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位于大陆内部的埃达克质岩通常来自于加厚下地壳或拆沉下地壳的部分熔融,对这类岩石的研究可以为我们了解地壳演化过程提供重要的信息.本文对产于华夏地块腹地的具有埃达克质岩特征的灵溪花岗闪长岩开展了详尽的研究工作.LA-ICP-MS锆石U-Pb年代学的结果显示其形成于早白垩世晚期((100±1)Ma).灵溪岩体的地球化学特征,如高SiO_2含量(大部分样品在64.4~68.9wt.%)和Sr含量(624~894ppm)、高的Sr/Y比值(49.9~60.8)和La/Yb比值(23.4~42.8),以及低Y含量(10.3~17.1ppm)、Ni含量(5.62~11.8)和MgO含量(绝大多数样品在0.86~1.57wt.%),表明其来自于下地壳物质的部分熔融.灵溪岩体的87Sr/86Sr初始比值为0.7086~0.7091,ε_(Nd)(t)值为.6.2~.5.9,而锆石的ε_(Hf)(t)值则主要变化于.10.1~.7.6.地球化学模拟的结果显示灵溪花岗闪长岩是由元古代地壳物质在至少40km的地壳深度下(或压力≥1.2kbar)部分熔融形成的,部分熔融的残留相为含石榴子石角闪岩相.结合前人对华夏地块构造演化进程的研究成果,本文认为华夏地块的地壳在早白垩世晚期的一次挤压事件中发生了一定程度的加厚,使地壳厚度达到至少40km,这与华夏地块内存在上白垩统红色砾岩角度不整合于下白垩统或侏罗系岩层之上的地质观察相吻合.在这次挤压事件之后,华夏地块受到古太平洋板块高角度俯冲的影响,进入岩石圈伸展减薄的构造环境.随着岩石圈的减薄,华夏地块的下地壳物质受到上涌的软流圈物质的加热并发生部分熔融,进而产生了灵溪花岗闪长岩以及其他同时代的花岗岩类.本文的研究为了解华夏地块早白垩世的地壳演化提供了新的信息.
The adakitic rocks located in the interior of the continent generally come from partial melting of thickening lower crust or subsidence lower crust, and the study of such rocks can provide important information for us to understand the evolution of the crust. A detailed study has been carried out on the Lingxi granodiorite, which is characterized by adakitic rocks in the hinterland. The zircon U-Pb dating of LA-ICP-MS shows that it was formed in the late Early Cretaceous ((100 ± 1) Ma). The geochemical characteristics of the Lingxi granitoid such as high SiO 2 content (64.4-68.9wt.% For most samples) and Sr (624- 894ppm) and high Sr / Y ratios And La / Yb ratios (23.4-42.8), as well as low Y (10.3-17.1 ppm), Ni (5.62-11.8) and MgO (0.86-1.57 wt.% For the vast majority of samples) The partial melting of the lower crust material shows that the 87Sr / 86Sr initial ratio of Lingxi pluton is 0.7086 ~ 0.7091 and the value of ε_ (Nd) (t) is between 6.2 ~ 5.9, while the ε_ (Hf) (t) The main changes are from .10.1 ~ .7.6. The results of geochemical modeling show that the Lingxi granodiorite is formed by the partial melting of Proterozoic crustal material at crustal depth of at least 40 km (or pressure ≥1.2 kbar), partial melting Of the residual phase is garnet-bearing amphibolite facies.Combining with previous studies on the tectonic evolution of the Huaxia block, this paper argues that the crust in the Cathaysia Block occurred in a certain degree during the early Cretaceous crushing event Thickened to a crustal thickness of at least 40 km, consistent with the geological observation that the Upper Cretaceous red conglomerate angle is not integrated with the Lower Cretaceous or Jurassic strata in the Huaxia block.After this crush event , The Huaxia block is affected by the high-angle subduction of the Paleo-Pacific plate and enters the tectonic setting where the lithosphere extends and is thinned.With the thinning of the lithosphere, the lower crustal material of the Huaxia block is heated by the upwelling asthenospheric material Partial melting occurs, and then Lingxi granodiorite and other granites of the same age are produced.The research in this paper provides new information for understanding the Early Cretaceous crustal evolution of the Huaxia block.