摘要:
利用LA-MC-ICP-MS锆石U-Pb测年获得马兰峪背斜核部前分水岭二长花岗岩、茅山二长花岗岩、王坪石二长花岗岩、高家店石英闪长岩、肖营子花岗闪长岩及钾长花岗岩的结晶年龄分别为(153.8±2.7) Ma、(162.7±1.5) Ma、(162.3±1.3) Ma、(170.5±1.8) Ma、(164.6±2.2) Ma和(186.8±1.3) Ma,同时获得180~175 Ma和201~186 Ma的继承岩浆锆石年龄,时代上分属于印支期和燕山期,以燕山期为主;岩石地球化学特征表明其岩浆来源于上地幔物质底侵引起下地壳部分熔融。结合区域地质资料分析,本文认为:1)马兰峪背斜开始形成于印支期,完成于燕山期;2)印支—燕山期强烈构造运动不但使地台基底与盖层同步卷入褶皱作用,地壳缩短加厚,而且使上地幔物质底侵,下地壳物质部分熔融,从而形成了一系列发育于背斜核部的侵入岩体;3)燕山地区中生代造山作用,并不只是地壳表层的物质运动,而是涉及全地壳以至上地幔的物质运动,它使中朝地块北部由原来稳定克拉通状态进入一个全面活化的新阶段。
Abstract:
LA-MC-ICP-MS U-Pb dating of zircons from the Qianfenshuiling monzonitic granite, Maoshan monzonitic granite, Wangpingshi monzonitic granite, Gaojiadian quartz diorite, Xiaoyingzi granodiorite and moyite yielded (153.8±2.7) Ma, (162.7±1.5) Ma, (162.3±1.3) Ma, (170.5±1.8) Ma, (164.6±2.2) Ma and (186.8±1.3) Ma respectively, and several inheritable magmatic zircons were dated at 180~175 Ma and 201~186 Ma. The results indicate that the Mesozoic intrusive bodies along the core of the Malanyu anticlinorium were emplaced in the Indosinian and Yanshanian, with the latter being predominant. Their geochemical characteristics show that the magma was generated from partial melting of lower crustal material caused by the upper mantle underplating. Combining these data with the regional geological information, the authors have reached some conclusions: 1) the Malanyu anticline was initiated in the Indosinian period, and formed finally in the Yanshanian period; 2) the Indosinian-Yanshanian orogeny not only contributed to the crust thickening characterized by basement-involved folding but also resulted in partial melting of the lower crust, bringing about the fromation of intrusive bodies along the anticlinal core; and 3) the Mesozoic orogeny in the Yanshan area was represented not only by the tectonic process of the surface of the crust but also by the movement of the lower crust and upper mantle, which caused the northern part of the Sino-Korean block to enter into a new evolutionary stage, i.e., from the original stability to overall activation.
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