Early Paleozoic Tectonic Transition from Ocean Subduction to Collisional Orogeny in the Eastern Kunlun Region: Evidence from Huxiaoqin Mafic Rocks
详细信息
- 责任者：Liu Bin (State Key Laboratory of Geological Processes and Mineral Resources ; China University of Geosciences ; Wuhan 430074 ; China) ; Ma Changqian
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(6)
- 关键词：镁铁质岩 ; mafic rocks ; 昆仑山 ; Kunlun Mountains
- 页码：p.2093-2106
- 图表：illus., 3 tables, 72 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The Huxiaoqin mafic rocks which distribute in the Central Kunlun Suture Zone,are mainly composed of hornblen dediabases. LA-ICP-MS zircon U-Pb analyses gave 438 ±2Ma ( MSWD = 1. 06,n = 15) of the crystallization age,suggesting Huxiaoqin mafic rocks are the products of the Early Silurian magmatism. All the rock samples are characterized by relatively low TiO2 ( 0.43%～1. 58% ) ,variable MgO (2. 83%～8.22% ) and Mg # (45 ～74) ,slight enriched Hf isotopic composition ( ε Hf ( t) =3. 68 ～8.20,t DM2 = 0. 90～1. 19Ga) ,enrichment of large ion lithophile elements ( LILE: eg. Rb,Ba,Th,U and LREE) and marked depletion of high field strength elements ( HFSE: eg. Nb,Ta,Ti) . Various binary diagrams taking Mg # as the abscissa,and adiagram plotting (2CaO + Na20)/TiO2 vs. Al203/TiO2 reveal fractional crystallization of clinopyroxene,olivine,and plagioclase. Crustal contamination was insignificant,as reflected by whole-rock relatively low Nb/La and Nb/Ce ratios,high Nb/Ta and Zr/Hf ratios. Based on our geochemical and Lu-Hf isotopic studies,we suggest the maficdykes likely were generated by partial melting of the spinel peridotites metasomatised by slab-derived fluids. Huxiaoqin mafic rocks have similar chemical composition to island arc basalts,and they formed earlier than metamorphic peaks of eclogite and epidote-amphibolite facies (428Ma and427Ma,respectively) ,indicating their formationwere closely related to the subduction of Early Paleozoic Eastern Kunlun 0ceanic lithosphere. Combining with regional studies,we suggest that Huxiaoqin mafic rocks may represent the latest magmatism which related to Early Paleozoic ocean subduction. Finally,we infer the tectonic transition fromocean subduction to collisional orogeny commenced at Early Silurian,the duration ofocean subduction is more than 79Myr and that of collisional orogeny is more than 8Myr.
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