医巫闾山地区早白垩世同伸展花岗岩就位机制  

Emplacement of Early Cretaceous syn-extension granitic in Yiwulüshan area,North China

作　　者：李刚[1] 刘正宏[1] 崔维龙 白相东[2] 

机构地区：[1]吉林大学地球科学学院,长春130061 [2]防灾科技学院,三河065201

出　　处：《岩石学报》2016年第9期2677-2689,共13页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41272223;41402169;41340024)资助

摘　　要：石山岩体形成的时间约为124Ma,是医巫闾山地区早白垩世NWW向伸展变形的同构造花岗岩体。花岗岩的主量、微量元素含量表现出埃达克质岩浆的特点,SiO 2、Al2O3及碱性组分含量较高,而Fe2OT3和MgO含量较低,岩浆锆石εHf(t)值=-26.7^-20.3、tDM2=2.0~2.3Ga,表明岩浆来源于华北陆块加厚下地壳的部分熔融。通过对围岩变形组构与岩体中岩浆组构的分析,可将石山岩体的就位过程划分为三个阶段。在岩浆底劈、膨胀作用和围岩伸展滑移的共同影响下,石山岩体最终形成了主体呈近圆形、西部发育两个岩墙的形态。岩浆就位过程与围岩变形组构的相互关系,表明中、浅部地壳的伸展变形可以控制岩浆的就位过程和最终形态,但与下地壳部分熔融的关系不大,岩石圈减薄及区域伸展应力场是下地壳发生部分熔融的诱因。The Shishan pluton formed at about 124Ma is the syn-tectonic granite of Early Cretaceous extension with NWW shear sense in Yiwultishan area. The major and trace element of the granite shows the characteristics of adakites. The high concentration of SiO2, A1203 , and alkaline content, and low Fe2O3 T and MgO concentration, indicate the magma may be come from the partial melting of crustal rocks. In addition, the magmatic zircons have εHf（t） values from -26. 7 to -20. 3 and t DM2 are between 2. 0Ga and 2. 3Ga indicate the adakitic magma was derived by partial melting of the lower part of the thickened crust of North China block. The magma emplacement of Shishan pluton has three stages could be identified by the analyses of the deformed fabrics from wall rocks and magmatic fabrics from the granites. The Shishan pluton shows a horizontal shape with the subrotund outcrop at major part and two banded granitic dikes at western part, which is the result of diapirism and ballooning of magma and the stretched shear of wall rock. We suggest that the extension at shallow crust could control the emplacement and shape of the pluton. But the partial melting of lower crust has no direct relationship with the shallow extension, instead, the lithospheric thinning and the field of regionally extensional stress may be the cause of partial melting.

关 键 词：岩浆就位 伸展变形 岩石成因 变质核杂岩 医巫闾山地区 华北陆块 

分 类 号：P542[天文地球—构造地质学] P588.121[天文地球—地质学]