Pub Date : 2024-01-31DOI: 10.5027/andgeov51n1-3633
R. Pilger
Two segments of subduction of the Nazca plate beneath the South American plate occur at low angles based on seismic hypocenter locations, approaching nearly horizontal below ~100 km in depth. In contrast with most of the rest of the subduction zone, the two segments, beneath central Chile, and central and northern Peru, lack active volcanoes along the crest of the Andes and have more subdued topography to the east of the Andean crest. Each low-angle subduction segment occurs to the east of the intersection of inferred mantle hotspot traces on the Nazca plate with the Peru-Chile Trench: the Nazca ridge (at the southern part of the Peruvian segment), and the Juan Fernández island-seamount chain (offshore the Chilean segment). A third inferred trace, the Galápagos-Carnegie ridge, may be correlated with a zone on incipient low-angle subduction beneath Colombia. The importance of such hotspot traces in contributing to low-angle subduction beneath the Andes is strengthened by updated South American-Nazca plate reconstructions, including three oceanic hotspot traces, in comparison with a new isotopic date compilation of igneous rocks from the mountain range. The Juan Fernández hotspot trace, reconstructed from Pacific-hotspot models to the Nazca-Farallon plate, encountered the subduction zone offshore southern Peru ~65 Ma, broadening arc volcanism to the east; the trace-trench intersection migrated gradually and then rapidly southward, widening the arc east to Bolivia and northern Argentina; it then stabilized about 13 Ma offshore central Chile, producing the contemporary low-angle Pampean segment. The Juan Fernández hotspot may also have been responsible for formation of the Manihiki Plateau on the Pacific plate much earlier, ~125 Ma. The Easter-Nazca hotspot trace intersected the subduction zone beneath Colombia before ~50 Ma and migrated southward beneath Ecuador beginning ~15 Ma, with progressive low-angle subduction implied by migrating volcanic cessation along the Andean crest to southern Peru. The Galápagos-Carnegie hotspot trace only recently encountered the subduction zone, apparently inducing a new low-angle segment and cessation of magmatism in Colombia. The reconstructions and magmatic history provided here strongly support a previously proposed genetic relationship of hotspot traces and low-angle subduction. Additionally, the reconstructions suggest remnants of older subducted traces in the asthenosphere may have sourced post-rift magmatism in eastern Brazil and Paraguay, which cannot be explained otherwise by simple hotspot mechanisms.
南美洲板块下方纳斯卡板块的两个俯冲段，根据地震震中位置，角度较小，在深度约 100 千米以下接近水平。与俯冲带其他大部分地区不同的是，这两段俯冲带位于智利中部、秘鲁中部和北部，安第斯山脉山脊一带没有活火山，安第斯山脉山脊以东地形较为平缓。每个低角度俯冲段都位于纳斯卡板块与秘鲁-智利海沟推断地幔热点痕迹交汇处的东部：纳斯卡海脊（秘鲁段南部）和胡安-费尔南德斯岛-海山链（智利段近海）。推断出的第三条迹线，即加拉帕戈斯-卡内基海脊，可能与哥伦比亚地下的初生低角度俯冲带有关。更新的南美洲--马斯卡板块重建（包括三条海洋热点痕迹）与来自山脉的火成岩的新同位素日期汇编进行了比较，从而加强了这些热点痕迹对安第斯山下低角俯冲的重要性。根据太平洋热点模型重建的纳斯卡-法拉隆板块胡安-费尔南德斯热点迹线，在秘鲁南部近海约 65 Ma 处遇到俯冲带，向东扩大了弧形火山活动；迹线-海沟交汇处逐渐向南迁移，然后迅速向南迁移，向东扩大了弧形火山活动，一直延伸到玻利维亚和阿根廷北部；然后在智利中部近海约 13 Ma 处稳定下来，形成了当代的低角度帕潘板块。胡安-费尔南德斯（Juan Fernández）热点也可能是太平洋板块上马尼希基（Manihiki）高原形成的原因，时间更早，约为 125 Ma。伊斯特-纳斯卡热点痕迹在约 50 Ma 之前与哥伦比亚下方的俯冲带相交，并从约 15 Ma 开始在厄瓜多尔下方向南迁移，沿安第斯山峰向秘鲁南部迁移的火山停止暗示了逐渐的低角度俯冲。加拉帕戈斯-卡内基热点痕量最近才遇到俯冲带，显然在哥伦比亚诱发了新的低角度段和岩浆活动的停止。这里提供的重建和岩浆历史有力地支持了之前提出的热点痕迹与低角度俯冲的遗传关系。此外，重建结果表明，天体层中较早的俯冲痕迹残留物可能是巴西东部和巴拉圭断裂后岩浆活动的源头，否则无法用简单的热点机制来解释。
{"title":"Tracing hotspot traces in the Andes","authors":"R. Pilger","doi":"10.5027/andgeov51n1-3633","DOIUrl":"https://doi.org/10.5027/andgeov51n1-3633","url":null,"abstract":"Two segments of subduction of the Nazca plate beneath the South American plate occur at low angles based on seismic hypocenter locations, approaching nearly horizontal below ~100 km in depth. In contrast with most of the rest of the subduction zone, the two segments, beneath central Chile, and central and northern Peru, lack active volcanoes along the crest of the Andes and have more subdued topography to the east of the Andean crest. Each low-angle subduction segment occurs to the east of the intersection of inferred mantle hotspot traces on the Nazca plate with the Peru-Chile Trench: the Nazca ridge (at the southern part of the Peruvian segment), and the Juan Fernández island-seamount chain (offshore the Chilean segment). A third inferred trace, the Galápagos-Carnegie ridge, may be correlated with a zone on incipient low-angle subduction beneath Colombia. \u0000The importance of such hotspot traces in contributing to low-angle subduction beneath the Andes is strengthened by updated South American-Nazca plate reconstructions, including three oceanic hotspot traces, in comparison with a new isotopic date compilation of igneous rocks from the mountain range. The Juan Fernández hotspot trace, reconstructed from Pacific-hotspot models to the Nazca-Farallon plate, encountered the subduction zone offshore southern Peru ~65 Ma, broadening arc volcanism to the east; the trace-trench intersection migrated gradually and then rapidly southward, widening the arc east to Bolivia and northern Argentina; it then stabilized about 13 Ma offshore central Chile, producing the contemporary low-angle Pampean segment. The Juan Fernández hotspot may also have been responsible for formation of the Manihiki Plateau on the Pacific plate much earlier, ~125 Ma. The Easter-Nazca hotspot trace intersected the subduction zone beneath Colombia before ~50 Ma and migrated southward beneath Ecuador beginning ~15 Ma, with progressive low-angle subduction implied by migrating volcanic cessation along the Andean crest to southern Peru. The Galápagos-Carnegie hotspot trace only recently encountered the subduction zone, apparently inducing a new low-angle segment and cessation of magmatism in Colombia. The reconstructions and magmatic history provided here strongly support a previously proposed genetic relationship of hotspot traces and low-angle subduction. Additionally, the reconstructions suggest remnants of older subducted traces in the asthenosphere may have sourced post-rift magmatism in eastern Brazil and Paraguay, which cannot be explained otherwise by simple hotspot mechanisms.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140477442","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}
Pub Date : 2024-01-31DOI: 10.5027/andgeov51n1-3667
John J. Sánchez, William A. Posada
Studying the different ways in which the concept of volcanism is represented is crucial in the understanding of communities’ perception of the volcanic phenomena. In this contribution, 129 modern (2021-2023) depictions of volcanoes in Colombia between latitudes 0.82 and 5.96° N are described and classified into different contexts of use. Prehispanic depictions of volcanism are investigated in rock art sites (3 pictographs and 33 petroglyphs), and 15 distinct mythical narratives compiled and confirmed through interviews in the State of Nariño. We suggest that many of the rock art sites contain motifs that are reminiscent of the idea of volcanism, and that many of the folk tales include allusions to the volcanic concept. By collating the information contained in modern and older depictions, a link is established with the reality of the volcanic phenomena that shows how mutualism takes root between communities and volcanoes. The beneficial aspects derived from this relationship influence the perception of volcanic hazards in the region.
{"title":"Old and modern volcanic depictions as evidence of communities-volcanoes mutualism in Colombia","authors":"John J. Sánchez, William A. Posada","doi":"10.5027/andgeov51n1-3667","DOIUrl":"https://doi.org/10.5027/andgeov51n1-3667","url":null,"abstract":"Studying the different ways in which the concept of volcanism is represented is crucial in the understanding of communities’ perception of the volcanic phenomena. In this contribution, 129 modern (2021-2023) depictions of volcanoes in Colombia between latitudes 0.82 and 5.96° N are described and classified into different contexts of use. Prehispanic depictions of volcanism are investigated in rock art sites (3 pictographs and 33 petroglyphs), and 15 distinct mythical narratives compiled and confirmed through interviews in the State of Nariño. We suggest that many of the rock art sites contain motifs that are reminiscent of the idea of volcanism, and that many of the folk tales include allusions to the volcanic concept. By collating the information contained in modern and older depictions, a link is established with the reality of the volcanic phenomena that shows how mutualism takes root between communities and volcanoes. The beneficial aspects derived from this relationship influence the perception of volcanic hazards in the region.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140471098","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}
Pub Date : 2024-01-31DOI: 10.5027/andgeov51n1-3668
Camila Alegría, Francisca Vergara-Pinto
Since the perceptions of communities at risk play a central role in managing future emergencies, contingency plans must consider the appropriate involvement of the perspectives of exposed populations. This article addresses the case of Ensenada (Puerto Varas, Chile), a settlement located in the area of direct influence of the Calbuco and Osorno volcanoes. They respectively rank 2nd and 8th in the list of highest-threat Chilean volcanoes. Here we depict the multiple risk perceptions of the inhabitants of Ensenada and the integration of human perceptions into volcanic emergency management through qualitative research, based on semi-structured interviews and documentary analysis. Our results illustrate that Ensenada represents a settlement critically exposed to multiple hazards from both volcanoes, intertwined with a series of social conditions that influence individuals’ self-perception as vulnerable to future eruptions and, simultaneously, as capable of acquiring conditions to strengthen disaster preparedness. Moreover, the locals are eager to participate in future emergency management planning and adopt preventive attitudes at community, household, and individual levels. Based on these results, we highlight the advantages of a better understanding of the causes of perceived risk and its integration into emergency management strategies for future eruptions, in order to visualise how people make sense of daily life and disaster preparedness in the midst of active volcanoes.
{"title":"Living in-between: Implications of local risk perceptions for the management of future eruptions at the Calbuco and Osorno volcanoes (Ensenada, Chile)","authors":"Camila Alegría, Francisca Vergara-Pinto","doi":"10.5027/andgeov51n1-3668","DOIUrl":"https://doi.org/10.5027/andgeov51n1-3668","url":null,"abstract":"Since the perceptions of communities at risk play a central role in managing future emergencies, contingency plans must consider the appropriate involvement of the perspectives of exposed populations. This article addresses the case of Ensenada (Puerto Varas, Chile), a settlement located in the area of direct influence of the Calbuco and Osorno volcanoes. They respectively rank 2nd and 8th in the list of highest-threat Chilean volcanoes. Here we depict the multiple risk perceptions of the inhabitants of Ensenada and the integration of human perceptions into volcanic emergency management through qualitative research, based on semi-structured interviews and documentary analysis. Our results illustrate that Ensenada represents a settlement critically exposed to multiple hazards from both volcanoes, intertwined with a series of social conditions that influence individuals’ self-perception as vulnerable to future eruptions and, simultaneously, as capable of acquiring conditions to strengthen disaster preparedness. Moreover, the locals are eager to participate in future emergency management planning and adopt preventive attitudes at community, household, and individual levels. Based on these results, we highlight the advantages of a better understanding of the causes of perceived risk and its integration into emergency management strategies for future eruptions, in order to visualise how people make sense of daily life and disaster preparedness in the midst of active volcanoes.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140475217","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}
Pub Date : 2024-01-31DOI: 10.5027/andgeov51n1-3657
Ricardo Amorocho-Parra, Cristhiam Calixto Rodríguez-Patiño, C. Ríos-Reyes, Juan Carlos Ramírez-Arias, Oscar Mauricio Castellanos-Alarcón
A comprehensive tectono-stratigraphic and sedimentological investigation of Early to Middle Devonian rocks was conducted in the southern Floresta Massif and adjacent regions in the Northern Andes of Colombia. A substantially reduced thickness of the Floresta Formation compared to prior studies is suggested here, attributable to pronounced stratal deformation and the prevalence of recumbent folds throughout the area. The deformation in the Floresta Formation manifests as atypical recumbent folds, diverging from the structural behavior observed in the underlying and overlying strata of the El Tibet and Cuche formations respectively, which exhibit minimal deformation. Our findings also reveal that the Floresta Formation accumulated under shallow-water platform conditions, subject to eustatic sea-level fluctuations. This resulted in distinct episodes of carbonate and siliciclastic deposition, with terrigenous sediments sourced from continental origins, potentially encompassing a combination of cratonic areas and uplifted blocks. The identification of a plausible stage of carbonate silicification signifies a post-diagenetic transformation. The sedimentary rocks of the Floresta Formation reached the upper epizone conditions, in proximity to the transition between the epizone and the upper anchizone, which suggests a maximum depth and temperature of ~5-7 km and ~300 °C, respectively. This contribution provides new insights into the geological history of the region, emphasizing the importance of scrutinizing Early to Middle Devonian rocks within the broader geological context of the Northern Andes.
{"title":"Tectono-stratigraphic and sedimentological analysis of the Early to Middle Devonian Floresta Formation: Insights from the Floresta Massif, Northern Andes, Colombia","authors":"Ricardo Amorocho-Parra, Cristhiam Calixto Rodríguez-Patiño, C. Ríos-Reyes, Juan Carlos Ramírez-Arias, Oscar Mauricio Castellanos-Alarcón","doi":"10.5027/andgeov51n1-3657","DOIUrl":"https://doi.org/10.5027/andgeov51n1-3657","url":null,"abstract":"A comprehensive tectono-stratigraphic and sedimentological investigation of Early to Middle Devonian rocks was conducted in the southern Floresta Massif and adjacent regions in the Northern Andes of Colombia. A substantially reduced thickness of the Floresta Formation compared to prior studies is suggested here, attributable to pronounced stratal deformation and the prevalence of recumbent folds throughout the area. The deformation in the Floresta Formation manifests as atypical recumbent folds, diverging from the structural behavior observed in the underlying and overlying strata of the El Tibet and Cuche formations respectively, which exhibit minimal deformation. Our findings also reveal that the Floresta Formation accumulated under shallow-water platform conditions, subject to eustatic sea-level fluctuations. This resulted in distinct episodes of carbonate and siliciclastic deposition, with terrigenous sediments sourced from continental origins, potentially encompassing a combination of cratonic areas and uplifted blocks. The identification of a plausible stage of carbonate silicification signifies a post-diagenetic transformation. The sedimentary rocks of the Floresta Formation reached the upper epizone conditions, in proximity to the transition between the epizone and the upper anchizone, which suggests a maximum depth and temperature of ~5-7 km and ~300 °C, respectively. This contribution provides new insights into the geological history of the region, emphasizing the importance of scrutinizing Early to Middle Devonian rocks within the broader geological context of the Northern Andes.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140473230","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}
Pub Date : 2024-01-31DOI: 10.5027/andgeov51n1-3644
Juan Cruz Ghilardi Truffa, L. Ruíz, Pierre Pitte, Lautaro Clavero
In recent decades, glacier retreat has been observed in all the world’s mountain ranges. Over the last 20 years, glaciers in the Andes have lost mass at one of the highest rates on record. Particularly, glaciers in the northern Patagonian Andes show the highest rate of loss of all the Andean regions for the last decade. Detailed records of long-term variations in glacier extent are crucial to put current climate change into context and quantify its impact on mountain areas. In the present study, a reconstruction of the extension (length and area) of the Alerce glacier (41.15° S-71.81° W) for the last 70 years was carried out. By means of historical documents and satellite images (Landsat and Pléiades), detailed maps of glacier fluctuations were generated for the period 1953-2020. Four methodologies were evaluated to measure the front position: i) central flow line; ii) curvilinear box; iii) multiline; and iv) variable box. The magnitude of the front position variations depends on the methodology applied. The method that best addresses glacier front variations over the period analyzed is the variable box method. Between 1953 and 2020, the Alerce glacier lost 35% of its area (1.1±0.1 km2) and 67% of its total length (1.49±0.04 km). It is possible to distinguish periods with different rates of retreat. A stage of slight retreat (-11.3±0.5 ma-1) between 1953 and 1976, followed by a period of stability (-6.7±0.5 ma-1) between 1977 and 1983, then a strong retreat (-58.7±0.5 ma-1) between 1984 and 1999, followed by another period of stability (-5.4±0.5 ma-1) between 2000 and 2009 and, finally, another retreat (-8.7±0.5 ma-1) between 2010 and 2020. The retreat rates for the Alerce glacier mimic those observed in other glaciers in the region, possibly representing a regional climatic signal.
{"title":"Fluctuaciones recientes del glaciar Alerce (1953-2020), Andes de Patagonia norte","authors":"Juan Cruz Ghilardi Truffa, L. Ruíz, Pierre Pitte, Lautaro Clavero","doi":"10.5027/andgeov51n1-3644","DOIUrl":"https://doi.org/10.5027/andgeov51n1-3644","url":null,"abstract":"In recent decades, glacier retreat has been observed in all the world’s mountain ranges. Over the last 20 years, glaciers in the Andes have lost mass at one of the highest rates on record. Particularly, glaciers in the northern Patagonian Andes show the highest rate of loss of all the Andean regions for the last decade. Detailed records of long-term variations in glacier extent are crucial to put current climate change into context and quantify its impact on mountain areas. In the present study, a reconstruction of the extension (length and area) of the Alerce glacier (41.15° S-71.81° W) for the last 70 years was carried out. By means of historical documents and satellite images (Landsat and Pléiades), detailed maps of glacier fluctuations were generated for the period 1953-2020. Four methodologies were evaluated to measure the front position: i) central flow line; ii) curvilinear box; iii) multiline; and iv) variable box. The magnitude of the front position variations depends on the methodology applied. The method that best addresses glacier front variations over the period analyzed is the variable box method. Between 1953 and 2020, the Alerce glacier lost 35% of its area (1.1±0.1 km2) and 67% of its total length (1.49±0.04 km). It is possible to distinguish periods with different rates of retreat. A stage of slight retreat (-11.3±0.5 ma-1) between 1953 and 1976, followed by a period of stability (-6.7±0.5 ma-1) between 1977 and 1983, then a strong retreat (-58.7±0.5 ma-1) between 1984 and 1999, followed by another period of stability (-5.4±0.5 ma-1) between 2000 and 2009 and, finally, another retreat (-8.7±0.5 ma-1) between 2010 and 2020. The retreat rates for the Alerce glacier mimic those observed in other glaciers in the region, possibly representing a regional climatic signal.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140473280","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}
Pub Date : 2024-01-31DOI: 10.5027/andgeov51n1-3441
Natalia Noemí Rios, Carla Ginesta Torcivia, M. R. Onorato, Valeria Sofia Cortez Taillant, María Yanina Esper Angillieri
The present work aims to determine flash flood occurrence prone areas, in the Jáchal river basin, San Juan Province, Argentina. The Jáchal river basin covers ~29,000 km2 and has a perimeter of ~2,400 km, while the eponymous river extends for nearly 570 km. It is a 7th order basin according to Strahler’s classification, subdivided into four 6th order sub-basins. Various morphometric basin characteristics are analysed and some basic and derived parameters are calculated. These calculations allow predicting the basin behaviour due to heavy rainfall, which translates into large volumes of water with peak flows capable of generating significant flash floods. The basin has a torrential character, so in case of intense rainfall the terrain conditions would contribute to increasing the flow of the main rivers. An inventory of alluvial deposits was carried out and their relationship with the conditioning variables of the terrain was evaluated. At the confluence zones, the river tributaries show more intense overflows than the main collector. This promotes the generation of flash floods. The areas most likely to be affected by flash flood events correspond to low-humidity, east-facing slightly rough terrains, with slopes of up to 15° as well as low-lying flood plain sectors, and at the confluence of tributaries with the main rivers. Populated centres and provincial and national routes are prone to be affected by alluvial events in the study area.
{"title":"Morfometría de una cuenca de los Andes Centrales, San Juan, Argentina: evaluación de los factores condicionantes del terreno a la ocurrencia de aluviones","authors":"Natalia Noemí Rios, Carla Ginesta Torcivia, M. R. Onorato, Valeria Sofia Cortez Taillant, María Yanina Esper Angillieri","doi":"10.5027/andgeov51n1-3441","DOIUrl":"https://doi.org/10.5027/andgeov51n1-3441","url":null,"abstract":"The present work aims to determine flash flood occurrence prone areas, in the Jáchal river basin, San Juan Province, Argentina. The Jáchal river basin covers ~29,000 km2 and has a perimeter of ~2,400 km, while the eponymous river extends for nearly 570 km. It is a 7th order basin according to Strahler’s classification, subdivided into four 6th order sub-basins. Various morphometric basin characteristics are analysed and some basic and derived parameters are calculated. These calculations allow predicting the basin behaviour due to heavy rainfall, which translates into large volumes of water with peak flows capable of generating significant flash floods. The basin has a torrential character, so in case of intense rainfall the terrain conditions would contribute to increasing the flow of the main rivers. An inventory of alluvial deposits was carried out and their relationship with the conditioning variables of the terrain was evaluated. At the confluence zones, the river tributaries show more intense overflows than the main collector. This promotes the generation of flash floods. The areas most likely to be affected by flash flood events correspond to low-humidity, east-facing slightly rough terrains, with slopes of up to 15° as well as low-lying flood plain sectors, and at the confluence of tributaries with the main rivers. Populated centres and provincial and national routes are prone to be affected by alluvial events in the study area.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140472179","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}
Pub Date : 2024-01-31DOI: 10.5027/andgeov50n3-3420
Jeny Alejandra Grajales, Á. F. Nieto-Samaniego, A. Tassara, Jairo Alonso Osorio, Luis Ernesto Ardila, Juan Fernando Martínez
Several authors have interpreted the Colombian Pacific margin as a succession of oceanic terrane accretions, with generation of forearc basins under a compressive-transpressive tectonic regime during the Late Cretaceous-Miocene. New data acquired in the last decade, consisting of reprocessed seismic lines, geological cross-sections, stratigraphic data from wells, and new stratigraphic columns, are analyzed in this study. We suggest that the proposed models of successive terrane accretions are not supported by the new data; rather, the onshore basins were likely controlled by a marine platform from the Late Cretaceous to the Middle-Late Eocene, with reef growth to the end of this period. In the Late Cretaceous, contemporary to the sedimentation stage, effusive magmatism, mainly basaltic, also occurred. Since Oligocene time, the basins were affected by three different tectonic processes. First, during the Oligocene-Early Miocene, an extensional-transtensional event occurred in the Tumaco Basin and San Juan Sub-basin, which produced horst and graben structures and domino faults, along with the emplacement of igneous bodies in the eastern flank of the basins. The Atrato Sub-basin was affected by local reverse faulting towards its eastern edge. Second, during the Mid-Late Miocene, the western side of the Tumaco Basin was uplifted, and transpressive deformation occurred in the San Juan Sub-basin as evidenced by the San Juan and Garrapatas fault systems. Finally, in the Atrato Sub-basin, a transpressional regime is evidenced by the Baudó anticline. Our results suggest there is no evidence of oceanic terrane accretions in the abovementioned basins during the Late Cretaceous-Middle Eocene. Furthermore, we do not see evidence of a subduction system during that period. We conclude that subduction in western Colombia could have begun during the Early Oligocene instead.
{"title":"Evolución de las cuencas Tumaco, Atrato y San Juan sobre una plataforma continua a lo largo del margen pacífico colombiano","authors":"Jeny Alejandra Grajales, Á. F. Nieto-Samaniego, A. Tassara, Jairo Alonso Osorio, Luis Ernesto Ardila, Juan Fernando Martínez","doi":"10.5027/andgeov50n3-3420","DOIUrl":"https://doi.org/10.5027/andgeov50n3-3420","url":null,"abstract":"Several authors have interpreted the Colombian Pacific margin as a succession of oceanic terrane accretions, with generation of forearc basins under a compressive-transpressive tectonic regime during the Late Cretaceous-Miocene. New data acquired in the last decade, consisting of reprocessed seismic lines, geological cross-sections, stratigraphic data from wells, and new stratigraphic columns, are analyzed in this study. We suggest that the proposed models of successive terrane accretions are not supported by the new data; rather, the onshore basins were likely controlled by a marine platform from the Late Cretaceous to the Middle-Late Eocene, with reef growth to the end of this period. In the Late Cretaceous, contemporary to the sedimentation stage, effusive magmatism, mainly basaltic, also occurred. Since Oligocene time, the basins were affected by three different tectonic processes. First, during the Oligocene-Early Miocene, an extensional-transtensional event occurred in the Tumaco Basin and San Juan Sub-basin, which produced horst and graben structures and domino faults, along with the emplacement of igneous bodies in the eastern flank of the basins. The Atrato Sub-basin was affected by local reverse faulting towards its eastern edge. Second, during the Mid-Late Miocene, the western side of the Tumaco Basin was uplifted, and transpressive deformation occurred in the San Juan Sub-basin as evidenced by the San Juan and Garrapatas fault systems. Finally, in the Atrato Sub-basin, a transpressional regime is evidenced by the Baudó anticline. Our results suggest there is no evidence of oceanic terrane accretions in the abovementioned basins during the Late Cretaceous-Middle Eocene. Furthermore, we do not see evidence of a subduction system during that period. We conclude that subduction in western Colombia could have begun during the Early Oligocene instead.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140473970","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}
Pub Date : 2023-06-07DOI: 10.5027/andgeov50n2-3503
Natalia Villalba, H. Murcia, Edith Jerez, Daniel Piedrahita, Dayana Schonwalder-Ángel, A. Pardo-Trujillo, S. Echeverri
The Combia Volcanic Province (~11-5 Ma), is a volcaniclastic sequence located in northwest Colombia between the Central and Western cordilleras at 5-6° N latitude. Its source is associated with the volcanic activity of the magmatic arc produced by the subduction of the Nazca plate under the South American plate in the northern Andes. The distribution, composition, and chronostratigraphy of the province’s deposits are well-known, with the volcanic sequences characterized as compositionally bimodal. The older rocks (ca. 11-9 Ma) display tholeiitic affinity, whereas the younger (ca. 9-5 Ma) are mostly calc-alkaline, with some adakite-like signature recognized. While the magmatic system for the calc-alkaline magmas has been previously extensively studied, the processes that occurred during the magma stagnation and ascent are unknown for the tholeiitic magmas. This work bridges this gap by the study of tholeiitic lava flows outcropping at the center of the province, through petrography, mineral chemistry, whole-rock analysis, and geothermobarometry calculations of the crystallization conditions. Texturally, the rocks are porphyritic with plagioclase (An50-90) and clinopyroxene (augite and pigeonite) phenocrysts and microphenocrysts, embedded in a glassy and microcrystalline groundmass. Compositionally, the rocks vary from basaltic andesite to andesite (52.8-57.8 wt% SiO2), with relative enrichments of LILE to HFSE and REE to chondrite. Crystallization conditions, based on several plagioclase-melt and pyroxene-melt geothermobarometers, were estimated at T=1,095-1,153 °C and P=0.22-0.60 GPa for the plagioclase, T=1,046-1,131 °C and P=0.09-0.21 GPa for the augite, and T=867-1,039 °C and P=0.40-0.60 GPa for the pigeonite. These results suggest a relatively rapid magma ascent for the tholeiitic products as well as an evolution mostly through fractional crystallization. The LILE elements enrichment, the negative trend in the FeOt, TiO2 and CaO versus SiO2 content, together with some disequilibrium textures, are also evidence of crustal contamination and magma recharge. Thus it is proposed that the Combia Volcanic Province started as a simple magmatic system, where the tholeiitic products were generated by a relatively rapid magma ascent. Then, a more complex magmatic system linked to long-term magma stagnation, allowed melt evolution to form calc-alkaline magmas as previously defined.
{"title":"Compositional and geothermobarometric analysis of the Upper Miocene tholeiitic volcanic products in the northern Andes at 5-6° N latitude: The Combia Volcanic Province","authors":"Natalia Villalba, H. Murcia, Edith Jerez, Daniel Piedrahita, Dayana Schonwalder-Ángel, A. Pardo-Trujillo, S. Echeverri","doi":"10.5027/andgeov50n2-3503","DOIUrl":"https://doi.org/10.5027/andgeov50n2-3503","url":null,"abstract":"The Combia Volcanic Province (~11-5 Ma), is a volcaniclastic sequence located in northwest Colombia between the Central and Western cordilleras at 5-6° N latitude. Its source is associated with the volcanic activity of the magmatic arc produced by the subduction of the Nazca plate under the South American plate in the northern Andes. The distribution, composition, and chronostratigraphy of the province’s deposits are well-known, with the volcanic sequences characterized as compositionally bimodal. The older rocks (ca. 11-9 Ma) display tholeiitic affinity, whereas the younger (ca. 9-5 Ma) are mostly calc-alkaline, with some adakite-like signature recognized. While the magmatic system for the calc-alkaline magmas has been previously extensively studied, the processes that occurred during the magma stagnation and ascent are unknown for the tholeiitic magmas. This work bridges this gap by the study of tholeiitic lava flows outcropping at the center of the province, through petrography, mineral chemistry, whole-rock analysis, and geothermobarometry calculations of the crystallization conditions. Texturally, the rocks are porphyritic with plagioclase (An50-90) and clinopyroxene (augite and pigeonite) phenocrysts and microphenocrysts, embedded in a glassy and microcrystalline groundmass. Compositionally, the rocks vary from basaltic andesite to andesite (52.8-57.8 wt% SiO2), with relative enrichments of LILE to HFSE and REE to chondrite. Crystallization conditions, based on several plagioclase-melt and pyroxene-melt geothermobarometers, were estimated at T=1,095-1,153 °C and P=0.22-0.60 GPa for the plagioclase, T=1,046-1,131 °C and P=0.09-0.21 GPa for the augite, and T=867-1,039 °C and P=0.40-0.60 GPa for the pigeonite. These results suggest a relatively rapid magma ascent for the tholeiitic products as well as an evolution mostly through fractional crystallization. The LILE elements enrichment, the negative trend in the FeOt, TiO2 and CaO versus SiO2 content, together with some disequilibrium textures, are also evidence of crustal contamination and magma recharge. Thus it is proposed that the Combia Volcanic Province started as a simple magmatic system, where the tholeiitic products were generated by a relatively rapid magma ascent. Then, a more complex magmatic system linked to long-term magma stagnation, allowed melt evolution to form calc-alkaline magmas as previously defined.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2023-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41455371","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}
Pub Date : 2023-06-07DOI: 10.5027/andgeov50n2-3469
F. Moreno, Ana Mestre, S. Heredia
The calcareous microfossils present in the Ordovician and Silurian carbonate successions around the world are limited to few studies and their biological affinities and environmental preferences remain indefinite. In the carbonate Ordovician San Juan Formation from the Cerro La Chilca section, a group of calcareous microfossils was recognized and, based on their size, they are included in the calcitarch classification. Two types of calcitarchs have been recognized, Type-III calcitarch: large spheres with a thin to medium wall (diameter ~250 μm), and Type-0 calcitarch: small spheres with a thin wall (diameter ~80 μm). The carbonate microfacies analysis of the lower part of the San Juan Formation allowed defining five successive microfacies: burrowed bioclastic wackestone (M1), peloidal intraclastic packstone-grainstone (M2), intraclastic floatstone (M3), intraclastic wackestone-packstone (M4) and bioclastic boundstone (M5). These microfacies are interpreted to range from shallow subtidal facies below wave action to shoal and reef facies. It is possible to infer that the recovered calcitarchs show variations in size in relation to the facies that contain them. The calcitarchs recognized in wackestone-type facies are the Type-0 calcitarch and those recovered from the packstone-grainstone facies are the Type-III calcitarch. The calcitarch sizes variation probably is related to a gradual increase of energy within a shallow subtidal environment. Occurrences of calcitarchs within the Floian Oepikodus evae-O. intermedius conodont zone extends their fossil record into the Early Ordovician.
奥陶系和志留系碳酸盐岩层序中存在的钙质微化石在世界范围内研究较少，其生物亲和性和环境偏好仍然不确定。在Cerro La Chilca剖面的奥陶系San Juan组中发现了一组钙质微化石，并根据其大小将其纳入钙质分类。可识别出两种类型的方解石:iii型方解石:薄壁至中壁大球体(直径~250 μm); 0型方解石:薄壁小球体(直径~80 μm)。通过对圣胡安组下部碳酸盐岩微相的分析，确定了5个连续的微相:洞状生物碎屑碎屑砾岩(M1)、球囊状碎屑内砾岩-颗粒岩(M2)、碎屑内浮岩(M3)、碎屑内碎屑-砾岩(M4)和生物碎屑边界岩(M5)。这些微相被解释为从波浪作用下的浅潮下相到浅滩和礁相。由此可以推断，所发现的方解石的大小随其所含相的不同而不同。微晶岩型相中发现的方解石为0型方解石，包岩-颗粒岩相中发现的方解石为ⅲ型方解石。钙质大小的变化可能与浅层潮下环境中能量的逐渐增加有关。Floian oepiikodus中钙质的出现。中牙形石带的化石记录延伸至早奥陶世。
{"title":"Lower Ordovician calcareous microfossils from the San Juan Formation, Argentina: a new type of calcitarch and its paleoenvironmental implications","authors":"F. Moreno, Ana Mestre, S. Heredia","doi":"10.5027/andgeov50n2-3469","DOIUrl":"https://doi.org/10.5027/andgeov50n2-3469","url":null,"abstract":"The calcareous microfossils present in the Ordovician and Silurian carbonate successions around the world are limited to few studies and their biological affinities and environmental preferences remain indefinite. In the carbonate Ordovician San Juan Formation from the Cerro La Chilca section, a group of calcareous microfossils was recognized and, based on their size, they are included in the calcitarch classification. Two types of calcitarchs have been recognized, Type-III calcitarch: large spheres with a thin to medium wall (diameter ~250 μm), and Type-0 calcitarch: small spheres with a thin wall (diameter ~80 μm). The carbonate microfacies analysis of the lower part of the San Juan Formation allowed defining five successive microfacies: burrowed bioclastic wackestone (M1), peloidal intraclastic packstone-grainstone (M2), intraclastic floatstone (M3), intraclastic wackestone-packstone (M4) and bioclastic boundstone (M5). These microfacies are interpreted to range from shallow subtidal facies below wave action to shoal and reef facies. It is possible to infer that the recovered calcitarchs show variations in size in relation to the facies that contain them. The calcitarchs recognized in wackestone-type facies are the Type-0 calcitarch and those recovered from the packstone-grainstone facies are the Type-III calcitarch. The calcitarch sizes variation probably is related to a gradual increase of energy within a shallow subtidal environment. Occurrences of calcitarchs within the Floian Oepikodus evae-O. intermedius conodont zone extends their fossil record into the Early Ordovician.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2023-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48492540","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}
Pub Date : 2023-06-07DOI: 10.5027/andgeov50n2-3617
F. E. Lopez, C. Kaufmann
New data and a biostratigraphic review on Silurian graptolites of the La Chilca Formation are presented. Silurian retiolitids and monoserial graptolites are described for the first time in the lower layers of the Salto Macho Member at the Poblete Norte section, exposed in the Central Precordillera, San Juan Province, western Argentina. This member (late Hirnantian-early Wenlock) begins with a pebble paraconglomerate covered by a sedimentary succession of dark grey shales and greenish-yellowish siltstones. Two graptolite assemblages were collected therein. The first association includes Pseudoplegmatograptus reticulatus, Stimulograptus sedgwickii, Talacastograptus leanzai, Metaclimacograptus asejradi, Coronograptus sp., and biserial and monoserial indeterminate graptolites. The second contains Retiolites geinitzianus, Monograptus priodon, Stimulograptus sp., Pristiograptus sp., and unknown monoserial colonies. The late Aeronian Stimulograptus sedgwickii Zone is recorded due to the presence of the index taxon in the middle levels of the Salto Macho Member. The second graptolite fauna has been related to the early Sheinwoodian Cyrtograptus murchisoni Zone, based on the presence of palynomorph assemblages from the La Chilca Formation, previously studied in another sections. The biotic changes of the graptolite faunas, sedimentary variations, and prevalent paleoenvironmental conditions observed in the lower beds of the Salto Macho Member, could indicate the first evidence of the Sedgwickii Event in Precordillera, which is recognized globally and involves comparable features.
{"title":"New insights on the Silurian graptolite biostratigraphy of the La Chilca Formation, Poblete Norte section, Central Precordillera of San Juan, Argentina: faunal replacement and paleoenvironmental implications","authors":"F. E. Lopez, C. Kaufmann","doi":"10.5027/andgeov50n2-3617","DOIUrl":"https://doi.org/10.5027/andgeov50n2-3617","url":null,"abstract":"New data and a biostratigraphic review on Silurian graptolites of the La Chilca Formation are presented. Silurian retiolitids and monoserial graptolites are described for the first time in the lower layers of the Salto Macho Member at the Poblete Norte section, exposed in the Central Precordillera, San Juan Province, western Argentina. This member (late Hirnantian-early Wenlock) begins with a pebble paraconglomerate covered by a sedimentary succession of dark grey shales and greenish-yellowish siltstones. Two graptolite assemblages were collected therein. The first association includes Pseudoplegmatograptus reticulatus, Stimulograptus sedgwickii, Talacastograptus leanzai, Metaclimacograptus asejradi, Coronograptus sp., and biserial and monoserial indeterminate graptolites. The second contains Retiolites geinitzianus, Monograptus priodon, Stimulograptus sp., Pristiograptus sp., and unknown monoserial colonies. The late Aeronian Stimulograptus sedgwickii Zone is recorded due to the presence of the index taxon in the middle levels of the Salto Macho Member. The second graptolite fauna has been related to the early Sheinwoodian Cyrtograptus murchisoni Zone, based on the presence of palynomorph assemblages from the La Chilca Formation, previously studied in another sections. The biotic changes of the graptolite faunas, sedimentary variations, and prevalent paleoenvironmental conditions observed in the lower beds of the Salto Macho Member, could indicate the first evidence of the Sedgwickii Event in Precordillera, which is recognized globally and involves comparable features.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2023-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46636934","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}
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