K.D. Nelson Lecture Series: Dr. Kennet Flores

The Department of Earth & Environmental Sciences in the College of Arts and Sciences presents the K.D. Nelson Lecture Series featuring speaker Kennet Flores. His talk is titled: “Petrological and Geochemical Record of Fluid Migration in the Subduction Interface.”

Abstract:

Subduction zones are the primary location for element recycling from the Earth’s surface into the mantle. Subducting plates release fluids that play a crucial role in generating intraslab earthquakes, serpentinization and flux melting of the mantle wedge to yield arc volcanism. Exhumed remnants of slab-mantle interfaces represent our only record, albeit incomplete, of the history of fluid transfer and fluid-rock interaction. Highly retrogressed eclogites within the North Motagua Mélange (central Guatemala) preserve extensive chemical alterations that record rehydration reactions at the plate interface at depths of ~80-30 km. Our new results suggest that these rocks reached peak burial at eclogite-facies conditions (550-600°C, 2.0-2.5 GPa) and were sliced off the slab at 114-113 Ma. These rocks also preserve two fluid-related retrogression events: (i) An initial rehydration event at blueschist-facies conditions (500-550°C, 1.5-2.0 GPa) at 100-89 Ma and characterized by significant whole-rock enrichment in fluid-mobile elements (e.g., K, Ba, Pb). (ii) At 82-73 Ma, a second retrogression stage occurred at Ep-amphibolite-facies conditions (450-500°C, 0.8-1.0 GPa) and was associated with the infiltration of Ca-Na-rich fluids. These two phases occurred during ~40 Myrs of storage-decompression within the subduction interface before a final exhumation stage. Throughout this residence time, slab-derived fluids infiltrated the subduction interface, triggering mantle serpentinization, fluid-related vein crystallization (e.g., jadeitites-phengitites) and rehydration of ascending eclogites. Our results suggest that retrograde eclogites and fluid-related rocks in serpentinite mélanges (frequently ignored due to their complexity) contain critical clues to reconstruct the record and timing of fluid migrations and fluid-rock interactions in subduction zones.