Cenozoic plutonism geochemistry in the extra-andean southern Patagonia as evidences of arc migration process

In this work, we present the results of the first study which involves most of several cenozoic satellite plutons located in a 'back-arc' position in west Patagonia, south of the present Chile Triple-Junction. 4 plutons were studied in the northern tip, and 3 in the southern one. The petrographic and geochemical character of these plutons is different enough between them to propose a further classification for them: alkaline (sensu stricto): only the Monte Balmaceda Igneous complex, in the southern extremity; "intra-plate transitional" calc-alkaline: Río de Las Nieves and San Lorenzo plutons in the northern area, and the Torres del Paine Igneous Complex, in the southern area; and "arc transitional" calc-alkaline: the Paso de Las Llaves and Cerro Negro del Ghío plutons in the northern area, and the Cerro Donoso Pluton in the southern area. The "transitional" character, together with the plutons location, and regional context, can be explained by a Mio-Pliocene eastward arc migration coeval with the beginning of the Chile Rise subduction . Slab flattening hypothesis is favoured to explain the arc-migration, and together with the different length and time of arrival of the Chile Rise segments, contributed to the plutons heterogeneous geochemistry.

Scratching the discs: evaluating alternative hypotheses for the origin of the Ediacaran discoidal structures from the Cerro Negro Formation, La Providencia Group, Argentina

In the Ediacaran marine succession of the Cerro Negro Formation (Tandilia System, NE Argentina), abundant microbially induced sedimentary structures indicate general conditions of substrate biostabilization. Numerous discoidal structures in this succession were previously interpreted as moulds of soft-tissue holdfasts of sessile organisms, within the form genus Aspidella. In this study, we performed a detailed re-analysis of some of these features and discuss two alternative hypotheses to explain their genesis: (1) as the result of soft-sediment deformation and fluid injection structures; and (2) as structures of active animal–sediment interaction (i.e. trace fossils). We show that the dome-shaped discs are internally laminated, with a cylindrical to a funnel-shaped vertical tube at their central region. The presence of these downwards vertical extensions and other intricate internal arrangements cannot be explained under the taphonomic spectrum of discoidal fossils, but shows striking similarities to Intrites-like structures and other sand-volcano-like pseudofossils (e.g. Astropolithon). However, some structures are hard to distinguish from vertical dwelling burrows with funnel-shaped apertures and thick-lined walls, commonly produced by suspension- and detritus-feeding invertebrates (e.g. Skolithos isp., Monocraterion isp. and, less likely, Rosselia isp.). Since reliable age constraints are unavailable, and further investigation concerning other palaeobiological indicators is needed, the most parsimonious hypothesis is that of a structure derived from fluid-escape processes. Our study demonstrates the importance of detailed investigation on discoidal structures in either upper Ediacaran or lower Cambrian strata.

Incorporation of Rheological Characterization in Grinding and Tailings Slurries to Optimize the CMP Magnetic Separation Plant

Compañía Minera del Pacífico (CMP) is the main iron producer on the Pacific coast of the American continent. The Cerro Negro Norte (CNN) operation of CMP is facing important challenges, such as the processing of low-grade ores containing complex gangue minerals which negatively affect the performance of the magnetic separation, grinding and solid–liquid separation stages. CMP is working on a program, aimed at optimizing the efficiency of the CNN plant, which considers a rheological characterization of the slurries produced by the different ores treated, information which will be useful to optimize the performance of the physical separation processes. The objective of this work was to characterize the slurries obtained from the secondary grinding and tailings thickener stages through rheological measurements. The rheological data were correlated with the physical, chemical and mineralogical characteristics of the different geological units (GU) tested. The results show that the rheological flow curves of the slurries taken from the secondary grinding product display a pseudoplastic behavior which follows a Casson model pattern. An exponential model was used to correlate the Casson yield stresses with the solids content of the slurries taken from the secondary grinding product. The results of this fitting process indicate that the yield stresses increase with the % −325# Tyler mesh and with the percentage of minerals with a tendency to generate fines (MTF = smectite + illite/mica + talc + chlorite + kaolinite), and in contrast the yield stresses decrease with the ore iron grade (Fe). For the tailings characterization, the results of settling rates and turbidity values of the supernatant obtained from tests with different GU samples show no significant differences. A linear regression model was used to correlate the results of yield stresses of compacted tailings with the chemical and mineralogical characteristics of the GU. The results of the fitting process indicate that the MTF content in the head ore samples influence the rheological properties of the tailings, which correlates with the behavior of the secondary grinding product. The increase in the GU iron grades also reduced the Casson yield stress. The experimental results were explained in terms of the microrheological effects and the physicochemical properties of the different types of phyllosilicates existing in the ore samples tested in this work.

Muon Tomography sites for Colombian volcanoes

By using a very detailed simulation scheme, we have calculated the cosmic ray background flux at 13 active Colombian volcanoes and developed a methodology to identify the most convenient places for a muon telescope to study their inner structure. Our simulation scheme considers three critical factors with different spatial and time scales: the geo-magnetic effects, the development of extensive air showers in the atmosphere, and the detector response at ground level. The muon energy dissipation along the path crossing the geological structure is modeled considering the losses due to ionization, and also contributions from radiative Bremßtrahlung, nuclear interactions, and pair production. By examining each particular volcano topography and assuming reasonable statistics for different instrument acceptances, we obtained the muon flux crossing each structure and estimated the exposure time for our hybrid muon telescope at several points around each geological edifice. After a detailed study from the topography, we have identified the best volcano to be studied, spotted the best points to place a muon telescope and estimated its time exposures for a significant statistics of muon flux. We have devised a mix of technical and logistic rules –the “rule of thumb” criteria– and found that only Cerro Machín, located at the Cordillera Central (4°29'N 75°22'W), can be feasibly studied today through muography. Cerro Negro and Chiles could be good candidates shortly.

Characterization of Tectonic - Magmatic Seismic Source at Chiles - Cerro Negro Volcanic Complex (CCNVC)

<p>The Chiles - Cerro Negro Volcanic Complex (CVCCN) is located in the Western cordillera at the Ecuador – Colombia border. This volcanic complex has showed an anomalous seismic activity since late 2013, with high activity peaks in 2014, specially in October and November with up to 6000 earthquakes per day mostly volcanic-tectonics events. The most important earthquake in this sequence occurred on October 20, 2014 with a 5.7 Mw. In order to obtain a better characterization of the seismic source in the CVCCN area, a new 1D velocity model was computed using 300 earthquakes with magnitudes larger than 3.0 MLv, and high quality of P and S pickings.  This model has 8 layers over a semi-space and starts with a Vp = 2.96 Km/s and  Vs = 1.69 Km/s highlighting strong variations at 7km with Vp = 5.87 Km/s and  Vs = 3.52 Km/s and at 24 km Vp = 6.58 Km/s and  Vs = 3.79 Km/s . A value of 1.73 of Vp/Vs was determined, which is a normal for the continental crust. Computed hypocenters with the new velocity model highlighted two sources: one is defined by a concentration of shallow earthquakes on the southern flank of Chiles Volcano, and the second one contains events deeper than 7 km and follows a N-S tectonic structure that crosses the CVCCN and matches the Cauca-Patía fault. This structure obtained with this new model is confirmed by interferograms from Sentinel images after the earthquake MLv 4.2 of September 27, 2019 where a mostly dextral movement is defined. Focal mechanisms were computed for earthquakes larger than MLV 4.0 using waveform inversion (SeisComp3). Most events show ~N-S planes and dextral with inverse component. Focal mechanisms exhibit a Non-Double Couple component (CLVD), which in most of these events is more than 40 percent including the CLVD = 71% calculated for the earthquake of Mw 5.7 on October 20, 2014. This value suggests the presence of a volumetric component that could be induced by magma or fluid movements. This is corroborated by the presence of LP and VLP events inside of the CVCCN system.</p>

Magnetostratigraphy and Carbon isotopes of Ediacaran Avellaneda Formation, Rio de La Plata Craton, Argentina

<p>The Ediacaran Period (635-542 Ma) witnessed a series of extraordinary events. It arises with the end of the Marinoan Glaciation and deposition of worldwide enigmatic cap carbonate deposits. This abrupt shift in paleoclimatic conditions coincides with major fluctuations in the  isotope ratios of carbon and sulfur, and with significant changes in the concentration of redox-sensitive elements in marine sediments. The Ediacaran is also a period marked by rapid changes in geomagnetic polarity. Magnetostratigraphy may therefore provide high-resolution correlation between Ediacaran successions worldwide. Here, we combine stratigraphy logs, carbon isotopes and magnetostratigraphy on the Avellaneda Formation (590-560 Ma) which at the Rio La Plata Craton, eastern Argentina. We investigated two drill cores (TSE-34 and TSE-7) with a 0.3-0.7 m resolution covering the entire Avellaneda Formation, corresponding to 98 standard specimens (25 mm in diameter). The basal contact of the Avellaneda Formation with the underlying mudstone rocks from Loma Negra Formation (~ 590 Ma) is present in both cores. The upper contact with the Alicia Formation, only observed in TSE-34 core, is transitional. The TSE-7 displays an erosional contact between Avellenda and Cerro Negro Formations (~ 560 Ma). After stepwise thermal demagnetization up to 600°C, almost all samples provided a characteristic magnetization between 350°C and 600°C, therefore Ti-poor magnetite or titanohematite is likely the main carrier of the stable remanence in these rocks. A high-temperature, dual-polarity component is persistent and coherent in the two drill cores. The base of the unit is marked by normal polarity, followed by a reverse interval, followed by persistent normal polarity across to the upper part of the Avellaneda Formation. This magnetostratigraphic framework, together with the carbon isotope signal, will be compared with results recently obtained for potentially coeval successions in China, Canada and United States.</p>

Geothermal Energy in Colombia as of 2018

Colombia is a country with great potential for the exploitation of geothermal energy due to its high volcanic activity caused by the subduction between the Nazca and South American tectonic plates. However, this energy is yet to be exploited. This article seeks to describe, by means of a literature review and information processing, the current status of geothermal energy in Colombia, including the current regulations, the limitations, the recommendations to develop the geothermal energy, and some of the most important projects, studies, and research papers that have been emerged on the discovery, exploration, and exploitation of geothermal energy within the country, emphasizing the areas where exploration projects have been initiated, such as the Nevado del Ruiz volcano, the Tufiño–Chiles–Cerro Negro volcanic system, the Azufral volcano geothermal area, and the Paipa geothermal area. Over the years, energy vulnerability in Colombia and a government policy of fostering sustainable development in different territories have generated favorable conditions for the exploitation of geothermal resources. Nevertheless, there are several technical, infrastructural, legal, and institutional barriers that slow the proper development of these projects.

Caracterización florística de las especies de aprovechamiento apícola en el complejo volcánico “Pilas el Hoyo”

El estudio se llevó a cabo en el área protegida “Complejo Volcánico Cerro Negro – Pilas – El Hoyo”, ubicada a 25 km al este de la ciudad de León. El objetivo de este estudio fue caracterizar las especies melíferas de la zona. Mediante la presente investigación los apicultores tendrán mayor conocimiento sobre las especies melíferas y su disponibilidad durante el año. Se eligieron 7 apiarios activos distribuidos entre la comunidad de Miramar y la comarca de los Terreros, donde se realizaron 4 muestreos semanales por apiario usando transectos de 20m x 50 m, tomando como punto de partida los apiarios para identificar y contar el número de especies de aprovechamiento apícola. Los datos obtenidos fueron exportados a Excel. Se identificaron 89 especies pertenecientes a 39 familias, dividas en: 59 especies de árboles, 15 especies de arbustos y 15 especies de hierbas. Las familias con mayor abundancia en árboles fueron las Bignoniáceae, Myrtaceae, Fabácea, Ebenácea y Boraginácea; en arbustos son la Verbenácea, Boraginaceae, Fabaceae, Apocynaceae y Solanaceae; en hierbas son la Plantaginacea, Malvaceae, Sterculiaceae, Lamiaceae y Convolvulacea. El uso de la tierra en los apiarios muestra un 53% de bosque silvestre, 12% de barbecho, 8% de maní, 12% entre maíz y sorgo, 9% entre eucalipto, frijol blanco y yuca, 4% entre potreros y caña, 2% entre pastizales y ajonjolí. Existe una mayor floración entre los meses de Diciembre a Mayo. De Junio a Noviembre hay escasez de floración, este fenómeno se trata de compensar con especies de floración prolongada y cultivos.