Decoupling of U–Pb ages and compositional zoning of garnet in a high–pressure marble from the eastern Iratsu body, Sanbagawa metamorphic terrane, Japan
Decoupling of U–Pb ages and compositional zoning of garnet in a high–pressure marble from the eastern Iratsu body, Sanbagawa metamorphic terrane, Japan
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DOI：
10.2465/jmps.210814
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发表时间：
2022
影响因子：
0.7
通讯作者：
S. Niki;Kenta Yoshida;H. Sawada;R. Oyanagi;T. Hirata
中科院分区：
文献类型：
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作者：
S. Niki;Kenta Yoshida;H. Sawada;R. Oyanagi;T. Hirata
本文首次报道了变质钙铝榴石石榴石（Grs）的原位U-Pb定年，并对内部分带结构进行了区分。本文所研究的花岗岩产于日本三钵川变质岩带东入津岩体中的榴辉岩相大理岩中。Grs具有斑片状结构，主要是在榴辉岩相和折返阶段分别形成的纯Grs核和富含钙铁榴石（Adr）的边缘。Grs核和富Adr边缘的U-Pb年龄分别为97 ± 10和106 ± 16 Ma（95%置信水平）。尽管在不同的P-T条件下形成了成分分带，但在分析不确定性范围内，核和边缘的U-Pb年龄值相似。这种化学分带与U-Pb年龄的分离表明，由于放射成因Pb在边缘形成过程中通过流体介导的溶解和再沉淀在核中重新分布，边缘的U-Pb年代学特征是从核中继承的。因此，Grs U-Pb年龄（97 ± 10 Ma）与前人报道的榴辉岩相变质作用期间岩芯形成的P-T条件直接对应。Grt岩石年代学的这一优点是将原位分析获得的放射性年龄与共生作用推断的P-T条件相结合，有助于重建
Here we fi rst report the in situ U – Pb dating of metamorphic grossular garnet (Grs) with distinction between internal zonation textures. The studied Grs occurs in an eclogite – facies marble collected from the eastern Iratsu body of the Sanbagawa metamorphic terrane, Japan. The Grs has a patchy texture, predominantly with pure Grs cores and andradite (Adr) – rich rims formed during eclogite – facies and exhumation stages, respectively. The U – Pb ages for the Grs core and Adr – rich rim were 97 ± 10 and 106 ± 16 Ma (95% con fi dence level), respectively. Despite the compositional zoning formed under di ff erent P – T conditions, the U – Pb ages of the core and rim were in similar values within analytical uncertainties. This decoupling of chemical zonation and U – Pb ages implies that the U – Pb chronological signatures of rims were inherited from cores owing to the redistribution of radiogenic Pb in cores during the rim formation through fl uid – mediated dissolution and reprecipitation. The Grs U – Pb age (97 ± 10 Ma) thus directly corresponds to previously reported P – T conditions of the core formation during the eclogite – facies metamorphism. This advantage of Grt petrochronology as the combination of radiometric ages obtained by in situ analysis and P – T conditions deduced from paragenesis can contribute to reconstruct