Thermal structure and paleo‐heat flow in the Shimanto accretionary prism, Southwest Japan
Thermal structure and paleo‐heat flow in the Shimanto accretionary prism, Southwest Japan
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日本西南部四万十吸积棱柱的热结构和古热流
DOI：
10.1046/j.1440-1738.1999.00246.x
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发表时间：
1999
期刊：
影响因子：
1.5
通讯作者：
A. Sakaguchi
中科院分区：
文献类型：
--
作者：
A. Sakaguchi
摘要热构造分析和古热流估算为了解增生杂岩的热演化提供了线索。通过镜质体反射率测量和流体包裹体分析，研究了日本西南部侏罗纪秩父和白垩纪至第三纪四万十增生杂岩的热结构和热流。据此，对本区的局部变质作用和多期变质作用进行了初步的认识。首先，中新世足折花岗岩周围的第三纪杂岩经历了超高温。其次，冲津混杂岩比周围的地层暴露在更高的温度下，并在始新世与日本群岛下方的库拉太平洋洋脊俯冲同时形成。最后，大部分白垩纪和南侏罗系杂岩的热结构与地质构造无关，表明这些地区遭受了热叠加。区域放射性测年研究表明，白垩纪四万十杂岩的大部分在始新世被加热;热叠加可能是由于洋脊俯冲而发生的。加热高峰期的热流估计为95-120 mW/m2，除了白垩纪冲津混杂岩和冲津混杂岩以北的白垩纪野之川组;冲津混杂岩中的热流估计值更高，约为200 mW/m2。非大川地层的热流估算失败，因为流体和岩石之间的热平衡尚未达到。南部地层可能经历了较高的热流。尽管始新世的热流要高得多，但这种热流的沟向增加与南海海槽的现状相似。
Abstract Thermal structural analysis and paleo‐heat flow estimation provide clues to understanding the thermal evolution of the accretionary complex. The thermal structure and heat flow in the Jurassic Chichibu and Cretaceous to Tertiary Shimanto accretionary complex, Southwest Japan, have been investigated by vitrinite reflectance measurement and fluid inclusion analysis. As a result, the local and multistage metamorphisms were recognized as follows. First, the Tertiary complex around the Miocene Ashizuri granite underwent exposure to extra‐high temperatures. Second, the Okitsu Melange underwent exposure to higher temperatures than the surrounding strata and was formed concurrently with the Kula‐Pacific ridge subduction beneath the Japanese Islands in the Eocene. Finally, the thermal structure of most of the Cretaceous and southern Jurassic complexes is independent of the geologic structure, indicating that these areas suffered thermal overprint. Regional radiometric dating studies show that most of the Cretaceous Shimanto complex was heated in the Eocene; the thermal overprint might have occurred as a result of ridge subduction. The heat flow during peak heating was estimated to be 95–120 mW/m2 except for the Cretaceous Okitsu melange and the Cretaceous Nonokawa formation, north of the Okitsu Melange; a much higher value of heat flow of ~200 mW/m2 was estimated in the Okitsu Melange. An estimation of heat flow failed for the non‐okawa formation because thermal equilibrium between the fluid and rocks has not yet been reached. It is probable that the southern strata underwent a higher heat flow. Such a trenchward increase in heat flow resembles the present situation of the Nankai Trough, although the heat flow in the Eocene was much higher.