In situ zircon U-Pb, oxygen and hafnium isotopic compositions of Jurassic granites from the North China craton: Evidence for Triassic subduction of continental crust and subsequent metamorphism-related 18O depletion
In situ zircon U-Pb, oxygen and hafnium isotopic compositions of Jurassic granites from the North China craton: Evidence for Triassic subduction of continental crust and subsequent metamorphism-related 18O depletion
复制标题
华北克拉通侏罗纪花岗岩原位锆石 U-Pb、氧和铪同位素组成：三叠纪大陆地壳俯冲和随后变质作用相关 18O 消耗的证据
DOI：
10.1016/j.lithos.2012.02.018
复制
发表时间：
2012-06-01
期刊：
影响因子：
3.5
通讯作者：
Chang, Guohu
中科院分区：
文献类型：
--
作者：
Jiang, Neng;Chen, Jingzhi;Chang, Guohu
华北克拉通东南缘玲珑花岗岩体的6个样品获得了相似的侏罗纪岩浆锆石U-Pb年龄和全岩Sr-Nd同位素组成。它们是弱过铝质到强过铝质，A/CNK（摩尔Al 2 O3/[CaO + Na 2 O + K2 O]）比为1.05至1.3，除了一个样品的A/CNK为0.98。然而，它们的继承锆石年龄和岩浆锆石Hf和O同位素组成却截然不同。两个样品具有相似的2.5Ga继承锆石和高δ O-18岩浆锆石，解释为主要来自华北克拉通下地壳。另外两个以三叠纪继承锆石和低三角洲O-18岩浆锆石为主的样品被认为主要来自华南克拉通的俯冲陆壳，并且在三叠纪变质作用期间被认为是O-18显著亏损的来源。其余两个样品以新元古代继承锆石和中三角洲O-18岩浆锆石为主，也被认为主要来自华南克拉通俯冲陆壳。但在三叠纪变质过程中，源区O-18没有明显亏损。不同岩性、全岩Nd（t）和锆石Hf（t）的差异也有力地支持了它们来自不同的来源。虽然来自六个样品的岩浆锆石的δ O-18从0.7到8.5千分之一不等，Hf（t）从-27.6到-11.8不等，但个别样品的Hf（t）和δ O-18更有限。样品中岩浆锆石的δ O-18和Hf（t）值表明玲珑花岗岩中没有幔源岩浆的贡献。这是由该地区没有同时代的幔源岩的事实支持。结果表明，Hf（t）和δ O-18的大的变化并不一定表明地幔和壳源岩浆之间的混合。相反，它们可能反映了来源的异质性。这些花岗岩是三叠纪华南克拉通陆壳俯冲到华北克拉通之下而增厚的地壳部分熔融的结果。岩石圈伸展和造山作用是花岗岩形成的主要机制。(C)2012爱思唯尔有限公司版权所有。
Six samples of the Linglong granitic pluton from the southeastern margin of the North China craton yield similar Jurassic magmatic zircon U-Pb ages and evolved whole-rock Sr-Nd isotopic compositions. They are weakly peraluminous to strongly peraluminous, with A/CNK (molar Al2O3/[CaO + Na2O + K2O]) ratios of 1.05 to 1.3 except one sample with an A/CNK of 0.98. However, they have contrasting inherited zircon ages and magmatic zircon Hf and O isotopic compositions. Two samples have similar to 2.5 Ga inherited zircons and high delta O-18 magmatic zircons and are interpreted to be derived dominantly from the lower crust of the North China craton. Another two samples with dominantly Triassic inherited zircons and low delta O-18 magmatic zircons are considered to be derived mainly from the subducted continental crust of the South China craton and the source was considered to be significantly depleted in O-18 during Triassic metamorphism. The rest two samples have dominantly Neoproterozoic inherited zircons and intermediate delta O-18 magmatic zircons and are also considered to be derived mainly from the subducted continental crust of the South China craton. But the source was not significantly depleted in O-18 during Triassic metamorphism. The different lithologies, whole-rock epsilon(Nd(t)) and zircon epsilon(Hf(t)) between the samples also strongly support that they are derived from different sources. Although magmatic zircons from the six samples have variable delta O-18 from 0.7 to 8.5 parts per thousand and epsilon(Hf(t)) from -27.6 to -11.8, individual samples have more limited epsilon(Hf(t)) and delta O-18. The delta O-18 and epsilon(Hf(t)) of magmatic zircons from the samples indicate no contribution of mantle- derived magmas to the Linglong granites. This is supported by the fact of no coeval mantle-derived rocks in the region. The results suggest that large variations of epsilon(Hf(t)) and delta O-18 do not necessarily indicate mixing between mantle- and crustal-derived magmas. Instead, they may reflect heterogeneity in the source. The granites are interpreted to result from partial melting of the thickened crust caused by Triassic subduction of the South China craton continental crust beneath the North China craton. Subsequent lithospheric extension and orogenic collapse are the most likely mechanism for the granites. (C) 2012 Elsevier B.V. All rights reserved.