Timescales and episodicity of fluid flow along the subduction interface | Dr. Sara Penniston-Dorland

Timescales and episodicity of fluid flow along the subduction interface – a petrological and geochemical perspective Talk provided by Dr. Sarah Penniston-Dorland from the University of Maryland on May 14, 2025 as part of the SZ4D International Webinar Series. For more information, visit www.sz4d.org Full Webinar Description: The source region of deep episodic tremor and slow slip (ETS) events at the subduction interface is likely fluid rich and subject to high pore fluid pressure, however the mechanistic role of fluid in producing these phenomena is debated. Exhumed subduction-related metamorphic rocks provide our only direct sampling of materials from the deep subduction interface. We provide evidence from these rocks that provides insight into timescales and episodicity of fluid flow at the subduction interface using Li isotope measurements on rocks from two different localities. The results of studies of fluid-related reaction features of the Catalina Schist indicate relatively short time-integrated durations of fluid flow at the subduction interface of ~40 years which are comparable to, or longer than, the longest slow slip events recorded in active subduction systems. The results suggest that fluid transport does not occur continuously at the subduction interface but rather reflects transport through fracture permeability consistent with fault-valve type models of fluid transport and related pore pressure fluctuation. Whether these timescales are a record of a single episode of fluid flow or the integration of multiple episodes of flow is uncertain. Episodicity can be evaluated through in situ Li isotope measurements of garnet. We show that in a fluid-related reaction feature of the Monviso Ophiolite there is evidence for at least four episodes of fluid transport along a subduction shear zone at eclogite facies. Combining these two methods will hopefully give us better constraints on the duration of individual fluid flow episodes that can be correlated to timescales of ETS occurring in active subduction zones and ultimately shed light on the processes that generate these events.