Garnet is a fundamental expression of metamorphism and one of the most important minerals used to constrain the thermal conditions of the crust. We used innovative in situ laser-ablation ICP-MS/MS Lu-Hf geochronology to demonstrate that garnet in metapelitic rocks enclosing Cambrian eclogite in southern Australia formed during Laurentian Mesoproterozoic metamorphism. Garnet porphyroblasts in amphibolite-facies metapelitic rocks yielded Lu-Hf ages between 1286 ± 58 Ma and 1241 ± 16 Ma, revealing a record of older metamorphism that was partially obscured by metamorphic overprinting during ca. 510 Ma Cambrian subduction along the East Gondwana margin. Existing detrital zircon age data indicate the protoliths to the southern Australian metapelitic rocks were sourced from western Laurentia. We propose that the metapelitic rocks of southern Australia represent a fragment of western Laurentian crust, which was separated from Laurentia in the Neoproterozoic and incorporated into the East Gondwana subduction system during the Cambrian. The ability to obtain Lu-Hf isotopic data from garnet at acquisition rates comparable to those for U-Pb analysis of detrital zircon means, for the first time, the metamorphic parentage of rocks as expressed by garnet can be efficiently accessed to assist paleogeographic reconstructions.

中文翻译：

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激光烧蚀 Lu-Hf 测年揭示了澳大利亚南部俯冲岩石中的劳伦石榴石

石榴石是变质作用的基本表现形式，也是用于限制地壳热条件的最重要矿物之一。我们使用创新的原位激光烧蚀 ICP-MS/MS Lu-Hf 地质年代学来证明澳大利亚南部寒武系榴辉岩周围的变泥质岩中的石榴石是在 Laurentian 中元古代变质作用期间形成的。角闪岩相变质岩中的石榴石斑岩产生的 Lu-Hf 年龄在 1286 ± 58 Ma 和 1241 ± 16 Ma 之间，揭示了较早变质作用的记录，该记录在大约 510 Ma 寒武纪沿东冈瓦纳边缘俯冲。现有的碎屑锆石年龄数据表明，澳大利亚南部变泥质岩的原岩来自劳伦蒂亚西部。我们认为澳大利亚南部的变泥质岩代表了西部劳伦地壳的一个片段，该地壳在新元古代与劳伦地壳分离，并在寒武纪被纳入东冈瓦纳俯冲系统。能够以与碎屑锆石的 U-Pb 分析相当的采集速率从石榴石中获取 Lu-Hf 同位素数据意味着，首次可以有效地获取石榴石所表示的岩石的变质亲本，以协助古地理重建。