Compositional diversity of late Mesozoic granites rooting from the subducted crust in the Qinling–Dabie orogenic belt

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
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Abstract

Continental subduction has been identified in many orogens, such as the Alps, the Himalayas, and the Dabie; however, better understanding of the mechanism and outcome of different subduction processes remains desirable. The Qinling–Dabie orogen in Central China shows an asymmetric distribution of Triassic ultrahigh-pressure metamorphic rocks and syn- and post-tectonic granitoid plutons, thereby providing an excellent means by which to probe the diverse processes of continental subduction. Many late Mesozoic granitoid plutons that formed in post-orogenic or even anorogenic settings are widely distributed in both the Qinling and Dabie tectonic units and can be useful for studying the composition of materials beneath the crust because of their conspicuous compositional diversity. In the present study, we report zircon ages and NdHf isotopic compositions for the Shangcheng and Heyu granite plutons, which represent late Mesozoic plutons in Dabie and Qinling. When compared with those of the Shangcheng pluton, the wide range of Nd isotopic values and the slightly depleted Hf isotopic compositions of the Heyu pluton indicate that there may be juvenile crust beneath the Qinling tectonic unit that is not present beneath the southern margin of North China. The currently undetectable juvenile material in this region may be an important candidate source of the late Mesozoic magmatism and metal mineralization in the southern margin of North China. The compositional diversity of these granites, as indicated by the NdHf isotopic compositions, is attributed to the nature of the deep crust within the orogenic belt, and the magmatic origins of this region are discussed in the present study.

扎根于秦岭-大别造山带俯冲地壳的中生代晚期花岗岩的成分多样性
在阿尔卑斯山、喜马拉雅山和大别山等许多造山带都发现了大陆俯冲现象,然而,人们仍然需要更好地了解不同俯冲过程的机制和结果。中国中部的秦岭-大别造山带显示出三叠纪超高压变质岩以及同步构造和后构造花岗岩柱的不对称分布,从而为探究大陆俯冲的各种过程提供了极好的手段。在秦岭构造单元和大别构造单元中,广泛分布着许多在后成因甚至无成因背景下形成的中生代晚期花岗岩质体,由于其明显的成分多样性,有助于研究地壳下的物质组成。本研究报告了代表大别和秦岭中生代晚期的商城花岗岩和河峪花岗岩的锆石年龄和钕铁硼同位素组成。与商城岩浆岩的同位素组成相比,河峪岩浆岩的钕同位素值范围较大,氦同位素组成略显贫化,这表明秦岭构造单元下可能存在华北南缘所没有的幼生地壳。该地区目前无法探测到的幼生物质可能是华北南缘中生代晚期岩浆活动和金属矿化的重要候选来源。从钕铁硼同位素组成来看,这些花岗岩的成分多样性与造山带深部地壳的性质有关,本研究对这一地区的岩浆起源进行了讨论。
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来源期刊
Lithos
Lithos 地学-地球化学与地球物理
CiteScore
6.80
自引率
11.40%
发文量
286
审稿时长
3.5 months
期刊介绍: Lithos publishes original research papers on the petrology, geochemistry and petrogenesis of igneous and metamorphic rocks. Papers on mineralogy/mineral physics related to petrology and petrogenetic problems are also welcomed.
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