Andean Geology最新文献

{"title":"Geochronology of the Real Cordillera, the inner magmatic arc of Bolivia","authors":"A. R. Iriarte, U. Cordani, Kei Sato","doi":"10.5027/ANDGEOV48N3-3326","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N3-3326","url":null,"abstract":"The Real Cordillera granitoids are a suite of Triassic and Oligocene plutons located at the core of the Eastern Cordillera of the Central Andes of Bolivia. Its geotectonical setting, chemical and ore composition make them part of the so called “Inner Magmatic Arc” which differs from the actual “Magmatic Arc” located immediately to the west. U-Pb SHRIMP ages were obtained in order to constrain their crystallization ages. The Triassic group yielded the following results: 240 ± 2 Ma for the Huato granite, 230.7 ± 1.3 Ma for the Illampu granodiorite, 222.2 ± 2.4 Ma for the Huayna Potosí granite and 221.9 ± 1.5 Ma for the Taquesi granodiorite. For the Oligocene group we obtained two ages of 26.87 ± 0.26 and 26.88 ± 0.21 Ma both for the Quimsa Cruz granite. Mafic enclaves from the Illampu and Taquesi granodiorites report ages that were older than their respective granitoid hosts, yielding 234.1 ± 1.3 Ma and 227 ± 1.3 Ma, respectively. Secondary processes related to regional thermal anomalies and magmatic melt-enrichment, reset the K/Ar and U/Pb isotopic systems, producing: a) younger ages by Ar loss and b) older ages by U/Pb isotopic ratios reorganization. As noted in previous studies, the Zongo/Kuticucho Triassic granite yielded extremely high U enrichment in most zircon analysed, producing reset of U/Pb ratios, wide span in age ranges and reverse discordia curves that obscure its actual crystallization age. Relatively abundant zircon inheritance was found in these “cold” and inheritance-rich granitoids, with ages suggesting provenance from early Paleozoic metapelites that also recycled older sources. This relatively abundant xenocrystic inheritance records the influence of the Gondwanide orogeny (336-205 Ma) as an overall subduction arc environment, punctuated at its final stage with the imprint of a continental rifting (245-220 Ma).","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":" ","pages":""},"PeriodicalIF":0.9,"publicationDate":"2021-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47583354","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Holocene tephra layer within coastal aeolian deposits north of Caleta Olivia (Santa Cruz Province, Argentina)","authors":"G. Zanchetta, M. Pappalardo, A. Roberto, M. Bini, I. Arienzo, I. Isola, A. Ribolini, G. Boretto, Enrique Fuck, D. Mele, M. D’Orazio, F. Marzaioli, I. Passariello","doi":"10.5027/ANDGEOV48N2-3290","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N2-3290","url":null,"abstract":"In this paper we illustrate the stratigraphy, geochronology, and geochemistry (major, minor, trace elements and Sr-isotopes) of a Holocene tephra layer found within coastal sedimentary deposits north of Caleta Olivia (Santa Cruz Province, Argentina). The stratigraphic succession comprises beach deposits with basal erosive surface resting on the local substrate (“Formacion Patagonia”) followed by a poorly developed paleosoil. The paleosoil is covered by a lenticular fine-grained (Mdφ: 5.2, 0.027 mm), well sorted (σφ: 1.2) volcanic ash layer and aeolian sands. The geochemical composition of shard fragments points to an origin from the Hudson volcano, located in the southern Andes, ca. 400 km to the west. The geochemistry, Sr-isotopes and the radiometric constraints (younger than the age of the underlying marine layer dated at ca. 4,100 a cal BP) further allow correlating this tephra with the so-called H2 eruption (ca. 3,900 a cal BP). This finding is of interest owing to the poor preservation potential of tephra within the Late Holocene sedimentary deposits of the Atlantic coast of Patagonia and represents the first finding of H2 eruption in this area, improving our knowledge of the dispersion of the fine-grained distal deposit of the Hudson volcanic explosive activity, thus allowing a better estimate of the eruptive dynamics and the risks associated with the Hudson volcano.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":"48 1","pages":"267-280"},"PeriodicalIF":0.9,"publicationDate":"2021-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48180728","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Magnetic fabric of the Parashi stock and related dyke swarm, Alta Guajira (Colombia): The Caribbean-South American plates oblique convergence","authors":"C. Bustamante, C. Archanjo, A. Cardona, Marcela Restrepo","doi":"10.5027/ANDGEOV48N2-3332","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N2-3332","url":null,"abstract":"Anisotropy of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) were used to evaluate the emplacement history of the Parashi stock and related dyke swarm situated in NW Colombia. The average magnetic susceptibility of 4.5×10-2 SI, in conjunction with low-coercivity components provided by the isothermal remanence and thermomagnetic curves with net Verwey and Curie transitions, indicates that multidomain magnetite records the anisotropy directions. The similar orientation and shape of the AMS and AAR ellipsoids indicate the absence of very fine magnetite with an inverse fabric. The magnetic foliation is the best-defined fabric element in these rocks and outlines a concentric structure, elongated parallel to the NE-SW direction of the pluton. Crystallisation age of the stock and dykes (51-47 Ma), along with pressure of emplacement determination indicate that the stock and the dyke swarm probably formed simultaneously, and they were emplaced in the shallow crust (","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":"48 1","pages":"219"},"PeriodicalIF":0.9,"publicationDate":"2021-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45814297","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The first Peruvian record of Enchodus (Actinopterygii, Aulopiformes, Enchodontidae) in the Upper Cretaceous Vivian Formation","authors":"Soledad Gouiric-Cavalli, A. L. Cione, D. Tineo, L. Pérez, Martín Iribarne, Miguel A. Allcca Torres, D. Poiré","doi":"10.5027/ANDGEOV48N2-3337","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N2-3337","url":null,"abstract":"We describe isolated teleostean teeth found in no association with the jaw bone. The specimens have been recovered in Late Cretaceous marine deposits of the Vivian Formation in the Peruvian Sub-Andean Region. The deposition sequence from where the teeth come is interpreted as a shallowing-upward sequence of low salinity. The fish material is identified as Enchodus aff. E. gladiolus based on the presence of a small but well-developed post-apical barb, an anterior cutting edge, the crown is symmetrical in cross-section, have a sigmoidal profile, and bears strong ridges (=striations). The Peruvian material differs from the typical E. gladiolus teeth in having a faintly serrated anterior cutting edge which is absent in most specimens referred to E. gladiolus. We also highlight that taxonomic assignments made based on isolated teeth must be taken with care. Despite scarce, the material recovered denotes that the marine units of Peru can give valuable information about the Pacific fish fauna during the Late Cretaceous.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":"48 1","pages":"303-315"},"PeriodicalIF":0.9,"publicationDate":"2021-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45638907","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Remotely-sensed time series of rapid terrace formation in the Laguna del Viedma valley (Patagonia)","authors":"V. Thorndycraft","doi":"10.5194/EGUSPHERE-EGU21-14866","DOIUrl":"https://doi.org/10.5194/EGUSPHERE-EGU21-14866","url":null,"abstract":"<p>The Patagonian Andes were subject to a range of geophysical drivers of landscape incision during the Last Glacial Interglacial Transition and Early Holocene, including tectonic and isostatic uplift, and base level fall triggered by rapid lake drainage events. Deciphering the drivers of river system response during this period is complex, and magnitudes and timescales of landscape change are poorly constrained. Herein, a remotely sensed time series of modern lake elevation change and terrace development is investigated for the Laguna del Viedma valley (Argentina) as a modern analogue of Late Quaternary landscape evolution. The aim of the research was to constrain the timing of terrace formation following lake-level fall of the Laguna del Viedma over a ~35 year period from 1985-2019. The objectives were to: 1) use satellite imagery from the period 1985-2019 to document landform, glacier and lake changes in the study area; 2) use remotely sensed imagery to map the landforms of the Laguna del Viedma valley; and 3) analyse terrace elevations using GIS. In total 7 terrace surfaces were distinguished by remotely sensed geomorphological mapping. The highest, and vegetated, T1 terrace surface (+75 m) was likely formed at the end of the last Holocene neoglacial advance. Viedma glacier recession at this time caused the abandonment of an ice-lateral spillway and allowed a subglacial drainage pathway leading to less stable lake level elevations and terrace formation. Whether the abandonment of T1 was associated with the 4 ka or 0.15 ka neoglacial termination constrains ~45 m of incision, at a rate of 0.01-0.33 m/yr, down to the T3 floodplain level by 1985. There then followed ~20 m of incision to the T4 level, which must have occurred by 2006, constraining a minimum rate of incision of 0.95 m/yr. The time series demonstrates rapid terrace formation occurred by vertical incision and lateral erosion, with mass movements contributing to lateral terrace recession. The implications of the data-set are discussed within the context of the Late Quaternary palaeohydrology of Patagonia where lake level falls of 10s to 100s of metres occurred within most large river systems from 42-52 &#8304;S demonstrating that base level falls from lake drainage, and catastrophic floods events, were likely a major driver of landscape change in the region.</p>","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":" ","pages":""},"PeriodicalIF":0.9,"publicationDate":"2021-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46353675","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Quaternary glaciolacustrine deposits around a Triple Junction site: Paleolakes at the foot of the Northern Patagonian Ice field (Argentina and Chile)","authors":"F. Isla, M. Espinosa","doi":"10.5027/ANDGEOV48N1-3173","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N1-3173","url":null,"abstract":"The area involved by the triple junction between the South American, Nazca and Antarctic plates activity was affected by Quaternary glaciations. Before 12,800 yrs BP an extended ice field occupied the top of the Patagonian Andes, irradiating glaciers towards the east and the west dominantly. Towards the east, the ice melted in piedmont lakes; towards the west, fjords melted into the Pacific Ocean. The Upper-Pleistocene climate amelioration caused the recession of those glaciers. Some piedmont lakes reversed their Atlantic outflow towards to the Pacific Ocean. The glaciers retreat caused the fluvial reactivations along crustal former faults that were located below the ice. The Patagonian ice field became therefore split into present Northern and Southern fields. At the second largest lake of South America, the Buenos Aires-General Carrera Lake, the water level dropped from about 500 m over present mean sea level to 230 m. Several glaciolacustrine deposits from this area are indicating significant variations caused by climatic changes, volcanism and tectonics, differing in spatial and temporal magnitudes. The triple junction activity involved subduction of the Chile Ridge below the continental South American plate, volcanic activity and faulting. During the glacier melting the Baker River captured three eastern-moving glacial systems towards the southwest, towards the Pacific Ocean. This rapid event is thought to occur 12,800 yrs BP. The lowering of these glaciolacustrine systems should be also interpreted in terms of the tectonic activity in the region and considering other processes operating in the lakes and within the watersheds.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":" ","pages":""},"PeriodicalIF":0.9,"publicationDate":"2021-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44734945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Gold Deposits in Chile","authors":"J. Cabello","doi":"10.5027/ANDGEOV48N1-3294","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N1-3294","url":null,"abstract":"A review of gold and gold bearing base metals deposits in Chile, indicate the existence of at least six different type of ore deposits, most largely formed during the Cenozoic with predominance in the Miocene. Mesozoic deposits are common but less relevant regarding their size and gold content. These hydrothermal ore deposits are genetically associated with subduction related Andean arc magmatism. Due to its relationship with episodic magmatism migrating eastward, there is a tendency for the deposits to be in distinct, north-south trending, belts with a progressive west to east decrease in mineralization age. After analysing 82 cases in total, main gold concentration can be assigned to high-sulfidation epithermal and porphyry type deposits. Low-sulfidation epithermal, IOCG and mesothermal type appears as less relevant. Gold bearing copper deposits constitute an important part of Chile’s total gold production. Both IOCG type but especially porphyry copper deposits are and will remain as a substantial source to supplement the future output of the gold in the country. The 82 deposits with their tonnage and grade studied, represent a total gold content of 11,662 t equivalent to 375 Moz, excluding past production for those exploited. A number of probable gold bearing base metals high tonnage deposits (IOCG and porphyry copper) do not include their gold content in public format, hence the number delivered could be estimated conservative. Methodical geochronological, ore types and zonation studies are required to better appreciate this metallogenic setting widening current understanding and future exploration results.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":"48 1","pages":"1-23"},"PeriodicalIF":0.9,"publicationDate":"2021-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44247345","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mid-Cenozoic SHRIMP U-Pb detrital zircon ages from metasedimentary rocks in the North Patagonian Andes of Aysén, Chile","authors":"P. Quezada, F. Hervé, Mauricio Calderón Nettle, C. Fanning, R. Pankhurst, E. Godoy, O. Urbina, R. Suárez","doi":"10.5027/ANDGEOV48N1-3282","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N1-3282","url":null,"abstract":"Previously undated low-grade metamorphic rocks from the Puerto Cisnes-Queulat area (44°30’ S) contain detrital zircons of mid-Oligocene age (ca. 28 Ma). Their outcrops represent the easternmost occurrence of the late Oligocene to early Miocene marine volcano-sedimentary Traiguén Formation; previous correlation with the Paleozoic metamorphic basement of this sector of the North Patagonian Andes is thus refuted. A similar age and provenance were obtained for a paraconglomerate bed of the La Junta Formation ca. 80 km to the north, which is thought to represent a high-energy lateral facies variation of the Traiguén Formation. Miocene plutonic rocks of the North Patagonian Batholith intruded these metasedimentary rocks, generating a contact metamorphic aureole that reaches biotite grade and overprints a previous metamorphic fabric probably formed during closure of the Traiguén Basin. Similar young ages for metamorphic rocks located immediately west of the Liquiñe-Ofqui Fault Zone 300 km north, near Ayacara, suggest a regional pattern of earliest Neogene metamorphism and rapid exhumation in this segment of the Patagonian Andes.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":" ","pages":""},"PeriodicalIF":0.9,"publicationDate":"2021-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45961183","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influencia de cuerpos discordantes de distinta cohesión en la geometría estructural de fajas plegadas y corridas: aproximación sobre la base de un modelamiento analógico","authors":"M. Villarroel, Pamela Jara, R. Charrier","doi":"10.5027/ANDGEOV48N1-3280","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N1-3280","url":null,"abstract":"Lithological heterogeneities in a rock series deformed by the development of a fold-and-thrust belt (FTB) affects the pattern of the resulting structures. We present a series of analogue experiments to determine the effect caused on the deformation pattern of a FTB by the presence of cohesive bodies, like plutons or basement blocks that oppose greater resistance than the host rocks to contractional deformation. The influence of these bodies on the deformation pattern of the FTB was studied by incorporating discordant bodies with different cohesions within a stratified granular sequence with negligible cohesion. We describe two sets of experiments in which the inserted body presents low (Co1) and high (Co2) cohesion respectively. The experiments show a tendency of the structural pattern to curve around the inserted body and to migrate towards the deformation front or the foreland, even when the cohesive body is not exposed. In the first case (Co1) the thrusts cut across the cohesive body, while in the second one (Co2) the cohesive body is not faulted, but transferred towards the deformation front along a basal detachment. Comparison of these results with natural examples at different scales shows a high degree of coincidence in the structural patterns recognized in both cases. Two of the main characteristics of these patterns are the tendency of the thrust faults traces to avoid the cohesive body and adopt the geometry of its distal edge. In order to explain curvatures in natural structural patterns in fold-and-thrust belts, we suggest consider the presence of unexposed bodies with higher strength than their environment.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":" ","pages":""},"PeriodicalIF":0.9,"publicationDate":"2021-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47196311","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Caracterización estructural del sistema de ledges y clavos mineralizados del sector Cachinalito, mina El Guanaco, región de Antofagasta, Chile","authors":"S. Jovic, G. Páez, Matías Galina, D. Guido, Conrado Permuy Vidal, Luciano López, Stabro Kasaneva","doi":"10.5027/ANDGEOV48N1-3171","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N1-3171","url":null,"abstract":"The high sulfidation epithermal gold deposit El Guanaco is located in the Palaeocene-Lower Eocene metallogenic belt in the Antofagasta Region, northern Chile, 215 km SE of Antofagasta city. The deposit is characterized by a system of sub-parallel ledges made of vuggy silica and quartz enargite veins. In the Cachinalito sector, on the north western side of the ore deposit, the ledges system has a discontinuous linear morphology, with a general ENE-OSO orientation, consisting of many ledges segments that change abruptly in orientation, thickness, length and inclination. Grade analysis distribution, detailed mapping at deposit scale, and identification of individual structures (ledges) shows that one of the key factors in deposit genesis is the structural control. The structural analysis allowed visualizing the different segmentations within a general structure, considering the sizes, horizontal and vertical continuity, degree of connection between ledge segments of different orientations, as well as determining the orientations with greater development of mineralized structures. The distribution of the grades allowed to characterize and identify the ore shoots within the ledges, and to interpret the ascending pathways of the mineralizing fluids by dimensioning and separating the high- and low-grade mineralized sectors. This type of analysis and identification represents an important exploration tool and helps exploration and / or production drilling in this type of deposit.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":" ","pages":""},"PeriodicalIF":0.9,"publicationDate":"2021-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41985938","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}