胶辽吉造山/活动带吉南地区集安群-老岭群地层时代、物源区特征及其构造意义研究

Jiao-Liao-Ji belt is the most important Paleoproterozoic orogenic/mobile belt in the North China Craton, which subdivides the Eastern Block into the Longgang and Langrim blocks. It is still controversial that the formation of Jiao-Liao-Ji belt is related to rifting or collision. In order to study on this issue, the important point is to recognize the Paleoproterozoic tectonic setting in the southern Jilin province, and it is crucial to identify tectonic setting represented by Ji’an and Laoling groups. Based on the detailed investigation of representative geological section and geological mapping, and combined with the U-Pb dating of monazite and xenotime from metasedimentary rocks and zircon from volcaniclasic rocks or interbedded volcanic rocks, detrital zircon investigations applying U-Pb and Hf-isotopes to zircons from the metasedimentary rocks of Ji’an and Laoling groups allow us to provide a maximum age for each of these clastic units, evaluate the provenance and determine tectonic settings. Combined with previous studies, we will understand whether Ji’an and Laoling groups formed in the same tectonic setting at the same time or not and further reconstruct the Paleoproterozoic tectonic evolution of the Jiao-Liao-Ji belt.

胶-辽-吉带是华北克拉通内部最具代表性的一条古元古代造山/活动带，是东部陆块中龙岗地块和狼林地块的分界，其形成与裂谷作用相关或与碰撞作用相关尚处于争议中。而胶-辽-吉带中研究程度较弱的吉南地区古元古代的构造环境为探讨这一问题的重要切入点，通过集安群和老岭群的研究确定构造环境则是重要途径。本申请拟以吉南地区集安群和老岭群的变碎屑沉积岩为重点研究对象，选取典型建组剖面进行详细的野外填图工作，通过详细的岩石学研究、系统的全岩地球化学、碎屑锆石U-Pb定年方法和Hf同位素分析，配合变沉积岩中原生磷钇矿或独居石及火山碎屑岩或者火山岩夹层中锆石的U-Pb定年研究，限定其原岩形成时代，追溯物质来源，推测其形成的构造环境，并结合前人的资料确定，吉南地区集安群和老岭群是同一时期、同一构造背景的产物还是不同时期、不同构造背景的产物；探讨胶-辽-吉带古元古代构造演化。

胶-辽吉带吉林南部通化-集安-浑江-白城等地区分布以含硼、含石墨、富铝的集安群和以碎屑沉积物和碳酸盐岩为主的老岭群。通过系统的全岩地球化学和两个群各组代表性的变碎屑沉积岩的锆石U-Pb年代学研究，表明集安群和老岭群的碎屑锆石年龄谱主要有2.57-2.41、2.23-2.09以及 2.04-2.02 Ga，沉积物主要来源于龙岗地块（和/或辽南地块）、2.2-2.1 Ga辽吉花岗岩类和~2.0Ga岩浆事件。据最年轻的碎屑锆石及最古老的变质锆石峰，集安群蚂蚁河组、荒岔沟组和大东岔组的沉积年龄分别限定为2.13-1.94、2.10-1.94和1.95-1.90Ga，老岭群达台山组、珍珠门组、花山组、临江组和大栗子组的沉积年龄分别为2.18-1.90、2.08-1.91、1.99-1.90、1.96-1.90和1.94-1.90Ga。结合区域大地构造、碎屑锆石与板块构造之间存在的耦合关系，可以判断晚古生代集安群和老岭群是2.2-1.9Ga沉积于弧后盆地不同位置的地层。岩浆弧形成的同时，弧后盆地张开，老岭群达台山组开始沉积；弧后盆地早期，集安群蚂蚁河组和荒岔沟组沉积于弧后盆地靠近岩浆弧的一侧，老岭群的珍珠门组沉积于靠近被动陆缘的一侧；集安群相比老岭群有更强烈的火山活动；晚期，集安群大东岔组和老岭群的花山组、临江组、大栗子组均具有类似复理石沉积，反映了造山前沉积的特征。