Granulite-faciesxenoliths from the Yuhuashan complex, central Jiangxi, South China: constraintson Late Palaeozoic orogeny and middle-lower crust components
Granulite-faciesxenoliths from the Yuhuashan complex, central Jiangxi, South China: constraintson Late Palaeozoic orogeny and middle-lower crust components
复制标题
江西中部雨花山杂岩麻粒岩相包体：晚古生代造山运动及中下地壳组成的制约
DOI：
10.1111/jmg.12170
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发表时间：
2016
影响因子：
3.4
通讯作者：
Shen LW
中科院分区：
文献类型：
--
作者：
Zhang Chunhui;Yu jinhai;O'Reilly SY;Griffin WL;Qian JH;Liu Q;Lou FS;Zhou XY;Shen LW
白垩纪雨花山火成杂岩中含有丰富的高级变质岩包体，其组合为石榴石+玄武岩+黑云母+斜长石+钾长石+石英。两个长英质麻粒岩的P-T计算表明，峰期变质温度分别为880~887℃和0.64~0.70 Gpa，为低压高温麻粒岩相。相平衡模拟给出了>；0.6 Gpa和>；840℃的长英质麻粒岩的峰组合的平衡条件，与p-T计算一致，并确定了逆时针的P-T-t路径。一个包体变质和碎屑锆石的La-ICPMS U-Pb定年结果表明，麻粒岩相变质作用发生在273.6 Ma±22.2 Ma，原岩为晚于683Ma的沉积岩。这是南中国地块首次发现的晚古生代(华力西)麻粒岩相事件。结合其他地质观察，Lp-HT变质条件和逆时针方向的P-T轨迹表明，华力西变质作用可能发生在与外部热输入有关的后造山或板内伸展构造环境中，与地幔岩浆底侵有关。根据ONP-T值估算和本区中低级变质岩的原岩成分对比，认为香山-雨花山地区的中下地壳主要由这些长英质麻粒岩和片麻岩组成，其原岩可能是在南海盆地早古生代造山期间俯冲到该深度，并在早古生代和晚古生代经历了两次变质作用。
The Cretaceous Yuhuashan igneous complex contains abundant xenoliths of high‐grade metamorphic rocks, with the assemblage garnet ± hypersthene + biotite + plagioclase + K‐feldspar + quartz. The biotite in these samples has high TiO2(>3.5%), indicating high‐Tmetamorphism (623–778 °C).P–Tcalculations for two felsic granulites indicate that the peak metamorphism took place at 880–887 °C and 0.64–0.70 GPa, in the low pressure/high temperature (LP‐HT) granulite facies. Phase equilibrium modelling gives equilibrium conditions for the peak assemblage of a felsic granulite of >0.6 GPa and >840 °C, consistent with theP–Tcalculations, and identifies an anticlockwiseP–T–tpath. LA‐ICPMS U–Pb dating of metamorphic and detrital zircon from one xenolith reveals that the granulite facies metamorphism took place at 273.6 ± 2.2 Ma, and the protolith was a sedimentary rock deposited later than 683 Ma. This represents the first Late Palaeozoic (Variscan) granulite facies event identified in the South China Block (SCB). Coupled with other geological observations, the LP‐HT metamorphic conditions and anticlockwiseP–T–tpath suggest that Variscan metamorphism probably occurred in a post‐orogenic or intraplate extensional tectonic setting associated with the input of external heat, related to the underplating of mantle‐derived magma. Based onP–Testimates and the comparison of the protolith composition with mid‐ to low‐grade metamorphic rocks in the area, it is suggested that the mid‐lower crust under the Xiangshan–Yuhuashan area consists mainly of these felsic granulites and gneisses, whose protoliths were probably subducted to these depths during the Early Palaeozoic orogeny in the SCB, and underwent two episodes of metamorphism during Early Palaeozoic and Late Palaeozoic time.