Petrogenesis of Early Silurian granitoids in the Longshoushan area and their implications for the extensional environment of the North Qilian Orogenic Belt, China
Petrogenesis of Early Silurian granitoids in the Longshoushan area and their implications for the extensional environment of the North Qilian Orogenic Belt, China
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DOI：
10.1016/j.lithos.2019.05.029
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发表时间：
2019-10
期刊：
影响因子：
3.5
通讯作者：
Kai‐Xing Wang;Chi Yu;Jie Yan;Xiao-dong Liu;Wen‐Heng Liu;Jiayong Pan
中科院分区：
文献类型：
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作者：
Kai‐Xing Wang;Chi Yu;Jie Yan;Xiao-dong Liu;Wen‐Heng Liu;Jiayong Pan
对阿拉善地块南缘沿着的吉岭岩体进行了锆石U-Pb年龄、矿物化学和全岩地球化学分析。这些分析结果将为研究北祁连造山带（NQOB）古生代壳幔相互作用以及阿拉善地块与祁连-柴达木地块碰撞期间挤压环境向伸展环境的过渡时代提供重要信息。锆石定年结果表明，吉岭岩体由早志留世花岗岩类（435-442 Ma）和同期的镁铁质微粒包体组成。多数花岗岩类含有角闪石和钛铁矿，A/CNK值<1，属于富角闪岩型钙碱性花岗岩类（ACG）和富钾钾长斑岩型钙碱性花岗岩类（KCG）。花岗岩类和MME样品显示可变的初始Sr和Nd同位素组成。我们认为，吉岭岩体是壳幔源岩浆混合作用的产物。MMEs的高HFSE含量表明，幔源岩浆来源于埃达克质岩浆交代的地幔楔熔融，壳源岩浆来源于龙首山群古元古代变质玄武质岩石的熔融。吉岭花岗岩类的发现表明，中奥陶世-早志留世北祁连造山带为挤压环境，是祁连-柴达木地块与阿拉善地块碰撞的产物，初始伸展环境始于442 Ma以前。
Analyses of the zircon U—Pb age, mineralogical chemistry and whole-rock geochemistry of the Jiling pluton along the southern margin of the Alxa Block were conducted. The results of these analyses will provide crucial information for investigations of Paleozoic crust-mantle interactions in the North Qilian Orogenic Belt (NQOB) and explorations of the transition age from a compressional to extensional environment during the collision between the Alxa Block and the Qilian-Qaidam Block. The zircon dating results reveal that the Jiling pluton is composed of Early Silurian granitoids (435–442 Ma) with contemporaneous mafic microgranular enclaves (MMEs). Most granitoids contain amphibole and titanite and have A/CNK values <1, illustrating that they belong to amphibolite-rich calc-alkaline granitoids (ACGs) and K-rich and K-feldspar porphyritic calc-alkaline granitoids (KCGs). Both the granitoid and MME samples display variable initial Sr and Nd isotopic compositions. We suggest that the Jiling pluton was formed by crust-mantle-derived magma mixing. The high HFSE content of the MMEs indicates that the mantle-derived magmas were derived from melting of the mantle wedge metasomatized by adakitic magma, and the crustal-derived magmas were derived from melting of Paleoproterozoic meta-basaltic rocks in the Longshoushan Group. The discovery of the Jiling granitoids indicates that the NQOB was dominated by a compressional environment during Middle Ordovician-Early Silurian in response to the collision between the Qilian-Qaidam Block and the Alxa Block, and the initial extensional environment began before 442 Ma.