扬子地块西北缘碑坝地区白玉～1.79Ga A型花岗岩的发现及其对构造演化的制约

发布时间：2018-05-02 06:39

本文选题：古元古代 + A型花岗岩　；参考：《地质学报》2017年07期

【摘要】：本文首次对扬子地块西北缘碑坝地区白玉花岗岩进行了锆石U-Pb年代学、全岩地球化学和锆石Hf同位素研究。锆石LA-ICP-MS U-Pb年龄测定结果表明,白玉花岗岩形成于~1790 Ma。在全岩地球化学组成上,白玉花岗岩高Si,富碱,高FeO~T/(FeO~T+MgO)比值,低Mg、Ca、Mn和P,A/CNK介于0.92~0.96之间,显示为准铝质的特点;微量元素中富集Ga、Th、Zr、Y,贫Sr、P、Ti;稀土元素总量较高,轻重稀土之间分异较明显,并表现出强烈的负Eu异常;这些特点与A型花岗岩一致。锆石负的εHf(t)值(-12.66~-10.69)显示,白玉花岗岩来源于古老地壳物质的部分熔融。地球化学和区域研究成果分析表明,白玉花岗岩最有可能形成于陆内裂谷盆地;结合前人研究成果我们认为,华南存在与Columbia超大陆有关的俯冲、拼合和裂解记录:碑坝地区与弧有关的后河群花岗岩类岩石证实了扬子地块西北缘在~2.10Ga为活动大陆边缘环境;华南与Columbia超大陆拼合有关的碰撞发生于2.00~1.88Ga,宜昌崆岭地区发生陆陆碰撞作用的时间(2.00~1.94Ga)要早于浙西南地区(1.93~1.88Ga),扬子地块本身(西、东扬子地块)及华夏地块(至少是华夏地块西部)在古元古代Columbia超大陆汇聚时期就已经拼贴形成统一的块体;1.87~1.82Ga期间,华南的A型酸性岩形成于后碰撞的构造背景,是由碰撞后的大洋岩石圈拆沉所致;而在~1.79Ga,华南进入了陆内裂解阶段,与华北及其他大陆记录的Columbia超大陆陆内裂解时限较为一致。
[Abstract]:In this paper, zircon U-Pb geochronology, whole rock geochemistry and zircon HF isotope have been studied for the first time in the Baiyu granite in the beiba area of the northwest margin of the Yangtze block. The results of zircon LA-ICP-MS U-Pb dating indicate that the Baiyu granite was formed at 1790 Ma. In terms of the geochemical composition of the whole rock, the Baiyu granite is characterized by high Si-rich, alkali rich, high FeO~T/(FeO~T MgO) ratios, and low MgO CaOmn and PMA / CNK between 0.92 and 0.96, indicating the characteristics of quasi-aluminite, and the enrichment in trace elements of GaAb / ZrY, which is poor in Sr-P _ 2O _ (Ti), and the high amount of rare earth elements. The difference between heavy and heavy rare earth elements is obvious and shows strong negative EU anomaly, which is consistent with A-type granite. The negative 蔚 Hft value of zircon (-12.66 ~ 10.69) shows that the albinite granite originated from the partial melting of the ancient crustal material. The geochemical and regional research results show that the Baiyu granite is most likely formed in the intracontinental rift basin, and we believe that there are subduction related to the Columbia supercontinent in South China. Assemblage and pyrolysis records: the arc related granite rocks of the Houhe Group in the Beida area confirmed that the northwestern margin of the Yangtze block is active continental margin environment at 2.10Ga; The collision between South China and Columbia supercontinent assemblage occurred in 2.00 ~ 1.88Ga. the time of continental collision occurred in Kongling area, Yichang. The East Yangtze block) and the Huaxia block (at least the western part of the Huaxia block) formed a unified block during the Paleoproterozoic Columbia supercontinent convergence period. Type A acidic rocks in South China were formed in the post-collision tectonic setting during the period of 1.87 ~ 1.82 Ga. At 1.79Ga, South China has entered the stage of intracontinental pyrolysis, which is consistent with the time limit of Columbia supercontinent cracking recorded in North China and other continents.
【作者单位】：中国地质调查局成都地质调查中心;国土资源部沉积盆地与油气资源重点实验室;
【基金】：国家自然科学基金项目(编号41402103,41372124,41502114,41672112) 中国地质调查局项目(编号DD20160193)联合资助的成果
【分类号】：P542;P588.121

【相似文献】