Terrane deletion in northern Guerrero state

Abstract

The tectonostratigraphic evolution of the southern margin of the North America Plate in Mexico is still in debate. Recent explanations assert Laramide age (Campanian-Eocene) accretion of oceanic terranes. Here we report new mapping results obtained from a 1:100,000 scale, 30 km x 250 km transect of northern Guerrero State, from Huetamo, Michoacan, to Papalutla, Guerrero. Our mapping objectives were to characterize terrane boundaries that have been proposed to cross the transect and to assess the tectonostratigraphic evolution of the transect. _ Our map, structural cross section and assessment of the 9 km thick stratigraphic section are consistent with regional information. The area that we mapped was the site of a Jurassic-Early Cretaceous (back-arc?) basin, filled with predominantly andesitic, submarine volcanics and sedimentary rocks, that formed on Late Permian-Early Triassic continental basement. Aptian/Albian transgression resulted in deposition of mid-Cretaceous carbonate platform and basinal facies on the western margin of the Tethys realm. The platform was drowned by Late Cretaceous flysch sedimentation. Late Cretaceous-Paleogene, Laramide age orogenesis resulted in approximately 60 km of shortening due to ENE directed folding and thrust faulting. Tertiary postorogenic extension led to terrestrial volcanism, fluvial siliciclastic sedimentation, and formation of a prominent, N -trending graben with 3 km of structural relief. Three different versions of the Guerrero-Mixteca terrane boundary and the Arcelia-Teloloapan subterrane boundary have been proposed to cross our transect. We found no stratigraphic incompatibilities or structures that require the existence of any of these boundaries. Therefore, these terranes and subterranes should be deleted in the area that we mapped.