巴基斯坦吉尼奥德矿区新元古代火山岩年代学及地质意义

Chronology and Tectonic Implications of Neoproterozoic Volcanics from Chiniot Deposit,Pakistan

罗迪尼亚超大陆的裂解及与之相关的吉尼奥德玢岩型铁矿的形成是目前研究的热点,对安山岩锆石进行了U-Pb年龄、Hf同位素和微量元素分析.所有锆石都属岩浆成因,具有一致的稀土配分型式以及明显的Ce正异常、Eu负异常和重稀土元素富集特征.锆石年龄主要分为两组,分别为947.8±4.0Ma和883.0±5.1Ma,代表两期安山岩的成岩年龄,指示安山岩为两期岩浆活动的混合产物;此外,捕获的基底锆石年龄为1 523.0±66 Ma,属于中元古代.εHf(t)值变化范围较大(-4.67^+13.10),指示其为壳幔物质混合的产物.安山岩产生于罗迪尼亚超大陆时期,是由高温幔源岩浆通过底侵作用,使得中元古代花岗质岩石组成的下地壳发生熔融,壳幔熔体混合形成的,与伸展裂谷有关的构造热事件及地幔柱的活动有着密切关系.吉尼奥德铁矿与凯特里铜矿在成矿地质背景方面具有诸多相似性,暗示其有大型IOCG型矿床的成矿潜力.在960~880 Ma期间,印度板块西北部与华北-刚果-圣弗朗西斯科板块可能连接在一起.

This is a hotpoint that the study the breakup of Rodinia supercontinent and the formation of Chiniot iron oxide-apatite deposit,we report zircon U-Pb ages,Hf isotopic composition and REE contents of andesite.All the zircons are magmatic origin with the similar REE patterns which are enriched in HREE with a positive Ce anomaly and a negative Eu anomaly.The zircon U-Pb isotopic analyses yields 206 Pb/238 U ages of 947.8±4.0 Ma and 883.0±5.1 Ma,which can be interpreted as the crystallization ages of two stages of andesites.Besides,the inherited zircons with U-Pb age of 1 523.0±66 Ma may indicate a Mesoproterozoic basement.The igneous zircons have highly variableεHf（t）values ranging from-4.67 to＋13.10,indicating that the andesites were derived from partial melting of a mixed mantle sourse.The geochemical and isotopic variation suggest that mantle-derived basic magmas have went through some degree of crustal commination during migration through Mesoproterozoic granitoids.The formation of the andesites were induced by a series of tectono-thermal events,associated with extensional rift and mantle plume during Rodinia supercontinent.There are many similarities between Chiniotiron deposit and Khetri Copper Belt in geological setting of ore-forming processes,indicating that the metallogenetic potentiality of giant IOCG is very well.The northwest of Indian craton may have connection with North China-Congo-S2 o Francisco craton between 960 Ma and 880 Ma.