Hunter–Bowen deformation in South Percy Island, northeastern Australia

South Percy Island is located approximately 50 km off the central Queensland coast and comprises a disrupted ophiolite mass alongside a diverse array of metamorphosed felsic and mafic rocks that record several episodes of magmatism, volcanism and deformation from the Permian to Early Cretaceous. This paper aims to constrain the age, affinity and deformation history of these units, as well as to establish the tectonic significance of the terrane. The trace-element compositions of mafic and felsic meta-igneous rocks record a change from MORB-like prior to <i>ca</i> 277 Ma to subduction-related by <i>ca</i> 258 Ma. Overprinting relationships between intrusive phases and deformation features reveal a relative chronology for the tectonothermal evolution of the area, while U–Pb and ⁴⁰Ar/³⁹Ar geochronology provides absolute age constraints. Deformation is localised around a NNE-striking tectonic contact that separates serpentinised ultramafic rocks from metamorphosed pillow lavas. Early formed ductile fabrics associated with the main episode of deformation (D₁) preserve bulk flattening strains at greenschist-facies conditions. Emplacement and post-kinematic cooling ages of a pre-D₁ quartz-monzonite dyke constrain the age of D₁/M₁ deformation and metamorphism to the period between <i>ca</i> 258 and <i>ca</i> 248 Ma. Minor brittle deformation (D₂) occurred at <i>ca</i> 230 Ma, based on U–Pb dating of a syn-D₂ diorite dyke (<i>ca</i> 231 ± 10 Ma) and several <i>ca</i> 230 Ma ⁴⁰Ar/³⁹Ar cooling ages. The deformation, metamorphism, and supra-subduction zone magmatism preserved on South Percy Island is correlated with the nearby Marlborough Terrane and more broadly with the second pulse of the Hunter–Bowen Orogeny, which affected much of the central and northern parts of eastern Australia in the late Permian and Early Triassic. Our results support previous suggestions that the second pulse of the Hunter–Bowen Orogeny involved coeval thrust systems in both the inboard and outboard parts of the orogen.

南珀西岛（South Percy Island）位于澳大利亚昆士兰州中部海岸外约50公里处，由受扰动的蛇绿岩块以及一套多样的变质长英质和镁铁质岩石组成，这些岩石记录了二叠纪至早白垩世期间多期岩浆作用、火山作用与变形事件。本文旨在限定这些地质单元的形成时代、成因属性与变形历史，并明确该地块的构造意义。镁铁质与长英质变质火成岩的微量元素组成记录了构造环境的转变：约277 Ma之前为类似洋中脊玄武岩（Mid-Ocean Ridge Basalt, MORB）的特征，至约258 Ma时转变为与俯冲作用相关的特征。侵入相与变形构造之间的穿切关系揭示了该区域构造热演化的相对年代序列，而铀-铅（U-Pb）和氩-氩（⁴⁰Ar/³⁹Ar）热年代学则提供了绝对年代约束。变形作用集中发育于一条北东北走向的构造接触带附近，该带将蛇纹石化超镁铁质岩石与变质枕状熔岩分隔开来。与主变形期（D₁）相关的早期韧性变形组构在绿片岩相条件下呈现整体压扁应变特征。前D₁期石英二长岩脉的侵位及运动后冷却年龄，将D₁/M₁变形与变质作用的时代限定在约258 Ma至约248 Ma之间。根据一条同D₂期闪长岩脉的铀-铅定年结果（约231 ± 10 Ma）以及多组约230 Ma的⁴⁰Ar/³⁹Ar冷却年龄，可判定次要脆性变形（D₂）发生于约230 Ma。南珀西岛所保存的变形作用、变质作用以及俯冲带上盘岩浆作用，可与附近的马尔伯勒地体（Marlborough Terrane）对比，更广泛地则可与晚二叠世至早三叠世期间影响澳大利亚东部中部与北部大部分区域的亨特-鲍恩造山运动第二幕相对应。本研究结果支持此前的观点，即亨特-鲍恩造山运动第二幕在造山带的内侧与外侧均发育同期的逆冲系统。