Aconcagua is the highest mountain in the Americas and the tallest mountain in the world outside of the Himalayas. Located in the Andes Mountains of Argentina, near the city of Mendoza, Aconcagua has ...been luring European mountain climbers since 1883, when a German ge-ologist nearly reached the mountain's summit. (A Swiss climber finally made the ascent in 1897.) In this fascinating book, Joy Logan explores the many impacts of mountaineering's "discovery" of Aconcagua including its effect on how local indigenous history is understood. The consequences still resonate today, as the region has become a magnet for "adventure travelers," with about 7,000 climbers and trekkers from all over the world visiting each year.Having done fieldwork on Aconcagua for six years, Logan offers keen insights into how the invention of mountaineering in the nineteenth century-and adventure tourism a century later-have both shaped and been shaped by local and global cultural narratives. She examines the roles and functions of mountain guides, especially in regard to notions of gender and nation; re-reads the mountaineering stories forged by explorers, scientists, tourism officials, and the gear industry; and considers the distinctions between foreign and Argentine climbers (some of whom are celebrities in their own right).In Logan's revealing analysis,Aconcaguais emblematic of the tensions produced by modernity, nation-building, tourism development, and re-ethnification. The evolution of mountain climbing on Aconcagua registers seismic shifts in attitudes toward adventure, the national, and the global. With an eye for detail and a flair for description, Logan invites her readers onto the mountain and into the lives it supports.
The glacier to rock glacier transformation problem is revisited from a previously unseen angle. A striking case in the Juncal Massif (located in the upper Aconcagua Valley, Chilean central Andes) is ...documented. There, the Presenteseracae debris-covered glacier has advanced several tens of metres and has developed a rock glacier morphology in its lower part over the last 60years. The conditions for a theoretically valid glacier to rock glacier transformation are discussed and tested. Permafrost probability in the area of the studied feature is highlighted by regional-scale spatial modelling together with on-site shallow ground temperature records. Two different methods are used to estimate the mean surface temperature during the summer of 2014, and the sub-debris ice ablation rates are calculated as ranging between 0.05 and 0.19cmd−1, i.e., 0.04 and 0.17m over the summer. These low ablation rates are consistent with the development of a coherent surface morphology over the last 60years. Furthermore, the rates of rock wall retreat required for covering the former glacier at Presenteseracae lie within the common 0.1–2mmy−1 range, assuming an average debris thickness and a range of debris-covering time intervals. The integration of the geomorphological observations with the numerical results confirms that the studied debris-covered glacier is evolving into a rock glacier.
•We study a debris-covered glacier whose morphology is turning into rock glacier morphology.•The common criteria defining a rock glacier are thoroughly tested and verified.•Permafrost conditions exist at the site with low sub-debris ice ablation rates.•According to potential debris-covering times, the glacier sediment store is consistent with common rock wall retreat rates.•The glacial landscape is shifting towards a periglacial landscape.
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The mummy of a seven-year-old child that was discovered in 1985 in Cerro Aconcagua (Mendoza, Argentina) was likely part of an Inka sacrificial religious practice known as capacocha. Previous ...uniparental DNA marker studies conducted by some scholars have suggested that the mummified child may be related to the southern Andean population of Peru. However, autosome genome-wide analysis performed by others has indicated that the child was more closely related to the population along the northern Peruvian coast than to that of the southern Andes. In this study, we aimed to determine possible genealogical connections in the male lineage of the mummified child. To achieve this, we compared the genetic profile of the mummy with an extensive database of contemporary individuals from the northern Peruvian coastal and southern Andean regions. We used single nucleotide polymorphisms and short tandem repeats from the nonrecombining region of the Y-chromosome for our analysis. Our results confirmed that the Inka child mummy was closely related to individuals from the north coast of Peru. This suggests that the child was likely descended from the Muchik–Chimor-speaking people.
The Andean belt is the only present‐day active case example of a subduction‐type orogeny. However, an existing controversy opposes classical views of Andean growth as an east verging retro wedge, ...against a recently proposed bivergent model involving a primary west vergent crustal‐scale thrust synthetic to the subduction. We examine these diverging views by quantitatively reevaluating the orogen structural geometry and kinematics at the latitude of 33.5°S. We first provide a 3‐D geological map and build an updated section of the east vergent Aconcagua fold‐and‐thrust belt (Aconcagua FTB), which appears as a critical structural unit in this controversy. We combine these data with geological constraints on nearby structures to derive a complete and larger‐scale section of the Principal Cordillera (PC) within the fore‐arc region. We restore our section and integrate published chronological constraints to build an evolutionary model showing the evolving shortening of this fore‐arc part of the Andes. The proposed kinematics implies uplift of the Frontal Cordillera basement since ~20–25 Ma, supported by westward thrusting over a crustal ramp that transfers shortening further west across the PC. The Aconcagua FTB is evidenced as a secondary east verging roof thrust atop the large‐scale basement antiform culmination of the Frontal Cordillera. We estimate a shortening of ~27–42 km across the PC, of which only ~30% is absorbed by the Aconcagua FTB. Finally, we combine these findings with published geological data on the structure of the eastern back‐arc Andean mountain front and build a crustal‐scale cross section of the entire Andes at 33.5°S. We estimate a total orogenic shortening of ~31–55 km, mainly absorbed by crustal west vergent structures synthetic to the subduction. Our results provide quantitative key geological inferences to revisit this subduction‐type orogeny and compare it to collisional alpine‐type orogenic belts.
Key Points
Three‐dimensional structural map and revisited geological cross section of the Aconcagua fold‐and‐thrust belt at 33°S and 33.5°S
Kinematics of crustal deformation and shortening of the Central Andes at 33.5°S since ~20–25 Ma
Bivergent crustal‐scale model of the Andes at 33.5°S with a total orogenic shortening of ~31–55 km
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We assess the role of inherited structures on the Meso‐Cenozoic tectonic evolution of the main Andean Cordillera in central Chile (33°30′S‐34°S). Based on extensive field mapping, U‐Pb geochronology ...and palinspastic restorations along the Yeso and Volcán river valleys, we propose a tectono‐stratigraphic model for the evolution of a hybrid fold‐and‐thrust belt, originated from the inversion of Mesozoic extensional basins. With these results, we highlight the structural graben configuration of the Yeguas Muertas and Nieves Negras depocenters, as evidenced by synextensional deposition of the Río Damas and Lo Valdés Formations, controlled by normal faulting. The uppermost Cretaceous evolution can be approached through the analysis of the Las Coloradas Unit (ULC), which overlies the volcanic rocks of the upper Colimapu Formation and can be correlated, north of 32°S, with the Juncal Formation, and south of 35°S, with the Plan Los Yeuques Formation. The contractional Neogene‐Quaternary deformation in the fold‐and‐thrust belt domain studied in this work, accommodated 27–28 km of minimum crustal shortening. The Neogene‐Quaternary deformation that generated the final uplift of the Andes, has a close relationship with preexisting inverted Mesozoic structures. These structures deform the volcano‐sedimentary Abanico Formation, deposited since the late Eocene, based on new U‐Pb detrital zircon data. We propose that the active seismicity observed in the eastern border of the Principal Cordillera, located to the east of Santiago, can be associated with major crustal faults, as the Estero de Yeguas Muertas‐Baños Colina fault system and the Chacayes‐Yesillo fault.
Key Points
The geochronological new data confirm the Andean Jurassic arc as a sediment source for the Río Damas Formation
The geometry of the western AFTB is controlled by heterogeneities inherited from the Neuquén Basin
The Chacayes‐Yesillo fault and the root of the Estero de Yeguas Muertas‐Baños Colina fault system concentrate the recent seismic activity
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Previous geologic studies and structural interpretations of the Meso-Cenozoic units in the Andean Principal Cordillera, between 32°- 33°S, have faced many difficulties due to the strong variability ...in volcanic deposits' thickness, the structural complexity that affects the involved units, and the scarcity of geochronological data that prevents defining a clear boundary between them. Structural-lithologic work carried out between 32°45′-33°S allowed us to recognize and define 4 different lithologic units along the Aconcagua-Juncal river valleys: one marine sedimentary unit assigned to the Cretaceous Mendoza Group and Late Jurassic exposures from the Río Damas/Tordillo Formation, and 3 volcano-sedimentary units mainly associated with Cenozoic volcanism represented by the Farellones, Abanico, and Cristo Redentor formations. The stratigraphic-structural model proposed in this work also allows for defining 3 structural domains throughout the study area: a western domain close to the Pocuro Fault Zone, a central domain, and an eastern domain close to the Alto del Juncal Fault Zone, next to the Chile-Argentina international border. The western and central domains show folds with larger wavelengths than the eastern domain, while the eastern domain shows intense deformation related to the emplacement and evolution of the Aconcagua fold and thrust belt. This deformation results from tectonic events which mainly occurred between the Upper Oligocene and Miocene. In the study region, these events caused a minimum shortening of ∼30 km in the Principal Cordillera. Based on the collected information, the Alto del Juncal Fault is also interpreted as the eastern Abanico basin bounding fault in which the Aconcagua fold-thrust belt is rooted.
•We perform a stratigraphical and structural mapping at the Principal Andes between 32°45′ and 33°S.•We recognize and define 4 different lithologic units along the Aconcagua-Juncal river valleys.•We recognize and define 3 structural domains throughout the study area.•We propose the Alto del Juncal Fault as the eastern Abanico basin bounding fault in which the AFTB belt is rooted.•A tentative evolution of the studied region from the late Eocene to the late Pliocene is presented.
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In Central Chile, the increment of withdrawals together with drought conditions has exposed the poor understanding of the regional hydrogeological system. In this study, we addressed the Western ...Andean Front hydrogeology by hydrogeochemical and water stable isotope analyses of 23 springs, 10 boreholes, 5 rain-collectors and 5 leaching-rocks samples at Aconcagua Basin. From the upstream to the downstream parts of the Western Andean Front, most groundwater is HCO3-Ca and results from the dissolution of anorthite, labradorite and other silicate minerals. The Hierarchical Cluster Analysis groups the samples according to its position along the Western Andean Front and supports a clear correlation between the increasing groundwater mineralization (31–1188 μS/cm) and residence time. Through Factorial Analysis, we point that Cl, NO3, Sr and Ba concentrations are related to agriculture practices in the Central Depression. After defining the regional meteoric water line at 33°S in Chile, water isotopes demonstrate the role of rain and snowmelt above ~2000 m asl in the recharge of groundwater. Finally, we propose an original conceptual model applicable to the entire Central Chile. During dry periods, water releases from high-elevation areas infiltrate in mid-mountain gullies feeding groundwater circulation in the fractured rocks of Western Andean Front. To the downstream, mountain-block and -front processes recharge the alluvial aquifers. Irrigation canals, conducting water from Principal Cordillera, play a significant role in the recharge of Central Depression aquifers. While groundwater in the Western Andean Front has a high-quality according to different water uses, intensive agriculture practices in the Central Depression cause an increment of hazardous elements for human-health in groundwater.
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•Central Depression aquifers receive recharge from mountain-block and -front area.•Focused recharge originates from rain and snowmelt above 2000 m asl.•Mountain recharge processes are critical for an effective water management.•At San Felipe alluvial aquifer, there is anthropogenic recharge by irrigation canals.•Agriculture impacts the groundwater quality in the Central Depression aquifers.
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The Chilean Central Andes near Santiago are a semi-arid region with substantial frozen water reserves in their high altitude cryosphere. Millions of people depend on the Andean cryosphere for ...freshwater supply. Over the last sixty years, global warming has altered the mountains’ water balance, as the temperature rose, precipitation decreased, and deglacierization exposed hundreds of square kilometers. The distribution of solid water stored in soil permafrost and the potential effects of climate change on it are unknown.
Here, we map favorable spots for permafrost occurrence at the “Monos de Agua” catchment, Aconcagua basin at 33°S, between 3600 and 5100 m a.s.l.. We identify these “cold spots” based on ground surface temperature and incoming solar radiation between 2017 and 2019. We suggest that these locations currently present permafrost and frozen water might actually be there. We confirmed a body of frozen water at one of these cold spots using an electrical resistivity survey.
Our mapping suggests that at least 15 ± 7% of the catchment's surface is underlain by permafrost. Permafrost occurrence begins around 3600 m a.s.l. with low probability and only at locations with favorable conditions of low exposure and isolation. Permafrost occurrence probability increases with altitude, with the largest fraction present above 4200 m a.s.l.
Our results suggest that the permafrost area in this region will decrease between 13 and 87% by the end of the century under the future global warming RCP scenarios. This event represents new challenges for the hydrological memory and water security planning in the Chilean Central Andes.
•We assessed mountain cryosphere elements within protected, water scarce areas.•Permafrost occurrence was confirmed, and its distribution was mapped.•A feedback between permafrost distribution and deglacierization is discussed.•Permafrost evolution, current and future distribution upon warming is presented.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The Jurassic-Cretaceous Mendoza Group is one of the most distinctive lithostratigraphic units of the widely surveyed Neuquén basin. This work focuses on its development in the Aconcagua basin, which ...crops out at the Aconcagua fold-and-thrust belt in the Principal Cordillera, and contrasts with its evolution in the main Neuquén basin by remarkable differences. By logging a series of stratigraphic sections, we performed a detailed revision of the Mendoza Group's stratigraphy and contact relations along the Blanco River valley (∼33°S). We reassigned several outcrops to the Mendoza Group based on our field observations and recent research, updating the current geological map of the study area. We identified an irregular development of the lower contact relation with the Auquilco Formation that denotes the existence of a paleo-topography at the time of deposition of the upper beds of the Mendoza Group. Moreover, we dismissed previous proposals of a lateral interfingering relation with the Juncal Formation, and in place, we describe an angular unconformity with an overlying Upper Miocene volcanic unit. Additional insight from the redefinition of the upper contact is brought by the characterization of an erosive surface at the top of the Mendoza Group, and the identification of a period of subaerial platform exposition and erosion. A previous paleogeographical model shows a good fit with the observed facies along the Blanco River valley and can be extended towards southern latitudes. Differences in the development of the Mendoza Group in the Aconcagua basin and the main Neuquén basin have been acknowledged, and a potential origin of this unusual behavior has been explored in the reactivation of an Early Jurassic structural high.
•A paleotopography has been identified towards the late Kimmeridgian-early Tithonian.•A traditional interfingering relation contact with the Cretaceous volcanic arc has been dismissed.•The anomalous development of the Mendoza Group in the study area may be related to a reactivation of early Jurassic structures.
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The Mountain-Block Recharge (MBR), also referred to as the hidden recharge, consists of groundwater inflows from the mountain block into adjacent alluvial aquifers. This is a significant recharge ...process in arid environments, but frequently discarded since it is imperceptible from the ground surface. In fault-controlled Mountain Front Zones (MFZs), the hydrogeological limit between the mountain-block and adjacent alluvial basins is complex and, consequently, the groundwater flow-paths reflect that setting. To cope with the typical low density of boreholes in MFZs hindering a proper assessment of MBR, a combined geoelectrical-gravity approach was proposed to decipher groundwater flow-paths in fault-controlled MFZs. The study took place in the semiarid Western Andean Front separating the Central Depression from the Principal Cordillera at the Aconcagua Basin (Central Chile). Our results, corroborated by field observations and compared with worldwide literature, indicate that: (i) The limit between the two domains consists of N-S-oriented faults with clay-rich core (several tens of meters width low electrical-resistivity subvertical bands) that impede the diffuse MBR. The “hidden recharge” along the Western Andean Front occurs through (ii) focused MBR processes by (ii.a) open and discrete basement faults (mass defect and springs) oblique to the MFZ that cross-cut the N-S-oriented faults, and (ii.b) high-hydraulic transmissivity alluvial corridors in canyons. Alluvial corridors host narrow unconfined mountain aquifers, which are recharged by indirect infiltration along ephemeral streams and focused inflows from oblique basement faults. This study also revealed seepage from irrigation canals highlighting their key role in the recharge of alluvial aquifers in the Central Depression. The proposed combined geophysical approach successfully incorporated (hydro)geological features and geophysical forward/inverse modelling into a robust hydrogeological conceptual model to decipher groundwater flow-paths in fault-controlled MFZs, even in the absence of direct observation points.
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•The study of faults in mountain settings is essential for water resources management.•NS oriented clay-rich faults are hydrogeologic barriers for mountain block recharge.•Oblique basement faults and alluvial corridors drive mountain block recharge.•Irrigation canals play a key role recharging alluvial aquifers in Central Chile.•The combined geophysical approach allows properly assessing mountain block recharge.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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