Sample records for geobarometry

  1. Geobarometry of ultramafic xenoliths from Loihi Seamount, Hawaii, on the basis of CO2 inclusions in olivine (United States)

    Roedder, E.


    Abundant fluid inclusions in olivine of dunite xenoliths (???1-3 cm) in basalt dredged from the young Loihi Seamount, 30 km southeast of Hawaii, are evidence for three coexisting immiscible fluid phases-silicate melt (now glass), sulfide melt (now solid), and dense supercritical CO2 (now liquid + gas)-during growth and later fracturing of some of these olivine crystals. Some olivine xenocrysts, probably from disaggregation of xenoliths, contain similar inclusions. Most of the inclusions (2-10 ??m) are on secondary planes, trapped during healing of fractures after the original crystal growth. Some such planes end abruptly within single crystals and are termed pseudosecondary, because they formed during the growth of the host olivine crystals. The "vapor" bubble in a few large (20-60 ??m), isolated, and hence primary, silicate melt inclusions is too large to be the result of simple differential shrinkage. Under correct viewing conditions, these bubbles are seen to consist of CO2 liquid and gas, with an aggregate ??{variant} = ??? 0.5-0.75 g cm-3, and represent trapped globules of dense supercritical CO2 (i.e., incipient "vesiculation" at depth). Some spinel crystals enclosed within olivine have attached CO2 blebs. Spherical sulfide blebs having widely variable volume ratios to CO2 and silicate glass are found in both primary and pseudosecondary inclusions, demonstrating that an immiscible sulfide melt was also present. Assuming olivine growth at ??? 1200??C and hydrostatic pressure from a liquid lava column, extrapolation of CO2 P-V-T data indicates that the primary inclusions were trapped at ??? 220-470 MPa (2200-4700 bars), or ??? 8-17 km depth in basalt magma of ??{variant} = 2.7 g cm-3. Because the temperature cannot change much during the rise to eruption, the range of CO2 densities reveals the change in pressure from that during original olivine growth to later deformation and rise to eruption on the sea floor. The presence of numerous decrepitated inclusions indicates that the inclusion sample studied is biased by the loss of higher-density inclusions and suggests that some part of these olivine xenoliths formed at greater depths. ?? 1983.

  2. Determination of pressure from measured Raman frequency shifts of anhydrite and its application in fluid inclusions and HDAC experiments (United States)

    Yuan, Xueyin; Mayanovic, Robert A.; Zheng, Haifei


    A new geobarometry was derived from the quantified relationships among Raman vibrational frequencies of anhydrite, pressure and temperature, as determined from in-situ micro-Raman spectroscopy of natural anhydrite crystals measured at p-T conditions up to 560 °C and 1400 MPa by using a hydrothermal diamond anvil cell (HDAC). With this geobarometry, the pressure in HDAC experiments and in anhydrite-bearing fluid inclusions can be determined directly from the ν1, 1016, ν3, 1128 and ν3, 1160 Raman frequency shifts of anhydrite at high p-T conditions relative to their values measured at ambient conditions. The pressure can be determined to an accuracy of better than 30 MPa based on the attainable accuracy of ±0.1 cm-1 for the fitted ν1 Raman peak positions, provided the measured spectra are calibrated using the emission peak of an external fluorescent light source. The feasibility and reliability of this geobarometry were verified by rebuilding the p-T history of two fluid inclusions from the ν1 frequency shifts of anhydrite daughter minerals from room to high temperatures, and by measuring the phase-transition pressures of calcite-CaCO3(II)-CaCO3(III) sequence at ambient temperature in a HDAC experiment using anhydrite as a Raman pressure sensor.

  3. Native iron in the continental lower crust: petrological and geophysical implications. (United States)

    Haggerty, S E; Toft, P B


    Lower crustal granulite xenoliths recovered from a kimberlite pipe in western Africa contain native iron (Fe(0)) as a decomposition product of garnet and ilmenite. Magnetic measurements show that less than 0.1 percent (by volume) of iron metal is present. Data from geothermometry and oxygen geobarometry indicate that the oxide and metal phases equilibrated between iron-wüstite and magnetite-wüstite buffers, which may represent the oxidation state of the continental lower crust, and the depleted lithospheric upper mantle. Ferromagnetic native iron could be stable to a depth of approximately 95 kilometers and should be considered in the interpretation of long-wavelength static magnetic anomalies.

  4. Observation on foreshore morphodynamics of microtidal sandy beaches

    Digital Repository Service at National Institute of Oceanography (India)

    Dora, G.U.; SanilKumar, V.; Philip, C.S.; Johnson, G.

    CURRENT SCIENCE, VOL. 107, NO. 8, 25 OCTOBER 2014 1324 *For correspondence. (e-mail: calc-alkaline granitoids, Eastern Desert of Egypt, and tectonic im- plications. J. Afr. Earth Sci., 2004, 38, 255–268. 15. Enami, M., Suzuki, K., Liou, J... transport from epidote dissolution kinet- ics. Science, 1996, 271, 1845–1848. 20. Ghent, E. D., Nicholls, J., Simony, P. S., Sevigny, J. H. and Stout, M. Z., Hornblende geobarometry of the Nelson Batholith, south- eastern British Columbia: tectonic...

  5. A 3D Magnetotelluric Perspective on the Galway Granite, Western Ireland (United States)

    Farrell, Thomas; Muller, Mark; Vozar, Jan; Feely, Martin; Hogg, Colin


    Magnetotelluric (MT) and audi-magnetotelluric (AMT) data were acquired at 75 locations across the exposed calc-alkaline Caledonian Galway granite batholith and surrounding country rocks into which the granite intruded. The Galway granite is located in western Ireland on the north shore of Galway bay, and has an ESE-WNW long axis. The granite is cut by trans-batholith faults, the Shannawona Fault Zone (SFZ) in the western part of the batholith, which has a NE-SW trend, and the Bearna Fault Zone (BFZ) in the eastern sector that has a NW-SE trend. Geobarometry data indicate that the central granite block between these fault zones has been uplifted, with the interpretation being that the granite in this central block is thinned. To the west of the SFZ, much of the Galway granite is below sea level, with the majority of the southern granite contact also beneath the sea in Galway bay. To the east of the batholith, the Carboniferous successions, consisting of mainly limestone with shale, overlie the basement rocks. The country rock to the north includes the metagabbro-gneiss suite, which itself intruded the deformed Dalradian successions that were deposited on the Laurentian margin of the Iapetus Ocean. The deformation of the Dalradian rocks, the intrusion of the metagabbro-gneiss suite and the intrusion of the Galway granite were major events in the protracted closure of the Iapetus Ocean. It is clear from geological mapping, from geobarometry and from the present submergence by the sea of a large part of the Galway granite, that inversion of MT data in this structurally complex geology is likely to require a 3D approach. We present a summary of 3D inversion of the Galway MT and AMT data. The study shows that the structure of the Galway granite is quite different from the pre-existing perspective. The central block, thought by its uplifting to be thinned, is shown to be the thickest part of the batholith. A geological model of granite intrusion is offered to explain this

  6. Granulites: Melts and fluids in the deep crust (United States)

    Valley, John W.


    Known examples of granulite facies metamorphism span at least 3.5 by. of Earth history. Mineralogic geobarometry indicates that such metamorphism has occurred in the deep crust, typically at 20 to 30 km (6 to 9 kbar). Geothermometry indicates that peak T = 700 to 900 C and therefore that T was elevated by at least 200 C over an anorgenic geotherm of 15 to 20 C/km. Commonly invoked sources of heat include rising magmas, radioactive decay insulated by continent/continent collision, mantle volatiles, or crustal thinning. Present day crustal thicknesses are normal beneath exposed granulite terranes and the common absence of evidence for post-metamorphic underplating suggests synmetamorphic thicknesses of 60 to 80 km. Thus granulites form in tectonically active regions of thickened crust and elevated geotherm. Xenolith suites suggest that granulite facies mineralogy persists in the deepest crust after tectonism in spite of declining temperature to greenschist/amphibolite facies conditions. The relative proportions of granulite terranes that are formed by Adirondack-type metamorphism dominantly magmatic/fluid-absent), India-type metamorphism (CO2 saturated), or some combination of 1 and 2 remains an important tectonic question.

  7. Crystallisation condition of the Quaternary basanites of volcanic centre Black Rock, monogenetic field Lunar Crater (United States)

    Turova, Mariia; Plechov, Pavel; Scherbakov, Vasily; Larin, Nikolay


    The Lunar Crater volcanic field is located in a tension zone Basin and Range Province (USA). This tension is connected with dives oceanic plate under the continental plate [1]. Lunar Crater consists of flows basalt, basanite, trachybasalt has a different age [2]. In this work we investigate the youngest rock - basanite. The basanite is highly crystalline consisting of about megacrysts (3-10 cm) 30-60 wt% phenocrysts ( 800-1500 µm) and microphenocrysts (100-800 µm) and 40-60% microlites (stress and style of tectonism of the Basin and Range province of the western United States //Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences. - 1981. - T. 300. - №. 1454. - C. 407-434. 2. Wood, X., and Keinle, Y., 1990, Volcanoes of North America: Cambridge,United Kingdom, Cambridge University Press, 354 p. 3. Nimis P. Clinopyroxene geobarometry of magmatic rocks. Part 2. Structural geobarometers for basic to acid, tholeiitic and mildly alkaline magmatic systems //Contributions to Mineralogy and Petrology. - 1999. - T. 135. - №. 1. - C. 62-74. 4. Ballhaus C., Berry R. F., Green D. H. High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: implications for the oxidation state of the upper mantle //Contributions to Mineralogy and Petrology. - 1991. - T. 107. - №. 1. - C. 27-40.

  8. Petrochemistry and mineral chemistry of Late Permian hornblendite and hornblende gabbro from the Wang Nam Khiao area, Nakhon Ratchasima, Thailand: Indication of Palaeo-Tethyan subduction (United States)

    Fanka, Alongkot; Tsunogae, Toshiaki; Daorerk, Veerote; Tsutsumi, Yukiyasu; Takamura, Yusuke; Endo, Takahiro; Sutthirat, Chakkaphan


    In the Wang Nam Khiao area, Nakhon Ratchasima, northeastern Thailand, there are various mafic-ultramafic plutons composed of hornblendite, hornblende gabbro and hornblende microgabbro. The rocks are generally dominated by hornblende, plagioclase and clinopyroxene. The mineral chemistry and whole-rock geochemistry of hornblendite, hornblende gabbro and hornblende microgabbro show their similarities, suggesting a close relationship of their magmatic evolution. The flat REE pattern and low HREE concentration indicate fractional crystallization from hydrous magma. The enrichment in LILE (e.g. Ba, K, Sr) and depletion of HFSE (e.g. Nb, Ta, Zr) together with compositions of clinopyroxene and hornblende reflect arc-related subduction. Hornblende-plagioclase geothermometry and Al-in-hornblende geobarometry indicate the PT conditions of crystallization are 5.3-9.8 kbar and 670-1000 °C, 7.6-9.0 kbar and 850-950 °C, and 7.6-8.8 kbar and 750-850 °C for hornblendite, hornblende gabbro and hornblende microgabbro, respectively, at the lower crustal depth (28-31 km). Zircon U-Pb age of hornblende microgabbro dike, that intruded into hornblendite, yields 257 Ma of intrusion age, suggesting the emplacement of the mafic-ultramafic rock in this area is related to Late Permian arc magmatism resulted from subduction of Palaeo-Tethys beneath Indochina Terrane.

  9. Tertiary tilting and dismemberment of the laramide arc and related hydrothermal systems, Sierrita Mountain, Arizona (United States)

    Stavast, W.J.A.; Butler, R.P.; Seedorff, E.; Barton, M.D.; Ferguson, C.A.


    Multiple lines of evidence, including new and published geologic mapping and paleomagnetic and geobarometric determinations, demonstrate that the rocks and large porphyry copper systems of the Sierrita Mountains in southern Arizona were dismembered and tilted 50?? to 60?? to the south by Tertiary normal faulting. Repetition of geologic features and geobarometry indicate that the area is segmented into at least three major structural blocks, and the present surface corresponds to oblique sections through the Laramide plutonic-hydrothermal complex, ranging in paleodepth from ???1 to ???12 km. These results add to an evolving view of a north-south extensional domain at high angles to much extension in the southern Basin and Range, contrast with earlier interpretations that the Laramide systems are largely upright and dismembered by thrust faults, highlight the necessity of restoring Tertiary rotations before interpreting Laramide structural and hydrothermal features, and add to the broader understanding of pluton emplacement and evolution of porphyry copper systems. ?? 2008 Society of Economic Geologists, Inc.


    Institute of Scientific and Technical Information of China (English)


    The Tan-Lu fault zone joins the Dabie Mountains on its eastern margin, and offsets the Dabie and Sulu orogenic belts sinistrally for about 500 km. On the basis of calculation of temperature and pressure experienced by the two phases of the fault zone as well as the thermo-chronological information on mylonite from the earlier and later Tan-Lu fault zones on the eastern margin of the Dabie Mountains, this paper discusses the delamination history and uplifting magnitudes of the Dabie Mountains from earlier Jurassic to earlier Cretaceous. From mineral assemblages, mineral deformation and muscovite-chlorite geothermometry calculation, it is known that the temperature experienced by the two phases of Tan-Lu fault zones are between 400℃ and 450℃, and the confining pressures are between 0.25Gpa and 0.36GPa for the earlier shear zones and 0.24-0.39GPa for the late shear zones. According to the geobarometry of Si-in-phengite and by considering shear heating and tectonic over-pressure, it is concluded that the maximum formation depths for the two phases of the ductile shear zones are not more than 12 km.Differential formation depths for the two phases of shear zones are 1-2 km at most. At about 190 Ma and 128 Ma, the Tan-Lu fault zone experienced two phases of cooling events. During this period, the eastern margin of the Dabie Mountains experienced a tectonic calm period and no uplifting. According to information from the Tan-Lu fault zone, the uplifting magnitudes of the Dabie orogenic belts are not more than 12 km during the earlier Cretaceous.

  11. Evolution of the Xiaotian-Mozitan fault and its implications for exhumation of Dabie HP-UHP rocks

    Institute of Scientific and Technical Information of China (English)

    Biwei Xiang; Yongsheng Wang; Changcheng Li; Guang Zhu; Yonghong Shi


    The Xiaotian-Mozitan fault (XMF) located north of the Dabie orogenic belt separates the North Dabie complex to the south from the Beihuaiyang low-grade metamorphic rocks to the north. It comprises several NW-striking ductile shear zones and brittle faults. The brittie faults obviously overprinted on the ductile shear zones and promoted the development of the volcanic basins in early Cretaceous to the north, which suggests that the brittle faults were normal faults formed in early Cretaceous during doming of the Dabie orogenic belt. The ductile shear zone superposed on the north Dabie gray gneiss. and it is an important channel where the Dabie HP-UHP rocks exhumed. For obtaining new structural constraint on exhumation of the HP-UHP rocks, we present here experimental results on the microstructure, quartz C-axis fabrics and the microprobe analyses of phengite. The ductile shear zone was determined to be formed at a temperature of 600-650℃ and pressure of 1.1GPa by the mineral deformation, microprobe analyses and geobarometry of Siin-phengite of the mylonite, the results suggest that the mylonite now exposed on the surface experienced an upper amphibolite-facies metamorphism in the lower crust. The mineral stretching lineation varies from horizontal in the east segment to sub-dip in the west. Shear sense indicators from outcrop and thin sections of orientated specimen and quartz C-axis fabrics suggest that the XMF is a sinistral normal fault. The kinematics analysis of the ductile shear zone indicates that the exhumation of Dabie HP-UHP rocks is the results of a SE-directed extrusion and an anticlockwise rotation around its eastern pivot simultaneously.

  12. 40Ar/39Ar hornblende and biotite geochronology of the Bulfat Igneous Complex, Zagros Suture Zone, NE Iraq: New insights on complexities of Paleogene arc magmatism during closure of the Neotethys Ocean (United States)

    Aswad, Khalid J.; Ali, Sarmad A.; Al. Sheraefy, Ruaa M.; Nutman, Allen P.; Buckman, Solomon; Jones, Brian G.; Jourdan, F.


    In NE Iraq, the eastern edge of the Arabian plate is overlain by arc rock allochthons whose genesis and tectonic emplacement were related to the consumption and closure of the Neotethys Ocean. This paper demonstrates the occurrence of unrelated Paleogene arc rocks in two adjacent allochthons. The Bulfat Igneous Complex at Wadi Rashid (NE Iraq) is an intrusion within the Upper Allochthon Albian-Cenomanian Gimo-Qandil sequence suprasubduction zone assemblage. A thrust separates this allochthon from the underlying Lower Allochthon of the Eocene-Oligocene Walash-Naopurdan volcanic-sedimentary arc rocks. The Bulfat Igneous Complex at Wadi Rashid consists of gabbro and granitic composite intrusions in which components mingle down to a small scale. Textural relationships in the Bulfat Igneous Complex rocks indicate emplacement at high crustal levels with rapid cooling, which is consistent with amphibole geobarometry indicating crystallisation pressures between 250 and 300 Mpa. Ti-rich igneous pargasite and Ti-rich igneous Fe-biotite from gabbroic and granitic components yielded 40Ar/39Ar ages of 39.23 ± 0.21 and 38.87 ± 0.24 Ma respectively. These ages agree within analytical error and suggest coeval emplacement and rapid cooling of mafic and felsic magmas in the Eocene, in an event that was distinct and much younger than the host Albian-Cenomanian rocks. This igneous event was unrelated to formation of Cenozoic rocks in the underlying, tectonically separate, lower allochthon. The trace element signatures of the Wadi Rashi volcanic rocks show volcanic-arc characteristics for the granites and the gabbroic rocks resemble E type MORB. The presence of Eocene arc-related rocks in two allochthons suggests complexity in Paleogene subduction systems, with possibly two subduction zones operating at that time.

  13. M1 Site Splitting Due to Next Nearest Neighbor Effects and Ferric Iron in Tetrahedral Site in Clinopyroxene Megacrysts

    Institute of Scientific and Technical Information of China (English)

    李一良; 李玉芝; 等


    It is well known that in pyroxene structure,there are two metal sites,M1 and M2.Generally speaking,Ferrous iron in each of these sites would normally be expected to give rise to a doublet,However,anomalies have been found in the relative areas of the peaks in the room temperature spectra of some clinopyroxene(CPX)when the above assignment is followed.According to the calculation of Next Nearest Neighbor configurations of divalent cations in M1,we found that the four configurations of M1 can be divided into two groups.One group is 3Ca configuration that increases with the content of Ca(p.f.u);the other group is made up of three No-3Ca configurations that decrease with the content of Ca.The two groups contribute to the spectrum structure of in this study we fit two doublets for ferrous iron in M1.Though there were several reports on Fe3+ in tetrahedral site previously,it was not sure that Fe3+ occupies the T site is a universal fact in CPX,despite of the content of Al.We found that the Fe3+ in the T site fitted by Moessbauer spectroscopy is negatively correlated to the Si content in the T site and positively correlated to the Fe3+ in the T site estimated on the supposition that Fe3+ and Al occupy the T site randomly.If it is is important in the modeling of ion exchange geobarometries and geothermomeries.

  14. Petrological significance of the abyssal peridotites from the ophiolite belt of Indo-Myanmar Range, northeastern India (United States)

    Maibam, B.; Foley, S.


    The ophiolite belt of the Indo-Myanmar Range of northeastern India is regarded as the continental extension of the Indonesia island arc. The ophiolite sequence forms a belt extending about 200 km from Pukhpur (Nagaland state) in the north to Moreh (Manipur state) in the south. Here we report preliminary mineralogical and phase geochemical data of peridotites collected from the ophiolite sequences of the Ukhrul district in Manipur. Primary minerals are clinopyroxene, orthopyroxene and spinel with scarce relicts of olivine. Andraditic garnet present in a few samples is of secondary origin. The clinopyroxene and orthopyroxene show limited compositional range. Well's (1977) single clinopyroxene thermometry yielded variable equilibrium temperature between 780-1250oC. The lower temperature value suggests post-crystallisation re-equilibration. Equilibrium pressure estimates based on Nimis and Ulmer's single clinopyroxene (1998) and Köhler and Brey's (1990) olivine-spinel geobarometries range from 19 to 25 kbars. Oxygen fugacity expressed in terms of quartz-fayalite-magnetite (Delta QFM) value is calculated as -1.32. Spinel Cr# (Cr/(Cr+Al)) of the peridotites reflects mantle residues after low degree of melting (F = 0.5 - 11%) if derived from primitive mantle. Mineral composition tectonomagmatic discrimination diagrams confirm the studied samples to be abyssal peridotites. Laser Ablation ICPMS analyses of the rare earth element patterns of clinopyroxene in the peridotites show depleted light rare earth element with flat middle and heavy rare earth element patterns, similar to the reported abyssal peridotites. References Wells P.R.A. (1977) CMP, 62, 129-139. Nimis P., Ulmer P. (1998) CMP, 133, 122-135. Köhler T., Brey G.P. (1990) GCA, 54, 2375-2388.

  15. Deciphering petrogenic processes using Pb isotope ratios from time-series samples at Bezymianny and Klyuchevskoy volcanoes, Central Kamchatka Depression (United States)

    Kayzar, Theresa M.; Nelson, Bruce K.; Bachmann, Olivier; Bauer, Ann M.; Izbekov, Pavel E.


    The Klyuchevskoy group of volcanoes in the Kamchatka arc erupts compositionally diverse magmas (high-Mg basalts to dacites) over small spatial scales. New high-precision Pb isotope data from modern juvenile (1956-present) erupted products and hosted enclaves and xenoliths from Bezymianny volcano reveal that Bezymianny and Klyuchevskoy volcanoes, separated by only 9 km, undergo varying degrees of crustal processing through independent crustal columns. Lead isotope compositions of Klyuchevskoy basalts-basaltic andesites are more radiogenic than Bezymianny andesites (208Pb/204Pb = 37.850-37.903, 207Pb/204Pb = 15.468-15.480, and 206Pb/204Pb = 18.249-18.278 at Bezymianny; 208Pb/204Pb = 37.907-37.949, 207Pb/204Pb = 15.478-15.487, and 206Pb/204Pb = 18.289-18.305 at Klyuchevskoy). A mid-crustal xenolith with a crystallization pressure of 5.2 ± 0.6 kbars inferred from two-pyroxene geobarometry and basaltic andesite enclaves from Bezymianny record less radiogenic Pb isotope compositions than their host magmas. Hence, assimilation of such lithologies in the middle or lower crust can explain the Pb isotope data in Bezymianny andesites, although a component of magma mixing with less radiogenic mafic recharge magmas and possible mantle heterogeneity cannot be excluded. Lead isotope compositions for the Klyuchevskoy Group are less radiogenic than other arc segments (Karymsky—Eastern Volcanic Zone; Shiveluch—Northern Central Kamchatka Depression), which indicate increased lower-crustal assimilation beneath the Klyuchevskoy Group. Decadal timescale Pb isotope variations at Klyuchevskoy demonstrate rapid changes in the magnitude of assimilation at a volcanic center. Lead isotope data coupled with trace element data reflect the influence of crustal processes on magma compositions even in thin mafic volcanic arcs.

  16. Early Alleghanian oblique dextral extension and magmatism along the Modoc fault zone, eastern Appalachian Piedmont, SC-GA

    Energy Technology Data Exchange (ETDEWEB)

    Sacks, P.E. (Western Michigan Univ., Kalamazoo, MI (United States). Geology); Secor, D.T. Jr. (Univ. of South Carolina, Columbia, SC (United States). Geological Sciences); Maher, H.D. Jr. (Univ. of Nebraska, Omaha, NE (United States). Geography and Geology); Wright, J. (Rice Univ., Houston, TX (United States). Geology and Geophysics); Dallmeyer, R.D. (Univ. of Georgia, Athens, GA (United States). Geology)


    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.

  17. The Petrogenesis of the Late Cretaceous Mamba Pluton from the Eastern Gangdese: Constraints from Mineralogy (United States)

    Li, X.


    Occurred as stock,the late Cretaceous Mamba pluton, located at the southeast part of the Gangdese terrane, was one of the granitoid intrusions in the Mesozoic-Cenozoic Gangdese gaint magmatic belt, which is composed of Southern Gangdese, Gangdese back-arc fault uplift belt, Middle Gangdes, The Shiquanhe-Laguo Tso-Yongzhu-Nam Tso-Jiali Ophiolitic Méange Zone, and northern Gangdese from south to north, bounded by Indus-Yarlung Zangbo suture zone to the south, and Bangong Tso-Nujiang suture zone to the north(Zhu et al., 2008a), and the Mamba Pluton intruded pre-Ordovician Sumdo Group and early formed intrusions(T3, J1, J3), was unconformably overlied by Eocene Pana Formation. The modal mineralogy of selected samples from Mamba Pluton are calculated via Matlab: quartz(25%), plagioclase(40%), K-feldspar(18%), biotite(9%) and hornblende(5%), with subordinate primary epidote(buffers, but very close to NNO buffer, indicationg relatively moderate oxdizing conditions.. Emplacement depths estimated from aluminum-in-hornblende geobarometry indicate that the Mamba Pluton was emplaced at the pressure of c.a.1.33kbar, corresponding to 4.75km in depth.Temperatures of emplacement calculated with the hornblende-plagioclase thermometer range from 645 Celsius to 780 Celsius.Since the Mamba Pluton and contemporary plutons are unconformably overlain by Eocene volcanic rocks, namley Pana Formation regionally, thus the Mamba pluton must have been exposed at(or near) the surface prior to the Eocene, indicating the existence of protoplateau as proposed by Wang et al(2008).

  18. Geochemical and isotopic evidence for the petrogenesis and emplacement tectonics of the Serra dos Órgãos batholith in the Ribeira belt, Rio de Janeiro, Brazil (United States)

    Machado, Rômulo; Philipp, Ruy Paulo; McReath, Ian; Peucat, Jean Jacques


    The Serra dos Órgãos batholith in the State of Rio de Janeiro (Brazil) is a NE-SW-trending elongated body that occupies ca. 5000 km2 in plan view. It is a foliated intrusion, especially at its borders and is crosscut by syn-magmatic shear zones, with foliations that are moderately-to steeply-dipping to the northwest and moderately-to shallow-dipping in the center and to the southeast, in a configuration of a large laccolith. It was emplaced between 560 and 570 Ma, during an extensional episode that was part of a series of events that comprise the Brasiliano Orogeny in SE Brazil, and which includes deformation, metamorphism and granite intrusion during the interval between 630 and 480 Ma. The two main rock types in the batholith are biotite-hornblende monzogranite, and biotite leucogranite, with subordinate tonalite, granodiorite, diorite, quartz diorite (enclaves), aplite and pegmatite. Harker-type diagrams help show two rock groups with similar trends of evolution: a dioritic and a granitic. The first one is tholeiitic, whereas the second is calc-alkaline, with medium-to high-K calc-alkaline affinity and metaluminous to slightly peraluminous character. In both groups strong decrease in Al2O3, MgO, FeOT and CaO relative to silica contents are observed, which is compatible with trends of fractional crystallization involving clinopyroxene and/or hornblende, plagioclase, opaque minerals, apatite, microcline and biotite. The Sr and Nd isotopic data suggest recycling of a Paleoproterozoic crust as an important petrological process to generate the batholith rocks. Geothermometry (amphibole composition) and geobarometry (saturation in zircon and apatite) indicate that most of the batholith solidified at mid to lower crustal levels at about 750 °C and between 5 and 5.5 kbar. We consider that Serra dos Órgãos crustal protoliths underwent melting caused by the interaction with hotter mafic magma at the base of the crust. These two magmas, with distinct initial

  19. Experimental investigation and application of the equilibrium rutile + orthopyroxene = quartz + ilmenite (United States)

    Hayob, J.L.; Bohlen, S.R.; Essene, E.J.


    Equilibria in the Sirf (Silica-Ilmenite-Rutile-Ferrosilite) system: {Mathematical expression} have been calibrated in the range 800-1100?? C and 12-26 kbar using a piston-cylinder apparatus to assess the potential of the equilibria for geobarometry in granulite facies assemblages that lack garnet. Thermodynamic calculations indicate that the two end-member equilibria involving quartz + geikielite = rutile + enstatite, and quartz + ilmenite = rutile + ferrosilite, are metastable. We therefore reversed equilibria over the compositional range Fs40-70, using Ag80Pd20 capsules with {Mathematical expression} buffered at or near iron-wu??stite. Ilmenite compositions coexisting with orthopyroxene are {Mathematical expression} of 0.06 to 0.15 and {Mathematical expression} of 0.00 to 0.01, corresponding to KD values of 13.3, 10.2, 9.0 and 8.0 (??0.5) at 800, 900, 1000 and 1100?? C, respectively, where KD=(XMg/XFe)Opx/(XMg/XFe)Ilm. Pressures have been calculated using equilibria in the Sirf system for granulites from the Grenville Province of Ontario and for granulite facies xenoliths from central Mexico. Pressures are consistent with other well-calibrated geobarometers for orthopyroxeneilmenite pairs from two Mexican samples in which oxide textures appear to represent equilibrium. Geologically unreasonable pressures are obtained, however, where oxide textures are complex. Application of data from this study on the equilibrium distribution of iron and magnesium between ilmenite and orthopyroxene suggests that some ilmenite in deep crustal xenoliths is not equilibrated with coexisting pyroxene, while assemblages from exposed granulite terranes have reequilibrated during retrogression. The Sirf equilibria are sensitive to small changes in composition and may be used for determination of activity/composition (a/X) relations of orthopyroxene if an ilmenite model is specified. A symmetric regular solution model has been used for orthopyroxene in conjunction with activity models

  20. Phase-equilibrium geobarometers for silicic rocks based on rhyolite-MELTS—Part 3: Application to the Peach Spring Tuff (Arizona-California-Nevada, USA) (United States)

    Pamukcu, Ayla S.; Gualda, Guilherme A. R.; Ghiorso, Mark S.; Miller, Calvin F.; McCracken, Reba G.


    Establishing the depths of magma accumulation is critical to understanding how magmas evolve and erupt, but developing methods to constrain these pressures is challenging. We apply the new rhyolite-MELTS phase-equilibria geobarometer—based on the equilibrium between melt, quartz, and two feldspars—to matrix glass compositions from Peach Spring Tuff (Arizona-California-Nevada, USA) high-silica rhyolite. We compare the results to those from amphibole geothermobarometry, projection of glass compositions onto the haplogranitic ternary, and glass SiO2 geobarometry. Quartz + 2 feldspar rhyolite-MELTS pressures span a relatively small range (185-230 MPa), consistent with nearly homogeneous crystal compositions, and are similar to estimates based on projection onto the haplogranitic ternary (250 ± 50 MPa) and on glass SiO2 (255-275 MPa). Amphibole geothermobarometry gives much wider pressure ranges (temperature-independent: ~65-300 MPa; temperature-dependent: ~75-295 MPa; amphibole-only: ~80-950 MPa); average Anderson and Smith (Am Mineral 80:549-559, 1995) + Blundy and Holland (Contrib Miner Petrol 104:208-224, 1990) or Holland and Blundy (Contrib Miner Petrol 116:433-447, 1994—Thermometer A, B) pressures are most similar to phase-equilibria results (~220, 210, 190 MPa, respectively). Crystallization temperatures determined previously with rhyolite-MELTS (742 °C), Zr-in-sphene (769 ± 20 °C), and zircon saturation (770-780 °C) geothermometry are similar, but temperatures from amphibole geothermometry (~450-955 °C) are notably different; the average Anderson and Smith + Holland and Blundy (1994—Thermometer B; ~710 °C) temperature is most consistent with previous estimates. The rhyolite-MELTS geobarometer effectively culls glass compositions affected by alteration or analytical issues; Peach Spring glass compositions that yield pressure estimates reveal a tight range of plausible Na2O and K2O contents, suggesting that low Na2O and high K2O contents of many

  1. Post-collisional high-Mg granitoids from the Paleoproterozoic East Sarmatian Orogen (East European Craton): Evidence for crust-mantle interaction (United States)

    Terentiev, R. A.; Santosh, M.


    The East Sarmatian Orogen (ESO) is located along the southwestern domain of the East European Craton and occupies a key tectonic link between the Sarmatian and Volgo-Uralian domains. Here we investigate the Paleoproterozoic Novaya Melovatka pluton and its mafic-ultramafic xenoliths to gain insights into the role of interaction between intermediate-felsic crustal melt with mantle rocks as a mechanism for the generation of high-Mg granitoids at crustal pressures. The pluton is composed of biotite-orthopyroxene quartz dioritic and monzodioritic porphyrites (Phase 1) and medium-grained biotite-amphibole quartz diorite, tonalite and granodiorite and commingled Phase 1 mafic magmatic enclaves (MME) (Phase 2). The general geochemical characteristics of these rocks are similar to those of Late-Archean high-Mg sanukitoids. The TDM (model) ages for intermediate Phase 1 and granitoid Phase 2 are similar and show a range of 2324-2439 and 2284-2519 M, respectively. The εNd(t) values are grouped around subchondritic values (=+1.4-+1.9 and + 1.1-+2.2) and the initial 87Sr/86Sr ratios are in the range of 0.70202-0.70390. The complex compositional zoning of minerals suggests that the rocks crystallized as synchronous but discrete magma pulses, with limited to significant mixing. Based on the geochemical features we infer that the Phase 1 rocks formed from partial melting of a mantle wedge metasomatized to different degrees by fluids/melts. The presence of MMEs, compositional zoning of minerals including reversely zoned amphiboles, plagioclases with thin calcic overgrowths, and acicular apatite, as well as the whole-rock geochemical features are consistent with a hybrid origin of the high-Mg granitoids belonging to Phase 2. Geobarometry indicates crystallization at upper-crustal depths (i.e. 1.7-2.4 kbar). The igneous suite evolved by fractional crystallization of orthopyroxene, hornblende, plagioclase and biotite. Here we propose a tectonic model involving partial melting of the

  2. Neoproterozic Re-Os age of a sulfide inclusion in a superdeep diamond: Implications for mantle convection beneath Juina, Brazil (United States)

    Shirey, S. B.; Smit, K.; Nestola, F.; Steele, A.; Bulanova, G.; Smith, C. B.


    Diamonds from the Juina area Brazil have long been known for their sublithospheric or superdeep (e.g. from depths of 300-800 km) origins. These diamonds have yielded new information about high pressure mantle mineralogy, deep crustal recycling, diamond source fluids, and mantle transition zone water content. A type II (low N) diamond (sample J1) from the 93.1±1.5 myr old (Heaman 7IKC 1998 ) Collier 4 kimberlite was studied previously (Walter et al. Nature 2008; Bulanova et al. CMP 2010) as part of a larger suite of eclogitic-composition, inclusion-bearing type II Collier 4 diamonds with complex internal growth structure. Major and trace element analyses of mineral inclusions in these diamonds include Ca-Ti-Si perovskite, Ca-rich majoritic-garnet, clinopyroxene, olivine, jeffbenite, minerals with stoichiometries of CAS and K-hollandite phases, SiO2, FeO, native iron, low-Ni sulfides, and Ca-Mg-carbonate. The C isotopic compositions of the diamond hosts range from a δ13C of -25 to -5‰ ( J1 being -15‰). Collier 4 diamonds have been interpreted to crystallize from carbonatitic melts derived from the recycling of oceanic lithosphere at TransitionZone depths (Walter et al. Nature 2008; Bulanova et al. CMP 2010). A rare Fe-sulfide inclusion in the core of diamond J1 has been dated with the Re-Os system in order to provide age and compositional constraints on the proposed oceanic slab recycling. The rim of J1 contained inclusions of Ca-Ti-Si perovskite that yielded U-Pb age of 101±7 Ma and eclogitic (low Cr, high Ca) majorite that yielded formation pressures (Si - Al+Cr geobarometry) >8 GPa (Bulanova et al. CMP 2010). The Fe-sulfide analyzed was low Ni pyrrhotite determined to be Fe10S11 of a rare 11T polytype by single-crystal X-ray diffraction. The 27 ug interior pyrrhotite had a high Re/Os (187Re/188Os = 854) typical of MORB (Re/Os ~100) and radiogenic Os isotopic composition (187Os/188Os = 8.50±1.38) that yields a 602±16 Ma model age relative to normal mantle

  3. Rapid transition to long-lived deep crustal magmatic maturation and the formation of giant porphyry-related mineralization (Yanacocha, Peru) (United States)

    Chiaradia, Massimo; Merino, Daniel; Spikings, Richard


    The Yanacocha magmatic field (northern Peru) hosts the largest high sulfidation gold deposit on Earth. Mineralization is associated with porphyritic intrusions distributed along a NE-trending magmatic structural corridor. Eight of these intrusions investigated in this study range in age from 12.4 to 8.4 Ma and show systematic chemical and isotopic changes through time. They are interpreted to derive from hydrous mafic magmas evolving through amphibole-clinopyroxene ± garnet fractionation and lower crust melting (leaving a garnet residue) at deeper levels, which led to variably strong adakite-like signatures, and through plagioclase-amphibole fractionation at shallower levels, both accompanied by crustal assimilation and recharge (recharge assimilation fractional crystallization, RAFC, processes). Systematic geochemical and isotopic changes with intrusion ages, coupled with plagioclase zoning and amphibole geobarometry, suggest that the evolution of the magmatic system occurred through interaction of mantle-derived melts with an increasing length of the crustal column and propagation from deep towards shallower crustal levels through time. This was probably the result of a steadily increasing compression that has progressively slowed down magma ascent forcing magmas to evolve at a series of intermediate level chambers between the lower and upper crust. Increased compression might have been related to the onset of subduction of the buoyant Inca oceanic plateau, estimated to occur at ˜ 12 Ma, i.e., the same time of the onset of the rapid transition from "normal" to adakite-like signatures. The giant Yanacocha ore system developed in coincidence with the ˜ 3.6-4.0 Ma-long intrusion of the adakite-like magmas (12.4/12.0-8.4 Ma) formed by the above processes into a small upper crustal volume and peaked during the last ˜ 2.4 Ma (10.8-8.4 Ma) of magmatic activity after a ˜ 1.4 Ma long (12.4-11.0 Ma) maturation of magmas at deep crustal levels. Further investigation is

  4. The Lopu Kangri High-Pressure Metamorphic Complex: A Tso Morari Analog in Southern Tibet (United States)

    Laskowski, A. K.; Kapp, P. A.


    The Lopu Range, located along the Yarlung-Tsangpo suture ~600 km west of Lhasa city in southern Tibet, exposes a high-pressure metamorphic complex composed of Indian passive margin (Tethyan) rocks. An integrated approach involving geologic mapping, kinematic analysis, phengite geobarometry, Zr-in-rutile geothermometry, garnet-phengite Fe-Mg exchange geothermometry and pseudosection modeling reveals that Lopu Range meta-Tethyan rocks reached peak pressures of 20-25 kbar (2.0-2.5 GPa) at temperatures <550-630 ºC along a clockwise P-T path. These data indicate subduction to mantle depths (~75 km) at eclogite facies conditions followed by exhumation to mid-crustal depths and retrogression at upper greenschist to amphibolite facies conditions. The structural geometry and interpreted P-T-t history of Lopu Kangri rocks is similar to the Tso Morari complex, located ~700 km along-strike to the northwest. Therefore, we interpret that these two localities formed in a similar manner following the onset of Tethyan Himalaya—Eurasia collision ca. 58-52 Ma. A previously published Ar-Ar date from Lopu Kangri suggests that exhumation to mid-crustal levels occurred by ~41 Ma. Two key differences exist between the Lopu Kangri and Tso-Morari complexes. 1) the high-grade nappe in the Lopu Kangri complex is composed entirely of Cambrian-Ordovician metasedimentary rocks whereas the high-grade nappe in the Tso Morari complex is composed of the Tso Morari orthogneiss, eclogite boudins (meta-mafic enclaves) and Cambrian-Ordovician metasediments. We interpret that the lack of eclogite boudins at Lopu Kangri resulted from the absence of a basic protolith. 2) Lopu Kangri is located along the Yarlung-Tsangpo segment of the Indus-Yarlung (India-Asia) suture whereas Tso Morari and nearby Kaghan Valley are located along the Indus suture. Prior to this study, no continental high-pressure metamorphic complexes were known along the Yarlung-Tsangpo suture. Previously formulated tectonic models

  5. Pressure conditions for the solidification of the Skaergaard intrusion: Eruption of East Greenland flood basalts in less than 300,000 years (United States)

    Larsen, Rune B.; Tegner, Christian


    Primary granophyres are differentiated from olivine tholeiitic magma and occur interstitially throughout the cumulus stratigraphy of the Skaergaard intrusion, East Greenland. Samples from the Lower Zones a-c (LZa-c), the Middle Zone (MZ) and the Sandwich Horizon (SH) are included in the present study together with granophyric accumulations in gabbroic pegmatite from LZa-c. Fluid inclusions in quartz and the mineral assemblage in the granophyres record the pressure under which the Skaergaard intrusion crystallised. Pegmatitic granophyre from LZa-c consists mainly of quartz, plagioclase (An 4-7) and alkali feldspar (Or 40-80) enclosing an earlier formed assemblage of ferrohastingsitic and ferroedenitic hornblende, fayalite (Fo 4-5), titanite, biotite and fluor-apatite. Granophyric quartz, albite and alkali feldspar crystallised from water-saturated granitic melts near eutectic minimum conditions between 680 and 660 °C. The pressure of granophyre crystallisation was modelled by the intercept between fluid inclusion isochores and the minimum melt solidus for granitic compositions. Pressures, recalculated to the roof pendant of the intrusion, are 0.7 ± 0.5 for LZa, 2.0 ± 0.2 for LZb-c, 2.3 ± 0.8 for MZ (the Triple Group level) and 3.3 ± 1.3 kb for SH. Amphibole geobarometry, independently, confirm the pressure estimates for pegmatitic granophyres in LZa-c. The granophyres formed as the intrusion cooled through the minimum melt solidus in LZa, LZb, LZc, MZ and SH, respectively. The pressure increase from LZa to SH granophyres is explained by progressive burial during cooling of the intrusion and contemporaneous outpouring of 5.3-6.3 ± 2.7 km of flood basalts during the initial opening of the Northeast Atlantic Ocean. Accordingly, the Skaergaard intrusion evolved from a subvolcanic magma chamber at emplacement to a more deep-seated igneous system during terminal crystallization when the majority of the intercumulus phases formed. The present cooling history suggests

  6. Progress Towards a Thermo-Mechanical Magma Chamber Forward Model for Eruption Cycles, Applied to the Columbia River Flood Basalts (United States)

    Karlstrom, L.; Ozimek, C.


    Magma chamber modeling has advanced to the stage where it is now possible to develop self-consistent, predictive models that consider mechanical, thermal, and compositional magma time evolution through multiple eruptive cycles. We have developed such a thermo-mechanical-chemical model for a laterally extensive sill-like chamber beneath free surface, to understand physical controls on eruptive products through time at long-lived magmatic centers. This model predicts the relative importance of recharge, eruption, assimilation and fractional crystallization (REAFC, Lee et al., 2013) on evolving chemical composition as a function of mechanical magma chamber stability regimes. We solve for the time evolution of chamber pressure, temperature, gas volume fraction, volume, elemental concentration in the melt and crustal temperature field that accounts for moving boundary conditions associated with chamber inflation (and the possibility of coupled chambers at different depths). The density, volume fractions of melt and crystals, crustal assimilation and the changing viscosity and crustal properties of the wall rock are also tracked, along with joint solubility of water and CO2. The eventual goal is to develop an efficient forward model to invert for eruptive records at long-lived eruptive centers, where multiple types of data for eruptions are available. As a first step, we apply this model to a new compilation of eruptive data from the Columbia River Flood Basalts (CRFB), which erupted 210,000 km3 from feeder dikes in Washington, Oregon and Idaho between 16.9-6Ma. Data include volumes, timing and geochemical composition of eruptive units, along with seismic surveys and clinopyroxene geobarometry that constrain depth of storage through time. We are in the process of performing a suite of simulations varying model input parameters such as mantle melt rate, emplacement depth, wall rock compositions and rheology, and volatile content to explain volume, eruption timescales, and

  7. Crustal structure in the Elko-Carlin Region, Nevada, during Eocene gold mineralization: Ruby-East Humboldt metamorphic core complex as a guide to the deep crust (United States)

    Howard, K.A.


    The deep crustal rocks exposed in the Ruby-East Humboldt metamorphic core complex, northeastern Nevada, provide a guide for reconstructing Eocene crustal structure ???50 km to the west near the Carlin trend of gold deposits. The deep crustal rocks, in the footwall of a west-dipping normal-sense shear system, may have underlain the Pin??on and Adobe Ranges about 50 km to the west before Tertiary extension, close to or under part of the Carlin trend. Eocene lakes formed on the hanging wall of the fault system during an early phase of extension and may have been linked to a fluid reservoir for hydrothermal circulation. The magnitude and timing of Paleogene extension remain indistinct, but dikes and tilt axes in the upper crust indicate that spreading was east-west to northwest-southeast, perpendicular to a Paleozoic and Mesozoic orogen that the spreading overprinted. High geothermal gradients associated with Eocene or older crustal thinning may have contributed to hydrothermal circulation in the upper crust. Late Eocene eruptions, upper crustal dike intrusion, and gold mineralization approximately coincided temporally with deep intrusion of Eocene sills of granite and quartz diorite and shallower intrusion of the Harrison Pass pluton into the core-complex rocks. Stacked Mesozoic nappes of metamorphosed Paleozoic and Precambrian rocks in the core complex lay at least 13 to 20 km deep in Eocene time, on the basis of geobarometry studies. In the northern part of the complex, the presently exposed rocks had been even deeper in the late Mesozoic, to >30 km depths, before losing part of their cover by Eocene time. Nappes in the core plunge northward beneath the originally thicker Mesozoic tectonic cover in the north part of the core complex. Mesozoic nappes and tectonic wedging likely occupied the thickened midlevel crustal section between the deep crustal core-complex intrusions and nappes and the overlying upper crust. These structures, as well as the subsequent large

  8. A LA-ICP-MS study of minerals in the Rocche Rosse magmatic enclaves: Evidence of a mafic input triggering the latest silicic eruption of Lipari Island (Aeolian Arc, Italy) (United States)

    Davì, Marcella; De Rosa, Rosanna; Barca, Donatella


    resident fractionated magmas and triggered the eruption. A plumbing system of this type has been shown to be active in the southern sector of the Aeolian Islands since the last 42 ka [Gioncada, A., Mazzuoli, R., Milton, A., 2005. Magma mixing at Lipari (Aeolian Islands, Italy): Insights from textural and compositional features of phenocrysts. J. Volcanol. Geotherm. Res. 145, 97-118; Peccerillo, A., Frezzotti, M.L., De Astis, G., Ventura, G., 2006. Modeling the magma plumbing system of Vulcano (Aeolian Islands, Italy) by integrated fluid-inclusion geobarometry, petrology and geophysics. Geology 34, 17-20]. It is concluded that the hazard assessment of Lipari Island should take into account the arrival of deep and never erupted mafic melts as eruption triggers of more evolved shallower magma bodies.

  9. High-Ti, bright-CL rims in volcanic quartz: a result of very rapid growth (United States)

    Pamukcu, Ayla S.; Ghiorso, Mark S.; Gualda, Guilherme A. R.


    Volcanic quartz commonly contains Ti-enriched zones and CO2-enriched melt inclusions, and crystallization temperatures and pressures derived from Ti-in-quartz geothermobarometry and H2O-CO2 glass geobarometry applied to these compositions are typically high. Consequently, these features are generally interpreted to represent high temperatures and/or pressures. Yet, growth rate estimates from some high-Ti/bright-CL quartz rims suggest they grew at rates orders of magnitude faster than did cores and interiors of the crystals. This observation is notable in light of studies that suggest that fast crystal growth rates can produce a boundary layer in the melt surrounding a growing crystal that is enriched in components that diffuse comparatively slowly in the melt. In these circumstances, the composition of zones or melt inclusions formed from such a boundary layer melt will not accurately represent that of the far-field melt, and temperatures and pressures estimated from these compositions will be anomalous. We use a numerical model based on the coupled growth-diffusion equation of Lasaga (1982) to assess the effect of growth rate on the production of high-Ti/bright-CL zones and high-CO2 melt inclusions in quartz in rhyolitic melts. Simulations span a wide range of growth rates (10-7 to 10-13 m/s) and timescales (1 minute-1 year), and results suggest that quartz growth at 10-10 m/s or faster can produce a boundary layer enriched in these components. This suggests that appropriate application of Ti-in-quartz and H2O-CO2 glass geothermobarometry is contingent upon the verification that the compositions used are not those of boundary layer melts. Applying our model to the Bishop Tuff, which contains quartz displaying high-Ti/bright-CL rims and high-CO2 rim-hosted melt inclusions, we find that growth rates of 10-7 to 10-9 m/s can produce the observed enrichments in these components over the timescales estimated for the growth of the rims (days-weeks); these growth rates

  10. Single inclusion piezobarometry confirms high-temperature decompression path for Variscan granulites (United States)

    Angel, Ross; Alvaro, Matteo; Mazzucchelli, Mattia; Nimis, Paolo; Nestola, Fabrizio


    temperatures. The extension of single inclusion piezobarometry to elastically anisotropic minerals will allow quantitative analysis of diamonds trapped in other minerals such as kyanite. This work was supported by ERC starting grant 307322 to Fabrizio Nestola and by the MIUR-SIR grant "MILE DEEp" (RBSI140351) to M. Alvaro. Angel R.J., Mazzucchelli M.L., Alvaro M., Nimis P. & Nestola F. (2014) Geobarometry from host-inclusion systems: the role of elastic relaxation. Am. Mineral., 99, 2146-2149. Angel R.J., Nimis P., Mazzucchelli M.L., Alvaro M. & Nestola F. (2015) How large are departures from lithostatic pressure? Constraints from host-inclusion elasticity. J. Metamorphic Geol., 33, 801-813. Kotková J, O'Brien P.J & Ziemann M.A. (2011)Diamond and coesite discovered in Saxony-type granulite: Solution to the Variscan garnet peridotite enigma. Geology, 39, 667-670.

  11. Thermobarometry for spinel lherzolite xenoliths in alkali basalts (United States)

    Ozawa, Kazuhito; Youbi, Nasrrddine; Boumehdi, Moulay Ahmed; Nagahara, Hiroko


    geothermobarometry based on reactions with large and distinct volume changes, is necessary. Specification of mineral domains and their components representing the thermal state of the mantle just before xenolith extraction is one of the major tasks for the establishment of reliable geothermobarometry for spinel lherzolite xenoliths. Systematic variations of such mineralogical information among xenoliths transported by a single volcanic eruption guarantees proper estimation of a mantle geotherm. For the development of such geobarometry, it is important to choose appropriate xenolith locality, where previous studies provide enough information and where many xenolith samples are available for extending a range of derivation depth. Spinel lherzolite xenoliths in alkali basalts from Bou Ibalhatene maars in the Middle Atlas in Morocco are suitable study target. Geochemical, geochronological, petrological, and rheological aspects of the spinel lherzolite xenoliths have been studied (Raffone et al. 2009; El Messbahi et al., 2015; Witting et al., 2010; El Azzouzi et al., 2010), which show that they represent fragments of the lithospheric mantle formed and modified since 1.7Ga before their extraction from Miocene to recent. We have pinpointed portions of minerals in the xenolith samples and their components representing condition just before their entrapment in magmas, on which appropriate geothermobarometers are applied and detected ~0.5GPa pressure difference (1.5-2.0GPa) for ~100°C variation in temperatures (950-1050°C).

  12. Grain-scale pressure variations recorded in orthopyroxene from the diamond grade ultra-high pressure Svartberget peridotite body, Western Gneiss Region, Norway (United States)

    Vrijmoed, Johannes C.


    The ultra-high pressure (UHP) area in the Western Gneiss Region (WGR) in Norway is recognized as a giant UHP domain that resulted from the collision of Baltica and Laurentia during the Caledonian Orogeny. Recent geochronological data suggest the WGR resided at UHP for several tens of millions of years and slowly exhumed near- isothermally to amphibolite facies conditions. The Svartberget peridotite body is located in the north-westernmost part of the UHP area of the WGR. The rocks record diamond grade peak metamorphism at ~800 ° C in crosscutting pyroxenite veins as evidenced by micro-diamond inclusions in Caledonian metamorphic garnet. The peridotite body preserves primary spinel-garnet-peridotite assemblages stable at much lower pressure (~2.0 GPa at ~800 ° C). Orthopyroxene typically shows bowl-shaped aluminium (Al) zoning and conventional geothermobarometry using core compositions of garnet-opx mineral pairs yields P-T estimates of 5.5 GPa at ~800 ° C. Besides Al increasing toward the rims of orthopyroxene grains, concentrations also increase in cracks and veins crosscutting the mineral. Here, recently developed unconventional geobarometry and Gibbs minimization methods are used to derive the grain-scale pressure variations corresponding to the observed Al-zoning. The methods independently result in pressure variations from core to rim on the order of 2.0 GPa. Interestingly, low-Al cores correspond to low pressures whereas high-Al rims correspond to high pressures, opposite to conventional geothermobarometry results. However, the new estimates are in agreement with the consideration that at high pressure the high density phases become more stable. In a binary orthopyroxene in the MAS-system, the Mg-Tschermak endmember thought to be the dominant Al-species in the mineral has a higher density then the Al-free enstatite endmember. Therefore at higher pressure the Mg-Tschermak endmember in orthopyroxene is favoured over the enstatite endmember. This is similar

  13. Magmatic-hydrothermal fluid evolution of the Dalli porphyry Cu-Au deposit; using Amphibole and Plagioclas mineral chemistry

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    Houshang Pourkaseb


    used as an indicator for characterizing the conditions involved during the evaluation of magma crystallization i.e., pressure, temperature, liquid water content and oxygen fugacity. Most recent studies on the porphyry copper intrusions in the Urumieh- Dokhtar magmatic arc by (Zarasvandi et al., 2015a, indicate that all of the mineralized porphyry systems (Dalli porphyry is included consistently show high levels of La/Sm and Sm/Yb, with concave upward patterns in the rare earth elements’ spider diagrams. Importantly, such features indicate high crustal assimilation in a relatively thickened crust and provide insight into the contribution of hornblende during the development of mineralized porphyry systems in the Urumieh- Dokhtar belt. The results of this study indicate that amphiboles of Dalli intrusions belong to the calsic group and range in composition from magnesio- hornblende, to edenite, magnesiohastingsite, and tschermakite. (Ridolfi et al., 2010, indicating that the alumina content of amphibole could be used for geobarometry. The calculations of geobarometry for quartz diorite intrusions of Dalli indicate that they formed in the pressure range of 136 to 287 (MPa. Also, calculation of magmatic water content using amphibole geochemistry indicates that the water content of quartz diorite intrusions in the Dalli were between 4.6- 5.7 (wt. %. The results of plagioclase chemistry indicate that there is a little zoning in this mineral. Also, the plagioclase composition varies from Or0.01 to Ab 0.48, An 0.50, Or 0.018, Ab 0.62 and An 0.35. They mostly have Andesine and Labradorite compositions. Discussion Amphibole minerals of the Dalli intrusions are calcic type and exhibit geochemical signatures of subduction zones. Also, characterizing the source of ore-hosting intrusions with amphibole chemistry indicate that parental magma of Dalli intrusion were generated from mixing of mantle melts with crustal materials. It seems that in an ongoing process of closure of Neo

  14. Application of Clinopyroxene Chemistry to Interpret the Physical Conditions of Ascending Magma, a Case Study of Eocene Volcanic Rocks in the Ghohrud Area (North of Isfahan

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    Mohammad Sayari


    authors would like to thank the University of Isfahan, and Dr. Seyed Mohsen Tabatabaei Manesh for his help for doing microprobe analyses. References Dilek, Y., Imamverdiyev, N. and Altunkaynak, S., 2010. Geochemistry and tectonics of Cenozoic volcanism in the Lesser Caucasus (Azerbaijan and the peri-Arabian region: collision-induced mantle dynamics and its magmatic fingerprint. International Geology Review, 52(4-6: 536-578. Nimis, P. and Ulmer, P., 1998. Clinopyroxene geobarometry of magmatic rocks. 1. An expanded structural geobarometer for anhydrous and hydrous, basic and ultrabasic systems. Contributions to Mineralogy and Petrology, 133(1-2: 122-135. Putirka, K., 2008. Thermometers and Barometers for Volcanic Systems. Reviews in Mineralogy and Geochemistry, 69(1: 61-120. Putirka, K., Johnson, M., Kinzler, R. and Walker, D., 1996. Thermobarometry of mafic igneous rocks based on clinopyroxene-liquid equilibria, 0-30 kbar. Contributions to Mineralogy and Petrology, 123(1: 92-108. Sayari, M., 2012. APG: An efficient software program for Amp-Pl thermobarometry based on graphical method. Journal of Sciences, Islamic Republic of Iran, 22(4: 345-349. Sayari, M., 2015. Petrogenesis and evolution of Oligocene-Pliocene volcanism in the central part of Urumieh-Dokhtar Magmatic Arc (NE of Isfahan. Ph.D Thesis, University of Isfahan, Isfahan, Iran, 195 pp (in Persian with English abstract. Sayari, M. and Sharifi, M., 2014. SCG: A computer application for single clinopyroxene geothermobarometry. Italian Journal of Geosciences 133(2: 315-322.

  15. The evaluation of physico-chemical parameters of the Nasrand Plutonic complex by using mineral composition

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    Fatemeh Sarjoughian


    al., 1997. Actinolitic probably crystallized as a subsolidus phase. Pyroxene in the dikes is clinopyroxene with augite- diopside composition (Morimoto, 1988. Discussion The total Al content of hornblende is a sensitive linear function of crystallization pressure and temperature (Schmidt 1992; Holland and Blundy, 1994. However, the computed pressure may reflect the level at which the hornblende crystallizes rather than the pressure at which the granite consolidates. Therefore, Al content in hornblende geobarometer is only applicable in the presence of quartz and plagioclase; alkali feldspars, biotite, hornblende, clearly limit compositional influences (Ague, 1997. Oxygen fugacity has a marked effect on the mineral system, so only hornblendes with Fe/(Fe+Mg < 0.65, Si ≤7.5 and Ca ≥1.6 were used for geobarometry and are not applicable to subsolidus actinolite (Stein and Dietl, 2001. The average formation pressure in the intrusive rocks is evaluated to be 1.54 kbar by Schmidt (Schmidt, 1992 and Anderson and Smith (Anderson and Smith, 1995 equations, which is consistent with a depth of 5.9 Km, whereas the average pressure of amphibole crystallization in the dioritic dikes is calculated to be about 2.96 Kbar by the Ridolfi equation (Ridolfi et al., 2010, indicating 11.4 Km depth. The estimated pressure for clinopyroxene crystallization in the dikes is calculated to be about 4–8 kbar by the Soesoo (Soesoo, 1997 and Putirka (Putirka, 2008 equations which is reflecting the initial crystallization pressure of pyroxene from magma which corresponds to depths of about 15-30 km. The average formation temperature of the intrusive rocks and amphiboles in dioritic dikes is estimated to be 700 and 940 °C respectively, by the Holland and Blundy (Holland and Blundy, 1994, Vyhnal et al. (Vyhnal et al., 1991, and Ridolfi et al. (Ridolfi et al., 2010 equations. The highest temperatures from pyroxene thermometry in the dikes is about 1150 – 1250 °C by Soesoo (Soesoo, 1997 and