Elements of a broad zone of northwesterly-trending lineaments, along the southwest margin of the North American craton, have been recurrently active since Middle Proterozoic time. Stratigraphic and structural data indicate the influence of this zone on Paleozoic, Mesozoic, Tertiary and Recent geology of northeastern Chihuahua. The Carrizo Mountain Group (estimated age 1,400-1,300 Ma) must have been deposited in a basin (northwesttrending graben?). Sparse examples of "older" granitic rocks (ca. 1,350-1,270 Ma) suggest widespread magmatism over a large area of Chihuahua, that is in part coeval with emplacement of granitic rocks to the north. The Carrizo Mountain Group depositional basin (graben?) may be the earliest manifestation of the dominant northwesterly-trending structural grain of the region; timing is consistent with oldest known strike-slip movement along the Texas Lineament zone (Stockton Pass, Arizona ca. 1,370±70 Ma). Following deposition of the Carrizo Mountain Group, inferred 1,260-1,160 Ma De Baca rifting affected areas to the north and northwest of the present Carrizo Mountain Group outcrop and subcrop. The rift probably extended into northern Chihuahua and metasedimentary rocks record a marine incursion; presumably from an ocean to the south. It is postulated that the De Baca/Swisher metasedimentary and basaltic rocks represent an intracontinental rift and that there is a genetic relationship between them and the Midcontinent rift. At about the same time as rifting, rocks of the Carrizo Mountain Group underwent their first metamorphism. At around 1,100 Ma, the region was subjected to "Grenville" diastrophism that includes extensive batholith emplacement, thrust faulting, retrograde metamorphism and synorogenic deposition of the Hazel Formation. Pre-Mississippian Paleozoic rocks of the region are the consequence of widespread cratonic shelf deposition along a relatively passive margin of the North American craton. Cambrian and Ordovician rocks include basal transgressive sandstones that reflect a general northeastern advance of seas onto North America. The major event during the early Paleozoic was a change in the boundary of the North American craton during Ordovician time. At about 450 Ma, the Cuyania terrane was separated from the craton and eventually was attached to South America. Local Ordovician, Silurian and Devonian faulting in Texas and New Mexico and disconformities on the Diablo Platform and in central New Mexico indicate periods of shelf exposure. These features may reflect tectonism over large areas, including northern Chihuahua, but their origin and significance is not clear. Four late Paleozoic tectonic pulses, affecting the Ouachita-Marathon system, are recognized in northeastern Chihuahua and adjacent parts of the United States: 1) Mississippian-Pennsylvanian deformation in Ouachita hinterland; 2) Pennsylvanian orogeny; 3) Pennsylvanian-Permian folding and thrusting; 4) Permian erosion/truncation and subsequent tilting
The Chihuahua trough is a right-lateral pull-apart basin that began to form ca. 159 to ca. 156 Ma (Oxfordian) during a period of relative counterclockwise rotation of the North American plate. The Chihuahua trough developed as a right step between two right-lateral fault systems-the Texas "zone" and the San Marcos fault zone, which has been interpreted as an element of the Mojave-Sonora megashear. By this interpretation, the Mojave-Sonora fault zone of the Caborca area cannot-and need not-be projected to join the San Marcos fault zone as a continuous system in medial Jurassic time.Jurassic seas were well established by latest Oxfordian time, and there was little change in basin confi guration throughout the remainder of Late Jurassic and Early Cretaceous time. Elements of a broad zone of intersecting preexisting northwesttrending and north-trending structures along the southwest border of the North American craton provide the fabric for development of the pull-apart basin between the Diablo and Aldama platforms. While the presence of Middle to Upper Jurassic marine rocks in Chihuahua and Sonora has received comment in previous articles, this paper provides a regionally consistent tectonic mechanism for creating two arms of the Mar Mexicano.
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