72 Toe to Toe: Cordilleran Systems from Trench to Retroarc Domains (Posters)

This session highlights research across geoscience disciplines to advance understanding of the deformation, magmatism, seismicity, topography, and sedimentation processes governing trench to retroarc evolution during ocean-continent plate convergence.

Sunday, 19 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Garnet Diffusion Chronometry Reveals Ultrafast Exhumation of the Subduction Mélange of Cedros Island, Baja California, Mexico

Paper number: 72-1
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Subduction mélanges, mixed fragments of subducted blocks in a fine-grained matrix, provide valuable constraints on how crustal and mantle materials move at the interface between the subducting slab and the overlying mantle wedge. The mechanism and timescale of their exhumation from great depths remain controversial. Cedros Island, Baja California, Mexico is composed of a late Jurassic–Cretaceous subduction mélange of various metamorphic grades tectonically emplaced beneath an ophiolite. Garnet grains in the garnet amphibolite blocks exhibit complex, sharply defined compositional zoning, requiring metamorphism and exhumation over a very short time scale. Using phase equilibria modeling and garnet diffusion chronometry, we show that garnet growth happened as discrete pulses during rapid compression and decompression by ~8 kbar, possibly due to local fluid overpressure. After peak metamorphism, the mélange cooled at approximately 10 °C/kyr, far exceeding the rates predicted by geodynamic models. Based on structural observations in the field, a possible explanation for such rapid cooling is exhumation by normal faulting and tectonic extrusion.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412771

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