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中国科学院地质与地球物理研究所2004学术年会

作者： ZHANG Hongfu,YING Jifeng,XU Ping & MA Yuguang Institute of Geology and Geophysics,Chinese Academy of Sciences, Beijing 100029,China

Mesozoic(125 Ma) Fangcheng basalts from Shandong Province contain clearly zoned olivines that are rare in terrestrial samples and provide first evidence for the replacement of lithospheric mantle from high-Mg peridotites to low-Mg peridotites through peridotite-melt reaction. Zoned olivines have compositions in the core(Mg#=87.2—90.7) similar to those olivines from the mantle peridotitic xenoliths entrained in Cenozoic basalts from the North China craton and in the rim(Mg#=76.8—83.9) close to olivine phenocrysts of the host basalts(75.7—79.0).These compositional features as well as rounded crystal shapes and smaller grain sizes(300—800μm) demonstrate that these zoned olivines are mantle xenocrysts,*** of mantle *** core compositions can represent those of olivines of mantle *** zoned texture of olivines was formed through rapid reaction between the olivine xenocryst and the host *** olivine-basaltic melt reaction could have been ubiquitous in the Mesozoic lithospheric mantle beneath the North China craton,*** important type of the replacement of lithospheric *** reaction resulted in the transformation of the Paleozoic refractory (high-Mg) peridotites to the late Mesozoic fertile (low-Mg) and radiogenic isotope-enriched peridotites,leading to the loss of old lithospheric mantle.

关键词： North China craton Mesozoic basalt xenocrysts lithospheric mantle

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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

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