赣南地区加里东期基性岩墙的性质及构造意义

发布时间：2018-04-25 02:12

本文选题：赣南地区 + 华南地块　；参考：《成都理工大学》2017年硕士论文

【摘要】：赣南地区在大地构造位置上属于南岭东西向构造岩浆带的东段,属于南岭稀有-有色金属成矿带(左祖发,2015)。该区岩浆活动强烈,部分岩浆岩体呈面状分布。其中,加里东期和燕山期的岩浆活动最为活跃。区内岩浆岩绝大部分为酸性岩浆岩,基性岩含量极少,零星分布于个别构造发育位置。基性岩墙在区域上与深大断裂构造关系紧密,常与区域内的伸展构造环境相关,他们起源于地壳深部(上地幔或下地壳),沿地壳薄弱位置上升到地壳中,在地壳不同层次发生侵位活动。华南地块是由西北部的扬子陆块和东南部的华夏陆块在新元古代早期沿着江南造山带拼贴而成,并经历后期多期次构造岩浆事件的叠加改造,其中加里东期造山作用就是其中一次非常重要的构造事件。但是,目前对华南加里东期构造岩浆事件的研究主要集中于花岗岩类,酸性火山岩和基性岩研究程度相对较低。目前发现的华南加里东期基性岩仅有3例,分别分布于南岭地区、云开地区和武夷地区,年龄主要集中于420-450 Ma之间,但是,基于相关地球化学和同位素的研究,目前对这些岩形成的构造环境还存在较大的争议,有人认为他们形成于板内环境,有人认为形成于岛弧俯冲环境(Yao et al.,2012;Wang et al.,2013)。本文主要以赣南遂川地区基性岩墙作为研究对象,开展了详细的野外观察和室内岩石学、地球化学以及锆石LA-ICP-MS U-Pb年龄和Lu-Hf同位素等测定分析研究,并对其岩石学、地球化学特征、形成时间、岩浆成因及构造环境等有关问题进行探讨。基性岩墙LA-ICP-MS锆石U-Pb定年法得到Th、U之比介于0.46-1.59之间,可以确定为岩浆成因形成的锆石。4个样品的测年结果为446±6.6Ma(N=30,MSWD=0.55)、431.9±5.7Ma(N=30,MSWD=0.65)、422.3±7.3Ma(N=30,MSWD=0.79)和426.6±6.9Ma(N=20,MSWD=0.52),侵入时代为早古生代志留纪,表明该岩体为赣南地区加里东运动后期构造环境由挤压转换为区域性伸展拉张环境后的产物。对两个样品进行的Lu-Hf同位素分析结果显示,初始176Hf/177Hf比值变化范围较小,对应的εHf(t)值都在-4~-0.1之间,全部为负值,显示锆石应为壳源岩石重熔作用的产物。锆石的二阶段Hf亏损地幔模式年龄TDM2值介于1424~1670 Ma之间,主要分布在中元古代,指示中元古代时期的新生基性地壳可能是研究区早古生代加里东期基性侵入岩形成的主要源区。主量元素特征和微量元素分析结果显示,基性岩墙为拉斑玄武岩系列和碱性系列,属于富钠基性岩类;TiO2含量较高,其中3个样品含量大于1%,属于钛较高的基性岩类;A/NCK均小于1,属于准铝质基性岩类,稀土配分曲线右倾明显,∑LREE/∑HREE在7.4~8.78之间,显示样品轻稀土相对富集,重稀土相对亏损的特征。曲线模式与地幔岩浆型稀土元素曲线模式大致相似,说明岩浆来源与地幔岩浆有密切关系。这说明早古生代加里东运动末期的岩浆作用是幔源岩浆与中元古代形成的基性地壳共同作用的结果;早古生代晚期基性岩浆作用以壳源为主。研究区出露了加里东期同造山期的黑云母二长花岗岩、花岗闪长岩和后造山期黑云母二长花岗岩两类中酸性岩体。在研究区同时出现加里东期的酸性和基性两类侵入岩,说明加里东期侵位岩浆岩由挤压型酸性岩渐变为拉张基性岩,反映了该地区区域地壳构造环境由早期的挤压应力环境逐渐变为后期伸展拉张环境的演化过程。
[Abstract]:The South Gannan area belongs to the east part of the Nanling East-West tectonic magma belt, which belongs to the Nanling rare nonferrous metal metallogenic belt (Zuo Zufa, 2015). The magma activity is strong and some magmatic rocks are distributed in a face like distribution. Among them, the magma activity in the Caledonian and Yanshan periods is most active. Most of the magmatism in the region is acidic magma. The rock and basic rock content is very small, scattered in a few tectonic development positions. The basic rock wall is closely related to the deep fault structure in the region, often related to the extensional tectonic environment within the region. They originated in the deep crust of the crust (upper mantle or lower crust), rising in the weak position of the crust to the crust, and emplacement activities at different levels of the earth's crust. The Southern China block is made up of the Yangtze block in the northwest and the Huaxia block in the southeast in the early Neoproterozoic Era along the Jiangnan orogenic belt, and experienced the superposition and transformation of the late multistage tectonic magma events. The Caledonian orogeny is one of the most important tectonic events. However, the Caledonian structure in Southern China is present. The study of magmatic events is mainly focused on granitoids, acid volcanic rocks and basic rocks relatively low. There are only 3 Caledonian basic rocks in Southern China, which are found in Nanling, Yunnan and Wuyi areas, mainly between 420-450 Ma, but based on related geochemistry and isotopes. At present, there is still a lot of controversy about the tectonic environment formed by these rocks. Some people think they are formed in the internal environment of the plate. Some people think that they are formed in the island arc subduction environment (Yao et al., 2012; Wang et al., 2013). This paper mainly takes the basic rock wall in Suichuan area of South Jiangxi as the research object, and has carried out detailed field observation and indoor petrology, The analysis of ball chemistry and zircon LA-ICP-MS U-Pb age and Lu-Hf isotopes is studied, and its petrology, geochemistry, formation time, magmatism and tectonic environment are discussed. The basic rock wall LA-ICP-MS zircon U-Pb dating method is Th, and the ratio of U to 0.46-1.59 can be determined as the formation of magma genesis. The dating results of.4 zircon samples are 446 + 6.6Ma (N=30, MSWD=0.55), 431.9 + 5.7Ma (N=30, MSWD=0.65), 422.3 + 7.3Ma (N=30, MSWD=0.79) and 426.6 + 6.9Ma (N=20,), and the intrusive age is the early Paleozoic Silurian, indicating that the rock mass was transformed from extrusion to regional extensional stretching environment in the later period of the Caledonian movement in the south of Jiangxi. The Lu-Hf isotopic analysis of the two samples shows that the initial 176Hf/177Hf ratio has a small change range and the corresponding Hf (T) values are all -4~-0.1 and all are negative, indicating that the zircon should be the product of the remelting of the shell source rocks. The TDM2 value of the two stage Hf loss mantle model age of the zircon is between the 1424~1670 Ma, and the main content of the zircon is between the 1424~1670 Ma. It is distributed in Mesoproterozoic, indicating that the new basal crust in the Mesoproterozoic period may be the main source area of the early Paleozoic Caledonian intrusive rocks in the study area. The main element characteristics and trace elements analysis showed that the basic rock wall was the La basalt series and the alkaline series, which belonged to the sodium rich base rock, and the TiO2 content was higher. The content of the 3 samples is more than 1%, which belongs to the high titanium base rock. A/NCK is less than 1. It belongs to the quasi aluminum base rock. The distribution curve of rare earth is right, and the sigma LREE/ Sigma HREE is between 7.4~8.78. It shows that the light rare earth is relatively rich and the heavy rare earth is relative to the loss. The Qu Xianmo formula is similar to the mantle magmatic rare earth element curve pattern. It indicates that the magma source is closely related to the mantle magma. This indicates that the magmatism at the end of the early Palaeozoic Caledonian movement was the result of the joint action of the mantle derived magma and the basic crust formed by Mesoproterozoic, and the primary magmatism of the late Early Paleozoic was mainly the crust source. The study area revealed the two long black mica granite in the eastern period of the Gary period. There are two acidic rocks in rock, granodiorite and post orogenic two feldspar granite. In the study area, there are two types of acid and basic intrusive rocks in the Caledonian period, indicating that the Caledonian emplacement magmatic rocks gradually changed from extruded acid rocks to extensional rocks, reflecting the regional tectonic setting of the region from the early compressive stress ring. The environment gradually evolved into the evolutionary process of extensional extension in later stage.

【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P542;P588.124

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