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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.
The Ningzhen area of Jiangsu Province is located at the easternmost end of the Yangtze River mineralization belt 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 mass is the only basic rock mass in Ningzhen area The zircon U-Pb geochronology, mineral chemistry, lithogeochemistry and Sr-Nd-Hf isotopes are studied, and their origin and mantle source region properties are discussed.The rock mass is mainly composed of olivine gabbro, hornblende gabbro and The zircon U-Pb dating of pyroxene diorite is 121 ± 1Ma and the εHf (t) value of zircon is between -2.9 ~ The whole rock geochemistry study showed that rock samples were rich in sodium and potassium, enriched in light rare earth elements, heavy rare earth elements loss was not obvious, the enrichment of large ion lithophile elements (such as K, Ba, Sr, etc.), loss of high field strength (Such as Nb, Ta, Ti, Zr, Hf, etc.) The Jiangmian-based intrusive rocks have the highest εNd (t) values and the lowest (87Sr / 86Sr) i values in Mesozoic magmatic rocks in the middle and lower reaches of the Yangtze River, The Sr-Nd isotopic composition lies between the depleted MORB mantle (DMM) and the enriched mantleⅡ (EMⅡ) Therefore, the Jiangmian pluton should originate from the mixed component of asthenospheric mantle and enriched lithospheric mantle. There may be a small amount of subducting slab material added to the source area and undergone some degree of crystallization differentiation during diagenesis. Combined with regional geology, geochronology, mineralogy and geochemistry data, it is concluded that the formation of Jiangmiao rock mass may be closely related to the subduction events of the Paleo-Pacific plate.