The presence of mélange at the subduction interface influences numerous geochemical and geophysical processes. However, the relationship between the timescales of mélange development, deformation, and resultant mass transport is poorly understood. Here, we use Sm-Nd garnet geochronology to elucidate the timing of peak metamorphism for five garnet amphibolite tectonic blocks from the amphibolite-facies mélange zone of the Catalina Schist (Santa Catalina Island, CA). Ages range from 108 to 116 Ma and do not appear to correlate with the peak metamorphic temperature recorded by each block (between 640 and 740°C). The lack of correlation between age and peak temperature favors the tectonic mixing model previously proposed for the unit. These ages overlap with previous estimates of 111–114 Ma for peak metamorphism of the mélange zone but are predominately younger than an estimate for the structurally lower coherent amphibolite unit of ca. 115 Ma. White mica ⁴⁰Ar/³⁹Ar ages from previous studies suggest that the units cooled asynchronously to 400–425°C by 106 to 97 Ma at rates between 18 and 43°C/Ma. Collectively, these results demonstrate that mélange formation occurred over at least 8 Myr from 116 to 108 Ma and was followed by cooling. The structural and chronologic relationship between the mélange zone and underlying lower-grade units indicates that the cooling occurred in conjunction with an underplating event between 109 and 108 Ma. The age discrepancy between the mélange zone and the underlying coherent amphibolite unit may indicate that the two units were juxtaposed either during or after the underplating event.

中文翻译：

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俯冲时代的混合体：俯冲界面剪切带发育和底侵时间尺度的约束，Catalina Schist（美国加利福尼亚州）

俯冲界面混杂物的存在影响了许多地球化学和地球物理过程。然而，人们对混色物发展、变形和由此产生的质量传输的时间尺度之间的关系知之甚少。在这里，我们使用 Sm-Nd 石榴石年代学来阐明来自 Catalina 片岩（加利福尼亚州圣卡塔利娜岛）的角闪岩相混合带的五个石榴石角闪岩构造块的峰值变质时间。年龄范围从 108 到 116 Ma，似乎与每个区块记录的峰值变质温度（640 到 740°C）无关。年龄和峰值温度之间缺乏相关性有利于先前为该单元提出的构造混合模型。这些年龄与先前估计的混杂带峰值变质作用的 111-114 Ma 重叠，但主要比对结构较低的相干角闪岩单元的估计更年轻。115 马。白云母来自先前研究的⁴⁰ Ar/ ³⁹ Ar 年龄表明，这些装置以 18 至 43°C/Ma 的速率异步冷却至 400-425°C 106 至 97 Ma。总的来说，这些结果表明，从 116 到 108 Ma，混色物的形成发生在至少 8 Myr 的时间里，然后冷却。混杂带与下伏低品位单元之间的结构和年代关系表明，冷却与 109 至 108 Ma 之间的底镀事件一起发生。混杂带和下伏的连贯角闪岩单元之间的年龄差异可能表明这两个单元在底镀事件期间或之后并列。