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西秦岭造山带李子园金矿区侵入岩对金成矿的约束:来自岩石地球化学特征、锆石U−Pb年龄及锆石微量元素的制约

Constraints of intrusive rocks on gold mineralization in Liziyuan Gold Deposit, West Qinling Orogenic Belt: Insights from petrogeochemical characteristics, zircon U−Pb ages, and zircon trace elements

  • 摘要: 为精确限定西秦岭造山带李子园金矿区侵入岩的形成时代,阐明岩石成因与构造背景,厘清其对区域金成矿时代的约束作用,对二长花岗岩和正长岩进行全岩分析、锆石U−Pb定年与微量元素分析,结合多种锆石微量元素判别图解,系统开展岩石类型、源区属性及构造环境判别。定年结果显示:二长花岗岩和正长岩的侵位年龄分别为217.2 Ma±2.6 Ma与210.4 Ma±2.3 Ma,归属印支早期岩浆活动产物。锆石微量元素特征表明:二长花岗岩和正长岩具典型I型花岗岩属性,源区以陆壳物质为主;锆石发育正Ce异常与负Eu异常,指示岩浆形成于较高氧逸度环境,且可能经历斜长石分离结晶作用。构造环境显示:二长花岗岩和正长岩形成于非造山向造山环境的转换阶段,伴随地壳增厚过程。综合分析表明:二长花岗岩和正长岩形成于晚三叠世印支期,为陆壳物质在碰撞造山背景下部分熔融的产物。结合前人成岩成矿锆石年龄数据,构建了“岩体侵位(210~214 Ma)→热液成矿(207 Ma)”的完整成矿时序,确立“岩体年龄+成矿年龄”的双重约束模型,为深入解析西秦岭造山带岩浆−成矿演化规律提供了关键年代学与地球化学依据。

     

    Abstract: To accurately constrain the emplacement age of intrusive rocks in the Liziyuan Gold Deposit, West Qinling Orogenic Belt, elucidate their petrogenesis and tectonic setting, and clarify their constraints on the regional gold mineralization timing, whole-rock analysis, zircon U−Pb dating, and trace element analysis were carried out on monzogranite and syenite. Combined with various zircon trace element discrimination diagrams, the rock types, source characteristics, and tectonic settings were systematically identified. The dating results show that the emplacement ages of monzogranite and syenite are 217.2 Ma ± 2.6 Ma and 210.4 Ma ± 2.3 Ma, respectively, indicating they were formed during the early Indosinian magmatic event. Zircon trace element characteristics reveal that the monzogranite and syenite exhibit typical I-type granite affinity and were mainly derived from continental crustal materials. Zircons display positive Ce anomalies and negative Eu anomalies, suggesting that the magma formed under relatively high oxygen fugacity and possibly underwent plagioclase fractionation. Tectonic discrimination indicates that the monzogranite and syenite were emplaced during the transition from anorogenic to orogenic settings, accompanied by crustal thickening. Comprehensive analysis demonstrates that the monzogranite and syenite were formed during the Late Triassic Indosinian and were generated by partial melting of continental crust materials under a collisional orogenic setting. Integrated with previously published zircon ages for magmatism and mineralization, a complete metallogenic temporal sequence of "pluton emplacement (210–214 Ma) →hydrothermal mineralization (207 Ma)" is established, and a dual-constraint model of "pluton age + mineralization age" is proposed. This study provides key geochronological and geochemical evidence for further understanding the magma-mineralization evolution in the West Qinling Orogenic Belt.

     

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