New U-Pb and Structural Data Constraining the Mesozoic Paleogeography and Tectonic Evolution of the Guerrero Terrane in Southern Mexico

The Mesozoic volcano-sedimentary successions of south-western Mexico have been interpreted as a single or multi-arc system (Guerrero terrane), built on oceanic crust far away from the continent, and subsequently accreted to nuclear Mexico and producing the late Cretaceous Early Tertiary Laramide orogeny. Here we present a stratigraphic and structural analysis backed by 40Ar/39Ar and U-Pb ages for a broad region located in the central-eastern part of the Guerrero terrane, which allow testing the accretion model. In the Huetamo-Ciudad Altamirano region, a first shortening of the marine succession between the Late Cenomanian and the Santonian was followed by an out-of-sequence coaxial refolding in Maastrichtian-Paleocene times. The ubiquitous occurrence of continental recycled material in the Huetamo Cretaceous succession and Grenvillian inherited zircons in the ~120 Ma Placeres del Oro pluton indicates that this region has been close to a continent during most of the Mesozoic. Moreover, detrital zircon ages from the pre-Cretaceous basement of the Huetamo succession and the pre-Early Jurassic basement of the Arcelia sub-terrane yielded very similar Late Permian and Ordovician age peaks, the latter being typical of the Acatlán complex, onto which the Guerrero terrane is supposed to have accreted in the Late Cretaceous. Models considering the Guerrero terrane as formed by intraoceanic island arcs separated by one or more subduction zones cannot explain the ubiquitous presence of older continental material in the Mesozoic succession. We favour a model in which most of the Guerrero terrane consist of autochthonous or parautochthonous units, deposited on the rifted continental margin of the North American plate and where the Mesozoic magmatic and sedimentary record can be explained in the frame of a west facing migrating arc and related extensional back-arc and fore-arc basins. Our results exclude the accretion of allochtonous terranes as the cause for the Laramide deformation in southern Mexico.