阴山及邻区三叠纪富碱侵入岩的成因意义  

Genetic significance of Triassic alkali-rich intrusive rocks in the Yinshan and neighboring areas

作　　者：汤艳杰[1] 张宏福[1,2] 英基丰[2] 

机构地区：[1]中国科学院地质与地球物理研究所、岩石圈演化国家重点实验室,北京100029 [2]西北大学地质学系、大陆动力学国家重点实验室,西安710069

出　　处：《岩石学报》2014年第7期2031-2040,共10页Acta Petrologica Sinica

基　　金：国家973项目(2013CB429802)资助

摘　　要：富碱侵入岩主要包括碱性岩和碱性花岗岩以及碱长花岗岩,其全碱含量(K2O+Na2O)一般>8%。碱性岩主要包括正长岩、霞石正长岩、辉石正长岩、霓霞正长岩、闪石正长岩等,在岩石化学上相对贫硅富铝高碱。碱性花岗岩是指含碱性角闪石、碱性辉石的花岗岩,相对富硅贫铝高碱。在各类侵入岩中,富碱侵入岩所占比例很小,其出露面积约占各类侵入岩出露总面积的2%。但是,富碱侵入岩却有重要的矿产和地质意义。富碱侵入岩的研究不仅对于揭示岩石圈地幔的组成特征、壳幔相互作用及其地球动力学背景具有重要的意义,而且,能为有关岩石圈演化、找矿勘查和资源评价工作提供科学依据。根据对现有资料的总结,燕辽-阴山地区目前已发现很多三叠纪的富碱侵入岩体,它们西起内蒙古包头市,东到吉林省的中部,向东一直延伸到朝鲜的北部,大体分布于北纬40°~42°之间(宽度约100km),构成一条近EW向、长达1500km的碱性岩带。阴山及邻区的三叠纪富碱侵入岩分布在包头、凉城、四子王旗、察哈尔右后旗和察哈尔右中旗地区,东边与之相邻的碱性侵入岩主要分布在天镇、阳原和矾山,它们形成于268~190Ma,其中凉城和包头富碱侵入岩的形成年龄较小(197~190Ma)。这些杂岩体的岩石学和地球化学组成变化较大,其SiO2含量变化可从35%到70%。相比之下,四子王旗和察哈尔地区的正长岩具有较高的SiO2和Al2O3含量,较低的TiO2、Fe2O3和MgO,这可能反映了它们是地幔源区物质较高程度部分熔融的产物,而且经历了相对较大程度的辉石、橄榄岩和角闪石的分离结晶作用。绝大多数正长岩具有很低的MgO含量,落在了板片熔融实验(1~4GPa)所产生的熔体范围之内,部分样品具有相对较高的MgO含量和Mg#,落在了来源于大洋板片熔融所产生的埃达克岩范围内,说明这些岩石的形成可能与再循环的俯冲板片熔Alkali-rich intrusive rocks mainly include alkaline rocks and alkaline granites as well as alkali-feldspar granites. The total alkali contents of these rocks are generally more than 8%. Alkaline rocks mainly include syenite, nepheline syenite, pyroxene syenite, aegirine-augite syenite and amphibole syenite. The most striking feature of their chemical composition is relatively poor in silica, but rich in aluminum and total alkali. Alkaline granites refer to the alkaline amphibole and alkaline pyroxene-bearing granites. They are relatively rich in silica and total alkali but poor in aluminum. Alkali-rich intrusive only account for a very small proportion of total intrusive recks. Their outcrop area approximately occupies 2% of the total area of all kinds of intrusive recks. However, alkali- rich intrusive rocks have very important mineral and geological significance. As a result, the investigations of alkali-rich intrusive rocks not only are of important significance to reveal the characteristics of lithospheric mantle, the processes of crust-mantle interaction and their associated geodynamic background, but also can provide scientific basis for the research of lithospheric evolution, mineral exploration and resource evaluation. Based on the comprehensive summary of available information, there are lots of Triassic alkali-rich intrusions occurred in the Yanshan-Liaoning-Yinshan regions in the northern margin of the North China Craton. These alkali-richintrusions start at the Baotou City in the Inner Mongolia in the west and end at the central part of Jilin Province and even the north part of North Korea in the east. They are generally located between north latitude 40° and north latitude 42° with width of about 100km and constitute a nearly east-west-direction and 1500-kilometer-long alkaline rock belt. The Triassic alkali-rich intrusive rocks in the Yinshan and its neighboring areas are mainly located in the territories of Baotou, Liangeheng, Siziwangqi, Chahar Right Back Banner and Chahar Right Middle Banner ci

关 键 词：富碱侵入岩 岩石成因 阴山 三叠纪 古亚洲洋 华北克拉通 

分 类 号：P588.121[天文地球—岩石学] P588.15[天文地球—地质学]