The Cuicateco Terrane: Z a Oceanic Basin with Subduction Influence in the Upper Cretaceous in the Southern Mexico? New Structural, Geochemical and Geochronological Data

The southestern portion of the Cuicateco terrane, between Matías Romero and Juchitán, Oaxaca, is made up by a low metamorphic grade vulcanosedimentary sequence that show at least three deformation events: D1) isoclinal-recumbent F1 folding of the S0 surfaces with northeastern verging and development of a S1 axial plane cleavage with southwestern dipping. Parallel to S1 surfaces is observed the development of hornblende, epidote, chlorite, muscovite and quartz. Such structure is related with a transcurrent event with left cinematic and post-maastrichtian age. D2) Paleocene event? distinguished by thrust faulting with displacement direction to north-northeastern, like to Vista Hermosa Fault, and development of the S2 cleavage without recrystallization associated. D3) miocenic event, defined by normal and lateral faulting.

Chemical composition of the amphibolitic rocks of the Cuicateco terrane is toleitic basalts MORB (SiO2 45-50%), with a depletion in light rare earths and flat high rare earths patterns. Trace elements show a pattern depleted in incompatible elements, a slight enrichment in compatible elements, and negative anomalies of Nb and Th. A contribution of subduction-related magmas is also shown.

U-Pb dating by LA-MC-ICPMS on zircons belonging to the amphibolite, which yielded a maastrichtian age (65.6 ± 0.2 Ma) interpreted as the crystallization age of the basaltic protolith. Detrital U-Pb analyses on zircons of a vulcanoclastic phyllite suggest a maximum depositional maastrichtian age (~ 78 Ma). Zircons belonging to a sandstone of the Todos Santos Formation indicate a maximum depositional age, later to Middle-Upper Triassic (228 Ma).

The data obtained suggest the development of a basic volcanism in an ocean basin environment with a subduction-related influence during the Late Cretaceous,. that suffered the effect of two events, a transpressive and other compressive, during the latest Cretaceous - Paleocene, following by normal-lateral faulting miocenic.