Translating burial and exhumation histories from the petrological and geochronological record of high-pressure assemblages in subduction channels is key to understanding subduction channel processes. Convective return flow, either serpentinite or sediment hosted, has been suggested as a potential mechanism to retrieve rocks from significant depths and exhume them. Numerical modelling predicts that during convective flow, subducted material can be cycled within a serpentinite-filled subduction channel. Geochronological and petrological evidences for such cycling during subduction are preserved in lawsonite eclogite from serpentinite melange in the Southern New England Orogen, eastern Australia. Ar–Ar, Rb–Sr phengite and U–Pb titanite geochronology, supported by phase equilibrium forward modelling and mineral zoning, suggest Cambro–Ordovician eclogite underwent two stages of burial separated by a stage of partial exhumation. The initial subduction of the eclogite at ca. 490 Ma formed porphyroblastic prograde-zoned garnet and lawsonite at approximate P–T conditions of at least 2.9 GPa and 600 °C. Partial exhumation to at least 2.0 GPa and 500 °C is recorded by garnet dissolution. Reburial of the eclogite resulted in growth of new Mg-rich garnet rims, growth of new prograde-zoned phengite and recrystallization of titanite at P–T conditions of approximately 2.7 GPa and 590 °C. U–Pb titanite, and Ar–Ar and Rb–Sr phengite ages constrain the timing of reburial to ca. 450 Ma. This was followed by a second exhumation event at approximately 1.9 GPa and 520 °C. These conditions fall along a cold approximate geotherm of 230 °C/GPa. The inferred changes in pressure suggest the lawsonite eclogite underwent depth cycling within the subduction channel. Geochronological data indicate that partial exhumation and reburial occurred over ca. 50 M y., providing some estimation on the timescales of material convective cycling in the subduction channel.

中文翻译：

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在充满蛇纹岩的俯冲通道内重新俯冲硬柱石榴辉岩

从俯冲通道中高压组合的岩石学和地质年代记录翻译埋藏和挖掘历史是理解俯冲通道过程的关键。对流回流，无论是蛇纹岩还是沉积物，都被认为是从重要深度取回岩石并挖掘它们的潜在机制。数值模拟预测，在对流过程中，俯冲物质可以在充满蛇纹岩的俯冲通道内循环。俯冲过程中这种循环的地质年代学和岩石学证据保存在澳大利亚东部新英格兰造山带南部蛇纹岩混杂岩中的硬钠铝榴石榴辉岩中。Ar-Ar、Rb-Sr phengite 和 U-Pb 钛白石年代学，由相平衡正向建模和矿物分带支持，表明 Cambro-Ordovician 榴辉岩经历了两个埋藏阶段，被一个部分挖掘阶段分开。榴辉岩的初始俯冲在约。490 Ma 在至少 2.9 GPa 和 600 °C 的近似 P-T 条件下形成了斑纹状顺行带石榴石和硬镁铝榴石。通过石榴石溶解记录到至少 2.0 GPa 和 500 °C 的部分折返。榴辉岩的再埋导致新的富镁石榴石边缘的生长、新的顺产带状菱镁矿的生长和钛铁矿在约 2.7 GPa 和 590 °C 的 P-T 条件下的再结晶。U-Pb 钛铁矿、Ar-Ar 和 Rb-Sr phentite 年龄将重新埋藏的时间限制在大约 450 毫安。随后在大约 1.9 GPa 和 520 °C 下发生了第二次折返事件。这些条件属于大约 230 °C/GPa 的冷地温。推断的压力变化表明硬柱石榴辉岩在俯冲通道内经历了深度循环。地质年代学数据表明，部分挖掘和重新埋葬发生在大约 50 M y.，提供了对俯冲通道中物质对流循环时间尺度的一些估计。