Petrografía, geoquímica y geocronología del cinturón ofiolítico Peltetec (Ecuador), implicaciones geodinámicas

Resumen

The Peltetec ophiolitic belt is discontinuously exposed along ca.310 km (N-S to NNE-SSW directed, <2 km in width) in the western margin of the Cordillera Real (Ecuador). It has been interpreted as a mélange of a dismembered Cretaceous ophiolite (Litherland et al., 1994; 134 Ma, Spikings et al., 2015). To the West and East the body is in contact with Jurassic to Cretaceous metasedimentary sequences; however, tectonic slivers of S-type Triassic granites (228 Ma, Tres Lagunas Unit) also occur in the western boundary. The lithologies, variably metamorphosed/altered and deformed, include serpentinites, gabbros (locally cummulate), basalts, discordant basaltic dykes, hydrothermal breccias, and sedimentary rocks. Immobile trace elements, rare earth elements and Nd isotopes of basaltic rocks show tholeiitic affinity and variable imprint of subduc- tion zone-derived fluids/melts. Geochemical considerations allow classifying these rocks in three groups, one with oceanic island arc affinity and other two with NMORB-like back-arc affinity. Zircon from a metadiabase yielded a U-Pb SHRIMP age of 230 Ma. These data allow interpreting Peltetec ophiolitic belt as an oceanic lithospheric section generated in an arc/ back-arc setting as a consequence of Upper Triassic extension in the continental lithosphere.