Thermal structure in subducted units from continental Moho depths in a palaeo subduction zone, the Asemigawa region of the Sanbagawa metamorphic belt, SW Japan
Thermal structure in subducted units from continental Moho depths in a palaeo subduction zone, the Asemigawa region of the Sanbagawa metamorphic belt, SW Japan
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日本西南部三波川变质带阿塞美川地区古俯冲带大陆莫霍面深处俯冲单元的热结构
DOI：
10.1111/jmg.12584
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发表时间：
2021
影响因子：
3.4
通讯作者：
Enami Masaki
中科院分区：
文献类型：
--
作者：
Kouketsu Yui;Sadamoto Kazushi;Umeda Hayato;Kawahara Hirokazu;Nagaya Takayoshi;Taguchi Tomoki;Mori Hiroshi;Wallis Simon;Enami Masaki
在11 km × 7 km的范围内采集了126个泥质片岩样品，利用Raman CM地温测量技术，以前所未有的细节揭示了日本西南部三巴川变质带Asemigawa地区的热结构。总的来说，估计温度在288-553°C范围内从南到北逐渐升高。然而，在绿泥石带和石榴石带的边界附近，发现了~380 ~ ~440℃的温差。这一温度区域与三巴川俯冲带大陆莫霍的深度相匹配。高温区温度梯度大于低温区温度梯度，在高温单元和温度断裂带附近发育了影响热结构的大规模致密褶皱。这些地质构造可能反映出，由于从蛇纹岩下向地壳岩覆盖的较浅区域的挖掘过程中，上覆岩石的耦合强度增加，阻碍了向上运动，因此在莫霍深度被挖出的板单元阻塞。沿俯冲边界耦合强度的变化导致了高温域的强烈褶皱，而莫霍深度发育的预成叶理作用可能起到了构造边界的作用，导致了温度不连续。这些结果将有助于阐明现代俯冲带弧前地区发生的各种地质现象。
Raman CM geothermometry applied to 126 samples of pelitic schists collected over an area of 11 km × 7 km reveals the thermal structure of the Asemigawa region of the Sanbagawa metamorphic belt, southwest Japan in unprecedented detail. In general, the estimated temperatures gradually increase from south to north in the range of 288–553°C. However, a temperature gap from ~380 to ~440°C is identified near the boundary between the chlorite and garnet zones. This temperature region matches the depth of the continental Moho of the Sanbagawa subduction zone. The temperature gradient in the higher‐temperature domain is higher than that in the lower‐temperature domain, and large‐scale tight folds that affect the thermal structure are developed in the high‐grade units and in the vicinity of the temperature discontinuity. These geological structures probably reflect that the exhumed slab units was dammed at the Moho depth due to the upward movement being impeded by increase in the coupling strength of the overlying rocks associated with exhumation from beneath serpentinite rocks to a shallower domain overlain by crustal rocks. Changes in the coupling strength along the subduction boundary led the strong folding at the higher‐temperature domain and the pre‐formed foliation developed at the Moho depth may have acted as the tectonic boundary, resulting in a temperature discontinuity. These results will contribute to elucidating various geological phenomena occurring in the forearc regions of modern subduction zones.