Miocene surface uplift and orogenic evolution of the southern Andean Plateau (central Puna), northwestern Argentina

Abstract

We present stable hydrogen-isotope analyses of volcanic glass ([Formula: see text]Dg) and radiometric ages (U-Pb zircon, U-Th calcite, AMS¹⁴C) from deformed sedimentary deposits in the vicinity of the intermontane Pocitos Basin in the central Puna of the Andean Plateau at about 24.5°S. Our results demonstrate 2-km surface uplift since the middle to late Miocene and protracted shortening that persists until the present day, while other sectors of the Puna show evidence for tectonically neutral and/or extensional settings. These findings are at odds with previous studies suggesting near-modern elevations (4 km) of the Puna Plateau since the late Eocene and formation of the intermontane Miocene Arizaro-Pocitos Basin associated with gravitational foundering of a dense lithosphere. Geophysical and geochemical data support the removal of continental lithosphere beneath the Puna, but the timing and mechanisms by which this removal occurs have remained controversial. We hypothesize that intermontane basin formation in the central Puna is the result of crustal shortening since about 20 Ma, followed by rapid surface uplift, likely related to lithospheric delamination.

Keywords: Central Andes; NW Argentina; Puna Plateau; stable isotope paleoaltimetry; tectonics.

Fig. 1.

Overview maps and cross-section of the study area in the central Puna Plateau. (A) Shaded relief map showing morphotectonic provinces of the Central Andes. AP, Andean Plateau; EC, Eastern Cordillera; SFTB, Subandean fold-and-thrust belt; SBS, Santa Bárbara System; SP, Sierras Pampeanas. (B) Topographic map of the southern Central Andes showing major basins and ranges discussed in the text. Numbered squares indicate age of deformation onset and range uplift in Ma compiled from the literature (e.g., refs. –, for a complete list see SI Appendix, Table S2). The white line delineates watershed between the internally drained Puna Plateau and adjacent provinces. (C) Geological map of the Salar de Pocitos basin and adjacent regions (Arizaro, Siete Curvas, and Pastos Grandes) modified after Alonso (27), Blasco et al. (28), DeCelles et al. (21), and Martínez et al. (29). PG, Salar de Pastos Grandes; TG, Salina Tolar Grande. Shown are a) a pseudo-fault-plane solution calculated from fault-kinematic indicators documenting thrust kinematics of the Macón Fault (SI Appendix, Table S3) and b) $\mathrm{\delta }$Dg and geochronologic sample locations with selected age estimates as listed in Table 1 and SI Appendix, Table S13. Black lines show the location of cross-sections shown in D and Fig. 3. The black star shows the location of the Quebrada Quirón site discussed in the text. (D) Schematic geologic cross-section (P’–P”’ in C) through the study area (modified after 21, 30). Bt, Batín Formation; Qt, Quaternary fill.

Fig. 2.

Simplified stratigraphy of the Pocitos area with a representative set of radiometric ages. Rose plots represent paleocurrent directions from imbricated clast measurements. BT, Batín Formation; BL, Blanca Lila Formation. Note: The Right column shows an enlarged excerpt of the Left column.

Fig. 3.

Simplified W–E cross-sections of key localities documenting Mio–Pleistocene deformation in the Pocitos Basin. Numbers refer to obtained U–Pb zircon and U–Th calcite^a ages in Ma. For profile locations see Fig. 1C.

Fig. 4.

Hydrogen stable isotope data and paleoaltimetry estimates for the southern Central Andes (24–25°S). (A) $\delta$Dg vs. depositional age ($\pm$2$\sigma$ error bars) from the low-elevation foreland [green, (41)], Eastern Cordillera [gray, (41)], Puna Plateau [red, (33, 41) this study], and Western Cordillera [WC, orange, (70)]. Asterisks indicate data from this study. Data excluded from paleoaltimetry calculations are presented in SI Appendix, Table S13 and Fig. S3. Note the stepwise decrease in $\delta$Dg in the Puna records, which we interpret to reflect surface uplift. Assuming an isotopic lapse rate of –15.8 $\pm$ 7.9$‱$/km (75), the isotopic difference of 34 $\pm$ 4$‱$ between the pre-13 Ma and post-10 Ma Puna implies an elevation gain of about 2.1 $\pm$ 1.1 km (from ca. 1.9 to 4.0 km asl). (B) Schematic illustration of the paleotopographic evolution across the southern Central Andes (Az–Arizaro, Poc/SC–Pocitos/Siete Curvas, and PG–Pastos Grandes). Colored bars show representation of paleotopography estimates for each time period calculated from the isotopic difference ($\mathrm{\Delta }\delta$Dg) between the foreland and the region of interest (SI Appendix, Table S14). The black curve and gray envelope show modern topography (min, mean, max) across the swath area shown in Fig. 1B. 20–14 Ma: While the present-day foreland and the Eastern Cordillera are at a similar elevation of about 1.1 $\pm$ 0.4 km (41) and 1.1 $\pm$ 0.2 km asl, respectively, the Puna Plateau is at about 1.9 $\pm$ 0.6 km asl. Limited data from the Western Cordillera indicate paleoelevations of 3.1 $\pm$ 1.1 km asl; 13–10 Ma: The Puna Plateau experiences surface uplift on the order 0.8 $\pm$ 0.5 km from ca. 1.9 to 2.7 km asl; 10–0 Ma: Between 9 and 8 Ma, the central Puna Plateau attained modern elevations of 4.0 $\pm$ 1.0 km asl, and although the Eastern Cordillera was deformed as early as the middle Miocene [ca. 13 Ma, e.g., ref. , signs of significant surface uplift to modern elevations (2.3 $\pm$ 0.7 km asl) are not evident until about 6.5 Ma (41).