Abstract

PEREZ-GUTIERREZ, Rosalva; SOLARI, Luigi A.; GOMEZ-TUENA, Arturo  and  VALENCIA, Víctor A.. The Cuicateco terrane: Upper Cretaceous oceanic basin with subduction influence in southern Mexico? New structural, geochemical and geochronological data. Rev. mex. cienc. geol [online]. 2009, vol.26, n.1, pp.222-242. ISSN 2007-2902.

The southestern portion of the Cuicateco terrane, between Matías Romero and Juchitán, Oaxaca, is made up by a low metamorphic grade vulcanosedimentary sequence that shows 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 can be observed the development of hornblende, epidote, chlorite, muscovite and quartz. Such structures are related to a post-Maastrichtian left transcurrent deformational event. D₂: Paleocene(?) event characterized by thrust faulting with displacement direction to north-northeast, such as the Vista Hermosa mesostructure fault, and the development of the S₂ cleavage without associated recrystallization. D₃: Miocenic event, defined by normal and lateral faulting. Chemical composition of the amphibolitic rocks of the Cuicateco terrane resembles that of tholeiitic basalts (SiO₂ 45-50%), with a depletion in LREE and flat HREE patterns. Trace elements show a pattern depleted in the highly incompatible elements with respect to the less incompatible elements, and negative anomalies of Nb and Th. A contribution of subduction-related magmas is also shown by the Ta/Yb vs. Th/Yb relationships. U-Pb dating by LA-MC-ICPMS on zircons belonging to the amphibolite yielded a Maastrichtian age (65.7 ± 1.2 Ma) that is interpreted as the crystallization age of the basaltic protolith. U-Pb analyses on detrital zircons of a vulcanoclastic phyllite suggest a maximum depositional Maastrichtian age (~78 Ma) with significant peaks at 113 Ma, 542 Ma, 1198 Ma, 1662 Ma, 2791 and 3062 Ma. Zircons from a sandstone belonging to the Todos Santos Formation indicate a maximum depositional age of the Middle-Upper Triassic (228 Ma), with important peaks at 571 Ma, 1026 Ma, 1530 Ma, 1978 Ma and 2909 Ma. Petrological, structural and geochronological data suggest the development of a mafic volcanism and sedimentation in an ocean basin and close relationships with a subduction process during the Late Cretaceous. This volcanic-sedimentary sequence was deformed by two events: a transpressive to compressive deformation, during the Latest Cretaceous - Paleocene, and a later, Miocenic normal-lateral faulting, which can be associated to the Polochic-Motagua faulting tectonic system.

Keywords : oceanic basin; U-Pb geochronology; transpressional deformation; Cuicateco terrane; Maastrichtian; Mexico.

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