Pub Date : 2021-11-22DOI: 10.5027/andgeov49n1-3387
J. A. Murra, Edgardo G. Baldo, Sebastián O. Verdecchia, Carlos D. Ramacciotti, C. Galindo
The El Escorial marbles (Cushamen Metamorphic Complex) along with amphibolites form metamorphic septa within the permian granitoids of the Mamil Choique Formation (261-286 Ma). The metamorphism, determined in granulite facies migmatic gneisses septa cropping out 120 km southwest of El Escorial, occurs at 311 ± 27 Ma (CHIME method in monazite). The marbles are calcitic (calcite > 95%, R.I.: 0.5 to 2.5%) and show 87Sr/86Sr values between 0.70768 and 0.70825 (n = 10). The data provided in this work, added to previous contributions, allow to constraints the sedimentation age of the silicic-carbonate successions of the Cushamen Metamorphic Complex between ca. 385 and 335 Ma. This suggests the existence of a mixed carbonate-siliciclastic platform at least in the southernmost portion of southwestern Gondwana between Middle Devonian and early Carboniferous (Middle Mississippian).
El Escorial大理岩（Cushamen变质杂岩）和角闪岩在Mamil Choique组（261-286 Ma）的二叠纪花岗岩中形成变质隔膜。变质作用发生在El Escorial西南120km的麻粒岩相混合片麻岩中，发生在311±27Ma（独居石中的CHIME方法）。大理石为钙质（方解石>95%，R.I.：0.5至2.5%），87Sr/86Sr值在0.70768至0.70825之间（n=10）。这项工作中提供的数据，加上之前的贡献，可以将库沙门变质杂岩的硅化碳酸盐序列的沉积年龄限制在约385至335 Ma之间。这表明至少在中泥盆纪和早石炭世（中密西西比纪）之间的冈瓦纳大陆西南部最南部存在混合碳酸盐-硅碎屑台地。
{"title":"Los mármoles cálcicos de El Escorial (Complejo Metamórfico Cushamen, Macizo Norpatagónico): caracterización isotópica de 87Sr-86Sr y edad de sedimentación","authors":"J. A. Murra, Edgardo G. Baldo, Sebastián O. Verdecchia, Carlos D. Ramacciotti, C. Galindo","doi":"10.5027/andgeov49n1-3387","DOIUrl":"https://doi.org/10.5027/andgeov49n1-3387","url":null,"abstract":"The El Escorial marbles (Cushamen Metamorphic Complex) along with amphibolites form metamorphic septa within the permian granitoids of the Mamil Choique Formation (261-286 Ma). The metamorphism, determined in granulite facies migmatic gneisses septa cropping out 120 km southwest of El Escorial, occurs at 311 ± 27 Ma (CHIME method in monazite). The marbles are calcitic (calcite > 95%, R.I.: 0.5 to 2.5%) and show 87Sr/86Sr values between 0.70768 and 0.70825 (n = 10). The data provided in this work, added to previous contributions, allow to constraints the sedimentation age of the silicic-carbonate successions of the Cushamen Metamorphic Complex between ca. 385 and 335 Ma. This suggests the existence of a mixed carbonate-siliciclastic platform at least in the southernmost portion of southwestern Gondwana between Middle Devonian and early Carboniferous (Middle Mississippian).","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2021-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46990113","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 : 2021-06-15DOI: 10.5027/ANDGEOV48N3-3350
S. Moragues, M. G. Lenzano, S. Rivera, Jonathan Oberreuter
{"title":"CARACTERIZACIÓN DE LA INESTABILIDAD DE LADERAS DEL CANAL UPSALA: DESLIZAMIENTO AGASSIZ, PATAGONIA AUSTRAL, ARGENTINA","authors":"S. Moragues, M. G. Lenzano, S. Rivera, Jonathan Oberreuter","doi":"10.5027/ANDGEOV48N3-3350","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N3-3350","url":null,"abstract":"","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2021-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43226827","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 : 2021-06-15DOI: 10.5027/ANDGEOV48N3-3362
P. C. Quero-Jiménez, Lester Alejandro Arias Felipe, Julio Omar Prieto García, M. E. Rodriguez, Jorge Lopez, O. Montenegro, Reinaldo Molina Ruiz, I. Tiscornia
The Cuban bentonite clays have a specific surface area of 79.9098 m2.g-1, a pore volume of about 0.077612 cm3.g-1 and both isotherms exhibited a hysteresis loop of IV type. X-ray diffractogram of raw bentonite shows that the main mineralogical component is montmorillonite (> 90%). The mineral object study presents the first endothermic peak, characteristic of montmorillonite, in 48.11 ºC and others less accentuated (80.81, 94.01, 119.81 ºC) characteristic of calcium montmorillonite, that corresponds to the loss of water, and can be extended up to 250 ºC. The FTIR spectra showed the existence of Si-OH, Al-Al-OH, Al-Fe-OH, Al-Mg-OH and Si-O-Si functional groups in all clay samples, confirmed the presence of hydrated aluminosilicate in the clay, bands between 1120 and 461 cm-1 correspond to phyllosilicate structures and OH stretching vibrations were observed. The pH at the point of zero charge (pHPZC) obtained has a value of 8.1, which allows montmorillonite to be classified as basic. The structural formula for one-layer unit of montmorillonite was determined as (Na3.99Al0.01)(Al1.11Fe3+0.49Mg0.18Ti0.07)(Ca0.24Na0.15K0.01)O10(OH)2, indicate the location of the different cations in metal oxide octahedrons or tetrahedrons, respectively. From the results obtained by different methods and the analysis of the calculated structural formula, it can be concluded that the bentonite under study is a calcium montmorillonite, with a low specific surface area and little porosity.
{"title":"Local Cuban bentonite clay: composition, structure and textural characterization","authors":"P. C. Quero-Jiménez, Lester Alejandro Arias Felipe, Julio Omar Prieto García, M. E. Rodriguez, Jorge Lopez, O. Montenegro, Reinaldo Molina Ruiz, I. Tiscornia","doi":"10.5027/ANDGEOV48N3-3362","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N3-3362","url":null,"abstract":"The Cuban bentonite clays have a specific surface area of 79.9098 m2.g-1, a pore volume of about 0.077612 cm3.g-1 and both isotherms exhibited a hysteresis loop of IV type. X-ray diffractogram of raw bentonite shows that the main mineralogical component is montmorillonite (> 90%). The mineral object study presents the first endothermic peak, characteristic of montmorillonite, in 48.11 ºC and others less accentuated (80.81, 94.01, 119.81 ºC) characteristic of calcium montmorillonite, that corresponds to the loss of water, and can be extended up to 250 ºC. The FTIR spectra showed the existence of Si-OH, Al-Al-OH, Al-Fe-OH, Al-Mg-OH and Si-O-Si functional groups in all clay samples, confirmed the presence of hydrated aluminosilicate in the clay, bands between 1120 and 461 cm-1 correspond to phyllosilicate structures and OH stretching vibrations were observed. The pH at the point of zero charge (pHPZC) obtained has a value of 8.1, which allows montmorillonite to be classified as basic. The structural formula for one-layer unit of montmorillonite was determined as (Na3.99Al0.01)(Al1.11Fe3+0.49Mg0.18Ti0.07)(Ca0.24Na0.15K0.01)O10(OH)2, indicate the location of the different cations in metal oxide octahedrons or tetrahedrons, respectively. From the results obtained by different methods and the analysis of the calculated structural formula, it can be concluded that the bentonite under study is a calcium montmorillonite, with a low specific surface area and little porosity.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2021-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44300773","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 : 2021-06-15DOI: 10.5027/ANDGEOV48N3-3361
J. A. Naranjo, F. Hevia, E. Polanco
The Mondaca volcano comprises a thick rhyolitic lava-field and a dome of similar composition, located near the Lontué River Valley headwaters in the northern part of the Southern Andes Volcanic Zone. It reaches a total volume of ~ 0.85 km, and it is formed by 4 subunits, named Mondaca 1, 2, 3 and 4, which correspond to successive rhyolitic blocky lava flows, emitted from a rounded dome structure. They present well-preserved flow structures and, in the surroundings, restricted to the south and east of the dome, pyroclastic fall, as well as block and ash deposits are also exhibited. Downstream, along the Lontué River, a laharic deposit is recognized. The lahar was produced after the collapse of an ephemeral ~0.44 km3 lake generated after the river obstruction by viscous lavas, during the 1762 first eruptive phase. Proximal lahar facies are well exposed between 5 and 30 km from their source. The profuse agricultural activity has completely obliterated the lahar's medium facies deposits along the Central Depression, but are well identified at the mouth of the Mataquito River, 180 km downstream, as a beige-coloured layer, interbedded within dark coastal beach-sands. The identification of overflows and super-elevation deposits formed during the debris flow emplacement along the Lontué River valley, allows to determine a high flow mobility, with estimated velocities that locally reached up to 114 km/h. Petrographic characteristics in addition to chemical composition of lavas from the volcano, pyroclasts and juvenile blocks of the laharic deposit, indicate that all they correspond to high K calcoalkaline rhyolites with subalkaline affinity. These backgrounds, together with the geographical continuity between the lavas and debris deposits along the Lontué and Mataquito rivers, verify facies correlation and common origin as the result of the 1762 Mondaca volcano eruption complex evolution. IN PR ES S Andean Geology 48 (3): xxx-xxx. September, 2021 doi: 10.5027/andgeoV48n3-3361 2 Although it was a mainly effusive eruption that could not be observed from Curicó, the collateral consequences would have been catastrophic over a vast area to the south of that city, and evidences one of the largest volcanic disasters in Chilean history. Probably because of the low density polulation at that time, the consequences could have been minor.
{"title":"MONDACA VOLCANO LAHAR OF DECEMBER 3, 1762, MAULE REGION (35°28’S): ONE OF THE LARGEST VOLCANIC DISASTERS IN CHILEAN HISTORY","authors":"J. A. Naranjo, F. Hevia, E. Polanco","doi":"10.5027/ANDGEOV48N3-3361","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N3-3361","url":null,"abstract":"The Mondaca volcano comprises a thick rhyolitic lava-field and a dome of similar composition, located near the Lontué River Valley headwaters in the northern part of the Southern Andes Volcanic Zone. It reaches a total volume of ~ 0.85 km, and it is formed by 4 subunits, named Mondaca 1, 2, 3 and 4, which correspond to successive rhyolitic blocky lava flows, emitted from a rounded dome structure. They present well-preserved flow structures and, in the surroundings, restricted to the south and east of the dome, pyroclastic fall, as well as block and ash deposits are also exhibited. Downstream, along the Lontué River, a laharic deposit is recognized. The lahar was produced after the collapse of an ephemeral ~0.44 km3 lake generated after the river obstruction by viscous lavas, during the 1762 first eruptive phase. Proximal lahar facies are well exposed between 5 and 30 km from their source. The profuse agricultural activity has completely obliterated the lahar's medium facies deposits along the Central Depression, but are well identified at the mouth of the Mataquito River, 180 km downstream, as a beige-coloured layer, interbedded within dark coastal beach-sands. The identification of overflows and super-elevation deposits formed during the debris flow emplacement along the Lontué River valley, allows to determine a high flow mobility, with estimated velocities that locally reached up to 114 km/h. Petrographic characteristics in addition to chemical composition of lavas from the volcano, pyroclasts and juvenile blocks of the laharic deposit, indicate that all they correspond to high K calcoalkaline rhyolites with subalkaline affinity. These backgrounds, together with the geographical continuity between the lavas and debris deposits along the Lontué and Mataquito rivers, verify facies correlation and common origin as the result of the 1762 Mondaca volcano eruption complex evolution. IN PR ES S Andean Geology 48 (3): xxx-xxx. September, 2021 doi: 10.5027/andgeoV48n3-3361 2 Although it was a mainly effusive eruption that could not be observed from Curicó, the collateral consequences would have been catastrophic over a vast area to the south of that city, and evidences one of the largest volcanic disasters in Chilean history. Probably because of the low density polulation at that time, the consequences could have been minor.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2021-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47189789","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 : 2021-06-15DOI: 10.5027/ANDGEOV48N3-3329
Carlos A Ríos, M. Vargas, Mario Garcia
In ANH-CR-Montecarlo-1X well located in the southern sector of the Cesar-Ranchería basin, Colombia, rocks of the middle Cretaceous outcrop, which have been defined as belonging to the Cogollo Group. The present study concerns with the diagenetic evolution and thermal maturity of this geological unit, integrating petrographic techniques (thin section microscopy and scanning electron microscopy), geochemistry (total organic carbon and pyrolysis rock-eval) and basic petrophysics, to establish the thermal maturity and the potential of rocks as reservoirs of conventional and unconventional hydrocarbons. The results of petrographic and diagenetic analysis revealed that the rocks compositionally correspond to quartz sandstones and graywackes and carbonate rocks to mudstones and wackestones; which were affected by diagenetic processes such as compaction, mineral neoformations distinguishing minerals from the group of clays that cover the grains of the framework, and other types of precipitates of cements such as silica, ferrous and non-ferrous carbonate, some of these present partial and/or total dissolution, for which secondary porosity is recognized, also metasomatisms, where processes of chloritization and illitization of the argillaceous matrix are observed, alteration of feldspars to ferrous and non-ferrous carbonate, which affects the porosity and permeability of the rock; and recrystallization from micrite to sparite and carbonate precipitation in calcareous rocks. The study also showed that the rocks were more affected by compaction than precipitation of the different cements. The research contributes to the understanding of the impact of diagenetic processes on porosity, as well as their spatial and temporal distribution, providing diagenetic paragenesis for both siliciclastic and carbonatic rocks. When we classifying siliciclastic rocks as potential reservoir rocks, low potential results were obtained as conventional reservoirs but has good potential as non-conventional reservoirs (tight sandstones), this respect to porosity and permeability data. The geochemical studies in the calcareous rocks exhibited low to good content of total organic carbon, overmaturity state and a low generation potential with type III and IV kerogens.
{"title":"Diagenesis and Thermal Maturity of the Cogollo Group rocks in the ANH-CR-Montecarlo-1X well, Cesar-Ranchería Basin, Colombia","authors":"Carlos A Ríos, M. Vargas, Mario Garcia","doi":"10.5027/ANDGEOV48N3-3329","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N3-3329","url":null,"abstract":"In ANH-CR-Montecarlo-1X well located in the southern sector of the Cesar-Ranchería basin, Colombia, rocks of the middle Cretaceous outcrop, which have been defined as belonging to the Cogollo Group. The present study concerns with the diagenetic evolution and thermal maturity of this geological unit, integrating petrographic techniques (thin section microscopy and scanning electron microscopy), geochemistry (total organic carbon and pyrolysis rock-eval) and basic petrophysics, to establish the thermal maturity and the potential of rocks as reservoirs of conventional and unconventional hydrocarbons. The results of petrographic and diagenetic analysis revealed that the rocks compositionally correspond to quartz sandstones and graywackes and carbonate rocks to mudstones and wackestones; which were affected by diagenetic processes such as compaction, mineral neoformations distinguishing minerals from the group of clays that cover the grains of the framework, and other types of precipitates of cements such as silica, ferrous and non-ferrous carbonate, some of these present partial and/or total dissolution, for which secondary porosity is recognized, also metasomatisms, where processes of chloritization and illitization of the argillaceous matrix are observed, alteration of feldspars to ferrous and non-ferrous carbonate, which affects the porosity and permeability of the rock; and recrystallization from micrite to sparite and carbonate precipitation in calcareous rocks. The study also showed that the rocks were more affected by compaction than precipitation of the different cements. The research contributes to the understanding of the impact of diagenetic processes on porosity, as well as their spatial and temporal distribution, providing diagenetic paragenesis for both siliciclastic and carbonatic rocks. When we classifying siliciclastic rocks as potential reservoir rocks, low potential results were obtained as conventional reservoirs but has good potential as non-conventional reservoirs (tight sandstones), this respect to porosity and permeability data. The geochemical studies in the calcareous rocks exhibited low to good content of total organic carbon, overmaturity state and a low generation potential with type III and IV kerogens.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2021-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45552739","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 : 2021-06-15DOI: 10.5027/ANDGEOV48N3-3158
Alejandro Sánchez Valenzuela, M. Saint-Blanquat, F. Hervé, M. Polvé, D. Morata, Phillipe De Parseval, M. Benoit
In this work, we present the results of the first study which involves most of several cenozoic satellite plutons located in a 'back-arc' position in west Patagonia, south of the present Chile Triple-Junction. 4 plutons were studied in the northern tip, and 3 in the southern one. The petrographic and geochemical character of these plutons is different enough between them to propose a further classification for them: alkaline (sensu stricto): only the Monte Balmaceda Igneous complex, in the southern extremity; "intra-plate transitional" calc-alkaline: Río de Las Nieves and San Lorenzo plutons in the northern area, and the Torres del Paine Igneous Complex, in the southern area; and "arc transitional" calc-alkaline: the Paso de Las Llaves and Cerro Negro del Ghío plutons in the northern area, and the Cerro Donoso Pluton in the southern area. The "transitional" character, together with the plutons location, and regional context, can be explained by a Mio-Pliocene eastward arc migration coeval with the beginning of the Chile Rise subduction . Slab flattening hypothesis is favoured to explain the arc-migration, and together with the different length and time of arrival of the Chile Rise segments, contributed to the plutons heterogeneous geochemistry.
在这项工作中，我们介绍了第一项研究的结果，该研究涉及位于巴塔哥尼亚西部“后弧”位置的几个新生代卫星深成岩体中的大多数，该位置位于现在的智利三联结以南。在北端研究了4个深成岩体，在南端研究了3个。这些深成岩体的岩相和地球化学特征在它们之间的差异足以为它们提出进一步的分类：碱性（严格意义上）：只有位于南端的Monte Balmaceda火成岩杂岩；“板块内过渡”钙碱性：北部地区的Río de Las Nieves和San Lorenzo深成岩体，以及南部地区的Torres del Paine火成岩杂岩；和“弧形过渡”钙碱性：北部地区的Paso de Las Llaves和Cerro Negro del Ghío深成岩体，以及南部地区的Cerro Donoso Pluton。这种“过渡”特征，加上深成岩体的位置和区域背景，可以用中新世向东弧迁移与智利隆起俯冲的开始同时代来解释。板块压扁假说有利于解释弧的迁移，加上智利隆起段的不同长度和到达时间，有助于形成深成岩体的非均质性地球化学。
{"title":"Cenozoic plutonism geochemistry in the extra-andean southern Patagonia as evidences of arc migration process","authors":"Alejandro Sánchez Valenzuela, M. Saint-Blanquat, F. Hervé, M. Polvé, D. Morata, Phillipe De Parseval, M. Benoit","doi":"10.5027/ANDGEOV48N3-3158","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N3-3158","url":null,"abstract":"In this work, we present the results of the first study which involves most of several cenozoic satellite plutons located in a 'back-arc' position in west Patagonia, south of the present Chile Triple-Junction. 4 plutons were studied in the northern tip, and 3 in the southern one. The petrographic and geochemical character of these plutons is different enough between them to propose a further classification for them: alkaline (sensu stricto): only the Monte Balmaceda Igneous complex, in the southern extremity; \"intra-plate transitional\" calc-alkaline: Río de Las Nieves and San Lorenzo plutons in the northern area, and the Torres del Paine Igneous Complex, in the southern area; and \"arc transitional\" calc-alkaline: the Paso de Las Llaves and Cerro Negro del Ghío plutons in the northern area, and the Cerro Donoso Pluton in the southern area. The \"transitional\" character, together with the plutons location, and regional context, can be explained by a Mio-Pliocene eastward arc migration coeval with the beginning of the Chile Rise subduction . Slab flattening hypothesis is favoured to explain the arc-migration, and together with the different length and time of arrival of the Chile Rise segments, contributed to the plutons heterogeneous geochemistry.","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2021-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46318933","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 : 2021-06-15DOI: 10.5027/ANDGEOV48N3-3351
Hans Niemeyer Rubilar
{"title":"EL PLUTÓN SINTECTÓNICO ORDOVÍCICO EL LEÓN, EXTREMO SUROCCIDENTAL DEL CORDÓN DE LILA, REGIÓN DE ANTOFAGASTA","authors":"Hans Niemeyer Rubilar","doi":"10.5027/ANDGEOV48N3-3351","DOIUrl":"https://doi.org/10.5027/ANDGEOV48N3-3351","url":null,"abstract":"","PeriodicalId":49108,"journal":{"name":"Andean Geology","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2021-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48144686","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 : 2021-06-15DOI: 10.5027/ANDGEOV48N3-3345
Leda Sánchez Bettucci, U. Cordani, J. Loureiro, E. Peel, S. Fort
Se realizó un estudio geocronológico U-Pb SHRIMP en circones en el Terreno Nico Pérez, localizado en la porción centro-oriental de Uruguay. El Terreno Nico Pérez es parte del Cratón del Río de La Plata y está limitado al oeste por el Terreno Piedra Alta a través de la mega zona de cizalla Sarandí del Yí. Al este se encuentra en contacto tectónico con el Cinturón Dom Feliciano, que constituye un elemento importante resultado el ciclo Orogénico Brasiliano. Litológicamente, está compuesto por cinturones metamórficos de grado medio a alto (bloques Pavas, Valentines y Rivera) representados principalmente por rocas de tipo granitoide, así como rocas orto y parametamórficas, como anfibolitas, metapiroxenitas, BIF, esquistos, cuarcitas con fucsita, entre otros. La corteza del Terreno Nico Pérez se generó principalmente durante el Riaciano, como lo muestran las edades isotópicas disponibles, que normalmente también están presentes en otras partes del Cratón del Río de la Plata, como los Terrenos Piedra Alta y Tandilia. Escamas tectónicas de edad Arqueanas retrabajadas arrojaron edades de 3.1 Ga y 2.7 Ga, corroborando resultados disponibles anteriores. También se obtuvo una edad de 1,73 Ga para el granito rapakivi de Illescas. Además, se obtuvieron edades robustas Ediacaranas (ca. 580 Ma) en plutones graníticos que se encuentran intruyendo el Terreno Nico Pérez. Estas se encuentran afectadas por el ciclo Orogénico Brasiliano. Se sugiere que las rocas de grado medio-alto del Terreno Piedra Alta y aquellas del Bloque Valentines formaban parte de un mismo fragmento cortical cuando se formó el cinturón Dom Feliciano, ya que muestran una evolución tectónica con arcos magmáticos maduros de edad Riaciana. Además, el enjambre de diques máficos de Florida, del Terreno Piedra Alta, y el granito rapakivi Illescas, del Terreno Nico Pérez, podrían ser parte del mismo episodio magmático que ocurrió alrededor de los 1.73 Ga. El Terreno Nico Pérez muestra como carácter distintivo el haber sido fuertemente afectado por la Orogenia brasiliana. Esto sugiere que es resultado de la metacratización Ediacarana del Cratón del Río de La Plata.
对位于乌拉圭中东部的Nico perez地块的锆石进行了U-Pb虾年代学研究。Nico perez地形是rio de La Plata克拉通的一部分，其西部与Piedra Alta地形接壤，穿过cizalla sarandi del yi mega zone。在东部，它与多姆费利西亚诺带构造接触，多姆费利西亚诺带是巴西造山循环的重要组成部分。在岩性上，它由中、高变质带(Pavas、Valentines和Rivera块体)组成，主要以花岗质岩石为代表，以及角闪岩、变质辉长岩、BIF、片岩、含岩心石的石英岩等正、副变质岩。Nico perez地壳主要是在riacian时期形成的，这可以从可用的同位素年龄中看出，通常也存在于rio de La Plata克拉通的其他部分，如Piedra Alta和Tandilia地壳。重建的太古宙构造鳞片的年龄分别为3.1 Ga和2.7 Ga，证实了以前的发现。我们还获得了Illescas rapakivi花岗岩的年龄为1.73 Ga。此外，在侵入Nico perez地形的花岗岩岩体中获得了埃迪卡拉纪的鲁棒年龄(约580 Ma)。它们受到巴西造山循环的影响。有人认为，在Dom Feliciano带形成时，Piedra Alta地形的中高级岩石和Valentines块的岩石是同一地壳碎片的一部分，因为它们显示了成熟的岩浆弧的构造演化。此外，来自Piedra Alta地形的佛罗里达基性岩脉群和来自Nico perez地形的rapakivi Illescas花岗岩可能是发生在1.73 Ga左右的同一岩浆事件的一部分。Nico perez地形的特点是受到巴西造山运动的强烈影响。这表明它是埃迪卡拉亚元化的结果，在拉普拉塔克拉通。
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Pub Date : 2021-06-15DOI: 10.5027/ANDGEOV48N3-3256
J. Araya, G. Pascale, S. Sepúlveda
Understanding the location and nature of Quaternary active crustal faults is critical to the reduction of both fault rupture and strong ground motions hazards in the built environment. Recent work along the San Ramon Fault in Santiago, Chile demonstrates that crustal seismic sources are important hazards. We present the results of a second likely Quaternary active fault (the El Arrayan Fault, EAF) that runs through the City of Santiago. The EAF was discovered at an outcrop in El Arrayan (Lo Barnechea) with up to the North reverse motion and sinistral (left-lateral) motion clearly visible and coincident with fault rocks (gouge, cataclasite, and breccia) and higher topography (i.e. uplift) in the hanging wall. The EAF is at least 12 km long, strikes North-Northwest to South-Southeast, and is steeply dipping (mean dip 77º NE). Clear geomorphic expression with sinistral displaced streams (up to ~210 m) suggest that this fault is Quaternary active and an important local source of fault rupture and crustal strong ground motions. Because no fault zone avoidance criteria in Chile, there is need for enhanced fault mapping, legislation, implementation of active fault rupture avoidance areas in Chile to reduce the risk posed by active crustal structures.
了解第四纪地壳活动断层的位置和性质对于减少断层破裂和强地震动对建筑环境的危害至关重要。最近在智利圣地亚哥沿着圣拉蒙断层进行的工作表明，地壳震源是重要的危险。我们提出了第二个可能的第四纪活动断层(El Arrayan断层，EAF)的结果，该断层穿过圣地亚哥市。EAF是在El Arrayan (Lo Barnechea)的一个露头上发现的，向上向北的反向运动和左旋(左旋)运动清晰可见，与断层岩(断层泥、碎裂岩和角砾岩)和上盘的较高地形(即隆起)一致。东寒带长度至少12公里，走向西北偏北至东南偏南，倾角陡(平均东经77度)。左旋位移流(~210 m)的清晰地貌表现表明，该断裂具有第四纪活动性，是断裂破裂和地壳强地震动的重要局地源。由于智利没有断层避免标准，因此需要加强断层制图、立法、实施活动断层避免破裂区域，以减少活动地壳结构带来的风险。
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Pub Date : 2021-06-15DOI: 10.5027/ANDGEOV48N3-3327
I. Pérez-Martínez, R. Villanueva-Estrada, A. Rodríguez-Díaz, C. Canet, R. García, Alfredo Ramos-Leal, D. Garcia, Froylan Cambrón
The Araró-Simirao geothermal system is in the southeast part of the Cuitzeo Lake depression. Physiographically, it is located in the eastern portion of the central part of the TransMexican Volcanic Belt province (TMVB). It is a convective hydrothermal system of dominant liquid, with chlorinated sodium waters and high boron content. The principal gas emitted by the thermal springs is CO2 and, in lower concentrations, H2S, H2 and noble gases (He, Ne, Ar). The aim of this study was to delimit fluid ascent areas in the geothermal system by determining the relationships between diffuse gas emission concentrations in soils and the greatest permeability plausible zones (principal faults). Three sampling campaigns were carried out during 2018 (August and November) and 2019 (May), in which diffuse gas emission measurements (CO2, Rn and mercury vapors) across the soils and soil temperature measurements were carried out. For a sampling campaign, the CO2 flux ranged between 4.38 and 94.61 g m-2 d-1 and the gaseous elemental mercury (GEM) concentration ranged between 0.5 and 365 ng/m3. For the other sampling campaign, the CO2 flux ranged between 0.8 and 1,421 g m-2 d-1 and the GEM values ranged between 0.49 and 2,914ng/m3. In the last sampling campaign the222Rn and 220Rn were also measured, and these values oscillated between 1,060 and 124,100 Bq/m3 and from 0 to 7,511 Bq7m3, respectively. Several anomalous zones of CO2 fluxes, GEM and 222Rn concentrations were found, which match the greatest permeability zones (faults and lineaments). The zone with the highest values in these three parameters is located in the so-called «mud pool», at the crossing of the Araró-Simirao fault with a lineament NW-SE (south zone), which is associated with the upflow zone of the system. Other anomalous zones were also located in the fracture and/or lineaments zones in the central and north parts of the system, which are associated with the outflow zone. According to the data obtained, CO2 could be functioning as a carrier of Hg and 222Rn in the area of vertical rise of gases and, in the outflow zone this gas may be found dissolved in the groundwater.
Araró-Simirao地热系统位于Cuitzeo湖凹陷的东南部。从地理上看，它位于跨墨西哥火山带省（TMVB）中部的东部。它是一个以液体为主的对流热液系统，含有氯化钠水和高硼含量。温泉释放的主要气体是CO2，以及较低浓度的H2S、H2和稀有气体（He、Ne、Ar）。本研究的目的是通过确定土壤中扩散气体排放浓度与最大渗透率合理区域（主要断层）之间的关系，来界定地热系统中的流体上升区域。在2018年（8月和11月）和2019年（5月）期间进行了三次采样活动，其中对土壤中的扩散气体排放量（CO2、Rn和汞蒸气）进行了测量，并对土壤温度进行了测量。对于采样活动，CO2通量在4.38至94.61 g m-2 d-1之间，气态元素汞（GEM）浓度在0.5至365 ng/m3之间。对于其他采样活动，CO2通量在0.8至1421 g m-2 d-1之间，GEM值在0.49至2914ng/m3之间。在上一次采样活动中，还测量了22Rn和220Rn，这些值分别在1060至124100 Bq/m3和0至7511 Bq7m3之间波动。发现了几个CO2通量、GEM和222Rn浓度的异常带，这些异常带与最大渗透率带（断层和线性构造）相匹配。这三个参数值最高的区域位于所谓的“泥浆池”中，位于Araró-Simirao断层与NW-SE线性构造（南区）的交叉处，该线性构造与系统的上流区有关。其他异常带也位于系统中部和北部的断裂和/或线性构造带中，与流出带有关。根据获得的数据，在气体垂直上升的区域，二氧化碳可能是汞和222Rn的载体，在流出区，这种气体可能溶解在地下水中。
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