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Geochemistry and Geochronology of Saga Alkaline Basalt in Southern Tibet

Geochemistry and Geochronology of Saga Alkaline Basalt in Southern Tibet Dec. 2015 ZHAO Hui, YANG JingSui, LIU Fei, XIONG Fahui, ZHANG Lan and LIAN Dongyang, 2015. Geochemistry and Geochronology of Saga Alkaline Basalt in Southern Tibet. Acta Geologica Sinica (English Edition), 89(supp. 2): 120. Geochemistry and Geochronology of Saga Alkaline Basalt in Southern Tibet ZHAO Hui1, 2, YANG JingSui1, 2,*, LIU Fei2, XIONG Fahui2, ZHANG Lan1, 2 and LIAN Dongyang2, 3 1 School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China 2 CARMA, State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China 3 Faculty of Earth Sciences, China University of Geoscience, Wuhan 430074, China The Yarlung Zangbo Suture Zone (YZSZ) to the west of Saga is divided into two sub-belts , namely the south subbelt and the north sub-belt. The Saga ophiolite is mainly composed of peridotites, gabbro, diabase and lava. In this paper, we report a suite of alkaline basalt to the south of the Saga ophiolite, which extends NWW along an outcrop 1–3 km in width. This suite of basaltic lava has a vesicular/amygdaloid structure and a porphyric texture with phenocrysts of plagioclase (15–20 modal%) and clinopyroxene (~5 modal%). The plagioclase is albitic and the clinopyroxene is titaniferous diopside (TiO2=1.46 wt %). Based on the composition and TAS diagram, the lava classifies as alkaline basalt. The SiO2 contents of the lava vary from 44.06–53.06 wt%, the Al2O3 contents vary from 14.68–18.44 wt%, the MgO contents vary from 4.96–7.95 wt%, and the TiO2 contents vary from 2.62–3.47 wt%. In all, the lava shows the characteristics of low SiO2 and high TiO2 and Al2O3, as well as enrichment in large ion lithophile elements ( LILE: Rb, Ba, Th) and high field strength elements (HFSE: Zr, Hf, Nb, Ta). The rare earth element (REE) content of the basalt is higher (ΣREE=266.93 ppm), with a strong fractionation between LREE and HREE [(Ce/Yb)N =7.30–14.18], simiar to typical OIB. This study shows that garnets exist as residual minerals in the source of Saga alkaline basalt. In addition, the early stage of magmatism is marked by fractional crystallization of olivine, clinopyroxene and other mafic minerals. Based on incompatible element ratios and tectonic discrimination diagrams, the Saga alkaline basalts plot as oceanic intraplate. U-Pb dating of zircons by LA-ICP-MS yields a wide range of ages. The mininum average age is 54.2±1.4)Ma, which can provide some important information about the evolution of the Tibetan plateau. Acknowledgements We thank the State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, China and the China National Research Center for the geochemical analyses. In addition, give my sincere thanks to Professor Pearce for reviewing. This research was funded by grants from the Ministry of Science and Technology of China (2014DFR21270), China Geological Survey (12120115026801, 12120115027201, 201511022) and the Fund from the State Key Laboratory of Continental Tectonics and Dynamics (Z1301-a20). * Corresponding author. E-mail: yangjsui@163.com http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Geologica Sinica (English Edition) Wiley

Geochemistry and Geochronology of Saga Alkaline Basalt in Southern Tibet

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Publisher
Wiley
Copyright
© 2015 Geological Society of China
ISSN
1000-9515
eISSN
1755-6724
DOI
10.1111/1755-6724.12308_71
Publisher site
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Abstract

Dec. 2015 ZHAO Hui, YANG JingSui, LIU Fei, XIONG Fahui, ZHANG Lan and LIAN Dongyang, 2015. Geochemistry and Geochronology of Saga Alkaline Basalt in Southern Tibet. Acta Geologica Sinica (English Edition), 89(supp. 2): 120. Geochemistry and Geochronology of Saga Alkaline Basalt in Southern Tibet ZHAO Hui1, 2, YANG JingSui1, 2,*, LIU Fei2, XIONG Fahui2, ZHANG Lan1, 2 and LIAN Dongyang2, 3 1 School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China 2 CARMA, State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China 3 Faculty of Earth Sciences, China University of Geoscience, Wuhan 430074, China The Yarlung Zangbo Suture Zone (YZSZ) to the west of Saga is divided into two sub-belts , namely the south subbelt and the north sub-belt. The Saga ophiolite is mainly composed of peridotites, gabbro, diabase and lava. In this paper, we report a suite of alkaline basalt to the south of the Saga ophiolite, which extends NWW along an outcrop 1–3 km in width. This suite of basaltic lava has a vesicular/amygdaloid structure and a porphyric texture with phenocrysts of plagioclase (15–20 modal%) and clinopyroxene (~5 modal%). The plagioclase is albitic and the clinopyroxene is titaniferous diopside (TiO2=1.46 wt %). Based on the composition and TAS diagram, the lava classifies as alkaline basalt. The SiO2 contents of the lava vary from 44.06–53.06 wt%, the Al2O3 contents vary from 14.68–18.44 wt%, the MgO contents vary from 4.96–7.95 wt%, and the TiO2 contents vary from 2.62–3.47 wt%. In all, the lava shows the characteristics of low SiO2 and high TiO2 and Al2O3, as well as enrichment in large ion lithophile elements ( LILE: Rb, Ba, Th) and high field strength elements (HFSE: Zr, Hf, Nb, Ta). The rare earth element (REE) content of the basalt is higher (ΣREE=266.93 ppm), with a strong fractionation between LREE and HREE [(Ce/Yb)N =7.30–14.18], simiar to typical OIB. This study shows that garnets exist as residual minerals in the source of Saga alkaline basalt. In addition, the early stage of magmatism is marked by fractional crystallization of olivine, clinopyroxene and other mafic minerals. Based on incompatible element ratios and tectonic discrimination diagrams, the Saga alkaline basalts plot as oceanic intraplate. U-Pb dating of zircons by LA-ICP-MS yields a wide range of ages. The mininum average age is 54.2±1.4)Ma, which can provide some important information about the evolution of the Tibetan plateau. Acknowledgements We thank the State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, China and the China National Research Center for the geochemical analyses. In addition, give my sincere thanks to Professor Pearce for reviewing. This research was funded by grants from the Ministry of Science and Technology of China (2014DFR21270), China Geological Survey (12120115026801, 12120115027201, 201511022) and the Fund from the State Key Laboratory of Continental Tectonics and Dynamics (Z1301-a20). * Corresponding author. E-mail: yangjsui@163.com

Journal

Acta Geologica Sinica (English Edition)Wiley

Published: Dec 1, 2015

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