Full Title: Geology of Part of Southern Sinaloa, Mexico Adjacent to the Gulf of California
Compilers: Christopher D. Henry and Goran Fredrikson
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One color sheet, 23" x 26". Scale 1:250,000. From text: Southern Sinaloa is a geologically complex area that has had repeated magmatic and tectonic activity at least since the Jurassic. The oldest known rocks are quartz diorite orthogneiss and folded, regionally metamorphosed, clastic sedimentary rocks, at least Jurassic in age, which probably accumulated upon the gneiss. Gabbro was emplaced as sills into the metasedimentary rocks. These rocks, along with Lower Cretaceous carbonates, were folded and regionally metamorphosed by about mid-Cretaceous time. A granitic batholithic complex of Late Cretaceous to early Tertiary age underlies almost all of the area. Individual plutons range in composition from diorite to granite. Comagmatic volcanic rocks, ranging from andesite to rhyolite, are abundant in the eastern part of the area but have largely been eroded from the Pacific coastal area. Oligocene to Miocene rhyolitic ash-flow tuffs and minor intermediate and mafic lava flows cap the high plateau of the Sierra Madre Occidental and fault blocks near the coast. Miocene and Pliocene sedimentary rocks accumulated in normal-fault-bounded basins. Small, late Tertiary felsic to mafic intrusions and domes and Quaternary basalt lavas and domes were emplaced along the coast. East-northeast-trending folds in the oldest rocks suggest north-northwest-oriented compression, associated with regional metamorphism before the Late Cretaceous. In the late Tertiary, east-northeast-oriented tension produced north-northwest-trending normal faults and grabens from the coast to the western edge of the Sierra Madre Occidental.
Published: 4/01/1987
Pages: 14 plus 1 sheet
Product Category: Maps and Charts