The long-lived partial melting of the Greater Himalayas in southern Tibet, constraints from the Miocene Gyirong anatectic pegmatite and its prospecting potential for rare element minerals  

作　　者：Hua-wen Cao Qiu-ming Pei Xiao Yu Ai-bin Cao Yong Chen Hang Liu Kai Zhang Xin Liu Xiang-fei Zhang 

机构地区：[1]Chengdu Center,China Geological Survey(Geosciences Innovation Center of Southwest China),Ministry of Natural Resources,Chengdu 610218,China [2]College of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China [3]Faculty of Geosciences and Environmental Engineering,Southwest Jiaotong University,Chengdu 611756,China [4]Research Center of Applied Geology,China Geological Survey,Ministry of Natural Resources,Chengdu 610036,China [5]School of Earth Resources,China University of Geosciences,Wuhan 430074,China

出　　处：《China Geology》2023年第2期303-321,I0004-I0015,共31页中国地质（英文）

基　　金：sponsored by the National Key R&D Programme of China(2021YFC2901803);National Natural Science Foundation of China(92055314 and 41802095);the China Geological Survey(DD20230049 and DD20220983);is a contribution to the International Geoscience Programme(IGCP-741);Academician Bao-jun Liu Foundation of Southwest Geological Science and Technology Innovation Center.

摘　　要：The Cenozoic Himalayan leucogranite-pegmatite belt has been a hotspot for rare metal exploration in recent years.To determine the genesis of the pegmatite in the Himalayan region and its relationship with the Greater Himalayan Crystalline Complex(GHC),the Gyirong pegmatite in southern Tibet was chosen for geochronological and geochemical studies.The dating analyses indicate that the U-Th-Pb ages of zircon,monazite,and xenotime exhibit large variations(38.6‒16.1 Ma),with the weighted average value of the four youngest points is 16.5±0.3 Ma,which indicates that the final stage of crystallization of the melt occurred in the Miocene.The age of the muscovite Ar-Ar inverse isochron is 15.2±0.4 Ma,which is slightly later than the intrusion age,showing that a cooling process associated with rapid denudation occurred at 16‒15 Ma.TheεHf(t)values of the Cenozoic anatectic zircons cluster between−12 and−9 with an average of−11.4.The Gyirong pegmatite shows high contents of Si,Al,and K,a high Al saturation index,and low contents of Na,Ca,Fe,Mn,P,Mg,and Ti.Overall,the Gyirong pegmatite is enriched in Rb,Cs,U,K,Th and Pb and depleted in Nb,Ta,Zr,Ti,Eu,Sr,and Ba.The samples show a high 87Sr/86Sr(16 Ma)ratio of ca.0.762 and a lowεNd(16 Ma)value of−16.0.The calculated average initial values of 208Pb/204Pb(16 Ma),207Pb/204Pb(16 Ma)and 206Pb/204Pb(16 Ma)of the whole rock are 39.72,15.79 and 19.56,respectively.The Sr-Nd-Pb-Hf isotopic characteristics of the Gyirong pegmatite are consistent with those of the GHC.This study concludes that the Gyirong pegmatite represents a typical crustal‒derived anatectic pegmatite with low metallogenic potential for rare metals.The Gyirong pegmatite records the long‒term metamorphism and partial melting process of the GHC,and reflects the crustal thickening caused by thrust compression at 39‒29 Ma and the crustal thinning induced by extensional decompression during 28‒15 Ma.

关 键 词：Partial melting of magma Anatectic pegmatite Zircon-monazite-xenotime U‒Pb dating Sr-Nd-Pb isotopes Greater Himalayan crystalline complex Mineral exploration engineering Gyirong Tibet 

分 类 号：P618.6[天文地球—矿床学]