榴辉岩部分熔融热力学及微量元素地球化学模拟:以柴达木盆地北缘锡铁山地体为例  

Thermodynamic and trace elements modelling of partial melting of eclogite:A case study of Xitieshan terrane,northern Qaidam basin,China

作　　者：蒋晓聪 李传志 于胜尧[1,2] 彭银彪 蒋兴洲 高翔宇 王林涛 JIANG Xiaocong;LI Chuanzhi;YU Shengyao;PENG Yinbiao;JIANG Xingzhou;GAO Xiangyu;WANG Lintao(MOE Key Lab of Submarine Geosciences and Prospecting Techniques,Institute for Advanced Ocean Study,College of Marine Geosciences,Ocean University of China,Qingdao,Shandong 266100,China;Laboratory for Marine Geology,Pilot National Laboratory for Marine Science and Technology,Qingdao,Shandong 266037,China)

机构地区：[1]中国海洋大学海洋地球科学学院,海洋高等研究院,海底科学与探测技术教育部重点实验室,山东青岛266100 [2]青岛海洋科学与技术国家实验室,海洋地质过程与环境功能实验室,山东青岛266037

出　　处：《地质学报》2025年第3期744-759,共16页Acta Geologica Sinica

基　　金：青岛海洋科学与技术试点国家实验室山东省专项经费(编号2022QNLM05032-3);国家自然科学基金项目(编号42121005,42372247);山东省自然科学基金杰出青年基金项目(编号ZR2020JQ16);泰山学者项目(编号ts20190918,tstp20221112)联合资助的成果。

摘　　要：地壳深熔作用是高级变质岩石中普遍存在的现象,也是造山带演化的重要地质过程之一。榴辉岩作为研究大陆俯冲、超高压变质以及壳幔相互作用的主要岩石类型,其部分熔融与地壳生长、板片折返过程以及俯冲隧道中元素的迁移与分配等具有紧密联系。柴北缘构造带锡铁山地体退变榴辉岩中普遍保留了代表深熔作用的原位和源区钠质浅色体,为研究超高压榴辉岩的深熔作用提供了有利条件。本文对锡铁山地体榴辉岩中的浅色体进行锆石U-Pb年代学研究,获得浅色体的结晶年龄为425.3±5.9 Ma(MSWD=0.74)。通过对锡铁山地体榴辉岩的深熔过程开展岩石热力学及微量元素地球化学模拟,结合区域上榴辉岩退变P-T轨迹获得了赋存于榴辉岩中的钠质浅色体平衡结晶的温压条件为794~797℃,1.227~1.071 GPa。锡铁山地体榴辉岩初始部分熔融发生在退变过程中的榴辉岩相阶段(~780℃,~1.954 GPa),熔融机制为在近升温降压过程中,以绿辉石主导,少量多硅白云母及黝帘石参与的脱水熔融。整个部分熔融过程中榴辉岩可产生约8%~9%体积熔体,满足熔体迁移的最低要求,表明锡铁山地体榴辉岩可能对于该区内的同折返花岗岩的源区有少量贡献。Anatexis is a commonly observed phenomenon in high-grade metamorphic rocks and plays a crucial role in the tectonic evolution of the orogenic belt.Eclogite,as the primary rock type,is extensively studied for its significance in continental subduction,ultra-high pressure(UHP)metamorphism,and crust-mantle interaction.Partial melting of eclogite is closely linked to crustal growth,slab exhumation,and the transport and distribution of elements within continental subduction channels.In the North Qaidam UHP metamorphic belt,the Xitieshan eclogite preserves in-situ and in-source leucosomes,which serve as indicators of anatexis.These leucosomes provide favorable conditions for understanding the effect of the anatexis on UHP eclogite.This paper focuses on the zircon U-Pb chronology analysis of the leucosomes within the Xitieshan eclogite.Through LA-ICP-MS U-Pb dating,a weighted mean^(206)Pb/^(238)U age of 425.3±5.9 Ma(MSWD=0.74)was obtained,representing the formation age of leucosomes.To further understand the anatexis of eclogite in the Xiteshan terrane,thermodynamic and trace element modelling techniques were employed.Combining these models with the retrograde P-T paths of eclogite in the area,the equilibrium crystallization of Na-rich leucosomes in eclogite was constrained to temperature and pressure conditions of 794~797℃and 1.227~1.071 GPa,respectively.The initial partial melting of the eclogite occurred during the eclogite phase(~780℃and~1.954 GPa).As the temperature increased and the pressure decreased,the partial melt formed in the UHP eclogite through the breakdown of omphacite,with minor involvement of phengite and zoisite.Throughout partial melting,eclogite generated 8~9 vol%melt,sufficient to initiate melt migration.This suggests that the eclogite likely had a limited contribution to the source area of the syn-exhumation granite in the Xitieshan terrane.

关 键 词：深熔作用 微量元素地球化学模拟 同折返花岗岩 

分 类 号：P61[天文地球—矿床学]