CONICET | Buscador de Institutos y Recursos Humanos

The thermal history of the Precordillera terrane of northwestern Argentina has beenconstrained by the conodont colour alteration index (CAI) in combination withpreviously published paleothermal data (e.g., illite crystallinity and clay mineralassemblages). The pattern of paleotemperatures displays a raise of paleotemperatures tothe west and south of the basin. This configuration shows a gradual and continuoustransition from diagenesis to low-grade metamorphism, which is apparently notcontrolled by any of the morpho-structural subdivisions of the Precordillera (i.e.,Western, Central, or Eastern). According to our results, the lower Paleozoic sedimentaryburial played a secondary role in the heating of the Precordillera. Instead, thepredominant component was loading by thrust sheets, which reflects the effects of theDevonian collision of Chilenia, particularly, in the Western Precordillera. Conversely,our paleothermometric data from the easternmost exposures of the Precordillera do notevidence anomalies referable to any of the accretionary events that contributed to theearly Paleozoic building of the southern proto-Andean margin of Gondwana. Instead,the expected thermally altered conodonts from the Cuyania accretion are represented bymetamorphosed conodont elements transported to the deeper settings of the west. TheCAI data also suggest that overburden depth varied from ca. 3.6 km in the shelf regionof the Eastern Precordillera to ca. 12 km in the slope to rise deposits of the WesternPrecordillera, thus providing constrains for the palinspastic restoration across theorogen. On the other hand, the smooth increase of peak paleotemperatures to the southof the Precordillera is associated with the exposure of deeper crustal levels at thatsector, probably related to larger shortening due to stronger collisional effects, oralternatively, a weaker mechanical response of its elastic lithosphere.