内蒙古苏尼特左旗地区古生代花岗岩岩石学特征

发布时间：2018-04-08 19:06

本文选题：晚石炭世　切入点：碱长花岗岩　出处：《石家庄经济学院》2015年硕士论文

【摘要】：研究区位于内蒙古苏尼特左旗地区西北部,大地构造位置属中亚造山带东段—兴蒙造山带。该区构造单元划分属兴蒙造山带北方造山带,南侧以二连—贺根山断裂带为界,北侧属西伯利亚活动大陆边缘,查干敖包—阿荣旗深断裂东西向穿过该区。该区古生代属于古亚洲洋构造域,进入中生代,则属滨西太平洋构造域。研究区出露地层包括石炭系宝力高庙组一段碎屑岩、白垩系白音高老组火山岩、白垩系大磨拐河组、古近系伊尔丁曼哈组及第四系。碱长花岗岩岩体周缘被白音高老组火山岩喷发不整合覆盖。研究区花岗岩类岩石组合主要为碱长花岗岩、二长花岗岩和花岗闪长岩。本文主要研究了碱长花岗岩体。碱长花岗岩基出露于查干敖包—阿荣旗断裂以北准和热音苏木一带,在楚图陶勒盖一带被斑状花岗闪长岩侵入。碱长花岗岩体发育发育东西向展布的斑状花岗闪长岩脉和斑状黑云母二长花岗岩脉。碱长花岗岩的锆石U-Pb同位素测年获得206Pb/U238加权平均年龄为312.2Ma±7.4Ma(MSWD=6.67),属于晚石炭世。地球化学分析结果显示,碱长花岗岩高硅、富碱,显示钙碱性岩浆地球化学特征;A/CNK=1.01~1.12,A/NK=1.05~1.40,属于准铝质-弱过铝质岩石。碱长花岗岩轻重稀土分馏不明显,具有明显的Eu负异常,呈典型的“海鸥型稀土配分曲线”。在原始地幔标准化微量元素蛛网图上,碱长花岗岩不相容元素Ba、Nb、Ce、Sr、Ti亏损明显,相容元素Rb、U、Th等富集,表明地壳岩浆源区特征。碱长花岗岩高10000Ga/Al比值和高Zn、Zr、Y、Ce含量,在花岗岩分类图解上分布于A型花岗岩区。它们高Ga和Y、低Nb,属于A2-花岗岩亚类。据微量元素构造辨别图解,研究区碱长花岗岩均落入同碰撞花岗岩区和火山弧花岗岩区,属于火山弧后环境。
[Abstract]:The study area is located in the northwest of Sunita Zuo Banner area, Inner Mongolia. The tectonic location is the east segment of Central Asian orogenic belt-Xingmeng orogenic belt.The tectonic units in this area are divided into the northern orogenic belt of Xingmeng orogenic belt, the Erlian-Hegenshan fault zone in the south and the active continental margin of Siberia in the north.The Paleozoic belongs to the Paleo-Asian oceanic tectonic domain and enters the Mesozoic and belongs to the West Coast Pacific tectonic domain.The exposed strata in the study area include the clastic rocks of the first member of the Baoligaomiao formation of the Carboniferous, the volcanic rocks of the Cretaceous and the Damokuahe formation of the Cretaceous system, the Paleogene Yerdingmanha formation and the Quaternary system.The margin of alkali-feldspar granite body is covered by the eruption unconformity of Baiyingao formation volcanic rocks.The granitic rock assemblages in the study area are mainly composed of alkali feldspar granite, monzomorphic granite and granodiorite.In this paper, the alkali-feldspar granite is studied.The alkali feldspar granite basement was exposed to the north of Chagan Aoba-Aronqi fault and was intruded by porphyry granodiorite in the area of Tudaulege.The alkali-feldspar granitic body developed the porphyry granodiorite vein and the porphyry biotite monzogranite vein.The zircon U-Pb isotopic dating of alkali feldspar granites obtained 206Pb/U238 weighted mean age of 312.2Ma 卤7.4 Ma-MSWDN 6.67, which belongs to the late Carboniferous.The geochemical analysis shows that the alkali feldspar granite is high in silicon and rich in alkali, indicating the geochemical characteristics of calc-alkaline magma.The fractionation of heavy and heavy rare earth elements in alkali feldspar granite is not obvious, and it has obvious negative EU anomaly, which is typical "seagull-type rare earth partition curve".On the primitive mantle-normalized trace element cobweb map, the alkali feldspar granite is characterized by obvious depletion of the incompatible element BaHNbNbCE-Sr-Ti and enrichment of the compatible element RbCU Th, which indicates the characteristics of the crustal magma source region.The alkali feldspar granites have a high 10000Ga/Al ratio and a high Zn ~ (2 +) Zr ~ (2 +) Y ~ (+) ce content, and are distributed in the A-type granite area on the classification diagram of the granites.They are high in Ga and Y, low in NB and belong to A 2-granite subclass.According to the trace element structure distinguishing diagram, the alkali feldspar granites in the study area all fall into the syncollision granite area and the volcanic arc granite area, which belong to the behind volcanic arc environment.
【学位授予单位】：石家庄经济学院
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121

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