显生宙碰撞造山带超高温变质作用的加热机制:来自二维数值模拟的约束  

Heating mechanisms of ultra-high temperature metamorphism in Phanerozoic collisional orogens: Constraints from 2-D numerical modelling

作　　者：樊银龙 张立飞[1] 李忠海 焦淑娟 王杨 邹雷 FAN YinLong;ZHANG LiFei;LI ZhongHai;JIAO ShuJuan;WANG Yang;ZOU Lei(MOE Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing 100871,China;Key Laboratory of Computational Geodynamics,College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]北京大学地球与空间科学学院,造山带与地壳演化教育部重点实验室,北京100871 [2]中国科学院大学地球与行星科学学院,计算地球动力学重点实验室,北京100049 [3]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

出　　处：《岩石学报》2024年第4期1044-1060,共17页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(91755206)资助。

摘　　要：大量的岩石学证据表明:碰撞造山带中常发育900~1100℃的超高温变质作用。然而,碰撞造山带中如何出现如此极端的超高温条件仍然存在争议。为了更好地理解超高温变质作用加热机制和碰撞造山带中主要热源的相对贡献,我们建立了一系列高分辨率二维热-动力学模型,借此探讨了俯冲大陆岩石圈密度亏损程度、大陆地壳放射性生热率和大陆汇聚速率等因素对碰撞造山过程中超高温变质主要热源的影响。当大陆岩石圈密度亏损(Δρ=ρ软流圈地幔-ρ岩石圈地幔)大于50kg/m^(3)时,有利于发生大陆平板俯冲,软流圈地幔无法上涌为地壳物质提供热源;此时,具有较高放射性生热率(>3μW/m^(3))的地壳可以发生“浅俯冲-折返”型超高温变质作用。而当大陆岩石圈密度亏损小于10kg/m^(3)时,大陆上地壳在深俯冲阶段首先发生超高压榴辉岩相变质作用,随后伴随着大陆岩石圈地幔后撤和软流圈上涌,进而出现以异常高的地幔热流加热为主的“深俯冲-折返”型超高温变质作用。此外,较低的大陆汇聚速率(<1cm/yr)更有利于“深俯冲-折返”型超高温变质作用的产生。将数值模拟结果与特提斯构造域的变质岩石数据和地球物理观测进行对比,我们认为在现今板块构造体制下,由具有密度亏损程度较高的大陆岩石圈平俯冲有利于“浅俯冲-折返”型超高温变质作用的发生,而由密度亏损程度较低的大陆岩石圈俯冲可能导致“深俯冲-折返”型超高温变质作用的产生。Many lines of petrological evidence show that ultra-high temperature (UHT) metamorphism of 900~1100℃ often developed in collisional orogens. However, how such extreme ultra-high temperature conditions arose in collision orogens is still a matter of debate. In order to better understand the heating mechanism of UHT metamorphism and the relative contribution of the main heat sources in collision orogens, we have established a series of high-resolution 2-D numerical models to investigate the influence of several key factors such as the degree of density depletion of the continental lithosphere, the radioactive heat production (RHP) of the continental upper crust and the rate of continental convergence on the main heat sources of ultrahigh temperature metamorphism. When the density depletion of a continental lithosphere (Δρ=ρasthenosphere-ρlithosphere) is greater than 50kg/m^(3), the flat subduction of the continental lithosphere is generally resulting, and the asthenosphere mantle cannot upwell to provide heat source for the continental crust. With a higher RHP (>3μW/m^(3)), the continental upper crust can undergo "shallow subduction-exhumation" type UHT metamorphism. However, when the density depletion of the continental lithosphere is less than 10kg/m^(3), the continental upper crust undergoes ultra-high pressure eclogite facies metamorphism during the deep subduction stage, followed by mantle retreat and asthenosphere upwelling, and then "deep subduction-exhumation" type ultra-high temperature metamorphism dominated by abnormally high mantle heat flow heating. In addition, the lower continental convergence rate (< 1cm/yr) is more favorable to the generation of "deep subduction-exhumation" type UHT metamorphism. By comparing the numerical modelling results with the metamorphic rock data and geophysical observations in the Tethyan tectonic domain, we conclude that, under the present plate tectonic system, the flat subduction of the continental lithosphere with higher density depletion is favorable to the occ

关 键 词：超高温变质作用 碰撞造山带 大陆岩石圈密度 数值模拟 特提斯构造域 

分 类 号：P313[天文地球—固体地球物理学] P588.3[天文地球—地球物理学]