Verónica Oliveros
University of Concepción
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Geological Society of America Bulletin | 2016
Alfonso Encinas; Andrés Folguera; Verónica Oliveros; Lizet De Girolamo Del Mauro; Francisca Tapia; Ricardo Riffo; Francisco Hervé; Kenneth L. Finger; Victor A. Valencia; Guido Gianni; Orlando Álvarez
The Chilean margin has been used as the model of an ocean-continent convergent system dominated by compression and active mountain building as a consequence of the strong mechanical coupling between the upper and the lower plates. The Andean Cordillera, however, shows evidence of alternating phases of compressional and extensional deformation. Volcano-sedimentary marine strata in the Aysen region of southern Chile contribute to an understanding of the causes of extensional tectonics and crustal thinning that occurred in the Andean orogeny because these deposits constitute the only reliable record of submarine suprasubduction volcanism during the Cenozoic in southern South America. In order to discern the age and tectono-sedimentary setting of these strata, referred to as the Traiguen Formation, we integrated sedimentology, ichnology, petrography, geochemistry, structural geology, foraminiferal micropaleontology, and U-Pb geochronology. Our results indicate that the Traiguen Formation was deposited in a deep-marine extensional basin during the late Oligocene–earliest Miocene. The geochemistry and petrography of the pillow basalts suggest that they formed in a convergent margin on a thinned crust rather than at an oceanic spreading center. We attribute the origin of the Traiguen Basin to a transient period of slab rollback and vigorous asthenospheric wedge circulation that was caused by an increase in trench-normal convergence rate at ca. 26–28 Ma and that resulted in a regional event of extension and widespread volcanism.
Journal of the Geological Society | 2017
Andrés Echaurren; Verónica Oliveros; Andrés Folguera; Federico Ibarra; Christian Creixell; Friedrich Lucassen
The Andes in northern Patagonia are mainly formed by Mesozoic magmatic units: the mostly Jurassic–Cretaceous North Patagonian Batholith and volcanism of the Jurassic Lago La Plata (Ibáñez) Formation as well as the mid-Cretaceous Divisadero Group. These rocks represent the development of a magmatic belt through Jurassic–mid-Cretaceous time, during a switch of the tectonic regime from extension to compression. To study arc evolution during this transition, we carried out fieldwork and geochemical sampling at c. 43°S, clarifying structural relationships and characterizing the magmatic sources. Multi-element diagrams for both volcanic units suggest a slab-derived signature, whereas isotopic ratios (Sr–Nd–Pb) indicate parental melts sourced from the subduction-modified asthenospheric mantle interacting with crustal sources during their emplacement. An angular unconformity is identified between the synextensional Jurassic volcanic rocks and Lower Cretaceous sedimentary rocks beneath the mid-Cretaceous sequences. Although this deformational event was simultaneous with generalized overriding plate compression, geochemical ratios indicate an immature Aptian–Albian arc with no associated crustal thickening. Late Jurassic to mid-Cretaceous arc settlement after a trenchward retraction of magmatism from the foreland between c. 41 and 45°S, with an associated increase in slab dip angle, may have provoked crustal softening facilitating the subsequent initial fold–thrust belt growth. Supplementary material: Petrographic descriptions and geochemical–isotopic data are available at https://doi.org/10.6084/m9.figshare.c.3677974
Journal of the Geological Society | 2016
Christian Creixell; Verónica Oliveros; P. Vásquez; J. Navarro; D. Vallejos; X. Valin; E. Godoy; Mihai N. Ducea
A large section of the Late Palaeozoic forearc is exposed along the coastal ranges of north–central Chile (28°–29°30′S). This is characterized by three lithotectonic units: (1) the Punta de Choros Metamorphic Complex (basal accretion series), composed mostly of micaschists and metabasites; (2) the Chañaral Epimetamorphic Complex (frontal accretion series), formed by metaturbidites and metasediments; (3) the Llano del Chocolate Beds (forearc basin deposits), composed of a sedimentary sequence of clastic sedimentary rocks with minor limestones and acidic volcanic rocks. Within the basal accretion series, two distinctive blocks of garnet-bearing schists with amphibolite-facies metamorphism have been preserved, recording early stages of the subduction system. The stratigraphic record and the U–Pb dating of igneous (291–318 Ma) and detrital zircons (maximal deposition ages between 273 and 292 Ma) in the forearc basin deposits, coupled with 40Ar/39Ar ages for metamorphic rocks (319–280 Ma), indicate that forearc sedimentation was broadly contemporaneous with metamorphism and exhumation of the basal accretion series. The radiometric dating on garnet-bearing rocks indicates that the onset of the subduction system took place in the Mississippian, at a high thermal gradient. These conditions were responsible for generation of limited volumes of acidic melt, now recognized as acidic domes and tuffs within the forearc basin stratigraphy. Supplementary material: Tables of sedimentary facies, U-Pb geochronological analyses and Ar-Ar geochronological data are available at: http://doi.org/10.6084/m9.figshare.c.2868307.
Archive | 2018
Alfonso Encinas; Andrés Folguera; Florencia Bechis; Kenneth L. Finger; Patricio Zambrano; Felipe Pérez; Pablo Bernabé; Francisca Tapia; Ricardo Riffo; Luis A. Buatois; Darío Orts; Sven N. Nielsen; Victor V. Valencia; José I. Cuitiño; Verónica Oliveros; Lizet De Girolamo Del Mauro; Victor A. Ramos
The most important Cenozoic marine transgression in Patagonia occurred during the late Oligocene–early Miocene when marine waters of Pacific and Atlantic origin flooded most of southern South America including the present Patagonian Andes between ~41° and 47° S. The age, correlation, and tectonic setting of the different marine formations deposited during this period are debated. However, recent studies based principally on U–Pb geochronology and Sr isotope stratigraphy, indicate that all of these units had accumulated during the late Oligocene–early Miocene. The marine transgression flooded a vast part of southern South America and, according to paleontological data, probably allowed for the first time in the history of this area a transient connection between the Pacific and Atlantic oceans. Marine deposition started in the late Oligocene–earliest Miocene (~26–23 Ma) and was probably caused by a regional event of extension related to major plate reorganization in the Southeast Pacific. Progressive extension and crustal thinning allowed a generalized marine flooding of Patagonia that reached its maximum extension at ~20 Ma. It was followed by a phase of compressive tectonics that started around 19–16 Ma and led to the growth of the Patagonian Andes. The youngest (~19–15 Ma) marine deposits that accumulated in the eastern Andean Cordillera and the extra-Andean regions are coeval with fluvial synorogenic deposits and probably had accumulated under a compressive regime.
Archive | 2018
Verónica Oliveros; Javiera González; Mauricio Espinoza Vargas; Paulina Vásquez; Pablo Rossel; Christian Creixell; Fernando J. Sepúlveda; Francisco Bastias
A temporal and tectonic framework for the initiation of the Andean magmatism at its earliest stages is presented in this work, based on the current geological, geochemical, and geochronological information available in northern Chile between 20o and 30o S. This information has been collected from Triassic and Jurassic plutonic, volcanic, and volcanosedimentary units cropping out at the Coastal, Domeyko, Frontal Cordilleras, and the Precordillera, as two roughly parallel belts that extend for more than 1,000 km in the Chilean territory. Petrological and geochemical data suggest that the magmatism during the Triassic and Jurassic was dominantly intermediate in composition and had arc or subduction affinities. Even though magma sources should have had a clear mantle component, a crustal influence was more important during the Triassic. Geochronological information shows a significant magmatic lull near the Triassic–Jurassic boundary, associated with the retraction of the arc to the present-day Coastal Cordillera. Based on these data, the early stages of the Andean magmatism can be tracked backup to the Triassic igneous units in northern Chile.
Lithos | 2013
Pablo Rossel; Verónica Oliveros; Mihai N. Ducea; Reynaldo Charrier; Stéphane Scaillet; Leonardo Retamal; Oscar Figueroa
Journal of South American Earth Sciences | 2012
Verónica Oliveros; Mariana Labbé; Pablo Rossel; Reynaldo Charrier; Alfonso Encinas
Lithos | 2015
Pablo Rossel; Verónica Oliveros; Mihai N. Ducea; Laura B. Hernández
Andean Geology | 2017
Felipe Coloma; Ximena Valin; Verónica Oliveros; Paulina Vásquez; Christian Creixell; Esteban Salazar; Mihai N. Ducea
Andean Geology | 2014
Pablo Rossel; Verónica Oliveros; José F. Mescua; Felipe Tapia; Mihai N. Ducea; Sergio Calderón; Reynaldo Charrier; Derek Hoffman