The Imleih layered mafic-ultramafic body is a Neoproterozoic intrusion covering about 45 km2 in southern Sinai. The field relations as well as the fine grained chilled margins indicate that the layered intrusion is younger than the surrounding calc-alkaline syn-tectonic granodiorite and Iqna Shar,a volcanics and older than the post-tectonic Iqna granite. There is a general consensus that there are no ophiolitic rocks younger than the syn-tectonic granitoids in the Arabian-Nubian Shield (ANS), which supports the non-ophiolitic origin of the Imleih layered intrusion. The studied layered intrusion is tilted to the north, with lower layers (peridotite and pyroxenite) exposed to the south and upper layers (cumulus gabbro and anorthosite) exposed to the north. Imleih rocks are cumulates, dominat...

Gebel Filat granites form one of Egyptian younger granite intrusions in Wadi Allaqi region, South Eastern Desert of Egypt. They are perthitic monzogranites composed mainly of K-feldspars, plagioclase, and quartz with minor biotite. Plagioclase feldspars are Na-rich and have low anorthite content (An2?3). Potash feldspars are mainly perthitic microcline and have chemical formula as (Or96?96.6 Ab3.4?4 An0). Biotite is Mg-rich and seems to be derived from calc-alkaline magma. Chlorite is pycnochlorite with high Mg content, revealing its secondary derivation from biotite. The estimated formation temperatures of biotite and chlorite are (689?711?C) and (602?622?C), respectively. Gebel Filat monzogranites are metaluminous, high-K calc-alkaline, I-type granites. They are late orogenic granites re...

Mineral alteration and fluid inclusion studies of drill cuttings and core samples indicate that the sedimentary basement rocks and the volcanic rocks associated with Tulancingo-Acoculco Caldera Complex have been the site of two distinct and major hydrothermal events. The complex, located in the eastern portion of the Trans-Mexican Volcanic Belt, is formed by the Pliocene Tulancingo Caldera and the younger (Pleistocene) Acoculco Caldera, which developed within the older depression. The volcanic rocks are underlain by Cretaceous sedimentary rocks of the Sierra Madre Oriental. The earliest important hydrothermal event occurred during the emplacement of Mid-Tertiary granitic intrusions that metamorphosed the sedimentary rocks; these intrusives are not exposed at the surface. However, granitic ...

Abukuma plutonic rocks in the central to western Abukuma plateau have been divided into ‘older' (weakly foliated and intermediate) and ‘younger'(massive and felsic) granitic rocks, as well as small amounts of gabbroic to dioritic rocks, based on field occurrences and their lithofacies. Although many radiometric ages have been reported for these rocks, it remains unclear whether the gabbroic to dioritic rocks represent the first stage of granitic magmatism or are pre-Cretaceous basement rocks. Moreover, the geochronological discrepancy in K-Ar biotite ages between ‘older' and ‘younger' granitic rocks are still ambiguous. These problems are expected to be resolved by the U-Pb dating of zircon, which has a significantly higher closure temperature, making this one of the best ways to estimate the crystallization age of the plutonic rocks.  We have determined U-Pb zircon ages for six samples of Abukuma plutonic rocks using laser-ablation ICP mass spectrometry. We found that these ages were 104.9 ± 0.9 Ma for the Utsushiga-take gabbroic body, 100.4 ± 0.7 Ma for the Nagaya body, 113.4 ± 0.5 Ma for the Shikayama body, 106.7 ± 0.8 Ma for the Ishimori body, 118.0 ± 0.7 Ma for the Miharu body and 101.9 ± 1.6 Ma for the Hatsumori body.   These results suggest that the Utsushiga-take gabbroic body did not result from first stage granitic magmatism or from magma contaminated by pre-Cretaceous basement rocks, but rather that gabbroic magmatism in this district occurred during the same stage as granitic magmatism. Although our results showed clear geochronological contrast among each granitic rock, there was no significant difference between ‘older' and ‘younger' granitic rocks. These findings indicate that the previous classification system, based only on lithofacies, should be re-examined based on other criteria, such as further field observations of intrusive relationships and/or U-Pb dating of zircon.   The cooling histories of each granitic rock were also estimated by K-Ar, Ar-Ar and U-Pb age. We found that the minimum cooling rate of the Utsushiga-take gabbroic rock at relatively higher temperatures (750-530 °C) was more rapid (~ <200 °C/m.y.) than at lower temperature (530-310 °C) and the other granitic samples (? 10-70 °C/m.y.).   

New U-Pb ages for zircon and titanite obtained by LA-MC-ICPMS are reported for post-collisional granites from the central Ribeira belt (Rio de Janeiro State, southeast Brazil). These post-collisional, I-type, megaporphyritic and equigranular leucogranite plutons and dykes intrude high-grade metasedimentary units, orthogneisses, and migmatites within the root zone of the deeply eroded Neoproterozoic-Cambrian Ribeira belt. The ages obtained are: 511.2 ± 6.9 Ma (zircon) for the Suruí Granite; 490.3 ± 8.7 Ma (zircon) for a cross-cutting dyke of the pegmatitic facies of the Andorinha Granite from the same outcrop; 480.7 ± 6.1 Ma (zircon) for the Frades Granite; 488.7 ± 4.2 Ma (titanite) for the Nova Friburgo Granite; and 490.9 ± 9.8 Ma (zircon) for the Sana Granite. These new U-Pb ages and those compiled from the literature for post-orogenic intrusions distributed ˜400 km along the strike of the orogen (Rio de Janeiro and Espírito Santo States), define two separate intervals for magmatic activity, which are consistent with mineralogical and structural signatures. The magmatic intervals consist of an older Cambrian magmatic pulse occurred at ca.512 Ma (Pedra Branca, Suruí and Buarama plutons), and a younger Ordovician event at ca. 486 Ma (Mangaratiba, Favela, Andorinha, Frades, Nova Friburgo and Sana granites). The Cambrian pulse post-dates the end of the first and main collisional phase by ca. 35 m.y. It also post-dates the onset of the second collisional episode by ca. 20 m.y. The late-Ordovician magmatic pulse post-dates the end of the second collisional episode by ca. 25 m.y. In map view, the alignment of the post-collisional plutons and stocks depicts a sinuous belt running along the eroded roots of central/northern Ribeira and Araçuaí belts. This granite belt probably marks the zone where preferential heating and melting of lower continental crust took place, either caused by breaking off of subducted slab, or by the extensional collapse of hot, overthickened continental crust.

Granitic intrusions, ranging from small plugs coring precursor stratocones to composite batholith-scale bodies, are exceptionally exposed within and adjacent to the numerous Tertiary calderas (37-23 Ma) of the Southern Rocky Mountain volcanic field (SRMVF), as result of high regional topography, large-scale faulting associated with the Rio Grande rift system, and associated deep erosion. Such plutons are variable in age, texture, composition, and size relative to associated ignimbrite calderas. Large caldera subsidence structures are direct evidence for batholith-scale magma bodies in the upper crust, for which these plutons are inferred to provide samples of shallow solidified residua. Most exposed plutons are smaller than associated calderas, but large negative gravity anomalies (to -50 mgal) document upper-crustal presence of vertically extensive composite batholiths that are much larger than individual calderas. Some granitic plutons within or near SRMVF calderas are indistinguishable in age from the time of ignimbrite eruption, but others are millions of years younger. Pluton textures range from nearly aphanitic to medium-grained equigranular or megacrystic granitic, reflecting variable cooling and crystallization rates in shallow crustal environments. Compositions of SRMVF intrusions vary from diorite to highly evolved granite; those most closely related in age and location to calderas commonly are compositionally similar to more mafic late-erupted portions of associated ignimbrites. These relations are consistent with interpretation of pluton compositions as mushy residua from prolonged fractionation energized by sustained mafic magma inputs, during which more evolved upper parts of the subcaldera magma chamber were largely erupted as ignimbrite. Sparse recent U-Pb-zircon age data for granitic rocks elsewhere suggest that deeper-level plutons in Cordilleran arcs may have longer crystallization histories than shallower subvolcanic cupolas, contrasts inferred to reflect more prolonged open-system recharge, mixing, and crystallization at greater depths in the batholithic environment. A continuing uncertainty is the proportion of the eventual subvolcanic batholith present at times of peak ignimbrite volcanism, versus continued later- and post-volcanic enlargement.

This paper describes the granitic rocks in Awaji Island with an emphasis on partly observed foliation. The granites in the island can be divided largely into Granitic Rocks 1, 2 and 3. The Granitic Rocks 1 are composed of rocks or tonalites with grown foliation. The Granitic Rocks 2 comprise clustered granodiorites without foliation, and capture in part the Granitic Rocks 1 exerting contact deformation activity on them. The Granitic Rocks 3 are clustered granites, piercing through the Granitic Rocks 1 and 2. The Granitic Rocks 1 and the Older Dikes piercing through the former exhibit foliations parallel to each other. In addition, the Granitic Rocks 1 and the Older Dikes show structures indicating plastic deformation, with the strongly deformed part of the Granitic Rocks 1 forming mylonite. These foliations are thought to have been formed by a wide range plastic deformation action (mylonitification) given before intrusion of the Granitic Rocks 2. 25 refs., 17 figs.

This study is concerned with the radioactivity and mineralogy of the younger granites and pegmatites in the Wadi Haleifiya area, southeastern Sinai Peninsula, Egypt. The area is occupied by metasediments, migmatites, older and younger granites. Most of these rocks, especially granites, are dissected by mafic and felsic dykes as well as pegmatites. The younger granites are represented by three main varieties: monzogranites, syenogranites and alkali feldspar granites. The monzogranite consists essentially of quartz, plagioclase, potash feldspar and biotite with minor muscovite. Iron oxide, titanite, zircon and allanite are the main accessory minerals. Syenogranite is massive, medium- to coarse-grained and commonly exhibits equigranular and hypidiomorphic textures. It is made up essentially o...

Mineral alteration and fluid inclusion studies of drill cuttings and core samples indicate that the sedimentary basement rocks and the volcanic rocks associated with Tulancingo-Acoculco Caldera Complex have been the site of two distinct and major hydrothermal events. The complex, located in the eastern portion of the Trans-Mexican Volcanic Belt, is formed by the Pliocene Tulancingo Caldera and the younger (Pleistocene) Acoculco Caldera, which developed within the older depression. The volcanic rocks are underlain by Cretaceous sedimentary rocks of the Sierra Madre Oriental. The earliest important hydrothermal event occurred during the emplacement of Mid-Tertiary granitic intrusions that metamorphosed the sedimentary rocks; these intrusives are not exposed at the surface. However, granitic rocks were encountered at the bottom of exploratory borehole EAC-1, drilled within the Caldera Complex. The second main event occurred during the formation of the Tulancingo and Acoculco Calderas. Both episodes lead to secondary mineralization that reduced the permeability of the reservoir rocks. A possible third hydrothermal event may be associated with the recent magmatic activity within the Acoculco Caldera.Thermal logs from well EAC-1 display a conductive thermal gradient with maximum temperatures exceeding 300 C at 2000 m depth. Although there are no active thermal springs in the area, there is extensive fossil surface hydrothermal alteration and cold gas discharges with high He{sup 3}/He{sup 4} ratios. (author)

The Late Mesozoic geology of Southeast China is characterized by extensive Jurassic to Cretaceous magmatism consisting predominantly of granites and rhyolites and subordinate mafic rocks, forming a belt of volcanic-intrusive complexes. The Xiangshan volcanic-intrusive complex is located in the NW region of the belt and mainly contains the following lithologies: rhyodacite and rhyodacitic porphyry, porphyritic lava, granite porphyry with mafic microgranular enclaves, quartz monzonitic porphyry, and lamprophyre dyke. Major and trace-element compositions, zircon U-Pb dating, and Sr-Nd-Hf isotopic compositions have been investigated for these rocks. The precise SHRIMP and LA-ICP-MS zircon U-Pb dating shows that the emplacement of various magmatic units at Xiangshan took place within a short time period of less than 2 Myrs. The stratigraphically oldest rhyodacite yielded a zircon U-Pb age of 135 ± 1 Ma and the overlying rhyodacitic porphyry has an age of 135 ± 1 Ma. Three porphyritic lava samples yielded zircon U-Pb ages of 136 ± 1 Ma, 132 ± 1 Ma, and 135 ± 1 Ma, respectively. Two subvolcanic rocks (granite porphyry) yielded zircon U-Pb ages of 137 ± 1 Ma and 137 ± 1 Ma. A quartz monzonitic porphyry dyke, which represented the final stage of magmatism at Xiangshan, also yielded a zircon U-Pb age of 136 ± 1 Ma. All these newly obtained precise U-Pb ages demonstrate that the entire magmatic activity at Xiangshan was rapid and possibly took place at the peak of extensional tectonics in SE China. The geochemical data indicate that all these samples from the volcanic-intrusive complex have an A-type affinity. Sr-Nd-Hf isotopic data suggest that the Xiangshan volcanic-intrusive complex derived mainly from remelting of Paleo-Mesoproterozoic crust without significant additions of mantle-derived magma. However, the quartz monzonitic porphyry, which has zircon Hf model ages older than the whole-rock Nd model ages, and which has ?Nd(T) value higher than the other rocks, may indicate involvement of a subordinate younger mantle-derived magma in its origin. Geochemical data indicate that the various rocks show variable REE patterns and negative anomalies of Ba, Nb, Sr, P, Eu and Ti in the trace element spidergrams, suggesting that these rocks may have undergone advanced fractional crystallization with separation of plagioclase, K-feldspar and accessory minerals such as allanite. We suggest that this Cretaceous volcanic-intrusive complex formed in an extensional environment, and the formation of the Xiangshan mafic microgranular enclaves can be explained by the injection of mafic magma from a deeper seated mantle magma chamber into a hypabyssal felsic magma chamber at the crustal emplacement levels.

We report field characteristics, petrography, geochemistry and isotopic ages of the Neoarchaean intrusive complex and the Paleoproterozoic metamorphic belt around Quruqtagh in the northern margin of the Tarim Block, NW China in an attempt to evaluate the evolution of the Precambrian basement of the Tarim Block. Zircon U-Pb ages indicate that the tonalite-trondhjemite complex with gabbroic enclaves and the slightly younger potassic granites crystallized at ca. 2.60Ga and ca. 2.53Ga respectively, and were metamorphosed at ca.1.85-1.80Ga. Zircon U-Pb ages indicate that the amphibolite to granulite facies assemblages in the strongly deformed Paleoproterozoic gneiss-schist belt were generated during a major thermal event at 1.85-1.80Ga, and were again overprinted by late Mesoproterozoic to earl...

The Silver Creek caldera, southern Black Mountains, AZ, is the source of the supereruption that produced the Miocene (18.8 Ma) Peach Spring Tuff (PST), an extensive ignimbrite found throughout much of northwestern Arizona, southern Nevada, and southeastern California. The caldera's eastern margin is intruded by a slightly younger (18.5 +/- 0.5 Ma), ~30 km2 complex of epizonal, intermediate to felsic plutonic rocks. Because it is the largest known suite of intrusive rocks associated with the Peach Spring supereruption and contiguous (~19.5-17.5 Ma) volcanic activity in the Black Mountains, the Silver Creek intrusive complex provides a valuable record of processes operating in the shallow crust in the aftermath of a major eruption and during a period of intense volcanic activity. Rocks in the Silver Creek intrusive complex have historically been divided into two units, the Moss porphyry and the Times porphyry, though the complex exhibits textural and compositional complexity that belies a simple two-unit classification scheme. Field observations and geochemical analysis indicate that the northern portion of the Silver Creek suite comprises porphyries and coarse-grained rocks with ~62 to ~68 wt. % SiO2 ("Moss porphyry"). Rounded, 2-10 cm enclaves (59 wt. % SiO2) with crenulate margins are sparse overall but locally abundant in this portion of the complex. The southern part of the complex consists of leucogranitic porphyry and coarse-grained granite with >70 wt. % SiO2 ("Times porphyry"). At the east/west-trending Times/Moss contact zone along Silver Creek, the coarse-grained component of the Times contains mixing, suggest that the Silver Creek intrusive complex records rapid reinvigoration of the magmatic system that fed the PST supereruption and its volcanic predecessors in the Black Mountains.

The Haestholmen study site is located within the anorogenic Wiborg rapakivi granite batholith, 1640 1630 Ma in age. The bedrock consists of various rapakivi granites, which can be divided into three groups or lithological units: (1) wiborgite and pyterlite, (2) porphyritic rapakivi granite, and (3) even-grained or weakly porphyritic rapakivi granite, pyterlite being the dominant rock type. The evengrained and weakly porphyritic rapakivi granite has been interpreted to form a younger intrusive unit with a thickness of ca. 500 m, dipping approx. 20 deg to the NNW-NNE. Surface fractures form a distinct orthogonal system, with three perpendicular fracture directions: fractures dipping steeply (dip >75 deg) to the NE-SW and NW-SE plus subhorizontal (dip <30 deg) fractures. The fracturing in the outcrops is sparse,the average fracture frequency being 0.6 fractures/m. The majority of the fractures in the drill cores are horizontal or very gently dipping and there is no difference in fracture orientations in regard to rock type or depth. Core samples are usually slightly fractured (1 - 3 fractures/m), even-grained rapakivi granites being in places abundantly fractured (3 10 fractures/m. The broken sections in Haestholmen core samples represent about 4.6 % of the total length of the samples. Calcite, dolomite, Fe- hydroxides and clay minerals (illite, montmorillonite and kaolinite) form the most typical fracture mineral phases throughout the drill cores. Core discing is locally seen as repeated fracture-like subparallel cracks in core with spacing of about some millimetres to tens of millimetres. The structural model contains 27 structures (denoted by the term R+number), more than half of which have been verified by direct observations from boreholes or from the VLJ repository. The remaining structures are mainly based on the geophysical interpretation, and have been classified as probable or possible fracture zones. In addition, local structures with uncertain orientation and continuity occur in the rock mass. They are not classified as R-structures but may still have hydraulic significance. The most significant features of the bedrock are the subhorizontal structures R1, R3, R18 and R19 located in boreholes over the depth ranges of 50 - 150 m, 150 - 350 m, 300 - 500 m and 700 - 950 m, respectively. Transmissivity values for the R-structures measured by the double packer system and the flowmeter lie in the range 1*10{sup -3} m{sup 2}/s to 1*10{sup -7} m{sup 2}/s, the average being 1-10{sup -5} m{sup 2}/s. (orig.)

The Paleozoic granites in the Chinese Altai are important for the study of tectonic evolution and crustal growth in the Central Asian Orogenic Belt (CAOB). Four representative peraluminous granitic intrusions were selected for systematic studies of zircon U-Pb and Hf isotopic compositions and whole-...

The Hartville uplift is the southeasternmost exposure of the Precambrian Wyoming province and is situated near the proposed junction of the Cheyenne Belt, Trans Hudson, and Central Plains orogens. Consequently, it is uncertain which orogen was responsible for the apparent metamorphism and N-S trending deformation in the Hartville uplift. Field relationships combined with U-Pb data from zircon, monazite, and apatite suggest an episode of regional metamorphism and deformation ca. 1.66 Ga. Based on U-Pb zircon data, the crystallization age of a gray gneissic phase of the Rawhide Buttes granite is [ge]2.4 Ga which is consistent with Rb/Sr data from similar granites by Z. Peterman. Monazite ages from the gray gneiss are nearly concordant at 1.66 Ga, and discordant apatite data yield a Pb/Pb age of 1.60 Ga. Metapelite assemblages adjacent to the Rawhide Buttes granite record second sillimanite facies metamorphism, which other workers have shown to be of sufficient grade to either reset monazite or recrystallize it below its closure temperature. The monazite age is thus interpreted to document the timing of a metamorphic event. Apatite ages from Rawhide Buttes and two other Proterozoic intrusions in the Hartville uplift are also consistent with resetting ca. 1.66 Ga. Regional deformation near the Rawhide Buttes post-dates crystallization of 1.69 Ga zircons from a strongly boudinaged pegmatitic dike. This episode of deformation may have accompanied the regional thermal resetting of apatite and monazite ca. 1.66 Ga. This age is distinctly younger than both the Cheyenne Belt and Trans Hudson orogenies but may be correlative with the Central Plains orogen.

The chemical Th-U-total Pb isochron method (CHIME) has been adopted for dating the syntectonic foliated and post-tectonic unfoliated granites in northwestern Cameroon. The CHIME ages are 532{+-}35 Ma for allanite and 523{+-}45 Ma for zircon from Sample I{sub 10} of foliated biotite granite, 530{+-}9 Ma for monazite from Sample N{sub 9} of foliated two-mica granite, and 510{+-}25 Ma for monazite from Sample I{sub 4} of unfoliated two-mica granite. Several monazite grains from Samples N{sub 9} and I{sub 4} yield 436{+-}13 and 420{+-}16 Ma CHIME ages, respectively. The 532-510 Ma ages are interpreted as the time of granite emplacement and the 436-420 Ma ages as the time of hydrothermal alteration. The CHIME ages coupled with the concordant relation between the foliated granites and migmatitic gneiss suggest a ca. 530 Ma metamorphic-plutonic episode in northwestern Cameroon rather than a thermal overprint by granite intrusion. (author)

Garam Chashma granitic rocks intrude discordantly into the Hindukush metamorphic complex on the southern margin of the Asian plate, Trans-Himalayas, northwestern Pakistan. The rocks are fine to coarse-grained, two-mica leucogranite. K-Ar biotite analyses of four samples from the Garam Chashma pluton yield 18-20 Ma ages. These ages are younger than those of the other post-collisional granitic rocks in Trans-Himalayas of Pakistan and resemble those of the Higher Himalayan granitic rocks.   

Rb-Sr isotope whole-rock dating of the Krossnes Granite has yielded an isochron age of 430+-6 Ma with I.R=0.7066 +- 0.0005, interpreted as the age of intrusion. This age is close to that of the Haakre Granite of the Sunnhordland Batholith, to which the Krossnes Granite is probably related. The age indicates that the Krossnes Granite probably intruded during the period of deposition of the Ashgillian-Llandoverian sediments of the Ulven and Holdhus Groups, Major Bergen Arc. It also demonstrates that strong ductile deformation of rocks in the Major Bergen Arc occurred during the Ordovician period, or close to the transition from the Ordovician to the Silurian period.

Radioelements and heat production rates of granitic rocks and stable isotopes of groundwaters were analyzed to investigate the geothermal potential of Wolchulsan granite complex in the southern Yeongam area. Wolchulsan granite complex is composed mainly by Cretaceous pink alkali-feldspar granite and partly Jurassic biotite granite. The main target for the geothermal exploration is the alkali-feldspar granite that is known in general to be favorable geothermal reservoir(e.g., Shap granite in UK). To develop exploration techniques for geothermal anomalies, all geochemical data were compared to those from the Jeonju granite complex. Heat production rates(HPR) of the alkali-feldspar granite is 1.8 - 10.6 {mu}Wm{sup -3}. High radio-thermal anomalies were revealed from the central western and northern parts of the granite body. These are relatively higher than the Caledonian hot dry granites in the UK. The integrated assessment of Wolchulsan granite complex suggests potential of the Cretaceous alkali-feldspar granite as a geothermal targets. Groundwater geochemistry of the Yeongam area reflects simple evaporation process and higher oxidation environment. Stable isotope data of groundwaters are plotted on or close to the Meteoric Water Line(MWL). These isotopic data indicate a significant meteoric water dominance and do not show oxygen isotope fractionation between groundwater and wall rocks. In despite of high HPR values of the Yeongam alkali-feldspar granite, groundwater samples do not show the same geochemical properties as a thermal water in the Jeonju area. This reason can be well explained by the comparison with geological settings of the Jeonju area. The Yeongam alkali-feldspar granite does not possess any adjacent heat source rocks despite its high radio-thermal HPR. While the Jeonju granite batholith has later heat source intrusive and suitable deep fracture system for water circulation with sedimentary cap rocks. (Abstract Truncated)

The Spanish Central System (SCS) is one of the largest granite batholiths in the European Variscan Belt. Zircons from five granitic intrusions from the eastern SCS have been separated and analysed for Hf isotopes by laser ablation MC-ICPMS, in order to evaluate the nature of granitic magma source. Two samples are cordierite-bearing S-type granites, the rest are amphibole-bearing I-type monzogranites. Hf-isotope composition of zircons from these granites defines a narrow range of negative Hf values (-1.1 to -5.8), typical of crustal protoliths. The within-sample variation of zircon Hf isotope composition is slightly above the analytical uncertainty (+/-1.5 units), suggesting the mixing of different magma batches during pluton assembly. The S- and I-type granites display the same range of in...

The Granny Smith (37 t Au production) and Wallaby deposits (38 t out of a 180 t Au resource) are located northeast of Kalgoorlie, in 2.7 Ga greenstones of the Eastern Goldfields Province, the youngest orogenic belt of the Yilgarn craton, Western Australia. At Granny Smith, a zoned monzodiorite-granodiorite stock, dated by a concordant titanite-zircon U-Pb age of 2,665 ± 3 Ma, cuts across east-dipping thrust faults. The stock is fractured but not displaced and sets a minimum age for large-scale (1 km) thrust faulting (D2), regional folding (D1), and dynamothermal metamorphism in the mining district. The local gold-pyrite mineralization, controlled by fractured fault zones, is younger than 2,665 ± 3 Ma. In augite-hornblende monzodiorite, alteration progressed from a hematite-stained alkali feldspar-quartz-calcite assemblage and quartz-molybdenite-pyrite veins to a late reduced sericite-dolomite-albite assemblage. Gold-related monazite and xenotime define a U-Pb age of 2,660 ± 5 Ma, and molybdenite from veins a Re-Os isochron age of 2,661 ± 6 Ma, indicating that mineralization took place shortly after the emplacement of the main stock, perhaps coincident with the intrusion of late alkali granite dikes. At Wallaby, a NE-trending swarm of porphyry dikes comprising augite monzonite, monzodiorite, and minor kersantite intrudes folded and thrust-faulted molasse. The conglomerate and the dikes are overprinted by barren (1,600-m-long replacement pipe, which is intruded by a younger ring dike of syenite porphyry pervasively altered to muscovite + calcite + pyrite. Skarn and syenite are cut by pink biotite-calcite veins, containing magnetite + pyrite and subeconomic gold-silver mineralization (Au/Ag = 0.2). The veins are associated with red biotite-sericite-calcite-albite alteration in adjacent monzonite dikes. Structural relations and the concordant titanite U-Pb age of the skarn constrain intrusion-related mineralization to 2,662 ± 3 Ma. The main-stage gold-pyrite ore (Au/Ag >10) forms hematite-stained sericite-dolomite-albite lodes in stacked D2 reverse faults, which offset skarn, syenite, and the biotite-calcite veins by up to 25 m. The molybdenite Re-Os age (2,661 ± 10 Ma) of the ore suggests a genetic link to intrusive activity but is in apparent conflict with a monazite-xenotime U-Pb age (2,651 ± 6 Ma), which differs from that of the skarn at the 95% confidence level. The time relationships at both gold deposits are inconsistent with orogenic models invoking a principal role for metamorphic fluids released during the main phase of compression in the fold belt. Instead, mineralization is related in space and time to late-orogenic, magnetite-series, high-Mg monzodiorite-syenite intrusions of mantle origin, characterized by Mg/(Mg + FeTOTAL) = 0.31-0.57, high Cr (34-96 ppm), Ni (22-63 ppm), Ba (1,056-2,321 ppm), Sr (1,268-2,457 ppm), Th (15-36 ppm), and rare earth elements (total REE: 343-523 ppm). At Wallaby, shared Ca-K-CO2 metasomatism and Th-REE enrichment (in allanite) link Au-Ag mineralization in biotite-calcite veins to the formation of the giant epidote skarn, implicating a Th + REE-rich syenite pluton at depth as the source of the oxidized hydrothermal fluid. At Granny Smith, lead isotope data and the Rb-Th-U signature of early hematite-bearing wall-rock alteration point to fluid released by the source pluton of the differentiated alkali granite dikes.

The Tianyu mafic-ultramafic intrusion is one of many important sulfide-bearing mafic-ultramafic intrusions in the eastern Tianshan terrane located in the southern margin of the Central Asian Orogenic Belt in north Xinjiang, NW China. The origin of sulfide mineralization in these intrusions, their relationship with Permian basalts and A-type granites, and the geodynamic setting of the bimodal magmatism in the region are controversial. In this paper we use zircon U-Pb age, Hf-Sr-Nd-Os isotope and lithophile-chalcophile trace element constraints from the Tianyu mafic-ultramafic intrusion to address these important issues. The U-Pb age of zircon from the Tianyu intrusion determined by SIMS is 280+/-2Ma. This confirms that the Tianyu intrusion is coeval with most sulfide-bearing mafic-ultramafi...

Tectonic subsidence curves show that the Illinois, Michigan, and Williston basins formed by initial fault-controlled mechanical subsidence during rifting and by subsequent thermal subsidence. Thermal subsidence began around 525 Ma in the Illinois Basin, 520-460 Ma in the Michigan Basin, and 530-500 Ma in the Williston Basin. In the Illinois Basin, a second subsidence episode (middle Mississippian through Early Permian) was caused by flexural foreland subsidence in response to the Alleghanian-Hercynian orogeny. Past workers have suggested mantle phase changes at the base of the crust, mechanical subsidence in response to isostatically uncompensated excess mass following igneous intrusions, intrusion of mantle plumes into the crust, or regional thermal metamorphic events as causes of basin initiation. Cratonic basins of North America, Europe, Africa, and South America share common ages of formation, histories of sediment accumulation, temporal volume changes of sediment fills, and common dates of interregional unconformities. Their common date of formation suggests initiation of cratonic basins in response to breakup of a late Precambrian supercontinent. This supercontinent acted as a heat lens that caused partial melting of the lower crust and upper mantle followed by emplacement of anorogenic granites during extensional tectonics in response to supercontinent breakup. Intrusion of anorogenic granites and other partially melted intrusive rocks weakened continental lithosphere, thus providing a zone of localized regional stretching and permitting formation of cratonic basins almost simultaneously over sites of intrusion of these anorogenic granites and other partially melted intrusive rocks.

Zircon U-Pb dating and whole-rock major oxide, trace element and Nd-Sr isotope compositions have been determined for four representative granitic intrusions in the SW Chinese Altai, in order to understand the orogenesis and history of crustal growth in the Central Asian Orogenic Belt (CAOB). The Ash...

Because many variable surface characteristics affect the response of an electromagnetic ... These so-called “cookie-cutter” granite intrusions vividly demonstrate the dominance of mechanical weathering processes in this arid environment. ..... Examination of the transformation matrix in table 2 shows the relative importance ...

The Spanish Central System (SCS) is one of the largest granite batholiths in the European Variscan Belt. Zircons from five granitic intrusions from the eastern SCS have been separated and analysed for Hf isotopes by laser ablation MC-ICPMS, in order to evaluate the nature of granitic magma source. Two samples are cordierite-bearing S-type granites, the rest are amphibole-bearing I-type monzogranites. Hf-isotope composition of zircons from these granites defines a narrow range of negative ?Hf values (? 1.1 to ? 5.8), typical of crustal protoliths. The within-sample variation of zircon Hf isotope composition is slightly above the analytical uncertainty (± 1.5 ? units), suggesting the mixing of different magma batches during pluton assembly. The S- and I-type granites display the same range of initial ?Hf values, that is in agreement with previous data showing that both SCS granite types have similar (Sr, Nd, O, Pb) isotope signatures. These isotopic data suggest that they derived from similar sources, while the variation in peraluminosity could be related to different partial melting conditions.The presence of a Lower Ordovician inherited zircon population (478–462 Ma), at least in I-type granites, suggests the involvement of Cambro–Ordovician orthogneisses as components in the source of some SCS granites. Inherited zircon population of similar age has also been identified in the SCS lower crustal granulites. The Hf-isotope composition of the analysed granite zircons is within that of zircons from the above granulites. Moreover, some evidence of a juvenile input at 560–595 Ma is recorded by Hf-isotope data in zircons from both the SCS granites and granulite xenoliths. Hf-isotope signature, in conjunction with other chemical, isotopic (Sr, Nd, O, Pb) and geochronological evidences, suggests that SCS granites were probably derived from metaigneous lower crustal sources. The Variscan magmatism in central Spain is dominantly a crustal reworking event.

Abstract in portuguese A seqüência vulcano-sedimentar de Arenópolis, localizada na porção sul do Arco Magmárico de Goiás, inclui uma associação de rochas vulcânicas calci-alcalinas de arco com ca. 900 Ma de idade, constituída de rochas variando em composição entre basaltos e riolitos, metamorfisados em fácies xisto verde a anfibolito. Pequenos corpos sub-vulcânicos de gabros a granitos calci-alcalinos são também reconhecidos. A intrusão do Morro do Baú é a maior dessas intru (more) sões, compreendendo dioritos e gabros. Cristais de zircão separados de uma amostra de gabro e analisados no SHRIMP I indicaram a idade 206Pb/238U média de 890 +/- 8 Ma, mostrando que a intrusão é grosseiramente contemporânea, ou talvez um pouco mais jovem que as rochas vulcânicas. Ao contrário das rochas metavulcânicas, que são juvenis, a composição isotópica de Nd do gabro do Morro do Baú indica forte contaminação com material siálico arqueano (T DM de 2.8 Ga e EpsilonNd(T) igual a -9.7), representado na área por uma pequena fatia tectônica de rocha gnáissica arqueana/paleoproterozóica (gnaisse Ribeirão), e que representa a rocha encaixante da intrusão gabro-diorítica. A idade de cristalização de ca. 890 Ma representa, portanto, um limite mínimo para a acresção tectônica do gnaisse Ribeirão às rochas mais jovens da seqüência de Arenópolis. Os dados sugerem que esse evento foi precoce na evolução da seqüência vulcano-sedimentar de Arenópolis, provavelmente entre ca. 920 e 890 Ma. Abstract in english The Arenópolis volcano-sedimentary sequence is located in the southern part of the Goiás Magmatic Arc and includes a ca. 900 Ma calc-alkaline arc sequence made of volcanic rocks ranging in composition from basalts to rhyolites, metamorphosed under greenschist to amphibolite facies. Small calc-alkaline gabbro to granite sub-volcanic bodies are also recognized. The Morro do Baú intrusion is the largest of these intrusions, and is made of gabbros and diorites. Zircon grai (more) ns separated from one gabbro sample and analyzed by SHRIMP I yielded the mean 206Pb/238U age of 890 +/- 8 Ma, indicating that the intrusion is roughly coeval or only slightly younger than the Arenópolis volcanics. Contrary to the metavolcanics, which are juvenile, the Nd isotopic composition of the Morro do Baú gabbro indicates strong contamination with archean sialic material (T DM of 2.8 Ga and EpsilonNd(T) of -9.7), represented in the area by an allochthonous sliver of archean/paleoproterozoic gneisses (Ribeirão gneiss) which are the country-rocks for the gabbro/dioritic intrusion. The emplacement age of ca. 890 Ma represents a minimum age limit for the tectonic accretion of the gneiss sliver to the younger rocks of the Arenópolis sequence. The data suggest that this happened early in the evolution of the Goiás Magmatic Arc, between ca. 920 and 890 Ma.

The Tianyu mafic-ultramafic intrusion is one of many important sulfide-bearing mafic-ultramafic intrusions in the eastern Tianshan terrane located in the southern margin of the Central Asian Orogenic Belt in north Xinjiang, NW China. The origin of sulfide mineralization in these intrusions, their relationship with Permian basalts and A-type granites, and the geodynamic setting of the bimodal magmatism in the region are controversial. In this paper we use zircon U-Pb age, Hf-Sr-Nd-Os isotope and lithophile-chalcophile trace element constraints from the Tianyu mafic-ultramafic intrusion to address these important issues. The U-Pb age of zircon from the Tianyu intrusion determined by SIMS is 280 ± 2 Ma. This confirms that the Tianyu intrusion is coeval with most sulfide-bearing mafic-ultramafic intrusions and some basalts and A-type granites in the Tianshan region. Similar to coeval basalts in the nearby Tuha basin, the Tianyu intrusive rocks are characterized by negative Nb anomaly and elevated ? Nd values varying between - 1 and + 4.6. The negative Nb anomaly in the Tianyu intrusion is not as pronounced as in the coeval A-type granites but the ? Nd values for these bimodal rocks are similar. The ? Hf values of zircon from the Tianyu intrusion are positive, varying between 3 and 8. These values suggest that the parental magma of the Tianyu intrusion was dominated by melt derived from a depleted source mantle. The ? Os values of pyrrhotite from the Tianyu intrusion are high, ranging from 725 to 995, which can be modeled by selective assimilation of sulfide from the lower and upper crusts. Negative Pt anomaly is present in relatively sulfide-rich samples such as semi-massive and massive sulfide ores but not in sulfide-poor samples, which is more consistent with the effect of post-magmatic hydrothermal alteration than the original signature of the parental magma. The results of modeling using the compositions of selected disseminated sulfide samples suggest that the parental magma of the Tianyu intrusion was depleted in all PGE, which is consistent with previous sulfide segregation at depth. Our data and modeling results support the model of decompression melting of upwelling asthenosphere due to slab break-off during a transition from oceanic subduction to arc-arc or arc-continent collision in the Permian. Decompression melting of the upwelling asthenosphere in the region produced mafic magma. Partial melting in the lower parts of a juvenile arc crust due to mafic magma underplating produced granitic melts. Mixing of the mafic magma with a small amount of granitic melts at depth followed by contamination with the upper crust at a higher level formed the parental magma of the Tianyu intrusion. PGE depletion in the parental magma of the Tianyu intrusion can be attributed to sulfide segregation associated to the first stage of crustal contamination at depth. We suggest that the formation of sulfide ores in the intrusion was related to the second stage of crustal contamination in the upper crust.

The Baishitouquan (BST) pluton is a topaz- and amazonite-bearing leucogranite intrusion located in the Middle Tianshan orogen of Xinjiang, northwestern China. This pluton exhibits five lithological zones gradational from the bottom upwards: leucogranite (zone-a), amazonite-bearing granite (zone-b), amazonite granite (zone-c), topaz-bearing amazonite granite (zone-d) and topaz albite granite (zone-e). Contents of REE and other trace elements were analysed on major and accessory minerals, including quartz, plagioclase, K-feldspar, white micas, topaz, fluorite, garnet, zircon and monazite, separated from above five zones of the BST pluton. Chondrite-normalized REE patterns of minerals from zone-a to zone-e display clear convex tetrad effect, and the TE"1","3 (quantification factor of tetrad e...

Abstract The Sharang porphyry Mo deposit is the first discovered Mo porphyry-type deposit in the Gangdese Metallogenic Belt. The orebody is hosted by the Eocene multi-stage composite intrusive complex which is emplaced in the Upper Permian Mengla Formation and cut by the Miocene dykes. Granite porphyry is recognized as the ore-bearing porphyry in the complex, which consists of quartz diorite, quartz monzonite, granite, prophyritic granite and post-mineral lamprophyre. Granodiorite porphyry and dacite porphyry intrude the granite porphyry. Geochemical data indicate that Sharang complex has a High-K calc-alkalinc to shoshonitic, metaluminous to slightly peraluminous composition. The Sharang complex rocks are enriched in large ion lithophile elements, depleted in high-field strength elements,...

Zircon U-Pb dating and geochemical data are reported for the Jiefangyingzi and Yongshenghao granitic plutons from the Jiefangyingzi area to the northeast (NE) of Chifeng city, Inner Mongolia, with the objective of revealing the tectonic nature of the northern margin of the Sino-Korean paleoplate in early Mesozoic. Zircons from these granitic intrusions are euhedral and subeuhedral in shape with typical oscillatory zoning, indicating magmatic origin. The dating results indicate that these plutons formed in late middle Triassic (229+/-2Ma and 229+/-1Ma respectively), rather than in late Paleozoic, as previously thought. The Jiefangyingzi and Yongshegnhao granitic plutons are composed primarily of granodiorite and granite, with compositions of SiO"2=63.23-68.91wt.%, K"2O=3.06-4.51wt.%, and A/...

deposits and shoreline features of Silver Lake and Soda Lake depositional basins of ...... of the beach deposits are mantled by younger eolian sediments .... stratigraphic relations have been described for Quaternary marine .... Subrounded to subangular clasts (up to 4 cm in size) of granite and lesser amount of limestone.

The Galician Hercynian segment constitutes the core of the Ibero-Armorican orogenic arc, characterized by few tectonic units that record three main phases of deformation (D1 to D3). Four generations of granite, syn- to post-D3 intruded the major tectonic units. From older to younger, we find: i) syn...

High-grade rocks of the Wilmington Complex, northern Delaware and adjacent Maryland and Pennsylvania, contain morphologically complex zircons that formed through both igneous and metamorphic processes during the development of an island-arc complex and suturing of the arc to Laurentia. The arc complex has been divided into several members, the protoliths of which include both intrusive and extrusive rocks. Metasedimentary rocks are interlayered with the complex and are believed to be the infrastructure upon which the arc was built. In the Wilmingto n Complex rocks, both igneous and metamorphic zircons occur as elongate and equant forms. Chemical zoning, shown by cathodoluminescence (CL), includes both concentric, oscillatory patterns, indicative of igneous origin, and patchwork and sector patterns, suggestive of metamorphic growth. Metamorphic monazites are chemically homogeneous, or show oscillatory or spotted chemical zoning in backscattered electron images. U-Pb geochronology by sensitive high resolution ion microprobe (SHRIMP) was used to date complexly zoned zircon and monazite. All but one member of the Wilmington Complex crystallized in the Ordovician between ca. 475 and 485 Ma; these rocks were intruded by a suite of gabbro-to-granite plutonic rocks at 434 ?? Ma. Detrital zircons in metavolcanic and metasedimentary units were derived predominantly from 0.9 to 1.4 Ga (Grenvillian) basement, presumably of Laurentian origin. Amphibolite to granulite facies metamorphism of the Wilmington Complex, recorded by ages of metamorphic zircon (428 ?? 4 and 432 ?? 6 Ma) and monazite (429 ?? 2 and 426 ?? 3 Ma), occurred contemporaneously with emplacement of the younger plutonic rocks. On the basis of varying CL zoning patterns and external morphologies, metamorphic zircons formed by different processes (presumably controlled by rock chemistry) at slightly different times and temperatures during prograde metamorphism. In addition, at least three other thermal episodes are recorded by monazite growth at 447 ?? 4, 411 ?? 3, and 398 ?? 3 Ma. ?? 2006 Geological Society of America.

Zircon U-Pb SHRIMP ages and crustal Sm-Nd signatures are reported for metasediments meta- volcanics. and a variety of pre- and post-tectonic granitoid intrusives in the Eastern Fold Belt of the Mt Isa inlier. These enable tracing of the broad crustal evolution of the rocks erection of a chrono- stratigraphic framework in the Eastern Fold Belt. and correlation of these rocks with those in other parts of the Mt Isa Inlier and in other Proterozoic inliers of northern Australia. The SHRIMP results and Sm-Nd model ages provide quantitative information related to the provenance history of the metasediments and the sources and crustal interactions of magmatic rocks. Most of the latter have Nd T{sub DM} of 2270-2200 Ma suggesting similar source(s) to the metasediments and gneisses (2360-2140Ma). The Nd T{sub DM} model ages are younger than those found in the Kalkadoon-Leichhardt Belt, suggesting that the Eastern Fold Belt crust received less Archaean source input, Rocks of Barramundi age (1870-1840 Ma) are not found in the Eastern Fold Belt. The geochronology of the Eastern Fold Belt country rocks and granites supports arguments based on lithostratigraphy and evidence from Pb-isotope data which imply that stratabound Pb-Zn mineralisation in the Eastern Fold Belt and Georgetown regions may have been generated in a similar tectonic environment and from similar source rocks at about the same time (ca 1680-1660Ma). A post-1700 Ma connection and correlation of these two terrains, and possibly the Broken Hill inlier has to be seriously considered. Copyright (1998) Blackwell Science Asia

In the early 1960s, new concepts and innovative techniques coalesced spectacularly to improve understanding of Tertiary pyroclastic volcanism in North America. Spotty recognition of welded tuff, among rocks mostly described as silicic lava flows, exploded with identification of individual ignimbrite sheets, some having volumes >103 km3 and extending >100 km from source calderas. R.l. Smith, during study of the Bandelier Tuff in New Mexico, documented complexities of welding and crystallization zones that provided a genetic framework (cooling units) for ignimbrite studies (even while confusion continues in some areas where talus and vegetation obscure bench-forming contact zones between densely welded cliffs). Also in the 1960s, application of isotopic age determinations (initially K-Ar, now largely superceded by 40Ar/39Ar laser fusion) and precise paleomagnetic pole directions became key tools for correlating ignimbrites, deciphering eruptive histories, and determining volcano-tectonic patterns. Dated ignimbrites provide unique stratigraphic markers within volcanic field, as well as datums for regional structures and the shifting patterns of volcanism related to global plate motions--another happy coincidence in the 1960s as plate-tectonic models were formulated. Tertiary ignimbrite flare-ups along the Cordilleran margin increasingly are recognized as coinciding with inception of regional extension, especially during transitions from episodes of low-angle convergence. Many large caldera sources for the Tertiary ignimbrites have now been identified, in place of prior vague concepts of “volcano-tectonic depressions”, especially as the contrasts between thin outflow and thickly ponded intracaldera ignimbrite with interleaved collapse breccia became appreciated. Multi-km-thick fills in many calderas document that collapse begins early during large ignimbrite eruptions, and downsag inception was succeeded by breakage along ring faults. Resurgent uplift has been identified at many ignimbrite calderas, building on the pioneering observations of van Bemmelen at Lake Toba, Indonesia. Still many Tertiary caldera systems remain poorly understood where buried beneath younger rocks, others completely eroded to levels of subvolcanic granitic plutons. Links between silicic volcanism and batholith formation in continental crust continue a major research focus; improved petrologic, isotopic, and geophysical techniques are helping evaluate compositional and age relations between extrusive and intrusive components, as well as present-day intrusion geometry relative to times of peak volcanism. Ignimbrites that preserve quenched compositional gradients, commonly from rhyolite upward into crystal-rich dacite, were early recognized as special opportunities for magma-chamber studies, especially as analytical methods improved (XRF and INAA rock chemistry, microprobe mineral compositions, radiogenic and stable isotope geochemistry). These demonstrated the importance of mafic magma from the mantle, melting/assimilation in the lower crust, and mixing of diverse magmas during rise and eruption, even as recent studies by electron and/or ion probe documented complex crystal cargos (mixed phenocrysts, xenocrysts, and antecrysts).

The Antongil Craton, along with the Masora and Antananarivo cratons, make up the fundamental Archaean building blocks of the island of Madagascar. They were juxtaposed during the late-Neoproterozoic to early Palaeozoic assembly of Gondwana. In this paper we give a synthesis of the geology of the Antongil Craton and present previously published and new geochemical and U-Pb zircon analyses to provide an event history for its evolution.The oldest rocks in the Antongil Craton form a nucleus of tonalitic gneiss, characteristic of Palaeo-Mesoarchaean cratons globally, including phases dated between 3320 ?? 14. Ma to 3231 ?? 6. Ma and 3187 ?? 2. Ma to 3154 ?? 5. Ma. A series of mafic dykes was intruded into the Mesoarchaean tonalites and a sedimentary succession was deposited on the craton prior to pervasive deformation and migmatisation of the region. The age of deposition of the metasediments has been constrained from a volcanic horizon to around 3178 ?? 2. Ma and subject to migmatisation at around 2597 ?? 49. Ma. A subsequent magmatic episode generated voluminous, weakly foliated granitic rocks, that also included additions from both reworked older crustal material and younger source components. An earlier granodiorite-dominated assemblage, dated between 2570 ?? 18. Ma and 2542 ?? 5. Ma, is largely exposed in xenoliths and more continuously in the northern part of the craton, while a later monzogranite-dominated phase, dated between 2531 ?? 13. Ma and 2513 ?? 0.4. Ma is more widely developed. Together these record the stabilisation of the craton, attested to by the intrusion of a younger dyke swarm, the age of which is constrained by a sample of metagabbro dated at 2147 ?? 6. Ma, providing the first evidence for Palaeoproterozoic rocks from the Antongil Craton.The youngest events recorded in the isotopic record of the Antongil Craton are reflected in metamorphism, neocrystallisation and Pb-loss at 792 ?? 130. Ma to 763 ?? 13. Ma and 553 ?? 68. Ma. These events are interpreted as being the only manifestation of the Pan-African orogeny seen in the craton, which led to the assembly of the tectonic blocks that comprise the island. ?? 2010 NERC.

New zircon U?Pb ages for a felsic volcanic rock (2,588???10?Ma) and an intrusive granite (?2,555???6?Ma) in the Gadag greenstone belt in the Western Dharwar Craton, southern India, are similar to dates for equivalent rocks in the Eastern Dharwar Craton and indicates docking of the two cratons prior to this time. The zircons in the intrusive granite are strongly overprinted, and coexisting titanites yielded two different age populations: the dominant group gives an age of 2,566???7?Ma, interpreted as the emplacement age, whereas the minor group gives an age of 2,516???10?Ma, reflecting a hydrothermal overprint. In situ U?Pb dating of monazite and xenotime in gold reefs of the Gadag (2,522???6?Ma) and Ajjanahalli (2,520???9?Ma) gold deposits reveal a previously undated episode of gold minera...

Summary The Dachang Sn-polymetallic ore district is one of the largest tin producing districts in China. Its origin has long been in dispute between magmatic-hydrothermal replacement and submarine exhalative-hydrothermal origin. The Dachang ore district comprises several types of ore deposits, including the Lamo magmatogenic skarn deposit near a granite intrusion, the Changpo-Tongkeng bedded and vein-type sulfide deposit, and the Gaofeng massive sulfide deposit. Sulfide minerals from the Lamo skarn ores show ?34S values in the range between ?3 and +4? with a mean close to zero, suggesting a major magmatic sulfur source that likely was the intrusive Longxianggai granite. Sulfide minerals from the Gaofeng massive ores show higher ?34S values between +5 and +12?, whereas sulfide minerals from...

The Paleozoic granites in the Chinese Altai are important for the study of tectonic evolution and crustal growth in the Central Asian Orogenic Belt (CAOB). Four representative peraluminous granitic intrusions were selected for systematic studies of zircon U-Pb and Hf isotopic compositions and whole-rock geochemical and Nd-Sr isotopic analyses. These rocks have high ASI (Alumina Saturation Index, Al2O3/(CaO+Na2O+K2O)=1.01-1.46 molecular ratios), with 0.6-5.6wt.% of normative corundum, and are characterized by moderately negative Eu anomalies (Eu/Eu*=0.38-0.98) and strong depletion in Ba, Nb and Sr elements. Our data suggest that these intrusions were emplaced from 419 to 393Ma, consistent with a period of intensive magmatic activities and high temperature metamorphism in the Chinese Altai. ...

The Aouli Pluton consists of four units: (1) granodiorite; (2) grey granite; (3) pink granite - these three units constituting a spatially continuous massif, and (4) muscovite granite, which is exposed in two small stocks somewhat removed from the other units. U-Pb ages obtained on zircon and titanite are 333 {+-} 2 Ma and 319 {+-} 1.5 Ma for the granodiorite and grey granite respectively. The 14 ma age difference between the granodiorite and the grey granite supports the multiple injection hypothesis which was the outcome of geochemical studies (Oukemeni and Bourne, 1993). These two rocks also contain an inherited component which has been dated at 1520 Ma in the granudiorite and at 1245 ma and 1804 Ma in the grey granite. The inherited components suggest the possible presence of Precambian crust below the Haute Moulouya. Since the intrusion is late-to post-tectonic (Oukemeni and Bourne, 1993), the age of the granodiorite (333 {+-} 2 Ma) indicates that the Hercynian deformation is pre-Visean in the Haute Moulouya area, and, by extension, throughout the eastern meseta region. (authors). 14 refs. 4 figs. 3 tabs.

The Abukuma Plateau is one of the major granitic terranes in the Japan Arc. Older granitic rocks (foliated and intermediate), younger granitic rocks (massive and felsic), and minor gabbroic rocks are complexly distributed in this region. In order to examine the cooling histories of the plutons, we have determined four 40Ar-39Ar hornblende ages and five K-Ar biotite ages of the plutonic rocks in the central Abukuma Plateau. The results are as follows:     Utsushiga-take gabbroic body: 103.8 ± 0.5 Ma (hbl)     Nagaya body (older): 97.3 ± 0.6 Ma (hbl), 93.4 ± 3.1 Ma (bt)     Shikayama body (older): 103.0 ± 0.4 Ma (hbl), 86.1 ± 3.8 Ma (bt)     Ishimori body (older): 99.0 ± 0.5 Ma (hbl), 94.2 ± 2.6 Ma (bt)     Miharu body (younger): 91.3 ± 2.3 Ma (bt)     Hatsumori body (younger): 90.5 ± 2.6 Ma (bt)     (hbl, 40Ar-39Ar hornblende age; bt, K-Ar biotite age).On the basis of these analytical results and the petrography of the samples, we made the following observations:(1) The cooling rates of the Nagaya and Ishimori bodies (56 and 46 °C/m.y.) are equivalent to the common cooling rates of the Japanese granitic batholiths. The cooling rate of the Shikayama body (13 °C/m.y.) is slow because its volume is large.(2) The excellent 40Ar-39Ar plateau age of and the scarcity of metamorphic minerals in the Utsushiga-take gabbroic body suggest that the hornblende age is not a rejuvenated age but the original cooling age.(3) We were unable to detect any distinct geochronological boundary between the older and younger granitic rocks in the central Abukuma Plateau, in terms of the K-Ar biotite ages.   

Large volumes of granitic magmas form through partial melting of the lower crust and are subsequently emplaced in the higher crustal levels [1]. In addition, granite-like liquids may form through partial melting of subducted sediments [2] or as an end-product of magmatic differentiation [3]. Moreover, water rich magmas of granitic composition are a major source of explosive volcanism. The physical properties of granitic melts, and particularly their density, are key controls on the migration rate and emplacement depth of granitic intrusions. However, because of the high viscosity of granitic liquids, density and compressibility measurements with the sink/float method and sound velocity measurements are challenging. As a result, the density and compressibility of dry and volatile-bearing granitic liquids is poorly constrained, particularly for the pressure-temperature conditions relevant for their formation and emplacement. In this study, we present in situ experimental data on the density of dry and hydrous haplogranitic melts (5 and 10 wt% water) at pressure and temperature conditions relevant for the crust and the subducting slab (1.0-2.7 GPa, 1350-1720 K). The experiments were performed with a panoramic Paris-Edinburgh press installed at the ID27 beamline of ESRF. The samples were contained in a cylindrical diamond capsule, capped with a platinum disk on either side, surrounded by hexagonal boron nitride (hBN) and placed inside a graphite heater and boron epoxy gasket. Pressure and temperature were determined from the X-ray diffraction patterns of hBN and platinum using the double-isochore method [4]. The density of the melts was determined from the X-ray absorption contrast between the sample and the diamond capsule (Mo edge, 20 keV). The molten state of the sample at the condition of the density measurements was verified by X-ray diffraction. The run products were analyzed by electron microprobe and infrared spectroscopy to verify the chemical composition and volatile content of the samples. Our results, combined with literature data on granite melt density at atmospheric pressure, provides the first experimentally derived equation of state of dry and hydrous granitic liquids at crustal and upper mantle conditions. This equation of state enables the prediction of the partial molar volume of water and granite melt density for the pressures, temperatures and water contents relevant for partial melting in the lower crust, melt migration through the middle crust and the emplacement of intrusions in the upper crust. [1] N. Petford, A.R. Cruden, K.J.W. McCaffrey, J.-L. Vigneresse, 2000, Nature, 408, 669. [2] Y. Tatsumi, 2000, Geology, 29, 323. [3] N.L. Bowen, 1956, The evolution of igneous rocks. [4] W.A. Chrichton, M. Mezouar, 2002, High Temp.-High Press, 34, 235.

The Paleozoic granites in the Chinese Altai are important for the study of tectonic evolution and crustal growth in the Central Asian Orogenic Belt (CAOB). Four representative peraluminous granitic intrusions were selected for systematic studies of zircon U-Pb and Hf isotopic compositions and whole-rock geochemical and Nd-Sr isotopic analyses. These rocks have high ASI (Alumina Saturation Index, Al2O3/(CaO + Na2O + K2O) = 1.01-1.46 molecular ratios), with 0.6-5.6 wt.% of normative corundum, and are characterized by moderately negative Eu anomalies (Eu/Eu* = 0.38-0.98) and strong depletion in Ba, Nb and Sr elements. Our data suggest that these intrusions were emplaced from 419 to 393 Ma, consistent with a period of intensive magmatic activities and high temperature metamorphism in the Chinese Altai. While in situ zircon Hf isotopic analyses for these granites give predominantly positive ?Hf(t) values (+ 0.8 to + 12.8), a few inherited zircons yield negative ?Hf(t) values from - 12.5 to - 1.53. The U-Pb age and Hf isotopic data of these inherited zircons are similar to that of the widespread metasediments. In addition, the peraluminous granitic rocks have near-zero or negative ?Nd(t) values (- 3.3 to - 0.5) and relatively high initial 87Sr/86Sr ratios (0.7079-0.7266), distinct from those of the I-type granites in the study region, but similar to the Early Paleozoic Habahe sediments. These isotopic compositions suggest that the newly accreted metasediments of Habahe Group may be the major source rock of the peraluminous granites. The geochemical compositions indicate that their precursor magmas were derived from a relatively shallow crustal level (P ? 5 kbar) and zircon saturation temperatures suggest that these granitic intrusions were emplaced at 672-861 °C. The peraluminous granitic magmas were generated by dehydration melting of newly accreted materials, which were possibly brought to at least middle crustal depth by subduction-related processes in an active margin, and were subsequently molten by strikingly high ambient temperature probably caused by upwelling of the hot asthenosphere associated with ridge subduction in the Paleozoic.

The local heterogeneity of K, Rb, Ti, Zr, P, Sr, and Ba was determined by x-ray fluorescence analysis as a first step in investigations of the regional heterogeneity of a whole granite body of larger extent. The first granite of this series is the Malsburg-Granite in the southwest of the Black Forest. The analytical results are reproducible and accurate, if the rock samples are ground below 450 mesh. The errors and mean deviations caused by counting, instrumentation, and preparation are small in comparison with those in a rock sample of an outcrop or the whole rock body. The method of x-ray fluorescence analysis can be applied for the study of the mechanism of magmatic intrusion and differentiation. (auth)

As the boundary between the Indochina and the South China blocks, the Ailao Shan-Red River (ASRR) shear zone underwent a sinistral strike-slip shearing which is characterized by ductile deformation structures along the Ailao Shan range. The timing issue of left-lateral shearing along the ASRR shear zone is of first-order importance in constraining the nature and regional significance of the shear zone. It has been, therefore, focused on by many previous studies, but debates still exist on the age of initiation and termination of shearing along the shear zone. In this paper, we dated 5 samples of granitic plutons (dykes) along the Ailao Shan shear zone. Zircon U-Pb ages of four sheared or partly sheared granitic rocks give ages of 30.9 ± 0.7, 36.6 ± 0.1, 25.9 ± 1.0 and 27.2 ± 0.2 Ma, respectively. An undeformed granitic dyke intruding mylonitic foliation gives crystallization age of 21.8 ± 1 Ma. The Th/U ratios of zircon grains from these rocks fall into two populations (0.17-1.01 and 0.07-0.08), reflecting magmatic and metamorphic origins of the zircons. Detailed structural and microstructural analysis reveals that the granitic intrusions are ascribed to pre-, syn- and post-shearing magmatisms. The zircon U-Pb ages of these granites provide constraints on timing of the initiation (later than 31 Ma from pre-shearing granitic plutons, but earlier than 27 Ma from syn-shearing granitic dykes) and termination (ca. 21 Ma from the post-shearing granitic dykes) of strong ductile left-lateral shearing, which is consistent with previous results on the Diancang Shan and Day Nui Con Voi massifs in the literature. We also conclude that the left-lateral shearing along the ASRR shear zone is the result of southeastward extrusion of the Indochina block during the Indian-Eurasian plate collision. Furthermore, the left-lateral shearing was accompanied by the ridge jump, postdating the opening, of the South China Sea.

Initiation of the Cordilleran magmatic arc in the southwestern United States is marked by intrusion of granitic plutons, predominantly composed of alkali-calcic Fe- and Sr-enriched quartz monzodiorite and monzonite, that intruded Paleoproterozoic basement and its Paleozoic cratonal-miogeoclinal cover. Three intrusive suites, recognized on the basis of differences in high field strength element and large ion lithophile element abundances, contain texturally complex but chronologically distinctive zircons. These zircons record heterogeneous but geochemically discrete mafic crustal magma sources, discrete Permo-Triassic intrusion ages, and a prolonged postemplacement thermal history within the long-lived Cordilleran arc, leading to episodic loss of radiogenic Pb. Distinctive lower crustal magma sources reflect lateral heterogeneity within the composite lithosphere of the Proterozoic craton. Limited interaction between derived magmas and middle and upper crustal rocks probably reflects the relatively cool thermal structure of the nascent Cordilleran continental margin magmatic arc. ?? 2006 by The University of Chicago. All rights reserved.

A geophysical signature associated with Nb?Ta?Sn mineralization of G. (G. : abbreviation to word Gebel which means mountain in Arabic) Nuweibi area, located the Central Eastern Desert of Egypt is presented. This signature was established by an integration of airborne gamma ray spectrometric and magnetic data. Variations seen in the gamma ray spectrometric data are used as a base to study the three granitic suites: younger-, albite-, and older granites in G. Nuweibi area. Graphical techniques such as frequency histograms and box-plots are used to visualize the shape of the distribution and determine the anomaly thresholds of the three radioelements eU, eTh, and K% data in these granitic suites. The box-plot graphical representations and calculations made on data sets indicate that no sample...

The Jomolhari region of NW Bhutan contains one of the largest and most accessible continuous exposures of the South Tibetan Fault System in the Himalaya. Lying immediately southeast of the Yadong Graben (Mount Jomolhari is part of the eastern rift flank uplift), the geology of this area is dominated by banded orthogneiss and paragneiss of the Greater Himalayan Sequence (GHS), Chekha Group pelitic schist and quartzite and carbonate units of the Tibetan Sedimentary Sequence (TSS). All contain abundant leucogranite sills and dikes. New mapping of the Jomolhari region combined with decorrelation stretched, multispectral ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) imagery has revealed two fault contacts that we interpret as two strands of the South Tibetan Fault System. The structurally lower of the two faults has been recognized by other research groups previously, although published maps of its trace differ from what we have established through field mapping and satellite data interpretation. The lower contact places Chekha Group quartzite over Greater Himalayan Sequence paragneiss. One extremely good exposure of the contact in the Paro Chhu valley expresses as a normal-sense, brittle-ductile shear zone marked by calcareous mylonite overlain by a chloritic breccia. This shear zone locally trends WSW-ENE and dips 35° to the SSE, before changing to a N-dip farther north as it disappears beneath the Chung La leucogranite pluton. The upper contact is marked by a major structural discontinuity between recumbently-folded TSS carbonate above and folded Chekha Group units below. TSS carbonate rock outcrops at Jomolhari base camp and farther west towards Mount Jomolhari suggest that the geology of this area may be more complex than previously described. Since outcrop in the region is generally poor, the Chekha-TSS Carbonate contact is inferred from changes in landslide material and a distinct change in weathering style. A suite of deformed granites that intrude all units have been dated by zircon U-Pb geochronology to ca. 21 Ma. This suggests that: (1) motion on the lower structure began prior to 21 Ma; and (2) folding of the carbonate unit is younger than 21 Ma. Rim ages of multiple zircons from a deformed leucogranite intrusion within the GHS-Chekha shear zone have more complex U-Pb systematics with ages as young as ca. 14 Ma, suggesting a prolonged history of fault motion. This study reinforces work done by other researchers across the Himalaya, demonstrating multiple strands of the South Tibetan Fault System, rather than a single detachment.

Petrochemical data for the igneous rocks in and around the Erdenetiin Ovoo Porphyry Cu-Mo deposit, Orkhon Selenge trough (part of the Mongol Okhotsk Fold Belt) are re-examined. Magmatic activity of the trough started by Permian bimodal volcanism formed in extensional regime changed in early Mesozoic by compressional regime by intrusion of calc-alkaline gabbro-granodiorite-granite of the Selenge Intrusive Complex with subsequent intrusion of Porphyry Association followed by trachybasalt-trachyandesite alkaline series volcanics of the Mogod Formation. Permian volcanics exhibits typical continental arc characteristics, the Selenge Complex intrusion and Porphyry Association are related to calc-alkaline, I-type, magnetite series, medium and high K rock, and enriched in LIL, depleted in Nb, Ta, Ti and P that typical for continental arc environment. The Mogod Formation is characterized by variation in K, enrichment in Al and LIL, depletion in Nb, Ta and Ti, showing magmas derived from a sub-arc mantle source. Petrochemistry and low initial 87Sr/86Sr isotope ratio of intrusive rocks are corresponding to the adakitic nature and consisting with arc condition.

The well preserved Bosumtwi crater (Ghana), 10.5 km in diameter and 1.07 Myr old (e.g., Koeberl and Reimold 2005), was excavated in rocks of the Early Proterozoic Birimian Supergroup. These rocks were deposited 2.1-2.15 Gyr ago in a volcanic arc environment and were metamorphosed to greenschist facies during the Eburnean tectono-thermal event (e.g., Jones et al. 1981, Feybesse et al. 2006). The Birimian Supergroup mainly consists of two contemporary units: volcanic belts and sedimentary basins aligned in multiple parallel features. Additionally, numerous granitoid intrusions were emplaced within the Birimian Supergroup (Wright et al. 1985). Two main types of granitoid intrusions are recognized in Ghana: belt granitoids and basin granitoids (Leube et al. 1990). Both types can be distinguished according to petrology, chemistry, and age. Whereas previous studies of target rocks from the Bosumtwi crater focused on metasedimentary rocks (e.g., Karikari et al. 2007), in this study we investigate felsic intrusive bodies. This work will also provide more data on the geological evolution of the Kumasi basin and Ashanti belt regions in Ghana. We analyzed thirteen samples for their major- and trace element compositions, as well as their U-Pb, Lu-Hf, and Sm-Nd systematics. Twelve samples come from three different felsic intrusive bodies. Two intrusions are located to the north of the crater, previously described as basin-type granitoids, whereas one intrusion was classified as belt-type granite (Koeberl and Reimold 2005). One sample represents a mafic (diabase) dyke. Analyses were performed using optical microscopy, XRF, and INAA at the University of Vienna, as well as by MC-ICPMS at the University of Bonn. Additional zircon U-Pb ages were obtained with VG Sector-54 multicollector TIMS at the Massachusetts Institute of Technology. Zircon ages for samples from four different intrusive bodies vary within a narrow range between 2091.96 ± 7 Ma and 2097.70 ± 7 Ma. A whole-rock 147Sm-143Nd regression line, defined by six samples coming from all sampled bodies, correlates to an age of 2048±63 Ma, in accordance with the U-Pb data for zircons. Notably, a sample from a mafic intrusion plots also on the regression line. Whole-rock 176Lu-176Hf data define a regression line yielding no meaningful geological age, possibly due to inherited old zircons from the source. Our first results suggest that, despite previous research (Koeberl and Reimold 2005), all studied intrusions genetically belong to the basin-type intrusions. All intrusions share common geochemical and petrologic properties, and were emplaced at approximately the same time.

Four major rock groups are defined in the Southern Complex: the Bell Creek Granite (BCG), the Clotted Granitoids (CGR), the Albite Granite (AGR), and the Migmatite Complex. Metatexites of the Migmatite Complex are the oldest rocks and include paleosome of a metasedimentary and metavolcanic protolith represented by Banded Iron Formation, Banded Amphibolite, and Banded Gneisses, and interlayered or crosscutting leucogranites. The CGR span the range from metatexite to diatexite and represent in-situ partial melting of metapelitic layers in the protolith during intrusion of the BCG. The BCG cuts the migmatites, is locally cut by the CGR, and was derived by partial melting of a dominantly metasedimentary protolith at some depth below the presently exposed migmatites during a regional tectonothermal event. The Albite Granite is a 2km diameter, muscovite-fluorite-columbite-bearing intrusive stock that cuts all other major units. The thorium history of the BCG is a function of the history of monazite. The thorium history of the CGR is also dominated by monazite but the thorium content of this unit cannot be entirely accounted for by original restite monazite. The uranium history of the BCG and CGR was dominated by magmatic differentiation and post magmatic, metamorphic and supergene redistributions and is largely independent of the thorium history. The thorium and uranium history of the AGR was dominated by magmatic/deuteric processes unlike the BCG and CGR.

The Santa Barbara Granite Massif is part of the Younger Granites of Rondonia (998 - 974 Ma) and is included in the Rondonia Tin Province (SW Amazonian Craton). It comprises three highly fractionated metaluminous to peraluminous within-plate A-type granite units emplaced in older medium-grade metamorphic rocks. Sn-mineralization is closely associated with the late-stage unit. U-Pb monazite conventional dating of the early-stage Serra do Cicero facies and late-stage Serra Azul facies yielded ages of 993 +- 5 Ma and 989 +- 13 Ma, respectively. Conventional multigrain U-Pb isotope analyses of zircon demonstrate isotopic disturbance (discordance) and the preservation of inherited older zircons of several different ages and thus yielded a 207 Pb/206 Pb weighted-mean age of 978 +- 13 Ma. The textural complexity of the zircon crystals of the Santa Barbara facies association, the variable concentrations of U, Th and Pb, as well as the mixed inheritance of zircon populations are major obstacles to using conventional multigrain U-Pb isotopic analyses. Sm-Nd model ages and epsilon{sub Nd}(T) values reveal anomalous isotopic data, attesting to the complex isotopic behaviour within these highly fractionated granites. Thus, SHRIMP U-Pb zircon and conventional U-Pb monazite dating methods are the most appropriate to constrain the crystallization age of the Sn-bearing granite systems in the Rondonia Tin Province. (author)

Detailed mapping of the Inconsolable Range in the east-central Sierra Nevada reveals a structurally and lithologically complex region of multi-phase intrusions. Some plutons are compositionally-zoned [e.g., Inconsolable (100 Ma) and Lamarck (90 Ma)]; others may be the result of magma mixing. Intrusive borders vary from brittle to ductile and sharp to gradational, and are bounded by contact aureoles of varying metamorphic grade. A shear zone (Long Lake shear zone -- LLSZ) bounds the western margin of the Inconsolable Range for 8 km; this is truncated in the south by the Cretaceous Lamarck intrusive suite, and is tectonically overlain in the north by the Bishop Creek Pendant (Ordovician ). The LLSZ is a complex zone of interleaved septa of biotite schists, orthogneisses, aplitic screens, and calc-silicate gneisses approximately 500 to 800 m wide. Preliminary interpretation suggests that the LLSZ is the sheared remnant of a Triassic-Jurassic igneous terrane complete with metasedimentary pendants. Juxtaposition of greenschist facies meta-sedimentary rocks of the Chocolate Peak klippe over highly deformed amphibolite grade meta-igneous rocks of the LLSZ postdates movement along the LLSZ. Metamorphic grades suggest that deeper structural levels are exposed within the LLSZ near its southern terminus. Twenty plutonic lithologies have been mapped and informally named (e.g., Spotted biotite quartz diorite), including 3 compositionally-zoned plutons. Zonation within the Lamarck, Inconsolable, and Spotted intrusions are the result of multiple emplacement events into partially crystallized host plutons. Along the eastern border of the Lamarck intrusive suite field evidence indicates four separate intrusive events. The Inconsolable body is a compositionally-zoned biotite, clinopyroxene, quartz diorite with irregular granodiorite margins. The base of the Spotted intrusion appears to have been magmatically eroded by a pulse of the younger Lamarck intrusion.

The Pangong range is an 8km wide shear zone corresponding to the exhumed root of the central Karakorum fault zone (KFZ), one of the great continental strike-slip faults of the India-Asia collision zone. Ductile deformation is the most intense in the Tangtse and Muglib strands which bracket the shear zone to the SW and NE respectively. Structural and microstructural data show that deformation was at least partly synchronous with partial melting and the intrusion of granitic bodies and dykes. New U/Pb SHRIMPII and LA-ICP-MS ages for 24 zircons populations, from 5 gneiss and mylonites as well as 10 leucocratic dykes, span in age from 105.1±1.1 Ma to 14.2±0.1 Ma. Old ages are inherited from the surrounding Cretaceous Ladakh and Karakorum batholiths, while 13 ages are younger than 25.6 Ma and reflect Miocene partial melting. The oldest dyke that can be shown to be syntectonic to the KFZ is 18.8±0.4 Ma old, suggesting that strike slip deformation started in the Tangtse strand at least at ~19 Ma. Other published U/Pb ages imply that deformation lasted until at least ~13.5 Ma. The absolute ages of dykes that are deformed or crosscut the foliation demonstrate that deformation was heterogeneous in space and time. 24 new Ar/Ar ages, together with published ones, allow reconstructing the shear zone cooling history. Cooling was diachronic across strike and ductile deformation (~300°C) stopped earlier in the SW than in the NE: at ~16 Ma in the south Tangtse granite, ~11 Ma in the Tangtse strand, ~9Ma in the Pangong range, and ~ 8Ma in the Muglib Strand. Deformation thus appears to have migrated / localized from the whole shear zone to the Muglib strand, the only locus showing evidence for brittle deformation and active faulting. Taking into account data previously collected along the KFZ, and a finite offset of 200 to 240 km, it appears that the fault has been active for at least 22 Ma, with a slip rate of 0.84 to 1.3 cm/yr in its central section. Stain rates measured in quartz ribbon with the QSR method from 5 samples across the Tangtse shear zone are higher in the two mylonitic strands than in the surrounding rocks. The corresponding integrated shear rate is on the order of 5.7 E-14 s-1, which would corresponds to an integrated fault rate on the order of 1.45 cm yr-1. Such rate is close to, but somewhat higher, than the fault rate deduced from geological constraints. This study conducted in the frontal part of the Himalayan orogen shows that large continental strike-slip faults can be linked with magmatism and be stable for more than 20 Ma, even in the hottest part of the orogen where strain localization is supposed to be at a minimum. While de fault zone propagates along strike, deformation also migrates across-strike within the ~8km wide shear zone.

The O?okiep Copper District is the oldest formal mining area in South Africa. Between 1852 and 2002, the 2,500 km2 area yielded two million tons of copper from 32 mines ranging in ore tonnages from 140,000 to 37 million tons. This paper summarizes the calendar of events from the formation of the first primitive crust 1,700?2,000?Ma ago to early Cambrian times ~500?Ma ago, with particular emphasis on the Namaquan (Grenville) Orogeny, notably: the O?okiepian Episode (1,180?1,210?Ma ago) of alpine-type folding, regional granite plutonism, and granulite facies metamorphism and the Klondikean Episode (1,020?1,040?Ma ago) of open and tight folding and the intrusion of the Rietberg Granite and the Koperberg Suite. Almost all of the copper in the O?okiep District occurs in the Koperberg Suite, of ...

Intrusions of the Irtysh Complex are spatially restricted to the regional Irtysh Shear Zone (ISZ) and are hosted in blocks of high-grade metamorphic rocks (Kurchum, Predgornenskii, Sogra, and others) in the greenschist matrix of the ISZ. The massifs consist of contrasting rock series from gabbro to plagiogranite and granite at strongly subordinate amounts of diorite and the practical absence of rocks of intermediate composition (tonalite and granodiorite). The complex was produced in the Early Carboniferous, simultaneously with the onset of the origin of the ISZ itself. The granitoids composing the complex affiliate with diverse petrochemical series (from subaluminous plagiogranite of the andesite series to granite of the calc-alkaline series) and contain similar REE and HFSE concentration...

The Spanish Central System (SCS) batholith, located in the Central Iberian Zone, is one of the largest masses of granite in the European Variscan Belt. This batholith is a composite unit of late- and post-kinematic granitoids dominated by S- and I-type series granite, with subordinate leucogranite and granodiorite. Zircon trace element contents, from two representative S-type and three I-type granitoids from the eastern portion of the SCS batholith, indicate a heterogeneous composition due to magma differentiation and co-crystallisation of other trace element-rich accessory phases. In situ, U?Pb dating of these zircons by SHRIMP and LA-ICP-MS shows 479?462-Ma inherited zircon ages in the I-type intrusions, indicating the involvement of an Ordovician metaigneous protolith, while the S-type ...

This paper investigates the influence exerted by brittle tectonic structures in the emplacement of granite plutons in contractional settings. We address both cases where contractional tectonics and magma intrusion are (1) coeval, to study how active contractional tectonics controls the transport of magma, and (2) diachronous, to study the role of pre-existing structures on the transport of magma. In light of new experimental models, we show that magma can rise along thrusts ramps and flats. This phenomenon occurs for both low-viscosity magma (basalts to andesite) and high-viscosity magma (dry granite). The experimental results also allow the evaluation of the role played by magma viscosity in determining pluton geometries. In addition, a review of literature demonstrates a spatial and caus...

The NW China region is characterised by tectonic and lithostratigraphic domains, such as the Tian Shan and Altay orogens, the Tarim, Junggar and Turpan Basins. The Tian Shan and Altay orogens are part of the Central Asian Orogenic Belt. The NW China region was affected by a series of thermal events that occurred between the Silurian and the Triassic, which resulted in the emplacement of numerous granitic plutons and mafic-ultramafic intrusions. A number of these granitic plutons are of A-type affiliation, which on the basis of the positive &z.epsiv;Nd values are likely to have been derived from mantle sources. In addition, at least two large igneous provinces (LIPs) can be recognised in NW China, namely the 345-325Ma Tian Shan LIP and the ca. 270-280Ma Tarim LIP. Age and field data suggest...

Abstract Ion microprobe dating of zircon from meta-igneous samples of the Hitachi metamorphic terrane of eastern Japan yields Cambrian magmatic ages. Tuffaceous schist from the Nishidohira Formation contains ca 510-Ma zircon, overlapping in age with hornblende gneiss from the Tamadare Formation (ca 507-Ma), and meta-andesite (ca 507-Ma) and metaporphyry (ca 505-Ma) from the Akazawa Formation. The latter is unconformably overlain by the Carboniferous Daioin Formation, in which a granite boulder from metaconglomerate yields a magmatic age of ca 500-Ma. This date overlaps a previous estimate for granite that intrudes the Akazawa Formation. Intrusive, volcanic, and volcaniclastic lithologies are products of a Cambrian volcanic arc associated with a continental shelf, as demonstrated by the pre...

U-Pb analyses from the Horrsjoe granite, south central Sweden, give an upper intercept with concordia of 1850 /sup +8/-/sub 7/Ma (1 sigma). The Horrsjoe granite accordingly belongs to the synkinematic Svecokarelian intrusions. The zircons have no visible cores. Their positions on discordia are reversed in relation to the normal case, the smallest crystals having less than half the uranium content of the largest. This may be due to uranium loss caused by superimposed events of ser- and postorogenic Svecokarelian magmatism in the area. However, a recalculation with the new U-Pb systematics of Wickman (Wickman, F.E., 1983: Uranium-lead isotope systematics: The case of crystals with discrete cores. Lithos 16) yields an age of 1946 Ma. The age of 1850 Ma is accordingly a minimum age.

The Sakharjok Y-Zr deposit in Kola Peninsula is related to the fissure alkaline intrusion of the same name. The intrusion ?7 km in extent and 4?5 km2 in area of its exposed part is composed of Neoarchean (2.68?2.61 Ma) alkali and nepheline syenites, which cut through the Archean alkali granite and gneissic granodiorite. Mineralization is localized in the nepheline syenite body as linear zones 200?1350 m in extent and 3?30 m in thickness, which strike conformably to primary magmatic banding and trachytoid texture of nepheline syenite. The ore is similar to the host rocks in petrography and chemistry and only differs from them in enrichment in zircon, britholite-(Y), and pyrochlore. Judging from geochemical attributes (high HSFE and some incompatible element contents (1000?5000 ppm Zr, 200?6...

The Mazraeh Cu?Fe skarn deposit, NW Iran is the result of the intrusion of an Oligocene?Miocene granitic pluton into Cretaceous calcareous rocks. The pluton ranges in composition from monzonite to quartz monzonite, monzogranite, tonalite and granodiorite with I-type, calc-alkaline, and weakly peraluminous characteristics. The Mazraeh pluton was emplaced in a volcanic arc setting in an active continental margin at a depth of ~8 km. Pyroxene skarn, garnet skarn, and epidote skarn zones were formed during the intrusive phase. The garnet skarn developed as exoskarn and endoskarn from the calcareous wall rocks and the pluton, respectively, prior to mineralization. Garnet skarn from the exoskarn zone is identified by relict layering inherited from the precursor calcareous lithologies. Mass balan...

K-Ar analyses of 20 hornblendes from skarns and associated metabasites in the Hjulsjoe area of the Bergslagen ore province, central Sweden, define an age of 1.83+-0.05 Ga. This age is interpreted in terms of the geological relationships as signalling a period of skarn-formation and metamorphism along with episodes of shearing and basic dike intrusion. Following the hypothesis that the skarn ores were formed by sea-floor hydrothermal metamorphism, this age should also be attributed to the deposition of the enclosing volcano-sedimentary leptite-haelleflinta sequence and the injection and extrusion of basic magma. Analyses of 13 biotites from the skarns and enclosing metavolcanic leptites produce K-Ar and Rb-Sr ages of 1.69+-0.05 Ga and 1.65+-0.04 Ga, respectively; these are related to an episode of mild crustal heating associated with nearby post-orogenic granite intrusion dated at 1.70 Ga.

The petrographic and chemical study of the Middle Jurassic-Lower Cretaceous rocks of the Lower Amur region revealed the important role of granitoids in their provenance. Intermediate, mafic, and ultramafic (?) intrusive rocks, as well as sedimentary, volcanic, and metamorphic complexes were less common. The orientation of the cross bedding and casts of whirlpool pits in the Tithonian-Valanginian turbidites indicates that the provenance was located in the west and southwest. It was mainly made up of the continental granite-metamorphic blocks of the Jiamusi-Khanka-Bureya Massif. At the same time, a significant part of the provenance was occupied by the fragments of the Late Paleozoic-Early Mesozoic active continental margin.

The study of deep structure of the Kirovograd ore district proceeds from a broad treatment of its geological boundaries and combination of metasomatic uranium, pegmatitic lithium, and hydrothermal gold deposits, as well as lodes of magmatic titanium ore within these boundaries. The spatial juxtaposition of the Novoukrainsk-Kirovograd granitoid massif and the Korsun-Novomirgorod rapakivi granite-anorthosite massif is a distinguishing feature of the Kirovograd ore district. The former massif along with stratified metamorphic rocks forms an intrusive-ultrametamorphic basement, whereas the latter massif is autonomous with respect to the basement. Taken together, both massifs make up the Novoukrainsk-Korsun-Novomirgorod composite pluton, which determines the architecture of the Kirovograd ore d...

For hundreds of years, two types of granite (Zarzalejo and Alpedrete) from the Madrid region, Spain, have been extensively used as building stones. Fresh specimens of both stone types have been sampled from their respective quarries and subjected to sodium sulphate salt crystallization test (SCT). The resulting physical and chemical weathering patterns have been characterized by polarized light optical and environmental scanning electron microscopy. Water absorption under vacuum conditions and mercury intrusion porosimetry techniques were used to determine the pre- and post-SCT porosity and pore size distribution. The following non-destructive techniques were performed to assess stone durability and decay: ultrasound velocity (US) and surface roughness determination (SR) of intra- and inte...

Sierra Leone lies within the south-western part of the West African Craton and comprises two major Archaean structural divisions: a low-grade granite-greenstone terrane characterised by N-S striking structures and a NW-SE striking highly metamorphosed belt of strained rocks that form the coastal margin of the craton. Intruded into the belt is the Freetown Layered Igneous Complex (FLIC), a tholeiitic magamtic body emplaced prior to or during the break-up of Pangea to form the Central Atlantic Ocean and, forming today the high ground of the coastal outline of Sierra Leone which is one of the most distinctive features on the West African coast. The break-up of Pangaea to form the Central Atlantic and its passive margins began in the Early Jurassic. Geo-tectonically, the break-up was particularly characterised by the formation of the Central Atlantic Magmatic Province (CAMP), covering once-contiguous parts of North America, Europe, Africa and South America. The FLIC forming part of the heart of CAMP is the largest single layered igneous intrusive yet known on either side of the Central Atlantic, measuring on surface, 65 x 14 x 7 km. Geophysical investigations indicate that the intrusion extends offshore to a depth of about 20 km. Geologically the Complex is a rhythmically layered elongated ultramafic-mafic lopolith divisible into 4 major zones each comprising repeated sequences of troctolitic, gabbroic and anorthositic rocks. An idealised unit of layering is from base upwards: dunite, troctolite, olivine-gabbro, leuco-gabbro, gabbro-norite and anorthosite cumulates. 40Ar-39Ar age spectra and 40Ar/36Ar versus 39Ar/36Ar isochron plots obtained by stepwise-heating experiments on plagioclases, biotites and amphiboles from troctolites, olivine-gabbros, gabbro-norites and anorthosites of the four zones yield plateau and isochron ages that seem to depict the cooling history of the Complex after emplacement. The biotites and some of the plagioclases and amphiboles give very good plateaus that range from 196.3 ± 3 Ma to 232.1 ± 9 Ma with the best-fit isochron plots showing a range from 193.3± 10 Ma to 234.1 ± 11 Ma. Because these dates represent cooling ages, we interpret them as representing a minimum intrusion-age of the Complex implying that its true emplacement age might be somewhat older than 230 Ma. Given that most established CAMP ages revolve around 200 Ma or younger, we hypothesise that FLIC represents a hitherto unknown pre-CAMP magmatic event that might have thermally triggered the initial break-up of Pangaea to form the Central Atlantic. This view is consistent with field-observations that the Complex is cross-cut by predominantly coast-parallel mafic dykes attributed to the CAMP dyke-swarm. To ascertain the hypothesis, we are currently carrying out U-Pb zircon dating to establish, precisely, the true emplacement age of the Complex. The Fission-track ages vary from 91.7 ± 7 Ma to 114.6 ± 9 Ma. This age range shows that after emplacement and crystallisation, the FLIC underwent an extremely slow cooling for a long period of time. This in turn implies that after the break-up of Pangea to form, in part, the Sierra Leone margin, a late and slow uplift (Erosion/denudation) that took place during the Cretaceous was a very important geological process that characterised the post-rift evolution of the margin. References: Barrie, I.J., P.A.M. Andriessen, F.F. Beunk, J.R. Wijbrans, V.E.H. Strasser-King, D.V.A.Fode. (2006). Tectonothermal Evolution of the Sierra Leone Passive Continental Margin, West Africa: Constraints from Thermochronology. Geochemica et Cosmochemica Acta 70 (18): A36- A36 Suppl. S Aug-Sep 2006. Marzoli, A., P.R. Renne, E.M. Piccirillo, M. Ernesto, G. Bellieni, A De Min. (1999). Extensive 200-Million-Year-Old Continental Flood Basalts of the Central Atlantic Magmatic Province. Science284: 616-618. McHone, J.G. (2000). Non-plume magmatism and rifting during the opening of the central Atlantic Ocean. Tectonophysics, 316: 287-296. Umeji, A.C. (1983). Geochemistry and Mineralogy of the Freetown Layered Basic Igneous Complex of Sierra Leone. Chemical Geology, 39: 17-38. Wells, M.K. (1962). Structure and Petrology of the Freetown Layered Basic Complex of Sierra Leone. Overseas Geol. Mineral. Res. Bull. Suppl., 4, 115 pp. Williams, H.R. (1986). The Archaean Kaila Group of Western Sierra Leone: Geology and Relations with adjacent Granite-Greenstone Terrane. Precambrian Research, 38: 201-213.

Mesoproterozoic granitic gneisses comprise most of the basement of the northern Blue Ridge geologic province in Virginia and Maryland. Lithology, structure, and U-Pb geochronology have been used to subdivide the gneisses into three groups. The oldest rocks, Group 1, are layered granitic gneiss (1153 ?? 6 Ma), hornblende monzonite gneiss (1149 ?? 19 Ma), porphyroblastic granite gneiss (1144 ?? 2 Ma), coarse-grained metagranite (about 1140 Ma), and charnockite (>1145 Ma?). These gneisses contain three Proterozoic deformational fabrics. Because of complex U-Pb systematics due to extensive overgrowths on magmatic cores, zircons from hornblende monzonite gneiss were dated using the sensitive high-resolution ion microprobe (SHRIMP), whereas all other ages are based on conventional U-Pb geochronology. Group 2 rocks are leucocratic and biotic varieties of Marshall Metagranite, dated at 1112??3 Ma and 1111 ?? 2 Ma respectively. Group 3 rocks are subdivided into two age groups: (1) garnetiferous metagranite (1077 ?? 4 Ma) and quartz-plagioclase gneiss (1077 ?? 4 Ma); (2) white leucocratic metagranite (1060 ?? 2 Ma), pink leucocratic metagranite (1059 ?? 2), biotite granite gneiss (1055 ?? 4 Ma), and megacrystic metagranite (1055 ?? 2 Ma). Groups 2 and 3 gneisses contain only the two younger Proterozoic deformational fabrics. Ages of monazite, seprated from seven samples, indicate growth during both igneous and metamorphic (thermal) events. However, ages obtained from individual grains may be mixtures of different age components, as suggested by backscatter electron (BSE) imaging of complexly zoned grains. Analyses of unzoned monazite (imaged by BSE and thought to contain only one age component) from porphyroblastic granite gneiss yield ages of 1070, 1060, and 1050 Ma. The range of ages of monazite (not reset to a uniform date) indicates that the Grenville granulite event at about 1035 Ma did not exceed about 750??C. Lack of evidence for 1110 Ma growth of monazite in porphyroblastic granite gneiss suggests that the Short Hill fault might be a Grenvillian structure that was reactivated in the Paleozoic. The timing of Proterozoic deformations is constrained by crystallization ages of the gneissic rocks. D1 occurred between about 1145 and 1075 Ma (or possibly between about 1145 and 1128 Ma). D2 and D3 must be younger than about 1050 Ma. Ages of Mesoproterozoic granitic rocks of the northern Blue Ridge are similar to rocks in other Grenville terranes of the eastern USA, including the Adirondacks and Hudson Highlands. However, comparisons with conventional U-Pb ages of granulite-grade rocks from the central and southern Appalachians may be specious because these ages may actually be mixtures of ages of cores and overgrowths.

Proterozoic silicic magmatic activity in the Tennant Creek area includes a suite of pre- to syn-orogenic granitoids (i.e. the Tennant Creek Granite and compositionally similar porphyries) predominantly intruded during the period 1870 1830 Ma, a group of silicic volcanics and volcaniclastics ( Flynn Subgroup) erupted shortly after the main D1 deformation, and apparently anorogenic silicic intrusives represented by the Warrego Granite. Chemical and petrographic data indicate that the majority of the pre- to syn-orogenic granitoids and porphyries are I-type or infracrustal-derived, whereas the peraluminous muscovite-rich Warrego Granite has many characteristics of supracrustal-derived (S-type) granitoids. The Warrego Granite also appears to be moderately fractionated with relatively low Ba, Sr, Zr, K/Rb, and high Th, Nb, Be, Bi, Rb/Sr compared with the associated I-type granitoids, porphyries and volcanics. Fractionation of feldspar and minor zircon has also resulted in substantial relative enrichment in LREE together with a pronounced negative Eu anomaly in the Warrego Granite. Previous studies suggest that the Cu-Au-Bi mineralisation at Tennant Creek post-dates formation of the host ironstones, but the absolute timing is imprecisely known. Mass-balance calculations utilising background Au concentrations for potential source rocks suggest it is feasible for the Au in some of the deposits to have been leached by relatively high-temperature (250 to 300 °C) deep basinal brines, and deposited by reaction with the ironstones. However, the inferred hydrothermal leaching cells would need to have been very large unless the leaching process was very effective. An alternative preferred model is that the mineralising fluids were exsolved from incompatible element-enriched, fractionated granitic magma, mixed with ground water, and reacted with the ironstones to deposit the base and precious metals. On the basis of chemical similarity to other granitoids closely associated with mineralisation, the Warrego Granite seems the most likely source of the fluids. However, problematic constraints imposed by the apparent age of the mineralisation (1810 Ma), and an emplacement age (Rb-Sr) of 1670 Ma for the Warrego Granite indicate a need for additional geochronological studies.

Phanerozoic granitoids are widespread in the Korean Peninsula and form a part of the East Asian Cordilleran-type granitoid belt extending from southeastern China to Far East Russia. Here we present SHRIMP zircon U-Pb ages and geochemical and Nd isotopic compositions of Late Paleozoic to Early Jurassic granitoid plutons in the northern Gyeongsang basin, southeastern Korea; namely the Jangsari, Yeongdeok, Yeonghae, and Satkatbong plutons. The granite and associated gabbroic rocks from the Jangsari pluton were coeval and respectively dated at 257.3+/-2.0Ma and 255.7+/-1.4Ma. This result represents the first finding of a Late Paleozoic pluton in South Korea. Three granite samples from the Yeongdeok pluton yielded a slightly younger age span ranging from 252.9+/-2.5Ma to 246.7+/-2.1Ma. Two dior...

Rubidium-strontium analyses of whole-rock samples of an Archean granite from the Owl Creek Mountains, Wyo., indicate an intrusive age of 2640 {plus minus} 125 Ma. Muscovite-bearing samples give results suggesting that these samples were altered about 2300 Ma. This event may have caused extensive strontium loss from the rocks as potassium feldspar was altered to muscovite. Alteration was highly localized in nature as evidence by unaffected rubidium-strontium mineral ages in the Owl Creek Mountains area. Furthermore, the event probably involved a small volume of fluid relative to the volume of rock because whole-rock {delta}{sup 18}O values of altered rocks are not distinct from those of unaltered rocks. In contrast to the rubidium-strontium whole-rock system, zircons from the granite have been so severely affected by the alteration event, and possibly by a late-Precambrian uplift event, that the zircon system yields little usable age information. The average initial {sup 87}Sr/{sup 86}Sr (0.7033 {plus minus} 0.0042) calculated from the isochron intercept varies significantly. Calculated initial {sup 87}Sr/{sup 86}Sr ratios for nine apparently unaltered samples yield a range of 0.7025 to 0.7047. These calculated initial ratios correlate positively with whole-rock {delta}{sup 18}O values; and, therefore, the granite was probably derived from an isotopically heterogeneous source. The highest initial {sup 87}Sr/{sup 86}Sr ratio is lower than the lowest reported for the metamorphic rocks intruded by the granite as it would have existed at 2640 Ma. Thus, the metamorphic sequence, at its current level of exposure, can represent no more than a part of the protolith for the granite.

The Neoproterozoic post-collisional period in southern Brazil (650-580Ma) is characterized by substantial volumes of magma emplaced along the active shear zones that compose the Southern Brazilian Shear Belt. The early-phase syntectonic magmatism (630-610Ma) is represented by the porphyritic, high-K, metaluminous to peraluminous Quatro Ilhas Granitoids and the younger heterogranular, slightly peraluminous Mariscal Granite. Quatro Ilhas Granitoids include three main petrographic varieties (muscovite-biotite granodiorite - mbg; biotite monzogranite - bmz; and leucogranite - lcg) that, although sharing some significant geochemical characteristics, are not strictly comagmatic, as shown by chemical and Sr-Nd-Pb isotope data. The most primitive muscovite-biotite granodiorite was produced by cont...

The ore deposits of the Mesozoic age in South China can be divided into three groups, each with different metal associations and spatial distributions and each related to major magmatic events. The first event occurred in the Late Triassic (230-210 Ma), the second in the Mid-Late Jurassic (170-150 Ma), and the third in the Early-Mid Cretaceous (120-80 Ma). The Late Triassic magmatic event and associated mineralization is characterized by peraluminous granite-related W-Sn-Nb-Ta mineral deposits. The Triassic ore deposits are considerably disturbed or overprinted by the later Jurassic and Cretaceous tectono-thermal episodes. The Mid-Late Jurassic magmatic and mineralization events consist of 170-160 Ma porphyry-skarn Cu and Pb-Zn-Ag vein deposits associated with I-type granites and 160-150 Ma metaluminous granite-related polymetallic W-Sn deposits. The Late Jurassic metaluminous granite-related W-Sn deposits occur in a NE-trending cluster in the interior of South China, such as in the Nanling area. In the Early-Mid Cretaceous, from about 120 to 80 Ma, but peaking at 100-90 Ma, subvolcanic-related Fe deposits developed and I-type calc-alkaline granitic intrusions formed porphyry Cu-Mo and porphyry-epithermal Cu-Au-Ag mineral systems, whereas S-type peraluminous and/or metaluminous granitic intrusions formed polymetallic Sn deposits. These Cretaceous mineral deposits cluster in distinct areas and are controlled by pull-apart basins along the South China continental margin. Based on mineral assemblage, age, and space-time distribution of these mineral systems, integrated with regional geological data and field observations, we suggest that the three magmatic-mineralization episodes are the result of distinct geodynamic regimes. The Triassic peraluminous granites and associated W-Sn-Nb-Ta mineralization formed during post-collisional processes involving the South China Block, the North China Craton, and the Indo-China Block, mostly along the Dabie-Sulu and Songma sutures. Jurassic events were initially related to the shallow oblique subduction of the Izanagi plate beneath the Eurasian continent at about 175 Ma, but I-type granitoids with porphyry Cu and vein-type Pb-Zn-Ag deposits only began to form as a result of the breakup of the subducted plate at 170-160 Ma, along the NNE-trending Qinzhou-Hangzhou belt (also referred to as Qin-Hang or Shi-Hang belt), which is the Neoproterozoic suture that amalgamates the Yangtze Craton and Cathaysia Block. A large subduction slab window is assumed to have formed in the Nanling and adjacent areas in the interior of South China, triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic W-Sn mineralization. A relatively tectonically quiet period followed between 150 and 135 Ma in South China. From 135 Ma onward, the angle of convergence of the Izanagi plate changed from oblique to parallel to the coastline, resulting in continental extensional tectonics and reactivation of regional-scale NE-trending faults, such as the Tan-Lu fault. This widespread extension also promoted the development of NE-trending pull-apart basins and metamorphic core complexes, accompanied by volcanism and the formation of epithermal Cu-Au deposits, granite-related polymetallic Sn-(W) deposits and hydrothermal U deposits between 120 and 80 Ma (with a peak activity at 100-90 Ma).

We report results of petrologic, geochronological and geochemical investigation of the Late Carboniferous diorites, granodiorites, amphibole (Am)-bearing granites, and associated dioritic and monzonitic enclaves and mafic and granitic dikes in the Keramay area, of the western Junggar region of Central Asian Orogenic Belt (CAOB). Zircon U-Pb dating suggests that they were generated in the Late Carboniferous (316-304 Ma). The diorite and granodiorite compositions extend over a wide range of SiO2 (53-70 wt.%), Sr (240-602 ppm), and Mg# (41-58) values, and are characterized by moderately fractionated rare earth element (REE) patterns, Nb-Ta depletion and relatively low Y and Yb contents. The mafic dikes consist of dolerites, diorite porphyries and minor granodiorite porphyries, and have variable SiO2 (51-59 wt.%) and high Mg#, Cr and Ni values. With the exception of two samples with relatively high heavy REE (HREE) contents, the mafic dikes exhibit trace element characteristics similar to diorites and granodiorites. The Am-bearing granites and a granite porphyry dike sample have high levels of SiO2 (73-77 wt.%), HREEs (e.g., Yb = 3.46-15.7 ppm) and low Mg#, Cr and Ni contents, along with clearly negative Eu, Ba and Sr anomalies, similar to typical A-type granites. All granitoids, enclaves and dikes in this region have high positive ?Nd(t) (+ 7.13 to + 9.74) and zircon ?Hf(t) (+ 10 to + 16) values and moderate initial 87Sr/87Sr ratios (0.7004-0.7049). Mineral composition data suggest that the parental magmas for mafic dikes are similar to Cenozoic sanukitoids in the Setouchi arc area (Japan) and were possibly generated under water-rich and high oxygen fugacity (NNO + 1.5 to NNO + 2.7) conditions. They most likely originated from partial melting of a mantle source variably modified by subducted oceanic crust-derived melts and minor fluids and subsequently underwent fractional crystallization. The diorites and granodiorites were possibly generated by magma mixing between enriched lithospheric mantle and juvenile lower crust-derived magmas coupled with minor crystal fractionation. The Am-bearing granites and granite porphyry dike were produced by partial melting of juvenile crustal materials at shallow crustal levels. Taking into account widespread contemporaneous magmatism including "MORB-type" basalts and slab-derived adakites in western Junggar, we suggest that the Keramay intrusive rocks were generated in a special arc setting related to ridge subduction and resultant slab window, which played an important role in the crustal growth of the CAOB.

40-20Ma marks a fundamental interval in the evolution of the 70-0Ma Panamanian magmatic arc system. During this period, there is no evidence of Panamanian magmatic arc activity to the east of the Panama Canal Basin while to the west and in localized regions to the east of the Panama Canal Basin a phase of intrusive-only activity is recorded. Fundamentally, geochemical and geochronological evidence presented herein indicate that this intrusive activity was predominantly 'adakitic-like' and becomes younger from west to east along an approximately W-E striking lineament. Granodiorites of the Petaquilla batholith, western Panama yield LAM-ICP-MS ^2^0^6Pb/^2^3^8U zircon ages of 29.0+0.7, -0.6Ma, 28.5+0.7, -0.5Ma, 28.3+0.5, -0.4Ma and 26.2+0.5, -0.9Ma. To the east of the Panama Canal Basin zirco...

The South Tianshan orogenic belt, the southwestern extension of the Central Asian orogenic belt, separates the Yili?Central Tianshan block to the north from the Tarim block to the south. This belt is marked by a Proterozoic metamorphic complex, ophiolites, granitoids, mafic intrusions and younger high-pressure and low-temperature metamorphic rocks. The Jingbulake mafic intrusion in this belt is a zoned body composed of pyroxene diorite, olivine gabbro and wehrlite. Pyroxenite locally intrudes all of these rocks but is most abundant along the boundaries between pyroxene diorite and olivine gabbro. Both the olivine gabbro and wehrlite contain disseminated sulfide mineralization, and a sulfide rich orebody intrudes the pyroxenite. The pyroxene diorite has a SHRIMP zircon U?Pb isotope age of 4...

Because most of the Permian basin region of west Texas and southern New Mexico is covered by Phanerozoic rocks, other means must be found to examine the Precambrian upper crustal geology of the region. We have combined geologic information on the Precambrian from outcrops and wells with geophysical information from gravity and magnetic surveys in an integrated analysis of the history and structure of basement rocks in the region. Geophysical anomalies can be related to six Precambrian events: formation of the Early Proterozoic outer tectonic belt, igneous activity in the southern Granite-Rhyolite province, an episode of pre-Grenville extension, the Grenville orogeny, rifting to form the Delaware aulacogen, and Eocambrian rifting to form the early Paleozoic continental margin. Two geophysical features were studied in detail: the Abilene gravity minimum and the Central Basin platform gravity high. The Abilene gravity minimum is shown to extend from the Delaware basin across north-central Texas and is interpreted to be caused by a granitic batholith similar in size to the Sierra Nevada batholith in California and Nevada. This batholith appears to be related to formation of the southern Granite- Rhyolite province, possibly as a continental margin arc batholith. Because of this interpretation, we have located the Grenville tectonic front southward from its commonly quoted position, closer to the Llano uplift. Middle Proterozoic mafic intrusions are found to core the Central Basin platform and the Roosevelt uplift. These intrusions formed at about 1.1 Ga and are related in time to both the Mid-Continent rift system and the Grenville orogeny in Texas. Precambrian basement structures and changes in lithology have influenced the structure and stratigraphy in the overlying Permian basin, and thus have potential exploration significance.

Rare-earth contents of 20 allanites and 13 monazites, accessory minerals from a restricted outcrop area of intrusive granitic rocks, are reported. A quantity called sigma (??), which is the sum of the atomic percentages of La, Ce and Pr, is used as an index of composition with respect to the rare-earth elements. Values of sigma vary from 61.3 to 80.9 at.% for these allanites and monazites, representing an appreciable range of composition in terms of the rare-earth elements. Degree of fractionation of rare earths varies directly with CaO content of the granitic rocks, which in turn depends largely on proximity of limestone. Four xenoliths included in the study suggest that spotty mosaic equilibria are superimposed on the regional gradients and that locally the degree of fractionation of rare earths responds to whole rock composition over distances of a few yards or less. The chemistry of the granitic rocks under study appears to be similar in some respects to that of alkalio rocks and carbonatites. Allanites from the most calcium-rich rocks show a pronounced concentration of the most basic rare earths, and whole-rock concentrations of such rare constituents as total cerium earths, Zr, F, Ti, Ba and Sr increase sympathetically with whole-rock calcium. The explanation for the concentration gradients observed in this chemical system must involve assimilation more than magmatic differentiation. ?? 1967.

In order to evaluate the mineral potential of the region a reconnaissance geochemical survey was conducted for uranium, lead, zinc, copper and nickel. Sediment samples were collected from the almost uncontaminated springs of the area. A new geochemical method for the extraction and determination of metal contents of samples of sediments was developed and applied. The sediment samples were leached with a solution of EDTA and sodium carbonate, the filtrates were then evaporized on special filter discs. These were finally utilized for analytical determinations by X-ray fluorescence. The survey resulted in the detection of a number of anomalies, some of which can be related to tectonic fracture zones: Strong uranium anomalies were detected particularly in a mylonitic shear zone in the Auerbachtal area and in the course of the Schwarzachtal fracture zone. Lead anomalies occured systematically in the proximity of the Pfahl mylonite zone. Within the eastern offshoot of the Neunburg granite which presumably constitutes a relatively independent intrusion within the Neunburg granite body, a larger area showing anomalous values of zinc, lead and uranium was detected. The very same part of the granite body is characterized by a higher level of alpha and gamma radiation. The statistical analysis of the data revealed some interdependencies between the uranium contents of the sediments and the pH-value, hydrogen carbonate content and electric conductivity of the spring waters as well as some correlations among the various metals.

The Tombstone, Mayo and Tungsten plutonic suites of granitic intrusions, collectively termed the Tombstone-Tungsten Belt, form three geographically, mineralogically, geochemically and metallogenically distinct plutonic suites. The granites (sensu lato) intruded the ancient North American continental margin of the northern Canadian Cordillera as part of a single magmatic episode in the mid-Cretaceous (96-90 Ma). The Tombstone Suite is alkalic, variably fractionated, slightly oxidised, contains magnetite and titanite, and has primary, but no xenocrystic, zircon. The Mayo Suite is sub-alkalic, metaluminous to weakly peraluminous, fractionated, but with early felsic and late mafic phases, moderately reduced with titanite dominant, and has xenocrystic zircon. The Tungsten Suite is peraluminous, entirely felsic, more highly fractionated, reduced with ilmenite dominant, and has abundant xenocrystic zircon. Each suite has a distinctive petrogenesis. The Tombstone Suite was derived from an enriched, previously depleted lithospheric mantle, the Tungsten Suite is from the continental crust including, but not dominated by, carbonaceous pelitic rocks, and the Mayo Suite is from a similar sedimentary crustal source, but is mixed with a distinct mafic component from an enriched mantle source. Each suite has a distinctive metallogeny that is related to the source and redox characteristics of the magma. The Tombstone Suite has a Au-Cu-Bi association that is characteristic of most oxidised and alkalic magmas, but also has associated, and enigmatic, U-Th-F mineralisation. The reduced Tungsten Suite intrusions are characterised by world-class tungsten skarn deposits with less significant Cu, Zn, Sn and Mo anomalies. The Mayo Suite intrusions are characteristically gold-enriched, with associated As, Bi, Te and W associations. All suites also have associated, but distal and lower temperature Ag-Pb- and Sb-rich mineral occurrences. Although processes such as fractionation, volatile enrichment and phase separation are ultimately required to produce economic concentrations of ore elements from crystallising magmas, the nature of the source materials and their redox state play an important role in determining which elements are effectively concentrated by magmatic processes.

Intra-basaltic sediments 50 m below the top of the Paleogene lava succession at Kap Dalton, East Greenland, contain dinoflagellate cysts of late Ypresian-earliest Lutetian age, while sediments immediately above the lavas contain an assemblage of early Lutetian age. Combined with paleomagnetic results, this constrains the termination of the East Greenland Paleogene Igneous Province to the Early-Middle Eocene transition (nannoplankton chronozones NP13-NP14/earliest NP15). This is 6-8 Ma younger than according to previous biostratigraphic age assignments. The new data show that flood basalt volcanism occurred simultaneously with major intrusions occurring further to the south. This corroborates previous assumptions of an important melting event much younger than the continental break-up.

The Modoc fault zone is a prominent zone of simple shear that has been mapped for 250 km from near Columbia, SC to the Ocmulgee River, in central GA. The steeply northwest-dipping fault zone is up to 5 km wide and contains variably mylonitic paragneiss and synkinematic sheets of mylonitic granite. Rotated tension gashes, reverse-slip-slip-crenulations, and asymmetric porphyroclasts in the fault zone are interpreted to indicate oblique dextral and normal movement. U/Pb zircon ages of 315--300 Ma yielded by some of these granite sheets are interpreted to date the time of movement on the Modoc fault zone, relatively early during the Alleghanian orogeny (ca 330--265Ma). Concurrent with movement along the Modoc fault zone, granite bodies (dated at 320--300 Ma) were intruded into both the hangingwall and the footwall sides of the fault. Cooling ages of ca 308 Ma (U/Pb monazite) and ca 305--288 Ma (40Ar/39Ar hornblende) from footwall rocks near the Savannah River indicate rapid cooling from temperatures above 700 starting with movement along the Modoc fault zone. Published geobarometry results suggest that footwall rocks were uplifted from depths of ca 29km and juxtaposed next to hangingwall rocks at depths of ca 11km by movement along the Modoc fault zone. Taken together, the crustal omission, uplift and rapid cooling of the footwall blocks, and the oblique normal sense of shear indicate at least a component of crustal extension along the Modoc fault zone. Intrusion of granite into and adjacent to the fault indicates magmatism accompanied movement on the fault at ca 315--300 Ma. Regardless of tectonic mechanism, extension associated with either crustal delamination or dextral transcurrent motion of accreted terranes, it is clear that crustal extension and magmatism was important during early phases of the Alleghanian orogeny in this part of the orogen, and it may have also been important elsewhere.

Abstract in spanish Los plutones Santa Cruz y Asha, afloran en el flanco nororiental de la sierra de Velasco, con dirección norte sur. El Granito Santa Cruz está constituido por granitos equigranulares evolucionados, con moscovita mayor que biotita y susceptibilidad magnética de 0,10 a 0,14 x 10-3 SI. Mientras que el Granito Porfídico Asha, tiene caracteres evolutivos calco-alcalinos normales, con biotita mayor que moscovita y susceptibilidad magnética de 2 a 16 x 10-3 SI. Ambos granito (more) s presentan valores de A/CNK > 1,1 y relaciones Rb/Sr >2. En el diagrama modal QAP ambos se proyectan superpuestos en el campo granítico. Estos granitos presentan diferencias entre si y muestran variaciones a leucogranitos. Las edades determinadas por U-Pb sobre monacitas, son de 361 +/- 4,1 Ma, para el Granito Porfídico Asha (GPA) y de 354,3 +/- 3,8 Ma, para el Granito Santa Cruz (GSC), estableciendo que las intrusiones se produjeron en el Devónico superior - Carbonífero inferior. Estos granitos son algo más antiguos que los granitos San Blas, Huaco y Sanagasta, de la Sierra de Velasco. El GSC tiene más bajos contenidos de Fe2O3t, MgO, CaO, TiO2 y valores más altos en SiO2, Al2O3, K2O, P2O5. Los elementos trazas (Sr, Ba, V, Sc y ? REE) son más altos que los del GSC, aunque ambos presentan marcada anomalía negativa de Eu. Muestra asimismo menor contenido en Tierras Raras totales que el GPA. Ambos granitos muestran bajos contenidos de Sr ( Abstract in english The Santa Cruz and Asha granites crop out as north-south striking associated plutons in the northeast sector of the Sierra de Velasco. Even though both granites have been emplaced nearly synchronous, they are clearly different in their textural and geochemical characteristics. The Santa Cruz Granite is a medium-grained equigranular monzogranite, in which muscovite predominates over biotite, and the magnetic susceptibility is 0.10 - 0.14 x 10-3 IS units. The Porphyritic As (more) ha Granite is a coarse-grained porphyritic monzogranite with biotite largely predominating over muscovite. The magnetic susceptibility is 2 to 16 x 10-3 IS units. Both granites present A/CNK > 1,1 and have Rb/Sr > 2. In a modal QAP, both granites are project on the granite field. A U-Pb monazite age was of 361+/- 4.1 Ma for the Porphyritic Asha Granite (GPA) and 354.3 +/-3.8 Ma for the Santa Cruz Granite (GSC). These data indicate that the intrusions took place during the Upper Devonian to the Lower Carboniferous. The Fe2O3, MgO, CaO and TiO2 values are significantly lower, and SiO2 , Al2O3 , K2O and P2O5 are higher than those in GPA. Trace elements (Sr, Ba, V, Sc and ? REE) are higher than those in GSC, although both showed marked negative Eu anomaly. Both granites show low content of Sr (

Re Os dating of molybdenite is an accurate means to date intrusions and intrusion-related ore deposits using the model age or isochron approach. But, molybdenite has a new niche in the greenschist- to granulite-facies metamorphic environment. Re Os ages for metamorphic molybdenite may be used to construct regional metamorphic histories. Age significance and accuracy are established by analyzing multiple molybdenite separates extracted from single, petrographically-characterized molybdenite occurrences. In this study, twelve geologically distinct molybdenite-bearing samples from two small Mo districts in northern Sweden trace a 150 m.y. Paleoproterozoic Svecofennian metamorphic history from ˜1900 to 1750 Ma. These data reveal a little-known, widespread and protracted, Late Svecofennian anatexis in northern Sweden. The Kåtaberget Mo (Cu, F) deposit is located in the Moskosel granite batholith north of the economically-renown Skellefte district. Four different molybdenite samples from outcrop at Kåtaberget indicate an intrusion age of 1895 ± 6 Ma with the formation of later pegmatite aplite at 1875 ± 6 Ma. The Allebuoda (Björntjärn) and Munka Mo (W) deposits in the Rappen district are represented by three outcrop and five drill core samples of molybdenite-bearing aplite pegmatite granite. These two deposits were previously described as intrusion-related Climax-type Mo mineralization. Re Os ages for molybdenites from these deposits range from 1865 to 1750 Ma and, significantly, Re concentrations are markedly low, extending to the sub-ppm level. Age agreement within the deposits is conspicuously lacking, whereas, with one exception, age agreement within any single sample (geologic occurrence), as established by analysis of additional molybdenite separates, is very good. These data, together with fundamental geologic observations discussed in this paper, suggest that Mo (W) mineralization in northern Sweden is not intrusion-related, but the local product of episodic melting of Archean Paleoproterozoic supracrustal gneisses related to the Svecofennian orogeny. Petrographic traverses across the boundary between widespread, foliation-parallel units of aplitic to pegmatitic pink granite and hosting biotite gneiss directly capture the process of ore formation. Dehydration breakdown of zircon-rich biotite aligned with the foliation in the gneiss is accompanied by formation of new pristine, post-deformational biotite plus sulfides, oxides, hydrothermal zircon and fluorite, all associated with microcline-dominant leucosomes. This process has profound implication for the traditional leucogranite, intrusion-related genesis attributed to the broad classification of Mo W Sn base and precious metal mineralization (e.g., South Mountain Batholith, Nova Scotia; Okiep, Namaqualand, South Africa; Mactung, Yukon; Pogo Liese, Tintina, Alaska; Carajás and Goiás Rio Tocantins, Brazil; New England Batholith, NSW, Australia; Bergslagen, Sweden; Nevoria, Western Australia; Alpeinerscharte, Austria; Erzgebirge, Germany; Sardinia Corsica Batholith). In addition to biotite, metallogenic contributions (e.g., Mo, W, Sn, U, Bi, Cu, Pb, Zn, Fe, Ni, Co, Au, Ag, Te, As, Sb, REE) in various combinations may also be controlled by breakdown of amphibole. In effect, the trace element composition of dehydrating or recrystallizing components in a gneissic rock essentially defines the local and district metallogenic suite. In the absence of focusing structures (e.g., shear zones, sheeted vein development), this process will generally form small and disconnected subeconomic deposits with erratic and unpredictable grades. Low Re content in associated molybdenite is a key indicator for a subeconomic origin by local melting of biotite gneiss (Mo W) or muscovite schist (Sn W).

The Chengchao and Jinshandian deposits in the southeast Hubei Province are the two largest skarn Fe deposits in the Middle-Lower Yangtze River Valley metallogenic belt (MLYRVMB), China. They are characterized by NW-striking orebodies that are developed along the contacts between the Late Mesozoic granitoid and Triassic carbonate and clastic rocks. New sensitive high-resolution ion microprobe and laser ablation inductively coupled plasma mass spectrometry zircon U-Pb dating of the mineralization-related quartz diorite and granite at Chengchao yield ages of 129 ± 2 and 127 ± 2 Ma, respectively, and those at Jinshandian of 127 ± 2 and 133 ± 1 Ma, respectively. These results are interpreted as the crystallization age of these intrusions. Hydrothermal phlogopite samples from the skarn ores at Chengchao and Jinshandian have the plateau 40Ar-39Ar ages of 132.6 ± 1.4 and 131.6 ± 1.2 Ma, respectively. These results confirm that both intrusions and associated skarn Fe mineralization were formed contemporaneously in the middle Early Cretaceous time. New zircon U-Pb and phlogopite 40Ar-39Ar ages in this study, when combined with available precise geochronological data, demonstrate that there were two discontinuous igneous events, corresponding to two episodes of skarn Fe-bearing mineralization in the southeast Hubei Province: (1) 140-136 Ma diorites and quartz diorites and 141-137 Ma skarn Cu-Fe or Fe-Cu deposits and (2) 133-127 Ma quartz diorites and granites and 133-132 Ma skarn Fe deposits. This scenario is similar to that proposed for the entire MLYRVMB. The intrusions related to skarn Fe deposits show obviously petrological and geochemical differences from those related to skarn Cu-Fe or Fe-Cu deposits. The former are quartz diorite and diorite in petrology and have similar adakitic geochemical signatures and in equilibrium with a garnet-rich residue, whereas the latter are petrologically granite and quartz diorite that are distinguishable from adakitic rocks and in equilibrium with a plagioclase residue. These features indicated that two episodes of magmatism and the formation of skarn Fe-bearing deposits in the southeast Hubei Province, MLYRVMB, might be associated lithosphere thinning induced by asthenosphere upwelling during the Late Mesozoic.

Nogal Peak quadrangle is located in the northern Sierra Blanca Igneous Complex (SBIC) and contains most of the White Mountain Wilderness (geologic map is available at http://geoinfo.nmt.edu/publications/maps/geologic/ofgm/details.cfml?Volume=134). The geology of the quad consists of a late Eocene to Oligocene volcanic pile (Sierra Blanca Volcanics, mostly alkali basalt to trachyte) intruded by a multitude of dikes, plugs and three stocks: Rialto, 31.4 Ma (mostly syenite), Three Rivers, ca. 29 to 27 Ma (quartz syenite intruded by subordinate alkali granite), and Bonito Lake, 26.6 Ma (mostly monzonite). Three Rivers stock is partially surrounded by alkali rhyolites that geochemically resemble the alkali granites. The circular shape of the stock and surrounding rhyolites suggests they form the root of a probable caldera. SBIC rocks have compositions typical of those found within the Rocky Mountain alkaline belt and those associated with continental rift zone magmatism. Because the volcanic host rocks are deeply eroded, intrusive relations with the stocks are well exposed. Most contacts at stock margins are near vertical. Roof pendants are common near some contacts and stoped blocks up to 700 m long are found within the Three Rivers stock. Contacts, pendants and stoped blocks generally display some combination of hornfelsing, brecciation, fracturing, faulting and mineralization. Sierra Blanca Volcanics display hydrothermal alteration increasing from argillic in the NW sector of the quad to high-temperature porpylitic near stock margins. Retrograde phyllic alteration occurs within breccia pipes and portions of the stocks. Mineral deposits consist of four types: Placer Au, fissure veins (mostly Ag-Pb-Zn±Au), breccia pipes (Au-Mo-Cu), and porphyry Mo-Cu. A singular pipe on the SW margin of Bonito Lake stock contains sapphire-lazulite-alunite. Although Au has been intermittently mined in the quad since 1865, best production of Au originated around the turn of the last century from the Parsons Mine, a breccia pipe in the southern Rialto stock. The Great Western Mine deposit, located within three breccia pipes on the north margin of Three Rivers stock, apparently contains 150,000 troy ounces of low-grade, disseminated Au. Three Rivers syenites and alkali granites are slightly enriched in REE compared to typical intrusive rock standards but are not high enough to be exploitable. One alkali granite sample contains 2850 ppm Zr, about 5 to 10 times the values of typical rock standards.

Metamorphic reactions, deformation mechanism and chemical changes during mylonitization and ultramylonitization of granite affected by a crustal-scale shear zone are investigated using microstructural observations and quantitative analysis. The Vivero Fault (VF) is a large extensional shear zone (>140Km) in NW of Iberia that follows the main Variscan trend dipping 60° toward the West. The movement accumulated during its tectonic history affects the major lithostratigraphic sequence of Palaeozoic and Neoproterozoic rocks and the metamorphic facies developed during Variscan orogenesis. Staurolite, and locally, andalucite plus biotite grew in the hangingwall during the development of VF, overprinted the previous regional Variscan greenschist facies metamorphism. Andalusite growth took place during the intrusion of syntectonic granitic bodies, such as the deformed granite studied here. The Penedo Gordo granite is coarse-grained two-mica biotite-rich granite intruding the VF and its hangingwall. This granite developed a localized deformation consisting of a set of narrow zones (mm to metric scales) heterogeneously distributed subsequently to its intrusion. Based on pseudosections for representative hangingwall pelites hosting the granite and the inferred metamorphic evolution, the shear zone that outcrops at present-day erosion surface was previously active at 14,7-17 km depth (390-450 MPa). Temperature estimates during deformation reach at least the range 500-600° C, implying a local gradient of 35±6°C/km. Microstructures in the mylonites are characterized by bulging (BLG) to subgrain rotation (SGR) recristallization in quartz with the increasing of deformation. Albitisation, flame-perthite and tartan twining are common in K-feldspar at the early stage of deformation. The inferred dominant deformation mechanisms are: i) intracrystalline plasticity in quartz, ii) cataclasis with syntectonic crystallisation of very fine albite-oligoclase and micas in K-feldspar, and iii) cataclasis with precipitation of K-feldspar in fractures and other dilatational sites in plagioclase. Ultramylonites consist of a matrix mainly containing feldspar, quartz and micas (mainly biotite) with an average grain size below 15 ?m, usually featuring some quartz pods and small feldspar porphyroclast. Quartz pods disintegrate into polycrystalline aggregates, and the resultant grains are mixed into the surrounding matrix reaching its average grain size. In the matrix, grain size is uniform and the distribution of mineral phases tends to be homogeneous. Mass balance analysis based on major elements indicates that the deformation process was not isochemical for some elements. Preliminary XRF results show that the mylonitic/ultramylonitic samples are depleted in Na and Mn and enriched in K and Ca respect to the original protolith, while others remains stable (Si, Al or Fe). This data suggests a large-scale transport of some components, and therefore, that fluids were involved during deformation. Similar feldspar microstructures in mylonites, implying cataclasis and neocrystallisation, have been previously reported in natural rocks where the temperature was estimated between 250 to 450°C (see Fitz-Gerald and Stünitz 1993, Hippertt 1998 or Ree et al. 2005). In opposition to this, petrological and mineralogical thermometry data indicate that temperatures during deformation of FV reached at 500-600°C, extending the temperature range previously reported.

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.

The Kabanga Ni-Cu sulfide deposits and the Luhuma Ni-Cu sulfide prospect are located in NW Tanzania roughly 200 km SW of Lake Victoria. Both areas are within the Meso-Proterozoic Karagwe-Ankolean tectonic domain, which consists of medium grade metasedimentary rocks, that are intruded by mafic to ultramafic intrusions, late syn- and post-orogenic granites.The two Ni-Cu sulfide deposits found in the Kabanga area are Kabanga Main and Kabanga North deposits; both of these deposits are associated wih ultramafic rocks. The ore zones are classified into (1) those located within ultramafic rocks, (2) those detached from ultramafic rocks and located within metasedimentary rocks and (3) those located at the contact between ultramafic rocks and metasedimentary rocks.This paper focuses on the identifi...

This paper studies the petrology of K-alkaline lamproite-carbonatite complexes, which are widespread in Siberia. They are exemplified by the Murun and Bilibino massifs in West and Central Aldan. In these massifs, the entire range of differentiates was first found, from K-ultrabasic-alkalic rocks through basic and intermediate ones to alkali granites and unique residual calc-silicate rocks (benstonite Ba-Sr carbonatites and charoite rocks). Also, intrusive equivalents of lamproites occur in these massifs, and the Murun massif was probably formed from highly differentiated lamproite magmas. In many K-alkaline complexes, silicate and silicate-carbonate magma layering takes place. Stages of magmatism are described for both massifs. Binary and ternary petrochemical diagrams exhibit the same com...

The southwestern margin of the Eastern Ghats Belt characteristically exposes mafic dykes intruding massif-type charnockites. Dykes of olivine basalt of alkaline composition have characteristic trace element signatures comparable with Ocean Island Basalt (OIB). Most importantly strong positive Nb anomaly and low values of Zr/Nb ratio are consistent with OIB source of the mafic dykes. K-Ar isotopic data indicate two cooling ages at 740 and 530 Ma. The Pan-African thermal event could be related to reactivation of major shear zones and represented by leuco-granite vein along minor shear bands. And 740 Ma cooling age may indicate the low grade metamorphic imprints, noted in some of the dykes. Although no intrusion age could be determined from the present dataset, it could be constrained by some...

A detailed 2-D modelling of the seismic structure and other geological and geophysical signatures across the Cuddapah basin of the southern Indian shield suggests upwarping of high-velocity and high-density layers, which are observed close to the surface below the southwestern part of the basin. This anomalous feature is constrained by (i) a strong gravity high anomaly of about 55 mGal, (ii) a 100 km wide high conductivity anomaly (resistivity < 100 ?-m) extending from surface to a minimum depth of 50 km in the mantle lithosphere and (iii) large scale massive intrusive activity. These features are interpreted to be an expression of a thermal anomaly, which may have acted like a plume during the Proterozoic and could well correspond to a 1.1 Ga kimberlitic activity. Below this region, the thin granitic-gneissic crust is underlain by well-differentiated, high-velocity layers, possibly due to underplating and densification of much of the crust by extruded magma.

The paper addresses the composition and genesis of endogenous borates from hypabyssal skarn deposits of Japan (Honshu Island) that were formed after dolomitic, rhodochrosite, and calcareous marbles in the contact aureoles of magmatic intrusions of diverse felsicity (from granites to diorite-monzonites). Metasomatic bodies formed at the prograde stage of the mineral formation are characterized by clearly expressed zoning of primitive type. Borates occur in the calciphyres at the Neichi, Kaso, and Rito mines, and are developed in calcitic marbles at the Fuka mine. Depending on initial composition of carbonate rocks, borates are represented by suanite, kotoite, jimboite, and takedaite in the outer zones of spinel-forsterite and galaxite-jacobsite-tephroite calciphyres or calcitic marbles, res...

The Siberian craton was affected by more voluminous plume events during last 1200?Ma than any other craton on the Earth. These events produced many economically important deposits, of which the tectonic setting of diamond deposits and related alkaline magmatism is analysed in this paper. In space and time, they can be grouped into several subprovinces: Meso- to Neoproterozoic Yenisei?Sayan; Late Devonian to Early Carboniferous Vilyui; Permo-Triassic Tunguska; Late Jurassic Olenek; and Late Jurassic to Early Cretaceous Aldan. Regardless of their age and subprovince affinity, the alkaline intrusions, including kimberlites, preferentially occur within the Archean granulite-gneiss terranes, forming a north?south-trending ?Central Horde?, framed by Archean granite?greenstone terranes. These ter...

The Phalaborwa carbonatite Complex, situated in the northeastern part of South Africa, is characterized by copper and zirconium mineralization, and is composed principally of pyroxenites, phoscorite and carbonatite (banded and transgressive). The complex is transected by mafic dykes, and is geographically associated with a satellite syenite and minor granite intrusions. Zircon and baddeleyite U-Pb isotopic age determinations using CAMECA 1280 secondary ion mass spectrometry have shown that the outer pegmatitic pyroxenite at the Loolekop pipe was emplaced at 2060+/-4Ma, and the main phoscorite at 2062+/-2Ma. Both ages are identical to those of 2060+/-2 and 2060+/-1Ma for the banded and transgressive carbonatites, respectively. The satellite syenite, which forms plug-like bodies outside of t...

Geologic and geochemical criteria were developed for the occurrence of economic uranium deposits in alkaline igneous rocks. A literature search, a limited chemical analytical program, and visits to three prominent alkaline-rock localities (Ilimaussaq, Greenland; Pocos de Caldas, Brazil; and Powderhorn, Colorado) were made to establish criteria to determine if a site had some uranium resource potential. From the literature, four alkaline-intrusive occurrences of differing character were identified as type-localities for uranium mineralization, and the important aspects of these localities were described. These characteristics were used to categorize and evaluate U.S. occurrences. The literature search disclosed 69 U.S. sites, encompassing nepheline syenite, alkaline granite, and carbonatite. It was possible to compare two-thirds of these sites to the type localities. A ranking system identified ten of the sites as most likely to have uranium resource potential.

Abstract The Nuri Cu-W-Mo deposit is located in the southern subzone of the Cenozoic Gangdese Cu-Mo metallogenic belt. The intrusive rocks exposed in the Nuri ore district consist of quartz diorite, granodiorite, monzogranite, granite porphyry, quartz diorite porphyrite and granodiorite porphyry, all of which intrude in the Cretaceous strata of the Bima Group. Owing to the intense metasomatism and hydrothermal alteration, carbonate rocks of the Bima Group form stratiform skarn and hornfels. The mineralization at the Nuri deposit is dominated by skarn, quartz vein and porphyry type. Ore minerals are chalcopyrite, pyrite, molybdenite, scheelite, bornite and tetrahedrite, etc. The oxidized orebodies contain malachite and covellite on the surface. The mineralization of the Nuri deposit is divi...

The Louzidian low-angle ductile shear detachment zone at the south of Chifeng is a SE-dipping, low-angle normal fault system. It is composed mainly of ductile shear zone, ductile-brittle shear zone and brittle fault zone. The ductile shear zone consists of, from bottom to top, mylonitic rocks, protomylonites and mylonites. Finite strain measurement of feldspar strain markers from those rocks using the R f /? method shows that strain intensities (Es) of the mylonite at core of the ductile shear zone (Es=0.65?0.96) are higher than those of the mylonitic rocks close to the granite intrusions (Es=0.59?0.62) and of the protomylonites at top of the ductile shear zone (Es= 0.47?0.70), and the strain types of the protomylonites and mylonties are elongate strain and plane-flattening strain, respect...

Paharpur gabbroic intrusive is an arcuate body running east?west paralleling the foliation of Chhotanagpur Granite Gneiss which acts as country rock. The main gabbroic body is intruded by a number of dolerite dykes running north?south. It is composed of clinopyroxene (Wo48En40Fs12?Wo51En40Fs09, mg no. 72?82), plagioclase (An52?An90), hornblende (magnesian hornblende to ferro-tschermackite), orthopyroxene (En76?En79) and ilmenite. Hornblende occurs as large poikilitic grain and constitutes around 60% of the rock. Both gabbro and associated dolerite dykes, show relatively primitive character (mg no. 65?73). Primitive mantle-normalized and MORB-normalized spider diagrams indicate enrichment in Rb, Ba, Th, La, Sr and depletion in Nb, Zr, Y, Ti and Nd. The LILE enrichment and Nb, Ti, Zr, Y depl...

The Xihuashan tungsten deposit in the central Nanling region, South China, is an important vein-type ore deposit hosted in Cambrian strata and Mesozoic granitic intrusions. Wolframite and molybdenite are the principal ore minerals. The gangue minerals are mainly quartz and muscovite. Wolframite and molybdenite are products of the first stage hydrothermal activity, whereas muscovite formed dominantly at the second stage. Molybdenite Re-Os and muscovite ^4^0Ar/^3^9Ar dating have been carried out to investigate the age of mineralization. Re-Os isotopic dating for molybdenite associated with wolframite yield a precise, well-constrained isochron age of 157.8+/-0.9Ma (MSWD=1.5). Ar-Ar isotopic analyses of muscovite yield a plateau age of 152.8+/-1.6Ma, in agreement with an inverse isochron age o...

The Maoduan Pb?Zn?Mo deposit is in hydrothermal veins with a pyrrhotite stage followed by a molybdenite and base metal stage. The Re?Os model ages of five molybdenite samples range from 138.6???2.0 to 140.0???1.9?Ma. Their isochron age is 137.7???2.7?Ma. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U?Pb dating of the nearby exposed Linggen granite porphyry gave a 206Pb/238U age of 152.2???2.2?Ma and the hidden Maoduan monzogranite yielded a mean of 140.0???1.6?Ma. These results suggest that the intrusion of the Maoduan monzogranite and Pb?Zn?Mo mineralization are contemporaneous. ? 34S values of sulfide minerals range from 3.4? to 4.8?, similar to magmatic sulfur. Four sulfide samples have 206Pb/204Pb?=?18.252?18.432, 207Pb/204Pb?=?15.609?15.779, and 208Pb...

Vostok-2???East Russia???s largest skarn deposit of high-grade sulfide-scheelite ore with substantial base-metal and gold mineralization???was formed during the Mesozoic orogenic epoch of evolution of the Far East marginal continental system as an element of the gold-tin-tungsten metallogenic belt. The deposit is related to the multistage monzodiorite-granodiorite-granite complex pertaining to the ilmenite series and spatially associated with a minor granodiorite porphyry (?) stock, which bears petrological features transi- tional to those of intrusive rocks occurring at Au-W and Au deposits. The hydrothermal metasomatic alteration of host rocks evolved from pyroxene skarn via retrograde postskarn and propylitic (hydrosilicate) metasomatic rocks to the late, low-temperature quartz-sericite...

Late Paleozoic and Early Mesozoic epochs in the formation history of the Central Asian Foldbelt are distinguished by high rare-metal productivity. A number of large REE, Ta, Nb, Zr, Be, Sn, Li, Mo, Re, and other deposits were formed at that time. As a rule, they are of the magmatic origin and related to the intrusions of highly evolved igneous rocks varying in composition from alkaline ultramafic with carbonatites to alkali and Li-F granites. In general, the occurrences of rare-metal magmatism are related to the rift zones of the Central Asian Rift System formed 310?190 Ma ago and conjugated with a consecutive series of the Barguzin, Hangay, and Hentiy zonal igneous provinces characterized by the large batholiths in their centers and rift zones in the framework. Such a structure indicates ...

The N-S trending 80 km long by 4-8 km wide Kolar Schist Belt in the Achean Dharwar craton of south India is bounded on its east and west by gneiss terranes. The contacts between the schist belt and surrounding gneisses are tectonic, rather than intrusive or unconformable. On the west side of the schist belt, monzodioritic to granitic gneisses have U-Pb zircon ages of 2631 +6.5/{minus}6 Ma, 2610 +10/{minus}10 Ma, and 2551 +3/{minus}3 Ma. The U-Pb sphene ages of these orthogneisses are between 2553 and 2551 Ma. Later granitic intrusions have U-Pb sphene and garnet ages as young as 2400 Ma. Gneisses occurring as tectonic and magmatic inclusions in the area contain zircons older than 3140 Ma. The dominant gneiss unit on the east side of the schist belt has a U-Pb zircon age of 2532 +3.5/{minus}3Ma; U-Pb sphene ages east of the belt range from 2520 to 2500 Ma. The last major shearing episode, probably represented by Pb-Pb K-feldspar-whole rock ages on both sides of the schist belt, and by an {sup 40}Ar/{sup 39}Ar muscovite plateau age from sheared gneisses, occurred between 2520 and 2420 Ma. Pb, Nd and Sr initial ratios for the western gneisses suggest that their parent magmas were mantle-derived, but were contaminated by continental crust older than 3200 Ma. Nd, Sr and Pb initial ratios for the eastern gneisses show no evidence of older continental crust either having contaminated the magmas, or acting as part of the source materials. The Kolar Schist Belt is interpreted as the site of a latest Archean or earliest Proterozoic (2520 to 2420 Ma) suture zone where newly generated continental crust on the east was tectonically accreted to the margin of an older (3400 to 2550 Ma) continental nucleus to the west.

The upper Eocene Kuh-e Dom granitoids in Central Iran comprise mafic microgranular enclaves ranging from a few centimeters to meters in size. The spherical to ellipsoidal enclaves consist of diorite, quartz-diorite, monzodiorite and quartz-monzodiorite whereas the more felsic host intrusions mainly comprise monzogranite and granodiorite. Most enclaves show sharp contacts with the host granites and distinct chilled margins in the small enclaves indicate rapid cooling after entering the felsic host magma. Disequilibrium textures include: (1) poikilitic and antirapakivi textures in feldspar megacrysts, (2) ocelli quartz rimmed by fine-grained mineral aggregates, (3) rounded and corroded plagioclase, (4) patchy plagioclase, (5) mafic clots, (6) blade biotite, (7) small lath-shaped plagioclase in larger tabular plagioclase, (8) acicular apatite, and (9) crenulated and cuspate contacts between enclaves and host rocks. These textures indicate mingling/mixing of two different magmas. Microprobe data show variable plagioclase compositions ranging between oligoclase and andesine in granodiorite, and between andesine to labradorite in the enclaves with normal zoning and oscillatory zoning. Geochemically, the enclaves are Na-rich whereas the host rocks are K-rich. In addition, the enclaves are depleted in LREE and LILE and enriched in HREE and Ti, P, Nb and Y, relative to their host granodiorites. Average initial Nd-Sr isotopic compositions for the host rocks are &z.epsiv;Nd (47 Ma) = -5.09 and Sri = 0.7068, compared to enclave Sri = 0.7060 and &z.epsiv;Nd (47 Ma) = -2.89. Fractionation of both enclaves and host rocks from the same melt cannot explain these petrological, geochemical and isotopic differences. Instead, enclaves and host rocks more likely originated from two separate magmas, which subsequently mingled and mixed. The mafic enclaves are modified mantle-derived melts while the granodioritic host rocks are partial melts of lower continental crust. The mafic enclave magma was at near liquidus conditions when injected into the granitic host melt, and the Kuh-e Dom intrusion reflects a hybrid product from mingling and partial (incomplete) mixing of these two melts.

The Barro Vermelho area is located in the border between municipalities of Custodia and Sertania - PE, Pajeu-Paraiba Fold Belt, Borborema Province. Geological mapping at 1/25.000 scale allowed to distinguish two metamorphic domains respectively built up of orthoderivated rocks and paraderivated ones. The orthoderivated domain is formed mainly by augen gneisses more or less migmatized of granitic, monzogranitic, granodioritic, tonalitic and quartz-dioritic composition inside of which are found metamafic enclaves of leucogabbros, gabbronorites, gabbros/diorites, and anorthosites, apart from banded amphibolites, with a small occurrence of Fe-Ti ore enclosed by some of these enclaves. In addition, inserted in the orthogneisses are found also others enclaves and intrusions (some apparently concordant and others certainly discordant in relation to the prominent foliation of the area, Sn) of metric to hectometric dimensions, built up of amphibolites/metadiorites, metaplite, calcissilicate rocks of mafic ultramafic protholiths, weakly deformed granites and diorites, and two hectometric bodies of olivine diabase to troctolite. Field relations and similarities in terms of composition, texture and lithogeochemistry allowed to place the lithotypes of the orthoderivated domain in the following groups, considering them in a relative sequence of events from the older to the newest ones: anorthositic-gabbros xenoliths; tonalite (protolith of the orthogneisse of equal composition); enclaves/ dikes of amphibolites/metadiorites, synplutonic in relation to tonalite and comagmatic to the xenoliths; granitic orthogneisses formed from migmatization of tonalite; enclaves/dikes of amphibolites/metadiorite, synplutonic in relation to migmatization of tonalites; granites and diorites late to post migmatization; and olivine diabase to troctolite post the last tectonic-metamorphic event recorded in the area. Concordia diagrams U/Pb with colinear regression of three zircon fractions to tonalitic and granitic orthogneisses, respectively, display ages of crystallization 2.44 Ga and 2.01 Ga to their protoliths. Model ages Sm/Nd (T{sub DM}) were determined in seven different lithotypes. However, only two yield meaningful ages, 2.30 and 2.73 Ga, respectively. These data suggest that some older Archean crustal material was incorporated during the genesis of the 2.44 Ga tonalitic gneisses, while the mafic enclaves appear to have been derived from a Paleoproterozoic source region. (author)

Abstract in spanish El plutón San Martín estáformado por una facies de borde granito biotítica, una facies centralleucogranítica y diques graníticos y aplitas cogenéticas. Corresponde a ungranito de tipo I metaluminoso, emplazado en niveles altos de la corteza en elPérmico medio alto (262 ± 5,2 Ma). Las rocas del plutón muestran una evolucióntextural desde granitos biotíticos hipidiomórficos de grano medio aleucogranitos alotriomórficos de grano fino, diques porfíricos y aplit (more) asmiarolíticas que dan cuenta de procesos de sobreenfriamiento del magma,saturación de agua y exolución de volátiles favorables para la remoción ytransporte de wolframio. Se reconocieron dos tipos de vetas alojadas en esteplutón: 1) vetas pre-mineralización y 2) vetas mineralizadas. La secuenciaparagenética comenzó con una primera etapa hidrotermal estéril (etapa I) queformó las vetas premineralización y generó feldespatización en la caja. Lasegunda etapa hidrotermal (etapa II) formó las vetas mineralizadas y depositóprimero cuarzo, feldespato potásico y wolframita, luego cuarzo y wolframita yfinalmente cuarzo, sulfuros, sulfosales de metales base y preciosos y fluorita.Se propone un modelo de sistema magmático-hidrotermal donde el plutón SanMartín es la roca de caja de las vetas hidrotermales cuya fuente es unintrusivo altamente diferenciado ubicado por debajo. Dicho intrusivo sería unafacies tardía del sistema granítico del plutón San Martín. Abstract in english The San Martín pluton is formed by abiotitic granite border facies, a leucogranite central facies and cogeneticgranitic dykes and aplites. This pluton is a I-type metaluminous granite. Itwas seated in high crust levels in the middle Upper Permian (262 ± 5.2 Ma). Thepluton rocks show a textural evolution from medium grained hypidiomorphicbiotitic granites to fine grained allotriomorphic leucogranites, porphyriticdykes and miarolitic aplites, which suggest magma undercool (more) ing, watersaturation and exsolution of magmatic volatiles to favor tungsten removal andtransportation. There are two vein types in the San Martín pluton: 1) pre-tungstenmineralization veins, and 2) tungsten-bearing veins. The paragenetic sequencebegan with the first hydrothermal sterile stage (stage I), which formedpre-tungsten mineralization veins and generated potassium alteration in thewall rock. The second hydrothermal stage (stage II) formed the tungsten-bearingveins and deposited quartz, alkali feldspar and wolframite followed by quartzand wolframite. At the end of the stage II, quartz, sulphides, base andprecious metal sulphosalts and fluorite were deposited. A magmatic-hydrothermalsystem model is proposed where the San Martin pluton is the wall rock of thehydrothermal veins whose source is a highly differentiated granite intrusionlocated below. The granite intrusion would be a late stage of the graniticsystem of San Martín pluton.

The footwall of the South Kawishiwi Intrusion (SKI) a part of the Mesoproterozoic (1.1 Ga) Duluth Complex consists of Archean granite-gneiss, diorite, granodiorite (Giant Range Batholith), thin condensed sequences of Paleoproterozoic shale (Virginia Fm.), as well as banded iron formation (Biwabik Iron Fm). Detailed (re)logging and petrographic analysis of granitic footwall rocks in the NM-57 drillhole from the Dunka Pit area has been performed to understand metamorphic processes, partial melting, deformation and geochemical characteristics of de-volatilization or influx of fluids. In the studied drillhole the footwall consists of foliated metagranite that is intersected by mafic (dioritic) dykes of older age than the SKI. In the proximal contact zones, in the mafic dykes, the orthopyroxene+clinopyroxene+plagioclase+quartz+Fe-Ti-oxide+hornblende±biotite porphyroblasts embedded in a plagioclase+K-feldspar+orthopyroxene+apatite matrix indicate pyroxene-hornfels facies conditions. Migmatitization is revealed by the euhedral crystal faces of plagioclase and pyroxene against anhedral quartz crystals in the in-situ leucosome and by the presence of abundant in-source plagioclase±biotite leucosome veinlets. Amphibole in the melanosome of mafic dykes was formed with breakdown of biotite and implies addition of H2O to the system during partial melting. Towards the deeper zones, the partially melted metatexite-granite can be characterized by K-feldspar+plagioclase+quartz+ortho/clinopyroxene+biotite+Fe-Ti-oxide+apatite mineral assemblage. The felsic veins with either pegmatitic or aplititic textures display sharp contact both to the granite and the mafic veins. They are characterized by K-feldspar+quartz±plagioclase±muscovite mineral assemblage. Sporadic occurrence of muscovite suggest local fluid saturated conditions. Emplacement of gabbroic rocks of the SKI generated intense shear in some zones of the granitic footwall resulting in formation of biotite-rich mylonites with lepidoblastic texture. High modal content of syn-tectonic biotite in these shear zones indicate involvement of large amount of fluids during deformation. Apatite is an omnipresent accessory mineral in all rock types, with up to 1-3% modal proportion. Crystal habit is columnar or rarely needle-like. XCl/XF and XOH/XF ratios of apatite were compared with depth in the drillhole and in relation to the host rock type. Apatite in the metagranite and in the mafic dyke is fluorine-rich (XFgranite?1,27-1,63; XFmafic dyke?1,51-1,83) and their XCl/XFgranite?0,083 to 0,051 and XCl/XFmafic dyke?0,051 to 0,044 ratios decrease towards the distal parts of the contact. Apatite in biotite-rich mylonite, as well as in the porphyroblasts of mafic dykes, is extremely depleted in chlorine- and hydroxyl-anions (XCl/XFmylonite?0,02 and XOH/XFmylonite?0,14), whereas apatite in felsic dykes and in the in-source leucosome are enriched in hydroxyl and chlorine relative to fluorine (XCl/XFfelsic vein?0,21 and XOH/XFfelsic vein?0,37). These variations suggest release of chlorine enriched fluids from the partially melted contact zones and movement and enrichments of these fluids in migration channels of partial melts. It has been for a long time accepted that fluids emerging from the metamorphosed Virginia Formation played an essential role in the formation of the Cu-Ni sulphide and PGE mineralization at the bottom of the gabbroic intrusions in the northwestern marginal zones of the Duluth Complex. Our study proves that the granitic footwall was also an important source of fluids and melts. We acknowledge the Austrian Science Found (FWF P23157-N21) to A. Mogessie for the financial support.

Dating the magmatic events in the Montagne Noire gneiss dome is a key point to arbitrate between the different interpretations of the Late Carboniferous-Early Permian tectonics in this southern part of the Variscan belt. The Saint-Eutrope orthogneiss crops out along the northern flank of the dome. We show that the protolith of this orthogneiss is an Ordovician granite dated at 455 ± 2 Ma (LA-ICP-MS U-Pb dating on zircon). This age is identical to that previously obtained on the augen orthogneiss of the southern flank, strongly suggesting that both orthogneiss occurrences have the same Ordovician protolith. The Saint-Eutrope orthogneiss experienced intense shearing along the Espinouse extensional detachment at ca. 295 Ma (LA-ICP-MS U-Pb-Th on monazite), an age close to that determined previously on mica by the 39Ar-40Ar method and contemporaneous with the emplacement age of the syntectonic Montalet granite farther to the west. This normal sense shearing reworked previous fabrics related to Variscan thrusting that can be still observed in the augen orthogneiss of the southern flank, and is responsible for the spectacular "C/S-like" pattern of the Saint-Eutrope orthogneiss. This work also shows that care is needed when dealing with C/S-type structures, since they can develop not only in syntectonic intrusions, but also in orthogneisses affected by an intense secondary deformation, at decreasing temperature.

Mesozoic mineral deposits in South China include world-class deposits of W, Sn and Sb and those that provide the major sources of Ta, Cu, Hg, As, Tl, Pb, Zn, Au and Ag for the entire country. These deposits can be classified into polymetallic hydrothermal systems closely related to felsic intrusive rocks (Sn-W -Mo granites, Cu porphyries, polymetallic and Fe skarns, and polymetallic vein deposits) and low-temperature hydrothermal systems with no direct connection to igneous activities (MVT deposits, epithermal Au and Sb deposits). Recent studies have shown that they formed in the Triassic (Indosinian), Jurassic-Cretaceous (Early Yanshanian), and Cretaceous (Late Yanshanian) stages. Indosinian deposits include major MVT (Pb-Zn-Ag) deposits and granite-related W-Sn deposits. Early Yanshanian deposits are low-temperature Sb-Au and high-temperature W-Sn and Cu porphyry types. Many Late Yanshanian deposits are low-temperature Au-As-Sb-Hg and U deposits, and also include high-temperature W-Sn polymetallic deposits. The formation of these deposits is linked with a specific tectonothermal evolution and igneous activities. This special issue brings together some of the latest information in eight papers that deal with the origins and tectonic environments of mineral deposits formed in these stages. We anticipate that this issue will stimulate more interests in these ore deposits in South China.

As the development of plate tectonic theory has provided a framework within which to interpret new geological and geophysical data, the need for an organized deep-drilling effort on the continents has become apparent. Since the expense of such a venture will be large, it is important to perform as many scientific experiments as practical on each hole drilled. This paper is a report on scientific, administrative, and financial aspects of a drilling program in Kansas. Experiences related here should be of some use to other groups planning scientific drilling ventures.Four holes were drilled to 0.5-1.1-km depth in Kansas as part of a hydrological study of the Arbuckle Formation. Two of the holes penetrated igneous rock of Precambrian age, and several meters of granitic core were recovered. At least one of the cores is highly magnetic and more radioactive than normal granite. Both cores have U/Pb zircon ages of 1340-1360 million years, presenting evidence for a previously unknown episode of intrusive activity. All four holes have been thermally logged with geothermal gradients ranging from 28° C/km to 36° C/km. The cased boreholes will be available in the future for additional experiments by other scientists.

Quitobaquito Springs, in Organ Pipe Cactus National Monument near the south end of the northwestward-trending Quitobaquito Hills, are less than 0.25 mile north of the international boundary between the United States and Mexico. The National Park Service is concerned that the natural flow from Quitobaquito Springs might be reduced by ground-water withdrawals in the adjacent State of Sonora, Mexico. Quitobaquito and other nearby springs flow from a highly fractured granite that forms the Quitobaquito Hills. Fractures in the granitic intrusive rocks provide conduits for ground water to flow from an alluvial flow system along Aguajita Wash to a line of springs on the southwest side of Quitobaquito Hills. The chemical composition of water from all the springs is similar. Carbon-14 analysis of water from Quitobaquito Springs indicates that the spring water probably is between 500 and several thousand years old. Discharge at Quitobaquito Springs averaged 28 gallons per minute and ranged from 15 to 40 gallons per minute for 1981-92. Rainfall at two gages in the area of recharge to the northeast of Quitobaquito Hills averaged 6.6 inches per year during the 11-year monitoring program ending in September 1992. The lack of correlation between spring discharge and local rainfall indicates that local annual recharge may be small relative to the total quantity of ground water in storage. Surface-geophysical data indicate that a thin alluvial aquifer overlies the shallow crystalline rocks northeast of Quitobaquito Hills along Aguajita Wash. Results of the study indicate that the ground-water flow system along Aguajita Wash provides a source of water to the springs and may be hydraulically connected to the ground-water system that is pumped for agricultural purposes in Mexico. The altitude and low permeability of the granite bedrock near the international boundary, however, may provide a barrier to and (or) delay the effect of a northwestward propagation of water- level declines caused by pumping near the Rio Sonoyta in Mexico.

Abstract in spanish El granito de Inti Huasi que aflora en el extremo sur de la sierra de Comechingones es uno de los tres ejemplos del magmatismo monzogranítico débilmente peraluminoso post-Famatiniano de las Sierras de Córdoba. Considerando datos de relevamiento geofísico se puede notar que el granito Inti Huasi está mayormente cubierto (> 90 %) por sedimentos modernos del Cuaternario. Esta relación de campo impide diferenciar el número de pulsos magmáticos independiente que pod (more) rían haber formado plutones discretos dentro del granito Inti Huasi. No obstante, la diversidad litológica de las rocas que afloran, reflejan que los tipos litológicos del granito están vinculadas genéticamente por la acción de procesos petrológicos que ocurrieron a nivel de epizona. La roca ígnea más abundante es un monzogranito con biotita y muscovita. Estos monzogranitos se caracterizan por ser félsico (SiO2 > 73 %, y FeO* + MgO + TiO2 Abstract in english The Inti Huasi granite at the southern end of the Sierra de Comechingones is one of three examples of post-Famatinian, alkali-rich, weakly-peraluminous monzogranitic magmatism of the Sierra de Córdoba. According to geophysical data the Inti Huasi granite is largely covered (> 90%) by Quaternary sediments. The sedimentary cover, however, makes it impossible to identify and map satisfactorily all the possible sub-intrusions units which represent individual magmatic puls (more) es that fed the Inti Huasi granite. Nevertheless, rock diversity seems to reflect the effect of high-level differentiation processes. The most common rock type is a biotite ± muscovite bearing monzogranite. Monzogranites are characteristically felsic (SiO2 > 73 %, and FeO* + MgO + TiO2

Reconnaissance and locally detailed geologic mapping and U-Pb zircon geochronology have been used to establish the style, kinematics, and timing of amalgamation of metamorphic terranes in a poorly understood region in the southeastern San Gabriel Mountains. The Cucamonga, San Antonio, and Tujunga terranes were juxtaposed along subparallel east-west trending, left-lateral ductile fault zones during emplacement of late Cretaceous granitic rocks. Displacement for each of the mylonitic fault zones was approximately several tens of kilometer and was part of a broad left-lateral shear system that was active between 90 and 81 Ma ago. The Cucamonga terrane consists of early Cretaceous granulite facies gneissic rocks. These rocks were intruded by late Cretaceous granitic rocks as the Cucamonga terrane was faulted against the San Antonio terrane. Metasedimentary pendants of the San Antonio terrane were metamorphosed under upper amphibolite facies conditions during emplacement of granitic rocks between 85 and 81 Ma ago. The San Antonio terrane was concurrently juxtaposed against the Tujunga terrane (consisting of Precambrian gneiss and Precambrian and Mesozoic intrusive rocks) to the north. No lithologic, isotopic, or structural data support suggestions that any of these rocks were accreted to North America during the Tertiary. Late Cretaceous synplutonic mylonitic deformation was followed by underthrusting of the oceanic rocks of the Baldy terrane along the Vincent thrust. After palinspastic restoration of Cenozoic fault displacements, the left-lateral mylonite belts in the southeastern San Gabriel Mountains appear to represent a tear fault within a major, synplutonic, ductile thrust system. This transcurrent zone may originally have linked west-directed thrusts in the central Transverse Ranges with those along the eastern side of the Peninsular Ranges.

Paharpur gabbroic intrusive is an arcuate body running east-west paralleling the foliation of Chhotanagpur Granite Gneiss which acts as country rock. The main gabbroic body is intruded by a number of dolerite dykes running north-south. It is composed of clinopyroxene (Wo48En40Fs12-Wo51En40Fs09, mg no. 72-82), plagioclase (An52-An90), hornblende (magnesian hornblende to ferro-tschermackite), orthopyroxene (En76-En79) and ilmenite. Hornblende occurs as large poikilitic grain and constitutes around 60% of the rock. Both gabbro and associated dolerite dykes, show relatively primitive character (mg no. 65-73). Primitive mantle-normalized and MORB-normalized spider diagrams indicate enrichment in Rb, Ba, Th, La, Sr and depletion in Nb, Zr, Y, Ti and Nd. The LILE enrichment and Nb, Ti, Zr, Y depletion suggest arc like geochemical signature for the gabbroic and doleritic rocks of Paharpur. Flat to slightly LREE fractionated pattern and variable degree of REE enrichment is observed. An early stage fractionation of clinopyroxene, plagioclase, orthopyroxene, ilmenite and late stage reaction of cumulate pile and evolved melt/hydrous fluid is suggested for magmatic evolution of gabbro. Associated dolerite dykes, which are geochemically similar to the gabbro, have tholeiitic with boninitic character. The mineralogical and chemical compositions of intrusive rocks also have some similarity with mafic rocks of ophiolite complex of subduction zone.

Abstract in spanish La zona central del extenso batolito Sierra Norte-Ambargasta, en el bloque más oriental de las Sierras Pampeanas orientales, está representada por granitoides de arco magmático tipo I (granodioritas, monzogranitos, pórfidos dacíticos y riolíticos denominados serie La Isla - Cerro de los Burros), intruidos por cuerpos menores félsicos postcolisionales, químicamente más evolucionados (denominados unidades Puesto de Los Caminos y Cerro Baritina), todos perteneciente (more) s al Neoproterozoico- Cámbrico inferior. Nueva información geológica y geoquímica de la región centro-oriental del mismo batolito permitió identificar un plutón de composición alcalifeldespática, denominado Granito Calasuya, el primero de esta naturaleza en el batolito. Su mineralogía distintiva la constituyen la composición albítica de la plagioclasa magmática (An Abstract in english The central-western portion of the extended Sierra Norte-Ambargasta batholith, in the easternmost block of the eastern Sierras Pampeanas, is largely characterized by pre-collisional I-type magmatic arc granitoids (granodiorites, monzogranites, dacite and rhyolite porphyries named La Isla - Cerro de los Burros series), and by smaller sized postcollisional felsic intrusives of higher evolved chemistry (named Puesto de los Caminos and Cerro Baritina units), all of which crys (more) tallized along the Late Proterozoic -Lower Cambrian time span. New geological and geochemical data from the central and oriental areas of the batholith allowed to identify an intrusive body of alkalifeldspar composition (the Calasuya granite), the first of its type in the batholith. Its distinctive mineralogy is highlighted by the albitic composition of magmatic plagioclase (molar An

The Clipper Gap pluton, composed mostly of quartz monzonite with minor granite, granodiorite, and crosscutting alaskite dikes, intrudes Paleozoic western facies strata. A narrow zone of contact metamorphism is present at the intrusive-sediment contact. No mineral production has been recorded from Clipper Gap, but quartz veins containing gold-silver-copper mineral occurrences have been prospected there from the late 1800's to the present. Areas of the Lone Mountain-Weepah plutons that were studied are located in Esmeralda County about 14 km west of Tonopah, Nevada. At Lone Mountain, a Cretaceous intrusive cuts folded Precambrian and Cambrian sediments. Lead-zinc ores have been mined from small replacement ore bodies in the Alpine district, west of Lone Mountain. Copper and molybdenum occurrences have been found along the east flank of Lone Mountain, and altered areas were noted in intrusive outcrops around the south end of Lone Mountain. Mineral occurrences are widespread and varied with mining activity dating back to the 1860's. The Pipe Spring pluton study area is flanked by two important mining districts, Manhattan to the north and Belmont to the northeast. Mining activity at Belmont dates from 1865. Activity at Manhattan was mainly between 1907 and 1947, but the district is active at the present time (1979). Four smaller mining areas, Monarch, Spanish Springs, Baxter Spring, and Willow Springs, are within the general boundary of the area. The Pipe Spring pluton study area contains numerous prospects along the northern contact zone of the pluton. Tungsten-bearing veins occur within the pluton near Spanish Springs, with potential for gold-tungsten placer in the Ralston Valley. Nickel and associated metals occur at Willow Spring and Monarch Ranch, where prospects may be associated with the margin of the Big Ten Peak Caldera.

The Bonfim Metamorphic Complex is one of the sialic fragments that make up the Archaen crust of the Southern Sao Francisco Craton, eastern Brazil. The northern part of the Bonfim Metamorphic Complex, located in the Quadrilatero Ferrifero region, was investigated on the basis of petrology, geochemistry and U-Pb and Sm-Nd geochronology. This complex comprises eight lithostratigraphic units, six of them Neo Archaen in age, composed of trondhjemitic to granitic gneisses, intrusive granitoids and and amphibolites. The other two units are Mesoproterozoic and probably Phanerozoic mafic dikes. The origin of rock protoliths of the Bonfim Metamorphic Complex goes back to the 3200 Ma ago, as suggested by inherited U-Pb age components and Sm-Nd (T{sub DM}) crus formation ages. The main evolution of the Northern Bonfim Metamorphic Complex was associated with the Rio das Velhas Tectonothermal Event (2780 - 2700 Ma) that correlates with major Neo Archean events in the Southern Sao Francisco Craton. The Rio das Velhas event, in the Northern Bonfim Metamorphic Complex, is characteriszed by widespread metamorphism, calc-alkaline (tonalite bodies) and tholeitic magmatism within both the sialic crust and Rio das Velhas greenstone belt. The geological features together with geochemical signatures suggest a convergent margin setting for the Neoproterozoic evolution, which final steps are represented by an intrusive granite activity dated by U-Pb zircon at 2703{+-} 24/20 Ma. During the proterozoic, the Neo-Archaen crust was affected by thermotectonic overprints, under low-grade facies metamorphic conditions, as suggested by resetting of the Rb-Sr (whole rock), and K-Ar (mineral) isotopic systems. Finally, from the petrological, geochemical and geochronological data, this paper presents a global tectonic model for the geological evolution from the Meso-to Neo Archaen in the Quadrilatero Ferrifero region. This model comprises the following geological setting and processes: active margins, mantelic plumes, magma mixing and mingling, partial melting of the lower Archaen sialic crust by mantelic underplating, extensional tectonics and ocean basin generation, ultramafic, mafic, calc alkaline and granite magmatism, tectonic inversion and closing basin during the Rio das Velhas Tectonothermal Event. (author) 51 refs., 9 figs., 4 tab.; e-mail: mauricio at degeo.ufop.br; wteixeir.usp.br; imcjr at hotmail.com.br; nafer at hotmail.com.br

The Huanggang Sn-Fe deposit, Inner Mongolia, is located in southern Great Hinggan Range metallogenic belt. LA-ICP-MS zircon U-Pb dating show that the K-feldspar granite and granite-porphyry in the Huanggang mine were formed at 136.7 ± 1.1 Ma and 136.8 ± 0.57 Ma, respectively. Sr-Nd-Pb isotope of the rocks and In situ zircon Hf isotopic systematics show that (87Sr/86Sr)i values range from 0.70211 to 0.70729, close to the (87Sr/86Sr)i of oceanic basalts and lower than those of continental crust. The &z.epsiv;Nd(t) values and Nd model ages (TDM) vary from -0.8 to 0.9 and 855 to 993 Ma, respectively. The Pb isotopic compositions are also variable with 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of 18.974-26.107, 15.554-15.914 and 38.894-39.890, respectively, suggesting that the lead is derived from a mixed source. The 176Hf/177Hf values range from 0.282744 to 0.282922, with corresponding &z.epsiv;Hf(t) values ranging from 1.9 to 18.3, and two-stage Hf model ages (TDM2) of between 561 and 888 Ma. The isotope composition shows that Huanggang granites were derived from partial melting of juvenile lower crust that originated from depleted mantle, perhaps contaminated by small amounts of ancient continental crust. Younger Nd, Hf isotope model ages imply that an important crustal growth event took place in this area during the Neoproterozoic. Integrating our data with previously published results and the Late Mesozoic regional tectonic setting, we conclude that the Huanggang granites were generated in an intraplate tectonic-magmatic setting. Asthenospheric mantle upwelling due to lithospheric delamination and magma underplating, caused the partial melting of a mantle wedge metasomatized by the fluids released from subducted oceanic crust or by decompression of depleted mantle. This resulted in remelting, differentiation and a continued evolution of the mafic juvenile crust, producing a large quantity of granitic magma. The tectonic setting for these processes may be linked to the NNW subduction of the Pacific plate (Izanagi) in the Mesozoic, which affected most of eastern China.

A Cu-bearing skarn zone occurs north of the Shayvar Mountain in northwestern Iran. Skarn-type metasomatic alteration and mineralization occur along the contact between Upper Cretaceous impure carbonates and a Miocene Cu-bearing granitic stock. Both endoskarn and exoskarn developed in the rocks. Exoskarn is the principal skarn zone and is enclosed by a skarnoid-hornfelsic zone. Skarn formation occured during stages: (1) prograde, (2) middle stage and (3) late stage. In the prograde stage, there were two main processes: (a) metamorphic-bimetasomatic and (b) prograde metasomatic. The metamorphic process began immediately after intrusion of the pluton into the enclosing impure carbonates. The prograde metasomatic stage commenced with segregation and evolution of a fluid phase in the pluton and movement into fractures and micro-fractures in the skarnoid-hornfelsic rocks developed in a metamorphic zone. The introduction of considerable amounts of Fe, Si and Mg led to the development of voluminous medium- to coarse-grained anhydrous calc-silicates. During the middle stage, the previously formed skarn zones were affected by intense multiple hydrofracturing in the Cu-bearing stock. In addition to Fe, Si and Mg, substantial amounts of Cu, Pb and Zn, along with volatile components such as H2S and CO2 were added to the skarn system. Consequently, substantial amounts of hydrous calc-silicates (epidote, tremolite-actinolite), sulfides (pyrite, chalcopyrite and molybdenite), oxides (magnetite, hematite) and carbonates (calcite) replaced the anhydrous calc-silicates. The retrograde stage was synchronous with the incursion of relatively low-temperature, more oxidized fluids into skarn system, resulting in partial alteration of the early-formed calc-silicates and development of a series of very fine-grained aggregates of chlorite, clay, hematite and calcite. Zircon grains from the endoskarn zone provide constraints on the timing of solidification of the granite stock (9.91 ± 0.31 Ma) that caused mineralization in the Anjerd area. One sample of primary hornblende from the monzogranitic Shayvar batholith has an 40Ar/39Ar age of 26.54 ± 0.65 Ma and indicates that intrusion of the Miocene stock and associated Cu skarn formation occurred a considerable time after intrusion of the batholith.

Northern Guangdong is an important part of Nanling tungsten?tin metallogenic belt, South China. The tungsten mineralization in this area consists of mainly quartz?wolframite vein-type mineralization, with W?Sn polymetallic deposits mostly distributed at the outer contact zone between concealed Late Jurassic granitic stocks and Cambrian?Ordovician low-metamorphosed sandstones and shales. Molybdenite Re?Os and muscovite 40Ar/39Ar isotopic dating of three typical tungsten vein-type deposits (Yaoling, Meiziwo, and Jubankeng) in northern Guangdong, show that two episodes of Late Jurassic W?Sn polymetallic mineralization occurred in this area: an early episode during the Late Jurassic (158?159 Ma) represented by the Yaoling, Hongling, and Meiziwo tungsten deposits, and a younger event during the...

The Katherina Volcanics of Gabal Ma'ain in the Sinai comprise an Ediacaran (580-590Ma) approximately 450m thick succession dominated by porphyritic rhyolite lava flows with subordinate related pyroclastics. These volcanics unconformably overlie the calc-alkaline Younger Granites (>=590Ma) and are intruded by alkaline granitoids (578+/-8Ma). The rhyolites have a potassic alkaline affinity and peraluminous to slightly metaluminous character. They exhibit many of the classic features of A-type magmas, including enrichment of incompatible elements, such as Zr, Nb, Y, Ga, Zn and Ce and total REE, as well as high FeO*/(FeO*+MgO) and 10,000*Ga/Al2O3 ratios. The A-type rhyolites have LREE-enriched patterns with pronounced negative Eu anomalies that are comparable with typical REE profiles for ''ho...

Over 50 magnetic bottom depths derived from spectra of magnetic anomalies in Eastern Egypt along the Red Sea margin show variable magnetic bottoms ranging from 10 to 34km. The deep magnetic bottoms correspond more closely to the Moho depth in the region, and not the depth of 580^oC, which lies significantly deeper on the steady state geotherms. These results support the idea of Wasilewski and coworkers that the Moho is a magnetic boundary in continental regions. Reduced-to-pole magnetic highs correspond to areas of Younger Granites that were emplaced toward the end of the Precambrian. Other crystalline Precambrian units formed earlier during the closure of ocean basins are not strongly magnetic. In the north, magnetic bottoms are shallow (10-15km) in regions with a high proportion of these...

To investigate the long-term alteration behavior of brannerite, we have undertaken a study of 13 natural samples from various geological environments, including granites, granitic pegmatites, quartz veins, and placer deposits. Literature data and U-Th-Pb chemical dating carried out in this work indicate that the samples range in age from approximately 20 Ma to 1580 Ma. Where independent age data or estimates are available for comparison, the U-Th-Pb chemical ages are in reasonable agreement for the younger samples, but the older samples tend to show evidence for Pb loss (up to about 80%), a common feature of metamict Nb, Ta, and Ti oxide minerals. Our results show that many of the samples exhibit only minor alteration, usually within small patches, microfractures, or around the rims of the brannerite crystals. Other samples consist of variable amounts of unaltered and altered brannerite. Heavily altered samples may contain anatase and thorite as fine-grained alteration products. Certain samples exhibited fracturing of the associated rock matrix or mineral phase in the immediate vicinity of the brannerite grains. These fractures contain U bearing material and indicate that some U migrated locally from the source brannerite.

The geochemistry of zircon from the granites that host the Sn-Rare-Metal-cryolite deposit of Pitinga Mine in northern Brazil, Amazonia, is discussed based on data obtained by LA-ICP-MS. The ore deposit is one of the largest in the world and is related with F-rich A-type granite intrusions of 1822 ± 2 Ma. REE, Y, U, Th, Nb, Ta, Pb, and Hf contents were determined in zircon grains from the albite-bearing facies that contains the ore deposit and from less evolved facies composed of amphibole-biotite and biotite granites. The trace-element contents of zircon were compared to those of their host rocks and the calculated zircon/rock ratios are like the values of zircon/melt partition coefficients for natural granitic compositions. The concentrations found for all analysed elements are highly variable, even for determinations made in the same grain. However, the average contents and patterns are like those of typical magmatic zircon and can indicate the composition of the melts from which they were crystallized. The interpretation of trace element contents in the zircon grains suggests that: (i) in the albite-bearing facies, zircon crystallized after the volatile phase exsolution and shows typical geochemical features such as: Th/U ratios from 1 to 10, Y/Ho is lower than 20, Sm/Nd ratios are generally higher than 0.5, Nb/Y is higher than 0.08, and Hf is over 2 wt%; (ii) M-type tetrad effects were produced in the REE patterns of most differentiated melts by F-complex stabilization, and were preserved in some zircon grains; (iii) ore deposition in the Pitinga mine initiated in the late stages of magmatic crystallization mainly following resurgent boiling. The trace element contents of zircon are particularly relevant for provenance studies if mineral/melt partition coefficients are taken into account, so that the approximate trace element pattern of their igneous source can be estimated. The geochemistry of trace elements in zircon, in spite of the wide range of contents, can produce a very significant set of information useful for metallogenetic, petrogenetic, exploration, geochronological, and provenance studies.

The Southeast Anatolian Orogen resulted from collision of the Afro-Arabian and the Eurasian plates following the Cretaceous to Miocene closure of the southern Neotethyan oceanic basin. In this orogenic belt, there are number of tectonomagmatic/stratigraphic units in the Kahramanmara?-Malatya-Elaz?? region that are important to understand the geological evolution of southeast Anatolia during the Late Cretaceous. These are (a) metamorphic massifs (i.e. Malatya-Keban platform), (b) ophiolites (i.e. Göksun, ?spendere, Kömürhan), (c) ophiolite-related metamorphics (i.e. Berit metaophiolite) and (d) granitoids (i.e. Göksun, Do?an?ehir and Baskil). The Baskil granitoid crops out to the northwest of Elaz?? and is a large magmatic body (170 km2) that intruded all of the above-mentioned units during Late Cretaceous time.The Baskil granitoid comprises both mafic and felsic plutonic/sub-plutonic rock associations. The felsic plutonic phase includes granite, granodiorite, tonalite and quartz monzonite whereas the felsic sub-plutonic phase is characterized by aplite, granophyre, granite porphyry and granodiorite porphyry. The granite and granodiorite contain mafic microgranular enclaves (MME). The mafic plutonic phase comprises gabbro, diorite, quartz diorite, whereas the mafic sub-plutonic phase is represented by diabase, microdiorite, quartz microdiorite, diorite porphyry, quartz diorite porphyry and dykes of orbicular gabbro dyke. Geochemically, the Baskil granitoid rocks have I-type, metaluminous-peraluminous calc-alkaline characteristics. The REE- and ocean ridge granite-normalized multi-element patterns and tectonomagmatic discrimination diagrams, together with biotite geochemistry suggest that the granitoids were formed in a volcanic arc setting. The40Ar/39Ar geochronology of the granitoid rocks yielded biotite ages of 81.9 ± 0.7 Ma and 81.5 ± 0.8 Ma (95% confidence level). Coexisting hornblende, and hornblende from additional samples, yielded ages ranging from 84.0 ± 0.7 Ma to 81.5 ± 1.1 Ma. The ophiolites are believed to have formed in a suprasubduction zone tectonic setting, whereas the ophiolite-related metamorphic rocks formed either during the initiation of intraoceanic subduction or later-stage thrusting (˜ 90 Ma). These units were then thrust beneath the Malatya-Keban platform during the progressive closure of the southern Neotethys. This was followed by intrusion of the granitoids (85-82 Ma) along the Tauride active continental margin of the southern Neotethys.

The Tien Shan form a high intracontinental mountain belt, lying north of the main India-Asia collision mountains, and consist of re-activated Paleozoic orogens. The western segment of the southern Tien Shan lies northwest of the Pamir and west of the Talas-Fergana fault. The stratigraphy, lithology, igneous and metamorphic petrology and geochemistry of this segment indicate that it was formed by the assembly of Lower Paleozoic arcs which developed into microcontinents with Upper Paleozoic mature shelf and slope clastic and carbonate sediments. Precambrian continental crust is confined to two small blocks along its southern margin. The bulk of the southern Tien Shan consists of ?Vendian to Silurian oceanic and slope clastic rocks, resting on oceanic lithosphere, and overlain by thick passive margin Devonian to mid-Carboniferous mature shelf clastics and carbonates. These are unconformably overlain by syn- and post-orogenic immature clastic sediments derived from mountains on the north formed by closure of a Carboniferus southern Tajik and a northern Vendian to Carboniferous Turkestan ocean with the southern Tien Shan microcontinent sandwiched between. Associated with these collisions are late Carboniferous to Permian intrusives, which form three south to north (though overlapping) suites; a southern calc-alkaline granodiorite-granite suite, an intermediate gabbro-monzodiorite-granite suite, and a northern alkaline monzodiorite-granite-alaskite suite. The gabbro-monzodiorite-granite suite forms the earliest subduction-related magmatism of the southern Tien Shan: rare earth element patterns are consistent with derivation from a primitive or slightly enriched mantle. The other suites show more crustal contamination. Rb and Sr vary with depth and degree of partial melting and are consistent with progressive involvement of crustal material in partial melts during collision. The gradual change in composition within each complex, lasting in some cases from 295 to 250Ma (the entire Permian), may be explained by a consecutive shift in the melting sedimentary cover of the subducting plate from oceanic crust through transitional crust to marginal continental crust. Like the Central Asian orogenic belt (the main focus of IGCP 420), the Tien Shan represent a net addition of continental crust during the Phanerozoic. Very little of the belt has any Precambrian precursor.

The Santa Lucia Shear Zone (SLSZ, Corsica) is a granulite-facies Permian shear zone that developed after the emplacement of a deep-seated gabbroic intrusion. New structural data shows that the SLSZ results from the juxtaposition of three spatially distinct mylonite belts, which are the product of the interaction between magmatism, metamorphism and shearing over a temperature range from ~800 to ~400°C. During the earlier high-grade deformation stage, which was accompanied by decompression from ~7 to ~5 kb at ~800°C, the SLSZ has accommodated high finite strain on a shear zone ?1 km wide. Strain became increasingly localized as temperature decreased, but rather than reactivating pre-existing shear zones as commonly expected, younger mylonites expanded into previously unsheared rock, extending the total width of the shear zone. The zonation of different fabrics across the SLSZ suggests that pre-existing compositional and grain size heterogeneities in the starting material played a key role in governing superposed generations of shear zones.

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A collection of 306 oriented samples from 43 Permian and Triassic intrusions from the Ukrainian Shield, the southwest portion of the East European Craton, has yielded valuable palaeomagnetic directions with new ages obtained using the 40Ar/39Ar method. Andesitic intrusions have Late Triassic ages (six dating samples) of 204.2 ± 1.6 Ma to 215.7 ± 2.0 Ma and dual-polarity Dec/Inc = 60.1°/+64.4°, k= 96, ?95= 4.5°, derived from N= 12 sites. Trachyte dykes have an early Artinskian (mid-Early Permian) age (one dating sample) of 282.6 ± 2.6 Ma, and yielded Dec/Inc = 204.3°/-23.8°, k= 27.7, ?95= 6.5°, from N= 19 sites. The palaeolatitude of the trachyte intrusions is 12.4°± 3.7° N. Because the Artinskian and younger Permian palaeopoles obtained from the Gondwana continents are subject to uncertainties, some studies have adopted a palaeopole (at 41°S, 61°E) largely based on results from ˜280 Ma Permian quartzporphyries in the Southern Alps of Italy as proxy to position Gondwana at that time. With this palaeoposition and our new ˜280 Ma palaeolatitude for Baltica, a Pangea A reconstruction cannot be supported. To avoid its inherent continental overlap of Africa and Eurasia, a Pangea B reconstruction has been favoured, wherein Eurasia's southern margin faces the northcoast of South America instead. However, the 280 ± 10 Ma palaeomagnetic data from the Gondwana continents themselves give a mean palaeopole at 30°S, 59°E, which results in a palaeogeographic position of Gondwana that allows a Pangea A type reconstruction. Thus, the choice between Pangea A versus B in the Artinskian hinges on data selection and reliability criteria and the assumptions about tectonic coherence of northern Adria (i.e. the Southern Alps) with Africa in Permian times. A more reliable mid-Early Permian palaeopole from cratonic Gondwana would provide a more definitive conclusion.

The Proterozoic volcano-sedimentary succession comprising successively younger Dhanjori, Chaibasa, Dhalbhum, Dalma and Chandil Formations of the Singhbhum crustal province, India records sedimentation and volcanism in a rapidly changing tectonic scenario. Cooling of the vast volume of Archaean Singhbhum granite possibly induced an isostatic readjustment. The associated tensional regime and deep-seated fractures controlled the formation of the Proterozoic Singhbhum basin. The Dhanjori Formation unconformably overlies the Singhbhum granite and is entirely terrestrial, dominantly fluvial. At the base, the conglomerate deposits, coarse-grained sandstone, and shale represent the distal fringe of an alluvial fan complex. The rest of the formation including the volcaniclastic rocks consists almost entirely of fining-upward fluvial cycles. The base of the Dhanjori Formation is a sequence boundary and the formation itself represents a lowstand systems tract. The Dhanjori volcano-sedimentary succession displays evidence of having passed through passive, as well as, active phases of continental rifting with an increasingly important influence of volcanism on the sedimentation through time. The Chaibasa Formation sharply overlies the Dhanjori Formation and a transgressive lag demarcates their contact. The basal part of the Chaibasa Formation immediately overlying the transgressive lag deposit represents a transgressive systems tract while offshore shales that sharply overlie the shallow marine sandstones up-section represent marine flooding surfaces. The shallow marine subtidal sandstones bear an excellent record of sandwave migration and provide a rare opportunity to unlock the Late Palaeoproterozoic lunar orbital periodicities. Unlike the Chaibasa, the overlying Dhalbhum Formation is entirely terrestrial (fluvial-aeolian) indicating that the Chaibasa-Dhalbhum contact is a sequence boundary. The Dalmas, overlying the Dhalbhum Formation, represents concordant lava outpourings without any break in sedimentation; these lavas are genetically related to mantle plume upwelling in an intracontinental rift setting. The volcano-sedimentary package lying north of the Dalma volcanic belt (Chandil Formation) is of Mesoproterozoic age. The entire Late Palaeoproterozoic volcano-sedimentary package displays post-depositional compressional deformation and greenschist to amphibolite facies metamorphism dated at ca. 1600 Ma, forming the so-called North Singhbhum fold belt. The volcano-sedimentary package lying south of the Dalma volcanic belt was pushed further south towards the Singhbhum granite batholith complex as a result of uplift related to the Dalma plume. The Singhbhum granite batholith acted as a rigid body. This gave rise to a compressional stress regime that induced shearing/thrusting at ca. 1600 Ma along the Singhbhum Shear Zone. The Dalma plume magmatism was possibly part of a ˜1600 Ma global tectono-thermal event.

The West Junggar, northwestern China, is located in the southwest of the Central Asian Orogenic Belt (CAOB) and consists of Paleozoic ophiolitic mélanges, arcs and accretionary complexes. The Mayile Mountain ultramafic-mafic mélange in the southern West Junggar is the northeastern part of the Mayile ophiolitic mélange. The Mayile Mountain mélange is represented by a ca. 30 km long, 5 km wide, north-northeast-striking serpentinite-matrix mélange, which encloses serpentinized harzburgite, dunite, chromitite, wehrlite, clinopyroxenite, gabbro, rodingite, and chert blocks. It is overlain by the Middle Silurian greenschist facies and Early-Middle Devonian unmetamorphic volcano-sedimentary strata.Chemically, chromian spinel from peridotite and clinopyroxenite is similar to those of island arc lava and depleted peridotite from supra-subduction zone (SSZ). Clinopyroxene from the ultramafic-mafic rocks shows the affinities of island arc tholeiite and boninite. The ultramafic-mafic rocks also show the subduction-related geochemical signatures, such as flat REE patterns with slight LREE depletion ((La/Yb)N = 0.66-0.89), LILE enrichment and HFSE depletion.The ultramafic-mafic mélange is crosscut by intrusions. Zircon U-Pb dating reveals four phases of magmatism: Late Cambrian (501-493 Ma), Early Ordovician (488-485 Ma), Early Silurian (444-439 Ma), and Late Carboniferous-Early Permian (318-296 Ma). The Late Cambrian gabbro, diorite and granite, Early Ordovician diorite and Early Silurian granodiorite intrude the mélange in places and predate the overlying Middle Silurian and Early-Middle Devonian successions. They are I-type calc-alkaline and show strong island arc affinities, with LILE and LREE enrichment ((La/Yb)N = 3.77-21.45) and HFSE depletion. On the contrary, the Late Carboniferous-Early Permian I-type diorite, granodiorite and granite and A-type alkali-feldspar granite crosscut both the mélange and overlying strata. They are coeval with the widespread post-collisional granitoids in the West Junggar.Our data for the mélange and intrusions suggest that this mélange might be a highly mixed SSZ-type ophiolitic mélange generated in the earliest stage of south-dipping subduction-accretion during the Early-Middle Cambrian, and then an island arc was successively built in the south in the Late Cambrian (501-493 Ma), in the center in the Early Ordovician (488-485 Ma) and in the north in the Early Silurian (444-439 Ma), as a result of northward arc migration. In the Middle Silurian, the mélange and island arc intrusions might be exposed and covered by deep or hemi-deep sea volcano-sedimentary strata in a back-arc setting, and they might have been accreted southward to another arc and continental margin before the Early-Middle Devonian. After the ocean was ultimately closed at the end of the Early Carboniferous, the mélange and island arc as well as other tectonic units in the West Junggar were stitched together by the Late Carboniferous-Permian post-collisional granitoids.

During the late Cryogenian-Ediacaran (650-542 Ma), the Arabian-Nubian Shield (ANS) underwent final assembly and accretion to the Saharan Metacraton concurrent with the assembly of eastern and western Gondwana. At the end of the Precambrian it lay at one end of the East African Orogen, with its northern margin (present coordinates) forming a low-relief stable shelf facing an open ocean; to the south the ANS transitioned into the Mozambique Belt. The geologic history of the ANS during this period provides insight into the closing developmental stages of one of the world's largest accretionary orogens. Following a 680-640 Ma orogenic event reflecting amalgamation of a core grouping of island-arc terranes (the proto-Arabian-Nubian Shield; pANS), the region underwent extensive exhumation, erosion, and subsidence. Depositional basins formed in the northern and eastern pANS, with those in the east below sea level and connected to an ocean. Periodic basin closure and formation of new basins in other parts of the ANS followed. Many basins were filled by terrestrial, molasse-type sediments interfingering with subordinate to predominant amounts of volcanic rocks. Magmatism was extensive throughout the period, initially characterized by tonalite-trondhjemite-granodiorite (TTG) and granite (monzogranite, syenogranite), but also characterized, from ˜610 Ma on, by increasing amounts of alkali-feldspar granite and alkali granite. The plutons are largely undeformed, except where cut by brittle-ductile shear zones. The magma sources of the late Cryogenian-Ediacaran granitoids were dominated by juvenile crust and(or) depleted mantle and magmas mostly originated in anorogenic, post-collisional, commonly extensional, settings. They were derived by melting and fractionation of anhydrous high-grade metamorphosed lower crust, mafic- to intermediate calc-alkaline crust, and(or) subduction-modified mantle wedges associated with slab break-off or delamination.By ˜630 Ma, the region was affected by oblique (transpressional) convergence of continental blocks that formed eastern and western Gondwana—the pANS was approaching the Saharan Metacraton; north-trending shear and shortening zones developed in the southern ANS; and northwest-trending strike-slip shear zones of the Najd fault system dominated farther north. In the northwestern ANS, convergence and Najd transpression buckled the crust causing structural highs with domes of gneissic infracrust overlain by supracrust composed of ophiolitic and volcanosedimentary assemblages dating from the Tonian-middle Cryogenian period of island-arc activity. The supracrust was extensively translated to the northwest above a high-strain zone. Extension and tectonic escape augmented exhumation of the gneissic infracrust particularly between ˜620-580 Ma. In the northeastern ANS, linear belts of gneiss formed from reworked older intrusive bodies or syntectonic intrusions that were emplaced along Najd faults. By ˜620 Ma a marine basin on the eastern margin of the pANS (present coordinates) was beginning to close. A thick sedimentary assemblage (Abt formation) in this basin underwent metamorphism and folding, and subduction-related magmatism and volcanism farther into this basin (Al Amar arc; >690-615 Ma) was coming to an end. Amalgamation of the Abt formation, Al Amar arc, and the pANS occurred between ˜620 and ˜605 Ma, and terminal collision between the pANS and the Saharan Metacraton was complete by ˜580 Ma. At this time, the ANS was fully assembled. Granite magmatism continued until ˜565-560 Ma and orogeny ceased by ˜550 Ma. During these terminal events, the region underwent strong chemical weathering and became a vast low-relief surface on which Lower Paleozoic sandstone was eventually deposited.

Extensive volcanism occurred along the Philippine Fault in the Tongonan region in the Miocene and produced the Bao Volcanic Formation (BVF) and the Mahiao Plutonic Complex (MPC). The BVF is composed of basaltic andesite lavas and volcaniclastic sediments interbedded with up to three thin horizons of shales and limestones containing Miocene fossils, and is cut by hornblende-dacite dykes. The MPC contains rocks ranging in composition from gabbro to granite. When the mafic magmas first intruded, they contact metamorphosed the overlying volcanic and plutonic rocks to produce hornblende hornfels. A low temperature (< 250{degree}C) geothermal system in the Miocene. In the Pliocene, the Philippine fault reactivated and this coincided with intrusion of granodiorite magma into the Malitbog (eastern) sector of the field. As the granodiorite crystallized, about 2 mole % of mainly CO{sub 2} and H{sub 2}s gas in geothermal steam dissociated to form a corrosive acidic condensate which intensely altered the host rocks and deposited kaolinite, alunite, pyrophyllite and diaspore to depths of about 500 m below sea level. However, epidote, illite, chlorite, quartz, anhydrite and garnet deposited from boiling, neutral pH, alkali-chloride, waters in the deep reservoir. The water exchanged oxygen isotopes with the reservoir rock. Fluid inclusion evidence shows that boiling has occurred, and the salinity and temperature of the deep fluid did not change significantly. In the Quaternary, calc-alkaline granite magma intruded the basement rocks in the Mahiao (western) sector of the field. Only minor gas released from this magma accounts for the lack of acid alteration in the Mahiao sector. The deep neutral-pH fluids deposited mainly quartz and epidote during boiling, and exchanged oxygen isotopes with the host rocks at temperatures above about 300{degree}C.

Abstract in spanish En el presente trabajo se realiza el estudio mineralógico y se define la edad de una mica de litio obtenida en las salbandas de las vetas cuarzo portadoras de wolframita de mina La Rosario, ubicada en las proximidades del granito Ayacucho, Sierra de Fiambalá, Sierras Pampeanas Occidentales de la provincia de Catamarca. Esta especie mineral fue identificada a través de diferentes técnicas analíticas que incluyen determinaciones por difracción de rayos X, análisis qu (more) ímicos y por espectrometría infrarroja. Los resultados de los estudios indican que su estructura corresponde a una zinnwaldita y su composición química permite ubicarla dentro de la serie biotita-siderofilita-zinnwaldita-lepidolita. Las edades isotópicas obtenidas para el Granito Ayacucho (340 ± 8 Ma) y esta mica hidrotermal (339 ± 8 Ma) confirman una edad carbonífera para este intrusivo y la estrecha relación temporal con la mineralización hidrotermal asociada. Abstract in english This work deals with a mineralogical study and the age of a lithium mica obtained from the selvage of wolframite quartz veins from La Rosario mine, which crops out close to Ayacucho Granite, Sierra de Fiambalá, Sierras Pampeanas Occidentales of Catamarca province. This mineral species was identified through different analytical techniques that include X-ray diffraction, chemical analyses and infrared spectrometry analyses. The results of the studies indicate that its str (more) ucture corresponds to zinnwaldite and its chemical composition allows locating it inside the biotite-siderophyllite-zinnwaldite-lepidolite series. The isotopic ages obtained for the Ayacucho granite (340 ± 8 Ma) and this hydrothermal mica (339 ± 8 Ma) confirm a Carboniferous age for this intrusive and the genetic link with hydrothermal mineralization.

The Torrington Landfill lies within the Western Connecticut Highlands and overlies the geologic contact between the interlayered schists and gneisses of the Hartland Formation from the medium grained granites and pegmatites of the Tyler Lake Granite. The contact separating the two formations, exposed to the south and north of the landfill, is sharp and discordant. Geologic structures observed at the outcrop scale include a dominant foliation, several generations of folding, and three dominant fracture orientations measuring N70W, N35W, and N15E. Bedrock controlled surface topography directs the flow of leachate from the landfill in the overburden aquifer and prevents the leachate from migrating in a radial pattern. Outcrops to the west, southwest, southeast, east, and north of the landfill act as barriers to leachate migration and funnel leachate through two bedrock valleys present along the south and northeast sides of the landfill. Leachate migration within the crystalline bedrock occurs primarily through fracture zones. Field observations suggest that neither the intrusive contact between the two formations nor the dominant foliation are likely leachate migration pathways. The ability of the fractured bedrock to transmit leachate depends on the extent of fracture development and the degree of fracture interconnection. Those areas where fractures are well developed generally show topographic expression, such as along the course of Peck Brook and the southern bedrock valley, and are documented pathways for leachate migration. These interpretations regarding leachate migration pathways from the landfill within both the overburden and bedrock aquifers are supported by historical groundwater monitoring data, and by data generated from a geophysical survey completed around the perimeter of the landfill.

The prograde deserpentinized peridotites from the talc zone in the Happo-O'ne complex, central Japan, show differences in their field relation and mineral assemblage with the high-P retrograde peridotites of the other part of the complex. They show a mineral assemblage, olivine + talc + antigorite ± prograde tremolite ± chlorite, formed by thermal metamorphism around the granitic intrusion at T, 500-650 °C and P talc display a spoon-shaped primitive mantle (PM)-normalized REE pattern (0.1-3 times PM) in which LREE are higher than HREE contents. The prograde tremolite is depleted in Al, Na, Cr, Sc, V, Ti, B, HREE and Li, but is enriched in Si, Cs, U, Th, HFSE (Hf, Zr, Nb, Ta), Rb and Ba relative to the retrograde tremolite; the immobile-element depletion in this tremolite is inherited from its source (antigorite + secondary diopside), whereas the depletion of mobile elements (e.g., Li, B, Na, Al) is ascribed to their mobility during the deserpentinization and/or the depleted character of the source of tremolite. The enrichment of HFSE and LILE in the prograde tremolite is related to an external addition of these elements from fluid/melt of the surrounding granitic magma and/or in situ equilibrium with LILE-bearing fluid released during dehydration of serpentinized retrograde metaperidotites and olivine-bearing serpentinites (protoliths). The prograde olivine is higher in REE and most trace-element contents than the retrograde one due to the external addition of these elements; it is enriched in B, Co and Ni, but depleted in Li that was liberated during deserpentinization by prograde metamorphism.

The South Mountain Batholith (SMB) of southwestern Nova Scotia (Canada) is a Late Devonian (~375 Ma) composite intrusion, which crops over an area of about 7,300 km2. This peraluminous granitoid body consists of rocks ranging from granodiorite through monzogranite and leucomonzogranite to leucogranite that locally host greisen tin-base metal mineralization. K-feldspar displays large compositional variations of trace elements and Pb isotopic ratios, particularly in the highly fractionated rocks. Many variations are consistent with processes of fractional crystallization, but a distinct enrichment of Rb, Li and Cs accompanied by low K/Rb, Ba/Rb, Eu/Eu* and K/Cs ratios point to the role of fluids during the late stages of magmatic evolution. The correlation of Pb isotopic ratios with the enriched elements and their ratios implies that the isotopic variations are an integral part of the evolution of the SMB. Together with well-defined isochronal relationships of Pb systems in the feldspars, the correlation suggests that fractional crystallization accompanied in the late stages by fluid fractionation led to the formation of Li-F-rich leucogranites. Internally derived U-rich fluids fractionated U/Pb ratios, which in turn produced distinct variations of 206Pb/204Pb and 238U/204Pb ratios in K-feldspars. This implies that the Pb isotopic values of K-feldspar, which have traditionally been used for tectonic reconstructions, might have been modified in many granitic rocks. Thus, only early magmatic K-feldspars, which show no discernible effects of fluid fractionation yield the initial Pb isotopic compositions of the parental granitic magmas and their sources. The data also show that the geochemical characteristics of the leucogranites are the results of magmatic evolution rather than a distinctive source.

The Mazraeh Cu-Fe skarn deposit, NW Iran is the result of the intrusion of an Oligocene-Miocene granitic pluton into Cretaceous calcareous rocks. The pluton ranges in composition from monzonite to quartz monzonite, monzogranite, tonalite and granodiorite with I-type, calc-alkaline, and weakly peraluminous characteristics. The Mazraeh pluton was emplaced in a volcanic arc setting in an active continental margin at a depth of ~8 km. Pyroxene skarn, garnet skarn, and epidote skarn zones were formed during the intrusive phase. The garnet skarn developed as exoskarn and endoskarn from the calcareous wall rocks and the pluton, respectively, prior to mineralization. Garnet skarn from the exoskarn zone is identified by relict layering inherited from the precursor calcareous lithologies. Mass balance calculation of garnet skarn in the endoskarn zone indicates that hydrothermal fluids originating from the cooling magma introduced Si, Fe, Mn, Ca, Mg, P, Ag, Cu, Zn, La, Pb, Cd, Mo, and Y. The main mass loss in the garnet skarn was due to destruction of feldspars in the Mazraeh plutonic rocks and leaching of K2O and Na2O. Released Ca has been fixed in the andraditic garnet. Garnetization of the Mazraeh pluton was accompanied by mass and volume increase. The magnitude of these changes depends mainly on the degree of alteration and composition of the precursor. The brittle behavior of the endoskarn zone was increased due to formation of massive garnet which subsequently fractured. These fractures not only facilitated movement of hydrothermal fluids but also provided new locations for Cu mineralization. Therefore locating strongly garnetized zones may be a vector to ore in skarn deposits.

In order to provide platforms for the development of new downhole geophysical and hydrodynamic sensors, 4 sites are being developped with a series of nearby 100 m deep boreholes located with a few meters to 100 meters, at the most. The objective is to set-up a cluster of extremely well characterized in-situ laboratories at scales where experiments cannot be conducted in traditionnal labs. At least one borehole is continuously cored at each of the sites, and the core is fully characterized in petrological, petrophysical and geochemical terms. An emphasis is placed on fundamental and environmental applications such as hydrogeology, waste storage or the study of seismogenic faults, whether for characterization purposes or the development of long-term monitoring sensors and methods. These sites are developped with the support of CNRS, the University of Montpellier and the ALIANCE program financed by the European Commission. The 4 sites span different lithologies with granite at Ploemeur (Brittany, France), Miocene carbonates from a reefal platform in south Mallorca (Baleares, Spain), Valanginian marly limestone at Lavalette, near Montpellier (Languedoc, France), and unconsolidated sands in a coastal setting also near Montpellier. In the context of ALIANCE, the goal is to improve the investigation, characterisation and monitoring of coastal aquifers for vulnerability assessment. For this, a set of geophysical approaches for the quantitative evaluation of brine intrusion will be developped. This includes the design of 5 new geophysical and hydrodynamical logging/testing sensors. Two end-member sites in terms of hydrogeological behavior will be set up for long-term experimentation, the testing of the new tools, and the validation of site-specific experimental and modelling protocols from µm- to 100 m-scale. Active in-situ testing from short and longer-term injections with variable salinity fluids will simulate overdrafting or saline water intrusion.

The U-Th-total Pb composition of monazite determined by electron microprobe methods has been successfully applied in geochronology using different age calculation procedures (1). One of the main problems in the use of this geochronological tool is the impossibility to asses the degree of discordance of the minerals analyzed. The Los Pedroches batholith of the Central-Iberian Zone (S Spain) is a late-Hercynian magmatic alignment essentially formed by a granodiorite unit and several granite intrusions. The batholith was emplaced subsequently to the main Hercynian deformation phase during upper Westphalian to lower Stephanian times (ca. 300 Ma). The emplacement was controlled by a crustal-scale shear zone trending N120--130E developed in a transtensional regime (2). There is no evidence of major deformational events after the emplacement. Thirty representative monazites from four granitic plutons (Santa Eufemia, El Guijo, Cerro Mogábar, Cardeña-Virgen de La Cabeza) of the Los Pedroches batholith have been analyzed by electron microprobe using standard procedures described in (3). Data obtained from 166 analyses were processed and plotted on different diagrams proposed for U-Th-total Pb dating assessment (1, 3, 4). In U/Pb vs. Th/Pb diagrams, analyzed monazites exhibit gradual variations in U, Th and Pb contents, but deviate from the reference isochron lines. Data sets for each pluton show considerable scatter on age histograms which also prevent obtaining ages with reasonable errors. Yet, individual monazite grains show variable patterns and generally present the higher frequency of data at ca. 300 Ma with tails down to ca. 250 Ma. On the other hand, data plotted on the ThO_2* (%) vs. PbO (%) diagrams generally crosscut in PbO negative values, indicating some Pb loss after mineral crystallization. It appears, therefore, that despite the absence of field, structural and geophysical evidence of post-emplacement deformation and recrystallization in granites, the analysis of monazites from the Los Pedroches batholith unveils late event(s) that have affected preferably this mineral. Taking into account the whole information available (including isotopic Pb data on galenas from related mineralizations, cf. accompanying abstract), it is suggested that such an event might have taken place at ca. 260 Ma. (1) Cocherie, A. &Albarede, F. Geochim. Cosmochim Acta 65: 4509--4522, 2001. (2) Aranguren, A. et al., C. R .Acad .Sci. Paris, 325: 601--606, 1997. (3) Montel, J.M. et al., Chem. Geol. 131: 37--53, 1996. (4) Suzuki, K. &Adachi, M. Geochem. Jour. 25: 357--376, 1991.

At Sams Creek, a gold-bearing, peralkaline granite porphyry dyke, which has a 7 km strike length and is up to 60 m in thickness, intrudes camptonite lamprophyre dykes and lower greenschist facies metapelites and quartzites of the Late Ordovician Wangapeka formation. The lamprophyre dykes occur as thin (siderite±biotite; Stage II consisting of thin quartz-pyrite veinlets; and Stage III (low fO2) consisting of sulphides, quartz and siderite veins, and pervasive silicification. The lamprophyre is altered to an ankerite-chlorite-sericite assemblage. Stage III sulphide veins are composed of arsenopyrite + pyrite ± galena ± sphalerite ± gold ± chalcopyrite ± pyrrhotite ± rutile ± graphite. Three phases of deformation have affected the area, and the mineralised veins and the granite and lamprophyre dykes have been deformed by two phases of folding, the youngest of which is Early Cretaceous. Locally preserved early-formed fluid inclusions are either carbonic, showing two- or three-phases at room temperature (liquid CO2-CH4 + liquid H2O ± CO2 vapour) or two-phase liquid-rich aqueous inclusions, some of which contain clathrates. Salinities of the aqueous inclusions are in the range of 1.4 to 7.6 wt% NaCl equiv. Final homogenisation temperatures (Th) of the carbonic inclusions indicate minimum trapping temperatures of 320 to 355°C, which are not too different from vein formation temperatures of 340-380°C estimated from quartz-albite stable isotope thermometry. ?18O values of Stage II and III vein quartz range from +12 and +17‰ and have a bimodal distribution (+14.5 and +16‰) with Stage II vein quartz accounting for the lower values. Siderite in Stage III veins have ?18O (+12 to +16‰) and ?13C values (-5‰, relative to VPDB), unlike those from Wangapeka Formation metasediments (?13Cbulk carbon values of -24 to -19‰) and underlying Arthur Marble marine carbonates (?18O = +25‰ and ?13C = 0‰). Calculated ?18Owater (+8 to +11‰, at 340°C) and ?^{13}{text{C}}_{CO2}(-5‰) values from vein quartz and siderite are consistent with a magmatic hydrothermal source, but a metamorphic hydrothermal origin cannot be excluded. ?34S values of sulphides range from +5 to +10‰ (relative to CDT) and also have a bimodal distribution (modes at +6 and +9‰, correlated with Stage II and Stage III mineralisation, respectively). The ?34S values of pyrite from the Arthur Marble marine carbonates (range from +3 to +13‰) and Wangapeka Formation (range from -4 to +9.5‰) indicate that they are potential sources of sulphur for sulphides in the Sams Creek veins. Another possible source of the sulphur is the lithospheric mantle which has positive values up to +14‰. Ages of the granite, lamprophyre, alteration/mineralisation, and deformation in the region are not well constrained, which makes it difficult to identify sources of mineralisation with respect to timing. Our mineralogical and stable isotope data does not exclude a metamorphic source, but we consider that the source of the mineralisation can best be explained by a magmatic hydrothermal source. Assuming that the hydrothermal fluids were sourced from crystallisation of the Sams Creek granite or an underlying magma chamber, then the Sams Creek gold deposit appears to be a hybrid between those described as reduced granite Au-Bi deposits and alkaline intrusive-hosted Au-Mo-Cu deposits.

The Tarim Block is an important tectonic unit to understand the Proterozoic tectonic framework of the Central Asian Orogenic Belt and the supercontinent Rodinia. The granitic, dioritic, gabbroic intrusive rocks and volcanic-volcanoclastic rocks are widely distributed in the Quruqtagh domain of NE-Tarim. The precise ages of these rocks and their tectonic implications in this part of the world are not well understood. This paper reports geochronological data of gabbro, diorite and granitic rocks from Quruqtagh. LA ICPMS U-Pb zircon ages suggest that numerous of gabbroic and granitic rocks were mainly crystallized at ca. 800 Ma. New geochronological data from the magmatic zircons of gabbro, granite and paragneiss can be preliminarily divided into four groups, which are (1) 2469 ± 12 Ma or 2470 ± 24 Ma, (2) 933 ± 11 Ma to 1048 ± 19 Ma, (3) 806 ± 8 Ma, 798 ± 7 Ma, 799 ± 24 Ma, 698 ± 51 Ma (lower intercept age of the paragneiss), and (4) 1930 Ma (upper intercept age of the paragneiss), respectively. These age data are consistent with four tectono-thermal events that took ever place in the Tarim Block. The 93 U-Pb age data (seven for average Concordia age from seven igneous plutons, 86 for xenocrystic and metamorphic ones) from eight samples can be divided into four evolutionary stages: 2360-2550 Ma (peak of 2510 Ma), 1800-2020 Ma (peak of 1870 Ma), 860-1140 Ma (peak of 920 Ma) and 680-840 Ma (peak of 800 Ma), respectively. The age peak of 2500 Ma, consistent with characteristic period of a global building-continent event, indicates that the late Neoarchean-early Paleoproterozoic magmatism had been ever taken place in Tarim. Two peaks at 1870 Ma and 920 Ma, being two assembly periods of the middle Paleoproterozoic Columbia and the Neoproterozoic Rodinia supercontinents, suggest that Tarim had connections with both Columbia and Rodinia, whereas structural evidence of these two events is absent in Tarim. Notable peak of 800 Ma is interpreted as a response to the break-up of Rodinia supercontinent. The geological indicators of break-up such as Neoproterozoic granite, bimodal igneous rocks, composite magmatic flow, basic dyke swarm and continental rift type basins are well developed, followed by a large-scale of late Neoproterozoic glacier event. Four stages of magmatism mentioned above constitute major events in the Precambrian evolution of Tarim and Central Asian. These data, combining with previous U-Pb ages from igneous rocks, provide a significant line of evidence for understanding the Rodinia evolution of Tarim and the relationships with South China, east India and east Antarctica, Lesser and Great Himalaya blocks in Proterozoic. A primary reconstruction of the Tarim Block, connecting it with South China, east India and east Antarctica, Lesser and Great Himalaya blocks, is finally proposed.

It was recognized that two important boundaries, the Farsund-RAP shear zone and the Sveconorwegian (=Grenvillian) opx-in isograd, controlled the composition of the post-collisional magmatism of southern Norway (0.97 to 0.92 Ga) (Vander Auwera et al., 2011). The Farsund-RAP shear zone (Bolle et al., 2010), a boundary between two contrasted lithothectonic units, separates magmatic bodies with different isotopic compositions mainly due to different contaminants. During the regional metamorphism (1.035 to 0.97 Ga: i.e. Bingen et al., 2005), southern Norway lower crustal segments were variably modified, with granulite facies conditions prevailing in the westernmost part of the orogen and producing dehydrated lower crustal sources west of the opx-in isograd, and more hydrated sources east of this isograd. The small Kleivan intrusion (? 20 km2, 930 ± 7 Ma, Rb-Sr; Pedersen & Falkum, 1975), located in the eastern hydrated part of the orogen, confirms these interpretations. This pluton contains two different trends. The main trend displays, from North to South and with increasing SiO2, a gradual variation from opx-bearing charnockites to amphibole-bearing and finally biotite-bearing granites (Petersen, 1980), in which titanite is absent. In the subsidiary Hbl+Tit trend, titanite is present, opx is absent and amphibole is the dominant ferromagnesian. The main trend has a significantly higher Fe# than the Hbl+Tit trend, echoed by higher Fe# in amphiboles and accompanied by a larger range in SiO2 (63.9 to 77% in the main trend; 63.5 to 68.9% in the Hbl+Tit trend). Both trends are ferroan and have overlapping compositions for trace and other major elements. The bulk magnetic susceptibility (Km) is higher in the Hbl+Tit trend, reflecting its higher magnetite/ilmenite ratio. The two trends have similar initial Sr, Nd and Pb isotopic compositions indicating contamination by the eastern crustal contaminant only, in agreement with the emplacement of the Kleivan intrusion east of the Farsund-RAP shear zone. Experimental data (Bogaerts et al., 2006) indicate a lower H2O content (5.5 wt% H2O). In addition, higher magnetite/ilmenite ratio and titanite occurrence within the Hbl+Tit trend agree with a higher fO2. The presence of two trends differing by their H2O content and fO2 is here related to straddling of the opx-in isograd (Sveconorwegian metamorphism) by the Kleivan intrusion (Vander Auwera et al., 2011). It is also worth noting that, despite similar rheologies (similar major elements composition and temperature), the two trends did not mix, preserving their characteristics towards their level of emplacement (3.5 to 5 kbar) through differentiation and upward migration from the lower crust.

The chemical composition was analyzed and the radioactivity, radon exhalation rate and emanation fraction were measured to investigate the characteristics of the granites sampled at Misasa and Badgastein, world famous for radon therapy. The Misasa granite was probably composed of quartz, albite and microcline. The Badgastein granite was probably composed of quartz and muscovite. The radon exhalation rates and emanation fractions of the Misasa granite were much higher than those of the Badgastein granite, regardless of the {sup 226}Ra activity concentrations.

The Tahoe and Truckee Basins fall within the NW-trending Walker Lane (WL), a northward-widening deformation zone accommodating 20-25% of Pacific/North American plate convergence. Separating the Sierra Nevada microplate to the west from the Great Basin to the east, the WL accommodates 10-14 mm/yr of dextral shear. Within the Tahoe-Truckee area, this deformation is thought to be partitioned both spatially and temporally between E/W extension and N/S shortening. We present results of a USGS geophysical study aimed at understanding the complex faulting pattern within the area. The Tahoe and Truckee basins are separated from one another by a range of Miocene and younger volcanics that tower 500 - 700 m above the nearby basins. Thirty magnetotelluric (MT) soundings were acquired in June, 2009 along a 25 km E/W transect between the Tahoe and Truckee Basins. Thes transect extends from the high Sierras to the Carson Range, and crosses the northward projection of several major normal faults in the Tahoe Basin, including the Tahoe Sierra Frontal Fault Zone, the West Tahoe Fault, the Dollar Point Fault, and the Agate Bay Fault. In contrast to south Lake Tahoe where Sierran granite is readily exposed, the majority of the transect is covered by Pleistocene volcanics and/or glacial deposits. The two-dimensional MT resistivity model images a symmetric 2.5-km-deep basin with significant vertical offset in the granitic basement (500 - 1000 m) along at least six faults, several of which can be traced northward from the Tahoe Basin. This general structure is strikingly similar to that of the Tahoe Basin proper (2 kms from range crest to lake bottom). Offsets within the imaged sediments further indicate that deposition began before the onset of Plio-Pleistocene extension. Taken together, these findings suggest that the Tahoe and Truckee Basins represent a single basin that has been subsequently divided by Pleistocene volcanism, N/S shortening, or a combination of the two.

In the Fra Cristobal Range near Truth or Consequences, New Mexico, 250 to 500 m(820 to 1640 ft) of relative basement uplift is present. The contact between Precambrian crystalline basement and cover strata (Cambrian and younger) is folded along a north-south deformation front defining the margin of the Laramide uplift. The style of deformation changes along strike from an overturned fold to a central domain of imbricate thrusts of Precambrian granite, overlying a gentle anticline of cover strata, and then back to an overturned fold. These changes in style occur across narrow transition zones characterized by transverse folds and tear faults, suggesting some control from basement structure. West-dipping, high-angle reverse faults and south-plunging S-folds on the overturned eastern limb of the south-plunging, basement-involved anticline suggest eastward vergence with the basement, in part forcing the fold in the cover strata. Closely spaced fractures are present in the granite hinge of the main overturned, basement-cored fold. Abundant microfaults with grains visibly offset are present in thin section. These features indicate a cataclastic flow mechanism to accommodate shortening strain in the core of the fold. The structural styles of the basement-involved Laramide deformation are similar to Berg's fold-thrust model; shortening in the basement is accommodated by imbricate thrusting in the central domain and cataclastic flow on a small scale in the basement-cored folds. Preexisting basement structure may have controlled the location of structural transitions within the belt of crustal shortening and uplift, and movement of basement blocks may have in part forced the observed folding.

The Hutti-Maski Greenstone Belt (HMGB), situated in the eastern block of the Dharwar Craton, India is dominated by bimodal volcanics with a minimum magmatic age of 2586 ± 59 Ma. Two phases of granitoid intruded into the belt, the syn-tectonic Kavital granitoid, homogeneous, medium-grained porphyritic granodiorite, with an intrusion age of 2543 ± 9 Ma, followed by the post-tectonic Yelagatti granitoid, heterogeneous, fine- to medium-grained granite to granodiorite. The extensively altered zircons from the Yelagatti granitoid have significant enrichments of U, Th (>1%) and common-Pb (up to 47%). Only two of the analyses were reproducible, providing a minimum 207Pb/206Pb age of 2221 ± 99 Ma, this may indicate an approximate magmatic age or more realistically a subsequent event. Felsic metavolcanic rocks contain cross-cutting veinlets, which formed during the Mesoproterozoic (ca. 1180 Ma), the final closure of the Pb system occurred between the Neoproterozoic and Ordovician, possibly related to the Pan-African orogeny. The tectono-magmatic evolution of the HMGB can be correlated with the collision between the eastern and western blocks of the Dharwar Craton subsequent to 2658 Ma and the craton wide magmatism from 2613 to 2513 Ma. These events can be accounted for by combining uniformitarian and non-uniformitarian models.

As part of EUROPROBE's SW Iberia project a deep seismic reflection profile was acquired along one of the most complete transects of the Variscan Orogen (IBERSEIS). The seismic profile crosses two sutures that separate three main tectonic terranes: the South Portuguese Zone, Ossa-Morena Zone and Central Iberian Zone. A preliminary interpretation of the seismic data includes the definition of the geometry of the most prominent sutures such as the Beja-Acebuches ophiolite and Badajoz-Cordoba shear zone. A prominent lower crustal seismic fabric is observed along the involved terranes. The South Portuguese Zone features a typical geometry of a thrust and fold belt architecture. The high resolution achieved by the relatively close receiver and shot spacing has imaged very detailed structures within this thin-skinned tectonic unit, including thrust stacks and duplexes. The Ossa-Morena Zone is characterized by the presence of folded recumbent folds and thrusts. Due to the high resolution, sub-vertical contacts can be identified, helping to understand the strain partitioning of the transpressional tectonics. Furthermore, the seismic data reveal contacts and internal structure of granitic intrusions.

The Umm Nar BIF was formed in a sedimentary environment. It is confined to an upper stratigraphic zone of pre-Pan-African metamorphosed shelf deposits. During the Pan-African deformational history, the BIF and the host metasediments were tectonically' overlain by ophiolitic melange succession. The metasediments and the mélange were subjected to a major folding phase and then thrust over the “Shaitian” sheared granite, prior to the intrusion of syn- to late- orogenic granitoids. The BIF is divisible into two main types: oxide-bands including magnetite and hematite, and oxide-silicate bands including magnetite, hematite and stilpnomelane. The associated gangues are quartz, calcite, epidote, garnet, plagioclase, graphite and muscovite. Rhythmic banding and lamination, cross-lamination and flaser structure are the most prominent primary features in the IF bands. The iron minerals and the associated gangue show a variety of textural aspects and microscopic interrelationships which indicate successive episodes of mineral accumulation and formation, involving deposition, recrystallization, blastic growths, overgrowths, replacement and deformations, during continuous burial and subsequent tectonic deformations.

Data acquired with the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) of the Mountain Pass, San Bernadino County, California, area were analyzed to evaluate the use of narrow-band imaging data for carbonatite exploration. Carbonatites are igneous carbonate-rich rocks that are economically important in part because they are the major source for rare-earth minerals. Because the 224 AVIRIS spectral channels have a nominal spectral resolution of 10 nm, narrow absorption features such as those displayed by the rare-earth elements neodymium (Nd) and samarium (Sm) may be detected. The Mountain Pass region encompasses a well-exposed sequence of sedimentary, metamorphic, and igneous rocks, including an alkalic carbonatite intrusion. The carbonatite was emplaced in Precambrian granitic rocks that are fault bounded by a thick suite of Paleozoic, sedimentary rock, predominantly dolomite. The carbonatite stock, the major source of light rare-earth elements (REE) in the United States, affords the opportunity to test AVIRIS capabilities for detecting REE absorption features. Nd-bearing minerals display narrow, sharp and distinctive spectral features at 580, 740, 800, and 870 nm. Minerals bearing Sm display similarly sharp features near 1090, 1250, 1410, and 1550 nm. The more common REE, lanthanum and cerium, do not display absorption features in the visible/near-infrared region in their natural oxidation states.

Southeastern New England is subdivided into three major fault bounded tectonic terranes, each with a distinctive metamorphic history. The easternmost, the Avalon Terrane, has generally been metamorphosed no higher than the lower greenschist facies. Evidence for pre-Alleghanian metamorphism includes a Proterozoic Z(.) event, contact metamorphism adjacent to Ord.-Dev. alkaline plutons, and granulite facies crustal xenoliths in Mesozoic dikes. To the west the Nashoba Terrane has been deformed and polymetamorphosed to the sill. and 2nd sill. zones between approximately 415 and 450 m.y., based on ages of associated granitic and migmatitic rocks. 730 m.y. assumed basement gneisses (fish Brook) have likely experienced Late PC metamorphism. In the Merrimack Trough, here including the Massabesic Gneiss, the metamorphic grade ranges from the greenschist facies on the east to the 2nd sillimanite zones on the west toward the Massabesic. The two metamorphic events present here must predate the intrusion of the Exeter Diorite (473 m.y .), indicating one or both may be PC. To the east, the fault bounded Rye Formation has also experienced two pre- 470 m.y. metamorphisms (and -sill.) However, the terrane east of the Turtle Head Fault Zone (THFZ) has many similarities to the Boston Platform including general (Late PC.) lower greenschist metamorphism. Also, the area between the Norumbega FZ and the THFZ has experienced high grade metamorphism of probable Silurian age and thus may be similar to the Nashoba Terrane.

A combined study of zircon U-Pb ages and Lu-Hf isotopes, whole-rock elements and Sr-Nd isotopes was carried out for two granitic intrusions at Changawuzi and Alasan in Muzhaerte River of Southwest Tianshan (NW China). SHRIMP zircon U-Pb dating gave two ^2^0^6Pb/^2^3^8U ages of 333+/-3Ma and 326+/-3Ma for the Changawuzi pluton. LA-ICP-MS zircon U-Pb dating yielded two ^2^0^6Pb/^2^3^8U ages of 293+/-3Ma and 294+/-2.2Ma for the Alasan pluton. The two groups of ages predate and postdate the UHP metamorphic event at 320-305Ma in this region, respectively, registering to syn-subduction and post-collisional magmatism. The Changawuzi pluton is composed of gneissic porphyritic tonalite and garnet-bearing gneissic granitoids, having SiO2 of 55.1-64.5wt.%, K2O+Na2O of 2.58-5.07wt.%, MgO of 2.07-4.32w...

Lithium isotope signatures of whole rock pegmatite samples and mineral separates from the rare element-bearing Little Nahanni Pegmatite Group, NWT, and whole rock samples from nearby granitic intrusions were measured. Correlation of the Li isotopic values from the pegmatite dikes with whole rock trace element geochemistry, mineralogy and primary textural evidence reflect mechanisms of Li isotopic fractionation during pegmatite formation. The heavier ?7Li signatures within the broad range measured from whole rock LNPG samples (- 0.94‰ to + 11.36‰) are related to the consolidation of the final ~ 15% melt fraction of a volatile-rich peraluminous magma in the late stages of magmatic fractionation. Rock-forming minerals (quartz, albite, spodumene and mica) display ?7Li signatures that indicate consolidation of the dikes under variable, non-equilibrium conditions. Lithium isotope signatures of relatively cool, highly evolved peraluminous magmas reflect the build-up of fluxes (e.g., H2O and F) and provide a qualitative assessment of the state of mineral/melt chemical equilibrium.

The central Appalachian Piedmont between the Occoquan River in Virginia and Liberty Reservoir in Maryland is characterized by tectonic motifs of precursory melange-thrust sheet pairs. In Virginia, the lowest tectonic motif (Indian Run-Melange-Annandale Group) (IA) is overlain by the Sykesville melange-Mather Gorge formation tectonic motif (SM), which is overlain by the Yorkshire melange-Piney Branch Complex tectonic motif. The Piney Branch is a tectonic melange of ultramafic and mafic rocks. The thrust sheets were deformed and metamorphosed prior to emplacement above their melanges. Hornblende from second generation amphibolite within the Mather gorge Formation cooled beneath 500 C isotherm at about 490 Ma. The assembled tectonic motifs were folded before emplacement of the Falls Church Intrusive Suite (481 Ma) and Occoquan Granite (479 Ma) that constitute part of a magmatitic arc in the area. In Maryland, the SM is tectonically underlain by the Laurel melange-Loch Raven Schist tectonic motif (LL), which appears to be more proximal in origin. These tectonic motifs are, in part, separated by a shear zone that experienced early sinistral strike slip and later dextral strike slip. Both tectonic motifs are intruded by the Kensington Tonalite (543 Ma), which experienced both the sinistral and dextral shear. This shear zone separates the LL from the IA, and their relation is unknown. All the motifs are interpreted to have been assembled during the Penobscot orogeny in an oceanic trench an unknown distance from the Laurentian margin.

Manley Hot Springs is one of several hot springs which form a belt extending from the Seward Peninsula to east-central Alaska. All of the hot springs are low-temperature, water-dominated geothermal systems, having formed as the result of circulation of meteoric water along deepseated fractures near or within granitic intrusives. Shallow, thermally disturbed ground at Manley Hot Springs constitutes an area of 1.2 km by 0.6 km along the lower slopes of Bean Ridge on the north side of the Tanana Valley. This area includes 32 springs and seeps and one warm (29.1/sup 0/C) well. The hottest springs range in temperature from 61/sup 0/ to 47/sup 0/C and are presently utilized for space heating and irrigation. This study was designed to characterize the geothermal system present at Manley Hot Springs and delineate likely sites for geothermal drilling. Several surveys were conducted over a grid system which included shallow ground temperature, helium soil gas, mercury soil and resistivity surveys. In addition, a reconnaissance ground temperature survey and water chemistry sampling program was undertaken. The preliminary results, including some preliminary water chemistry, show that shallow hydrothermal activity can be delineated by many of the surveys. Three localities are targeted as likely geothermal well sites, and a model is proposed for the geothermal system at Manley Hot Springs.

Each Circum-Pacific Tectonic Map sheet gives a tectonic synopsis of one-eighth of the earth's surface and contains enough detail to illustrate specifics of individual regions. The maps show the active plate margins and the contrasting oceanic and continental crustal domains. Crustal domains are further subdivided into cover rocks and basement complexes. In the oceanic crustal domain, successive episodes of sea-floor spreading are color coded. These episodes seem to correlate between distant oceanic regions and may reflect worldwide changes in plate kinematics. Oceanic plateau, seamount, and island volcanic rocks are shown by patterns; their ages are color coded. Sedimentary cover is indicated by isopachs. At convergent plate margins, where allochthonous microcontinents represent older basement complexes, three main types of units are shown: magmatic arcs, forearc sediments, and accretionary prism rocks. The continental crustal domain is divided into basement rocks, transitional and reactivation sequences, and cover rocks. Basement includes metamorphic, intrusive, and deformed sedimentary and volcanic rocks. Color coding indicates age of metamorphism, emplacement, and deformation. Transitional sequences are defined as deposits directly succeeding major deformation in orogenic regions and preceding platform-strata deformation. Igneous rocks include most felsic volcanics, bimodal volcanics in rifts, and postkinematic granites and associated volcanics. Sedimentary rocks include molasselike deposits, commonly in foreland basins, foredeeps or intradeeps, and grabens. Reactivation sequences comprise deposits unrelated to preceding tectonism, except for inherited structural control. These sequences are related to plate collisions exemplified by basin related to collision of the Indian plate with the Asian plate.

Hulsite, Sn bearing Fe borate, was found from the Sengendera skarn deposit which formed by high temperature pneumatolytic metasomatism derived from intrusion of the Okueyama granite mass. It occurred as radiating aggregate of acicular and columnar crystals up to 1 cm, associated closely with magnetite, diopside and tremolite-actinolite, and rarely occurred as chemical sector zone within vonsenite crystals. It is black in color and opaque zones with metallic luster. Cleavages is not distinct. Color of reflection is gray. Monoclinic cell dimensions are a=10.695(4), b=3.102(1), c=5.431(1) Å, ?=94.21(3)°. The empirical formula of hulsite from Sengendera skarn deposit is (Fe1.5132+Mg0.459Mn0.023)?1.995(Fe0.7923+ Sn0.204Al0.002)?0.998B1.015O5, and range of Sn content is 9.06 to 11.88 wt%. The average Sn content of vonsenite, an Fe-borate, from Sengendera mine is 1.40 wt%. Hulsite domain within vonsenite crystals was probably formed at lower temperature on account of high Sn content more than 4 wt% SnO2.

Precambrian and Paleozoic basements are present in southern Mexico and Central America, where several crustal blocks are recognized by their different geologic record, and juxtaposed along lateral faults. Some of those crustal blocks are currently located between southernmost north America (the Maya block) and Central America (Chortis block).To better understand the geology of these crustal blocks, and to establish comparisons between their geologic history, U-Pb ages of both igneous and metasedimentary key units cropping out in central and western Guatemala are presented here. In the Altos Cuchumatanes (Maya block) granites yield both Permian (269 +/- 29 Ma) and Early Devonian (391 +/- 7.4 Ma) U-Pb ages. LA-ICPMS detrital zircon ages from rocks of the San Gabriel sequence, interpreted as the oldest metasedimentary unit of the Maya block, and overlain by the Late Paleozoic Upper Santa Rosa Group, yield Precambrian detrital zircons bracketed between 920 Ma and 1,000 Ma. The presence of these metasedimentary units, as well as Early Devonian to Silurian granites in the Mayan continental margin, from west (Altos Cuchumatanes), to east (Maya Mountains of Belize) indicate a more or less continuous belt of Lower Paleozoic igneous activity, also suggesting that the continental margin of the Maya block can be extended south of the Polochic fault, up to the Baja Verapaz shear zone. A metasedimentary sample belonging to the Chuacus Complex yielded detrital zircons with ages between 440 Ma and 1,325 Ma. The younger ages are similar to the igneous ages reported from the entire southern Maya continental margin, and show proximity of the Complex in the Middle-Late Palaeozoic. The S. Diego Phyllite, which overlies high-grade basement units of the Chortis block, contains zircons that are Lower Cambrian (538 Ma), Mesoproterozoic (980 to 1,150 Ma) and even Paleoproterozoic (1,820 Ma). Absence of younger igneous zircons in the San Diego Phyllite indicates that either its sedimentation took place in a close range of time, during the Late Cambrian, or absence of connection between Chortis and Maya blocks during the Early-Mid Palaeozoic. The Precambrian zircons could have come from southern Mexico (Oaxaca and Guichicovi Complexes), or from Mesoprterozoic Massifs exposed in Laurentia and Gondwana. Paleogeographic models for Middle America are limited to post-Jurassic time. The data presented here shed light on Paleozoic and, possibly, Precambrian relationships. They indicate that Maya and the Chortis did not interact directly until the Mesozoic or Cenozoic, as they approached their current position.

Age determinations were conducted on detrital zircon grains from two stratigraphic levels in the Postmasburg Group, Transvaal Supergroup - the top of the Makganyene Formation and the base of the Hotazel Formation - to constrain the age of the group and for comparison with purported correlatives in the Segwagwa Group of the Kanye basin and Pretoria Group of the Transvaal basin. Detrital zircon grains are interpreted as being derived mainly from the underlying Ghaap Group and its basement of Ventersdorp Supergroup and Kraaipan granite/greenstone rocks, indicating a proximal source to the east and north on the Vryburg arch. The maximum age of the Postmasburg Group was constrained by the youngest detrital-zircon age to 2436 ± 7 Ma and the broad age range of the group, as a consequence, to somewhere between 2.43 and 2.38 Ga. Comparison with various stratigraphic units in the Kanye and Transvaal basins indicated close similarities in zircon populations with the Duitschland Formation in the Transvaal basin. The Pretoria and Segwagwa Groups contain younger zircon populations at 2350-2320 and 2240-2200 Ma that are related to syn-depositional volcanic activity and are not present in the Postmasburg Group samples, indicating the younger age of these groups. Based on compatibility of zircon populations, new stratigraphic correlations between the upper groups of the Transvaal Supergroup in the Griqualand West, Kanye and Transvaal basins are proposed. These include the probable restriction of the lower Timeball Hill - Hekpoort portion of the Pretoria Group to the Transvaal basin. An older age for the Postmasburg Group - ?2.4 Ga as opposed to the generally accepted 2.22 Ga - will affect various models proposed for the evolution of the Earth's atmosphere/hydrosphere that have been based on studies of rocks of the group, supporting an older ?2.4 Ga age for global oxidation transformations.

The Alnö complex on the central Swedish east coast is composed of a main composite intrusion (the main intrusion) and four smaller satellite intrusions (Söråker, Sälskär, Långharsholmen and Båräng) distributed around the main intrusion on Alnö Island and on the mainland north of the island. The m...

The alkali-calcic Castle Mountains Volcanic rocks (CMV) are host to major gold mineralization. They are located about 100 km south of Las Vegas, Nevada and are on the boundary between the Basin and Range Province and Colorado River extensional corridor (35[degree]18 minutes 45 seconds N, 115[degree]05 minutes 10 seconds W). New data show the following chronology. 22 Ma. A regional rhyolite ash-flow tuff, the Castle Mountain Tuff member, was deposited on a Proterozoic-Paleozoic basement of low relief. <22 Ma - > 17 Ma. Normal faulting (N30--60[degree]W, 60--65[degree]NE) formed half-grabens. Latite and basalt flows, minor ash-flow tuffs, lahars and sediments (Jacks Well member - JW) were deposited unconformably. JW magmas are enriched in light REE compared to the younger CMV. <17 Ma to 15.5 Ma. Oxidizing upper portions (796 C) of a shallowly emplaced silicic melt erupted to form the high-silica rhyolite dome complexes and intrusives (Linder Peak member - LP) of the NNE-striking Castle Mountains. NW-striking transverse structures caused discontinuities in strike direction of the subvolcanic intrusive and domes and helped form a synvolcanic depression. During a hiatus in volcanism, early Hart Peak member (HP) sediments were deposited marginal to the Castle Mountains. Major gold mineralization and widespread hydrothermal alteration occurred at about 15.5 Ma. 16 Ma to 14 Ma. Early HP volcaniclastic sediments, rhyolite pyroclastic-surge tuff, and basaltic flows, were deposited during late hydrothermal alteration and then fractured and displaced by NNE-striking normal faults, especially in the eastern and northeastern CMV. < 14 Ma. Tectonically significant flat-lying boulder conglomerate and unconformably overlying, largely andesitic flows fill depressions in the Castle Mountains and the Piute Range to the east.

Archean greenstones occur in South Pass area and southern Wind River Canyon area in central Wyoming State, U.S.A. These two areas are near about 100 km away from each other and belong to the same sub- province named Wyoming greenstone province (WGP, composed of meta-mafic rocks and meta- sedimentary rocks) (Mueller et al., 1998). The South Pass area is one of the greenstone belts in the southern Wyoming Province and is located in the northwestern part of the WGP. The greenstones (15 km long) occur along the later Archean granitic batholith (Louis Lake batholith, 2.63 Ga) and are composed of meta-pillow lavas, meta diabasic rocks, meta-gabbroic rocks, meta basaltic tuffs, and other meta sediments. The meta diabasic rocks occur as dykes. Banded iron formation lies along the contact between these greenstones and the batholith. Several previous studies suggested that these greenstones were metamorphosed under conditions of amphibolite, and locally greenschist (Harper et al., 1985; Wilks and Harper, 1997; Frost et al., 2000). However we found evidence indicating limited distribution of the amphibolite facies zone which is restricted along the batholith. Greenstones in this area were regionally metamorphosed under low-grade and the amphibolite facies greenstones were formed by the thermal effects by the batholith. Many characteristics of the protolith are well preserved. The following textures are preserved; pillow lava structure, relic igneous augite grains in meta basaltic rocks, relic igneous brown hornblende grains in meta diabasic rocks, gabbroic textures, and some sedimentary textures. The pillow lavas (5-10 cm x 15-30 cm) are composed of pale green core and thin dark gray rim (about 0.5 cm wide) and the core domain is rich in carbonate. The southern Wind River Canyon area is located in the northern part of the WGP. Archean greenstones in this area are composed of meta pillow lavas, meta gabbroic rocks, and meta pelites. From south toward north, mafic rocks generally grade into pelitic rocks. All the greenstones were metamorphosed under a condition of amphibolite and no relic of protolith minerals are preserved. Ring structures suggesting pillow lavas (core, 20- 30 cm x 30-50 cm; rim, 1.0-3.0 cm wide) occur in fine-grained mafic greenstones. Skarn (several cm to several tens cm in scale) occurs only near these ring structures and cuts the greenstones. This skarn is cut by granite intrusions. Both the South Pass area and the southern Wind River Canyon area are possibly regarded as upper part of Archean oceanic crust. The South Pass greenstones were regionally metamorphosed under low-grade (lower greenschist facies). Amphibolite facies greenstones were formed by thermal effects by the granitic batholith. The southern Wind River Canyon greenstones were subjected to amphibolite facies regional metamorphism and no thermal effect by the granites was observed. Archean skarn occurs only in the southern Wind River Canyon area. What did make these differences between Archean greenstones in the South Pass area and the southern Wind River Canyon area? Comparisons of greenstones between these two areas are significant for the formation of the Archean greenstones and the formation of Archean skarn in these areas.

Seventeen {sup 40}Ar/{sup 39}Ar ages for hornblende, celadonitic muscovite, and biotite from the Pelona, Orocopia, Rand, and Portal Ridge (POR) schists range from 39 to 85 Ma. Two muscovites and one hornblende from the Rand Schist have ages of 72 to 74 Ma, indistinguishable from the K-Ar age of 74 Ma for hornblende from a posttectonic granodiorite that intrudes the schist, but younger than the 70 Ma U-Pb age of the intrusion. Four muscovite and two hornblende ages for schist and mylonite from the East Fork area of the San Gabriel Mountains range from 55 to 61 Ma. Concordance of schist and upper plate ages confirms structural and metamorphic evidence that the Vincent thrust in the San Gabriel Mountains has not undergone significant postmetamorphic disruption. Ages from the Orocopia Mountains are 75 Ma for hornblende from nonmylonitic upper plate, 52 Ma for muscovite from structurally high Orocopia Schist that is mylonitic, and 41 Ma for muscovite from nonmylonitic Orocopia Schist. These are consistent with field evidence that the Orocopia thrust is a postmetamorphic normal fault. Muscovite and hornblende from the Gavilan Hills have ages of 48 to 50 Ma, younger than ages from the San Gabriel Mountains but similar to schist ages from the Orocopia Mountains. The geochronologic and structural complexities of the Vincent, Chocolate Mountains, Orocopia, and Rand thrusts imply that previously cited northeastward vergence may not relate to prograde metamorphism (subduction) of the POR schists. The data indicate substantial uplift of the POR schists prior to middle Tertiary detachment faulting, which confirms other geochronologic evidence of uplift in southern California and southern Arizona during the Late Cretaceous-early Tertiary.

U-Pb ages were determined on metamorphic sphenes and monazites from the Late Proterozoic Adirondack Highlands and Lowlands in the vicinity of the Carthage-Colton mylonite zone. Monazites were extracted from metapelites, and sphenes were separated from marbles, calc-silicate gneisses, and granite gneisses in order to determine the timing and the duration of metamorphism as well as the cooling histories for rocks on either side of the mylonite zone. Monazite ages from the Lowlands range from 1,171-1,137 Ma; sphene ages in the Lowlands range from 1,156-1,103 Ma, those from the Highlands immediately to the east of the mylonite zone range from 1,050-982 ma. The ages indicate that the last high-grade metamorphism in the Highlands is ca. 100 m.y. younger than in the Lowlands and that both terranes had separate cooling histories at least until ca. 1,000 Ma. Sphenes from within the Carthage-Colton mylonite zone yield ages of about 1,098 Ma, which are distinct from sphene ages on either side of the shear zone. The mineral ages, structures, and metamorphic histories suggests that the Carthage-Colton mylonite zone is a fundamental tectonic boundary within the Proterozoic Grenville Orogen of North America.

La Crosa de Sant Dalmai volcano is one of the most representative volcanic edifices of the Catalan Volcanic Zone (NE Spain). It is a very well preserved maar-type structure, of 1.5 km in diameter, which was excavated at the contact between a hard and a soft substrate formed by Palaeozoic granites and Quaternary gravels, respectively. In order to infer the uppermost inner structure of La Crosa de Sant Dalmai maar we have performed a multiparametric geophysical study including gravimetry, magnetometry, self potential, and electric resistivity tomography. The results obtained, together with a field geology revision and a 15 m probing information from a borehole drilled inside the maar crater, have permitted to get a detailed 3D picture of the post-eruptive maar infill sequence as well as of the uppermost part of the maar-diatreme structure, which helps to understand its origin and posterior evolution. In this sense, it is worth mentioning the little erosion and degradation suffered by original tuff ring, which accounts for a much younger age, probably Holocene, of La Crosa de Sant Dalmai maar than it was previously stated

Tha data on natural radioactivity of rocks (U, Th and K contents) from the Moon, Venus and Mars obtained by means of cosmic means are analyzed. The Moon rock radioactivity has been measured in situ (from orbital vehicles) as well as in the samples of lunar material delivered to the Earth and as for Venus and Mars rocks - by landing vehicles. It has been found that the main specific feature of the Moon and the Earth group planets is the presence of two geomorphological types of the structure of their surface composed by two different types of the matter. The ancient continent regions are made up by feldspar rock - gabbroanorthosite at the Moon (and possibly at the Mars) and granite-metamorphic at the Earth (and possibly at the Venus). The younger ''marine'' regions are composed by basalt rock. The presence at the Moon of two types of crust (marine and continental ones) having a different nature is clearly reflected on the Moon radioactivity map where marine regions (15% of the total surface) which have high radioactivity and continental regions with a relatively low radioactivity can be seen. The discovery of rocks on the Venus surface highly enriched by U, Th and K speaks of their melting from the primary matter in the depth of the Earth. The Marsian rock by the natural radioelement content is close to igneous rocks of the Earth crust of the basic composition and lunar marine basalts.

The emplacement of anorogenic magmas, be they mantle-derived or crust-derived and silica-undersaturated or silica-oversaturated, marks a period of rifting or tectonic relaxation and apparent quiescence. In a given area, such magmatism commonly recurs episodically, and can yield even more strongly alkaline products than in the first cycle, in spite of the depletion that resulted from that episode of melting. Anorogenic magmatism is said to be punctuated where it recurs, in response to a triggering mechanism. The second cycle reflects an influx of heat and a fluid phase responsible for the fertilization of the depleted source-rock. In cases of an anorogenic stage after a major collision, the first cycle of magmatism, yielding an AMCG suite, arises by gravity-induced sinking of lithosphere and the diapiric rise of an asthenospheric mantle; renewed magmatism may involve localized and renewed detachment as late as 200 m.y. after the collision. Where the hiatus is much longer, as in Nigeria, we appeal to a propagating zipper-like zone of extension, possibly related to rotation of a crustal block. The economic ramifications of punctuated anorogenic magmatism are important; the second-generation magmas may well crystallize products that are mineralized in the high-field-strength elements and any other elements enriched in the source rocks. Such a model would account for the rich deposits of alluvial columbite, zircon and cassiterite associated with the Younger Granites of Nigeria.

The Eoarchaean (>3,600 Ma) Itsaq Gneiss Complex of southern West Greenland is dominated by polyphase orthogneisses with a complex Archaean tectonothermal history. Some of the orthogneisses have c. 3,850 Ma zircons, and they vary from rare single phase metatonalites to more common complexly banded migmatites. This is due to heterogeneous strain, in situ anatexis and granitic veining superimposed during younger tectonothermal events. In the single-phase tonalites with c. 3,850 Ma zircon, oscillatory-zoned prismatic zircon is all 3,850 Ma old, but shows patchy ancient loss of radiogenic Pb. SHRIMP spot analyses and laser ablation ICP-MS depth profiling show that thin (usually shells of lower Th/U metamorphic zircon are present on these 3,850 Ma zircons. Several samples with this simple zircon population occur on islands near Akilia. In contrast, migmatites usually contain more complex zircon populations, with often more than one generation of igneous zircon present. Additional zircon dating of banded gneisses across the Complex shows that samples with c. 3,850 Ma igneous zircon are not just a phenomenon restricted to Akilia and adjacent islands. For example, migmatites from Itilleq (c. 65 km from Akilia) contain variable amounts of oscillatory-zoned 3,850 Ma and 3,650 Ma zircon, interpreted, respectively, as the rock age and the time of crustal melting under Eoarchaean metamorphism. With only 110-140 ppm Zr in the tonalites and likely magmatic temperatures of >850°C, zircon solubility-melt composition relationships show that they were only one-third saturated in zircon. Any zircon entrained in the precursor magmas would thus have been highly soluble. Combined with the cathodoluminesence imaging, this demonstrates that the c. 3,850 Ma oscillatory zoned zircon crystallised out of the melt and hence gives a magmatic age. Thus the rare well-preserved tonalites and palaeosome in migmatites testify that c. 3,850 Ma quartzo-feldspathic rocks are a widespread (but probably minor) component in the Itsaq Gneiss Complex. C. 3,850 Ma zircon with negative Eu anomalies (showing growth in felsic systems) also occurs as detrital grains in rare c. 3,800 Ma metaquartzites and as inherited grains in some 3,660 Ma granites ( sensu stricto). These demonstrate that still more c. 3,850 Ma rocks were present, but were recycled into Eoarchaean sediments and crustally derived granites. The major and trace element characteristics (e.g. LREE enrichment, HREE depletion, low MgO) of the best-preserved c. 3,850 Ma rocks are typical of Archaean TTG suites, and thus argue for crust formation processes involving important contributions from melting of hydrated mafic crust to the earliest Archaean. Five c. 3,850 Ma tonalites were selected as the best preserved on the basis of field criteria and zircon petrology. Four of these samples have overlapping initial ?Nd (3,850 Ma) values from +2.9 to +3.6± 0.5, with the fourth having a slightly lower value of +0.6. These data provide additional evidence for a markedly LREE-depleted early terrestrial mantle reservoir. The role of c. 3,850 Ma crust should be considered in interpreting isotope signatures of the younger (3,800-3,600 Ma) rocks of the Itsaq Gneiss Complex.