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Thermochronometry unveils ancient thermal regimes in the NW Pampean Ranges, Argentina: From Mesozoic rifting to Miocene flat‐slab subduction

Authors:
Miguel Ezpeleta at National Scientific and Technical Research Council
Miguel Ezpeleta
Mauricio Parra at University of São Paulo
Mauricio Parra
Gilda Collo at National University of Córdoba
Gilda Collo
Cecilia Ayelén Wunderlin at Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de Anillaco (La Rioja)
Cecilia Ayelén Wunderlin
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Abstract

Reconstructing thermal histories in thrust belts is commonly used to infer the age and rates of thrusting and hence the driving mechanisms of orogenesis. In areas where ancient basins have been incorporated into the orogenic wedge, a quantitative reconstruction of the thermal history helps distinguish among potential mechanisms responsible for heating events. We present such a reconstruction for the Ischigualasto‐Villa Unión basin in the western Pampean Ranges of Argentina, where Triassic rifting and late Cretaceous‐Cenozoic retroarc foreland basin development, including Miocene flat‐slab subduction have been widely documented. We report results of organic and inorganic thermal indicators acquired along three stratigraphic sections, including vitrinite reflectance and X‐ray diffractometry in claystones and new thermochronological [(apatite fission‐track and apatite and zircon (U‐Th)/He)] analyses. Despite an up to 5 km‐thick Cenozoic overburden and unlike previously thought, the thermal peak in the basin is not due to Cenozoic burial but occurred in the Triassic, associated with a high heat flow of up to 90 mWm‐2 and less than 2 km of burial, which heated the base of the Triassic strata to ~160°C. Following exhumation, attested by the development of an unconformity between the Triassic and Late‐Cretaceous‐Cenozoic sequences, Cenozoic re‐burial increased the temperature to ~110°C at the base of the Triassic section and only ~50°C 7 km upsection, suggesting a dramatic decrease in the thermal gradient. The onset of Cenozoic cooling occurred at ~10‐8 Ma, concomitant with sediment accumulation and thus preceding the latest Miocene onset of thrusting that has been independently documented by stratigraphic‐cross‐cutting relationships. We argue that the onset of cooling is associated with lithospheric refrigeration following establishment of flat‐slab subduction, leading to the eastward displacement of the asthenospheric wedge beneath the South American plate. Our study places time and temperature constraints on flat‐slab cooling calls for a careful interpretation of exhumation signals in thrustbelts inferred from thermochronology only.
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Ezpeleta et al 2022 Basin research Thermochronometry unveils ancient thermal regimes in the NW Pampean Ranges Argentina From Mesozoic rifting to Miocene flat-slab subducti
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Article
Full-text available
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Article
Full-text available
  • Aug 2020
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Fault reactivation in the Sierras Pampeanas resolved across Andean extensional and compressional regimes using thermochronologic modeling
Article
  • Aug 2021
  • J S AM EARTH SCI
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Triassic-Jurassic thermal evolution and exhumation of the western Gondwana foreland: Thermochronology and basalt thermobarometry from the Argentine Sierras Pampeanas
Article
  • Oct 2020
  • J S AM EARTH SCI
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New thermocronological data of the Cretaceous-Cenozoic clastic sequences from the VINCHINA basin: Linkage between burial, exhumation and thermal flow variations
Article
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  • J S AM EARTH SCI
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Linking thermochronological data to transient geodynamic regimes; new insights from kinematic modeling and Monte Carlo sampling of thermal boundary conditions
Article
  • Nov 2020
  • J S AM EARTH SCI
It is common practice to assume values for basal heat flow or basal temperatures as a lower boundary condition for thermo-kinematic models of crustal tectonics. Here, we infer spatial and temporal variations of the paleo-basal temperature from integrated modelling of thermochronological ages, to relate the inferred variations to the geodynamic setting. To this end, we consider the Argentine Precordillera as a natural laboratory, given that its kinematic evolution is relatively well constrained and therefore, the focus can be placed on the variations of its basal thermal state. By means of a simple Monte Carlo sampling approach with thermochronological data as constraints, we infer the paleo-basal temperature history. This is compared to estimates posed by models existing in the literature concerning flat-slab subduction. Our results imply that, given the kinematic models used to date in the area, extremely low temperature gradients (<15 °C/km) are required to adequately predict the observed thermochronological ages. Substantial cooling of the lithosphere around 10 Ma is also required in order to fit measured values. This agrees with previous thermal simulations carried out in the region. Furthermore, major controls of the thermal architecture on the Argentine Precordillera are implied, thus reigniting the debate on thermal driving mechanisms in the evolution of mountainous settings and their relationship with deeper processes within the Earth, such as on the effects of the flat-slab subduction.
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Evidence for the Carnian Pluvial Episode in Gondwana: New multiproxy climate records and their bearing on early dinosaur diversification
Article
  • Jun 2020
  • GONDWANA RES
The Triassic hothouse world experienced dynamic changes in climate and ecosystems that set the Earth's climate and biotic states for part of the Mesozoic Era. A critical time interval was the Carnian Stage (~237–227 Ma), which not only saw the first appearance of dinosaurs in the fossil record but witnessed a large igneous province (Wrangellia LIP) and a sudden climate shift, the Carnian Pluvial Episode (CPE). Compelling hypotheses suggest that the Wrangellia eruptions caused the CPE, which in turn set the stage for the origin and initial diversification of dinosaurs. Unfortunately, testing these hypotheses is difficult because most relevant Carnian sedimentary archives possess few if any absolute age constraints, and there is little detailed paleoclimatic data for the CPE outside of the Tethys region. There is little existing evidence for the CPE in Gondwana, even though this region contains by far the best fossil record of early dinosaurs and their close relatives. We present new high-resolution geochronologic and paleoclimatic data from Carnian-aged strata in the Ischigualasto-Villa Unión Basin of northwest Argentina, which also preserves fossils of the earliest-known dinosaurs. New CA-TIMS UPb zircon age of 234.47 ± 0.44 Ma from the lower Los Rastros Formation demonstrates that most of the overlying lacustrine strata within this basin was deposited during or after the CPE, including large dinosauriforms fossil footprint. Multiproxy paleoenvironmental data (sedimentology, clay mineralogy, C and O stable isotopes, and fossils) from the same strata are the first detailed paleoclimate data for the CPE in Gondwana, and provide evidence that the CPE interval in western Gondwana was indeed warmer and more humid than before or after. These data are consistent with the interpretation of the CPE as a global event, but direct linkages in Gondwana and the Tethys with the origin and initial diversification of dinosaurs are less clear.
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Recognizing drainage reorganization in the stratigraphic record of the Neogene foreland basin of the Central Andes
Article
  • Jun 2020
  • SEDIMENT GEOL
Changes in drainage basin reorganization as preserved in the stratigraphic record have direct implications for the composition, organization, and scaling relationships of sedimentary systems. However, isolating the stratigraphic signature of drainage basin reorganization in response to tectonic and/or climatic drivers can be challenging. In the Neogene foreland basin of the southern Central Andes between 28°–31°S, the tectonically-controlled reorganization of basin catchment area has been cited as an important control on the basin stratigraphy. To resolve the signature of drainage basin reorganization in the Central Andean foreland, we conducted a basin-scale study integrating detailed sedimentology from four measured sections with multi-method provenance analysis to reconstruct foreland sediment routing pathways between 28°–31°S. Our regional synthesis suggests that the foreland basin has been connected by an axial sediment routing system since the early Miocene. Statistical analysis and graphical comparison using multidimensional scaling of new and published detrital zircon data from 45 samples resolves tectonically controlled changes in the catchment area in the late Miocene, including an eastward shift of the Andean drainage divide. This study provides the first evidence for expansion of the catchment area east of the basin draining the emerging basement-cored highlands of the Sierras Pampeanas. This study demonstrates that, when combined, provenance and detailed sedimentologic data sets provide a powerful tool to recognize and interpret drainage basin reorganization in the stratigraphic record and thus reconstruct the tectono-climatic and paleogeographic evolution of sedimentary systems.
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