48-1 Unraveling the Andes: Exhumed Subduction Metamorphic Rocks in a Long-Lived Non-Collisional Orogen

Session: Tectónica de las Américas: Sesión en español

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Authors:

Abstract:

Exhumed subduction-related metamorphic rocks (ESRMRs) offer critical insights into the tectonic and thermal evolution of convergent margins. In non-collisional orogens like the Andes, these rocks help delineate paleo-plate boundaries, constrain pressure-temperature (P–T) histories, and elucidate the timing and style of long-term deformation. Andean ESRMRs are exposed discontinuously along a ~7,000 km belt from Venezuela to Chile and record a protracted exhumation history spanning from the Paleozoic to the Cenozoic (~465–28 Ma). This record captures three principal tectonic phases: (i) amalgamation of western Gondwana (~465–323 Ma), (ii) long-lived, non-collisional subduction along the paleo-Andean margin (~361–55 Ma), and (iii) Caribbean–South American plate convergence (~97–28 Ma). The Andean ESRMRs are characterized by relatively warm thermal gradients, comparable to those of modern Cascadia-type subduction; however, they mostly occur as discontinuous, coherent metamorphic units, rather than mélanges. This difference suggests alternative exhumation mechanisms from those in collisional orogens, where mélange formation in rheologically weak subduction channels is more prevalent. Notably, Andean ESRMR exhumation often coincides with periods of back-arc extension and closure, indicating a strong link to upper-plate deformation cycles. These cycles may be modulated by shifts in subduction dynamics, including transitions between trench retreat—associated with extensional regimes—and trench anchoring—associated with compression. While increased subduction rates can enhance shear stress and hinder exhumation, trench retreat may reduce drag, facilitating exhumation of high-pressure rocks. The Andean ESRMR record underscores the importance of convergent margin style and upper-plate tectonics in governing exhumation pathways in long-lived cordilleran systems.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6617

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