长江中下游地区燕山晚期基性岩浆活动的记录

发布时间：2018-03-30 06:03

  本文选题：蒋庙岩体　切入点：锆石U-Pb定年　出处：《地球科学》2017年06期

【摘要】：江苏省宁镇地区位于长江中下游沿江成矿带的最东端,是长江中下游成矿带的重要组成部分,蒋庙岩体是宁镇地区唯一的基性岩体.对此岩体进行了锆石U-Pb年代学、矿物化学、岩石地球化学和Sr-Nd-Hf同位素研究,讨论了其成因及地幔源区性质.岩体主要由橄榄辉长岩、角闪辉长岩和辉石闪长岩组成,其中辉石闪长岩的锆石LA-ICP-MS(laser ablation inductively coupled plasma mass spectrometry)U-Pb年龄为121±1Ma.锆石εHf(t)值介于-2.9~-6.4.全岩地球化学研究显示岩石样品富钠低钾,富集轻稀土元素,重稀土元素亏损不明显,富集大离子亲石元素(如K、Ba、Sr等),亏损高场强元素(如Nb、Ta、Ti、Zr、Hf等).蒋庙基性侵入岩在长江中下游地区中生代岩浆岩中具有最高的εNd(t)值以及最低的(87Sr/86Sr)i值,其Sr-Nd同位素组成介于软流圈地幔(depleted MORB mantle,DMM)-富集岩石圈地幔(enriched mantleⅡ,EMⅡ)之间.研究认为,蒋庙岩体应来源于软流圈地幔和富集岩石圈地幔的混合组分,可能有少量的俯冲板片物质加入源区,并在成岩过程中经历了一定程度的结晶分异.结合区域地质、年代学、矿物学和地球化学资料,表明蒋庙岩体的形成可能与古太平洋板块俯冲事件密切相关.
[Abstract]:The Ningzhen area of Jiangsu Province is located at the easternmost end of the metallogenic belt along the Yangtze River in the middle and lower reaches of the Yangtze River, and is an important part of the metallogenic belt in the middle and lower reaches of the Yangtze River. The Jiangmiao rock body is the only basic rock body in the Ningzhen area. The zircon U-Pb chronology and mineralogical chemistry have been carried out. Petrogeochemistry and Sr-Nd-Hf isotopic studies are used to discuss its genesis and mantle origin. The rock body is mainly composed of olivine gabbro, hornblende gabbro and pyroxene diorite. Among them, the zircon LA-ICP-MS(laser ablation inductively coupled plasma mass spectrometry)U-Pb age of pyroxene diorite is 121 卤1Ma.The zircon 蔚 HF t) value is between -2.9 ~ 6.4.The whole rock geochemical study shows that the rock samples are rich in sodium and low potassium, enriched in light rare earth elements, but not depleted in heavy rare earth elements. It is rich in large ion lithophile elements (such as Ki, Baer, Sr, etc., and depleted in high field strength elements, such as NbBU Tajiao TiTiZR, HF, etc.). The Jiangmiao basic intrusive rocks have the highest 蔚 Ndtl value in the Mesozoic magmatic rocks in the middle and lower reaches of the Yangtze River, and the lowest value of 87-Sr-86SrI. Its Sr-Nd isotopic composition is somewhere between the asthenospheric mantle depleted MORB mantletle- enriched mantle 鈪，

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