Miocene Crustal Anatexis of Paleozoic Orthogneiss in the Zhada Area,Western Himalaya  

作　　者：CHEN Han HU Guyue ZENG Lingsen YU Xuhui LI Yike 

机构地区：[1]College of Earth Science,Chengdu University of Technology,Chengdu 610059,China [2]MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China [3]Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China

出　　处：《Acta Geologica Sinica(English Edition)》2022年第3期954-971,共18页地质学报（英文版）

基　　金：This work was supported by the National Natural Science Foundation of China(Grant Nos.42072114,41503006);the Deep Resources Exploration and Mining,the National Key R&D Program of China(Grant No.2018YFC0604106);the Chinese Geological Survey(Grant No.DD20190167);the China Scholarship Council(Grant No.201808110080).

摘　　要：Granitic gneiss(orthogneiss)and Himalayan leucogranite are widely distributed in the Himalayan orogen,but whether or not the granitic gneiss made a contribution to the Himalayan leucogranite remains unclear.In this study,we present the petrological,geochronological and geochemical results for orthogneisses and leucogranites from the Zhada area,Western Himalayas.Zhada orthogneiss is composed mainly of quartz,plagioclase,K-feldspar,biotite and muscovite,with accessory zircon and apatite.Orthogneiss zircon cathodoluminescence(CL)images show that most grains contain a core with oscillatory zoning,which indicates an igneous origin.Sensitive high-resolution ion microprobe(SHRIMP)U-Pb dating of the zircon cores in the orthogneiss shows a weighted ^(206)Pb/^(238)U age of 515±4 Ma(early Paleozoic),with sponge-like zircon rims of 17.9±0.5 Ma(Miocene).Zhada leucogranite shows^(206)Pb/^(238)U ages ranging from 19.0±0.4 Ma to 12.4±0.2 Ma,the weighted average age being 16.2±0.4 Ma.The leucogranites have a low Ca content(<1 wt%),FeOt content(<1 wt%),Rb content(67.0-402 ppm),Sr content(<56.6 ppm),Ba content(3.35-238 ppm)and Rb/Sr ratio(0.5-14.7),which are similar to the geochemical characteristics of the Himalayan leucogranite derived from muscovite dehydration partial melting of metasediments and representative of most Himalayan leucogranites.The highly variable Na_(2)O+K_(2)O(4.33 wt%-9.13 wt%),Al_(2)O_(3)(8.44 wt%-13.51 wt%),ΣREE(40.2-191.0 ppm),Rb(67.0-402 ppm)and Nb(8.23-26.4 ppm)contents,^(87)Sr/^(86)Sr(t)ratios(0.7445-0.8605)andεNd(t)values(−3.6 to−8.2)indicate that the leucogranite is derived from a heterogenetic source.The nonradiogenic Nd isotope values of the studied Zhada leucogranite and orthogneiss range from−8.2 to−3.6 and from−8.7 to−4.1,respectively.Therefore,the general mixing equation was used to perform the Sr and Nd isotope mixing calculations.The results indicate that the heterogenetic source was the Tethyan Himalayan Sequence(THS)/Higher Himalayan Crystalline(HHC)metasediments and Zhada

关 键 词：LEUCOGRANITE ORTHOGNEISS PETROGENESIS crustal anatexis Zhada area Himalayan orogen 

分 类 号：P534.4[天文地球—古生物学与地层学] P588.3[天文地球—地质学]