孔岭复合体中约2.0 Ga花岗岩的岩石成因:对长江克拉通从压缩到延伸的构造转变的影响

IF 3.2 2区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY
Liang Zhang , Shao-Bing Zhang , Zhen-Xin Li , Ting Liang , Zheng-Xiang Li , Xiang-Ping Zha
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引用次数: 0

摘要

Ca.中国南方长江克拉通的2.1-1.9 Ga构造热事件与超大陆周期初期的全球大陆组装是同时发生的。然而,该地区约 2.0 Ga 构造热事件的构造机制仍未确定。2.0 Ga事件的构造机制仍悬而未决,因为有报道称岩浆岩同时处于压缩和伸展环境中。在此,我们报告了对长江克拉通孔岭复合区约2.0 Ga花岗岩的综合研究结果,包括全岩主要元素和微量元素结果、锆石U-Pb年龄、锆石Lu-Hf和氧同位素结果。2.0 Ga花岗岩分为两组:第 1 组花岗岩的 HREEs、HFSEs 和 Eu 异常值均为正值,锆石 εHf(t)值相对较高;而第 2 组花岗岩的 HREEs 和 HFSE 含量较高,Eu/Eu* 和锆石 εHf(t)值较低。锆石 Hf 同位素特征表明,两类花岗岩的来源物质可能分别为奥陶系托勒密岩和奥陶系孔岭复合体 TTGs。热力学建模结果表明,与这两组花岗岩类似的岩浆可能是在800-900 °C、10-12千巴的相同熔融条件下,由中新世孔岭富集阿奇安透辉岩(kEAT)(第1组花岗岩)和TTGs(第2组花岗岩)部分熔融生成的。这样的P-T条件与同一地区2.0Ga黑云母花岗岩的变质峰值P-T估计值相一致,表明阿基坦地壳是在很深(>1 GPa)的地方重熔的。此外,扬子克拉通北部2.1-1.9 Ga花岗岩的MgO/CaO比值在约2.0 Ga之后向高值转变,这可能是由于在2.1-1.9 Ga花岗岩中的MgO/CaO比值较高所致。此外,长江克拉通北部2.1-1.9 Ga花岗岩的MgO/CaO比值在约2.0 Ga之后转为较高值,这可能是由于熔融温度/压力(T/P)比值升高,即热梯度升高所致。基于这些结果,我们认为长江克拉通的构造体系在约2.0 Ga时由压缩转为伸展。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Petrogenesis of ca. 2.0 Ga granites in the Kongling Complex: Implications for a tectonic transition of the Yangtze Craton from compression to extension
Ca. 2.1–1.9 Ga tectono-thermal events in the Yangtze Craton, South China, are coeval with global continental assembly in the dawn of supercontinent cycle. However, the tectonic regime for the ca. 2.0 Ga events there remains unresolved because magmatic rocks of both compressional and extensional environments have been reported. Here, we report the results of an integrated study of ca. 2.0 Ga granitic rocks in the Kongling Complex of the Yangtze Craton, including whole-rock major and trace element results, zircon U–Pb ages, and zircon Lu–Hf and oxygen isotope results. The 2.0 Ga granites are divided into two groups: Group 1 granites show highly depleted HREEs, HFSEs and positive Eu anomalies with relatively higher zircon εHf(t) values, whereas Group 2 granites have higher HREE and HFSE contents with lower Eu/Eu* and zircon εHf(t) values. Zircon Hf isotopic signatures indicate the source materials for the two types of granites were likely Archean tholeiite and Archean TTGs of the Kongling Complex, respectively. Thermodynamic modelling results suggest that magmas similar to the two groups of granites could be generated from partial melting of Mesoarchean Kongling Enriched Archean Tholeiite (kEAT) (Group 1 granites) and TTGs (Group 2 granites) under the same melting conditions of 800–900 °C, 10–12 kbar. Such a PT condition is consistent with the peak metamorphic PT estimates constrained from 2.0 Ga mafic granulites in the same area, indicating that the Archean crust was remelted at great depth (>1 GPa). Furthermore, the MgO/CaO ratios of the 2.1–1.9 Ga granitic rocks in northern Yangtze Craton shifted to higher values after ca. 2.0 Ga, likely caused by an increased melting temperature/pressure (T/P) ratio, i.e., the higher thermal gradient. Based on these results, we propose that the tectonic regime of the Yangtze Craton switched from compression to extension at ca. 2.0 Ga.
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来源期刊
Precambrian Research
Precambrian Research 地学-地球科学综合
CiteScore
7.20
自引率
28.90%
发文量
325
审稿时长
12 months
期刊介绍: Precambrian Research publishes studies on all aspects of the early stages of the composition, structure and evolution of the Earth and its planetary neighbours. With a focus on process-oriented and comparative studies, it covers, but is not restricted to, subjects such as: (1) Chemical, biological, biochemical and cosmochemical evolution; the origin of life; the evolution of the oceans and atmosphere; the early fossil record; palaeobiology; (2) Geochronology and isotope and elemental geochemistry; (3) Precambrian mineral deposits; (4) Geophysical aspects of the early Earth and Precambrian terrains; (5) Nature, formation and evolution of the Precambrian lithosphere and mantle including magmatic, depositional, metamorphic and tectonic processes. In addition, the editors particularly welcome integrated process-oriented studies that involve a combination of the above fields and comparative studies that demonstrate the effect of Precambrian evolution on Phanerozoic earth system processes. Regional and localised studies of Precambrian phenomena are considered appropriate only when the detail and quality allow illustration of a wider process, or when significant gaps in basic knowledge of a particular area can be filled.
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