Origin of two types of rhyolites in the Tarim Large Igneous Province: Consequences of incubation and melting of a mantle plume
Origin of two types of rhyolites in the Tarim Large Igneous Province: Consequences of incubation and melting of a mantle plume
复制标题
塔里木火成岩省两种流纹岩的成因：地幔柱孕育和融化的后果
DOI：
10.1016/j.lithos.2014.02.007
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发表时间：
2014-09-01
期刊：
影响因子：
3.5
通讯作者：
Shang-Guan, Shi-Mai
中科院分区：
文献类型：
--
作者：
Liu, Hai-Quan;Xu, Yi-Gang;Shang-Guan, Shi-Mai
中国西北塔里木早二叠世大火成岩省（LIP）包含大面积（约48，000 km（2））与镁铁质-超镁铁质岩在空间和时间上相关的火山岩。为了了解地幔柱上地壳的行为，对流纹岩样品进行了锆石U-Pb定年、地球化学和同位素分析。塔里木流纹岩具有高的A/CNK比值（=摩尔Al_2O_3/CaO + Na_2O + K_2O）、Fe #、Ga/Al比值、高场强元素（HFSE）如Zr和Nb的浓度以及稀土元素（REE），沿着具有高的锆石饱和温度（872 - 940 ℃），是典型的铝质A型花岗岩。两种截然不同的岩石类型已被确认。低Nb-Ta型流纹岩主要与290Ma左右的塔里木第一期溢流玄武岩岩浆活动有关。它们具有Nb-Ta负异常、低Nd（t）和Hf（t）值、高Sr-87/Sr-88（t）和δ（18）O-锆石值等特征，与大陆壳源一致。高Nb-Ta型流纹岩及其深成等价物与塔里木第二期岩浆活动（283 - 272Ma）有关。其特征是Nb Ta负-正异常小，微量元素比值似洋岛玄武岩（0113），Sr-87/Sr-88（t）低，Nd（t）和Hf（t）高。这些高Nb-Ta韵律最好解释为镁铁质岩浆的晶体分馏的混合产物，再加上地壳同化。塔里木流纹岩的时间和成分演化反映了地幔柱上方幔源玄武岩浆与地壳物质之间不同程度的热交换和物质交换。当地幔柱头上升到塔里木克拉通底部时，首先熔融了岩石圈地幔中富集的组分（约290Ma），其中一部分可能在壳幔边界附近形成了积水，并诱发了地壳深熔作用，形成了低Nb-Ta型流纹。在280 Ma左右，由于地幔柱减压熔融过程中岩浆供应速率增加，形成了大型岩浆房和管道系统。这导致形成了一个镁铁质-超镁铁质和长英质组合，其中高铌钽型韵律的一部分。(C)© 2014 Elsevier B.V.版权所有
The Early Permian Tarim Large Igneous Province (LIP) in northwestern China contains a large area of silicic volcanics (similar to 48,000 km(2)) which are spatially and temporally associated with mafic-ultramafic rocks. In order to understand the behavior of crust above a mantle plume, selected rhyolitic samples are investigated in terms of U-Pb zircon dating, geochemical and isotopic analyses. The Tarim rhyolites have high A/CNK ratios (= molar Al2O3/CaO + Na2O + K2O), Fe#, Ga/Al ratios, concentrations of high field strength elements (HFSEs) such as Zr and Nb, and rare earth elements (REEs), along with high zircon saturation temperatures (872-940 degrees C), typical of aluminous A-type granitoids. Two contrasting rock types have been recognized. The low Nb-Ta type rhyolites are mainly associated with the first phase of the Tarim flood basalt magmatism at similar to 290 Ma. They are characterized by negative Nb-Ta anomalies, low epsilon(Nd)(t) and epsilon(Hf)(t) values, and high Sr-87/Sr-88(t) and delta(18) O-zircon values, consistent with a derivation from continental crustal source. The high Nb-Ta type rhyolites and their plutonic equivalents are associated with the second episode of Tarim magmatism (283-272 Ma). They are characterized by small negative to positive Nb-Ta anomalies, oceanic island basalt (0113)-like trace element ratios, low Sr-87/Sr-88(t) and high epsilon(Nd)(t) and epsilon(Hf)(t) values. These high Nb-Ta rhyolites are best interpreted as hybrid products of crystal fractionation of mafic magmas, coupled with crustal assimilation. The temporal and compositional evolution of the Tarim rhyolites reflects various extents of thermal and mass exchange between mantle-derived basaltic magma and crustal material above a mantle plume. When the plume head rises to the base of the Tarim craton, it first melts enriched components in the lithospheric mantle (similar to 290 Ma), part of which may have ponded near the crust-mantle boundary and induced crustal anatexis leading to the formation of the low Nb-Ta type rhyolites. At similar to 280 Ma, large magma chambers and plumbing systems were formed due to increasing magma supply rate during decompression melting of the mantle plume. This led to the formation of a mafic-ultramafic and felsic association of which the high Nb-Ta type rhyolites are a part. (C) 2014 Elsevier B.V. All right reserved