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The Cretaceous igneous rocks in southeastern Guangxi and their implication for tectonic environment in southwestern South China Block
Open Geosciences ( IF 2 ) Pub Date : 2020-07-30 , DOI: 10.1515/geo-2020-0160
Yang Liu 1 , Nianqiao Fang 1 , Menglin Qiang 2 , Lei Jia 3 , Chaojie Song 4
Affiliation  

Abstract Southeastern Guangxi is located in the southwestern South China Block and to the northwest of the South China Sea (SCS), with abundant records of the Cretaceous magmatism. A detailed study of igneous rocks will contribute to a better understanding of the late Mesozoic tectonic environment. Zircon U–Pb dating yields ages of 93.37 ± 0.43 Ma for Yulin andesites and 107.6 ± 1.2 Ma for Luchuan granites. Yulin andesites are hornblende andesites, of which w(MgO) is between 7.72% and 8.42%, and Mg# is between 66.7 and 68.0, belonging to high magnesian andesites (HMAs) from peridotite sources. Luchuan granites are medium- to fine-grained monzogranites. Monzogranites and clastoporphyritic lava are high-K calc-alkaline series and metaluminum to weakly peraluminous series, which belong to the I-type granites. Those are enriched in Rb, Th, K and LREEs and depleted in Nb, Ta, P and Eu, showing the geochemical characteristics related to subduction. Unlike the contemporary “bimodal igneous rock assemblages” in Zhejiang and Fujian, the intermediate-acid magmatites in the southeastern Guangxi imply the compressive tectonic environment. The assemblage of HMAs and adakitic rocks indicates that the southwestern South China Block was under the Neo-Tethyan subduction during Cretaceous, and slab melting contributed to the magma in this area.

中文翻译:

桂东南白垩纪火成岩及其对华南地块西南部构造环境的意义

摘要 广西东南部地处华南地块西南部,南海西北部,白垩纪岩浆活动记录丰富。对火成岩的详细研究将有助于更好地了解晚中生代构造环境。榆林安山岩的锆石 U-Pb 定年结果为 93.37 ± 0.43 Ma,陆川花岗岩的年龄为 107.6 ± 1.2 Ma。榆林安山岩为角闪石安山岩,其中w(MgO)在7.72%~8.42%之间,Mg#在66.7~68.0之间,属于橄榄岩来源的高镁安山岩(HMA)。陆川花岗岩为中至细粒二长花岗岩。二长花岗岩和碎斑状熔岩为高钾钙碱性系列和金属铝至弱过铝系列,属于I型花岗岩。那些富含 Rb、Th、K 和 LREEs 以及 Nb、Ta、P 和 Eu 的贫化,显示出与俯冲相关的地球化学特征。与当代浙江和福建的“双峰火成岩组合”不同,广西东南部的中酸性岩浆岩暗示着挤压构造环境。HMAs与埃达克岩的组合表明华南地块西南部在白垩纪处于新特提斯俯冲作用之下,板块熔融形成了该地区的岩浆。
更新日期:2020-07-30
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