U-Pb ages of detrital and volcanic zircons of the Toro Negro Formation,northwestern Argentina: Age,provenance and sedimentation rates |
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| Institution: | 1. Geology Department, Middlebury College, Middlebury, VT, 05753, USA;2. Departamento de Ciencias Geológicas, IGeBA, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires-CONICET. Pabellón 2, 1° piso, Ciudad Universitaria, C1428EHA Buenos Aires, Argentina;3. Jackson School of Geosciences, University of Texas at Austin, Austin, TX, 78712, USA;4. Earth Research Institute, University of California, Santa Barbara, CA, 93106, USA;1. Instituto Superior de Correlación Geológica (INSUGEO-CONICET), Universidad Nacional de Tucumán, Miguel Lillo 205, T4000JFE, San Miguel de Tucumán, Argentina;2. Facultad de Ciencias Naturales e Instituto Miguel Lillo, Universidad Nacional de Tucumán, Miguel Lillo 205, T4000JFE, San Miguel de Tucumán, Argentina;3. Paleontología, Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), Centro Científico Tecnológico CONICET Mendoza, Avda. Ruiz Leal s/n, 5500, Mendoza, Argentina;1. INGEOSUR-CONICET, Departamento de Geología Universidad Nacional del Sur, San Juan 670, 8000, Bahía Blanca, Buenos Aires, Argentina;2. Departamento de Geología Universidad Nacional del Sur, San Juan 670, 8000, Bahía Blanca, Buenos Aires, Argentina;3. Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa, Avenida Uruguay 151, 6300, Santa Rosa, La Pampa, Argentina;1. Laboratorio de Paleomagnetismo Daniel A. Valencio, Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires (IGEBA), Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160, Pabellón II, Ciudad Universitaria, C1428EGA, Buenos Aires, Argentina;2. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina;1. Museo Argentino de Ciencias Naturales B. Rivadavia, A. Gallardo 470, C1405DJR Buenos Aires, Argentina;2. Facultad de Ciencias, Departamento de Evolución de Cuencas, Universidad de la República, Iguá 4225, 11400 Montevideo, Uruguay;3. Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom;4. Museo de La Plata, 1900 La Plata, Argentina;1. Centro de Investigaciones en Ciencias de la Tierra (CICTERRA), CONICET-Universidad Nacional de Córdoba, Haya de la Torre s/n, Ciudad Universitaria, X5016CGA Córdoba, Argentina;2. Departamento de Petrología y Geoquímica, Universidad Complutense – IGEO (CSIC), 28040 Madrid, Spain;1. Laboratorio de Análisis de Cuencas, CICTERRA, CONICET-Universidad Nacional de Córdoba, Córdoba X5016GCA, Argentina;2. Instituto de Geociencias, Universidade de Brasilia, Brazil |
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| Abstract: | The Toro Negro Formation is a foreland sequence in western La Rioja province, Argentina, which records the 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 in northwest Argentina. The Vinchina basin is uniquely situated between the Toro Negro and Umango blocks of the Western Sierra Pampeanas to the north and south, the Precordillera to the west, and the Sierra de Famatina to the east. New U-Pb dating of volcanic tephra provides improved age constraints on the pace of sedimentation, and U-Pb ages of detrital zircons serve to strengthen existing provenance interpretations. We show that deposition of the Toro Negro Formation spans roughly 6.9 to 2.3 Ma: Late Miocene to Early Pleistocene. A high-relief, erosional unconformity with the underlying Vinchina Formation developed sometime between 9.3 and 6.9 Ma, although stratigraphic considerations suggest it spanned only the later part of this time interval (perhaps 7.5–6.9 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 5.0 and 3.0 Ma, probably beginning not long after 5.0 Ma. The timing of both unconformities broadly Matches the timing of inferred tectonic events in the Sierra Famatina ～50 km to the east, the Fiambalá 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 previous interpretations based on sediment petrography. They show that provenance did not change significantly during the course of Toro Negro deposition, precluding major tectonically-induced drainage reorganization 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 Precordillera beginning around 6.5 Ma. |
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| Keywords: | Tephra Vinchina Fiambala Bermejo Famatina U-Pb Zircon Precordillera Valle Fertil |
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