ALBERT

Description: The El Oro metamorphic province of SW Ecuador is a composite massif made of juxtaposed terranes of both continental and oceanic affinity that has been located in a forearc position since Late Paleozoic times. Various geochemical, geochronological and metamorphic studies have been undertaken on the El Oro metamorphic province, providing an understanding of the origin and age of the distinct units. However, the internal structures and geodynamic evolution of this area remain poorly understood. Our structural analysis and thermal modeling in the El Oro metamorphic province show that this forearc zone underwent four main geological events. (1) During Triassic times (230-225 Ma), the emplacement of the Piedras gabbroic unit at crustal-root level (~9 kbar) triggered partial melting of the metasedimentary sequence under an E-W extensional regime at pressure-temperature conditions ranging from 4.5 to 8.5 kbar and from 650 to 900 °C for the migmatitic unit. (2) At 226 Ma, the tectonic underplating of the Arenillas-Panupalí oceanic unit (9 kbar and 300 °C) thermally sealed the forearc region. (3) Around the Jurassic-Cretaceous boundary, the shift from trench-normal to trench-parallel subduction triggered the exhumation and underplating of the high-pressure, oceanic Raspas Ophiolitic Complex (18 kbar and 600 °C) beneath the El Oro Group (130-120 Ma). This was followed by the opening of a NE-SW pull-apart basin, which tilted the massif along an E-W subhorizontal axis (110 Ma). (4) In Late Cretaceous times, an N-S compressional event generated heterogeneous deformation due to the presence of the Cretaceous Celica volcanic arc, which acted as a buttress and predominantly affected the central and eastern part of the massif.

Description: Continental lithosphere extension results in complex basin types with differing structural styles, subsidence, thermal histories and melt production. Many studies have examined the role of initial rheological layering, geothermal gradients and extension rates during a single rifting event. This approach neglects the tectonic history of many basins that are marked by multiple rifting events. Here, we address the role of repeated extension on long-term lithospheric strain modes and the resulting basins, highlighting cases most affected by previous rifting events. We use numerical models of a lithosphere undergoing two rifting events of differing extension rates and separated by cooling, to show the effect of early events on subsequent evolution. The combination of boundary displacement velocity in both events leads to the formation of various rift basin types, ranging from narrow to wide to hyper-extended, and with variation of subsidence patterns, degrees of symmetry and melt yield. We show that basin type, subsidence and melt production might be strongly affected by previous rifting events, illustrating cases in which the previous rifting history cannot be neglected. Our models reproduce the first-order features of Earth's sedimentary basins, and propose a classification to guide the interpretation of extensional basins and their evolution.