Geochemistry and zircon U-Pb chronology of Shuangshanzi Group in the eastern Hebei province, North China Craton: Constraints on petrogenesis and tectonic setting

冀东双山子群是一套出露于青龙县东部变质程度较低的火山沉积地层,其中火山岩地层主要由变质玄武岩、安山岩和英安岩-流纹岩组成。全岩地球化学分析表明变玄武岩呈现拉斑玄武岩的地球化学特征,起源于尖晶石二辉橄榄岩12%~25%的部分熔融,变质安山岩与变质英安岩-流纹岩形成于弧下地幔部分熔融,该熔体受到地壳物质混染。LA-ICPMS锆石U-Pb定年表明本群变质安山岩形成于2514±16Ma,而变质流纹岩形成于2522±8Ma,二者均受到~2450和~2300Ma的后期热事件扰动。结合本群变质火山岩的岩石组合、地球化学特征和岩石成因,该套岩石可能形成于活动大陆边缘弧相关构造背景。Shuangshanzi Group locates in the Shuangshanzi-Zhuzhangzi area of eastern Hebei Province and is composed of low-grade metamorphosed volcanic-sedimentary rocks, mainly comprising plagioclase amphibolite, biotite amphibole plagioclase gneiss, felsic schist or gneisses. Whole-rock geochemical analyses reveal that magmatic precursors of metamorphosed volcanic rocks from the Shuangshanzi Group are comparable to basalts, andesites and dacite-rhyolites, among which the metabasalts show tholeiitic basalt features with low SiO2 of 49. 7% similar to 50. 1%, high TiO2 of 1.51% similar to 1. 84%, MgO of 5. 68% similar to 6. 53% and low Al2O3 of 12. 2% similar to 12. 7%, and nearly flat REE patterns with (La/Yb)(N) ratios of 1. 51 similar to 2. 15 as well as minor negative Nb anomalies. These geochemical features are similar to primitive arc basalts, indicating that their magmatic precursors may be derived from 12% similar to 25% partial melting of spinel iherzolite. Metamorphic andesites and dacite-rhyolites are characterized by high SiO2 of 53.7% similar to 71. 8%, low MgO of 0. 88% similar to 14. 1% and TiO2 of 0. 32% similar to 0. 54%, with pronounced LREE enrichments and negative Nb, Ta and Ti anomalies, indicating their magmatic precursors have typical features of the arc volcanic rocks. Therefore, the lithological assemblage of metamorphic volcanic rocks is considered as sub-arc depleted mantle melts with minor contaminations of crustal materials. LA-ICPMS zircon U-Pb dating indicates the magmatic precursors of meta-andesites erupted at 2514 +/- 16Ma, and meta-felsic rocks at 2522 +/- 8Ma, both of which underwent similar to 2450Ma and similar to 2300Ma thermal events. The two dated samples exhibit their Hf isotopic model ages (t(DM)) of 2. 6 similar to 2. 9Ga, suggesting an important crustal growth period. Integrated with lithology, geochemistry and petrogenesis, we suggest Shuangshanzi Group was formed under a Neoarchean tectonic setting of active continental margin.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000344215200008&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701SCI(E)中文核心期刊要目总览(PKU)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)7guorong0219@163.com; swliu@pku.edu.cn102885-29043