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Metamorphic olivine after dehydration embrittlement in Serpentinite: Case study from the Shiraga Serpentinite mass in the Sanbagawa high P/T metamorphic belt, central Shikoku, Japan
Island Arc ( IF 1.5 ) Pub Date : 2019-01-27 , DOI: 10.1111/iar.12293
Seiya Fukumura 1 , Kazuaki Okamoto 1, 2 , Masaru Terabayashi 3
Affiliation  

Metamorphic olivine veins in serpentinites are considered to be a metamorphism dehydration product. However, the previous descriptions of these veins have been from paleo‐collision belts such as those in the Alps, Norwegian Caledonides, and Spain. Here the unique metamorphic olivine veins in a mass of serpentinite in the high‐pressure/low‐temperature (high P/T) Sanbagawa belt was reported. The Sanbagawa belt is a product of the subduction of oceanic plates during the Cretaceous. Elongated olivine‐talc veins were observed along shear bands in serpentine mylonite. The olivine's chemical composition is nearly pure forsterite; magnetite is distributed along the boundary of the olivine vein. This clearly suggests that the olivine was formed by the antigorite terminal reaction at a pressure less than 1.5 GPa. The reaction was caused by local heating in the mylonite as there is little evidence of the continuous antigorite breakdown reaction in the serpentinite. Metamorphic olivines are possibly formed in the intraslab earthquake zone of a relatively warm subduction zone such as southwest Japan after the antigorite terminal reaction at P less than 1.5 GPa.

中文翻译:

蛇纹石脱水脆变后的变质橄榄石:以日本四国中部三河川高P / T变质带中的Shiraga蛇纹岩块为例

蛇纹岩中的变质橄榄石脉被认为是变质脱水产物。但是,以前对这些静脉的描述来自古碰撞带,例如阿尔卑斯山,挪威古苏格兰和西班牙。在这里,据报道在高压/低温(高P / T)三叶川带蛇纹岩中有独特的变质橄榄石脉。Sanbagawa带是白垩纪洋板俯冲的产物。沿蛇纹石绵长岩的剪切带观察到橄榄石滑石带拉长。橄榄石的化学成分几乎是纯镁橄榄石。磁铁矿沿橄榄石脉的边界分布。这清楚地表明,橄榄石是通过在小于1.5 GPa的压力下的抗蛇纹石末端反应形成的。该反应是由anti石中的局部加热引起的,因为几乎没有证据表明蛇纹石中有连续的反蛇纹石分解反应。在P小于1.5 GPa的反蛇纹石末端反应之后,变质橄榄石可能形成在相对温暖的俯冲带的板内地震带中,例如日本西南部。
更新日期:2019-01-27
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