Thermal Structure of a Hot Accretionary Complex: Upper Shimanto Group, Shikoku, Japan

大多数俯冲杂岩内的热结构模型预测出现小地温梯度和低热流。然而，南开海槽附近的地温梯度计算和测量结果并不支持这一范式。此外，异常高的埋藏温度可能影响了整个新生代日本南部的增生边缘。南开增生楔的隆起部分沿若干日本列岛明显暴露；最年轻的增生地层（始新世-中新世）属于上石曼托群。该项目将收集来自Shimanto吸积棱镜的样品的热成熟度数据，康奈尔大学和布朗大学的工作人员正在对其进行研究。实验室方法包括镜质组反射率和伊利石结晶度。目的包括使用热成熟度数据和复杂的单个单元内的热历史记录来测试构造模型。结果数据的重要性将远远超出具体地点的问题。数据将为现有的热结构理论模型提供急需的经验检验。更重要的是，南开/Shimanto的例子似乎代表了热状态光谱中的一端成员。因此，研究结果可能会促使对俯冲复合体的基本概念框架进行扩展和完善。

Most models of thermal structure within subduction complexes predict the occurrences of small geothermal gradients and low heat flow. Calculated and measured geothermal gradients in the vicinity of Nankai Trough, however, do not support this paradigm. Moreover, abnormally high burial temperatures may have affected the accretionary margin of southern Japan throughout Cenozoic time. Uplifted portions of the Nankai accretionary wedge are well exposed along several of the Japanese Islands; the youngest of these accreted strata (Eocene-Miocene) are assigned to the Upper Shimanto Group. This project will collect thermal-maturity data on samples from the Shimanto accretionary prism, which is being studied by workers at Cornell and Brown Universities. Laboratory methods include vitrinite reflectance and illite crystallinity. Objectives include testing tectonic models using thermal-maturity data and documentation of thermal history within individual units of the complex. The significance of the resulting data will extend well beyond site-specific issues. Data will provide a much-needed empirical check on existing theoretical models of thermal structure. More importantly, the Nankai/Shimanto example appears to represent one end member within a spectrum of thermal regimes. Consequently, results will likely force an expansion and refinement of the fundamental conceptual framework of subduction complexes.