关于东天山花岗岩与陆壳垂向增生的若干认识  

Some problems on granites and vertical growth of the continental crust in the eastern Tianshan Mountains,NW China.

作　　者：顾连兴[1] 张遵忠[1] 吴昌志[1] 王银喜[2] 唐俊华[1] 汪传胜[1] 郗爱华[1] 郑远川[1] 

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室(南京大学)南京大学地球科学系,南京210093 [2]南京大学现代分析中心,南京210093

出　　处：《岩石学报》2006年第5期1103-1120,共18页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2001CB409802);国家自然科学基金项目(40472042)

摘　　要：东天山海西期主碰撞以后形成的花岗岩可分为三个阶段:挤压-伸展转折阶段(310～285Ma)、碰撞后伸展阶段(285～250Ma)和板内阶段(250～208Ma)。这三个阶段在岩石圈厚度、等温线形态和动力学状态等方面的差异,造成了不同阶段花岗岩岩体形态、岩石组合、岩相学和地球化学等方面的差异。除了底侵以外,幔源岩浆的内侵可以造成地壳不同层次岩石的部分熔融,也是花岗质岩浆生成的重要机制和地壳垂向增生的重要方式。东天山的片麻状花岗岩有一部分是变质交代成因的,这类花岗岩的形成与碰撞后幔源岩浆的底侵和内侵有关。变质峰期后韧性剪切带中构造细粒化的岩石是形成片麻状花岗岩的最有利部位。虽然这类花岗岩多数定位于地壳较深层次,但在内侵热量的影响下也可以定位于较浅层次。康古尔韧性剪切带的形成除了构造动力作用以外,还与地壳垂向增生,尤其是内侵有着密切联系,是构造动力、岩浆活动、变质作用和流体运移等复杂反馈的结果。博格达造山带碰撞前和碰撞后岩浆岩均具有正的ε_(Nd)(t)值,表明该造山带地幔早在碰撞前就已亏损,而碰撞后的地幔则继承了碰撞前地幔的亏损特征。东天山在印支期有一次重要的地壳垂向增生事件,其岩浆活动和成矿作用与古特提斯洋的俯冲和随后的碰撞密切有关,因此是东天山从中亚构造体制向特提斯体制转换的产物。Granite formation after major continental collision in the eastern Tianshan Mountains can be divided into three stages： the compression-extension transition stage （310- 285Ma）, the post-collision extension stage （285 - 250Ma） and the intra-plate stage （250 -208Ma）. Distinguishable granite features of each stage in pluton morphology, rock association, petrography and geochemistry depend upon lithosphere thickness, isotherm shapes and geodynamics of these stages. Apart from underplating, intraplating, which is capable to induce partial melting at various crustal levels, is another essential mechanism for generation of granite magmas and crustal growth. Some of the gneissic granites in eastern Tianshan were formed by metamorphism-metasomatism with ultimate genetic affiliation to post-eollisional underplating and intraplating of mantle magmas. Post-metamorphic peak ductile shear zones with highly reduced grain sizes are most favorable sites for the formation of gneissic granites. Despite that most of the gneissic granites are emplaced at deep crustal levels, they can also be formed at relatively shallower levels depending upon the assistance of heat from underplating. Apart from tectonic forces, formation of the Kanguer ductile shear zone is closely connected to continental vertical growth, particularly intraplating, and includes complicated feedback between teetonism, magmatism, metamorphism, and fluid migration. Both the preeollisional and post-eollisional magmatie rocks from the Bogda orogen are characterized by positive εNd （t） values, indicating that the mantle of this orogen were already depleted before collision and that post-collisional depletion could have been inherited from prceollisional mantle. An Indosinian （Triassic） event of vertical crustal growth is discerned in eastern Tianshan. Magmatism and oreformation in accompany with this event was related to the subduction and subsequent collision of the Palaeo-Tethys, and hence represent the tectonic transition of eastern Tianshan fro

关 键 词：碰撞后花岗岩 板内岩浆活动 韧性剪切带 陆壳增生 底侵 内侵 天山 

分 类 号：P588.121[天文地球—岩石学]