MAGMA-TECTONIC STRUCTURAL CONTROLS ON SUBLACUSTRINE HYDROTHERMAL SYSTEMS IN MONO LAKE, CALIFORNIA

Heat and volatile transport in tectonically active regions are strongly controlled by active crustal deformation driven by tectonics and magmatism. The respective influence of magmatic and tectonically induced deformation on heat and volatile transport is both spatially and temporally variable. In this study we couple new campaign heat flow measurements with data from seismic and bathymetric surveys to constrain the shallow tectonic and magmatic structures that control heat, fluid, and gas transport in the Mono Basin, located in eastern California. We collected 62 new shallow temperature gradient measurements. In general, temperature fluctuations in the shallow sediments induced by annual lake temperature fluctuations dominate the shallow temperature gradients. Nonetheless, temperature gradient measurements exceeded seasonal background levels at (1) Hot Springs Cove southeast of Paoha Island where a lava dome formed approximately 300-350 years BP and (2) South Tufa along a fault mapped onshore and identified offshore through seismic reflection data. Repeat surveys in March 2022 and August 2022 near Hot Springs Cove confirm a temperature gradient anomaly at the bottom of the lake even during summer conditions when lake floor temperature is broadly elevated. High temperature gradients in the lake at Hot Springs Cove and South Tufa are associated with sublacustrine hydrothermal systems. We couple geophysical observations with basin wide numerical modeling of non-isothermal fluid flow in porous media to assess the distribution of thermal anomalies in Mono Lake. Our analysis reveals that shallow fractured lava domes within the Mono Basin form conduits for vertical fluid flow whereby volatiles can transport heat through advection to the surface producing fumaroles and hot springs and sublacustrine hydrothermal systems. This study demonstrates the need for high spatial and temporal resolution heat flow sampling systems to constrain highly localized structural controls on the distribution of sublacustrine hydrothermal systems.