Talc-bearing serpentinized peridotites from the southern Mariana forearc:implications for aseismic character within subduction zones

The serpentinized peridotites overlying the subducted zones in the Izu-Bonin-Mariana(IBM) arc system have been interpret as the cause of the low-velocity layer identified beneath the IBM froearc,in turn few earthquakes occurred along the plate boundary.Chrysotile,which is a low temperature and highly hydrated phase of serpentine with low frictional strength,has been suggested as the low velocity material in the serpentinized peridotites,besides,brucite is inferred to be likely conducive to stable sliding.However,such idea encounters challenging in our serpentinized peridotites from the southern Mariana forearc,which absent both the above minerals.The presence of talc,which characterized by its weak,low-friction and inherently stable sliding behavior,provides new clue.Here we report the occurrence of talc in serpentinized peridotites collected from the landward trench slope of the southern Mariana forearc.We infer that talc is mainly forming as a result of the reaction of serpentine minerals with silica-saturated fluids released from the subducting slab,and talc also occurs as talc veins sometimes.Due to its unique physical properties,talc may therefore play a significant role in aseismic slip in the IBM subduction zone.

塔里木盆地地震剖面地质解释及其构造演化

从地震剖面显示塔里木盆地发育为手风琴式演化史,大体上形成三层"断-坳"结构:(l)震旦系的"断",古生界—三叠系的"坳";(2)侏罗系的"断",白垩系的"坳";(3)古近系的"断",新近系的"坳"。断陷与坳陷分别由拉张与挤压应力场所致,这种应力场的变化是由相邻洋壳板块俯冲倾角由小到大的变化所引起的。由于地壳的多旋回运动,多次发生构造沉积演变,构成了多套生储盖组合,多领域、多种圈闭类型的油气藏,从震旦系—古生界—中生界—新生界,各断陷-坳陷结构的盆地都具有可能形成油气藏的地质条件。