Geochemical Evidence for Thickening and Thinning of Lower Crust beneath the Jiaodong Peninsula: Implications for Late Mesozoic Destruction of the Eastern North China Craton
Geochemical Evidence for Thickening and Thinning of Lower Crust beneath the Jiaodong Peninsula: Implications for Late Mesozoic Destruction of the Eastern North China Craton
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胶东半岛下地壳增厚减薄的地球化学证据：对华北克拉通东部晚中生代破坏的启示
DOI：
10.2113/2020/8831664
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发表时间：
2020-06
期刊：
影响因子：
2.4
通讯作者：
Enquan Zhao
中科院分区：
文献类型：
--
作者：
Yayun Liang;Wenhui Guo;Yao Ma;Enquan Zhao
华北克拉通东部（NCC）被认为在中生代经历了克拉通破坏；然而，其破坏机制仍不清楚。所提出的模型之间的主要区别在于下大陆地壳（LCC）是否经历了减薄。本次研究对华北克拉通东南缘胶东半岛晚中生代长英质侵入岩进行了综合分析，包括晚侏罗世花岗岩（166~146Ma）、早白垩世花岗闪长岩（136~123Ma）和最新早白垩世花岗岩（123~108Ma）。这些岩石使我们能够研究该地区LCC厚度的变化，并进一步讨论华北克拉通东部的破坏机制。在这里，可以使用长英质侵入岩的全岩 La/Yb 比率来跟踪地壳厚度的时间变化。我们的研究表明，由于早侏罗世以来华北克拉通下方古太平洋岩石圈的挤压和向西俯冲，华北克拉通东部的大陆地壳在晚侏罗世（>40km）增厚。大陆地壳在早白垩世进一步增厚，这是由于~144Ma之后俯冲板片变陡，在拉张环境中产生了地幔衍生熔体的地壳底侵。然而，在早白垩世末期，大陆地壳变薄（20-40公里），这是由于~123Ma之后俯冲板块的回滚造成的。三个阶段长英质侵入岩的地球化学成分也表明，影响华北克拉通东部的区域构造应力在~144Ma之后从挤压环境转变为板内伸展环境。因此，华北克拉通东部晚中生代的破坏及其伴随的岩浆作用受到古太平洋岩石圈低角度俯冲、陡峭和回滚造成的长期热机械化学侵蚀的控制。
The eastern North China Craton (NCC) has been recognised as undergoing cratonic destruction during the Mesozoic; however, the mechanism of its destruction is still unclear. The main difference between the proposed models is whether the lower continental crust (LCC) underwent thinning. In this study, we conducted comprehensive analyses of Late Mesozoic felsic intrusive rocks, including Late Jurassic granites (166–146 Ma), Early Cretaceous granodiorites (136–123 Ma), and latest Early Cretaceous granites (123–108 Ma) from the Jiaodong Peninsula, located on the southeastern margin of the NCC. These rocks allowed us to investigate variations in the LCC thickness in this region and to further discuss the destruction mechanism of the eastern NCC. Here, temporal variations in crustal thickness can be tracked using whole-rock La/Yb ratios of the felsic intrusive rocks. Our study shows that the continental crust in the eastern NCC thickened during the Late Jurassic (>40 km) due to compression and the westward subduction of the Palaeo-Pacific Ocean lithosphere beneath the NCC since the Early Jurassic. The continental crust further thickened during the Early Cretaceous, caused by the steepening of the subducting slab after ~144 Ma that produced crustal underplating of mantle-derived melts in an extensional setting. However, the continental crust thinned (20–40 km) during the latest Early Cretaceous, caused by the rollback of the subducting slab after ~123 Ma. The geochemical compositions of three stages of felsic intrusions also suggest that the regional tectonic stress that affects the eastern NCC altered from a compressional to an intraplate extensional environment after ~144 Ma. Thus, the Late Mesozoic destruction of the eastern NCC and its accompanying magmatism were controlled by prolonged thermomechanical-chemical erosion due to low-angle subduction, steepening, and rollback of the Palaeo-Pacific Oceanic lithosphere.
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