张广才岭南部帽儿山岩体二长花岗岩年代学、地球化学特征及其构造意义

Geochronology, Geochemistry and Tectonic Significance of the Monzonitic Granites of Maoershan Pluton from the Southern Zhangguangcai Range in Heilongjiang Province, China

张广才岭是松嫩地块与佳木斯地块之间的碰撞造山带,是东北"巨型花岗岩省"的重要组成部分。本文通过锆石U-Pb定年和岩石地球化学分析,研究了张广才岭南部帽儿山二长花岗岩年代学、地球化学特征和构造背景。锆石U-Pb年代学结果显示:张广才岭南部细粒二长花岗岩成岩年龄为(176.4±1.1)Ma,中粒二长花岗岩成岩年龄为(178.9±1.3)、(177.7±1.1)Ma,粗粒二长花岗岩成岩年龄为(180.0±1.8)、(179.9±1.2)Ma,成岩时代均属于早侏罗世。岩石地球化学研究显示:细粒二长花岗岩、中粒二长花岗岩和粗粒二长花岗岩均具有富硅、贫铝、高碱、低钙,富集Zr、Hf、Rb、K,亏损Ba、Sr、Nb、P、Ti,燕式型稀土配分模式等特征,成岩类型属于造山后A2型花岗岩。结合年代学和地球化学特征,研究区早侏罗世二长花岗岩形成于碰撞后构造背景,代表佳木斯地块和松嫩地块碰撞—拼合过程中的一次伸展作用,表明早侏罗世区域构造环境逐渐由挤压造山向造山后伸展环境转变。

The Zhangguangcai Range is a collision orogenic belt between the Songnen massif and the Jiamusi massif, and is an important part of the "Giant Granite Province" in Northeast China. Based on zircon U-Pb dating and petrogeochemical analysis, we have studied the chronology, geochemical characteristics and tectonic setting of the Early Jurassic monzogranites in the southern Zhangguangcai Range. The zircon U-Pb dating results show that the diagenetic age of the fine-grained monzogranite granite sample is(176.4±1.1) Ma;The medium-grained monzogranite samples are(178.9±1.3)Ma,(177.7±1.1)Ma;The coarse-grained monzogranite samples are(180.0±1.8)Ma,(179.9±1.2)Ma. These ages belong to the Early Jurassic. Petrogeochemical results show that the fine-grained monzogranite samples, medium-grained monzogranite samples and coarse-grained monzogranite samples are rich in silicon, poor in aluminum, high in alkali, low in calcium, enriched in Zr, Hf, Rb, K, depleted in Ba, Sr, Nb, P, Ti, swallow-type rare earth distribution model and other characteristics, the diagenetic type belongs to post-orogenic A2 granite. Combining the characteristics of chronology and geoch emistry, the authors believe that the Early Jurassic monzonitic granite in the study area was formed in the post-collision tectonic setting, representing an extension during the collision-assembly process of the Jiamusi and Songnen blocks, indicating the Early Jurassic the regional tectonic environment gradually changed from compression orogenic to post-orogenic extensional environment.