Modelling White Mica Pressure-Temperature-time (P-T-t) Paths Using Thermobarometric and 40ar/39ar Thermochronologic Data

White micas are major rock forming minerals in igneous and metamorphic rocks, and their chemical and isotopic variations can be used to determine pressure, temperature and time (P-T-t) histories. We apply 40Ar/39Ar multi-diffusion domain modelling to white micas from blueschists blocks in serpentinite matrix melange from the exhumed Baja California subduction complex. Thermal history models yielded T-t paths suggesting that 40Ar* resides within multiple diffusion domains with varying 40Ar* retentivity. Modelled white mica thermal histories and thermobarometric data were used to forward model continuous P-T-t paths. P-T-t paths are consistent with previous studies and are interpreted to constrain blueschist block exhumation paths within the Baja accretionary wedge. Our P-T-t models use temperature controlled 40Ar/39Ar step heat data in which argon loss by volume diffusion can be demonstrated, and for which the white mica petrogenesis is known.