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Sample records for i-type granitoid magmatism

  1. A-type and I-type granitoids and mylonitic granites of Hassan Salaran area of SE Saqqez, Kurdistan, Iran

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    Abdullah, Fakhraddin Mohammad; Saeed Ahmad, Sheler

    2014-05-01

    The Hassan Salarn area is located 20km to southeast of Saqqez city in Kurdistan Province, western Iran. In this area there are two distinct granitic rock suites consisting A-type and I-type granites and also mylonitic granites. These A-type and I-type granites have various petrological and geochemical characteristics. They also have different origins and petrogenesis. A-type granitoids comprise alkali feldspar granite, syenogranite and quartz alkali feldspar syenite, whereas I-type granitoids are composed of monzogranite, granodiorite and tonalite. Geochemically, A-type granitoids are peralkaline and acmite-normative but I-type granitoids are subalkaline (calc-alkaline), metaluminous and diopside-normative. A-type granitoids are also ferroan alkali and ferroan alkali-calcic whereas I-type granitoids are magnesian and calcic. A-type granitoids resemble to within plate granites and post-orogenic granites whereas I-type granitoids resemble to volcanic arc granites. A-type granitoids contain higher concentrations of alkalies, Zr, Rb, Nb, Y, Th, Ce, high FeO/MgO ratios and lower concentrations of Mg, Ca and Sr, resembling post-orogenic A-type granites. It is possible that heat from a mantle-derived magma which intruded into the lower crust, and/or rapid crustal extension have been essential generation of approriate melts producing A-type granitoids. Thus we can conclude that A-type granitoids were generated from a mixed mantle-crust source. Negative Nb anomalies and low contents of Ti and P probably indicate a subduction-related origin for protolith of I-type granitoids. Negative Nb anomalies and enrichment in Ce relative to its adjacent elements can be related to involvement of continental crust in magmatic processes. I-type granitoids are also enriched in Rb, Ba, K, Th, Ce and depleted in Nb, Zr and Y, indicating that they have had interacted with crust. I-type granitoids may result from contamination of mantle-derived magmas by continental crust during a subduction

  2. The differentiation process of the I-type granitoids in southwest Japan and New South Wares in Australia

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    Kawakatsu, K.; Iwamoto, Y.; Ebisu, S.; Hasegawa, M.; Hiraiwa, N.; Kawakatsu, T.; Kitano, A.; Masuta, T.; Ootsubo, H.; Wakazono, R.

    2013-12-01

    Cretaceous-Paleogene Granitoids in the inner zone of southwest Japan have been divided into two series: the magnetite series that is distributed mainly in the San-in belt and the ilmenite series that is distributed mainly in San-yo belt. For 8 years, we have been investigating the two series to clear their processes of magmatic differentiation. Recently, we discovered oscillatory zoned structure, exsolution lamellae of amphibole, and relics of pyroxene left in the core of amphibole from Harima granodiorite, Nunobiki granodiorite (San-yo belt) and Daito-Yokota quartz diorite (San-in belt). The amphibole that has microstructure coexists with magnetite, ilmenite and pyrrhotite. We compared the two series for crystallization and re-equilibrium by ion substitution using the microstructure of the amphibole as 'time measure' during the differentitation process of acidic magma. While magnetites and ilmenites coexist with the core of the amphiboles, the oxygen fugacity of the San-yo belt magma was low until the later stage of magmatic differentiation where H2S from the Earth's crust mixed with it. In the subsolidus process, hydrothermal solutions circulated. On the other hand, the oxygen fugacity of the San-in belt magma began to rise in the early stage of magmatic differentiation. In the later stage, mafic magma was contaminated with SO2. The rims of amphiboles coexist with pyrrhotites in both of belts. Furthermore, the re-equilibrium of minerals underwent progressive oxidation and hydrothermal fluid circulated actively in the subsolidus process. Bingie Bingie Point at New South Wares (Eurobodalla National Park) is a peninsula about a meter around. The plutonic rocks were formed in the Devonian period and belong to the magnetite series. They are classified I-type granitoids such as those found in the inner zone of southwest Japan. They have only trace amounts of oxide minerals and pyrrhotite. The amphiboles of the granitoids have oscillatory zoned structures at pale green

  3. Granitoid magmatism of Alarmaut granite-metamorphic dome, West Chukotka, NE Russia

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    Luchitskaya, M. V.; Sokolov, S. D.; Bondarenko, G. E.; Katkov, S. M.

    2009-04-01

    relation between magmatism, metamorphism and deformations, accompanying formation of dome structure. Structural data also indicate the dome formation between two regional strike-slips. Strike-slip deformations of terminal stage of collision might have resulted in local zones of extensions [6, 8]. Intrusive contacts of studied granitoid plutons with already deformed host deposits indicate their postcollisional origin. Wide petrographical spectrum of granitoids, hornblende and biotite existence in granites, metaluminous high-K and shoshonite character, biotites compositions allow belonging them to high-K granites of I-type. Appearance of I-type granites in postcollisional setting is usually related to crustal anatexis under the influence of hot asthenospheric mantle due to delamination of lower parts of lithosphere. At the same time the processes of mingling of magmas of different composition, assimilation, fractional crystallization take place. Thus, in tectonic scenario of Alarmaut dome formation except dominating submergence of Chukotka microcontinent margin beneath the structures of North-Asian craton active margin we should assume slab-breakoff or delamination of lithospheric mantle which might have facilitated heat transfer, necessary for melting of granite magma. Aptian-Albian volcanism, localized in postcollisional extensional structures, confirms this assumption. Interrelations of major oxides in granitoids show that compositions of Alarmaut intermediate rocks fall in the fields of melts, experimentally obtained during partial melting of amphibolites, and compositions of granodiorites and granites, along the boundary zone of partial melts of greywackes and dacites, tonalites. Heterogeneity of granitoids source composition or different level of magma contamination by ancient crustal material is confirmed by Sr-Nd data. It is expressed in significant dispersal of ɛNd(Т) and 87Sr/86Sr values in granitoids. Work is carried out at the financial support of RFBR

  4. Geochemistry Petrography, thermobarometry and investigation of magmatic series in Mirabad- Chehel Khane granitoid body (east of Bouin– Miandasht, Isfahan province

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    Seyed Mohsen Tabatabaei Manesh

    2017-11-01

    Full Text Available On the base of petrology, the Mirabad- Chehel Khane granitoid, east of Bouin-Miandasht, dominantly consists of syenogranite, monzogranite, alkali granite and granodiorites. The main minerals of these rocks are quartz, alkali feldspar (Orthoclase, plagioclase (Albite - Oligoclase, biotite, ± amphibole with minor amount of allanite, zircon, titanite, apatite, ± tourmaline.  The biotite from the granites are Fe-rich type (annite and primary magmatic in origin. The composition of the biotites studied principally falls in the calc-alkaline subduction related I-type granite on the tectonomagmatic discrimination diagrams, which stand on their major element oxides. Which is consistent with the nature of their host rocks. The studied amphiboles are classified as calcic (ferro-hornblende which points to the I-type nature of the granitoid.  The tourmaline composition plots on the schorl - foitite field. The temperature for the alteration, on the base of chlorite composition from the syenogranite, is estimated around 350°C and from the monzogranite rocks about 341°C.  Based on the application of Al-in amphibole, a 3 Kbar pressure was determined for the syenogranite unit corresponding to the depth of 8-11 Km for the emplacement of the pluton. Hornblende- plagioclase thermometer shows 694 to 700°C for the equilibrium of these two minerals.

  5. Geochemical studies, magmatic evolution, microstructures and replacement mechanisms in Jebale-Barez granitoid Complex (East and Southeast Jiroft

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    Jamal Rasouli

    2017-08-01

    samples and full matrix correction, the sum of all major oxides was equal to about 100 wt.%. The concentration of trace elements in the selected samples has been performed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS. The uncertainty is <10% for trace element contents higher than 2 ppm (except for Pb, <15% and <15% for all the other trace elements. Results The microstructures observed in thin sections in this study were grouped into three types: (i magmatic microstructures; (ii submagmatic microstructures and (iii mylonitic microstructures. Magmatic and submagmatic microstructures occurred simultaneously with the emplacement of granitoid complex and mylonitic microstructures that occurred after emplacement of granitoid complex. The magma nature of these rocks is sub-alkaline-(calc-alkaline, which fall into calc-alkaline series with high potassium in SiO2-K2O plots. The geochemical variation diagrams of major oxides, the continuous spectrum of rock compositions has been carried out which indicates the crystallization of magmatic differentiation and extensive appendices. Field observations, petrographic and geochemical studies suggest that the rocks in this area have type I and CAG subsections. Studying the geochemical diagrams of the rocks in the studied area indicates that these rocks have been formed in active continental margin tectononic settings. It seems that the Jebale-Barez granitoid Complex is located within a shear zone. Magma has been percolated through Mijan caldera and emplacement Forms of Sill along the shear zone during various periods and the structural setting of granitoid complex in the Jebale-Barez is extensional-shear fractures which are the product of transpression tectonic regime. Discussion The JBPC is calc-alkaline, high-K, subalkaline, and mostly metaluminous except granite and alkali-granite units which are slightly peraluminous and I type in character. These geochemical properties of the studied granitoids suggest subduction

  6. DURATION OF GRANITOID MAGMATISM IN PERIPHERAL PARTS OF LARGE IGNEOUS PROVINCES (BASED ON 40AR/39AR ISOTOPIC STUDIES OF ALTAI PERMIAN-TRIASSIC GRANITOIDS

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    O. A. Gavryushkina

    2017-01-01

    Full Text Available In large igneous provinces (LIP of fold areas, granitoid rocks are dominant, while mantle-derivated rocks play a subordinate role in rock formation. If magma emissions are impulsive, it may take 25–30 million years for a LIP to form and take shape. In this paper, we present the results of 40Ar/39Ar isotopic studies of Permian-Triassic grani­toids in the Altai region, Russia, and clarify the evolution of this region located at the periphery of the Siberian LIP. These granitoids are very diverse and differ not only in their rock set, but also in the composition features. In the study region, the granodiorite-granite and granite-leucogranite association with the characteristics of I- and S-types as well rare metal ore-bearing leucogranites are observed along with gabbro- and syenite-granite series, including mafic and intermediate rocks with the A2-type geochemical features. The 40Ar/39Ar data obtained in our study suggest that most of the studied granitoids intruded within a short period of time, 254–247 Ma. This timeline is closely related to the formation of granitoids in theKuznetsk basin and dolerite dikes in the Terekta complex (251–248 and 255±5 Ma, respectively, as well as intrusions of lamproite and lamprophyre dikes of the Chuya complex (245–242 and 237–235 Ma. Thus, we conclude that the Altai Permian-Triassic granitoids are varied mainly due to the evolution of mafic magmatism.

  7. Possible genetic link between I-type granite and orogenic gold deposits in Egypt (metamorphic-magmatic interaction?)

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    Abd El Monsef, Mohamed

    2015-04-01

    The orogenic gold deposits are a distinctive type of deposits that revealed unique temporal and spatial association with an orogeny. Where, the system of gold veins and related ore minerals was confined to hydrothermal solutions formed during compressional to transpressional deformation processes at convergent plate margins in accretionary and collisional orogens, with the respect to ongoing deep-crustal, subduction-related thermal processes. In Egypt, most of vein-type and dyke-type gold mineralization are restricted to granitic rocks or at least near of granitic intrusion that seems to have had an important influence on gold mineralization. Shear zone-related, mesothermal gold deposits of Fatira and Gidami mines in the northern Eastern Desert of Egypt are found within granitic bodies or at the contact between granites and metavolcanic rocks. The hosting-granitic rocks in Fatira and Gidami areas are mainly of granodioritic composition (I-Type granite) which is related to calc-alkaline magmatic series. However, Fatira granitoids were developed within island arc tectonic settings related to mature island arc system (Late-orogenic stage), at relatively low temperature (around 660° C) and medium pressure between (5 - 10 Kbar). On the other hand, Gidami granitoids were developed during the collision stage in continental arc regime related to active continental margin (Syn-orogeny), which were crystallized at relatively high temperature (700-720° C) and low pressure (around 0.1 Kbar). The ore mineralogy includes pyrite, chalcopyrite, sphalerite, covellite, ilmenite, goethite ± pyrrhotite ± pentlandite ± galena ± molybdenite. Native gold is detected only in Gidami mineralization as small inclusions within pyrite and goethite or as tiny grains scattered within quartz vein (in close proximity to the sulfides). In Fatira deposits, it is detected only by microprobe analysis within the crystal lattice of pyrite and jarosite. Fluid inclusions study for the mineralized

  8. Emplacement, petrological and magnetic susceptibility characteristics of diverse magmatic epidote-bearing granitoid rocks in Brazil, Argentina and Chile

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    Sial, A. N.; Toselli, A. J.; Saavedra, J.; Parada, M. A.; Ferreira, V. P.

    1999-03-01

    Magmatic epidote (mEp)-bearing granitoids from five Neoproterozoic tectonostratigraphic terranes in Northeastern (NE) Brazil, Early Palaeozoic calc-alkalic granitoids in Northwestern (NW) Argentina and from three batholiths in Chile have been studied. The elongated shape of some of these plutons suggests that magmas filled fractures and that dyking was probably the major mechanism of emplacement. Textures reveal that, in many cases, epidote underwent partial dissolution by host magma and, in these cases, may have survived dissolution by relatively rapid upward transport by the host magma. In plutons where such a mechanism is not evident, unevenly distributed epidote at outcrop scale is armoured by biotite or near-solidus K-feldspar aggregates, which probably grew much faster than epidote dissolution, preventing complete resorption of epidote by the melt. Al-in-hornblende barometry indicates that, in most cases, amphibole crystallized at P≥5 kbar. Kyanite-bearing thermal aureoles surrounding plutons that intruded low-grade metamorphic rocks in NE Brazil support pluton emplacement at intermediate to high pressure. mEp show overall chemical variation from 20 to 30 mol% (mole percent) pistacite (Ps) and can be grouped into two compositional ranges: Ps 20-24 and Ps 27-30. The highest Ps contents are in epidotes of plutons in which hornblende solidified under Pcorrosion of individual epidote crystals included in plagioclase in high-K calc-alkalic granitoids in NE Brazil, emplaced at 5-7 kbar pressure, yielded estimates of magma transport rate from 70 to 350 m year -1. Most of these plutons lack Fe-Ti oxide minerals and Fe +3 is mostly associated with the epidote structure. Consequently, magnetic susceptibility (MS) in the Neoproterozoic granitoids in NE Brazil, as well as Early Palaeozoic plutons in Argentina and Late Palaeozoic plutons in Chile, is usually low (3.0×10 -3 SI, typical of magnetite-series granitoids crystallized under higher oxygen fugacity. In NE

  9. Ordovician A-type granitoid magmatism on the Ceará Central Domain, Borborema Province, NE-Brazil

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    Castro, Neivaldo A.; Ganade de Araujo, Carlos E.; Basei, Miguel A. S.; Osako, Liliane S.; Nutman, Alan A.; Liu, Dunyi

    2012-07-01

    We present field relationships, major and trace element geochemistry and U-Pb SHRIMP and ID-TIMS geochronology of the A-type Ordovician Quintas pluton located in the Ceará Central Domain of the Borborema Province, in northeastern Brazil. This pluton presents a concentric geometry and is composed mainly of syenogranite, monzogranite, quartz syenite to quartz monzodiorite, monzogabbro and diorite. Its geochemical characteristics [SiO2 (52-70%), Na2O/K2O (1.55-0.65), Fe2O3/MgO (2.2-7.3), metaluminous to sligthly alkaline affinity, post-collisional type in (Y + Nb) × Rb diagram, and A-type affinity (Ga > 22 ppm, Nb > 20 ppm, Zn > 60 ppm), REE fractioned pattern with negative Eu anomaly] are coherent with post-collisional A2-type granitoids. However, the emplacement of this pluton is to some extent temporally associated with the deposition of the first strata of the Parnaíba intracratonic basin, attesting also to a purely anorogenic character (A1-type granitoid). The emplacement of this pluton is preceded by one of the largest known orogenesis of the planet (Neoproterozoic Pan-African/Brasiliano) and, if it is classified as an A2-type granitoid, it provides interesting constraints about how long can last A2-type magmatic activity after a major collisional episode, arguably triggered by disturbance of the underlying mantle, a topic extensively debated in the geoscience community.

  10. Petrogenesis of shoshonitic granitoids, eastern India: Implications for the late Grenvillian post-collisional magmatism

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    B. Goswami

    2014-11-01

    Full Text Available Many elongated, lenticular plutons of porphyritic granitoids are distributed mainly near the southern and northern margin of the Chhotanagpur Gneissic Complex (CGC which belongs to the EW to ENE–WSW tending 1500 km long Proterozoic orogenic belt amalgamating the North and South Indian cratonic blocks. The late Grenvillian (1071 ± 64 Ma Raghunathpur porphyritic granitoid gneiss (PGG batholith comprising alkali feldspar granite, granite, granodiorite, tonalite, quartz syenite and quartz monzonite intruded into the granitoid gneisses of southeastern part of CGC in the Purulia district, West Bengal and is aligned with ENE–WSW trending North Purulia shear zone. Mineral chemistry, geochemistry, physical condition of crystallization and petrogenetic model of Raghunathpur PGG have been discussed for the first time. The petrographic and geochemical features (including major and trace-elements, mineral chemistry and 87Sr/86Sr ratio suggest these granitoids to be classified as the shoshonitic type. Raghunathpur batholith was emplaced at around 800 °C and at 6 kbar pressure tectonic discrimination diagrams reveal a post-collision tectonic setting while structural studies reveal its emplacement in the extensional fissure of North Purulia shear zone. The Raghunathpur granitoid is compared with some similar granitoids of Europe and China to draw its petrogenetic model. Hybridization of mantle-generated enriched mafic magma and crustal magma at lower crust and later fractional crystallization is proposed for the petrogenesis of this PGG. Mafic magma generated in a post-collisional extension possibly because of delamination of subducting slab. Raghunathpur batholith had emplaced in the CGC during the final amalgamation (∼1.0 Ga of the North and South Indian cratonic blocks. Granitoid magma, after its generation at depth, was transported to its present level along megadyke channel, ways within shear zones.

  11. Genesis of Neoproterozoic granitoid magmatism in the Eastern Aracuai Fold Belt, eastern Brazil: field, geochemical and Sr-Nd isotopic evidence

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    Celino, Joil Jose; Botelho, Nilson Francisquini; Pimentel, Marcio Martins

    2000-01-01

    The Neoproterozoic granitoid magmatism of the Aracuai Fold Belt (AFB) is an important element for the discussion of the evolution of this belt and its relationships with the African counterpart, the West Congo Belt. In the eastern part of the AFB, four different granitoid suites were recognized. The Nanuque Suite (NQS) comprises syn-tectonic peraluminous cordierite-bearing monzogranites. The Sao Paulinho Suite (SPS) consists of Th-rich peraluminous two mica or biotite-only granitoids. Calc-alkalic granitoids with magmatic epidote were grouped into the Itagimirim Suite (ITS) and post-tectonic charnockitic rocks were grouped into the Salomao Suite (SLS). Sm-Nd mineral isochron and Rb- isochron yielded ages of yielded ages of respectively 761 Ma and 714 Ma for the Nanuque and Sao Paulino suites. The general Sr-Nd isotopic characteristics of the granitoid suites and some country rocks indicate that the parental magmas were mostly the product of melting of the Paraiba do Sul metasediments. The chronological and genetic evolution the Neoproterozoic plutonism can be envisaged in a model of est-dipping subduction zone, followed by a continental collision between the Brasiliano/Pan-African (Brazil) and Congo (Africa cratons and final episodes of uplift and collapse. (author)

  12. Electron probe micro analyser chemical zircon ages of the Khetri granitoids, Rajasthan, India: records of widespread late palaeoproterozoic extension-related magmatism

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    Kaur, Parampreet; Chaudhri, Naveen; Biju-Sekhar, S.; Yokoyama, K.

    2006-01-01

    A number of granitoid plutons were emplaced in the northernmost entity of the Aravalli craton, the Khetri Copper Belt (KCB). We report here Th-U-Pb electron probe micro analyser chemical ages for zircon and monazite from two granitoid plutons of the north KCB, the Biharipur and Dabla. Zircons occurring in the granitoids depict well-developed magmatic zoning and are chronologically unzoned. Both the plutons and their diverse granitoid facies are coeval and provide ages around 1765-1710 Ma. Geochemical attributes of the studied plutons are typical of A-type within-plate granites and consistent with an extensional tectonic environment. Our new age data are comparable to the petrologically similar A-type granitoids of the Alwar region, which have provided zircon chemical ages around 1780-1710 Ma. These analogous ages imply a widespread late palaeoproterozoic extension-related plutonism in the northern part of the Aravalli craton. The monazites, which were recovered only from the mafic magmatic rocks of the Biharipur pluton, yielded an isochron age of 910 ±10 Ma, signifying an over- print of a younger neoproterozoic thermal event in the region. (author)

  13. Les granitoïdes hercyniens post-collisionnels du Maroc oriental : une province magmatique calco-alcaline à shoshonitiqueThe post-collisional Hercynian granitoids from eastern Morocco: a calc-alkaline to shoshonitic magmatic province

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    El Hadi, Hassan; Tahiri, Abdelfatah; Reddad, Aicha

    2003-11-01

    The post-collisional Hercynian granitoids crop out in the easternmost part of the Moroccan Hercynian belt. Petrographical and geochemical studies show a composition similarity in the various granitoids. The granitoids belong to per-aluminous and metaluminous magmatic associations. They have evolved according to a scheme similar to high-K calc-alkaline to shoshonitic associations. To cite this article: H. El Hadi et al., C. R. Geoscience 335 (2003).

  14. Multiple sources of magmatism. granitoids from southeast Kohistan, NW Himalayas, Pakistan

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    Khan, M. A.; Qazi, M. S.

    2005-01-01

    The Kohistan island arc terrane in the northwestern Himalayas of N. Pakistan is sandwiched between the Indian and Karakoram plated. The base of the arc is occupied by a major stratiform ultramafic-gabbroic complex (the Sapat-Babusar complex), which overrides the crust of the Indian plate along the Indus suture (i.e., the Main Mantle Thrust; MMT). It was intruded into the base of a thick pile of metavolcanics (the Kamila belt), which comprise a tectonic collage of MORB-type tholeiitic basalts, island-arc tholeiites and calc-alkaline andesites. The Chilas complex, comprising ultramafic and gabbronorite rocks, is also intrusive into the Kamila belt, it is emplaced onto the top rather than the base of the Kamila belt. A sizeable proportion of granitoid rocks are present in the south-eastern part of Kohistan, which intruded the Kamila amphibolites. These are predominantly dioritic in composition, but include gabbros, granodiorites, granites and trondhjemites. The granitoids occur in two types. (1) large sheet-like lenticular masses, and (2) minor intrusives in the form of veints, sills or dykes. Three large sheets like bodies are mapped. All these bodies are composite, comprising gabbros, diorite/tonalite, granodiorite and granite. The minor intrusion of granitic and trondhjemitic composition are abundantly present in the form of veins, sills and dykes; and are characterized by variation in distribution. Strong shearing transformed the rocks into blastomylonite gneisses. The mineral assemblage consists of quartz, plagioclase, emphibole, epidote, chlorite, biotite, muscovite, sphene, magnetite and apatite. (author)

  15. Multiple sources of magmatism: granitoids from southeast kohistan, nw himalayas Pakistan

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    Sayab, M.; Qazi, M.S.

    2005-01-01

    The Kohistan island arc terrane in the northwestern Himalayas of N. Pakistan is sandwiched between the Indian and Karakoram plates. The base of the arc is occupied by a major stratiform ultramafic-gabbroic complex (the Sapat-Babusar complex). which overrides the crust of the Indian plate along the Indus suture (i. e., the Main Mantle Thrust; MMT). It was intruded into the base of a thick pile of metavolcanics (the Kamila belt), which comprise a tectonic collage of MORB-type tholeiitic basalts, island-arc tholeiites and calc-alkaline andesites. The Chilas complex, comprising ultramafic and gabbronorite rocks, is also intrusive into the Kamila belt. It is emplaced onto the top rather than the base of the Kamila belt. A sizeable proportion of granitoid rocks are present in the south-eastern part of Kohistan. Which intruded the Kamila amphibolites. These are predominantly dioritic in composition but include gabbros, granodiorites, granites and trondhjemites. The granitoids occur in two types: (I) large sheet-like lenticular masses, and (2) minor intrusives in the form of veins sills or dykes. Three large sheets like bodies are mapped. All these bodies are composite, comprising gabbros, diorite/tonalite. granodiorite and granite. The minor intrusions of granitic and trondhjemitic composition are abundantly present in the form of veins, sills and dykes and are characterized by variation in distribution. Strong shearing transformed the rocks into blastomylonite gneisses. The mineral assemblage consists of quartz, plagioclase, Amphibole, epidote, chlorite, biotite, muscovite, sphene, magnetite and apatite. (author)

  16. Geochemistry of the Serifos calc-alkaline granodiorite pluton, Greece: constraining the crust and mantle contributions to I-type granitoids

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    Stouraiti, C.; Baziotis, I.; Asimow, P. D.; Downes, H.

    2017-11-01

    The Late Miocene (11.6-9.5 Ma) granitoid intrusion on the island of Serifos (Western Cyclades, Aegean Sea) is composed of syn- to post-tectonic granodiorite with quartz monzodiorite enclaves, cut by dacitic and aplitic dikes. The granitoid, a typical I-type metaluminous calcic amphibole-bearing calc-alkaline pluton, intruded the Cycladic Blueschists during thinning of the Aegean plate. Combining field, textural, geochemical and new Sr-Nd-O isotope data presented in this paper, we postulate that the Serifos intrusion is a single-zoned pluton. The central facies has initial 87Sr/86Sr = 0.70906 to 0.7106, ɛNd(t) = - 5.9 to - 7.5 and δ18Οqtz = + 10 to + 10.6‰, whereas the marginal zone (or border facies) has higher initial 87Sr/86Sr = 0.711 to 0.7112, lower ɛ Nd(t) = - 7.3 to - 8.3, and higher δ18Οqtz = + 10.6 to + 11.9‰. The small range in initial Sr and Nd isotopic values throughout the pluton is paired with a remarkable uniformity in trace element patterns, despite a large range in silica contents (58.8 to 72 wt% SiO2). Assimilation of a crustally derived partial melt into the mafic parental magma would progressively add incompatible trace elements and SiO2 to the evolving mafic starting liquid, but the opposite trend, of trace element depletion during magma evolution, is observed in the Serifos granodiorites. Thermodynamic modeling of whole-rock compositions during simple fractional crystallization (FC) or assimilation-fractional crystallization (AFC) processes of major rock-forming minerals—at a variety of pressure, oxidation state, and water activity conditions—fails to reproduce simultaneously the major element and trace element variations among the Serifos granitoids, implying a critical role for minor phases in controlling trace element fractionation. Both saturation of accessory phases such as allanite and titanite (at SiO2 ≥ 71 wt%)(to satisfy trace element constraints) and assimilation of partial melts from a metasedimentary component (to

  17. Metallogenetic systems associated with granitoid magmatism in the Amazonian Craton: An overview of the present level of understanding and exploration significance

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    Bettencourt, Jorge Silva; Juliani, Caetano; Xavier, Roberto P.; Monteiro, Lena V. S.; Bastos Neto, Artur C.; Klein, Evandro L.; Assis, Rafael R.; Leite, Washington Barbosa, Jr.; Moreto, Carolina P. N.; Fernandes, Carlos Marcello Dias; Pereira, Vitor Paulo

    2016-07-01

    The Amazonian Craton hosts world-class metallogenic provinces with a wide range of styles of primary precious, rare, base metal, and placer deposits. This paper provides a synthesis of the geological database with regard to granitoid magmatic suites, spatio temporal distribution, tectonic settings, and the nature of selected mineral deposits. The Archean Carajás Mineral Province comprises greenstone belts (3.04-2.97 Ga), metavolcanic-sedimentary units (2.76-2.74 Ga), granitoids (3.07-2.84 Ga) formed in a magmatic arc and syn-collisional setting, post-orogenic A2-type granites as well as gabbros (ca. 2.74 Ga), and anorogenic granites (1.88 Ga). Archean iron oxide-Cu-Au (IOCG) deposits were synchronous or later than bimodal magmatism (2.74-2.70 Ga). Paleoproterozoic IOCG deposits, emplaced at shallow-crustal levels, are enriched with Nb-Y-Sn-Be-U. The latter, as well as Sn-W and Au-EGP deposits are coeval with ca. 1.88 Ga A2-type granites. The Tapajós Mineral Province includes a low-grade meta-volcano-sedimentary sequence (2.01 Ga), tonalites to granites (2.0-1.87 Ga), two calc-alkaline volcanic sequences (2.0-1.95 Ga to 1.89-1.87 Ga) and A-type rhyolites and granites (1.88 Ga). The calc-alkaline volcanic rocks host epithermal Au and base metal mineralization, whereas Cu-Au and Cu-Mo ± Au porphyry-type mineralization is associated with sub-volcanic felsic rocks, formed in two continental magmatic arcs related to an accretionary event, resulting from an Andean-type northwards subduction. The Alta Floresta Gold Province consists of Paleoproterozoic plutono-volcanic sequences (1.98-1.75 Ga), generated in ocean-ocean orogenies. Disseminated and vein-type Au ± Cu and Au + base metal deposits are hosted by calc-alkaline I-type granitic intrusions (1.98 Ga, 1.90 Ga, and 1.87 Ga) and quartz-feldspar porphyries (ca. 1.77 Ga). Timing of the gold deposits has been constrained between 1.78 Ga and 1.77 Ga and linked to post-collisional Juruena arc felsic magmatism (e.g., Col

  18. Les granitoïdes néoprotérozoïques de Khzama, Anti-Atlas central, Maroc: marqueurs de l'évolution d'un magmatisme d'arc à un magmatisme alcalineNeoproterozoic granitoids from Khzama, central Anti-Atlas, Morocco: evolution markers from arc magmatism to alkaline magmatism

    Science.gov (United States)

    El-Khanchaoui, T.; Lahmam, M.; El-Boukhari, A.; El-Beraaouz, H.

    2001-05-01

    Petrological study and zircon typology provide important information that is related to the classification and genesis of Neoproterozoic granitoids in the Khzama area (northeast Siroua). The Pan-African granitoids show a transition from island-arc magmatism to alkaline magmatism. A space and time zonation of magmatism from the north to the south is evident. Early Pan-African granitoids were generated from various magma sources through different petrogenetic mechanisms. The first association corresponds to the low-K calc-alkaline plutons of Ait Nebdas, the second one correponds to high-K calc-alkaline post-collisional granites (Tamassirte-Tiferatine and Ifouachguel). Finally, shoshonitic magmatism (Irhiri) ends the magmatic evolution of the region. Thus, the late Pan-African granitic plutonism began with calc-alkaline associations and ended with K-alkaline magmatism in a transtensional setting, heralding the onset of the Moroccan Palæozoic cycle.

  19. Carboniferous Granitoid Magmatism of Northern Taimyr: Results of Isotopic-Geochemical Study and Geodynamic Interpretation

    Science.gov (United States)

    Kurapov, M. Yu.; Ershova, V. B.; Makariev, A. A.; Makarieva, E. V.; Khudoley, A. K.; Luchitskaya, M. V.; Prokopiev, A. V.

    2018-03-01

    Data on the petrography, geochemistry, and isotopic geochronology of granites from the northern part of the Taimyr Peninsula are considered. The Early-Middle Carboniferous age of these rocks has been established (U-Pb, SIMS). Judging by the results of 40Ar/39Ar dating, the rocks underwent metamorphism in the Middle Permian. In geochemical and isotopic composition, the granitic rocks have much in common with evolved I-type granites. This makes it possible to specify a suprasubduction marginal continental formation setting. The existence of an active Carboniferous margin along the southern edge of the Kara Block (in presentday coordinates) corroborates the close relationship of the studied region with the continent of Baltia.

  20. A- and I-type metagranites from the North Shahrekord Metamorphic Complex, Iran: Evidence for Early Paleozoic post-collisional magmatism

    Science.gov (United States)

    Badr, Afsaneh; Davoudian, Ali Reza; Shabanian, Nahid; Azizi, Hossein; Asahara, Yoshihiro; Neubauer, Franz; Dong, Yunpeng; Yamamoto, Koshi

    2018-02-01

    The North Shahrekord Metamorphic Complex (NSMC) of the central Sanandaj-Sirjan Zone (SaSZ) consists of metagranitoid bodies, which were metamorphosed within high pressure-low temperature conditions. Whole rock chemistry shows relatively high amounts of SiO2 (65-77 wt%) and Al2O3 (12-15 wt%), low amounts of Nb, P, Sr, Ti, a high ratio of Ga/Al (4-9) and a negative Eu anomaly. The chemical compositions of metagranites are reasonably similar to A- and I-type granites. U-Pb zircon ages of three samples of metagranites indicate that crystallization of the granites occurred at 521.6 ± 9.1 to 513.5 ± 8.5 Ma, Middle Cambrian. The initial 87Sr/86Sr and 143Nd/144Nd ratios of samples vary from 0.7057-0.7239 and 0.511801-0.511890, respectively. High initial 87Sr/86Sr ratios and low εNd(t) values (- 3.39 to - 1.07) associated with high ratios of 206Pb/204Pb(t) = 17.8557-18.8045, 207Pb/204Pb(t) = 15.6721-15.7220, and 208Pb/204Pb(t) = 37.7490-38.4468 infer a significant contribution of continental crust in generating the source magma of the metagranite bodies. The results reveal that the metagranites were mainly produced through mixing of basaltic melts with components similar to metasedimentary sources. The new results show that crystallization of the metagranites occurred in Early Paleozoic times and much earlier than break-up and drifting of the SaSZ from the Arabian plate, suggesting that the metagranites were mainly produced in the western Iran after the closure of the Proto-Tethys Ocean. This model is consistent with the previously suggested models for formation of an Early Paleozoic granitoid belt along the northern rim of Gondwana.

  1. U-Pb (LA-ICPMS) zircon ages and Nd isotopes for granitoids of the Tamboril-Santa Quiteria Complex, Ceara Central Domain: implication for neoproterozoic syncollisional magmatism in north Borborema Province, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Costa, Felipe Grandjean da; Araujo, Carlos Eduardo Ganade de; Vasconcelos, Antonio Maurilio, E-mail: felipe.costa@cprm.gov.br, E-mail: caegeo@gmail.com, E-mail: maurilio.vasconcelos@cprm.gov.br [Servico Geologico do Brasil (CPRM), Fortaleza, CE (Brazil); Amaral, Wagner da Silva, E-mail: wamaral@ufc.br [Universidade Federal do Ceara (UFC), Fortaleza, CE (Brazil). Departamento de Geologia; Rodrigues, Joseneusa Brilhante, E-mail: joseneusa.rodrigues@cprm.gov.br [Servico Geologico do Brasil (CPRM), Brasilia, DF (Brazil)

    2013-06-15

    The Tamboril-Santa Quiteria Complex (TSQC) is one of the largest Neoproterozoic plutonic manifestations in the north Borborema Province (NE Brazil). It represents an anatectic/igneous association characterized by a number of magmatic pulses that occurred in the 650-610 Ma interval. In this paper, we present U-Pb (LA-MC-ICP-MS) zircon ages and Nd isotopes for quartz monzonite and quartz diorites of the southern part of TSQC. The quartz monzonite belong to a hybrid granitoid association, including monzonite, syenites and quartz syenites, all with abundant mafic magmatic enclaves. A quartz monzonite sample yielded a U-Pb zircon age of 634 {+-} 10 Ma and a TDM age of 2.69 Ga. The quartz diorites are much more homogeneous in composition and yielded a U-Pb zircon age of 618 {+-} 23 Ma and a TDM age of 2.19 Ga. The presence of coeval mantle-derived magmatism and diatexites (crustal anatexis) post-dating high-pressure metamorphism (ca. 650 Ma), and together with high-temperature metamorphism (ca. 630-610 Ma), suggests that this large magmatic manifestation evolved in a collisional setting, probably related to slab break off during the Western Gondwana amalgamation. (author)

  2. Geological, petrogical and geochemical characteristics of granitoid rocks in Burma: with special reference to the associated WSn mineralization and their tectonic setting

    Science.gov (United States)

    Zaw, Khin

    Burma, but trace element data show the tendency for granitoid plutons which bear W-Sn mineralization to be comparatively more enriched in Be, Bi, Cu, Mo, Pb, Sn, Y, and Zn, but less depleted in Ba and Zr than those plutons in which no W-Sn occurrences are recorded. The eastern belt granitoids are still largely unknown but characterized by medium to coarsely porphyritic textures and country rocks of regionally metamorphosed, turbiditic sediments of Chaung Magyi Group (Upper Precambrian). This eastern granitoid belt lies immediately to the north of mostly Triassic granitoids in northern Thailand, and the Sn-W bearing, mesozonal, Permo-Triassic, Main Range granitoids in the western part of the Malay Peninsula. The latter granitoid swere considered to have been emplaced during continental collision, but geologic and tectonic information for the eastern belt grantoids in Burma are still incomplete to confirm this contention. Alternatively, present available geologic evidences cannot rule out the possibility that the eastern belt granitoids were emplaced in a continental margin above an eastward subducting ocean floor during the Lower Paleozoic. According to the criteria given by Chappell and White ( Pacific Geol.8, 173-174, 1974), the porphyry Cu(Au)-related, western granitoid belt plutons have I-type characteristics, whereas the W-Sn related, central granitoid belt contains both the hornblende-bearing I-type granitoids as older intrusive phases and the W-Sn bearing, S-type granitoids as younger plutonic phases. The eastern belt granitoids cannot be classified as being of either I- or S-type, as petrochemical data are still lacking.

  3. Ar-Ar dating and petrogenesis of the Early Miocene Taşkapı-Mecitli (Erciş-Van) granitoid, Eastern Anatolia Collisional Zone, Turkey

    Science.gov (United States)

    Oyan, Vural

    2018-06-01

    The Early Miocene Taşkapı-Mecitli granitoid that is located in the northern section of the Eastern Anatolia Collision Zone has typical I-type, metaluminous and calk-alkaline characteristics. It also contains mafic microgranular / magmatic enclaves (MMEs). New Ar-Ar dating results show that the age of the Taşkapı-Mecitli granitoid is ∼23 Ma and it crystallised in the Early Miocene, in contrast to its previously known Cretaceous age. Identical crystallisation ages (∼23 Ma), similar mineral assemblages and geochemical compositions, and indistinguishable isotopic compositions of MMEs and host rocks imply that the MMEs are most consistent with a cumulate origin formed at earlier stages of the same magmatic system that produced the Taşkapı-Mecitli granitoid. MELTS modelling suggests that magma of the Taşkapı-Mecitli granitoid was the result of fractionation under a crustal pressure of 4 kbar, with a H2O content of 1.5%. EC-AFC model calculation reveals that the Taşkapı-Mecitli granitoid includes from 0.5% to 2% crustal assimilation rates. These rates indicate that crustal contamination can be negligible when compared to fractional crystallisation in the evolution of the magma beneath the Taşkapı-Mecitli granitoid. The partial melting model calculations and MORB-normalised trace element concentrations of the least evolved samples of the Taşkapı-Mecitli granitoid are consistent with those of mafic melts obtained from partial melting of interacting mantle- lower crust with a melting degree of 18%. The age (23 Ma) of the post- or syn-collisional Taşkapı-Mecitli granitoid suggests that the collision between Arabian and Eurasian plates could be before/around ∼23 Ma (Late Oligocene to Early Miocene).

  4. [Analysis of X-Ray Fluorescence Spectroscopy and Plasma Mass Spectrometry of Pangxidong Composite Granitoid Pluton and Its Implications for Magmatic Differentiation].

    Science.gov (United States)

    Zeng, Chang-yu; Ding, Ru-xin; Li, Hong-zhong; Zhou, Yong-zhang; Niu, Jia; Zhang, Jie-tang

    2015-11-01

    Pangxidong composite granitoid pluton located in the southwestern margin of Yunkai massif. The metamorphic grade of this pluton increases from outside to inside, that is, banded-augen granitic gneisses, gneissoid granites and granites distribute in order from edge to core. X-Ray Fluorescence Spectroscopy and Plasma Mass Spectrometry are conducted to study the geochemical characteristics of the three types of rocks. The result shows that all the three types of rocks are peraluminous rocks and their contents of main elements and rare earth elements change gradually. From granitic gneisses to granites, the contents of Al₂O₃, CaO, MgO, TiO₂, total rare earth elements and light rare earth elements increase, but the contents of SiO₂ and heavy rare earth elements decrease. It is suggested that the phylogenetic relationship exists between granitic gneisses, gneissoid granites and granites during the multi-stage tectonic evolution process. Furthermore, the remelting of metamorphosed supracrustal rocks in Yunkai massif is probably an important cause of granitoid rocks forming. The evolutionary mechanism is probably that SiO₂ and heavy rare earth elements were melt out from the protolith and gradually enriched upward, but Al₂O₃, CaO, MgO, TiO₂ and light rare earth elements enriched downward.

  5. Geochronology, geochemical and Sr-Nd-Hf-Pb isotopic compositions of the granitoids in the Yemaquan orefield, East Kunlun orogenic belt, northern Qinghai-Tibet Plateau: Implications for magmatic fractional crystallization and sub-solidus hydrothermal alteration

    Science.gov (United States)

    Yin, Shuo; Ma, Changqian; Xu, Jiannan

    2017-12-01

    A general consensus has emerged that high field strength elements (HFSE) can mobile to some extent in a hydrothermal fluid. However, there are hot debates on whether sub-solidus hydrothermal alteration can lower the Nb/Ta ratio in evolved melts. In this study, we present petrography, geochronology and geochemistry of the barren and mineralized rocks in the Yemaquan skarn iron deposit, northern Qinghai-Tibet Plateau, to probe magmatic-hydrothermal transition. The barren rocks consist of diorites, granodiorites, granites and syenogranites, whereas the porphyritic granodiorites are associated with mineralization for an excellent consistency between the magmatic zircon U-Pb age (225 ± 2 Ma) and the hydrothermal phlogopite 40Ar-39Ar age (225 ± 1.5 Ma). The Sr-Nd-Hf-Pb isotopic data demonstrate that the Yemaquan granitoids are originated from a relatively homogenous enriched mantle with different degrees of crust contamination (assimilation fractional crystallization, AFC). Trace elements signatures indicate that the porphyritic granodiorites related to mineralization display amphibole crystallization for high water contents, whereas the barren granites have gone through biotite crystallization due to potassium enrichment by continuous upper crust contamination, both of which are responsible for their Nb/Ta ratios, respectively. Modeling results suggest that a basaltic melt with Nb/Ta ratio of 15.3 can reach a minimum Nb/Ta ratio of 12 in the producing granodioritic melt by amphibole fractional crystallization based on partition coefficients of Nb and Ta between amphibole and melts from previous experiments. This may explain the average Nb/Ta ratio (13.7) of the barren granodiorites, while it cannot account for the average Nb/Ta ratio (8.4) of the mineralized porphyritic granodiorites, and it is even lower than that of the granites (10.3) with biotite fractional crystallization. Exsolution of a magmatic-hydrothermal fluid is inevitable when a water saturated magma

  6. Crustal basement controls granitoid magmatism, and implications for generation of continental crust in subduction zones: A Sr-Nd-Hf-O isotopic study from the Paleozoic Tongbai orogen, central China

    Science.gov (United States)

    Wang, Hao; Wu, Yuan-Bao; Yang, Jin-Hui; Qin, Zheng-Wei; Duan, Rui-Chun; Zhou, Lian; Yang, Sai-Hong

    2017-06-01

    Ascertaining the petrogenesis of granitoid rocks in subduction zones holds the key for understanding the processes of how continental crust is produced. The synchronous Taoyuan and Huanggang plutons occur in two different geological units of the Paleozoic Tongbai orogen of central China. They provide an optimal opportunity for a study to address the role of the crustal basement in generating voluminous granitoid magmatism in subduction zones. The Taoyuan and Huanggang plutons have identical U-Pb zircon crystallization ages of 440-444 Ma, which are temporally related to northward subduction of the Paleotethyan Ocean. The Taoyuan samples show high SiO2 (73.36-79.16%) and low Al2O3 (12.00-13.45%) contents, Mg numbers (20.6-38.2), and Sr/Y (2.04-10.1) and (La/Yb)N (2.34-7.32) ratios with negative Eu anomalies (Eu/Eu* = 0.33-0.93). They yielded positive εNd(t) (+ 3.0 to + 6.7) and εHf(t) (+ 11.8 to + 13.2) values, elevated initial Sr isotopic ratios (0.7040-0.7057) and relatively low zircon δ18O values of 4.62-5.39‰. These suggest that they were produced through partial melting of hydrothermally altered lower crust of the accreted Erlangping oceanic arc. In contrast, the Huanggang samples exhibit variable whole-rock geochemical and isotopic compositions with SiO2 contents of 57.01-64.42 wt.%, initial Sr isotopic ratios of 0.7065-0.7078, and εNd(t) values of - 5.7 to - 9.4. Additionally, they have high zircon δ18O values of 7.57-8.45‰ and strongly negative zircon εHf(t) values of - 14.4 to - 10.5. They were suggested to have been mainly derived from ancient continental crust of the Kuanping crustal unit with the addition of 20-40% juvenile, mantle-derived material. Accordingly, the granitoids in both oceanic and continental arcs are likely to be mainly derived from intracrustal melting of their crustal basement. It is revealed by the Huanggang pluton that little net continental crust growth occurs in continental arcs, and addition of new volume of continental

  7. Comparison of hydrothermal alteration patterns associated with porphyry Cu deposits hosted by granitoids and intermediate-mafic volcanic rocks, Kerman Magmatic Arc, Iran: Application of geological, mineralogical and remote sensing data

    Science.gov (United States)

    Yousefi, Seyyed Jabber; Ranjbar, Hojjatollah; Alirezaei, Saeed; Dargahi, Sara; Lentz, David R.

    2018-06-01

    The southern section of the Cenozoic Urumieh-Dokhtar Magmatic Arc (UDMA) of Iran, known as Kerman Magmatic Arc (KMA) or Kerman copper belt, is a major host to porphyry Cu ± Mo ± Au deposits, collectively known as PCDs. In this study, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and spectral angle mapper (SAM) method, combined with field data, mineralogical studies, and spectral analysis are used to determine hydrothermal alteration patterns related to PCDs in the KMA. Gossans developed over some of these porphyry type deposits were mapped using Landsat 8 data. In the NKMA gossans are more developed than in the SKMA due to comparatively lower rate of erosion. The hydrothermal alteration pattern mapped by ASTER data were evaluated using mineralogical and spectral data. ASTER data proved to be useful for mapping the hydrothermal alteration in this semi-arid type of climate. Also Landsat 8 was useful for mapping the iron oxide minerals in the gossans that are associated with the porphyry copper deposits. Our multidisciplinary approach indicates that unlike the PCDs in the northern KMA that are associated with distinct and widespread propylitic alteration, those in the granitoid country rocks lack propylitic alteration or the alteration is only weakly and irregularly developed. The porphyry systems in southern KMA are further distinguished by development of quartz-rich phyllic alteration zones in the outer parts of the PCDs that could be mapped using remote sensing data. Consideration of variations in alteration patterns and specific alteration assemblages are critical in regional exploration for PCDs.

  8. Geochemical criteria for distinguishing magmatic and metasomatic albite-enrichment in granitoids — examples from the Ta-Li granite Yichun (China) and the Sn-W deposit Tikus (Indonesia)

    Science.gov (United States)

    Schwartz, M. O.

    1992-03-01

    Two examples of albite-rich granitoids of different genesis are discussed: the Ta-Li granite at Yichun (China) exhibits dominantly igneous textures, and the sodium-enrichment zone in biotite granite of the Sn-W deposit at Tikus is characterized by metasomatic textures. The Yichun stock shows a magmatic evolution from biotite-muscovite granite to lepidolite granite with an increase of Na2O and F concentrations and a decrease of CaO and Sr concentrations. The composition of the different granite phases is close to pseudoternary minima in the haplogranite-H2O(-Li-F) system. The composition of the F-rich albitization zone at Tikus deviates strongly from the pseudoternary minima and shows a tendency to become monomineralic (nearly pure albitite). CaO and Sr concentrations are increased or remain unchanged with respect to the unaltered biotite granite at Tikus. Albitization produced by fluid-rock interaction in F-rich systems is characterized by that CaO or Sr released by the breakdown of plagioclase in the granite protolith, are fixed in newly formed fluorite or albite, respectively.

  9. Geochronology and Geochemistry of a Late Cretaceous Granitoid Suite, Santa Rosa Range, Nevada: Linking Arc Magmatism in Northwestern Nevada to the Sierra Nevada Batholith

    Science.gov (United States)

    Brown, K.; Stuck, R.; Hart, W. K.

    2010-12-01

    Throughout the Mesozoic, an arc-trench system dominated the western margin of North America. One of the principal records of this system’s evolution is a discontinuous alignment of deeply eroded batholiths, which represent the once-active roots of ancient volcanic systems. Although these batholiths extend from Alaska to Mexico, there is a prominent (~500 km) gap located in present-day Nevada that contains scattered plutons that are hypothesized to be similar in age and origin to the larger batholiths. The current understanding of these isolated plutons, however, remains limited to regional isotopic studies aimed at identifying major crustal boundaries and structural studies focused on emplacement mechanisms. Therefore, detailed petrogenetic studies of the plutons exposed within the Santa Rosa Range (SRR) of NW Nevada will better characterize magmatism in this region, placing them within a regional context that explores the hypothesized links between the intrusions of NW Nevada to the Sierra Nevada batholith (SNB). A compilation of published geochronology from this region shows that plutons in the SRR are broadly coeval with the Cathedral Range Intrusive Epoch (~95-83 Ma) and the Shaver Sequence (~118-105 Ma) of the SNB. Preliminary Rb-Sr geochronology from the Granite Peak stock reveals a previously unrecognized period of magmatism (ca. 85.0 Ma) in this region. Therefore, ongoing work will more completely characterize the timing of magmatic pulses in this region and their relationships to the SNB. Preliminary petrographic, geochemical, and isotopic observations suggest that two distinct compositional/textural groups exist: the Santa Rosa/ Andorno group (SRA) and Granite Peak/ Sawtooth group (GPS). The chemical and isotopic variations between the two groups suggest that they were not consanguineous. Whereas the SRA group is generally more mafic (64-72 wt% SiO2) and metaluminous, the GPS group is more felsic (72- 76 wt% SiO2) and peraluminous. This observation is

  10. Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harsit Pluton, Eastern Turkey

    NARCIS (Netherlands)

    Karsli, O.; Dokuz, A.; Uysal, I.; Aydin, F.; Chen, B.; Kandemir, R.; Wijbrans, J.R.

    2010-01-01

    We present elemental and Sr-Nd-Pb isotopic data for the magmatic suite (~79 Ma) of the Harşit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO

  11. Early Cretaceous Na-rich granitoids and their enclaves in the Tengchong Block, SW China: Magmatism in relation to subduction of the Bangong-Nujiang Tethys ocean

    Science.gov (United States)

    Zhu, Ren-Zhi; Lai, Shao-Cong; Santosh, M.; Qin, Jiang-Feng; Zhao, Shao-Wei

    2017-08-01

    The Na-rich intermediate-to-felsic granitic rocks provide insights into the generation of magmas in subduction zones. This paper presents zircon LA-ICP-MS U-Pb ages as well as whole-rock geochemical, mineral chemical, and in situ zircon Hf isotopic data on Na-rich granitic rocks from the Tengchong Block, SW China. The granodiorites and associated mafic magmatic enclaves (MMEs) from the Menglian batholith yield zircon U-Pb ages of 116.1 ± 0.8 to 117.8 ± 0.6 Ma and 117.7 ± 0.7 Ma, respectively. Both host granodiorites and enclaves show calc-alkaline and sodium-rich nature, enrichment in large-ion lithophile elements (LILEs), and variable depletion in zircon Hf isotopic compositions. Euhedral amphiboles in both granodiorites and associated enclaves are magnesian-hornblende with high Mg and Ca and contain euhedral plagioclase inclusions of labradorite to andesine (An36-57) composition. The granodiorite was most likely derived through the mixing of partial melts derived from juvenile basaltic lower crust and a minor evolved component of ancient crustal sources. The quartz monzodiorite-granodiorites and associated MMEs from the Xiaotang-Mangdong batholith yield zircon U-Pb ages of 120.3 ± 1.3 to 122.6 ± 0.8 Ma and 120.7 ± 1.5 Ma. These rocks are also sodium-rich and show calc-alkaline trend with negative zircon Hf isotopic compositions (- 5.55 to + 0.58). The MMEs in the host intrusions are monzogabbro with variable and depleted zircon Hf isotopic compositions. The amphiboles in the both host intrusions and the enclaves show Al-rich ferro-tschermakite composition. We infer that the quartz monzodiorite-granodiorites were derived from magmas generated by the melting of ancient basaltic rocks in the lower arc crust induced by the underplating of mantle-derived mafic magmas. The formation of the different types of Na-rich granitic rocks is correlated to the subduction of Bangong-Nujiang Tethyan ocean. A comparison with magmatism in the northern magmatic belt suggests

  12. Rb-Sr isochronous age of Vepor pluton granitoids

    International Nuclear Information System (INIS)

    Bagdasaryan, G.P.; Gykasyan, R.Kh.; Cambel, B.

    1986-01-01

    The result are presented of geochronological investigations of the Vepor pluton granitoids by the Rb-Sr isochronous method. The results prove the Variscan age of granodiorite magmatism of the Sihla type (387±27 m.y.) and the Early Variscan age of leucocratic granitoids of the Vepor and the Ipel types (284±22 m.y.). Since the initial ratio of 87 Sr/ 86 Sr in granitoids of the Sihla type is 0.7054 and of the Vepor type 0.7060, it can be assumed that during the formation of the granitoids of veporides there was an increased supply of matter from the main source affecting genesis of granitoids. The results prove a polyphase character of the Variscan granitoids of Veporicum. (author)

  13. Geochemistry and Nd-Sr isotopic signatures of the Pensamiento Granitoid Complex, Rondonian-San Ignacio Province, eastern precambrian shield of Bolivia: petrogenetic constraints for a mesoproterozoic magmatic arc setting

    International Nuclear Information System (INIS)

    Matos, Ramiro; Teixeira, Wilson; Bettencourt, Jorge Silva; Geraldes, Mauro Cesar

    2009-01-01

    The Pensamiento Granitoid Complex (PGC), located in the northern part of the eastern Precambrian shield of Bolivia, is tectonically assigned to the Rondonian-San Ignacio Province (1.55 - 1.30 Ga) of the Amazonian Craton that is made up by Archean and Proterozoic provinces. The Proterozoic ones result from accretionary orogens that become successively younger south westwards, such as the Rondonian/San Ignacio (1.37 - 1.32 Ga) and the Sunsas orogenies (1.20 - 1.00 Ga). The PGC crops out mainly on the 'Paragua craton' bounded to the south by the Sunsas belt, and composed of granites and subvolcanic terms, and subordinately of syenites, granodiorites, tonalites, trondhjemites and diorites as orogenic representatives of the Rondonian/San Ignacio Orogeny, intrusive into the Lomas Maneches (ca. 1.68 Ga) and Chiquitania (ca. 1.7 Ga) complexes. Thirteen whole rock chemical analyses for major, trace and REE elements were performed for the La Junta, San Martin, Diamantina, Porvernir, San Cristobal, Piso Firme plutons of the PGC. The negative trends of MgO, Al 2 O 3 and CaO contents with increasing SiO 2 suggest that fractional crystallization played an important role in the petrogenesis of the investigated rocks. The data also indicate a mainly peraluminous, sub-alkaline to high-K calc-alkaline composition, and fractionated LREE/HREE patterns are consistent with a magmatic arc character for these plutons. SHRIMP U-Pb zircon ages of the La Junta and San Martin syn- to late-kinematic plutons are 1347 ± 21 Ma and 1373 ± 20 Ma respectively, and the Sm-Nd T DM model ages are between 1.9 to 2.0 Ga, while ε Nd(1330) values range from +1.8 to -4.3, respectively. In addition, the late- to post-kinematic Diamantina pluton yields SHRIMP U-Pb zircon age of 1340 ± 20 Ma, and variable Sm-Nd T DM model ages (1.6 to 1.9 Ga) and ε Nd(1330) values (+0.4 to -1.2) that are comparable with previous results found for other coeval plutons. The Porvenir, San Cristobal and Piso Firme plutons

  14. Petrogenesis of Luchuba and Wuchaba granitoids in western Qinling: geochronological and geochemical evidence

    Science.gov (United States)

    Kong, Juanjuan; Niu, Yaoling; Duan, Meng; Zhang, Yu; Hu, Yan; Li, Jiyong; Chen, Shuo

    2017-12-01

    The West Qinling Orogenic Belt (WQOB) is a major portion of the Qinling-Dabie-Sulu Orogen and holds essential information for understanding the prolonged evolution of the northeastern branch of the Paleo-Tethys in East Asia. This study focuses on the petrogenesis of granitoids from Luchuba and Wuchaba plutons in the WQOB. We obtained zircon U-Pb ages of 211 ± 1.4 Ma for the Luchuba pluton and 218.7 ± 1.3 Ma for the Wuchaba pluton, which are the same as the proposed timing of continental collision at ˜220 Ma. We thus interpret the granitoids to represent a magmatic response to the collision between the North China Craton (NCC) and the Yangtze Block (YB). The two plutons are metaluminous to weakly peraluminous I-type granitoids. Samples from the two plutons show strong light rare earth element (REEs) enrichment and weak heavy REE depletion, with varying negative Eu anomalies, which is most consistent with significant plagioclase fractionation although the possible effect of plagioclase as residual phase in the magma source region cannot be ruled out. In primitive mantle normalized multi-element variation diagrams, nearly all the samples show negative Nb, Ta, P and Ti anomalies and relative enrichment in Rb, Pb, U and K. These characteristics resemble those of the average continental crust. The Luchuba pluton has lower (87Sr/86Sr)i (0.7051 to 0.7104), higher ɛNd(t) (-8.11 to -5.73) and ɛHf(t) (-6.70 to -1.65) than mature continental crust ([87Sr/86Sr] i > 0.72, ɛNd(t) pluton also has lower (87Sr/86Sr)i (0.7069 to 0.7080), higher ɛNd(t) (-9.86 to -3.34) and ɛHf(t) (-5.69 to 1.58) than mature continental crust. We conclude that the Luchuba and Wuchaba granitoids in the WQOB are best explained as resulting from fractional crystallization with crustal assimilation of parental magmas derived from melting of Mianlue oceanic crust under amphibolite facies conditions during the initial stage of continental collision between the North China Craton and the Yangtze Block

  15. Geochemistry and Nd-Sr isotopic signatures of the Pensamiento Granitoid Complex, Rondonian-San Ignacio Province, eastern precambrian shield of Bolivia: petrogenetic constraints for a mesoproterozoic magmatic arc setting;Geoquimica e assinaturas Nd-Sr do Complexo Granitoide Pensamiento, provincia Rondoniana-San Ignacio, pre-cambriano de Bolivia Oriental: caracterizacao petrogenetica de um arco magmatico no mesoproterozoico

    Energy Technology Data Exchange (ETDEWEB)

    Matos, Ramiro, E-mail: rmatoss@igc.usp.b [Universidad Mayor de San Andre (UMSA), La Paz (Bolivia, Plurinational State of). Inst. de Investigaciones Geologicas y del Medio Ambiente; Teixeira, Wilson; Bettencourt, Jorge Silva, E-mail: wteixeir@usp.b, E-mail: jsbetten@usp.b [Universidade de Sao Paulo (IGC/USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica; Geraldes, Mauro Cesar, E-mail: geraldes@uerj.b [Universidade do Estado do Rio de Janeiro (FG/UERJ), RJ (Brazil). Faculdade de Geologia

    2009-07-01

    The Pensamiento Granitoid Complex (PGC), located in the northern part of the eastern Precambrian shield of Bolivia, is tectonically assigned to the Rondonian-San Ignacio Province (1.55 - 1.30 Ga) of the Amazonian Craton that is made up by Archean and Proterozoic provinces. The Proterozoic ones result from accretionary orogens that become successively younger south westwards, such as the Rondonian/San Ignacio (1.37 - 1.32 Ga) and the Sunsas orogenies (1.20 - 1.00 Ga). The PGC crops out mainly on the 'Paragua craton' bounded to the south by the Sunsas belt, and composed of granites and subvolcanic terms, and subordinately of syenites, granodiorites, tonalites, trondhjemites and diorites as orogenic representatives of the Rondonian/San Ignacio Orogeny, intrusive into the Lomas Maneches (ca. 1.68 Ga) and Chiquitania (ca. 1.7 Ga) complexes. Thirteen whole rock chemical analyses for major, trace and REE elements were performed for the La Junta, San Martin, Diamantina, Porvernir, San Cristobal, Piso Firme plutons of the PGC. The negative trends of MgO, Al{sub 2}O{sub 3} and CaO contents with increasing SiO{sub 2} suggest that fractional crystallization played an important role in the petrogenesis of the investigated rocks. The data also indicate a mainly peraluminous, sub-alkaline to high-K calc-alkaline composition, and fractionated LREE/HREE patterns are consistent with a magmatic arc character for these plutons. SHRIMP U-Pb zircon ages of the La Junta and San Martin syn- to late-kinematic plutons are 1347 {+-} 21 Ma and 1373 {+-} 20 Ma respectively, and the Sm-Nd T{sub DM} model ages are between 1.9 to 2.0 Ga, while {epsilon}{sub Nd(1330)} values range from +1.8 to -4.3, respectively. In addition, the late- to post-kinematic Diamantina pluton yields SHRIMP U-Pb zircon age of 1340 {+-} 20 Ma, and variable Sm-Nd T{sub DM} model ages (1.6 to 1.9 Ga) and {epsilon}{sub Nd(1330)} values (+0.4 to -1.2) that are comparable with previous results found for other coeval

  16. Early Permian intrusions of the Alai range: Understanding tectonic settings of Hercynian post-collisional magmatism in the South Tien Shan, Kyrgyzstan

    Science.gov (United States)

    Konopelko, D.; Wilde, S. A.; Seltmann, R.; Romer, R. L.; Biske, Yu. S.

    2018-03-01

    We present geochemical and Sr-Nd-Pb-Hf isotope data as well as the results of single grain U-Pb zircon dating for ten granitoid and alkaline intrusions of the Alai segment of Kyrgyz South Tien Shan (STS). The intrusions comprise four geochemically contrasting series or suites, including (1) I-type and (2) shoshonitic granitoids, (3) peraluminous granitoids including S-type leucogranites and (4) alkaline rocks and carbonatites, closely associated in space. New geochronological data indicate that these diverse magmatic series of the Alai segment formed in a post-collisional setting. Five single grain U-Pb zircon ages in the range 287-281 Ma, in combination with published ages, define the main post-collisional magmatic pulse at 290-280 Ma, which is similar to ages of post-collisional intrusions elsewhere in the STS. An age of 287 ± 4 Ma, obtained for peraluminous graniodiorite of the Liayliak massif, emplaced in amphibolite-facies metamorphic rocks of the Zeravshan-Alai block, is indistinguishable from ca. 290 Ma age of peraluminous granitoids emplaced coevally with Barrovian-type metamorphism in the Garm block, located ca. 40 km south-west of the research area. The Sr-Nd-Pb-Hf isotopic compositions of the studied intrusions are consistent with the reworking of crustal material with 1.6-1.1 Ga average crustal residence times, indicating the formation of the Alai segment on a continental basement with Mesoproterozoic or older crust. The pattern of post-collisional magmatism in the Alai segment, characterized by emplacement of I-type and shoshoninitic granitoids in combination with coeval Barrovian-type metamorphism, is markedly different from the pattern of post-collisional magmatism in the adjacent Kokshaal segment of the STS with predominant A-type granitoids that formed on a former passive margin of the Tarim Craton. We suggest that during the middle-late Carboniferous the Alai segment probably comprised a microcontinent with Precambrian basement located between

  17. Petrology, geochronology, geochemistry and petrogenesis of Bajestan granitoids, North of Ferdows, Khorasan Razvi Province

    Directory of Open Access Journals (Sweden)

    Reyhaneh Ahmadirouhani

    2017-02-01

    -Pb dating results, there are two magmatism phases (Upper Cretaceous and Oligocene in the area which have not reported in the north of Lut Block yet. During the Upper Cretaceous, three localities of granitoids are reported, excluding Bajestan: Bazman (initial 87Sr/86Sr =0.7056 is located in the southern part of the Lut Block, Gazu (initial 87Sr/86Sr =0.7045 is located near the Nayband fault in the Tabas Block and Kaje is located in Ferdows (initial 87Sr/86Sr =0.7061-0.7080. All of these granitoids were formed due to the subduction zone and their magma (I type originated from mantle. However, granitoids in Bajestan with the initial 87Sr/86Sr =0.711-0.718 were formed during the continental collision while their magma was originated from the continental crust. In addition, the Middle Jurassic granitoids in the Lut Block (Shah Kuh, KlatehAhani and SurkhKuh with the origin of continental crustal magma have an initial 87Sr/86Sr = 0.7068-0.7081. That is, the continental crust from which Bajestan granitoid magma is originated, is different from the other parts of the Lut Block due to very high (87Sr/86Sr. This indicates that Bajestan perhaps joined the Lut Block after the Upper Cretaceous collision. In addition to Bajestan, the Oligocene granitoids in the Lut block are reported in the Chah-Shaljami, Dehsalm, Mahoor and Khunik areas. Except Bajestan, all of these granitoids were formed in the subduction zone and their magma is I type. Mineralization in Chah-shaljami, Dehsalm, and Mahoor is related to the porphyric system, whereas no mineralization in Khunik and Bajestan Granitoids has been reported yet. References Ahmadirouhani, R., Karimpour, M.H., Rahimi, B. and Malekzadeh Shafaroudi, A., 2015. Enhance of alteration zones and lineation in the east of Bajestan using SPOT, ASTER, ETM+ and Geophysics data. Scientific Quaternary Journal Geosciences, 24: 253-262. Karimpour, M.H., Malekzadeh-Shafaroudi. A., Stern. C.R. and Hidarian, M.R., 2008. Using ETM+ and airborne geophysics data to

  18. Petrology of Oligocene Ghaleh Yaghmesh granitoids in the west of Yazd province

    Directory of Open Access Journals (Sweden)

    Bahareh Fazeli

    2017-02-01

    calculation of amphibole minerals by Cameca SX50 microprobe device at the Oklahomacity University (Norman - USA. Results The studied plutonic rocks are dominated by plagioclase, orthoclase, quartz, amphibole (magnesio hornblende and actinolite hornblende, biotite, and pyroxene. Zircon, apatite, sphene, tourmaline and opaque minerals as the common accessory and chlorite, epidote and calcite are the secondary minerals. On the base of petrographic observation as well as mineral-chemistry and geochemical data, the granitoid massif is classified as I-type (magnetite series, calc – alkaline and metaluminous composition. The rocks under discussion are characterized by the high level of LILE (Ba, Sr, K and Cs and the negative anomaly of HFS elements (Ti, Nb, Zr and Y indicating the subduction related magmatism. The Ghaleh Yaghmesh granitoids are cogenetic and possibly developed in subduction zone related to active continental margin calc – alkaline volcanic arcs. Mixing process of acidic and basic magmas is likely involved in generation of the rocks being studied. Discussion The parent magma probably formed by partial melting of amphibolites with some sedimentary materials. Fractional crystallization of melt in the higher levels of crust gave rise to various rock types. Mantle – derived basaltic magmas emplaced into the lower crust most likely provide heat for partial melting Clemens et al., 2011(. Field evidences such as the presence of mafic microgranular enclaves having sharp boundaries with the host rocks (Zorpi et al., 1989; Didier, 1991, petrographic observations (similar mineralogy of MME and the host rock (Didier, 1991; Didier and Barbarin, 1991, the occurrence of accicular apatite (Zorpi et al., 1989; Didier, 1991, the corroded margin of amphibole and plagioclase (Zorpi et al., 1989; Shelley, 1993 and the abundance of biotite and hornblende in MME compared to the host rock (Ellis and Thompson, 1986 and geochemical criteria (range of silica from 51.35 to 70.78 indicate

  19. Chronology of neoproterozoic-cambrian granitic magmatism in the Aracuai Belt, Eastern Brazil, based on single zircon evaporating dating

    International Nuclear Information System (INIS)

    Noce, Carlos Mauricio; Soares, Antonio Carlos Pedrosa; Macambira, Moacir Jose Buenano

    2000-01-01

    Granitic magmatism related to the orogenic stages of the Aracuai Belt took place at 595-575 Ma, and are represented by two distinct suites. One is composed of I-type granitoids and includes the following plutons: Brasilandia (595±3 Ma), Sao Vitor (576±4 Ma) and Guarataia (574± 2 Ma). The other suite comprises S-type granites like the Ataleia (591±5 Ma) and Wolf (582±5 Ma) plutons. After a long period of magnetic quiescence, a batholith composed of the Caladao granite and Padre Paraiso charnockite intruded at 519±2 Ma. This magmatic episode is probably associated to the collapse of the orogen. (author)

  20. Granitoids of the Dry Valleys area, southern Victoria Land : geochemistry and evolution along the early Paleozoic Antarctic Craton margin

    International Nuclear Information System (INIS)

    Allibone, A.H.; Cox, S.C.; Smillie, R.W.

    1993-01-01

    Field relationships and geochemistry indicate granitoid plutons of the Dry Valleys area comprise at least three petrogenetically distinct suites. The older Dry Valleys 1a (DV1a) suite, comprising the Bonney, Catspaw, Denton, Cavendish, and Wheeler Plutons and hornblende-biotite orthogneisses, and Dry Valleys 1b (DV1b) suite, comprising the Hedley, Valhalla, St Johns, Dun, Calkin, and Suess Plutons, biotite granitoid dikes and biotite orthogneisses, were emplaced before prominent swarms of Vanda mafic and felsic dikes. Both the DV1a and DV1b suites are time transgressive, with older intrusions in each suite being emplaced during the later stages of deformation of the Koettlitz Group. Younger granitoids that postdate the majority of the Vanda dikes include: the Dry Valleys 2 (DV2) suite, comprising the Pearse and Nibelungen Plutons plus several smaller, unnamed plugs; and the Harker, Swinford, Orestes, and Brownworth Plutons with identical field relationships and enclaves but distinct chemistries. Chemical characteristics and limited Rb-Sr isotopic dating indicate plutonism before c. 500 Ma was dominated by the Cordilleran I-type DV1a suite, inferred to have developed during melting above a west-dipping subduction zone along the Antarctic Craton margin. The chemical characteristics of the DV1b suite indicate large-scale melting of a quartzo-feldspathic protolith lacking residual plagioclase, but containing refractory garnet. Potential DV1b suite source rocks include metamorphosed immature sediments, possibly underplated along the subduction zone associated with DV1a magmatism, or older granitoid orthogneisses. Major DV1b plutonism at 490 Ma marks the end of subduction-related plutonism in southern Victoria Land. Younger DV2 alkali-calcic, Caledonian I-type plutonism is inferred to have formed in response to uplift and extension between 480 and 455 Ma. Lack of DV2 suite correlatives and Vanda mafic and felsic dikes in northern Victoria Land suggests significantly

  1. SHRIMP zircon dating of granitoids from Myanmar: constraints on the tectonic evolution of Southeast Asia

    International Nuclear Information System (INIS)

    Barley, M.E.; Pickard, A.L.; Zaw, K.; University of Tasmania, Hobart, TAS

    1999-01-01

    Full text: Situated south of the eastern syntaxis of the Himalayas, Myanmar occupies a key position in the tectonic evolution of Southeast Asia. However, there is almost no modern geochronology for this region. In this contribution we present new SHRIMP zircon dates for granitoids from the Shan Scarp (Mogok Metamorphic Belt), Taninthayi (Tenasserim) Region in the Myeik (Mergui) Archipelago and Central Valley (Western Myanmar) regions of Myanmar. The oldest ages obtained were from Jurassic granitoids, gneisses and amphibolites interlayered with marbles that were metamorphosed and deformed during the Eocene-Oligiocene and Miocene in the Mogok Metamorphic Belt. The occurrence of mid-Jurassic metamorphosed igneous rocks in the Mogok Metamorphic Belt is similar to that in the Hunza Karakoram and confirms interpretations that the southern margin of Asia became an Andean-type convergent margin at that time. Ages between 120 and 80 Ma for l-type granitoids intruding the Mogok Metamorphic Belt, Myeik Archipelago and Western Myanmar confirm that an up to 200km wide mid Cretaceous magmatic belt extended along the Eurasian margin from Tibet to Sumatra. Fractionated l-Type granitoids, that locally host Sn-W mineralisation, were emplaced in the Myeik Archipelago (and adjacent Thailand) in the latest Cretaceous to Early Eocene (80 to 50 Ma). These granitoids formed a wide convergent margin magmatic belt as the Indian plate rapidly approached Eurasia. Deformation and high-grade metamorphism occurred in the Mogok Metamorphic Belt during the Eocene-Oligiocene as the collision between India and Eurasia initiated crustal thickening prior to extrusion, or rotation, of Indochina and northward movement of Western Myanmar. Arc magmatism continued in Western Myanmar with emplacement of granitoids in the Central Valley. Deformation, extensional uplift and further granitoid magmatism occurred in the Mogok Metamorphic Belt during the Early Miocene northward movement of Western Myanmar

  2. Petrography, geochemistry and tectonic setting of Rigi granitoid body (east of Lut Block, Central Iran)

    International Nuclear Information System (INIS)

    Ghonjalipour, R.; Biabangard, H.; Ahmadi, A.

    2016-01-01

    The Rigi Granitoid Mountain is located in 5 Km West of Dehsalm and 85 Km West of Nehbandan city, southeast of Birjand province and east of Lut Block. This granitoid with Eocene-Oligocene age was penetrated into sedimentary rocks (shale, limestone and sandstone) and changes theses rocks to skarn, hornfels and calcsilicate rocks. This granitoid consist of granodiorite, quartz monzonite and syenogranite with plagioclase, orthose, biotite, hornblende and quartz minerals. Sericite, chlorite, and Magnetite are secondary mineral in these rocks. Geochemical properties this pluton showes that it subalkaline and has metaluminous. Geochemical diagrams and presence of hornblende mineral in this pluton shows that belong to I-type granite. The rocks in granitoid pluton are enrichment LREE compare to HREE, high contents of LILE relative to HFSE and negative anomalies of Nb, Ti and P show it granitoid related to subduction zone. Also, tectonomagmatic diagrams improve that this pluton has belong to active continental margin.

  3. Metasedimentary, granitoid, and gabbroic rocks from central Stewart Island, New Zealand

    International Nuclear Information System (INIS)

    Allibone, A.H.; Tulloch, A.J.

    1997-01-01

    A NNE-NE trending strip, 3-8 km wide, extending from the Freshwater valley across Mt Rakeahua Table Hill, and Mt Allen to the northern end or the Tin Range was mapped at a scale of 1:12,500 to locate and investigate the boundary between the Median Tectonic Zone (MTZ) and Western Province on Stewart Island. A NNE-trending fault, herein termed the Escarpment Fault, separates predominantly ductily deformed rocks on its south side from essentially undeformed rocks to the north. North of the Escarpment Fault, a small (2-3 km 2 ) pluton of alkali-feldspar granite (Freds Camp) intruded gabbroic rocks tentatively considered to be associated with gabbro/anorthosite/diorite of the Rakeahua pluton, centred on Mt Rakeahua. Both units were subsequently intruded by I-type biotite granite of the South West Arm pluton. South of the Escarpment Fault the oldest intrusions are biotite tonalite-granite orthogneisses (Ridge and Table Hill plutons) intercalated with the sillimanite-cordierite-bearing Pegasus Group metasedimentary rocks, considered to represent the Western Province. They contain titanite, allanite, and magmatic epidote-bearing assemblages, implying affinities with I-type granitoids. These older granitoids have been affected by at least three phases of ductile deformation. Immediately south of the Escarpment Fault, the Escarpment pluton (hornblende, biotite, quartz, monzonite-quartz monzodiorite) only exhibit effects of the third phase of deformation. Minor gabbroic intrusives concordant with the S 3 fabric intrude the Pegasus Group and intercalated orthogneisses. Plutons of two-mica, garnet ±cordierite granite (Blaikies and Knob) and younger biotite-titanite-magmatic epidote granite (Campsite) cut fabrics associated with the third phase of ductile deformation. Preliminary U-Pb dating indicate Devonian-Carboniferous, Jurassic, and Early Cretaceous emplacement ages for Ridge Orthogneiss, Freds Camp pluton, South West Arm pluton, and Blaikies pluton, respectively. South

  4. A petrochemical investigation of a group of granitoids in the Cnydas area, West of Upington

    International Nuclear Information System (INIS)

    Jankowitz, J.A.C.

    1981-01-01

    Detailed mapping in the eastern Namaqualand Metamorphic Complex west of Upington, indicates that the Cnydas batholith can be divided into ten different granitoidal phases. The classification is based on the intrusive field relationships supported by variation in mineralogy, texture, petrography and geochemistry. A differentiation sequence from granodiorite through mesocratic granite to leucogranite is proposed on the basis of geochemical evidence. The chemistry and petrography suggests an I-type origin for these granitoids

  5. The Rb/Sr ages for granitoids of the Middle Chukotka: a new approach to the geological history of the region

    International Nuclear Information System (INIS)

    Efremov, S.V.; Kozlov, V.D.; Sandimirova, G.P.

    2000-01-01

    For studying the history of geological evolution of the Middle Chukotka in the Mesozoic by the method of Rb-Sr dating the age of granitoids in the region was determined. It was ascertained that the granitoids have different genetic nature, their formation involving the most intensive tectonic restructuring. Magmatism was manifested in two stages. Formation of the first stage granitoids (126-144 mln. years) relates to orogenesis, while that of the second stage granitoids (∼ 80 mln. years) - to the process of the Chukotka folded region activation [ru

  6. Two-phase southward subduction of the Mongol-Okhotsk oceanic plate constrained by Permian-Jurassic granitoids in the Erguna and Xing'an massifs (NE China)

    Science.gov (United States)

    Liu, Huichuan; Li, Yinglei; He, Hongyun; Huangfu, Pengpeng; Liu, Yongzheng

    2018-04-01

    Geodynamics of the Mongol-Okhotsk oceanic plate southward subduction are still pending problems. This paper presents new zircon LA-ICP-MS U-Pb age and whole-rock geochemical data for the middle Permian to Middle Jurassic granitoids in the western Erguna and central Xing'an massifs. 267-264 Ma, 241 Ma and 173 Ma I-type granites, and 216 Ma A-type granites were identified in the Erguna and Xing'an massifs (NE China). The I-type granites were produced by partial melting of the lower mafic crust. The 216 Ma A-type granites were derived from partial melting of crustal materials with tonalitic to granodioritic compositions. The 267-264 Ma and 241 Ma I-type granites were generated in an Andean-type arc setting, wheras the 216 Ma A-type and 173 Ma granites were formed in supra subduction extensional setting. We summarized previous age data of the middle Permian to Middle Jurassic magmtaic rocks in the Erguna and Xing'an Massifs and identified two isolated phases of magmatic activity including the ca. 267-225 Ma and ca. 215-165 Ma periods, with a significant magmatic gap at ca. 225-215 Ma. These middle Permian to Middle Jurassic magmatic rocks are closely related to the southward subduction of the Mongol-Okhotsk ocean. A two-stage tectonic evolutionary model was proposed to account for these geological observations in the Erguna and Xing'an massifs, involving Permian to Middle Triassic continuous southward subduction of the Mongol-Okhotsk oceanic plate and Late Triassic to Jurassic slab-rollback and supra subduction extension.

  7. Petrology and isotope systematics of magma mushes: some porphyritic granitoids of northeastern Brazil

    International Nuclear Information System (INIS)

    McMurry, J.; Long, L.E.; Sial, A.N.

    1987-01-01

    More than 80 coarsely porphyritic granitoid plutons with K-feldspar megacrysts (Itaporanga-type granites) intrude metamorphic rocks of Northeastern Brazil. Textural evidence for filter pressing and flow foliation indicates that these bodies were emplaced as viscous, crystal-laden mushes. A representative Itaporanga-type pluton, the Monte das Gameleiras intrusion, consists of a variety of rock types with SiO 2 ranging from 49.5 to 71.6 weight percent. Chemically and petrographically, this hornblende-bearing pluton has I-type characteristics with some S-type affinities. Whole-rock oxygen isotope data are in keeping with the distribution of δO 18 , for unaltered granitic rocks. Similarly, REE data suggest a single magmatic process, at least for the more felsic rock types, without post-intrusive effects. A 5-point, whole-rock Rb-Sr isochron for the Monte das Gameleiras pluton gives t = 511 ± 26 Ma andan initial, 87 Sr/ 86 Sr = 0.7099 ± 0.0004. This is contrasted with disparate ages calculated from texturally similar bodies such as the Fazenda Nova pluton, for which a 5-point whole-rock isochron gives t = 630 ± 24 Ma with initial 87 Sr/ 86 Sr = 0.7065 ± 0.0005, and the type locality Itaporanga pluton, for which a 6-point isochron gives t= 625 ± 22 Ma. (author) [pt

  8. Understanding the evolution of S- and I-type granitic plutons through analysis of apatite.

    Science.gov (United States)

    Hess, B. L.; Fiege, A.; Tailby, N.

    2017-12-01

    The major and trace element composition of apatites from the Lachlan fold belt (LFB) S- and I-type granitoids (Australia) and the Central French Massif (CFM) S-type leucogranites (France) were analyzed to investigate their compositional and redox variation. Apatite is a common accessory mineral in magmatic systems that can incorporate a variety of trace elements, including the polyvalent elements sulfur (S), iron (Fe), and manganese (Mn). It was recently discovered that apatite can incorporate three oxidation states of S (S6+, S4+, S2-) into its structure as a function of oxygen fugacity [1]. However, the oxidation states of Mn and Fe in apatite are essentially unknown (2+ and/or 3+). In this study, we collected many electron probe line transects across apatites in several different host phases from a variety of S- and I-type plutons. The F-H-Cl contents of the S- and I-type LFB samples were similar ( 2.9 wt% F, 0.4 wt% Cl, 0.5 wt% OH). The CFM S-types contained virtually no Cl and ranged from near-endmember OH-apatite to near-endmember F-apatite. The apatites of all studied the S- and I-type plutons are characterized by similar ranges of Fe content (X-ray absorption near-edge structure (XANES) spectroscopy. The spectra show variability in S oxidation states ranging from mostly sulfate down to nearly equal S6+/S2- ratios, indicating redox variations during apatite formation. The S-type Mn + Fe content plots in a 1:1 ratio against calcium (Ca) in atoms per formula unit, while the I-type apatites have too low Mn and Fe to show a clear trend. Thus, divalent Mn and Fe probably replace Ca2+ in the S-types' apatite structure, while the incorporation of trivalent Mn or Fe in apatite is rather unlikely. We suggest that Mn and Fe contents in apatite may become a useful tracer of melt evolution once the distributions coefficients are experimentally calibrated. [1] Konecke et al. (2017), Am Mineral

  9. Geochemical characteristics of Proterozoic granite magmatism from Southern Granulite Terrain, India: Implications for Gondwana

    Science.gov (United States)

    Yellappa, T.; Rao, J. Mallikharjuna

    2018-03-01

    Granitoid intrusions occur widely in the Southern Granulite Terrain (SGT) of India, particularly within the Cauvery Suture Zone (CSZ), which is considered as the trace of the Neoproterozoic Mozambique ocean closure. Here we present the petrological and geochemical features of 19 granite plutons across the three major tectonic blocks of the terrain. Our data show a wide variation in the compositions of these intrusions from alkali feldspathic syenite to granite. The whole rock geochemistry of these intrusions displays higher concentrations of SiO2, FeO*, K2O, Ba, Zr, Th, LREE and low MgO, Na2O, Ti, P, Nb, Y and HREE's. The granitoids are metaluminous to slightly peraluminous in nature revealing both I-type and A-type origin. In tectonic discrimination plots, the plutons dominantly show volcanic arc and syn-collisional as well as post-collisional affinity. Based on the available age data together with geochemical constrains, we demonstrate that the granitic magmatism in the centre and south of the terrain is mostly associated with the Neoproterozoic subduction-collision-accretion-orogeny, followed by extensional mechanism of Gondwana tectonics events. Similar widespread granitic activity has also been documented in the Arabian Nubian shield, Madagascar, Sri Lanka and Antarctica, providing similarities for the reconstruction of the crustal fragments of Gondwana supercontinent followed by Pan-African orogeny.

  10. Cyclic formation and stabilization of Archean lithosphere by accretionary orogenesis: Constraints from TTG and potassic granitoids, North China Craton

    Science.gov (United States)

    Wang, Wei; Cawood, Peter A.; Liu, Shuwen; Guo, Rongrong; Bai, Xiang; Wang, Kang

    2017-09-01

    Accretionary orogens are major sites of modern continental growth, yet their role in the development of Archean continental crust remains enigmatic. Diverse granitoid suites from tonalite-trondhjemite-granodiorite (TTG) to potassic granitoids appeared during late Archean, representing a period of major continental formation and stabilization. In this study, whole-rock geochemical and zircon U-Pb and Lu-Hf isotopic data are reported for Neoarchean granitoid gneisses from the Northern Liaoning Terrane, northeastern North China Craton (NCC). Older granitoid gneisses ( 2592-2537 Ma) define three magmatic zones migrating from southeast to northwest, each showing a common magmatic evolution from high-pressure TTGs to medium-/low-pressure TTGs and potassic granitoids. They have depleted zircon ƐHf(t) of +0.5 to +8.7. Younger 2529-2503 Ma potassic granitoids and TTGs occur throughout the terrane, which are marked by variable zircon ƐHf(t) of -4.7 to +8.1, and are coeval with regional high-grade metamorphism. Petrogenetic modeling and changing Sr/Y and (La/Yb)N of the granitoids suggest that the crust experienced episodic thickening and thinning and became progressively evolved through development of potassic granitoids and sedimentary successions. The metavolcanic basement to the granitoids display tholeiitic to calc-alkaline affinities, together with the top-to-the-northwest thrusting and associated volcanogenic massive sulfide-type Cu-Zn deposits, suggesting cyclic crustal formation of Northern Liaoning within an accretionary orogen with a SE-dipping subduction polarity. Cyclic crustal thickening and thinning is related to tectonic switching from advancing to retreating relations between the downgoing and overriding plate. After 2530 Ma, this accretionary system accreted to the ancient continental nucleus of NCC (Anshan-Benxi Terrane), signifying final lithosphere stabilization.

  11. Early Cretaceous I-type granites in the Tengchong terrane: New constraints on the late Mesozoic tectonic evolution of southwestern China

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    Yi Fang

    2018-03-01

    Full Text Available The Early Cretaceous granitoids that are widespread in the Tengchong terrane of Southwest China play a critical role in understanding the tectonic framework associated with the Tethyan oceans. In this study, we present a detailed description of zircon U–Pb ages, whole-rock geochemistry and Hf isotopes for the Laoxiangkeng pluton in the eastern Tengchong terrane and elucidate their petrogenesis and geodynamic implications. Zircon U–Pb dating of the Laoxiangkeng pluton yields ages of 114 ± 1 Ma and 115 ± 1 Ma, which imply an Early Cretaceous magmatic event. The Laoxiangkeng pluton enriched in Si and Na, is calc-alkaline and metaluminous, and has the characteristics of highly fractionated I-type granites. Zircons from the pluton have calculated εHf(t values of −12.7 to −3.7 and two-stage model ages of 1327–1974 Ma, respectively, indicating a mixed source of partial melting of Paleo-Neoproterozoic crust-derived compositions with some inputs of mantle-derived magmas. By integrating all available data for the regional tectonic evolution of the eastern Tethys tectonic domain, we conclude that the Early Cretaceous magmatism in the Tengchong terrane was produced by the northeastward subduction of the Meso-Tethyan Bangong–Nujiang Ocean.

  12. U-Pb SHRIMP data and geochemical characterization of granitoids intruded along the Coxixola shear zone, Provincia Borborema, NE Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Guimaraes, Ignez de Pinho; Silva Filho, Adejardo Francisco da; Silva, Francis M.J.V. da, E-mail: ignez@ufpe.br [Universidade Federal de Pernanmbuco (UFPE), Recife, PE (Brazil). Dept. de Geologia; Armstrong, Richard [Australian National University (Australia)

    2011-07-01

    A large volume of granitic magmatism associated with large scale shear zone and metamorphism under high-T amphibolite facies conditions characterize the Brasiliano Orogeny in the Borborema Province, NE Brazil. Granitoids from two plutons and later dykes intruded along the Coxixola shear zone show distinct crystallization ages and geochemical signature. The oldest granitoids (618 ± 5 Ma), Serra de Inacio Pereira Pluton are coeval with the peak of regional metamorphism and they were probably originated by melting of a paleoproterozoic source. The granitoids from the Serra do Marinho Pluton show crystallization age of 563 ± 4 Ma and geochemical signature of post-collisional A-type granites. The later dykes have crystallization age of 526 ± 7 Ma, geochemical signature of A-type granitoids. (author)

  13. Ams Fabric and Deformation of The Jawornik Granitoids In The Zloty Stok - Skrzynka Deformation Zone (sudetes, SW Poland)- Preliminary Interpretations.

    Science.gov (United States)

    Werner, T.; Bialek, D.

    Jawornik granitoids comprise the NE-SW trending sequences of the 1cm up to 1 km thick granitoid veins surrounded by schists and gneisses of the Zloty Stok - Skrzynka deformation zone in Eastern Sudetes (SW Poland). According to conflicting theories granitoids are of magmatic origin or were formed from blastomylonitic rocks that underwent multiphase deformation. AMS studies were performed for the 53 sites lo- calized within granitoid veins and within the surrounding gneisses. AMS foliations for granitoid veins of various thickness as well as for gneisses dip at moderate to steep an- gles to N-NW. AMS lineations in the surrounding gneisses plunge subhorizontally to NE-SW that reflects the regional NE-SW shearing components. Magnetic lineations for sites within wider veins of granitoids plunge at low angles (mostly from S to W) but with more varying trends between sites. Mezoscopic tectonic foliations are record- able only in 50% of sites. They show good correlation with AMS planar fabric on the site scale. The uniformity of AMS fabric on the site scale and high AMS anisotropy within all sites (P of 1.05-1.30, T of 0.3-0.6 on average) suggest syntectonic gener- ation of granitoids. Further interpretations of the AMS and tectonic fabrics will be performed when microtectonic studies and chemical analyses results are available.

  14. Petrography and geochronology of the Sao Jose dos Quatro Marcos granitoids, southwestern Mato Grosso, Brazil

    International Nuclear Information System (INIS)

    Carneiro, M.A.; Ulbrich, H.H.G.J.; Kawashita, K.

    1989-01-01

    An area of about 400Km 2 was mapped in the region of Sao Jose dos Quatro Marcos, southwestern State of Mato Grosso, western Brazil. Various granitoid rocks were recognized, intrusive into basement gneisses, and mapped as two distinct units, one of massive late granitoids (mostly 3a and 3b granites) and one of foliated granitoids, with oriented mafic minerals, consisting mainly of tonalites and, to a lesser degree, of granodiorites. The sequence of intrusion is from tonalites to granodiorites to late granites. Magmatic textures are usually preserved in the rocks, with the exception of some clearly recrystallized samples. Field aspects, as well as petrography and mineralogy, suggest a genetic relationship between the various granitoid types, showing overall features commonly cited as typical of 'I' lineages. A Rb/Sr whole-rock isochron obtained from 3b granites (six points) shows an age of 1,472 +- 19 Ma, and Sr 87 86 initial ratio of 0.7037 +- 0.0004; a nine point isochron (adding two tonalites and one granodiorite) yelds similar results (age of 1,505 +- 20 Ma, initial ratio of 0.7029+- 0.0003). The obtained ages confirm the existence of a thermal-magmatic event at about 1,500 Ma at the southern border of the Amazon Craton. (author) [pt

  15. Banatitic magmatic and metallogenetic belt: metallogeny of the Romanian Carpathians segment

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    S̡erban-Nicolae Vlad

    2003-04-01

    Full Text Available The Romanian Carpathians sector of the Late Cretaceous Banatitic Magmatic and Metallogenetic belt (BMMB contains 1 plutons and volcano-plutonic complexes, i. e. calc-alkaline, I-type granitoids, with related ores; 2 shoshonitic plutons that lack economic interest. Two provinces have been delineated: the Apuseni Mts. Province in the North and the Western South Carpathians in the South. Apuseni Mts. Province is a non-porphyry environment related to more evolved (granodioritic-granitic magmatism. It is subdivided into three zones: Vlădeasa (Pb-Zn ores of restricted metallogenetic potential; Gilău-Bihor (Fe, Bi, Mo, Cu, W, Au, Ni, Co, Pb, Zn, Ag, U, B ores / conspicuous peri-batholitic arrangement and South Apuseni (only one minor Fe-skarn occurrence. Western South Carpathians Province occurs in Romania and extends in Eastern Serbia. It is subdivided into South Banat Mts.–Timok Zone (SBTZ and Poiana Ruscă Mts.– North Banat Mts.– Ridanj-Krepoljin Zone (PR-NB-RKZ. SBTZ is a typical porphyry environment of high metallogenetic potential (Cu, Au, Pb, Zn, while PR-NB-RKZ is a non-porphyry environment with small to medium size Pb, Zn, Fe, Cu deposits/prospects exhibiting commonly a peri-plutonic zoning. The metallogenetic model of the Romanian Carpathians segment of BMMB is conceived based on correlating magma composition/level of emplacement and ore types.

  16. U-Pb zircon geochronology, Sr-Nd isotope geochemistry, and petrogenesis of oxidant granitoids at Keybarkuh, southwest of Khaf

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    Ehsan Salati

    2012-10-01

    Full Text Available Keybarkuh area is located 70 km southwest of Khaf, Khorasan Razavi province. The study area is situated in northeastern Lut block. The rock units in the area are Paleozoic metamorphic rocks and Cretaceous to Tertiary subvolcanic intrusions intruded as dike, stock and batholith; their composition varies from granite to diorite. Based on magnetic susceptibility, the intrusive rocks are divided into oxidant and reduced series. In this study, the oxidant intrusions are discussed. These intrusions are mostly high-K to shoshonitic and also meta-aluminous type. Their magma formed in subduction magmatic arc and they belong to I-type granitoid series. Enrichment of Large Ion Lithophile Elements (LILE such as Rb, Cs, K, Ba, and Th relative to High Field Stength Elements (HFSE such as Nb, Zr, and Ti supported the idea. Enrichment of Light Rare Earth Elements (LREE and depletion of Heavy Rare Earth Elements (HREE are also typical of subduction magmatism. Negative anomalies of Eu/Eu* can be attributed to the presence of residual plagioclase in a mantle source and contamination of magma by reduced continental crust. The amount of Nb > 11 ppm, lower ratio of Zr/Nb 0.706, initial 143Nd/144Nd (> 0.512 and εNd (< -3.5 indicate that magma contaminated by reduced continental crust. Hornblende biotite granodiorite porphyry dated using U-Pb zircon geochronology at 43.44 Ma (Middle Eocene. Based on calculated TDM, magma derived from ancient slab with 820 Ma age in the Keybarkuh area, was affected by the highest continental crust contamination during its ascent.

  17. Episodic melting and magmatic recycling along 50 Ma in the Variscan belt linked to the orogenic evolution in NW Iberia

    Science.gov (United States)

    Gutiérrez-Alonso, G.; López-Carmona, A.; García Acera, G.; Martín Garro, J.; Fernández-Suárez, J.; Gärtner, A.; Hofmann, M.

    2017-12-01

    The advent of a large amount of more precise U-Pb age data on Variscan granitoids from NW Iberia in recent years has provided a more focused picture of the magmatic history of the Western European Variscan belt (WEVB). Based on these data, three main pulses of magmatic activity seem to be well established.

  18. Gold contents of sulfide minerals in granitoids from southwestern New Brunswick, Canada

    Science.gov (United States)

    Yang, Xue-Ming; Lentz, David R.; Sylvester, Paul J.

    2006-07-01

    The abundance of gold and selected trace elements in magmatic sulfide and rock-forming minerals from Silurian-Devonian granitoids in southwestern New Brunswick were quantitatively analyzed by laser-ablation inductively coupled plasma mass-spectrometry. Gold is mainly hosted in sulfide minerals (i.e., chalcopyrite, pyrrhotite, and pyrite), in some cases perhaps as submicron inclusions (nanonuggets). Gold is below detection (caca % qGTbGaaeyzaiaabYgacaqG0baaaOGaeyypa0JaaGymaiaaiwdacaaI % WaGaeyySaeRaaGioaiaaiodacaGGSaGaaeiiaiaabggacaqGUbGaae % izaiaabccacaWGebWaa0baaSqaaiaabgeacaqG1baabaGaaeiCaiaa % bMhacaqGVaGaaeyBaiaabwgacaqGSbGaaeiDaaaakiabg2da9iaaio % dacaaI2aGaaGOmaiabgglaXkaaiMdacaaI2aaaaa!6E8F! D^{{{text{cpy/melt}}}}_{{{text{Au}}}}= 948 ± 269,{text{ }}D^{{{text{po/melt}}}}_{{{text{Au}}}} = 150 ± 83,{text{ and }}D^{{{text{py/melt}}}}_{{{text{Au}}}} = 362 ± 96. This result suggests that gold behavior in the granitoid systems is controlled by the conditions of sulfur saturation during magmatic evolution; the threshold of physiochemical conditions for sulfur saturation in the melts is a key factor affecting gold activity. Gold behaves incompatibly prior to the formation of sulfide liquids or minerals, but it becomes compatible at their appearance. Gold would be enriched in sulfur-undersaturated granitoid magmas during fractionation, partitioning into evolved magmatic fluids and favoring the formation of intrusion-related gold deposits. However, gold becomes depleted in residual melts if these melts become sulfur-saturated during differentiation, leading to gold precipitation in the early sulfide phases of a granitoid suite. Late-stage Cl-bearing magmatic-hydrothermal fluids with low pH and relatively high oxidation state derived from either progressively cooling magmas at depth or convective circulation of meteoric water buffered by reduced carbon-bearing sediments, may scavenge gold from early sulfide minerals. If a significant amount of gold produced in this

  19. Magmatic tritium

    International Nuclear Information System (INIS)

    Goff, F.; Aams, A.I.; McMurtry, G.M.; Shevenell, L.; Pettit, D.R.; Stimac, J.A.; Werner, C.

    1997-01-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory. Detailed geochemical sampling of high-temperature fumaroles, background water, and fresh magmatic products from 14 active volcanoes reveal that they do not produce measurable amounts of tritium ( 3 H) of deep origin ( 2 O). On the other hand, all volcanoes produce mixtures of meteoric and magmatic fluids that contain measurable 3 H from the meteoric end-member. The results show that cold fusion is probably not a significant deep earth process but the samples and data have wide application to a host of other volcanological topics

  20. Rare earth element lithogeochemistry of granitoid mineral deposits

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, R.P.; Fryer, B.J. (Memorial Univ. of Newfoundland, St. John' s (Canada). Dept. of Earth Sciences)

    1983-12-01

    As a monitor of the processes involved in the formation of granitoid mineral deposits the coherent group behaviour of the rare earth elements (REE) actively reflects changing fluid characteristics. For example, in the porphyry environment, magmatic-hydrothermal fluids produce potassic alteration with strong enrichment in the light rare earth elements, reflecting their high pH, low fluid/rock ratios, and the dominant role of Cl/sup -/ complexing in metal (i.e. Cu, Au) transport. With increasing fluid/rock ratios and decreasing pH accompanying the progressive involvement of meteoric fluids (and the production of propylitic, argillic, and phyllic alteration) anionic species such as F/sup -/ and CO/sub 3//sup 2 -/ become important in metal (e.g. Mo, W) transport through complexing, and their activity in the hydrothermal fluids is illustrated by mobilization of the heavy rare earth elements. The relative involvement of Cl/sup -/ versus F/sup -/ versus CO/sub 3//sup 2 -/ in metal transport in other granite-related systems can also be monitored through REE behaviour. Hence granitoid tin-tungsten mineralization and associated greisenization typically exhibit heavy rare earth enrichment and evidence the importance of F/sup -/ and CO/sub 3//sup 2 -/ in metal transport. Similarly, heavy rare earth element enrichment in hydrothermal uranium deposits can be related to the transport of uranium as carbonate complexes. REE are widely accepted as powerful tools in the study of rock petrogenesis, but their use has been neglected in the investigation of mineral deposits. The recognition of the systematic variation of REE distributions in granitoid mineral deposits suggests that the application of REE geochemistry, particularly when integrated with fluid inclusion and isotope studies, can provide l) an effective method for identifying the physiochemical controls of metal transport and 2) a useful criterion of elucidating metal distribution.

  1. Rare earth element lithogeochemistry of granitoid mineral deposits

    International Nuclear Information System (INIS)

    Taylor, R.P.; Fryer, B.J.

    1983-01-01

    As a monitor of the processes involved in the formation of granitoid mineral deposits the coherent group behaviour of the rare earth elements (REE) actively reflects changing fluid characteristics. For example, in the porphyry environment, magmatic-hydrothermal fluids produce potassic alteration with strong enrichment in the light rare earth elements, reflecting their high pH, low fluid/rock ratios, and the dominant role of Cl - complexing in metal (i.e. Cu, Au) transport. With increasing fluid/rock ratios and decreasing pH accompanying the progressive involvement of meteoric fluids (and the production of propylitic, argillic, and phyllic alteration) anionic species such as F - and CO 3 2- become important in metal (e.g. Mo, W) transport through complexing, and their activity in the hydrothermal fluids is illustrated by mobilization of the heavy rare earth elements. The relative involvement of Cl - versus F - versus CO 3 2- in metal transport in other granite-related systems can also be monitored through REE behaviour. Hence granitoid tin-tungsten mineralization and associated greisenization typically exhibit heavy rare earth enrichment and evidence the importance of F - and CO 3 2- in metal transport. Similarly, heavy rare earth element enrichment in hydrothermal uranium deposits can be related to the transport of uranium as carbonate complexes. REE are widely accepted as powerful tools in the study of rock petrogenesis, but their use has been neglected in the investigation of mineral deposits. The recognition of the systematic variation of REE distributions in granitoid mineral deposits suggests that the application of REE geochemistry, particularly when integrated with fluid inclusion and isotope studies, can provide l) an effective method for identifying the physiochemical controls of metal transport and 2) a useful criterion of elucidating metal distribution

  2. Geochemical characteristics of granitoids and related mafic granulites from the Pan-African Dahomeyide belt, southeastern Ghana

    International Nuclear Information System (INIS)

    Aidoo, F.

    2012-07-01

    The Dahorneyide orogenic belt marks the southeastern limit of the West Africa craton (WAC). The belt consists of three structural units which include the deformed eastern edge of the WAC with its cover rocks made up of the Togo and the Buern Structural Units (external nappes), a suture zone assemblage of mafic and ultramafic rocks, and granitoid gneiss-rnigmatite assemblages (east of the suture zone). Geochemical and petrographic characteristics of the granitoids from the external nappes and mafic and ultramafic granulites roeks from the suture zone have been studied with the objective of inferring their petrogenesis and tectonic setting in which they were formed. Twenty five (25) representative samples were selected for petrographic studies and fifteen samples for major and trace elements composition using ICP-AES and ICP-MS respectively. The granitoids gneisses are mainly biotite muscovite gneisses, migmatites and granodiorites made up of quartz (25-68%), biotite (7-30%), plagioclase (8-40%), muscovite (4-20%) with some few pyroxene, sericite and calcite observed in some oF the samples. Within these rocks is an amphibole rich gneiss composed of about 45% amphiboles. The granitoid gneisses contain SiO 2 content of 40.60-68.90 wt. % with low Mg# of 36-46. Geochernically, they are classified as I-type, mctaluminous to peraluminous, magnessian to ferroan, calcic to calc alkali granitoids. They exhibit fractionated REE patterns with (La/Sm) N = 1.80-5.85 and (La/Yb) N = 3.76-76.30, and negative to positive Eu anomalies (Eu/Eu*'' = 0.68-2.10. The primitive mantle-normalised, trace element patterns show that the granitoid gneisses are characterised by enrichment in LILE relative to HFSE and in LREE relative HREE. They display subduction-related trace element characteristics of positive Ba and negative Ti, Ta, Nb and Hf anomalies. The mafic granulites are composed of quartz (16-43%), hornblende (12-45%), plagioclase (13-23%), pyroxene (13-17%), garnet (4

  3. Molybdenite Re/Os dating, zircon U-Pb age and geochemistry of granitoids in the Yangchuling porphyry W-Mo deposit (Jiangnan tungsten ore belt), China: Implications for petrogenesis, mineralization and geodynamic setting

    Science.gov (United States)

    Mao, Jingwen; Xiong, Bikang; Liu, Jun; Pirajno, Franco; Cheng, Yanbo; Ye, Huishou; Song, Shiwei; Dai, Pan

    2017-08-01

    ) in the north, as well as the Southeastern Coast porphyry-skarn Cu-Mo-Au ore belt (SCB) recognized in South China in this paper, we propose that the latest Jurassic to earliest Cretaceous granitoids and associated ores were formed during a tearing of the subducting Izanagi slab. This tearing of the subduction slab caused the upwelling of asthenosphere and the resulting mantle-crust interaction. The granitoid-related W ore systems in JNB resulted from the remelting of the Proterozoic crust. The mafic-ultramafic volcanic rocks of the Shuangqiaoshan Group intercalated with phyllite and slate, ophiolitic mélange and magmatic arc rocks, mainly comprising I-type granite, basalt, andesite, rhyolite, pyroclastics, together with subduction-related metasomatized lithospheric mantle, would have provided additional mantle material. In this case, the partial melting of rocks of the Shuangqiaoshan Group can produce S-, I- and transitional type granitoids. After strong differentiation it formed tungsten-bearing granitoids characterized by enrichment of high alkali, silicon and volatile components. In the Yangchuling mine area the small monzogranitic porphyry stock has stronger fractionation, volatile content and ore-forming components than the older granodiorite, resulting in the development of the porphyry W-Mo ore system.

  4. Age, geochemical affinity and geodynamic setting of granitoids and felsic volcanics in the basement of Wrangel Island

    Science.gov (United States)

    Luchitskaya, Marina; Moiseev, Artem; Sokolov, Sergey; Tuchkova, Marianna; Sergeev, Sergey

    2016-04-01

    volcanics have high contents of alkalis (K2O= 4.15-5.79%, Na2O= 2.28-3.78%) and belong to high-K calc-alkaline series. In TAS classification granites and gneisses, mylonitic ones are classed with granites and felsic volcanic, with rhyolites. In the Frost et al., 2001 classification granites and felsic volcanics are classed with magnesian (Fe*=FeO*/(FeO*+ MgO)=0.71-0.79), calc-alkalic and alkali-calcic (MALI=Na2O+K2O-CaO=6.92-7.68) and peraluminous (ASI=1.13-1.35) granitoids. Spidergrams of granites and felsic volcanics are enriched in LILEs in respect to HFSE, show negative anomalies of Ba, Nb, Ta, LREE, Sr, Ti and positive anomaly for Pb. On FeO*/MgO vs (Zr+Nb+Ce+Y) and Zr vs 104Ga/Al (Whalen et al., 1987) diagrams, muscovite granites and granitic gneisses fall in the field of I- and S-types granites, mylonitic granites and felsic volcanics, on the line between I-, S-granites and A-type granites fields or in the A-type granites field. Conclusions. 1. U-Pb zircon data indicate two stages of felsic magmatic activity in Wrangel complex at ~700 and ~600 Ma. 2. Granitoids of Wrangel complex belong to highly fractionated peraluminous I-type granites; felsic volcanics have similarity to A-type granites. 3. Granitoids of the 600 Ma stage may be derivates of I-types granites of Andian continental margin or postcollisional ones; felsic volcanics are part of bymodal rift-related assemblage, associated with extention setting. The latter is confirmed by rifting nature of spatially associated basalts (Moiseev et. al, 2009; Moiseev et al., 2015). This work was supported by Rosneft' company, Russian Fund of Basic Researches (projects № 16-05-00146, 14-05-00031), and Scientific school (NSh-9581.2016.5).

  5. Syn-collisional felsic magmatism and continental crust growth: A case study from the North Qilian Orogenic Belt at the northern margin of the Tibetan Plateau

    Science.gov (United States)

    Chen, Shuo; Niu, Yaoling; Xue, Qiqi

    2018-05-01

    The abundant syn-collisional granitoids produced and preserved at the northern Tibetan Plateau margin provide a prime case for studying the felsic magmatism as well as continental crust growth in response to continental collision. Here we present the results from a systematic study of the syn-collisional granitoids and their mafic magmatic enclaves (MMEs) in the Laohushan (LHS) and Machangshan (MCS) plutons from the North Qilian Orogenic Belt (NQOB). Two types of MMEs from the LHS pluton exhibit identical crystallization age ( 430 Ma) and bulk-rock isotopic compositions to their host granitoids, indicating their genetic link. The phase equilibrium constraints and pressure estimates for amphiboles from the LHS pluton together with the whole rock data suggest that the two types of MMEs represent two evolution products of the same hydrous andesitic magmas. In combination with the data on NQOB syn-collisional granitoids elsewhere, we suggest that the syn-collisional granitoids in the NQOB are material evidence of melting of ocean crust and sediment. The remarkable compositional similarity between the LHS granitoids and the model bulk continental crust in terms of major elements, trace elements, and some key element ratios indicates that the syn-collisional magmatism in the NQOB contributes to net continental crust growth, and that the way of continental crust growth in the Phanerozoic through syn-collisional felsic magmatism (production and preservation) is a straightforward process without the need of petrologically and physically complex processes.

  6. Petrology and geochemistry of Granitoids at Khanchay-Aliabad region, Tarom sub-zone, East of Zanjan

    Directory of Open Access Journals (Sweden)

    Arefeh Saiedi

    2018-03-01

    Full Text Available Khanchay-Aliabad area as a part of Tarom magmatic belt contains some shallow depth intrusions which are intruded the Eocene volcanic- sedimentary rocks and have very close association with Cu mineralization. The Eocene volcanic- sedimentary rocks include alternation of basalt, basaltic andesite and andesite, various kinds of tuff, tuffaceous sandstone, sandstone, siltstone and occasionally shale. Petrographical studies demonstrate that intrusions are pyroxene quartz monzonite and olivine gabbro in composition. The Khanchay pyroxene quartz monzonite have porphyritic to porphyroidic, hetero-granular to sereitic, ophitic and sub- ophitic textures and composed of plagioclase, clinopyroxene, hornblende, quartz, K-feldspar and biotite. The Aliabad pyroxene quartz monzonite shows porphyritic to porphyroidic textures composing of plagioclase, clinopyroxene and hornblende in the quartz- feldspatic matrix. The Khanchay olivine gabbro is characterized by the presence of coarse grained granular, ophitic and sub- ophitic textures as well as the occurrence of plagioclase, clinopyroxene and olivine. Geochemical studies indicate that the Khanchay- Aliabad pyroxene quartz monzonitic intrusions have SiO2 content varying from 59.58 to 61.34 %. These intrusions have high- K calc- alkaline nature and are classified as I-type metaluminous granitoids. Their similar patterns on spider diagrams are indication of genetic relation of these intrusions. On these diagrams LILEs (Ba, K, Th and Pb enrichment along with negative anomalies of HFSEs (Nb and Ti are observed. Moreover, the Chondrite normalized REE patterns demonstrate LREE enrichment with high ratio of LREE/HREE and Lan/Ybn ratio ranging from 3.08 to 3.72. The overall  field investigation, petrological and geochemical studies as well as  tectonic setting discrimination diagrams confirm that the Khanchay- Aliabad high-K intrusions were formed from a subduction related metasomatized lithospheric mantle in a post

  7. Geochemistry and petrogenesis of the Kolah-Ghazi granitoid assemblage, south of Esfahan

    Directory of Open Access Journals (Sweden)

    Jamshid Ahmadian

    2018-04-01

    Full Text Available Introduction The Kolah-Ghazi granitoid assemblage is located in the south of Esfahan and in the Sanandaj-Sirjan magmatic-metamorphic zone. The Sanandaj-Sirjan zone is extended for 1500 km from Sirjan in the southeast to Sanandaj in the northwest of Iran and is situated in the west of Central Iranian terrane. The Sanandaj-Sirjan zone represents the metamorphic belt of the Zagros orogeny which is part of the Alpine- Himalayan orogenic belt. The Kolah-Ghazi granitoid assemblage consists of granodiorite, granites, quartz-rich granitoid and minor tonalite. The aim of this paper is to represent the mineralogy, geochemistry, petrogenesis and tectonic setting of this plutonic assemblage. Materials and methods More than 60 samples representing all of the rock units in the study area were chosen for microscopic studies. Then, 22 samples were selected for geochemical studies. The major elements were determined with XRF in the Naruto University, Japan. The trace and rare earth elements were analyzed by ICP-MS in the Acmelab, Canada. The geochemical results are presented in Table 1. Results and Discussion The Kolah-Ghazi granitoid assemblage intruded into the Jurassic sedimentary units and overlaid by lower Cretaceous sandstone and conglomerate which suggest Upper Jurassic as the possible age of the Kolah-Ghazi intrusion. Based on the modal studies, this granitoid assemblage is comprised of granite, granodiorite, quartz-rock granitoid and tonalite with different igneous textures including symplectic, myrmekitic, rapakivi, poikilitic and porphyroid. There are some xenoliths, microgranular enclaves and sur micaceous enclaves in the Kolah-Ghazi granitoid assemblage. Xenoliths are mostly derived from Jurassic shale and sandstones which have been trapped in the magma. The sur micaceousenclaves have tonalite composition. The sur micaceous enclaves are biotite-rich rock fragments which display metamorphic texture. The sur micaceous enclaves are classified as

  8. Petrology and Geochemistry of Shakh Sefid Granitoid and related skarn in the North of Rayen (southeastern of Kerman

    Directory of Open Access Journals (Sweden)

    Habib biabangard

    2017-11-01

    Full Text Available The Shakh Sefid Granitoid pluton and related Skarn are located 80 Km in the southeastern of Kerman and 20 Km north of Rayen. This area   is geologically located in the southeastern of the Lut block in the Central Iran. The Shakh Sefid Granitoid with Eocene-Oligocene age cuts the Cretaceous sedimentary rocks and led to the formation of Skarn. The granitoids are granite and granodiorite in composition composing of quartz, plagioclase, orthoclase, as primary minerals, biotite as minor and chlorite and sericite as secondary minerals. The sedimentary rocks are shale, sandstone, siltstone and limestone. Metamorphic rocks are marble and Skarns. The Skarn is calcic type. Garnet (grossular-andradite, tremolite and magnetite are the main minerals that are often accompanied with hematite, goethite and limonite. Pyrite, chalcopyrite and copper carbonate (malachite and azurite are the other minerals in Skarn. Geochemical studies show that the amount of major and minor elements of granitoid with increasing SiO2 content do not change due to the uniform mass, low dispersion of elements which result from heterogeneous textures and low alteration zone. Spider diagrams from minor elements normalized to Chondrite and primitive mantle show enrichment of all elements except for Ti, positive anomalies of Th, Pb and negative anomalies of Ti, P and Sr for the Sakh Sefid granitoids are probably due to crustal contamination. They are enriched in light rare earth elements (LREE between 10 to 100 times and heavy elements (HREE enrichment between 1 to 10 times compared to the reference (chondrite and regular pattern with approximately the same slope , the parallel trends indicate that the granitoid rocks share  a common source rock . The Shakh Sefid granitoid is I-type, metaluminous to peraluminous belonging to an active continental margin. Mineral and Mineralization in Kuh Shakh Sefid skarn is remarkably similar to iron skarn deposits. Minerals such as garnet and

  9. Origin of the mafic microgranular enclaves (MMEs) and their host granitoids from the Tagong pluton in Songpan-Ganze terrane: An igneous response to the closure of the Paleo-Tethys ocean

    Science.gov (United States)

    Chen, Qiong; Sun, Min; Zhao, Guochun; Yang, Fengli; Long, Xiaoping; Li, Jianhua; Wang, Jun; Yu, Yang

    2017-10-01

    The Songpan-Ganze terrane is mainly composed of a Triassic sedimentary sequence and late Triassic-Jurassic igneous rocks. A large number of plutons were emplaced as a result of tectono-magmatic activity related to the late stages of Paleo-Tethys ocean closure and ensuing collision. Granitoids and their hosted mafic enclaves can provide important constraints on the crust-mantle interaction and continental crustal growth. Mesozoic magmatism of Songpan-Ganze remains enigmatic with regard to their magma generation and geodynamic evolution. The Tagong pluton (209 Ma), in the eastern part of the Songpan-Ganze terrane, consists mainly of monzogranite and granodiorite with abundant coeval mafic microgranular enclaves (MMEs) (ca. 208-209 Ma). The pluton comprises I-type granitoid that possesses intermediate to acidic compositions (SiO2 = 61.6-65.8 wt.%), high potassium (K2O = 3.2-4.1 wt.%), and high Mg# (51-54). They are also characterized by arc-type enrichment of LREEs and LILEs, depletion of HFSEs (e.g. Nb, Ta, Ti) and moderate Eu depletions (Eu/Eu* = 0.46-0.63). Their evolved zircon Hf and whole-rock Nd isotopic compositions indicate that their precursor magmas were likely generated by melting of old lower continental crust. Comparatively, the MMEs have lower SiO2 (53.4-58.2 wt.%), higher Mg# (54-67) and show covariation of major and trace elements, coupled with field and petrographic observations, such as the disequilibrium textures of plagioclase and amphibole, indicating that the MMEs and host granitoids were originated from different magma sources but underwent mafic-felsic magma mixing process. Geochemical and isotopic data further suggest that the precursor magma of the MMEs was formed in the continental arc setting, mainly derived from an ancient metasomatized lithospheric mantle wedge. The Triassic granitoids from the Songpan-Ganze terrane show remarkable temporal-spatial-petrogenetic affinities to the counterparts of subduction zones in the Yidun and Kunlun arc

  10. Melting of subducted continental crust: Geochemical evidence from Mesozoic granitoids in the Dabie-Sulu orogenic belt, east-central China

    Science.gov (United States)

    Zhao, Zi-Fu; Liu, Zhi-Bin; Chen, Qi

    2017-09-01

    Jurassic and Early Cretaceous, respectively, for granitic magmatism. While partial melting in the Late Triassic is responsible for syn-exhumation magmatism, the Late Jurassic and Early Cretaceous granitoids are independent of the continental collision and thus belong to postcollisional magmatism.

  11. Tectonic implications of U-Pb (zircon) Geochronology of Chor Granitoids of the Lesser Himalaya, Himachal Pradesh, NW Himalaya

    Science.gov (United States)

    Singh, P.; Bhakuni, S. S.

    2017-12-01

    Granitoids of various ages ranging from Proterozoic to Tertiary occur throughout the Himalayan fold-thrust belt. The occurrence of the Neoproterozoic granitoids are very less in the Himalayan orogen. One of the best example of Neoproterozoic granitoids is Chor granitoids, which are the intrusive granite bodies in the Paleoproterozoic of the Lesser Himalayan Crystallines of the Jutogh Group. In the central part these granites are non-foliated homogeneous that are porphyritic and peraluminous in nature (Singh et al., 2002; Bhargava et al., 2014, 2016), whereas in the peripheral part these are foliated showing south directed shear sense of movement. In this work we present the U-Pb (zircon) geochronology of two different granites samples of the Chor granitoids of Himachal Pradesh, NW Himalaya. The Jutogh Group of rocks is thrust over the Lesser Himalayan Sequence along the Jutogh Thrust or MCT. The geochronology of the Chor Granitoids and Lesser Himalayan Crystallines and their relationship with each other, including with the Indian shield are sparsely obscure. U-Pb zircon geochrnological age populations from these granitoids yield ages between 780 and 980 Ma. One sample gives the prominent age spectra for 206Pb/238U with weighted mean age of 908.3 ± 6.7 Ma (2σ) MSWD = 2.4 (n = 18). Similarly another sample gives the age of crystallization with weight mean age of 917 ± 17 Ma (2σ) MSWD = 3 (n = 11) and Th/U ratios of both samples are >0.1, indicating their magmatic origin. As a result of ductile shearing of granites along the MCT during the Cenozoic Himalayan Orogeny, the age has reduced to 780 Ma. The Neoproterozoic age of Chor granite matches with the Neoproterozoic detrital zircon age (800 to 1000 Ma by Parrish and Hodges 1996, Decelles et al., 2000) of the HHC. On the basis of U-Pb (zircon) geochronological ages, it is revealed that the source of zircons of the Chor granite and HHC rocks was the northern margin of the Pan-African orogen. The Chor granitoids was

  12. A historical overview of Moroccan magmatic events along northwest edge of the West African Craton

    Science.gov (United States)

    Ikenne, Moha; Souhassou, Mustapha; Arai, Shoji; Soulaimani, Abderrahmane

    2017-03-01

    Located along the northwestern edge of the West African Craton, Morocco exhibits a wide variety of magmatic events from Archean to Quaternary. The oldest magmatic rocks belong to the Archean Reguibat Shield outcrops in the Moroccan Sahara. Paleoproterozoic magmatism, known as the Anti-Atlas granitoids, is related to the Eburnean orogeny and initial cratonization of the WAC. Mesoproterozoic magmatism is represented by a small number of mafic dykes known henceforth as the Taghdout mafic volcanism. Massive Neoproterozoic magmatic activity, related to the Pan-African cycle, consists of rift-related Tonian magmatism associated with the Rodinia breakup, an Early Cryogenian convergent margin event (760-700 Ma), syn-collisional Bou-Azzer magmatism (680-640 Ma), followed by widespread Ediacaran magmatism (620-555 Ma). Each magmatic episode corresponded to a different geodynamic environment and produced different types of magma. Phanerozoic magmatism began with Early Cambrian basaltic (rift?) volcanism, which persisted during the Middle Cambrian, and into the Early Ordovician. This was succeeded by massive Late Devonian and Carboniferous, pre-Variscan tholeiitic and calc-alkaline (Central Morocco) volcanic flows in basins of the Moroccan Meseta. North of the Atlas Paleozoic Transform Zone, the Late Carboniferous Variscan event was accompanied by the emplacement of 330-300 Ma calc-alkaline granitoids in upper crustal shear zones. Post-Variscan alkaline magmatism was associated with the opening of the Permian basins. Mesozoic magmatism began with the huge volumes of magma emplaced around 200 Ma in the Central Atlantic Magmatic Province (CAMP) which was associated with the fragmentation of Pangea and the subsequent rifting of Central Atlantic. CAMP volcanism occurs in all structural domains of Morocco, from the Anti-Atlas to the External Rif domain with a peak activity around 199 Ma. A second Mesozoic magmatic event is represented by mafic lava flows and gabbroic intrusions in

  13. Petrotectonic characteristics, geochemistry, and U-Pb geochronology of Jurassic plutons in the Upper Magdalena Valley-Colombia: Implications on the evolution of magmatic arcs in the NW Andes

    Science.gov (United States)

    Rodríguez, G.; Arango, M. I.; Zapata, G.; Bermúdez, J. G.

    2018-01-01

    Field, petrographic, and geochemical characterization along with U-Pb zircon geochronology of the Jurassic plutons exposed in the Upper Magdalena Valley (Colombia) allowed recognizing distinct western and eastern suites formed in at least three magmatic pulses. The western plutons crop out between the eastern flank of the Central Cordillera and the Las Minas range, being limited by the Avirama and the Betania-El Agrado faults. The western suite comprises a quartz monzonite - quartz monzodiorite - quartz diorite series and subordinate monzogranites. Chemically, the rocks are high-K calc-alkaline I-type granitoids (some reaching the shoshonitic series) with metaluminous of magnesium affinity. Trace-element tectonic discrimination is consistent with magmatism in a continental arc environment. Most rocks of this suite crystallized between 195 and 186 Ma (Early Jurassic, Pliensbachian), but locally some plutons yielded younger ages between 182 and 179 Ma (Early Jurassic, Toarcian). The eastern suite crops out in the eastern margin of the Upper Magdalena Valley, east of the Betania - El Agrado fault. Plutons of this unit belong to the monzogranite series with rock types ranging between syenogranites and granodiorites. They are high-K calc-alkaline continental granitoids, some metaluminous and some peraluminous, related to I-type granites generated in a volcanic arc. Crystallization of the suite was between 173 and 169 Ma (Middle Jurassic, Aalenian-Bajocian), but locally these rocks contain zircon with earlier inherited ages related to the magmatic pulse of the western suite between 182 and 179 Ma (Early Jurassic, Toarcian). The evolution of the Jurassic plutons in the Upper Magdalena Valley is best explained by onset or increase in subduction erosion of the accretionary prism. This explains the eastward migration of the arc away from the trench. Subduction of prism sediments increased the water flux from the subducting slab, decreasing solidus temperatures, therefore

  14. Tectonomagmatic evolution of the proto Andean Margin: Geochemical characterization and zircon U-Pb geochronologic constraints from the Ecuadorian Eastern Cordilleran granitoids

    Science.gov (United States)

    Buchwaldt, R.; Toulkeridis, T.

    2013-05-01

    The timing of pan-Pacific Gondwanide Orogeny in the proto-Andes, and its driving mechanisms are still highly debated and relies predominantly upon whole-rock Rb-Sr and K-Ar chronology and rudimentary mineralogy and geochemistry. In order to decipher these uncertainties we have studied the composition, age and provenance of granitoids along the strike of the Eastern Cordillera of Ecuador and related these deep-seated and surface tectonic processes attending the Late Cretaceous-Palaeogene history of the northern Andes. The plutonic rocks constitute a metaluminous to peraluminous (A/CNK ~ 0.8-1.2), calc-alkaline suite. A unimodal and wide compositional range of the intrusives (49-78 wt. % SiO2) is characteristic of this I-type orogenic suites. Mantle-normalized trace element patterns reveal typical subduction-related signature. Chondrite-normalized REE patterns do not show significant HREE fractionation suggesting the absence of high-pressure residual mineralogy in the source and formation in a "normal thickness", garnet-free crust. Slight Eu anomalies, lowering Sr contents, and concave-up REE patterns of samples dioritic in composition indicate a model involving fractionation of plagioclase, amphibole and pyroxene from a basaltic parent. The analyzed zircon crystals are colorless - transparent ranging in size from 50 to 250 μm. In CL images, 95% of the zircons exhibit oscillatory zonation, characteristic of a magmatic origin. This observation is consistent with the REE zircon composition showing a are characteristic steep positive slope from La to Lu with a significantly positive Ce-anomaly and slight negative Eu-anomaly. There is very little variation in Hf isotopic composition with most of the crust maintains near chondritic Zr/Hf ratios of around 35-40. Our results indicate the development of two tectonic episodes; with the first varying between 210-250 Ma and the second approximate 170-180 Ma. These results are consistent with similar events observed throughout

  15. Petrogenesis and geodynamic implications of Ediacaran highly fractionated A-type granitoids in the north Arabian-Nubian Shield (Egypt): Constraints from whole-rock geochemistry and Sr-Nd isotopes

    Science.gov (United States)

    Sami, Mabrouk; Ntaflos, Theodoros; Farahat, Esam S.; Mohamed, Haroun A.; Hauzenberger, Christoph; Ahmed, Awaad F.

    2018-04-01

    magma that have injected and partly mixed with the colder and more felsic TMGs magma. Geochemical and isotopic data along with petrogenetic modelling, suggest that the TMGs were formed by low degrees of partial melting of the pre-existing I-type granodiorites, followed by extensive fractional crystallization and fluid fractionation to produce the geochemically specialized rare metals GMGs and MGs in the margin of Abu-Diab pluton. During the post-collisional stage of ANS and due to lithospheric delamination processes, the underplated fluid/volatile rich mantle magma had interplated and migrated upward to shallow crustal levels, through extensional faults/shear zones, and enhanced the partial melting and fractionation of granodiorites to eventually form Abu-Diab A-type granitoids.

  16. Lithogeochemistry of rare-earth elements in the characterization of granitoids from the Cachoeirinha belt, Northeast Brazil

    International Nuclear Information System (INIS)

    Sial, A.N.

    1984-01-01

    Detailed rare-earth element study on about 40 samples from 14 granitic bodies distributed within and in adjacent areas of the Cachoeirinha belt, states of Pernambuco and Paraiba, between 37 0 and 40 0 W long. and 7 0 and 8 0 15' lat., was performed. These bodies include potassic, calc-alkalic, and peralkalic granitic associations, besides one with trondhjemitic affinities. The REE patterns for the potassic granitoids (Bodoco, Serra da Lagoinha and Itaporanga) which pierced basement migmatites, are strongly fractionated, mutually similar, LREE-enriched, and lack En anomaly. The calc-alkalic granitoids (Conceicao-type) intruded the low-grade metamorphics, and display strongly fractionated REE patterns, LREE-enriched relative to HREE, and exhibit a discrete, yet significative negative Eu anomaly. The granitoids with trondhjemitic affinities (Serrita-type) which intruded the Salgueiro schists, exhibit Σ REE much lower than in the previously mentioned granituids - REE patterns are strongly fractionated, LREE - enriched in relation to HREE, with discrete positive Eu anomaly and HREE approaching chondrite abundances. REE patterns of the peralkalic granitoids (Catingueira-type) ressemble those of rocks with trondhjemitic affinities and show a discrete positive Eu anomaly. The REE geochemistry agrees essentially with the major chemistry of the 4 granitoid associations, and is consistent with the 18 O/ 1 6O behavior which of ten varies sympathetically with Σ REE and S;O 2 . The presence of magmatic epidote, a high pressure phase, in three of these associations suggests that these rocks crystallized at a relatively great depth. (D.M.) [pt

  17. Isotope geochemistry of brasiliano age, coarsely porphyritic, K-calc-alkalic granitoids and associated K-diorites, northeast Brazil

    International Nuclear Information System (INIS)

    Sial, A.N.; Mariano, G.; Ferreira, V.P.

    1989-01-01

    Several porphyritic, K-calc-alkalic were syntectonically intruded in NE Brazil during the Brasiliano orogeny. They show bi-(qz) diorite and coarsely porphyritic granodiorite to qz monzonite ('Itaporanga-type') in commingling zones on a scale of cm to m irrespective of whether plutons are at the margins of the NE-trending Cachoeirinha-Salgueiro Fold Belt (CSF) or intruded metasediments of the Serido Fold Belt (SFB). The bi(qz) diorites are found in magmatic or stromatic structures and narrow dikes wich intruded the felsic facies. SiO 2 in the porphyritic facies ranges from 61 to 72% with K 2 O usually > Na 2 O. K-diorities exhibit SiO 2 from 50 to 58%, MgO from 2 to 10% and K 2 O from 2 to 5%. Both facies are usually Ba and Sr-enriched, with similar, highly fractionated REE patterns, lacking free of Eu anomaly. Quartz 180 values are considered homogeneous on the scale of these intrusions in the CSF, (8 to 10 per milSMOW). Bi-(qz) diorites exhibit slightly higher 180 (9.5 to 10.5 per milSMOW). In the SFB both facies are lower than 180. The oxygen isotope data for the porphyritic facies are compatible with I-type source with some metasedimentary component of variable proportion. As bi(qz) diorites were formed pre- to post-porphyritic facies intrusion, their high LREE, K and 180 reflect their source rather than the interaction with the potassic felsic magma. Preliminarly sulfur isotope values suggest that porphyritic facies of granitoids in the SBF are lower in 34S than those in the CSF. Rb and Sr isotopes reflect source heterogeneity, complicated by mixing relations. Ages span from 510 to 630 Ma suggesting that the Itaporanga-type association was formed during uplift and cooling of the Pan-African I and onset of the Pan-African II orogenies, recognized in West Africa. (author) [pt

  18. Petrotectonic framework of granitoids and associated granulites at ...

    Indian Academy of Sciences (India)

    tion that wraps around the feldspar augen. The sheared granitoid ..... 1987) has been used to classify the granitoids ... The data for all the analyses used in the diagrams are given in table 1. ..... Different stages of crystal-plastic deformation are.

  19. New monazite U-Pb age constraints on the evolution of the Paleoproterozoic Vaasa granitoid batholith, western Finland

    Directory of Open Access Journals (Sweden)

    A.K. Kotilainen

    2016-09-01

    Full Text Available The Vaasa batholith, western Finland, is a large, peraluminous granitoid pluton that crystallized at 1.88–1.87 Ga during the culmination of the Svecofennian orogeny. The batholith has gradual contacts, through metatexites and diatexites, with the enveloping metasedimentary rocks of the Bothnian Belt. We present ID-TIMS U-Pb age data on monazite from granitoids and xenoliths of the Vaasa batholith and combine these with published U–Pb zircon ages in order to shed further light on the evolution of the Vaasa batholith. The apparent monazite ages for seven of the examined samples are 1870–1863 Ma, and 1855±3 Ma for one further sample from the southern part of the batholith. Combined with pre-existing data, the monazite ages of the granitoids are 9 to 18 Ma (face values or 3 to 9 Ma (external errors considered younger than the U–Pb zircon crystallization ages from respective samples. Our new data suggest slow cooling for the Vaasa batholith – the closure/saturation temperature of the monazite U–Pb system was probably reached in ~10 m.y. after the crystallization of magmatic zircon in the examined rocks.

  20. Linking Tengchong Terrane in SW Yunnan with Lhasa Terrane in southern Tibet through magmatic correlation

    Science.gov (United States)

    Xie, Jincheng; Zhu, Dicheng; Dong, Guochen; Zhao, Zhidan; Wang, Qing

    2016-04-01

    New zircon U-Pb data, along with the data reported in the literature, reveal five phases of magmatic activity in the Tengchong Terrane since the Early Paleozoic with spatial and temporal variations summarized as: Cambrian-Ordovician (500-460 Ma) to the eastern, minor Triassic (245-206 Ma) in the eastern and western, abundant Early Cretaceous (131-114 Ma) in the eastern, extensive Late Cretaceous (77-65 Ma) in the central, and Paleocene-Eocene (65-49 Ma) in the central and western Tengchong Terrane, in which the Cretaceous-Eocene magmatism was migrated from east to west (Xu et al., 2012). The increased zircon eHf(t) of the Early Cretaceous granitoids from -12.3 to -1.4 at ca. 131-122 Ma to -4.6 to +7.1 at ca. 122-114 Ma identified for the first time in this study and the magmatic flare-up at ca. 53 Ma in the central and western Tengchong Terrane (Wang et al., 2014, Ma et al., 2015) indicate the increased contributions from mantle- or juvenile crust-derived components. The spatial and temporal variations and changing magmatic compositions with time in the Tengchong Terrane closely resemble the Lhasa Terrane in southern Tibet. Such similarities, together with the data of stratigraphy and paleobiogeography (Zhang et al., 2013), enable us to propose that the Tengchong Terrane in SW Yunnan is most likely linked with the Lhasa Terrane in southern Tibet, both of which experience similar tectonomagmatic histories since the Early Paleozoic. References Ma, L.Y., Wang, Y.J., Fan, W.M., Geng, H.Y., Cai, Y.F., Zhong, H., Liu, H.C., Xing, X.W., 2014. Petrogenesis of the early Eocene I-type granites in west Yingjiang (SW Yunnan) and its implication for the eastern extension of the Gangdese batholiths. Gondwana Research 25, 401-419. Wang, Y.J., Zhang, L.M., Cawood, P.A., Ma, L.Y., Fan, W.M., Zhang, A.M., Zhang, Y.Z., Bi, X.W., 2014. Eocene supra-subduction zone mafic magmatism in the Sibumasu Block of SW Yunnan: Implications for Neotethyan subduction and India-Asia collision

  1. Crustal evolution of granitoids and gneisses from the Cambaizinho belt, southern Brazil: Review zircon Pb-Pb evaporation ages and Pb-Nd-Sr isotopes

    International Nuclear Information System (INIS)

    Remus, M.V.D; Macambira, M.B; Hartmann, L.A.; Beilfuss, M

    2001-01-01

    Deformed granitoids and gneisses from the Cambai Complex (900-700 Ma) along Cambaizinho Creek and in the Vila Nova do Sul region, state of Rio Grande do Sul, Brazil, were formed in a remarkably short time, about 10 m.y., between 704±13 and 697±3 Ma. The data base of this work includes eighteen zircon Pb/Pb evaporation analyses, five Pb isotope in feldspar and whole rock. The oldest known rocks in the region are polydeformed dioritic gneisses dated by conventional U-Pb zircon at 704±13 Ma. New Pb-Pb zircon evaporation data on the late transcurrent, less deformed and more evolved granitoids (Sanga do Jobim Granitoids) yield a 697± Ma age and indicates that the evolution of the plutonic magmatism in the area was nearly contemporaneous. These data contrast with previous interpretations based on Rb-Sr data which considered that these rock associations were formed during a longer time period (700-640 Ma). All these granitoids intruded the supracrustal sequence. These granitoids yield a minimum age of about 700 Ma for the formation of the supracrustal sequence and its regional dynamothermal metamorphism. Lead isotope composition of K-feldspar from Sanga do Jobim Granitoids plot close to, but slightly below the lead isotope evolution curve of orogeny in the Zartmann and Doe model (1981). This indicates that the setting for these granitoids was that of a juvenile magmatic arc. These new data plus previous data in the region also corroborate that the crustal evolution involved juvenile crust accreted between 760-700 Ma. In contrast, the Cacapava and Sao Sepe Granites intruded the supracrustal sequences along the eastern side of the Sao Gabriel Block at 562 Ma and 550 Ma, respectively, and show Pb and Nd isotope signatures from an old basement. This evidence suggests that the juvenile terrane was thrusted over the older basement situated along the eastern part of the shield during the Dom Feliciano collisional orogeny at about 620-590 Ma (au)

  2. Granitoides paleozoicos de la Sierra de Narváez, Sistema de Famatina, Argentina: Hibridización de magmas en un margen continental activo

    Directory of Open Access Journals (Sweden)

    Cisterna, C. E.

    1992-12-01

    Full Text Available The granitoids from the Sierra de Narváez were investigated for their geochemical and petrographical characteristics. They are composed of calc-alkaline granites, granodiorites and tonalites, similar to the other paleozoic granitoids of the Famatina System. These rocks are intrusive in the Las Planchadas (volcanic rocks and Suri (sedimentary rocks Formations, which are probably cogenetic with the granitoids within the same magmatic cycle.The study of the granitoids reveals the close relationship between their composition and the abundance of the enclosed magmatic inclusions. The latter represent rocks and granodioritic tonalitic and diorite composition, and have a great number of mineralogical characteristic that suggest the presence of two magmas, mafic and felsic for the origin of such enclaves.The close chemical relationship existing between the inclusions and their host rocks shows that the mafic and felsic components are compositionally modified and that the granitoids are more or less hybridized.Trace elements discrimination diagrams have been used as a tools for fingerprinting the tectonic setting of the Sierra de Narváez granitoids. The geochemistry as well as the geologic relations of the granitoids with the roughly coeval ordovician vulcanism indicate a volcanic arc environment.Las rocas que afloran en el extremo septentrional de la Sierra de Narváez están representadas por una asociación de monzogranitos, granodioritas y tonalitas que definen una serie calcoalcalina, de características similares a las de otros intrusivos del Paleozoico del Sistema de Famatina. Estos granitoides se hallan intruyendo las Formaciones Las Planchadas y Suri, representadas por vulcanitas y metasedimentitas, respectivamente, y corresponderían a un mismo evento magmático del Paleozoico Inferior.Los granitoides estudiados presentan abundantes inclusiones ígneas de composición granodiorítica o tonalítica y diorítica. La estrecha relación que

  3. Geochronology, geochemistry, and Sr-Nd-Pb-Hf isotopes of the Zhunsujihua granitoid intrusions associated with the molybdenum deposit, northern Inner Mongolia, China: implications for petrogenesis and tectonic setting

    Science.gov (United States)

    Zhang, Xiaojun; Lentz, David R.; Yao, Chunliang; Liu, Rui; Yang, Zhen; Mei, Yanxiong; Fan, Xianwang; Huang, Fei; Qin, Ying; Zhang, Kun; Zhang, Zhenfei

    2018-03-01

    The Zhunsujihua porphyry molybdenum deposit, located in northern Inner Mongolia of China that belongs to Central-Asian Orogenic Belt (CAOB), is the only Mo deposit formed in the late Carboniferous in this area so far. Its mineralization is mainly restricted to the Zhunsujihua granitoid intrusions, which are composed of the main granodiorite (GD) and crosscutting, virtually coeval minor syn-ore leucogranite (LG) and diorite porphyry (DP) dykes. LA-ICP-MS zircon U-Pb dating yields crystallization ages of 300.0 ± 2.0, 299.3 ± 2.0, and 299.0 ± 2.6 Ma for the GD, LG, and DP, respectively. The major and trace element lithogeochemical data show that the GD and LG are metaluminous to weakly peraluminous, high-K calc-alkaline series with I-type granite characteristics, strongly oxidized, with low concentrations of Ba, Nb, Sr, P, and Ti and elevated K and Rb contents, indicating typical arc magmatic features. The LG is a product derived by extensive fractional crystallization of a parental magma similar to the GD as evident from the lower Eu/Eu*, Nb/Ta, Zr/Hf, and T Zr. The moderately altered DP exhibits high concentrations of K, Rb, Cs, LREE, Y, and low Sr/Y, with a positive ɛ Nd (300 Ma), which indicates a mantle or juvenile source associated with an arc setting. The Sr-Nd-Hf isotope data show low I Sr (0.70406-0.70461) and moderate ɛ Nd (300 Ma) (-0.9 to 1.5) for the GD and LG, and relatively high ɛ Hf (300 Ma) values (-3.6 to +11.2) for the GD, suggesting the magma mainly originated from the juvenile lower crust that was derived from depleted mantle, with a minor component of ancient continental crust. Lead isotope data have characteristics of a lower crust source with minor contamination by upper crustal material. Combined with previous research, the Zhunsujihua granitoid intrusions developed in an intracontinental volcanic arc (Uliastai) associated with northward subduction of the Paleo-Asian Ocean plate during late Carboniferous to early Permian; this suggests

  4. Interaction between felsic granitoids and basic dykes in ...

    Indian Academy of Sciences (India)

    37

    Many workers gave detailed petrographical and geochemical data of the ... greenstone complex (Malviya et al., 2006; Kumar et al., 2013; Singh and ...... Mafic rock shows lobate shape pointing towards granitoids (marked by the white arrows);.

  5. Geodynamic setting of mesozoic magmatism and its relationship to uranium metallogenesis in southeastern China

    International Nuclear Information System (INIS)

    Chen Peirong

    2004-01-01

    In the southeastern China, magmatism was developed quite intensely in Mesozoic forming a large quantity of rare and nonferrous metal deposits. The Indosinian orogenic movement ( Early Mesozoic) and the Yanshanian movement (Late Mesozoic) provided the dynamic force for magmatism and metallogenesis in this region. The intra-plate extension was induced by the Indosinian orogenic movement in South China continent under a regionally compressional framework to form Indosinian granites. The Yanshanian movement was a post-orogenic geologic event in relation to the Indosinian orogeny, and characterized by intense lithosphere breaking-up, resulting in large scale magmatic activities and a great amount of mineral resources was formed. The Indosinian granites overprinted by the Yanshanian tectono-magma event were closely related to uranium metallogenesis and were likely a kind of uranium source rock. Therefore, research on the distribution pattern of Indosinian granitoids and factors favorable to uranium ore-formation should be enhanced during prospecting in southern China. (author)

  6. Distribution of natural radioactive elements in Western Carpathians granitoids

    International Nuclear Information System (INIS)

    Katlovsky, V.

    1979-01-01

    The content of natural radioactive elements was determined using the 1024-channel analyser NTA-512 B with NaI(Tl) scintillators or with a Ge(Li) detector. The following groups of samples were processed: 1. granitoids, pegmatites and weathered rocks in the Small Carpathians; 2. acid magmatites of exotic rocks of the klippen zone; 3. granitoids of the Western Carpathians. The results of the measurements are summed up. (Ha)

  7. Geochemical and isotopic characterization of the granitic magmatism along the Remígio - Pocinhos shear zone, Borborema Province, NE Brazil

    Science.gov (United States)

    de Lima, Jefferson V.; Guimarães, Ignez de P.; Santos, Lucilene; Amorim, José Victor A.; Farias, Douglas José S.

    2017-04-01

    Two granitoid plutons (Pilõezinhos and Curral de Cima) intruded along the Remígio - Pocinhos shear zone, eastern part of the Borborema Province. The Pilõezinhos and Curral de Cima granites were dated at 566 ± 3 Ma and 618 ± 5 Ma respectively. The granitoids from both plutons have distinct initial 143Nd/144Nd ratios, expressed by εNd(t) values, i.e. the granitoids of Pilõezinhos pluton have lower εNd(t) values (-15.47 to -15.81) and negative εHf (t = 570 Ma) values (-16.0 to -18.6), while the granitoids of the Curral de Cima pluton have εNd(t) values between -1.12 and -5.23. The granitoids of the Curral de Cima pluton are epidote bearing, magnesian calcalkaline I-type granitoids, crystallized under high fO2 conditions. The granitoids of the Pilõezinhos pluton are alkaline, low-fO2, ferroan, ilmenite-series, A2-type granite intrusions. The geochemical and isotopic signatures suggest that the origin of magma of the Curral de Cima granitoids involved mixing/mingling at depth between crustal and mantle magmas, associated to decompression (lateral escape) during the convergent stage of Brasiliano/Pan/African orogeny, which lead the asthenosphere melts to rise into the lower crust. The source of magma of the granitoids of the Pilõezinhos pluton involved a strong crustal component with geochemical and isotopic signatures similar to the orthogneisses of the Serrinha-Pedro Velho Complex, and small mantle component. The emplacement of the Pilõezinhos pluton is associated to an extensional space formed during high-T strike-slip shearing developed by the synchronic movement of the Matinhas sinistral shear zone and Remígio - Pocinhos dextral shear zone.

  8. Formation of continental crust by intrusive magmatism

    Science.gov (United States)

    Rozel, A. B.; Golabek, G. J.; Jain, C.; Tackley, P. J.; Gerya, T.

    2017-09-01

    How were the continents formed in the Earth? No global numerical simulation of our planet ever managed to generate continental material self-consistently. In the present study, we show that the latest developments of the convection code StagYY enable to estimate how to produce the early continents, more than 3 billion years ago. In our models, melting of pyrolitic rocks generates a basaltic melt and leaves behind a depleted solid residue (a harzburgite). The melt generated in the mantle is transported to the surface. Only basaltic rocks melting again can generate continental crust. Should the basaltic melt always reach the open air and cool down? Should the melt be intruded warm in the pre-existing crust? The present study shows that both processes have to be considered to produce continents. Indeed, granitoids can only be created in a tight window of pressure-temperature. If all basalt is quickly cooled by surface volcanism, the lithosphere will be too cold. If all basalt is intruded warm below the crust then the lithosphere will be too warm. The key is to have both volcanism and plutonism (intrusive magmatism) to reach the optimal temperature and form massive volumes of continental material.

  9. Geochronology, petrogenesis and metallogeny of Piaotang granitoids in the tungsten deposit region of South China

    International Nuclear Information System (INIS)

    He Zhenyu; Xu Xisheng; Wang Xudong; Yu Yao; Zou Haibo

    2010-01-01

    stages of magmatism and W mineralization in the Piaotang tungsten deposit, and the similarities with other granite related W-Sn deposits in the same region, it is proposed that the regional tectonic setting and lithosphere dynamics are the key factors controlling the metallogenic capacity of granitoids in South China. (author)

  10. Magma sources during Gondwana breakup: chemistry and chronology of Cretaceous magmatism in Westland, New Zealand

    DEFF Research Database (Denmark)

    van der Meer, Quinten Har Adriaan; Waight, Tod Earle; Scott, James M.

    2013-01-01

    by emplacement of granitoid plutons, the deposition of terrestrial Pororari Group sediments in extensional half-grabens across on- and offshore Westland, and the intrusion of mafic dikes from 90 Ma. These dikes are concentrated in the swarms of the Paparoa and Hohonu Ranges and were intruded prior...... to and simultaneous with volumetrically minor A-type plutonism at 82 Ma. The emplacement of mafic dikes and A-type plutonism at 82 Ma is significant as it coincides with the age of the oldest seafloor in the Tasman Sea, therefore it represents magmatism coincident with the initiation of seafloor spreading which...

  11. A prolonged granitoid formation in Saglek Block, Labrador: Zonal growth and crustal reworking of continental crust in the Eoarchean

    Directory of Open Access Journals (Sweden)

    Tsuyoshi Komiya

    2017-03-01

    We made a detailed sketch of a small outcrop in St. John's Harbour South (SJHS area, and classified the orthogneisses and mafic enclaves into seven generations based on the geologic occurrence. The first and second generations comprise mafic rocks and lack magmatic zircons. We conducted CL imaging and U-Pb dating of zircons from the third, sixth and seventh generation of the orthogneisses to estimate the protolith ages at 3902 ± 25, 3892 ± 33 and 3897 ± 33 Ma for each, supporting the presence of the over 3.9 Ga Iqaluk Gneiss. The geological occurrence that the mafic rocks occur as enclaves within the 3.9 Ga Iqaluk Gneiss indicates that they are the oldest supracrustal rocks in the world. Our geochronological and geological studies show the Uivak Gneiss is quite varied in lithology and age from 3.6 to >3.9 Ga, and tentatively classified into six groups based on their ages. The oldest Uivak Gneiss components including the Iqaluk Gneiss are present around the SJHS area, and the orthogneisses become young as it is away. The lines of evidence of overprinting of younger granitoid on older granitoid in small outcrops and geological-map scale as well as presence of inherited zircons even in the oldest suite suggests that crustal reworking played an important role on erasing the ancient crusts.

  12. Magmatic and Crustal Differentiation History of Granitic Rocks from Hf-O Isotopes in Zircon

    Science.gov (United States)

    Kemp, , A. I. S.; Hawkesworth, , C. J.; Foster, , G. L.; Paterson, , B. A.; Woodhead, , J. D.; Hergt, , J. M.; Gray, , C. M.; Whitehouse, M. J.

    2007-02-01

    Granitic plutonism is the principal agent of crustal differentiation, but linking granite emplacement to crust formation requires knowledge of the magmatic evolution, which is notoriously difficult to reconstruct from bulk rock compositions. We unlocked the plutonic archive through hafnium (Hf) and oxygen (O) isotope analysis of zoned zircon crystals from the classic hornblende-bearing (I-type) granites of eastern Australia. This granite type forms by the reworking of sedimentary materials by mantle-like magmas instead of by remelting ancient metamorphosed igneous rocks as widely believed. I-type magmatism thus drives the coupled growth and differentiation of continental crust.

  13. Rb-Sr isochrone dating of granitoids from Tribec Mts

    International Nuclear Information System (INIS)

    Bagdasaryan, G.P.; Gukasyan, R.Kh.; Cambel, B.; Broska, I.

    1990-01-01

    The results of Rb-Sr isochrone dating of granitoids from the Tribec-Zobor crystalline complex region are presented. Whole-rock Rb-Sr isochrone indicates an age of 352±5 m.y., the initial ratio being ( 87 Sr/ 86 Sr) 0 =0.70582±0.00008, which approaches the hitherto published initial ratios from the Tatric-Veporide part of the crystalline complex. This indicates a common source of granitoid rocks over the entire region studied. (author). 2 figs., 1 tab., 15 refs

  14. Age and geochemistry of Neoproterozoic granitoids in the Songnen-Zhangguangcai Range Massif, NE China: Petrogenesis and tectonic implications

    Science.gov (United States)

    Luan, Jin-Peng; Xu, Wen-Liang; Wang, Feng; Wang, Zhi-Wei; Guo, Peng

    2017-10-01

    This study presents new zircon U-Pb ages and geochemical data for Neoproterozoic granitoids in the Songnen-Zhangguangcai Range Massif (SZRM) of NE China. This dataset provides insights into the Neoproterozoic tectonic setting of the SZRM and the links between this magmatism and the evolution of the Rodinia supercontinent. The zircon U-Pb dating indicates that the Neoproterozoic magmatism within the SZRM can be subdivided into two stages: (1) a ∼917-911 Ma suite of syenogranites and monzogranites, and (2) an ∼841 Ma suite of granodiorites. The 917-911 Ma granitoids contain high concentrations of SiO2 (67.89-71.18 wt.%), K2O (4.24-6.91 wt.%), and Al2O3 (14.89-16.14 wt.%), and low concentrations of TFe2O3 (1.63-3.70 wt.%) and MgO (0.53-0.88 wt.%). They are enriched in the light rare earth elements (LREE) and the large ion lithophile elements (LILE), are depleted in the heavy REE (HREE) and the high field strength elements (HFSE; e.g., Nb, Ta, and Ti), and have slightly positive Eu anomalies, indicating that they are geochemically similar to high-K adakitic rocks. They have zircon εHf (t) values and TDM2 ages from -4.4 to +1.5 and 1915 Ma to 1592 Ma, respectively, suggesting that they were derived from a primary magma generated by the partial melting of ancient thickened lower crustal material. In comparison, the 841 Ma granodiorites contain relatively low concentrations of Al2O3 (14.50-14.58 wt.%) and K2O (3.27-3.29 wt.%), relatively high concentrations of TFe2O3 (3.78-3.81 wt.%) and the HREE, have negative Eu anomalies, and have zircon εHf (t) values and TDM2 ages from -4.7 to +1.0 and 1875 to 1559 Ma, respectively. These granodiorites formed from a primary magma generated by the partial melting of ancient crustal material. The ∼917-911 Ma magmatism within the SZRM is inferred to have formed in an orogenic setting, whereas the ∼841 Ma magmatism formed in an anorogenic setting related to either a post-orogenic tectonic event or the onset of Neoproterozoic

  15. Geochronology of granitic magmatism from Caraculo-Bibala region (SW Angola) and its correlation with Ribeira fold belt (SE Brazil)

    International Nuclear Information System (INIS)

    Carvalho, Heitor de; Tassinari, Colombo C.G.

    1992-01-01

    Rb-Sr whole-rock analyses of representative granitic rocks from the Bibala-Caraculo region, southwestern Angola, are used to determine the age and evolution of the acid plutonic events in this segment of the Angolan continental crust. The granitoids present a wide range of lithological types and compositions. Three time-intervals have been defined for the magmatism: 1,950 - 1,900 Ma; 1,750 - 1,700 Ma; 1,550 - 1,500 Ma. The oldest, though not very well defined, was obtained for the Chicalengue granitoid, the second one represents the Serra dos Gandarengos and Chonga granitoids and Luchipa-Pungue Granitic Complex and the youngest one comprises the Chicate and Caraculo granitic bodies and Numhino Granitic Complex. The initial 87 Sr/ 86 Sr ratios show characteristic values for each time-interval, as follows; 1,950 -1,900 Ma = 0,7015; 1,750 - 1,700 Ma = 0,7060 to 0,7075; 1,550 - 1,500 Ma 0,7048 - 0,7057, suggesting different sources for the granitoids within each geological period. In addition are presented two K-Ar ages for the basic rocks in SW Angola, with values of 1700 and 600 Ma, which represent a minimum ages for these rocks and are probably related to the Damara Orogeny. (author). 24 refs., 11 figs., 2 tabs

  16. the origin of late archaean granitoids in the sukumaland greenstone

    African Journals Online (AJOL)

    Mgina

    melting at the base of a late Archaean thickened sub-arc basaltic crust. Melting to form the Suite 1 granitoids occurred in the eclogite stability field whereas Suite 2 formed by melting at shallower ... of TTG in terms of slab melting processes.

  17. Petrogenesis of Jurassic granitoids at the northeastern margin of the North China Craton: New geochemical and geochronological constraints on subduction of the Paleo-Pacific Plate

    Science.gov (United States)

    Liu, Jin; Zhang, Jian; Liu, Zhenghong; Yin, Changqing; Zhao, Chen; Peng, Youbo

    2018-06-01

    At the junction between the North China Craton (NCC) and the Central Asian Orogenic Belt (CAOB), northern Liaoning province, NE China, there are widespread Jurassic igneous rocks. The tectonic setting and petrogenesis of these rocks are unresolved. Zircon U-Pb dating, whole-rock geochemistry, and Hf isotopic compositions of Jurassic granitoids were investigated to constrain their ages and petrogenesis in order to understand the tectonic evolution of the Paleo-Pacific Ocean along the northeastern margin of the NCC. Geochronological data indicate that magmatism occurred between the early and late Jurassic (180-156 Ma). Despite the wide range in ages of the intrusions, Jurassic granitoids were likely derived from a similar or common source, as inferred from their geochemical and Hf isotopic characteristics. Compared to the island arc andesite-dacite-rhyolite series, the Jurassic granitoids are characterized by higher SiO2, Al2O3, and Sr contents, and lower MgO, FeOT, Y, and Yb contents, indicating that the primary magmas show typical characteristics of adakitic magmas derived from partial melting of thickened lower crust. These findings, combined with their εHf(t) values (+1.4 to +5.4) and two-stage model ages (1515-1165 Ma), indicate the primary magmas originated from partial melting of juvenile crustal material accreted during the Mesoproterozoic. They are enriched in large-ion lithophile elements (e.g., Rb, K, Th, Ba, and U) and light rare-earth elements (REE), and depleted in high-field-strength elements (e.g., Nb, Ta, Ti, and P) and heavy REE. Based on these findings and previous studies, we suggest that the Jurassic adakitic granitoids (180-156 Ma) were formed in an active continental margin and compressive tectonic setting, related to subduction of the Paleo-Pacific Plate.

  18. Devonian granitoids and their hosted mafic enclaves in the Gorny Altai terrane, northwestern Central Asian Orogenic Belt: crust-mantle interaction in a continental arc setting

    Science.gov (United States)

    Chen, Ming; Sun, Min

    2016-04-01

    Granitoids are a major component in the upper continental crust and hold key information on how did the continental crust grow and differentiate. This study focuses on the Yaloman intrusive complex from the Gorny Altai terrane, northwestern Central Asian Orogenic Belt (CAOB). The association of granitoids and mafic enclaves can provide important clues on the source nature, petrogenetic processes and geodynamic setting of the Yaloman intrusive complex, which in turn will shed light on the crustal evolution in the northwestern CAOB. Zircon U-Pb dating shows that the granitoids, including quartz diorites and granodiorites, were emplaced in ca. 389-387 Ma. The moderate Na2O + K2O contents and low A/CNK values indicate that these rocks belong to the sub-alkaline series with metaluminous to weakly peraluminous compositions. The granitoids yield two-stage zircon Hf model ages of ca. 0.79-1.07 Ga and whole-rock Nd model ages of ca. 0.90-0.99 Ga, respectively, implying that they were mainly sourced from Neoproterozoic juvenile crustal materials. The mafic enclaves show an almost identical crystallization age of ca. 389 Ma. The identification of coarse-grained xenocrysts and acicular apatites, together with the fine-grained texture, makes us infer that these enclaves are likely to represent magmatic globules commingled with the host magmas. The low SiO2 and high MgO contents of the mafic enclaves further suggest that substantial mantle-derived mafic melts were probably involved in their formation. Importantly, the SiO2 contents of the granitoids and mafic enclaves are well correlated with other major elements and most of the trace elements. Also a broadly negative correlation exists between the SiO2 contents and whole-rock epsilon Nd (390 Ma) values of the granitoids. Given the observation of reversely zoned plagioclases within the granitoids and the common occurrence of igneous mafic enclaves, we propose that magma mixing probably played an important role in the formation

  19. Syn-collisional I-type Esenköy Pluton (Eastern Anatolia-Turkey): An indication for collision between Arabian and Eurasian plates

    Science.gov (United States)

    Açlan, Mustafa; Altun, Yusuf

    2018-06-01

    The Esenköy pluton which is situated in the East Anatolian Accretionary Complex (EACC) is represented by I-type, metalumino, calc-alkaline, VAG + syn-COLG, gabbro, diorite, quartz diorite, tonalite and granodiorite type rocks. This paper presents the characteristics of the above granitoids on their major, trace, rare earth elements (REE) and their zircon U-Pb dating. Zircon U-Pb crystallisation ages for gabbro, tonalite and granodiorite are 22.3 ± 0.2 Ma, 21.7 ± 0.2 Ma and 21.8 ± 0.2 Ma respectively. Esenköy granitoids show medium and high-K calc-alkaline character, with six exceptional K-poor sample plot in tholeiitic series field. The Rb/Y-Nb/Y diagram for Esenköy granitoids display subduction zone enrichment trend. The data which obtained from major, trace and REE geochemical characteristics and 206Pb/238U ages indicate that the collision which is take place between Arabian and Eurasian plates along the Bitlis-Zagros suture zone has begun in the Early Miocene (Aquitanian) or before from Early Miocene.

  20. The tardi-Pan-African granitoids of South-Westerner Anti-Atlas (Morocco: Evolution from magnesian to ferroan type. Example of the Ifni inlier

    Directory of Open Access Journals (Sweden)

    El Aouli, E. H.

    2007-06-01

    Full Text Available The study of the neoproterozoic granitoids in the Ifni Inlier and those of the other inliers in south-westerner Anti-Atlas shows that this magmatism evolves from magnesian to ferroan type. In the Ifni inlier, these granitoids outcrop within the sedimentary and volcanogenic formations of the Ouarzazate Super- Group SGO (615 to 540 My. They belong to two distinct magmatic episodes (i an early one composed of magnesian granitoids with alkali-calcic and metaluminous to slightly aluminous character (quartz bearing diorite, granodiorite and monzogranite intrusive in the lower formations of the SGO, and (ii a late episode associated to the summit of the SGO volcanites, which includes granites and sub-volcanic syenogranites of iron-bearing type and alkali-calcic to alkaline affinity. These magmatisms resulting from the partial melting of mixed material mark the end of the last Panafrican episode and would be set up in a transition from orogenic to anorogenic settings which announce the Paleozoic cycle. They would be contemporary to posterior with the exhumation of the extensive metamorphic domes of the Western Anti-Atlas.El estudio de los granitoides neoproterozoicos de la “boutonnière” (complejo plutono-metamórfico profundo con geometría subcircular de Ifni y de los de otras “boutonnières” del dominio suroccidental del Anti-Atlas, demuestra que este magmatismo evoluciona desde un tipo magnésico hacia un tipo férrico. En la “boutonnière” de Ifni, estos granitoides afloran en el interior de formaciones sedimentarias y volcano-sedimentarias del Supergrupo de Ouarzazate SGO (615 a 540 Ma. Pertenecen a dos episodios magmáticos diferentes (i un episodio precoz compuesto de granitoides magnésicos, calcoalcalinos y metaluminosos a poco aluminosos (dioritas con cuarzo, granodioritas y monzogranitos que intruyen en las formaciones inferiores del SGO, (ii un episodio tardío asociado con un vulcanismo terminal a techo del

  1. Tibetan Magmatism Database

    Science.gov (United States)

    Chapman, James B.; Kapp, Paul

    2017-11-01

    A database containing previously published geochronologic, geochemical, and isotopic data on Mesozoic to Quaternary igneous rocks in the Himalayan-Tibetan orogenic system are presented. The database is intended to serve as a repository for new and existing igneous rock data and is publicly accessible through a web-based platform that includes an interactive map and data table interface with search, filtering, and download options. To illustrate the utility of the database, the age, location, and ɛHft composition of magmatism from the central Gangdese batholith in the southern Lhasa terrane are compared. The data identify three high-flux events, which peak at 93, 50, and 15 Ma. They are characterized by inboard arc migration and a temporal and spatial shift to more evolved isotopic compositions.

  2. Permo-Triassic arc-like granitoids along the northern Lancangjiang zone, eastern Tibet: Age, geochemistry, Sr-Nd-Hf isotopes, and tectonic implications

    Science.gov (United States)

    Wang, Xinyu; Wang, Shifeng; Wang, Chao; Tang, Wenkun

    2018-05-01

    Large volumes of Permo-Triassic granitoids are exposed along the Northern Lancangjiang zone, eastern Tibet, and these rocks provide insights into the tectonic evolution of the Paleo-Tethys Ocean. We conducted detailed geological fieldwork and geochemical analysis of the Xiaochangdu and Kagong plutons that crop out along the Northern Lancangjiang magmatic belt. Zircon U-Pb data constrain the emplacement of the Xiaochangdu quartz diotites to between 263 and 257 Ma, and the Kagong granites and diorites to between 234 and 232 Ma. The Xiaochangdu quartz diorites are enriched in light rare earth (LREE) and large ion lithophile elements (LILE), depleted in high field strength elements (HFSE), have low (87Sr/86Sr)i ratios, and near-positive εNd(t) (-0.26 to 1.58) and εHf(t) (0.68-8.83) values, similar to typical subduction- related mantle-derived arc magmas. They are also characterized by high Al2O3 concentrations and low Nb/U (3.48-7.59) and Ce/Pb (3.22-4.86) ratios, indicating that their mantle source was modified by subducted pelagic sediments; Coeval granites and diorites from the Kagong pluton exhibit low A/CNK values, high LREE/HREE (heavy rare earth element) ratios, enrichment in LILE, and depletion in HFSE, also characteristic of typical arc magmas. Their variable SiO2 contents (57%- 75%), (87Sr/86Sr)i ratios, and εNd(t) (1.02-4.49) and εHf(t) (2.52-6.93) values, and relatively high zircon saturation temperatures (721-827 °C), suggest underplating of mantle-derived mafic melts beneath the lower crust. Their magmatic evolution can be explained using a MASH model. In combination with regional geological studies, our geochemical and geochronological results suggest that the late Permian Xiaochangdu and Late Triassic Kagong arc-like granitoids represent a section of a Permo-Triassic magmatic arc that was associated with the eastward subduction of the Paleo-Tethys oceanic slab beneath the Northern Qiangtang-Changdu terrane. Combined with other geological evidence

  3. Evolution of Brasiliano-age granitoid types in a shear-zone environment, Umarizal-Caraubas region, Rio Grande do Norte, northeast Brazil

    Science.gov (United States)

    Galindo, A. C.; Dall'Agnol, R.; McReath, I.; Lafon, J. M.; Teixeira, N.

    1995-01-01

    A sequence of Brasiliano-age granitoid types is exposed in a small area near the cities of Umarizal and Caraúbas in Rio Grande do Norte State, Northeast Brazil. Porphyritic K-alkali-calcic monzogranite is an important facies of the oldest Caraúbas intrusion (RbSr whole rock isochron age of ca. 630 Ma), which suffered solid-state deformation due to movements on a major NE-trending shear zone. The intrusion of the Prado and part of the Quixaba bodies was probably controlled by the shear zone. These two bodies include mafic/intermediate rocks, some of which contain two pyroxenes, and have hybrid, partly alkaline and partly shoshonitic geochemical characteristics. Rock types and ages are similar to those of some Pan-African occurrences in southwestern Nigeria. The Tourão body, intruded at ca. 590 Ma, presents preferred mineral orientations which are probably largely magmatic, since little evidence is found for widespread solid-state deformation. On the other hand, its intrusion may have been facilitated by the presence of the shear-zone faults. The rocks form a monomodal felsic K-alkali-calcic suite. With the exception of the Quixaba body, all these earlier granitoids are magmatic epidote- and magnetite-bearing porphyritic monzogranites with trace element geochemical characteristics of modern syn-collisional granites. The latest intrusion at ca. 545 Ma is mainly represented by potassic quartz syenites and related rocks, some of which contain fayalite or ferrohypersthene. These rocks possess neither well developed mineral orientations of magmatic origin nor signs of solid-state deformation. They are mineralogically similar to, but younger than some of the "bauchites" of central Nigeria. Geochemical signatures are comparable with those of modern within-plate granites. All granitoids present high ( 87Sr/ 86Sr)i ratios which range from 0.708 to 0.712, and increase with decreasing age. Such ratios are compatible with important or dominant crustal contributions. On the

  4. Geochemical characteristics of Proterozoic granite magmatism from ...

    Indian Academy of Sciences (India)

    T Yellappa

    MS received 20 November 2016; revised 12 July 2017; accepted 14 July 2017; published online 6 March 2018. Granitoid ...... India; Oxford University Press, New York, 223p. Nathan N P ..... Kwon, Chansoo Park, Nagesh P, Mohanty D P and.

  5. Petrography and geochronology (U/Pb-Sm/Nd) the Passagem Granite, Pensamiento Granitoid Complex, Paragua Terrane, SW Amazon Craton, Mato Grosso, Brazil

    International Nuclear Information System (INIS)

    Jesus, Gisely Carmo de; Sousa, Maria Zelia Aguiar de; Ruiz, Amarildo Salina; Matos, Joao Batista de

    2010-01-01

    The Passagem granite includes stocks, plugs and dikes located in the Ricardo Franco hill - Vila Bela da Santissima Trindade region - state of Mato Grosso, central Brazil. The Passagem Granite is included in the Paragua terrane - SW Amazonian Craton. It consists of isotropic monzogranite, sienogranite and more rarely granodiorites with leucocratic dark gray to white color. These rocks range from hypidomorphic inequigranular to xenomorphic texture, fine to medium grained. Biotite is the only primary mafic present as essential phase and characterize an expanded slightly acid sequence formed by a sub-alkaline magmatism of high-potassium calc-alkaline, slightly peraluminous composition from arc magmatic tectonic environment during a post-collisional period. Mechanism of fractional crystallization of plagioclase, biotite, titanite, apatite and zircon associated with simultaneous crustal assimilation are suggested for the evolution of these rocks. The results support the hypothesis of a post-collisional magmatism in the Paragua terrane at 1284 +- 20 Ma corresponding to the crystallization age of the Passagem granite. This paper propose that Passagem Granite represents as an extension in Brazilian terrane of the Pensamiento Granitoid Complex. (author)

  6. Three tier transition of Neoarchean TTG-sanukitoid magmatism in the Beit Bridge Complex, Southern Africa

    Science.gov (United States)

    Rajesh, H. M.; Belyanin, G. A.; Van Reenen, D. D.

    2018-01-01

    Neoarchean TTG-sanukitoid associations of contrasting scales occur within the Beit Bridge Complex terrane of the Limpopo Complex in southern Africa. These include the smaller 2.65-2.63 Ga Avoca granitoid and the voluminous 2.73-2.64 Ga Alldays granitoid. This study characterizes the wide compositional spectrum preserved in these two granitoids. The elliptical Avoca pluton consists of a biotite-amphibole-orthopyroxene ± clinopyroxene-bearing core that is dominantly trondhjemite with less dominant tonalite and granodiorite variants, and a thin amphibole-biotite-bearing granite rim, with local occurrence of two-pyroxene-bearing metabasite boudins. While both the core and rim rocks exhibit a linear fabric, the granite in addition preserves a penetrative foliation. Field relations of granite enclaves in the core rocks together with available ages indicate that the core rocks intruded the granite. The foliated biotite ± amphibole-bearing Alldays granitoid contains inclusions of older supracrustals and rocks of the Messina layered intrusion, and is widely distributed. Compositionally, it include tonalites and granodiorites and to a lesser extent trondhjemites. Both the Avoca core and rim rocks are characterized by difference in mineral chemistry, with the mafic minerals Mg-rich in the TTG core, while they are Fe-rich in the granite and metabasite. In comparison, biotite is Mg-rich and amphibole is Fe-rich in the Alldays granitoid. Two groups of Alldays TTG can be delineated in terms of whole-rock geochemical characteristics, and are comparable to the low- to medium-pressure TTG groups delineated by Moyen (2011), while the Avoca TTG is similar to the high-pressure TTG group. The lowest silica samples from each group of granitoid have geochemical characteristics comparable to Archean sanukitoids, with those from the Avoca granitoid similar to low-Ti sanukitoids, and those from the Alldays granitoid similar to low-Ti and high-Ti sanukitoids. Separate petrogenetic models

  7. Insights into crystal growth rates from a study of orbicular granitoids from western Australia

    Science.gov (United States)

    Zhang, J.; Lee, C. T.

    2017-12-01

    The purpose of this study is to develop new tools for constraining crystal growth rate in geologic systems. Of interest is the growth of crystals in magmatic systems because crystallization changes the rheology of a magma as well as provides surfaces on which bubbles can nucleate. To explore crystal growth in more detail, we conducted a case study of orbicular granitoids from western Australia. The orbicules occur as spheroids dispersed in a granitic matrix. Most orbicules have at least two to three concentric bands, composed of elongate and radially oriented hornblende surrounded by interstitial plagioclase. We show that mineral modes and hence bulk composition at the scale of the band is homogeneous from rim to core. Crystal number density decreases and crystal size increases from rim to core. These observations suggest that the orbicules crystallized rapidly from rim to core. We hypothesize that the orbicules are blobs of hot dioritic liquid injected into a cold granitic magma and subsequently cooled and solidified. Crystals stop growing when the mass transport rate tends to zero due to the low temperature. We estimated cooling timescales based on conductive cooling models, constraining crystal growth rates to be 10-6 to 10-5 m/s. We also show that the oscillatory banding is controlled by disequilibrium crystallization, wherein hornblende preferentially crystallizes, resulting in the diffusive growth of a chemical boundary layer enriched in plagioclase component, which in turns results in crystallization of plagioclase. We show that the correlation between the width of each crystallization couplet (band) with distance from orbicule rim is linear, with the slope corresponding to the square root of the ratio between chemical diffusivity in the growth medium and thermal diffusivity. We estimate chemical diffusivity of 2*10-7 m2/s, which is remarkably fast for silicate liquids but reasonable for diffusion in hot aqueous fluids, suggesting that crystallization

  8. The mechanics of granitoid systems and maximum entropy production rates.

    Science.gov (United States)

    Hobbs, Bruce E; Ord, Alison

    2010-01-13

    A model for the formation of granitoid systems is developed involving melt production spatially below a rising isotherm that defines melt initiation. Production of the melt volumes necessary to form granitoid complexes within 10(4)-10(7) years demands control of the isotherm velocity by melt advection. This velocity is one control on the melt flux generated spatially just above the melt isotherm, which is the control valve for the behaviour of the complete granitoid system. Melt transport occurs in conduits initiated as sheets or tubes comprising melt inclusions arising from Gurson-Tvergaard constitutive behaviour. Such conduits appear as leucosomes parallel to lineations and foliations, and ductile and brittle dykes. The melt flux generated at the melt isotherm controls the position of the melt solidus isotherm and hence the physical height of the Transport/Emplacement Zone. A conduit width-selection process, driven by changes in melt viscosity and constitutive behaviour, operates within the Transport Zone to progressively increase the width of apertures upwards. Melt can also be driven horizontally by gradients in topography; these horizontal fluxes can be similar in magnitude to vertical fluxes. Fluxes induced by deformation can compete with both buoyancy and topographic-driven flow over all length scales and results locally in transient 'ponds' of melt. Pluton emplacement is controlled by the transition in constitutive behaviour of the melt/magma from elastic-viscous at high temperatures to elastic-plastic-viscous approaching the melt solidus enabling finite thickness plutons to develop. The system involves coupled feedback processes that grow at the expense of heat supplied to the system and compete with melt advection. The result is that limits are placed on the size and time scale of the system. Optimal characteristics of the system coincide with a state of maximum entropy production rate. This journal is © 2010 The Royal Society

  9. Granitoids of South Korea and Southwest Japan. Trace element evidence regarding their differentiation

    International Nuclear Information System (INIS)

    Tsusue, Akio; Mizuta, Toshio; Tamai, Tadaharu.

    1994-01-01

    Although we have already published our trace element data for granitoids of South Korea and Southwest Japan, and we have interpreted REE patterns and Ba, Rb and Sr relationships of the granitoids (Tsusue et al., 1986, 1987a, 1987b, 1988), we intend to review briefly the trace element data of South Korea and Southwest Japan in this report. (J.P.N.)

  10. Magmatism on the Moon

    Science.gov (United States)

    Michaut, Chloé; Thorey, Clément; Pinel, Virginie

    2016-04-01

    Volcanism on the Moon is dominated by large fissure eruptions of mare basalt and seems to lack large, central vent, shield volcanoes as observed on all the other terrestrial planets. Large shield volcanoes are constructed over millions to several hundreds of millions of years. On the Moon, magmas might not have been buoyant enough to allow for a prolonged activity at the same place over such lengths of time. The lunar crust was indeed formed by flotation of light plagioclase minerals on top of the lunar magma ocean, resulting in a particularly light and relatively thick crust. This low-density crust acted as a barrier for the denser primary mantle melts. This is particularly evident in the fact that subsequent mare basalts erupted primarily within large impact basins where at least part of the crust was removed by the impact process. Thus, the ascent of lunar magmas might have been limited by their reduced buoyancy, leading to storage zone formation deep in the lunar crust. Further magma ascent to shallower depths might have required local or regional tensional stresses. Here, we first review evidences of shallow magmatic intrusions within the lunar crust of the Moon that consist in surface deformations presenting morphologies consistent with models of magma spreading at depth and deforming an overlying elastic layer. We then study the preferential zones of magma storage in the lunar crust as a function of the local and regional state of stress. Evidences of shallow intrusions are often contained within complex impact craters suggesting that the local depression caused by the impact exerted a strong control on magma ascent. The depression is felt over a depth equivalent to the crater radius. Because many of these craters have a radius less than 30km, the minimum crust thickness, this suggests that the magma was already stored in deeper intrusions before ascending at shallower depth. All the evidences for intrusions are also preferentially located in the internal

  11. The age of Male Karpaty Mts. granitoid rocks determined by Rb-Sr isochrone method

    International Nuclear Information System (INIS)

    Badgasaryan, G.P.; Gukasyan, R.Kh.; Veselsky, J.

    1982-01-01

    The results are presented of nuclear geochronological datings of Male Karpaty Mts. granitoids by Rb-Sr isochrone method. Using the method the age of Bratislava massif granitoids was established to be 347+-4 mil. y. at ( 87 Sr/ 86 Sr)=0.7076+-0.0013 and the age of Modra massif granitoids to be 324+-18 mil. y. at ( 87 Sr/ 86 Sr)=0.7075+-0.00032 (2σ). The relative agreement of age of both massifs as well as the agreement of the primary ratio ( 87 Sr/ 86 Sr) 0 not only testifies to their continuity in age but also in genesis. The same relations also confirm the genetic dependence of pegmatites and leucocratic granitoids on fundamental types of granitoids building up the Bratislava and Modra massifs. (author)

  12. Emplacement and deformation of the Cerro Durazno Pluton delineates stages of the lower Paleozoic tectono-magmatic evolution in NW-Argentina

    Science.gov (United States)

    Hongn, F.; Riller, U.

    2003-04-01

    Regional-scale transpression and transtension are considered to be important in the lower Paleozoic tectono-magmatic evolution of metamorphic and granitoid basement rocks of the southern central Andes. In order to test whether such kinematic changes affected Paleozoic basement rocks on the local scale, i.e. in the Eastern Cordillera of NW-Argentina, we performed a detailed field-based structural analysis of the 456 Ma granitoid Cerro Durazno pluton (CDP). The results of our analysis point to the following stages in the geodynamic evolution of this area: (1) Metamorphism and deformation of Neoproterozoic-Paleozoic basement rocks occurred at high T and low to medium P prior to emplacement of the CDP. This lead to the formation of schists and migmatites characterized by pervasive planar and linear mineral shape fabrics and the growth of andalusite, cordierite and fibrolite. (2) Magmatic foliation in the CDP is defined by the shape-preferred orientation of euhedral feldspar phenocrysts and microgranitoid enclaves. These fabrics are concordant to the NE-SW striking intrusive contact with migmatitic host rocks. The lack of submagmatic or high-T solid-state fabrics in the CDP may indicate that cooling and solidification of granitoid magma was not accompanied by regional deformation. Alternatively, emplacement of granitoid magma may have been facilitated by the creation of open space at mid-crustal level induced by regional deformation. (3) Ductile deformation under greenschist metamorphic conditions overprinted magmatic fabrics of the CDP. This is evident by NW-SE striking metamorphic foliation surfaces transecting magmatic shape fabrics at high angles. During this deformation, the pluton was thrust on a SW-dipping shear zone toward the NE over low-grade metamorphic host rocks which lead to a condensation of metamorphic isograds in the host rocks. Ages of strained pegmatitic dikes indicate that this deformation occurred at about 430 Ma. In summary, the difference in age

  13. Granites and granitoids of the southern region - Granite molybdenite system

    International Nuclear Information System (INIS)

    Issler, R.S.

    1987-01-01

    Economic concentrations of molybdenum are genetically closely associated with acidic and moderately acid granitoids-granites, granodiorites, monzonites and diorites, and are located in two geotectonic settings: subduction-related and rift-related. The aim of this paper is twofold, first succinctly approach the geology, tectonic setting and chemical parameters of the 'granite molybdenite system' as defined by Mutschler and/or alcali granite porphyry bodies emplaced in the North American continent for occasion of a Mesozoic-Fanerozoic extensile event; second to relate the computer-assisted evaluation of 422 major element chemical analysis of granites and granitoids of southern region of Brazil, using chemical fingerprints (SiO 2 ≥ 74. Owt%, Na 2 O ≤ 3.6wt%, K 2 O ≥ 4.5wt%), and K 2 O/Na 2 O ratio > 1.5 developed and testified from North American and Finnish occurrences, may locate molybdenite-bearing granite bodies with high exploration potential. These techniques suggest that some late Precambrian to early Paleozoic granite-rhyolite assemblages inserted at domains of the SG. 22/23 Curitiba/Iguape, SH. 21/22 Uruguaiana/Porto Alegre and SI.22 Lagoa Mirim Sheets, have exploration potential for molybdenum. (author) [pt

  14. Magmatism and polymetallic mineralization in southwestern Qinzhou-Hangzhou metallogenic belt, South China

    Science.gov (United States)

    Huang, Xudong; Lu, Jianjun; Wang, Rucheng; Ma, Dongsheng

    2016-04-01

    As Neoproterozoic suture zone between the Yangtze Block and Cathaysia Block, Qinzhou-Hangzhou metallogenic belt is one of the 21 key metallogenic belts in China. Intensive multiple-aged felsic magmatism and related polymetallic mineralization take place in this belt. Although Neoproterozoic, Paleozoic, Triassic granites and associated deposits have been found in southwestern Qinzhou-Hangzhou metallogenic belt, Middle-Late Jurassic (150-165 Ma) magmatism and related mineralization is of the most importance. Three major kinds of Middle-Late Jurassic granitoids have been distinguished. (Cu)-Pb-Zn-bearing granitoids are slightly differentiated, calc-alkaline and metaluminous dioritic to granodioritic rocks. Sn-(W)-bearing granites contain dark microgranular enclaves and have high contents of REE and HFSE, suggesting affinities of aluminous A-type (A2) granites. W-bearing granites are highly differentiated and peraluminous rocks. (Cu)-Pb-Zn-bearing granitoids have ɛNd(t) values of -11 ˜ -4 and ɛHf(t) values of -12 ˜ -7, corresponding to TDMC(Nd) from 1.4 to 1.8 Ga and TDMC(Hf) from 1.6 to 2.0 Ga, respectively. The ɛNd(t) values of W-bearing granites vary from -11 to -8 with TDMC(Nd) of 1.6 ˜ 1.9 Ga and ɛHf(t) values change from -16 to -7 with TDMC(Hf) of 1.5 ˜ 2.0 Ga. Compared with (Cu)-Pb-Zn-bearing granitoids and W-bearing granites, the Sn-(W)-bearing granites have higher ɛNd(t) (-8 ˜ -2) and ɛHf(t) (-8 ˜ -2) values and younger TDMC(Nd) (1.1 ˜ 1.6 Ga) and TDMC(Hf) (1.2 ˜ 1.8 Ga) values, showing a more juvenile isotopic character. Sn-(W)-bearing granites originate from partial melting of granulitized lower crust involved with some mantle-derived materials. W-bearing granites are derived from partial melting of crust. (Cu)-Pb-Zn-bearing granitoids are also derived from crust but may be influenced by more mantle-derived materials. For (Cu)-Pb-Zn deposits, skarn and carbonate replacement are the most important mineralization types. Cu ore bodies mainly

  15. Gallium and germanium geochemistry during magmatic fractionation and post-magmatic alteration in different types of granitoids: A case study from the Bohemian Massif (Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Breiter, Karel; Gardenová, N.; Kanický, V.; Vaculovič, T.

    2013-01-01

    Roč. 64, č. 3 (2013), s. 171-180 ISSN 1335-0552 R&D Projects: GA ČR GAP210/10/1309 Institutional support: RVO:67985831 Keywords : gallium * geochemistry * germanium * granites * ICP -MS Subject RIV: DD - Geochemistry Impact factor: 0.835, year: 2013

  16. Petrography and geochronology (U/Pb-Sm/Nd) the Passagem Granite, Pensamiento Granitoid Complex, Paragua Terrane, SW Amazon Craton, Mato Grosso, Brazil; Petrologia e geocronologia (U/Pb-Sm/Nd) do Granito Passagem, Complexo Granitoide Pensamiento, SW do Craton Amazonico (MT)

    Energy Technology Data Exchange (ETDEWEB)

    Jesus, Gisely Carmo de, E-mail: giselycarmo@hotmail.co [Universidade Federal de Mato Grosso (ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Programa de Pos-Graduacao em Geociencias; Sousa, Maria Zelia Aguiar de, E-mail: mzaguiar@terra.com.b [Universidade Federal de Mato Grosso(ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Dept. de Recursos Minerais; Ruiz, Amarildo Salina; Matos, Joao Batista de, E-mail: asruiz@gmail.co, E-mail: jmatos@cpd.ufmt.b [Universidade Federal de Mato Grosso (ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Dept. de Geologia Geral

    2010-09-15

    The Passagem granite includes stocks, plugs and dikes located in the Ricardo Franco hill - Vila Bela da Santissima Trindade region - state of Mato Grosso, central Brazil. The Passagem Granite is included in the Paragua terrane - SW Amazonian Craton. It consists of isotropic monzogranite, sienogranite and more rarely granodiorites with leucocratic dark gray to white color. These rocks range from hypidomorphic inequigranular to xenomorphic texture, fine to medium grained. Biotite is the only primary mafic present as essential phase and characterize an expanded slightly acid sequence formed by a sub-alkaline magmatism of high-potassium calc-alkaline, slightly peraluminous composition from arc magmatic tectonic environment during a post-collisional period. Mechanism of fractional crystallization of plagioclase, biotite, titanite, apatite and zircon associated with simultaneous crustal assimilation are suggested for the evolution of these rocks. The results support the hypothesis of a post-collisional magmatism in the Paragua terrane at 1284 +- 20 Ma corresponding to the crystallization age of the Passagem granite. This paper propose that Passagem Granite represents as an extension in Brazilian terrane of the Pensamiento Granitoid Complex. (author)

  17. Record of Permian-Early Triassic continental arc magmatism in the western margin of the Jiamusi Block, NE China: petrogenesis and implications for Paleo-Pacific subduction

    Science.gov (United States)

    Yang, Hao; Ge, Wenchun; Dong, Yu; Bi, Junhui; Wang, Zhihui; Ji, Zheng; Yang, H.; Ge, W. C.; Dong, Y.; Bi, J. H.; Wang, Z. H.; Ji, Z.

    2017-09-01

    In this paper, we report zircon U-Pb ages, Hf isotopes and whole-rock geochemical data for the Permian to Early Triassic granitoids from the western margin of the Jiamusi Block (WJB), NE China. The intermediate to felsic (SiO2 = 59.67-74.04 wt%) granitoids belong to calc-alkaline series and are characterized by enrichments in light rare earth elements and large ion lithophile elements with pronounced negative Nb, Ta and Ti anomalies, revealing typical continental magmatic arc geochemical signatures. The zircon U-Pb determinations on the granodiorite, monzogranite, syenogranite and quartz diorite samples yielded ages between ca. 275-245 Ma, which, together with the published coeval intrusive rocks, indicates that Permian to Early Triassic continental arc magmatism occurred extensively in the WJB. The low and mainly negative zircon ɛ Hf( t) values between -7.6 and +1.6 and the zircon Hf model ages of 1.2-1.8 Ga, which are significantly older than their crystallization ages, suggest that they were mainly derived from reworking of ancient crustal materials with a limited input of juvenile components. The geochemical systematics and petrogenetic considerations indicate that the studied granitoids were generated from a zone of melting, assimilation, storage, and homogenization, i.e., a MASHed zone at the base of Paleo- to Mesoproterozoic continental crust, where large portions of igneous rocks and minor clay-poor sediments involved in the source region. In combination with regional geological data, we argue that the Jiamusi Block was unlikely the rifted segment of the Songliao Block and two possible geodynamical models were proposed to interpret the formation of the ca. 275-245 Ma granitoids in the WJB. In the context of Permian global plate reconstruction, we suggest that Paleo-Pacific plate subduction was initiated in the Permian to Early Triassic beneath the Jiamusi Block, and even whole eastern NE China.

  18. Geochemical studies, magmatic evolution, microstructures and replacement mechanisms in Jebale-Barez granitoid Complex (East and Southeast Jiroft)

    OpenAIRE

    Jamal Rasouli; Mansour Ghorbani; Vahid Ahadnejad

    2017-01-01

    Introduction The Jebale-Barez Plutonic Complex (JBPC) is composed of many intrusive bodies and is located in the southeastern province of Kerman on the longitude of the 57◦ 45 ' east to 58◦ 00' and Northern latitudes 28◦ 30' to 29◦ 00'. The petrologic composition is composed of granodiorite, quartzdiorite, granite, alkali-granite, and trace amounts of tonalite with dominant granodiorite composition. Previously, the JBPC was separated into three plutonic phases by Ghorbani (2014). The fi...

  19. The magmatism and metamorphism at the Malayer area, Western Iran

    Science.gov (United States)

    Ahadnejad, V.; Valizadeh, M. V.; Esmaeily, D.

    2009-04-01

    The Malayer area is located in the NW-SE aligned Sanandaj-Sirjan metamorphic belt, western Iran and consists mainly of Mesozoic schists so-called Hamadan Phyllites, Jurassic to Tertiary intrusive rocks and related contact metamorphic aureoles, aplites and pegmatites. The Sanandj-Sirjan Zone is produced by oblique collisional event between Arabian plate and Central Iran microcontinent. Highest level of regional metamorphism in the area is greenschist facies and injection of felsic magmas is caused contact metamorphism. Magmatism is consist of a general northwest trend large felsic to intermediate intrusive bodies. The main trend of structural features i.e. faults, fractures and other structural features is NW-SE. The Malayer granitoid complex is ellipsoid in shape and has NW-SE foliation especially at the corners of the intrusions. Petrography of the magmatic rocks revealed recrystallization of quartz and feldspars, bending of biotite, and aligment of minerals paralle to the main trend of magmatic and metamorphic country rocks. These indicated that intrusion of felsic magma is coincide to the regional metamorphism and is syn-tectoinc. Non-extensive contact metamorphism aureoles and rareness of pegmatite and aplite in the area are interpreted as injection of felsic magmas into the high-strain metamorphic zone. The regional metamorphic rocks mainly consist of meta-sandstone, slate, phyllite, schist. These gray to dark metasedimentary rocks are consist of quartz, muscovite, turmaline, epidote, biotite and chlorite. Sheeted minerals form extended schistosity and study of porphyroblast-matrix relationships shows that injection of granitic magma into the country rocks is syn to post-tectonic. Syn-tectonic indicating porphyroblast growth synchronous with the development of the external fabric. The thermal contact area of the granite can be observed in the contact margin of granite and regional metamorphic rocks, where it produced hornfelses, andalusit-garnet schists and

  20. Oxidation state inherited from the magma source and implications for mineralization: Late Jurassic to Early Cretaceous granitoids, Central Lhasa subterrane, Tibet

    Science.gov (United States)

    Cao, MingJian; Qin, KeZhang; Li, GuangMing; Evans, Noreen J.; McInnes, Brent I. A.; Li, JinXiang; Zhao, JunXing

    2018-03-01

    Arc magmas are more oxidized than mid-ocean ridge basalts; however, there is continuing debate as to whether this higher oxidation state is inherited from the source magma or developed during late-stage magmatic differentiation processes. Well-constrained Late Jurassic to Early Cretaceous arc-related intermediate to felsic rocks derived from distinct magma sources provide us with a good opportunity to resolve this enigma. A series of granitoids from the western Central Lhasa subterrane were analyzed for whole-rock magnetic susceptibility, Fe2O3/FeO ratios, and trace elements in zircon. Compared to Late Jurassic samples (1.8 ± 2.0 × 10-4 emu g-1 oe-1, Fe3+/Fetotal = 0.32 ± 0.07, zircon Ce4+/Ce3+* = 15.0 ± 13.4), Early Cretaceous rocks show higher whole-rock magnetic susceptibility (5.8 ± 2.5 × 10-4 emu g-1 oe-1), Fe3+/Fetotal ratios (0.43 ± 0.04), and zircon Ce4+/Ce3+* values (23.9 ± 22.3). In addition, positive correlations among whole-rock magnetic susceptibility, Fe3+/Fetotal ratios, and zircon Ce4+/Ce3+* reveal a slight increase in oxidation state from fO2 = QFM to NNO in the Late Jurassic to fO2 = ˜NNO in the Early Cretaceous. Obvious linear correlation between oxidation indices (whole-rock magnetic susceptibility, zircon Ce4+/Ce3+*) and source signatures (zircon ɛHf(t), TDM C ages) indicates that the oxidation state was predominantly inherited from the source with only a minor contribution from magmatic differentiation. Thus, the sources for both the Late Jurassic and Early Cretaceous rocks were probably influenced by mantle wedge-derived magma, contributing to the increased fO2. Compared to ore-forming rocks at giant porphyry Cu deposits, the relatively low oxidation state (QFM to NNO) and negative ɛHf(t) (-16 to 0) of the studied granitoids implies relative infertility. However, this study demonstrates two potential fast and effective indices ( fO2 and ɛHf(t)) to evaluate the fertility of granitoids for porphyry-style mineralization. In an

  1. Post-collisional magmatism in the central East African Orogen: The Maevarano Suite of north Madagascar

    Science.gov (United States)

    Goodenough, K.M.; Thomas, Ronald J.; De Waele, B.; Key, R.M.; Schofield, D.I.; Bauer, W.; Tucker, R.D.; Rafahatelo, J.-M.; Rabarimanana, M.; Ralison, A.V.; Randriamananjara, T.

    2010-01-01

    Late tectonic, post-collisional granite suites are a feature of many parts of the Late Neoproterozoic to Cambrian East African Orogen (EAO), where they are generally attributed to late extensional collapse of the orogen, accompanied by high heat flow and asthenospheric uprise. The Maevarano Suite comprises voluminous plutons which were emplaced in some of the tectonostratigraphic terranes of northern Madagascar, in the central part of the EAO, following collision and assembly during a major orogeny at ca. 550 Ma. The suite comprises three main magmatic phases: a minor early phase of foliated gabbros, quartz diorites, and granodiorites; a main phase of large batholiths of porphyritic granitoids and charnockites; and a late phase of small-scale plutons and sheets of monzonite, syenite, leucogranite and microgranite. The main phase intrusions tend to be massive, but with variably foliated margins. New U-Pb SHRIMP zircon data show that the whole suite was emplaced between ca. 537 and 522 Ma. Geochemically, all the rocks of the suite are enriched in the LILE, especially K, and the LREE, but are relatively depleted in Nb, Ta and the HREE. These characteristics are typical of post-collisional granitoids in the EAO and many other orogenic belts. It is proposed that the Maevarano Suite magmas were derived by melting of sub-continental lithospheric mantle that had been enriched in the LILE during earlier subduction events. The melting occurred during lithospheric delamination, which was associated with extensional collapse of the East African Orogen. ?? 2009 Natural Environment Research Council.

  2. Magmatism and mineralization ages from northeast area of La Sierra de San Luis, Argentina

    International Nuclear Information System (INIS)

    Ulacco, Jose H

    2001-01-01

    Three igneous rock groups, characterized as pre, sin and post-kinematics, have intruded the crystalline basement of Sierra de San Luis, Argentina. The ore deposits are associated with Devonian to Carboniferous epizonal granite stocks and batholiths in an area underlain by metamorphic rocks. This granitoids are characterized as post-kinematics magmatism. Model lead ages on the ore deposits (338,8 - 292,1 Ma) are strongly supported by K-Ar ages of the intrusives. The bulk of the north Sierra de San Luis ore deposits are genetically related to late Carboniferous granite plutons. The ore bodies are tungsten veins with greisen envelopes, lead veins, epithermal fluorite veins and REE and Th deposit. A generalized scheme of ore bodies related to granites is proposed. The ore deposits and their lithotectonic setting are characteristic of Gondwana metallogenetic Epoch in the Sierra de San Luis (au)

  3. Determination of emplacement mechanism of Zafarghand granitoid Pluton (Southeast of Ardestan by using anisotropy of magnetic susceptibility method (AMS

    Directory of Open Access Journals (Sweden)

    Mahmoud Sadeghian

    2017-03-01

    Full Text Available Zafarghand granitoid pluton with compositional range from gabbro to granite and early to middle Miocene age cropped out about 35 km of SE Ardestan. This pluton intrudedthe Eocene volcanic and volcanosedimentary rocks of the Urumieh - Dokhtar structuralzone. In this research, for the first time, the emplacement mechanism of Zafarghandgranitoidic pluton method has been investigated using of anisotropy of magneticsusceptibility (AMS. Based on field observations, as well as petrography andinterpretations of magnetic parameters, Zafarghand pluton divided into 5 domains (1A,1B, 2, 3, 4 and 5. Domain 1, in turn, is divided into 1A and 1B. Domains 2 and 4 arelithologically, gabbro to quartzdiorite and have been emplaced first. They have playedas feeder zones. Domains 1A, 1B, 3, and 5 are dominantly granodioritic to graniticcomposition and have been emplaced as a big and low dip magmatic flow (or possibly as a sill. The occurrence of gabbro to quartzdiorite as well as grandiorite, granite andtonalite in the margin borders of the body, are all indication of magma mixing. It isshould be noted that during emplacement of the pluton studied, fractionalcrystallization, magma mixing and crustal contamination contributed to its generationand the evolution as well.

  4. Repeated granitoid intrusions during the Neoproterozoic along the western boundary of the Saharan metacraton, Eastern Hoggar, Tuareg shield, Algeria: An AMS and U-Pb zircon age study

    Science.gov (United States)

    Henry, B.; Liégeois, J. P.; Nouar, O.; Derder, M. E. M.; Bayou, B.; Bruguier, O.; Ouabadi, A.; Belhai, D.; Amenna, M.; Hemmi, A.; Ayache, M.

    2009-09-01

    The N-S oriented Raghane shear zone (8°30') delineates the western boundary of the Saharan metacraton and is, with the 4°50' shear zone, the most important shear zone in the Tuareg shield. It can be followed on 1000 km in the basement from southern Aïr, Niger to NE Hoggar, Algeria. Large subhorizontal movements have occurred during the Pan-African orogeny and several groups of granitoids intruded during the Neoproterozoic. We report U-Pb zircon datings (laser ICP-MS) showing that three magmatic suites of granitoids emplaced close to the Raghane shear zone at c. 790 Ma, c. 590 and c. 550 Ma. A comprehensive and detailed (158 sites, more than 1000 cores) magnetic fabric study was performed on 8 plutons belonging to the three magmatic suites and distributed on 200 km along the Raghane shear zone. The main minerals in all the target plutons do not show visible preferential magmatic orientation except in narrow shear zones. The AMS study shows that all plutons have a magnetic lineation and foliation compatible with the deformed zones that are zones deformed lately in post-solidus conditions. These structures are related to the nearby mega-shear zones, the Raghane shear zone for most of them. The old c. 793 Ma Touffok granite preserved locally its original structures. The magnetic structures of the c. 593 Ma Ohergehem pluton, intruded in the Aouzegueur terrane, are related to thrust structures generated by the Raghane shear zone while it is not the case of the contemporaneous plutons in the Assodé-Issalane terrane whose structures are only related to the subvertical shear zones. Finally, the c. 550 Ma granite group has magnetic structure related to the N-S oriented Raghane shear zone and its associated NNE-SSW structures when close to them, but NW-SE oriented when further. These NW-SE oriented structures appear to be characteristic of the late Neoproterozoic evolution of the Saharan metacraton and are in relation to the convergence with the Murzuq craton. This

  5. Piedra lata terrane of Uruguay: Rb-Sr geochronological data of two new paleoproterozoic (transamazonian) granitoids

    International Nuclear Information System (INIS)

    Cingolani, C; Bossi, J; Varela, R; Maldonado, S.; Pineyro, D.; Schipilov, A

    2001-01-01

    The Precambrian basement of Uruguay consists of three major terranes separated and crosscut by wide NE-striking subvertical transcurrent shear zones. The western terrane as a part of the Rio de la Plata Craton is known as the Piedra Alta Terrane (PAT). This is separated from the Nico Perez Terrane by the Sarandi del Yi-Piri olis subvertical shear zone (Bossi et al., 1993). A mafic dykes complex intruded the PAT at 1.8 Ga and was not later deformed. The PAT has equivalent rocks in the igneous-metamorphic basement of Tandilia region and the Martin Garcia Island, Buenos Aires Province, Argentina (Dalla Salda et al., 1988; Cingolani and Dalla Salda, 2000). The PAT shows no evidence of the Neoproterozoic orogenies and is considered a best preserved Paleoproterozoic block (Transamazonian Cycle). It contains three E-W trending belts of volcano-sedimentary rocks with low grade metamorphism. These are from south to north: Pando, San Jose and Andresito belts (Bossi et al., 1996). Associated with them, three granitic-gneissic zones he Ecilda Paullier, Florida and Feliciano- were recognized with magmatic intrusives emplaced at different crustal levels. The San Jose belt is the largest supracrustal unit and contains abundant volcanic and volcaniclastic rocks of low grade metamorphic (Paso Severino Fm.) with sheets of granitic rocks intercalated (Mutti et al., 1996; Bossi et al., 1996). The associated granitic rocks are of large areal extension, mostly granodiorites and tonalites, and minor monzogranite and gabbro (e.g. Cerro Rospide region), including xenoliths from Paso Severino Fm. Towards the north of the San Jose belt an important Florida granitized zone is developed in the central part of the PAT, where the Pintos massif was recognized. The main purpose of this contribution is to offer new Rb-Sr geochronological data from two granitoid units, The Cerro Rospide intrusive in Paso Severino Fm. and Pintos massif included in medium grade migmatic-metamorphic complex and its

  6. Geological evolution of the center-southern portion of the Guyana shield based on the geochemical, geochronological and isotopic studies of paleoproterozoic granitoids from southeastern Roraima, Brazil

    International Nuclear Information System (INIS)

    Almeida, Marcelo Esteves

    2006-01-01

    This study focuses the granitoids of center-southern portion of Guyana Shield, southeastern Roraima, Brazil. The region is characterized by two tectonic-stratigraphic domains, named as Central Guyana (GCD) and Uatuma-Anaua (UAD) and located probably in the limits of geochronological provinces (e.g. Ventuari-Tapajos or Tapajos-Parima, Central Amazonian and Maroni-Itacaiunas or Transamazon). The aim this doctoral thesis is to provide new petrological and lithostratigraphic constraints on the granitoid rocks and contribute to a better understanding of the origin and geo dynamic evolution of Guyana Shield. The GCD is only locally studied near to the UAD boundary, and new geological data and two single zircon Pb-evaporation ages in mylonitic biotite granodiorite (1.89 Ga) and foliated hastingsite-biotite granite (1.72 Ga) are presented. These ages of the protholiths contrast with the lithostratigraphic picture in the other areas of Cd (1.96-1.93 Ga). Regional mapping, petrography, geochemistry and zircon geochronology carried out in the Urad have showed widespread Paleoproterozoic calc-alkaline granitic magmatism. These granitoid rocks are distributed into several magmatic associations with different Paleoproterozoic (1.97-1.89 Ga) ages, structural and geochemical affinities. Detailed mapping, petrographic and geochronological studies have distinguished two main sub domains in the UAD. In the northern UAD, the high-K calc-alkaline Martins Pereira (1.97 Ga) and Serra Dourada S-type granites (1.96 Ga) are affected by NE-SW and E-W ductile dextral shear-zones, showing coexistence of magmatic and deformational fabrics related to heterogeneous deformation. Inliers of basement (2.03 Ga) crop out northeast of this area, and are formed by meta volcano-sedimentary sequence (Cauarane Group) and TTG-like calc-alkaline association (Anaua Complex). Xenoliths of meta diorites (Anaua Complex) and para gneisses (Cauarane Group) reinforce the intrusive character of Martins Pereira

  7. Diversity, origin and tectonic significance of the Mesoarchean granitoids of Ourilândia do Norte, Carajás province (Brazil)

    Science.gov (United States)

    da Silva, Luciano Ribeiro; de Oliveira, Davis Carvalho; dos Santos, Maria Nattânia Sampaio

    2018-03-01

    Norte granitoids can be grouped into two suites: (i) Fe-K suite formed by BMzG and spTEBGd; and (ii) Mg-K suite composed of sanukitoids (including hEBGd and pBHGd) and (quartz) diorites of BADR affinity. The origin of the eBMzG is attributed to anatexis of a 2.92-2.98 Ga old TTG crust. The hEBGd has sanukitoid affinity and was produced by intense fractionation of hornblende ± clinopyroxene from the Rio Maria Granodiorite. The granitoids of spTEBGd, hBMzG, pBHGd and pEBTd facies show mingling evidence between contrasting magmas, indicating that their origins require interaction between metassomatized mantle- and crustal derived magmas. Geochemical data and modeling were used to identify their different formation processes: (i) spTEBGd is enriched in HFSE (Ti, Zr and Y) and LILE (Ba and Sr) and it was interpreted as product of the partial melting of an enriched mantle source, with participation of crustal liquids; (ii) hBMzG is generated by the interaction between spTEBGd (60%) and eBMzG (40%) magmas; (iii) pBHGd by hybridization between sanukitoid (80%) and eBMzG (20%); and (iv) pEBTd by mixture between trondhjemitic (70-80%) and BARD-affinity (20-30%) liquids. Therefore, at ∼2.87-2.86 Ga a significant crustal growth and reworking occurred in the final stages of stabilization of the first geotectonic cycle of Carajás province, where all the Ourilândia do Norte Mesoarchean granitoids were emplacement during the second stage of a tectono-magmatic two-stage (subduction-collision) model: (i) first stage (2.98-2.92 Ga) - low-angle subduction with emplacement of slab-melt and mantle wedge metasomatism; (ii) second stage (∼2.87-2.86 Ga) - collisional environment, where shear zones conditioned the rise and emplacement of the Ourilândia do Norte magmas.

  8. Using apatite to discriminate synchronous ore-associated and barren granitoid rocks: A case study from the Edong metallogenic district, South China

    Science.gov (United States)

    Duan, Deng-Fei; Jiang, Shao-Yong

    2018-06-01

    In order to find criteria to discriminate the synchronous ore-associated and barren granitoid rocks, we have determined apatite chemistry associated with ore-associated (Cu-Au) and barren granitoid rocks in the Edong district of the Middle and Lower Yangtze River metallogenic belt, South China. Both rock types give zircon U-Pb ages between 135.0 and 138.7 Ma. Apatite has a higher volatile and Li content (Cl: 0.19-0.57 wt%, average 0.35 wt%, SO3: 0.08-0.71 wt%, average 0.32 wt%, Li: 0.49-7.99 ppm, average 3.23 ppm) in ore-associated rocks than those in barren rocks (Cl: 0.09-0.31 wt%, average 0.16 wt%, SO3: 0.06-0.28 wt%, average 0.16 wt%, Li: 0.15-0.89 ppm, average 0.36 ppm). Apatite (La/Yb)N ratios and Eu/Eu* values are relatively high and show wider variation in ore-associated rocks than those in barren rocks. Apatite (La/Sm)N and (Yb/Sm)N show positive correlation in ore-associated rocks but negative in barren rocks. The higher volatile content occurs in ore-associated magma, favoring Cu-Au transportation and deposition. Furthermore, amphibole fractional crystallization in ore-associated magma further enriched the ore elements in the residual melt. Barren rocks may have undergone fluid exsolution before emplacement, which makes it barren in Cl, S and ore elements (Cu, S). These signatures emphases the significance of volatile and magma evolution in mineralization and indicate that analyses of magmatic apatite can serve to distinguish ore-associated from barren intrusions.

  9. Potassium-argon ages of two granitoids northwest of Kumasi, Ghana

    International Nuclear Information System (INIS)

    Agyei, E.K.

    1989-01-01

    Four granitic samples from two granitoids northwest of Kumasi,Ghana, have been dated using the conventional K-Ar method. Two samples NB1 NB2 from a road-cutting at Nyamebekyere village, located about 60 km from Kumasi on the Kumasi-Sunyani road gave biotite ages of 2144+/= 11 Ma and 2144+/=7 Ma, respectively. The biotite ages for two samples NTN1 and NTN2 from Kassardjan quarry, located about 3 km south of the Kumasi-Sunyani road at Ntensere village some 20 km northwest of Kumasi were 2070+/= 10 Ma and 2099+/=14 Ma, respectively. A hornblende age of 2169+/=26 Ma was obtained for NTN2 which suggests a slow cooling during the uplift of the granitoid. Although the biotite ages obtained here for the two G2 granitoids are older than most of the reported biotite ages which happen to be for G1 granites, it is too premature to generalize that G2 granitoids are older than G1 granitoids. (author). 21 refs. 1 fig. 1 tab

  10. Petrogenesis of the middle Jurassic appinite and coeval granitoids in the Eastern Hebei area of North China Craton

    Science.gov (United States)

    Fan, Wenbo; Jiang, Neng; Xu, Xiyang; Hu, Jun; Zong, Keqing

    2017-05-01

    An integrated study of zircon U-Pb ages and Hf-O isotopic compositions, whole rock elemental and Sr-Nd isotope geochemistry was conducted on three lithologically diverse middle Jurassic plutons from the Eastern Hebei area of the North China Craton (NCC), in order to reveal both their petrogenesis and possible tectonic affinity. The three plutons have consistent magmatic zircon U-Pb ages from 167 ± 1 Ma to 173 ± 1 Ma. The Nianziyu pluton has typical characteristics of appinite with low SiO2 (43.7-52.6%), high Ca, Mg, Fe and H2O contents. It possesses subduction-related trace element patterns, enriched Nd-Hf isotopic signatures as well as elevated zircon δ18O values (6.2-7.2‰), arguing for an enriched mantle source metasomatized by fluids related to subduction. The Shuihutong monzogranites have high silica (SiO2 = 75.4-75.9%) and alkali contents, low Ca contents and striking negative Ba, Sr and Eu anomalies. Samples from the pluton have more evolved Nd-Hf isotopic values and are considered to be most likely derived from anatexis of ancient lower continental crust. Hybridization between mantle- and ancient lower crust-derived magmas is proposed for the mafic microgranular enclave-bearing Baijiadian granitoids, which are characterized by variable εNd (t) and εHf(t) values. Integrated with the regional geologic history, we suggest that the formation of the three middle Jurassic plutons were related to the subduction of the Paleo-Pacific ocean plate beneath the NCC. Their petrogenetic differences reflect complex magmatic processes in subduction settings involving melting of multiple sources, possible partly facilitated by fluid metasomatism and water-rich magma injection, accompanied with various degrees of magma mixing. The appearance of middle Jurassic appinitic rocks leads us to propose that the NCC destruction and lithosphere thinning were facilitated and controlled by the weakening of the lithospheric mantle after hydration because of the subduction of the

  11. Geological evolution of the center-southern portion of the Guyana shield based on the geochemical, geochronological and isotopic studies of paleoproterozoic granitoids from southeastern Roraima, Brazil; Evolucao geologica da porcao centro-sul do escudo das Guianas com base no estudo geoquimico, geocronologico e isotopico dos granitoides paleoproterozoicos do sudeste de Roraima, Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Almeida, Marcelo Esteves

    2006-07-01

    This study focuses the granitoids of center-southern portion of Guyana Shield, southeastern Roraima, Brazil. The region is characterized by two tectonic-stratigraphic domains, named as Central Guyana (GCD) and Uatuma-Anaua (UAD) and located probably in the limits of geochronological provinces (e.g. Ventuari-Tapajos or Tapajos-Parima, Central Amazonian and Maroni-Itacaiunas or Transamazon). The aim this doctoral thesis is to provide new petrological and lithostratigraphic constraints on the granitoid rocks and contribute to a better understanding of the origin and geo dynamic evolution of Guyana Shield. The GCD is only locally studied near to the UAD boundary, and new geological data and two single zircon Pb-evaporation ages in mylonitic biotite granodiorite (1.89 Ga) and foliated hastingsite-biotite granite (1.72 Ga) are presented. These ages of the protholiths contrast with the lithostratigraphic picture in the other areas of Cd (1.96-1.93 Ga). Regional mapping, petrography, geochemistry and zircon geochronology carried out in the Urad have showed widespread Paleoproterozoic calc-alkaline granitic magmatism. These granitoid rocks are distributed into several magmatic associations with different Paleoproterozoic (1.97-1.89 Ga) ages, structural and geochemical affinities. Detailed mapping, petrographic and geochronological studies have distinguished two main sub domains in the UAD. In the northern UAD, the high-K calc-alkaline Martins Pereira (1.97 Ga) and Serra Dourada S-type granites (1.96 Ga) are affected by NE-SW and E-W ductile dextral shear-zones, showing coexistence of magmatic and deformational fabrics related to heterogeneous deformation. Inliers of basement (2.03 Ga) crop out northeast of this area, and are formed by meta volcano-sedimentary sequence (Cauarane Group) and TTG-like calc-alkaline association (Anaua Complex). Xenoliths of meta diorites (Anaua Complex) and para gneisses (Cauarane Group) reinforce the intrusive character of Martins Pereira

  12. Paired Magmatic-Metallogenic Belts in Myanmar - an Andean Analogue?

    Science.gov (United States)

    Gardiner, Nicholas; Robb, Laurence; Searle, Michael; Morley, Christopher

    2015-04-01

    contrasting minerals endowment. The Mogok-Mandalay-Mergui (MMM) Belt hosts crustal-melt S-type granites with significant tin-tungsten mineralization, and contains the historically major tungsten deposit of Mawchi. The Wuntho-Popa Arc comprises I-type granites and granodiorites with porphyry-type copper-gold and epithermal gold mineralization, and includes the world-class Monywa copper mine. Recent U-Pb radiometric age dating has shown the potential for the two belts to be both active from the Late Cretaceous to Eocene. The spatial juxtaposition of these two sub-parallel belts, the implication of contemporary magmatism, and their distinct but consistent metallogenic endowment bears strong similarities to the metallogenic belts of the South American Cordillera. Here we investigate whether they together represent the magmatic and metallogenic expression of an Andean-type setting in Myanmar during the subduction of Neo-Tethys. In this analogue the Wuntho-Popa Arc represents a proximal I-type magmatic belt sited immediately above the eastwards-verging Neo-Tethys subduction zone. Exhibiting porphyry-type copper-gold and epithermal gold mineralization, this would therefore be the Myanmar equivalent of the Andean coastal copper belts. Conversely, the parallel MMM Belt, comprised of more distal crustal-melt S-type tin granites, would have an analogue in the Bolivian tin belt.

  13. Carbonatite magmatism in northeast India

    Science.gov (United States)

    Kumar, D.; Mamallan, R.; Dwivedy, K. K.

    The Shillong Plateau of northeast India is identified as an alkaline province in view of the development of several carbonatite complexes e.g. the Sung Valley (Jaintia Hills), Jasra (Karbi-Anglong), Samchampi and Barpung (Mikir Hills) and lamprophyre dyke swarms (Swangkre, Garo-Khasi Hills). On the basis of limited KAr data, magmatic activity appears to have taken place over a protracted period, ranging from the Late Jurassic to the Early Cretaceous. The carbonatite complexes of the Shillong Plateau share several common traits: they are emplaced along rift zones, either within Archaean gneisses or Proterozoic metasediments and granites, and exhibit enrichment in the light rare-earth elements, U, Th, Nb, Zr, Ti, K and Na. The enrichment in incompatible trace elements can best be accounted for if the parental magmas were of alkali basaltic type (e.g. mela-nephelinite or carbonate-rich alkali picrite).

  14. Crustal melting and recycling: geochronology and sources of Variscan syn-kinematic anatectic granitoids of the Tormes Dome (Central Iberian Zone). A U-Pb LA-ICP-MS study

    Science.gov (United States)

    López-Moro, F. J.; López-Plaza, M.; Gutiérrez-Alonso, G.; Fernández-Suárez, J.; López-Carmona, A.; Hofmann, M.; Romer, R. L.

    2018-04-01

    In this study, we report U-Pb Laser Ablation ICP-MS zircon and ID-TIMS monazite ages for peraluminous granitoid plutons (biotite ± muscovite ± cordierite ± sillimanite) in the Tormes Dome, one of the gneiss-cored domes located in the Central Iberian Zone of the Variscan belt of northern Spain. Textural domains in zircon, interpreted to represent the magmatic crystallization of the granitoids (and one monazite fraction in the Ledesma pluton) yielded ages around 320 Ma, in agreement with other geochronological studies in the region. This age is interpreted to date the timing of decompression crustal melting driven by the extensional collapse of the orogenic belt in this domain of the Variscan chain of western Europe. In addition, there are several populations of inherited (xenocrystic) zircon: (1) Carboniferous zircon crystals (ca. 345 Ma) as well as one of the monazite fractions in the coarse-grained facies of the Ledesma pluton that also yielded an age of ca. 343 Ma. (2) Devonian-Silurian zircon xenocrysts with scattered ages between ca. 390 and 432 Ma. (3) Middle Cambrian-Ordovician (ca. 450-511 Ma). (4) Ediacaran-Cryogenian zircon ages (ca. 540-840 Ma). (5) Mesoproterozoic to Archaean zircon (900-2700 Ma). The abundance of Carboniferous-inherited zircon shows that crustal recycling/cannibalization may often happen at a fast pace in orogenic scenarios with only short lapses of quiescence. In our case study, it seems plausible that a "crustal layer" of ca. 340 Ma granitoids/migmatites was recycled, partially or totally, only 15-20 My after its emplacement.

  15. 222Rn activity concentration differences in groundwaters of three Variscan granitoid massifs in the Sudetes (NE Bohemian Massif, SW Poland)

    International Nuclear Information System (INIS)

    Przylibski, Tadeusz A.; Gorecka, Joanna

    2014-01-01

    Based on research conducted in three Variscan granitoid massifs located within the crystalline Bohemian Massif, the authors confirmed that the higher the degree of their erosional dissection, the smaller the concentration of 222 Rn in groundwaters circulating in these massifs. This notion implies that radon waters and high-radon waters, from which at least some of the dissolved radon should be removed before feeding them as drinking water to the water-supply system, could be expected in granitoid massifs which have been poorly exposed by erosion. At the same time, such massifs must be taken into account as the areas of possible occurrence of radon medicinal waters, which in some countries can be used for balneotherapy in health resorts. Slightly eroded granitoid massifs should be also regarded as very probable radon prone areas or areas of high radon potential. - Highlights: • The concentration of 222 Rn in groundwater depends on the zone of the granitoid massif which is exposed on the ground surface. • The highest 222 Rn concentrations occur in the least eroded granitoid massifs, the lowest in massifs with exposed root parts. • The stronger the erosional dissection of a granitoid massif, the lower 222 Rn concentration in groundwaters in this massif. • Not all granitoid massifs are areas with groundwaters containing high concentrations of 222 Rn. • The least eroded granitoid massifs are radon prone areas with the occurrence of high-radon and radon groundwaters

  16. Age of granitoids from the Kohut Veporic zone according to Rb-Sr isochrone analysis

    International Nuclear Information System (INIS)

    Cambel, B.; Bagdasaryan, G.P.; Gukasyan, R.K.; Dupej, J.

    1988-01-01

    Rb-Sr isochrone analyses of granitoid rocks from the southern part of the Veporic zone - the so-called Kohut zone - are presented. In this region, the Sinec (Rimavica) type of granitoids formerly considered to be Late Palaeozoic to Neoide, is found. The present isochrone research determines them as equivalents of granitoids of the Sihla type (387±27 m.y.). The Sinec (Rimavica) granite reaches an age of 392±5 m.y. This extended age must partly be attributed to additional processes which took place in the stage of retrograde alterations. The conclusions are of considerable importance in clarifying the metamorphic age and stratigraphy of the crystalline complex in the region of the southern Veporic zone. (author). 9 figs., 4 tabs., 38 refs

  17. Isotopic signature of Madeira basaltic magmatism

    International Nuclear Information System (INIS)

    Kogarko, L.N.; Karpenko, S.F.; Bibikova, E.V.; Mato, Zh.

    2000-01-01

    Chemical composition of the basalts of Madeira Island is studied. To assess the isotopic sources of magmatism the Pb-Sr, Sm-Nd, U-Th-Pb systems were investigated in a number of basalts. It is shown that the island's rocks are characterized by the mostly deplet sources in relation to Pb-Sr and Sm-Nd systems ( 87 Sr/ 86 Sr - 0.70282-0.70292, 143 Nd/ 144 Nd - 0.52303-0.51314). Isotopic composition of lead testifies that the magmatism reservoir is some enriched. It is concluded that the magmatism of Madeira Island is a new example of world ocean island's volcanism [ru

  18. Geochemistry, U-Pb SHRIMP zircon dating and Hf isotopes of the Gondwanan magmatism in NW Argentina: petrogenesis and geodynamic implications

    International Nuclear Information System (INIS)

    Poma, Stella; Zappettini, Eduardo O; Quenardelle, Sonia; Santos, Joao O; Koukharsky, Magdalena; Belousova, Elena; McNaughton, Neil

    2014-01-01

    We have carried out zircon U-Pb SHRIMP dating and Hf isotope determinations as well as geochemical analyses on three plutonic units of Gondwanan magmatism that crop out in NW Argentina. Two episodes of different age and genesis have been identified. The older one includes gabbros and diorites (Rio Grande Unit) of 267±3 Ma and granitoids (belonging to the Llullaillaco Unit) of 263±1 Ma (late Permian, Guadalupian); the parent magmas were generated in an intraplate environment and derived from an enriched mantle but were subsequently contaminated by crustal components. The younger rocks are granodiorites with arc signature (Chuculaqui Unit) and an age of 247±2 Ma (middle Triassic-Anisian). Hf isotope signature of the units indicates mantle sources as well as crustal components. Hf model ages obtained are consistent with the presence of crustal Mesoproterozoic (mainly Ectasian to Calymnian (T DM(c) =1.24 to 1.44 Ga-negative ε Hf m) and juvenile Cryogenian sources (T DM =0.65 to 0.79 Ga-positiveε Hf(T) , supporting the idea of a continuous, mostly Mesoproterozoic, basement under the Central Andes, as an extension of the Arequipa-Antofalla massif. The tectonic setting and age of the Gondwanan magmatism in NW Argentina allow to differentiate: a. Permian intra-plate magmatism developed under similar conditions to the upper section of the Choiyoi magmatism exposed in the Frontal Cordillera and San Rafael Block, Argentina; b. Triassic magmatism belonging to a poorly known subduction-related magmatic arc segment of mostly NS trend with evidence of porphyry type mineralization in Chile, allowing to extend this metallotect into Argentina

  19. Felsic magmatism and uranium deposits

    International Nuclear Information System (INIS)

    Cuney, Michel

    2014-01-01

    The strongly incompatible behaviour of uranium in silicate magmas results in its concentration in the most felsic melts and a prevalence of granites and rhyolites as primary U sources for the formation of U deposits. Despite its incompatible behavior, U deposits resulting directly from magmatic processes are quite rare. In most deposits, U is mobilized by hydrothermal fluids or ground water well after the emplacement of the igneous rocks. Of the broad range of granite types, only a few have U contents and physico-chemical properties that permit the crystallization of accessory minerals from which uranium can be leached for the formation of U deposits. The first granites on Earth, which crystallized uraninite, dated at 3.1 Ga, are the potassic granites from the Kaapval craton (South Africa) which were also the source of the detrital uraninite for the Dominion Reef and Witwatersrand quartz pebble conglomerate deposits. Four types of granites or rhyolites can be sufficiently enriched in U to represent a significant source for the genesis of U deposits: per-alkaline, high-K met-aluminous calc-alkaline, L-type peraluminous and anatectic pegmatoids. L-type peraluminous plutonic rocks in which U is dominantly hosted in uraninite or in the glass of their volcanic equivalents represent the best U source. Per-alkaline granites or syenites are associated with the only magmatic U-deposits formed by extreme fractional crystallization. The refractory character of the U-bearing minerals does not permit their extraction under the present economic conditions and make them unfavorable U sources for other deposit types. By contrast, felsic per-alkaline volcanic rocks, in which U is dominantly hosted in the glassy matrix, represent an excellent source for many deposit types. High-K calc-alkaline plutonic rocks only represent a significant U source when the U-bearing accessory minerals (U-thorite, allanite, Nb oxides) become metamict. The volcanic rocks of the same geochemistry may be

  20. Felsic magmatism and uranium deposits

    International Nuclear Information System (INIS)

    Cuney, M.

    2014-01-01

    Uranium strongly incompatible behaviour in silicate magmas results in its concentration in the most felsic melts and a prevalence of granites and rhyolites as primary U sources for the formation of U deposits. Despite its incompatible behaviour, U deposits resulting directly from magmatic processes are quite rare. In most deposits, U is mobilized by hydrothermal fluids or ground water well after the emplacement of the igneous rocks. Of the broad range of granite types, only a few have have U contents and physico-chemical properties that permit the crystallization of accessory minerals from which uranium can be leached for the formation of U deposits. The first granites on Earth which crystallized uraninite appeared at 3.1 Ga, are the potassic granites from the Kaapval craton (South Africa) which were also the source of the detrital uraninite for the Dominion Reef and Witwatersrand quartz pebble conglomerate deposits. Four types of granites or rhyolites can be sufficiently enriched in U to represent a significant source for the genesis of U deposits: peralkaline, high-K metaluminous calc-alkaline, L-type peraluminous ones and anatectic pegmatoids. L-type peraluminous plutonic rocks in which U is dominantly hosted in uraninite or in the glass in their volcanic equivalents represent the best U source. Peralkaline granites or syenites represent the only magmatic U-deposits formed by extreme fractional crystallization. The refractory character of the U-bearing minerals does not permit their extraction at the present economic conditions and make them unfavourable U sources for other deposit types. By contrast, felsic peralkaline volcanic rocks, in which U is dominantly hosted in the glassy matrix, represent an excellent source for many deposit types. High-K calc-alkaline plutonic rocks only represent a significant U source when the U-bearing accessory minerals [U-thorite, allanite, Nb oxides] become metamict. The volcanic rocks of the same geochemistry may be also a

  1. Semi-brittle flow of granitoid fault rocks in experiments

    Science.gov (United States)

    Pec, Matej; Stünitz, Holger; Heilbronner, Renée.; Drury, Martyn

    2016-03-01

    Field studies and seismic data show that semi-brittle flow of fault rocks probably is the dominant deformation mechanism at the base of the seismogenic zone at the so-called frictional-viscous transition. To understand the physical and chemical processes accommodating semi-brittle flow, we have performed an experimental study on synthetic granitoid fault rocks exploring a broad parameter space (temperature, T = 300, 400, 500, and 600°C, confining pressure, Pc ≈ 300, 500, 1000, and 1500 MPa, shear strain rate, γṡ ≈ 10-3, 10-4, 10-5, and 10-6 s-1, to finite shear strains, γ = 0-5). The experiments have been carried out using a granular material with grain size smaller than 200 µm with a little H2O added (0.2 wt %). Only two experiments (performed at the fastest strain rates and lowest temperatures) have failed abruptly right after reaching peak strength (τ ~ 1400 MPa). All other samples reach high shear stresses (τ ~ 570-1600 MPa) then weaken slightly (by Δτ ~ 10-190 MPa) and continue to deform at a more or less steady state stress level. Clear temperature dependence and a weak strain rate dependence of the peak as well as steady state stress levels are observed. In order to express this relationship, the strain rate-stress sensitivity has been fit with a stress exponent, assuming γ˙ ∝ τn and yields high stress exponents (n ≈ 10-140), which decrease with increasing temperature. The microstructures show widespread comminution, strain partitioning, and localization into slip zones. The slip zones contain at first nanocrystalline and partly amorphous material. Later, during continued deformation, fully amorphous material develops in some of the slip zones. Despite the mechanical steady state conditions, the fabrics in the slip zones and outside continue to evolve and do not reach a steady state microstructure below γ = 5. Within the slip zones, the fault rock material progressively transforms from a crystalline solid to an amorphous material. We

  2. Late Paleozoic-Early Mesozoic tectonic evolution of the Paleo-Asian Ocean: geochronological and geochemical evidence from granitoids in the northern margin of Alxa, Western China

    Science.gov (United States)

    Sha, Xin; Wang, Jinrong; Chen, Wanfeng; Liu, Zheng; Zhai, Xinwei; Ma, Jinlong; Wang, Shuhua

    2018-03-01

    The Paleo-Asian Ocean (Southern Mongolian Ocean) ophiolitic belts and massive granitoids are exposed in the Alxa block, in response to oceanic subduction processes. In this work, we report petrographic, geochemical, and zircon U-Pb age data of some granitoid intrusions from the northern Alxa. Zircon U-Pb dating for the quartz diorite, tonalite, monzogranite, and biotite granite yielded weighted mean 206Pb/238U ages of 302±9.2 Ma, 246.5±4.6 Ma, 235±4.4 Ma, and 229.5±5.6 Ma, respectively. The quartz diorites ( 302 Ma) exhibit geochemical similarities to adakites, likely derived from partial melting of the initially subducted Chaganchulu back-arc oceanic slab. The tonalites ( 246.5 Ma) display geochemical affinities of I-type granites. They were probably derived by fractional crystallization of the modified lithospheric mantle-derived basaltic magmas in a volcanic arc setting. The monzogranites ( 235 Ma) are characterized by low Al2O3, but high Y and Yb with notably negative Eu anomalies. In contrast, the biotite granites ( 229.5 Ma) show high Al2O3 but low Y and Yb with steep HREE patterns and the absence of negative Eu anomalies. Elemental data suggested that the biotite granites were likely derived from a thickened lower crust, but the monzogranites originated from a thin crust. Our data suggested that the initial subduction of the Chaganchulu oceanic slab towards the Alxa block occurred at 302 Ma. This subduction process continued to the Early Triassic ( 246 Ma) and the basin was finally closed before the Middle Triassic ( 235 Ma). Subsequently, the break-off of the subducted slab triggered asthenosphere upwelling (240-230 Ma).

  3. Spinels of Variscan olivine hornblendites related to the Montnegre granitoids revisited (NE Spain): petrogenetic evidence of mafic magma mixing

    Energy Technology Data Exchange (ETDEWEB)

    Galán, G.; Enrique, P.; Butjosa, L.; Fernández-Roig, L.

    2017-07-01

    Olivine hornblendites (cortlandtites) form part of the Montnegre mafic complex related to late-Variscan I-type granitoids in the Catalan Coastal Ranges. Two generations of spinel are present in these hornblendites: Spl1 forms euhedral crystals included in both olivine and Spl2. Spl2 forms euhedral to anhedral crystals associated with phlogopite and fibrous colourless amphibole forming pseudomorphs after olivine. Compositions of Spl1 are picotite-Al chromite (Fe#: 77.78-66.60; Cr#: 30.12-52.22; Fe3+/R3+: 6.99-21.89; 0.10< TiO2%< 0.62). Compositions of Spl2 are pleonaste (Fe#: 37.86-52.12; Cr#: 1.00-15.45; Fe3+/R3+: 0.31-5.21; TiO2% <0.10%). The two types of spinel follow a CrAl trend, mainly due to the substitution (Fe2+)-1Cr-1= MgAl, which is interpreted as the result of mixing between two different mantle-derived melts. The compositions of early Spl1 crystals included in olivine are characteristic of Al-rich basalts. More aluminous Spl2 would result from reaction of olivine with a less evolved, Al and K-rich mantle-derived melt after new refilling of the magma chamber or channel. As a whole, spinels from similar examples of Variscan olivine hronblendites also follow a CrAl trend with high Fe# and starting at higher Cr# than other trends of this type. Cr# heterogeneity in the early spinels from these Variscan hornblendites would be inherited from the variable Al content of the mafic melts involved in their genesis.

  4. The evolutionary characteristics and study of uranium mineralization conditions of early precambrian basement and old granitoids in Northern Hebei province of China

    International Nuclear Information System (INIS)

    Xia Yuliang; Rong Jiashu; Lin Jinrong; Zheng Maogong; Wen Xiyuan

    1993-05-01

    Based on the systematic studies of petrology, geochemistry and isotope geochronology, the Early Precambrian metamorphic complex in Northern Hebei province of China can be divided into three different series, i.e. granulite series, khondalite series and amphibolitic-felsic rock series. The so called 'magmatic granitoids' in that area are actually some magmagranites with different ages and different geneses, and they are not formed by migmatization. Up to now, the discovered Huaian complex which was formed in 3.5 Ga ago is the oldest nuclear area in the northern margin of North-China Platform. The granulite series, khondalite series and amphibolitic-felsic rock series belong to Early Archaean (>3.0 +- 0.1 Ga), Middle Archaean (>2.7 +- 0.1 Ga) and Later Archaean (>2.4 +- 0.1 Ga) respectively. The geological time scale of the Early Precambrian for Northern Hebei Province has been built. According to the synthetic analyses of various factors there is no prospect of uranium mineralization in the ancient terrain. However, the Mesozoic volcanic basins covering over the Hercynian Period granites would be main goal for looking for large uranium deposits in north part in that area

  5. Oxygen isotope regional pattern in granitoids from the Cachoeirinha Belt, northeast Brazil

    International Nuclear Information System (INIS)

    Sial, A.N.

    1984-01-01

    Four groups of granitoids are present within the Cachoeirinha belt and in the adjacent migmatitic basement, between 37 0 and 40 0 W long. and 7 0 and 8 0 15' S lat., States of Pernambuco and Paraiba: a) K 2 O - enriched, very porphyritic; b) a calc-alkalic slightly porphyritic group; c) group with trondjemitic affinities; and d) peralkalic group. Petrology and oxygen isotope geochemistry for over 100 samples from these groups were studied. Almost all plutons for which 5 or more samples were analyzed, exhibit a total range of gamma 18 O less than 2% o. A broad range of mean oxygen isotope composition is observed, varying from 6.93 to 12.79% o. There is a systematic regional trend in which the calc-alkalic granitoids (conceicao-type) found within the Cachoeirinha space are the most 18 O - enriched rocks (10.6 to 12.9% o) while the lowest mean gamma 18 O values (4.5 to 9.7% o) are found in the K 2 O - enriched granitoids (Itaporanga-type). Intermediate gamma 18 O values were recorded in the bodies with trondhjemitic affinities (8.9 to 9.8% o) which intruded metasediments of the Salgueiro Group and in the peralkalic granitoids of Catingueira (8.1 to 9.8% o) which intruded Cachoeirinha metamorphics. Among the potassic granitoids, mean gamma 18 O increases from Bodoco to Itaporanga (from west to east). As a whole, the W.R. gamma 18 O of these plutons correlate with the type of grade of metamorphism of the host rocks and, therefore, with the tectonic framework, increasing from those which intruded the gneiss-migmatites to those which intruded the low-grade metamorphics of the Cachoeirinha Group. The possible origin of each rock group is discussed in light of the oxygen isotope geochemistry. (Author) [pt

  6. Indoor radon related to uranium in granitoids of the Central Bohemian plutonic complex

    International Nuclear Information System (INIS)

    Barnet, I.; Fojtikova, I.

    2004-01-01

    The study is based on the indoor radon data (one year measurements, Kodak LR 115 track etch detectors), vectorized geological maps 1:50000, vectorized coordinates of dwellings and uranium data for granitoid types of the Central Bohemian Plutonic Complex (CBPC). Using ArcGis 8.2 programme, the position of 16145 dwellings was linked to a geological database covering the CBPC (approx. 3200 km 2 ), and the type of underlying rock type was specified for each house. The resulting databases enabled us to calculate the mean EEC indoor Rn data for particular granitoid types and to study the relationship between the indoor Rn and the U concentrations. The petrogenetically variable CBPC was emplaced during Variscan orogenesis (330-350 Ma) and is among the most radioactive rock types within the Bohemian Massif. A long-term process of CBPC genesis resulted in more than 20 granitoid types, differing by their petrogenetic characteristics as well as mineralogical and chemical composition, including uranium concentration. The relation between the mean indoor radon values and uranium concentrations in particular rock types was examined. A positive regression between indoor Rn and uranium as the source of Rn soil gas clearly demonstrates how regional geology influences the indoor radon activity concentration in dwellings. The highest indoor Rn concentrations were observed in the Sedlcany granodiorite and Certovo bremeno syenite, where also the highest gamma dose rates (150-210 nGy.h -1 ) within all granitoid types in the Czech Republic were observed. The two rock types differ from other granitoids by a relatively high zircon concentration, which is the main source of U and subsequently of soil gas Rn being released from the bedrock. The lower indoor Rn values of Certovo bremeno syenite which do not correspond with the high U concentrations can be explained by a relatively low permeability of its clayey weathering crust. This feature was also observed for soil gas radon concentration

  7. Study of rare earth elements for the characterization and metalogenetic evaluation of granitoids of the paranaense shield

    International Nuclear Information System (INIS)

    Chiodi Filho, C.; Santos, J.F. dos; Moretzsohn, J.S.

    1989-01-01

    REE geochemistry combined with major and trace elements data, provide some diagnostic criteria regarding the origin, the geotectonic setting and the metallogenesis of granitoid intrusions in the Parana Shield. The intrusions were grouped as mantle (Sintexis Series) and crustal (Transformation Series) origins. The two lineages include six suites, with pre, syn, tardi-to-post and post-collisional emplacement. From the metallogenetic standpoint, the 'Sintexis' granitoids can be labelled as ''0Mo-W-Cu-Au porphyry-granites''and the 'Transformation' granitoids as Sn-W greisengranites. (author) [pt

  8. Extensive crustal melting during craton destruction: Evidence from the Mesozoic magmatic suite of Junan, eastern North China Craton

    Science.gov (United States)

    Yang, Fan; Santosh, M.; Tang, Li

    2018-05-01

    The cratonic destruction associated with the Pacific plate subduction beneath the eastern North China Craton (NCC) shows a close relationship with the widespread magmatism during the Late Mesozoic. Here we investigate a suite of intrusive and extrusive magmatic rocks from the Junan region of the eastern NCC in order to evaluate the role of extensive crustal melting related to decratonization. We present petrological, geochemical, zircon U-Pb geochronological and Lu-Hf isotopic data to evaluate the petrogenesis, timing and tectonic significance of the Early Cretaceous magmatism. Zircon grains in the basalt from the extrusive suite of Junan show multiple populations with Neoproterozoic and Early Paleozoic xenocrystic grains ranging in age from 764 Ma to 495 Ma as well as Jurassic grains with an age range of 189-165 Ma. The dominant population of magmatic zircon grains in the syenite defines three major age peaks of 772 Ma, 132 Ma and 126 Ma. Zircons in the granitoids including alkali syenite, monzonite and granodiorite yield a tightly restricted age range of 124-130 Ma representing their emplacement ages. The Neoproterozoic (841-547 Ma) zircon grains from the basalt and the syenite possess εHf(t) values of -22.9 to -8.4 and from -18.8 to -17.3, respectively. The Early Paleozoic (523-494 Ma) zircons from the basalt and the syenite also show markedly negative εHf(t) values of -22.7 to -18.0. The dominant population of Early Cretaceous (134-121 Ma) zircon grains presented in all the samples also displays negative εHf(t) values range from -31.7 to -21.1, with TDM of 1653-2017 Ma and TDMC in the range of 2193-3187 Ma. Accordingly, the Lu-Hf data suggest that the parent magma was sourced through melting of Mesoarchean to Paleoproterozoic basement rocks. Geochemical data on the Junan magmatic suite display features similar to those associated with the arc magmatic rocks involving subduction-related components, with interaction of fluids and melts in the suprasubduction

  9. Abundances of chemical elements in granitoids of different geological ages and their characteristics in China

    Directory of Open Access Journals (Sweden)

    Changyi Shi

    2011-04-01

    Full Text Available Actual granitoid analytical data of 767 composited samples are presented here. The data source is 6080 samples collected mainly from 750 large- to middle-sized granitoid bodies across China. Data from the composited samples, which includes that of 70 elements, is analyzed according to geological age — Archeozoic (Ar, Proterozoic (Pt, Eopaleozoic (Pz1, Neopaleozoic (Pz2, Mesozoic (Mz, and Cenozoic (Cz — and three major compositional varieties, e.g. alkali-feldspar granite, syenogranite and adamellite. Petrochemical parameters, trace-element content and rare-earth element (REE distributions of the different rock types and geological ages are characterized, and change tendencies through Archean to Cenozoic time are recorded. The comprehensive analytical data presented here has not been previously published. This significant data set can be used as fundamental information in studies of basic China geology, magma petrogenesis, ore exploration and geochemistry.

  10. INTERACTIONS BETWEEN GABBROID AND GRANITOID MAGMAS DURING FORMATION OF THE PREOBRAZHENSKY INTRUSION, EAST KAZAKHSTAN

    Directory of Open Access Journals (Sweden)

    S. V. Khromykh

    2017-01-01

    Full Text Available The paper reports on studies of the Preobrazhensky gabbro‐granitoid intrusion, East Kazakhstan, com‐ posed of the rocks that belong to four phases of intrusion, from quartz monzonites and gabbroids to granite‐ leucogranites. Specific relationships between basite and granitoid rocks are usually classified as the result of interac‐ tions and mixing of liquid magmas, i.e. magma mingling and mixing. Basite rocks are represented by a series from biotite gabbros to monzodiorites. Granitoids rocks are biotite‐amphibole granites. Porphyric granosyenites, com‐ bining the features of both granites and monzodiorites, are also involved in mingling. It is established that the primary granitoid magmas contained granosyenite/quartz‐monzonite and occurred in the lower‐medium‐crust conditions in equilibrium with the garnet‐rich restite enriched with plagioclase. Monzodiorites formed during fractionation of the parent gabbroid magma that originated from the enriched mantle source. We propose a magma interaction model describing penetration of the basite magma into the lower horizons of the granitoid source, which ceased below the viscoplastic horizon of granitoids. The initial interaction assumes the thermal effect of basites on the almost crystal‐ lized granitic magma and saturation of the boundary horizons of the basite magma with volatile elements, which can change the composition of the crystallizing melt from gabbroid to monzodiorite. A ‘boundary’ layer of monzodiorite melt is formed at the boundary of the gabbroid and granitoid magmas, and interacts with granitoids. Due to chemical interactions, hybrid rocks – porphyric granosyenites – are formed. The heterogeneous mixture of monzodiorites and granosyenites is more mobile in comparison with the overlying almost crystallized granites. Due to contraction frac‐ turing in the crystallized granites, the heterogeneous mixture of monzodiorites and granosyenites penetrate into the

  11. Chemical Zoning of Feldspars in Lunar Granitoids: Implications for the Origins of Lunar Silicic Magmas

    Science.gov (United States)

    Mills, R. D; Simon, J. I.; Alexander, C.M. O'D.; Wang, J.; Christoffersen, R.; Rahman, Z..

    2014-01-01

    Fine-scale chemical and textural measurements of alkali and plagioclase feldspars in the Apollo granitoids (ex. Fig. 1) can be used to address their petrologic origin(s). Recent findings suggest that these granitoids may hold clues of global importance, rather than of only local significance for small-scale fractionation. Observations of morphological features that resemble silicic domes on the unsampled portion of the Moon suggest that local, sizable net-works of high-silica melt (>65 wt % SiO2) were present during crust-formation. Remote sensing data from these regions suggest high concentrations of Si and heat-producing elements (K, U, and Th). To help under-stand the role of high-silica melts in the chemical differentiation of the Moon, three questions must be answered: (1) when were these magmas generated?, (2) what was the source material?, and (3) were these magmas produced from internal differentiation. or impact melting and crystallization? Here we focus on #3. It is difficult to produce high-silica melts solely by fractional crystallization. Partial melting of preexisting crust may therefore also have been important and pos-sibly the primary mechanism that produced the silicic magmas on the Moon. Experimental studies demonstrate that partial melting of gabbroic rock under mildly hydrated conditions can produce high-silica compositions and it has been suggested by that partial melting by basaltic underplating is the mechanism by which high-silica melts were produced on the Moon. TEM and SIMS analyses, coordinated with isotopic dating and tracer studies, can help test whether the minerals in the Apollo granitoids formed in a plutonic setting or were the result of impact-induced partial melting. We analyzed granitoid clasts from 3 Apollo samples: polymict breccia 12013,141, crystalline-matrix breccia 14303,353, and breccia 15405,78

  12. Petrological mineralogical and geochemical characterization of the granitoids and fracture fillings developed in Ratones Mines (Spain)

    International Nuclear Information System (INIS)

    Buil Gutierrez, B.

    2002-01-01

    The petrological, mineralogical and geochemical characterisation of the granitoids and fracture fillings developed in the Ratones Mine (Caceres, Spain) has been done in order to understand rock-water interaction processes which control water geochemical parameters. Special interest has been devoted to the analysis and interpretation of REE patterns in the solid phase (granitoids and fracture fillings) because they constitute geochemical tracers in water-rock interaction process. Moreover, REE are considered as actinide analogues. In order to characterise the solid phase (granitoids and fracture fillings) several investigation scales (system, outcrop, whole rock, mineral and geochemical components) have been considered and different types of samples have been analysed. These factors control the methodological approach used in this investigation. The analytical methods we have used in this investigation are microscope, qualitative and semi-quantitative methods (XRD, SEM,EDAX) and quantitative methods (ICP-MS, XRF, EM, LAM-IC-MS). The bulk of the granitoids located around the Ratones Mine Belongs to the alkaline feldspar granite-sienogranite lihotype and they show a peraluminous and subalkaline pattern. From the mineralogical point of view, they are composed by quartz, K-feldspar (Or>90%), showing sericitation, moscovitization and turmolinization altherations, alkaline plagioclase (An-=-3%), usually altered to sericite, saussirite and less frequently affected by moscovitization processes, Fe-Al biotite, frequently affected by chloritization processes and sometimes replaced by muscovite, and finally muscovite (>2% celadonite and <4% paragonite) both of primary and secondary origin. The differences observed between the different lithotypes are related with the modal proportion of the principal minerals,with the presence or absence of certain accessory minerals ( turmaline, cordierite), with specific textural patterns, grain size and also with the richness in specific

  13. Cretaceous magmatism in North-Eastern India and Gondwanaland ...

    Indian Academy of Sciences (India)

    jsray

    Cretaceous magmatism of NEI: Major Objectives. • Age and duration of Sylhet Traps and its connection to Kerguelene hotspot and Gondwanaland breakup? • Age of carbonatite magmatism associated with the traps? • Relationship of basaltic-carbonatite magmatism with. Aptian (~116 Ma) Mass Extinction event? • Nature of ...

  14. Tok-Algoma magmatic complex of the Selenga-Stanovoi Superterrain in the Central Asian fold belt: Age and tectonic setting

    Science.gov (United States)

    Kotov, A. B.; Larin, A. M.; Salnikova, E. B.; Velikoslavinskii, S. D.; Sorokin, A. A.; Sorokin, A. P.; Yakovleva, S. Z.; Anisimova, I. V.; Tolmacheva, E. V.

    2012-05-01

    According to the results of U-Pb geochronological investigations, the hornblende subalkali diorite rocks making up the Tok-Algoma Complex in the eastern part of the Selenga-Stanovoi Superterrain of the Central Asian fold belt were formed in the Middle Jurassic rather than in the Middle Archean as was suggested previously. Thus, the age of the regional amphibolite facies metamorphism manifested itself in the Ust'-Gilyui rock sequence of the Stanovoi Complex and that superimposed on granitoids of the Tok-Algoma Complex is Mesozoic rather than Early Precambrian. The geochemical features of the Tok-Algoma granitoids are indicative of the fact that they were formed in the geodynamic setting of the active continental margin or a mature island arc. Hence, it is possible to suggest that the subduction processes along the southern boundary between the Selenga-Stanovoi Superterrain and the Mongolian-Okhotsk ocean basin in the Middle Jurassic resulted in the formation of a magmatic belt of over 500 km in length.

  15. Petrological and geochemical characterization of the plutonic rocks of the Sierra de La Aguada, Province of San Luis, Argentina: Genetic implications with the Famatinian magmatic arc

    Directory of Open Access Journals (Sweden)

    E. Cristofolini

    2017-07-01

    Full Text Available This study presents a synthesis on the geology of the crystalline complex that constitute the Sierra de la Aguada, San Luis province, Argentine, from an approach based on field relations, petrologic and structural features and geochemical characteristic. This mountain range exposes a basement dominated by intermediate to mafic calcalkaline igneous rocks and peraluminous felsic granitoids, both emplaced in low to medium grade metamorphic rocks stabilized under low amphibolite facies. All this lithological terrane has been grouped in the El Carrizal-La Aguada Complex. Field relations, petrographic characterization and geochemical comparison of the plutonic rocks from the study area with those belonging to the Ordovician Famatinian suit exposed in the Sierra Grande de San Luis, suggest a genetic and temporal relation linked to the development of the Famatinian magmatic arc.

  16. Petrology and geochemistry of the orbicular granitoid of Caldera, northern Chile. Models and hypotheses on the formation of radial orbicular textures

    Science.gov (United States)

    Díaz-Alvarado, Juan; Rodríguez, Natalia; Rodríguez, Carmen; Fernández, Carlos; Constanzo, Ítalo

    2017-07-01

    columnar and equiaxial crystallization. According to the obtained results, the formation of the orbicular granitoid of Caldera may have initiated 1) during the generation of a magmatic fracture in the crystallization front of the Relincho pluton, where the water released by the host crystal mush was dissolved in the new batch of dioritic magma. 2) The high influx of water-rich liquids induced superheating conditions in the newly intruding magma that became a depolymerized liquid, where the only solid particules were the small irregular fragments of the host mush dragged from the fracture walls. 3) Volatile exsolution promoted crystallization under undercooling conditions. 4) Undercooling and nucleation around the core (cold germs) involved the physical and geochemical fractionation between two sub-systems: a gabbroic sub-system that comprises the solid paragénesis with a residual water-rich liquid and a granodioritic sub-system. 5) The orbicules, including core and inner shell, behaved as viscous bodies (crystals + residual liquid) floating in the granodioritic magma. 6) Higher undercooling rates occurred at the starting stage, close to the liquidus, promoting columnar crystallization around the cores and formation of the shells. Conversely, in the granodioritic matrix sub-system, equiaxial crystallization was promoted by low relative crystallization rates. 7) The rest of the crystallization process evolved later in the outer shell and the matrix, as suggested by the poikilitic textures observed in both sides of the orbicule contact, and under conditions close to the solidus of both sub-systems (shell and matrix). The water-rich residual liquid expelled during the orbicular shell crystallization was mingled with the partially crystallized matrix magma, generating the pegmatitic domains with large Kfs megacrysts.

  17. Magmatic sulphides in Quaternary Ecuadorian arc magmas

    Science.gov (United States)

    Georgatou, Ariadni; Chiaradia, Massimo; Rezeau, Hervé; Wälle, Markus

    2018-01-01

    New petrographic and geochemical data on magmatic sulphide inclusions (MSIs) are presented and discussed for 15 Quaternary volcanic centers of the Ecuadorian frontal, main and back volcanic arc. MSIs occur mostly in Fe-Ti oxides (magnetite and/or magnetite-ilmenite pair) and to a lesser extent in silicate minerals (amphibole, plagioclase, and pyroxene). MSIs are present in all volcanic centers ranging in composition from basalt to dacite (SiO2 = 50-67 wt.%), indicating that sulphide saturation occurs at various stages of magmatic evolution and independently from the volcano location along the volcanic arc. MSIs also occur in dioritic, gabbroic and hornblenditic magmatic enclaves of the volcanic rocks. MSIs display variable sizes (1-30 μm) and shapes (globular, ellipsoidal, angular, irregular) and occur mostly as polymineralic inclusions composed of Fe-rich and Cu-poor (pyrrhotite) and Cu-rich (mostly chalcopyrite) phases. Aerial sulphide relative abundances range from 0.3 to 7 ppm in volcanic host rocks and from 13 to 24 ppm in magmatic enclaves. Electron microprobe analyses of MSIs indicate maximum metal contents of Cu = 65.7 wt.%, Fe = 65.2 wt.%, Ni = 10.1 wt.% for those hosted in the volcanic rocks and of Cu = 57.7 wt.%, Fe = 60.9 wt.%, Ni = 5.1 wt.%, for those hosted in magmatic enclaves. Relationships of the sulphide chemistry to the host whole rock chemistry show that with magmatic differentiation (e.g., increasing SiO2) the Cu and Ni content of sulphides decrease whereas the Fe and S contents increase. The opposite behavior is observed with the increase of Cu in the whole rock, because the latter is anti-correlated with the SiO2 whole rock content. Laser ablation ICP-MS analyses of MSIs returned maximum values of PGEs and noble metals of Pd = 30 ppm, Rh = 8.1 ppm, Ag = 92.8 ppm and Au = 0.6 ppm and Pd = 43 ppm, Rh = 22.6 ppm, Ag = 89 ppm and Au = 1 ppm for those hosted in volcanic rocks and magmatic enclaves, respectively. These PGE contents display a

  18. The final pulse of the Early Cenozoic adakitic activity in the Eastern Pontides Orogenic Belt (NE Turkey): An integrated study on the nature of transition from adakitic to non-adakitic magmatism in a slab window setting

    Science.gov (United States)

    Eyuboglu, Yener; Dudas, Francis O.; Santosh, M.; Eroğlu-Gümrük, Tuğba; Akbulut, Kübra; Yi, Keewook; Chatterjee, Nilanjan

    2018-05-01

    The Eastern Pontides Orogenic Belt, one of the best examples of a fossil continental arc in the Alpine-Himalayan system, is characterized by adakitic magmatism during the Early Cenozoic. Popular models correlate the adakitic magmatism to syn- or post-collisional processes occurring after the collision between the Eastern Pontides Orogenic Belt and the Tauride Platform at the end of Late Mesozoic and/or beginning of the Cenozoic. We present new geological, petrological and chronological data from andesites and felsic tuffs exposed in the Bayburt area, in the southern part of the Eastern Pontides Orogenic Belt, and discuss the nature of the transition from adakitic to non-adakitic activities in a continental arc. Major, trace and rare earth element concentrations of both andesites and felsic tuffs clearly suggest that they are related to arc magmatism in a continental arc with adakitic composition. The isotopic compositions are permissive of mixing between a component similar to depleted mantle and a second component that is either mafic lower crust or subducted oceanic crust. 39Ar/40Ar hornblende and U/Pb zircon dating indicate that this adakitic magmatism in the Bayburt area ended by about 47 Ma, and transformed into non-adakitic, granitoid arc magmatism in the area immediately north of Bayburt in the Lutetian (∼46 Ma). Based on our new results in conjunction with available data, we propose that the beginning of northward rollback of a south-directed subducting slab, and simultaneous opening of a slab window related to ridge subduction, triggered both adakitic magmatism for approximately a 10 Myr period between 57.6 and 47 Ma and arc-parallel extension that caused the opening of the Early Cenozoic sedimentary basins. We also suggest that the shallow marine environment, in which Nummulite-bearing sandy limestones accumulated in the Early Cenozoic, was transformed into a saline-lake environment during the pyroclastic activity that produced the studied felsic tuffs

  19. The W (Sn-Mo)-specialized catinga suite and other granitoids of the Brusque Group, neo proterozoic of the state of Santa Catarina, Southern Brazil

    International Nuclear Information System (INIS)

    Castro, Neivaldo Araujo de; Crosta, Alvaro Penteado; Basei, Miguel Angelo Stipp

    1999-01-01

    The petrographic, geochemical and isotopic data on the granitoids intrusive in the Brusque Group, State of Santa Catarina, southern Brazil, are presented in this paper. These are late-to post-tectonic rocks, being the most evolved ones those that constitute the Catinga Suite. The granitoids intrusive in the southern domain of the Brusque Group are grayish rocks, in which biotite (when present) is practically the only mafic mineral. They are rather reduced, slightly alkalic, transitional between meta-and peraluminous. An acid subvolcanic pluton, the Ribeirao da Velha pluton, has similar petrographic and geochemical characteristics, and seems to be genetically related to these granitoids. LREE fractionation relative to HREE is incipient for the Catinga suite, and the REE patterns showing strong negative Eu anomaly. Initial 87 Sr/ 86 Sr ratios, from the literature for these granitoids are around 0.721 (Sao Joao Batista granitoid) and the only available t DM model age (Valsungana granitoid) points to a genesis from a continental crust of ca. 2020 Ma old. Gneiss-migmatitic rocks such as those that occur in the eastern portion of Brusque Group domain and as enclaves in the Nova Italia granitoid are strong candidates for protoliths of these granitoids. Little available information on the granitoids intrusive in the northern domain of the Brusque Group reports the presence of pink K-feldspar hornblende granitoids (Faxinal pluton) and light pink K-feldspar biotite granitoid (Guabiruba pluton). These granitoids are more enriched in K and more oxidized than those in the southern domain, and the LREE fractionation relative to HREE is strong, with the REE patterns showing incipient negative Eu anomaly. It is suggested that part of the Au concentrations found in the northern domain may be genetically associated with the granitoids, since they present characteristics favorable to promote Au mineralizations than the granitoids in the southern domain. Distinct protoliths and

  20. Microchemistry, geochemistry and geochronology of the Lagoa Real Uranium Province (BA) magmatic association: petrological and evolutionary significance

    International Nuclear Information System (INIS)

    Amorim, Lucas Eustaquio Dias

    2016-01-01

    The Lagoa Real Uranium Province (PULR) is located in the center-south of the Bahia State, in the central part of Sao Francisco Craton and consists of an association of Paleoproterozoic meta-granites, alkali-gneiss, albitites, meta-leucodiorite and charnockites. This work has as objective the studies of the magmatic association, trying to understand its petrological and evolutionary meaning. For this purpose, representative bodies were sampled in order to develop unpublished studies of litogeochemistry, isotopes, geochronology and mineral chemistry. These analyzes were performed in: different preserved granitoid facies (Lagoa do Barro, Sao Timoteo, Juazeirinho and late pegmatitic phases), the meta-leucodiorites and charnockite. The data obtained using several modern methodologies, such as geochronology and mineral chemistry by LA-ICP-MS, provided results that allowed the characterization of two magmatic lithologies not described in the literature (Juazeirinho granite e late pegmatitic phases), and also a lithology preliminarily described (Lagoa do Barro granite). Moreover, these data contributed to elucidate the origin and meaning of the leucodiorite and charnoquito varieties, and made it possible to verify new compositional and mineral chemistry tendencies of Sao Timoteo granite. The data presented show that the studied granites were affected by albititization events (tardi or post-magmatic), which have different micro-chemical characteristics from the processes of albite formation related to the non-mineralized albitites bodies. Three albititization events were identified: a) An event that affected the granites characterized by the formation of albite with Rb and U, (b) Another event related to fluids associated with late pegmatitic bodies that formed albite with high levels of U, Rb and Ba, and partially affected the granites of the next pegmatoids portions; and (c) a final albititization event that caused the formation of the albite gneiss bodies, with albite

  1. Datation U_Pb : âge de mise en place du magmatisme bimodal des Jebilet centrales (chaîne Varisque, Maroc). Implications géodynamiquesU_Pb dating: emplacement age of the bimodal magmatism of central Jebilet (Variscan Belt, Morocco). Geodynamic implications

    Science.gov (United States)

    Essaifi, Abderrahim; Potrel, Alain; Capdevila, Ramon; Lagarde, Jean-Louis

    2003-01-01

    The bimodal magmatism of central Jebilet is dated to 330.5 +0.68-0.83 Ma by UPb dating on zircons. This age, similar to that of the syntectonic Jebilet cordierite-bearing granitoids, corresponds to the age of the local major tectonometamorphic event. The syntectonic plutonism of the Jebilet massif, composed of tholeiitic, alkaline, and peraluminous calc-alkaline series, is variegated. Magmas emplacement was favoured by the local extension induced by the motion along the western boundary of the Carboniferous basins of the Moroccan Meseta. The Jebilet massif exemplifies the activation of various magmas sources during an episode of continental convergence and crustal wrenching.

  2. The distribution, geochronology and geochemistry of early Paleozoic granitoid plutons in the North Altun orogenic belt, NW China: Implications for the petrogenesis and tectonic evolution

    Science.gov (United States)

    Meng, Ling-Tong; Chen, Bai-Lin; Zhao, Ni-Na; Wu, Yu; Zhang, Wen-Gao; He, Jiang-Tao; Wang, Bin; Han, Mei-Mei

    2017-01-01

    Abundant early Paleozoic granitoid plutons are widely distributed in the North Altun orogenic belt. These rocks provide clues to the tectonic evolution of the North Altun orogenic belt and adjacent areas. In this paper, we report an integrated study of petrological features, U-Pb zircon dating, in situ zircon Hf isotope and whole-rock geochemical compositions for the Abei, 4337 Highland and Kaladawan Plutons from north to south in the North Altun orogenic belt. The dating yielded magma crystallization ages of 514 Ma for the Abei Pluton, 494 Ma for the 4337 Highland Pluton and 480-460 Ma for the Kaladawan Pluton, suggesting that they are all products of oceanic slab subduction because of the age constraint. The Abei monzogranites derived from the recycle of Paleoproterozoic continental crust under low-pressure and high-temperature conditions are products of subduction initiation. The 4337 Highland granodiorites have some adakitic geochemical signatures and are sourced from partial melting of thickened mafic lower continental crust. The Kaladawan quartz diorites are produced by partial melting of mantle wedge according to the positive εHf(t) values, and the Kaladawan monzogranite-syenogranite are derived from partial melting of Neoproterozoic continental crust mixing the juvenile underplated mafic material from the depleted mantle. These results, together with existing data, provide significant information about the evolution history of oceanic crust subduction during the 520-460 Ma. The initiation of subduction occurred during 520-500 Ma with formation of Abei Pluton; subsequent transition from steep-angle to flat-slab subduction at ca.500 Ma due to the arrival of buoyant oceanic plateaus, which induces the formation of 4337 Highland Pluton. With ongoing subduction, the steep-angle subduction system is reestablished to cause the formation of 480-460 Ma Kaladawan Pluton. Meanwhile, it is this model that account for the temporal-spatial distribution of these early

  3. Magmatism and deformation during continental breakup

    Science.gov (United States)

    Keir, Derek

    2013-04-01

    The rifting of continents and the transition to seafloor spreading is characterised by extensional faulting and thinning of the lithosphere, and is sometimes accompanied by voluminous intrusive and extrusive magmatism. In order to understand how these processes develop over time to break continents apart, we have traditionally relied on interpreting the geological record at the numerous fully developed, ancient rifted margins around the world. In these settings, however, it is difficult to discriminate between different mechanisms of extension and magmatism because the continent-ocean transition is typically buried beneath thick layers of volcanic and sedimentary rocks, and the tectonic and volcanic activity that characterised breakup has long-since ceased. Ongoing continental breakup in the African and Arabian rift systems offers a unique opportunity to address these problems because it exposes several sectors of tectonically active rift sector development spanning the transition from embryonic continental rifting in the south to incipient seafloor spreading in the north. Here I synthesise exciting, multidisciplinary observational and modelling studies using geophysical, geodetic, petrological and numerical techniques that uniquely constrain the distribution, time-scales, and interactions between extension and magmatism during the progressive breakup of the African Plate. This new research has identified the previously unrecognised role of rapid and episodic dike emplacement in accommodating a large proportion of extension during continental rifting. We are now beginning to realise that changes in the dominant mechanism for strain over time (faulting, stretching and magma intrusion) impact dramatically on magmatism and rift morphology. The challenge now is to take what we're learned from East Africa and apply it to the rifted margins whose geological record documents breakup during entire Wilson Cycles.

  4. Barren Miocene granitoids in the Central Andean metallogenic belt, Chile: Geochemistry and Nd-Hf and U-Pb isotope systematics

    International Nuclear Information System (INIS)

    Deckart, Katja; Godoy, Estanislao; Bertens, Alfredo; Jerez, Daniela; Saeed, Ayesha

    2010-01-01

    Four Middle-to-Late Miocene barren plutonic complexes that occur between the giant porphyry copper deposits of the central Chilean Andes were selected for U-Pb LA-ICPMS geochronology and Hf-isotope systematics on single zircon grains. Major and trace elements and Sr-Nd-Hf isotope whole rock geochemical studies were undertaken to compare with slightly younger or coeval barren and fertile intrusive rocks between 32 o and 34 o S. The studied granitoids yield resolvable crystallization ages of 11.3±0.1 Ma (Cerro Meson Alto massif), 10.3±0.2 Ma (La Gloria pluton), 14.9±0.2 Ma/14.9±0.1 Ma (Yerba Loca stock) and 11.2±0.1 Ma/14.7±0.1 Ma (San Francisco Batholith). Major and trace elements discard an adakitic signature as suggested for coeval porphyric intrusions at 32 o S, slightly younger mineralized porphyries at Rio Blanco-Los Bronces deposit and other Cenozoic adakites. Volcanic host rocks are less fractionated than the intrusive rock units. The same observation can be made for the unmineralized northern plutons compared to the southern ones. Initial Sr-Nd isotope data show insignificant variation (0.703761-0.704118 and 0.512758- 0.512882), plotting in the mantle array. Trace element enrichment can be explained by addition of subducted-slab fluids and/or terrigenous sediments to the mantle wedge prior to and/or slight crustal input during magma ascent. Zircon grains separated from these barren intrusives share a similar initial εHf-data variation for the younger age group (10-12 Ma; 7.04-9.54) and show a more scattered range for the older one (14-15 Ma; 8.50-15.34); both sets plot between the DM and CHUR evolution lines. There is evidence that magma evolution was slightly distinct through time from older to younger barren magmatism, compared to a few fertile porphyritic rocks from Rio Blanco-Los Bronces porphyry copper deposit. It is suggested that chronological inconsistencies within these complexes might be related to differential shortening across the NE

  5. Granitoids of the Dry Valleys area, southern Victoria Land, Antarctica : plutons, field relationships, and isotopic dating

    International Nuclear Information System (INIS)

    Allibone, A.H.; Cox, S.C.; Johnstone, R.D.

    1993-01-01

    Detailed mapping throughout much of the Dry Valleys area indicates the region is underlain by 15 major granitoid plutons and numerous smaller plugs and dikes. Intrusive relationships of these plutons and dikes indicate repeated intrusion of superficially similar granitoids at different times. Sufficient internal lithologic variation occurs within individual plutons, to allow correlation with several of the previously defined granitoid units based on lithologic character. Consequently, previous subdivision schemes based on lithology are no longer tenable and are here replaced with a subdivision scheme based on the identification of individual plutons. The elongate, concordant Bonney, Denton, Cavendish, and Wheeler Plutons, which range in composition between monzodiorite and granodiorite, are the oldest relatively undeformed plutons in the Dry Valleys area. Each pluton is characterised by flow alignment of K-feldspar megacrysts, hornblende, biotite, and mafic enclaves. Field relationships and radiometric dating indicate these are deep-level plutons, emplaced synchronous with upper amphibolite facies metamorphism of the adjacent Koettlitz Group between 589 and 490 Ma ago. Elongate, discordant plutons of equigranular homogeneous biotite granodiorite and granite (Hedley, Valhalla, St Johns, Suess) were subsequently emplaced by stoping at a relatively high crustal level at 490 Ma. These eight plutons are cut by numerous swarms of Vanda mafic and felsic porphyry dikes. The ovoid, discordant, high level Pearse, Nibelungen, Orestes, Brownworth, Swinford, and Harker Plutons, emplaced between c. 486 and 477 Ma, display mutually crosscutting relationships with the youngest of the Vanda dikes. These younger plutons range in composition between monzonite and granite. Some are characterised by K-feldspar megacrystic textures superficially similar to some of the oldest concordant plutons. (author). 57 refs.; 2 tabs.; 4 figs

  6. A review of the ascent and emplacement of granitoid bodies into the crust

    Directory of Open Access Journals (Sweden)

    Katarína Bónová

    2005-03-01

    Full Text Available This paper relates to basic information (i.e. mechanical aspects of ascent, indicators faciliting the discriminability of various ascent styles about the models of ascent and emplacement of granitoid bodies, since the purely mechanical aspect of intrusion of magmas is a fascinating subject and it has generated a considerable controversy over many years. Individual models are demonstrated by world-known occurrences and examples from Western Carpathian’s region. The conditions of magma migration are demonstrated as well.

  7. Permian alkali granitoids of the transbaikal region (new Rb-Sr dates)

    Energy Technology Data Exchange (ETDEWEB)

    Sukhanov, M K; Ryakhovskij, V M; Abramov, A V

    1984-01-01

    Rubidium-strontium isotopic investigations of granitoids from Khorinsk and Middle Oninsk massifs were conducted. Isochrones for two chief-modifications of rocks - subalkaline syenites and alkaline granites-were constructed. The age of syenites is determined to be (293 + 20) x 10/sup 6/ at (/sup 87/Sr//sup 86/Sr)/sub 0/=0.7044 +- 0.0106 that of alkaline granites - (253 +- 3) x 10/sup 6/ at (/sup 87/Sr//sup 86/Sr)/sub 0/=0.7077 +- 0.0033. Analytical data for determination of rubidium-strontium age of rocks of the mentioned massits are presented as well.

  8. Geology and geochemistry of Massangana Granitoid Complex, Brazil, and its relation with tin mineralization

    International Nuclear Information System (INIS)

    Romanini, S.J.

    1982-01-01

    The geochemical and petroLogical characteristics of the Massangana Granitoid Complex, situated in the Rondonia Federal Territory, Brazil, aiming to discriminate the tin mineralized granitic rocks from the no mineralized ones. The collected samples consists of examples in tin mineralized and sterile phases. The elements traces were determined by x-ray fluorescence analysis, emission spectrography, molecular absorption spectrophotometry and atomic absorption spectrophotometry. The complex edifying evolved in four sucessive episodes called Massangana Phase, Bom Jardim Phase, Sao domingos Phase and Taboca Phase ordered stratigraphycally in this sequence. (author/M.C.K.) [pt

  9. On the metamorphic history of an Archaean granitoid greenstone terrane, East Pilbara, Western Australia, using the 40Ar/39Ar age spectrum technique

    International Nuclear Information System (INIS)

    Wijbrans, J.R.; McDougall, I.

    1987-01-01

    Age spectrum analyses of blue-green hornblendes from amphibolites from the Western Shaw Belt, East Pilbara, Western Australia, indicate an age of at least 3200 Ma for early regional metamorphism. Ages on hornblende and muscovite from the narrow contact zone with the adjacent Yule Batholith probably data updoming of the granitoid gneiss terranes at 2950 Ma. Hornblendes from within the Shaw Batholith and from a contact zone of a post-tectonic granitoid yield ages of 2840-2900 Ma, indicating either prolonged high temperatures within the granitoid gneiss terranes or a separate thermal pulse associated with the intrusion of post-tectonic granitoids. The preservation of very old hornblendes in a narrow greenstone belt surrounded by massive granitoid gneiss domes indicates that remarkable contrasts in metamorphic geotherms existed over short distances during the Late Archaean, suggesting that updoming occurred during a period of rapid tectonism. (orig.)

  10. On the metamorphic history of an Archaean granitoid greenstone terrane, East Pilbara, Western Australia, using the /sup 40/Ar//sup 39/Ar age spectrum technique

    Energy Technology Data Exchange (ETDEWEB)

    Wijbrans, J.R.; McDougall, I.

    1987-07-01

    Age spectrum analyses of blue-green hornblendes from amphibolites from the Western Shaw Belt, East Pilbara, Western Australia, indicate an age of at least 3200 Ma for early regional metamorphism. Ages on hornblende and muscovite from the narrow contact zone with the adjacent Yule Batholith probably data updoming of the granitoid gneiss terranes at 2950 Ma. Hornblendes from within the Shaw Batholith and from a contact zone of a post-tectonic granitoid yield ages of 2840-2900 Ma, indicating either prolonged high temperatures within the granitoid gneiss terranes or a separate thermal pulse associated with the intrusion of post-tectonic granitoids. The preservation of very old hornblendes in a narrow greenstone belt surrounded by massive granitoid gneiss domes indicates that remarkable contrasts in metamorphic geotherms existed over short distances during the Late Archaean, suggesting that updoming occurred during a period of rapid tectonism.

  11. Some genetic aspects of hydrothermal uranium deposits in the Bakulja granitoide (Serbia)

    International Nuclear Information System (INIS)

    Jelenkovic, Rade

    1998-01-01

    This paper discusses the influence of temperature and the way of hydrothermal fluids flow in function of both the degree of tectonized granitoid and the origin of solutions, and partly the processes accompanying mineralization expressed through physico-chemical, mineralogical and mechanical alterations of the mother rock. It has been concluded that heat energy exchange is in function of: 1) petrochemical characteristic of a rock the hydrothermal fluids flow through; 2) degree of tectonization of the surrounding mineralized rocks; 3) volume and morphology of the fissured-porous space; 4) form of uranium bonding in mineral carriers; 5) degree of uranium leaching in hydrothermal solutions; 6) the way of hydrothermal fluids flow, and 7) coefficient of heat exchange expressed by distribution of heat energy within a fluid-rock system. It has also been established that contraction of granite volume results from physico-chemical processes that take place within a granitoid-hydrothermal fluid system and its quantification has been carried out. (Author)

  12. An isotopic study of granitoids in the Litchfield Block, Northern Territory

    International Nuclear Information System (INIS)

    Page, R.W.; Bower, M.J.; Guy, D.B.

    1984-01-01

    The Litchfield Block contains a variety of granitoids, gneissic rocks, and migmatites that are intrusive into metasediments of probable Early Proterozoic age at the western margin of the Pine Creek Inlier. Isotopic data, which include U-Pb measurements on cogenetic zircon and xenotime and Rb-Sr total-rock measurements on the least metamorphosed granodiorites, show that these rocks crystallised from mantle-derived melts between 1840 Ma and 1850 Ma ago. Radiogenic Pb was lost from zircon in the early Palaeozoic (about 435 Ma), but xenotime remained a closed system until recent time. Many granitoids in the Litchfield Block have a gneissic fabric imposed during greenschist to amphibolite-grade regional metamorphism. This disturbance allowed partial isotopic re-equilibration of Rb-Sr total-rock systems, at about 1770 +- 16 Ma. As this igneous and metamorphic evolution is mirrored in other parts of the Pine Creek Inlier, the Halls Creek Inlier, and many other orogenic belts in northern Australia, its recognition and isotopic definition in the Litchfield Block further emphasise the magnitude and chronological integrity of this early Proterozoic tectonic event

  13. Neoproterozoic alkaline magmatism in Ilha do Cardoso, southeastern coast of Sao Paulo State, Brazil

    International Nuclear Information System (INIS)

    Weber, Werner; Basei, Miguel A.S.; Siga Junior, Oswaldo; Sato, Kei

    2001-01-01

    This work focuses on the geology and geochronology of rocks cropping out on Cardoso Island, on the southeastern coast of Sao Paulo State, close to the boundary with Parana State. The island, with an area of about 151 km 2 is a protected area administered by the Forest Institute of the Secretariat for the Environment of the State of Sao Paulo. It is mountainous, with a peak at 814 m, and is covered by dense Atlantic Forest vegetation. The island is made up mainly of an igneous complex with light grey leucocratic, inequigranular, medium to coarse-grained syenites. The Tres Irmaos Syenite (STI), composed of pyroxene, hornblende, and perthitic to mesoperthitic microcline, predominates has magmatic flow structures, and it cut by the pinkish grey, leucocratic medium-grained Cambriu alkali-feldspar granites (GC). Geochemical analysis of STI and GC demonstrate their metaluminous alkaline nature and late orogenic to anorogenic character. The bodies formed between 620 and 570 Ma according to U-Pb dating of zircons and cooled between 597 and 531 Ma (K-Ar in amphiboles). Whole rock Sm-Nd analyses yield Meso- and Paleoproterozoic TDM ages (1,500 - 2,200 Ma). A belt of low-grade metasedimentary rocks occurs in the northern part of the island. Quartz schist, quartz-mica schist and mica-quartz schist, often-containing andalusite and cordierite, predominate. Geochemical and geochronological data suggest that the sources of the metasediments were continental arc andesites of whose protoliths separated from the mantle between 1,800 and 2,200 Ma during the Paleoproterozoic. These metasediments probably continue on the continent in the Taquari region and extend southwards in narrow strips between the granitoids of the Paranagua Domain. (author)

  14. The neoproterozoic Goias magmatic arc, central Brazil: a review and new Sm-Nd isotopic data

    International Nuclear Information System (INIS)

    Pimentel, Marcio Martins; Fuck, Reinhardt Adolfo; Gioia, Simone Maria Costa Lima

    2000-01-01

    In this study we review the main characteristics and geochronological/isotopic data of metaigneous rocks of the juvenile Neoproterozoic Goias Magmatic Arc in central Brazil. Some new Sm-Nd isotopic data are also presented for both the southern (Arenopolis) and northern (Mara Rosa) sections of the arc. In the south, granitoids of the Choupana-Turvania area yielded a Sm-Nd whole-rock isochron age of 863± 97 Ma and e Nd (T) of +4.1 T D M model ages vary between 0.94 and 1.13 Ga. Metavolcanic rocks in the Pontalina region have a Sm-Nd whole rock isochron age of 762 ± 77 Ma and e Nd (T) of +2.9. T DM values are between 0.96 and 1.10 Ga. In the northern section of the Goias Arc, mylonitic gneisses of the Serra Azul ridge, an important N30E shear zone, were investigated and have a Sm-Nd isochron age of 3058 ± 120 Ma and initial e Nd value of ca.+ 2.1. This data suggests that the Serra Azul ridge might represent either a mylonitized fragment of the Archaen terranes exposed just to the south, or the sialic basement of the Araguaia Belt supracrustal, along the eastern margin of the Amazon Craton. The geochronological data available so far indicate a long history of arc formation and amalgamation on the western margin of the Sao Francisco-Congo continent during the Neoproterozoic. The history of convergence of continental masses is partially coeval with the fragmentation of Rodinia, indicating that the western margin (present geographic reference) of that continent occupied a peripheral setting in the Rodinia super continent. (author)

  15. The neoproterozoic Goias magmatic arc, central Brazil: a review and new Sm-Nd isotopic data

    Energy Technology Data Exchange (ETDEWEB)

    Pimentel, Marcio Martins; Fuck, Reinhardt Adolfo; Gioia, Simone Maria Costa Lima [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail: marcio@unb.br

    2000-03-01

    In this study we review the main characteristics and geochronological/isotopic data of metaigneous rocks of the juvenile Neoproterozoic Goias Magmatic Arc in central Brazil. Some new Sm-Nd isotopic data are also presented for both the southern (Arenopolis) and northern (Mara Rosa) sections of the arc. In the south, granitoids of the Choupana-Turvania area yielded a Sm-Nd whole-rock isochron age of 863{+-} 97 Ma and e{sub Nd} (T) of +4.1 T{sub D}M model ages vary between 0.94 and 1.13 Ga. Metavolcanic rocks in the Pontalina region have a Sm-Nd whole rock isochron age of 762 {+-} 77 Ma and e{sub Nd} (T) of +2.9. T {sub DM} values are between 0.96 and 1.10 Ga. In the northern section of the Goias Arc, mylonitic gneisses of the Serra Azul ridge, an important N30E shear zone, were investigated and have a Sm-Nd isochron age of 3058 {+-} 120 Ma and initial e{sub Nd} value of ca.+ 2.1. This data suggests that the Serra Azul ridge might represent either a mylonitized fragment of the Archaen terranes exposed just to the south, or the sialic basement of the Araguaia Belt supracrustal, along the eastern margin of the Amazon Craton. The geochronological data available so far indicate a long history of arc formation and amalgamation on the western margin of the Sao Francisco-Congo continent during the Neoproterozoic. The history of convergence of continental masses is partially coeval with the fragmentation of Rodinia, indicating that the western margin (present geographic reference) of that continent occupied a peripheral setting in the Rodinia super continent. (author)

  16. Modulation of magmatic processes by carbon dioxide

    Science.gov (United States)

    Caricchi, L.; Sheldrake, T. E.; Blundy, J. D.

    2017-12-01

    Volatile solubility in magmas increases with pressure, although the solubility of CO2 is much lower than that of H2O. Consequently, magmas rising from depth release CO2-rich fluids, which inevitably interact with H2O-poor magmas in the upper crust (CO2-flushing). CO2-flushing triggers the exsolution of H2O-rich fluids, leading to an increase of volume and magma crystallisation. While the analyses of eruptive products demonstrates that this process operates in virtually all magmatic system, its impact on magmatic and volcanic processes has not been quantified. Here we show that depending on the initial magma crystallinity, and the depth of magma storage, CO2-flushing can lead to volcanic eruptions or promote conditions that favour the impulsive release of mineralising fluids. Our calculations show that the interaction between a few hundred ppm of carbonic fluids, and crystal-poor magmas stored at shallow depths, produces rapid pressurisation that can potentially lead to an eruption. Further addition of CO2 increases magma compressibility and crystallinity, reducing the potential for volcanic activity, promoting the formation of ore deposits. Increasing the depth of fluid-magma interaction dampens the impact of CO2-flushing on the pressurisation of a magma reservoir. CO2-flushing may result in surface inflation and increases in surface CO2 fluxes, which are commonly considered signs of an impending eruption, but may not necessarily result in eruption depending on the initial crystallnity and depth of the magmatic reservoir. We propose that CO2-flushing is a powerful agent modulating the pressurisation of magma reservoirs and the release of mineralising fluids from upper crustal magma reservoirs.

  17. Role of Sulfur in the Formation of Magmatic-Hydrothermal Copper-Gold Deposits

    Science.gov (United States)

    Seo, J.; Guillong, M.; Heinrich, C.

    2009-05-01

    Sulfur plays essential roles in hydrothermal ore-forming processes [1], which calls for precise and accurate quantitative sulfur determination in fluid inclusions. Feasibility tests for sulfur quantification by comparing data from both LA-Quadrupole (Q) - ICP-MS and LA-High Resolution (HR) - ICP-MS show that reliable sulfur quantification in fluid inclusions is possible [2], provided that a very careful baseline correction is applied. We investigate the metal transporting capabilities of sulfur by measuring sulfur together with copper and other elements in cogenetic brine and vapor inclusions ('boiling assemblages') in single healed crack hosted by quartz veins. Samples are from high-temperature magmatic-hydrothermal ore deposits and miarolitic cavities of barren granitoid. Clear compositional correlations of sulfur with copper and gold were found. A molar S/Cu ratio commonly close to 2 but never above 2, indicates sulfur-complexed metal transportation in the high-temperature hydrothermal vapor, and probably also in the Na-Fe-K-Cl-enriched brines. Vapor/brine partitioning trends of the S and Cu are shown to be related with the chemistry of the fluids (possibly by various sulfur speciations in varying pH, fO2) and causative magma source. In the boiling hydrothermal environments, higher vapor partitioning of Cu and S is observed at reduced and peraluminous Sn-W granite, whereas oxidized and perakaline porphyry-style deposits have a lower partitioning to the vapor although the total concentration of S, Cu, Au in both fluid phase is higher than in the Sn-W granite [3]. Vapor inclusion in the boiling assemblages from magmatic-hydrothermal ore deposits and granitic intrusions generally contain an excess of sulfur over ore metals such as Cu, Fe, and Mo. This allows efficient sulfide ore precipitation in high-temperature porphyry-type deposits, and complexation of gold by the remaining sulfide down to lower temperatures. The results confirm earlier interpretations [1] and

  18. Late Mesozoic basin and range tectonics and related magmatism in Southeast China

    Directory of Open Access Journals (Sweden)

    Dezi Wang

    2012-03-01

    Full Text Available During the Late Mesozoic Middle Jurassic–Late Cretaceous, basin and range tectonics and associated magmatism representative of an extensional tectonic setting was widespread in southeastern China as a result of Pacific Plate subduction. Basin tectonics consists of post-orogenic (Type I and intra-continental extensional basins (Type II. Type I basins developed in the piedmont and intraland during the Late Triassic to Early Jurassic, in which coarse-grained terrestrial clastic sediments were deposited. Type II basins formed during intra-continental crustal thinning and were characterized by the development of grabens and half-grabens. Graben basins were mainly generated during the Middle Jurassic and were associated with bimodal volcanism. Sediments in half-grabens are intercalated with rhyolitic tuffs and lavas and are Early Cretaceous in age with a dominance of Late Cretaceous–Paleogene red beds. Ranges are composed of granitoids and bimodal volcanic rocks, A-type granites and dome-type metamorphic core complexes. The authors analyzed lithological, geochemical and geochronological features of the Late Mesozoic igneous rock assemblages and proposed some geodynamical constraints on forming the basin and range tectonics of South China. A comparison of the similarities and differences of basin and range tectonics between the eastern and western shores of the Pacific is made, and the geodynamical evolution model of the Southeast China Block during Late Mesozoic is discussed. Studied results suggest that the basin and range terrane within South China developed on a pre-Mesozoic folded belt was derived from a polyphase tectonic evolution mainly constrained by subduction of the western Pacific Plate since the Late Mesozoic, leading to formation of various magmatism in a back-arc extensional setting. Its geodynamic mechanism can compare with that of basin and range tectonics in the eastern shore of the Pacific. Differences of basin and range

  19. Magmatism at different crustal levels in the ancient North Cascades magmatic arc

    Science.gov (United States)

    Shea, E. K.; Bowring, S. A.; Miller, R. B.; Miller, J. S.

    2013-12-01

    The mechanisms of magma ascent and emplacement inferred from study of intrusive complexes have long been the subject of intense debate. Current models favor incremental construction based on integration of field, geochemical, geochronologic, and modeling studies. Much of this work has been focused on a single crustal level. However, study of magmatism throughout the crust is critical for understanding how magma ascends through and intrudes surrounding crustal material. Here, we present new geochronologic and geochemical work from intrusive complexes emplaced at a range of crustal depths in the Cretaceous North Cascades magmatic arc. These complexes were intruded between 92 and 87 Ma at depths of at ≤5 -10 km, ~20 km, and ~25 km during this time. U-Pb CA-TIMS geochronology in zircon can resolve Jack-Entiat intrusive complex, a highly elongate amalgamation of intrusions recording two episodes of magmatism between~92-88 Ma and ~80-77 Ma. Each of these complexes provides a window into crustal processes that occur at different depths. Our data suggest assembly of the Black Peak intrusive complex occurred via a series of small (0.5-2 km2) magmatic increments from ~92 Ma to ~87 Ma. Field relations and zircon trace element geochemistry indicate each of these increments were emplaced and crystallized as closed systems-we find no evidence for mixing between magmas in the complex. However, zircon inheritance becomes more common in younger intrusions, indicating assimilation of older plutonic material, possibly during magma production or transport. The Seven-Fingered Jack intrusive complex, emplaced around 15-20 km, preserves a much more discontinuous record of intrusion than the Black Peak. Our data indicate major magmatism in the complex occurred between ~92.1-91.1 Ma. Inheritance in the Seven-Fingered Jack is common, particularly along contacts between intrusions. The Tenpeak intrusive complex, assembled between ~92 Ma and 89 Ma, represents one of the deepest exhumed

  20. Geochemistry and petrogenesis of Mesoproterozoic A-type granitoids from the Danish island of Bornholm, southern Fennoscandia

    DEFF Research Database (Denmark)

    Johansson, Åke; Waight, Tod Earle; Andersen, Tom

    2016-01-01

    Granitoids and gneisses from the Danish island of Bornholm have been investigated using whole rock geochemistry, Sr and Nd isotope geochemistry and Hf isotopes in zircon. Recent U–Pb dating shows that the rocks were formed during a short time interval at 1.45 to 1.46 Ga, penecontemporaneous...

  1. Pre- and syn-Ross orogenic granitoids at Drake Head and Kartografov Island, Oates Coast, northern Victoria Land, East Antarctica

    International Nuclear Information System (INIS)

    Adams, C.J.; Roland, N.W.

    2002-01-01

    The majority of the Oates Coast, northern Victoria Land granitoids, typified by those at Drake Head and Kartografov Island (Harald Bay), are monzogranites with lesser granodiorites and minor quartz-monzodiorite and syenogranite. All are plagioclase-K-feldspar-biotite granitoids with additional muscovite, garnet and/or hornblende, and are subalkaline and peraluminous. Berg Granite typifies the early Ordovician, Granite Harbour Instrusive (GHI) suite of the Ross Orogen at the Oates Coast. Granitoids from Kartografov Island have higher amounts of Fe+Mg+Ti and an ambiguous Rb-Sr geochronology: they could be either pre-Ross Orogeny in age, or syn-Ross Orogeny and representing a lower structural level of GHI. The Drake Head granite gneiss has a fractionated leuco-granite composition similar to Berg Granite, and is intruded by granite and granodiorite. Rb-Sr ages indicate that all are Neoproterozoic, although the granite gneiss result is probably an errorchron age, reflecting its less uniform nature (granodiorite:649 ± 30 Ma, initial ratio 0.7065 +/- 6; granite gneiss: 682 ± 140 Ma, initial ratio 0.7107 ± 50). These late Neoproterozoic granitoids provide a source for distinctive detrital zircon age components in extensive early Paleozoic turbidites of Australia-New Zealand-Antarctica. (author). 24 refs., 5 figs., 1 tab

  2. Geochemical modeling of magmatic gas scrubbing

    Directory of Open Access Journals (Sweden)

    B. Gambardella

    2005-06-01

    Full Text Available The EQ3/6 software package, version 7.2 was successfully used to model scrubbing of magmatic gas by pure water at 0.1 MPa, in the liquid and liquid-plus-gas regions. Some post-calculations were necessary to account for gas separation effects. In these post-calculations, redox potential was considered to be fixed by precipitation of crystalline a-sulfur, a ubiquitous and precocious process. As geochemical modeling is constrained by conservation of enthalpy upon water-gas mixing, the enthalpies of the gas species of interest were reviewed, adopting as reference state the liquid phase at the triple point. Our results confirm that significant emissions of highly acidic gas species (SO2(g, HCl(g, and HF(g are prevented by scrubbing, until dry conditions are established, at least locally. Nevertheless important outgassing of HCl(g can take place from acid, HCl-rich brines. Moreover, these findings support the rule of thumb which is generally used to distinguish SO2-, HCl-, and HF-bearing magmatic gases from SO2-, HCl-, and HF-free hydrothermal gases.

  3. Mineral chemistry and geochemistry of the Late Neoproterozoic Gabal Abu Diab granitoids, Central Eastern Dessert, Egypt: Implications for the origin of rare metal post-orogenic A-type granites

    Science.gov (United States)

    Sami, Mabrouk; Ntaflos, Theodoros; Farahat, Esam S.; Ahmed, Awaad F.; Mohamed, Haroun A.

    2015-04-01

    The Neoproterozoic Gabal Abu Diab pluton is a part of the Arabian Nubian shield (ANS) continental crust and located in the Central Eastern Desert (CED) of Egypt. It constitutes multiphase granitic pluton intruded into granodiorite and metagabbro-diorite rocks with sharp and nonreactive contacts. Based on field observations, colors, structural variations and petrographic investigations, this granitic outcrop consists of an inner core of two-mica granite (TMG) followed outward by garnet bearing muscovite granite (GBMG) and albite granite (AG). Petrographical study indicated that medium to coarse-grained TMG is dominated by K-feldspar (Or88-98), quartz, plagioclase (albite, An0-7), muscovite and biotite with hypidiomorphic texture. With exception the appearance of garnet and the disappearance of biotite the GBMG resembles the TGM, while AG is leucocratic without any mafic mineral. The main accessories are zircon, Nb and Ta-bearing rutile, columbite, ilmenorutile, ilmenite, magnetite and apatite. This mineralogical similarity and the existence of columbite group minerals (CGM) in all granitoids, indicates a cogenetic relationship. Microprobe analyses reveal that, besides the CGM, rutile and ilmenite are the main repository phases for Nb-Ta-Ti. Columbite-(Mn) exists as individual subhedral crystals (up to 100μm in size) or intimate intergrowth with Nb-bearing rutile and/or ilmenite. The CGM are represented mostly by columbite-(Mn) with Ta/(Ta+Nb) and Mn/(Mn+Fe) ratio ranging from 0.02-0.08 and 0.4-0.9, respectively suggesting extreme degree of magmatic fractionation. Rutile contains significant amounts of Ta (up to 4 wt.% Ta2O5) and Nb (up to 22 wt.% Nb2O5). Biotites are phlogopite-annite in composition (Ann47-60Phlog40-53,on average) and are enriched with AlIV that characterize peraluminous granites. Garnets contain 60-69 mol.% spessartine and 28-36 mol.% almandine where, the ratio of spessartine and almandine together exceeds 95 mole percent, similar to garnet occur

  4. Petrogenesis of late Paleozoic-to-early Mesozoic granitoids and metagabbroic rocks of the Tengchong Block, SW China: implications for the evolution of the eastern Paleo-Tethys

    Science.gov (United States)

    Zhu, Ren-Zhi; Lai, Shao-Cong; Qin, Jiang-Feng; Zhao, Shao-Wei

    2018-03-01

    mantle-derived material associated with late Permian-to-Early Triassic subduction of the Paleo-Tethys, and a second stage that generated granitoid magmas by the partial melting of crustal-derived sources during the Late Triassic collision between the Lhasa and Tengchong blocks and the northern margin of the Australian continent. These rocks, therefore, provide evidence of a systematic late Permian-to-Late Triassic transition from a pre-collision/volcanic arc setting through a collisional setting to a final within-plate phase of magmatism. The previous research involving bulk-rock Sr-Nd analyses of units from the southern Sanjiang orogenic belt and zircon Hf isotopic analyses of units from the Tengchong Block suggests that these areas may record similar magmatic evolutionary trends from mantle- to crustal-derived sources during the evolution of the eastern Paleo-Tethys.

  5. New data on barguzinsky granitoids age of the Angaro-Vitimsky batholith

    International Nuclear Information System (INIS)

    Budnikov, S.V.; Kovalenko, V.I.; Yarmolyuk, V.V.

    1995-01-01

    The age batholith rocks was studied by the Sm-Nd and U-Pb methods in terms of zircon. The boundary of masses being of Late carboniferous age of batholith rocks has been defined. Early and Middle Proterozoic age is possible for magmatic rocks of this part of batholith. 12 refs.; 3 refs.; 1 tab

  6. Role of deep-Earth water cycling in the growth and evolution of continental crust: Constraints from Cretaceous magmatism in southeast China

    Science.gov (United States)

    Li, Zhen; Wang, Xuan-Ce; Wilde, Simon A.; Liu, Liang; Li, Wu-Xian; Yang, Xuemei

    2018-03-01

    The late Mesozoic igneous province in southeast China provides an excellent opportunity to understand the processes that controlled the growth and evolution of Phanerozoic continental crust. Here we report petrological, whole-rock geochemical and isotopic data, and in situ zircon U-Pb-Lu-Hf isotopic data from granitoids and associated gabbros in the Pingtan and Tong'an complexes, southeast China. Through combining the new results with published datasets in southeast China, we show that the Early Cretaceous magmatic rocks are dominated by juvenile Nd-Hf isotopic compositions, whereas the Late Cretaceous ones display less radiogenic Nd-Hf isotope signatures. Furthermore, Nd-Hf isotope systematics are coupled with decreasing abundance of hydrous minerals and an increase of zircon saturation temperatures. Compiled zircon Hf-O data indicates that the 117-116 Ma granites have zircon δ18O values ranging from mantle values (close to 5.3‰) to as low as 3.9‰, but with dominantly positive initial epsilon Hf (εHf(t)) values. Zircon grains from 105 to 98 Ma rocks have δ18O values plotting within the mantle-like range (6.5‰ - 4.5‰), but mainly with negative εHf(t) values. Zircon grains from ca. 87 Ma rocks have positive εHf(t) values (+ 9.8 to + 0.7) and a large range of δ18O values (6.3‰ - 3.5‰). The variations in Hf-Nd-O isotopic compositions are correlated with decreasing abundance of magma water contents, presenting a case that water-fluxed melting generated large-scale granitic magmatism. Deep-Earth water cycling provides an alternative or additional mechanism to supply volatiles (e.g., H2O) for hydrous basaltic underplating, continental crustal melting, and magmatic differentiation.

  7. The possibility of use of Kremicj granitoid (Serbia) as an architectural stone

    International Nuclear Information System (INIS)

    Kureshevicj, Lidja

    2010-01-01

    The stone from the granitoid pluton of Kremić in southern Serbia has been examined in order to evaluate the possibility of its use as an architectural stone. Both field observations and laboratory testing of specimens have been performed. Although the specimens were collected from the field surface level, their physicomechanical lab test results have shown that the rock mass itself fulfils all the requirements for use as an architectural stone set by the State through Serbian standards. Also, the stone quality is higher in deeper ground levels, where the weathering agents have less intense effects. This stone does not have high ornamental properties, but it has a finegrained texture and low mica content which has a positive effect on its technical characteristics and susceptibility to processing. (Author)

  8. Rb-Sr isochronous dating of granitoids of Dumbier zone of Low Tatras (Western Carpathians)

    International Nuclear Information System (INIS)

    Bagdasaryan, G.P.; Gukasyan, R.Kh.; Cambel, B.; Vesel'skij, J.

    1985-01-01

    The results are discussed of isotopic-geochronological research and age determination of characteristic samples of granitoid rocks, obtained by the Rb/Sr isochronous method. The samples were biotite granodiorites and granites taken from various parts of the Dumbier massif and small granite bodies of the Kralicka type. Rb/Sr isochrones of the rock samples show identical age values: 362+-21 m.y. for the Dumbier massif and 365+-17 m.y. correspnding to the Middle - Upper Devonian. Initial 87 Sr/ 86 Sr ratios equal to 0.7079 and 0.7157, respectively, allow to make a presumption that the rocks of the Dumbier massif may have been derived both from crustal and from mantle sources while granites of the Kralicka type are close to the rocks of the crustal origin

  9. Geotectonic evolution of granitoid-greenstone belts from Crixas, Guarinos, Pilar de Goias - Hidrolina (Goias), Brazil

    International Nuclear Information System (INIS)

    Montalvao, R.M.G. de.

    1985-01-01

    The area in discussion, in a geologic context, constitutes one of the most interesting and complex, within the South American Platform, in Brazilian territory, over which granitoid-greenstone belts are outstanding. The Goiano Complex is the oldest unit in the geologic column herein adopted and composed largely of granitoids, gneiss and migmatites, in the amphibolite facies. Dated samples of the complex have shown two isochrones of Rb/Sr reference, the oldest one is 2.926 +- 65 m.y. and the 87 Sr/ 86 Sr initial ratio of 0.7001 and the youngest on of 2.471 + 20 m.y. and 87 Sr/ 86 Sr initial ratio of 0.701. Although the initial ratios data of the Rb/Sr isochron, as well as the parameters in the Pb/Pb analyses may indicate material of mantle source, it may be interpreted, with the help of field data, that the youngest values may indicate the reworking of crustal sialic rocks formed 2.925 +- 65 m.y. ago (oldest isochron), with primitive material contribution. Before such reworking volcanic-sedimentary sequence was deposited over the already formed sialic crust, and it is denominated Pilar de Goias Supergroup which characterizes the Greenstone Belts in the region. The Archean age for the supergroup was evident through the age results of its ultramafic rocks, showing 2.600 m.y. isochron age, with Sm/Nd methods. Besides the geochronology and field studies, basic information for the construction of the geologic column herein presented, there has been done petrographic and litho geochemical studies, both in the Goiano Complex and Pilar de Goias Supergroup, as for the Pilar de Goias Supergroup, the studies were concentrated on its mafic-ultramafic rocks. (author)

  10. Moho and magmatic underplating in continental lithosphere

    DEFF Research Database (Denmark)

    Thybo, Hans; Artemieva, Irina M.

    2013-01-01

    interacts with the surrounding crustal rocks which leads to smearing of geophysical signals from the underplated material. In terms of processes, there is no direct discriminator between the traditional concept of underplated material and lower crustal magmatic intrusions in the form of batholiths and sill......Underplating was originally proposed as the process of magma ponding at the base of the crust and was inferred from petrologic considerations. This process not only may add high density material to the deep crust, but also may contribute low density material to the upper parts of the crust by magma...... fractionation during cooling and solidification in the lower crust. Separation of the low density material from the high-density residue may be a main process of formation of continental crust with its characteristic low average density, also during the early evolution of the Earth. Despite the assumed...

  11. Efficient cooling of rocky planets by intrusive magmatism

    Science.gov (United States)

    Lourenço, Diogo L.; Rozel, Antoine B.; Gerya, Taras; Tackley, Paul J.

    2018-05-01

    The Earth is in a plate tectonics regime with high surface heat flow concentrated at constructive plate boundaries. Other terrestrial bodies that lack plate tectonics are thought to lose their internal heat by conduction through their lids and volcanism: hotter planets (Io and Venus) show widespread volcanism whereas colder ones (modern Mars and Mercury) are less volcanically active. However, studies of terrestrial magmatic processes show that less than 20% of melt volcanically erupts, with most melt intruding into the crust. Signatures of large magmatic intrusions are also found on other planets. Yet, the influence of intrusive magmatism on planetary cooling remains unclear. Here we use numerical magmatic-thermo-mechanical models to simulate global mantle convection in a planetary interior. In our simulations, warm intrusive magmatism acts to thin the lithosphere, leading to sustained recycling of overlying crustal material and cooling of the mantle. In contrast, volcanic eruptions lead to a thick lithosphere that insulates the upper mantle and prevents efficient cooling. We find that heat loss due to intrusive magmatism can be particularly efficient compared to volcanic eruptions if the partitioning of heat-producing radioactive elements into the melt phase is weak. We conclude that the mode of magmatism experienced by rocky bodies determines the thermal and compositional evolution of their interior.

  12. The Taitao Granites: I-type granites formed by subduction of the Chile Ridge and its implication in growth of continental crusts

    Science.gov (United States)

    Anma, Ryo

    2016-04-01

    Late Miocene to Early Pliocene granite plutons are exposed at the tip of the Taitao peninsula, the westernmost promontory of the Chilean coast, together with a contemporaneous ophiolite with a Penrose-type stratigraphy. Namely, the Taitao granites and the Taitao ohiolite, respectively, are located at ~30 km southeast of the Chile triple junction, where a spreading center of the Chile ridge system is subducting underneath the South America plate. This unique tectonic setting provides an excellent opportunity to study the generation processes of granitic magmas at a ridge subduction environment, and the complex magmatic interactions between the subducting ridge, overlying crust and sediments, and mantle. This paper reviews previous studies on the Taitao ophiolite/granite complex and use geochemical data and U-Pb age distributions of zircons separated from igneous and sedimentary rocks from the area to discuss the mechanism that formed juvenile magma of calc-alkaline I-type granites during ridge subduction. Our model implies that the magmas of the Taitao granites formed mainly due to partial melting of hot oceanic crust adjacent to the subducting mid-oceanic ridge that has been under influence of deep crustal contamination and/or metasomatized sub-arc mantle through slab window. The partial melting took place under garnet-free-amphibolite conditions. The juvenile magmas then incorporated a different amount of subducted sediments to form the I-type granites with various compositions. The Taitao granites provide an ideal case study field that shows the processes to develop continental crusts out of oceanic crusts through ridge subduction.

  13. Direct evidence for the origin of low-18O silicic magmas: Quenched samples of a magma chamber's partially-fused granitoid walls, Crater Lake, Oregon

    International Nuclear Information System (INIS)

    Bacon, C.R.; Adami, L.H.; Lanphere, M.A.

    1989-01-01

    Partially fused granitoid blocks were ejected in the climactic eruption of Mount Mazama, which was accompanied by collapse of Crater Lake caldera. Quartz, plagioclase, and glass in the granitoids have much lower δ 18 O values (-3.4 to +4.9per mille) than any fresh lavas of Mount Mazama and the surrounding region (+5.8 to +7.0per mille). Oxygen isotope fractionation between phases in granitoids is consistent with equilibrium at T≥900deg C following subsolidus exchange with hydrothermal fluids of meteoric origin. Assimilation of ≅ 10-20% of material similar to these granitoids can account for the O and Sr isotopic compositions of lavas and juvenile pyroclasts derived from the climactic magma chamber, many of which have δ 18 O values ≅ 0.5per mille or more lower than comparable lavas of Mount Mazama. The O isotope data provide the only clear evidence for such assimilation because the mineralogy and chemical and radiogenic isotopic compositions of the granitoids (dominantly granodiorite) are similar to those of erupted juvenile magmas. The granitoid blocks from Crater Lake serve as direct evidence for the origin of 18 O depletion in large, shallow silicic magma bodies. (orig.)

  14. Oxigen isotope compositions as indicators of epidote granite genesis in the Borborema Provinces, NE Brazil

    International Nuclear Information System (INIS)

    Ferreira, V.P.; Valley, J.W; Sial, A.N; Spicuzza, M.J

    2001-01-01

    Neoproterozoic magmatic epidote-bearing granitoids intrude low-grade metapelites in the Cachoeirinha-Salgueiro terrane (CST), and gneisses and migmatites in the Serido terrane (ST), in the Borborema structural province, northeastern Brazil. Granitoids in both terranes contain biotite and hornblende, and are metaluminous, calc-alkalic, and oxidized I-type granites according to White's (1992) classification. However, in spite of these similarities, this work shows that mineral oxygen isotope data from plutons of the two terranes indicate different magma sources, and that magmatic epidote besides crystallizing at different pressure conditions, can have variable isotopic composition (au)

  15. Magmatic intrusions in the lunar crust

    Science.gov (United States)

    Michaut, C.; Thorey, C.

    2015-10-01

    The lunar highlands are very old, with ages covering a timespan between 4.5 to 4.2 Gyr, and probably formed by flotation of light plagioclase minerals on top of the lunar magma ocean. The lunar crust provides thus an invaluable evidence of the geological and magmatic processes occurring in the first times of the terrestrial planets history. According to the last estimates from the GRAIL mission, the lunar primary crust is particularly light and relatively thick [1] This low-density crust acted as a barrier for the dense primary mantle melts. This is particularly evident in the fact that subsequent mare basalts erupted primarily within large impact basin: at least part of the crust must have been removed for the magma to reach the surface. However, the trajectory of the magma from the mantle to the surface is unknown. Using a model of magma emplacement below an elastic overlying layer with a flexural wavelength Λ, we characterize the surface deformations induced by the presence of shallow magmatic intrusions. We demonstrate that, depending on its size, the intrusion can show two different shapes: a bell shape when its radius is smaller than 4 times Λ or a flat top with small bended edges if its radius is larger than 4 times Λ[2]. These characteristic shapes for the intrusion result in characteristic deformations at the surface that also depend on the topography of the layer overlying the intrusion [3].Using this model we provide evidence of the presence of intrusions within the crust of the Moon as surface deformations in the form of low-slope lunar domes and floor-fractured craters. All these geological features have morphologies consistent with models of magma spreading at depth and deforming an overlying elastic layer. Further more,at floor-fractured craters, the deformation is contained within the crater interior, suggesting that the overpressure at the origin of magma ascent and intrusion was less than the pressure due to the weight of the crust removed by

  16. Post-Hercynian subvolcanic magmatism in the Serre Massif (Central-Southern Calabria, Italy)

    Science.gov (United States)

    Romano, V.; Cirrincione, R.; Fiannacca, P.; Mazzoleni, P.; Tranchina, A.

    2009-04-01

    In the Serre Massif (Central-Southern Calabria, Italy) dykes and subvolcanic bodies intrude diffusively both Hercynian metamorphic rocks and late-Hercynian granitoids. They range in composition from basaltic andesites to dacite-rhyodacites and can be ascribed to the extensive magmatic activity that affects the entire Hercynian orogenic belt in late Paleozoic - early Mesozoic time. The geodinamic framework of the magmatic activity is still matter of debate, nevertheless most authors agree in correlating magmatism both to the late-orogenic collapse of the Hercynian belt and to the lithosphere thinning responsible for the subsequent continental rifting. In this work, we propose a petrogenetic model for acidic to basic hypabissal bodies from southern Calabria in order to define the nature of sources, discriminate magmatic processes and supply a contribution in the geodynamic reconstruction of the Late Palaeozoic in the Calabria-Peloritani Orogen. In relation to their geochemical affinity, studied dykes have been divided in two groups: a medium- to high-K calc-alkaline and a tholeiitic one. Dykes belonging to the former group, andesitic and dacitic-rhyodacitic in composition, show typical features of subduction-related magmatism, such as LILE and LREE enrichments, depletions in HFSE, peaks in Rb, Th and Ce, accentuated troughs in Ba, Nb-Ta, P and Ti (White and Dupré, 1986; McCulloch and Gamble, 1991), contrasting with the late Hercynian collisional context. On the other side, features typical of intra-plate magmatic activity, such as a moderate enrichment in Ta, Nb, Ce, P, Zr, Hf and Sm relative to MORB composition are also present in studied rocks (Shimizu & Arculus, 1975; Pearce, 1982). REE-patterns are strongly to weakly fractionated for the andesitic rocks (Lan/Ybn = 10.03-13.98) and the dacitic-rhyodacitic ones (Lan/Ybn = 6.00 to 2.82), respectively. The latter rocks exhibit a very slight negative Eu anomaly, whereas no Eu anomaly is recognizable in the andesite

  17. From steep feeders to tabular plutons - Emplacement controls of syntectonic granitoid plutons in the Damara Belt, Namibia

    Science.gov (United States)

    Hall, Duncan; Kisters, Alexander

    2016-01-01

    Granitoid plutons in the deeply eroded south Central Zone of the Damara Belt in Namibia commonly show tabular geometries and pronounced stratigraphic controls on their emplacement. Subhorizontal, sheet-like pluton geometries record emplacement during regional subhorizontal shortening, but the intrusion of spatially and temporally closely-related granitoid plutons at different structural levels and in distinct structural settings suggests independent controls on their levels of emplacement. We describe and evaluate the controls on the loci of the dyke-to-sill transition that initiated the emplacement of three syntectonic (560-530 Ma) plutons in the basement-cover stratigraphy of the Erongo region. Intrusive relationships highlight the significance of (1) rigidity anisotropies associated with competent sedimentary packages or pre-existing subhorizontal granite sheets and (2) rheological anisotropies associated with the presence of thick ductile marble horizons. These mechanical anisotropies may lead to the initial deflection of steep feeder conduits as well as subsequent pluton assembly by the repeated underaccretion of later magma batches. The upward displacement of regional isotherms due to the heat advection associated with granite emplacement is likely to have a profound effect on the mechanical stratification of the upper crust and, consequently, on the level at which granitoid pluton emplacement is initiated. In this way, pluton emplacement at progressively shallower crustal depths may have resulted in the unusually high apparent geothermal gradients recorded in the upper crustal levels of the Damara Belt during its later evolution.

  18. Drilling to investigate processes in active tectonics and magmatism

    OpenAIRE

    J. Shervais; J. Evans; V. Toy; J. Kirkpatrick; A. Clarke; J. Eichelberger

    2014-01-01

    Coordinated drilling efforts are an important method to investigate active tectonics and magmatic processes related to faults and volcanoes. The US National Science Foundation (NSF) recently sponsored a series of workshops to define the nature of future continental drilling efforts. As part of this series, we convened a workshop to explore how continental scientific drilling can be used to better understand active tectonic and magmatic processes. The workshop, held in Park C...

  19. Constraints on timescales and mechanics of magmatic underplating from InSAR observations of large active magma sills in the Earth's crust.

    Science.gov (United States)

    Fialko, Y.

    2002-12-01

    Theoretical models of the granitoid magma generation due to magmatic underplating predict that anatectic melts are produced on quite short timescales of the order of the crystallization time of typical mafic underplates (e.g., 102-10^3 years for sill intrusions that are a few tens to a few hundred meters thick). If so, the intrusion of mafic underplates, the volume changes associated with in situ melting, and the subsequent evacuation of the resulting granitoid magmas can each generate geodetically observable deformation. Geodetic measurements in areas of contemporaneous large active magma bodies may therefore provide critical constraints on the timescales and dynamics of crustal anatexis. We use Interferometric Synthetic Aperture Radar (InSAR) observations in regions of the ongoing crustal magmatism to constrain typical rates of the large-scale melt generation and/or migration, and to test the proposed models of the granitic melt production. Our primary targets include large mid-crustal magma bodies imaged by seismic studies, in particular, the Socorro (New Mexico, USA), the Altiplano-Puna (south America), and the south Tibet (Asia) magma bodies. All these magma bodies are located at depth of 19-20 km, suggesting a strong rheological or buoyancy control on the transition from a vertical to a horizontal magma flow. Stacked interferometric data from the Socorro magma body indicate a quasi-steady uplift with a maximum rate of 3-4 mm/yr over the last 10 years covered by the InSAR observations. The uplift morphology can be well described by an elastic inflation of the Socorro sill. We show that deformation models that allow for the viscous-like rheology of the mid-to-lower crust cannot be easily reconciled with the geodetic data. However, thermodynamic modeling, in conjunction with inferences of the nearly constant uplift rates, suggest that the deformations associated with the intrusion emplacement must involve a significant inelastic component. Such inelastic

  20. Backarc extension, detachments and granitoids in the Aegean, their relations to slab tear and asthenospheric flow

    Science.gov (United States)

    Jolivet, Laurent; Menant, Armel; Rabillard, Aurélien; Arbaret, Laurent; Augier, Romain; Gumiaux, Charles

    2013-04-01

    The Cycladic granitoids (Ikaria, Mykonos, Naxos, Kos, Lavrion, Serifos, Tinos) intruded the Aegean crust during a rather short period (17-10 Ma) compared to the much longer Oligo-Miocene crustal thinning phase (35 Ma to the Present). Their geochemical characteristics show that their sources have changed through time and space, with a progressive decreasing component of continental crust contamination with time and from east to west. They all interacted with large-scale detachments, namely the North Cycladic Detachment System (NCDS) in the north and the West Cycladic Detachment System (WCDS) in the south. In Mykonos, Naxos, Serifos and Ikaria the plutons are also associated with a high-temperature metamorphic dome of Miocene age. Their intrusion period roughly covers the same time window as the fast clockwise rotation of the western Aegean evidenced by paleomagnetic measurements and they are contemporaneous with a surge of alkaline volcanism in the eastern Aegean that can be related to a slab tear imaged below western Anatolia. The continental crust component in the Middle Miocene Cycladic plutons is not found in the early Miocene plutons of the northern Aegean, like in Kavala and Vrondou. They thus probably record a quite sudden thermal event in the Cyclades that led to the partial melting of the extending deep crust. We propose a model involving slab tear starting at ~17 Ma, fast retreat of the slab west of the tear and southwestward influx of hot asthenospheric material below the Aegean crust, leading to melting of the lower crust. Partial melting of the whole lower crust above the hot asthenospheric flow could explain the flat Moho observed below the Cyclades. The close proximity of plutons with the detachments suggests that their ascent toward the upper crust is favoured by the extreme extension at work there. The first granitoids in the region of the tear (Ikaria) are the richest in crustal component and this component decreases while the crust thins more and

  1. Transformation of juvenile Izu-Bonin-Mariana oceanic arc into mature continental crust: An example from the Neogene Izu collision zone granitoid plutons, Central Japan

    Science.gov (United States)

    Saito, Satoshi; Tani, Kenichiro

    2017-04-01

    Granitic rocks (sensulato) are major constituents of upper continental crust. Recent reviews reveal that the average composition of Phanerozoic upper continental crust is granodioritic. Although oceanic arcs are regarded as a site producing continental crust material in an oceanic setting, intermediate to felsic igneous rocks occurring in modern oceanic arcs are dominantly tonalitic to trondhjemitic in composition and have lower incompatible element contents than the average upper continental crust. Therefore, juvenile oceanic arcs require additional processes in order to get transformed into mature continental crust enriched in incompatible elements. Neogene granitoid plutons are widely exposed in the Izu Collision Zone in central Japan, where the northern end of the Izu-Bonin-Mariana (IBM) arc (juvenile oceanic arc) has been colliding with the Honshu arc (mature island arc) since Middle Miocene. The plutons in this area are composed of various types of granitoids ranging from tonalite to trondhjemite, granodiorite, monzogranite and granite. Three main granitoid plutons are distributed in this area: Tanzawa plutonic complex, Kofu granitic complex, and Kaikomagatake granitoid pluton. Tanzawa plutonic complex is dominantly composed of tonalite and trondhjemite and characterized by low concentration of incompatible elements and shows geochemical similarity with modern juvenile oceanic arcs. In contrast, Kofu granitic complex and Kaikomagatake granitoid pluton consists mainly of granodiorite, monzogranite and granite and their incompatible element abundances are comparable to the average upper continental crust. Previous petrogenetic studies on these plutons suggested that (1) the Tanzawa plutonic complex formed by lower crustal anatexis of juvenile basaltic rocks occurring in the IBM arc, (2) the Kofu granitic complex formed by anatexis of 'hybrid lower crust' comprising of both basaltic rocks of the IBM arc and metasedimentary rocks of the Honshu arc, and (3) the

  2. Mafic microgranular enclave swarms in the Chenar granitoid stock, NW of Kerman, Iran: evidence for magma mingling

    Science.gov (United States)

    Arvin, M.; Dargahi, S.; Babaei, A. A.

    2004-10-01

    Mafic microgranular enclaves (MME) are common in the Early to Middle Miocene Chenar granitoid stock, northwest of Kerman, which is a part of Central Iranian Eocene volcanic belt. They occur individually and in homogeneous or heterogeneous swarms. The MME form a number of two-dimensional structural arrangements, such as dykes, small rafts, vortices, folded lens-shapes and late swarms. The enclaves are elongated, rounded to non-elongated and subrounded in shape and often show some size-sorting parallel to direction of flow. Variation in the elongation of enclaves could reflect variations in the viscosity of the enclave, the time available for enclave deformation and differential strain during flow of the host granitoid magma. The most effective mechanism in the formation of enclave swarms in the Chenar granitoid stock was velocity gradient-related convection currents in the granitoid magma chamber. Gravitational sorting and the break-up of heterogeneous dykes also form MME swarms. The MME (mainly diorite to diorite gabbro) have igneous mineralogy and texture, and are marked by sharp contacts next to their host granitoid rocks. The contact is often marked by a chilled margin with no sign of solid state deformation. Evidence of disequilibrium is manifested in feldspars by oscillatory zoning, resorbed rims, mantling and punctuated growth, together with overgrowth of clinopyroxene/amphibole on quartz crystals, the acicular habit of apatites and the development of Fe-Ti oxides along clinopyroxene cleavages. These observations suggest that the MMEs are derived from a hybrid-magma formed as a result of the intrusion of a mafic magma into the base of a felsic magma chamber. The density contrast between hybrid-magma and the overlying felsic magma was reduced by the release of dissolved fluids and the ascent of exsolved gas bubbles from the mafic magma into the hybrid zone. Further convection in the magma chamber dispersed the hybridized magma as globules in the upper parts of

  3. Intraplate mafic magmatism: New insights from Africa and N. America

    Science.gov (United States)

    Ebinger, C. J.; van der Lee, S.; Tepp, G.; Pierre, S.

    2017-12-01

    Plate tectonic concepts consider that continental interiors are stable, with magmatism and strain localized to plate boundaries. We re-evaluate the role of pre-existing and evolving lithospheric heterogeneities in light of perspectives afforded by surface to mantle results from active and ancient rift zones in Africa and N. America. Our process-oriented approach addresses the localization of strain and magmatism and stability of continental plate interiors. In both Africa and N. America, geophysical imaging and xenolith studies reveal that thick, buoyant, and chemically distinct Archaean cratons with deep roots may deflect mantle flow, and localize magmatism and strain over many tectonic cycles. Studies of the Colorado Plateau and East African rift reveal widespread mantle metasomatism, and high levels of magma degassing along faults and at active volcanoes. The volcanoes and magmatic systems show a strong dependence on pre-existing heterogeneities in plate structure. Syntheses of the EarthScope program ishow that lateral density contrasts and migration of volatiles that accumulated during subduction can refertilize mantle lithosphere, and enable volatile-rich magmatism beneath relatively thick continental lithosphere. For example, the passive margin of eastern N. America shows uplift and magmatism long after the onset of seafloor spreading, demonstrating the dynamic nature of coupling between the lithosphere, asthenosphere, and deeper mantle. As demonstrated by the East African Rift, the Mid-Continent Rift, and other active and ancient rift zones, the interiors of continents, including thick, cold Archaean cratons are not immune to mafic magmatism and tectonism. Recent studies in N. America and Africa reveal ca. 1000 km-wide zones of dynamic uplift, low upper mantle velocities, and broadly distributed strain. The distribution of magmatism and volatile release, in combination with geophysical signals, indicates a potentially convective origin for widespread

  4. Structural control of weathering processes within exhumed granitoids: Compartmentalisation of geophysical properties by faults and fractures

    Science.gov (United States)

    Place, J.; Géraud, Y.; Diraison, M.; Herquel, G.; Edel, J.-B.; Bano, M.; Le Garzic, E.; Walter, B.

    2016-03-01

    In the latter stages of exhumation processes, rocks undergo weathering. Weathering halos have been described in the vicinity of structures such as faults, veins or dykes, with a lateral size gradually narrowing with depth, symmetrically around the structures. In this paper, we describe the geophysical characterisation of such alteration patterns on two granitoid outcrops of the Catalan Coastal Ranges (Spain), each of which is affected by one major fault, as well as minor faults and fractures. Seismic, electric and ground penetrating radar surveys were carried out to map the spatial distribution of P-wave velocity, electrical resistivity and to identify reflectors of electromagnetic waves. The analysis of this multi-method and complementary dataset revealed that, at shallow depth, geophysical properties of the materials are compartmentalised and asymmetric with respect to major and subsidiary faults affecting the rock mass. This compartmentalisation and asymmetry both tend to attenuate with depth, whereas the effect of weathering is more symmetric with respect to the major structure of the outcrops. We interpret such compartmentalisation as resulting from the role of hydraulic and mechanical boundaries played by subsidiary faults, which tend to govern both the chemical and physical alterations involved in weathering. Thus, the smoothly narrowing halo model is not always accurate, as weathering halos can be strongly asymmetrical and present highly irregular contours delimiting sharp contrasts of geophysical properties. These results should be considered when investigating and modelling fluid storage and transfer in top crystalline rock settings for groundwater applications, hydrocarbon or geothermal reservoirs, as well as mineral deposits.

  5. Geología de la parte sur de la Sierra de San Luis y granitoides asociados, Argentina

    Directory of Open Access Journals (Sweden)

    Llambías, E. J.

    1992-12-01

    Full Text Available The lower Palaeozoic basement of the southern part of Sierra de San Luis, Argentina, is made up of metamorphic rocks, granitoids and ultramafic rocks. The metamorphic grade ranges from the lower limit of greenschist facies through the upper limit of amphibolite facies, in apparent transition. The lower grade metamorphic rocks include slates, metavolcanics, metaconglomerates, quartzites and phyllites. Rocks with intermediate metamorphism are biotite-quartz-oligoclase schists with abundant pegmatoid veins. The higher grade metamorphism is represented by gneisses, amphibolites and migmatites, to which mafic and ultramafic bodies are associated. Three deformation phases have been recognized, being the last one (D3, of ordovician age, responsible of the most marked structures.The granitoids were grouped into pre-, syn- and post-kynematic bodies respect to D3. The pre-kynematic granitoids are located within the belt of lower grade metamorphic rocks and are composed of tonalites, granodiorites and monzogranites, strongly deformed. Their age is unknown. The syn-kynematic bodies are mainly garnet-moscovite-bearing leucogranodiorites. They show low thermal and rheological contrasts respect to the country rocks, and the age is 454 ± 21 m.a. The post-kynematic granitoids are mainly monzogranites with K-feldspar megacrysts and abundant sphene. They are subcircular and discordant, and are associated with an extensional regime. Their age is comprised between 423 and 320 m.a., and corresponds to the end of the Famatinian cycle.El basamento cristalino de la parte sur de la Sierra de San Luis, de edad Paleozoico Inferior, está constituido por rocas metamórficas, granitoides y rocas ultramáficas. El grado de metamorfismo varía desde la parte baja de esquistos verdes hasta la parte alta de la facies anfibolita, siendo sus relaciones de aparente transicionalidad. Las rocas con menor grado metamórfico consisten en pizarras, metavolcanitas, metaconglomerados

  6. Review of the geochemistry and metallogeny of approximately 1.4 Ga granitoid intrusions of the conterminous United States

    Science.gov (United States)

    du Bray, Edward A.; Holm-Denoma, Christopher S.; Lund, Karen; Premo, Wayne R.

    2018-03-27

    The conterminous United States hosts numerous volumetrically significant and geographically dispersed granitoid intrusions that range in age from 1.50 to 1.32 billion years before present (Ga). Although previously referred to as A-type granites, most are better described as ferroan granites. These granitoid intrusions are distributed in the northern and central Rocky Mountains, the Southwest, the northern midcontinent, and a swath largely buried beneath Phanerozoic cover across the Great Plains and into the southern midcontinent. These intrusions, with ages that are bimodally distributed between about 1.455–1.405 Ga and 1.405–1.320 Ga, are dispersed nonsystematically with respect to age across their spatial extents. Globally, although A-type or ferroan granites are genetically associated with rare-metal deposits, most U.S. 1.4 Ga granitoid intrusions do not contain significant deposits. Exceptions are the light rare-earth element deposit at Mountain Pass, California, and the iron oxide-apatite and iron oxide-copper-gold deposits in southeast Missouri.Most of the U.S. 1.4 Ga granitoid intrusions are composed of hornblende ± biotite or biotite ± muscovite monzogranite, commonly with prominent alkali feldspar megacrysts; however, modal compositions vary widely. These intrusions include six of the eight commonly identified subtypes of ferroan granite: alkali-calcic and calc-alkalic peraluminous subtypes; alkalic, alkali-calcic, and calc-alkalic metaluminous subtypes; and the alkalic peralkaline subtype. The U.S. 1.4 Ga granitoid intrusions also include variants of these subtypes that have weakly magnesian compositions. Extreme large-ion lithophile element enrichments typical of ferroan granites elsewhere are absent among these intrusions. Chondrite-normalized rare-earth element patterns for these intrusions have modest negative slopes and moderately developed negative europium anomalies. Their radiogenic isotopic compositions are consistent with mixing involving

  7. Textures, trace element compositions, and U-Pb ages of titanite from the Mangling granitoid pluton, East Qinling Orogen: Implications for magma mixing and destruction of the North China Craton

    Science.gov (United States)

    Hu, Hao; Li, Jian-Wei; McFarlane, Christopher R. M.; Luo, Yan; McCarron, Travis

    2017-07-01

    The Mangling granitoid pluton, located along the southern margin of the North China Craton, consists mainly of monzogranite with minor amounts of diorite. The monzogranite contains abundant mafic microgranular enclaves (MMEs) and is intruded by numerous mafic dikes, providing an opportunity to study magma mixing and its role in the formation of the granitioid pluton. In this paper, we present in situ analysis of U-Pb isotopes and trace element compositions of titanite from the MMEs and the host monzogranite using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry to document the role of magma mixing in the formation of the Mangling granitoid pluton. Titanite grains from the MMEs (type 1) are euhedral with patchy zoning, whereas the varieties from the closely associated host monzogranite are euhedral and consist of two types (type 2 and type 3). Type 2 titanite is more abundant and has oscillatory zoning without Fe-Ti oxide inclusions, whereas type 3 grains commonly have Fe-Ti oxide inclusions in the core that is rimmed by inclusion-free overgrowths with weak oscillatory zoning. Titanite from monzogranite without MMEs (type 4) is euhedal and has weak oscillatory zoning, with rare ilmenite inclusions in the core. Titanite from a mafic dike intruding the monzogranite (type 5) is anhedral and has sector zoning. Titanite grains from MMEs and the monzogranite (type 1, 2 and 3) have U-Pb ages that are indistinguishable (149 ± 1 Ma, 148 ± 1 Ma and 148 ± 2 Ma, respectively). These ages agree well with zircon U-Pb ages of 150 ± 1 Ma, 150 ± 1 Ma and 149 ± 1 Ma for the MMEs, host monzogranite, and mafic dike, respectively. The age consistency thus confirms coeval formation of the MMEs, the host monzogranite, and the mafic dikes, demonstrating a mafic magmatic, rather than extraneous or restitic origin for the MMEs. Titanite grains from the MMEs (type 1) and mafic dike (type 5) have much lower Al2O3, REE, Nb/Zr, Y/Zr, and Lu/Hf, but higher (Ce + Nd)/Y and La

  8. Comparative study T-type and I-type layout of PWR nuclear power plants

    International Nuclear Information System (INIS)

    Eko Rudi Iswanto and Siti Alimah

    2010-01-01

    Determining plant layout is one of the five major stages during the life time of a nuclear power plant. Some important factors that affect in the selecting of plant layout are availability of infrastructure, economic aspects, social aspects, public and environment safety, and also easy to do. Another factor to be considered is requirements as seismic design, which refers to the principles of good security workers, communities and the environment of radiological risks. There are many layout types of nuclear power plant, two of them are T-type layout and I-type layout. Each type of the plant layout has advantage and disadvantage, therefore this study is to understand them. Good layout is able to provide a high level of security against earthquakes. In term of earthquake design, I-type layout has a higher security level than T-type layout. Therefore, I-type layout can be a good choice for PWR nuclear power plants 1000 MWe that will be built in Indonesia. (author)

  9. Magmatic-hydrothermal fluids and volatile metals in the Spirit Lake pluton and Margaret Cu-Mo porphyry system, SW Washington, USA

    Science.gov (United States)

    Iveson, Alexander A.; Webster, James D.; Rowe, Michael C.; Neill, Owen K.

    2016-03-01

    The halogen-bearing minerals tourmaline, amphibole, and biotite formed during magmatic-hydrothermal processes associated with the late-stage cooling of the Spirit Lake granitoid pluton (Mt. St. Helens, WA) and with the younger sulphide-mineralised rocks of the Margaret Cu-Mo porphyry deposit located entirely within the pluton. Major- and trace-element discrimination suggests that one tourmaline population crystallised from fractionated late-stage melt pockets in granodiorite-monzogranitic dykes of the pluton. These coarse, euhedral, oscillatory, and complexly sector-zoned uvite tourmalines span a limited range in Mg/(Mg + Fe) [Mg#] space (0.4-0.7 apfu) and show the highest Ti, Ca, F, Nb, and Ta contents, and low X-site vacancies (X-site vacancies (>0.6 apfu), lower Ca and F contents, and the highest Li, As, and HREE contents (>80 ppm Li, >1200 ppm As). This population appears to record direct, rapid crystallisation from magmatic ± meteoric fluid(s) bearing the signature of the breakdown of primary feldspars and pyroxenes, with fluid exsolution from fractionated melt patches likely triggered by the formation of the previous generation of tourmaline. Mineralised porphyry deposit tourmaline compositions from the stockwork span a much larger range in Mg# space (0.05-0.9 apfu) and are almost entirely Ca-free. X-sites of these schorl tourmalines are dominated by Na or vacancies, and the Y-sites are strongly Fe enriched. The highest Mn and Zn concentrations (>4000 and >1000 ppm, respectively) potentially reflect the composition of mineralising fluids during ore deposition. A number of boron isotopic analyses yield predominantly heavy boron, but δ11B values range from -5.2 to 6.2 ‰ and average 1.4 ‰. Whilst most plutonic tourmalines conform to reported a- and c-sector element partitioning models, those from the mineralised porphyry show large and variable sector fractionation differences, suggesting that external controls may also be important. Wider evidence for

  10. First record of 1.2 Ga quartz dioritic magmatism in the Archaean Yilgarn Craton, Western Australia, and its significance

    Energy Technology Data Exchange (ETDEWEB)

    Qiu, Y.; McNaughton, N.J.; Groves, D.I.; Dunphy, J.M. [University of Western Australia, Nedlands, WA (Australia). Centre for Strategic Mineral Deposits, Department of Geology and Geophysics

    1999-06-01

    Ion microprobe (SHRIMP) U-Pb zircon dating. Pb-Nd isotope tracer studies and major, trace and rare-earth element analyses have identified, for the first time. a Mesoproterozoic (1.2 Ga) quartz diorite intrusion in the central part of the Archaean Yilgarn Craton. Western Australia The quartz diorite is characterised by intergrowths of quartz and plagioclase, having low A/CNK (0 8). low K{sub 2}O (0.28 wt%), Ba (54 ppm), Rb (11 ppm), Sr (92 ppm), Pb (13 ppm), U (1.7 ppm) and Th (6 ppm) contents, high Nd (41 ppm), Sm (10.5 ppm), Zr (399 ppm). Nb (18.5 ppm). Y (57.5 ppm) and Sc (19 ppm) contents. a low Pb isotope two-stage model {mu} value (6.3), and a primitive initial e{sub Nd} value (+3.4) at 1.2 Ga. It is interpreted that the 1.2 Ga quartz diorite was derived from a predominantly mantle source, with minor crustal contamination, possibly from the surrounding Archaean monzogranites or their source region, during magma ascent. The age (1215 {+-} 11 Ma) of the intrusion overlaps with the timing of a major continental collisional orogeny in the Albany-Fraser Orogen, about 400km south, and is broadly coeval with the diamond-bearing Argyle lamproites in the east Kimberley Block. This study extends the history of granitoid magmatism in the central craton by more than 1.0 billion years (2.6 to 1.2 Ga), and has implications for isotopic data interpretations of tectonothermal events in the craton. Copyright (1999) Blackwell Science Pty Ltd 33 refs., 3 tabs., 6 figs.

  11. Thermal modeling of the Clear Lake magmatic system, California: Implications for conventional and hot dry rock geothermal development

    Energy Technology Data Exchange (ETDEWEB)

    Stimac, J.; Goff, F.; Wohletz, K.

    1997-06-01

    The combination of recent volcanism, high heat flow ({ge} HFU or 167 mW/m{sup 2}), and high conductive geothermal gradient (up to 120{degree} C/km) makes the Clear Lake region of northern California one of the best prospects for hot dry rock (HDR) geothermal development in the US. The lack of permeability in exploration wells and lack of evidence for widespread geothermal reservoirs north of the Collayomi fault zone are not reassuring indications for conventional geothermal development. This report summarizes results of thermal modeling of the Clear Lake magmatic system, and discusses implications for HDR site selection in the region. The thermal models incorporate a wide range of constraints including the distribution and nature of volcanism in time and space, water and gas geochemistry, well data, and geophysical surveys. The nature of upper crustal magma bodies at Clear Lake is inferred from studying sequences of related silicic lavas, which tell a story of multistage mixing of silicic and mafic magma in clusters of small upper crustal chambers. Thermobarometry on metamorphic xenoliths yield temperature and pressure estimates of {approximately}780--900 C and 4--6 kb respectively, indicating that at least a portion of the deep magma system resided at depths from 14 to 21 km (9 to 12 mi). The results of thermal modeling support previous assessments of the high HDR potential of the area, and suggest the possibility that granitic bodies similar to The Geysers felsite may underlie much of the Clear Lake region at depths as little as 3--6 km. This is significant because future HDR reservoirs could potentially be sited in relatively shallow granitoid plutons rather than in structurally complex Franciscan basement rocks.

  12. Mesozoic to Cenozoic magmatic history of the Pamir

    Science.gov (United States)

    Chapman, James B.; Scoggin, Shane H.; Kapp, Paul; Carrapa, Barbara; Ducea, Mihai N.; Worthington, James; Oimahmadov, Ilhomjon; Gadoev, Mustafo

    2018-01-01

    New geochronologic, geochemical, and isotopic data for Mesozoic to Cenozoic igneous rocks and detrital minerals from the Pamir Mountains help to distinguish major regional magmatic episodes and constrain the tectonic evolution of the Pamir orogenic system. After final accretion of the Central and South Pamir terranes during the Late Triassic to Early Jurassic, the Pamir was largely amagmatic until the emplacement of the intermediate (SiO2 > 60 wt.%), calc-alkaline, and isotopically evolved (-13 to -5 zircon εHf(t)) South Pamir batholith between 120-100 Ma, which is the most volumetrically significant magmatic complex in the Pamir and includes a high flux magmatic event at ∼105 Ma. The South Pamir batholith is interpreted as the northern (inboard) equivalent of the Cretaceous Karakoram batholith and the along-strike equivalent of an Early Cretaceous magmatic belt in the northern Lhasa terrane in Tibet. The northern Lhasa terrane is characterized by a similar high-flux event at ∼110 Ma. Migration of continental arc magmatism into the South Pamir terrane during the mid-Cretaceous is interpreted to reflect northward directed, low-angle to flat-slab subduction of the Neo-Tethyan oceanic lithosphere. Late Cretaceous magmatism (80-70 Ma) in the Pamir is scarce, but concentrated in the Central and northern South Pamir terranes where it is comparatively more mafic (SiO2 roll-back of the Neotethyan oceanic slab, which is consistent with similarly aged extension-related magmatism in the Karakoram terrane and Kohistan. There is an additional pulse of magmatism in the Pamir at 42-36 Ma that is geographically restricted (∼150 km diameter ellipsoidal area) and referred to as the Vanj magmatic complex. The Vanj complex comprises metaluminous, high-K calc-alkaline to shoshonitic monzonite, syenite, and granite that is adakitic (La/YbN = 13 to 57) with low Mg# (35-41). The Vanj complex displays a range of SiO2 (54-75 wt.%) and isotopic compositions (-7 to -3 εNd(i), 0.706 to

  13. New U-Pb ages in the Diablillos Intrusive Complex, Southern Puna, Argentina: A long magmatic event in the Paleozoic Arc, SW Gondwana

    Energy Technology Data Exchange (ETDEWEB)

    Ortiz, Agustin; Hauser, Natalia [Universidade de Brasilia (UnB), DF (Brazil). Instituto de Geociencias. Lab. de Geocronologia; Becchio, Raul; Nieves, Alexis; Suzano, Nestor [Universidad Nacional de Salta (UNSa)-CONICET, Salta (Argentina)

    2015-07-01

    The Puna geological region comprises Salta, Jujuy and Catamarca provinces, northwestern Argentina. This 4000 meter above sea level high-plateau region lies between the Central Argentinian Andes. The Puna basement in the central Andes consists of Proterozoic–Paleozoic metamorphic rocks and granitoids. Diverse authors, proposed different models to explain the origin of the basement, where two orogenic events are recognized: the Pampean (Upper Precambrian–Lower Cambrian) and Famatinian (Upper Cambrian–Lower Silurian) (e.g. Ramos et al., 1986; Ramos, 1988; Loewy et al., 2004; for opposite points of view see Becchio et al., 1999; Bock et al., 2000; Buttner et al., 2005). Hence, Lucassen et al. (2000) proposed for the Central Andean basement, an evolution in a mobile belt, where the Pampean and Famatinian cycles are not distinct events but, they are one single, non-differentiable event from 600 to 400 Ma. The mobile belt culminated in low-P/ high-T metamorphism at approximately 525-500 Ma. Then, these were followed by a long-lasting high-thermal gradient regime in the mid-crust until Silurian times. Becchio et al., (2011) defined the Diablillos Intrusive Complex (CID, by its Spanish name), emplaced in the Inca Viejo Range. This range splits the Salares Ratones-Centenario with the Salar Diablillos (Fig.1). This Complex is located in the Eastern Magmatic Belt, Southern Puna, Argentina. Here we present new zircons U-Pb ages by LA-MC-ICPMS in the Diablillos Intrusive Complex, contributing to understanding the magmatic event in the lower Paleozoic arc, SW Gondwana. (author)

  14. New U-Pb ages in the Diablillos Intrusive Complex, Southern Puna, Argentina: A long magmatic event in the Paleozoic Arc, SW Gondwana

    International Nuclear Information System (INIS)

    Ortiz, Agustin; Hauser, Natalia

    2015-01-01

    The Puna geological region comprises Salta, Jujuy and Catamarca provinces, northwestern Argentina. This 4000 meter above sea level high-plateau region lies between the Central Argentinian Andes. The Puna basement in the central Andes consists of Proterozoic–Paleozoic metamorphic rocks and granitoids. Diverse authors, proposed different models to explain the origin of the basement, where two orogenic events are recognized: the Pampean (Upper Precambrian–Lower Cambrian) and Famatinian (Upper Cambrian–Lower Silurian) (e.g. Ramos et al., 1986; Ramos, 1988; Loewy et al., 2004; for opposite points of view see Becchio et al., 1999; Bock et al., 2000; Buttner et al., 2005). Hence, Lucassen et al. (2000) proposed for the Central Andean basement, an evolution in a mobile belt, where the Pampean and Famatinian cycles are not distinct events but, they are one single, non-differentiable event from 600 to 400 Ma. The mobile belt culminated in low-P/ high-T metamorphism at approximately 525-500 Ma. Then, these were followed by a long-lasting high-thermal gradient regime in the mid-crust until Silurian times. Becchio et al., (2011) defined the Diablillos Intrusive Complex (CID, by its Spanish name), emplaced in the Inca Viejo Range. This range splits the Salares Ratones-Centenario with the Salar Diablillos (Fig.1). This Complex is located in the Eastern Magmatic Belt, Southern Puna, Argentina. Here we present new zircons U-Pb ages by LA-MC-ICPMS in the Diablillos Intrusive Complex, contributing to understanding the magmatic event in the lower Paleozoic arc, SW Gondwana. (author)

  15. Lithospheric delamination in post-collisional setting: Evidence from intrusive magmatism from the North Qilian orogen to southern margin of the Alxa block, NW China

    Science.gov (United States)

    Zhang, Liqi; Zhang, Hongfei; Zhang, Shasha; Xiong, Ziliang; Luo, Biji; Yang, He; Pan, Fabin; Zhou, Xiaochun; Xu, Wangchun; Guo, Liang

    2017-09-01

    Post-collisional granitoids are widespread in the North Qilian and southern margin of the Alxa block and their petrogenesis can provide important insights into the lithospheric processes in a post-collisional setting. This paper carries out an integrated study of U-Pb zircon dating, geochemical and Sr-Nd-Hf isotopic compositions for five early Paleozoic intrusive plutons from the North Qilian to southern margin of the Alxa block. The geochronological and geochemical results show that their magmatism can be divided into three periods with distinct geochemical features. The early-period intrusive rocks ( 440 Ma) include the Lianhuashan (LHS) and Mengjiadawan (MJDW) granodiorites. Both of them display high Sr/Y ratios (52-91), coupled with low Y and HREE contents, implying that they were derived from partial melting of thickened lower crust, with garnet in the residue. The middle-period intrusive rocks ( 430 Ma), including the MJDW quartz diorites and Yangqiandashan (YQDS) granodiorites, are high-K calc-alkaline with low Sr/Y values. The geochemical and isotopic data suggest that they are generated from partial melting of lower crust without garnet in the residue. The late-period intrusive rocks (414-422 Ma), represented by the Shengrongsi (SRS) and Xinkaigou (XKG) plutons, are A-type or alkali-feldspar granites. They are possibly derived from partial melting of felsic crustal material under lower pressure condition. Our data show decreasing magma crystallization ages from MJDW pluton in the north and LHS pluton in the south to the SRS and XKG plutons in the central part of the study area. We suggest that such spatial and temporal variations of magmatic suites were caused by lithospheric delamination after the collision between the Central Qilian and the Alxa block. A more plausible explanation is that the delamination propagated from the margin part of the thickened lithosphere to inward beneath the North Qilian and southern margin of the Alxa block.

  16. The geochemical evolution of syncollisional magmatism and the implications for significant magmatic-hydrothermal lead-zinc mineralization (Gangdese, Tibet)

    Science.gov (United States)

    Zhou, Jinsheng; Yang, Zhusen; Hou, Zengqian; Liu, Yingchao; Zhao, Xiaoyan; Zhang, Xiong; Zhao, Miao; Ma, Wang

    2017-09-01

    In addition to well-known subduction processes, the collision of two continents also generates abundant ore deposits, as in the case of the Tibetan Plateau, which is the youngest and most spectacular collisional belt on Earth. During the building history of the Gangdese magmatic belt, several magmatic flare-up events developed, however, significant magmatic-hydrothermal lead-zinc mineralization dominantly accompanied the magmatism during the syncollisional period ( 65-41 Ma). Based on integrated geochemical and isotopic data, we provide insights into the genesis and evolution of syncollisional magmas, and their implications for significant magmatic-hydrothermal lead-zinc mineralization. The Sr-Nd isotopic compositions of most syncollisional igneous rocks (87Sr/86Sr = 0.7034-0.7123; εNd(t) = - 9.0 to + 1.8) indicate a mixing origin between mantle-derived basaltic magmas and ancient crustal melts, and fractional crystallization is a fundamental mechanism by which syncollisional magmas evolve towards intermediate to silicic compositions. Most lead-zinc mineralization-related plutons are high silica (76.14% wt.% SiO2 on average), high oxygen fugacity (average ΔFMQ + 2.5) granites with highly evolved chemical signatures [average Eun/Eun* = 0.33, high Rb/Sr (average = 3.9)], and they represent the final products from primary magmas. Due to the contribution of ancient crustal melts to the genesis of mineralization-related parent magmas, the spatial distribution of Pb-Zn deposits within the northern Gangdese magmatic belt is controlled by the lithospheric architecture. In compressional environments, magmas have low evacuation efficiency and long magma chamber lifespan, which is favorable for basaltic parents evolved to high silica granites through sufficient fractional crystallization. This scenario contributes to our understanding of the significant magmatic-hydrothermal lead-zinc mineralization that occurred in the syncollisional period.

  17. Magmatism and Tectonics in the Meso-Archean Pongola Supergroup, South Africa

    Science.gov (United States)

    Wilson, Allan

    2013-04-01

    The Pongola Supergroup is one of the most extensive and well preserved volcano-sedimentary successions emplaced in a continental setting in the Meso-Archean (c. 2.95 Ga). It contrasts with both the older (Barberton type c.3.5 Ga) and younger (Belingwe type c.2.7 Ga) greenstone belts in southern Africa in that the sequence has not undergone the strong horizontal compressional tectonics typically related to greenstone belt-TTG environments. However, it is appropriate to compare this sequence with rocks of the Barberton greenstone belt by which the final phase of deposition preceded that of the juxtaposed Pongola basin with a relatively small time interval. The Pongola succession, which commenced with the first major magmatic event after the Barberton greenstone belt, overlies granitoids and remnants of greenstone belts in SE South Africa and in SW Swaziland. Formation was not in a continental rift environment but most likely in a marginal epicontinental basin with syn-depositional subsidence in a half-graben fault system in the type area. The Pongola rocks occur in two domains related to a NW-trending central basement high in the Kaapvaal Craton and achieving a maximum thickness of 8 km in the northern areas. The lower section (Nsuze group 3.7 km thick) is made up mainly of lavas and pyroclastic rocks and the upper section (Mozaan Group 4.3 km thick) is aranaceous sediments and argillites with a thick volcanic unit observed in the south-eastern facies. Chemical affinities of the lavas include tholeiite and calc-alkaline over the compositional range of basalt to rhyolite. There is a preponderance of andesites in the compositional array. The preservation of these rocks gives insight into the range of volcanic processes that took place at this stage of Earth history and in some areas it is possible to identify eruptions from a single source over several kilometres, as well as feeder-dyke systems to the lava flows. Simultaneous eruption of contrasting magmas from several

  18. Magmatic Flow Record From AMS Data La Gloria Pluton, Central Chile

    Science.gov (United States)

    Gutierrez, F.; Payacan, I. J.; Calderon, S.

    2011-12-01

    La Gloria Pluton (LGP) is a 10 Ma epizonal intrusion in the Southern Andes, located 40 km east of Santiago, in central Chile. 20 km long and 5 km wide LPG has a thickness of 2.5 km, in the form of a NW elongating inverted canoe. LGP intrudes Miocene volcanics as NS extending cluster of Miocene granitoids. LGP was emplaced at the west of an inverse fault system without exhibiting significant post-intrusion deformation. The fault system includes the Laguna Negra Fault and the El Coironal Fault, at its southern and northern ends respectively. LGP has been interpreted to have had a short cooling time, where subsolidus reequilibration was not pervasive, allowing identification of early and late magmatic conditions and suggesting it to be a single closed chamber. LGP is zoned vertically from granodiorite/quartz monzodiorite to quartz monzonite towards the roof, where hornblende and biotite and minor magnetite-ilmenite are omnipresent. AMS samples were collected at 39 sites to determine of the magnetic anisotropy susceptibility tensor. Magnetic fabric is generally oblate and anisotropy values range from 1.3 to 13.9%, consistent with the prescience magnetite and ilmenite. Magnetic lineation (ML) has a NNW trend, a subhorizontal dip and values between 0.4 and 5.3%. Magnetic foliation (MF) has a NW trend and dip varying from vertical at the walls of the intrusive to subhorizontal inside and under the roof. MF values ranges between 0.8 and 13.3%. Since linear trend of MF is restricted to the LGP interior only and can not be caused by a simple inverse fault system, we interpret the AMS results as a consequence of magmatic flow. ML represents the main flow direction, where several shallow plutons intrude at 10Ma in NW direction. MF is consequence of convection, related to cooling and differentiation, and is comparable to numerical simulations of magma fluid-dynamics during differentiation (R4). Two profiles (EW and NS) indicate that MF linear trend is from 29°/km to 50

  19. Magma hybridization in the Western Tatra Mts. granitoid intrusion (S-Poland, Western Carpathians).

    Science.gov (United States)

    Burda, Jolanta; Gawęda, Aleksandra; Klötzli, Urs

    In the Variscan Western Tatra granites hybridization phenomena such as mixing and mingling can be observed at the contact of mafic precursors of dioritic composition and more felsic granitic host rocks. The textural evidence of hybridization include: plagioclase-K-feldspar-sphene ocelli, hornblende- and biotite-rimmed quartz ocelli, plagioclase with Ca-rich spike zonation, inversely zoned K-feldspar crystals, mafic clots, poikilitic plagioclase and quartz crystals, mixed apatite morphologies, zoned K-feldspar phenocrysts. The apparent pressure range of the magma hybridization event was calculated at 6.1 kbar to 4.6 kbar, while the temperature, calculated by independent methods, is in the range of 810°C-770°C. U-Pb age data of the hybrid rocks were obtained by in-situ LA-MC-ICP-MS analysis of zircon. The oscillatory zoned zircon crystals yield a concordia age of 368 ± 8 Ma (MSWD = 1.1), interpreted as the age of magma hybridization and timing of formation of the magmatic precursors. It is the oldest Variscan magmatic event in that part of the Tatra Mountains.

  20. Argon isotopes as recorders of magmatic processes

    Science.gov (United States)

    Layer, P. W.; Gardner, J. E.; Mora Chaparro, J. C.; Arce, J. L.

    2003-12-01

    Argon isotopic ratios vary enough between different reservoirs (atmosphere, crust, mantle) and diffuse fast enough through most minerals at magmatic temperatures (700-1200 C) to make them ideal for looking at magma chamber dynamics. Indeed, diffusion is sufficiently fast to allow short time scales to be deciphered, setting argon apart from many other isotopic methods. A mineral's ability to retain "excess" argon (40Ar/36Ar ratios greater than the atmospheric value and apparent ages older than the known eruption age) during post-eruption cooling is key to Ar studies. Previous work shows that both phenocrysts (crystallizing in the magma chamber; e.g. Mt St. Helens; Layer and Gardner, 2001) and xenocrysts (introduced into the magma chamber; e.g Toba; Gardner et al., 2002) preserve excess argon, which enables magma chamber processes to be deciphered through the variable diffusion rates between crystal phases. Single crystal 40Ar/39Ar step-heating of biotite from the 10.5 ka eruption of Nevado de Toluca volcano, Mexico indicates that they are xenocrystic and resided for only a short (< 1 year) time in the magma before it erupted. The biotite has reaction rims of hornblende, orthopyroxene and plagioclase, and failed to grow experimentally at pressure-temperature conditions of the magma, confirming the xenocrystic nature of this phase. Single-step fusion of plagioclase phenocrysts from eruptions of El Chichon volcano, Mexico, shows evidence of excess (mantle) argon, whereas hornblende from the same eruptions contains little or none. In this case, faster diffusion of Ar in plagioclase than in hornblende allow plagioclase to incorporate excess argon during magma recharge; hornblende does not. Combining such results with other isotopic systems may in fact better determine magma chamber processes. At El Chichon, Sr isotopes suggest magma recharges ocurred (Tepley et al., 2000), whereas the argon isotopes suggest such pulses occurred just before each eruption. The fast and

  1. 1.88 Ga São Gabriel AMCG association in the southernmost Uatumã-Anauá Domain: Petrological implications for post-collisional A-type magmatism in the Amazonian Craton

    Science.gov (United States)

    Valério, Cristóvão da Silva; Macambira, Moacir José Buenano; Souza, Valmir da Silva; Dantas, Elton Luiz; Nardi, Lauro Valentim Stoll

    2018-02-01

    In the southernmost Uatumã-Anauá Domain, central Amazonian craton (Brazil), crop out 1.98 Ga basement inliers represented by (meta)leucosyenogranites and amphibolites (Igarapé Canoas Suite), 1.90-1.89 Ga high-K calc-alkaline granitoids (Água Branca Suite), a 1.88-1.87 Ga alkali-calcic A-type volcano-plutonic system (Iricoumé-Mapuera), Tonian SiO2-satured alkaline granitoids, 1.45-1.25 Ga orthoderived metamorphic rocks (Jauaperi Complex) and Orosirian-Upper Triassic mafic intrusions. New data on petrography, multielementar geochemistry, in situ zircon U-Pb ages and Nd and Hf isotopes of alkali-calcic A-type granites (São Gabriel Granite, Mapuera Suite) and related rocks are indicative of a 1.89-1.87 Ga volcano-plutonic system integrated to the São Gabriel AMCG association. Its magmatic evolution was controlled by the fractional crystallization combined with magma mixing and cumulation processes. Nd isotope values (εNdt values = - 3.71 to + 0.51 and Nd TDM model age = 2.44 to 2.12 Ga) and U-Pb inherited zircon crystals (2115 ± 22 Ma; 2206 ± 21 Ma; 2377 ± 17 Ma, 2385 ± 17 Ma) of the São Gabriel system indicate a large participation of Siderian-Rhyacian crust (granite-greenstones and granulites) and small contribution of Rhyacian mantelic magma. εHft values (+ 5.2 to - 5.8) and Hf TDM ages (3.27-2.14 Ga) also point to contribution of Paleoarchean-Rhyacian crustal melts and small participation of Siderian-Rhyacian mantle melts. Residual melts from the lower crust have been mixed with basaltic melts generated by partial melting of the subcontinental lithospheric mantle (peridotite) in a post-collisional setting at 1.89-1.87 Ga. The mafic melts of such a mixture could have been originated through partial melting of residual ocean plate fragments (eclogites) which ascended onto a residual mantle wedge (hornblende peridotite) and melted it, resulting in modified basaltic magma which, by underplating, led heat to the anatexis of the lower continental crust

  2. The Pedregal granite (Portugal: petrographic and geochemical characterization of a peculiar granitoid

    Directory of Open Access Journals (Sweden)

    Ferreira, J. A.

    2014-12-01

    Full Text Available The Pedregal granite outcrops in the Central Iberian Zone, northern Portugal, in the eastern border of a synorogenic variscan granite-migmatite complex sub-concordant with the regional metamorphic structures. It is a granitoid (ca. 3 km2 with an elongated NW-SE shape intruded in staurolite-micaschist and banded gneiss-migmatite rocks, with local igneous breccias in the contact. The country rocks belong to a metapelitic and metasammitic sequence of Edicarian-Cambrian age, known as the “Complexo Xisto-Grauváquico” (CXG which shows a main regional foliation with a NW-SE to NNW-SSE direction. The Pedregal granite is peraluminous (its A/CNK parameter ranges from 1.18 to 1.62, with a magnesian and alkali to alkali-calcic signature. The peculiar features of the granite are high contents of Zr (389 to 435 ppm and a LREE flat pattern, which are uncommon characteristics for granitic rocks, as well as the corroded shape of the biotite, and the large amount of secondary muscovite. These peculiar features distinguish it from the adjacent synorogenic granites. The field, petrographical and chemical features of the Pedregal granite are in accordance with a second phase of partial melting of a residuum, depleted by melt segregation during a first melting episode with the involvement of peritectic garnet and abundant residual biotite with LREE- and Zr-bearing accessory minerals. Besides, the intrusive character of the granite, and the presence of metasedimentary xenoliths point out to a secondary diatexite.El granito de Pedregal aflora en la Zona Centro-Ibérica, en el norte de Portugal, en el borde oriental de un complejo granito-migmatítico sinorogénico varisco, subconcordante con las estructuras metamórficas regionales. Es un granitoide (ca. 3 km2 de forma elongada NW-SE, que intruye en micaesquistos estaurolíticos y en rocas gneissico- migmatíticas bandeadas, con brechas ígneas locales en el contacto. Las rocas encajantes pertenecen a una

  3. Mass changes during hydrothermal alteration/mineralization in the gold-bearing Astaneh granitoid, western Iran

    Science.gov (United States)

    Zahra Afshooni, Seyedeh; Esmaeily, Dariush

    2010-05-01

    The Astaneh granitoid massif, located in western Iran, is a part of Sanandaj-Sirjan structural Zone. This body, mainly consist of granodioritic rocks, is widely affected under hydrothermal alteration and four alteration zones including phyllic (sericitic), chloritic, propylitic and argillic zones could be identified in this area. Four main mineralization- related alteration episodes have been studied in terms of mass transfer and element mobility during the hydrothermal evolution of Astaneh deposit. In order to illustrate these changes quantitatively, isocon plots have been applied. Isocon plots illustrate that Al, Ti, Ga and Tm was relatively immobile during alteration and that mass were essentially conserved during alteration. Phyllic alteration was accompanied by the depletion of Na and Fe and the enrichment of Si and Cu. The loss of Na and Fe reflects the sericitization of alkali feldspar and the destruction of ferromagnesian minerals. The addition of Si is consistent with widespread silicification wich is a major feature of phyllic alteration. All of the HFSE (except in Y), were enriched but all REEs were depleted in this zone. The overall obtained results show that major oxides such as SiO2, Al2O3, Fe2O3, MnO, MgO, CaO, Na2O, K2O, P2O5 and TiO2 and also LOI show dissimilar behaviors in the different zones. All of the LFSE, HFSE and FTSM (except in Cu and Mo) were depleted in argillic alteration but show dissimilar behaviors in the other alteration zones. The results shown strong depletion in REE, in particular LREE, in all of the alteration facies (except in chloritic zone), equivalent fresh rocks. In chloritic zone, compared with HREE, the LREE represent more enrichment.

  4. A radiological survey of the Eğrigöz granitoid, Western Anatolia/Turkey.

    Science.gov (United States)

    Canbaz Öztürk, B; Yaprak, G; Çam, N F; Candan, O

    2015-06-01

    A radiological survey of the granitoid areas throughout Western Anatolia was conducted during 2007-14. As a part of this radiological survey, this article presents results obtained from Eğrigöz pluton, which lies in the northeastern region of Western Anatolia. In the investigated area, the activity measurements of the natural gamma-emitting radionuclides ((226)Ra, (232)Th and (40)K) in the granitic rock samples and soils have been carried out by means of the NaI(Tl) gamma-ray spectrometry system. The activity concentrations of the relevant natural radionuclides in the granite samples appeared in the ranges as follows: (226)Ra, 28-95 Bq kg(-1); (232)Th, 50-122 Bq kg(-1) and (40)K, 782-1365 Bq kg(-1), while the typical ranges of the (226)Ra, (232)Th and (40)K activities in the soil samples were found to be 7-184, 11-174 and 149-1622 Bq kg(-1), respectively. Based on the available data, the radiation hazard parameters associated with the surveyed rocks/soils are calculated. The corresponding absorbed dose rates in air from all those radionuclides were always much lower than 200 nGy h(-1) and did not exceed the typical range of worldwide average values noted in the UNSCEAR (2000) report. Furthermore, the data are also used for the mapping of the surface soil activity of natural radionuclides and the corresponding gamma dose rates of the surveyed area. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  5. THE GEOCHEMICAL CHARACTERISTIC OF MAJOR ELEMENT OF GRANITOID OF NATUNA, SINGKEP, BANGKA AND SIBOLGA

    Directory of Open Access Journals (Sweden)

    Ediar Usman

    2017-07-01

    Full Text Available A study of geochemical characteristic of major elelemnt of granitoid in Western Indonesia Region was carried out at Natuna, Bangka, Singkep and Sibolga. The SiO2 contents of the granites are 71.16 to 73.02 wt%, 71.77 to 75.56wt% and 71.16 to 73.02wt% at Natuna, Bangka, and Singkep respectively, which are classified as acid magma. While in Sibolga the SiO2 content from 60.27 to 71.44wt%, which is classified as intermediate to acid magma. Based on Harker Diagram, the granites from Natuna, Bangka and Singkep as a co-genetic. In other hand the Sibolga Granite show as a scatter pattern. Granites of Natuna, Bangka and Singkep have the alkaline-total (Na2O + K2O between 6.03 to 8.51 wt% which are classified as granite and alkali granite regime. K2O content ranges from 3.49 to 5.34 wt% and can be classified as calc-alkaline type. The content of alkaline-total of Sibolga granite between 8.12 to 11.81 wt% and classified as a regime of syenite and granite. The range of K2O is about 5.36 to 6.94wt%, and assumed derived from high-K magma to ultra-potassic types. Granites of Natuna, Bangka and Singkep derived from the plutonic rock types and calc-alkaline magma, while Sibolga granite magma derived from K-high to ultra-potassic as a granite of islands arc. Based on the chemical composition of granite in Western Indonesian Region can be divided into two groups, namely Sibolga granite group is representing the Sumatera Island influenced by tectonic arc system of Sumatera Island. Granites of Bangka and Singkep are representing a granite belt in Western Indonesian Region waters which is influenced by tectonic of back arc.

  6. Modulation of magmatic processes by CO2 flushing

    Science.gov (United States)

    Caricchi, Luca; Sheldrake, Tom E.; Blundy, Jon

    2018-06-01

    Magmatic systems are the engines driving volcanic eruptions and the source of fluids responsible for the formation of porphyry-type ore deposits. Sudden variations of pressure, temperature and volume in magmatic systems can produce unrest, which may culminate in a volcanic eruption and/or the abrupt release of ore-forming fluids. Such variations of the conditions within magmatic systems are commonly ascribed to the injection of new magma from depth. However, as magmas fractionating at depth or rising to the upper crust release CO2-rich fluids, the interaction between carbonic fluids and H2O-rich magmas stored in the upper crust (CO2 flushing), must also be a common process affecting the evolution of subvolcanic magma reservoirs. Here, we investigate the effect of gas injection on the stability and chemical evolution of magmatic systems. We calculate the chemical and physical evolution of magmas subjected to CO2-flushing using rhyolite-MELTS. We compare the calculations with a set of melt inclusion data for Mt. St. Helens, Merapi, Etna, and Stromboli volcanoes. We provide an approach that can be used to distinguish between melt inclusions trapped during CO2 flushing, magma ascent and decompression, or those affected by post-entrapment H2O-loss. Our results show that CO2 flushing is a widespread process in both felsic and mafic magmatic systems. Depending upon initial magma crystallinity and duration of CO2 input, flushing can either lead to volcanic eruption or fluid release. We suggest that CO2 flushing is a fundamental process modulating the behaviour and chemical evolution of crustal magmatic systems.

  7. Petrochemical and Tectonogenesis of Granitoids in the Wuyo-Gubrunde Horst, Northeastern Nigeria: Implication for Uranium Enrichment

    Energy Technology Data Exchange (ETDEWEB)

    Bolarinwa, Anthony Temidayo, E-mail: atbola@yahoo.com; Bute, Saleh Ibrahim [University of Ibadan, Department of Geology (Nigeria)

    2016-06-15

    The Wuyo-Gubrunde Horst in the northeastern Nigeria consists of migmatite gneiss, unaltered, altered, and sheared porphyritic granites, pegmatites, aplites, basalts, and sandstone. Uranium has been reported in rhyolite, sheared rocks, and sandstone within the area. The petrogenesis of the granitoids and associated rocks in the area was evaluated in the light of new geochemical data, which showed that the U content of altered porphyritic granite is highest and hydrothermal-related. The granitoids are metaluminous, sub-alkaline, and S-type granite, and have evolved by partial melting of crustal material emplaced at moderate depth of 20–30 km in a syn-to late-collisional within-plate tectonic setting. The negative Eu/Eu* anomaly and high (La/Yb){sub N} ratio of the granitoids indicate magma fractionation. The low SiO{sub 2} (<53%) and high Fe{sub 2}O{sub 3} (10%) of the altered porphyritic granite compared to other similar rock units suggest pervasive alteration. The associated basalts are tholeiitic, emplaced within continental plate tectonic setting, and enriched in Ni, V, Nb, Sr, and light rare earth elements, and they have SiO{sub 2}, Fe{sub 2}O{sub 3}, V, Th, and Co contents that are similar to those of the altered porphyritic granites. The U occurrence in the Wuyo-Gubrunde Horst is believed to be sourced from the adjoining Bima sandstone in the Benue Trough, which locally contains carbonaceous zones with anomalously high concentrations of U. The Fe{sup 2+}/Fe{sup 3+} redox fronts formed by alteration of the iron-rich basalts provided the requisite geochemical barrier for U-bearing hydrothermal fluid, causing enrichment of U leached and mobilized from the sandstone through fractures in the rocks.

  8. Rock strength measurements on Archaean basement granitoids recovered from scientific drilling in the active Koyna seismogenic zone, western India

    Science.gov (United States)

    Goswami, Deepjyoti; Akkiraju, Vyasulu V.; Misra, Surajit; Roy, Sukanta; Singh, Santosh K.; Sinha, Amalendu; Gupta, Harsh; Bansal, B. K.; Nayak, Shailesh

    2017-08-01

    Reservoir triggered earthquakes have been occurring in the Koyna area, western India for the past five decades. Triaxial tests carried out on 181 core samples of Archaean granitoids underlying the Deccan Traps provide valuable constraints on rock strength properties in the Koyna seismogenic zone for the first time. The data include measurements on granite gneiss, granite, migmatitic gneiss and mylonitised granite gneiss obtained from boreholes KBH-3, KBH-4A, KBH-5 and KBH-7 located in the western and eastern margins of the seismic zone. Salient results are as follows. (i) Increase of rock strength with increasing confining pressure allow determination of the linearized failure envelopes from which the cohesive strength and angle of internal friction are calculated. (ii) Variable differential stresses at different depths are the manifestations of deformation partitioning in close association of fault zone(s) or localized fracture zones. (iii) Fractures controlled by naturally developed weak planes such as cleavage and fabric directly affect the rock strength properties, but the majority of failure planes developed during triaxial tests is not consistent with the orientations of pre-existing weak planes. The failure planes may, therefore, represent other planes of weakness induced by ongoing seismic activity. (iv) Stress-strain curves confirm that axial deformation is controlled by the varying intensity of pre-existing shear in the granitoids, viz., mylonite, granite gneiss and migmatitic gneiss. (v) Frequent occurrences of low magnitude earthquakes may be attributed to low and variable rock strength of the granitoids, which, in turn, is modified by successive seismic events.

  9. Uranium in accessory sphene from granitoids and its behaviour during mineral's alteration (Muzbekskij pluton at Mogol-Tau, Central Asia)

    International Nuclear Information System (INIS)

    Simonova, L.I.; Maksimova, I.G.; Nad'yarnykh, V.G.; Voronikhin, V.A.

    1982-01-01

    Uranium behaviour in accessory spbene and products of its alteration at different stages of granitoid transformation with characteristic association of zirconium-apatite-sphene and magnetite of accessory minerals, is shown. The products of sphene alteration (due to propylitization of granatoids the sphene is replaced by leucoxene) are determined by MS-46 electron probe microanalyzer and MA-1 lazer microanalyzer. Uranium distribution in leucoxene is studied by the method of fragmentary radiography. Leucoxene pseudomorphoses at a high oxygen potential are capable of giving into solution Uranium previously sorbed by leucoxene. This fact should be taken into account when determining source of metal of hydrogenous deposits

  10. Quaternary Magmatism in the Cascades - Geologic Perspectives

    Science.gov (United States)

    Hildreth, Wes

    2007-01-01

    Foreward The Cascade magmatic arc is a belt of Quaternary volcanoes that extends 1,250 km from Lassen Peak in northern California to Meager Mountain in Canada, above the subduction zone where the Juan de Fuca Plate plunges beneath the North American Plate. This Professional Paper presents a synthesis of the entire volcanic arc, addressing all 2,300 known Quaternary volcanoes, not just the 30 or so visually prominent peaks that comprise the volcanic skyline. Study of Cascade volcanoes goes back to the geological explorers of the late 19th century and the seminal investigations of Howel Williams in the 1920s and 1930s. However, major progress and application of modern scientific methods and instrumentation began only in the 1970s with the advent of systematic geological, geophysical, and geochemical studies of the entire arc. Initial stimulus from the USGS Geothermal Research Program was enhanced by the USGS Volcano Hazards Program following the 1980 eruption of Mount St. Helens. Together, these two USGS Programs have provided more than three decades of stable funding, staffing, and analytical support. This Professional Paper summarizes the resultant USGS data sets and integrates them with the parallel contributions of other investigators. The product is based upon an all-encompassing and definitive geological database, including chemical and isotopic analyses to characterize the rocks and geochronology to provide the critical time constraints. Until now, this massive amount of data has not been summarized, and a systematic and uniform interpretation firmly grounded in geological fact has been lacking. Herein lies the primary utility of this Cascade volume. It not only will be the mandatory starting point for new workers, but also will provide essential geological context to broaden the perspectives of current investigators of specific Cascade volcanoes. Wes Hildreth's insightful understanding of volcanic processes and his uncompromising scientific integrity make him

  11. Barren Miocene granitoids in the Central Andean metallogenic belt, Chile: Geochemistry and Nd-Hf and U-Pb isotope systematics Granitoides estériles del Mioceno en la franja metalogénica de los Andes Centrales, Chile: geoquímica e isotopía de Nd-Hf y U-Pb

    Directory of Open Access Journals (Sweden)

    Katja Deckart

    2010-01-01

    Full Text Available Four Middle-to-Late Miocene barren plutonic complexes that occur between the giant porphyry copper deposits of the central Chilean Andes were selected for U-Pb LA-ICPMS geochronology and Hf-isotope systematics on single zircon grains. Major and trace elements and Sr-Nd-Hf isotope whole rock geochemical studies were under-taken to compare with slightly younger or coeval barren and fertile intrusive rocks between 32° and 34°S. The studied granitoids yield resolvable crystallization ages of 11.3±0.1 Ma (Cerro Mesón Alto massif, 10.3±0.2 Ma (La Gloria pluton, 14.9±0.2 Ma/14.9±0.1 Ma (Yerba Loca stock and 11.2±0.1 Ma/14.7±0.1 Ma (San Francisco Batholith. Major and trace elements discard an adakitic signature as suggested for coeval porphyric intrusions at 32°S, slightly younger mineralized porphyries at Río Blanco-Los Bronces deposit and other Cenozoic adakites. Volcanic host rocks are less fractionated than the intrusive rock units. The same observation can be made for the unmineralized northern plutons compared to the southern ones. Initial Sr-Nd isotope data show insignificant variation (0.703761-0.704118 and 0.512758-0.512882, plotting in the mantle array. Trace element enrichment can be explained by addition of subducted-slab fluids and/or terrigenous sediments to the mantle wedge prior to and/or slight crustal input during magma ascent. Zircon grains separated from these barren intrusives share a similar initial εHf i-data variation for the younger age group (10-12 Ma; 7.04-9.54 and show a more scattered range for the older one (14-15 Ma; 8.50-15.34; both sets plot between the DM and CLTUR evolution lines. There is evidence that magma evolution was slightly distinct through time from older to younger barren magmatism, compared to a few fertile porphyritic rocks from Río Blanco-Los Bronces porphyry copper deposit. It is suggested that chronological inconsistencies within these complexes might be related to differential shortening

  12. Magmatic densities control erupted volumes in Icelandic volcanic systems

    Science.gov (United States)

    Hartley, Margaret; Maclennan, John

    2018-04-01

    Magmatic density and viscosity exert fundamental controls on the eruptibility of magmas. In this study, we investigate the extent to which magmatic physical properties control the eruptibility of magmas from Iceland's Northern Volcanic Zone (NVZ). By studying subaerial flows of known age and volume, we are able to directly relate erupted volumes to magmatic physical properties, a task that has been near-impossible when dealing with submarine samples dredged from mid-ocean ridges. We find a strong correlation between magmatic density and observed erupted volumes on the NVZ. Over 85% of the total volume of erupted material lies close to a density and viscosity minimum that corresponds to the composition of basalts at the arrival of plagioclase on the liquidus. These magmas are buoyant with respect to the Icelandic upper crust. However, a number of small-volume eruptions with densities greater than typical Icelandic upper crust are also found in Iceland's neovolcanic zones. We use a simple numerical model to demonstrate that the eruption of magmas with higher densities and viscosities is facilitated by the generation of overpressure in magma chambers in the lower crust and uppermost mantle. This conclusion is in agreement with petrological constraints on the depths of crystallisation under Iceland.

  13. Bimodal magmatism produced by progressively inhibited crustal assimilation 2 (PICA)

    NARCIS (Netherlands)

    Meade, F.C.; Troll, V.R.; Ellam, R.M.; Freda, C.; Font Morales, L.; Donaldson, C.H.; Klonowska, I.

    2014-01-01

    The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous

  14. Magmatic Densities Control Erupted Volumes in Icelandic Volcanic Systems

    Directory of Open Access Journals (Sweden)

    Margaret Hartley

    2018-04-01

    Full Text Available Magmatic density and viscosity exert fundamental controls on the eruptibility of magmas. In this study, we investigate the extent to which magmatic physical properties control the eruptibility of magmas from Iceland's Northern Volcanic Zone (NVZ. By studying subaerial flows of known age and volume, we are able to directly relate erupted volumes to magmatic physical properties, a task that has been near-impossible when dealing with submarine samples dredged from mid-ocean ridges. We find a strong correlation between magmatic density and observed erupted volumes on the NVZ. Over 85% of the total volume of erupted material lies close to a density and viscosity minimum that corresponds to the composition of basalts at the arrival of plagioclase on the liquidus. These magmas are buoyant with respect to the Icelandic upper crust. However, a number of small-volume eruptions with densities greater than typical Icelandic upper crust are also found in Iceland's neovolcanic zones. We use a simple numerical model to demonstrate that the eruption of magmas with higher densities and viscosities is facilitated by the generation of overpressure in magma chambers in the lower crust and uppermost mantle. This conclusion is in agreement with petrological constraints on the depths of crystallization under Iceland.

  15. Unusual Rb-Sr data on the age of two typical peralkaline granitoid plutons in West Transbeikalia

    International Nuclear Information System (INIS)

    Litvinovskij, B.A.; Posokhov, V.F.; Zanvilevich, A.N.

    1995-01-01

    Rb-Sr isotope study of two typical plutons in West Transbaikalia (Bryansk and Kharitonov) has been carried out. For alkaline and peralkaline suits of the Bryansk pluton the obtained data are 287 ± m.y., I Sx =0.7054 ± 3 and 285 ± 1 m.y., I Sr =0.7037 ± 3 respectively. Rb-Sr age of peralkaline syenites and granites from the Kharitonov pluton are in more or less consistency with those on the Malokunal pluton (233 ± 5 m.y.) and much less than the age of the Khorinsk pluton (253 ± 3 m.y.). Taking into account the K-Ar data on amphibole from the peralkaline granitoids it is concluded that probable age of these rocks span the interval 250-220 m.y. However results obtained from the Bryansk pluton suggest that within the Mongolia-Transbaikalia belt one more stage of peralkaline granitoid generation i.e. the Early Permian stage could be manifested as well. 20 refs.; 5 figs.; 3 tabs

  16. The geochemistry and geochronology of some proterozoic granitoid rocks from the Natal structural and metamorphic province, Southeastern Africa

    International Nuclear Information System (INIS)

    Kerr, A.; Milne, G.C.; Eglington, B.M.

    1987-01-01

    The Natal Structural and Metamorphic Province is thought to be an eastern extension of the Namaqua Metamorphic Province. Until recently few geochemical and isotopic data have been available on many of the rocks of this mobile belt. This paper presentes initial geochemical and geochronological information on the granitoids and associated rocks from three areas NSMP. Together, these areas provide a traverse through central and southern parts of the Mapumulo Group. Supracrustal gneisses, of uncertain age, are the oldest rocks in all areas, while the granitic intrusives range from 1,200-850 Ma, with a tendency for younger dates towards dates towards the south. Low initial 87 Sr/ 86 Sr ratios for these plutonic units suggest that the rocks were the products of partial melting of a relatively juvenile (circa 1,400 Ma) protolith. A type granites are common within the NSMP and give a range of ages, indicating that conditions suitable for their formation persited in this part of the African continent for an extended period of time. Economic deposits are lacking in eastern (Natal) sector of the mobile belt. Reconnaissance studies, however indicate that syn-tolate-Kinematic granitoids, intruded circa 1,000 Ma, are enriched in uranium and thorium irrespective of bulk chemistry, textural nature,mineralogy,structural setting, and isotopic characteristics. (author) [pt

  17. Geochronology of granitoids and gnaisses from the Rio Maria, Mata Geral farm and Itacaiunas river regions, southern Para, Brazil

    International Nuclear Information System (INIS)

    Montalvao, R.M.G. de; Tassinari, C.C.G.; Bezerra, P.E.L.; Prado, P.

    1984-01-01

    Granitoids and gneisses occurring at Rio Maria, Mata Geral farm and Itacaiunas river regions, southern Para, underwent radiometric age determinations by Rb/Sr method using conventional isochrons. Results obtained from the Rio Maria and Mata Geral farm regions allowed te establishment of a reference 2,600 my Rb/Sr isochron with an initial Sr 87 /Sr 86 ratio of 0.7009. This result resembles the one obtained for granitoids and gneisses hosting rocks of the Serra do Inaja greenstone belt, located some what south of this area, which yielded, in Rb/Sr isochron, a radiometric age of 2,696 + - 79 my with an initial Sr 87 /Sr 86 ratio of 0.701. Results obtained from the Itacaiunas river region allowed for the establishment of a Rb/Sr referential isochron of 2,480 + - 40 my wth an initial Sr 87 /.Sr 86 ratio of 0.7072. Due to low initial ratios, it is suggested that the rocks from the Rio Maria, Mata Geral farm and Serra do Inaja regions formed from Mafic crust or superior mantle reworking, while those from the Itacaiunas river region, due to a high initial ratio, result from reworking at high crustal levels. (Author) [pt

  18. Re-evaluating Gondwana breakup: Magmatism, movement and microplates

    Science.gov (United States)

    Ferraccioli, F.; Jordan, T. A.

    2017-12-01

    Gondwana breakup is thought to have initiated in the Early- to Mid-Jurassic between South Africa and East Antarctica. The critical stages of continental extension and magmatism which preceded breakup remain controversial. It is agreed that extensive magmatism struck this region 180 Ma, and that significant extension occurred in the Weddell Sea Rift System (WSRS) and around the Falkland Plateau. However, the timing and volume of magmatism, extent and mechanism of continental extension, and the links with the wider plate circuit are poorly constrained. Jordan et al (Gondwana Research 2017) recently proposed a two-stage model for the formation of the WSRS: initial extension and movement of the Ellsworth Whitmore Mountains microplate along the margin of the East Antarctic continent on a sinistral strike slip fault zone, followed by transtensional extension closer to the continental margin. Here we identify some key questions raised by the two-stage model, and identify regions where these can be tested. Firstly, is the magmatism inferred to have facilitated extension in the WSRS directly linked to the onshore Dufek Intrusion? This question relates to both the uncertainty in the volume of magmatism and potentially the timing of extension, and requires improved resolution of aeromagnetic data in the eastern WSRS. Secondly, did extension in the WSRS terminate against a single strike slip fault zone or into a distributed fault system? By integrating new and existing aeromagnetic data along the margin of East Antarctica we evaluate the possibility of a distributed shear zone penetrating the East Antarctic continent, and identify critical remaining data gaps. Finally we question how extension within the WSRS could fit into the wider plate circuit. By integrating the two-stage model into Gplates reconstructions we identify regions of overlap and areas where tracers of past plate motion could be identified.

  19. Active Magmatic Underplating in Western Eger Rift, Central Europe

    Science.gov (United States)

    Hrubcová, Pavla; Geissler, Wolfram H.; Bräuer, Karin; Vavryčuk, Václav; Tomek, Čestmír.; Kämpf, Horst

    2017-12-01

    The Eger Rift is an active element of the European Cenozoic Rift System associated with intense Cenozoic intraplate alkaline volcanism and system of sedimentary basins. The intracontinental Cheb Basin at its western part displays geodynamic activity with fluid emanations, persistent seismicity, Cenozoic volcanism, and neotectonic crustal movements at the intersections of major intraplate faults. In this paper, we study detailed geometry of the crust/mantle boundary and its possible origin in the western Eger Rift. We review existing seismic and seismological studies, provide new interpretation of the reflection profile 9HR, and supplement it by new results from local seismicity. We identify significant lateral variations of the high-velocity lower crust and relate them to the distribution and chemical status of mantle-derived fluids and to xenolith studies from corresponding depths. New interpretation based on combined seismic and isotope study points to a local-scale magmatic emplacement at the base of the continental crust within a new rift environment. This concept of magmatic underplating is supported by detecting two types of the lower crust: a high-velocity lower crust with pronounced reflectivity and a high-velocity reflection-free lower crust. The character of the underplated material enables to differentiate timing and tectonic setting of two episodes with different times of origin of underplating events. The lower crust with high reflectivity evidences magmatic underplating west of the Eger Rift of the Late Variscan age. The reflection-free lower crust together with a strong reflector at its top at depths of 28-30 km forms a magma body indicating magmatic underplating of the late Cenozoic (middle and upper Miocene) to recent. Spatial and temporal relations to recent geodynamic processes suggest active magmatic underplating in the intracontinental setting.

  20. A preserved early Ediacaran magmatic arc at the northernmost portion of the Transversal Zone central subprovince of the Borborema Province, Northeastern South America

    Directory of Open Access Journals (Sweden)

    Benjamim Bley de Brito Neves

    Full Text Available ABSTRACT: Magmatic arcs are an essential part of crust-forming events in planet Earth evolution. The aim of this work was to describe an early Ediacaran magmatic arc (ca. 635-580 Ma exposed in the northernmost portion of the Transversal Zone, central subprovince of Borborema Province, northeast Brazil. Our research took advantage of several syntheses by different authors, including theses and dissertations, carried out on magmatic rocks of the study area for the last 30 years. The ca. 750 km long and up to 140 km wide arc, trending ENE-WSW, is preserved to the south of the Patos Lineament, between 35º15' and 42º30'W and 7º15' and 8ºS. About 90 different stocks and batholiths of I-type granitic rocks were mapped along this orogenic zone, preferentially intruding low-grade schists of the Cryogenian-Ediacaran Piancó-Alto Brígida (SPAB belt. Three igneous supersuites are recognized: a epidote-bearing granodiorites and tonalites ("Conceição" type; b high-K calc-alkaline granites ("Itaporanga" type; c biotite granodiorites of trondhjemite affinity ("Serrita" type. A fourth group of peralkalic and shoshonitic rocks occurs to the south of the previous ones, reflecting special tectonic conditions. NNE-SSW trending Paleoproterozoic fold belts, surrounding Archean nuclei, characterize the continental part of the northern lower plate. The oceanic fraction of this lower plate was recycled by subduction and scarce remnants of which may be seen either within the enclosing low-grade schists or as xenoliths within the arc intrusions. The upper continental plate presents WSW-ENE structural trends and is composed of Neoproterozoic fold belts and Paleoproterozoic reworked basement inliers. Available data bear clear evidence of an Ediacaran magmatic arc built at the northern portion of the Transversal Zone in the Borborema Province, northeast Brazil.

  1. Hybrid type I-type II superconducting behavior in magnesium diboride

    International Nuclear Information System (INIS)

    Kunchur, M.N.; Saracila, G.; Arcos, D.A.; Cui, Y.; Pogrebnyakov, A.; Orgiani, P.; Xi, X.X.

    2006-01-01

    In traditional type-II superconductors, an applied magnetic field depresses the transition temperature and introduces magnetic flux vortices that cause resistive losses accompanied by a broadening of the transition. High-field high-pulsed-current measurements have revealed a new hybrid behavior in disordered magnesium diboride films: The superconductivity survives high magnetic fields by entering a mixed state with vortices (like a type II superconductor) but holds its vortices nearly motionless and avoids dissipation (like a type I superconductor). A study of this phenomenon in magnesium diboride films with varying degrees of scattering indicate that the hybrid type I-type II behavior arises from the two-band nature of the superconductivity and the different degrees of influence that disorder exerts on its different bands. (author)

  2. Mode I type delamination fracture toughness of YBCO coated conductor with additional Cu layer

    International Nuclear Information System (INIS)

    Miyazato, T.; Hojo, M.; Sugano, M.; Adachi, T.; Inoue, Y.; Shikimachi, K.; Hirano, N.; Nagaya, S.

    2011-01-01

    A fracture toughness test method was developed for a YBCO coated conductor with an additional Cu layer. Mode I type tests were carried out using double cantilever beam (DCB) specimens. Delamination propagated into the YBCO layer, and sometimes reached the Ag/YBCO interface. The fracture toughness for YBCO was about 10 J/m 2 . That for Ag/YBCO interface was about 100 J/m 2 . Although interlaminar fracture at a YBa 2 Cu 3 O 7-δ (YBCO)/CeO 2 interface was reported for YBCO coated conductors, this has not yet been investigated by a fracture mechanical approach. In the present study, we developed a mode I type fracture toughness test method for a YBCO coated conductor with an additional Cu layer using double cantilever beam (DCB) specimens. Fracture mechanism was investigated by microscopic observation by a scanning electron microscope (SEM), together with composition analysis by an energy dispersive X-ray spectroscope (EDS). A pre-crack introduced at the YBCO/CeO 2 interface deviated from the interface, and propagated into the YBCO layer, and sometimes reached the Ag/YBCO interface. The fracture toughness, G R , for YBCO and the Ag/YBCO interface was evaluated to be 7-10 J/m 2 and 80-120 J/m 2 , respectively. The complex stress intensity factor ratio, K 2 /K 1 , at YBCO/CeO 2 interface was evaluated to be -0.19, and this ratio controlled the formation of microcracks in the YBCO layer. The main crack propagated into the YBCO layer accompanied with the formation of microcracks.

  3. Magmatism, ash-flow tuffs, and calderas of the ignimbrite flareup in the western Nevada volcanic field, Great Basin, USA

    Science.gov (United States)

    Christopher D. Henry,; John, David A.

    2013-01-01

    Sierra Nevada, which was not a barrier to westward flow of ash flows at that time. At least three tuffs flowed eastward across a north-south paleodivide through central Nevada. That tuffs could flow significant distances apparently uphill raises questions about the absolute elevation of the region and the elevation, relief, and location of the paleodivide.Calderas are equant to slightly elongate, at least 12 km in diameter, and as much as 35 km in longest dimension. Exceptional exposure of two caldera complexes that resulted from extensional faulting and tilting show that calderas subsided as much as 5 km as large piston-like blocks; caldera walls were vertical to steeply inward dipping to depths ≥4–5 km, and topographic walls formed by slumping of wall rock into the caldera were only slightly outboard (≤1 km) of structural margins.Most calderas show abundant post-collapse magmatism expressed as resurgent intrusions, ring-fracture intrusions, or intracaldera lavas that are closely related temporally (∼0–0.5 Ma younger) to caldera formation. Granitoid intrusions, which were emplaced at paleodepths ranging from Mountain epithermal gold deposit, few known caldera-related hydrothermal systems are strongly mineralized. Major middle Cenozoic precious and base metal mineral deposits in and along the margins of the western Nevada volcanic field are mostly related to intrusive rocks that preceded caldera-forming eruptions.

  4. Rb-Sr and Sm-Nd isotopic relations and ages of the Brasiliano granitic magmatism of the eastern region of the Dom Feliciano belt in the Rio Grande do Sul State, South region Brazil: evidences of the reworking of a paleoproterozoic continental crust, South region, Brazil

    International Nuclear Information System (INIS)

    Frantz, Jose Carlos; Koester, Edinei; Teixeira, Roberto Santos; Botelho, Nilson Francisquini; Pimentel, Marcio Martins; Potrel, Alan

    1999-01-01

    The granitoids belonging to the brasiliano cycle from the eastern region at the Dom Feliciano Belt in the Rio Grande do Sul state have had Rb-Sr data that indicated bodies which were intruded between 800 and 585 Ma. The T DM ages are suggesting the participation of an older source in their generation. This source could be represented by a long period enriched mantle, much than would be expected during the evolution of the magmatic arcs, or could be represented by the interaction between an older continental crust and mantle during a continental collision regime. The tectonic evolution of this area., the existence of a long period of time between the granitic intrusions associated to the tangential regime and to the transpressive regime and to the transpressive regime ones, the isotopic relations between Sr and nd and the very low negative values of ε N dt are suggesting a strong participation of an older continental crust. This older continental crust, may be constituted by gneissic protoliths of paleoproterozoic ages and generated during the evolution of the Transamazonic Cycle, has participated in the formation of the sources of the granitic magmatism of this part of the belt. The variations of the T DM ages and of the Nd ratios in the calc-alkaline granitoids are suggesting different proportions of mixture between and older continental crust and mantle or different homogenization grades in the magmas sources. For the peraluminous granites, that have be resulted from continental crustal melt, there are indications of different sources to the different bodies. (author)

  5. Structural analysis and magmatism characterization of the Major Gercino shear zone, Santa Catarina State, Brazil

    International Nuclear Information System (INIS)

    Passarelli, Claudia Regina

    1996-01-01

    This work describes the geometric and kinematic characteristics of the Major Gercino Shear Zone (MGSZ) in the Canelinha-Garcia area. This shear zone is one of the major lineaments that affect all southern Brazilian precambrian terrains. In Santa Catarina State, it separates, along its whole extension, the supracrustal rocks of the Brusque belt (northern part) from the Granitoid belt (southern). This zone is characterized by a regional NE trend and a dextral sense of movement where ductile-brittle structures predominate. The MGSZ is composed of two mylonitic belts separated by granitoid rocks probably associated to the development of the shear zone. Both shear zones show cataclastic to ultra mylonitic rocks, but mylonites and protomylonites conditions at high strain rate. The calc-alkaline granitoids present in the area can be grouped in two granitoid associations with meta to peraluminous affinities. The Rolador Granitoid Association is characterized by grayish porphyritic biotite-monzogranites and the Fernandes Granitoid Association by coarsed-grained to porphyritic pinkish amphibole-syenogranites. The U-Pb and Rb-Sr ages range from 670 to 590 Ma with the Sr 87 / Sr 86 initial ratios suggesting a crustal contribution in the generation of these rocks. The importance of the pure shear component is also emphasized by the results of the Fry method. Many z axes of the strain ellipses are at high angle to the shear foliation. Symmetric porphyroclasts also corroborate this hypothesis. The micaceous minerals formed during the shear development indicate K-Ar ages around 555 ± 15 Ma. Brittle reactivations of the shear zone have been placed by K-Ar in fine-fraction materials at Triassic time (215 ± 15 Ma.)

  6. Superposition de la tectonique éburnéenne et panafricaine dans les granitoïdes de la bordure nord du craton ouest africain, boutonniére de Zenaga, Anti-Atlas central, Maroc(Pan-african overprint on Eburnian granitoids at the northern boundary of the West African Craton, Zenaga Inlier, central Anti-Atlas, Morocco)

    Science.gov (United States)

    Ennih, N.; Laduron, D.; Greiling, R. O.; Errami, E.; de Wall, H.; Boutaleb, M.

    2001-05-01

    The Zenaga Inlier shows a comprehensive record of the Eburnian and Pan-African Orogenies. The Eburnian is characterised by high-temperature regional metamorphism and complex magmatism. The early (Azguemerzi) granodiorite has an isotopic mantle signature and was emplaced diapirically during the Eburnian Orogeny causing local thermal metamorphism. The foliation observed in this granitoid is a result of the interference between its primary syn-emplacement foliation and the regional foliation under amphibolite-facies conditions. The northern part of Zenaga has been intruded by the leucocratic granites of Tazenakht. These granites are cut by mylonites and phyllonites, corresponding to the Pan-African shear zones and accompanied with sub-greenschist-facies metamorphism during the Pan-African Orogeny. The deformation was the result of a regional sinistral transpressive event. This study in the northern part of the West African Craton shows the superposition of the Pan-African on the Eburnian Orogeny and the presence of a major fault in the Anti-Atlas.

  7. The Rooiwater complex and associated rocks, Murchison granitoid-greenstone terrane, Kaapvaal Craton

    International Nuclear Information System (INIS)

    Vearncombe, J.R.; Walsh, K.L.

    1987-01-01

    The greater than 2625 Ma Rooiwater Complex is a thick, on-end differentiated basic igneous body exposed along the northern margin of the Murchison schist belt. It is metamorphosed to amphibolite facies and regionally retrograded and hydrothermally altered. Metamorphosed anorthosite, gabbro, pyroxenite, sulphide-bearing gabbros, thick magnetite layers, and granites are compatible with the hypothesis that the Complex is a layered intrusion, tectonically rotated and intruded by younger, genetically unrelated granites. Increasing TiO 2 and decreasing V 2 O 3 contents southwards in the magnetites layers combined with a general southern disposition of differentiated hornblende granite suggest that the Rooiwater Complex faces south. Although the Rubbervale Formation is pervasively deformed and metamorphosed at the greenschist facies, field relations and isotopic and rare earth element data tentatively suggest that a genetic relationship exists, the Rubbervale Formation being a possible roof to the Rooiwater intrusion, being derived from the same or a similar undepleted magmatic source. A paucity of ultramafic cumulates and up to 1,5 km of hornblende granites may relate to a source magma more felsic than that of other layered intrusions. In order to determine model ages for the Eden pluton, the Free State hornblende granite, the Quagga quartz amphibolite, the Rubbervale formation, and the Novengilla gabbro-anorthosite series. Rb-Sr and Pb isotopic analyses were undertaken

  8. Magmatic gases in fluid inclusions from hydrothermal ore deposits

    Energy Technology Data Exchange (ETDEWEB)

    Graney, J.; Kesler, S. (University of Michigan, MI (United States))

    1992-08-31

    In this study, magmatic gases in fluid inclusions from hydrothermal ore deposits have been analyzed. The gas composition of fluid inclusions from a wide range of extinct hydrothermal systems as represented by different ore deposit types was determined using a quadrupole mass spectrometer. Most samples used for analysis consisted of transparent quartz, although barite, jasperoid, opal, sphalerite, pyrite, chalcopyrite, and bornite were also analyzed. H2O was the dominant volatile component in fluid inclusions, and composed 95-99 mole percent of the inclusion fluid. CO2 comprised most of the remaining volatile component and the other gases were generally present in amounts smaller than 0.1 mole percent. Analysis from porphyry and acid-sulfate deposits, in which magmatic gas contributions are considered to be largest, plotted closest to the fumarolic gas compositions. These inclusion fluid volatile component comparisons have shown that there are systematic differences in inclusion fluids from different hydrothermal systems. 9 refs., 3 figs.

  9. Magmatic formations in the Okhotsk--Chukotka volcanogenic belt

    Energy Technology Data Exchange (ETDEWEB)

    Osipov, A.P.

    1976-05-01

    The relationship between the Okhotsk-Chukotka volcanogenic belt of Northeast USSR and the stage of evolution of magnetism and tectonic development of the region are examined. Recognizing the associations of effusive and intrusive rocks that are typical of the southern part of the volcanogenic belt and that are joined together by some characteristic features, a basic plan is presented for examination of the problem of magnetic formations. On the basis of the distinctive characteristics of epigeosynclinal tectonic development of the territory and the sequence of formation of the magmatic rocks within it, three main groups: volcanic, coleanoplutonic, and plutonic, can be distinguished; and a general scheme of development of these types in space and time within the volcanogenic belt can be developed. According to this scheme, four main stages can be recognized in the Mesozoic and Cenozoic magmatic evolution of the Okhotsk-Chukotka belt. This scheme of classification takes into consideration the factor of the structural development of this tectonomagmatic element.

  10. Active Magmatic Underplating in Western Eger Rift, Central Europe

    Czech Academy of Sciences Publication Activity Database

    Hrubcová, Pavla; Geissler, W.H.; Bräuer, K.; Vavryčuk, Václav; Tomek, Č.; Kämpf, H.

    2017-01-01

    Roč. 36, č. 12 (2017), s. 2846-2862 ISSN 0278-7407 R&D Projects: GA ČR GA17-19297S; GA ČR GC16-19751J Institutional support: RVO:67985530 Keywords : active intraplate magmatic underplating * mantle-derived fluids * high-velocity lower crust * reflection-free magma body Subject RIV: DC - Siesmology, Volcanology, Earth Structure OBOR OECD: Volcanology Impact factor: 3.784, year: 2016

  11. The Magmatic Plumbing System of the Campi Flegrei Caldera.

    Science.gov (United States)

    Lucia, C.; Ilenia, A.; Massimo, D.; Valeria, D.; Mauro, D.; Giovanni, O.

    2006-12-01

    The Campi Flegrei caldera is a nested and resurgent structure generated by at least two major collapses. Large sectors of the structural boundary of both calderas resulted from partial reactivation of pre-existing faults generated by regional tectonism. Its magmatic system is still active with the last eruption occurring in 1538 A.D. (Monte Nuovo), widespread fumaroles and hot springs activity, and the unrest episodes in the last 35 years, with a maximum net uplift of about 3.5 m in the Pozzuoli area. The definition of the history of the magmatic feeding system of this caldera, in terms of composition, time- scale and depth of crystallization, relation between composition of the erupted magma and structural position of the vent, and magma chamber processes, is of extreme importance for a better understanding of the dynamic conditions of the present day magma chamber and for evaluating of the extent to which the behavior of the magmatic system can be predicted. The Campi Flegrei caldera magmatic plumbing system is characterized by deep and shallow reservoirs. Campi Flegrei magmas originated in a subduction modified mantle source, stagnate at mid crustal level (20- 10 km depth), where they differentiated and are contaminated with the continental crust. From the "deep reservoir" shoshonitic to latitic magmas rise towards the surface along the NE aligned regional fault reactivated during the caldera collapse, whereas trachytic magmas rise mostly along faults and fractures bordering the resurgent block and the southern part of the Campi Flegrei caldera. Repeated arrival of trachytic to phonolitic magmas form shallow reservoirs at 4-3 km depth, in which differentiation and mixing processes occur before and during the eruption.

  12. Failed magmatic eruptions: Late-stage cessation of magma ascent

    Science.gov (United States)

    Moran, S.C.; Newhall, C.; Roman, D.C.

    2011-01-01

    When a volcano becomes restless, a primary question is whether the unrest will lead to an eruption. Here we recognize four possible outcomes of a magmatic intrusion: "deep intrusion", "shallow intrusion", "sluggish/viscous magmatic eruption", and "rapid, often explosive magmatic eruption". We define "failed eruptions" as instances in which magma reaches but does not pass the "shallow intrusion" stage, i. e., when magma gets close to, but does not reach, the surface. Competing factors act to promote or hinder the eventual eruption of a magma intrusion. Fresh intrusion from depth, high magma gas content, rapid ascent rates that leave little time for enroute degassing, opening of pathways, and sudden decompression near the surface all act to promote eruption, whereas decreased magma supply from depth, slow ascent, significant enroute degassing and associated increases in viscosity, and impingement on structural barriers all act to hinder eruption. All of these factors interact in complex ways with variable results, but often cause magma to stall at some depth before reaching the surface. Although certain precursory phenomena, such as rapidly escalating seismic swarms or rates of degassing or deformation, are good indicators that an eruption is likely, such phenomena have also been observed in association with intrusions that have ultimately failed to erupt. A perpetual difficulty with quantifying the probability of eruption is a lack of data, particularly on instances of failed eruptions. This difficulty is being addressed in part through the WOVOdat database. Papers in this volume will be an additional resource for scientists grappling with the issue of whether or not an episode of unrest will lead to a magmatic eruption.

  13. Development of irradiation rig in HTTR and dosimetry method. I-I type irradiation equipment

    Energy Technology Data Exchange (ETDEWEB)

    Shibata, Taiju; Kikuchi, Takayuki [Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Oarai Research Establishment; Miyamoto, Satoshi; Ogura, Kazutomo [Japan Atomic Power Co., Tokyo (Japan)

    2002-12-01

    The High Temperature Engineering Test Reactor (HTTR) is a graphite-moderated, helium gas-cooled test reactor with a maximum power of 30 MW. The HTTR aims not only to establish and upgrade the technological basis for the HTGRs but also to perform the innovative basic research on high temperature engineering with high temperature irradiation fields. It is planned that the HTTR is used to perform various engineering tests such as the safety demonstration test, high temperature test operation and irradiation test with large irradiation fields at high temperatures. This paper describes the design of the I-I type irradiation equipment developed as the first irradiation rig for the HTTR and does the planned dosimetry method at the first irradiation test. It was developed to perform in-pile creep test on a stainless steel with large standard size specimens in the HTTR. It can give great loads on the specimens stably and can control the irradiation temperature precisely. The in-core creep properties on the specimens are measured by newly developed differential transformers and the irradiation condition in the core is monitored by thermocouples and self-powered neutron detectors (SPNDs), continuously. The irradiated neutron fluence is assessed by neutron fluence monitors of small metallic wires after the irradiation. The obtained data at the first irradiation test can strongly be contributed to upgrade the technological basis for the HTGRs, since it is the first direct measurement of the in-core irradiation environments of the HTTR. (author)

  14. Magmatic context of Bou Skour copper deposit (Eastern Anti-Atlas, Morocco): Petrogrography, geochemistry and alterations

    Science.gov (United States)

    EL Azmi, Daoud; Aissa, M.; Ouguir, H.; Mahdoudi, M. L.; El Azmi, M.; Ouadjo, A.; Zouhair, M.

    2014-09-01

    The Bou Skour copper deposit is located in the western part of the Saghro massif (Eastern Anti-Atlas), about 50 km East of the city of Ouarzazate. It is subdivided into several areas that are, from North to South: “Panthère”, “Chaigne”, “Anne Marie”, “Chapeau de fer” and “Patte d'Oie”. The latter is economically the most important and is the object of this study. The “Patte d'Oie” district consists mainly of extrusive and intrusive igneous rocks. The extrusive rocks are represented by andesites spatially associated with pyroclastic terms (ignimbrites and pyroclastic breccias). This volcanic unit is intruded by a pink granite pluton and a I-type granodiorite with equigranular texture (Bou Skour granodiorite) showing to the border a microgranular facies (microgranodiorite). All these magmatic formations are intersected by rhyolitic dykes (NNE-SSW) and doleritic dykes (WNW-ESE to NW-SE). The granodiorite and andesite have undergone a polyphase hydrothermal alteration: (i) potassic alteration, (ii) phyllitic alteration, (iii) silicification, (iv) argillic alteration and (v) propylitic alteration. The analysis of geochemical data of granodiorite, granite, andesite and dolerite confirmed: (i) their petrographic natures, (ii) the medium-K calc-alkaline affiliation of andesite and granodiorite, which would have been set up into an active geotectonic environment, probably of island arc or collision, during the Pan-African orogeny, (iii) The high-K calc-alkaline character of granite indicating a post-collision development during the Pan-African orogeny and (iv) The alkaline affinity of the dolerite which is linked to an extensive post-orogenic setting (post-Pan-African). The copper mineralization of “Patte d'Oie” area is hosted, exclusively, in the andesitic and granodioritic facies. It is represented, essentially, by chalcopyrite and bornite minerals and is, probably, related to a porphyry system (disseminated and stockwork mineralization

  15. Semi-adakitic magmatism of the Satkatbong diorite, South Korea: Geochemical implications for post-adakitic magmatism in southeastern Eurasia

    Science.gov (United States)

    Lim, Hoseong; Woo, Hyeon Dong; Myeong, Bora; Park, Jongkyu; Jang, Yun-Deuk

    2018-04-01

    The Satkatbong diorite (190 Ma) and the older Yeongdeok granite (250 Ma) in the Yeongnam massif, which is part of the southeastern margin of the Eurasian plate, are affected by a subduction system that is associated with the Izanagi and Farallon plates. The Satkatbong diorite is characterized by its abundant mafic magmatic enclaves (MMEs), mantle affinity, and intermediate adakitic Sr/Y vs. Y signature, whereas the Yeongdeok granite is distinctly adakitic and felsic and contains few MMEs. These differences in adakitic features might be due to differences in the lithospheric mantle material and/or different mafic MME sources. The results of rare earth element (REE) analyses and newly proposed Sr/La modeling in this study indicate that these two plutons were both generated by slab-mantle mixing and continental assimilation, whereas the Satkatbong diorite was additionally affected by the injection of a mafic source of MMEs, which "diluted" its adakitic chemistry. The young and hot subducting ridge passing toward the northeast due to the oblique subduction of the Izanagi and Farallon plates during the Early Mesozoic could have given rise to slab melting and asthenospheric influence through slab melting regions and a slab window, respectively. This implies that the adakitic Yeongdeok granite produced by slab melting and then the semi-adakitic Satkatbong diorite produced by asthenospheric influence, including other similar adakitic to semi-adakitic magmatism, might have occurred along the areas affected by ridge subduction. We suggest that this sequential magmatism would be applicable for many continental arcs which experienced ridge subduction being one of the mechanisms of adakite to semi-adakite magmatism.

  16. Petrogenesis of the postcollisional Middle Devonian monzonitic to granitic magmatism of the Sierra de San Luis, Argentina

    Science.gov (United States)

    López de Luchi, Mónica G.; Siegesmund, Siegfried; Wemmer, Klaus; Nolte, Nicole

    2017-09-01

    Middle Devonian granitoids intruded the Eastern Sierras Pampeanas basement ca. 600 km east of the inferred proto-Pacific margin of Gondwana along which a ca. 390 Ma collisional event developed. In the Sierra de San Luis, voluminous Middle Devonian (393-382 Ma) batholiths are composed of I- to A-type hybrid Monzonite and Granite suites. Shoshonite and subordinated high-K series, stocks, synplutonic dikes and enclaves make up the Monzonite Suite; rocks are metaluminous alkali-calcic magnesian porphyritic or equigranular monzonite, quartz monzonite, monzodiorite and scarce monzogabbro. High-K and subordinated shoshonite series metaluminous to mildly peraluminous magnesian alkali-calcic to calc-alkalic porphyritic or equigranular quartz monzonite, granodiorite, monzogranite and equigranular leucomonzogranites make up the Granite Suite plutons and batholiths. Only a small group of highly evolved granites are ferroan. SiO2 (46-62%), Cr, Ni, V, Sc, LILE, LREE, Th, Zr and variable, Sr/Y, (La/Yb)N and (Tb/Yb)N, smooth Eu/Eu*, moderate Na2O (ca 3.5), and troughs at Nb and Ta for Monzonite Suite rocks suggest an subduction-related enriched lithospheric mantle source. Sm-Nd data (TDM 0.98-1.08 Ga, εNd(380 Ma) 0.66-1.47) and 87Sr/86Sri (0.703520-0.704203) are compatible with an enriched mantle source. The metaluminous porphyritic quartz monzonite-monzogranite and the mildly peraluminous equigranular biotite monzogranites of the Granite Suite are characterized by relatively moderate Al2O3, CaO, and 87Sr/86Sri, high LILE, Cr, variable Sr/Y, (La/Yb)N and Eu/Eu* and low Rb/Sr ( 1.5, ASI 1.05-1.18, and Ga/Al 2.6-3.9, εNd(380 Ma) - 3.74 to - 3.95 and (87Sr/86Sr)i 0.710743-0.712955 which would point to metasedimentary or felsic igneous crustal sources. Nevertheless their TDM 1.36-1.38 Ga is considerably younger than the mean 1.8-1.6 Ga Eastern Sierras Pampeanas crustal residence age and less radiogenic. Middle Devonian magmatism would record an episode of crustal growth by enriched

  17. Behaviour of {sup 238}U, {sup 234}U, {sup 228}Ra and {sup 226}Ra in rock alterations: study of Morungaba granitoids, SP-Brazil and ground water in its fractures; Comportamento de {sup 238}U, {sup 234}U, {sup 228}Ra e {sup 226}Ra na alteracao de rochas: estudo dos granitoides de Morungaba (SP) e aguas subterraneas de suas fraturas

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Rosana N. dos [Pontificia Univ. Catolica de Sao Paulo, SP (Brazil). Dept. de Fisica]. E-mail: rosana@pucsp.br; Marques, Leila S. [Sao Paulo Univ., SP (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas. Dept. de Geofisica]. E-mail: leila@iag.usp.br

    2005-07-01

    This work presents the first results obtained on the investigation of the behavior of uranium and radium radioisotopes in the processes of weathering and rock-water interaction of Morungaba granitoids belonging to Meridional Pluton (Valinhos Town-SP-Brazil). Specific activities of {sup 238}U, {sup 234}U, {sup 228}Ra and {sup 226}Ra were determined in non altered granitoids (Group A), as well as in those affected by different degrees of weathering (Groups B, C and D). The uranium specific activities were determined by alpha spectrometry method, whereas for the determination of radium isotopes high resolution gamma-ray spectrometry technique was employed. The data indicate that {sup 238}U and {sup 234}U are in radioactive equilibrium in the fresh analyzed granitoids, but show a slight depletion of {sup 234}U in relation to {sup 238}U in the weathered rocks. The ({sup 226}Ra/{sup 238}U) and ({sup 226}Ra/{sup 234}U) activity ratios of all investigated rocks are similar, showing a significant {sup 226}Ra depletion, which is probably caused by its preferential leaching. These results indicate that even samples macroscopically classified as fresh rocks, their systems have been opened for some geochemical changes. The high ({sup 234}U/{sup 238}U) activity ratios of groundwaters which are found in the fractures of these granitoids suggest their prolonged residence times in the aquifer and/or their percolation by other rocks presenting different geochemical properties. (author)

  18. On the Hydrogranular Dynamics of Magmatic Gravity Currents

    Science.gov (United States)

    McIntire, M. Z.; Bergantz, G. W.; Schleicher, J.; Burgisser, A.

    2016-12-01

    Magmatic processes are generally governed by multi-phase interactions of silicate liquid, crystals, and bubbles. However, the modes of dissipation and the manner that stress is transmitted are poorly understood. We use a model of a simple but widely applicable gravity current as a means to exemplify the hydrogranular dynamics in crystal-rich magmas. Viscous and lubrication forces are of special interest because they have a dual role in dispersal and mixing in a crystal-rich gravity current. For example, lubrication forces provide an initial apparent yield strength by inducing a negative pore pressure as crystals move apart. However, once the gravity current is underway, lubrication forces reduce the dissipation due to collision and frictional contact.The gravity current is initiated by a combination of toppling and sliding along a well-defined granular fault. This produces three distinct regimes: a quasi-static base, an overlying particle hump that translates in a quasi-plastic fashion by grain-passing and rolling until the angle of repose is reached, and a viscous particle current. The current initially forms a leading vortex at the head, but the loss of crystals by sedimentation-assisted granular capture by an upward growing particle front drains energy from the flow. The vortex is soon abandoned, but persists in the reservoir as a fossil feature of orphaned crystals in a smear of previous intercumulate fluid. The kinetic energy of the most active crystals decays in a dual fashion, initially linearly, then parabolically with a near symmetrical increase and loss of kinetic energy.There is very little entrainment and mixing between intercumulate and reservoir fluids from magmatic gravity currents. Only a thin seam of reservoir melt is captured by the base of the flow as it descends across the floor. Hence magmatic gravity currents, while producing modest amounts of crystal sorting, are not effective agents of mixing as lubrication and viscous forces inhibit

  19. Magmatic development of the outer Vøring Margin

    Science.gov (United States)

    Breivik, Asbjorn; Faleide, Jan Inge; Mjelde, Rolf; Flueh, Ernst; Murai, Yoshio

    2013-04-01

    The Vøring Plateau off mid-Norway is a volcanic passive margin, located north of the East Jan Mayen Fracture Zone (EJMFZ). Large volumes of magmatic rocks were emplaced during Early Eocene margin formation. In 2003, an ocean bottom seismometer survey was acquired on the Vøring and Lofoten margins. One profile crosses from the Vøring Plateau to the Vøring Spur, an oceanic plateau north of the EJMFZ. The P-wave data were modeled by ray-tracing in a 2D velocity model of the crust. The process behind the excess magmatism can be estimated by comparing seismic velocity (VP) with igneous thickness (H). This profile and two other profiles farther north show a positive H-VP correlation, consistent with a hot mantle reservoir of finite extent under the margin at breakup. However, during the first two million years, magma production appears to be augmented by a secondary process. By 51-51.5 Ma melting may be caused by elevated mantle temperature alone. Seismic stratigraphy around the Vøring Spur shows at least two inversion events, with the main episode tentatively in the Upper Miocene, apparently through igneous growth to create the up to 15 km crustal thickness. The H-VP correlation of the spur is low, indicating constant and moderate-degree mantle melting not tied to the breakup magmatism. The admittance function between bathymetry and free-air gravity shows that the high is near local isostatic equilibrium, discounting that compressional flexure at the EJMFZ shaped the high. We also find no evidence for the proposed Early Eocene triple junction in the area.

  20. Magmatic carbon dioxide emissions at Mammoth Mountain, California

    Science.gov (United States)

    Farrar, Christopher D.; Neil, John M.; Howle, James F.

    1999-01-01

    Carbon dioxide (CO2) of magmatic origin is seeping out of the ground in unusual quantities at several locations around the flanks of Mammoth Mountain, a dormant volcano in Eastern California. The most recent volcanic activity on Mammoth Mountain was steam eruptions about 600 years ago, but seismic swarms and long-period earthquakes over the past decade are evidence of an active magmatic system at depth. The CO2 emission probably began in 1990 but was not recognized until 1994. Seismic swarms and minor ground deformation during 1989, believed to be results of a shallow intrusion of magma beneath Mammoth Mountain, probably triggered the release of CO2, which persists in 1998. The CO2 gas is at ambient temperatures and emanates diffusely from the soil surface rather than flowing from distinct vents. The CO2 has collected in the soil by displacing air in the pore spaces and reaches concentrations of greater than 95 percent by volume in places. The total area affected by high CO2 concentrations and high CO2 flux from the soil surface was estimated at 60 hectares in 1997. Coniferous forest covering about 40 hectares has been killed by high CO2 concentrations in the root zone. In more than 300 soil-gas samples collected from depths of 0.5 to 2 m in 1995, CO2 concentrations ranged from background levels (less than 1 percent) to greater than 95 percent by volume. At 250 locations, CO2 flux was measured using a closed chamber in 1996; values, in grams per square meter per day, ranged from background (less than 25) to more than 30,000. On the basis of these data, the total emission of magmatic CO2 in 1996 is estimated to be about 530 megagrams per day. Concentrations of CO2 exceeding Occupational Safety and Health Administration standards have been measured in pits dug in soil and snow, in poorly ventilated buildings, and in below-ground valve-boxes around Mammoth Mountain. CO2 concentrations greater than 10 percent in poorly ventilated spaces are not uncommon on some parts

  1. The Nokomis Cu-Ni-PGE Deposit, Duluth Complex: A sulfide-bearing, crystal-laden magmatic slurry

    Science.gov (United States)

    Peterson, D. M.

    2009-12-01

    deposit. A fundamental aspect of the ever-developing ore deposit model is an understanding of the initial conditions of the magmatic system - its crystallinity, sulfur capacity, geochemistry, and geometry - and how the sulfur saturated SKI magma lived, worked, and died. Such understanding includes the realization that the magma was a crystal-liquid (silicate and sulfide liquids) slurry and the identification of magma channelways and sub-channels and their associated thermal anomalies. In addition, the SKI magmas locally melted the footwall granitoid rocks, and such melts have been incorporated into the sulfide-bearing troctolitic melts of the SKI. In the end, hard work (>16,000 outcrops mapped, ~20,000 geochemical analyses completed, and >155,000 meters of core drilled) and intellectual geologic thought has been used to identify one of the world’s largest resources of Cu-Ni-PGEs.

  2. Orogenic potassic mafic magmatism, a product of alkaline-peraluminous mixing ? Variscan 'calc-alkaline' rocks from the Central Iberian and Ossa Morena Zones, Central Spain.

    Science.gov (United States)

    Scarrow, Jane H.; Cambeses, Aitor; Bea, Fernando; Montero, Pilar; Molina, José F.; Moreno, Juan Antonio

    2013-04-01

    Orogenic magmatic rocks provide information about mantle and crust melt-generation and -interaction processes. In this context, minor potassic mafic stocks which are formed of enriched mantle and crustal components and are common as late-orogenic intrusions in granitic plutons give insight into the timing of new crust formation and crustal recycling. Potassic mafic stocks are prevalent, albeit low volume, constituents of granite batholiths all through the European Variscan (350-280 Ma). In the Central Iberia Zone, Spanish Central System, crustal-melt, S-type, granitoid plutons are intruded by minor concomitant ultramafic-intermediate appinitic-vaugneritic stocks. Notwithstanding their whole-rock calc-alkaline composition, the stocks apparently did not have a subduction-related origin. Recent studies have attributed their genesis to mixing of alkaline mantle and peraluminous crustal melts. Their primary alkaline character, as indicated by amphibole and biotite mineral chemistry data, points, rather, towards an extension-related genesis. In the Ossa Morena Zone, south of the Central Iberian Zone, the igneous rocks also have a whole-rock calc-alkaline composition which has been considered to be the result of northward subduction of the South Portuguese Zone. Nevertheless, identification of a 'sill' of significant volume of mafic magma in the middle crust, the ´IBERSEIS reflective body', in a seismic profile across the Ossa Morena and South Portuguese Zones has cast doubt upon the calc-alkaline magmatism-subduction model; leading, instead, to the magmatism being attributed to intra-orogenic extension related to a mantle plume active from 340 Ma to 330 Ma. The aim here, then, is to reinvestigate the petrogenesis and age of the calc-alkaline rocks of the Ossa Morena Zone to determine their tectonomagmatic context be it subduction-, plume- or extension-related, and establish what they may reveal about mantle-crust interactions. Focussing, initially, on the Valencia del

  3. U-Th-Pb systematics of some granitoids from the northeastern Yilgarn Block, Western Australia and implications for uranium source rock potential

    Energy Technology Data Exchange (ETDEWEB)

    Stuckless, J S; Nkomo, I T [Geological Survey, Denver, CO (USA); Bunting, J A [Geological Survey of Western Australia, Perth

    1981-11-01

    The Mount Boreas-type granite and spatially associated syenitic granitoid of Western Australia yield Pb-Pb ages of 2370 +- 100 Ma and 2760 +- 210 Ma, respectively. Th-Pb ages, although less precise, are concordant with these ages, and therefore the apparent ages are interpreted to be the crystallisation ages for these two units. U-Pb ages are variable and for the most part anomalously old, which suggests a Cainozoic uranium loss. However, this loss is generally small (3..mu..g/g); therefore, neither granitoid in its fresh state provides a good source for nearby calcrete-hosted uranium deposits. The possibility remains that the Mount Boreas-type granite that has been completely weathered during the Tertiary could have been a source for the calcrete-type uranium deposits in W.A. Although the Mount Boreas-type granite is highly fractionated, it does not bear a strong geochemical imprint of a sedimentary precursor. This feature contrasts it with apparently fresh granitoids from other parts of the world that have lost large amounts of uranium (approx. 20..mu..g/g) and are associated with large roll-type and other low temperature-type uranium deposits.

  4. A-type granitoid in Hasansalaran complex, northwestern Iran: Evidence for extensional tectonic regime in northern Gondwana in the Late Paleozoic

    Science.gov (United States)

    Azizi, Hossein; Kazemi, Tahmineh; Asahara, Yoshihiro

    2017-07-01

    The Hasansalaran plutonic complex is one of the main intrusive bodies with a wide range of granite, monzonite, diorite and syenite that crop out in northwest Iran. This body includes Paleozoic granitoids that are surrounded and cut by Cretaceous granitoids. Zircon U-Pb age dating shows that the crystallization of this body occurred at 360 Ma ago in the Early Carboniferous. Whole rock compositions of the investigated intrusive body, show high contents of Ga (11.1-76.3 ppm), Zr (73.5-1280 ppm), Zn (43.7-358 ppm), Y(17.9-177 ppm), enrichment of rare earth elements (REEs) together with high Ga/Al ratios and a strong Eu negative anomaly, fairly consistent with typical A-type signature. The low εNd(t = 360 Ma) value (model for evolution of northwest Iran in the Late Paleozoic. Based on our model, the upwelling of a mantle plume, probably due to the proto-Tethys oceanic rollback activity beneath northern Gondwana, had a crucial role in the uplifting of the continental crust and resulted in the crystallization of A-type granitoids with some gabbroic rocks in northwest Iran.

  5. Hot subduction: Magmatism along the Hunter Ridge, SW Pacific

    International Nuclear Information System (INIS)

    Crawford, A.J.; Verbeeten, A.; Danyushevsky, L.V.; Sigurdsson, I.A.; Maillet, P.; Monzier, M.

    1997-01-01

    The Hunter 'fracture zone' is generally regarded as a transform plate boundary linking the oppositely dipping Tongan and Vanuatu subduction systems. Dredging along the Hunter Ridge and sampling of its northernmost extent, exposed as the island of Kadavu in Fiji, has yielded a diversity of magmatic suites, including arc tholeiites and high-Ca boninites, high-Mg lavas with some affinities to boninites and some affinities to adakites, and true adakitic lavas associated with remarkable low-Fe, high-Na basalts with 8-16 ppm Nb (herein high-Nb basalts). Lavas which show clear evidence of slab melt involvement in their petrogenesis occur at either end of the Hunter Ridge, whereas the arc tholeiites and high-Ca boninites appear to be restricted to the south central part of the ridge. Mineralogical and whole rock geochemical data for each of these suites are summarized, and a tectono-magmatic model for their genesis and distribution is suggested. Trace element features and radiogenic isotope data for the Hunter Ridge lavas indicate compositions analogue to Pacific MORB-like mantle

  6. Genetic relationships between skarn ore deposits and magmatic activity in the Ahar region, Western Alborz, NW Iran

    Directory of Open Access Journals (Sweden)

    Mollai Habib

    2014-06-01

    Full Text Available Paleocene to Oligocene tectonic processes in northwest Iran resulted in extensive I-type calc-alkaline and alkaline magmatic activity in the Ahar region. Numerous skarn deposits formed in the contact between Upper Cretaceous impure carbonate rocks and Oligocene-Miocene plutonic rocks. This study presents new field observations of skarns in the western Alborz range and is based on geochemistry of igneous rocks, mineralogy of the important skarn deposits, and electron microprobe analyses of skarn minerals. These data are used to interpret the metasomatism during sequential skarn formation and the geotectonic setting of the skarn ore deposit related igneous rocks. The skarns were classified into exoskarn, endoskarn and ore skarn. Andraditic garnet is the main skarn mineral; the pyroxene belongs to the diopside-hedenbergite series. The skarnification started with pluton emplacement and metamorphism of carbonate rocks followed by prograde metasomatism and the formation of anhydrous minerals like garnet and pyroxene. The next stage resulted in retro gradation of anhydrous minerals along with the formation of oxide minerals (magnetite and hematite followed by the formation of hydrosilicate minerals like epidote, actinolite, chlorite, quartz, sericite and sulfide mineralization. In addition to Fe, Si and Mg, substantial amounts of Cu, along with volatile components such as H2S and CO2 were added to the skarn system. Skarn mineralogy and geochemistry of the igneous rocks indicate an island arc or subduction-related origin of the Fe-Cu skarn deposit.

  7. Variability of orogenic magmatism during Mediterranean-style continental collisions : A numerical modelling approach

    NARCIS (Netherlands)

    Andrić, N.; Vogt, K.; Matenco, L.; Cvetković, V.; Cloetingh, S.; Gerya, T.

    The relationship between magma generation and the tectonic evolution of orogens during subduction and subsequent collision requires self-consistent numerical modelling approaches predicting volumes and compositions of the produced magmatic rocks. Here, we use a 2D magmatic-thermomechanical numerical

  8. Magmatic activity stages of the El'brus volcanic center (Great Caucasus): isotope geochronological data

    International Nuclear Information System (INIS)

    Chernyshev, I.V.; Lebedev, V.A.; Bubnov, S.N.; Arakelyants, M.M.; Gol'tsman, Yu.V.

    2001-01-01

    The age of volcanites in the Elbrus volcanic center was determined by the methods of K-Ar- and Rb-Sr-dating to ascertain stages of magmatic activity in the area. The data obtained suggest existence of at least two stages of magmatic activity: Middle Neopleistocene (225-180 thous. years) and Late Neopleistocene-Holocene ( [ru

  9. A Palaeoproterozoic tectono-magmatic lull as a potential trigger for the supercontinent cycle

    Science.gov (United States)

    Spencer, Christopher J.; Murphy, J. Brendan; Kirkland, Christopher L.; Liu, Yebo; Mitchell, Ross N.

    2018-02-01

    The geologic record exhibits periods of active and quiescent geologic processes, including magmatism, metamorphism and mineralization. This apparent episodicity has been ascribed either to bias in the geologic record or fundamental changes in geodynamic processes. An appraisal of the global geologic record from about 2.3 to 2.2 billion years ago demonstrates a Palaeoproterozoic tectono-magmatic lull. During this lull, global-scale continental magmatism (plume and arc magmatism) and orogenic activity decreased. There was also a lack of passive margin sedimentation and relative plate motions were subdued. A global compilation of mafic igneous rocks demonstrates that this episode of magmatic quiescence was terminated about 2.2 billion years ago by a flare-up of juvenile magmatism. This post-lull magmatic flare-up is distinct from earlier such events, in that the material extracted from the mantle during the flare-up yielded significant amounts of continental material that amalgamated to form Nuna — Earth's first hemispheric supercontinent. We posit that the juvenile magmatic flare-up was caused by the release of significant thermal energy that had accumulated over some time. This flux of mantle-derived energy could have provided a mechanism for dramatic growth of continental crust, as well as the increase in relative plate motions required to complete the transition to modern plate tectonics and the supercontinent cycle. These events may also be linked to Palaeoproterozoic atmospheric oxygenation and equilibration of the carbon cycle.

  10. Magmatic control along a strike-slip volcanic arc: The central Aeolian arc (Italy)

    KAUST Repository

    Ruch, Joel; Vezzoli, L.; De Rosa, R.; Di Lorenzo, R.; Acocella, V

    2016-01-01

    -slip motion; consistent with an E-W extension direction, with minor dextral and sinistral shear. Our data highlight six eruptive periods during the last 55 ka, which allow considering both islands as a single magmatic system, in which tectonic and magmatic

  11. Magmatic Hydrothermal Fluids: Experimental Constraints on the Role of Magmatic Sulfide Crystallization and Other Early Magmatic Processes in Moderating the Metal Content of Ore-Forming Fluids

    Science.gov (United States)

    Piccoli, P. M.; Candela, P. A.

    2006-05-01

    It has been recognized for some time that sulfide phases, although common in intermediate-felsic volcanic rocks, are not as common in their plutonic equivalents. That sulfide crystallization, or the lack thereof, is important in the protracted magmatic history of porphyry Cu and related systems is supported by the work of e.g., Rowins (2000). Candela and Holland (1986) suggested that sulfide crystallization could moderate the ore metal concentrations in porphyry environments. Experiments show clearly that Au and Cu can partition into Cl-bearing vapor and brine. This effect can be enhanced by S (Simon, this session). However, in some instances enhances this effect. That is, the partitioning of Au and Cu into vapor+brine is highly efficient (e.g. Simon et al. 2003; Frank et al 2003). This suggests that if sulfides do not sequester ore metals early during the history of a magma body from the melt, they will partition strongly into the volatile phases. Whether volatile release occurs in the porphyry ore environment, or at deeper levels upon magma rise, is a yet unsolved question. Little is known about deep release of volatiles (during magma transport at lower- to mid-crustal levels). Saturation of melts with a CO2-bearing fluid could happen at levels much deeper than those typical of ore formation. CO2 is released preferentially, so a high CO2 concentration in fluids in the porphyry ore environment argues against deep fluid release. Of course, this depends upon the specific processes of crystallization and fluid release, which may be complex. Our experiments on sulfides have concentrated on pyrrhotite and Iss. Our partitioning data for Po/melt exhibit wide variations from metal to metal: Cu (2600); Co (170); Au (140); Ni (100); Bi, Zn and Mn (2). These results suggest that crystallization of Po can contribute to variable ore metal ratios (e.g. Cu/Au). Other sulfides behave differently. If a melt is Iss (Cpy) saturated, then Cu will be buffered at a high value, and Au

  12. Natural radioactivity (226Ra, 232Th and 40K) and assessment of radiological hazards in the Kestanbol granitoid, Turkey.

    Science.gov (United States)

    Canbaz, Buket; Cam, N Füsun; Yaprak, Günseli; Candan, Osman

    2010-09-01

    The surveys of natural gamma-emitting radionuclides in rocks and soils from the Ezine plutonic area were conducted during 2007. Direct dose measurement using a survey meter was carried out simultaneously. The present study, which is part of the survey, analysed the activity concentrations of (238)U, (232)Th and (40)K in granitoid samples from all over the region by HPGe gamma spectrometry. The activity concentrations of (226)Ra ranged from 94 to 637 Bq kg(-1), those of (232)Th ranged from 120 to 601 Bq kg(-1)and those of (40)K ranged from 1074 to 1527 Bq kg(-1) in the analysed rock samples from different parts of the pluton. To evaluate the radiological hazard of the natural radioactivity in the samples, the absorbed dose rate (D), the annual effective dose rate, the radium equivalent activity (Ra(eq)) and the external (H(ex)) hazard index were calculated according to the UNSCEAR 2000 report. The thorium-to-uranium concentration ratios were also estimated.

  13. Oxygen and U-Th isotopes and the timescales of hydrothermal exchange and melting in granitoid wall rocks at Mount Mazama, Crater Lake, Oregon

    Science.gov (United States)

    Ankney, Meagan E.; Bacon, Charles R.; Valley, John W.; Beard, Brian L.; Johnson, Clark M.

    2017-01-01

    We report new whole rock U-Th and in-situ oxygen isotope compositions for partially melted (0–50 vol% melt), low-δ18O Pleistocene granitoid blocks ejected during the ∼7.7 ka caldera-forming eruption of Mt. Mazama (Crater Lake, Oregon). The blocks are interpreted to represent wall rocks of the climactic magma chamber that, prior to eruption, experienced variable amounts of exchange with meteoric hydrothermal fluids and subsequent partial melting. U-Th and oxygen isotope results allow us to examine the timescales of hydrothermal circulation and partial melting, and provide an “outside in” perspective on the buildup to the climactic eruption of Mt. Mazama. Oxygen isotope compositions measured in the cores and rims of individual quartz (n = 126) and plagioclase (n = 91) crystals, and for transects across ten quartz crystals, document zonation in quartz (Δ18OCore-Rim ≤ 0.1–5.5‰), but show homogeneity in plagioclase (Δ18OCore-Rim ≤ ±0.8‰). We propose that oxygen isotope zonation in quartz records hydrothermal exchange followed by high-temperature exchange in response to partial melting caused by injection of basaltic to andesitic recharge magma into the deeper portions of the chamber. Results of modeling of oxygen diffusion in quartz indicates that hydrothermal exchange in quartz occurred over a period of ∼1000–63,000 years. Models also suggest that the onset of melting of the granitoids occurred a minimum of ∼10–200 years prior to the Mazama climactic eruption, an inference which is broadly consistent with results for magnetite homogenization and for Zr diffusion in melt previously reported by others.Uranium-thorium isotope compositions of most granitoid blocks are in 238U excess, and are in agreement with a 238U enriched array previously measured for volcanic rocks at Mt. Mazama. Uranium excess in the granitoids is likely due to enrichment via hydrothermal circulation, given their low δ18O values. The sample with the

  14. Magmatic and non-magmatic history of the Tyrrhenain backarc Basin: new constraints from geophysical and geological data

    Science.gov (United States)

    Prada, Manel; Sallares, Valenti; Ranero, Cesar R.; Zitellini, Nevio; Grevemeyer, Ingo

    2016-04-01

    The Western Mediterranean region is represented by a system of backarc basins associated to slab rollback and retreat of subduction fronts. The onset of formation of these basins took place in the Oligocene with the opening of the Valencia Through, the Liguro-Provençal and the Algero-Balearic basins, and subsequently, by the formation of the Alboran and Tyrrhenian basins during the early Tortonian. The opening of these basins involved rifting that in some regions evolved until continental break up, that is the case of the Liguro-Provençal, Algero-Balearic, and Tyrrhenian basins. Previous geophysical works in the first two basins revealed a rifted continental crust that transitions to oceanic crust along a region where the basement nature is not clearly defined. In contrast, in the Tyrrhenian Basin, recent analysis of new geophysical and geological data shows a rifted continental crust that transitions along a magmatic-type crust to a region where the mantle is exhumed and locally intruded by basalts. This basement configuration is at odds with current knowledge of rift systems and implies rapid variations of strain and magma production. To understand these processes and their implications on lithospheric backarc extension we first need to constrain in space and time these observations by further analysis of geophysical and geological data. Here we present two analyses; the first one is focused on the spatial variability of magmatism along the Cornaglia Terrace axis, where magmatic-type crust has been previously interpreted. The comparison of three different seismic refraction transects, acquired across the basin axis from North to South, allows to infer that the highest magmatic activity occurred beneath the central and most extended region of the terrace; while it was less important in the North and almost non-existent in the South. The second analysis focuses on the presence of exhumed mantle in the deepest region of the Tyrrhenian, previously interpreted by

  15. Flux tubes and the type-I/type-II transition in a superconductor coupled to a superfluid

    International Nuclear Information System (INIS)

    Alford, Mark G.; Good, Gerald

    2008-01-01

    We analyze magnetic-flux tubes at zero temperature in a superconductor that is coupled to a superfluid via both density and gradient ('entrainment') interactions. The example we have in mind is high-density nuclear matter, which is a proton superconductor and a neutron superfluid, but our treatment is general and simple, modeling the interactions as a Ginzburg-Landau effective theory with four-fermion couplings, including only s-wave pairing. We numerically solve the field equations for flux tubes with an arbitrary number of flux quanta and compare their energies. This allows us to map the type-I/type-II transition in the superconductor, which occurs at the conventional κ≡λ/ξ=1/√(2) if the condensates are uncoupled. We find that a density coupling between the condensates raises the critical κ and, for a sufficiently high neutron density, resolves the type-I/type-II transition line into an infinite number of bands corresponding to 'type-II(n)' phases, in which n, the number of quanta in the favored flux tube, steps from 1 to infinity. For lower neutron density, the coupling creates spinodal regions around the type-I/type-II boundary, in which metastable flux configurations are possible. We find that a gradient coupling between the condensates lowers the critical κ and creates spinodal regions. These exotic phenomena may not occur in nuclear matter, which is thought to be deep in the type-II region but might be observed in condensed-matter systems

  16. Magmatism and petroleum exploration in the Brazilian Paleozoic basins

    Energy Technology Data Exchange (ETDEWEB)

    Thomaz Filho, Antonio; Antonioli, Luzia [Universidade do Estado do Rio de Janeiro, Faculdade de Geologia, Rua Sao Francisco Xavier, no 524/2030, CEP 20550-900, Rio de Janeiro, RJ (Brazil); Mizusaki, Ana Maria Pimentel [Universidade Federal do Rio Grande do Sul, Instituto de Geociencias, Avenida Bento Goncalves, no 9500, Campus do Vale, CEP 91509-900, Porto Alegre, RS (Brazil)

    2008-02-15

    Petroleum exploration in the Paleozoic sedimentary basins of Brazil has proven very challenging for explorationists. Except for the Solimoes Basin, in which transcurrent tectonism formed prospective structural highs, Brazilian Paleozoic basins lack intense structural deformation, and hence the detection and prospecting of place is often difficult. Magmatic intrusive and associated rocks in all these basins have traditionally been considered heat sources and hydrocarbon traps. The role of tholeiitic basic dikes in the generation, migration and accumulation of petroleum in the Anhembi oil occurrence (Sao Paulo State) is discussed herein. It follows that similar geological settings in other Paleozoic basins can be regarded as promising sites for oil accumulation that warrant investigation via modern geological and geophysical methods. (author)

  17. Uranium metallogeny, magmatism and structure in southeast China

    International Nuclear Information System (INIS)

    Simpson, P.R.

    1989-01-01

    Granite magmatism and the associated uranium metallogeny in southeast China are considered in relation to a plate tectonic model previously developed for Jiangxi Province which envisages the suturing of three separate continental fault blocks or plates which are thought to have existed as separate continental microplates until the Permian, namely the Sino-Korean, Yangtze and South China Plates. In Jiangxi Province, most of the granitic magmas, including those considered in the paper to be associated with U ore deposits, can be shown to be systematically distributed in relation to the postulated destructive plate margins which are thought to have existed along all the plate boundaries between the continental microplates. The granitic intrusions in Jiangxi range from those more proximal to the inferred location of the subduction zone in a modified Andean type model, such as porphyries of Cu, Cu-Mo and W-Cu type, to more distal granites of U-W-Sn-F-Nb-REE type. They range in age from Indosinian to Yanshanian (but mainly the latter) and are intruded in tensional settings along major lithospheric fracture zones, with sinistral strike slip, many of which continued to move both during and after granite emplacement. These U, W, Sn, F, Nb and REE rich metalliferous granites, which all intruded post-tectonically long after the principal metamorphic events, which are Jinningian (Late Proterozoic on the Yangtze Plate) and Caledonian (South China Plate), and the younger suturing events, are considered in the study to be essentially of juvenile magmatic rather than crustal origin. Such a tectonic model helps to account for the well developed and structurally zoned metallogeny of southeast China and the genesis of the Southeast China Uranium Province. Selected examples of U ore deposits which occur within the Southeast China Uranium Province are considered in order to develop the basis for a genetic model for U which would be more generally applicable to this region and possibly

  18. The mineralogy and petrology of I-type cosmic spherules: Implications for their sources, origins and identification in sedimentary rocks

    Science.gov (United States)

    Genge, Matthew J.; Davies, Bridie; Suttle, Martin D.; van Ginneken, Matthias; Tomkins, Andrew G.

    2017-12-01

    I-type cosmic spherules are micrometeorites that formed by melting during atmospheric entry and consist mainly of iron oxides and FeNi metal. I-types are important because they can readily be recovered from sedimentary rocks allowing study of solar system events over geological time. We report the results of a study of the mineralogy and petrology of 88 I-type cosmic spherules recovered from Antarctica in order to evaluate how they formed and evolved during atmospheric entry, to constrain the nature of their precursors and to establish rigorous criteria by which they may be conclusively identified within sediments and sedimentary rocks. Two textural types of I-type cosmic spherule are recognised: (1) metal bead-bearing (MET) spherules dominated by Ni-poor (100 and suggest that metal from H-group ordinary, CM, CR and iron meteorites may form the majority of particles. Oxidation during entry heating increases in the series MET 80 wt% Ni comprising a particle mass fraction of exchange of Ni between wüstite and metal, and magnetite and wüstite are suggested as proxies for the rate of oxidation and cooling rate respectively. Variations in magnetite and wüstite crystal sizes are also suggested to relate to cooling rate allowing relative entry angle of particles to be evaluated. The formation of secondary metal in the form of sub-micron Ni-rich or Pt-group nuggets and as symplectite with magnetite was also identified and suggested to occur largely due to the exsolution of metallic alloys during decomposition of non-stoichiometric wüstite. Weathering is restricted to replacement of metal by iron hydroxides. The following criteria are recommended for the conclusive identification of I-type spherules within sediments and sedimentary rocks: (i) spherical particle morphologies, (ii) dendritic crystal morphologies, (iii) the presence of wüstite and magnetite, (iv) Ni-bearing wüstite and magnetite, and (v) the presence of relict FeNi metal.

  19. Petrology, geochemistry and LA-ICP-MS U-Pb geochronology of Paleoproterozoic basement rocks in Bangladesh: An evaluation of calc-alkaline magmatism and implication for Columbia supercontinent amalgamation

    Science.gov (United States)

    Hossain, Ismail; Tsunogae, Toshiaki; Tsutsumi, Yukiyasu; Takahashi, Kazuki

    2018-05-01

    The Paleoproterozoic (1.7 Ga) basement rocks from Maddhapara, Bangladesh show a large range of chemical variations (e.g. SiO2 = 50.7-74.7%) and include diorite, quartz diorite, monzodiorite, quartz monzonite and granite. The pluton overall displays metaluminous, calc-alkaline orogenic suite; mostly I-type suites formed within subduction-related magmatism. The observed major elements show general trends for fractional crystallization. Trace element contents also indicate the possibility of a fractionation or assimilation; explain the entire variation from diorite to monzonite, even granite. The pluton may have evolved the unique chemical features by a process that included partial melting of calc-alkaline lithologies and mixing of mantle-derived magmas, followed by fractional crystallization, and by assimilation of country rocks. The pluton shows evidence of crystal fractionation involving largely plagioclase, amphibole and possibly biotite. Some of the fractionated magmas may have mixed with more potassic melts from distinct parts of the continental lithosphere to produce granites and/or pegmatites. New geochronological results of granitic pegmatite (1722 ± 10 Ma) are indisputably consistent with diorite and tonalite and those data showing credible geochronological sequence (i.e., diorite - tonalite - granitic pegmatite). Identical Paleoproterozoic age (1.7 Ga) with distinctive magmatism of the Maddhapara basement rocks have agreeable relationship with the CITZ, India. The consistent magmatism is also common in the Transamazonian of South America, Trans-Hudson orogeny in North America, Bohemian Massif and the Svecofennian, Poland, have identified the sequential growth of the continent through the amalgamation of juvenile terrains, succeeded by a major collisional orogeny. Such Paleoproterozoic subduction-related orogens in Australia have similar counterparts in Antarctica and other part of the world. These types of Paleoproterozoic magmatism dominantly contributed

  20. K-Ar age and tectonic setting of brannerite-mineralized Futagojima granodiorite, Koshiki Islands, Southern Kyushu

    International Nuclear Information System (INIS)

    Ishihara, Shunso; Shibata, Ken; Terashima, Shigeru

    1984-01-01

    Futagojima granodiorite, which was previously thought to be a part of Cretaceous Ryoke granitoids, is turned out to be upper Miocene granitoids (7.5 Ma). The granodiorite contains magnetite and is depleted in lithophile components. This is characteristics of magnetite-series granitoids in the Green Tuff terrains. All the Miocene granitoids in Koshiki Islands are relatively mafic consisting of hornblende-bearing facies such as quartz diorite, tonalite and granodiorite; thus belonging to I-type magnetite series. These rocks are considered to have generated at depth and formed along a rift zone during Miocene time (13 - 7 Ma). Thus, Koshiki Islands may represent an aborted rift at margin of the Danjo basin. Miocene granitoids of Koshiki Islands are small stocks but magmatic-hydrothermal ore deposits are only seen in Futagojima. This localization of mineralization is explained by a high degree of magmatic fractionation, which is only observed in Futagojima and by a low rate of erosion to preserve the mineralized horizons. Mineralization here is unique having brannerite-magnetite and chalcopyrite-molybdenite-quartz assemblages. No gold and silver were detected from the vein-type deposit. (author)

  1. Mesozoic Magmatism and Base-Metal Mineralization in the Fortymile Mining District, Eastern Alaska - Initial Results of Petrographic, Geochemical, and Isotopic Studies in the Mount Veta Area

    Science.gov (United States)

    Dusel-Bacon, Cynthia; Slack, John F.; Aleinikoff, John N.; Mortensen, James K.

    2009-01-01

    We present here the initial results of a petrographic, geochemical, and isotopic study of Mesozoic intrusive rocks and spatially associated Zn-Pb-Ag-Cu-Au prospects in the Fortymile mining district in the southern Eagle quadrangle, Alaska. Analyzed samples include mineralized and unmineralized drill core from 2006 and 2007 exploration by Full Metal Minerals, USA, Inc., at the Little Whiteman (LWM) and Fish prospects, and other mineralized and plutonic samples collected within the mining district is part of the USGS study. Three new ion microprobe U-Pb zircon ages are: 210 +- 3 Ma for quartz diorite from LWM, 187 +- 3 Ma for quartz monzonite from Fish, and 70.5 +- 1.1 Ma for altered rhyolite porphyry from Fish. We also present 11 published and unpublished Mesozoic thermal ionization mass spectrometric U-Pb zircon and titanite ages and whole-rock geochemical data for the Mesozoic plutonic rocks. Late Triassic and Early Jurassic plutons generally have intermediate compositions and are slightly foliated, consistent with synkinematic intrusion. Several Early Jurassic plutons contain magmatic epidote, indicating emplacement of the host plutons at mesozonal crustal depths of greater than 15 km. Trace-element geochemical data indicate an arc origin for the granitoids, with an increase in the crustal component with time. Preliminary study of drill core from the LWM Zn-Pb-Cu-Ag prospect supports a carbonate-replacement model of mineralization. LWM massive sulfides consist of sphalerite, galena, and minor pyrite and chalcopyrite, in a gangue of calcite and lesser quartz; silver resides in Sb-As-Ag sulfosalts and pyrargyrite, and probably in submicroscopic inclusions within galena. Whole-rock analyses of LWM drill cores also show elevated In, an important metal in high-technology products. Hypogene mineralized rocks at Fish, below the secondary Zn-rich zone, are associated with a carbonate host and also may be of replacement origin, or alternatively, may be a magnetite

  2. The Magmatic Budget of Rifted Margins: is it Related to Inheritance?

    Science.gov (United States)

    Manatschal, G.; Tugend, J.; Gillard, M.; Sauter, D.

    2017-12-01

    High quality reflection and refraction seismic surveys show a divergent style of margin architecture often referred to as magma-poor or magma-rich. More detailed studies show, however, that the evolution of these margins can be similar, despite the variable quantity and distribution of magmatism. These observations suggest that simple relations between magmatic and extensional systems are inappropriate to describe the magmatic history of rifted margins. Moreover, the study of magmatic additions indicates that they may occur, prior to, during or after lithospheric breakup. Furthermore, the observation that the magmatic budget may change very abruptly along strike and across the margin is difficult to reconcile with the occurrence of plumes or other deep-seated large-scale mantle phenomena only. These overall observations result in questions on how magmatic and tectonic processes are interacting during rifting and lithospheric breakup and on how far the inherited composition and temperature of the decompressing mantle may control the magmatic budget during rifting. In our presentation we will review examples from present-day and fossil rifted margins to discuss their structural and magmatic evolution and whether they are considered as magma-rich or magma-poor. The key questions that we aim to address are: 1) whether decompression melting is the driving force, or rather the consequence of extension, 2) how far the magmatic budget is controlled by inherited mantle composition and temperature, and 3) how important magma storage is during initial stages of rifting. Eventually, we will discuss to what extent the evolution of margins may reflect the interplay between inheritance (innate/"genetic code") and the actual physical processes (acquired/external factors).

  3. Petrological mineralogical and geochemical characterization of the granitoids and fracture fillings developed in Ratones Mines (Spain); Caracterizacion petrologica, mineralogica, geoquimica y evaluacion del comportamiento geoquimico de las REE en la fase solida (granitoides y rellenos fisurales) del sistema de interaccion agua-roca delentorno de la Mina Ratones

    Energy Technology Data Exchange (ETDEWEB)

    Buil Gutierrez, B [Ciemat. Madrid (Spain)

    2002-07-01

    The petrological, mineralogical and geochemical characterisation of the granitoids and fracture fillings developed in the Ratones Mine (Caceres, Spain) has been done in order to understand rock-water interaction processes which control water geochemical parameters. Special interest has been devoted to the analysis and interpretation of REE patterns in the solid phase (granitoids and fracture fillings) because they constitute geochemical tracers in water-rock interaction process. Moreover, REE are considered as actinide analogues. In order to characterise the solid phase (granitoids and fracture fillings) several investigation scales (system, outcrop, whole rock, mineral and geochemical components) have been considered and different types of samples have been analysed. These factors control the methodological approach used in this investigation. The analytical methods we have used in this investigation are microscope, qualitative and semi-quantitative methods (XRD, SEM,EDAX) and quantitative methods (ICP-MS, XRF, EM, LAM-IC-MS). The bulk of the granitoids located around the Ratones Mine Belongs to the alkaline feldspar granite-sienogranite lihotype and they show a peraluminous and subalkaline pattern. From the mineralogical point of view, they are composed by quartz, K-feldspar (Or>90%), showing sericitation, moscovitization and turmolinization altherations, alkaline plagioclase (An-=-3%), usually altered to sericite, saussirite and less frequently affected by moscovitization processes, Fe-Al biotite, frequently affected by chloritization processes and sometimes replaced by muscovite, and finally muscovite (>2% celadonite and <4% paragonite) both of primary and secondary origin. The differences observed between the different lithotypes are related with the modal proportion of the principal minerals,with the presence or absence of certain accessory minerals ( turmaline, cordierite), with specific textural patterns, grain size and also with the richness in specific

  4. Comparison of the distribution of large magmatic centers on Earth, Venus, and Mars

    Science.gov (United States)

    Crumpler, L. S.

    1993-01-01

    Volcanism is widely distributed over the surfaces of the major terrestrial planets: Venus, Earth, and Mars. Anomalous centers of magmatic activity occur on each planet and are characterized by evidence for unusual concentrations of volcanic centers, long-lived activity, unusual rates of effusion, extreme size of volcanic complexes, compositionally unusual magmatism, and evidence for complex geological development. The purpose of this study is to compare the characteristics and distribution of these magmatic anomalies on Earth, Venus, and Mars in order to assess these characteristics as they may relate to global characteristics and evolution of the terrestrial planets.

  5. Tectono-metamorphic evolution and magmatic processes in the thermo-metamorphic aureole of the Monte Capanne pluton (Elba Island, Northern Tyrrhenian Sea, Italy).

    Science.gov (United States)

    Morelli, M.; Pandeli, E.; Principi, G.

    2003-04-01

    Introduction In this work we present new structural and petrographic data collected in the thermo-metamorphic aureole of Monte Capanne (western Elba Island) and its metamorphic evolution. In the western Elba Island the Monte Capanne monzogranitic body (ca. 7 Ma) and its thermo-metamorphic aureole crop out. At least two different tectonic units can be distinguished: the Punta Le Tombe Unit, weak re-crystallized, and the Punta Nera Unit. In the latter one the re-crystallization is strong and a pre-intrusion tectono-metamorphic framework is evident (Morelli et al., 2002). The latter is mainly constituted by thermo-metamorphosed meta-ophiolites and meta-sedimentary successions previously correlated by Barberi et al. (1969) with the un-metamorphic ones (Complex IV and V of Trevisan, 1950) cropping out in the central-eastern Elba. According to Perrin (1975) and Reutter &Spohn (1982) a pre-intrusion tectono-metamorphic framework was recognized into such rocks. As suggested by Daniel &Jolivet (1995) complex relationships between metamorphic evolution and magmatic events are also recognizable. Geological Data The Punta Nera Unit crops out all around the Monte Capanne magmatic body and the primary contact with the underlying granitoid is somewhere preserved. This unit, strongly re-crystallized and locally crosscut by aplitic and porphyritic dikes, is represented by (Coli &Pandeli, 1997; Morelli, 2000) tectonized meta-serpentinites, meta-gabbros with rodingitic dikes, rare meta-basalts and meta-ophicalcites, meta-cherts, marbles, cherty meta-limestones, phyllites and meta-limestones with rare meta-arenites intercalations. A "pre-magmatic" tectono-metamorphic framework of this unit is well evident only in its meta-sedimentary portion. The meta-sediments are deformed by syn-metamorphic isoclinal folds caractherized by N-S trending axes, west dipping axial planes and easternward vergence. A later folding and flattening event clearly post-dated the above said folds and associated

  6. A cryptic Early Palaeozoic event in the Nacea Antiform? 40Ar/39Ar amphibole data in the Puente de Selce granitoid

    OpenAIRE

    Gutiérrez Alonso, Gabriel; Fernández Suárez, Javier; Ortega Rivera, M. A.; Lee, J. k. W.; Murphy, J. B.

    2005-01-01

    Las edades 40Ar/39Ar obtenidas a partir de anfíboles del granitoide Neoproterozoico de Puente de Selce, localizado en el Antiforme del Narcea junto con la existencia de fábricas de deformación relictas generadas en condiciones de media-alta temperatura en las mismas rocas puede ser interpretada como debida a un evento críptico de edad Paleozoico Inferior fuertemente retrabajado durante la deformación varisca. La naturaleza y la cinemática de este posible evento no pueden precisarse pero si se...

  7. A cryptic Early Palaeozoic event in the Narcea Antiform? 40Ar/39Ar amphibole data in the Puente de Selce granitoid

    OpenAIRE

    Gutiérrez Alonso, Gabriel; Fernández Suárez, J.; Keppie, J. D.; Ortega Rivera, M. A.; Lee, J. K. W.; Murphy, J. B.

    2005-01-01

    Las edades 40Ar/39Ar obtenidas a partir de anfíboles del granitoide Neoproterozoico de Puente de Selce, localizado en el Antiforme del Narcea junto con la existencia de fábricas de deformación relictas generadas en condiciones de media-alta temperatura en las mismas rocas puede ser interpretada como debida a un evento críptico de edad Paleozoico Inferior fuertemente retrabajado durante la deformación varisca. La naturaleza y la cinemática de este posible evento no pueden precisars...

  8. Geochronology Intermediary Laboratory implantation at the Rio Grande do Norte Federal University: the dating of the Serrinha Granitoid (RN) and the correlate Brasiliana extensional deformation

    International Nuclear Information System (INIS)

    Macedo, Maria Helena F.; Sa, Emanuel F. Jardim de; Souza, Zorano S.; Mendes, Franklin S.; Ramalho, Karlos A.C.

    1997-01-01

    The article describes the activities developed by the Geochronology Intermediary Laboratory at the Federal University of the Rio Grande do Norte, a Brazilian university, where there were the preoccupation of establishing strategies for a geochronological development. It relates the Rubidium-Strontium (Rb/Sr) and Samarium-Neodymium (Sm/Nd) methods, describing the analysis realized in these methodologies. Afterward, it presents the geological and petrographic situation of the Granitoide de Serrinha, located at Rio Grande do Norte State, Brazil and its geochronological data

  9. Drilling to investigate processes in active tectonics and magmatism

    Science.gov (United States)

    Shervais, J.; Evans, J.; Toy, V.; Kirkpatrick, J.; Clarke, A.; Eichelberger, J.

    2014-12-01

    Coordinated drilling efforts are an important method to investigate active tectonics and magmatic processes related to faults and volcanoes. The US National Science Foundation (NSF) recently sponsored a series of workshops to define the nature of future continental drilling efforts. As part of this series, we convened a workshop to explore how continental scientific drilling can be used to better understand active tectonic and magmatic processes. The workshop, held in Park City, Utah, in May 2013, was attended by 41 investigators from seven countries. Participants were asked to define compelling scientific justifications for examining problems that can be addressed by coordinated programs of continental scientific drilling and related site investigations. They were also asked to evaluate a wide range of proposed drilling projects, based on white papers submitted prior to the workshop. Participants working on faults and fault zone processes highlighted two overarching topics with exciting potential for future scientific drilling research: (1) the seismic cycle and (2) the mechanics and architecture of fault zones. Recommended projects target fundamental mechanical processes and controls on faulting, and range from induced earthquakes and earthquake initiation to investigations of detachment fault mechanics and fluid flow in fault zones. Participants working on active volcanism identified five themes: the volcano eruption cycle; eruption sustainability, near-field stresses, and system recovery; eruption hazards; verification of geophysical models; and interactions with other Earth systems. Recommended projects address problems that are transferrable to other volcanic systems, such as improved methods for identifying eruption history and constraining the rheological structure of shallow caldera regions. Participants working on chemical geodynamics identified four major themes: large igneous provinces (LIPs), ocean islands, continental hotspot tracks and rifts, and

  10. Hydrothermal plume anomalies over the southwest Indian ridge: magmatic control

    Science.gov (United States)

    Yue, X.; Li, H.; Tao, C.; Ren, J.; Zhou, J.; Chen, J.; Chen, S.; Wang, Y.

    2017-12-01

    Here we firstly reported the extensive survey results of the hydrothermal activity along the ultra-slow spreading southwest Indian ridge (SWIR). The study area is located at segment 27, between the Indomed and Gallieni transform faults, SWIR. The seismic crustal thickness reaches 9.5km in this segment (Li et al., 2015), which is much thicker than normal crustal. The anomaly thickened crust could be affected by the Crozet hotspot or highly focused melt delivery from the mantle. The Duanqiao hydrothermal field was reported at the ridge valley of the segment by Tao et al (2009). The Deep-towed Hydrothermal Detection System (DHDS) was used to collect information related with hydrothermal activity, like temperature, turbidity, oxidation-reduction potential (ORP) and seabed types. There are 15 survey lines at the interval of 2 to 3 km which are occupied about 1300 km2 in segment 27. After processing the raw data, including wiping out random noise points, 5-points moving average processing and subtracting the ambient, we got anomalous Nephelometric Turbidity Units values (ΔNTU). And dE/dt was used to identify the ORP anomalous as the raw data is easily influenced by electrode potentials drifting (Baker et al., 2016). According to the results of water column turbidity and ORP distributions, we confirmed three hydrothermal anomaly fields named A1, A2 and A3. The three fields are all located in the western part of the segment. The A1 field lies on the ridge valley, west side of Duanqiao field. The A2 and A3 field lie on the northern and southern of the ridge valley, respectively. We propose that recent magmatic activity probably focus on the western part of segment 27.And the extensive distribution of hydrothermal plume in the segment is the result of the discrete magma intrusion. References Baker E T, et al. How many vent fields? New estimates of vent field populations on ocean ridges from precise mapping of hydrothermal discharge locations. EPSL, 2016, 449:186-196. Li J

  11. Geophysical Observations Supporting Research of Magmatic Processes at Icelandic Volcanoes

    Science.gov (United States)

    Vogfjörd, Kristín. S.; Hjaltadóttir, Sigurlaug; Roberts, Matthew J.

    2010-05-01

    Magmatic processes at volcanoes on the boundary between the European and North American plates in Iceland are observed with in-situ multidisciplinary geophysical networks owned by different national, European or American universities and research institutions, but through collaboration mostly operated by the Icelandic Meteorological Office. The terrestrial observations are augmented by space-based interferometric synthetic aperture radar (InSAR) images of the volcanoes and their surrounding surface. Together this infrastructure can monitor magma movements in several volcanoes from the base of the crust up to the surface. The national seismic network is sensitive enough to detect small scale seismicity deep in the crust under some of the voclanoes. High resolution mapping of this seismicity and its temporal progression has been used to delineate the track of the magma as it migrates upwards in the crust, either to form an intrusion at shallow levels or to reach the surface in an eruption. Broadband recording has also enabled capturing low frequency signals emanating from magmatic movements. In two volcanoes, Eyjafjallajökull and Katla, just east of the South Iceland Seismic Zone (SISZ), seismicity just above the crust-mantle boundary has revealed magma intruding into the crust from the mantle below. As the magma moves to shallower levels, the deformation of the Earth‘s surface is captured by geodetic systems, such as continuous GPS networks, (InSAR) images of the surface and -- even more sensitive to the deformation -- strain meters placed in boreholes around 200 m below the Earth‘s surface. Analysis of these signals can reveal the size and shape of the magma as well as the temporal evolution. At near-by Hekla volcano flanking the SISZ to the north, where only 50% of events are of M>1 compared to 86% of earthquakes in Eyjafjallajökull, the sensitivity of the seismic network is insufficient to detect the smallest seismicity and so the volcano appears less

  12. Magmatic and fragmentation controls on volcanic ash surface chemistry

    Science.gov (United States)

    Ayris, Paul M.; Diplas, Spyros; Damby, David E.; Hornby, Adrian J.; Cimarelli, Corrado; Delmelle, Pierre; Scheu, Bettina; Dingwell, Donald B.

    2016-04-01

    The chemical effects of silicate ash ejected by explosive volcanic eruptions on environmental systems are fundamentally mediated by ash particle surfaces. Ash surfaces are a composite product of magmatic properties and fragmentation mechanisms, as well as in-plume and atmospheric alteration processes acting upon those surfaces during and after the eruption. Recent attention has focused on the capacity of alteration processes to shape ash surfaces; most notably, several studies have utilised X-ray photoelectron spectroscopy (XPS), a technique probing the elemental composition and coordination state of atoms within the top 10 nm of ash surfaces, to identify patterns of elemental depletions and enrichments relative to bulk ash chemical composition. Under the presumption of surface and bulk equivalence, any disparities have been previously attributed to surface alteration processes, but the ubiquity of some depletions (e.g., Ca, Fe) across multiple ash studies, irrespective of eruptive origin, could suggest these to be features of the surface produced at the instant of magma fragmentation. To investigate this possibility further, we conducted rapid decompression experiments at different pressure conditions and at ambient and magmatic temperature on porous andesitic rocks. These experiments produced fragmented ash material untouched by secondary alteration, which were compared to particles produced by crushing of large clasts from the same experiments. We investigated a restricted size fraction (63-90 μm) from both fragmented and crushed materials, determining bulk chemistry and mineralogy via XRF, SEM-BSE and EPMA, and investigated the chemical composition of the ash surface by XPS. Analyses suggest that fragmentation under experimental conditions partitioned a greater fraction of plagioclase-rich particles into the selected size fraction, relative to particles produced by crushing. Trends in surface chemical composition in fragmented and crushed particles mirror that

  13. Geocronología y geoquímica isotópica (Sr, Nd) de los granitoides de Pola de Allande (Asturias): ¿Relictos de un arco magmático cadomiense en la Zona Asturoccidental Leonesa?

    OpenAIRE

    Gutiérrez Alonso, Gabriel; Fernández Suárez, Javier

    1998-01-01

    [ES] Los granitoides pre-Variscos de Pola de Allande se sitúan en el Antiforme del Narcea, en el límite entre las zonas Cantábrica y Asturoccidental Leonesa de la cadena Varisca Ibérica. Estos granitoides, formados por tonalitas y granodioritas con afinidades geoquímicas de arco magmático, intruyeron en sedimentos siliciclásticos Neoproterozoicos y fueron posteriormente afectados por la deformación tangencial Varisca. La datación U-Pb de circones de dos intrusiones por el método de Ablación L...

  14. Petrogenesis of granitoids and associated xenoliths in the early Paleozoic Baoxu and Enping plutons, South China: Implications for the evolution of the Wuyi-Yunkai intracontinental orogen

    Science.gov (United States)

    Yu, Yang; Huang, Xiao-Long; Sun, Min; He, Peng-Li

    2018-05-01

    orogenic event. These early Paleozoic granites occur near the ancient suture zone between the Yangtze and Cathaysia blocks and have high La/Yb and Sr/Y ratios, likely due to the existence of residual garnet in the source, suggesting the thickened crust at ca. 440 Ma. The 450-440 Ma gneissic S-type granites near the suture zone are earlier than those in the central part of the Cathaysia block (∼430 Ma). The crustal thickening along the ancient suture zone at 440 Ma propagated into the central part of the Cathaysia block as evidenced by the 430 Ma granites. Early Paleozoic I-type granites near the suture zone clearly show involvement of significant mantle-derived materials, in contrast to granites in the central part of the Cathaysia block. The ancient suture zone may have acted as channels for the emplacement of mafic magmas during the collapse of an intracontinental orogen.

  15. Observational constraints on the identification of shallow lunar magmatism : insights from floor-fractured craters

    OpenAIRE

    Jozwiak, Lauren; Head, James; Neumann, G. A.; Wilson, Lionel

    2017-01-01

    Floor-fractured craters are a class of lunar crater hypothesized to form in response to the emplacement of a shallow magmatic intrusion beneath the crater floor. The emplacement of a shallow magmatic body should result in a positive Bouguer anomaly relative to unaltered complex craters, a signal which is observed for the average Bouguer anomaly interior to the crater walls. We observe the Bouguer anomaly of floor-fractured craters on an individual basis using the unfiltered Bouguer gravity so...

  16. Transient magmatic control in a tectonic domain: the central Aeolian volcanic arc (South Italy)

    KAUST Repository

    Ruch, Joel; Vezzoli, Luigina; Di Lorenzo, Riccardo; De Rosa, Rosanna; Acocella, Valerio

    2015-01-01

    The background stress field in volcanic areas may be overprinted by that produced by transient magmatic intrusions, generating local faulting. These events are rarely monitored and thus not fully understood, generating debate about the role of magma and tectonics in any geodynamic setting. Here we carried out a field structural analysis on the NNW-SSE strike-slip system of the central Aeolian Arc, Italy (Lipari and Vulcano islands) with ages constrained by stratigraphy to better capture the tectonic and magmatic evolution at the local and regional scales. We consider both islands as a single magmatic system and define 5 principal stratigraphic units based on magmatic and tectonic activity. We collected >500 measurements of faults, extension fractures and dikes at 40 sites, mostly NNE-SSW to NNW-SSE oriented with a dominant NS orientation. These structures are governed quasi exclusively by pure dip-slip motion, consistent with an E-W extension direction, with minor dextral and sinistral slip, the latter being mostly related to old deposits (>50 ka). We further reconstructed the evolution of the Vulcano-Lipari system during the last ~20 ka and find that it consists of an overall half-graben-like structure, with faults with predominant eastward dips. Field evidence suggests that faulting occurs often in temporal and spatial relation with magmatic events, suggesting that most of the observable deformation derived from transient magmatic activity, rather than from steady regional tectonics. To explain the dominant magmatic and episodic extension in a tectonic dominant domain, we propose a model where the regional N-S trending maximum horizontal stress, responsible for strike-slip activity, locally rotates to vertical in response to transient pressurization of the magmatic system and magma rise below Lipari and Vulcano. This has possibly generated the propagation of N-S trending dikes in the past 1 ka along a 10 km long by 1 km wide crustal corridor, with important

  17. Transient magmatic control in a tectonic domain: the central Aeolian volcanic arc (South Italy)

    KAUST Repository

    Ruch, Joel

    2015-04-01

    The background stress field in volcanic areas may be overprinted by that produced by transient magmatic intrusions, generating local faulting. These events are rarely monitored and thus not fully understood, generating debate about the role of magma and tectonics in any geodynamic setting. Here we carried out a field structural analysis on the NNW-SSE strike-slip system of the central Aeolian Arc, Italy (Lipari and Vulcano islands) with ages constrained by stratigraphy to better capture the tectonic and magmatic evolution at the local and regional scales. We consider both islands as a single magmatic system and define 5 principal stratigraphic units based on magmatic and tectonic activity. We collected >500 measurements of faults, extension fractures and dikes at 40 sites, mostly NNE-SSW to NNW-SSE oriented with a dominant NS orientation. These structures are governed quasi exclusively by pure dip-slip motion, consistent with an E-W extension direction, with minor dextral and sinistral slip, the latter being mostly related to old deposits (>50 ka). We further reconstructed the evolution of the Vulcano-Lipari system during the last ~20 ka and find that it consists of an overall half-graben-like structure, with faults with predominant eastward dips. Field evidence suggests that faulting occurs often in temporal and spatial relation with magmatic events, suggesting that most of the observable deformation derived from transient magmatic activity, rather than from steady regional tectonics. To explain the dominant magmatic and episodic extension in a tectonic dominant domain, we propose a model where the regional N-S trending maximum horizontal stress, responsible for strike-slip activity, locally rotates to vertical in response to transient pressurization of the magmatic system and magma rise below Lipari and Vulcano. This has possibly generated the propagation of N-S trending dikes in the past 1 ka along a 10 km long by 1 km wide crustal corridor, with important

  18. Colorado Plateau magmatism and uplift by warming of heterogeneous lithosphere.

    Science.gov (United States)

    Roy, Mousumi; Jordan, Thomas H; Pederson, Joel

    2009-06-18

    The forces that drove rock uplift of the low-relief, high-elevation, tectonically stable Colorado Plateau are the subject of long-standing debate. While the adjacent Basin and Range province and Rio Grande rift province underwent Cenozoic shortening followed by extension, the plateau experienced approximately 2 km of rock uplift without significant internal deformation. Here we propose that warming of the thicker, more iron-depleted Colorado Plateau lithosphere over 35-40 Myr following mid-Cenozoic removal of the Farallon plate from beneath North America is the primary mechanism driving rock uplift. In our model, conductive re-equilibration not only explains the rock uplift of the plateau, but also provides a robust geodynamic interpretation of observed contrasts between the Colorado Plateau margins and the plateau interior. In particular, the model matches the encroachment of Cenozoic magmatism from the margins towards the plateau interior at rates of 3-6 km Myr(-1) and is consistent with lower seismic velocities and more negative Bouguer gravity at the margins than in the plateau interior. We suggest that warming of heterogeneous lithosphere is a powerful mechanism for driving epeirogenic rock uplift of the Colorado Plateau and may be of general importance in plate-interior settings.

  19. The inception of a Paleotethyan magmatic arc in Iberia

    Directory of Open Access Journals (Sweden)

    M.F. Pereira

    2015-03-01

    Full Text Available This paper presents a compilation of recent U-Pb (zircon ages of late Carboniferous–early Permian (LC–EP calc-alkaline batholiths from Iberia, together with a petrogenetic interpretation of magma generation based on comparisons with Mesozoic and Tertiary Cordilleran batholiths and experimental melts. Zircon U-Pb ages distributed over the range ca. 315–280 Ma, indicate a linkage between calc-alkaline magmatism, Iberian orocline generation and Paleotethys subduction. It is also shown that Iberian LC–EP calc-alkaline batholiths present unequivocal subduction-related features comparable with typical Cordilleran batholiths of the Pacific Americas active margin, although geochemical features were partially obscured by local modifications of magmas at the level of emplacement by country rock assimilation. When and how LC–EP calc-alkaline batholiths formed in Iberia is then discussed, and a new and somewhat controversial interpretation for their sources and tectonic setting (plume-assisted relamination is suggested. The batholiths are proposed to have formed during the subduction of the Paleotethys oceanic plate (Pangaea self-subduction and, consequently, they are unrelated to Variscan collision. The origin of the Iberian batholiths is related to the Eurasian active margin and probably represents the inception of a Paleotethyan arc in the core of Pangaea.

  20. Updated Magmatic Flux Rate Estimates for the Hawaii Plume

    Science.gov (United States)

    Wessel, P.

    2013-12-01

    Several studies have estimated the magmatic flux rate along the Hawaiian-Emperor Chain using a variety of methods and arriving at different results. These flux rate estimates have weaknesses because of incomplete data sets and different modeling assumptions, especially for the youngest portion of the chain (little or no quantification of error estimates for the inferred melt flux, making an assessment problematic. Here we re-evaluate the melt flux for the Hawaii plume with the latest gridded data sets (SRTM30+ and FAA 21.1) using several methods, including the optimal robust separator (ORS) and directional median filtering techniques (DiM). We also compute realistic confidence limits on the results. In particular, the DiM technique was specifically developed to aid in the estimation of surface loads that are superimposed on wider bathymetric swells and it provides error estimates on the optimal residuals. Confidence bounds are assigned separately for the estimated surface load (obtained from the ORS regional/residual separation techniques) and the inferred subsurface volume (from gravity-constrained isostasy and plate flexure optimizations). These new and robust estimates will allow us to assess which secondary features in the resulting melt flux curve are significant and should be incorporated when correlating melt flux variations with other geophysical and geochemical observations.

  1. Dating the magmatism of Maio, Cape Verde Islands

    Energy Technology Data Exchange (ETDEWEB)

    Mitchell, J G [Newcastle upon Tyne Univ. (UK). School of Physics; Le Bas, M J [Leicester Univ. (UK). Dept. of Geology; Furnes, H [Bergen Univ. (Norway). Geologisk Inst.

    1983-07-01

    Conventional K-Ar and /sup 40/Ar//sup 39/Ar studies of Mesozoic ocean floor basalts and Tertiary plutonic and volcanic rocks from Maio, Cape Verde Islands, have been determined to elucidate the magmatic evolution of this ocean island. Pillow lavas of the Basement Complex yield a minimum age of 113 +- 8 Ma though thermal overprinting of their formation age by the younger Central Intrusive Complex (CIC) and subsequent sheet intrusions is in some cases almost total. Activity in the CIC began before 20 Ma and plutons continued to develop until about 8 Ma, the youngest ages possibly indicating a cooling history of more than 2 Ma for these bodies relative to their volcanic counterparts. Sheet intrusion occurred throughout the period 20 to 9 Ma though the peak of this activity probably occurred 11 Ma ago. Field relations allow the time of thrusting(s) on the Monte Branco Thrust to be bracketed between 9 and 7 Ma. Volcanic activity began in the Tertiary, probably before 12 Ma, and culminated in the development of a stratovolcano at 7 Ma.

  2. The Mozambique Ridge: a document of massive multistage magmatism

    Science.gov (United States)

    Fischer, Maximilian D.; Uenzelmann-Neben, Gabriele; Jacques, Guillaume; Werner, Reinhard

    2017-01-01

    The Mozambique Ridge, a prominent basement high in the southwestern Indian Ocean, consists of four major geomorphological segments associated with numerous phases of volcanic activity in the Lower Cretaceous. The nature and origin of the Mozambique Ridge have been intensely debated with one hypothesis suggesting a Large Igneous Province origin. High-resolution seismic reflection data reveal a large number of extrusion centres with a random distribution throughout the southern Mozambique Ridge and the nearby Transkei Rise. Intrabasement reflections emerge from the extrusion centres and are interpreted to represent massive lava flow sequences. Such lava flow sequences are characteristic of eruptions leading to the formation of continental and oceanic flood basalt provinces, hence supporting a Large Igneous Province origin of the Mozambique Ridge. We observe evidence for widespread post-sedimentary magmatic activity that we correlate with a southward propagation of the East African Rift System. Based on our volumetric analysis of the southern Mozambique Ridge we infer a rapid sequential emplacement between ˜131 and ˜125 Ma, which is similar to the short formation periods of other Large Igneous Provinces like the Agulhas Plateau.

  3. K/Ar dating of the Eastern Rhodope Paleogene magmatism

    Energy Technology Data Exchange (ETDEWEB)

    Lilov, P.; Yanev, Y.; Marchev, P.

    1987-12-01

    Paleogene magmatic rocks from the Eastern Rhodope Mountains have seldom been an object of radiogeochronological studies and very few data are available from the geological literature. Until now their dating relied heavily on paleontological data from fossil-bearing sediments, alternating with the lava flows. However, there are also many cross bodies (extrusions, dikes and intrusions) as well as volcanic areas of no sediments or of fossil-free sediments which require the combined use of both methods. This paper aims at characterizing geochronologically the Eastern Rhodope Paleogene volcanism. The K/Ar method was used to date reference volcanoes (mostly with well-defined positions in the Paleogene sequence) associated with the various phases of volcanic activity, as well as some separate intrusive bodies. Nomenclature of volcanics followed the classification of the Soviet Petrographic Commission and that of Peccerillo and Taylor as supplemented by Marchey. The paper characterizes only two of the three main volcanic districts, the Momcilgrad-Arda and the Borovica districts. The third one, Susica district, has restricted exposures near the state boundary between Bulgari and Greece and was excluded from the study. The results obtained are compared with the geochronological scales proposed by Odin and Cavelier and Pomerol which correlate radiogeochronological and paleontological data (nannoplancton data included).

  4. Old inherited zircons in two synkinematic variscan granitoids: the 'granite du Pinet' and the 'Orthogneiss de Marvejols' (Southern French Massif Central)

    International Nuclear Information System (INIS)

    Pin, C.

    1981-01-01

    Two granitic bodies outcropping in the metamorphic basement of the Southern French Massif Central have been studied with the zircon U-Pb method: the Pinet granite (Rouergue area) and the Marvejols orthogneisses (Serie du Lot). It is shown that neither of them are pre-Variscan intrusions but that they were emplaced synkinematically, during the early stages of the Hercynian tectonometamorphic event. As numerous other S-type granitoids, both formations are characterized by an important inherited zircon component, whose apparent age is 1800 +- 200 m.y. Lower intersections with the Concordia curve allow to settle an emplacement age around 350-360 m.y., although the Pinet zircons display a complex pattern, owing both to heterogeneity of the inherited component and to late isotopic disturbances. Regional consequences of the synkinematic character of these S-type granitoids are outlined. It is shown that inherited zircons occurences often hinder accurate dating and the possible petrogenetic significance of the old proterozoic component is discussed. (orig.)

  5. Zircon U-Pb ages and Hf isotopic compositions of neoarchaean granitoids from Karimnagar, Eastern Dharwar craton, Southern India: LA-ICPMS results

    International Nuclear Information System (INIS)

    Babu, E.V.S.S.K.; Vijaya Kumar, T.; Sreenivas, B.; Khadke, Namrata; Vijaya Gopal, B.; Bhaskar Rao, Y.J.

    2015-01-01

    The Archaean Dharwar and Bastar cratons of Peninsular India are separated by the NE-SW trending Godavari Graben. This zone is involved in recurrent rifting. It is generally believed that earlier phase of rifting dates back to Mesoproterozoic and the younger phase is related to the deposition of Permo-carboniferous coal-bearing sediments. A belt of high-grade rocks (∼ 150 x 45 km) - the Karimnagar granulite terrane (KGT) along the southern flank of the graben. The KGT comprises high-grade lithologies such as orthopyroxene-bearing quarto-feldspathic gneiss, amphibolite-granulite facies supracrustal belts that include metamorphosed quartz-arenites, pelites, carbonates, iron formation and mafic rocks as well as several zones of migmatite and younger granitoid intrusives. The study presented new LA-ICPMS zircon U-Pb age data for five granitoid (charnockite and granite) samples (KRN-90-24, KRN-90-30, KRN-13-02, KRN-13-03 and KRN-13-05; a closer constraint of the age crystallization of protoliths and high-grade metamorphism of felsic granulites and orthogneisses from the KGT. Hf isotopic compositions were also obtained for selected zircons from two samples (KRN-90-24 and KRN-90-30) using New Wave UP-213 Laser Ablation system coupled to Nu Plasma HR MC-ICPMS to constraint the nature of the felsic protoliths of the charnockite and granite gneisses in the KGT

  6. Petrochemical and Mineralogical Constraints on the Source and Processes of Uranium Mineralisation in the Granitoids of Zing-Monkin Area, Adamawa Massif, NE Nigeria

    International Nuclear Information System (INIS)

    Haruna, I. V.; Orazulike, D. M.; Ofulume, A. B.; Mamman, Y. D.

    2011-01-01

    Zing-Monkin area, located in the northern part of Adamawa Massif, is underlain by extensive exposures of moderately radioactive granodiorites, anatectic migmatites, equigranular granites, porphyritic granites and highly radioactive fine-grained granites with minor pegmatites. Selected major and trace element petrochemical investigations of the rocks show that a progression from granodiorite through migmatite to granites is characterised by depletion of MgO, CaO, Fe 2 O 3, Sr, Ba, and Zr, and enrichment of SiO 2 and Rb. This trend is associated with uranium enrichment and shows a chemical gradation from the more primitive granodiorite to the more evolved granites. Electron microprobe analysis shows that the uranium is content in uranothorite and in accessories, such as monazite, titanite, apatite, epidote and zircon. Based on petrochemical and mineralogical data, the more differentiated granitoids (e.g., fine-grained granite) bordering the Benue Trough are the immediate source of the uranium prospect in Bima Sandstone within the Trough. Uranium was derived from the granitoids by weathering and erosion. Transportation and subsequent interaction with organic matter within the Bima Sandstone led to precipitation of insoluble secondary uranium minerals in the Benue Trough.

  7. The Sr:Ba:Rb ratio and zircon typology in granitoid complexes of Sao Paulo, Parana and Minas Gerais states (Brazil)

    International Nuclear Information System (INIS)

    Wernick, E.; Galembeck, T.M.B.; Artur, A.C.; Rigo Junior, L.; Weber-Diefenbach, K.

    1990-01-01

    Chemical (Sr: Ba: Rb) and zircon typology data from the Nazare Paulista, Mairipora/Cantareira, Cunhaporanga, Tres Corregos, Morungaba, Socorro, Itu, Graciosa and Serra Carambei granitoid complexes from the states of Minas Gerais, Sao Paulo and Parana (SE/S Brazil) are presented and discussed. By the zircon typology method these complexes are reffered, respectively, to the 2nd crustal, 3rd crustal/low temperature C-A, low temperature C-A, medium temperature C-A, medium/high temperature C-A, K-SA/Alkaline and alkaline serie which are considered as generated under increasing temperature associated with a progressive major participation of mantellic material. All these series, with the exception of the medium to high temperature calc-alkaline complexes Socorro and Morungaba whose chemical data come from several laboratories, display different positions and behaviour in the Sr: Ba: Rb diagram which reinforce the use of the zircon typology method in the study of granitoids. From the 2nd crustal serie up to the medium temperature C-A serie the complexes show a regular shift in their chemical composition which became progressively richer in Sr and depleted in Rb. The highly differentiades hypersolvus Serra do Carambei granite is strongly enriched in Rb and impoverish in Ba with respect to the Itu and the Graciosa complex which itself is slighly more depleted in Sr than the Itu granite. (author)

  8. Geochronology and geochemistry of the granitoids and ore - forming age in the Xiaoyao tungsten polymetallic skarn deposit in the Jiangnan Massif tungsten belt, China: Implications for their petrogenesis, geodynamic setting, and mineralization

    Science.gov (United States)

    Su, Qiangwei; Mao, Jingwen; Wu, Shenghua; Zhang, Zhaochong; Xu, Shengfa

    2018-01-01

    The Xiaoyao tungsten polymetallic skarn deposit in the eastern Jiangnan Massif of Yangtze Block is located at the contact between a granodiorite pluton and Sinian-Cambrian limestone. The intrusions in the tungsten-rich district comprise the Xiaoyao and other granodiorite plutons and granite porphyry dikes. The age determinations by LA-ICP-MS U-Pb dating of zircons indicate that the granodiorite formed at 149.4 ± 1.1 Ma, whereas the granite porphyry was emplaced at 133.2 ± 0.7 Ma. Re-Os dating of molybdenite from the skarn orebodies yielded a weighted average age of 148.7 ± 2.3 Ma (n = 5). These ages indicate that the tungsten mineralization is temporally related to the granodiorite. The granodiorites are metaluminous (A/CNK = 0.86-0.98) and in the high-K calc-alkaline series. They contain hornblende and have a negative correlation between P2O5 and SiO2, indicating that they are typical I-type intrusions. The granite porphyries exhibit high alkali contents (Na2O + K2O = 7.97-9.53%), elevated FeOT/(FeOT + MgO) ratios (0.83-0.94), high concentrations of Zr, Nb, Ce, and Y, and high Zr saturation temperatures (average of 812 °C); thus, they are geochemically similar to A-type intrusions. The initial 87Sr/86Sr and εNd(t) values range respectively from 0.7074 to 0.7083 and from - 7.9 to - 1.3 for the granodiorite, and from 0.7008 to 0.7083 and from - 6.3 to - 4.7 for the granite porphyry. In addition, two-stage Nd model ages (T2DM) of 1.0-1.6 Ga for the granodiorite and 1.3-1.4 Ga for the granite porphyry indicate that the Proterozoic crustal rocks of the Shangxi Group could have contributed to the Xiaoyao magmas. The rhenium contents of the molybdenite grains vary from 32 to 136 ppm, suggesting that the molybdenum was derived mainly from a mixture of mantle and crustal sources. Based on the new geochemical data and regional geological investigations, we propose that the Late Jurassic mineralization-related I-type granodiorite was derived from the Neoproterozoic

  9. Zircon U-Pb geochronology and Sr-Nd-Pb-Hf isotopic constraints on the timing and origin of Mesozoic granitoids hosting the Mo deposits in northern Xilamulun district, NE China

    Science.gov (United States)

    Shu, Qihai; Lai, Yong; Zhou, Yitao; Xu, Jiajia; Wu, Huaying

    2015-12-01

    Located in the east section of the Central Asian orogen in northeastern China, the Xilamulun district comprises several newly discovered molybdenum deposits, primarily of porphyry type and Mesozoic ages. This district is divided by the Xilamulun fault into the southern and the northern parts. In this paper, we present new zircon U-Pb dating, trace elements and Hf isotope, and/or whole rock Sr-Nd-Pb isotopic results for the host granitoids from three Mo deposits (Yangchang, Haisugou and Shabutai) in northern Xilamulun. Our aim is to constrain the age and petrogenesis of these intrusions and their implications for Mo mineralization. Zircon U-Pb LA-ICP-MS dating shows that the monzogranites from the Shabutai and Yangchang deposits formed at 138.4 ± 1.5 and 137.4 ± 2.1 Ma, respectively, which is identical to the molybdenite Re-Os ages and coeval well with the other Mo deposits in this region, thereby indicating an Early Cretaceous magmatism and Mo mineralization event. Zircon Ce/Nd ratios from the mineralized intrusions are significantly higher than the barren granites, implying that the mineralization-related magmas are characterized by higher oxygen fugacity. These mineralized intrusions share similar zircon in-situ Hf and whole rock Sr-Nd isotopic compositions, with slightly negative to positive εHf(t) ranging from - 0.8 to + 10.0, restricted εNd(t) values from - 3.7 to + 1.6 but a little variable (87Sr/86Sr)i ratios between 0.7021 and 0.7074, indicative of formation from primary magmas generated from a dominantly juvenile lower crust source derived from depleted mantle, despite diverse consequent processes (e.g., magma mixing, fractional crystallization and crustal contamination) during their evolution. The Pb isotopes (whole rock) also show a narrow range of initial compositions, with (206Pb/204Pb)i = 18.03-18.88, (207Pb/204Pb)i = 15.48-15.58 and (208Pb/204Pb)i = 37.72-38.28, in agreement with Sr-Nd-Hf isotopes reflecting the dominance of a mantle component

  10. Age and tectonomagmatic setting of the Eocene Çöpler-Kabataş magmatic complex and porphyry-epithermal Au deposit, East Central Anatolia, Turkey

    Science.gov (United States)

    İmer, Ali; Richards, Jeremy P.; Creaser, Robert A.

    2013-06-01

    The Çöpler epithermal Au deposit and related subeconomic porphyry Cu-Au deposit is hosted by the middle Eocene Çöpler-Kabataş magmatic complex in central eastern Anatolia. The intrusive rocks of the complex were emplaced into Late Paleozoic-Mesozoic metamorphosed sedimentary basement rocks near the northeastern margin of the Tauride-Anatolide Block. Igneous biotite from two samples of the magmatic complex yielded 40Ar/39Ar plateau ages of 43.75 ± 0.26 Ma and 44.19 ± 0.23, whereas igneous hornblende from a third sample yielded a plateau age of 44.13 ± 0.38. These ages closely overlap with 40Ar/39Ar ages of hydrothermal sericite (44.44 ± 0.28 Ma) and biotite (43.84 ± 0.26 Ma), and Re-Os ages from two molybdenite samples (44.6 ± 0.2 and 43.9 ± 0.2 Ma) suggesting a short-lived (history at Çöpler. No suitable minerals were found that could be used to date the epithermal system, but it is inferred to be close in age to the precursor porphyry system. The Çöpler-Kabataş intrusive rocks show I-type calc-alkaline affinities. Their normalized trace element patterns show enrichments in large ion lithophile and light rare earth elements and relative depletions in middle and heavy rare earth elements, resembling magmas generated in convergent margins. However, given its distance from the coeval Eocene Maden-Helete volcanic arc, the complex is interpreted to be formed in a back-arc setting, in response to Paleocene slab roll-back and upper-plate extension. The tectonomagmatic environment of porphyry-epithermal mineralization at Çöpler is comparable to some other isolated back-arc porphyry systems such as Bajo de la Alumbrera (Argentina) or Bingham Canyon (USA).

  11. Spatiotemporal evolution of magmatic pulses and regional metamorphism during a Cretaceous flare-up event: Constraints from the Ryoke belt (Mikawa area, central Japan)

    Science.gov (United States)

    Takatsuka, Kota; Kawakami, Tetsuo; Skrzypek, Etienne; Sakata, Shuhei; Obayashi, Hideyuki; Hirata, Takafumi

    2018-05-01

    The spatiotemporal relationship between granitoid intrusions and low-pressure/temperature type regional metamorphism in the Ryoke belt (Mikawa area) is investigated to understand the tectono-thermal evolution of the upper- to middle-crust during a Cretaceous flare-up event at the Eurasian active continental margin. Three plutono-metamorphic stages are recognized; (1) 99-84 Ma: intrusion of granitoids (99-95 Ma pulse) into the upper crust and high-T regional metamorphism reaching sillimanite-grade (97.0 ± 4.4 Ma to 88.5 ± 2.5 Ma) in the middle crust, (2) 81-75 Ma: intrusion of gneissose granitoids (81-75 Ma Ma pulse) into the middle crust at 19-24 km depth, and (3) 75-69 Ma: voluminous intrusions of massive to weakly-foliated granitoids (75-69 Ma pulse) at 9-13 km depth and formation of contact metamorphic aureoles. Cooling of the highest-grade metamorphic zone below the wet solidus of granitic rocks is estimated at 88.5 ± 2.5 Ma. At ca. 75 Ma, the upper-middle crustal section underwent northward tilting, resulting in the exhumation of regional metamorphic zones to 9-13 km depth. Although the highest-grade metamorphic rocks and the 99-95 Ma pulse granitoids preserve similar U-Pb zircon ages, the absence of spatial association suggests that the regional metamorphic zones were mainly produced by a transient thermal anomaly in the mantle and thermal conduction through the crust, supplemented by localized advection due to granitoid intrusions. The successive emplacement of granitoids into shallow, deep and shallow levels of the crust was probably controlled by the combination of change in thermal structure of the crust and tectonics during granitoid intrusions.

  12. A Parent Magma for the Nakhla Martian Meteorite: Reconciliation of Estimates from 1-Bar Experiments, Magmatic Inclusions in Olivine, and Magmatic Inclusions in Augite

    Science.gov (United States)

    Treiman, Allan H.; Goodrich, Cyrena Anne

    2001-01-01

    The composition of the parent magma for the Nakhla (martian) meteorite has been estimated from mineral-melt partitioning and from magmatic inclusions in olivine and in augite. These independent lines of evidence have converged on small range of likely compositions. Additional information is contained in the original extended abstract.

  13. Modelling Subduction Zone Magmatism Due to Hydraulic Fracture

    Science.gov (United States)

    Lawton, R.; Davies, J. H.

    2014-12-01

    The aim of this project is to test the hypothesis that subduction zone magmatism involves hydraulic fractures propagating from the oceanic crust to the mantle wedge source region (Davies, 1999). We aim to test this hypothesis by developing a numerical model of the process, and then comparing model outputs with observations. The hypothesis proposes that the water interconnects in the slab following an earthquake. If sufficient pressure develops a hydrofracture occurs. The hydrofracture will expand in the direction of the least compressive stress and propagate in the direction of the most compressive stress, which is out into the wedge. Therefore we can calculate the hydrofracture path and end-point, given the start location on the slab and the propagation distance. We can therefore predict where water is added to the mantle wedge. To take this further we have developed a thermal model of a subduction zone. The model uses a finite difference, marker-in-cell method to solve the heat equation (Gerya, 2010). The velocity field was prescribed using the analytical expression of cornerflow (Batchelor, 1967). The markers contained within the fixed grid are used to track the different compositions and their properties. The subduction zone thermal model was benchmarked (Van Keken, 2008). We used the hydrous melting parameterization of Katz et.al., (2003) to calculate the degree of melting caused by the addition of water to the wedge. We investigate models where the hydrofractures, with properties constrained by estimated water fluxes, have random end points. The model predicts degree of melting, magma productivity, temperature of the melt and water content in the melt for different initial water fluxes. Future models will also include the buoyancy effect of the melt and residue. Batchelor, Cambridge UP, 1967. Davies, Nature, 398: 142-145, 1999. Gerya, Cambridge UP, 2010. Katz, Geochem. Geophys. Geosy, 4(9), 2003 Van Keken et.al. Phys. Earth. Planet. In., 171:187-197, 2008.

  14. Magmatic control along a strike-slip volcanic arc: The central Aeolian arc (Italy)

    Science.gov (United States)

    Ruch, J.; Vezzoli, L.; De Rosa, R.; Di Lorenzo, R.; Acocella, V.

    2016-02-01

    The regional stress field in volcanic areas may be overprinted by that produced by magmatic activity, promoting volcanism and faulting. In particular, in strike-slip settings, the definition of the relationships between the regional stress field and magmatic activity remains elusive. To better understand these relationships, we collected stratigraphic, volcanic, and structural field data along the strike-slip central Aeolian arc (Italy): here the islands of Lipari and Vulcano separate the extensional portion of the arc (to the east) from the contractional one (to the west). We collected >500 measurements of faults, extension fractures, and dikes at 40 sites. Most structures are NNE-SSW to NNW-SSE oriented, eastward dipping, and show almost pure dip-slip motion, consistent with an E-W extension direction, with minor dextral and sinistral shear. Our data highlight six eruptive periods during the last 55 ka, which allow considering both islands as a single magmatic system, in which tectonic and magmatic activities steadily migrated eastward and currently focus on a 10 km long × 2 km wide active segment. Faulting appears to mostly occur in temporal and spatial relation with magmatic events, supporting that most of the observable deformation derives from transient magmatic activity (shorter term, days to months), rather than from steady longer-term regional tectonics (102-104 years). More in general, the central Aeolian case shows how magmatic activity may affect the structure and evolution of volcanic arcs, overprinting any strike-slip motion with magma-induced extension at the surface.

  15. Magmatic control along a strike-slip volcanic arc: The central Aeolian arc (Italy)

    KAUST Repository

    Ruch, Joel

    2016-01-23

    The regional stress field in volcanic areas may be overprinted by that produced by magmatic activity, promoting volcanism and faulting. In particular, in strike-slip settings, the definition of the relationships between the regional stress field and magmatic activity remains elusive. To better understand these relationships, we collected stratigraphic, volcanic and structural field data along the strike-slip Central Aeolian arc (Italy): here the islands of Lipari and Vulcano separate the extensional portion of the arc (to the east) from the contractional one (to the west). We collected >500 measurements of faults, extension fractures and dikes at 40 sites. Most structures are NNE-SSW to NNW-SSE oriented, eastward dipping, and show almost pure dip-slip motion; consistent with an E-W extension direction, with minor dextral and sinistral shear. Our data highlight six eruptive periods during the last 55 ka, which allow considering both islands as a single magmatic system, in which tectonic and magmatic activity steadily migrated eastward and currently focus on a 10 km long x 2 km wide active segment. Faulting appears to mostly occur in temporal and spatial relation with magmatic events, supporting that most of the observable deformation derives from transient magmatic activity (shorter-term, days to months), rather than from steady longer-term regional tectonics (102-104 years). More in general, the Central Aeolian case shows how magmatic activity may affect the structure and evolution of volcanic arcs, overprinting any strike-slip motion with magma-induced extension at the surface.

  16. The Interplay Between Saline Fluid Flow and Dynamic Permeability in Magmatic-Hydrothermal Systems

    Science.gov (United States)

    Weis, P.

    2014-12-01

    Magmatic-hydrothermal ore deposits document the interplay between saline fluid flow and rock permeability. Numerical simulations of multi-phase flow of variably miscible, compressible H20-NaCl fluids in concert with a dynamic permeability model can reproduce characteristics of porphyry copper and epithermal gold systems. This dynamic permeability model incorporates depth-dependent permeability profiles characteristic for tectonically active crust as well as pressure- and temperature-dependent relationships describing hydraulic fracturing and the transition from brittle to ductile rock behavior. In response to focused expulsion of magmatic fluids from a crystallizing upper crustal magma chamber, the hydrothermal system self-organizes into a hydrological divide, separating an inner part dominated by ascending magmatic fluids under near-lithostatic pressures from a surrounding outer part dominated by convection of colder meteoric fluids under near-hydrostatic pressures. This hydrological divide also provides a mechanism to transport magmatic salt through the crust, and prevents the hydrothermal system to become "clogged" by precipitation of solid halite due to depressurization of saline, high-temperature magmatic fluids. The same physical processes at similar permeability ranges, crustal depths and flow rates are relevant for a number of active systems, including geothermal resources and excess degassing at volcanos. The simulations further suggest that the described mechanism can separate the base of free convection in high-enthalpy geothermal systems from the magma chamber as a driving heat source by several kilometers in the vertical direction in tectonic settings with hydrous magmatism. This hydrology would be in contrast to settings with anhydrous magmatism, where the base of the geothermal systems may be closer to the magma chamber.

  17. Granitoid emplacement during syn-convergent transtension: An example from the Huamenlou pluton in North Qinling, central China

    Directory of Open Access Journals (Sweden)

    Yang Li

    2018-01-01

    Full Text Available The Huamenlou pluton, is an elongated granite intrusion with high aspect ratio, emplaced within the southern margin of the North Qinling (central China. Here we investigate this pluton through multiple techniques including the fabric study, microstructural observation and zircon geochronology. Our zircon U–Pb data confirm that the granite crystallized at ca. 462 Ma which is consistent with the ages of other linear plutons in North Qinling. Microstructural observations of the Huamenlou granites illustrate that the pluton has undergone superimposed deformation during its emplacement, from magmatic to high-temperature solid state conditions. The internal fabric obtained by anisotropy of magnetic susceptibility (AMS and shape preferred orientation (SPO show similar results. The fabrics are relatively concordant and generally vary from NE–SW to NEE–SWW which are roughly oblique to the trend of the pluton elongation and the regional structures. Meanwhile, scalar parameters reflect two completely different strain regimes for the pluton and its host rocks, i.e., the fabrics within host rocks are mainly oblate while the central part of the intrusion displays mainly prolate fabrics. It is inferred that the structural pattern recorded in this pluton was caused by local dextral transtension in consequence of oblique convergence between the South and North China Blocks. We propose that the local transtension in convergence setting probably evolved from vertical extrusion tectonics that provided room for the magma emplacement and imparted prolate fabrics in the Huamenlou pluton.

  18. Breakup Style and Magmatic Underplating West of the Lofoten Islands, Norway, Based on OBS Data.

    Science.gov (United States)

    Breivik, A. J.; Faleide, J. I.; Mjelde, R.; Murai, Y.; Flueh, E. R.

    2014-12-01

    The breakup of the Northeast Atlantic in the Early Eocene was magma-rich, forming the major part of the North Atlantic Igneous Province (NAIP). This is seen as extrusive and intrusive magmatism in the continental domain, and as a thicker than normal oceanic crust produced the first few million years after continental breakup. The maximum magma productivity and the duration of excess magmatism varies along the margins of Northwest Europe and East Greenland, to some extent as a function of the distance from the Iceland hotspot. The Vøring Plateau off mid-Norway is the northernmost of the margin segments in northwestern Europe with extensive magmatism. North of the plateau, magmatism dies off towards the Lofoten Margin, marking the northern boundary of the NAIP here. In 2003, as part of the Euromargins Program we collected an Ocean Bottom Seismometer (OBS) profile from mainland Norway, across the Lofoten Islands, and out into the deep ocean. Forward velocity modeling using raytracing reveals a continental margin that shows transitional features between magma-rich and magma-poor rifting. On one hand, we detect an up to 2 km thick and 40-50 km wide magmatic underplate of the outer continent, on the other hand, continental thinning is greater and intrusive magmatism less than farther south. Continental breakup also appears to be somewhat delayed compared to breakup on the Vøring Plateau, consistent with increased extension. This indicates that magmatic diking, believed to quickly lead to continental breakup of volcanic margins and thus to reduce continental thinning, played a much lesser role here than at the plateau. Early post-breakup oceanic crust is up to 8 km thick, less than half of that observed farther south. The most likely interpretation of these observations, is that the source for the excess magmatism of the NAIP was not present at the Lofoten Margin during rifting, and that the excess magmatism actually observed was the result of lateral transport from the

  19. Late magmatic controls on the origin of schorlitic and foititic tourmalines from late-Variscan peraluminous granites of the Arbus pluton (SW Sardinia, Italy): Crystal-chemical study and petrological constraints

    Science.gov (United States)

    Bosi, Ferdinando; Naitza, Stefano; Skogby, Henrik; Secchi, Francesco; Conte, Aida M.; Cuccuru, Stefano; Hålenius, Ulf; De La Rosa, Nathaly; Kristiansson, Per; Charlotta Nilsson, E. J.; Ros, Linus; Andreozzi, Giovanni B.

    2018-05-01

    Tourmalines from the late-Variscan Arbus pluton (SW Sardinia) and its metamorphic aureole were structurally and chemically characterized by single-crystal X-ray diffraction, electron and nuclear microprobe analysis, Mössbauer, infrared and optical absorption spectroscopy, to elucidate their origin and relationships with the magmatic evolution during the pluton cooling stages. The Arbus pluton represents a peculiar shallow magmatic system, characterized by sekaninaite (Fe-cordierite)-bearing peraluminous granitoids, linked via AFC processes to gabbroic mantle-derived magmas. The Fe2+-Al-dominant tourmalines occur in: a) pegmatitic layers and pods, as prismatic crystals; b) greisenized rocks and spotted granophyric dikes, as clots or nests of fine-grained crystals in small miaroles locally forming orbicules; c) pegmatitic veins and pods close to the contacts within the metamorphic aureole. Structural formulae indicate that tourmaline in pegmatitic layers is schorl, whereas in greisenized rocks it ranges from schorl to fluor-schorl. Tourmalines in thermometamorphosed contact aureole are schorl, foitite and Mg-rich oxy-schorl. The main substitution is Na + Fe2+ ↔ □ + Al, which relates schorl to foitite. The homovalent substitution (OH) ↔ F at the O1 crystallographic site relates schorl to fluor-schorl, while the heterovalent substitution Fe2+ + (OH, F) ↔ Al + O relates schorl/fluor-schorl to oxy-schorl. Tourmaline crystallization in the Arbus pluton was promoted by volatile (B, F and H2O) enrichment, low oxygen fugacity and Fe2+ activity. The mineralogical evolutive trend is driven by decreasing temperature, as follows: sekaninaite + quartz → schorl + quartz → fluor-schorl + quartz → foitite + quartz. The schorl → foitite evolution represents a distinct trend towards (Al + □) increase and unit-cell volume decrease. These trends are typical of granitic magmas and consistent with Li-poor granitic melts, as supported by the absence of elbaite and other

  20. Late Paleozoic to Triassic magmatism in the north-central High Andes, Chile: New insights from SHRIMP U-Pb geochronology and O-Hf isotopic signatures in zircon

    Science.gov (United States)

    Hernández González, Álvaro; Deckart, Katja; Fanning, Mark; Arriagada, César

    2014-05-01

    The Chilean High Andes (28o- 31oS) comprises a vast number of late Paleozoic - Triassic granitoids which give information about the last stages of Gondwana assemblage. Particularly, previous studies determined two tectonic configurations during this time: subduction related compressional setting (late Carboniferous - Late Permian) and non-subduction post-collisional extensional setting (Late Permian - Triassic), as the last stage of Gondwana assemblage. However, new O-Hf isotopic data along new U-Pb SHRIMP ages in zircon have shown that this model should be modified and updated to the new analytical data available. δ18O values indicate a strong change in the tectonic configuration approximately 270 Ma (earliest middle Permian) and thus, units can be divided into 2 mayor groups: late Carboniferous to earliest middle Permian and middle Permian to Triassic. The oldest group shows slightly low values of ɛHfi (ca. +1 to -4) with high δ18O (ca. >6.5 o/oo), indicating an elevated supracrustal component and the addition of less radiogenic continental-like material, which along significant residence time (TDM2: Mesoproterozoic) can be interpreted as magmas formed at depth in a subduction-related continental arc, and contaminated with supracrustal material and/or oceanic sediments transported through the subducted slab to the mantle-wedge. Subsequently, middle Permian - Triassic rocks show a wider range of ɛHfi values (ca. +3 to -3) with relatively low, mantle-like δ18O (ca. 4.5-6.5 o/oo), indicating a source of magmas without the addition of supracrustal material for some plutons, whilst for others, a slight input. The higher positive values of ɛHfi can be related to the influence of new juvenile material in the source of some magmas. This isotopic data can be interpreted as rocks formed as the result of melting of an old thinned mafic crust (with mantle-like δ18O values characteristic of this type of rocks) with limited addition of supracrustal material; in

  1. Geologic Mapping, Volcanic Stages and Magmatic Processes in Hawaiian Volcanoes

    Science.gov (United States)

    Sinton, J. M.

    2005-12-01

    rise to various Hawaiian lithologies. This analysis indicates that the important magmatic process that links geologic mapping to volcanic stage is thermal state of the volcano, as manifest by depth of magma evolution. The only criterion for rejuvenation volcanism is the presence of a significant time break (more than several hundred thousand years) preceding eruption.

  2. Shallow magmatic degassing into the hydrothermal system of Copahue, Argentina

    Science.gov (United States)

    Varekamp, J.; Ouimette, A.; Kreulen, R.; Delpino, D.; Bermudez, A.

    2001-05-01

    Copahue volcano has a crater lake and acid hot springs that discharge into the Rio Agrio river system. These fluids are very concentrated (up to 6 percent sulfate), rich in rock-forming elements (up to 2000 ppm Mg) and small spheres of native sulfur float in the crater lake. The stable isotope composition of the waters (delta 18O =-2.1 to + 3.6 per mille; delta D = -49 to -26 per mille) indicates that the hot spring waters are at their most concentrated about 70 percent volcanic brine and 30 percent glacial meltwater. The crater lake waters have similar mixing proportions but added isotope effects from intense evaporation. Further dilution of the waters in the Rio Agrio gives values closer to local meteoric waters (delta 18O = -11 per mille; delta D = -77 per mille), whereas evaporation in closed ponds led to very heavy water (up to delta 18O = +12 per mille). The delta 34S value of dissolved sulfate is +14.2 per mille, whereas the native sulfur has values of -8.2 to -10.5 per mille. The heavy sulfate probably formed when SO2 disproportionated into bisulfate and native sulfur. We measured the sulfate fluxes in the Rio Agrio, and from these flux values and the stoichiometry of the disproportionation reaction we calculated the rate of liquid sulfur storage inside the volcano (6000 m3/year). During the eruptions of 1995/2000, large amounts of that stored liquid sulfur were ejected as pyroclastic sulfur. The calculated rate of rock dissolution (from rock- forming element fluxes in the Rio Agrio) suggests that the void space generated by rock dissolution is largely filled by native sulfur. The isotopic signature of the magmatic sulfur can be reconstituted at about +7 per mille, which is a source signature with superposed effects of shallow degassing. Lead isotope and 129Iodine data from the fluids indicate that subducted components may have played a role in the Copahue magma formation. Primary glass inclusions in plagioclase and olivine have 1110-1670 ppm Cl, 90-400 ppm

  3. Exhumation History Of Brasilian Highlands After Late Cretaceous Alcaline Magmatism

    Science.gov (United States)

    Doranti Tiritan, Carolina; Hackspacher, Peter Christian; Carina Siqueira Ribeiro, Marli; Glasmacher, Ulrich Anton; Françoso de Godoy, Daniel

    2017-04-01

    The southeast Brazilian margin recorded a long history of tectonic and magmatic events after the Gondwana continent break up. The drifting of the South American Platform over a thermal anomaly generated a series of alkaline intrusions that are distributed from the interior to the coast from west to east. Several exhumation events are recorded on the region and we are providing insights on the landscape evolution of the region since Late Cretaceous, comparing low temperature thermochronology results from two alkaline intrusions regions. Poços de Caldas Alkaline Massif (PCAM), is lied in the interior, 300km from the coastline, covering over 800km2 intruding the Precambrian basement around 83Ma, nepheline syenites, phonolites and tinguaites intruded in a continuous and rapid sequence lasting between 1 to 2 Ma. São Sebastião Island (SSI) on the other hand is located at the coast, 200 km southeast of São Paulo. It is characterized by an intrusion in Precambrian/Brazilian orogen and intruded by Early Cretaceous sub-alkaline basic and acid dykes, as well as by Late Cretaceous alkaline stocks (syenites) and dykes (basanite to phonolite). Will be presenting the apatite fission track (AFT) and (U-Th)/He results that shows the main difference between the areas is that PCAM region register older history then the coastal area of SSI, where thermal history starts register cooling event after the South Atlantic rifting process, while in the PCAM area register a previous history, since Carboniferous. The results are giving support to studies that indicate the development of the relief in Brazil being strongly influenced by the local and regional tectonic movements and the lithological and structural settings. The landscape at the Late Cretaceous was witness of heating process between 90 and 60Ma due the intense uplift of South American Platform. The elevation of the isotherms is associated with the mantellic plumes and the crustal thickness that caused thermal anomalies due

  4. Sulfur concentration at sulfide saturation (SCSS) in magmatic silicate melts

    Science.gov (United States)

    Liu, Yanan; Samaha, Naji-Tom; Baker, Don R.

    2007-04-01

    the MELTS software to calculate the saturation of natural magmas with a sulfide phase and evolution of the SCSS during magmatic differentiation.

  5. Magma Mixing: Magmatic Enclaves in Morne Micotrin, Dominica

    Science.gov (United States)

    Hickernell, S.; Frey, H. M.; Manon, M. R. F.; Waters, L. E.

    2017-12-01

    Magmatic enclaves in volcanic rocks provide direct evidence of magma mingling/mixing within a magma reservoir and may reinvigorate the system and trigger eruption, as documented at the Soufriere Hills in Montserrat. Lava domes on the neighboring island of Dominica also contain multiple enclave populations and may be evidence for similar magma chamber processes. The central dome of Micotrin is at the head of the Roseau Valley, which was filled with 3 km3 of pyroclastic deposits from eruptions spanning 65 - 25 ka. There appear to be two distinct types of enclaves in the crystal-rich Micotrin andesites (60 wt% SiO2), fine-grained and coarse-grained. Fine-grained mafic enclaves (52 wt% SiO2) vary in size from 1 to 15 cm in diameter, whereas the coarse-grained enclaves are generally larger and range from 3-20 cm. Fine-grained enclaves are saturated in plag (35%) + opx (35%) + cpx (20%) + oxides (10%). Average pyroxenes are 0.01 to 0.02 cm in size, whereas plagioclase averages 0.05 cm and up to 0.1 cm. The texture of the fine-grained enclaves is cumulate-like, devoid of microlites and matrix glass. Coarse-grained enclaves lack cpx and have different modal abundances and textures: plag (75%) + opx (10%) + oxides (5%) + plag microlites (10%). Plagioclase are 0.1 cm in size and orthopyroxenes average 0.05 cm. The coarse-grained enclaves are highly vesicular, a notable difference from the host as well as the fine-grained enclaves. The boundaries of both the fine- and coarse-grained enclaves are quite sharp and distinct and there do not appear to be enclave minerals disaggregated in the host rock. Temperatures were determined by two oxides. The fine-grained enclaves had two populations of magnetite, yielding 847 + 21° and 920 + 17°C. The coarse-grained enclave was 890 + 42 °C, but the oxides were extensively exsolved. Plagioclase composition in both coarse and fine-grained samples was comparable, ranging from An50 to An80. Despite compositional similarity the textures of

  6. Magmatic Volatiles as an Amplifier of Centrifugal Volcanism

    Science.gov (United States)

    Pratt, V. R.

    2017-12-01

    There is a striking correlation between negated Length of Day -LOD and the 60-70 year period in 20th century global climate, associated by some with the so-called Atlantic Multidecadal Oscillation or AMO. A number of authors have suggested mechanisms by which the former might cause the latter. One such that this author finds quite compelling is that gravity fluctuations at low latitudes increase essentially linearly with LOD fluctuations and therefore moves magma towards or away from the surface as LOD decreases or increases, i.e. angular velocity increases or decreases, respectively. At AGU FM2016 we proposed the term "centrifugal volcanism" for this mechanism and listed four possible objections to it, explaining three to our satisfaction. The remaining objection is the very obvious one that the 4 ms increase in LOD between 1880 and 1910 seems far too small to be able to account for the observed variation of about a quarter of a degree. A basic mechanism underlying many violent eruptions is the strong positive feedback between reduction of pressure in magma and evaporation of dissolved volatiles found in some magmas, driving the magma outwards and thereby further reducing the pressure. The normal state of magma is equilibrium. Any fluctuation in gravity, even a very small one, can be sufficient to shift this equilibrium sufficiently far to set this positive feedback in motion. The relevant electrical analogy would be an operational amplifier whose amplification is greatly increased by a positive feedback. We therefore propose that the same mechanism responsible for some violent eruptions also serves to amplify the tiny changes in gravity sufficiently to increase or decrease the vertical component of the movement of magma in general. This movement, felt throughout the planet albeit most strongly at low latitudes, influences the temperature at ocean bottoms wherever there is a significant level of magmatic volatiles. This in turn creates thermals that are large

  7. Phase equilibria constraints on models of subduction zone magmatism

    Science.gov (United States)

    Myers, James D.; Johnston, Dana A.

    Petrologic models of subduction zone magmatism can be grouped into three broad classes: (1) predominantly slab-derived, (2) mainly mantle-derived, and (3) multi-source. Slab-derived models assume high-alumina basalt (HAB) approximates primary magma and is derived by partial fusion of the subducting slab. Such melts must, therefore, be saturated with some combination of eclogite phases, e.g. cpx, garnet, qtz, at the pressures, temperatures and water contents of magma generation. In contrast, mantle-dominated models suggest partial melting of the mantle wedge produces primary high-magnesia basalts (HMB) which fractionate to yield derivative HAB magmas. In this context, HMB melts should be saturated with a combination of peridotite phases, i.e. ol, cpx and opx, and have liquid-lines-of-descent that produce high-alumina basalts. HAB generated in this manner must be saturated with a mafic phase assemblage at the intensive conditions of fractionation. Multi-source models combine slab and mantle components in varying proportions to generate the four main lava types (HMB, HAB, high-magnesia andesites (HMA) and evolved lavas) characteristic of subduction zones. The mechanism of mass transfer from slab to wedge as well as the nature and fate of primary magmas vary considerably among these models. Because of their complexity, these models imply a wide range of phase equilibria. Although the experiments conducted on calc-alkaline lavas are limited, they place the following limitations on arc petrologic models: (1) HAB cannot be derived from HMB by crystal fractionation at the intensive conditions thus far investigated, (2) HAB could be produced by anhydrous partial fusion of eclogite at high pressure, (3) HMB liquids can be produced by peridotite partial fusion 50-60 km above the slab-mantle interface, (4) HMA cannot be primary magmas derived by partial melting of the subducted slab, but could have formed by slab melt-peridotite interaction, and (5) many evolved calc

  8. Petrologic Modeling of Magmatic Evolution in The Elysium Volcanic Province

    Science.gov (United States)

    Susko, D.; Karunatillake, S.; Hood, D.

    2017-12-01

    The Elysium Volcanic Province (EVP) on Mars is a massive expanse of land made up of many hundreds of lava flows of various ages1. The variable surface ages within this volcanic province have distinct elemental compositions based on the derived values from the Gamma Ray Spectrometer (GRS) suite2. Without seismic data or ophiolite sequences on Mars, the compositions of lavas on the surface provide some of the only information to study the properties of the interior of the planet. The Amazonian surface age and isolated nature of the EVP in the northern lowlands of Mars make it ideal for analyzing the mantle beneath Elysium during the most recent geologic era on Mars. The MELTS algorithm is one of the most commonly used programs for simulating compositions and mineral phases of basaltic melt crystallization3. It has been used extensively for both terrestrial applications4 and for other planetary bodies3,5. The pMELTS calibration of the algorithm allows for higher pressure (10-30 kbars) regimes, and is more appropriate for modeling melt compositions and equilibrium conditions for a source within the martian mantle. We use the pMELTS program to model how partial melting of the martian mantle could evolve magmas into the surface compositions derived from the GRS instrument, and how the mantle beneath Elysium has changed over time. We attribute changes to lithospheric loading by long term, episodic volcanism within the EVP throughout its history. 1. Vaucher, J. et al. The volcanic history of central Elysium Planitia: Implications for martian magmatism. Icarus 204, 418-442 (2009). 2. Susko, D. et al. A record of igneous evolution in Elysium, a major martian volcanic province. Scientific Reports 7, 43177 (2017). 3. El Maarry, M. R. et al. Gamma-ray constraints on the chemical composition of the martian surface in the Tharsis region: A signature of partial melting of the mantle? Journal of Volcanology and Geothermal Research 185, 116-122 (2009). 4. Ding, S. & Dasgupta, R. The

  9. Geochronology Intermediary Laboratory implantation at the Rio Grande do Norte Federal University: the dating of the Serrinha Granitoid (RN) and the correlate Brasiliana extensional deformation; Implantacao do Laboratorio Intermediario de Geocronologia na UFRN: a datacao do granitoide de Serrinha (RN) e da deformacao extensional brasiliana correlata

    Energy Technology Data Exchange (ETDEWEB)

    Macedo, Maria Helena F.; Sa, Emanuel F. Jardim de; Souza, Zorano S. [Pernambuco Univ., Recife, PE (Brazil). Nucleo de Pesquisa em Geodinamica e Geofisica; Mendes, Franklin S. [Pernambuco Univ., Recife, PE (Brazil). Curso de Quimica; Ramalho, Karlos A.C. [Pernambuco Univ., Recife, PE (Brazil). Curso de Geologia

    1997-12-31

    The article describes the activities developed by the Geochronology Intermediary Laboratory at the Federal University of the Rio Grande do Norte, a Brazilian university, where there were the preoccupation of establishing strategies for a geochronological development. It relates the Rubidium-Strontium (Rb/Sr) and Samarium-Neodymium (Sm/Nd) methods, describing the analysis realized in these methodologies. Afterward, it presents the geological and petrographic situation of the Granitoide de Serrinha, located at Rio Grande do Norte State, Brazil and its geochronological data 8 refs., 2 figs.

  10. Investigating Magmatic Processes in the Lower Levels of Mantle-derived Magmatic Systems: The Age & Emplacement of the Kunene Anorthosite Complex (SW Angola)

    Science.gov (United States)

    Hayes, B.; Bybee, G. M.; Owen-Smith, T.; Lehmann, J.; Brower, A. M.; Ashwal, L. D.; Hill, C. M.

    2017-12-01

    Our understanding of mantle-derived magmatic systems has shifted from a notion of upper crustal, melt-dominated magma chambers that feed short-lived volcanic eruptions, to a view of more long-lived trans-crustal, mush-dominated systems. Proterozoic massif-type anorthosite systems are voluminous, plagioclase-dominated plutonic suites with ubiquitous intermediate compositions (An 50 ± 10) that represent mantle-derived magmas initially ponded at Moho depths and crystallized polybarically until emplacement at mid-crustal levels. Thus, these systems provide unique insight into magma storage and processing in the lower reaches of the magma mush column, where such interpretation has previously relied on cumulate xenoliths in lavas, geophysical data and experimental/numerical modeling. We present new CA-ID-TIMS ages and a series of detailed field observations from the largest Proterozoic anorthosite massif on Earth, the Kunene Anorthosite Complex (KAC) of SW Angola. Field structures indicate that (i) the bulk of the material was emplaced in the form of crystal mushes, as both plutons and sheet-like intrusions; (ii) prolonged magmatism led to cumulate disaggregation (block structure development) and remobilization, producing considerable textural heterogeneity; (iii) crystal-rich magmatic flow induced localized recrystallization and the development of protoclastic (mortar) textures; and (iv) late residual melts were able to migrate locally prior to complete solidification. Dating of pegmatitic pods entrained from cumulate zones at the base of the crust (1500 ± 13 Ma) and their host anorthosites (1375-1438 Ma) reveals time periods in the range of 60-120 Myr between the earliest products of the system and the final mushes emplaced at higher crustal levels. Therefore, the KAC represents a complex, mushy magmatic system that developed over a long period of time. Not only do these observations help in refining our understanding of Proterozoic anorthosite petrogenesis, they

  11. Uranium distributions in the mineral constituents of granitoid rocks and the associated pegmatites at Wadi Abu Had, north eastern desert, Egypt

    International Nuclear Information System (INIS)

    Nossair, L.M.; Moharem, A.F.; Abdel Warith, A.

    2007-01-01

    Wadi Abu Had area is located at the northern part of the Eastern Desert of Egypt. It covers about 55 km2 of the crystalline basement rocks stretching between latitudes 28o 15'- 28o 25' N and longitudes 32o 25' - 32o 35' E. Abu Had younger granites are fertile (uraniferous) granites as they possess U-contents greater than 11 ppm. Their associated pegmatites show higher U-contents than those of granitoid rocks and hosting secondary uranium minerals. Numerous unzoned and zoned pegmatite pockets are associated with the marginal parts of granodiorite and within younger granites. Zoned pegmatites are the most radioactive ones. They are composed of extremely coarse-grained milky quartz core, intermediate zone of mica and wall zone of feldspars. An alteration zone with secondary uranium minerals (uranophane and beta-uranophane) is found at the contact between quartz core and the intermediate zone.

  12. Japan-U. S. seminar on magmatic contributions to hydrothermal systems

    Energy Technology Data Exchange (ETDEWEB)

    Muffler, L. (U. S. Geological Survey, CA (United States)); Hedenquist, J. (Geological Survey of Japan, Tsukuba (Japan)); Kesler, S. (University of Michigan, MI (United States)); Izawa, E. (Kyushu University, Fukuoka (Japan). Faculty of Engineering)

    1992-08-31

    A multidisciplinary Seminar on Magmatic Contributions to Hydrothermal Systems'' was held at Ebino and Kagoshima at Kyushu, November, 1991. The principal purpose of the Ebino/Kagoshima Seminar was to bring together a small group of individuals which have been conducting active research on magmatic contributions to hydrothermal systems. The Seminar focussed on the porphyry and epithermal ore environments because of the potential to relate these environments to active volcanic and geothermal systems. Disciplines included valcanology, volcanic gas geochemistry, water geochemistry, isotope geochemistry, geochemical modeling, experimental geochemistry, igneous petrology, geothermal geology, economic geology, fluid-inclusion study, geophysics, and physical modeling. This paper summarizes the outline and significance of the Seminar. It was pointed out that understanding magmatic contributions to hydrothermal systems would require augmented experimental investigations, numerical modeling, field studies, and drilling.

  13. Red-Sea rift magmatism near Al Lith, Kingdom of Saudi Arabia

    Science.gov (United States)

    Pallister, J.S.

    1986-01-01

    A newly recognized Tertiary dike complex and comagmatic volcanic rocks exposed on the central Saudi Arabian coastal plain record early stages of magmatism related to Red Sea rifting. Intrusive and stratigraphic relationships, and new potassium-argon dating indicate episodic magmatism from about 30 Ma to the present. Additional stratigraphic and radiometric evidence suggests that limited rift-related magmatism may have began as early as about 50 Ma ago. An early phase of crustal extension in the region was accompanied by faulting and graben formation and by dike-swarm intrusion. The style of extension and intrusion changed approximately 20 Ma ago. Localized volcanism and sheeted dike injection ceased and were replaced by the intrusion of thick gabbro dikes. This change may mark the onset of sea-floor spreading in the central Red Sea.

  14. Pluton emplacement and magmatic arc construction: A model from the Patagonian batholith

    Science.gov (United States)

    Bruce, Robert; Nelson, Eric; Weaver, Stephen

    1988-01-01

    A model of batholithic construction in Andean arcs and its applicability to possibly similar environments in the past is described. Age and compositional data from the Patagonian batholith of southern Chile show a long history of magmatism in any given area (total age range is 15 to 157 Ma), but different regions appear to have different magmatic starting ages. Furthermore, mafic rocks seem to be the oldest components of any given region. An assembly line model involving semicontinuous magmatism and uplift was outlined, which has implications for other terranes: uplift rates will be proportional to observed ranges in age, and total uplift will be proportional to the age of the oldest pluton in any given area. It is suggested that misleading results would be obtained if only small areas of similar terranes in the Archean were available for study.

  15. Characteristics of mesozoic magmatic rocks in western Zhejiang and their relation with uranium mineralization

    International Nuclear Information System (INIS)

    Zhou Jiazhi

    2000-01-01

    The author summarizes characteristics of Mesozoic (Yangshanian Period) acid-intermediate volcanics, sub-volcanics and basic intrusive from aspects of formation time of rock series, petrogenic sequence, chemical composition, rock -controlling factors and petrogenic environments. It is suggested that these rocks were originated from different source areas of crust and mantle. Based on the time-space relation between different types uranium deposits and magmatic rocks, the author proposes that: the earlier stage (Earlier Cretaceous) U-hematite ores were originated from acid volcanic magmatism of crustal source, but the later stage (Late Cretaceous) pitchblende-polymetallic sulfide and pitchblende-purple fluorite rich ores were derived from basic magmatism of mantle source. Finally, the author proposes prospecting criteria of the above two types of uranium deposits

  16. Decreasing Magmatic Footprints of Individual Volcanos in a Waning Basaltic Field

    Energy Technology Data Exchange (ETDEWEB)

    G.A> Valentine; F.V. Perry

    2006-06-06

    The distribution and characteristics of individual basaltic volcanoes in the waning Southwestern Nevada Volcanic Field provide insight into the changing physical nature of magmatism and the controls on volcano location. During Pliocene-Pleistocene times the volumes of individual volcanoes have decreased by more than one order of magnitude, as have fissure lengths and inferred lava effusion rates. Eruptions evolved from Hawaiian-style eruptions with extensive lavas to eruptions characterized by small pulses of lava and Strombolian to violent Strombolian mechanisms. These trends indicate progressively decreasing partial melting and length scales, or magmatic footprints, of mantle source zones for individual volcanoes. The location of each volcano is determined by the location of its magmatic footprint at depth, and only by shallow structural and topographic features that are within that footprint. The locations of future volcanoes in a waning system are less likely to be determined by large-scale topography or structures than were older, larger volume volcanoes.

  17. The study of the mineralogy and rare earth elements behavior in the hydrothermal alteration zones of the Astaneh granitoid massif (SW Arak, Markazi province, Iran)

    International Nuclear Information System (INIS)

    Esmaeily, D.; Afshooni, S. Z.; Valizadeh, M. V.

    2009-01-01

    The Astaneh granitoid massif is located about 40 km to Arak city, central Iran, is a part of Sanandaj-Sirjan structural zone. These intrusive rocks which are mainly composed of gronodioritic rocks, widely affected under hydrothermal alteration. The alteration zones, on the basis of field studies and mineralogy as well as the study of the REE behavior, are investigated in this paper. Eight alteration zones including phyllic (sericitic) with quartz, sericite and pyrite; chloritic with quartz, sericite and chlorite; propylitic with chlorite, epidot, calcite and albite; argillic with clay minerals (chlorite and illite); silicic with abundant quartz; albitic with albite, chlorite and quartz; hematitisation with hematite, Fe-carbonates (ankerite and siderite) and tourmalinisation with tourmaline (dravite) are identified. The results demonstrate notable differences in the REE behavior in the different alteration zones. Accordingly, comparison with the fresh rocks, in the phyllic (sericitic) alteration, LREE are enriched, but HREE, except Yb which enriched, unchanged. Also in chloritic alteration zone, LREEs are depleted, but HREEs represent different behaviors. In the argillic and propylitic alteration zones, all REE are depleted, but compared with HREE, the LREE represent more depletion. In the silicic and hematitisation alteration zones, compared with HREE, the LREE are enriched. Finally, in the albitic and tourmalinisation alteration zones all REE are depleted. These features indicate that the behavior of REE in the hydrothermal alteration zones of the Astaneh granitoid rocks is mainly controlled by p H, availability of complexing ions in the fluid as well as the presence of secondary phases as host REE minerals

  18. Understanding the Yellowstone magmatic system using 3D geodynamic inverse models

    Science.gov (United States)

    Kaus, B. J. P.; Reuber, G. S.; Popov, A.; Baumann, T.

    2017-12-01

    The Yellowstone magmatic system is one of the largest magmatic systems on Earth. Recent seismic tomography suggest that two distinct magma chambers exist: a shallow, presumably felsic chamber and a deeper much larger, partially molten, chamber above the Moho. Why melt stalls at different depth levels above the Yellowstone plume, whereas dikes cross-cut the whole lithosphere in the nearby Snake River Plane is unclear. Partly this is caused by our incomplete understanding of lithospheric scale melt ascent processes from the upper mantle to the shallow crust, which requires better constraints on the mechanics and material properties of the lithosphere.Here, we employ lithospheric-scale 2D and 3D geodynamic models adapted to Yellowstone to better understand magmatic processes in active arcs. The models have a number of (uncertain) input parameters such as the temperature and viscosity structure of the lithosphere, geometry and melt fraction of the magmatic system, while the melt content and rock densities are obtained by consistent thermodynamic modelling of whole rock data of the Yellowstone stratigraphy. As all of these parameters affect the dynamics of the lithosphere, we use the simulations to derive testable model predictions such as gravity anomalies, surface deformation rates and lithospheric stresses and compare them with observations. We incorporated it within an inversion method and perform 3D geodynamic inverse models of the Yellowstone magmatic system. An adjoint based method is used to derive the key model parameters and the factors that affect the stress field around the Yellowstone plume, locations of enhanced diking and melt accumulations. Results suggest that the plume and the magma chambers are connected with each other and that magma chamber overpressure is required to explain the surface displacement in phases of high activity above the Yellowstone magmatic system.

  19. Geology of the Baskil (Elazığ Area and the Petrology of Baskil Magmatics

    Directory of Open Access Journals (Sweden)

    H. Jerf ASUTAY

    1986-06-01

    Full Text Available The study area which covers the region around Baskil on Eastern Taurus Range comprises of Keban metamorphics and Baskil magmatics overlain by a Tertiary sedimentary cover. The Keban metamorphics are represented by regional and contact metamorphic rocks in the study area. Calc schist and marble associations are widespread on the regional scale. Between Baskil granite and Keban metamorphics exomorphism and endomorphism zones have been developed. Metasomatic effects are observed in the contact metamorphic rocks which reflect the pyroxene-hornfels facies. The sedimentary sequence begins with Middle Paleocene (Thanetian aged rocks in the study area. The same sequence, however, has been deposited starting in Santonian-Campanian in the surrounding area. The sedimentary rock sequence which is composed of Kuşçular conglomerate, Seske formation, Kırkgeçit formation (Paleocene-Plio-Quaternary are represented by conglomerate, carbonates and flysch kind of sedimentary rocks. Baskil magmatics are an association of plutonic, hypabyssal and volcanic rocks. Of this association, Baskil granite contains dioritic, monzonitic and tonalitic kind of magmatic rocks which are mostly observed as transitional. Baskil granite, in the study area, is frequently cut across by basic and acidic dykes which locally intrudes between the granite and the basaltic, andesitic rocks overlying the granite and are transitional with the volcanics. Chemically, Baskil granite is of calc-alkaline type. It is rich in silica and alkaline. Trace element distribution is quite regular. Baskil granite which is determined as of type 'I' is generally rich in hornblende but poor in muscovite and biotite. It shows the features of continental margin magmatism and is an example of systematic differentiation. Considering their features and under the light of plate tectonics concept, Baskil magmatics may be said to be a product of continental margin magmatism. They are, presumably, the products of an

  20. Formation of heterogeneous magmatic series beneath North Santorini, South Aegean island arc

    DEFF Research Database (Denmark)

    Bailey, John C; Jensen, E.S.; Hansen, A.

    2008-01-01

    magma formation beneath North Santorini throughout its 500 ka history is attributed to variable transfer of sedimentary components - either terrigenous or pelagic, as bulk sediments or high-temperature partial melts rather than fluids or low-temperature partial melts - from a rupture zone...... in the subducted slab to the overlying mantle. The three main magmatic series followed independent paths of assimilation of upper crustal materials during fractional crystallization. Assimilation was more pronounced at the basaltic stage. The long-lived histories of the three main magmatic series imply repetitive...... melting of isolated mantle regions, ascent of magmas through independent feeder systems, and their residence in separate crustal magma chambers....

  1. Duration of Parana magmatism and implications for the evolution and source regions of continental flood basalts

    International Nuclear Information System (INIS)

    Mantovani, M.S.M.; Stewart, K.; Turner, S.; Hawkesworth, C.J.

    1995-01-01

    Duration of Continental Floods Basalts magmatism has generally been considered to be extremely short. Ar-Ar data for different magma type, over a broad region within Parana, demonstrate a duration of 10 Ma, an order of magnitude greater than the usually accepted duration of magmatism. The dating method included rigorous geochemical selection tests, to discard altered samples, combined with the analysis of laser spot technique using the isochron approach. This methodology allows discrimination between rocks which yield precise ages and those which are too altered or heterogeneous. The agreement between the determined age and the relative stratigraphic position of samples supports the above statement. 4 figs

  2. Duration of Parana magmatism and implications for the evolution and source regions of continental flood basalts

    Energy Technology Data Exchange (ETDEWEB)

    Mantovani, M.S.M. [Sao Paulo Univ., SP (Brazil). Inst. Astronomico e Geofisico; Stewart, K.; Turner, S.; Hawkesworth, C.J. [Open Univ., Milton Keynes (United Kingdom). Dept. of Earth Sciences

    1995-12-31

    Duration of Continental Floods Basalts magmatism has generally been considered to be extremely short. Ar-Ar data for different magma type, over a broad region within Parana, demonstrate a duration of 10 Ma, an order of magnitude greater than the usually accepted duration of magmatism. The dating method included rigorous geochemical selection tests, to discard altered samples, combined with the analysis of laser spot technique using the isochron approach. This methodology allows discrimination between rocks which yield precise ages and those which are too altered or heterogeneous. The agreement between the determined age and the relative stratigraphic position of samples supports the above statement. 4 figs.

  3. Asymmetric rifting, breakup and magmatism across conjugate margin pairs: insights from Newfoundland to Ireland

    Science.gov (United States)

    Peace, Alexander L.; Welford, J. Kim; Foulger, Gillian R.; McCaffrey, Ken J. W.

    2017-04-01

    Continental extension, subsequent rifting and eventual breakup result in the development of passive margins with transitional crust between extended continental crust and newly created oceanic crust. Globally, passive margins are typically classified as either magma-rich or magma-poor. Despite this simple classification, magma-poor margins like the West Orphan Basin, offshore Newfoundland, do exhibit some evidence of localized magmatism, as magmatism to some extent invariably accompanies all continental breakup. For example, on the Newfoundland margin, a small volcanic province has been interpreted near the termination of the Charlie Gibbs Fracture Zone, whereas on the conjugate Irish margin within the Rockall Basin, magmatism appears to be more widespread and has been documented both in the north and in the south. The broader region over which volcanism has been identified on the Irish margin is suggestive of magmatic asymmetry across this conjugate margin pair and this may have direct implications for the mechanisms governing the nature of rifting and breakup. Possible causes of the magmatic asymmetry include asymmetric rifting (simple shear), post-breakup thermal anomalies in the mantle, or pre-existing compositional zones in the crust that predispose one of the margins to more melting than its conjugate. A greater understanding of the mechanisms leading to conjugate margin asymmetry will enhance our fundamental understanding of rifting processes and will also reduce hydrocarbon exploration risk by better characterizing the structural and thermal evolution of hydrocarbon bearing basins on magma-poor margins where evidence of localized magmatism exists. Here, the latest results of a conjugate margin study of the Newfoundland-Ireland pair utilizing seismic interpretation integrated with other geological and geophysical datasets are presented. Our analysis has begun to reveal the nature and timing of rift-related magmatism and the degree to which magmatic asymmetry

  4. Magmatic Diversity of the Wehrlitic Intrusions in the Oceanic Lower Crust of the Northern Oman Ophiolite

    Science.gov (United States)

    Kaneko, R.; Adachi, Y.; Miyashita, S.

    2014-12-01

    The Oman ophiolite extends along the east coast of Oman, and is the world's largest and best-preserved slice of obducted oceanic lithosphere. The magmatic history of this ophiolite is complex and is generally regarded as having occurred in three stages (MOR magmatism, subduction magmatism and intraplate magmatism). Wehrlitic intrusions constitute an important element of oceanic lower crust of the ophiolite, and numerous intrusions cut gabbro units in the northern Salahi block of this ophiolite. In this study area, we identified two different types of wehrlitic intrusions. One type of the intrusions mainly consists of dunite, plagioclase (Pl) wehrlite and mela-olivine (Ol) gabbro, in which the crystallization sequence is Ol followed by the contemporaneous crystallization of Pl and clinopyroxene (Cpx). This type is called "ordinary" wehrlitic intrusions and has similar mineral compositions to host gabbros (Adachi and Miyashita 2003; Kaneko et al. 2014). Another type of the intrusions is a single intrusion that crops out in an area 250 m × 150 m along Wadi Salahi. This intrusion consists of Pl-free "true" wehrlite, in which the crystallization sequence is Ol and then Cpx. The forsterite contents (Fo%) of Ol from the "ordinary" wehrlitic intrusions and "true" wehrlitic intrusions have ranges of 90.8-87.0 (NiO = 0.36-0.13 wt%) and 84.7 (NiO = 0.31 wt%), respectively. Cr numbers (Cr#) of Cr-spinel from the "true" wehrlitic intrusions show higher Cr# value of 0.85 than those of the "ordinary" wehrlitic intrusions (0.48-0.64). But the former is characterized by very high Fe3+ values (YFe3+ = 0.49-0.68). Kaneko et al. (2014) showed that the "ordinary" ubiquitous type has similar features to MOR magmatism and the depleted type in the Fizh block (Adachi and Miyashita 2003) links to subduction magmatism. These types are distinguished by their mineral chemistries (TiO2 and Na2O contents of Cpx). The TiO2 and Na2O contents of Cpx from the "true" wehrlitic intrusions have 0

  5. Continental crust melting induced by subduction initiation of the South Tianshan Ocean: Insight from the Latest Devonian granitic magmatism in the southern Yili Block, NW China

    Science.gov (United States)

    Bao, Zihe; Cai, Keda; Sun, Min; Xiao, Wenjiao; Wan, Bo; Wang, Yannan; Wang, Xiangsong; Xia, Xiaoping

    2018-03-01

    The Tianshan belt of the southwestern Central Asian Orogenic Belt was generated by Paleozoic multi-stage subduction and final closure of several extinct oceans, including the South Tianshan Ocean between the Kazakhstan-Yili and Tarim blocks. However, the subduction initiation and polarity of the South Tianshan Ocean remain issues of highly debated. This study presents new zircon U-Pb ages, geochemical compositions and Sr-Nd isotopes, as well as zircon Hf isotopic data of the Latest Devonian to Early Carboniferous granitic rocks in the Wusun Mountain of the Yili Paleozoic convergent margin, which, together with the spatial-temporal distributions of regional magmatic rocks, are applied to elucidate their petrogenesis and tectonic linkage to the northward subduction initiation of the South Tianshan Ocean. Our zircon U-Pb dating results reveal that these granites were emplaced at the time interval of 362.0 ± 1.2-360.3 ± 1.9 Ma, suggesting a marked partial melting event of the continental crust in the Latest Devonian to Early Carboniferous. These granites, based on their mineral compositions and textures, can be categorized as monzogranites and K-feldspar granites. Geochemically, both monzogranites and K-feldspar granites have characters of I-type granites with high K2O contents (4.64-4.83 wt.%), and the K-feldspar granites are highly fractionated I-type granites, while the monzogranites have features of unfractionated I-type granites. Whole-rock Sr-Nd isotopic modeling results suggest that ca. 20-40% mantle-derived magmas may be involved in magma mixing with continental crust partial melts to generate the parental magmas of the granites. The mantle-derived basaltic magmas was inferred not only to be a major component of magma mixture but also as an important heat source to fuse the continental crust in an extensional setting, which is evidenced by the high zircon saturation temperatures (713-727 °C and 760-782 °C) of the studied granites. The Latest Devonian to

  6. Sources of Magmatic Volatiles Discharging from Subduction Zone Volcanoes

    Science.gov (United States)

    Fischer, T.

    2001-05-01

    Subduction zones are locations of extensive element transfer from the Earth's mantle to the atmosphere and hydrosphere. This element transfer is significant because it can, in some fashion, instigate melt production in the mantle wedge. Aqueous fluids are thought to be the major agent of element transfer during the subduction zone process. Volatile discharges from passively degassing subduction zone volcanoes should in principle, provide some information on the ultimate source of magmatic volatiles in terms of the mantle, the crust and the subducting slab. The overall flux of volatiles from degassing volcanoes should be balanced by the amount of volatiles released from the mantle wedge, the slab and the crust. Kudryavy Volcano, Kurile Islands, has been passively degassing at 900C fumarole temperatures for at least 40 years. Extensive gas sampling at this basaltic andesite cone and application of CO2/3He, N2/3He systematics in combination with C and N- isotopes indicates that 80% of the CO2 and approximately 60% of the N 2 are contributed from a sedimentary source. The mantle wedge contribution for both volatiles is, with 12% and 17% less significant. Direct volatile flux measurements from the volcano using the COSPEC technique in combination with direct gas sampling allows for the calculation of the 3He flux from the volcano. Since 3He is mainly released from the astenospheric mantle, the amount of mantle supplying the 3He flux can be determined if initial He concentrations of the mantle melts are known. The non-mantle flux of CO2 and N2 can be calculated in similar fashion. The amount of non-mantle CO2 and N2 discharging from Kudryavy is balanced by the amount of CO2 and N2 subducted below Kudryavy assuming a zone of melting constrained by the average spacing of the volcanoes along the Kurile arc. The volatile budget for Kudryavy is balanced because the volatile flux from the volcano is relatively small (75 t/day (416 Mmol/a) SO2, 360 Mmol/a of non-mantle CO2 and

  7. Is there excess argon in the Fish Canyon magmatic system?

    Science.gov (United States)

    Wilkinson, C. M.; Sherlock, S.; Kelley, S. P.; Charlier, B. L.

    2010-12-01

    Some phenocrysts from the Fish Canyon Tuff (San Juan volcanic field, south-western Colorado, USA) have yielded anomalously old 40Ar/39Ar apparent ages and yet the sanidine ages are sufficiently reproducible to allow its use as an international standard. The eruption age of the Fish Canyon tuff has recently been determined by high precision analysis and recalibration of the decay constants based on the sanidine standard at 28.305 ± 0.036 Ma [1], slightly younger than the generally accepted U-Pb age. Previously, minerals from the tuff have been used in various geochronological studies e.g., fission-track; U-Pb; Rb-Sr; K-Ar and 40Ar/39Ar, but U-Pb zircon ages which range 28.37 - 28.61 Ma appear to be older than the sanidine and other minerals, including biotite, yield older ages (27.41 - 28.25 Ma for biotite) [2]. In the Fish Canyon volcanic system, the erupted products are thought to exist in the magma chamber for significant periods prior to eruption [3] and then pass rapidly from a high temperature magmatic environment (where Ar is free to re-equilibrate among the minerals), to effectively being quenched upon eruption (where Ar becomes immobile). Artificially elevated ages, older than eruption age, have been identified in some 40Ar/39Ar geochronological studies (e.g. [4]). These older ages may either reflect; 1) argon accumulation in pheno- or xenocrysts (by radioactive decay of parent 40K), 2) excess argon (40ArE) incorporated into a mineral during crystallisation (via diffusion into the mineral lattice or hosted within fluid or melt inclusions) or 3) inherited radiogenic argon (the dated material contains a component older than the age of eruption) [5]. To better understand the effects of 40ArE on 40Ar/39Ar apparent ages we have conducted a detailed study of intra-grain grain age variations by UV-LAMP Ar-analysis. Analysis of polished thick sections has been performed in-situ using a 213nm laser and Nu Instruments Noblesse which is able to discriminate against

  8. D/N and /sup 18/O//sup 16/O in magmatic waters and gases of the Great Tolbachik fissure eruption, Kamchatka

    Energy Technology Data Exchange (ETDEWEB)

    Menyailov, I A; Vetshtein, V E; Nikitina, L P; Artemchuk, V G [AN SSSR, Petropavlovsk-Kamchatskii. Inst. Vulkanologii; AN Ukrainskoj SSR, Kiev. Inst. Geokhimii i Fiziki Mineralov)

    1981-01-01

    Isotope content of magmatic gases and their condensates (magmatic waters) is studied on the basis of the Great Tolbachik fissure eruption, Kamchatka. The phenomenon of regular increase of deuterium content in magmatic water and protium content in gases is found out. It is supposed that this fact is conditioned by isotope fractionation during phase transitions in liquid-steam-gas system in the process of the formation of magmatic hearth and gas release from magma during eruption.

  9. The Kalatongke magmatic Ni-Cu deposits in the Central Asian Orogenic Belt, NW China: product of slab window magmatism?

    Science.gov (United States)

    Li, Chusi; Zhang, Mingjie; Fu, Piaoer; Qian, Zhuangzhi; Hu, Peiqing; Ripley, Edward M.

    2012-01-01

    The Permian Kalatongke Ni-Cu deposits in the Central Asian Orogenic Belt are among the most important Ni-Cu deposits in northern Xinjiang, western China. The deposits are hosted by three small mafic intrusions comprising mainly norite and diorite. Its tectonic context, petrogenesis, and ore genesis have been highly contested. In this paper, we present a new model involving slab window magmatism for the Kalatongke intrusions. The origin of the associated sulfide ores is explained in the context of this new model. Minor amounts of olivine in the intrusions have Fo contents varying between 71 and 81.5 mol%, which are similar to the predicted values for olivine crystallizing from coeval basalts in the region. Analytic modeling based on major element concentrations suggests that the parental magma of the Kalatongke intrusions and the coeval basalts represent fractionated liquids produced by ˜15% of olivine crystallization from a primary magma, itself produced by 7-8% partial melting of depleted mantle peridotite. Positive ɛ Nd values (+4 to +10) and significant negative Nb anomalies for both intrusive and extrusive rocks can be explained by the mixing of magma derived from depleted mantle with 6-18% of a partial melt derived from the lower part of a juvenile arc crust with a composition similar to coeval A-type granites in the region, plus up to 10% contamination with the upper continental crust. Our model suggests that a slab window was created due to slab break-off during a transition from oceanic subduction to arc-arc or arc-continent collision in the region in the Early Permian. Decompression melting in the upwelling oceanic asthenosphere produced the primary magma. When this magma ascended to pond in the lower parts of a juvenile arc crust, it underwent olivine crystallization and at the same time triggered partial melting of the arc crust. Mixing between these two magmas followed by contamination with the upper crust after the magma ascended to higher crustal

  10. Observational Constraints on the Identification of Shallow Lunar Magmatism: Insights from Floor-Fractured Craters

    Science.gov (United States)

    Jozwiak, L. M.; Head, J. W., III; Neumann, G. A.; Wilson, L.

    2016-01-01

    Floor-fractured craters are a class of lunar crater hypothesized to form in response to the emplacement of a shallow magmatic intrusion beneath the crater floor. The emplacement of a shallow magmatic body should result in a positive Bouguer anomaly relative to unaltered complex craters, a signal which is observed for the average Bouguer anomaly interior to the crater walls. We observe the Bouguer anomaly of floor-fractured craters on an individual basis using the unfiltered Bouguer gravity solution from GRAIL and also a degree 100-600 band-filtered Bouguer gravity solution. The low-magnitude of anomalies arising from shallow magmatic intrusions makes identification using unfiltered Bouguer gravity solutions inconclusive. The observed anomalies in the degree 100-600 Bouguer gravity solution are spatially heterogeneous, although there is spatial correlation between volcanic surface morphologies and positive Bouguer anomalies. We interpret these observations to mean that the spatial heterogeneity observed in the Bouguer signal is the result of variable degrees of magmatic degassing within the intrusions.

  11. Magmatic tempo of Earth's youngest exposed plutons as revealed by detrital zircon U-Pb geochronology.

    Science.gov (United States)

    Ito, Hisatoshi; Spencer, Christopher J; Danišík, Martin; Hoiland, Carl W

    2017-09-29

    Plutons are formed by protracted crystallization of magma bodies several kilometers deep within the crust. The temporal frequency (i.e. episodicity or 'tempo') of pluton formation is often poorly constrained as timescales of pluton formation are largely variable and may be difficult to resolve by traditional dating methods. The Hida Mountain Range of central Japan hosts the youngest exposed plutons on Earth and provides a unique opportunity to assess the temporal and spatial characteristics of pluton emplacement at high temporal resolution. Here we apply U-Pb geochronology to zircon from the Quaternary Kurobegawa Granite and Takidani Granodiorite in the Hida Mountain Range, and from modern river sediments whose fluvial catchments include these plutons in order to reconstruct their formation. The U-Pb data demonstrate that the Kurobegawa pluton experienced two magmatic pulses at ~2.3 Ma and ~0.9 Ma; whereas, to the south, the Takidani pluton experienced only one magmatic pulse at ~1.6 Ma. These data imply that each of these magmatic systems were both spatially and temporally distinct. The apparent ~0.7 Myr age gap between each of the three magmatic pulses potentially constrains the recharge duration of a single pluton within a larger arc plutonic complex.

  12. The timing and sources of intraplate magmatism related to continental breakup in southern New Zealand

    DEFF Research Database (Denmark)

    van der Meer, Quinten

    related I- to I/S-type plutons of the Rahu suite up to 105 Ma. Isolated plutonism continued on a smaller scale after 105 Ma. O and Hf isotopes in zircon from later felsic plutons indicate waning subduction related magmatism up to 101 Ma. This is followed by the regional dominance of intraplate signatures...

  13. Evidence for triple-junction rifting focussed on local magmatic centres along Parga Chasma, Venus

    Science.gov (United States)

    Graff, J. R.; Ernst, R. E.; Samson, C.

    2018-05-01

    Parga Chasma is a discontinuous rift system marking the southern boundary of the Beta-Atla-Themis (BAT) region on Venus. Along a 1500 km section of Parga Chasma, detailed mapping of Magellan Synthetic Aperture Radar images has revealed 5 coronae, 11 local rift zones distinct from a regional extension pattern, and 47 graben-fissure systems with radiating (28), linear (12) and circumferential (7) geometries. The magmatic centres of these graben-fissure systems typically coincide with coronae or large volcanoes, although a few lack any central magmatic or tectonic feature (i.e. are cryptic). Some of the magmatic centres are interpreted as the foci of triple-junction rifting that form the 11 local rift zones. Cross-cutting relationships between graben-fissure systems and local rift faults reveal synchronous formation, implying a genetic association. Additionally, cross-cutting relationships show that local rifting events postdate the regional extension along Parga Chasma, further indicating multiple stages of rifting. Evidence for multiple centres of younger magmatism and local rifting against a background of regional extension provides an explanation for the discontinuous morphology of Parga Chasma. Examination of the Atlantic Rift System (prior to ocean opening) on Earth provides an analogue to the rift morphologies observed on Venus.

  14. Sr-Nd-Pb isotopes of the post-paleozoic magmatism from eastern Paraguay

    International Nuclear Information System (INIS)

    Comin-Chiaramonti, P; Gasparon, M; Gomes, C.B; Antonini, P

    2001-01-01

    The Parana Angola-Namibia igneous province (PAN) is characterized by Early Cretaceous flood tholeiites and tholeiitic dyke swarms associated with alkaline rocks of Early and Late Cretaceous ages, respectively, and with scarce post-Mesozoic magmatic rocks (Comin-Chiaramonti et al., 1997; 1999; Marques et al., 1999). The Eastern Paraguay, at the westernmost side of the Parana Basin, is of special interest because: (1) it is located between two main cratonic blocks, i.e. the southernmost tip of the Amazon Craton, and the northermost exposure of the Rio de La Plata Craton; (2) it was the site of repeated Na-K-alkaline magmatism since Late-Permian-Triassic times (i.e.: 250-240 Ma, Na-alkaline; c. 145 Ma, K-alkaline; 128-126 Ma, K-alkaline; 120-90 Ma, Na-alkaline; 61-33 Ma, Na-alkaline; cf. Comin-Chiaramonti and Gomes, 1996; Comin-Chiaramonti et al., 1999), and of Early Cretaceous tholeiitic magmatism, both low- and high-Ti variants, L-Ti and H-Ti, respectively (133-131 Ma; cf. Marzoli et al., 1999); (3) the younger sodic magmatic rocks are closely associated in space to the potassic analogues (Comin- Chiaramonti et al., 1999). The paper aims discussing the most important Sr- Nd-Pb isotope features of the alkaline and tholeiitic magmas from Eastern Paraguay in comparison with the PAN analogues (au)

  15. History of the magmatic feeding system of the Campi Flegrei caldera (Italy)

    Science.gov (United States)

    Civetta, L.; Arienzo, I.; D'Antonio, M.; di Renzo, V.; di Vito, M. A.; Orsi, G.

    2007-05-01

    The definition of the magmatic feeding system of active volcanoes in terms of architecture, composition, crystallization time-scale, relationships between composition of the erupted magmas and structural position of the vents, and magma processes, is of paramount importance for volcanic hazards evaluation. Investigations aimed at defining the Campi Flegeri magmatic system, include detailed mineralogical, geochemical and isotopic analyses (Sr, Nd, Pb, Th,U). The magmatic feeding system of the Campi Flegrei caldera is characterized by deep and shallow magma reservoirs. In the deep reservoirs (20-10 km depth) mantle- derived magmas differentiated and were contaminated by continental crust. In the shallow reservoirs isotopically distinct magmas, further differentiated, contaminated, and mixed and mingled before eruptions. These processes generated isotopically distinct components, variably interacting with the different structural elements of the Campi Flegrei caldera through time. The relationships between the structural position of the eruption vents, during the last 15 ka of activity, and the isotopic composition of the magmas erupted at the Campi Flegrei caldera allow us to reconstruct the architecture of the magmatic feeding system and to infer the chemical and isotopic composition of the magma feeding a future eruption, according to vent position.

  16. History of the Magmatic Feeding System of the Campi Flegrei Caldera

    Science.gov (United States)

    Orsi, G.; Civetta, L.; Arienzo, I.; D'Antonio, M.; di Renzo, V.; di Vito, M. A.

    2007-12-01

    The definition of the magmatic feeding system of active volcanoes, in terms of composition, time-scale of crystallization, relation between composition of the erupted magma and structural position of vents, magma chamber processes and architecture, is of extreme importance for the hazard evaluation. The studies that are carried out for the definition of the magmatic systems include detailed mineralogical, geochemical and isotopic analyses (Sr, Nd, Pb). The Campi Flegrei caldera magmatic structure is characterized by deep and shallow magma chambers. In the deep reservoir (20-10 km depth) mantle derived magmas differentiate and are contaminated with continental crust. In the shallow reservoirs isotopically distinct magmas further differentiate, mix and mingle before the eruptions. These processes generated isotopically distinct components that were variably involved along different structures of the Campi Flegrei caldera during time. At Campi Flegrei caldera the relation between the structural position of the eruptive vent, for the last 14 ka of activity, and the isotopic composition of the emitted magma allow us to reconstruct the architecture of the magmatic feeding system and to infer the chemical and isotopic composition, and the magma chamber location and processes, of the future eruption, according to the position of the vent

  17. An isotopic perspective on growth and differentiation of Proterozoic orogenic crust: From subduction magmatism to cratonization

    Science.gov (United States)

    Johnson, Simon P.; Korhonen, Fawna J.; Kirkland, Christopher L.; Cliff, John B.; Belousova, Elena A.; Sheppard, Stephen

    2017-01-01

    The in situ chemical differentiation of continental crust ultimately leads to the long-term stability of the continents. This process, more commonly known as 'cratonization', is driven by deep crustal melting with the transfer of those melts to shallower regions resulting in a strongly chemically stratified crust, with a refractory, dehydrated lower portion overlain by a complementary enriched upper portion. Since the lower to mid portions of continental crust are rarely exposed, investigation of the cratonization process must be through indirect methods. In this study we use in situ Hf and O isotope compositions of both magmatic and inherited zircons from several felsic magmatic suites in the Capricorn Orogen of Western Australia to highlight the differentiation history (i.e. cratonization) of this portion of late Archean to Proterozoic orogenic crust. The Capricorn Orogen shows a distinct tectonomagmatic history that evolves from an active continental margin through to intracratonic reworking, ultimately leading to thermally stable crust that responds similarly to the bounding Archean Pilbara and Yilgarn Cratons. The majority of magmatic zircons from the main magmatic cycles have Hf isotopic compositions that are generally more evolved than CHUR, forming vertical arrays that extend to moderately radiogenic compositions. Complimentary O isotope data, also show a significant variation in composition. However, combined, these data define not only the source components from which the magmas were derived, but also a range of physio-chemical processes that operated during magma transport and emplacement. These data also identify a previously unknown crustal reservoir in the Capricorn Orogen.

  18. Beating the Heat: Magmatism in the Low-Temperature Thermochronologic Record

    Science.gov (United States)

    Murray, K. E.; Reiners, P. W.; Braun, J.; Karlstrom, L.; Morriss, M. C.

    2017-12-01

    The low-temperature thermochronology community was quick to recognize upper-crustal complexities in the geotherm that reflect landscape evolution, but the complex effects of crustal magmatism on thermochronometers can be difficult to independently document and remain underexplored. Because magmatism is common in many regions central to our understanding of tectonics, this is a significant gap in our ability to robustly interpret rock cooling. Here, we use several different numerical approaches to examine how local and regional crustal magmatism affects cooling age patterns and present examples from the western US that demonstrate the importance—and utility—of considering these effects. We modified the finite-element code Pecube to calculate how thermochronometers document the emplacement of simple hot bodies at different crustal levels. Results demonstrate the potential for mid-crustal plutons, emplaced at 10-15 km depth, to reset cooling ages in the overlying rocks at partial-retention depths at the time of magmatism. Permo-Triassic sandstones from the Colorado Plateau's Canyonlands region have apatite cooling ages that exemplify the resulting ambiguity: Oligocene rock cooling can be attributed to either 1 km of erosion or relaxation of a geothermal gradient transiently doubled by mid-crustal magmatism. Despite these complexities, there are compelling reasons to target rocks with magmatic histories. Shallowly emplaced plutons can usefully reset cooling ages in country rocks with protracted near-surface histories, as we have demonstrated in the Colorado Plateau's Henry Mountains. Cooling age patterns are also useful for quantifying magmatic processes themselves. In an ongoing project, we use the pattern of thermochronometer resetting around individual dikes that fed the Columbia River flood basalts, which are exposed in the Wallowa Mountains, to identify long-lived feeder dikes and model their thermal aureoles to further constrain eruptive dynamics. The pattern

  19. Crustal inheritance and arc magmatism: Magnetotelluric constraints from the Washington Cascades on top-down control

    Science.gov (United States)

    Bedrosian, P.; Peacock, J.; Bowles-martinez, E.; Schultz, A.; Hill, G.

    2017-12-01

    Worldwide, arc volcanism occurs along relatively narrow magmatic arcs, the locations of which are considered to mark the onset of dehydration reactions within the subducting slab. This `bottom-up' approach, in which the location of arc volcanism reflects where fluids and melt are generated, explains first-order differences in trench-to-arc distance and is consistent with known variations in the thermal structure and geometry of subducting slabs. At a finer scale, arc segmentation, magmatic gaps, and anomalous forearc and backarc magmatism are also frequently interpreted in terms of variations in slab geometry, composition, or thermal structure.The role of inherited crustal structure in controlling faulting and deformation is well documented; less well examined is the role of crustal structure in controlling magmatism. While the source distribution of melt and subduction fluids is critical to determining the location of arc magmatism, we argue that crustal structure provides `top-down' control on patterns or seismicity and deformation as well as the channeling and ascent of arc magmas. We present evidence within the Washington Cascades based upon correlation between a new three-dimensional resistivity model, potential-field data, seismicity, and Quaternary volcanism. We image a mid-Tertiary batholith, intruded within an Eocene crustal suture zone, and extending throughout much of the crustal column. This and neighboring plutons are interpreted to channel crustal fluids and melt along their margins within steeply dipping zones of marine to transitional metasedimentary rock. Mount St. Helens is interpreted to be fed by fluids and melt generated further east at greater slab depths, migrating laterally (underplating?) beneath the Spirit Lake batholith, and ascending through metasedimentary rocks within the brittle crust. At a regional scale, we argue that this concealed suture zone controls present-day deformation and seismicity as well as the distribution of forearc

  20. Purification and Characterization of Suicin 65, a Novel Class I Type B Lantibiotic Produced by Streptococcus suis.

    Science.gov (United States)

    Vaillancourt, Katy; LeBel, Geneviève; Frenette, Michel; Fittipaldi, Nahuel; Gottschalk, Marcelo; Grenier, Daniel

    2015-01-01

    Bacteriocins are antimicrobial peptides of bacterial origin that are considered as a promising alternative to the use of conventional antibiotics. Recently, our laboratory reported the purification and characterization of two lantibiotics, suicin 90-1330 and suicin 3908, produced by the swine pathogen and zoonotic agent Streptococcus suis (serotype 2). In this study, a novel bacteriocin produced by S. suis has been identified and characterized. The producing strain S. suis 65 (serotype 2) was found to belong to the sequence type 28, that includes strains known to be weakly or avirulent in a mouse model. The bacteriocin, whose production was only possible following growth on solid culture medium, was purified to homogeneity by cationic exchange and reversed-phase high-pressure liquid chromatography. The bacteriocin, named suicin 65, was heat, pH and protease resistant. Suicin 65 was active against all S. suis isolates tested, including antibiotic resistant strains. Amino acid sequencing of the purified bacteriocin by Edman degradation revealed the presence of modified amino acids suggesting a lantibiotic. Using the partial sequence obtained, a blast was performed against published genomes of S. suis and allowed to identify a putative lantibiotic locus in the genome of S. suis 89-1591. From this genome, primers were designed and the gene cluster involved in the production of suicin 65 by S. suis 65 was amplified by PCR. Sequence analysis revealed the presence of ten open reading frames, including a duplicate of the structural gene. The structural genes (sssA and sssA') of suicin 65 encodes a 25-amino acid residue leader peptide and a 26-amino acid residue mature peptide yielding an active bacteriocin with a deducted molecular mass of 3,005 Da. Mature suicin 65 showed a high degree of identity with class I type B lantibiotics (globular structure) produced by Streptococcus pyogenes (streptococcin FF22; 84.6%), Streptococcus macedonicus (macedocin ACA-DC 198; 84

  1. Purification and Characterization of Suicin 65, a Novel Class I Type B Lantibiotic Produced by Streptococcus suis.

    Directory of Open Access Journals (Sweden)

    Katy Vaillancourt

    Full Text Available Bacteriocins are antimicrobial peptides of bacterial origin that are considered as a promising alternative to the use of conventional antibiotics. Recently, our laboratory reported the purification and characterization of two lantibiotics, suicin 90-1330 and suicin 3908, produced by the swine pathogen and zoonotic agent Streptococcus suis (serotype 2. In this study, a novel bacteriocin produced by S. suis has been identified and characterized. The producing strain S. suis 65 (serotype 2 was found to belong to the sequence type 28, that includes strains known to be weakly or avirulent in a mouse model. The bacteriocin, whose production was only possible following growth on solid culture medium, was purified to homogeneity by cationic exchange and reversed-phase high-pressure liquid chromatography. The bacteriocin, named suicin 65, was heat, pH and protease resistant. Suicin 65 was active against all S. suis isolates tested, including antibiotic resistant strains. Amino acid sequencing of the purified bacteriocin by Edman degradation revealed the presence of modified amino acids suggesting a lantibiotic. Using the partial sequence obtained, a blast was performed against published genomes of S. suis and allowed to identify a putative lantibiotic locus in the genome of S. suis 89-1591. From this genome, primers were designed and the gene cluster involved in the production of suicin 65 by S. suis 65 was amplified by PCR. Sequence analysis revealed the presence of ten open reading frames, including a duplicate of the structural gene. The structural genes (sssA and sssA' of suicin 65 encodes a 25-amino acid residue leader peptide and a 26-amino acid residue mature peptide yielding an active bacteriocin with a deducted molecular mass of 3,005 Da. Mature suicin 65 showed a high degree of identity with class I type B lantibiotics (globular structure produced by Streptococcus pyogenes (streptococcin FF22; 84.6%, Streptococcus macedonicus (macedocin ACA

  2. Mantle dynamics and Cretaceous magmatism in east-central China: Insight from teleseismic tomograms

    Science.gov (United States)

    Jiang, Guoming; Zhang, Guibin; Zhao, Dapeng; Lü, Qingtian; Li, Hongyi; Li, Xinfu

    2015-11-01

    Both the rich mineralization in the Lower Yangtze Block (LYB) and the post-collisional mafic rocks in the Dabie Orogen (DBO) are closely related to the Cretaceous magmatism in east-central China. Various geodynamic models have been proposed for explaining the mechanism of the Cretaceous magmatism, but these models are controversial and even contradictory with each other, especially on the mechanism of adakites. A unified geodynamic model is required for explaining the magmatism in east-central China, in particular, the spatial and temporal correlations of magmatic activity in the DBO and that in the LYB. For this purpose, we apply teleseismic tomography to study P-wave velocity structure down to 800 km depth beneath east-central China. A modified multiple-channel cross-correlation method is used to collect 28,805 high-quality P-wave arrival-time data from seismograms of distant earthquakes recorded by permanent seismic stations and our temporary stations in the study region. To remove the influence of crustal heterogeneity on the mantle tomography, we used the CRUST1.0 model to correct the teleseismic relative residuals. Our tomography revealed distinct high-velocity (high-V) anomalies beneath the DBO and two flanks of the LYB, and low-velocity (low-V) anomalies above the high-V zones. Combining our tomographic images with previous geological, geochemical and geophysical results, we infer that these high-V and low-V anomalies reflect the detached lithosphere and upwelling asthenospheric materials, respectively, which are associated with the Late Mesozoic dynamic process and the Cretaceous magmatism. We propose a double-slab subduction model that a ridge subduction yielded the adakitic rocks in the LYB during 150-135 Ma and the subsequent Pacific Plate subduction played a crucial role in not only the formation of igneous rocks in the LYB but also remelting of the subducted South China Block beneath the DBO during 135-101 Ma.

  3. Major, Trace Element Concentration and Triple-Oxygen Isotope Compositions of G- and I-Type Spherules from the Sør Rondane Mountains, East Antarctica

    Science.gov (United States)

    Soens, B.; Goderis, S.; Greenwood, R. C.; McKibbin, S.; Van Ginneken, M.; Vanhaecke, F.; Debaille, V.; Franchi, I. A.; Claeys, Ph.

    2017-07-01

    We present new major, trace element concentration (LA-ICP-MS) and triple-oxygen isotope (LF-IRMS) data for G- and I-type cosmic spherules. This study suggests that both types of micrometeorites may originate from ordinary chondrite parent bodies.

  4. A Silurian-early Devonian slab window in the southern Central Asian Orogenic Belt: Evidence from high-Mg diorites, adakites and granitoids in the western Central Beishan region, NW China

    Science.gov (United States)

    Zheng, Rongguo; Xiao, Wenjiao; Li, Jinyi; Wu, Tairan; Zhang, Wen

    2018-03-01

    The Beishan orogenic belt is a key region for deciphering the accretionary processes of the southern Central Asian Orogenic Belt. Here in this paper we present new zircon U-Pb ages, bulk-rock major and trace element, and zircon Hf isotopic data for the Baitoushan, and Bagelengtai plutons in the western Central Beishan region to address the accretionary processes. The Baitoushan pluton consists of quartz diorites, monzonites and K-feldspar granites, with zircon LA-ICP-MS U-Pb ages of 435 Ma, 421 Ma and 401 Ma, respectively. The Baitoushan quartz diorites and quartz monzonites exhibit relatively high MgO contents and Mg# values (63-72), display enrichments in LILEs and LREEs, and exhibit high Ba (585-1415 ppm), Sr (416-570 ppm) and compatible element (such as Cr and Ni) abundances, which make them akin to typical high-Mg andesites. The Baitoushan quartz diorites and quartz monzonites were probably generated by the interaction of subducted oceanic sediment-derived melts and mantle peridotites. The Baitoushan K-feldspar granites are ascribed to fractionated I-type granites with peraluminous and high-K calc-alkaline characteristics. They exhibit positive εHf(t) values (2.43-7.63) and Mesoproterozoic-Neoproterozoic zircon Hf model ages (0.92-1.60 Ga). Those early Devonian granites, including Baitoushan K-feldspar granite and Gongpoquan leucogranites (402 Ma), are derived from melting of the mafic lower crust and/or sediments by upwelling of hot asthenospheric mantle. The Bagelengtai granodiorites exhibit similar geochemical signatures with that of typical adakites, with a zircon SHRIMP U-Pb age of 435 Ma. They exhibit relatively high Sr (502-628 ppm) and Al2O3 (16.40-17.40 wt.%) contents, and low MgO (1.02-1.29 wt.%), Y (3.37-6.94 ppm) and HREEs contents, with relatively high Sr/Y and (La/Yb)N ratios. The Bagelengtai granodiorites were derived from partial melting of subducted young oceanic crust, with significant contributions of subducted sediments, subsequently

  5. Sr and Nd isotopic compositions, age and petrogenesis of A-type granitoids of the Vernon Supersuite, New Jersey Highlands, USA

    Science.gov (United States)

    Volkert, R.A.; Feigenson, M.D.; Patino, L.C.; Delaney, J.S.; Drake, Avery A.

    2000-01-01

    Voluminous late Mesoproterozoic monzonite through granite of the Vernon Supersuite underlies an area of approximately 1300 km2 in the Highlands of northern New Jersey. The Vernon Supersuite consists of hastingsite ?? biotite-bearing granitoids of the Byram Intrusive Suite (BIS) and hedenbergite-bearing granitoids of the Lake Hopatcong Intrusive Suite (LHIS). These rocks have similar major and trace element abundances over a range of SiO2 from 58 to 75 wt.%, are metaluminous to weakly peraluminous, and have a distinctive A-type chemistry characterized by high contents of Y, Nb, Zr, LREE, and Ga/Al ratios, and low MgO, CaO, Sr and HREE. Whole-rock Rb-Sr isochrons of BIS granite yield an age of 1116 ?? 41 Ma and initial 87Sr/86Sr ratio of 0.70389, and of LHIS granite an age of 1095 ?? 9 Ma and initial 87Sr/86Sr ratio of 0.70520. Both suites have similar initial 143Nd/144Nd ratios of 0.511267 to 0.511345 (BIS) and 0.511359 to 0.511395 (LHIS). Values of ??(Nd) are moderately high and range from +1.21 to +2.74 in the BIS and +2.24 +2.95 in the LHIS. Petrographic evidence, field relationships, geochemistry, and isotopic data support an interpretation of comagmatism and the derivation of both suites from a mantle-derived or a juvenile lower crustal parent with little crustal assimilation. Both suites crystallized under overlapping conditions controlled by P-T-f(H(2)O). Lake Hopatcong magma crystallized at a liquidus temperature that approached 900??C and a pressure of about 6 kbar, and remained relatively anhydrous throughout its evolution. Initial P-T conditions of the Byram magma were ??? 850??C and about 5.5 kbar. BIS magma was emplaced contemporaneous with, or slightly preceding LHIS magma, and both magmas were emplaced during a compressional tectonic event prior to granulite facies metamorphism that occurred in the Highlands between 1080 and 1030 Ma. (C) 2000 Elsevier Science B.V. All rights reserved.

  6. Weathering profiles in granitoid rocks of the Sila Massif uplands, Calabria, southern Italy: New insights into their formation processes and rates

    Science.gov (United States)

    Scarciglia, Fabio; Critelli, Salvatore; Borrelli, Luigi; Coniglio, Sabrina; Muto, Francesco; Perri, Francesco

    2016-05-01

    In this paper we characterized several weathering profiles developed on granitoid rocks in the Sila Massif upland (Calabria, southern Italy), integrating detailed macro- and micromorphological observations with physico-mechanical field tests and petrographic, mineralogical and geochemical analyses. We focused our attention on the main weathering and pedogenetic processes, trying to understand apparent discrepancies between weathering grade classes based on field description and geomechanical properties, and two common weathering indices, such as the micropetrographic index (Ip) and the chemical index of alteration (CIA). Our results showed that sericite on plagioclase and biotite chloritization, that represent inherited features formed during late-stage hydrothermal alteration of granitoid rocks, may cause an overestimation of the real degree of weathering of primary mineral grains under meteoric conditions, especially in lower weathering grade classes. Moreover, the frequent identification of Fe-Mn oxides and clay coatings of illuvial origin (rather than or in addition to those formed in situ), both at the macro- and microscale, may also explain an overestimation of the weathering degree with respect to field-based classifications. Finally, some apparent inconsistencies between field geomechanical responses and chemical weathering were interpreted as related to physical weathering processes (cryoclastism and thermoclastism), that lead to rock breakdown even when chemical weathering is not well developed. Hence, our study showed that particular caution is needed for evaluating weathering grades, because traditional field and geochemical-petrographic tools may be biased by inherited hydrothermal alteration, physical weathering and illuvial processes. On the basis of chronological constraints to soil formation obtained from a 42 ka-old volcanic input (mixed to granite parent materials) detected in the soil cover of the Sila Massif upland, a first attempt to estimate

  7. Comparison of the behaviour of rare earth elements in surface waters, overburden groundwaters and bedrock groundwaters in two granitoidic settings, Eastern Sweden

    International Nuclear Information System (INIS)

    Roennback, Pernilla; Astroem, Mats; Gustafsson, Jon-Petter

    2008-01-01

    This work, which was done within the Swedish nuclear waste management program, was carried out in order to increase the understanding of the mobility and fate of rare earth elements (REEs) in natural boreal waters in granitoidic terrain. Two areas were studied, Forsmark and Simpevarp, one of which will be selected as a site for spent nuclear fuel. The highest REE concentrations were found in the overburden groundwaters, in Simpevarp in particular (median ΣREE 52 μg/L), but also in Forsmark (median ΣREE 6.7 μg/L). The fractionation patterns in these waters were characterised by light REE (LREE) enrichment and negative Ce and Eu anomalies. In contrast, the surface waters had relatively low REE concentrations. They were characterised either by an increase in relative concentrations throughout the lanthanide series (Forsmark which has a carbonate-rich till) or flat patterns (Simpevarp with carbonate-poor till), and had negative Ce and Eu anomalies. In the bedrock groundwaters, the concentrations and fractionation patterns of REEs were entirely different from those in the overburden groundwaters. The median La concentrations were low (just above 0.1 μg/L in both areas), only in a few samples were the concentrations of several REEs (and in a couple of rare cases all REEs) above the detection limit, and there was an increase in the relative concentrations throughout the lanthanide series. In contrast to these large spatial variations, the temporal trends were characterised by small (or non existent) variations in REE-fractionation patterns but rather large variations in concentrations. The Visual MINTEQ speciation calculations predicted that all REEs in all waters were closely associated with dissolved organic matter, and not with carbonate. In the hydrochemical data for the overburden groundwater in particular, there was however a strong indication of association with inorganic colloids, which were not included in the speciation model. Overall the results showed

  8. Structural analysis and magmatism characterization of the Major Gercino shear zone, Santa Catarina State, Brazil; Analise estrutural e caracterizacao do magmatismo da zona de cisalhamento Major Gercino, SC

    Energy Technology Data Exchange (ETDEWEB)

    Passarelli, Claudia Regina

    1996-12-31

    This work describes the geometric and kinematic characteristics of the Major Gercino Shear Zone (MGSZ) in the Canelinha-Garcia area. This shear zone is one of the major lineaments that affect all southern Brazilian precambrian terrains. In Santa Catarina State, it separates, along its whole extension, the supracrustal rocks of the Brusque belt (northern part) from the Granitoid belt (southern). This zone is characterized by a regional NE trend and a dextral sense of movement where ductile-brittle structures predominate. The MGSZ is composed of two mylonitic belts separated by granitoid rocks probably associated to the development of the shear zone. Both shear zones show cataclastic to ultra mylonitic rocks, but mylonites and protomylonites conditions at high strain rate. The calc-alkaline granitoids present in the area can be grouped in two granitoid associations with meta to peraluminous affinities. The Rolador Granitoid Association is characterized by grayish porphyritic biotite-monzogranites and the Fernandes Granitoid Association by coarsed-grained to porphyritic pinkish amphibole-syenogranites. The U-Pb and Rb-Sr ages range from 670 to 590 Ma with the Sr{sup 87} / Sr{sup 86} initial ratios suggesting a crustal contribution in the generation of these rocks. The importance of the pure shear component is also emphasized by the results of the Fry method. Many z axes of the strain ellipses are at high angle to the shear foliation. Symmetric porphyroclasts also corroborate this hypothesis. The micaceous minerals formed during the shear development indicate K-Ar ages around 555 {+-} 15 Ma. Brittle reactivations of the shear zone have been placed by K-Ar in fine-fraction materials at Triassic time (215 {+-} 15 Ma.) 220 refs., 107 figs., 18 tabs., 4 maps

  9. The evolution of Yellowstone's magmatic system over the past 630 kyr: Insights from the crystal record

    Science.gov (United States)

    Stelten, M. E.

    2017-12-01

    The Yellowstone Plateau volcanic field in northwestern Wyoming is one of the world's largest, active silicic volcanic centers, and has produced three caldera-forming "super eruptions" over the past 2.1 Myr. As a result, the petrologic evolution of Yellowstone's magmatic system has been the focus of numerous studies over the past 60 years. Early studies at Yellowstone focused on characterizing whole-rock chemical and isotopic variations observed in magmas erupted over Yellowstone's lifetime. While these have provided important insights into the source of Yellowstone magmas and the processes controlling their compositional evolution though time, whole-rock studies are limited in their ability to identify the mechanisms and timescales of rhyolite generation. In contrast, much of the recent work at Yellowstone has focused on applying micro-analytical techniques to characterize the age and composition of phenocrysts hosted in Yellowstone rhyolites. These studies have greatly advanced our understanding of the magmatic system at Yellowstone and have provided crucial new insights into the mechanisms and timescales of rhyolite generation. In particular, recent work has focused on applying micro-analytical techniques to study the age and origin of the [1] three caldera-forming eruptions that produced the Huckleberry Ridge, Mesa Falls, Lava Creek tuffs and [2] post-Lava Creek tuff intracaldera rhyolites that compose the Plateau Rhyolite. As a result, a wealth of crystal-chemical data now exists for rhyolites erupted throughout Yellowstone's 2.1 Myr history. These data provide a unique opportunity to create a detailed reconstruction of Yellowstone's magmatic system through time. In this contribution, I integrate available age, chemical, and isotopic data for phenocrysts hosted in Yellowstone rhyolites to construct a model for the evolution of Yellowstone's magmatic system from the caldera-forming eruption of the Lava Creek tuff at ca. 0.63 Ma to the present day. In particular

  10. Continental extension, magmatism and elevation; formal relations and rules of thumb

    Science.gov (United States)

    Lachenbruch, A.H.; Morgan, P.

    1990-01-01

    To investigate simplified relations between elevation and the extensional, magmatic and thermal processes that influence lithosphere buoyancy, we assume that the lithosphere floats on an asthenosphere of uniform density and has no flexural strength. A simple graph relating elevation to lithosphere density and thickness provides an overview of expectable conditions around the earth and a simple test for consistancy of continental and oceanic lithosphere models. The mass-balance relations yield simple general rules for estimating elevation changes caused by various tectonic, magmatic and thermal processes without referring to detailed models. The rules are general because they depend principally on buoyancy, which under our assumptions is specified by elevation, a known quantity; they do not generally require a knowledge of lithosphere thickness and density. The elevation of an extended terrain contains important information on its tectonic and magmatic history. In the Great Basin where Cenozoic extension is estimated to be 100%, the present high mean elevation ( ~ 1.75 km) probably requires substantial low-density magmatic contributions to the extending lithosphere. The elevation cannot be reasonably explained solely as the buoyant residue of a very high initial terrane, or of a lithosphere that was initially very thick and subsequently delaminated and heated. Even models with a high initial elevation typically call for 10 km or so of accumulated magmatic material of near-crustal density. To understand the evolution of the Great Basin, it is important to determine whether such intruded material is present; some could replenish the stretching crust by underplating and crustal intrusion and some might reside in the upper mantle. The elevation maintained or approached by an intruded extending lithosphere depends on the ratio B of how fast magma is supplied from the asthenosphere ( b km/Ma) to how fast the lithosphere spreads the magma out by extension (?? Ma-1). For a

  11. Mg isotope systematics during magmatic processes: Inter-mineral fractionation in mafic to ultramafic Hawaiian xenoliths

    Science.gov (United States)

    Stracke, A.; Tipper, E. T.; Klemme, S.; Bizimis, M.

    2018-04-01

    Observed differences in Mg isotope ratios between bulk magmatic rocks are small, often on a sub per mill level. Inter-mineral differences in the 26Mg/24Mg ratio (expressed as δ26Mg) in plutonic rocks are on a similar scale, and have mostly been attributed to equilibrium isotope fractionation at magmatic temperatures. Here we report Mg isotope data on minerals in spinel peridotite and garnet pyroxenite xenoliths from the rejuvenated stage of volcanism on Oahu and Kauai, Hawaii. The new data are compared to literature data and to theoretical predictions to investigate the processes responsible for inter-mineral Mg isotope fractionation at magmatic temperatures. Theory predicts up to per mill level differences in δ26Mg between olivine and spinel at magmatic temperatures and a general decrease in Δ26Mgolivine-spinel (=δ26Mgolivine - δ26Mgspinel) with increasing temperature, but also with increasing Cr# in spinel. For peridotites with a simple petrogenetic history by melt depletion, where increasing depletion relates to increasing melting temperatures, Δ26Mgolivine-spinel should thus systematically decrease with increasing Cr# in spinel. However, most natural peridotites, including the Hawaiian spinel peridotites investigated in this study, are overprinted by variable extents of melt-rock reaction, which disturb the systematic primary temperature and compositionally related olivine-spinel Mg isotope systematics. Diffusion, subsolidus re-equilibration, or surface alteration may further affect the observed olivine-spinel Mg isotope fractionation in peridotites, making Δ26Mgolivine-spinel in peridotites a difficult-to-apply geothermometer. The available Mg isotope data on clinopyroxene and garnet suggest that this mineral pair is a more promising geothermometer, but its application is restricted to garnet-bearing igneous (garnet pyroxenites) and metamorphic rocks (eclogites). Although the observed δ26Mg variation is on a sub per mill range in bulk magmatic rocks

  12. The 226Ra isotope activities in ground water samples drawn of two wells from the Meridional Pluton, Morungaba Granitoids, eastern Sao Paulo State; Atividades do 226Ra em aguas subterraneas extraidas de dois pocos localizados no pluton meridional, granitoides de Morungaba, SP

    Energy Technology Data Exchange (ETDEWEB)

    Lucas, Fabio de Oliveira; Silva Junior, Mario Goncalves da; Bertolla, Luciana; Ribeiro, Fernando Brenha [Sao Paulo Univ., SP (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas. Dept. de Geofisica]. E-mail: brenha@iag.usp.br

    2005-07-01

    The 226Ra activities, both in solution and associated with suspended solids, were measured in ground water samples drawn from two wells drilled in a fractured granitic aquifer from the Meridional Pluton, Morungaba Granitoids, eastern Sao Paulo State. The 226Ra isotope activities were measured in a sequence of samples collected about one month apart between March, 2003 and April 2004. The 226Ra activities were measured by radon gas emanometry. The mean dissolved 226Ra activity concentration activities observed in the two wells were (44.9 {+-} 7.1) mBq/L and (51.6 {+-} 8.8) mBq/L. The 226Ra activity of the suspend solids in a liter of these waters varied between (0,6 {+-} 0,1) mBq and (13 {+-} 1) mBq, respectively. (author)

  13. Field, geochemistry and Sr-Nd isotopes of the Pan-African granitoids from the Tifnoute Valley (Sirwa, Anti-Atlas, Morocco): a post-collisional event in a metacratonic setting

    Science.gov (United States)

    Toummite, A.; Liegeois, J. P.; Gasquet, D.; Bruguier, O.; Beraaouz, E. H.; Ikenne, M.

    2013-10-01

    In the Tifnoute Valley, three plutonic units have been defined: the Askaoun intrusion, the Imourkhssen intrusion and the Ougougane group of small intrusions. They are made of quartz diorite, granodiorite and granite and all contain abundant mafic microgranular enclaves (MME). The Askaoun granodiorite and the Imourkhssen granite have been dated by LA-ICP-MS on zircon at 558 ± 2 Ma and 561 ± 3 Ma, respectively. These granitic intrusions are subcontemporaneous to the widespread volcanic and volcano-detrital rocks from the Ouarzazate Group (580-545 Ma), marking the post-collisional transtensional period in the Anti-Atlas and which evolved towards alkaline and tholeiitic lavas in minor volume at the beginning of the Cambrian anorogenic intraplate extensional period. Geochemically, the Tifnoute Valley granitoids belong to an alkali-calcic series (high-K calc-alkaline) with typical Nb-Ta negative anomalies and no alkaline affinities. Granitoids and enclaves display positive ɛNd-560Ma (+0.8 to +3.5) with young Nd-TDM between 800 and 1200 Ma and relatively low 87Sr/86Sr initial ratios (Sri: 0.7034 and 0.7065). These values indicate a mainly juvenile source corresponding to a Pan-African metasomatized lithospheric mantle partly mixed with an old crustal component from the underlying West African Craton (WAC). Preservation in the Anti-Atlas of pre-Pan-African lithologies (c. 2.03 Ga basement, c. 800 Ma passive margin greenschist-facies sediments, allochthonous 750-700 Ma ophiolitic sequences) indicates that the Anti-Atlas lithosphere has not been thickened and was never an active margin during the Neoproterozoic. After a transpressive period, the late Ediacaran period (580-545 Ma) is marked by movement on near vertical transtensional faults, synchronous with the emplacement of the huge Ouarzazate Group and the Tifnoute Valley granitoids. We propose here a geodynamical model where the Tifnoute Valley granitoids as well as the Ouarzazate Group were generated during the post

  14. Petrology and geochemistry of charnockites (felsic ortho-granulites) from the Kerala Khondalite Belt, Southern India: Evidence for intra-crustal melting, magmatic differentiation and episodic crustal growth

    Science.gov (United States)

    Ravindra Kumar, G. R.; Sreejith, C.

    2016-10-01

    -alkaline granitoids as the product of final phases of crustal-remelting marking subduction cessation. All these magmatic events are fairly well correlated with the major episodes of crustal growth observed in the once contiguous continental fragments (Sri Lanka and Madagascar) and worldwide events (2.7, 1.9, and 1.2 Ga) implying similar episodic nature in the lower crustal evolution of the KKB.

  15. Heat flux from magmatic hydrothermal systems related to availability of fluid recharge

    Science.gov (United States)

    Harvey, M. C.; Rowland, J.V.; Chiodini, G.; Rissmann, C.F.; Bloomberg, S.; Hernandez, P.A.; Mazot, A.; Viveiros, F.; Werner, Cynthia A.

    2015-01-01

    Magmatic hydrothermal systems are of increasing interest as a renewable energy source. Surface heat flux indicates system resource potential, and can be inferred from soil CO2 flux measurements and fumarole gas chemistry. Here we compile and reanalyze results from previous CO2 flux surveys worldwide to compare heat flux from a variety of magma-hydrothermal areas. We infer that availability of water to recharge magmatic hydrothermal systems is correlated with heat flux. Recharge availability is in turn governed by permeability, structure, lithology, rainfall, topography, and perhaps unsurprisingly, proximity to a large supply of water such as the ocean. The relationship between recharge and heat flux interpreted by this study is consistent with recent numerical modeling that relates hydrothermal system heat output to rainfall catchment area. This result highlights the importance of recharge as a consideration when evaluating hydrothermal systems for electricity generation, and the utility of CO2 flux as a resource evaluation tool.

  16. Magmatism during Gondwana break-up : new geochronological data from Westland, New Zealand

    International Nuclear Information System (INIS)

    Van der Meer, Q.H.A.; Scott, J.M.; Waight, T.E.; Sudo, M.; Schersten, A.; Cooper, A.F.; Spell, T.L.

    2013-01-01

    Newly determined Late Cretaceous 40 Ar/ 39 Ar ages on megacrystic kaersutite from four lamprophyre dikes, and a U-Pb zircon age on a trachyte, from central and north Westland (New Zealand) are presented. These ages suggest that the intrusion of mafic dikes (88-86 and 69 Ma) was not necessarily restricted to the previously established narrow age range of 80-92 Ma. The younger lamprophyre and trachyte dikes (c. 68-70 Ma) imply that tensional stresses in the Western Province were either renewed at this time, or that extension and related magmatism continued during opening of the Tasman Sea. Extension-related magmatism in the region not only preceded Tasman seafloor spreading initiation (starting at c. 83 Ma, lasting to c. 53 Ma), but may have sporadically continued for up to 15 Ma after continental break-up. (author)

  17. Role of magmatism in continental lithosphere extension: an introduction to tectnophysics special issue

    Energy Technology Data Exchange (ETDEWEB)

    Van Wijk, Jolante W [Los Alamos National Laboratory

    2008-01-01

    The dynamics and evolution of rifts and continental rifted margins have been the subject of intense study and debate for many years and still remain the focus of active investigation. The 2006 AGU Fall Meeting session 'Extensional Processes Leading to the Formation of Basins and Rifted Margins, From Volcanic to Magma-Limited' included several contributions that illustrated recent advances in our understanding of rifting processes, from the early stages of extension to breakup and incipient seafloor spreading. Following this session, we aimed to assemble a multi-disciplinary collection of papers focussing on the architecture, formation and evolution of continental rift zones and rifted margins. This Tectonophysics Special Issue 'Role of magmatism in continental lithosphere extension' comprises 14 papers that present some of the recent insights on rift and rifted margins dynamics, emphasising the role of magmatism in extensional processes. The purpose of this contribution is to introduce these papers.

  18. Dating emplacement and evolution of the orogenic magmatism in the internal Western Alps

    DEFF Research Database (Denmark)

    Berger, Alfons; Thomsen, Tonny B.; Ovtcharova, Maria

    2012-01-01

    The Canavese Line in the Western Alps represents the position in the Alpine chain, where alkaline and calc-alkaline magmatism occur in close spatial and temporal association. In addition to available data on the alkaline Valle del Cervo Pluton, we present petrological and geochemical data...... on the Miagliano tonalite. The latter is of special interest, because it is located in the south-eastern side of the Canavese Line, in contrast to most Periadriatic Plutons. The dioritic to tonalitic rocks of the Miagliano Pluton represent an intermediate stage of a calc-alkaline differentiation, demonstrated...... by relics of two different pyroxenes as well as the texture of allanite. Hornblende barometry indicates pressures of similar to 0.46 GPa consistent with the presence of magmatic epidote. Field relationships between the two Plutons, the volcanic and volcaniclastic rocks of the Biella Volcanic Suite...

  19. The influence of inherited structures on magmatic and amagmatic processes in the East African Rift.

    Science.gov (United States)

    Biggs, J.; Lloyd, R.; Hodge, M.; Robertson, E.; Wilks, M.; Fagereng, A.; Kendall, J. M.; Mdala, H. S.; Lewi, E.; Ayele, A.

    2017-12-01

    The idea that crustal heterogeneities, particularly inherited structures, influence the initiation and evolution of continental rifts is not new, but now modern techniques allow us to explore these controls from a fresh perspective, over a range of lengthscales, timescales and depths. In amagmatic rifts, I will demonstrate that deep fault structure is controlled by the stress orientation during the earliest phase of rifting, while the surface expression exploits near-surface weaknesses. I will show that pre-existing structures control the storage and orientation of deeper magma reservoirs in magmatic rifts, while the tectonic stress regime controls intra-rift faulting and shallow magmatism and stresses related to surface loading and cycles of inflation and deflation dominate at volcanic edifices. Finally, I will show how cross-rift structures influence short-term processes such as deformation and seismicity. I will illustrate the talk throughout using examples from along the East African Rift, including Malawi, Tanzania, Kenya and Ethiopia.

  20. ALPINE MAGMATIC-METALLOGENIC FORMATIONS OF THE NORTHWESTERN AND CENTRAL DINARIDES

    Directory of Open Access Journals (Sweden)

    Jakob Pamić

    1997-12-01

    Full Text Available In the paper are presented basic geological, petrologieca1, geochemi-cal and mineral deposit data for five main magmatic-metallogenic formations of the northwestern and central Dinarides: (lThe Permo Triassic rifting related andesite-diorite formations; (2 The Jurassic-Lower Cretaceous accretionary (ophiolite formations; (3 The Upper Cretaceous-Paleogene subduction related basalt-rhyohite formations; (4 The Paleogene collisional granite formations, and (5 The Oligo-cene-Neogene postsubduction andesite formations. All these magmatic-metallogenic formations originated in different geotectonic settings during the Alpine evolution of the Dinaridic parts of thc Tethys and the postorogenic evolution of the Paratethys and the Pannonian Basin, respectively.

  1. Trouble Upstairs: Reconstructing Permian-Triassic Climate during Siberian Traps Magmatism

    Science.gov (United States)

    Black, B. A.; Neely, R. R., III; Lamarque, J. F.; Elkins-Tanton, L. T.; Mills, M. J.

    2014-12-01

    The eruption of large igneous provinces can transfer significant masses of volatiles from Earth's interior to the atmosphere. What are the consequences of this degassing for habitability and extinction? In this presentation, we consider this question in the context of Siberian Traps magmatism, which has been shown to overlap within geochronologic uncertainty with catastrophic deterioration of Permian-Triassic marine and terrestrial ecosystems. To investigate the impacts of endogenic gases on climate, atmospheric chemistry, and ocean circulation, we conducted a series of numerical experiments with a comprehensive global model for the Permian-Triassic. Our simulations predict the intensity and distribution of acid rain and ozone depletion, with implications for terrestrial biota. We further explore feedbacks between sulfur emissions, transient cooling, and shifts in ocean circulation. We suggest that Siberian Traps magmatism may have triggered several distinct kill mechanisms in the oceans and on land, contributing to a complex combined pattern of environmental stress and latest Permian ecological failure.

  2. THE GEOMORPHOLOGIC FEATURES OF INTRUSIVE MAGMATIC STRUCTURES FROM BÂRGĂU MOUNTAINS (EASTERN CARPATHIANS, ROMANIA

    Directory of Open Access Journals (Sweden)

    Ioan Bâca

    2016-08-01

    Full Text Available Igneous intrusive structures from Bârgău Mountains belong to the group of central Neogene volcanic chain of the Eastern Carpathians of Romania. The evolution of the relief developed on these structures are three main stages: the stage of injection of structures (Pannonian, the stage of uncovering of igneous intrusive bodies from Oligo-Miocene sedimentary cover (Pliocene, and the stage of subaerial modeling of magmatic bodies (Pliocene-current.In those circumstances, the geodiversity of intrusive magmatic structures from Bârgău Mountains is represented by several types of landforms such as: polycyclic landforms (erosional levels, structural landforms (the configuration of igneous intrusive structures, petrographic landforms (andesites, lithological contact, fluvial landforms (valleys, slopes, ridges, periglacial landforms (cryogenic and crionival landforms, biogenic and anthropogenic landforms. This study highlights certain features of the landforms modeled on igneous intrusive bodies with the aim of developing some strategy for tourism recovery by local and county authorities.

  3. Rb-Sr geochronology of neoproterozoic syenites in parts of northern Tamil Nadu: implication on Pan-African magmatism

    International Nuclear Information System (INIS)

    Pandey, U.K.; Prasad, R.N.; Krishna, Veena; Paneer Selvam, A.; Chabria, Tikam

    1996-01-01

    This paper presents Rb-Sr whole rock isochron age data on two syenite plutons viz. Elagiri and Rasimalai, and results of this study may constrain the timing of magmatic event and crystal evolution in northern granulite segment

  4. Physical processes of magmatism and effects on the potential repository: Synthesis of technical work through Fiscal Year 1995

    International Nuclear Information System (INIS)

    Valentine, G.A.

    1996-01-01

    This chapter summarizes data collection and model calculations through FY 95 under Study Plan 8.3.1.8.1.2 Physical Processes of Magmatism and Effects on the Potential Repository. The focus of this study plan is to gather information that ultimately constrains the consequences of small-volume, basaltic magmatic activity at or near a potential repository. This is then combined with event probability estimates, described elsewhere in this synthesis report, to yield a magmatic risk assessment. Tere are two basic classes of effects of magmatisms that are considered here: (1) Eruptive effects, whereby rising magma intersects a potential repository, entrains radioactive waste, and erupts it onto the earth's surface. (2) Subsurface effects, which includes a wide range of processes such as hydrothermal flow, alteration of mineral assemblages in the potential repository system, and alteration of hydrologic flow properties of the rocks surrounding a potential repository

  5. Physical processes of magmatism and effects on the potential repository: Synthesis of technical work through Fiscal Year 1995

    Energy Technology Data Exchange (ETDEWEB)

    Valentine, G.A.

    1996-09-01

    This chapter summarizes data collection and model calculations through FY 95 under Study Plan 8.3.1.8.1.2 Physical Processes of Magmatism and Effects on the Potential Repository. The focus of this study plan is to gather information that ultimately constrains the consequences of small-volume, basaltic magmatic activity at or near a potential repository. This is then combined with event probability estimates, described elsewhere in this synthesis report, to yield a magmatic risk assessment. Tere are two basic classes of effects of magmatisms that are considered here: (1) Eruptive effects, whereby rising magma intersects a potential repository, entrains radioactive waste, and erupts it onto the earth`s surface. (2) Subsurface effects, which includes a wide range of processes such as hydrothermal flow, alteration of mineral assemblages in the potential repository system, and alteration of hydrologic flow properties of the rocks surrounding a potential repository.

  6. Gondwana subduction-modified mantle domain prevents magmatic seafloor generation in the Central Indian Ridge

    Science.gov (United States)

    Morishita, T.; Nakamura, K.; Senda, R.; Suzuki, K.; Kumagai, H.; Sato, H.; Sato, T.; Shibuya, T.; Minoguchi, K.; Okino, K.

    2013-12-01

    The creation of oceanic crust at mid-ocean ridges is essential to understanding the genesis of oceanic plate and the evolution of the Earth. Detailed bathymetric measurements coupled with dense sample recovery at mid-ocean ridge revealed a wide range of variations in the ridge and seafloor morphologies, which cannot be simply explained by a spreading rate, but also by ridge geometry, mantle compositions and thermal structure (Dick et al., 2003 Nature; Cannat et al. 2006 Geology). It is now widely accepted that very limited magmatic activity with tectonic stretching generates oceanic core complex and/or smooth seafloor surface in the slow to ultraslow-spreading ridges, where serpentinized peridotite and gabbros are expected to be exposed associated with detachment faults (Cann et al., 1997 Nature; Cannat et al., 2006), although magmatism might be an essential role for the formation of oceanic core complexes (Buck et al., 2005 Nature; Tucholke et al 2008 JGR). A rising question is why magmatic activity is sometimes prevented during the oceanic plate formation. Ancient melting domain, that are too refractory to melt even in adiabatically upwelling to the shallow upper mantle, might cause the amagmatic spreading ridges (Harvey et al., 2006 EPSL, Liu et al.,2008 Nature). Its origin and effect on seafloor generations are, however, not well understood yet. We report an oceanic hill as an example of an ancient subduction-modified mantle domain, probably formed at continental margin of the Gondwanaland~Pangea supercontinent, existing beneath the Central Indian Ridge. This domain is the most likely to have prevented magmatic seafloor generation, resulting in creation of very deep oceanic valley and serpentine diaper (now the studied oceanic hill) at the present Central Indian ridge.

  7. 50 Myr of pulsed mafic magmatism in the High Arctic Large Igneous Province

    Science.gov (United States)

    Pearson, D. G.; Dockman, D. M.; Heaman, L. M.; Gibson, S. A.; Sarkar, C.

    2017-12-01

    Extensive and voluminous Cretaceous mafic magmatism in the Sverdrup Basin of Arctic Canada forms the circum-Arctic High Arctic Large Igneous Province (HALIP). The small number of published high-precision ages for this LIP indicate its eruption over a considerable timespan raising concerns over whether the HALIP can be strictly defined as a single LIP and questioning the role of a single or multiple plumes in its genesis. Here we present an integrated geochemical and geochronological study to better constrain the timing and cause of mafic magma genesis in the Canadian HALIP. Six new U-Pb and four 40Ar/39Ar ages of mafic lavas and intrusive sheets range from 121 Ma to 78 Ma. The U-Pb ages are the first analyzed from the mafic intrusions of Axel Heiberg and Ellesmere Islands. The new geochronology, combined with other published high-precision ages, reveal a > 50 Myr duration of mafic magmatism in the HALIP defined by three main pulses. Tholeiites dominate the initial 25 Myr of magmatism, transitioning to coeval emplacement of alkali and tholeiitic basalts. Whole-rock Sr-Nd isotope ratios indicate that both magma types are derived from a similar source dominated by convecting mantle. Rare-earth-element inversion models reveal that the alkalic and tholeiitic magmas were generated beneath a bimodal lithospheric `lid' thickness of 65 ± 5 and 45 ± 4 km, respectively. We suggest that the early 128 - 122 Ma tholeiitic event is primarily plume-generated and correlates across the circum-Arctic with the other HALIP tholeiites. Younger HALIP magmatism, with coeval alkalic and tholeiitic magmas erupting over 25 Myr, may be explained by alternating modes of edge-driven mantle convection as the primary control on magma genesis. A distal plume may have intensified magma production by edge-driven convection.

  8. Magmatic versus tectonic influence in the Eolian arc: the case of Vulcano and Lipari islands revisited

    Science.gov (United States)

    Ruch, Joel; Di Lorenzo, Riccardo; Vezzoli, Luigina Maria; De Rosa, Rosanna; Acocella, Valerio; Catalano, Stefano; Romagnoli, Gino

    2014-05-01

    The prevalent influence of magma versus tectonics for the edification and the evolution of volcanic zones is matter of debate. Here we focus on Vulcano and Lipari, two active volcanic islands located in the central sector of the Eolian arc (North of Sicily). Both systems are influenced by regional tectonics and affected by historical magmatic events taking place along a NS oriented structure, connecting both islands. We revisit and implement previous structural studies performed during the 1980's considering several new geophysical, geochemical and geodynamical findings. Four extensive structural campaigns have been performed on both islands and along the shorelines in 2012-2013 covering about 80% of the possible accessible outcrops. We collected ~500 measurements (e.g. faults, fractures and dikes) at 40 sites. Overall, most of the observed structures are oriented N-S and NNW-SSE, confirming previous studies, however, almost all features are strikingly dominated by an EW-oriented extensive regime, which is a novelty. These findings are supported by kinematic indicators and suggest a predominant dip-slip component (pitch from 80 and 130°) with alternating left and right kinematics. Marginal faulting in most recent formations have been observed, suggesting that the deformation may occur preferentially during transient deformation related to periods of magmatic activity, instead of resulting from continuous regional tectonic processes. Overall, fault and dike planes are characterized by a dominant eastward immersion, suggesting an asymmetric graben-like structure of the entire area. This may be explained by the presence of a topographic gradient connecting both islands to the deep Gioia basin to the East, leading to a preferential ample gravitational collapse. Finally, we propose a model in which the stress field rotates northward. It transits from a pure right lateral strike-slip regime along the Tindari fault zone (tectonic-dominant) to an extensive regime

  9. Late Carboniferous Monzonite-Granosyenite Magmatism in the Northern Balkhash Region (Central Kazakhstan)

    Science.gov (United States)

    Ermolov, P. V.; Degtyarev, K. E.; Salnikova, E. B.; Tretyakov, A. A.; Kotov, A. B.; Anisimova, I. V.; Plotkina, Yu. V.

    2018-02-01

    U-Pb dating of the Torangalyk Complex (Northern Balkhash) yielded a Late Carboniferous age of 305 ± 2 Ma. Taking into account the previous data, a new scheme for Late Paleozoic granitic magmatism in this region has been proposed. It includes the Early Carboniferous granite-granodiorite Balkhash Complex, Late Carboniferous monzonite-granosyenite Kokdombak and Torangalyk complexes, and the Late Carboniferous-Early Permian granite-leucogranite Akchatau Complex.

  10. Evidence for extreme partitioning of copper into a magmatic vapor phase

    International Nuclear Information System (INIS)

    Lowenstern, J.B.; Mahood, G.A.; Rivers, M.L.; Sutton, S.R.

    1991-01-01

    The discovery of copper sulfides in carbon dioxide- and chlorine-bearing bubbles in phenocryst-hosted melt inclusions shows that copper resides in a vapor phase in some shallow magma chambers. Copper is several hundred times more concentrated in magmatic vapor than in coexisting pantellerite melt. The volatile behavior of copper should be considered when modeling the volcanogenic contribution of metals to the atmosphere and may be important in the formation of copper porphyry ore deposits

  11. Hierarchically porous graphene in natural graphitic globules from silicate magmatic rocks

    OpenAIRE

    PONOMARCHUK V.A.; TITOV A.T.; MOROZ T.N.; PYRYAEV A.N.; PONOMARCHUK A.V.

    2014-01-01

    Naturally-occurring nanostructured graphites from silicate magmatic rocks, which are rare, were characterized using electron microscope and X-ray spectroscopy. This graphite consists of porous carbon, nanographite layers, microand nanotubes. The porous carbon is classified as macroporous matter with a small amount of mezopores. Evidence for the unusual properties of porous carbon are given: nanographite layers are created at the exposed surface of sample and the nanotubes occurs in the bulk o...

  12. Evolution of the earliest mantle caused by the magmatism-mantle upwelling feedback: Implications for the Moon and the Earth

    Science.gov (United States)

    Ogawa, M.

    2017-12-01

    The two most important agents that cause mantle evolution are magmatism and mantle convection. My earlier 2D numerical models of a coupled magmatism-mantle convection system show that these two agents strongly couple each other, when the Rayleigh number Ra is sufficiently high: magmatism induced by a mantle upwelling flow boosts the upwelling flow itself. The mantle convection enhanced by this positive feedback (the magmatism-mantle upwelling, or MMU, feedback) causes vigorous magmatism and, at the same time, strongly stirs the mantle. I explored how the MMU feedback influences the evolution of the earliest mantle that contains the magma ocean, based on a numerical model where the mantle is hot and its topmost 1/3 is partially molten at the beginning of the calculation: The evolution drastically changes its style, as Ra exceeds the threshold for onset of the MMU feedback, around 107. At Ra 107, however, the mantle remains compositionally more homogeneous in spite of the widespread magmatism, and the deep mantle remains hotter than the shallow mantle, because of the strong convective stirring caused by the feedback. The threshold value suggests that the mantle of a planet larger than Mars evolves in a way substantially different from that in the Moon does. Indeed, in my earlier models, magmatism makes the early mantle compositionally stratified in the Moon, but the effects of strong convective stirring overwhelms that of magmatism to keep the mantle compositionally rather homogeneous in Venus and the Earth. The MMU feedback is likely to be a key to understanding why vestiges of the magma ocean are so scarce in the Earth.

  13. Repeated magmatic intrusions at El Hierro Island following the 2011-2012 submarine eruption

    Science.gov (United States)

    Benito-Saz, Maria A.; Parks, Michelle M.; Sigmundsson, Freysteinn; Hooper, Andrew; García-Cañada, Laura

    2017-09-01

    After more than 200 years of quiescence, in July 2011 an intense seismic swarm was detected beneath the center of El Hierro Island (Canary Islands), culminating on 10 October 2011 in a submarine eruption, 2 km off the southern coast. Although the eruption officially ended on 5 March 2012, magmatic activity continued in the area. From June 2012 to March 2014, six earthquake swarms, indicative of magmatic intrusions, were detected underneath the island. We have studied these post-eruption intrusive events using GPS and InSAR techniques to characterize the ground surface deformation produced by each of these intrusions, and to determine the optimal source parameters (geometry, location, depth, volume change). Source inversions provide insight into the depth of the intrusions ( 11-16 km) and the volume change associated with each of them (between 0.02 and 0.13 km3). During this period, > 20 cm of uplift was detected in the central-western part of the island, corresponding to approximately 0.32-0.38 km3 of magma intruded beneath the volcano. We suggest that these intrusions result from deep magma migrating from the mantle, trapped at the mantle/lower crust discontinuity in the form of sill-like bodies. This study, using joint inversion of GPS and InSAR data in a post-eruption period, provides important insight into the characteristics of the magmatic plumbing system of El Hierro, an oceanic intraplate volcanic island.

  14. Neogene magmatism and its possible causal relationship with hydrocarbon generation in SW Colombia

    Science.gov (United States)

    Vásquez, Mónica; Altenberger, Uwe; Romer, Rolf L.

    2009-07-01

    The Cretaceous oil-bearing source and reservoir sedimentary succession in the Putumayo Basin, SW Colombia, was intruded by gabbroic dykes and sills. The petrological and geochemical character of the magmatic rocks shows calc-alkaline tendency, pointing to a subduction-related magmatic event. K/Ar dating of amphibole indicates a Late Miocene to Pliocene age (6.1 ± 0.7 Ma) for the igneous episode in the basin. Therefore, we assume the intrusions to be part of the Andean magmatism of the Northern Volcanic Zone (NVZ). The age of the intrusions has significant tectonic and economic implications because it coincides with two regional events: (1) the late Miocene/Pliocene Andean orogenic uplift of most of the sub-Andean regions in Peru, Ecuador and Colombia and (2) a pulse of hydrocarbon generation and expulsion that has reached the gas window. High La/Yb, K/Nb and La/Nb ratios, and the obtained Sr-Nd-Pb isotopic compositions suggest the involvement of subducted sediments and/or the assimilation of oceanic crust of the subducting slab. We discuss the possibility that magma chamber(s) west of the basin, below the Cordillera, did increase the heat flow in the basin causing generation and expulsion of hydrocarbons and CO2.

  15. Geothermal constraints on Emeishan mantle plume magmatism: paleotemperature reconstruction of the Sichuan Basin, SW China

    Science.gov (United States)

    Zhu, Chuanqing; Hu, Shengbiao; Qiu, Nansheng; Jiang, Qiang; Rao, Song; Liu, Shuai

    2018-01-01

    The Middle-Late Permian Emeishan Large Igneous Province (ELIP) in southwestern China represents a classic example of a mantle plume origin. To constrain the thermal regime of the ELIP and contemporaneous magmatic activity in the northeastern Sichuan Basin, maximum paleotemperature profiles of deep boreholes were reconstructed using vitrinite reflectance (Ro) and apatite fission track data. Two heating patterns were identified: (1) heating of the overlying lithosphere by magma storage regions and/or magmatic activity related to the mantle plume, which resulted in a relatively strong geothermal field and (2) direct heating of country rock by stock or basalt. Borehole Ro data and reconstructed maximum paleotemperature profiles near the ELIP exhibit abrupt tectonothermal unconformities between the Middle and Late Permian. The profiles in the lower subsections (i.e., pre-Middle Permian) exhibited significantly higher gradients than those in the upper subsections. Distal to the basalt province, high paleo-geotemperatures (hereafter, paleotemperatures) were inferred, despite deformation of the paleogeothermal curve due to deep faults and igneous rocks within the boreholes. In contrast, Ro profiles from boreholes without igneous rocks (i.e., Late Permian) contained no break at the unconformity. Paleotemperature gradients of the upper and the lower subsections and erosion at the Middle/Late Permian unconformity revealed variations in the thermal regime. The inferred spatial distribution of the paleothermal regime and the erosion magnitudes record the magmatic and tectonic-thermal response to the Emeishan mantle plume.

  16. Present-day Opening of the Natron Rift: Tectonic and Magmatic Processes at Work

    Science.gov (United States)

    Calais, E.; Dalaison, M.; Saria, E.; Doubre, C.; Masson, F.

    2017-12-01

    The young Natron basin (system, is an important locale to study the initial stage of continental rifting. It was the locus of a rarely observed tectono-magmatic event in July 2007, with slow slip on an intra-basin normal fault followed by a 10 km-long dike intrusion underneath the Gelai shield volcano. Here we report on a series of GPS observations over a 20-site network spanning the basin, measured repeatedly since 2013. We observe a long wavelength ( 200 km wide) extension with a horizontal rate of about 2 mm/yr, consistent with recentlty published regional kinematic models, and a velocity gradient centered on the west-bounding fault of the Natron basin. Initial models show that the data is best fit by a normal fault dipping 60 degrees to the east and slipping at a rate of 6 mm/yr. Superimposed on this long wavelength extension, we observe a smaller scale ( 30 km wide) extensional signal in the middle of the basin, roughly coincident with the location of the Gelai volcano, which was the locale of the 2007 seismic-magmatic crisis. We investigate the relative importance of tectonic faulting, post-diking relaxation following the 2007 intrusion (as observed for instance in Afar or Iceland after similar events), and melt recharge of the intra-basin magmatic system in present-day extension across this young segment of the East African Rift.

  17. Post-rift magmatism in the Pearl River Mouth Basin, northern South China Sea

    Science.gov (United States)

    Xu, H.; Zhao, F.; Xia, S.; Sun, J.; Fan, C.

    2017-12-01

    Multi-beam, 2D seismic reflection and borehole data reveal that post-rift magmatism are widespread in the northern margin of South China Sea. A large-scale volcanic complex was identified at water depths of 500 to 3000 m, covering an area of ca. 8000 km2. This volcanic complex includes seamounts, igneous sills, dykes and intruded volcanic bodies. Combining data from exploration wells BY7-1 and BY2 with published seismic stratigraphic data, we can highlight multiple extrusive events from the Early Oligocene to Early Miocene, reflecting progressive continental breakup in the South China Sea. Most intruded magma through the continental crust also uplifted sediments up to the T6 unconformity. Given the evidence in this work that Early Miocene magmatic bodies were developed above or along faults, we suggest that post-rift magmatism in the northern margin of the South China Sea was largely controlled by the faults. Reactivation events in the faults are suggested to have generated preferential vertical pathways for the ascent of magma within a context of progressive continental breakup and thinned continental crust, as the South China Sea was being formed.

  18. Structural controls on the emission of magmatic carbon dioxide gas, Long Valley Caldera, USA

    Science.gov (United States)

    Lucic, Gregor; Stix, John; Wing, Boswell

    2015-04-01

    We present a degassing study of Long Valley Caldera that explores the structural controls upon emissions of magmatic carbon dioxide gas. A total of 223 soil gas samples were collected and analyzed for stable carbon isotopes using a field-portable cavity ring-down spectrometer. This novel technique is flexible, accurate, and provides sampling feedback on a daily basis. Sampling sites included major and minor volcanic centers, regional throughgoing faults, caldera-related structures, zones of elevated seismicity, and zones of past and present hydrothermal activity. The classification of soil gases based on their δ13C and CO2 values reveals a mixing relationship among three end-members: atmospheric, biogenic, and magmatic. Signatures dominated by biogenic contributions (~4 vol %, -24‰) are found on the caldera floor, the interior of the resurgent dome, and areas associated with the Hilton Creek and Hartley Springs fault systems. With the introduction of the magmatic component (~100 vol %, -4.5‰), samples acquire mixing and hydrothermal signatures and are spatially associated with the central caldera and Mammoth Mountain. In particular, they are concentrated along the southern margin of the resurgent dome where the interplay between resurgence-related reverse faulting and a bend in the regional fault system has created a highly permeable fracture network, suitable for the formation of shallow hydrothermal systems. This contrasts with the south moat, where despite elevated seismicity, a thick sedimentary cover has formed an impermeable cap, inhibiting the ascent of fluids and gases to the surface.

  19. Remote detection of magmatic water in Bullialdus crater on the Moon

    Science.gov (United States)

    Klima, Rachel L.; Cahill, John; Hagerty, Justin J.; Lawrence, David

    2013-01-01

    Once considered dry compared with Earth, laboratory analyses of igneous components of lunar samples have suggested that the Moon’s interior is not entirely anhydrous. Water and hydroxyl have also been detected from orbit on the lunar surface, but these have been attributed to nonindigenous sources, such as interactions with the solar wind. Magmatic lunar volatiles—evidence for water indigenous to the lunar interior—have not previously been detected remotely. Here we analyse spectroscopic data from the Moon Mineralogy Mapper (M3) and report that the central peak of Bullialdus Crater is significantly enhanced in hydroxyl relative to its surroundings. We suggest that the strong and localized hydroxyl absorption features are inconsistent with a surficial origin. Instead, they are consistent with hydroxyl bound to magmatic minerals that were excavated from depth by the impact that formed Bullialdus Crater. Furthermore, estimates of thorium concentration in the central peak using data from the Lunar Prospector orbiter indicate an enhancement in incompatible elements, in contrast to the compositions of water-bearing lunar samples. We suggest that the hydroxyl-bearing material was excavated from a magmatic source that is distinct from that of samples analysed thus far.

  20. Effects of magmatic processes on the potential Yucca Mountain repository: Field and computational studies

    International Nuclear Information System (INIS)

    Valentine, G.A.; Groves, K.R.; Gable, C.W.; Perry, F.V.; Crowe, B.M.

    1993-01-01

    Assessing the risk of future magmatic activity at a potential Yucca Mountain radioactive waste repository requires, in addition to event probabilities, some knowledge of the consequences of such activity. Magmatic consequences are divided into an eruptive component, which pertains to the possibility of radioactive waste being erupted onto the surface of Yucca Mountain, and a subsurface component, which occurs whether there is an accompanying eruption or not. The subsurface component pertains to a suite of processes such as hydrothermal activity, changes in country rock properties, and long term alteration of the hydrologic flow field which change the waste isolation system. This paper is the second in a series describing progress on studies of the effects of magmatic activity. We describe initial results of field analog studies at small volume basaltic centers where detailed measurements are being conducted of the amount of wall rock debris that can be erupted as a function of depth in the volcanic plumbing system. Constraints from field evidence of wall rock entrainment mechanisms are also discussed. Evidence is described for a mechanism of producing subhorizontal sills versus subvertical dikes, an issue that is important for assessing subsurface effects. Finally, new modeling techniques, which are being developed in order to capture the three dimensional complexities of real geologic situations in subsurface effects, are described

  1. Genesis of the Hengling magmatic belt in the North China Craton: Implications for Paleoproterozoic tectonics

    Science.gov (United States)

    Peng, Peng; Guo, Jinghui; Zhai, Mingguo; Windley, Brian F.; Li, Tiesheng; Liu, Fu

    2012-09-01

    The 2200-1880 Ma igneous rocks in the central and eastern parts of the North China Craton (NCC) constitute a new Hengling magmatic belt (HMB), which includes the ~ 2147 Ma Hengling mafic sill/dyke swarm, the ~ 2060 Ma Yixingzhai mafic dyke swarm, and the ~ 1973 Ma Xiwangshan mafic dyke swarm. The three swarms are contiguous and have experienced variable degrees of metamorphism from greenschist to low amphibolite facies (Hengling), medium granulite facies (Yixingzhai), and medium/high-pressure granulite facies (Xiwangshan). They are all tholeiitic in composition typically with 47-52 wt.% SiO2 and 4-10 wt.% MgO, and all show light rare earth element enrichments and Nb- and Ta-depletion. Their Nd TDM ages are in the range of 2.5-3.0 Ga. Specifically, the Hengling and Yixingzhai dykes/sills are depleted in Th, U, Zr, Hf and Ti, whereas the Xiwangshan dykes are enriched in U and weakly depleted in other elements. Variable Sr-anomalies indicate significant feldspar accumulation (positive anomalies) or fractionation. The ɛNd(t) values of the three swarms are: - 3.2-+3.0 (Hengling), - 1.7-+ 1.8 (Yixingzhai) and - 1.4-+ 1.0 (Xiwangshan). These mafic representatives of the HMB originated from the > 2.5 Ga sub-continental lithospheric mantle of the NCC, and with A-type granites and other igneous associations in this belt they likely evolved in an intra-continental rift. The progressive changing compositions of the three swarms are interpreted in terms of their source regions at different depths, i.e., shallower and shallower through time. And the decrease in scale and size of the intrusions and their magma volumes indicate the progressive weakening of magmatism in this rift. The rocks in this belt are different chronologically, petrologically and chemically from those in the Xuwujia magmatic belt (XMB). We propose that the two magmatic belts represent two different magmatic systems in different blocks of the NCC, i.e., an eastern block (with the HMB) and a western block

  2. Unravelling the sulphur isotope systematics of an alkaline magmatic province: implications for REE mineralization and exploration

    Science.gov (United States)

    Hutchison, W.; Finch, A.; Boyce, A.; Friis, H.; Borst, A. M.; Horsburgh, N. J.

    2017-12-01

    Some of the world's best alkaline rare earth element (REE) deposits are formed in magmatic systems that are sealed (i.e., those that are autometasomatised and maintain reducing conditions). Conversely, in open systems where oxidizing fluids infiltrate, it is commonly assumed that REE are redistributed over a wider (less concentrated) zone. Sulphur isotope fractionation is sensitive to variations in temperature and redox, and, although sulphide minerals are relatively abundant in alkaline systems, there have been few attempts to test these hypotheses and develop a sulphur isotope proxy for alkaline metasomatism and formation of associated REE deposits. The Gardar Rift Province in southern Greenland was volcanically active in two periods between 1300 and 1100 Ma and is an ideal natural laboratory to explore sulphur isotope systematics because a near-complete alkaline magmatic lineage is exposed. We present new δ34S from across the province with a particular focus on three alkaline systems (Ilímaussaq, Motzfeldt and Ivigtût) that also host major REE deposits. Primitive mafic rocks from regional Gardar dykes and lavas have a restricted range of δ34S between 0 and 3 ‰ and fractional crystallization imparts no observable change in δ34S. In a few cases high-δ34S rocks (>15 ‰) occur when intrusive units have assimilated local sedimentary crust (δ34S = 25 ‰). Most δ34S variation takes place in the roof zones of alkaline intrusions during late-magmatic and hydrothermal stages, and we identify clear differences between the complexes. At Ilímaussaq, where the magmatic series is exceptionally reduced (below QFM buffer), roof zone δ34S remains narrow (0-3 ‰). At Motzfeldt, a more open oxidizing roof zone (MH buffer), δ34S ranges from -12 ‰ in late-stage fluorite veins to +12 ‰ where local crust has been assimilated. Ivigtût is intermediate between these end-members varying between -5 to +5 ‰. The δ34S variations primarily relate to temperature and

  3. High salinity volatile phases in magmatic Ni-Cu-platinum group element deposits

    Science.gov (United States)

    Hanley, J. J.; Mungall, J. E.

    2004-12-01

    The role of "deuteric" fluids (exsolved magmatic volatile phases) in the development of Ni-Cu-PGE (platinum group element) deposits in mafic-ultramafic igneous systems is poorly understood. Although considerable field evidence demonstrates unambiguously that fluids modified most large primary Ni-Cu-PGE concentrations, models which hypothesize that fluids alone were largely responsible for the economic concentration of the base and precious metals are not widely accepted. Determination of the trace element composition of magmatic volatile phases in such ore-forming systems can offer considerable insight into the origin of potentially mineralizing fluids in such igneous environments. Laser ablation ICP-MS microanalysis allows researchers to confirm the original metal budget of magmatic volatile phases and quantify the behavior of trace ore metals in the fluid phase in the absence of well-constrained theoretical or experimental predictions of ore metal solubility. In this study, we present new evidence from major deposits (Sudbury, Ontario, Canada; Stillwater Complex, Montana, U.S.A.) that compositionally distinct magmatic brines and halide melt phases were exsolved from crystallizing residual silicate melt and trapped within high-T fluid conduits now comprised of evolved rock compositions (albite-quartz graphic granite, orthoclase-quartz granophyre). Petrographic evidence demonstrates that brines and halide melts coexisted with immiscible carbonic phases at the time of entrapment (light aliphatic hydrocarbons, CO2). Brine and halide melt inclusions are rich in Na, Fe, Mn, K, Pb, Zn, Ba, Sr, Al and Cl, and homogenize by either halite dissolution at high T ( ˜450-700° C) or by melting of the salt phase (700-800° C). LA-ICPMS analyses of single inclusions demonstrate that high salinity volatile phases contained abundant base metals (Cu, Fe, Sn, Bi) and precious metals (Pt, Pd, Au, Ag) at the time of entrapment. Notably, precious metal concentrations in the inclusions

  4. Early paleozoic granitoids in the southern Vanoise basement: U-Pb geochronology of the Arpont meta-granite (Savoy, French Alps); Granitoides d`age paleozoique inferieur dans le socle de Vanoise meridionale: geochronologie U-Pb du metagranite de l`Arpont (Alpes de Savoir, France)

    Energy Technology Data Exchange (ETDEWEB)

    Bertrand, J.M. [Laboratoire de geodynamique des chaines alpines, LGCA-CISM, 73 - Le Bourget-du-Lac (France); Leterrier, J. [Centre de recherches petrographiques et geochimique, 54 - Vandoeuvre-les-Nancy (France)

    1997-12-01

    The U-Pb age of a meta-granite from southern Vanoise (Brianconnais` domain) at 479{+-} 4 Ma confirms hat the micaschists which dominate this pre-alpine basement are, at least, of Early Paleozoic age. The rare magmatic rocks occurring in Vanoise and showing alkaline affinities, may be compared to the orthogneisses belonging to the Cambrian-Ordovician extensional event well known in other parts of the Varican belt. (authors) 27 refs.

  5. Similar and Contrasting Response of Rifting and Transtension in the Gulf of California and Walker Lane to Preceding Arc Magmatism

    Science.gov (United States)

    Henry, C. D.; Faulds, J. E.

    2006-12-01

    The Gulf of California (GC) and Walker Lane (WL) have undergone strikingly similar development with strike- slip faulting following initial extension. They differ significantly in the amount of Pacific-North American plate motion taken up by each: essentially all relative motion in the GC and ~25% in the WL. In both areas, ancestral arc magmatism preceded and probably focused deformation, perhaps because heating and/or hydration weakened the lithosphere. However, differences in migration of the Rivera (RTJ) and Mendocino triple junctions (MTJ) related to differences in the orientation of plate boundaries determined how strike-slip faulting developed. Abrupt southward jumps in the RTJ led to abrupt cessation of magmatism over arc lengths of as much as 1000 km and initiation of east-northeast extension within the future GC. The best known jump was at ~13 Ma, but an earlier jump occurred at ~18 Ma. Arc magmatism has been best documented in Baja California, Sonora, and Nayarit, although Baja constituted the most-trenchward fringe of the ancestral arc. New and published data indicate that Sinaloa underwent a similar history of arc magmatism. The greatest volume of the arc immediately preceding RTJ jumps was probably in mainland Mexico. Arc magmatism shut off following these jumps, extension began in the future GC, and strike-slip faulting either followed or accompanied extension in the GC. In contrast, the MTJ migrated progressively northward. New and published data indicate magmatism generally shut off coincident with this retreat, but distinct nodes or zones of magmatism, presumably unrelated to subduction, persisted or initiated after arc activity ceased. We have suggested that the WL has grown progressively northward, following the retreating arc, and that the northern WL is its youngest part. However, the timing of initiation of strike-slip faulting in most of the WL is poorly known and controversial. Testing our hypothesis requires determining initiation and

  6. Magma flow recorded by magmatic and magnetic fabrics in a shallow granitic pluton: La Gloria Pluton, central Chile

    Science.gov (United States)

    Payacán, I. J.; Gutiérrez, F. J.; Gelman, S. E.; Bachmann, O.; Parada, M. A.

    2013-12-01

    To better understand the dynamics of a small, shallow, silicic magma reservoir, magmatic and magnetic (AMS) fabrics are compared in samples obtained from La Gloria Pluton (LGP), a 10 Ma granitic intrusion located in southern Andes. The magnetic fabric of LGP, mainly given by magnetite, is characterized by oblate shapes. Magnetic lineations have a NW trend with subhorizontal dip, following the main pluton elongation, while magnetic foliation planes have dips varying gradually from vertical at the walls to subhorizontal toward the center and the roof of the pluton. On the basis of numerical simulations, magnetic fabric was interpreted to represent the shear record induced by magmatic convection along solidification fronts as the reservoir reached its rheological locking point. Magmatic fabric (mineral orientation) was determined on 12 samples along the pluton. Three mutually orthogonal thin sections were produced for each sample, perpendicular to the AMS tensor axes. Size and orientation of individual crystals were obtained by image analysis. A 2-D tensor for two mineral groups (plagioclase and amphibole+biotitie) was defined in each mineral plane projecting the crystal lengths on the main crystal orientation (given by Bingham statistics). A 3-D magmatic fabric tensor was obtained. In order to compare the magmatic and magnetic fabrics, magmatic anisotropy parameters were defined similar to the AMS tensors. Magmatic fabric and anisotropy parameter values vary depending on the location inside the pluton: (1) Samples located at the borders exhibit vertical foliations and lineations with a NW trend, similar to the magnetic fabric tensors and higher anisotropy values for plagioclase than amphibole+biotite,; (2) samples located at the center of the LGP commonly present subvertical foliations/lineations, which differ from the magnetic fabric, and higher magmatic anisotropy degree values for amphibole+biotite than plagioclase. Based on numerical simulations of the fluid

  7. Early Paleozoic dioritic and granitic plutons in the Eastern Tianshan Orogenic Belt, NW China: Constraints on the initiation of a magmatic arc in the southern Central Asian Orogenic Belt

    Science.gov (United States)

    Du, Long; Long, Xiaoping; Yuan, Chao; Zhang, Yunying; Huang, Zongying; Sun, Min; Zhao, Guochun; Xiao, Wenjiao

    2018-03-01

    Early Paleozoic dioritic and granitic plutons in the Eastern Tianshan Orogenic Belt (ETOB) have been studied in order to constraint the initiation of a magmatic arc formed in this region. Zircon U-Pb dating indicates that two dioritic plutons in the northern ETOB were generated in the Late Ordovician (452 ± 4 Ma) and the Early Silurian (442 ± 3 Ma), respectively. Diorites from the two plutons are characterized by enrichments in large ion lithophile elements (LILE) and highly incompatible elements, with depletions in high field strength elements (HSFE) displaying typical geochemical features of a subduction-related origin. They have positive εNd(t) values (+5.08-+6.58), relatively young Nd model ages (TDM = 0.71-1.08 Ga), with Ta/Yb (0.05-0.09) and Nb/Ta ratios (12.06-15.19) similar to those of depleted mantle, suggesting a juvenile mantle origin. Their high Ba/La (13.3-35.9), low Th/Yb (0.72-2.02), and relatively low Ce/Th (4.57-14.7) and Ba/Th (47.8-235) ratios indicate that these diorites were probably produced by partial melting of a depleted mantle wedge metasomatized by both subducted sediment-derived melts and slab-derived aqueous fluids. Zircon U-Pb dating of a granitic pluton in the northern ETOB yielded a Late Ordovician intrusion age of 447 ± 5 Ma. Granites from this pluton show calc-alkaline compositions with geochemical characteristics of I-type granites. They also show positive εNd(t) values (+6.49-+6.95) and young Nd model ages (TDM = 0.69-0.87 Ga), indicating that the granites were most likely derived from juvenile lower crust. Our new dating results on the dioritic and granitic plutons suggest that arc-type magmatism in the northern ETOB began prior to or at the Late Ordovician (452-442 Ma). In addition, north-dipping subduction of the Kangguertage oceanic lithosphere may account for the arc-type magmatism and the geodynamic process of the ETOB in the Early Paleozoic.

  8. Early Carboniferous adakite-like and I-type granites in central Qiangtang, northern Tibet: Implications for intra-oceanic subduction and back-arc basin formation within the Paleo-Tethys Ocean

    Science.gov (United States)

    Liu, Jin-Heng; Xie, Chao-Ming; Li, Cai; Wang, Ming; Wu, Hao; Li, Xing-Kui; Liu, Yi-Ming; Zhang, Tian-Yu

    2018-01-01

    correlations with Rb. The above characteristics indicate that the syenogranites are typical I-type granites. The results of this study also show that the LSG were produced by magma mixing between the mantle and juvenile oceanic crust. The field study found that the Early Carboniferous suite of granites intruded into contemporaneous ophiolites that formed in an intra-oceanic back-arc basin, and were associated with coeval A-type granites in this region. Based on the geochemical and isotopic data presented in this paper and regional geological data, we consider that the HSG were formed during intra-oceanic subduction of the Paleo-Tethys Ocean in the Early Carboniferous. The LSG and A-type granites were formed in an intra-oceanic back-arc basin setting caused by roll-back of the Paleo-Tethys Ocean slab. This confirms that the subduction of the Paleo-Tethys Ocean in the Early Carboniferous was intra-oceanic subduction, and provides important evidence for the existence of an intra-oceanic back-arc basin during the Late Devonian to Early Carboniferous.

  9. Martian Magmatic-Driven Hydrothermal Sites: Potential Sources of Energy, Water, and Life

    Science.gov (United States)

    Anderson, R. C.; Dohm, J. M.; Baker, V. R.; Ferris, J. C.; Hare, T. M.; Tanaka, K. L.; Klemaszewski, J. E.; Skinner, J. A.; Scott, D. H.

    2000-01-01

    Magmatic-driven processes and impact events dominate the geologic record of Mars. Such recorded geologic activity coupled with significant evidence of past and present-day water/ice, above and below the martian surface, indicate that hydrothermal environments certainly existed in the past and may exist today. The identification of such environments, especially long-lived magmatic-driven hydrothermal environments, provides NASA with significant target sites for future sample return missions, since they (1) could favor the development and sustenance of life, (2) may comprise a large variety of exotic mineral assemblages, and (3) could potentially contain water/ice reservoirs for future Mars-related human activities. If life developed on Mars, the fossil record would presumably be at its greatest concentration and diversity in environments where long-term energy sources and water coexisted such as at sites where long-lived, magmatic-driven hydrothermal activity occurred. These assertions are supported by terrestrial analogs. Small, single-celled creatures (prokaryotes) are vitally important in the evolution of the Earth; these prokaryotes are environmentally tough and tolerant of environmental extremes of pH, temperature, salinity, and anoxic conditions found around hydrothermal vents. In addition, there is a great ability for bacteria to survive long periods of geologic time in extreme conditions, including high temperature hydrogen sulfide and sulfur erupted from Mount St. Helens volcano. Our team of investigators is conducting a geological investigation using multiple mission-derived datasets (e.g., existing geologic map data, MOC imagery, MOLA, TES image data, geophysical data, etc.) to identify prime target sites of hydrothermal activity for future hydrological, mineralogical, and biological investigations. The identification of these sites will enhance the probability of success for future missions to Mars.

  10. Intense magmatic degassing through the lake of Copahue volcano, 2013-2014

    Science.gov (United States)

    Tamburello, G.; Agusto, M.; Caselli, A.; Tassi, F.; Vaselli, O.; Calabrese, S.; Rouwet, D.; Capaccioni, B.; Di Napoli, R.; Cardellini, C.; Chiodini, G.; Bitetto, M.; Brusca, L.; Bellomo, S.; Aiuppa, A.

    2015-09-01

    Here we report on the first assessment of volatile fluxes from the hyperacid crater lake hosted within the summit crater of Copahue, a very active volcano on the Argentina-Chile border. Our observations were performed using a variety of in situ and remote sensing techniques during field campaigns in March 2013, when the crater hosted an active fumarole field, and in March 2014, when an acidic volcanic lake covered the fumarole field. In the latter campaign, we found that 566 to 1373 t d-1 of SO2 were being emitted from the lake in a plume that appeared largely invisible. This, combined with our derived bulk plume composition, was converted into flux of other volcanic species (H2O ~ 10989 t d-1, CO2 ~ 638 t d-1, HCl ~ 66 t d-1, H2 ~ 3.3 t d-1, and HBr ~ 0.05 t d-1). These levels of degassing, comparable to those seen at many open-vent degassing arc volcanoes, were surprisingly high for a volcano hosting a crater lake. Copahue's unusual degassing regime was also confirmed by the chemical composition of the plume that, although issuing from a hot (65°C) lake, preserves a close-to-magmatic signature. EQ3/6 models of gas-water-rock interaction in the lake were able to match observed compositions and demonstrated that magmatic gases emitted to the atmosphere were virtually unaffected by scrubbing of soluble (S and Cl) species. Finally, the derived large H2O flux (10,988 t d-1) suggested a mechanism in which magmatic gas stripping drove enhanced lake water evaporation, a process likely common to many degassing volcanic lakes worldwide.

  11. Do Hf isotopes in magmatic zircons represent those of their host rocks?

    Science.gov (United States)

    Wang, Di; Wang, Xiao-Lei; Cai, Yue; Goldstein, Steven L.; Yang, Tao

    2018-04-01

    Lu-Hf isotopic system in zircon is a powerful and widely used geochemical tracer in studying petrogenesis of magmatic rocks and crustal evolution, assuming that zircon Hf isotopes can represent initial Hf isotopes of their parental whole rock. However, this assumption may not always be valid. Disequilibrium partial melting of continental crust would preferentially melt out non-zircon minerals with high time-integrated Lu/Hf ratios and generate partial melts with Hf isotope compositions that are more radiogenic than those of its magma source. Dissolution experiments (with hotplate, bomb and sintering procedures) of zircon-bearing samples demonstrate this disequilibrium effect where partial dissolution yielded variable and more radiogenic Hf isotope compositions than fully dissolved samples. A case study from the Neoproterozoic Jiuling batholith in southern China shows that about half of the investigated samples show decoupled Hf isotopes between zircons and the bulk rocks. This decoupling could reflect complex and prolonged magmatic processes, such as crustal assimilation, magma mixing, and disequilibrium melting, which are consistent with the wide temperature spectrum from ∼630 °C to ∼900 °C by Ti-in-zircon thermometer. We suggest that magmatic zircons may only record the Hf isotopic composition of their surrounding melt during crystallization and it is uncertain whether their Hf isotopic compositions can represent the primary Hf isotopic compositions of the bulk magmas. In this regard, using zircon Hf isotopic compositions to trace crustal evolution may be biased since most of these could be originally from disequilibrium partial melts.

  12. Physical processes and effects of magmatism in the Yucca Mountain region

    International Nuclear Information System (INIS)

    Valentine, G.A.; Crowe, B.M.; Perry, F.V.

    1991-01-01

    This paper describes initial studies related to the effects of volcanism on performance of the proposed Yucca Mountain radioactive waste repository, and to the general processes of magmatism in the Yucca Mountain region. Volcanism or igneous activity can affect the repository performance by ejection of waste onto the earth's surface (eruptive effects), or by subsurface effects of hydrothermal processes and altered hydrology if an intrusion occurs within the repository block. Initial, conservative calculations of the volume of waste that might be erupted during a small-volume basaltic eruption (such as those which occurred in the Yucca Mountain region) indicate that regulatory limits might be exceeded. Current efforts to refine these calculations, based upon field studies at analog sites, are described. Studies of subsurface effects are just beginning, and are currently focused on field studies of intrusion properties and contact metamorphism at deeply eroded analog sites. General processes of magmatism are important for providing a physical basis for predictions of future volcanic activity. Initial studies have focused on modeling basaltic magma chambers in conjunction with petrographic and geochemical studies. An example of the thermal-fluid dynamic evolution of a small basaltic sill is described, based on numerical simulation. Quantification of eruption conditions can provide valuable information on the overall magmatic system. We are developing quantitative methods for mapping pyroclastic facies of small basaltic centers and, in combination with two-phase hydrodynamic simulation, using this information to estimate eruption conditions. Examples of such hydrodynamic simulations are presented, along with comparison to an historical eruption in Hawaii

  13. Magmatic plumbing system of Kilauea Volcano: Insights from Petrologic and Geochemical Monitoring

    Science.gov (United States)

    Garcia, M. O.; Pietruszka, A. J.; Marske, J.; Greene, A.; Lynn, K. J.

    2016-12-01

    Monitoring the petrology and geochemistry of lavas from active volcanoes in near realtime affords the opportunity to formulate and evaluate models for magma transport, mixing, and storage to help predict eruption scenarios with greater confidence and better understand magmatic plumbing systems (e.g., Poland et al. 2012, Nat. Geosci. 5, 295-300). Continous petrologic and geochemical monitoring of two ongoing eruptions at the summit and east rift zone of Kilauea Volcano on the Island of Hawaii have revealed much about the dynamics of magmatic processes. When the composition of lava shifted to a more MgO-rich composition in April 1983, we predicted that the Puu Oo eruption would not be short-lived. We had no idea it would continue for over 33 years. Subsequent changes in lava composition have highlighted the interplay between mixing pockets of rift-zone stored magma with new mantle-derived magma and the cooling-induced crystal fractionation during brief (usually days) eruption hiatuses. Surprisingly, the mantle derived magma has continued to change in composition including several 10-year cycles in Pb isotope ratios superimposed on a progressive depletion in highly incompatible elements (Greene et al. 2013, G3, doi: 10.1002/ggge.20285). These compositional trends are contrary to those observed for sustained basaltic eruptions on continents and argue for melt extraction from a multi-component source with 1-3 km wide heterogeneities. Compositional zoning within olivine phenocrysts, created by diffusive re-equilibration, also provide insights into magma mixing, storage, and transport at Kilauea. Timescales modeling of Fe-Mg and Ni concentration gradients within Puu Oo olivine indicate that crystals can be stored at magmatic temperatures for months to a few years before eruption (Shea et al. 2015, Geology 43, 935-938). Kilauea's ongoing eruptions continue to provide a dynamic laboratory for positing and testing models for the generation and evolution of basaltic magma.

  14. Porphyry Cu-Au mineralization in the Mirkuh Ali Mirza magmatic complex, NW Iran

    Science.gov (United States)

    Maghsoudi, A.; Yazdi, M.; Mehrpartou, M.; Vosoughi, M.; Younesi, S.

    2014-01-01

    The Mirkuh Ali Mirza Cu-Au porphyry system in East Azerbaijan Province is located on the western part of the Cenozoic Alborz-Azerbaijan volcanic belt. The belt is also an important Cu-Mo-Au metallogenic province in northwestern Iran. The exposed rocks in the study area consist of a volcaniclastic sequence, subvolcanic rocks and intermediate to mafic lava flows of Neogene age. The volcanic rocks show a typical subduction-related magmatic arc geological and geochemical signature, with low concentration of Nb, Ta, and Ti. Mineralization is hosted by Neogene dacitic tuff and porphyritic dacite situated at the intersections of northeast and northwest faults. Field observations, alteration zonation, geochemical haloes and isotopic data of the Mirkuh Ali Mirza magmatic complex show similarities with typical convergent margin Cu-Au porphyry type deposits. The following features confirm the classic model for Cu-Au porphyry systems: (a) close spatial association with high-K calcalkaline to shoshonitic rock related to post-collision extensional setting (b) low grade Cu (0.57%) (c) stockworks as well as disseminated sulfides (c) zonality of the alteration patterns from intense phyllic at the center to outward weak-phyllic, argillic, and propylitic (d) the presence of a pyritic halo (e) accompanied by sheeted veins and low-sulfidation epithermal gold (f) mineralization spatially associated with intersection of structures, (g) genetically related to diorite porphyry stocks at depth (h) geochemical zonation of (Cu ± Au ± Ag ± Bi) → (Cu + Mo ± Bi ± Au ± Pb ± Zn ± As) → (Au + Mo ± Pb ± Zn) → (As + Ag + Sb + Mn + Ba + Pb + Zn + Hg) → Hg from center to outwards (i) The range of sulfur isotopic values is approximately zero (interpreted to have magmatic source) and similar to other subduction-related porphyry Cu deposits.

  15. Magmatic development of the outer Vøring margin from seismic data

    Science.gov (United States)

    Breivik, Asbjørn; Faleide, Jan Inge; Mjelde, Rolf; Flueh, Ernst; Murai, Yoshio

    2014-09-01

    The Vøring Plateau off mid-Norway is a volcanic passive margin, located north of the East Jan Mayen Fracture Zone (EJMFZ). Large volumes of magmatic rocks were emplaced during Early Eocene margin formation. In 2003, an ocean bottom seismometer survey was acquired over the margin. One profile crosses from the Vøring Plateau to the Vøring Spur, a bathymetric high north of the EJMFZ. The P wave data were ray traced into a 2-D crustal velocity model. The velocity structure of the Vøring Spur indicates up to 15 km igneous crustal thickness. Magmatic processes can be estimated by comparing seismic velocity (VP) with igneous thickness (H). This and two other profiles show a positive H-VP correlation at the Vøring Plateau, consistent with elevated mantle temperature at breakup. However, during the first 2 Ma magma production was augmented by a secondary process, possibly small-scale convection. From ˜51.5 Ma excess melting may be caused by elevated mantle temperature alone. Seismic stratigraphy around the Vøring Spur shows that it was created by at least two uplift events, with the main episode close to the Miocene/Pliocene boundary. Low H-VP correlation of the spur is consistent with renewed igneous growth by constant, moderate-degree mantle melting, not related to the breakup magmatism. The admittance function between bathymetry and free-air gravity shows that the high is near local isostatic equilibrium, precluding that compressional flexure at the EJMFZ uplifted the high. We find a proposed Eocene triple junction model for the margin to be inconsistent with observations.

  16. Imaging the magmatic system of Mono Basin, California with magnetotellurics in three--dimensions

    Science.gov (United States)

    Peacock, Jared R.; Mangan, Margaret T.; McPhee, Darcy K.; Ponce, David A.

    2015-01-01

    A three–dimensional (3D) electrical resistivity model of Mono Basin in eastern California unveils a complex subsurface filled with zones of partial melt, fluid–filled fracture networks, cold plutons, and regional faults. In 2013, 62 broadband magnetotelluric (MT) stations were collected in an array around southeastern Mono Basin from which a 3D electrical resistivity model was created with a resolvable depth of 35 km. Multiple robust electrical resistivity features were found that correlate with existing geophysical observations. The most robust features are two 300 ± 50 km3 near-vertical conductive bodies (3–10 Ω·m) that underlie the southeast and north-eastern margin of Mono Craters below 10 km depth. These features are interpreted as magmatic crystal–melt mush zones of 15 ± 5% interstitial melt surrounded by hydrothermal fluids and are likely sources for Holocene eruptions. Two conductive east–dipping structures appear to connect each magma source region to the surface. A conductive arc–like structure (resistivity (200 Ω·m) suggestive of a cooled connection. A third, less constrained conductive feature (4–10 Ω·m) 15 km deep extending to 35 km is located west of Mono Craters near the eastern front of the Sierra Nevada escarpment, and is coincident with a zone of sporadic, long–period earthquakes that are characteristic of a fluid-filled (magmatic or metamorphic) fracture network. A resistive feature (103–105 Ω·m) located under Aeolian Buttes contains a deep root down to 25 km. The eastern edge of this resistor appears to structurally control the arcuate shape of Mono Craters. These observations have been combined to form a new conceptual model of the magmatic system beneath Mono Craters to a depth of 30 km.

  17. Paleomagnetism of Siberian Trap Intrusions: Implications for the Timing and Intensity of the Magmatic Activity

    Science.gov (United States)

    Latyshev, Anton; Veselovskiy, Roman; Mirsayanova, Elina; Ulyahina, Polina

    2016-04-01

    Large Igneous Provinces (LIPs) are the areas of the exceptional interest due to associated Cu-Ni-Pt deposits, problems of the causal link between volcanic hazards and mass extinctions, and questions about mantle plume dynamics. High-precise U-Pb and 40Ar/39Ar dating determined the duration of the main phase of the most voluminous Siberian Trap province formation as 1-2 Ma (Kamo et al., 2003; Reichow et al., 2008). Recent paleomagnetic investigations demonstrated the predominance of pulsating volcanic activity during LIPs formation (Chenet et al., 2009; Pavlov et al., 2015). We perform the results of detailed paleomagnetic study of intrusive complexes from Tunguska syncline and Angara-Taseeva depression (Siberian Trap province). Our data taken together with the previous paleomagnetic results from trap intrusions revealed two different styles of magmatic activity. In the central part of Tunguska syncline emplacement of was rather even without sharp bursts. Local intrusive events coeval to volcanic eruptions took place within spatially limited areas. In contrast, in the periphery of Tunguska syncline several short and powerful peaks of magmatic activity happened on the background of weak prolonged magmatism. These events resulted in huge Padunsky, Tulunsky and some other sills in the southern part of the Siberian platform. According to our paleomagnetic data, the duration of such pulses did not exceed 10-100 thousand years. Taking into account our paleomagnetic data and recent U-Pb ages for Siberian trap intrusions from (Burgess, Bowring, 2015), it is possible to correlate intrusive complexes with the volcanic section. In particular, formation the largest Tulunsky and Padunsky sills happened right after the termination of the main phase of Permian-Triassic volcanic activity on the Siberian platform. This work was supported by grants RFBR # 16-35-60114 and 15-35-20599 and Ministry of Education and Science of the Russian Federation (grant 14.Z50.31.0017).

  18. Mantle refertilization and magmatism in old orogenic regions: The role of late-orogenic pyroxenites

    Science.gov (United States)

    France, Lydéric; Chazot, Gilles; Kornprobst, Jacques; Dallai, Luigi; Vannucci, Riccardo; Grégoire, Michel; Bertrand, Hervé; Boivin, Pierre

    2015-09-01

    Pyroxenites and garnet pyroxenites are mantle heterogeneities characterized by a lower solidus temperature than the enclosing peridotites; it follows that they are preferentially involved during magma genesis. Constraining their origin, composition, and the interactions they underwent during their subsequent evolution is therefore essential to discuss the sources of magmatism in a given area. Pyroxenites could represent either recycling of crustal rocks in mantle domains or mantle originated rocks (formed either by olivine consuming melt-rock reactions or by crystal fractionation). Petrological and geochemical (major and trace elements, Sr-Nd and O isotopes) features of xenoliths from various occurrences (French Massif-Central, Jordan, Morocco and Cameroon) show that these samples represent cumulates crystallized during melt percolation at mantle conditions. They formed in mantle domains at pressures of 1-2 GPa during post-collisional magmatism (possibly Hercynian for the French Massif-Central, and Panafrican for Morocco, Jordan and Cameroon). The thermal re-equilibration of lithospheric domains, typical of the late orogenic exhumation stages, is also recorded by the samples. Most of the samples display a metasomatic overprint that may be either inherited or likely linked to the recent volcanic activity that occurred in the investigated regions. The crystallization of pyroxenites during late orogenic events has implications for the subsequent evolution of the mantle domains. The presence of large amounts of mantle pyroxenites in old orogenic regions indeed imparts peculiar physical and chemical characteristics to these domains. Among others, the global solidus temperature of the whole lithospheric domain will be lowered; in turn, this implies that old orogenic regions are refertilized zones where magmatic activity would be enhanced.

  19. Surface deformation induced by magmatic processes at Pacaya Volcano, Guatemala revealed by InSAR

    Science.gov (United States)

    Wnuk, K.; Wauthier, C.

    2017-09-01

    Pacaya Volcano, Guatemala is a continuously active, basaltic volcano with an unstable western flank. Despite continuous activity since 1961, a lack of high temporal resolution geodetic surveying has prevented detailed modeling of Pacaya's underlying magmatic plumbing system. A new, temporally dense dataset of Interferometric Synthetic Aperture Radar (InSAR) RADARSAT-2 images, spanning December 2012 to March 2014, show magmatic deformation before and during major eruptions in January and March 2014. Inversion of InSAR surface displacements using simple analytical forward models suggest that three magma bodies are responsible for the observed deformation: (1) a 4 km deep spherical reservoir located northwest of the summit, (2) a 0.4 km deep spherical source located directly west of the summit, and (3) a shallow dike below the summit. Periods of heightened volcanic activity are instigated by magma pulses at depth, resulting in rapid inflation of the edifice. We observe an intrusion cycle at Pacaya that consists of deflation of one or both magma reservoirs followed by dike intrusion. Intrusion volumes are proportional to reservoir volume loss and do not always result in an eruption. Periods of increased activity culminate with larger dike-fed eruptions. Large eruptions are followed by inter-eruptive periods marked by a decrease in crater explosions and a lack of detected deformation. Co-eruptive flank motion appears to have initiated a new stage of volcanic rifting at Pacaya defined by repeated NW-SE oriented dike intrusions. This creates a positive feedback relationship whereby magmatic forcing from eruptive dike intrusions induce flank motion.

  20. Paleomagnetic evidence for counterclockwise rotation of the Dofan magmatic segment, Main Ethiopian Rift

    Science.gov (United States)

    Nugsse, Kahsay; Muluneh, Ameha A.; Kidane, Tesfaye

    2018-04-01

    Twenty-six paleomagnetic sites in basalt and trachyte flows and ignimbrite deposits sampled in the Dofan magmatic segment, Main Ethiopian Rift (MER). From each site, 6 to 8 core samples were collected. The samples were then cut into 200 standard specimens and their Natural Remanent Magnetization (NRM) directions were measured using a JR6A spinner magnetometer. Most specimens were subjected to stepwise alternating field (AF) and at least one specimen per site to thermal (TH) demagnetization. The directional analysis of these individual specimens revealed either one or two components of NRM. Where two components are present, the first is isolated below a temperature of 300 °C or AF field below 20 mT; the second is isolated above those steps and mostly defined straight lines directed towards the origin and are interpreted as the Characteristic Remanent Magnetization (ChRM) acquired during cooling. Rock magnetic experiments on representative specimens indicate that the dominant magnetic minerals are titanium poor titanomagnetite and in few cases titanohematites. The overall mean directions calculated for the 23 sites of Dofan is Dec = 354.1°, Inc. = +11.6° (N = 23, K = 35.1, α95 = 5.2°). When these values are compared with the 1.5 Ma expected mean geomagnetic dipole reference field directions Dec = 1.0°, Inc. = +16.4° (N = 32, K = 105.6, α95 = 2.3°), obtained from African Apparent Polar Wander Path Curve; a difference in declination ΔD = -6.9° ± 4.7° and inclination ΔI = +4.8° ± 5.5° are determined. The declination difference is interpreted as a very slight counterclockwise rotation about vertical axis of the Dofan magmatic segment and the result is consistent with previous paleomagnetic reports and analogue modeling in Fentale magmatic segment.

  1. The McMurdo Dry Valleys Magmatic Laboratory Workshop of 2005 in Antarctica

    Science.gov (United States)

    Marsh, B. D.; Simon, A.; Charrier, A. D.; Hersum, T. G.; Eschholz, E.

    2005-12-01

    In January of 2005, twenty-five petrologists, volcanologists, geochemists, structural geologists, and magma dynamicists spent two weeks studying and discussing the Magmatic Mush Column represented by the 180 Ma Ferrar Dolerites of the McMurdo Dry Valleys, Antarctica. This exceptionally well-exposed system shows a series of massive interconnected sills culminating in a capping of regional flood basalts. The lowermost sill, the Basement Sill, contains a massive ultramafic tongue of large phenocrysts of orthopyroxene (Opx) with subordinate Cpx and much smaller plagioclase. The 3-D distribution of this Opx Tongue serves as a tracer for the filling dynamics and local motion of the magma. Ponding of the Basement Sill has resulted in a small (500 m), but exceedingly diversified and extensively layered ultramafic intrusion, the Dais Intrusion. Because of the relatively rapid cooling time of this body, the Dais textures have been preserved before extensive annealing, which presents the possibility of using these textures to understand those of much larger, slowly cooled bodies. The combination of seeing in detail a wide variety of exceptional field relations depicting layering, sill emplacement mechanics, internal ordering and crystal sorting in the Opx Tongue, dike and fissure distributions, wall rock thermal effects, and many other first order features of central interest to understanding magmatic processes and performing research in real time was a new challenge to all involved. Facilities were set up at McMurdo Station for rock cutting, thin-section making, map making, GIS analysis, petrographic analysis, and computer modeling using existing chemical and physical data on a spectrum of the representative rock types. At any one time half the group was housed in the field in Bull Pass near Wright Valley and the remaining group was shuttled in by helicopter each day. The principal groups were switched about every three days. Areas for daily field-work were decided upon by

  2. Oceanic magmatic evolution during ocean opening under influence of mantle plume

    Science.gov (United States)

    Sushchevskaya, Nadezhda; Melanholina, Elena; Belyatsky, Boris; Krymsky, Robert; Migdisova, Natalya

    2015-04-01

    Petrology, geochemistry and geophysics as well as numerical simulation of spreading processes in plume impact environments on examples of Atlantic Ocean Iceland and the Central Atlantic plumes and Kerguelen plume in the Indian Ocean reveal: - under interaction of large plume and continental landmass the plume can contribute to splitting off individual lithosphere blocks, and their subsequent movement into the emergent ocean. At the same time enriched plume components often have geochemical characteristics of the intact continental lithosphere by early plume exposure. This is typical for trap magmatism in Antarctica, and for magmatism of North and Central Atlantic margins; - in the course of the geodynamic reconstruction under the whole region of the South Atlantic was formed (not in one step) metasomatized enriched sub-oceanic mantle with pyroxenite mantle geochemical characteristics and isotopic composition of enriched HIMU and EM-2 sources. That is typical for most of the islands in the West Antarctic. This mantle through spreading axes jumping involved in different proportions in the melting under the influence of higher-temperature rising asthenospheric lherzolite mantle; - CAP activity was brief enough (200 ± 2 Ma), but Karoo-Maud plume worked for a longer time and continued from 180 to 170 Ma ago in the main phase. Plume impact within Antarctica distributed to the South and to the East, leading to the formation of extended igneous provinces along the Transantarctic Mountains and along the east coast (Queen Maud Land province and Schirmacher Oasis). Moreover, this plume activity may be continued later on, after about 40 million years cessation, as Kerguelen plume within the newly-formed Indian Ocean, significantly affects the nature of the rift magmatism; - a large extended uplift in the eastern part of the Indian Ocean - Southeastern Indian Ridge (SEIR) was formed on the ancient spreading Wharton ridge near active Kerguelen plume. The strongest plume

  3. Geophysical evidence for the crustal variation and distribution of magmatism along the central coast of Mozambique

    Science.gov (United States)

    Mueller, Christian Olaf; Jokat, Wilfried

    2017-08-01

    For our understanding of the timing and geometry of the initial Gondwana break-up, still a consistent image of the crustal composition of the conjugated margins of central Mozambique and Antarctica and the location of their continent-ocean boundaries is missing. In this regard, a main objective is the explanation for the source of the different magnetic signature of the conjugate margins. Based on a revised investigation of wide-angle seismic data along two profiles across the Mozambican margin by means of an amplitude modelling, this study presents the crustal composition across and along the continental margin of central Mozambique. Supported by 2D magnetic modelling, the results are compared to the conjugate margin in Antarctica and allow new conclusions about their joined tectonic evolution. An observed crustal diversity between the north-eastern and south-western parts of the central Mozambican margin, testifies to the complex break-up history of this area. Conspicuous is the equal spatial extent of the HVLCB along the margin of 190-215 km. The onset of oceanic crust at the central Mozambican margin is refined to chron M38n.2n (164.1 Ma). Magnetic modelling supports the presence of reversed polarized SDRs in the continent-ocean transition that were mainly emplaced between 168.5 and 166.8 Ma (M42-M40). Inferred SDRs in the Riiser-Larsen Sea might be emplaced sometime between 166.8 and 164.1 Ma (M39-M38), but got overprinted by normal polarized intrusions of a late stage of rift volcanism, causing the opposite magnetic signature of the conjugate margins. The distribution of the magmatic material along the central coast of Mozambique clearly indicates the eastern extension of the north-eastern branch of the Karoo triple rift along the entire margin. The main magmatic phase affecting this area lasted for at least 12 Myr between 169 and 157 Ma, followed by the cease of the magmatism, perhaps due to the relative southwards motion of the magmatic centre.

  4. Floor-fractured craters on the Moon: an evidence of past intrusive magmatic activity

    Science.gov (United States)

    Thorey, C.; Michaut, C.

    2012-12-01

    Floor-fractured lunar craters (FFC's) are a class of craters modified by post impact mechanisms. They are defined by distinctive shallow, often plate-like or convex floors, wide floor moats and radial, concentric and polygonal floor-fractures, suggesting an endogenous process of modification. Two main mechanisms have been proposed to account for such observations : 1) viscous relaxation and 2) spreading of magmatic intrusions at depth below the crater. Here, we propose to test the case of magmatic intrusions. We develop a model for the dynamics of magma spreading below an elastic crust with a crater-like topography and above a rigid horizontal surface. Results show first that the lithostatic pressure increase at the crater rim prevents the intrusion from spreading horizontally giving rise to intrusion thickening and to an uplift of the crater floor. Second, the deformation of the overlying crust exerts a strong control on the intrusion shape, and hence, on the nature of the crater floor uplift. As the deformation can only occur over a minimum flexural wavelength noted Λ, the intrusion shape shows a bell-shaped geometry for crater radius smaller than 3Λ, or a flat top with smooth edges for crater radius larger than 3Λ. For given crustal elastic properties, the crust flexural wavelength increases with the intrusion depth. Therefore, for a large intrusion depth or small crater size, we observe a convex uplift of the crater floor. On the contrary, for a small intrusion depth or large crater size, the crater floor undergoes a piston-like uplift and a circular moat forms just before the rim. The depth of the moat is controlled by the thickening of the crust at the crater rim. On the contrary to viscous relaxation models, our model is thus able to reproduce most of the features of FFC's, including small-scale features. Spreading of a magmatic intrusion at depth can thus be considered as the main endogenous mechanism at the origin of the deformations observed at FFC

  5. Influence of volatile degassing on the eruptibility of large igneous province magmatic systems

    Science.gov (United States)

    Mittal, T.; Richards, M. A.

    2017-12-01

    Magmatic volatiles, in particular their buoyancy, may play a critical role in determining whether a magma reservoir can build up enough overpressure leading to drive flood basalt eruptions (Black & Manga 2017). Thus, it is important to understand the extent to which volatiles can remain trapped in a magmatic system and how they influence the eruptibility. Although the high-temperature metamorphic aureloe around a magma chamber is typically considered to have low permeability due to ductile creep, recent theoretical, experimental, and field work (e.g. Noriaki et al. 2017) have highlighted the role of dynamic permeability in magmatic systems. Consequently, the effective permeability of the crust when magma is present in the system can be orders of magnitude larger than that of exhumed rock samples. We model dynamic permeability changes as a competition between hydro-fracturing (increased porosity) and fracture closure by ductile creep and hydrothermal mineral precipitation (reduced porosity) and find yearly-to-decadal time-scales for periodic fracturing and fluid loss events and an increase in average permeability. We then use a fully coupled poro-thermo-elastic framework to model to explore the macroscopic influence of volatile loss on the stress state of the crust in this higher time-averaged permeability setting. We derive new semi-analytical solutions and combine them with a magma chamber box model (modified from Degruyter & Huber 2014) to analyze system-scale dynamics for both basaltic and silicic magmatic systems. We find that passive degassing likely has a substantial temporal influence on the stress distribution in the crust and the highly crystalline mush zone immediately surrounding a magma reservoir, and find an additional scale : pore-pressure diffusion timescale that exerts a first-order control on the magnitude and frequency of volcanic eruptions. We also explore how disconnected magma batches interact indirectly with each other and its implications for

  6. Lithospheric low-velocity zones associated with a magmatic segment of the Tanzanian Rift, East Africa

    Science.gov (United States)

    Plasman, M.; Tiberi, C.; Ebinger, C.; Gautier, S.; Albaric, J.; Peyrat, S.; Déverchère, J.; Le Gall, B.; Tarits, P.; Roecker, S.; Wambura, F.; Muzuka, A.; Mulibo, G.; Mtelela, K.; Msabi, M.; Kianji, G.; Hautot, S.; Perrot, J.; Gama, R.

    2017-07-01

    Rifting in a cratonic lithosphere is strongly controlled by several interacting processes including crust/mantle rheology, magmatism, inherited structure and stress regime. In order to better understand how these physical parameters interact, a 2 yr long seismological experiment has been carried out in the North Tanzanian Divergence (NTD), at the southern tip of the eastern magmatic branch of the East African rift, where the southward-propagating continental rift is at its earliest stage. We analyse teleseismic data from 38 broad-band stations ca. 25 km spaced and present here results from their receiver function (RF) analysis. The crustal thickness and Vp/Vs ratio are retrieved over a ca. 200 × 200 km2 area encompassing the South Kenya magmatic rift, the NTD and the Ngorongoro-Kilimanjaro transverse volcanic chain. Cratonic nature of the lithosphere is clearly evinced through thick (up to ca. 40 km) homogeneous crust beneath the rift shoulders. Where rifting is present, Moho rises up to 27 km depth and the crust is strongly layered with clear velocity contrasts in the RF signal. The Vp/Vs ratio reaches its highest values (ca. 1.9) beneath volcanic edifices location and thinner crust, advocating for melting within the crust. We also clearly identify two major low-velocity zones (LVZs) within the NTD, one in the lower crust and the second in the upper part of the mantle. The first one starts at 15-18 km depth and correlates well with recent tomographic models. This LVZ does not always coexist with high Vp/Vs ratio, pleading for a supplementary source of velocity decrease, such as temperature or composition. At a greater depth of ca. 60 km, a mid-lithospheric discontinuity roughly mimics the step-like and symmetrically outward-dipping geometry of the Moho but with a more slanting direction (NE-SW) compared to the NS rift. By comparison with synthetic RF, we estimate the associated velocity reduction to be 8-9 per cent. We relate this interface to melt ponding

  7. Uranium mineralization associated with late Palaeozoic acid magmatism in northeast Queensland

    International Nuclear Information System (INIS)

    Bain, J.H.C.

    1977-01-01

    The late Palaeozoic acid igneous petrographic province, covering some 120,000 km 2 in the Cairns-Townsville hinterland, has associated uranium mineralization characterized by various combinations of uranium, fluorine, and molybdenum. Mineralization of this type has been described from other parts of the world, but is best known in the USSR. Information about the Australian deposits and occurrences is very limited, but it is apparent that the mineralization is mainly of hydrothermal origin and genetically related to extensive late Palaeozoic magmatism. A detailed description of the mineralization and the prospect of additional discoveries of uranium deposits of similar and related types in other parts of Australia are discussed. (J.R.)

  8. Extrusive and Intrusive Magmatism Greatly Influence the Tectonic Mode of Earth-Like Planets

    Science.gov (United States)

    Lourenco, D.; Tackley, P. J.; Rozel, A.; Ballmer, M.

    2017-09-01

    Plate tectonics on Earth-like planets is typically modelling using a strongly temperature-dependent visco-plastic rheology. Previous analyses have generally focussed on purely thermal convection. However, we have shown that the influence of compositional heterogeneity in the form of continental or oceanic crust can greatly influence plate tectonics by making it easier (i.e. it occurs at a lower yield stress or friction coefficient). Here we present detailed results on this topic, in particular focussing on the influence of intrusive vs. extrusive magmatism on the tectonic mode.

  9. Radioactivity and decay heat generation in precambrian magmatic rocks (with the South Pamirs as an example)

    International Nuclear Information System (INIS)

    Batyrmurzaev, A.S.; Alibekov, G.I.; Bekieva, A.A.

    2003-01-01

    The evaluation of the heat generation share in the results of the long-living radioactive elements (RAE) decay in the Earth surface layers is accomplished on the basis of the data on the uranium and thorium concentration in the precambrian magmatic rocks of the South Pamirs. It was supposed by the calculations, that the value of the heat flux, generated by the rocks, is determined mainly by the RAE content in the Earth upper layer crust itself of 10-15 km. It is shown that the radioheat generation share is within the range of 5-10% from the measured values of the geothermal flows [ru

  10. Regional setting and geochronology of the Late Cretaceous Banatitic Magmatic and Metallogenetic Belt

    Science.gov (United States)

    Ciobanu, Cristiana L.; Cook, Nigel J.; Stein, Holly

    2002-08-01

    The 1,500-km-long Banatitic Magmatic and Metallogenetic Belt (BMMB) of Romania, Serbia and Bulgaria is a complex calc-alkaline magmatic arc of Late Cretaceous age. It hosts a variety of magmatic-hydrothermal Cu, Au, Mo, Zn, Pb and Fe deposits, including Europe's only world-class porphyry-copper deposits. Regional metallogeny can be linked to subduction of the Vardar Ocean during the Late Cretaceous, as part of the closure of the Neotethys Ocean that had separated Europe and Africa in the Mesozoic. Porphyry Cu-(Au)-(Mo) and intimately associated epithermal massive sulphides dominate in the central segments of the belt in southernmost Banat (Romania), Serbia and north-west Bulgaria. These districts are the economically most important today, including major active Cu-Au mines at Moldova Nouă in Romania, Majdanpek, Veliki Krivelj and Bor in Serbia, and Elatsite, Assarel and Chelopech in Bulgaria. More numerous (and mostly mined in the past) are Fe, Cu and Zn-Pb skarns, which occur mainly at the two ends of the belt, in Eastern Bulgaria and in Romania. This paper summarises some of the deposit characteristics within the geodynamic framework of terminal Vardar subduction. Heterogeneous terranes of the belt, including the Apuseni Mountains at the western end, are aligned parallel to the Vardar front following continental collision of the Dacia and Tisza blocks. All available geochronological data (numerous K-Ar and some U-Pb and Re-Os ages) are compiled, and are complemented by a new high-precision Re-Os date for the Dognecea skarn deposit, south-west Romania (76.6±0.3 Ma). These data indicate that magmatism extended over at least 25 million years, from about 90 to 65 Ma in each segment of the belt. Within Apuseni Mountains and Banat, where magma emplacement was related to syn-collisional extension in the orogenic belt of Carpathians, ore formation seems to be restricted in time and maybe constrained by a shared tectonic event.

  11. Monitoring the State of the Magmatic Structures of Elbrus Volcano Based on Observation of Lithosphere Strains

    International Nuclear Information System (INIS)

    Milyukov, Vadim; Myasnikov, Andrey; Mironov, Alexey

    2008-01-01

    An analysis of crustal strain recorded by the Baksan laser interferometer revealed a shallow magma chamber in the structure of Elbrus Volcano (The Northern Caucasus, Russia). The analysis is based on estimation of parameters of magmatic structures resonant modes excited by teleseismic signals. The resonance parameters we have found were interpreted in the framework of contemporary models of magma resonators. The depth and dimension of the magma chamber, as well as the properties of the magma fluid were estimated. It was suggested the changing the magma state due to rising the intrachamber pressure

  12. Apatite: A New Tool For Understanding The Temporal Variability Of Magmatic Volatile Contents

    Science.gov (United States)

    Stock, M. J.; Humphreys, M.; Smith, V.; Pyle, D. M.; Isaia, R.

    2015-12-01

    The apatite crystal structure is capable of incorporating H2O, F and Cl, as well as trace CO2 and sulphur. These can be related to parental magma compositions through application of a series of pressure and temperature-dependent exchange reactions (Piccoli and Candela, 1994), permitting apatite crystals to preserve a record of all major volatile species in the melt. Furthermore, due to the general incompatibility of P in other rock-forming minerals, apatite is ubiquitous in igneous systems and often begins crystallising early, such that apatite inclusions within phenocrysts record melt volatile contents throughout magmatic differentiation. In this work, we compare the compositions of apatite inclusions and microphenocrysts with pyroxene-hosted melt inclusions from the Astroni 1 eruption of Campi Flegrei, Italy. These data are coupled with magmatic differentiation models (Gualda et al., 2012), experimental volatile solubility data (Webster et al., 2014) and thermodynamic models of apatite compositional variations (Piccoli and Candela, 1994) to determine a time-series of magmatic volatile evolution in the build-up to eruption. We find that apatite halogen/OH ratios decreased through magmatic differentiation, while melt inclusion F and Cl concentrations increased. Melt inclusion H2O contents are constant at ~2.5 wt%. These data are best explained by volatile-undersaturated differentiation over most of the crystallisation history of the Astroni 1 melt, with melt inclusion H2O contents reset during ascent, due to rapid H diffusion through the phenocryst hosts (Woods et al., 2000). Given the rapid diffusivity of volatiles in apatite (Brenan, 1993), preservation of undersaturated compositions in microphenocrysts suggests that saturation was only achieved a few days to months before eruption and that it may have been the transition into a volatile-saturated state that ultimately triggered eruption. Piccoli and Candela, 1994. Am. J. of Sc., 294, 92-135. Gualda et al., 2012

  13. Unraveling the dynamics of magmatic CO2 degassing at Mammoth Mountain, California

    Science.gov (United States)

    Peiffer, Loïc; Wanner, Christoph; Lewicki, Jennifer L.

    2018-02-01

    The accumulation of magmatic CO2 beneath low-permeability barriers may lead to the formation of CO2-rich gas reservoirs within volcanic systems. Such accumulation is often evidenced by high surface CO2 emissions that fluctuate over time. The temporal variability in surface degassing is believed in part to reflect a complex interplay between deep magmatic degassing and the permeability of degassing pathways. A better understanding of the dynamics of CO2 degassing is required to improve monitoring and hazards mitigation in these systems. Owing to the availability of long-term records of CO2 emissions rates and seismicity, Mammoth Mountain in California constitutes an ideal site towards such predictive understanding. Mammoth Mountain is characterized by intense soil CO2 degassing (up to ∼1000 t d-1) and tree kill areas that resulted from leakage of CO2 from a CO2-rich gas reservoir located in the upper ∼4 km. The release of CO2-rich fluids from deeper basaltic intrusions towards the reservoir induces seismicity and potentially reactivates faults connecting the reservoir to the surface. While this conceptual model is well-accepted, there is still a debate whether temporally variable surface CO2 fluxes directly reflect degassing of intrusions or variations in fault permeability. Here, we report the first large-scale numerical model of fluid and heat transport for Mammoth Mountain. We discuss processes (i) leading to the initial formation of the CO2-rich gas reservoir prior to the occurrence of high surface CO2 degassing rates and (ii) controlling current CO2 degassing at the surface. Although the modeling settings are site-specific, the key mechanisms discussed in this study are likely at play at other volcanic systems hosting CO2-rich gas reservoirs. In particular, our model results illustrate the role of convection in stripping a CO2-rich gas phase from a rising hydrothermal fluid and leading to an accumulation of a large mass of CO2 (∼107-108 t) in a shallow

  14. Origin of fumarolic fluids from Tupungatito Volcano (Central Chile): interplay between magmatic, hydrothermal, and shallow meteoric sources

    Science.gov (United States)

    Benavente, Oscar; Tassi, Franco; Gutiérrez, Francisco; Vaselli, Orlando; Aguilera, Felipe; Reich, Martin

    2013-08-01

    Tupungatito is a poorly known volcano located about 100 km eastward of Santiago (Chile) in the northernmost sector of the South Volcanic Zone. This 5,682 m high volcano shows intense fumarolic activity. It hosts three crater lakes within the northwestern portion of the summit area. Chemical compositions of fumarolic gases and isotopic signatures of noble gases (3He/4He and 40Ar/36Ar are up to 6.09 Ra and 461, respectively), and steam (δ18O and δD) suggest that they are produced by mixing of fluids from a magmatic source rich in acidic gas compounds (SO2, HCl, and HF), and meteoric water. The magmatic-hydrothermal fluids are affected by steam condensation that controls the outlet fumarolic temperatures (contamination from the subducting slab, (2) the sedimentary basement, and (3) limited contribution from crustal sediments. Gas geothermometry based on the kinetically rapid H2-CO equilibria indicates equilibrium temperatures 200 °C and redox conditions are consistent with those inferred by the presence of the SO2-H2S redox pair, typical of fluids that have attained equilibrium in magmatic environment. A comprehensive conceptual geochemical model describing the circulation pattern of the Tupungatito hydrothermal-magmatic fluids is proposed. It includes fluid source regions and re-equilibration processes affecting the different gas species due to changing chemical-physical conditions as the magmatic-hydrothermal fluids rise up toward the surface.

  15. The 3.26-3.24 Ga Barberton asteroid impact cluster: Tests of tectonic and magmatic consequences, Pilbara Craton, Western Australia

    Science.gov (United States)

    Glikson, Andrew; Vickers, John

    2006-01-01

    The location in the Barberton Greenstone Belt (Kaapvaal Craton) of ∼3.26-3.24 Ga asteroid impact ejecta units at, and immediately above, a sharp break between a > 12 km-thick mafic-ultramafic volcanic crust (Onverwacht Group ∼3.55-3.26 Ga, including the ∼3.298 > 3.258 Ga Mendon Formation) and a turbidite-felsic volcanic rift-facies association (Fig Tree Group ∼3.258-3.225 Ga), potentially represents the first documented example of cause-effect relations between extraterrestrial bombardment and major tectonic and igneous events [D.R. Lowe, G.R. Byerly, F. Asaro, F.T. Kyte, Geological and geochemical record of 3400 Ma old terrestrial meteorite impacts, Science 245 (1989) 959-962; D.R. Lowe, G.R. Byerly, F.T. Kyte, A. Shukolyukov, F. Asaro, A. Krull, Spherule beds 3.47-3.34 Ga-old in the Barberton greenstone belt, South Africa: a record of large meteorite impacts and their influence on early crustal and biological evolution, Astrobiology 3 (2003) 7-48; A.Y. Glikson, The astronomical connection of terrestrial evolution: crustal effects of post-3.8 Ga mega-impact clusters and evidence for major 3.2 ± 0.1 Ga bombardment of the Earth-Moon system, J. Geodyn. 32 (2001) 205-229]. Here we correlate this boundary with a contemporaneous break and peak magmatic and faulting events in the Pilbara Craton, represented by the truncation of a 3.255-3.235 Ga-old volcanic sequence (Sulphur Springs Group-SSG) by a turbidite-banded iron formation-felsic volcanic association (Pincunah Hill Formation, basal Gorge Creek Group). These events are accompanied by ∼3.252-3.235 Ga granitoids (Cleland plutonic suite). The top of the komatiite-tholeiite-rhyolite sequence of the SSG is associated with a marker chert defined at 3.238 ± 3-3.235 ± 3 Ga, abruptly overlain by an olistostrome consisting of mega-clasts of felsic volcanics, chert and siltstone up to 250 × 150 m-large, intercalated with siliciclastic sedimentary rocks and felsic volcanics (Pincunah Hill Formation-basal Gorge

  16. Arc magmatism as a window to plate kinematics and subduction polarity: Example from the eastern Pontides belt, NE Turkey

    Directory of Open Access Journals (Sweden)

    Yener Eyuboglu

    2011-01-01

    Full Text Available The Eastern Pontides orogenic belt in the Black Sea region of Turkey offers a critical window to plate kinematics and subduction polarity during the closure of the Paleotethys. Here we provide a brief synthesis on recent information from this belt. We infer a southward subduction for the origin of the Eastern Pontides orogenic belt and its associated late Mesozoic–Cenozoic magmatism based on clear spatial and temporal variations in Late Cretaceous and Cenozoic arc magmatism, together with the existence of a prominent south-dipping reverse fault system along the entire southern coast of the Black Sea. Our model is at variance with some recent proposals favoring a northward subduction polarity, and illustrates the importance of arc magmatism in evaluating the geodynamic milieu associated with convergent margin processes.

  17. Expansion of the granitic post-orogenic magmatism in the formation of Serrinha (Northeastern Bahia, B R), Sao Francisco craton

    International Nuclear Information System (INIS)

    Rios, Debora Correia; Conceicao, Herbet; Rosa, Maria de Lourdes da Silva; Marinho, Moacyr Moura; Davis, Donaldo Wayne

    2005-01-01

    The Pedra Vermelha Granitic Massif, located at the North area of Serrinha Nucleus, presents a circular shape, being intrusive at the Archaean geoscience-magmatic basement rocks and the Paleoproterozoic volcano sedimentary sequences. The single zircon U-Pb dating yield a crystallization age of 2080 ± 8 Ma. The geological, petrographic al and litogeochemical characteristics of the studied rocks are similar to those of the Morro do Lopes granitic magmatism (2076 ± 6 a 2071 ± 6 Ma), which is located at the South area of this nucleus. These allow us to infer that those post-orogenic alkaline bodies are widespread throughout the Serrinha Nucleus and constitute its last Paleoproterozoic magmatic expression. (author)

  18. Stable-isotope geochemistry of the Pierina high-sulfidation Au-Ag deposit, Peru: Influence of hydrodynamics on SO42--H2S sulfur isotopic exchange in magmatic-steam and steam-heated environments