T242 Fluids and Deformation during Subduction from the Trench to the Subarc

Wednesday, 25 September 2024
8:00 AM - 12:00 PM
304B

APATITE U-Pb PETROCHRONOLOGY RECORDS SUBDUCTION-RELATED DEFORMATION AND FLUID FLOW IN THE CATALINA SCHIST, CA

Paper number: T242-10
Program: Technical Sessions
Time: 10:15 AM – 10:30 AM

Authors

Abstract

The subduction plate interface is a region of intense deformation, metamorphism, and fluid flow—processes that influence slip behaviors at the base of the seismogenic zone such as slow slip events, non-volcanic tremor, and megathrust earthquakes. The timing and complexities of these processes are difficult to reconstruct over geologic time without consulting the exhumed rock record. Deformation, metamorphism, and fluid flow are challenging to date in blueschist-greenschist facies rocks due to a lack of geochronometers that record processes at these high-pressure and low-temperature conditions. Apatite is common in subduction-related metasedimentary and metavolcanic rocks and has a U-Pb closure temperature of 350-550 °C coinciding with temperatures at the base of the seismogenic zone. Apatite also dissolves and reprecipitates and records the timing and petrogenic conditions of these processes. We link apatite U-Pb dates with microstructures and geochemistry to directly date and characterize deformation and fluid flow from blueschist to amphibolite facies conditions in the Catalina Schist, CA. Apatite grains at all pressure-temperature conditions in the Catalina Schist show no evidence of intragranular deformation but often have synkinematic morphologies likely achieved by dissolution-reprecipitation creep. U-Pb dates from apatite separates from each unit range from 97-113 Ma which overlap with previous peak metamorphic ages, indicating (re)crystallization during prograde to peak metamorphism. In situ U-Pb dates from apatite grains likely represent the timing of (re)precipitation from metasomatic fluids during prograde fluid-rock interactions. This is corroborated by trace element geochemistry that suggests co-genetic growth of apatite with prograde mineral assemblage (e.g., garnet) and high Sr/Y ratios that reflect fluid involvement during (re)crystallization. This work, collectively demonstrates that apatite U-Pb petrochronology is a robust tool for investigating the timing and nature of deformation and fluid flow along the subduction plate interface at blueschist-greenschist facies conditions in exhumed subduction complexes.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-403514

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