Early Mesozoic Crust-and Mantle-Derived Magmatic Mixing in the Qinling Orogeny:Evidence From Geochemistry of Mafic Microgranular Enclaves in the Dongjiangkou Pluton
Early Mesozoic Crust-and Mantle-Derived Magmatic Mixing in the Qinling Orogeny:Evidence From Geochemistry of Mafic Microgranular Enclaves in the Dongjiangkou Pluton
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发表时间：
2012
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通讯作者：
Liao Lei;Zhang Chengli;Zhou Ying;Tian Huiquan;L. Xiaofei
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作者：
Liao Lei;Zhang Chengli;Zhou Ying;Tian Huiquan;L. Xiaofei
分别获得了东江口花岗岩及其镁铁质包体的锆石U-Pb年龄为218 Ma和224 Ma。镁铁质包体中发现了不平衡的岩浆结构,其中含有一些与主体花岗岩相似的钾长石和淬火条件下形成的针状磷灰石,表明存在两端元岩浆混合。早中生代，两端元岩浆混合导致了主花岗岩与其基性包体之间地球化学成分相似，Sr-Nd-Pb同位素强烈均一化。然而，镁铁质包体的Hf同位素组成显示e Hf(t)变化范围较宽，从-4.58到3.31，记录了两端元的物源特征因此，当代镁铁质包体中锆石的正e Hf(t)值(10)为该镁铁质岩浆来源于贫乏地幔提供了证据。而锆石负Hf(t)值(10)的主花岗岩则是中元古代幔源基岩部分熔融的产物。从此，形成了明显的壳幔源岩浆。 224 Ma左右混合,导致秦岭造山运动早中生代出现大量花岗岩侵入体,并发育丰富的镁铁质包体。
The zircon U-Pb ages of 218 Ma and 224 Ma have been obtained from the Dongjiangkou granitoids and their mafic enclaves,respectively.The disequilibrium magmatic textures can be found in the mafic enclaves,which have some K-feldspars similar to those of host granitoids and needle-like apatite formed under a quenching condition,indicating a two-end member magmatic mixing in the early Mesozoic.The two-end member magmatic mixing resulted in similar geochemical compositions and strong homogenization of Sr-Nd-Pb isotopes between host granitoids and their mafic enclaves.However,Hf isotopic composition of the mafic enclaves shows a wide range of e Hf(t) that varies from-4.58 to 3.31,registering the source features of two-end member magma.Thus,the positive e Hf(t) values(10) of zircons from the contemporary mafic enclaves provide evidence that the mafic magma was derived from the depleted mantle.While,host granitoids with negativee Hf(t) values(10) of zircons were products of partial melting of the Mid-Proterozoic mantle-derived basic rocks.Since then,the distinct crust-and mantle-derived magmas were mixed around 224 Ma,resulting in a large number of granitic intrusions with abundant mafic enclaves during the early Mesozoic in the Qinling orogeny.