METAMORPHISM-DEFORMATION RELATION IN THE ACATLAN COMPLEX, MEXICO

The Paleozoic Acatlán Complex, Puebla, Mexico, consist of two structural plates, a lower plate with the Magdalena, Chazumba and Cosoltepec formations; and an upper plate with Xayacatlán and Esperanza Granitoids units. We can recognize two metamorphic events (ME) associated with two deformation phases (DP) in the Chazumba Formation, the first one with amphibolite facies paragenesis of biotite, muscovite and garnet (locally with sillimanite), the second with biotite and muscovite recrystallization. In the Cosoltepec Formation we found at least the same two main ME and DP. In the east region, the first metamorphic event reach the upper greenschist facies zone with biotite, muscovite and garnet, while in the greater part of the formation only reach the lowest greenschist facies zone (chlorite zone) with a fine grained fabric. In the Xayacatlan Formation metabasites have paragenesis of blueschist, greenschist, epidote-amphibolite, and eclogite facies. In Olinalá area (Guerrero state), two blueschist metamorphic events are related with two deformation phases, a latter phase is related to retrogression into greenschist facies. The eclogite facies paragenesis (omphacite, garnet, amphibole, muscovite, zoisite, rutile) is preserved only in small outcrops. Metabasites and metapelites present a first DP as internal foliation in garnets and chloritoids; a second phase coeval with the peak metamorphism (eclogite facies) and a third phase coeval with retrogressive greenschist facies metamorphism. This third DP and ME is heterogeneous and is the only one that can be seen in some outcrops. In thin sections, the Esperanza Granitoid rocks present a mylonitic fabric formed by one DP, but outcrop observations allow us to define at least two DP associated with two ME in the typical Esperanza gneiss (with large Kfeldspar porphyroclasts). The Tecomate Formation, which unconformably overlies both structural plates, have two main ME associated with two DP, both of lower to middle greenschist facies, typical paragenesis in metabasites is: actinolite, epidote, albite, chlorite, sphene. The accurate understanding of the ME and associated DP in the Acatlán Complex, must help to decipher the tectonic events that originated the metamorphic complex.