EARLY MESOZOIC CORDILLERAN TERRANES IN NORTHEASTERN MEXICO

Triassic-Jurassic sedimentary and volcanic sequences exposed in central and northeastern Mexico are interpreted as related to the southwestern margin of North America and to the Mesozoic Cordilleran Volcanic arc. Carnian-Norian submarine fan deposits occurred in Zacatecas and San Luis Potosí (Zacatecasas Formation) and probably related fluvial deposits are present in Nuevo León and Tamaulipas (Lower Huizachal Group). Jurassic volcanic rocks (Nazas Formation) overlying both Triassic facies are interpreted as products of the cordilleran volcanic arc. Finally, alluvial deposits and partially lagoon to shallow marine deposits overlying the volcanogenic sequences, represent an increased rate of erosion on the arc and older exposed units during the early evolution of the Gulf of Mexico Basin in Late Jurassic Time. To this point , the studied region was separated from southwestern North America and the Cordilleran system but probably partially connected to the Pacific, prior to deposition of the Gulf sequences starting from Late Jurassic time.