Provenance and tectonic implications of Orán Group foreland basin sediments, Río Iruya canyon, NW Argentina (23° S)

Abstract

Foreland basins are important recorders of tectonic and climatic processes in evolving mountain ranges. The R ıo Iruya canyon of NW Argentina (23°S) exposes ca. 7500 m of Or an Group foreland basin sediments, spanning over 8 Myr of near continuous deposition in the Central Andes. This study presents a record of sedimentary provenance for the Iruya Section in the context of a revised stratigraphic chronology. We use U-Pb zircon ages from six interbedded ash layers and new magnetostratigraphy to constrain depositional ages in the section between 1.94 and 6.49 Ma, giving an average sedimentation rate of 0.93 AE 0.02 (2r) km Myr À1 . We then pair U-Pb detrital zircon dating with quartz trace-element analysis to track changes in sedimentary provenance from ca. 7.6 to 1.8 Ma. Results suggest that from ca. 7.6 to ca. 6.3 Ma, the Iruya watershed did not tap the Salta Group or Neogene volcanics that are currently exposed in the eastern Cordillera and Puna margin. One explanation is that a long-lived topographic barrier separated the eastern Puna from the foreland for much of the mid-late Miocene, and that the arrival of Jurassic-Neogene zircons records regional tectonic reactivation at ca. 6.3 Ma. A second major provenance shift at ca. 4 Ma is marked by changes in the zircon and quartz populations, which appear to be derived from a restricted source region in Proterozoic-Ordovician meta-sediments. Considered in conjunction with the onset of coarse conglomerate deposition, we attribute this shift to accelerated uplift of the Santa Victoria range, which currently defines the catchment's western limit. A third shift at ca. 2.3 Ma records an apparent disconnection of the Iruya with the eastern Puna, perhaps due to defeat of the proto RioIruya by the rising Santa Victoria range. This study is one of the first applications of quartz traceelement provenance analysis, which we show to be an effective complement to U-Pb detrital zircon dating when appropriate statistical methods are applied.

Foreland Basin Record of Uplift and Exhumation of the Eastern Cordillera, Northwest Argentina

“…The thick and thin bars around each point represent the 1σ and 2σ confidence intervals that contain 68 and 95% of the values from 10,000 bootstrapped data sets, respectively. The light grey symbols are data from Amidon et al (); the white symbols are from this study. The grey background boxes correspond to the 2σ confidence intervals for data from the Puncoviscana Formation and Santa Victoria Group.…”

“…Casa Grande data are from Siks and Horton (). Stratigraphic ages estimated from the magnetostratigraphy calibrated by absolute ages from interbedded tuffs (Amidon et al, ; Echavarria et al, ). The light grey and dark grey boxes show the age windows used to construct the d value (see text for details).…”

“…Near the town of Isla de Cañas, the Neogene sediment is exposed in a well‐studied coarsening‐upward section that exposes over 7‐km sediment. Depositional ages of this section are known from magnetostratigraphy, calibrated by radiometric ages of airfall tuffs intercalated through the section (Amidon et al, ; Echavarria et al, ; Hernandez et al, ; Reynolds et al, ). Deposition of the Tariquia Formation began around 12 Ma, but the age of the underlying Tranquitas Formation is not well known because of low‐quality paleomagnetic data.…”

“…We aim to document the provenance of foreland basin sediment to assess the long‐term history of growth and erosion of the plateau margin, building upon descriptions of the sedimentology and paleomagnetism of these units (Amidon et al, ; Hernandez et al, ). In the next two sections, we describe each of the various methods and the results from conglomerate clast counts, sandstone petrography, and detrital geochronology.…”

“…To trace the provenance of this material, we describe new sedimentologic and geochronologic data from a stratigraphic section that exposes over 7 km of detritus deposited over the past 12 Ma, including 1331 detrital grain age determinations from nine samples. We build upon prior studies that provide a sedimentologic framework and a detailed depositional chronology based on paleomagnetic results and dating of interbedded volcanics (Amidon et al, ; Echavarria et al, ; Hernandez et al, ). We also present new detrital apatite and zircon fission track data to document the cooling and exhumation history of the sediment source regions.…”