Lower Mesozoic facies and crosscutting sequence boundaries: Constraints on displacement of the Caborca terrane

Abstract

Five Triassic and Jurassic tectonosequences recognized on the Colorado Plateau have been identifi ed within the Caborca terrane in Sonora, Mexico. Piercing lines defi ned by truncation of tectonosequence boundaries constrain the pre-offset position of the terrane. Restoration of 1040 ± 290 km of Middle to Late Jurassic left slip along the Mojave-Sonora megashear places the Caborca block in a paleogeographic position that satisfi es the constraints provided by truncated tectonosequences and yields predictable regional facies distributions for all tectonosequences. The restoration is consistent with previous estimates of displacements based upon offset of correlative(1) terrains of crystalline basement and (2) pre-Oxfordian cover.

The Triassic/Jurassic boundary and the Jurassic stratigraphy and biostratigraphy of northern Sonora, northwest Mexico

“…It is considered as a continental extensional arc that in northeastern Sonora was constructed across the Proterozoic and Paleozoic basement and in northwestern most Sonora the plutons intruded the Permo-Triassic arc rocks. In north-central Sonora, the region known as the southern Papago domain lacks exposures of an older basement (Anderson et al, 2005). The Middle Jurassic arc magmatism ended when the NW-SE, fault-bounded basins in the region of Sonora and Arizona formed contemporaneously with the opening of the Gulf of Mexico.…”

“…A sparse and younger magmatism that is mostly present in the Papago domain falls in the age range from 160 to 145 Ma and consists of alkaline volcanic and plutonic rocks and interbedded sedimentary strata (Tosdal et al, 1989). Anderson et al (2005) considered this magmatism unrelated to the calc-alkaline Jurassic arc magmatism and instead they relate it to trans-tensional mechanisms associated with the megashear. Alternatively, Mauel et al (2011) considered it related to early extension of the Cucurpe-Altar rift, in which the Cucurpe Formation was deposited and identified as the likely source of zircon grains of 149 Ma that are present in the younger part of this formation ( Figure 6B).…”

“…Nevertheless, interpretations of the original position of this basin are speculative. Strata of the Monos Formation and El Antimonio Group altogether have been interpreted either as an allochthonous terrane that accreted to the Caborca block based mostly on its fossil content, or as strata that were relocated during the Jurassic by the Mojave-Sonora megashear, along with the Caborca block from southern California to its present-day position (Stanley and González-León, 1995;González-León, 1997a;Marzolf and Anderson, 2005). However, a different interpretation for these rocks is that they were deposited close to the arc and near the present-day location, on the Caborca block, which had been previously displaced from southern California by the California-Coahuila transform fault .…”

“…The Middle Jurassic arc magmatism ended when the NW-SE, fault-bounded basins in the region of Sonora and Arizona formed contemporaneously with the opening of the Gulf of Mexico. Opening of the basins may be related to opening of the Gulf of Mexico, or they may be related either to rollback of the subducting slab (Lawton and McMillan, 1999;Dickinson and Lawton, 2001) associated with the Jurassic arc, or to strike-slip faulting related to the Mojave-Sonora megashear (Anderson et al, 2005;Busby et al, 2005). A sparse and younger magmatism that is mostly present in the Papago domain falls in the age range from 160 to 145 Ma and consists of alkaline volcanic and plutonic rocks and interbedded sedimentary strata (Tosdal et al, 1989).…”