Petrogenesis of granitic pegmatite veins:Perspectives from major element and B isotope in tourmalines,Chakabeishan,Northern Tibetan Plateau

查看全文 作　　者：Wenli [1,2,3]Sun;Zhidan [1]Zhao;Yaoling [1,4]Niu;Chunjing [2]Wei;Guochen [1]Dong;Xiaowei [1]Li;Wanming [1]Yuan;Tao [5]Wang;Bingzhang [5]Wang;Tong [5]Pan;Jie [5]Han;Hongliang [5]Cao;Yan [1]Tang;Dicheng [1]Zhu 机构地区：[1]State Key Laboratory of Geological Processes and Mineral Resources,and School of Earth Science and Resources,China University of Geosciences,Beijing 100083,China;[2]MOE Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing 100871,China;[3]Gansu Industry Polytechnic College,Tianshui 741025,China;[4]Laoshan Laboratory,Qingdao 266237,China;[5]Bureau of Geological Exploration and Development of Qinghai Province,Xining 810012,China 出　　处：《Geoscience Frontiers》索引2023年第14卷第5期,共13页 基　　金：supported by the National Natural Science Foundation of China(Grant Nos.92062217,42121002,42073035);Second Tibetan Plateau Scientific Expedition and Research(STEP)program(Grant No.2019QZKK0702);111 Project of the Ministry of Science and Technology of China(Grant No.B18048);the University Innovation Foundation of Gansu Education Department(Grant No.2021A-230). 摘　　要：The petrogenesis of regionally zoned granitic pegmatite veins remains debated.Because of the economic significance,we carried out a study on the Chakabeishan(CKBS)pegmatite-type Li-Be deposit,eastern North Qaidam Tectonic Belt,Northern Tibetan Plateau,by means of in-situ major element and B isotope compositions of tourmalines in the beryl-bearing and spodumene-bearing pegmatite veins.Tourmalines(Tur-Be)from the beryl-bearing pegmatite are homogeneous schorl with low Mg/(Mg+Fe),high Na/(Na+Ca)and Y Al,suggesting that they are of magmatic origin.Two generations of tourmalines(TurLi)from the spodumene-bearing pegmatite are identified:(i)the crystal cores(mostly elbaite and Lirich schorl with subordinate schorl)are consistent with being of magmatic origin crystallized at the magmatic stage;(ii)the crystal rims(schorl)are best understood as the overgrowth at the later hydrothermal stage.Tur-Be and Tur-Li show an obvious difference in core-to-rim B isotopic variation trend with d11B decrease in Tur-Be and increase in Tur-Li.The core-to-rim d11B decrease in Tur-Be results from degassing during its host pegmatitic melt evolution,whereas the core-to-rim d11B increase in Tur-Li is related to fluid exsolution.The estimated d11B values for the initial melts of the beryl-bearing and spodumenebearing pegmatites are10.46‰and10.78‰,respectively,indicating that they most likely originate from protracted fractional crystallization/differentiation of granitic intrusions rather than partial melting of metapelite.Both Mg/(Mg+Fe)ratios and Li abundances in the cores of Tur-Be are lower than those of Tur-Li,suggesting that Tur-Li crystallizes from chemically more evolved melts. 关 键 词：PETROGENESIS PEGMATITE TOURMALINE Boron isotope Major element