秦-祁结合部位陇山杂岩变泥质岩变质作用及年代学研究

Metamorphism and geochronology of metapelites from the Longshan Complex at the Qinling-Qilian junction zone

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DOI 10.20086/j.cnki.yskw.2025.4204
刊名
Acta Petrologica et Mineralogica
年,卷(期) 2025, 44(4)
作者
作者单位

西北大学地质学系, 大陆演化与早期生命全国重点实验室, 陕西 西安 710069

摘要
陇山杂岩位于秦-祁结合部位,是研究此结合部位构造演化的重要岩石构造单元。为探讨秦-祁结合部位的构造演化历史,本研究对陇山杂岩的变泥质岩进行了岩相学、矿物化学、变质相平衡模拟和LA-ICP-MS独居石U-Pb年代学研究。岩相观察及矿物成分分析结果显示,陇山杂岩石榴黑云斜长片麻岩样品21LS30-1记录了2个变质演化阶段: 早期进变质阶段(M1)(Bt+Pl+Qz+Rt+Ilm)和峰期变质阶段(M2)(Bt+Grt+Pl+Qz+Rt+Ilm+Liq)。含矽线石榴黑云斜长片麻岩样品21LS37同样记录了2个变质演化阶段: 早期进变质阶段(M1)(Bt+Sil+Pl+Qz)和峰期变质阶段(M2)(Bt+Sil+Grt+Kfs+Pl+Qz+Ilm+Liq)。视剖面图模拟计算显示2个样品的峰期变质温压条件分别为813~821℃、1.08~1.1 GPa和815~819℃、0.93~0.97 GPa,达到了中压麻粒岩相变质。LA-ICP-MS独居石U-Pb定年得到4个石榴黑云斜长片麻岩样品的年龄分别为451~425 Ma、455~431 Ma、415~395 Ma、415~394 Ma。陇山杂岩与北秦岭造山带在古生代经历了相似的构造过程,推测陇山杂岩可能是北秦岭造山带向西延伸的部分,经历了古生代的陆陆碰撞造山作用。
Abstract
The Longshan Complex located in the Qinling-Qilian junction zone is the key to understanding the tectonic evolution of this junction. This study conducted petrographic observations, phase equilibrium modeling and monazite U-Pb dating, to better discuss the tectonic implication. Based on petrographical observation and mineral composition analysis, the garnet biotite plagioclase gneisses sample 21LS30-1 of the Longshan Complex display two metamorphic mineral assemblages: the prograde stage (M1) (biotite + plagioclase + quartz + rutile + ilmenite) and the peak stage (M2) (biotite + garnet + plagioclase + quartz + rutile + ilmenite + melt). Sample 21LS37 exhibits two sets of metamorphic minerals during different formation stages: the prograde stage (M1) (biotite+sillimanite+plagioclase+quartz) and the peak stage (M2) (biotite+sillimanite+garnet+K-feldspar+plagioclase+quartz+ilmenite+melt). Phase equilibrium modeling constrained the peak p-t conditions of the two samples to be 813~821℃, 1.08~1.1 GPa and 815~819℃, 0.93~0.97 GPa, reaching the medium-pressure granulites facies metamorphism. LA-ICP-MS monazite data from the garnet biotite plagioclase gneisses show 206Pb/238U ages of 451~425 Ma, 455~431 Ma, 415~395 Ma and 415~394 Ma, respectively. The Longshan Complex and the North Qinling Orogenic Belt underwent similar tectonic processes during the Paleozoic. We preliminarily proposed that the Longshan Complex belongs to the western extension of the North Qinling orogenic belt and has experienced Paleozoic continental-continental collisional orogeny.
关键词
秦-祁结合部位;陇山杂岩;相平衡模拟;独居石U-Pb定年;陆陆碰撞造山作用
KeyWord
Qinling-Qilian junction zone; Longshan Complex; phase equilibrium modeling; monazite U-Pb ages; continental collisional orogeny
基金项目
页码 895-923
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栗娟娟,卢俊生*. 秦-祁结合部位陇山杂岩变泥质岩变质作用及年代学研究 [J]. 岩石矿物学杂志. 2025; 44; (4). 895 - 923.

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