华北克拉通东北部新太古代晚期地壳生长:来自板石沟表壳岩年代学和Hf同位素的证据

Late Neoarchean crustal growth in the northeast of the North China Craton:Evidence from the geochronology and Hf isotope composition of Banshigou supracrustal rocks

对板石沟表壳岩中的斜长角闪岩和角闪片岩进行了锆石U-Pb年代学、地球化学以及Hf同位素分析,以探讨华北克拉通东北部新太古代晚期的构造环境和地壳演化。板石沟表壳岩主要岩石类型包括斜长角闪岩、斜长片麻岩、角闪片岩和磁铁石英岩,LA-ICP-MS锆石U-Pb测年显示斜长角闪岩(BA-1)岩浆锆石形成于2548±11Ma,绿帘角闪片岩(BA-6)岩浆锆石形成于2548±23Ma,代表了表壳岩的形成时代,在绿帘角闪片岩中识别出3颗年龄为2754±80Ma^2710±92Ma的捕获锆石,表明板石沟地区可能存在新太古代早期岩浆事件。斜长角闪岩和角闪片岩的原岩为玄武质火山岩,微量元素特征指示其形成于岛弧环境。Hf同位素分析结果显示斜长角闪岩εHf(t)为正值(0.29~8.89),单阶段模式年龄(tDM1)分布在2877~2469Ma之间,绿帘角闪片岩多具正的εHf(t)值(-0.78~8.03),tDM1介于2871~2544Ma,表明岩浆主要来源于亏损地幔,伴随少量古老地壳物质的再造,部分tDM1与207Pb/206Pb年龄相近,并同时具有高εHf(t)值的锆石反映板石沟地区新太古代晚期(2550Ma)发生过地壳增生事件。结合其他地区表壳岩研究成果,认为华北克拉通可能存在新太古代吉-辽-冀弧陆碰撞造山带,板石沟地区属于该造山带的一部分。

This paper reports zircon U-Pb age, geochemistry and Hf isotopic data of Banshigou supracrustal rocks in order to discuss the tectonic setting and crustal evolution in the northeast of the North China Craton in the Late Neoarchean. The main rock types of Banshigou supracrustal rocks are include amphibolite, plagioclase gneiss, hornblende schist and magnetite quartzite. LA-ICP-MS zircon U-Pb dating shows the magmatic zircons in the amphibolite （ BA-1 ） were crystallized at 2548 ± 11Ma while the magmatic zircons in the epidote-horublende schist （BA-6） were crystallized at 2548 ± 23Ma, representing the formation age of supracrustal rocks. Besides, we found three captured zircons in BA-6 which age are between 2754 ± 80Ma and 2710 ± 92Ma, indicate Banshigou area may have occurred magmatic events during the Early Neoarchean. The protoliths of amphibolite and hornblende schist are basaltic rocks, trace element characteristics reveal that the protoliths formed in an island-arc setting. Hf isotopic data indicate that the zircons in amphibolite have positive εHf （t） values between 0. 29 and 8. 89, one-stage model ages （tDM1 ） are between 2877Ma and 2544Ma, while most of the zircons in epidote-hornblende schist also have positive 8Hf（t） values between -0. 78 and 8.03, theirs tDM1 are between 2871Ma and 2544Ma, implying that the magma provenance was mainly made up of materials from depleted mantle with contamination of recycled old crust. Some zircons which tDM1 are similar to theirs 207 pb/ 206Pb ages suggested Banshigou area occurred crustal growth during the late Neoarehean. Combine with the supracrustal rocks in other regions, we propose there was likely existed the Neoarehean Ji-Liao-Ji （Jilin- Liaoning-Hebei） arc-continent collision orogenic belt in the North China Craton, besides, Banshigou area is one part of this orogenic belt.