Structure and kinematic history of the Acatlán Complex in the Nuevos Horizontes - San Bernardo region, Puebla

Abstract

Paleozoic metamorphites and magmatites forming the basement of the northern Mixteca terrane in southern Mexico define the Acatlán Complex. Six stages of dcformation are defined by metamorphic facies, structural behaviour, and ovcr- printing relationships. The first deformation (D1) is accompanied by high temperature metamorphism (M1), which over- prints pre-existing eclogites (D0), and culminates in intrusions of granites. During this deformation, large crystals of mica and megablasts of potassic feldspar grew. The second deformation (D2) is indicated by diaphtoresis up to greenschist facies. Mica crystals of the M1 are preserved as relictic porphyroclasts in the S1 foliation planes. On D2 planes they were broken and substituted by sericite. 0 2 caused elongation and recrystallization of quartz. During the third deformation (03) the Acatlán Complex was folded into W-vergent, tight to isoclinal folds. Sediments deposited between D2 and D3 were metamorphosed by very low grade metamorphism during D3. As the granites intruded into an upper crustal leve], they show S3 foliation. The fourth deformation phase is characterized by kinkfolds, cataclastic shearzones, and faults with slicken- sides. Calculations of the paleostress tensors yiclded subhorizontal cr1- and cr3-axis indicating NE-SW orientation of cr1. Most of the fault populations belong to the fifth deformation (D5) with subhorizontal and axis with ESE-WNW cr1 direction. Normal faults define the sixth deformation (D6) with subvertical and N-S trending crTaxes.