IGEBA   23946
INSTITUTO DE GEOCIENCIAS BASICAS, APLICADAS Y AMBIENTALES DE BUENOS AIRES
Unidad Ejecutora - UE
artículos
Título:
U-Pb ages of detrital and volcanic zircons of the Toro Negro Formation, northwestern Argentina: Age, provenance and sedimentation rates
Autor/es:
MARENSSI, S.A.; BURBANK, D; CICCIOLI, PATRICIA; FISHER, G; AMIDON, W; LIMARINO, C.; CLARK, A.; MARENSSI, S.A.; BURBANK, D; CICCIOLI, PATRICIA; FISHER, G; AMIDON, W; LIMARINO, C.; CLARK, A.
Revista:
JOURNAL OF SOUTH AMERICAN EARTH SCIENCES
Editorial:
PERGAMON-ELSEVIER SCIENCE LTD
Referencias:
Lugar: Amsterdam; Año: 2016 vol. 70 p. 237 - 250
ISSN:
0895-9811
Resumen:
The Toro Negro Formation is a foreland sequence in western La Rioja province, Argentina, which recordsthe late-stage tectonic evolution of the Vinchina Basin. Together with the underlying Vinchina Formation,these two units represent one of the thickest and longest continually exposed foreland sections innorthwest Argentina. The Vinchina basin is uniquely situated between the Toro Negro and Umangoblocks of the Western Sierra Pampeanas to the north and south, the Precordillera to the west, and theSierra de Famatina to the east. New U-Pb dating of volcanic tephra provides improved age constraints onthe pace of sedimentation, and U-Pb ages of detrital zircons serve to strengthen existing provenanceinterpretations. We show that deposition of the Toro Negro Formation spans roughly 6.9 to 2.3 Ma: LateMiocene to Early Pleistocene. A high-relief, erosional unconformity with the underlying Vinchina Formationdeveloped sometime between 9.3 and 6.9 Ma, although stratigraphic considerations suggest itspanned only the later part of this time interval (perhaps 7.5e6.9 Ma). Above this unconformity,undecompacted sedimentation rates are remarkably high at ~1.2 mm/yr, slowing to ~0.3 mm/yr after~6 Ma. An unconformity in the upper part of the section is constrained to occur sometime between 5.0and 3.0 Ma, probably beginning not long after 5.0 Ma. The timing of both unconformitiesbroadly Matches the timing of inferred tectonic events in the Sierra Famatina ~50 km to the east, theFiambala basin to the north, and the Bermejo basin to the south, suggesting they May record regional tectonism at these times. Provenance interpretations of detrital zircon spectra are consistent with previousinterpretations based on sediment petrography. They show that provenance did not changesignificantly during the course of Toro Negro deposition, precluding major tectonically-induced drainagereorganization events. Sediments were derived primarily from the north (Toro Negro Block) and west(Precordillera). The data are consistent with a subtle increase in sediment supply from the Precordillerabeginning around 6.5 Ma.