Zircon SHRIMP U-Pb dating and geochemical characteristics of Daning batholith in northeast Guangxi
Zircon SHRIMP U-Pb dating and geochemical characteristics of Daning batholith in northeast Guangxi
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发表时间：
2009
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通讯作者：
Pang Ying-chun
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作者：
Pang Ying-chun
大宁岩基位于扬子板块与华夏板块交界处，主要由二长闪长岩、花岗闪长岩和二长花岗岩组成，夹有少量花岗岩。本文通过对大宁岩基的锆石SHRIMP U-Pb定年和地球化学特征进行研究，探讨了华南桂北加里东期侵入体的岩浆来源和成因。年龄为（419.1±6.4）Ma（MSWD=1.03），为晚加里东岩基形成提供了上限。主量元素组成显示花岗岩呈弱过铝质、强钾钙碱性。花岗岩地球化学特征表明，该岩体来源于变质长石碎屑下地壳的部分熔融。花岗岩普遍富集大离子。高Rb/Sr、低Nb/Ta比的亲石元素和轻稀土元素，表现出高Sr、低Nd同位素组合行为。但花岗岩的TDM明显低于该区正常花岗岩的平均值，这与加里东花岗岩低TDM的区域线性分布相一致。结合岩基中广泛分布的镁铁质微粒包体的现场观察，认为强烈的地幔-地壳相互作用可能发生在晚加里东的深熔岩事件期间。地幔成分明显参与了深熔岩的形成。
Daning batholith,located in the border area between Yangtze plate and Cathaysia plate,consists mainly of monzodiorite,granodiorite and monzogranite with minor granite.In this paper,zircon SHRIMP U-Pb dating and geochemical characteristics of Daning batholith are reported to discuss the magma source and genesis of this Caledonian intrusion in northern Guangxi of South China.Zircon SHRIMP U-Pb dating of the late stage granite yielded an age of(419.1±6.4)Ma(MSWD=1.03),which provides the upper constraint of the batholith formation in Late Caledonian.The major element compositions show that the granites are weakly peraluminous and strongly potassic-calc-alkaline.Geochemical characteristics of the granites indicate that this pluton was derived from partial melting of metamorphosed feldspathic clastic lower crust.The granites are commonly enriched with large ion lithophile elements and light rare earth elements with high Rb/Sr and low Nb/Ta ratios,showing behaviors of high Sr and low Nd isotopic combination.However,TDM of the granites are obviously lower than the average value of normal granite in this area,which is consistent with the regional linear distribution of lower TDM of Caledonian granites.Combined with field observation of widely spread mafic microgranular enclaves in the batholith,the authors consider that an intense mantle-crust interaction probably occurred during the anatectic event in Late Caledonian.Mantle constituents were obviously involved in the formation of anatectite.