The habitat of slow slip phenomena in the Hikurangi subduction zone

俯冲带——大洋板块俯冲到大陆板块之下的地方——是地球上最具地质动力的系统之一。在过去的十年中，随着地震学和大地测量仪器的进步，我们对这一领域断层滑动行为的认识大大增加。新发现的断层滑动模式可以持续数月，因此被称为慢震。控制这种滑动行为的地质因素仍然存在争议。探险队375计划于2018年3月8日至5月5日进行，R/V JOIDES Resolution将对新西兰近海Hikurangi北部俯冲边缘浅层慢滑地震的栖息地进行采样和记录，包括前缘冲断、上板块和进入的沉积物以及海洋地壳。在前缘逆冲带和上板块目标断裂带的钻探点，流体有望向海底迁移，这将为研究慢滑震源区提供一个窗口。本研究旨在通过成岩作用、粘土脱水作用和流体运移，识别和表征重要成岩作用及其对俯冲逆冲流体力学状态的影响。该研究将通过流体和全岩石地球化学协调策略，结合硼和锂同位素分析来确定水岩相互作用过程。通过热液压实试验确定地球化学指纹图谱的温度依赖性，并将地球化学数据与反应输运模型相结合，以约束弧前俯冲带水岩相互作用和流体运移的时空分布。

Subduction zones - where an oceanic plate is subducting beneath a continental plate – are among the most geologically dynamic systems on earth. In the last decade our knowledge of fault slip behavior in this realm has tremendously increased in response to advances in seismological and geodetic instruments. The newly discovered fault slip modes can last for months and thus are termed slow earthquakes. The geological factors that control such slip behavior is still subject to debate. Expedition 375 has been scheduled from March 8th, 2018, to May 5th, 2018, for R/V JOIDES Resolution to sample and log the frontal thrust, upper plate and incoming sediment plus oceanic crust in order to characterize the habitat that hosts shallow slow slip earthquakes in the northern Hikurangi subduction margin offshore New Zealand. Drill sites at the frontal thrust and on the upper plate target fault zones where fluid migration to the seafloor is expected, which will provide a window to the slow slip source region. The proposed research aims at the identification and spatio-temporal characterization of important diagenetic processes and their influence on the hydro-mechanical state of the subduction thrust through diagenesis, clay dehydration processes and fluid migration. The research will be implemented by a coordinated strategy of fluid and whole rock geochemistry in combination with boron and lithium isotope analysis to identify water-rock interaction processes, hydrothermal compaction tests to determine the temperature-dependence of the geochemical fingerprints from the identified processes and integration of the geochemical data with reaction-transport models to constrain the spatio-temporal occurrence of water-rock interaction and fluid migration in the subduction zone forearc.