二叠纪地幔柱与地表系统演变

Permian Mantle Plumes and Earth's Surface System Evolution

本文简要总结了国家重点基础研究发展计划项目《二叠纪地幔柱构造与地表系统演变》的主要研究进展:(1)峨眉山大火成岩省形成于~259 Ma,持续时间小于1 Ma,是地幔柱头熔融的产物;塔里木大火成岩省为多阶段喷发(~300,~290,280 Ma),持续时间超过20 Ma,是孕育地幔柱活动的产物。(2)利用综合地球物理方法发现峨眉山大火成岩省内带上下地壳界面"消失"、下地壳增厚且具高波速特征、岩石圈地幔减薄,是地幔柱熔融产物在地壳不同深度底侵和内侵的结果。(3)完善了大火成岩省岩浆矿床的形成机理,构建了地幔柱成矿系统的基本框架,提出地幔柱结构、岩浆源区特征、结晶分异过程、硫化物饱和、地壳混染和岩浆侵位过程等是地幔柱成矿的关键控制因素。(4)从相对和绝对时间角度确证了西伯利亚和峨眉山大火成岩省分别对应于二叠纪末(PTB)和瓜德鲁普统-乐平统界线(GLB)生物灭绝事件;重建了华南二叠-三叠纪海水温度和p H值的演变历史,使甄别二叠纪末生物大灭绝的直接诱因成为可能。

This paper highlights the main research progresses made under the support of the National 973 project entitled ＂Permian Large Igneous Province and Surface System Evolution＂. （ 1 ） The Emeishan Large Igneous Province （ LIP ） was emplaced at ~ 259 Ma with a duration of 〈 1 Ma, most likely resulted from melting of a mantle plume head. The Tarim LIP was emplaced at three episodes with a duration of 〉20 Ma, most likely related to an incubating mantle plume under a thick craton. （2）Comprehensive geophysical survery revealed that the crust in the inner zone of the Emeishan LIP is character- ized by the lack of the upper-lower crust boundary, presence of a thick and high velocity lower crust and a thinned lithos- pheric mantle. All these features are attributable to upwelling of an ancient mantle plume and associated magmatic under- plating and intraplating at different level of the crust. （3） The formation mechanism of magmatic ore deposits associatedwith LIPs is refined, and a framework of plume-related mineralization system is established. Following has been identified as key controlling factors in plume-related mineralization： Structure of a plume, magma source, crystal fractionation, sul- fide saturation, crustal contamination, and intrusion processes. （4）Both relative temporal correlation and absolute dating confirm the links between the Siberian Traps and Permo-Triassic Boundary（PTB）mass extinction, and between the Emeis- han LIP and Guadlupian-Lopingian Boundary（GLB） mass extinction. The reconstruction of Permian-Triassic seawater tem- perature and pI-I makes it possible to discriminate the triggers of the end-Permian mass extinction.