Pub Date : 2025-12-31DOI: 10.1016/j.jsames.2025.105935
Lucca Martins Franco , Miguel Tupinambá , Emanuele Francesco La Terra , Liliane Paiva Panetto , Rogério Guitarrari Azzone
Here, we provide some structural and mineralogical evidence about what happens below a volcanic field during precursor seismic events. Based on outcrops and borehole material, we analyzed volcanic-related structures within the Cretaceous volcanic sequence of the Alto Paranaíba Igneous Province and the underlying Areado Group sandstones in southeastern Brazil, focusing on the role of magmatic volatiles and magmatic fluid circulation. Structural, petrographic, and geochemical data indicate that magma ascent through subvertical conduits generated overpressure conditions, promoting carbonate-rich hydrothermal activity and widespread deformation. The resulting structural assemblage includes normal faults, deformation bands, localized folding, subhorizontal creeping faults, and soft-sediment deformation structures, particularly concentrated at sandstone–volcanic contacts. Geological profiles highlight the mechanical and hydraulic interaction between alkaline rocks and their sedimentary host. Overall, the results indicate that volatile exsolution during magma ascent was a key driver of fluid-assisted brittle deformation and induced seismicity, exerting first-order control on fault development, sediment destabilization, and hydrothermal alteration.
{"title":"Degassing-driven seismicity and deformation: Evidence from the Cretaceous Alto Paranaíba Igneous Province, southeastern Brazil","authors":"Lucca Martins Franco , Miguel Tupinambá , Emanuele Francesco La Terra , Liliane Paiva Panetto , Rogério Guitarrari Azzone","doi":"10.1016/j.jsames.2025.105935","DOIUrl":"10.1016/j.jsames.2025.105935","url":null,"abstract":"<div><div>Here, we provide some structural and mineralogical evidence about what happens below a volcanic field during precursor seismic events. Based on outcrops and borehole material, we analyzed volcanic-related structures within the Cretaceous volcanic sequence of the Alto Paranaíba Igneous Province and the underlying Areado Group sandstones in southeastern Brazil, focusing on the role of magmatic volatiles and magmatic fluid circulation. Structural, petrographic, and geochemical data indicate that magma ascent through subvertical conduits generated overpressure conditions, promoting carbonate-rich hydrothermal activity and widespread deformation. The resulting structural assemblage includes normal faults, deformation bands, localized folding, subhorizontal creeping faults, and soft-sediment deformation structures, particularly concentrated at sandstone–volcanic contacts. Geological profiles highlight the mechanical and hydraulic interaction between alkaline rocks and their sedimentary host. Overall, the results indicate that volatile exsolution during magma ascent was a key driver of fluid-assisted brittle deformation and induced seismicity, exerting first-order control on fault development, sediment destabilization, and hydrothermal alteration.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"172 ","pages":"Article 105935"},"PeriodicalIF":1.5,"publicationDate":"2025-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145886269","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 : 2025-12-26DOI: 10.1016/j.jsames.2025.105934
Harrizon Lima de Almeida , Jucieny Sousa de Moura Barros
The gold mineralizations of the Borborema Province are structurally controlled and hosted in amphibolite facies metamorphic rock sequences. These gold mineralizations are closely related to the Brasiliano/Neoproterozoic orogeny and classified as orogenic gold deposits. The São Francisco gold deposit (SFGD), located in the Rio Grande do Norte Domain, Borborema Province, has emerged as the most significant gold mine in the region. The SFGD is hosted in biotite schists of the Seridó belt and consists of a planar and elongated, SW-NE-oriented ore shoot spatially associated with F3 antiform fold. The gold occurs both within quartz veins and disseminated in the mica schist, in paragenetic association with pyrite, pyrrhotite, arsenopyrite, and galena. A structural mapping conducted in this study shows that the SFGD occurs in the hinge zone of a F3 fold, which is primarily controlled by an intersection lineation developed during the D3 deformation event. A 3D-dimensional strain analysis was conducted on the mica schists of the area, encompassing different segments of the mineralization-hosting structure. The deformation in the hinge zone and in the limbs of the fold was dominated by constriction strain and flattening strain, respectively. It is proposed that the emplacement and occurrence of the SFGD resulted from the increase in structural permeability in the hinge zone, which, combined with a localized constriction strain regime, enabled the pipe-like channelling of a high volume of hydrothermal fluids. The SFGD represents an alternative model for the formation of saddle reef-type ore shoots in F3 antiform folds hosted in the Seridó belt, Borborema Province.
borborrema省金矿成矿受构造控制，赋存于角闪岩相变质岩层序中。这些金矿化与巴西利亚/新元古代造山运动密切相关，可归类为造山型金矿床。s o Francisco金矿（SFGD）位于borborrema省里约热内卢Grande do Norte Domain，已成为该地区最重要的金矿。SFGD赋存于Seridó带的黑云母片岩中，由一个平面细长的sw - ne向矿床组成，空间上与F3反形褶皱有关。金既赋存于石英脉中，又浸染于云母片岩中，与黄铁矿、磁黄铁矿、毒砂、方铅矿共生。本研究的构造作图表明，SFGD发生在F3褶皱的铰区，主要受D3变形事件期间形成的交点线理控制。对该地区的云母片岩进行了三维应变分析，包括矿化-承载结构的不同段。褶皱铰区和褶皱翼部的变形分别以收缩应变和压扁应变为主。认为SFGD的就位和发生是由于铰链区结构渗透率的增加，加上局部收缩应变状态，使得大量热液形成了管道状通道。SFGD代表了borborrema省Seridó带F3反形褶皱中鞍礁型矿脉形成的另一种模式。
{"title":"Structural control and deformational evolution of the São Francisco gold deposit, Borborema Province (NE Brazil)","authors":"Harrizon Lima de Almeida , Jucieny Sousa de Moura Barros","doi":"10.1016/j.jsames.2025.105934","DOIUrl":"10.1016/j.jsames.2025.105934","url":null,"abstract":"<div><div>The gold mineralizations of the Borborema Province are structurally controlled and hosted in amphibolite facies metamorphic rock sequences. These gold mineralizations are closely related to the Brasiliano/Neoproterozoic orogeny and classified as orogenic gold deposits. The São Francisco gold deposit (SFGD), located in the Rio Grande do Norte Domain, Borborema Province, has emerged as the most significant gold mine in the region. The SFGD is hosted in biotite schists of the Seridó belt and consists of a planar and elongated, SW-NE-oriented ore shoot spatially associated with F<sub>3</sub> antiform fold. The gold occurs both within quartz veins and disseminated in the mica schist, in paragenetic association with pyrite, pyrrhotite, arsenopyrite, and galena. A structural mapping conducted in this study shows that the SFGD occurs in the hinge zone of a F<sub>3</sub> fold, which is primarily controlled by an intersection lineation developed during the D<sub>3</sub> deformation event. A 3D-dimensional strain analysis was conducted on the mica schists of the area, encompassing different segments of the mineralization-hosting structure. The deformation in the hinge zone and in the limbs of the fold was dominated by constriction strain and flattening strain, respectively. It is proposed that the emplacement and occurrence of the SFGD resulted from the increase in structural permeability in the hinge zone, which, combined with a localized constriction strain regime, enabled the pipe-like channelling of a high volume of hydrothermal fluids. The SFGD represents an alternative model for the formation of saddle reef-type ore shoots in F<sub>3</sub> antiform folds hosted in the Seridó belt, Borborema Province.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"172 ","pages":"Article 105934"},"PeriodicalIF":1.5,"publicationDate":"2025-12-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145927675","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 : 2025-12-26DOI: 10.1016/j.jsames.2025.105932
Roberto Silva Jr. , Elisabetta Erba , Aristóteles de Moraes Rios-Netto , Silvia Clara Silva , Mauro Daniel Rodrigues Bruno , Lília Dias Sabaraense , Milene Freitas Figueiredo , Leonardo Borghi , João Graciano Mendonça Filho
This study investigates paleoceanographic and paleobiogeographic changes in the South Atlantic Ocean between the late Albian and early Santonian, integrating quantitative analyses of calcareous nannofossil assemblages with new geochemical data from 123 samples collected at Site 356 (São Paulo Plateau). A total of 109 calcareous nannofossil taxa and nine bioevents were identified. Two major hiatuses, corresponding to the late Albian–Cenomanian (∼6.9 Myr) and late Turonian/early Coniacian (∼2.7 Myr), are evident in the calcareous nannofossil record. The integration of nannofossil assemblages, diversity indices, and paleoecological proxies (mTI and mNI) with Total Organic Carbon (TOC) and stable isotope data (δ13C and δ18O) reveals nine distinct paleoceanographic intervals. Notably, the OAE 2 interval is confirmed by a plateau in the positive δ13C excursion and a sharp spike in TOC, reflecting enhanced organic carbon burial, although the onset of this event was truncated by the late Albian–Cenomanian hiatus. The paleoceanographic reconstruction indicates a predominance of warm, oligotrophic surface waters from the late Albian through the Turonian. Subsequently, a distinct positive shift in δ18O values during the late Coniacian signals a transition towards cooler surface waters. The paleobiogeographic affinity of the assemblages shows a dominance of cosmopolitan and mid-to low-latitude taxa, consistent with paleogeographic reconstructions and paleolatitude estimates (24°S–30°S) for the studied section. However, the increased abundance of high-latitude taxa between the late Coniacian and early Santonian appears to reflect a phase of enhanced surface-water connectivity and/or more effective oceanic circulation between the Central and South Atlantic, possibly driven by sea-level rise and/or a reduced influence of geological barriers (e.g., the Rio Grande Rise–Walvis Ridge System).
本研究通过对356 Site （s o Paulo Plateau）收集的123个样品的钙质纳米化石组合的定量分析和新的地球化学数据，研究了南大西洋Albian晚期至Santonian早期的古海洋学和古生物地理变化。共鉴定出109个钙质纳米化石分类群和9个生物事件。在钙质纳米化石记录中，有两个主要的间歇期，对应于晚Albian-Cenomanian （~ 6.9 Myr）和晚Turonian/早Coniacian （~ 2.7 Myr）。综合纳米化石组合、多样性指数、古生态指标（mTI和mNI）、总有机碳（TOC）和稳定同位素（δ13C和δ18O）数据，揭示了9个不同的古海洋层序。值得注意的是，OAE 2的间隔由δ13C正偏移的平台和TOC的急剧上升证实，反映了有机碳埋藏的增强，尽管这一事件的开始被晚Albian-Cenomanian中断所截断。古海洋学重建表明，从晚阿尔比世到Turonian，温暖的、少营养的地表水占主导地位。随后，在Coniacian晚期δ18O值的明显正移标志着向较冷的地表水过渡。这些组合的古地理亲和性显示出世界性和中低纬度分类群的优势，与研究剖面的古地理重建和古纬度估计（24°S - 30°S）一致。然而，在晚Coniacian和早sanantonian之间高纬度分类群的增加似乎反映了一个增强的地表水连通性和/或中大西洋和南大西洋之间更有效的海洋环流阶段，可能是由于海平面上升和/或地质屏障（例如里约热内卢Grande rise - walvis Ridge系统）影响的减少。
{"title":"Paleoceanographic and paleobiogeographic inferences from late Albian to early Santonian calcareous nannofossils at DSDP Site 356, South Atlantic","authors":"Roberto Silva Jr. , Elisabetta Erba , Aristóteles de Moraes Rios-Netto , Silvia Clara Silva , Mauro Daniel Rodrigues Bruno , Lília Dias Sabaraense , Milene Freitas Figueiredo , Leonardo Borghi , João Graciano Mendonça Filho","doi":"10.1016/j.jsames.2025.105932","DOIUrl":"10.1016/j.jsames.2025.105932","url":null,"abstract":"<div><div>This study investigates paleoceanographic and paleobiogeographic changes in the South Atlantic Ocean between the late Albian and early Santonian, integrating quantitative analyses of calcareous nannofossil assemblages with new geochemical data from 123 samples collected at Site 356 (São Paulo Plateau). A total of 109 calcareous nannofossil taxa and nine bioevents were identified. Two major hiatuses, corresponding to the late Albian–Cenomanian (∼6.9 Myr) and late Turonian/early Coniacian (∼2.7 Myr), are evident in the calcareous nannofossil record. The integration of nannofossil assemblages, diversity indices, and paleoecological proxies (mTI and mNI) with Total Organic Carbon (TOC) and stable isotope data (δ<sup>13</sup>C and δ<sup>18</sup>O) reveals nine distinct paleoceanographic intervals. Notably, the OAE 2 interval is confirmed by a plateau in the positive δ<sup>13</sup>C excursion and a sharp spike in TOC, reflecting enhanced organic carbon burial, although the onset of this event was truncated by the late Albian–Cenomanian hiatus. The paleoceanographic reconstruction indicates a predominance of warm, oligotrophic surface waters from the late Albian through the Turonian. Subsequently, a distinct positive shift in δ<sup>18</sup>O values during the late Coniacian signals a transition towards cooler surface waters. The paleobiogeographic affinity of the assemblages shows a dominance of cosmopolitan and mid-to low-latitude taxa, consistent with paleogeographic reconstructions and paleolatitude estimates (24°S–30°S) for the studied section. However, the increased abundance of high-latitude taxa between the late Coniacian and early Santonian appears to reflect a phase of enhanced surface-water connectivity and/or more effective oceanic circulation between the Central and South Atlantic, possibly driven by sea-level rise and/or a reduced influence of geological barriers (e.g., the Rio Grande Rise–Walvis Ridge System).</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"172 ","pages":"Article 105932"},"PeriodicalIF":1.5,"publicationDate":"2025-12-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145927674","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 : 2025-12-24DOI: 10.1016/j.jsames.2025.105929
Federico J. Saponara , Maria F. Lajoinie , Mabel E. Lanfranchini , Christopher J. Spencer , Belén Marone
This study looks at the origin and development of anatectic pegmatites in the Paleoproterozoic basement of the Tandilia Belt (TB), Río de la Plata Craton, Argentina. It combines new field observations with petrography, whole-rock geochemistry, and stable isotope (δ18O) data from the Barker and Balcarce regions. The pegmatites, which have granitic and slightly peralkaline compositions, formed mainly during the post-collisional stage from 2026 to 1948 Ma. This occurred under an extensional regime linked to asthenospheric upwelling and they represent the final products of partial melting of metasedimentary and metaigneous rocks through dehydration and fluid-flux melting processes. Field observations show both concordant and discordant intrusions into gneiss, migmatite, amphibolite, granulite, marble, and skarn, which are controlled by tectonic domains and existing structures. Petrographic features include bimodal grain-size distributions, perthitic microcline, heavily sericitized plagioclase, poikilitic and myrmekitic textures, and abundant tourmaline and garnet. These features reflect crystallization from volatile-rich, evolved melts. Geochemical data indicate enrichment in SiO2, K2O, and total alkalis. They also show high levels of LILE (Rb, Th, U), a decrease in HFSE (Nb, Zr, Y), and REE patterns marked by LREE/HREE fractionation and varying Eu anomalies. δ18O values range from +6.5 ‰ to +11.3 ‰, supporting a crustal origin with different degrees of fluid interaction. Higher values in Barker suggest more assimilation from the upper-middle crust, while lower values in Balcarce indicate a stronger influence from mafic lithology and fluid participation. These combined results suggest that the TB pegmatites reflect the late-stage evolution of Paleoproterozoic anatectic magmas. They link the formation to crustal recycling processes and the merging of the Atlantica supercontinent during the 2.2–1.8 Ga interval.
本文研究了阿根廷Río de la Plata克拉通坦迪利亚带（TB）古元古代基底的无晶长伟晶岩的起源和发育。它结合了Barker和Balcarce地区的岩石学、全岩地球化学和稳定同位素（δ18O）数据。伟晶岩主要形成于2026 ~ 1948 Ma的后碰撞阶段，具有花岗质和微过碱性成分。这是在与软流圈上升流有关的伸展状态下发生的，它们是变质沉积岩和变质岩通过脱水和流体通量熔融过程部分熔融的最终产物。野外观测显示，片麻岩、混辉岩、角闪岩、麻粒岩、大理岩和矽卡岩中均有和合型和不和合型侵入，受构造域和现有构造控制。岩石学特征包括：双峰型粒度分布、粗长微斜长石、绢云母斜长石、易绿质和绢云母质织构、丰富的电气石和石榴石。这些特征反映了富含挥发物的熔融物的结晶。地球化学数据表明，SiO2、K2O和总碱富集。它们还显示出高水平的LILE (Rb, Th， U), HFSE （Nb, Zr， Y）的减少，以及以LREE/HREE分异和变化的Eu异常为标志的REE模式。δ18O值在+6.5‰~ +11.3‰之间，表明该区存在不同程度流体相互作用的地壳成因。Barker地区较高的值表明更多的是来自中上地壳的同化作用，而Balcarce地区较低的值表明基性岩性和流体参与的影响更大。这些综合结果表明，结核伟晶岩反映了古元古代深熔岩浆的晚期演化。他们将其形成与2.2-1.8 Ga期间的地壳再循环过程和大西洋超大陆的合并联系起来。
{"title":"Anatectic pegmatites and partial melting evolution in the Paleoproterozoic basement of the Tandilia Belt, Río de la Plata Craton: Insights from Barker and Balcarce regions (Argentina)","authors":"Federico J. Saponara , Maria F. Lajoinie , Mabel E. Lanfranchini , Christopher J. Spencer , Belén Marone","doi":"10.1016/j.jsames.2025.105929","DOIUrl":"10.1016/j.jsames.2025.105929","url":null,"abstract":"<div><div>This study looks at the origin and development of anatectic pegmatites in the Paleoproterozoic basement of the Tandilia Belt (TB), Río de la Plata Craton, Argentina. It combines new field observations with petrography, whole-rock geochemistry, and stable isotope (δ<sup>18</sup>O) data from the Barker and Balcarce regions. The pegmatites, which have granitic and slightly peralkaline compositions, formed mainly during the post-collisional stage from 2026 to 1948 Ma. This occurred under an extensional regime linked to asthenospheric upwelling and they represent the final products of partial melting of metasedimentary and metaigneous rocks through dehydration and fluid-flux melting processes. Field observations show both concordant and discordant intrusions into gneiss, migmatite, amphibolite, granulite, marble, and skarn, which are controlled by tectonic domains and existing structures. Petrographic features include bimodal grain-size distributions, perthitic microcline, heavily sericitized plagioclase, poikilitic and myrmekitic textures, and abundant tourmaline and garnet. These features reflect crystallization from volatile-rich, evolved melts. Geochemical data indicate enrichment in SiO<sub>2</sub>, K<sub>2</sub>O, and total alkalis. They also show high levels of LILE (Rb, Th, U), a decrease in HFSE (Nb, Zr, Y), and REE patterns marked by LREE/HREE fractionation and varying Eu anomalies. δ<sup>18</sup>O values range from +6.5 ‰ to +11.3 ‰, supporting a crustal origin with different degrees of fluid interaction. Higher values in Barker suggest more assimilation from the upper-middle crust, while lower values in Balcarce indicate a stronger influence from mafic lithology and fluid participation. These combined results suggest that the TB pegmatites reflect the late-stage evolution of Paleoproterozoic anatectic magmas. They link the formation to crustal recycling processes and the merging of the Atlantica supercontinent during the 2.2–1.8 Ga interval.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"172 ","pages":"Article 105929"},"PeriodicalIF":1.5,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145886267","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 : 2025-12-24DOI: 10.1016/j.jsames.2025.105933
Luis Gerardo Vázquez-Guevara , René Ventura-Houle , Tomás Alejandro Peña-Alonso , Oscar Guevara-Mansilla , Glenda Nelly Requena-Lara , Elizabeth del Carmen Andrade-Limas , Bárbara Azucena Macías-Hernández
Karst aquifers in northeastern Mexico constitute the primary source of freshwater for more than 900,000 inhabitants, yet the hydrogeochemical functioning of their recharge zones and the mechanisms controlling groundwater evolution remain insufficiently documented. This study examines the origin, circulation, and degree of hydrochemical evolution of groundwater in the Upper Guayalejo–Tamesí Basin, a carbonate-dominated karst system characterized by complex structural controls and seasonal recharge dynamics. Thirteen groundwater samples collected between 2023 and 2024 were integrated with previously reported hydrochemical datasets to evaluate water–rock interaction processes and identify flow components within the local, intermediate, and regional Mifflin framework. Three hydrochemical facies were identified from the results: (1) Ca–Mg–Cl–SO4, associated with evaporation processes and salt dissolution; (2) Ca–Mg–HCO3, typical of recharge zones in carbonate rocks; and (3) Na–K–Cl–SO4, corresponding to evolved waters with high mineralization. Major ion relationships indicate that calcite dissolution predominates (Ca2+ > Mg2+ and HCO3− > Ca2+), with a minor contribution from gypsum dissolution (SO42− > Ca2+), as well as halite dissolution and cation exchange. Flow classification reveals a progression from local to intermediate and regional systems, controlled by increasing residence time, circulation depth, and the influence of structural pathways. These results enhance the understanding of hydrogeochemical processes governing groundwater evolution in a major karst recharge zone of northeastern Mexico and provide a transferable conceptual framework applicable to karst basins worldwide. This contributes to improving regional-scale interpretations of groundwater flow dynamics and supports informed water-resource management in structurally complex carbonate terrains.
{"title":"Groundwater origin and circulation within a karst watershed recharge zone: the case of the Upper Guayalejo-Tamesí River Basin, southern Tamaulipas, Mexico","authors":"Luis Gerardo Vázquez-Guevara , René Ventura-Houle , Tomás Alejandro Peña-Alonso , Oscar Guevara-Mansilla , Glenda Nelly Requena-Lara , Elizabeth del Carmen Andrade-Limas , Bárbara Azucena Macías-Hernández","doi":"10.1016/j.jsames.2025.105933","DOIUrl":"10.1016/j.jsames.2025.105933","url":null,"abstract":"<div><div>Karst aquifers in northeastern Mexico constitute the primary source of freshwater for more than 900,000 inhabitants, yet the hydrogeochemical functioning of their recharge zones and the mechanisms controlling groundwater evolution remain insufficiently documented. This study examines the origin, circulation, and degree of hydrochemical evolution of groundwater in the Upper Guayalejo–Tamesí Basin, a carbonate-dominated karst system characterized by complex structural controls and seasonal recharge dynamics. Thirteen groundwater samples collected between 2023 and 2024 were integrated with previously reported hydrochemical datasets to evaluate water–rock interaction processes and identify flow components within the local, intermediate, and regional Mifflin framework. Three hydrochemical facies were identified from the results: (1) Ca–Mg–Cl–SO<sub>4</sub>, associated with evaporation processes and salt dissolution; (2) Ca–Mg–HCO<sub>3</sub>, typical of recharge zones in carbonate rocks; and (3) Na–K–Cl–SO<sub>4</sub>, corresponding to evolved waters with high mineralization. Major ion relationships indicate that calcite dissolution predominates (Ca<sup>2+</sup> > Mg<sup>2+</sup> and HCO<sub>3</sub><sup>−</sup> > Ca<sup>2+</sup>), with a minor contribution from gypsum dissolution (SO<sub>4</sub><sup>2−</sup> > Ca<sup>2+</sup>), as well as halite dissolution and cation exchange. Flow classification reveals a progression from local to intermediate and regional systems, controlled by increasing residence time, circulation depth, and the influence of structural pathways. These results enhance the understanding of hydrogeochemical processes governing groundwater evolution in a major karst recharge zone of northeastern Mexico and provide a transferable conceptual framework applicable to karst basins worldwide. This contributes to improving regional-scale interpretations of groundwater flow dynamics and supports informed water-resource management in structurally complex carbonate terrains.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"172 ","pages":"Article 105933"},"PeriodicalIF":1.5,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145886265","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 : 2025-12-23DOI: 10.1016/j.jsames.2025.105930
Guadalupe Maro , Juan Pablo Villalba Ulberich , Gabriel I. Alemán , Alba C. Muñoz Dada , Tai Wen , Chao Zhang , Patrocinio Flores , Edgar D. González , Pablo J. Caffe
The Campanorco Subvolcanic Complex (25°38′S–65°33′W) is a poorly known unit that comprises pheno-andesitic sills and dikes located approximately 600 km east of the Nazca Plate subduction trench, an unusual setting for typical Andean back-arc magmatism. This contribution offers new petrographic, geochemical and geochronological data. U-Pb dating on zircon yielded crystallization ages of 6.8 Ma, confirming its belonging to Upper-Miocene back-arc magmatism. This igneous system consists of amphibole-bearing rocks of the high-K calc-alkaline and shoshonitic series, related to an enriched mantle source, likely metasomatized by subduction-derived fluids. Magmatic differentiation primarily occurred through fractional crystallization of water-rich parental magmas, with low crustal contamination, typical of steady-state andesites. Magmatic enclaves are widespread and are good physical evidence for the influence of multiple episodes of magma mixing on magma evolution.
The formation of the Campanorco Subvolcanic Complex is attributed to slab shallowing during Middle to Late Miocene times, likely driven by the subduction of the Taltal and Copiapó aseismic ridges, which facilitated mantle hydration and magma generation far from the volcanic arc. This unit serves as a key indicator of the maximum extent of slab shallowing during this period in the segment between 24° and 26°S. The study of this system provides critical insights into the petrogenesis, tectonic setting, and mineralization potential of the easternmost Neogene back-arc magmatism in the Central Andes.
{"title":"The Campanorco Subvolcanic Complex: Insights into Miocene back-arc magmatism and slab shallowing in the 24°–26°S segment of the Central Andes","authors":"Guadalupe Maro , Juan Pablo Villalba Ulberich , Gabriel I. Alemán , Alba C. Muñoz Dada , Tai Wen , Chao Zhang , Patrocinio Flores , Edgar D. González , Pablo J. Caffe","doi":"10.1016/j.jsames.2025.105930","DOIUrl":"10.1016/j.jsames.2025.105930","url":null,"abstract":"<div><div>The Campanorco Subvolcanic Complex (25°38′S–65°33′W) is a poorly known unit that comprises pheno-andesitic sills and dikes located approximately 600 km east of the Nazca Plate subduction trench, an unusual setting for typical Andean back-arc magmatism. This contribution offers new petrographic, geochemical and geochronological data. U-Pb dating on zircon yielded crystallization ages of 6.8 Ma, confirming its belonging to Upper-Miocene back-arc magmatism. This igneous system consists of amphibole-bearing rocks of the high-K calc-alkaline and shoshonitic series, related to an enriched mantle source, likely metasomatized by subduction-derived fluids. Magmatic differentiation primarily occurred through fractional crystallization of water-rich parental magmas, with low crustal contamination, typical of steady-state andesites. Magmatic enclaves are widespread and are good physical evidence for the influence of multiple episodes of magma mixing on magma evolution.</div><div>The formation of the Campanorco Subvolcanic Complex is attributed to slab shallowing during Middle to Late Miocene times, likely driven by the subduction of the Taltal and Copiapó aseismic ridges, which facilitated mantle hydration and magma generation far from the volcanic arc. This unit serves as a key indicator of the maximum extent of slab shallowing during this period in the segment between 24° and 26°S. The study of this system provides critical insights into the petrogenesis, tectonic setting, and mineralization potential of the easternmost Neogene back-arc magmatism in the Central Andes.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"171 ","pages":"Article 105930"},"PeriodicalIF":1.5,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145885134","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 : 2025-12-23DOI: 10.1016/j.jsames.2025.105931
Maria Aline Pereira Dino , Rafael César Lima Pedroso de Andrade , Naiara Cipriano Oliveira , Fábio Hideki Yamada , Antônio Álamo Feitosa Saraiva , Renan Alfredo Machado Bantim
Coprolites can provide clues about the diet and behavior of extinct organisms. We investigated 66 coprolites from the Romualdo Formation (Lower Cretaceous, Araripe Basin, Brazil), housed in the paleontological collection of the Paleontology Laboratory of the Universidade Regional do Cariri (LPU). All specimens were collected over the last decade at the Café das Antigas site (Lameiro district, Crato, Ceará), a locality that exposes laminated carbonates, carbonatic concretions, and shales of the Romualdo Formation and has yielded a diverse assemblage of vertebrate and plant remains. Using stereomicroscopy and morphometric documentation, we classified specimens into diagnostic morphotypes following previous established criteria, based on end morphology (isopolar and anisopolar) and overall outline. Five morphotypes were identified, such as cylindrical (n = 16), conical (n = 5), spiral (n = 3), ovoid (n = 14), and amorphous/irregular (n = 2), in addition to 26 indeterminate specimens. Seven coprolites (10.6 %) preserve expressive phosphatic fragments consistent with fish bones and scales, adding independent ichnological evidence that complements body-fossil evidence that teleosts were one of the main producers. Rare spiral forms may relate to fish with a spiral valve. These observations are constrained by the low proportions of inclusions and the descriptive scope of our analyses. We highlight the value of coprolites for reconstructing trophic interactions in this Konservat-Lagerstätte and outline avenues for future work to refine producer identification and detect microinclusions.
{"title":"Coprolites from the Romualdo Formation (Lower Cretaceous, Araripe Basin, Brazil): brief comments on morphology and trophic interactions","authors":"Maria Aline Pereira Dino , Rafael César Lima Pedroso de Andrade , Naiara Cipriano Oliveira , Fábio Hideki Yamada , Antônio Álamo Feitosa Saraiva , Renan Alfredo Machado Bantim","doi":"10.1016/j.jsames.2025.105931","DOIUrl":"10.1016/j.jsames.2025.105931","url":null,"abstract":"<div><div>Coprolites can provide clues about the diet and behavior of extinct organisms. We investigated 66 coprolites from the Romualdo Formation (Lower Cretaceous, Araripe Basin, Brazil), housed in the paleontological collection of the Paleontology Laboratory of the Universidade Regional do Cariri (LPU). All specimens were collected over the last decade at the Café das Antigas site (Lameiro district, Crato, Ceará), a locality that exposes laminated carbonates, carbonatic concretions, and shales of the Romualdo Formation and has yielded a diverse assemblage of vertebrate and plant remains. Using stereomicroscopy and morphometric documentation, we classified specimens into diagnostic morphotypes following previous established criteria, based on end morphology (isopolar and anisopolar) and overall outline. Five morphotypes were identified, such as cylindrical (n = 16), conical (n = 5), spiral (n = 3), ovoid (n = 14), and amorphous/irregular (n = 2), in addition to 26 indeterminate specimens. Seven coprolites (10.6 %) preserve expressive phosphatic fragments consistent with fish bones and scales, adding independent ichnological evidence that complements body-fossil evidence that teleosts were one of the main producers. Rare spiral forms may relate to fish with a spiral valve. These observations are constrained by the low proportions of inclusions and the descriptive scope of our analyses. We highlight the value of coprolites for reconstructing trophic interactions in this Konservat-Lagerstätte and outline avenues for future work to refine producer identification and detect microinclusions.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"171 ","pages":"Article 105931"},"PeriodicalIF":1.5,"publicationDate":"2025-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145885135","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 : 2025-12-18DOI: 10.1016/j.jsames.2025.105921
Michele Iemma, Vinicius Carneiro, André Gondim Brandão, João Paulo Oliveira, Leonardo Borghi
In the distal southern Campos Basin, the reservoirs consist of pre-salt carbonates (Macabu Fm.), which underwent successive diagenetic processes such as silicification and dolomitization. These processes are responsible for changing the original mineral composition as well as their pore system categorized into matrix and non-matrix features. Therefore, advanced techniques such as Artificial Intelligence (AI) and related methodologies have been increasingly applied to improve the prediction of reservoir characteristics. This study aims to use open-hole wireline logs and borehole image logs (BHI) from six wells in the BM-C-33 block to investigate the distribution of non-matrix features and permeability–porosity properties, across mineralogical (calcite, dolomite, silica and clay) and reservoir facies of the Macabu Formation carbonates. The study's findings reveal a notable prevalence of silicified carbonates interbedded with restricted dolomitized layers. These highly silicified intervals exhibit a higher fracture density, with a mean P10 of around 3 fractures/m. Petrophysical models indicate average porosity and permeability values of 9 % and 0.34 mD, respectively among the six wells. The highest values occur in silicified carbonates, contrasting with the lower ones observed in dolomitized intervals. Overall the study suggest a certain favoring of the silicification process in the quality of the reservoirs.
{"title":"Linking mineralogical facies, petrophysical properties, and non-matrix features in silicified carbonates, BM-C-33, Campos Basin","authors":"Michele Iemma, Vinicius Carneiro, André Gondim Brandão, João Paulo Oliveira, Leonardo Borghi","doi":"10.1016/j.jsames.2025.105921","DOIUrl":"10.1016/j.jsames.2025.105921","url":null,"abstract":"<div><div>In the distal southern Campos Basin, the reservoirs consist of pre-salt carbonates (Macabu Fm.), which underwent successive diagenetic processes such as silicification and dolomitization. These processes are responsible for changing the original mineral composition as well as their pore system categorized into matrix and non-matrix features. Therefore, advanced techniques such as Artificial Intelligence (AI) and related methodologies have been increasingly applied to improve the prediction of reservoir characteristics. This study aims to use open-hole wireline logs and borehole image logs (BHI) from six wells in the BM-C-33 block to investigate the distribution of non-matrix features and permeability–porosity properties, across mineralogical (calcite, dolomite, silica and clay) and reservoir facies of the Macabu Formation carbonates. The study's findings reveal a notable prevalence of silicified carbonates interbedded with restricted dolomitized layers. These highly silicified intervals exhibit a higher fracture density, with a mean P10 of around 3 fractures/m. Petrophysical models indicate average porosity and permeability values of 9 % and 0.34 mD, respectively among the six wells. The highest values occur in silicified carbonates, contrasting with the lower ones observed in dolomitized intervals. Overall the study suggest a certain favoring of the silicification process in the quality of the reservoirs.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"171 ","pages":"Article 105921"},"PeriodicalIF":1.5,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145841810","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 : 2025-12-18DOI: 10.1016/j.jsames.2025.105922
I.A. Petrinovic , I.R. Hernando , J. Martí Molist
The Caviahue caldera represents one of the largest topographic depressions identified in the Southern Volcanic Zone of the Andes. Here we present volcanological, stratigraphic, geochronological, and structural data of the Caviahue caldera, complemented by available subsurface information. These data support the interpretation of two caldera collapse cycles: the first at 1.27 Ma (Caviahue Caldera) and the second at 0.134 Ma (Las Mellizas Caldera). Both cycles are predominantly intermediate in composition and share several key features, including the formation of multiple lava vents, widespread deposition of ignimbrite and lava sheets associated with caldera collapse, and inter-eruptive epiclastic sedimentation. The 1.27 Ma Caviahue caldera did not result from a single, catastrophic collapse event, but from incremental collapses driven by substantial lava effusion episodes similar to those observed in mafic calderas, interspersed with explosive events characteristic of silicic systems.
The Las Mellizas caldera, dated at 0.134 Ma, began with pre-caldera lava flows and syn-to inter-eruptive sedimentation within deltaic, fluvial, and alluvial settings related to a glacial environment. This was followed by a single ignimbritic eruption accompanying caldera collapse, concluding with the growth of the post-caldera Copahue volcano.
Both caldera collapse cycles show evidence of interactions between effusive and explosive volcanism and glacial conditions, as recorded in both volcanic and sedimentary deposits. This indicates the presence and persistence of glaciations in the Southern Andes prior to 1.27 Ma. The pattern of incremental caldera collapse, characterized by both effusive and explosive activity within glaciated environments, may represent a defining feature of calderas in the Southern Volcanic Zone.
卡维亚休火山口代表了安第斯山脉南部火山带中最大的地形洼地之一。在这里，我们提供了火山学、地层学、地质年代学和Caviahue火山口的结构数据，并辅以现有的地下信息。这些数据支持对两个火山口崩塌周期的解释：第一个在1.27 Ma (Caviahue caldera)，第二个在0.134 Ma （Las Mellizas caldera）。这两个旋回的主要成分都是中等的，并具有几个关键特征，包括多个熔岩喷口的形成，与火山口崩塌相关的火成岩和熔岩板的广泛沉积，以及喷发间的碎屑沉积。1.27 Ma Caviahue火山口不是由单一的灾难性崩塌事件造成的，而是由大量熔岩流出事件驱动的渐进式崩塌造成的，类似于在基性火山口中观察到的，其间穿插着硅系特征的爆炸事件。Las Mellizas火山口的年代为0.134 Ma，开始于火山口前的熔岩流和与冰川环境相关的三角洲，河流和冲积环境中的同期喷发间沉积。随后是一次火成岩喷发，伴随着火山口的崩塌，最后形成了后火山口的科帕韦火山。两个破火山口崩塌旋回都显示了火山喷发和火山爆发与冰川条件之间相互作用的证据，这些都记录在火山和沉积物中。这表明在1.27 Ma之前，南安第斯山脉存在并持续着冰川作用。在冰川环境中，以喷涌和爆炸活动为特征的增量破火山口崩塌模式可能代表了南部火山岩带破火山口的一个决定性特征。
{"title":"Geological and volcanological constraints on a long-lived and multi-stage collapse caldera: The Caviahue caldera, southern volcanic zone of the Andes","authors":"I.A. Petrinovic , I.R. Hernando , J. Martí Molist","doi":"10.1016/j.jsames.2025.105922","DOIUrl":"10.1016/j.jsames.2025.105922","url":null,"abstract":"<div><div>The Caviahue caldera represents one of the largest topographic depressions identified in the Southern Volcanic Zone of the Andes. Here we present volcanological, stratigraphic, geochronological, and structural data of the Caviahue caldera, complemented by available subsurface information. These data support the interpretation of two caldera collapse cycles: the first at 1.27 Ma (Caviahue Caldera) and the second at 0.134 Ma (Las Mellizas Caldera). Both cycles are predominantly intermediate in composition and share several key features, including the formation of multiple lava vents, widespread deposition of ignimbrite and lava sheets associated with caldera collapse, and inter-eruptive epiclastic sedimentation. The 1.27 Ma Caviahue caldera did not result from a single, catastrophic collapse event, but from incremental collapses driven by substantial lava effusion episodes similar to those observed in mafic calderas, interspersed with explosive events characteristic of silicic systems.</div><div>The Las Mellizas caldera, dated at 0.134 Ma, began with pre-caldera lava flows and syn-to inter-eruptive sedimentation within deltaic, fluvial, and alluvial settings related to a glacial environment. This was followed by a single ignimbritic eruption accompanying caldera collapse, concluding with the growth of the post-caldera Copahue volcano.</div><div>Both caldera collapse cycles show evidence of interactions between effusive and explosive volcanism and glacial conditions, as recorded in both volcanic and sedimentary deposits. This indicates the presence and persistence of glaciations in the Southern Andes prior to 1.27 Ma. The pattern of incremental caldera collapse, characterized by both effusive and explosive activity within glaciated environments, may represent a defining feature of calderas in the Southern Volcanic Zone.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"171 ","pages":"Article 105922"},"PeriodicalIF":1.5,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145841809","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 : 2025-12-15DOI: 10.1016/j.jsames.2025.105920
Uilliams Alves de Oliveira Paz , Luis Felipe Ferreira de Mendonça , Arthur Antônio Machado
Topographic irregularities act as mechanisms of flow convergence or divergence, affecting the vertical distribution of motion and creating velocity gradients. In estuarine regions, this process favors the formation of persistent residual structures, which play the role of concentrating or dispersing matter. This study investigates spatial variations in estuarine tidal flow induced by bathymetric variations on scales of 1–70 m, using Acoustic Doppler Current Profilers (ADCP). ADCP results show that in channels near Frades Island, bathymetric deepening generates more intense flows, with velocities reaching 0.6 m/s northward in the meridional component and 0.8 m/s westward in the zonal component, consistent with three-dimensional fluid dynamics. In regions farther from the mainland, bathymetric deepening causes attenuation and reversal of currents. Near to Itaparica Island, bathymetry deepens from 15 m to 50 m over a 2 km stretch, with the meridional component showing a variation from 0.4 m/s northward to 0.7 m/s southward. In the center of BTS, the reversal of the zonal component leads to the formation of cyclonic vortices. The ADCP data show that deepening in confined regions accelerates the flow, while in open areas it decelerates the flow, occasionally creating recirculation zones and localized vorticity. These results corroborate the existing literature on the influence of bathymetry on estuarine circulation and provide in situ evidence, highlighting the importance of incorporating high-resolution bathymetry and stratification to reproduce the complexity of flow in estuarine regions.
{"title":"Influence of bathymetric variation on the flows of Baía de Todos os Santos","authors":"Uilliams Alves de Oliveira Paz , Luis Felipe Ferreira de Mendonça , Arthur Antônio Machado","doi":"10.1016/j.jsames.2025.105920","DOIUrl":"10.1016/j.jsames.2025.105920","url":null,"abstract":"<div><div>Topographic irregularities act as mechanisms of flow convergence or divergence, affecting the vertical distribution of motion and creating velocity gradients. In estuarine regions, this process favors the formation of persistent residual structures, which play the role of concentrating or dispersing matter. This study investigates spatial variations in estuarine tidal flow induced by bathymetric variations on scales of 1–70 m, using Acoustic Doppler Current Profilers (ADCP). ADCP results show that in channels near Frades Island, bathymetric deepening generates more intense flows, with velocities reaching 0.6 m/s northward in the meridional component and 0.8 m/s westward in the zonal component, consistent with three-dimensional fluid dynamics. In regions farther from the mainland, bathymetric deepening causes attenuation and reversal of currents. Near to Itaparica Island, bathymetry deepens from 15 m to 50 m over a 2 km stretch, with the meridional component showing a variation from 0.4 m/s northward to 0.7 m/s southward. In the center of BTS, the reversal of the zonal component leads to the formation of cyclonic vortices. The ADCP data show that deepening in confined regions accelerates the flow, while in open areas it decelerates the flow, occasionally creating recirculation zones and localized vorticity. These results corroborate the existing literature on the influence of bathymetry on estuarine circulation and provide in situ evidence, highlighting the importance of incorporating high-resolution bathymetry and stratification to reproduce the complexity of flow in estuarine regions.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"171 ","pages":"Article 105920"},"PeriodicalIF":1.5,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145799274","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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