今天是2018年09月24日

延边官地铁矿构造背景与和龙地块太古宙地壳增生: 来自岩石地球化学、锆石 U-Pb年代学及Hf 同位素证据

DOI:10.3799/dqkx.2017.611

作者:商青青,任云生,陈聪,段明新,孙琦,薛世远

联系地址:吉林大学地球科学学院,吉林长春 130061

摘要:延边地区官地铁矿床地处华北克拉通北缘与兴蒙造山带东段接合带附近的和龙地块北部,是东北地区发现和开发较早的典型BIF型铁矿床之一.该矿床的主矿体呈层状、似层状、透镜状赋存于鞍山群甲山组上段.为确定该矿床的形成与变质时代以及构造背景,重点对含矿岩系中的斜长片麻岩、角闪斜长片麻岩和斜长角闪岩进行岩石地球化学、锆石U-Pb年代学以及Hf同位素研究.原岩恢复表明,斜长片麻岩的原岩为流纹英安质-英安质火山碎屑岩,角闪斜长片麻岩的原岩为安山岩,斜长角闪岩的原岩为玄武岩.LA-ICPMS锆石U-Pb年代学研究发现,官地地区在新太古代末-古元古代初期发生了岩浆作用(2508~2483Ma)和变质事件(2472~2459Ma),且该期岩浆-变质事件与铁矿的形成有着密切的联系.斜长角闪岩的原岩-玄武岩形成于弧后盆地环境,反映了官地铁矿形成时的构造环境;角闪斜长片麻岩中锆石的εHf(t)值介于-5.0~+4.2,二阶段Hf模式年龄(tDM2)为3182~2889Ma,表明岩浆源区以中太古代古老地壳物质的熔融为主.通过与国内外典型BIF型铁矿床的对比研究认为,官地铁矿属Algoma型BIF,与新太古代晚期华北克拉通大规模BIF成矿事件密切相关;官地地区在新太古代初期(2.8~2.7Ga)可能存在地壳增生事件;和龙地块亲华北克拉通的构造属性,为索伦-西拉木伦-长春缝合带的东延问题研究提供了新的证据.

关键字:Hf同位素;锆石U-Pb定年;地壳增生;官地铁矿;和龙地块;地球化学.

Tectonic Setting of Guandi Iron Deposit and Archean Crustal Growth of Helong Massif in NE China: Evidence from Petrogeochemistry, Zircon U-Pb Geochronology and Hf Isotope

Author:Shang Qingqing, Ren Yunsheng, Chen Cong, Duan Mingxin, Sun Qi, Xue Shiyuan

Author Address:College of Earth Sciences, Jilin University, Changchun 130061, China

Abstract:The Guandi iron deposit has been discovered and developed for several years and has been considered as a typical BIF-type iron deposit in Yanbian area, Northeast China. This deposit is located at the north part of the Helong massif, at the joint of the North China craton and the Xingan-Mongolia orogenic belt. The stratiform and lenticular iron orebodies are dominantly hosted within the metamorphic rocks of Jiashan Formation, Anshan Group. In order to determine the formation age, metamorphic age and tectonic setting of the Guandi deposit, in this paper, the geochemistry, LA-ICP-MS zircon U-Pb dating and zircon Hf isotope for the ore-hosting plagiogneiss, amphibole plagiogneiss and amphibolite were conducted. The results indicate that the protolith of the plagiogneiss is rhyodacite and dacite pyroclastic rock, the protolith of the amphibole plagiogneiss is andesite, the protolith of the amphibolite is basalt. The LA-ICP-MS zircon U-Pb dating data imply that the Guandi area experienced the late Neoarchean to early Paleoproterozoic magmatic event (ca. 2508~2483Ma) and metamorphic event (ca. 2472~2459Ma), both of which have closely genetic relationship with the iron formation of the Guandi iron deposit. Geochemical characteristics of the ore-hosting amphibolite indicate that they formed in the back-arc basin setting, which is also interpreted as the tectonic setting of the Guandi iron deposit. The εHf(t) values of zircon grains from amphibole plagiogneiss range from -5.0 to +4.2, and the corresponding two-stage Hf model ages (tDM2) are from 3182Ma to 2889Ma, both of which indicate that the initial magma was mainly derived from the partial melting of the Mesoarchean crust. On the basis of comparison with several representative banded iron formations (BIFs) at home and abroad, it can be concluded that the Guandi iron deposit belongs to the Algoma-type BIFs, and was caused by the late Neoarchean large-scale BIF metallogenic event, which were widely developed in the North China craton. The Guandi area took place a crustal growth event at the early Neoarchean (2.8-2.7 Ga). Moreover, this paper proposes that the Helong massif has affinities to the North China Craton, which provides new evidence for the eastward termination of the Solonker-Xar Moron-Changchun suture in the Yanbian area.

Keyword:Hf isotope; zircon U-Pb dating; crustal growth; Guandi iron deposit; Helong massif; geochemistry.

 

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作者简介:商青青(1991-),女,硕士研究生,矿产普查与勘探专业.ORCID:0000-0002-6038-411X.E-mail:2276353157@qq.com

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