Abstract
Tectonic instability is the most distinctive feature of the geologic evolution of southern Mexico since the Precambrian. Although geochronometrical records in this region do not extend beyond about 1,100 m.y. b.p., clearly there were older sedimentary, magmatic and tectonic events that were obscured by subsequent geological activity. The granulitic Oaxacan Complex developed as a result of the first orogeny known in the area. Its tectonothermic culmination, some 1,025 ± 75 m.y. ago, eventhough did not destroy the original character of the involved rocks completely, their isotopic systems were disturbed to the extent that absolute dating has not yet penetrated beyond this pervasive orogenic event. Paragneissic (calcareous, pelitic and arkosic) and orthogneissic (anorthositic, gabbroid and graniticsyenitic) rocks, composing the Oaxacan Complex represent, respectively, miogeoclinal sedimentation and cratonic magmatism of unknown age, but probably restricted to the Proterozoic. The following 500 m.y. include a protracted event of uplift and erosion, that exposed the Oaxacan Complex after its generation at depths of 20 to 30 km and temperaturas exceeding 700°C, as suggested by its petrology. In order to continue, download the full paper in PDF.
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