【作者】 杨承海；

【导师】 许文良；

【作者基本信息】 吉林大学 ， 矿物学、岩石学、矿床学， 2007， 博士

【摘要】 本文以鲁西中生代高镁侵入岩为研究对象,利用锆石LA-ICP-MS U-Pb定年技术,确定了鲁西中生代高Mg侵入岩的形成时代;利用继承锆石和/或捕获锆石以及痕量元素和同位素地球化学示踪技术,结合高镁闪长岩中地幔橄榄岩包体的岩石地球化学研究,讨论了高Mg侵入岩岩浆源区的性质和形成的构造背景;在上述研究基础上,结合相邻地区adakitic岩石中榴辉岩包体的年代学与地球化学研究成果,提出了中生代早期华北克拉通东部陆壳加厚过程的存在;中生代早期扬子克拉通俯冲板片的断离以及华北克拉通东部加厚陆壳的拆沉是造成华北克拉通岩石圈破坏的主要动因,同时也是华北克拉通岩石圈减薄的开始;拆沉或断离板片的熔融以及相继出现的与地幔橄榄岩的反应是造成研究区中生代侵入岩中高Mg特征的主要原因。该项研究对全面了解华北克拉通东部中生代岩石圈演化的深部作用过程以及岩石圈破坏的地球动力学背景均具有十分重要的意义。更多还原

【Abstract】 Zircon U-Pb chronology and trace element and Sr-Nd-Pb isotopic geochemistry are carried out for Mesozoic high-Mg diorites in western Shandong to constrain the time and mechanism of the North China Craton （NCC） destruction. Main results are as follows:1. Mesozoic high-Mg diorites from the western Shandong consist mainly of gabbro-diorite- monzodiorite and formed in the Early Cretaceous.2. High-Mg diorites, being most common, are characterized by enrichment in MgO and Na2O, light rare earth elements （LREEs） and large ion lithophile elements （LILEs）, and depletion in heavy REE （HREEs） and high field strength elements （HFSEs）. Their ⁸⁷Sr/⁸⁶Sr（t） ratios andεNd（t）values range from 0.7048 to 0.7108 and -3.95 to -16.60, respectively. Their Pb isotopic compositions can be divided into two groups, i.e., Group I: the initial ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios being 17.18-17.67, 15.44-15.55 and 37.54-38.47, respectively; and Group II: the initial ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios being 16.42-17.11, 15.25-15.38 and 36.56-37.10, respectively. 3. Mesozoic high-Mg intrusions are characterized by high initial ⁸⁷Sr/⁸⁶Sr ratios and lowεNd（t）values. Their Pb isotopic compositions display spatially a variation trend, i.e., ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios gradually decrease from the Tan-Lu fault zone to northwest Combined with the mantle peridotite xenoliths and Archean inherited zircons in the host rocks, it is suggested that the primary magma was derived from the lithospheric mantle or asthenosphere to be involved by lower crust. From southeast to northwest, the Yangtze craton （YC） basement gradually decreases and the NCC basement increases in the magmatic source.The mantle xenoliths from Mesozoic high-Mg diorites consist mainly of spinel harzburgite and chromite-bearing dunite. The mineral equilibration temperatures （less than 1000°C） and chemical data （average Mg # =91.4） indicate that they represent the residues after large degrees of polybaric melting. However, the enrichment in LREEs and LILEs and high initial ⁸⁷Sr/⁸⁶Sr ratios as well as lowεNd（t）values imply that they was later subjected to modification by the infiltration of an adakitic melt.4. The formation of Mesozoic high-Mg diorites requires a thickened continental crust, which is proved by the discovery of eclogite xenoliths in coeval adakitic rocks in the Xu-Huai area. The thickening of the eastern NCC resulted from the subduction of the YC beneath the NCC in Early Mesozoic. The silica-rich melt metasomatism in the mantle peridotite xenoliths, i.e., melt-peridotite interaction, provide direct evidence for high-Mg feature of the Mesozoic diorites in western Shandong.更多还原