Regional implications of the Jurassic-cretaceous volcanosedimentary cuicateco terrane, Oaxaca, Mexico

Abstract

The 235 km long and 20 km wide Cuicateco Terrane is located between the eastern margin of the Precambrian Zapoteco Terrane and the northwestern margin of the Permian Batholith of Chiapas. The study area is about 800 sq. km, located in the northwestern limit of the terrane. The association of andesitic lavas and tuffs with sedimentary rocks which grade eastward from feldspatic wackes, calcareous wackes to limestones is comparable to an island arc which includes small internal basins. The "roots" of the magmatic province are exposed in the western side of the terrane corresponding to granodioriticmonzonitic rocks showing ultramafic segregations (pyroxenites and amphibolites). The crystalline rocks show a strong mylonitic solid-1ltate ductile flow fabric decreasing toward inner zones, where the intrusives are almost isotropic. Where the intrusives are absent, the western side of the magmatic belt is occupied by metaandesites showing the same metamorphic fabric. A large wedge of serpentinized ultramafics and leucodiorites are tectonically emplaced in the sequence of metatuffs. In accordance with the present-day meteoric water, chrysotile and lizardite structural water shows a DIH average ratio of -59 per mil, indicating its tectonically related formation.Structurally, the sedimentary sequence dermes a thrust-faulted, folded and weakly metamorphosed belt verging eastward. It is considered that the contact zone between the older terranes, which have a difference in thickness of about 20 km, is a major factor lithostatics on the location of the Cuicateco magmatic province.