辽东清河地区晚三叠世侵入岩锆石U-Pb年龄、地球化学特征及其对华北克拉通东部构造演化的指示

吴文彬; 申亮; 李海洋; 王玉平; 李超; 王晓亮; 杜继宇; 常世伟

doi:10.12097/j.issn.1671-2552.2023.07.005

辽东清河地区晚三叠世侵入岩锆石U-Pb年龄、地球化学特征及其对华北克拉通东部构造演化的指示

Zircon U-Pb age and geochemistry of Late Triassic intrusive rocks in Qinghe area, eastern Liaoning Province and its indication to the tectonic evolution of the eastern North China Craton

摘要

摘要: 辽东清河地区发育二长闪长岩和二长花岗岩2类侵入岩, 通过对其开展系统的LA-ICP-MS锆石U-Pb测年及地球化学研究, 探讨晚三叠世辽东清河地区的岩浆侵位机制及大地构造背景。二长闪长岩和二长花岗岩的LA-ICP-MS锆石U-Pb年龄加权平均值分别为212±2 Ma和221±2 Ma, 时代为晚三叠世。地球化学分析结果显示: 二长闪长岩SiO₂含量(50.44%~55.18%, 平均52.20%)中等, MgO(3.18%~6.2%, 平均5.20%)、TFe₂O₃(7.83%~8.85%, 平均8.37%)和总碱(7.04%~8.00%, 平均7.50%)含量较高, 表明清河地区二长闪长岩属于准铝质钾玄岩系列岩石; 岩石富集大离子亲石元素(LILE), 相对亏损高场强元素(HFSE), 中等的Nd/Th(3.70~9.75, 平均5.83)和Rb/Sr值(0.07~0.12, 平均值为0.09), 较高的Nb/U值(9.11~13.2, 平均10.8), 显示了主要由壳源物质组成, 同时有少量幔源物质的加入。二长花岗岩具有富SiO₂(76.10%~76.80%, 平均77.12%)、贫MgO和TFe₂O₃的特征, 其岩浆成分以地壳中的硅铝质成分为主, 属于过铝质的Ⅰ型花岗岩, 同时亏损高场强元素Nb、Ta、P、Ti, Nd/Th值(0.62~1.73, 平均1.23)接近壳源岩石值, 暗示其原始岩浆应是起源于陆壳物质的部分熔融。通过岩石学、年代学、岩石地球化学、构造环境分析, 并结合辽东半岛区域构造演化研究, 认为二长闪长岩为扬子克拉通深俯冲与华北克拉通后伸展作用的结果, 二长花岗岩花岗岩为同碰撞挤压环境。

Abstract: Monzodiorite and monzogranite are developed in Qinghe area of Liaodong Peninsula, which is located in the east of North China Craton.We have carried out systematic LA-ICP-MS zircon U-Pb dating and geochemistry of the two types of intrusive rocks to explore the magmatic emplacement mechanism and tectonic background of Qinghe area of Liaodong Peninsula in the Late Triassic.The weighted average zircon U-Pb ages of monzodiorite and monzogranite are 212 ±2 Ma and 221 ±2 Ma, respectively.According to geochemical analysis, monzodiorite has medium SiO₂ content(50.44%~55.18%, with an average of 52.20%), high MgO(3.18%~6.2%, with an average of 5.20%), TFe₂O₃(7.83%~8.85%, with an average of 8.37%)and total alkali(7.04%~8.00%, with an average of 7.50%), indicating that the monzodiorite in Qinghe area belongs to quasi aluminous shoshonite series.The rocks are enriched with large ion lithophile elements(LILE), relatively deficient in high field strength elements(HFSE), medium Nd/Th(3.70~9.75, average 5.83)and Rb/Sr(0.07~0.12, average 0.09)ratios, and high Nb/U(9.11~13.2, average 10.8)ratios, indicating that they are mainly composed of crust derived materials and a small amount of mantle derived materials.Monzogranite is rich in SiO₂(76.10%~76.80%, with an average of 77.12%), poor in MgO and TFe₂O₃.Its magmatic composition is mainly composed of siliceous and aluminous components in the crust, belonging to peraluminous Ⅰ-type granite.At the same time, it is deficient in high field strength elements Nb, Ta, P and Ti, and the Nd/Th(0.62~1.73, average 1.23)ratios are close to the value of crust source rock, suggesting that the original magma should be a partial melting of continental crust materials.Through the analysis of petrology, geochronology, geochemistry and tectonic environment, combined with the study of regional tectonic evolution of Liaodong Peninsula, it is considered that the monzodiorite is the result of deep subduction of the Yangtze craton and post extension of the North China craton, and the monzogranite is in the syn-collision and compression environment.

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