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Mineral Chemistry Indicates the Petrogenesis of Rhyolite From The Southwestern Okinawa Trough

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Journal of Ocean University of China 2017年第6期16卷 1097-1108页

作者： CHEN Zuxing ZENG Zhigang WANG Xiaoyuan ZHANG Yuxiang YIN Xuebo CHEN Shuai MA Yao LI Xiaohui QI Hanyan Key Laboratory of Marine Geology and Environment Institute of Oceanology Chinese Academy of SciencesQingdao 266071 P. R. China Laboratory for Marine Mineral Resources Qingdao National Laboratory for Marine Science and TechnologyQingdao 266071 P. R. China University of Chinese Academy of Sciences Beijing 100049 P. R. China

To reveal the petrogenesis of rhyolite from the southwestern Okinawa Trough, the mineral chemistry of plagioclase, orthopyroxene, amphibole, quartz and Fe-Ti oxide phenocrysts were analyzed using an electron microprobe, and in suit Sr and Ba contents of plagioclase analysed by LA-ICPMS were chosen for fingerprinting plagioclases of different provenances. Results indicate an overall homogeneous composition for each of the mineral phases except for plagioclase phenocrysts which have a wide range of composition(An=39~88). Plagioclase crystals characterized by An contents of >70 are not in equilibrium with their whole-rock compositions, and coarse-sieved plagioclase phenocryst interiors record high An contents(>70) and Sr/Ba ratios(>7), which are similar to the those of plagioclase crystals in basalt. Therefore, these crystals must have been introduced to the rhyolitic magma from a more mafic source. Equilibrium temperatures estimated using orthopyroxene-liquid, iron–titanium oxide, titanium-in-quartz and amphibole geothermometers show consistent values ranging from 792 to 869℃. The equilibrium pressure calculated using amphibole compositions is close to 121 MPa which corresponds to an approximate depth of 4 km. The fO_2 conditions estimated from Fe-Ti oxides and amphiboles plot slightly above the NNO buffer, which indicates that the rock formed under more oxidized conditions. Our results suggests that petrogenesis of the rhyolite due to basaltic magma ascend with the high An and Sr/Ba plaigoclases from deep magma chamber into the shallow chamber where the fractional crystallization and crustal assimilation happened. It also indicates that a two-layer magma chamber structure may occur under the southwestern Okinawa Trough.

关键词： geothermobarometry oxygen fugacity xenocrysts magma evolution rhyolite Okinawa Trough

Mica Types as Indication of Magma Nature,Central Anatolia,Turkey

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Acta Geologica Sinica(English Edition) 2022年第3期96卷 844-857页

作者： Kiymet DENIZ Department of Geological Engineering Ankara UniversityAnkaraTurkey Ankara University Faculty of EngineeringDepartment of Geological Engineering06830Golbasi-AnkaraTurkey

This study focuses on the nature of giant micas occurring at the contact between theÖzvatan(foid-bearing)syenites and the metamorphic basement in Central *** studied micas are dark greenish-black in color and crystallized within vein shape like bodies as a narrow *** origin and processes responsible for the formation of these independent crystals of the giant micas were investigated by mineralogical,petrographical and geochemical analyses with the use of Confocal Raman Spectroscopy(CRS),Fourier Transform Infrared(FTIR)Spectroscopy,X-Ray Diffraction(XRD),Polarized Energy Dispersive X-Ray Fluorescence Spectrometer(PED-XRF)and Electron Probe Micro Analysis(EPMA).According to XRD,CRS,FTIR and EPMA data,the giant micas are *** results reveal that studied mica minerals represent the products of re-equilibrated primary mica characterized by high MgO and FeO and low Al2O3 and TiO2 *** trace element concentrations of the giant micas display similar patterns with the upper *** giant micas are crystallized within small cubicles from an alkaline magma and their composition is possibly modified by a mixing event between the crust-and mantle-derived magmas and contaminated at varying extent by the basement metamorphic rocks.

关键词： phlogopite spectroscopy geothermobarometry oxygen fugacity Central Anatolia Turkey

Petrology,geochemistry,and zircon U-Pb geochronology of the Zambezi Belt in Zimbabwe:Implications for terrane assembly in southern Africa

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Geoscience Frontiers 2019年第6期10卷 2021-2044页

作者： Yusuke Kuribara Toshiaki Tsunogae Yusuke Takamura Yukiyasu Tsutsumi Graduate School of Life and Environmental Sciences University of TsukubaIbaraki 305-8572Japan Department of Geology University of JohannesburgAuckland Park 2006South Africa Department of Geology and Paleontology National Museum of Nature and ScienceIbaraki 305-0005Japan

The Zambezi Belt in southern Africa has been regarded as a part of the 570-530 Ma Kuunga Orogen formed by a series of collision of Archean cratons and Proterozoic orogenic ***,we report new petrological,geochemical,and zircon U-Pb geochronological data of various metamorphic rocks(felsic to mafic orthogneiss,pelitic schist,and felsic paragneiss)from the Zambezi Belt in northeastern Zimbabwe,and evaluate the timing and P-T conditions of the collisional event as well as protolith *** data of felsic orthogneiss indicate within-plate granite signature,whereas those of mafic orthogneiss suggest MORB,ocean-island,or within-plate *** P-Testimates for orthogneisses indicate significant P-T variation within the study area(700-780 C/6.7-7.2 kbar to 800-875 C/10-11 kbar)suggesting that the Zambezi Belt might correspond to a suture zone with several discrete crustal *** cores from felsic orthogneisses yielded two magmatic ages:2655±21 Ma and 813士5 Ma,which suggests Neoarchean and Early Neoproterozoic crustal growth related to within-plate *** zircons from metasediments display various ages from Neoarchean to Neoproterozoic(ca.2700-750 Ma).The Neoarchean(ca.2700-2630 Ma)and Paleoproterozoic(ca.2200-1700 Ma)zircons could have been derived from the adjacent Kalahari Craton and the Magondi Belt in Zimbabwe,*** Choma-Kalomo Block and the Lufilian Belt in Zambia might be proximal sources of the Meso-to Neoproterozoic(ca.1500-950 Ma)and early Neoproterozoic(ca.900-750 Ma)detrital zircons,*** detrital zircons from adjacent terranes possibly deposited during late Neoproterozoic(744-670 Ma),and subsequently underwent highgrade metamorphism at 557-555 Ma possibly related to the collision of the Congo and Kalahari Cratons during the latest Neoproterozoic to *** contrast,670-627 Ma metamorphic ages obtained from metasediments are slightly older than previous reports,but consistent with^68

关键词： geothermobarometry Detrital zircon Neoproterozoic Congo Craton Kalahari Craton Gondwana

GEOBAROMETRIC CONSTRAINTS ON THE DEPTH OF EMPLACEMENT OF GRANITE FROM THE LADAKH BATHOLITH, NORTHWEST HIMALAYA, INDIA

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地学前缘 2000年第S1期7卷 110-111页

作者： T. N. Jowhar(Wadia Institute of Himalayan Geology,33 General Mahadeo Singh Road, Dehra Dun\|248001, India,E\|mail: wihg@***)

The Ladakh batholith is exposed along the 600km long and 20 to 80km wide NW—SE trending Ladakh range north of the Indus\|Tsangpo Suture Zone. It was emplaced into an unmetamorphosed thick pile of mafic and felsic volcanics, ultramafics and sediments of Upper Cretaceous\|Eocene age (Dras Volcanics, Khardung Volcanics). The granites from the Ladakh batholith within the Leh\|Khardung La and Sakti—Chang La sections (samples collected between altitude of 3600m and 5440m above mean sea level, Fig.1) have been estimated for pressure and temperature of crystallization employing the hornblende geobarometer of Schmidt (1992) and hornblende\|plagioclase geothermometer of Blundy and Holland (1990), with the results of pressure of (250±60)MPa and temperature of (695±22)℃. Therefore, these granites were solidified at a depth of (8 6±2)km suggesting an unroofing of this thickness in this region. The importance of this geobarometric data in conjunction with age data on the cooling and unroofing history of the Trans\|Himalayan Ladakh batholith and geodynamic implications of the India—Asia collision are discussed.

关键词： Himalaya Ladakh batholith geothermobarometry granite

Spinel-Bearing Lherzolite Xenoliths from Hossere Garba(Likok,Adamawa-Cameroon):Mineral Compositions and Geothermobarometric Implications

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International Journal of Geosciences 2014年第12期5卷 1435-1444页

作者： Nguihdama Dagwai Chazot Gilles Kamgang Pierre Mbowou Gbambie Isaac Bertrand Ngounouno Ismaila Ecole Normale Supérieure Universite de MarouaMarouaCameroun Universite Europeenne de Bretagne BrestFrance Departement des sciences de la Terre Faculte de SciencesUniversite de Yaounde IYaoundeCameroun Ecole de Géologie et d’Exploitation Miniere(EGEM) Departement de Mines et de la GeologieUniversite de NgaoundereMeigangaCameroun

Spinel-bearing lherzolite xenoliths from the Hossere Garba (1272 m.a.s.l) volcano on the Adamawa Plateau, is located in Likok village, at about 35 km to WSW of Ngaoundere. These xenoliths (~11 cm size) have been sampled into the host basaltic lava flows from the NE flank of the Hossere Garba volcano. These xenoliths characterized by porphyroclastic texture consisted of olivine (~55 vol.%), orthopyroxene (~19 vol.%) and clinopyroxene (~21 vol.%) crystals. Spinel crystals (~5 vol.%) are red brown and interstitial between the crystals of olivine and pyroxenes. CaO contents are low (<0.08 wt%) in olivine and similar to those estimated (CaO: 0.05 - 0.1 wt%) for the mantle origin. The values of AlVI/AlIV ratio range between 1.1 and 1.3 for the Cr-diopside crystals from Hossere Garba xenoliths. The constant value of the volumes V(Cell) and V(M1) for clinopyroxene compositions, indicates the similar pressures. Hossere Garba represents a residual sequence issued from partial melting of a mantle source. Similar compositions have been recorded in minerals of ultramafic xenoliths from other ultramafic xenoliths domains of the Cameroon Line and the Adamawa Plateau.

关键词： Xenoliths lherzolite geothermobarometry Likok Adamawa

Tectono-metamorphic discontinuities in the Greater Himalayan Crystalline,central Himalaya

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Tectono-metamorphic discontinuities in the Greater Himalayan...