Anomalously deep earthquakes related to the Ojo de Agua Lineament and its tectonic significance,Sierras Pampeanas of Córdoba,Central Argentina

The Sierras de Cordoba are the easternmost uplifted ranges of the Sierras Pampeanas geological province of Argentina. They are composed of a Neoproterozoic-Paleozoic basement arranged in north-south aligned mountain ranges, limited by west-vergent reverse faults, reactivated or formed by compressive tectonics during the Andean orogeny. The ranges are also affected by oblique subvertical lineaments,probably related to pan-Gondwanan structures. The recorded seismicity shows anomalously deep earthquakes（up to 80 km depth） concentrated in the northwestern area. We attribute this seismicity to the current tectonic activity of the Ojo de Agua Lineament. This lineament is a N13°-135° strike, 70°-80° NE dip,macrostructure with more than 80 km depth and 160 km length. A sinistral transcompressional kinematics（convergent oblique shear） is deduced by the focal mechanism of a deep earthquake, together with hydrological and geomorphological features strongly modified. The continental lithosphere under the Sierras de Cordoba would be colder and more rigid than in a normal subduction area, due to the retraction of the asthenospheric wedge to the foreland, causing seismicity to depths greater than 40 km, below the Mohorovicic discontinuity. Neogene volcanism would be closely related to this lineament, allowing the rapid ascent of melts from the mantle.

Global pattern of conodont similarity and faunal constraints during the highstand of the Evae eustatic event(late Floian,Lower Ordovician)

One of the largest Ordovician sea-level rises is the Evae transgression,which occurs in the lower part of the Oepikodus evae Biozone,indicative of a late Floian age.Specifically,the characteristics associated with the highstand of this event included:a higher proportion of specimens of the index species O.evae than other species,a diversity acme in the evae Biozone,and a reduction of biogeographic barriers that resulted in a high proportion of species with cosmopolitan distribution.In the present contribution,the pattern of species similarity among Laurentia,Argentine Precordillera,Baltica,Kazakhstania,South China,and Australia is evaluated with a multiple coefficient analysis including only the sections that recorded the highstand of the Evae transgression.Moreover,the effect of possible terrestrial,latitudinal,physicochemical barriers and palaeogeographic distance on the species distribution is statistically analysed.Our results show a global pattern of conodont species distribution that is highly constrained by the tested palaeoenvironmental factors.This suggests that contrary to what was expected for a prominent transgression,faunal barriers did not decrease significantly during the Evae drowning peak.