Dispersion of low‐temperature thermochronologic data from nine samples collected on a deformed paleosurface preserved on the Cuevas range (Central Andes) can be exploited to unravel complex thermal ...histories. The nine samples yielded data that have both intersample and intrasample dispersions; the data set includes apatite fission‐track ages (180–110 Ma), mean track lengths (11–13 μm), apatite helium (10–250 Ma), and zircon helium ages (180–348 Ma). We ran inverse thermal history models for each sample that reveal spatial variations of the Miocene reheating along the paleosurface. Next, we ran a multiple‐sample joint model to infer a common form for thermal history for all samples. Our results suggest that initial exhumation during the Famatinian orogeny was followed by a residence between ~2.5 and 7.0 km depth during the Paleozoic and the Triassic. The onset of Mesozoic rifting was responsible for an increase of the geothermal gradient and extensive horst exhumation, which brought the basement of the Cuevas range close to the surface (~1–2 km) in the Late Jurassic. Between the Late Cretaceous and the Paleocene, the combination of low relief, a humid climate, and low erosion rates (0.006–0.030 km/Ma) facilitated the development of the Cuevas paleosurface. During the Miocene, this paleosurface experienced differential reheating with a high geothermal gradient (>25 °C/km) due to the sedimentary cover and local magmatic heat sources. During the Andean orogeny, in the Pliocene, the Cuevas paleosurface was deformed, exhumed, and uplifted.
Key Points
Multiple‐sample thermal history model performed with samples from a continuous paleosurface
Intersample and intrasample thermochronologic dispersions can be exploited to refine the tectonic evolution of the Campo‐Arenal basin
Spatiotemporal variations of geothermal gradient can explain basement thermal histories
Marked along‐strike changes in stratigraphy, mountain belt morphology, basement exhumation, and deformation styles characterize the Andean retroarc; these changes have previously been related to ...spatiotemporal variations in the subduction angle. We modeled new apatite fission track and apatite (U‐Th‐Sm)/He data from nine ranges located between 26°S and 28°S. Using new and previously published data, we constructed a Cretaceous to Pliocene paleogeographic model that delineates a four‐stage tectonic evolution: extensional tectonics during the Cretaceous (120–75 Ma), the formation of a broken foreland basin between 55 and 30 Ma, reheating due to burial beneath sedimentary rocks (18–13 Ma), and deformation, exhumation, and surface uplift during the Late Miocene and the Pliocene (13–3 Ma). Our model highlights how preexisting upper plate structures control the deformation patterns of broken foreland basins. Because retroarc deformation predates flat‐slab subduction, we propose that slab anchoring may have been the precursor of Eocene–Oligocene compression in the Andean retroarc. Our model challenges models which consider broken foreland basins and retroarc deformation in the NW Argentinian Andes to be directly related to Miocene flat subduction.
Key Points
The formation of Paleogene and Miocene broken foreland basins segmented the Andean retroarc
Inherited structures controlled the formation and the evolution of broken foreland basins
Slab anchoring may have promoted retroarc deformation
The Caviahue–Copahue volcanic complex in the Southern Volcanic Zone of the Andes is composed of the Pliocene–Pleistocene Caviahue depression and the active Copahue volcano. This volcanic complex is ...located in a zone of profuse volcanic and tectonic activity, and thus, the origin of the depression includes both tectonic and volcanic hypothesis (e.g., formation of a collapse caldera and a pull-apart basin). According to current knowledge, the oldest rocks filling the depression are lavas and ignimbrites of the Pleistocene Las Mellizas Formation. However, clastic sedimentary deposits underlying this unit have been recognized. Here, we document the characteristics of these deposits at the south shore of the Caviahue lake using field data and digital outcrop models (DOM). We have concluded that the deposits are deltaic and alluvial in origin and made up by a prodelta/distal deltaic front, delta front deposits, delta plain sediments and alluvial deposits. An unconformity separates the deltaic deposits from overlying alluvial deposits, indicating the decrease in the stratigraphic base level probably associated with a sudden coarse-grained clastic input and a drop in the lake level. Our study has implications on the timing and evolution of the Caviahue depression and indicates that the depression precedes the Las Mellizas Formation. Thus, Las Mellizas ignimbrite should not be interpreted as the main unit related to the Caviahue caldera as it has been proposed by some authors. If the depression had indeed been formed by a collapse caldera, this event would be previous to the described sediments.
Two end‐member models have been proposed for the Paleogene Andean foreland: a simple W‐E migrating foreland model and a broken‐foreland model. We present new stratigraphic, sedimentological and ...structural data from the Paleogene Quebrada de los Colorados (QLC) Formation, in the Eastern Cordillera, with which to test these two different models. Basin‐wide unconformities, growthstrata and changes in provenance indicate deposition of the QLC Formation in a tectonically active basin. Both west‐ and east‐vergent structures, rooted in the basement, controlled the deposition and distribution of the QLC Formation from the Middle Eocene to the Early Miocene. The provenance analysis indicates that the main source areas were basement blocks, like the Paleozoic Oire Eruptive Complex, uplifted during Paleogene shortening, and that delimits the eastern boundary of the present‐day intraorogenic Puna plateau. A comparison of the QLC sedimentary basin‐fill pattern with those of adjacent Paleogene basins in the Puna plateau and in the Santa Bárbara System highlights the presence of discrete depozones. These reflect the early compartmentalization of the foreland, rather than a stepwise advance of the deformation front of a thrust belt. The early Tertiary foreland of the southern central Andes is represented by a ca. 250‐km‐wide area comprising several deformation zones (Arizaro, Macón, Copalayo and Calchaquí) in which doubly vergent or asymmetric structures, rooted in the basement, were generated. Hence, classical foreland model is difficult to apply in this Paleogene basin; and our data and interpretation agree with a broken‐foreland model.
Since 2006 the Quantum Electronics and Plasma Physics (QEP) Research Group together with ENEA FusTech of Frascati have been working on dust re-suspension inside tokamaks and its potential capability ...to jeopardize the integrity of future fusion nuclear plants (i.e. ITER or DEMO) and to be a risk for the health of the operators. Actually, this team is working with the improved version of the "STARDUST" facility, i.e. "STARDUST-Upgrade". STARDUST-U facility has four new air inlet ports that allow the experimental replication of Loss of Vacuum Accidents (LOVAs). The experimental campaign to detect the different pressurization rates, local air velocity, temperature, have been carried out from all the ports in different accident conditions and the principal results will be analyzed and compared with the numerical simulations obtained through a CFD (Computational Fluid Dynamic) code. This preliminary thermo fluid-dynamic analysis of the accident is crucial for numerical model development and validation, and for the incoming experimental campaign of dust resuspension inside STARDUST-U due to well-defined accidents presented in this paper.
A loss of vacuum in a vessel, containing or not dust, is the typical case study considered in the STARDUST-UPGRADE facility of the Quantum Electronics and Plasma Group of the university of Rome Tor ...Vergata. This kind of accident was simulated numerically, without including the presence of dust, for two mass flow rates and three different inlet ports (C, E and F). Numerical settings are explained and the results obtained in each case are shown and discussed. At the end of the work, conclusions about what seen and further foreseen developments of this research are presented.
En este trabajo analizamos cómo en el Museo de La Plata (Argentina) las colecciones de restos humanos fueron intervenidas, identificadas, clasificadas, documentadas, exhibidas y guardadas entre los ...últimos años del siglo XIX y hasta la década de 1940. El análisis de archivos y publicaciones, la composición de los conjuntos óseos, los espacios de guarda y las características osteológicas permite afirmar, en primer lugar, que el criterio anatómico fue el privilegiado, pero no el único. Así se hicieron colecciones de cráneos, pelvis, huesos largos, esqueletos y preparados en formol, subdivididos a veces por regiones geográficas. En segundo lugar, la exhibición incorporó reordenamientos determinados por los curadores del museo y sus intereses de investigación, más que por políticas institucionales o intereses estatales. En tercer lugar, muchos cráneos y esqueletos fueron identificados y referenciados a veces como producto de memorias vagas u olvidos; luego, reordenados como resultado de la exhibición e investigación. Discutimos el impacto que estas prácticas tienen actualmente en los procesos de restitución a los pueblos indígenas.
The Palaeogene Maíz Gordo Formation is one of the main lacustrine events recorded in northwestern Argentina. It consists of sandstone, mudstone, and limestone beds 200 m thick, deposited in a ...brackish–alkaline lake and braided alluvial systems. The Maíz Gordo Lake evolved mainly as a closed system, with brief periods as an open one. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study samples from seven sites, corresponding respectively to proximal, intermediate, and transitional positions of the fluvial environment and marginal and inner-lake environment, focusing on the clay mineralogy and analcime formation. The basinward zonation of diagenetic minerals identified in the Maíz Gordo Lake was: mordenite → analcime → K-feldspar. Although not a typical zonation of saline–alkaline lakes, it does indicate an increase in salinity and alkalinity towards the centre.
In proximal fluvial settings, smectite predominates at the base of the sequence, with scarce kaolinite. Towards the top, a striking increase in kaolinite content suggests a change from a relatively arid climate with alternating humid and dry seasons, towards a warm and humid climate. Kaolinite content clearly decreases in a basinward direction. Such a variation is attributable to changes in hydro-geochemistry, denoting the progressive influence of the brackish and alkaline lake water on interstitial pores. SEM images of intermediate fluvial samples reveal authigenesis of illite at the expense of kaolinite booklets.
In littoral and inner-lake settings the clay fraction is composed of muscovite, sometimes with subordinate smectite. Analcime occurs in variable amounts in all sedimentary facies, in rock pores or filling veins. It forms subhedral square to hexagonal, or anhedral rounded crystals, denoting that they coarsened at low to moderate degrees of supersaturation. Although the mordenite identified in a fluvial level would have been the precursor of analcime in the Maíz Gordo Basin, no textural evidence of analcime formation through replacement of mordenite or other precursor zeolite was found. Hence it is more probable that analcime formation took place by direct authigenic precipitation or through the reaction between interstitial brines and clay minerals or plagioclase.
The limit between the Puna and the Eastern Cordillera is an area of geological complexity where Cenozoic tectonic, volcanic and sedimentary processes overlap. In this contribution, we describe the ...Early Miocene volcanic and subvolcanic manifestations located on the border between Northern Puna and Eastern Cordillera, analyzing their relationship with the foreland basin sedimentary succession. We present a new age of 17.94 ± 0.17 Ma (40Ar/39Ar hornblende) for the volcanic rocks, located in the middle Member of the Moreta Formation, as well as new geochemical analysis, showing andesitic-trachydacitic compositions belonging to the high K-calcalkaline series. In addition, we have studied the subvolcanic bodies intruded in the Río Grande Formation, from we which propose an early post-depositional emplacement. In both cases, we present brief considerations about the chemical composition of both study sites, since in the case of Moreta Formation the rocks are high K-calcalkaline andesites while in the case of Río Grande Formation, they are somewhat more undersaturated in silica and enriched in K (shoshonitic series). The new data we presented evinces an event of intra-foreland basin volcanism, mafic to intermediate in composition, at 18 Ma in the Northern Puna-Eastern Cordillera transition.
•Onset of volcanism at northern Puna-Eastern Cordillera limit is Early Miocene•Ductile emplacement of subvolcanic products revealed intra-basin volcanic events•∼18 Ma Río Grande Formation displays active intra-basin faults
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