赣江下游南昌段河流沉积物碎屑锆石U-Pb年代学和Lu-Hf同位素研究及其地质意义

发布时间：2018-07-22 19:43

【摘要】：作为长江八大支流之一的赣江是江西省的最大河流,它自南向北流贯江西全省。地质上,赣江流经的区域主要位于华夏地块腹地、江南造山带内和扬子地块东南缘。河流是构造与气候共同作用的产物,河流沉积物携带了源岩剥蚀、搬运以及流域源区的信息。而河流碎屑锆石记录了源自地壳物质的信息,这些地壳物质可能没有被保存下来,或者已经不在出露。无疑,赣江河流沉积物中的碎屑锆石主要来源于流经区域地质体中,这些锆石携带有源岩的重要信息。本文分别利用LA-ICP-MS和LA-MC-ICP-MS原位分析技术,对赣江下游南昌段河流沉积物中碎屑锆石的U-Pb年代学和Lu-Hf同位素开展系统研究,旨在讨论赣江流域水系沉积物的物质来源及其所经历的岩浆事件和构造活动,并结合已有资料探讨源区地壳生长和演化规律。文章取得的认识如下:(1)赣江下游南昌段河流沉积物碎屑锆石U-Pb年龄主要集中于134-197 Ma、221-290 Ma、398-484 Ma、520-625 Ma、727-895 Ma、980-1110 Ma、2502-2861 Ma等7个年龄组段。其中最主要的年龄组段为398-484 Ma(峰值为433 Ma,占总数的43%)和134-197 Ma(峰值为151 Ma,占总数的15%)。(2)赣江下游南昌段河流沉积物碎屑锆石所表现出来的主要年龄区间可分别与已知的岩浆事件时间相对应。2502-2861 Ma是全球地壳增长的一个阶段,该事件导致了原始稳定大陆以及古老陆核的形成;980-1110 Ma为全球罗迪尼亚超级大陆聚合、格林威尔期造山带形成的特征年龄;727-895 Ma对应扬子地块与华夏地块拼合及全球罗迪尼亚超级大陆裂解阶段;520-625 Ma对应泛非事件,目前地表尚无相应的岩浆岩石和构造形迹的记录;398-484 Ma正是全球各地褶皱造山-岩浆活动的高峰期,被称加里东构造运动事件;221-290 Ma对应印支-海西期,是古特提斯洋的闭合及其对应的碰撞作用阶段;134-197 Ma对应为燕山期,该时期的岩浆活动是在华南板块形成后的背景上发生的。(3)赣江下游南昌段河流沉积物中碎屑锆石年龄分布特征与华夏地块的年龄分布非常一致,说明赣江碎屑锆石主要来源于华夏地块的物质贡献。有效地从年代学方面对赣江流域的主要地壳物质来源进行了限定。(4)赣江下游南昌段河流沉积物碎屑锆石U-Pb年龄和Lu-Hf同位素组成能够反映华夏地块的形成与演化历史。新太古代锆石的εHf(t)值近似为0,表明该时期发生了强烈的壳幔混合作用;中-新元古代锆石εHf(t)值既有正值也有负值,说明源区物质既有古老地壳物质的再循环,也有新生地壳物质的加入;显生宙以来,εHf(t)值绝大多数为负值,且对应的两阶段模式年龄以古元古代-中元古代的年龄为主,说明显生宙以来的岩浆活动主要来源于古元古代-中元古代新生地壳的熔融和再造,直接来源于亏损地幔的新生地壳物质很少。2.1-1.1Ga是华夏地块地壳生长的主要阶段,此阶段形成的物质构成现今华夏地块全部地壳物质的80%以上。
[Abstract]:As one of the eight tributaries of the Yangtze River, the Ganjiang River is the largest river in Jiangxi Province, which flows from south to north through Jiangxi Province. Geologically, Ganjiang flow is mainly located in the hinterland of the Huaxia block, in the Jiangnan orogenic belt and in the southeastern margin of the Yangtze block. River is the product of tectonic and climatic interaction. Fluvial sediments carry information of source rock erosion, transport and basin source area. The river debris zircon records information from crustal materials that may not be preserved or are no longer exposed. There is no doubt that the detrital zircons in the sediments of the Ganjiang River are mainly derived from the regional geological bodies which carry important information of the active rocks. Using LA-ICP-MS and LA-MC-ICP-MS in situ analysis techniques, U-Pb geochronology and Lu-Hf isotopes of detrital zircons in the sediments of Nanchang section of the lower Ganjiang River have been systematically studied in this paper. The purpose of this paper is to discuss the source of material and magmatic events and tectonic activities in the sediments of the Ganjiang River basin, and to discuss the crustal growth and evolution law of the source region in the light of the available data. The results are as follows: (1) the zircon U-Pb ages of river sediments in Nanchang section of the lower Ganjiang River are mainly concentrated in seven age groups, 134-197 Ma-221-290 Ma-221-290 Ma-398-484 Ma-520-625 Ma-727-895 Ma-980-1110 Ma-Li 2502-2861 Ma and so on. The main age groups were 398-484 Ma (with a peak value of 433 Ma, accounting for 43% of the total) and 134-197 Ma (a peak value of 151Ma, accounting for 15% of the total). The magmatic event time corresponding to .2502-2861 Ma is a stage of global crustal growth. This event led to the formation of the primordial stable continent and the formation of ancient continental nuclei. The characteristic age of formation of the Greenville orogenic belt is 727-895 Ma, corresponding to the combination of Yangtze block and Cathaysian block, and 520-625 Ma to pan-African event at the stage of global Lordinia supercontinent pyrolysis. At present, there are no corresponding records of magmatic rocks and tectonic traces on the surface of the earth. The peak of the fold-orogenic and magmatic activity is 398-484 Ma, which is called Caledonian tectonic event (221-290 Ma) corresponding to the Indo-Hercynian epoch. The closure of the PaleoTethys Ocean and its corresponding collision stage, 134-197 Ma, correspond to the Yanshanian epoch. The magmatic activity in this period occurred after the formation of the South China plate. (3) the age distribution characteristics of the detrital zircon in the sediments of the Nanchang section of the lower Ganjiang River are very consistent with the age distribution of the Huaxia block. The results show that the zircon from the Ganjiang River is mainly derived from the material contribution of the Huaxia block. The main crustal material sources in Ganjiang River basin are effectively limited from chronology. (4) the zircon U-Pb age and Lu-Hf isotopic composition of river sediments in Nanchang section of the lower Ganjiang River can reflect the formation and evolution history of the Huaxia block. The 蔚 HF (t) value of NeoArchean zircon is approximately 0, which indicates that strong crust mantle mixing occurred in this period, and the 蔚 HF (t) value of Mesoproterozoic zircon has both positive and negative values, indicating that the source material has the recirculation of ancient crustal material. Since the Phanerozoic, 蔚 HF (t) values have been mostly negative, and the corresponding two-stage model ages are mainly from Gu Yuan to Mesoproterozoic. It is suggested that the magmatic activity since Phanerozoic mainly originated from the melting and reconstructing of the new crust of Gu Yuan and Mesoproterozoic, and that the material of the new crust derived directly from the depleted mantle is very little .2.1-1.1 Ga is the main stage of crustal growth in the Huaxia block. The materials formed in this stage constitute more than 80% of all crustal materials in the present Huaxia block.
【学位授予单位】：东华理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P597.3;P512.2

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