Formation age and tectonic setting of the Shirengou Neoarchean banded iron deposit in eastern Hebei Province: Constraints from geochemistry and SIMS zircon U–Pb dating
Formation age and tectonic setting of the Shirengou Neoarchean banded iron deposit in eastern Hebei Province: Constraints from geochemistry and SIMS zircon U–Pb dating
复制标题
DOI：
10.1016/j.precamres.2011.09.007
复制
发表时间：
2012-12
影响因子：
3.8
通讯作者：
Lianchang Zhang;M. Zhai;Xiaojing Zhang;Peng Xiang;Yanpei Dai;Changle Wang;F. Pirajno
中科院分区：
文献类型：
--
作者：
Lianchang Zhang;M. Zhai;Xiaojing Zhang;Peng Xiang;Yanpei Dai;Changle Wang;F. Pirajno
石人沟铁矿存款是产于冀东新太古代变质岩系中的一个典型BIF型存款矿床。变质岩包括角闪石斜长片麻岩、斜长角闪岩和磁铁石英岩。利用主量元素的含量和比值对原岩进行重构，结果表明角闪斜长片麻岩和斜长角闪岩的原岩分别为英安岩和玄武安山岩。根据赋矿岩石的地质特征和地球化学特征，推测石人沟BIF为新太古代弧相关盆地中形成的阿尔戈马型存款。石人沟铁矿围岩和夹层中锆石的西姆斯U-Pb定年和氧同位素分析结果表明：（1）两个斜长角闪岩和片麻岩样品中的岩浆锆石U-Pb年龄分别为2541± 21 Ma和2553± 31 Ma，为新太古代原岩提供了年龄;由于石人沟BIF为阿尔戈马型存款，因此，对含矿火山岩中锆石U-Pb年龄（2541- 2553 Ma）的测定，可以对BIF的形成时间进行限定。(2)斜长角闪岩和片麻岩中变质增生锆石U-Pb年龄分别为2512± 13 Ma和2510± 21 Ma，与新太古代变质作用相对应。(3)δ 18 O值为5.9-7.6‰的锆石也指示岩浆成因。锆石的δ 18 O值为6.8-9.9‰，表明变质作用中有外来的高δ 18 O流体参与。根据BIF的地质、地球化学特征，结合锆石年龄和氧同位素系统学研究，认为石人沟铁矿存款形成于与大洋板片俯冲有关的海底火山岩环境。
The Shirengou iron deposit, a typical BIF deposit located in eastern Hebei province in the North China Craton, is hosted in Neoarchean metamorphic rocks. The metamorphic rocks include hornblende plagiogneiss, plagioclase amphibolite and magnetite quartzite. We use contents and ratios of major elements for protolith reconstruction, showing that protoliths of the hornblende plagiogneiss and plagioclase amphibolite should be dacite and basaltic andesite, respectively. Based on geology and geochemistry of the hosting rocks, we infer that the Shirengou BIF is an Algoma type deposit formed in an arc-related basin in the Neoarchean. Constrains from SIMS U–Pb dating and oxygen isotopic analysis of zircon from wall-rocks and interlayer of the Shirengou iron bodies can be summarized as follow: (1) igneous zircons from two samples of amphibolite and gneiss yield U–Pb ages of 2541±21Ma and 2553±31Ma, respectively, providing the age of the Neoarchean protolith. Because the Shirengou BIF is an Algoma-type deposit, determined U–Pb age (2541–2553Ma) for zircons from hosting volcanic rocks can constrain the BIF-forming time. (2) Metamorphic overgrowth zircons from amphibolite and gneiss give two U–Pb ages of 2512±13Ma and 2510±21Ma, respectively, corresponding to the Neoarchean matemorphism. (3) The zircons with δ18O values of 5.9–7.6‰ also indicate magmatic origin. The zircons have δ18O values of 6.8–9.9‰, suggesting that exotic high δ18O fluids were involved during metamorphism. Based on the geology and geochemistry of BIF, and combing with zircon age and oxygen isotopic systematics, we suggest that the Shirengou iron deposit was formed in a submarine volcanic setting related to subduction of an oceanic slab.