辽南岩体LA-ICP-MS锆石U-Pb年龄、岩石地球化学特征及其地质意义——以盖州万福—岫岩龙潭地区三叠纪侵入岩为例

Geochemical Characteristics, LA-ICP-MS Zircon U-Pb Dating and Geological Significance of South Liaoning Pluton:A Case Study of Triassic Pluton in Gaizhou Wanfu-Xiuyan Longtan Area

辽宁南部盖州万福—岫岩龙潭地区位于华北板块北缘东段,辽东-辽南中生代岩浆弧带上。该地区中生代早期侵入岩主要由黑砬沟岩体和前豹沟岩体两个岩体构成,其中黑砬沟岩体岩性为中细粒黑云母二长花岗岩,前豹沟岩体岩性为似斑状黑云母二长花岗岩。中细粒黑云母二长花岗岩和似斑状黑云母二长花岗岩LA-ICP-MS锆石206Pb/238U年龄加权平均值分别为(219.8±0.7)和(220.9±2.1) Ma,时代为晚三叠世。岩体均属于钙碱性、准铝质岩石系列,K、Rb、Sr质量分数较高,Ta、Yb、Y质量分数偏低,稀土配分曲线右倾,负Eu异常不明显,轻稀土较富集,重稀土相对亏损。通过岩石学、年代学、岩石地球化学、构造环境及就位机制的分析,并结合邻区构造演化研究,认为该地区侵入岩为扬子板块与华北板块碰撞,在挤压的环境下地壳硅铝层增厚重熔,产生的同碰撞S型花岗岩。

Gaizhou Wanfu-Xiuyan Longtan area is located in the north margin of the North China block, which is on the Mesozoic magmatic arc belt of southeast Liaoning. It is mainly composed of two plutonic rocks. The Heilagou plutonic rocks are fine-grained biotite monzogranite, and the Qianbaogou plutonic rocks are porphyritic biotite monzogranite. The Late Triassic plutonic rocks belong to the calc-alkaline, per aluminous series. The plutonic rocks contain high content of K,Rb,and Sr,low content of Ta,Yb, and Y. The REE distribution pattern is obvious right dipping, with LREE enrichment, HREE depletion, and weak negative Eu anomaly. According to LA-ICP-MS zircon U-Pb dating, the fine-grained biotite monzogranite and porphyritic biotite monzogranite were formed in the Late Triassic((219.8±0.7) Ma and(220.9±2.1) Ma). Based on the analyses of petrology, petro-chemistry, chronology, and tectonic environment, combined with the study of the tectonic evolution in the adjacent area, it is considered that the intrusive rocks are syncollisional S type granites, which were produced by the thickening and remelting of the silicon aluminum layer in the crust during the collision between the Yangtze plate and the North China craton.