25-3 Blueschist-facies overprint of high-pressure–low-temperature blocks within the mélange of Cedros Island, Northwestern Mexico

Session: Integrating metamorphism, mass transfer, and magmatism across the American Cordillera (Posters)

Poster Booth No.: 47

Presenting Author:

Anthony Ramírez-Salazar

Authors:

Ramírez-Salazar, Anthony¹, Gutiérrez-Trejo, Luis Javier², Contreras-López, Manuel³, Colás, Vanessa⁴, Fitz-Díaz, Elisa⁵, Ramos-Arias, Mario Alfredo⁶

Abstract:

The preservation of mineral assemblages recording different high-pressure (HP)–low-temperature (LT) metamorphic conditions in partially overprinted rocks could shed light on the hydration and dehydration mechanisms that control fluid movement, mass transfer and metamorphic reactions that occur during subduction of oceanic lithosphere. These processes are observed in the Cedros Island, Northwestern Mexico, where blocks within a Late Jurassic-Early Cretaceous subduction-related mélange show blueschist facies assemblages overprinting HP-LT bright-green Na-rich pyroxene-garnet bearing rocks.

The HP-LT blocks preserve remnants of Na-rich pyroxene-garnet-white mica portions with mainly very fine-grained textures and rare polygonal granoblastic textures crosscut by glaucophane veins or enveloped by foliated glaucophane-rich domains. Garnet tends to occur as vein-like (micro)structures with inclusion-rich cores and displaying a low-birefringence typical of garnets in LT rocks (probably consequence of a tetragonal symmetry). Glaucophane is also associated to carbonate veins and calcite pseudomorphs. In this work, we present geochemical, mineralogical and geothermobarometric preliminary data to constraint the metamorphic history of the HP-LT blocks, as well as to provide insights into the phase transformation and fluid movement that caused the retrogression, in order to provide novel data to expand our understanding of the petrological and coupled tectonic processes occurring at the subducted slab interface and to refine the geological and tectonic evolution of the Northwestern convergent margin of Mexico.

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