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Geochronological and geochemical constraints on the petrogenesis of late Mesoproterozoic mafic and granitic rocks in the southwestern Yangtze Block
Geoscience Frontiers ( IF 8.9 ) Pub Date : 2020-08-05 , DOI: 10.1016/j.gsf.2020.07.005
Guichun Liu , Jing Li , Xin Qian , Qinglai Feng , Wei Wang , Guangyan Chen , Shaobin Hu

Late Mesoproterozoic igneous rocks in the SW Yangtze Block are important for understanding the role of it in reconstruction of the Rodinia supercontinent. In the present study, we report new geochronological, geochemical, and Nd–Hf isotopic data for the Cuoke plagioclase amphibolites and granites in the SW Yangtze Block. Geochronological results show that the plagioclase amphibolites and granites have similar late Mesoproterozoic zircon U–Pb ages of 1168–1162 ​Ma, constituting a bimodal igneous assemblage. The plagioclase amphibolites have high and variable TiO2 contents (1.15–4.30 ​wt.%) and Mg# (34–66) values, similar to the tholeiitic series. They are characterized by enrichment in LREEs and LILEs, and have OIB-like affinities with positive Nb and Ta anomalies. The plagioclase amphibolites have positive whole-rock εNd(t) (+3.2 to +4.3) and zircon εHf(t) (+4.3 to +10.7) values, indicating that they were derived from an OIB-like asthenospheric mantle source. The granites belong to the reduced peralkaline A-type series and have negative εNd(t) value of −6.0 and εHf(t) values of −5.8 to −13.8, indicating a derivation from the partial melting of ancient mafic lower crust. In combination with the ∼1.05–1.02 ​Ga bimodal igneous assemblage in the SW Yangtze Block, we propose that the Cuoke 1168–1162 ​Ma igneous rocks were likely formed in a continental rift basin and argue against the existance of Grenvillian Orogen in the SW Yangtze Block during the late Mesoproterozoic.



中文翻译:

西南扬子地块中晚古生代镁铁质和花岗岩岩石成因的地质年代学和地球化学约束

西南扬子地块的晚中古生代火成岩对于了解其在罗丹尼亚超大陆重建中的作用非常重要。在本研究中,我们报告了西南扬子地块中Cuoke斜长石闪石和花岗岩的新的地球年代,地球化学和Nd-Hf同位素数据。地质年代学结果表明,斜长石闪石和花岗岩具有类似的中元古生代锆石U-Pb年龄,年龄为1168-1162 Ma,构成了双峰火成岩组合。斜长石两闪石具有高且可变的TiO 2含量(1.15-4.30 wt。%)和Mg#(34-66)值,类似于可塑系列。它们的特点是富含LREE和LILE,并具有类似Nb和Ta异常的OIB相似性。斜长石闪岩具有正全岩ε)(3.2至4.3)和锆石ε)(4.3至10.7)的值,这表明它们是从一个OIB状软流圈地幔来源。花岗岩属于减少过碱性A型系列,并具有负ε的Nd的-6.0和)值ε的Hf)的值在-5.8到-13.8之间,表示源自古代铁镁质下地壳的部分熔融。结合西南扬子地块的〜1.05〜1.02 Ga双峰火成岩组合,我们提出在大陆裂谷盆地可能形成了库克1168–1162 Ma火成岩,并反对西南格林威猛造山带的存在。中元古代晚期的扬子地块。

更新日期:2020-08-05
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