Petrogenesis, Tectonic Evolution and Geothermal Implications of Mesozoic Granites in the Huangshadong Geothermal Field, South China
Petrogenesis, Tectonic Evolution and Geothermal Implications of Mesozoic Granites in the Huangshadong Geothermal Field, South China
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DOI：
10.1007/s12583-019-1242-9
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发表时间：
2019-08
影响因子：
3.3
通讯作者：
Zhicai Xiao;Shuai Wang;S. Qi;Jian Kuang;Min Zhang;Feng Tian;Yongjie Han
中科院分区：
文献类型：
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作者：
Zhicai Xiao;Shuai Wang;S. Qi;Jian Kuang;Min Zhang;Feng Tian;Yongjie Han
华南陆块中生代多期构造-岩浆事件产生了广泛分布的花岗岩类。黄沙洞位于华南陆块东南部，中生代花岗岩出露，温泉密集分布。本文通过全岩地球化学、锆石U-Pb年代学和锆石Lu-Hf同位素等新资料，研究了花岗岩的成因和构造演化，探讨了花岗岩与地热异常的关系。锆石U-Pb同位素显示HSD地区花岗岩有3个时期：印支期（约1000年）; 253 Ma，G4）含白云母的二长花岗岩，燕山早期（约253 Ma）。175-155 Ma，G5和G3）二长花岗岩和花岗闪长岩，燕山晚期（约175 - 155 Ma）。140 Ma，G1和G2）黑云二长花岗岩。在成因类型上，三期花岗岩均为I型花岗岩。其中G1、G2、G3和G4以高分馏为特征，SiO2、碱金属、Ga/Al和Rb/Sr值高，Sr、Ba、Zr、Nb、Ti和REE亏损，（La/Yb）N、Nb/Ta和Zr/Hf比值低，Eu负异常。在构造背景方面，253 Ma的G4可能是在后造山伸展构造下的古下地壳部分熔融的产物，古特提斯洋的关闭导致了陆内造山。175 Ma时，太平洋板块俯冲成为主导构造体系，古太平洋板块低角度俯冲促使俯冲洋壳和基底部分熔融，形成含角闪石的I型花岗闪长岩。随着俯冲板块倾角的增大，大陆弧构造环境向弧后拉张构造环境转变，导致下地壳在约400 ℃时发生强烈的部分熔融。158 Ma，是华南腹地最频繁的花岗质岩浆活动期。当板坯沉降发生在约。140 Ma，幔源岩浆底侵作用导致陆壳熔融，产生了大面积的高分异花岗岩。结合HSD及邻区花岗岩的演化和放射性产热率，认为花岗岩的高度分馏与岩浆演化中U、Th的富集有关。燕山期花岗岩的高放射性热是地壳热量的重要组成部分，对大地热流有重要贡献。钻孔ZK 8揭示了深，约。140 Ma花岗岩，结合地表花岗岩分布，推测地热异常热源主要为隐伏燕山期花岗岩。
Mesozoic multi-stage tectono-magmatic events produced widely distributed granitoids in the South China Block. Huangshadong (HSD) is located in south-eastern South China Block, where closely spaced hot springs accompany outcrops of Mesozoic granites. New data on whole-rock geochemistry, zircon U-Pb geochronology, and zircon Lu-Hf isotopes are presented, to study the petrogenesis and tectonic evolution of the granites, and to explore the relationship between granites and geothermal anomalies. Zircon U-Pb isotopes display three periods of granites in the HSD area: Indosinian (ca. 253 Ma, G4) muscovite-bearing monzonitic granite, early Yanshanian (ca. 175-155 Ma, G5 and G3) monzonitic granite and granodiorite, and late Yanshanian (ca. 140 Ma, G1 and G2) biotite monzonitic granite. In petrogenetic type, granites of the three periods are I-type granite. Among them, G1, G2, G3, and G4 are characterized by high fractionation, with high values of SiO2, alkalis, Ga/Al, and Rb/Sr, and depletion in Sr, Ba, Zr, Nb, Ti, REEs, with low (La/Yb)N, Nb/Ta, and Zr/Hf ratios and negative Eu anomalies. In terms of tectonic setting, 253 Ma G4 may be the product of partial melting of the ancient lower crust under post-orogenic ex-tensional tectonics, as the closure of the Paleo-Tethys Ocean resulted in an intracontinental orogeny. At 175 Ma, the subduction of the Pacific Plate became the dominant tectonic system, and low-angle subduction of the Paleo-Pacific Plate facilitated partial melting of the subducted oceanic crust and basement to generate the hornblende-bearing I-type granodiorite. As the dip angle of the subducting plate increased, the continental arc tectonic setting was transformed to back-arc extension, inducing intense partial melting of the lower crust at ca. 158 Ma and resulting in the most frequent granitic magmatic activity in the South China hinterland. When slab foundering occurred at ca. 140 Ma, underplating of mantle-derived magmas caused melting of the continental crust, generating extensive highly fractionated granites in HSD. Combining the granitic evolution of HSD and adjacent areas and radioactive heat production rates, it is suggested that highly fractionated granites are connected to the enrichments in U and Th with magma evolution. The high radioactive heat derived from the Yanshanian granites is an important part of the crustal heat, which contributes significantly to the terrestrial heat flow. Drilling ZK8 reveals deep, ca. 140 Ma granite, which implies the heat source of the geothermal anomalies is mainly the concealed Yanshanian granites, combining the granite distribution on the surface.