Revista de la Asociación Geológica Argentina

U-Th-Pb chemical dating in monazite in the andalusite-garnet-staurolite-sillimanite schists of the Cushamen Complex (Chubut, Argentina): reconstructing the P-T-t path

2024-12-26T14:19:49+00:00

This study presents the first U-Th-Pb CHIME monazite dating in andalusite-garnet-staurolite-sillimanite schists from the Cushamen Complex (Chubut, Argentina). It represents the first age obtained by this method in Argentina. X-ray elemental distribution maps were performed to assess possible zoning patterns resulting in zoned monazites with Th depletion and Ce enrichment toward the rims. Results reveal a correlation between the polymetamorphic P-T evolution with three groups of ages calculated from punctual analyses of monazite with ages of ca. 354, 333 and 300 Ma, consistent with main metamorphic events identified regionally in North Patagonia.

Paleogeographic model to the Upper Section of Pozo D-129 Formation in Los Perales, West Flank San Jorge Gulf Basin.

2023-11-28T13:01:03+00:00

This study presents a workflow for seismic and geological interpretation of the Upper Section of the Pozo D-129 Formation in the western flank of the San Jorge Gulf Basin. By integrating seismic data with wellbore information, the distribution of potential hydrocarbon reservoirs is analyzed and understood. Rock samples and electrical well logs were examined to characterize the sedimentary succession and identify the locations of productive reservoirs within the Upper Section of the formation. Based on this analysis, a sedimentary model was developed, providing a coherent explanation for the spatial distribution of productive reservoirs in the study area.

Low-sulfidation epithermal systems related to the upper section of the Choiyoi Group in south-central of La Pampa province.

2024-07-22T21:50:47+00:00

Studies conducted in three hydrothermal alteration zones in La Pampa province have identified textures and mineral assemblages characteristic of low-sulfidation epithermal systems. The alteration styles include pervasive silicification, siliceous breccias, stockworks, and veins, exhibiting complex primary, replacement, and recrystallization textures, along with adularia displaying rhombic and pseudo-acicular morphologies. These features suggest that the system corresponds to an ascending boiling paleozone. This study represents the first reported occurrence of a low-sulfidation epithermal system in La Pampa province, potentially linked to Gondwanan magmatism based on the age of its host rocks.

Analysis Of The Horizontal Stress Field Acting On Vaca Muerta Formation In The Neuquen Basin, Argentina

2024-10-17T18:38:23+00:00

The Vaca Muerta Formation in the Neuquén Basin, Argentina, is a significant hydrocarbon reservoir characterized by complex geological and tectonic forces that influence the horizontal stress field. This study isolates and analyzes the orientations of maximum horizontal stress (SHmax) using borehole breakout for VacaMuerta Formation data from 30 wells across the basin. The results indicate a predominant SHmax orientation trending SW-NE to E-W, influenced by regional tectonic forces, including the convergence of the Nazca and South American plates and topographic axes. However, deviations in SHmax orientations towards SSW-NNE and SE-NW suggest additional controls by basement structures, notably Triassic-Jurassic hemi-grabens. The integration of breakout analysis with geological models highlights the interplay of first-, second-, and third-order stress controls, which are crucial for optimizing hydraulic fracturing strategies in this prolific shale formation. Understanding these stress regimes enhances the efficiency and sustainability of resource extraction in the Vaca Muerta Formation.

Multiscale petrotectonic control of gold mineralization in the El Bagre-Nechí District (Antioquia, Colombia): a review of previous model

2024-08-15T15:42:27+00:00

Existing data and new observations indicate that gold mineralization with grades in the order of tens of grams per tonne in quartz veinlets and hypogene sulphides in the El Bagre and Nechí districts is closely related to the Carboniferous granitic plutonism of the El Carmen stock and its analogue in the Nechí area. The ore bodies, tend to be preferentially located in flexures where the dilatant character of the controlling fractures increases. They are arranged in echelon patterns along NNW-trending kilometric corridors, preferentially subparallel to the contacts of the intrusive with its metamorphic country rock. This arrangement favours the influence of thermal volumetric contraction during late magmatic emplacement as a complementary mechanism controlling the distribution of mineralizing fluids. Since most of the mineralized bodies develop a mantiform geometry sub-parallel to the intrusive-host contact, they define a spatial relationship that is difficult to reconcile with an exclusively subvertical transcurrent environment attributed to the Otú Fault. Thus, a substantial involvement of petrotectonic control combined with differential thermal contraction-expansion of the granitic host rocks is suggested to dominate over the pre-existing structural model of fracture-related emplacement of the vetiform bodies in a transcurrent context. Therefore, the traditional relationship proposed for this mineralization with the activity of the Otú fault transcurrent corridor, associated with the Andean deformation, needs to be reconsidered as it produces temporal inconsistencies. Despite the limited surface expression and the thick edaphic cover, this alternative model favours the location of unexplored sectors with high potential to define remaining primary gold targets.

GEOMORPHOLOGICAL CHARACTERIZATION AND HYDROLOGICAL RESPONSE OF THE PULULOS AND CHAUPIJARA LAKE SYSTEMS (NORTHERN PUNA, ARGENTINA)

2024-04-08T13:09:38+00:00

The Chaupijara and Pululos lakes are part of the Vilama lake system (4500 m a.s.l.; Northern Puna of Jujuy), which is located in a little explored and studied area of the Central Andes, characterized by the absence of scientific information in large areas of knowledge. The present work focuses on the characterization and recent geomorphological and hydrological analysis (1975-2017) of these lakes, under highly variable and extreme climatic conditions that characterize this region. The aim is to understand the environmental and landscape dynamics associated with the recent hydrological response of these lakes to regional rainfall variability. To this end, hydrographic and geomorphological information was generated and integrated to identify and delimit various landforms and sub-environments associated with each lake. Likewise, the current functioning of both lake systems was analyzed considering the climatic periods with the most extreme droughts and precipitations of the last decades. This climatic variability and its effects on the landscape were analyzed and evaluated from changes reflected in the lake surfaces and in the different sub-environments during the extreme precipitation/drought stages identified. The results obtained evidenced the great environmental and landscape variability shown by these Andean systems in the face of interannual hydroclimatic changes. These outcomes are essential for understanding the geomorphological and environmental dynamics of these high-Andean lake systems and set a precedent for the analysis of how these ecosystems could be affected by future environmental conditions, especially in the context of current climate change.

Beach nourishment on the coast of Playa Dorada (Mar Chiquita, province of Buenos Aires): geomorphological and sedimentological changes in natural coastal dynamics

2024-10-07T18:31:21+00:00

In this contribution, we studied the case of a beach nourishment work completed in June 2022 on the coastal front of the Playa Dorada neighborhood, south of the Mar Chiquita district (37°52' 13"S - 57°30' 53"O) in the province of Buenos Aires, Argentina. The aim of this contribution is to analyze the geomorphological and morphometric changes of the beach before and after nourishment, the textural and compositional variations of the sediments, and the evolution of the deposit over time to estimate its durability.

The results show that the granulometric and compositional differences between the crushing material used for recharge and the original material did not considerably affect the durability of the work. In relation to geomorphological processes, an important participation of continental processes (fluvial, wind and mass removal) has been detected in the redistribution of sediments over marine processes, giving rise to the development of new morphologies in the beach profile, such as sand flows, alluvial fans and gullies.

The effectiveness of the work has been relatively good compared to other similar nourishments in the area. It is estimated that during the first year from the end of the work 42 % of the original material was lost and, regarding the useful life, approximately 50 % is lost after 16 months after the work is completed (in November 2023).

Estimation of the geothermal potential of the deep hydrothermal system in the Bahía Blanca area

2024-08-15T22:33:54+00:00

The objective of this work is to determine the geothermal potential of the Deep Hydrothermal System in the metropolitan area of Bahía Blanca, by estimating the thermal energy reserves and its capacity to generate electrical energy.

For this, the USGS volumetric “heat in place” method was implemented, in combination with the Monte Carlo simulation method. The heat stored in the reservoir, the recoverable heat, and the net extractable thermal and electrical powers will be determined based on the lifetime of the resource use, considering variations in the heat recovery and conversion factors.

The probability density functions of the parameters involved in the calculation of the reserves were adjusted according to measurement values obtained in previous hydrogeological and petrophysical studies.

Thus, for the Bahía Blanca area, a productive potential of 80 MW of net electrical power (745 MW of net thermal power) with probability > 0.5, and 25 MW of net electrical power (240 MW of thermal power net) with probability > 0.9, during a period of 10 years of uninterrupted use of the resource without reestablishment of the initial recoverable heat, were estimated.

From the analysis of the results, it is concluded that the Deep Hydrothermal System represents a geothermal resource with significant energy potential, and therefore with the possibility of being used as an alternative and complementary source of thermal and electrical energy supply to the Bahía Blanca region.

Stratigraphy and geochronology of the Naupa Huen Formation: implications for the North Patagonian Foreland

2024-09-25T18:23:07+00:00

The Naupa Huen Formation represents a sedimentary fluvial unit distributed across the North Patagonian Foreland and has been assigned to the late Oligocene – Early Miocene based on fossil content and stratigraphic relations. These observations have led to the correlation of the unit with continental synorogenic volcaniclastic deposits of the tectono-stratigraphic cycle configured the Patagonian Broken Foreland (PBF) during the Early to Middle Miocene Andean contractional regime. However, the stratigraphic and sedimentary characteristics, and the predominantly epiclastic composition of the Naupa Huen Formation, contrast with the depositional synorogenic features and volcaniclastic composition of other units preserved in the Neogene depocenters of the PBF. To understand the tectono-stratigraphic framework under which the Naupa Huen Formation was deposited, a stratigraphic and geochronological analysis using U-Pb LA-ICP-MS dating on detrital zircons was conducted. The results obtained in this study constrain the Naupa Huen Formation to the early Eocene – earliest Miocene, suggesting that its deposition corresponds to a tectono-stratigraphic cycle preceding the configuration of the PBF in the Early to Middle Miocene contractional regime, as previously proposed. Although the results presented have enabled the evaluation of possible stratigraphic correlations with different Paleogene units of the Patagonian Foreland, additional studies of this nature are necessary to further deepen the understanding of Cenozoic sedimentation in this region.

Petrology and Geochemistry of felsic and intermediate rocks from the south-central of La Pampa province, Argentina. Its correspondence with the Choiyoi magmatism.

2024-12-05T13:18:35+00:00

Permian and Triassic igneous rocks from La Pampa province were initially part of the Choiyoi magmatism later, this rocks where included in the Permian-Triassic Intracratonic Magmatic Corridor of La Pampa excluding them from Choiyoi magmatism because they were considered of intraplate environment with an anorogenic signature. Petrological and geochemical studies on ignimbrites, lavas and porphyries from south-central of La Pampa province, identified rocks with arc characteristics and with transitional characteristics between magmatic arc and intraplate. A comparative analysis with Permo-Triassic rocks from other sectors of La Pampa province and the San Rafael Block, Mendoza province indicates that south-central of La Pampa rocks have similar characteristics in geochemistry and age to the units of the lower and upper sections of the Choiyoi magmatism.