Abstract

The geologic framework of Mexico evolved through the Phanerozoic assembly and fragmentation of crustal elements derived from Laurentia, Gondwana, and an intra-Pacific volcanogenic terrane. In middle Paleozoic time, an inactive south-facing Laurentian continental margin of transform origin passed through northern Mexico to connect the miogeoclinal Cordilleran margin with the passive continental margin formed by Cambrian rifting in Texas. Gondwanan blocks of eastern Mexico were accreted to Laurentia by juxtaposition along the Ouachita-Marathon suture belt in earliest Permian time. Subsequent Jurassic opening of the Gulf of Mexico by seafloor spreading displaced the Yucatán-Chiapas block southward, as it rotated anticlockwise from edge-driven shear between Colombia and Florida, along a gulf-flank transform passing through the Isthmus of Tehuantepec. The continuity of a linear north-trending Permian–Triassic arc (now represented by a granite belt) in eastern Mexico precludes strike-slip slivering of Mexico during gulf opening and implies that Colombia lay east of internally coherent Gondwanan crust of southeastern Mexico, but south of Yucatán-Chiapas, prior to Pangean breakup. During subsequent intracontinental rifting, crustal elements of eastern Mexico were displaced southeastward, along a transform between basement blocks of present northeastern and east-central Mexico, in the wake of Colombia's retreat from Laurentia. The Chortis block of nuclear Central America also lay within Pangea west of Colombia and remained attached to southern Mexico prior to its Cenozoic displacement eastward along the Cayman transform. The Caborca block of northwestern Mexico was displaced southeastward from the Cordilleran miogeocline by Permian–Triassic slip along a transform that linked the convergent Sonoma orogen with the northern end of a subduction zone in central Mexico that paralleled the Permian–Triassic magmatic arc built on Gondwanan crust of eastern Mexico. Subsequent post–Middle Triassic initiation of a west-facing continental-margin arc-trench system (i.e., with the subducting slab moving down to the east) along the structurally modified paleo–Pacific flank of Pangea produced middle Mesozoic arc assemblages extending southeastward from California and Arizona through east-central Mexico into Colombia. Beyond a compound suture belt lying outboard of the middle Mesozoic continental margin, western Mexico is underlain by Mesozoic volcanogenic crust formed beneath an east-facing intraoceanic island arc that was accreted to Laurentian and Gondwanan Mexico by arc-continent collision late in Early Cretaceous time. The accreted arc assemblage was overlapped by late Early Cretaceous–early Late Cretaceous carbonate platforms linked depositionally with comparable facies in eastern Mexico. As the offshore island arc approached the continent, progressive consumption of the intervening oceanic plate induced slab rollback beneath the Jurassic magmatic arc on the mainland, terminating arc magmatism and promoting development of associated rift troughs that extend from northeastern Mexico to southeastern California. Following arc collision and accretion, reversal of subduction polarity along the expanded western flank of Mexico created a west-facing continental-margin arc- trench system that was continuous with the Cordilleran arc and Franciscan trench of California. Subsequent subduction produced volcanic-plutonic arc assemblages on the mainland and in Baja California, which was contiguous with the mainland prior to Neogene seafloor spreading that opened the Gulf of California. A paired late Early Cretaceous subduction complex and late Mesozoic forearc basin occurred along the Pacific flank of Baja California.

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