华北克拉通东部中生代岩石圈减薄的过程与机制:中生代火成岩和深源捕虏体证据  

Processes and mechanism of Mesozoic lithospheric thinningin eastern North China Craton: Evidence from Mesozoicigneous rocks and deep-seated xenoliths

作　　者：许文良[1] 王清海[1] 王冬艳[1] 裴福萍[1] 高山[2] 

机构地区：[1]吉林大学地球科学学院,吉林长春130061 [2]中国地质大学地球科学学院,湖北武汉430074

出　　处：《地学前缘》2004年第3期309-317,共9页Earth Science Frontiers

基　　金：国家自然科学基金资助项目 (4 0 1 72 0 30 ;40 1 330 2 0 ) ;高校博士学科点基金资助项目 (2 0 0 1 0 1 830 0 7)

摘　　要：基于最新的同位素年代学资料 ,华北克拉通东部中生代的岩浆作用可划分成四个阶段 ,即晚三叠世 ( 2 0 5～ 2 2 5Ma)碱性岩浆作用 ;中晚侏罗世 ( 1 5 5～ 1 6 0Ma)花岗质岩浆作用 ;早白垩世 ( 1 1 2～ 1 32Ma)双峰式岩浆作用和晚白垩世 ( 92～ 73Ma)碱性玄武质岩浆作用。徐淮地区中生代侵入岩中榴辉岩捕虏体的发现及其地质年代学资料 ( 2 1 9Ma)表明 ,华北克拉通东部中生代早期曾发生过一次重要的陆壳加厚过程。俯冲板片的断离以及高压—超高压变质岩的快速折返和晚三叠世 ( 2 0 5～ 2 2 5Ma)的碱性岩浆作用的存在均暗示 ,华北克拉通中生代岩石圈减薄已经开始。拆沉作用则是引起中生代早期岩石圈减薄的主要机制。中、晚侏罗世 ( 1 5 5～ 1 6 0Ma)花岗质岩浆作用形成于造山期后的伸展环境 ,代表了中生代岩石圈减薄的继续和发展。早白垩世 ( 1 1 2～ 1 32Ma)双峰式岩浆作用表明中生代岩石圈减薄达到了峰期。而幔源纯橄岩捕虏体中富硅质熔体的交代作用和玄武岩的高87Sr/ 86Sr值、低ε(Nd ,t)值特征表明 ,软流圈对岩石圈底部的化学侵蚀可能是导致该阶段岩石圈减薄的主导机制。晚白垩世 ( 92～ 73Ma)碱性玄武质岩浆作用和“海洋型”Mesozoic magmatisms in the eastern North China Craton (NCC) can be subdivided into four periods on the basis of the last isotopic geochronological data, i.e., the late Triassic (205～225 Ma) alkaline magmatism, the middle-late Jurassic (155～160 Ma) granitic magmatism, the early Cretaceous (112～132 Ma) bi-modal magmatism, and the late Cretaceous (73～92 Ma) alkaline basaltic magmatism. The discovery of eclogite xenoliths and their geochronological data (220 Ma±) in Mesozoic intrusive in the Xu-Huai region imply that the thickening of continental crust happened in the eastern North China craton in the Early Mesozoic. The break-off of subducted slab, quick exhumation of high- and ultrahigh-pressure metamorphic (UHPM) rocks, and the late Triassic (205～225 Ma) alkaline magmatism suggest the beginning of Mesozoic lithospheric thinning in the NCC. The delamination could be a major mechanism to result in the thinning of lithospheric mantle in the Early Mesozoic. The middle-late Jurassic (155～160 Ma) granitic magmatism formed in post-orogenic extensional environment, implying the continuity and development of Mesozoic lithospheric thinning. The early Cretaceous (112～132 Ma) bi-modal magmatism implys the coming of the peak period of Mesozoic lithospheric thinning. The silica-rich melt metasomatism in the mantle-derived dunite xenoliths and high^(87)Sr/^(86)Sr ratios and low ε(Nd,t) values of basalts indicate that the chemical erosion of the asthenosphere to the lithospheric mantle could be a major mechanism to result in the thinning of lithospheric mantle in the period. The late Cretaceous (73～92 Ma) alkaline basaltic magmatism and the existence of “oceanic-like” mantle xenoliths indicate the decreasing of isothermal plane and the accretion of lithospheric mantle.

关 键 词：华北克拉通 中生代 岩石圈减薄 火成岩 深源捕虏体 

分 类 号：P588.12[天文地球—岩石学] P542[天文地球—地质学]