40Ar/39Ar muscovite geochronology of Arperos Basin inversion in Southern Mexico: new insights into cretaceous shortening initiation in southernmost North America

Abstract

ABSTRACT During Cretaceous–Eocene time, North America was involved in a succession of shortening events that produced major orogenic belts. Previous work permitted the characterization of the kinematics and dynamics of some of these orogenic events along various transects. However, the timing of shortening is not well constrained everywhere. This has led to misinterpretation of the tectonic history of some sectors of the North American Pacific margin and to an incomplete understanding of the subduction dynamics. Mexico is one of those sectors in which the shortening history is not completely defined. We present structural and 40Ar/39Ar isotopic data from major shortening structures in southern Mexico, documenting two episodes of shortening: a first one at ~ 118–112 Ma, not considered in previous works, and a second one at ~ 104–90 Ma, which was previously interpreted as the record of shortening initiation. Integrated with previous data, our 40Ar/39Ar results indicate that, in Mexico, the shortening history was developed in two main stages: 1) a Late Aptian–Early Albian stage of localized shortening, during which the oceanic Arperos Basin was closed and the Guerrero terrane arc accreted to nuclear Mexico forming a ~ 80 km-wide suture belt, and 2) a latest Albian–Eocene stage, in which shortening was propagated from the North American trench to the plate interior, producing the development of a critically tapered wedge. Whether these two stages represent two superposed orogenic cycles or two steps within the same orogenic cycle remains to be established. In any case, the Late Aptian–Early Albian stage of deformation, which was not fully recognized in most previous works, is a key for our understanding of the causes that triggered shortening in southern North America after ~ 100 m.y. of extension associated with Pangea break-up