Road Log Geology of Mexico: The Mexican State of Sinaloa: A Mesozoic Subduction Zone Complex

The Mexican State of Sinaloa consists of two physiographic provinces: the Pacific Coastal Plain along the Western Mexican coast and the Sierra Madre Occidental in the eastern half of the state. The Sinaloan subduction zone complex is characterized by subduction, accretion, and volcanic activity tied to oceanic island and continental arc systems. Sinaloa is part of the Guerrero Composite Terrane which belongs entirely to the Tahue Terrane portion of the composite terrane. The Tahue Terrane consists of Paleozoic accreted arc and eugeoclinal sedimentary rocks, Triassic rift related meta-igneous rocks overlain by pillow basalts, limestone, and volcaniclastic rocks.Ordovician oceanic rhyolitic andesite lavas, clastic, and calcareous rocks are deformed, metamorphosed to greenschist facies originating in an oceanic arc which accreted to Pennsylvanian and Permian deep marine sedimentary rocks. Cretaceous marine arc volcanics overlie the Paleozoic rock complex.A subduction trench began migrating from northeast to southwest across Sinaloa beginning in Jurassic time Tithonian Stage 150 mya. By Early Cretaceous time 140 mya, the trench was positioned along the northwestern Sinaloan boundary extending southeasterly in central southern Sinaloa exiting along the southeastern boundary into Durango. Observed exposures in north and south Sinaloa included oceanic crustal, upper, mantle, and arc type volcanic lava flows and ash deposits occurring in a cyclical pattern in the north more obvious than in the south. Southern exposures were partially covered by Upper Cretaceous volcanic rocks before limited oceanic crustal and upper mantle exposures were observed. Some areas of Late Jurassic and Late Cretaceous rocks were intensely deformed, metamorphosed, mineralized, and faulted by subduction zone related accretionary processes. Several orogenic events played a role in altering rocks most notably during deep and shallow slab subduction associated with the Sevier and Laramide uplifts. During flat slab subduction, coupling of the oceanic plate with the overlying continental plate increased the affect on regional and localized folding with hydration of the lower continental lithosphere. Rifting associated with the Chihuahua Trough and Mohave-Sonoran Megashear during Late Jurassic into Early Cretaceous time played a role in trench migration across Sinaloa. Read more