小兴安岭-张广才岭早古生代岩浆作用及其构造意义

The eastern section of the Central Asian Orogenic Belt (CAOB) contains several microcontinental massifs, and it is a controversial issue about the amalgamation history of these massifs. Lesser Xing’an Range-Zhangguangcai Range is located in the eastern margin of the Songnen–Zhangguangcai Range massif. Fortunately, the discovery of Early Paleozoic igneous rocks in this region has the potential to answer the amalgamation history of the Songnen–Zhangguangcai Range and Jiamusi massifs. This program studies the field geology, zircon U-Pb geochronology, and geochemistry of the Early Paleozoic igneous rocks in the Lesser Xing’an Range and Zhangguangcai Range, to determine the magmatism episodes, rock association and spatial variation of the Early Paleozoic igneous rock. Based on the igneous rock associations with different ages, we recognize the tectonic setting under which they formed. We shall use the element-isotopic tracing techniques to determine the nature of magma sources for igneous rocks with different ages and their evolution. Combined with the previous data for the tectonic evolution of the eastern section of the CAOB, this program will further provide new insights to the amalgamation history of the Songnen–Zhangguangcai Range and Jiamusi massifs. The program can be of important significance for investigating the Early Paleozoic tectonic evolution of the CAOB and the growth mechanism of continental crust in the Phanerozoic.

中亚造山带东段存在多个微陆块，这些块体的拼贴演化历史一直存在争议。小兴安岭-张广才岭位于松嫩-张广才岭地块东缘，该地区早古生代火成岩的存在为解决松嫩-张广才岭地块和佳木斯地块的拼贴历史提供了可能。本项目通过对小兴安岭-张广才岭早古生代火成岩野外地质、锆石U-Pb年代学和地球化学的系统研究，查明小兴安岭-张广才岭早古生代火成岩的岩浆期次、岩石组合及其空间展布；研究小兴安岭-张广才岭早古生代不同期次岩浆作用的岩石组合，确定不同时代火成岩所反映的构造背景；利用元素-同位素地球化学示踪技术，查明不同时代火成岩的岩浆源区性质及其演化；结合中亚造山带东段构造演化历史研究的成果，最终揭示松嫩-张广才岭地块和佳木斯地块的拼贴演化历史。本项研究对于探讨中亚造山带东段早古生代演化历史以及显生宙大陆地壳增生机制均具有重要意义。

本项目对松嫩—张广才岭地块东部早古生代火成岩进行了LA-ICP MS和SIMS 锆石U-Pb年代学、岩石学、全岩地球化学及锆石Hf同位素的研究，查明了早古生代岩浆作用的时空分布、岩石组合及成因。同时对松嫩—张广才岭地块东部和南部早古生代地层中碎屑锆石进行了年代学及物源研究。最终重建了松嫩—张广才岭地块新元古代—早古生代的演化历史，探讨了中亚造山带东段各块体来源。松嫩—张广才岭地块早古生代火成岩可划分为五期：516Ma、505-490Ma、482-461Ma、460-450Ma、435-420Ma。中—晚寒武世期间松嫩—张广才岭地块北部和佳木斯地块北部首先发生陆—陆碰撞，两陆块的拼贴呈剪刀式逐渐向南发展，晚志留世末期松嫩—张广才岭地块和佳木斯地块完成最终碰撞拼合。松嫩—张广才岭地块以及中亚造山带东段的其它块体可能来源于罗迪尼亚超大陆，经历了超大陆的聚合和裂解过程。松嫩—张广才岭地块以古元古代时期地壳增生作用为主，深部陆壳物质组成存在不均一性，新元古代罗迪尼亚超大陆的聚合和裂解作用以及早古生代期间洋陆相互作用再次造成了古老基底物质的再造和地壳的增生。上述成果对于研究中亚造山带东段各块体的来源及演化历史具有重要意义。