Reconstructing the metamorphic history of rock complexes implies the full characterization of the variations of chemical composition (including mineral zoning) of mineral phases and mineral assemblages in their textural and (micro) structural settings. This task constitutes the necessary first step in unraveling the P-T conditions of formation and paths that allow deciphering the tectonic processes involved in the formation and evolution of such complexes. Among these complexes, those formed at high pressure (HP) in paleo subduction settings are of the main interest, for they impose first-order constraints in the evolution of orogenic wedges. The geological record at the remote Diego de Almagro island, Chilean Patagonia (51º 30' S), includes a very rare almost unexplored occurrence of an early Cretaceous HP rock complex formed at the long-lived subduction zone of the western margin of Gondwana/South America (active since, at least, mid-Paleozoic times) and accreted against the Chilean basement. The complex is formed by blueschists and amphibolites, previously described as vestiges of moderate-depth portions of the subduction-zone/paleo-accretionary complex. After a more recent exploratory research conducted by researchers from this group (FAPESP 2004/10203-7), however, relicts of eclogitic rocks were identified for the first time at this locality, which represent the only occurrence reported so far of exhumed fragments of oceanic crust subducted down to ca. 60 km depth in the Patagonian accretionary complexes. Because metamorphism is a dynamic process that involves changes in pressure, temperature and strain, the progressive and retrogressive P-T conditions, deformation styles, phases, and geochronologic ages preserved in rock complexes formed in subduction zone settings, under high dP/dT conditions, constitute first order information for constraining the dynamics of deep zones of the subduction interface. Detailed chemical-textural studies using X-ray compositional maps, phase relations analysis in projective phase diagrams, and pseudosections for modeling the evolving equilibrium mineral assemblage comprise an essential methodology to conduct metamorphic studies, which has been applied by this research group on the study of the Proto Andean margin at central Chile (FAPESP 2012/01191-1). By means of the application of these petrologic techniques to the high pressure complex of the Diego de Almagro island (retroeclogitic rocks, amphibolites, blueschists, garnet-mica schists), this proposal aims unraveling the dynamics of a subduction channel and the processes involved in the building of an accretionary prism, including accretion, exhumation, and thermal evolution of the unexplored Diego de Almagro Complex.
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