An official website of the United States government
Abstract Understanding the effects of flat slab subduction on mountain building, arc magmatism, and basin evolution is fundamental to convergent‐margin tectonics, with implications for potential feedbacks among geodynamic, magmatic, and surface processes. New stratigraphic and geochronological constraints on Cenozoic sedimentation and magmatism in the southern Central Andes of Argentina (31°S) reveal shifts in volcanism, foreland/hinterland basin development, sediment accumulation, and provenance as the retroarc region was structurally partitioned during slab flattening. Detrital zircon U‐Pb age distributions from the western (Calingasta basin), central (Talacasto and Albarracín basins), and eastern (Bermejo foreland basin) segments of the retroarc basin system preserve syndepositional volcanism and orogenic unroofing of multiple tectonic provinces. Initial shortening‐related exhumation of the Principal Cordillera at 24–17 Ma was recorded by the accumulation of distal eolian deposits bearing Oligocene–Eocene zircons from the Andean magmatic arc. The Calingasta basin chronicled volcanism and basement shortening in the Frontal Cordillera at ~17–11 Ma, as marked by an upward coarsening succession of fluvial to alluvial fan deposits with a sustained zircon U‐Pb age component that matches pervasive Permian‐Triassic bedrock in the hinterland. An ~450 km eastward inboard sweep of volcanism at 11 Ma coincided with the inception of flat slab subduction, and subsequent thin‐skinned shortening in the Precordillera fold‐thrust belt that exhumed wedge‐top deposits and induced cratonward (eastward) advance of flexural subsidence into the Bermejo foreland basin. This foreland basin was structurally partitioned as basement uplifts of the Sierras Pampeanas transformed a fluvial megafan sediment routing network into smaller isolated alluvial fan systems fed by adjacent basement blocks.
more »
« less
Cenozoic Basin Evolution During Alternating Extension and Shortening in the Southern Central Andes Along the Chile-Argentina Border, 37–38°S
The south-central Chile and Argentina margin experienced a regional phase of extensional tectonics during the Oligocene–early Miocene, forming several basins across the forearc, Andean Cordillera, and retroarc regions. These basins accumulated thick successions of volcanic and sedimentary rocks. Subsequently, Neogene contractional tectonics led to the development of the current Andean Cordillera and the deposition of synorogenic clastic deposits in foreland basins. Traditionally, the Cura Mallín Formation, comprising a lower volcanic unit (CMV) and an upper sedimentary unit (CMS), has been interpreted to have formed during the Oligocene–early Miocene extensional phase. However, some studies propose deposition of the CMS in a foreland basin during the early–late Miocene. To unravel the transition from extensional to contractional tectonics in the Andes of south-central Chile and Argentina, we conducted new geochronological analyses (U-Pb, LA-ICP-MS) and integrated these results with structural, stratigraphic, and sedimentological observations in key sections within the CMS and the overlying Trapa-Trapa Formation in the Principal Cordillera along the Chile-Argentina border (37°–38°S). Our findings indicate that only the lower part of the CMS was deposited in an extensional setting, as evidenced by the presence of an inverted extensional wedge dated at ∼20 Ma. The middle-upper CMS (∼19 to 9 Ma) and contemporaneous units to the east exhibit evidence of syncontractional deformation, suggesting deposition in a foreland basin generated by shortening of the western Principal Cordillera. Around 9 Ma, uplift of the Agrio and Chos Malal fold and thrust belts, east of the Principal Cordillera, led to segmentation of the foreland basin. The Trapa Trapa Formation was deposited in a hinterland basin, with sediment sourced from the east. After ∼6.5 Ma, major contractional deformation shifted westward, resulting in intense folding of the CMS and Trapa Trapa Formation and subsequent thrusting of the western Principal Cordillera over the Central Depression. Our study suggests that deformation progressed toward the eastern foreland during the early to late Miocene and then shifted toward the western forearc during the late Miocene to Pleistocene.
more »
« less
- Award ID(s):
- 1918541
- PAR ID:
- 10546773
- Publisher / Repository:
- American Journal of Science
- Date Published:
- Journal Name:
- American Journal of Science
- Volume:
- 324
- ISSN:
- 0002-9599
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Koutz, F.R.; Pennell, W.M. (Ed.)A key question in the tectonic evolution of the Sevier orogenic belt of the western U.S. Cordillera is when and why the overthickened crust of the hinterland plateau began to collapse giving rise to the modern extensional tectonic regime. Delineating the exhumation history of the Ruby Mountains, East Humboldt Range and Wood Hills metamorphic core complex (REHW) of Elko County, Nevada offers important evidence bearing on this question. Recent work from the northern REHW records a three-phase extensional history: (1) ~15–20 km of Late Eocene extension, (2) a second pulse of extension of similar rate and magnitude beginning in the late Oligocene or early Miocene (by 21 Ma) and continuing to approximately 11 Ma, and (3) the Basin-and-Range extensional regime continuing at reduced rate to today. In contrast, previous work from the Harrison Pass area in the southern REHW does not recognize an imprint from the Late Eocene phase of extension, and places the onset of the second extensional phase after ~17 Ma. New intermediate closure temperature thermochronology from the Harrison Pass pluton indicates that it remained at significant depth until at least ~25 Ma, severely limiting any possible Late Eocene to early Oligocene extension, consistent with previous interpretations. However, the new results challenge the previously proposed post-17 Ma onset for extension at Harrison Pass. New, intermediate closure temperature (U-Th)/He titanite and zircon ages from the eastern half of the pluton almost entirely predate 17 Ma and instead support an extensional onset bracketed between the Early Miocene (21 Ma) and the late Oligocene (25 Ma). Integrating potassium feldspar 40Ar/39Ar multi-diffusion domain modeling with the lower closure temperature thermochronometric systems reveals an inflection to faster cooling rates after ~25 Ma and further supports this inference. Nevertheless, all but the farthest east and structurally shallowest of the samples also show a second inflection point at ~17 Ma. We argue that previously reported apatite fission track and apatite (U-Th)/He data captured this post-17.5 Ma reacceleration event but missed the earlier, late Oligocene-early Miocene extension recorded by the higher temperature thermochronometers. The latest Oligocene to early Miocene extensional phase correlates with extensional events reported from southern Nevada and Arizona that may relate to the relaxation of contractional boundary conditions during the early evolution of the San Andreas margin. However, the post-17.5 Ma resurgence in extension probably correlates with large-scale crustal weakening across the northern Basin and Range province attending the arrival of the Yellowstone thermal plume.more » « less
-
F.R. Koutz W.M. Pennell (Ed.)A key question in the tectonic evolution of the Sevier orogenic belt of the western U.S. Cordillera is when and why the overthickened crust of the hinterland plateau began to collapse giving rise to the modern extensional tectonic regime. Delineating the exhumation history of the Ruby Mountains, East Humboldt Range and Wood Hills metamorphic core complex (REHW) of Elko County, Nevada offers important evidence bearing on this question. Recent work from the northern REHW records a three-phase extensional history: (1) ~15–20 km of Late Eocene extension, (2) a second pulse of extension of similar rate and magnitude beginning in the late Oligocene or early Miocene (by 21 Ma) and continuing to approximately 11 Ma, and (3) the Basin-and-Range extensional regime continuing at reduced rate to today. In contrast, previous work from the Harrison Pass area in the southern REHW does not recognize an imprint from the Late Eocene phase of extension, and places the onset of the second extensional phase after ~17 Ma. New intermediate closure temperature thermochronology from the Harrison Pass pluton indicates that it remained at significant depth until at least ~25 Ma, severely limiting any possible Late Eocene to early Oligocene extension, consistent with previous interpretations. However, the new results challenge the previously proposed post-17 Ma onset for extension at Harrison Pass. New, intermediate closure temperature (U-Th)/He titanite and zircon ages from the eastern half of the pluton almost entirely predate 17 Ma and instead support an extensional onset bracketed between the Early Miocene (21 Ma) and the late Oligocene (25 Ma). Integrating potassium feldspar 40Ar/39Ar multi-diffusion domain modeling with the lower closure temperature thermochronometric systems reveals an inflection to faster cooling rates after ~25 Ma and further supports this inference. Nevertheless, all but the farthest east and structurally shallowest of the samples also show a second inflection point at ~17 Ma. We argue that previously reported apatite fission track and apatite (U-Th)/He data captured this post-17.5 Ma reacceleration event but missed the earlier, late Oligocene-early Miocene extension recorded by the higher temperature thermochronometers. The latest Oligocene to early Miocene extensional phase correlates with extensional events reported from southern Nevada and Arizona that may relate to the relaxation of contractional boundary conditions during the early evolution of the San Andreas margin. However, the post-17.5 Ma resurgence in extension probably correlates with large-scale crustal weakening across the northern Basin and Range province attending the arrival of the Yellowstone thermal plume.more » « less
-
ABSTRACT The topographic growth of the Eastern Cordillera in the northern Andes of Colombia is a critical event in the tectonic and paleogeographic evolution of the western Amazon Basin. Documentation of early orogenic growth is enabled through multi‐proxy provenance signatures recorded in the adjacent retro‐foreland basin. In broken foreland basins, basement highs interrupt the lateral continuity of facies belts and potentially mask provenance signals. The Putumayo Basin is a broken foreland basin in western Amazonia at ~1°–3° N, where the Florencia, Macarena, and El Melón‐Vaupes basement highs have compartmentalised discrete depocentres during basin development. This study presents new evidence from stratigraphic, conglomerate clast count, sandstone petrography, detrital zircon U–Pb geochronology and novel apatite detrital U–Pb age trace element geochemistry analyses. The results show that the southern Eastern Cordillera (i.e., Garzon Massif) and Putumayo Basin basement highs were initially uplifted during the Late Cretaceous coeval with the Central Cordillera, most likely associated with the collision of the Caribbean Large Igneous Province (CLIP). Distinctive facies distributions and provenance changes characterise the Putumayo Basin over a ~300 km distance from south to north, in the Rumiyaco Formation and Neme Sandstone. Detrital zircon U–Pb ages record a sharp reversal from easterly derived Proterozoic to westerly sourced late Mesozoic–Cenozoic Andean zircons derived principally from the Central Cordillera. Provenance signatures of the synorogenic Eocene Pepino Formation demonstrate the continued exhumation of the Eastern Cordillera as a second‐order source area. However, the emergence of the northern intraplate highs modulated the provenance signature due to the rapid unroofing of relatively thinner marine sedimentary cover strata that overlie the Putumayo basement, in comparison to the thicker sequences of the southern basin. The provenance data and facies distributions of the Oligocene–Miocene Orito Group were more heterogeneous due to strike‐slip deformation, associated with major plate tectonic reorganisation as the Nazca Plate subducted under the South American margin.more » « less
-
null (Ed.)The Ruby Mountains, East Humboldt Range and Wood Hills (REHW) of Elko County Nevada, one of the classic metamorphic core complexes of the Cordillera, preserves a protracted and episodic record of both ancient and modern crustal extension that has only recently been unraveled based on its thermochronometrically constrained cooling history. Extension began during the Late Eocene synchronously with a major pulse of intermediate to felsic magmatism preserved locally by plutonic rocks intruded into the REHW and regionally by widespread Late Eocene to early Oligocene volcanism (“the ignimbrite flare-up”). The Eocene-Oligocene event accommodated at least 15 km of extension concentrated in the northern half of the complex and associated with deposition in the Elko Basin to the west, a relatively thin (~1 km), broad sequence of Late Eocene lacustrine and related strata that contrasts with the younger sedimentation patterns represented by the narrower, thicker (up to 4+km), coarse clastics of the Miocene Humboldt Basin. Though locally significant, the Eocene-Oligocene extensional phase appears not to have been associated with broadly distributed regional extension, again contrasting with Miocene and younger events. The initial phase of extension slowed or halted by the mid-Oligocene, after which extension re-accelerated in the latest Oligocene to early Miocene (~25 – 21 Ma), correlative with deposition of a coarse clastic and lacustrine sequence known as the Clover Formation. This extensional phase propagated farther south than the earlier phase along the full length of the REHW. Extension likely slowed again between ~21 Ma and ~17.5 Ma, after which it abruptly re-accelerated through the Middle Miocene to ~10 Ma, synchronous with deposition of the thick, coarse clastics of the Humboldt Formation. Middle Miocene extension likely initiated with crustal-scale heating marking the impingement of the Yellowstone hot spot in NW Nevada. Sometime after 10 Ma, the interior of the core complex was transected by east-dipping normal faults that today define the steep eastern face of the Ruby Mountains and East Humboldt Range; these face west-dipping normal faults along the west flank of the Pequop Mountains and Spruce Mountains. Extension continues today at a rate of ~1 mm/yr as represented by the 2008 MW 6.0 Wells Earthquake.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.2475/001c.115328
