Andean Mountain Building and Foreland Basin Evolution During Thin‐ and Thick‐Skinned Neogene Deformation (32–33°S)

Abstract

The southern Central Andes recorded retroarc shortening, basin evolution, and magmatic arc migration during Neogene changes in subduction. At 31-33°S, above the modern flat-slab segment, spatial and temporal linkages between thin-and thick-skinned foreland shortening, basement-involved exhumation of the main Cordillera, and lower-crustal hinterland thickening remain poorly resolved. We integrate new geochronological and thermochronological data for thrust sheets and Neogene foreland basin fill with structural, sedimentological, and passive seismic results to reconstruct the exhumation history and evaluate potential geometric linkages across structural domains. 40 Ar/ 39 Ar ages for volcanic horizons and zircon U-Pb ages for synorogenic clastic deposits in the Manantiales Basin constrain the minimum duration of synorogenic sedimentation to~22-14 Ma. Detrital zircon age distributions record sequential unroofing of hinterland thrust sheets until~15 Ma, followed by eastward (cratonward) advance of the deformation front, shutoff of western sediment sources, and a shift from fluvial to alluvial fan deposition at 14 Ma. Apatite (U-Th)/He cooling ages confirm rapid exhumation of basement-involved structural blocks and basin partitioning by~14-5 Ma, consistent with the timing of the Manantiales facies and provenance shifts and a coeval (~12-9 Ma) pulse of thin-skinned shortening and exhumation previously identified in the eastern foreland. Late Miocene-Pliocene (~8-2 Ma) cooling ages along the Chile-Argentina border point to hinterland uplift during the latest stage of Andean orogenesis. Finally, geophysical constraints on crustal architecture and low-temperature thermochronometry results are compatible with a hybrid thin-and thick-skinned décollement spanning retroarc domains.

Neogene Retroarc Foreland Basin Evolution, Sediment Provenance, and Magmatism in Response to Flat Slab Subduction, Western Argentina

“…(Figure 5a; C4, C5, and C6). These trends suggest progressive exhumation of young Andean volcanic cover and then underlying Carboniferous -Triassic igneous units (Mackaman-Lofland et al, 2020;Pinto et al, 2018).…”

“…Early Miocene thermochronometric cooling ages attest to shortening-related exhumation in the Frontal Cordillera (Hoke, Graber, et al, 2014;Riesner et al, 2019). Erosion of the Frontal Cordilleran further expressed in middle-Miocene deposits to the southwest (Manantiales basin; Mackaman-Lofland et al, 2020: Pinto et al, 2018, southeast (Cachueta basin: Buelow et al, 2018), northern Bermejo basin (Fosdick et al, 2015;Jordan et al, 1996), and northeastern Bermejo basin (Ischigualasto-Villa Unión basin: Lemos-Santos et al, 2019). Igneous geochemical signatures suggest increased crustal contributions related to continued crustal thickening (>50 km) (Litvak et al, 2018;Jones et al, 2015;Kay et al, 1991).…”

“…Miocene to Quaternary (23-0 Ma) zircons from Andean arc rocks and recycled volcaniclastic rocks across the Frontal Cordillera (Figure 2a; Jones et al, 2015;Kay et al, 1991;Kay & Mpodozis, 2001). Predicted provenance variations associated with orogenic unroofing along Frontal Cordillera structures involves initial erosion of Neogene volcanic and volcaniclastic cover 10.1029/2019TC005958 Tectonics (RBLA01) followed by increased contributions from Carboniferous to Triassic igneous rocks (RMDZ01) (Figure 6b; Mackaman-Lofland et al, 2020;Pinto et al, 2018).…”

Late Miocene Deformation Kinematics Along the NW Zagros Fold‐Thrust Belt, Kurdistan Region of Iraq: Constraints From Apatite (U‐Th)/He Thermochronometry and Balanced Cross Sections

“…This study employed structurally integrated low‐temperature apatite (U‐Th)/He (AHe) thermochronometry to constrain the timing of faulting and folding. AHe dating has been widely applied in structural and geomorphic studies to define the timing of faulting and erosional exhumation (e.g., Anderson et al, 2018; Ehlers & Farley, 2003; Fosdick et al, 2015; Gavillot et al, 2010; Levina et al, 2014; Lock & Willett, 2008; McQuarrie & Ehlers, 2017; Mackaman‐Lofland et al, 2020; Stockli et al, 2000). The technique is based on radiogenic ingrowth of 4 He from the radioactive decay of 238 U, 235 U, 232 Th, and 147 Sm.…”

“…These inflection points were used to determine whether samples were fully thermally reset, partially reset, or not reset (i.e., retaining detrital ages) and hence to pinpointing the timing of rapid cooling and exhumation (Harrison & Zeitler, 2005; Stockli et al, 2000). For example, samples with AHe ages invariant with stratigraphic level and younger than the depositional age were considered to be thermally reset (e.g., Carrapa et al, 2011; Mackaman‐Lofland et al, 2020).…”