Discovery of Early Devonian Adakite in West Junggar, Xinjiang: Implications for Geotectonics and Cu Mineralization
详细信息
- 责任者：Wang Jinrong (Key Laboratory of Mineral Resources in Western China ; School of Earth Sciences ; Lanzhou University ; Lanzhou 730000 ; China) ; Jia Zhilei
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(3)
- 关键词：埃达克岩 ; adakite ; 大地构造 ; tectonics ; 准噶尔盆地 ; Junggar Basin
- 页码：p.840-852
- 图表：illus., 2 tables, 92 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The accretionary orogenic belt of West Junggar,Xijiang,are accepted as the products of subduction,accretion,and tectonic assembly of the oceanic terranes due to the closure of paleo-Asian ocean in Paleozoic,in which the many ophiolitic mélange zones,subduction-related plutons,volcanic-sedimentary rocks and arc igneous rocks,and post-collisional granitoids developed and studied well,but early Late-Paleozoic adakites are not definitely reported.The Akeqiaoke Cu-bearing granotoids,located about 100km southeast of Erming County,tectonically in the south margin of Boshchekul-Chingiz island arc of the West Junggar,formed in Early Devonian,and are 410.5±2.9Ma of LA-ICP-MS zircon U-Pb ages.They have geochemical features suggestive of the adakites from the circum-Pacific.The plutons exhibit high-K and calc-alkaline composition with SiO2(61%～66%),high Al(Al2O3=15.67%～16.87%),Sr(475×10-6～879×10-6),Na(Na2O=4.25%～5.58%) contents,and Sr/Y(36～77) and Na2O/K2O(1.40～2.47)ratios,as well as MgO(1.51%～2.58%) and Mg#(41～48),coupled with low Y(9.87×10-6～14.46×10-6) and Yb(0.96×10-6～1.49×10-6).Furthermore,they display obviously rich in strongly incompatible elements(Ba,Rb,Sr,Th and U)and LREE with(La/Yb)N,Rb/Sr,La/Ce ratios of 6.0～10.2,0.04～0.07,0.42～0.51,respectively,but depleted in HFSEs(Nb-Ta and Ti),HREE with Y/Yb ratio of 10,no Eu anomaly(Eu/Eu*≈1.0).However,compared with the modern adakites,they exhibit lower Cr,Ni contents and(La/Yb)N and Nb/U ratios,as well as flat HREE patterns,indicating these adakitic magmas were formed by relatively high degree of slab-melting,low reaction of the melt with mantle and input of subducted sedimentary components.The studied results show that the plutons of Early Devonian from Akeqiaoke were products resulted from the slab melting of the southward subduction of paleo-ocean represented by the Kujibai-Hebukesaier and Hongguleleng ophiolitic belts,with the residual minerals(eg.amphibole + pyroxene + garnet) in the source of garnet amphibolite,and that the mid-Paleozoic tectono-magmatic belt of the Akeqiaoke adakites and the alkali-feldspar granitoids(422～405Ma,Chen et al.,2010)in the Xiemisitai Shan,formed in arc setting,could extend eastward to the island arc north of the Zaheba-Aermantai ophiolite;and that the Cu-bearing adakite indicative of good Cu(Au) mineralization potential of porphyry type in the Mid-Paleozoic mega-tectonomagmatic belt.