Origin of the Darongshan-Shiwandashan S-type granitoid belt from southeastern Guangxi:geochemical and Sr-Nd-Hf isotopic constraints
Origin of the Darongshan-Shiwandashan S-type granitoid belt from southeastern Guangxi:geochemical and Sr-Nd-Hf isotopic constraints
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发表时间：
2007
影响因子：
1.8
通讯作者：
Qi Chang;Deng Xi;Li Wu;X. Lie
中科院分区：
文献类型：
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作者：
Qi Chang;Deng Xi;Li Wu;X. Lie
本文报道了以桂东南大荣山-十万大山花岗岩带为主的浦北岩体、九州岩体和泰马岩体的综合地球化学、锶-钕同位素和锆石Hf同位素资料。岩石学和元素地球化学特征表明，这些深成岩体是典型的S型花岗岩。高I_(Sr)(0.721)和低I_(ND)(T)值(-13.0~-9.9)表明它们来自于演化的地壳物质。在~230 Ma的岩浆锆石中，大多数的e_(Hf)(T)值在-11~-9之间，对应于T_(DM2)年龄约1.9~1.8Ga。1681~384 Ma年龄的继承锆石的Hf(T)值为-17.1~+3.4，T_(DM2)年龄为2.4Ga、1.9Ga和1.5Ga。考虑到大多数~230 Ma的岩浆锆石的Hf(T)值与Hf-ND同位素阵列的估计值一致。我们认为平均停留时间为1.9Ga的地壳是花岗岩的主要物质来源。一些岩浆和继承锆石的T_(DM2)年龄接近1.5Ga，表明平均停留时间为1.5Ga的地壳也参与了这些花岗岩类的形成。由于没有发现T_(DM2)大于2.0Ga的火成岩锆石，因此也可能涉及少量平均停留时间为2.4Ga的再循环地壳物质。由于没有从锆石Hf同位素中识别出新的地幔输入，地幔岩浆可能不参与S型花岗岩带的形成。
Comprehensive geochemical,Sr-Nd isotopic and in-situ zircon Hf isotopic data are reported for the Pubei pluton,the Jiuzhou pluton and the Taima pluton,which consist dominantly of the Darongshan-Shiwandashan granitoid belt in SE Guangxi. Petrographic and element geochemical features show that these plutons are typical S-type granites.High I_(Sr)(0.721)and lowe_(Nd)(t) values(-13.0～-9.9)indicate that they were originated from evolved crustal materials.Among the～230Ma magmatic zircons, most have a limited range ofe_(Hf)(t)values between -11 and -9 corresponding to T_(DM2)ages of ca.1.9～1.8Ga,and the remainder have relatively highe_(Hf)(t)values up to -4.5 corresponding to younger T_(DM2)ages of ca.1.5Ga.Inherited zircons in age of 1681～384Ma havee_(Hf)(t)of -17.1～+3.4,and T_(DM2)ages clustering at 2.4Ga,1.9Ga and 1.5Ga.Considering that most～230Ma magmatic zircons havee_(Hf)(t)values consistent with the estimated values in terms of Hf-Nd isotopic array,we interpret that the crust with average residential time of 1.9Ga is the dominant material source for the studied granites.Some magmatic and inherited zircons have nearly the same T_(DM2)ages of～1.5Ga,indicating that the crust with average residential time of 1.5Ga is also involved in formation of these granitoids.Given that no igneous zircons with T_(DM2)older than 2.0Ga have been detected,minor amount of recycled crustal materials with average residential time of 2.4Ga could also be involved.Because new mantle inputs have not been identified in terms of zircon Hf isotopes,mantle-derived magmas might not have been involved in formation of this S-type granitoid belt.