造山崩塌过程的岩浆作用响应:以北京薛家石梁-黑山寨岩浆杂岩体为例  

Magmatic Response to the Orogenic Collapse: An Example from the Xuejiashiliang-Heishanzhai Magmatic Complex in Beijing

作　　者：汪洋[1] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《大地构造与成矿学》2014年第3期656-669,共14页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(批准号:40572128;40376013;40104003);中央高校基本科研业务费专项资金(编号:2652013021;2010ZD15)资助

摘　　要：薛家石梁-黑山寨岩浆杂岩体出露于北京市昌平区东部,由上庄辉长岩、薛家石梁闪长岩、黑山寨石英二长岩、湖门二长岩和黑熊山花岗岩组成。结合薛家石梁-黑山寨杂岩体的地质产状、各类岩性的空间分布和接触关系以及侵位深度的估算结果,我们认为该杂岩体是一个被剥露出来的掀斜岩浆房。根据岩石学特征和地球化学分析结果,可将杂岩体的岩石归为5大类:(1)堆晶成因的含钒钛磁铁矿辉长岩;(2)低Ti辉长岩;(3)高Ti闪长岩;(4)高Sr低Y中酸性岩(低Ti闪长岩、二长岩、石英二长岩)和(5)黑熊山铁质花岗岩。其岩浆活动分为3批次:第1批次的原始幔源岩浆经AFC过程演化形成该杂岩体所包含的堆晶辉长岩、低Ti辉长岩、低Ti闪长岩、石英二长岩和二长岩;在岩浆房未固结时第2批次的高Ti闪长岩浆注入其中;然后是第3批次的壳源铁质花岗岩浆注入岩浆房上部。岩浆固结后该岩浆房经历了大角度掀斜,是云蒙山变质核杂岩下盘在拆离运动过程中发生背形穹弯变形的结果。该杂岩体所含的高Ti闪长岩的地球化学和Sr-Nd-Pb同位素特征指示当时存在亏损放射性Pb同位素的岩石圈地幔,不支持岩石圈拆沉的动力学模式。薛家石梁-黑山寨杂岩体是燕山造山带挤压变形导致的地壳增厚和增温所引起的重力崩塌过程的岩浆事件响应。The Xuejiashiliang-Heishanzhai magmatic complex is exposed in the east part of Changping District of Beijing, and is composed of the Shangzhuang gabbro, Xuejiashiliang diorite, Heishanzhai quartz-monzonite, Humen monzonite and Heixiongshan granite. It is suggested that the Xuejiashiliang-Heishanzhai complex represents a tilted magma chamber, based on the field occurrence, contact relationships, spatial distribution, and the estimated emplacement depth of the plutons. According to the petrology and geochemistry, the rocks of the plutons are classified as five categories：（1） the cumulated gabbro which contains vanadium-titanium magnetite ore;（2） low-Ti gabbro;（3） high-Ti diorite;（4） high Sr and low Y intermediate to acid rocks; and（5） the Heixiongshan ferroan granite. The magmatic pulses of the complex can be divided into three batches. The first batch of a primitive mantle-derived magma generated the sequence of cumulated gabbro, low-Ti gabbro, low-Ti diorite, quartz-monzonite and monzonite by assimilated fractional crystallization（AFC） process. The second batch of high-Ti dioritic magma was injected into the magma chamber before the complete consolidation of the low-Ti diorite, quartz-monzonite and monzonite. And finally, the third batch of crust-derived ferroan granitic magma intruded into the upper part of the magma chamber. The high-angle tilting of the magma chamber after consolidation was resulted from the domal uplifting of the footwall of the Yunmenshan metamorphic core complex. The geochemistry and Sr-Nd-Pb isotopic characteristics of the high-Ti diorite in the complex indicate the presence of the lithospheric mantle characterized by less radioactive-Pb isotopes, beneath the Yanshan belt in the Early Cretaceous. This fact does not favor the dynamic model of lithosphere delamination. The Xuejiashiliang-Heishanzhai complex is a good example of the magmatism related to the gravitational collapse of the Yanshan orogenic belt.

关 键 词：岩石成因 岩浆房 地球化学 造山崩塌 薛家石梁-黑山寨杂岩 北京 

分 类 号：P595[天文地球—地球化学]