The metamorphic configuration of the Piaxtla high-pressure suite inferred from geological mapping and its metasedimentary rocks

The Piaxtla high-pressure suite (Acatlán Complex) in southern Mexico represents a part of an ancient subduction zone. This suite consists of slices of oceanic and continental affinity containing blueschist- and eclogite-facies relics. Geological mapping of three key areas showed that rocks and mineral assemblages vary systematically and predictably across the region allowing us to divide the Piaxtla suite into two different low- and medium-temperature units (i.e., blueschist- and eclogite-facies, respectively). Field relationships suggest that rock intercalation within each unit resulted from an early subduction-related deformation stage (D1) subsequently overprinted by two deformation phases (D2 and D3). In the high-pressure–low-temperature unit, metasedimentary rocks are predominant and compositionally heterogeneous and share a common high-pressure history with the enclosed blueschists. The high-pressure–medium-temperature unit is characterized by the abundance of granitic gneisses as well as a relatively homogeneous metasedimentary package that is also co-metamorphic with the hosted eclogites. Together, field relationships and petrography indicate that low- and medium-temperature units within the Piaxtla high-pressure suite might have evolved as independent, relatively coherent tectonic slices.