Early Silurian (~ 440 Ma) adakitic, andesitic and Nb-enriched basaltic lavas in the southern Altay Range, Northern Xinjiang (western China): Slab melting and implications for crustal growth in the Central Asian Orogenic Belt
Early Silurian (~ 440 Ma) adakitic, andesitic and Nb-enriched basaltic lavas in the southern Altay Range, Northern Xinjiang (western China): Slab melting and implications for crustal growth in the Central Asian Orogenic Belt
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DOI：
10.1016/j.lithos.2014.07.024
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发表时间：
2014-10
期刊：
影响因子：
3.5
通讯作者：
Xiaoming Shen;Haixiang Zhang;Qiang Wang;Lin Ma;Yue-heng Yang
中科院分区：
文献类型：
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作者：
Xiaoming Shen;Haixiang Zhang;Qiang Wang;Lin Ma;Yue-heng Yang
阿尔泰山是中亚造山带的重要组成部分，发育大型古生代岩浆岩。然而，由于缺乏精确的年龄限制，该区岩浆岩的构造背景和成因一直存在争议，导致了对CAOB中生代地壳生长机制和增生造山过程的争论。本文报道了阿尔泰山南缘索尔库都克埃达克质、安山质和富铌玄武质（NEB）熔岩的年代学和地球化学资料。5个埃达克质、安山质和NEB样品的LA-ICP-MS锆石U-Pb分析表明，它们形成于早志留世（~ 440 Ma）。埃达克岩和玄武安山岩的地球化学特征为高Na_2 O/K_2 O、Sr/Y、Al_2 O_3、Sr、εNd（t）和锆石εHf（t）值及较低的（87 Sr/86 Sr）比值。与典型的弧玄武岩相比，NEBs富钠，具有更高的TiO 2、P2 O 5、Zr、Nb和Nb/U值。它们也具有正的εNd（t）值和正的和可变的锆石εHf（t）值。索尔库都克埃达克岩是俯冲洋壳部分熔融形成的，其上覆沉积物较少，且埃达克岩与玄武安山岩之间的连续成分变化证实了板片熔体与地幔橄榄岩的相互作用在玄武安山岩的形成中起着重要作用。相关的NEBs可能是由地幔楔橄榄岩的部分熔融所产生的板片衍生埃达克质熔体和微量流体交代。结合大量志留纪-泥盆纪花岗岩类、同时代蛇绿混杂岩和一系列弧内盆地的产出，提出了索尔库都克埃达克岩-玄武安山岩-NEB岩套形成的板片撕裂触发窗模式。软流圈地幔通过板片窗口的上涌可能导致上覆岩石圈的显著伸展;俯冲洋壳、地幔和幼年下地壳的大规模熔融;以及板片源熔体或流体与地幔楔之间的强烈相互作用。板块撕裂和随后的软流圈上涌可能在中生代CAOB的地壳生长中起了重要作用。
As an important part of the Central Asian Orogenic Belt (CAOB), the Altay Range contains large-scale Paleozoic magmatic rocks. However, owing to the lack of precise age constraints, the tectonic setting and petrogenesis of the magmatic rocks in this area have been controversial, which has led to the debate on Phanerozoic crustal growth mechanisms and accretionary orogenic processes in the CAOB. Herein, we report geochronological and geochemical data of the Suoerkuduke adakitic, andesitic and Nb-enriched basaltic (NEB) lavas in the southern margin of the southern Altay Range. LA-ICP-MS zircon U–Pb analyses for five adakitic, andesitic and NEB samples indicate that they were coevally generated in the Early Silurian (~ 440 Ma). The adakites and basaltic andesites are geochemically characterized by high Na2O/K2O, Sr/Y, Al2O3, Sr, εNd(t) and zircon εHf(t) values and relatively low (87Sr/86Sr)iratios. The NEBs are sodium-rich and have higher TiO2, P2O5, Zr, Nb, and Nb/U values than those of typical arc basalts. They also have positive εNd(t) values and positive and variable zircon εHf(t) values. We suggest that the Suoerkuduke adakites were derived by a partial melting of the subducted oceanic crust with minor overlying sediments, and the continuous compositional variations between adakites and basaltic andesites confirm that the interaction between slab melts and mantle peridotite played an important role in the formation of basaltic andesites. The associated NEBs were possibly generated by a partial melting of mantle wedge peridotites metasomatized by slab-derived adakitic melts and minor fluids. In combination with the occurrence of voluminous Silurian–Devonian granitoids, coeval ophiolite mélanges, and a series of intra-arc basins, a slab window model triggered by slab tearing is proposed to account for the formation of the Suoerkuduke adakite–basaltic andesite–NEB suites. The upwelling of the asthenospheric mantle through the slab window probably caused significant extension in the overlying lithosphere; extensive melting of the subducted oceanic crust, mantle and juvenile lower crust; and intense interaction between slab-derived melts or fluids and the mantle wedge. Slab tearing and subsequent asthenospheric upwelling possibly played an important role in the crustal growth of the CAOB during the Phanerozoic.