华夏地块早白垩世埃达克质岩的岩石成因及地质意义

发布时间：2018-05-25 09:47

  本文选题：Sr-Nd-Hf同位素 + 埃达克质岩　； 参考：《中国科学:地球科学》2017年07期

【摘要】：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.
[Abstract]:The adakite located in the interior of the continent usually comes from the partial melting of the thickened or desunk lower crust. The study of these rocks can provide important information for us to understand the evolution process of the crust. In this paper, a detailed study of Lingxi granodiorite with the characteristics of adakitic rocks in the hinterland of the Huaxia massif has been carried out. The results of U-Pb geochronology of zircon from LA-ICP-MS indicate that it was formed in the late early Cretaceous period. Geochemical characteristics of Lingxi rock mass, For example, high SiO_2 content (most samples are at 64.4 ~ 68.9 wt.), Sr content of 624894 ppm-1, high Sr/Y ratio of 49.9% ~ 60.8% and La/Yb ratio of 23.4 ~ 42.8%, as well as a low Y content of 10.3 ~ 17.1 ppm-1, Ni content of 5.6211.8) and MgO content (the vast majority of the samples are at 0.86 ~ 1.57 wt.), indicating that they originated from partial melting of the lower crust material. The initial 87Sr/86Sr ratio of Lingxi rock mass is 0.7086 / 0.7091, and the value of 蔚 _ S _ D _ (+) _ (t) is .6.2 ~ 5.9. while the value of zircon's 蔚 ~ (-1) is mainly changed from .10.1 ~ (?) ~ 7.6. The geochemical simulation results show that the Lingxi granodiorite was formed by partial melting of the Proterozoic crustal material at the crustal depth of at least 40km (or pressure 鈮，

本文编号：1932978