苏鲁造山带北部多期岩浆与变质事件及其构造意义

发布时间：2018-02-14 01:50

  本文关键词： 超高温麻粒岩 古元古代增生造山作用 三叠纪碰撞造山作用 苏鲁造山带 扬子板块　出处：《中国地质大学(北京)》2015年硕士论文　论文类型：学位论文

【摘要】：苏鲁造山带是扬子与华北板块三叠纪俯冲-碰撞造山作用的产物,是研究大陆造山作用与动力学的天然实验室。尽管对三叠纪的大陆深俯冲及超高压变质作用进行了大量的研究,并取得了大量成果,但对于造山带核部出露的少量前寒武变质表壳岩的长期构造演化历史还存在争议。本文对苏鲁造山带北部威海市西南的变质表壳岩和后期侵入岩进行了详细的岩石学和锆石年代学研究。结果显示这一地区的变质表壳岩主要是由片岩、片麻岩、大理岩、钙硅酸盐岩、斜长角闪岩、石英岩和麻粒岩等组成。泥质麻粒岩(S12-06-1)由石榴石、夕线石、斜长石、条纹长石、反条纹长石、石英、黑云母、白云母和金红石组成。黑云母和白云母呈石榴石和夕线石的冠状体产出,为退变质矿物。相平衡模拟表明,麻粒岩峰期变质的温度和压力条件为≥940?C和~1.2GPa。石英的Ti温压计计算给出的麻粒岩峰期变质温度下限为~980?C。泥质麻粒岩(S12-06-1)中锆石近等粒状或椭圆形,具扇状或冷杉状分带,大多数具有平坦甚至亏损的重稀土配分模式,并有Eu的负异常,为泥质岩麻粒岩相变质过程中生长锆石的典型特征。LA-ICP-MS锆石U-Pb定年结果给出了1845±9Ma的207Pb/206Pb加权平均年龄。与泥质麻粒岩伴生的斜长角闪岩(S12-06-3)的锆石具有典型的岩浆锆石特征,其定年结果给出了758±26Ma的206Pb/238U的加权平均年龄。与钙硅酸盐岩伴生的斜长角闪岩(S12-02-3)中有两种变质锆石,一种CL发光较强、具平坦HREE配分模式的锆石给出了230±4.7Ma的206Pb/238U的加权平均年龄,另一种发光较弱、富集HREE的锆石给出了214±6.5Ma的206Pb/238U的加权平均年龄。表壳岩中的含榴花岗岩脉(S12-02-4)的锆石具有核边结构,锆石边部具岩浆成因特征,获得了200±3.0Ma的206Pb/238U的加权平均年龄。基于以上成果,我们得出如下认识:(1)研究区变质表壳中的泥质麻粒岩记录了古元古代的超高温变质作用,其峰期变质作用的温、压条件分别是≥980?C和~1.2GPa,变质年龄为~1845Ma;(2)变质表壳岩中的基性侵入岩(斜长角闪岩)的原岩年龄为~758Ma的新元古代;(3)变质表壳岩和基性岩浆岩经历了三叠纪(~230Ma)的超高压变质作用和稍晚期(~214Ma)的角闪岩相退变质作用,并被约~200Ma的含榴花岗岩脉侵入。结合现有的其他研究结果,我们认为古元古代超高温变质作用很可能形成在扬子板块北缘的增生造山过程中,新元古代岩浆作用很可能与扬子板块北缘裂解相关,而三叠纪变质和岩浆事件形成在扬子与华北板块的碰撞造山过程中。
[Abstract]:The Sulu orogenic belt is the product of the Triassic subduction and collision orogeny between Yangtze and North China plate. Is a natural laboratory for the study of continental orogeny and dynamics. Although a great deal of research has been done on the Triassic continental deep subduction and ultrahigh pressure metamorphism, a great deal of results have been achieved. However, the long-term tectonic evolution history of a small amount of Precambrian metamorphic crust rocks exposed from the core of the orogenic belt is still controversial. In this paper, the metamorphic epidermal rocks and late intrusive rocks in the southwest of Weihai City, northern Sulu orogenic belt, are discussed in detail. The results show that the metamorphic crust rocks in this area are mainly composed of schist. Gneiss, marble, calcium silicate rock, amphibolite, quartzite and granulite are composed of garnet, skirite, plagioclase, striped feldspar, antistripe feldspar, quartz, biotite, etc. The composition of Muscovite and rutile. Biotite and Muscovite are coronal bodies of garnet and sillimanite, which are retrograde metamorphic minerals. The phase equilibrium simulation shows that the temperature and pressure conditions of granulite metamorphism are 鈮，

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