北京昌平薛家石梁杂岩体岩浆混合作用及其成因

发布时间：2018-04-16 07:42

  本文选题：岩浆混合 + 薛家石梁　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：薛家石梁杂岩体位于华北克拉通中部,北京地区燕山山脉南麓,由五个小岩体组成,按年龄从早到晚依次为上庄岩体、薛家石梁岩体、黑山寨岩体、湖门岩体和黑熊山岩体,其中薛家石梁岩体和黑山寨岩体中含有大量闪长质包体及伴生的细粒闪长岩岩脉。上庄岩体由四种岩石组成,从下至上分别为橄长岩、辉长苏长岩、辉长岩和辉长闪长岩,其中橄长岩和辉长苏长岩中富含钛磁铁矿矿体,并与橄长岩互层状产出;薛家石梁岩体主体岩性为角闪闪长岩,在靠近上庄岩体和黑山寨岩体边界附近为辉石闪长岩;黑山寨岩体为角闪二长岩,靠近湖门岩体边界附近为黑云母二长岩;湖门岩体为正长岩,由北向南岩石中矿物粒径逐渐减小,显示其冷凝速度不均衡;黑熊山岩体主体岩性为正长花岗岩-二长花岗岩。五个小岩体中除了薛家石梁岩体和黑山寨岩体为过渡型接触带外,其他岩体之间均为侵入接触关系。按照马昌前等(1994)的包体分类,将薛家石梁杂岩体中的包体分为混杂包体和混成包体两类,并通过对包体和岩脉及寄主岩的岩浆粘度、密度计算,并结合岩相学特征和主量元素Harker图解分析,得出薛家石梁岩体内靠近上庄岩体边界附近发生岩浆机械混合作用,混合区域内所含包体为混杂包体,黑山寨岩体内部也可见到与之成分相同的混杂包体,也为机械混合作用的结果,而黑山寨岩体与薛家石梁岩体的过渡型接触带为岩浆化学混合作用的结果,接触带内所含包体为混成包体,其中薛家石梁闪长质岩浆所占比率较高,最高可达76%。薛家石梁岩体、黑山寨岩体和湖门岩体的稀土元素、微量元素的配分曲线近似平行,显示三者具有相同的源区,富集Ba、Sr、Nb、Ta元素和亏损Pb元素暗示三个岩体来源于下地壳并有幔源物质混入。薛家石梁岩体与黑山寨岩体内的混杂包体的稀土元素和微量元素配分曲线一致,且与上庄岩体的配分曲线近于平行,结合上庄橄长岩中发育大量斜长石残留晶的证据,暗示该混杂包体为富铁含矿流体灌入到上庄岩体中发生部分熔融的产物,部分熔融温度在1130℃以上。通过SHRIMP锆石U-Pb测年,测得混杂包体年龄为127.5Ma,比薛家石梁岩体大约晚3Ma,暗示华北克拉通的抬升速度很快,是岩石圈拆沉作用的直接响应。
[Abstract]:The Xuejia Shiliang complex is located in the central part of the North China Craton, and the southern foot of the Yanshan Mountains in Beijing area. It consists of five small rock masses, which are the Shangzhuang rock mass, the Xuejialiang rock body, the Heishanzhai rock body, the Humen rock body and the Heixiong mountain rock body from early to late according to the age.There are a large number of diorite inclusions and associated fine diorite veins in the Xue Jia Shiliang and Heishanzhai rocks.The Shangzhuang rock body is composed of four kinds of rocks, which are olivine, pyroxene, gabbro and pyrodiorite from the bottom to the top, among which the olivine and pyroxenite are rich in titanomagnetite ore bodies and interbedded with olivine.The main lithology of the Xue Jia Shiliang rock body is hornblende, near the boundary of Shangzhuang and Heishanzhai rock bodies is pyroxene diorite, the Heishanzhai rock body is hornblende monzonite, and near the boundary of Humen rock body is biotite monzonite.The Humen rock body is a syenite, and the size of minerals in the rock decreases gradually from north to south, which indicates that the condensation velocity is uneven, and the lithology of the main body of the Heixiongshan rock body is syenite-monzogranite.In the five small rock masses, except Xue Jia Shiliang and Heishanzhai rock bodies are transitional contact zones, the other rock masses are intrusive contact relationship.According to the classification of inclusions in Machang Qianliang (1994), the inclusions in Xue Jia Shiliang complex are divided into two types: hybrid inclusions and mixed inclusions. The magmatic viscosity and density of inclusions and veins and host rocks are calculated.Combined with petrographic characteristics and principal element Harker diagram analysis, it is concluded that magmatic mechanical mixing occurs near the boundary of Shangzhuang rock body in Xue Jia Shiliang rock body, and the inclusions contained in the mixing area are mixed inclusions.In the interior of the Heishanzhai rock mass, the same mixed inclusions are also found, which are also the result of mechanical mixing, while the transitional contact zone between the Heishanzhai rock body and the Xue Jia Shiliang rock body is the result of the chemical mixing of magma.The inclusions contained in the contact zone are mixed inclusions, of which the ratio of Xue Jialiang diorite magma is high, the highest is 76g.The distribution curves of rare earth elements and trace elements in the Xue Jia Shiliang, Heishanzhai and Humen rock bodies are approximately parallel, indicating that the three bodies have the same source region.The enrichment of Ta and Pb suggests that the three intrusions are derived from the lower crust and are mixed with mantle materials.The REE and trace element partitioning curves of the xenoliths in Xue Jia Shiliang and Heishanzhai rocks are consistent, and are nearly parallel to those of the Shangzhuang rock mass, and combined with the evidence that a large number of plagioclase residual crystals are developed in Shangzhuang olivine.It is suggested that the hybrid inclusion is the product of partial melting of the iron-rich ore-rich fluid into the Shangzhuang rock mass, and the partial melting temperature is above 1130 鈩，

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