塔里木大火成岩省金伯利质岩石—霞石岩—碳酸岩研究

发布时间：2018-04-18 03:06

  本文选题：金伯利岩 + 霞石岩　； 参考：《中国地质大学(北京)》2016年博士论文

【摘要】：二叠纪塔里木大火成岩省不同于其他大火成岩省,以复杂的岩石组合为特征。本文在前人研究的基础上,选取塔里木大火成岩省瓦吉里塔格杂岩体中的金伯利质岩石、碳酸岩和霞石岩为研究对象,对其岩石成因进行研究并对塔里木大火成岩省深部地质过程进行初步的探讨,取得的主要研究成果和新认识如下:1、通过金红石SIMS U-Pb定年及详细地野外观察,基本厘定了霞石岩的喷发时间为270Ma,证明其是代表了塔里木大火成岩省晚期的岩浆活动。结合前人的年代学成果,说明塔里木大火成岩省的活动时限较长,持续了约30Ma。2、对金伯利质岩石中发现的碳酸质和硅酸质球粒展开详细研究,其中,碳酸质球粒几乎由纯的方解石组成,硅酸质球粒除了含有方解石外,还含有大量钙铁榴石、金云母和辉石。研究表明,这些球粒的地球化学特征与实验岩石学得到的液态不混溶熔体并不相符,因此它们不能代表由液态不混溶作用形成的熔体。碳酸质球粒的出现,说明岩浆本身富含CO2组分,指示着金伯利质岩浆起源于一个发生了碳酸盐化的地幔源区。3、本论文报道了金伯利质岩石、碳酸岩、霞石岩的镁同位素特征,δ26Mg值变化范围分别为-0.36‰~-0.75‰,-1.09‰~-0.68‰,-0.35‰~-0.55‰,它们均低于正常地幔的δ26Mg值(-0.25‰),指示它们的源区很可能受到早-中古生代俯冲的沉积碳酸盐岩交代的影响。霞石岩具有幔源的Sr-Nd同位素和壳源的Mg-O同位素特征,而碳酸岩也具有幔源的Sr-Nd-O和壳源的Mg-C同位素特征,这种同位素解耦现象对俯冲过程中碳酸盐矿物的相转变提供了非常重要的约束:随着俯冲深度的增加,碳酸盐矿物可由白云石经菱镁矿向方镁石、钙钛矿转变,且其俯冲深度可达900km甚至地球核幔边界。研究表明,霞石岩源区的碳酸盐矿物主要以菱镁矿的形式存在,而碳酸岩源区多以方镁石的相态存在。4、霞石岩在野外呈熔岩状直接覆盖在泥盆纪地层之上,二者之间缺少石炭纪地层,说明在霞石岩喷出之前存在公里级的地壳隆升造成石炭系的剥蚀丢失。菱镁矿分解需要相对于正常地幔绝热线的一个高的热异常。高的热异常和大规模的地壳隆升为塔里木大火成岩省的地幔柱成因提供了更多的支持。5.提出地幔柱-岩石圈相互作用的模型来解释塔里木大火成岩省的重要特征,论证了在地幔柱作用的晚期,塔里木岩石圈地幔发生了一定程度的减薄。塔里木大火成岩省所具有的丰富的岩石系列可归因于地幔柱-岩石圈相互作用的不同阶段的产物。
[Abstract]:The Permian Tarim igneous province is different from other major igneous provinces and is characterized by complex rock assemblages.On the basis of previous studies, the kimberlite, carbonatite and hayite in the Wagiritag complex of Tarim great igneous rock province are selected as the research objects in this paper.The petrogenesis and the deep geological process in Tarim great igneous province are studied. The main research results and new understandings are as follows: 1. Through the age determination and detailed field observation of rutile SIMS U-Pb,The eruption time of the igneous rocks is determined to be 270 Ma, which indicates that it represents the magmatic activity in the late stage of Tarim igneous province.Combined with previous geochronological results, it is shown that the activity time of Tarim great igneous province is relatively long, which lasted about 30 Ma.2.The carbonated and silicic acid spherulites found in kimberlite rocks are studied in detail, among which,The carbonated spheroids are almost composed of pure calcite, and the silicic acid spherulite contains not only calcite, but also a large amount of calcium ferrite, phlogopite and pyroxene.It is shown that the geochemical characteristics of these spherulites are not consistent with the liquid immiscible melts obtained from experimental petrology, so they cannot represent the melts formed by liquid immiscibility.The appearance of carbonaceous spherulites indicates that the magma itself is rich in CO2 components, indicating that the kimberlite magma originated from a carbonated mantle source region .3.This paper reports kimberlite, carbonatite, and kimberlite.The 未 26Mg values vary from -0.36 鈥，

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