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首页> 外文期刊>Contributions to Mineralogy and Petrology >Transition from dehydration to hydration during exhumation of the Sanbagawa metamorphic belt, Japan, revealed by the continuous P-T path recorded in garnet and amphibole zoning
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Transition from dehydration to hydration during exhumation of the Sanbagawa metamorphic belt, Japan, revealed by the continuous P-T path recorded in garnet and amphibole zoning

机译：石榴石和角闪石分区中记录的连续P-T路径揭示了日本Sanbagawa变质带发掘期间从脱水到水化的过渡

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摘要

To investigate the water budget in deep accretionary prisms, we undertook a detailed petrologic analysis of garnet-bearing amphibolites in the subduction-origin high-pressure Sanbagawa metamorphic belt, Japan. We obtained a continuous P-T path of exhumation by the application of differential thermodynamics to compositional zoning in both garnet and amphibole. The P-T path is characterized by three stages of decompression: (1) heating decompression from 1.5 GPa and 550 degrees C to 1.1 GPa and 600 degrees C; (2) isothermal decompression toward 0.8 GPa and 580 degrees C; and (3) cooling decompression to 0.3 GPa and 400 degrees C. Comparison with the results of numerical modeling of the thermal structures of subduction zones suggests that the peak-pressure condition is warmer than the slab surface temperature in a typical subduction zone, but is consistent with subduction of a young slab during the Sanbagawa metamorphism. The heating decompression just after the peak-pressure condition is explained by heating from the mantle wedge during ascent of the metamorphic body in the accretionary prism; heating stops when the metamorphic body reaches crustal depths. Mass balance calculations for the mineral reactions in an amphibolite reveal that the dehydration associated with the growth of Ca-poor garnet takes place during heating decompression, whereas hydration takes place during cooling decompression by the breakdown of garnet and pargasite to form chlorite and actinolite. Such a transition from dehydration to hydration in the exhuming metabasite body in an accretionary prism generates fluids between the continental Moho and the slab surface and may explain the seismic activity above the subduction plate boundary, such as supra-slab earthquakes.
机译：为了研究深部增生棱镜中的水预算，我们对俯冲起源的高压三河川变质带中含石榴石的闪石进行了详细的岩石学分析。通过将差分热力学应用于石榴石和角闪石的成分分区，我们获得了连续的P-T掘尸途径。 P-T路径的特征在于减压的三个阶段：（1）从1.5 GPa和550摄氏度的加热减压到1.1 GPa和600摄氏度的加热; （2）等温减压至0.8 GPa和580摄氏度; （3）将冷却减压至0.3 GPa和400摄氏度。与俯冲带热结构数值模拟的结果比较表明，在典型的俯冲带中，峰值压力条件要比平板表面温度高，但这与在三叶川变质中俯冲的年轻板块一致。峰值压力条件之后的加热减压是通过变质体在增生棱镜中上升时来自地幔楔的加热来解释的。当变质体到达地壳深度时，加热停止。闪石中矿物反应的质量平衡计算表明，与贫钙石榴石生长有关的脱水发生在加热减压过程中，而冷却过程中由于石榴石和辉石矿的分解形成绿泥石和阳起石，而发生水合作用。在增生棱柱体中，变质异位块体内从脱水到水化的过渡在大陆莫霍面和板状表面之间产生了流体，并可以解释俯冲板边界上方的地震活动，例如超板状地震。

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