Journal of South American Earth Sciences最新文献

{"title":"Magma storage conditions of Navidad cone and its relation with the latest eruptions of Lonquimay volcano, Andean Southern Volcanic Zone","authors":"Soledad Riquelme-Ríos ,&nbsp;Inés Rodríguez ,&nbsp;Benigno Godoy ,&nbsp;Osvaldo González-Maurel ,&nbsp;Petrus le Roux ,&nbsp;Elisa Ramírez ,&nbsp;Harri Geiger ,&nbsp;Aracelly Acuña ,&nbsp;Gabriela Guzmán-Marusic ,&nbsp;Scarlett Chanqueo","doi":"10.1016/j.jsames.2026.105975","DOIUrl":"10.1016/j.jsames.2026.105975","url":null,"abstract":"<div><div>The Lonquimay-Tolguaca Volcanic Complex is constituted by Lonquimay volcano and Cordón Fisural Oriental, including the Navidad cone. An initial emplacement at 35–40 km depth, with different levels of crustal storage during ascent is proposed for Loquimay volcano. However, even though Navidad cone is in the vacinity of Loquimay volcano, a detailed relationship between the evolution and magmatic plumbing system of both volcanic structures is missing.</div><div>Considering its historical record (eruption occurred in 1988–1990), the Navidad cone is proposed to represent the active system of the Lonquimay Volcanic Complex, becoming an important target when trying to understand the active volcanic system of the SVZ. Therefore, the goal of this study is to determine the magmatic relationship between the Navidad cone and Lonquimay volcano, through various techniques, with a main focus on pyroxenes.Petrographically lavas from the last products of Lonquimay volcano (i.e. Lonquimay 5) show plagioclase, clinopyroxene, orthopyroxene and olivine phenocrystals, whilts orthopyroxene are absent at Navidad. Our geochemical data show that samples from Navidad are mainly andesitic, with some trachy-andesitic and trachytic compositions, whilst lavas from unit Lonquimay 5 vary from basaltic-andesite to andesite. Groundmass from Navidad has a trachy-andesite composition, whilst from Lonquimay 5 is mainly andesitic. Decreasing FeOt and MgO content with differentiation, and constant ⁸⁷Sr/⁸⁶Sr ratios (0.703960–0.703990) suggest that fractional crystallization controlled the magma evolution at both volcanic structures, with increasing ⁸⁷Sr/⁸⁶Sr ratios with differentiation suggesting more assimilation of crustal material for Lonquimay volcano.</div><div>Different thermobarometers were used for determining pre-eruptive conditions for Navidad (2–8 kbar; 1019–1068 °C), compared with those of Lonquimay volcano (0–8 kbar; 994–1150 °C). For both systems, magma ascent to chambers located at 6, 13, 17 and 22 km, connected by dikes or fissures. However, the petrographic and the geochemical signatures suggest that, even though the magmatic system feeding the volcanoes involved magma storage at similar depths, the feeding systems of Lonquimay volcano and Navidad acted slightly independently from each other.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"174 ","pages":"Article 105975"},"PeriodicalIF":1.5,"publicationDate":"2026-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146098575","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Assessment of soil loss and amount of sediment exported and deposited in Upper Grande River Basin (Brazil) considering different scenarios","authors":"R. Cassaro ,&nbsp;J.Z. Lima ,&nbsp;R.R.M. Ferreira ,&nbsp;V.G.S. Rodrigues","doi":"10.1016/j.jsames.2026.105977","DOIUrl":"10.1016/j.jsames.2026.105977","url":null,"abstract":"<div><div>Understanding erosion patterns and drivers of soil in tropical catchments is essential for its effective conservation, especially under increasing climate change uncertainties. In this study, the Integrated Valuation of Ecosystem Services and Tradeoffs – Sediment Delivery Ratio (InVEST-SDR) model assessed soil loss, sediment export, and deposition in the Upper Grande River Basin (UGRB) in Brazil. The model inputs included digital terrain model (30 m × 30 m), 40 years of rainfall data, soil map, land use and land cover data, biophysical table, and calibration parameters. The results showed soil loss varied significantly in response to rainfall erosivity, with the lowest estimated soil loss of 11.29 Mg ha⁻¹ year⁻¹ occurring in 2014, when a severe drought in southeastern Brazil reduced rainfall erosivity to 2734.50 MJ mm ha⁻¹ h⁻¹ year⁻¹. Total soil loss hotspots due to steep slopes and high erosivity were identified in the southern basin region; however, the local soils are shallow and poorly evolved, limiting actual erosion rates. InVEST's reliance on USLE factors such as slope and erosivity leads to an overestimation of soil loss in areas with steeper terrain. Two future land use scenarios were analyzed considering climate change uncertainties. In Scenario 1, the replacement of pastures with temporary crops reduced soil losses from 33.27 Mg ha⁻¹ year⁻¹ (actual use) to 29.76 Mg ha⁻¹ year⁻¹ in 2004–2013, with a slight increase occurring in 2014–2023 (from 25.21 Mg ha⁻¹ year⁻¹ to 27.12 Mg ha⁻¹ year⁻¹). In Scenario 2, replacing pastures with planted forests reduced losses from 6.74 Mg ha⁻¹ year⁻¹ (actual use) to 3.11 Mg ha⁻¹ year⁻¹ in 2004–2013, with stable values in the following decade (2.94 Mg ha⁻¹ year⁻¹). The findings emphasize the potential of land use changes, such as adoption of planted forests, as a sustainable strategy to reduce soil loss, enhance climate change resilience, and keep a profitable activity for farmers. InVEST-SDR effectively assessed soil erosion and sedimentation, offering valuable insights for soil conservation and ecological restoration in tropical regions.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"173 ","pages":"Article 105977"},"PeriodicalIF":1.5,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146080256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reassessment of the Holocene eruptive history of atitlán stratovolcano, Guatemala","authors":"Eduard Pico Rodriguez ,&nbsp;Lucia Capra ,&nbsp;Rafael Torres-Orozco ,&nbsp;Daniel Eduardo Secaira Ziegler ,&nbsp;Gustavo Adolfo Chigna Marroquín ,&nbsp;María Moncada Vásquez","doi":"10.1016/j.jsames.2026.105973","DOIUrl":"10.1016/j.jsames.2026.105973","url":null,"abstract":"<div><div>Atitlán volcano, one of the youngest and most active stratovolcanoes in the Central American Volcanic Arc, poses a significant threat to the densely populated regions surrounding Lake Atitlán. Despite its eruptive potential and historic activity, the volcano's recent Holocene stratigraphy and eruptive history remain poorly constrained. This study presents a comprehensive reassessment of Atitlán stratovolcano's eruptive activity through detailed stratigraphic, petrological, and geochemical analysis carried out on 17 new sections across all flanks of the volcano. Field observations, supported by radiocarbon dating, geochemistry, grain-size, componentry, and petrography, allowed us to identify 10 volcanic units spanning from ∼1421 BC to 1856 AD. These eruptive successions reveal a recurring pattern of multi-phase activity comprising fallout, pyroclastic density currents (PDCs), and lava flows. Petrographic and geochemical analyses confirm that the volcano's products display basaltic-andesite compositions (53.03–56.73 SiO₂ wt%) within the calc-alkaline series, showing conspicuous mineralogical variability across eruptive phases. Grain-size and componentry analyses highlight the alternation between explosive and effusive dynamics, and the widespread distribution of deposits across all flanks underscores the volcano's high hazard potential. Volume estimates for the youngest fallout unit (0.01 to 0.12 km³ at a 1σ confidence level) suggest a VEI 3–4 event, consistent with strombolian to sub-Plinian eruptive styles, reaffirming that moderate-magnitude eruptions at Atitlán can produce regionally significant impacts. This work updates the geological map of Atitlán, establishes a robust stratigraphic framework for hazard assessment, and provides new insights into the volcano's eruptive behavior. These findings hold important implications for volcanic risk management at Atitlán and contribute to the broader understanding of stratovolcano evolution and hazards in similar volcanic systems worldwide.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"173 ","pages":"Article 105973"},"PeriodicalIF":1.5,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146080254","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The fate of back-arc basins: a constrained geodynamic model for the Bransfield basin case","authors":"Gonzalo Yanez ,&nbsp;Jorge Sanhueza ,&nbsp;Juan Carlos Parra","doi":"10.1016/j.jsames.2026.105963","DOIUrl":"10.1016/j.jsames.2026.105963","url":null,"abstract":"<div><div>Back-arc basin development is a relatively common and episodic geological process. In all the models proposed subducting slab play a key role. The most common setting is old/cold subducting slabs with island arcs/oceanic overriding plates, and strong corner flow. In contrast, young subducting slabs, continental overriding plates and weak asthenospheric flow is a rare combination for the development of back-arc basins In this particular tectonic setting the driving mechanisms are poorly understood.</div><div>In this communication, we develop a well-constrained thermomechanical geodynamic model to offer insights into the geological processes that allow the development of back-arc basins with a young slab as a driving force. As a case study, we use the Bransfield back-basin in the Antarctic Peninsula. This back-arc basin is a relatively well-constrained case, where independent geophysical proxies can be used to validate the scenarios obtained by the geodynamic model. Geophysical data used for validation purposes include, satellite-derived gravity, regional and local airborne magnetic surveys, natural seismicity, and heat-flow measurements. Geodynamic models, data and information derived from the geophysical proxies offer consistent results.</div><div>The implication of the modelling effort is that, back-arc basins can develop when plate kinematics suddenly stop. In such a particular tectonic setting the subducting slab collapses producing a roll-back effect. The strong corner flow produced drives the upward flow of asthenospheric hot material, enabling the development of a back-arc basin.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"173 ","pages":"Article 105963"},"PeriodicalIF":1.5,"publicationDate":"2026-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146080252","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Biochronocorrelation of K/Pg-Danian sections near Chicxulub: application of new planktic foraminiferal scales","authors":"Ignacio Arenillas ,&nbsp;Vicente Gilabert ,&nbsp;Iván Aparicio ,&nbsp;Hermann D. Bermúdez ,&nbsp;Liliana Bolívar ,&nbsp;Thierry Calmus ,&nbsp;Daniel Ferrer ,&nbsp;José M. Grajales-Nishimura ,&nbsp;Carlos L. Liesa ,&nbsp;Kenya E. Núñez-Cambra ,&nbsp;Ligia Pérez-Cruz ,&nbsp;Reinaldo Rojas-Consuegra ,&nbsp;María del Carmen Rosales-Domínguez ,&nbsp;Ana R. Soria ,&nbsp;Jaime Urrutia-Fucugauchi ,&nbsp;José A. Arz","doi":"10.1016/j.jsames.2026.105959","DOIUrl":"10.1016/j.jsames.2026.105959","url":null,"abstract":"<div><div>Using qualitative and quantitative planktic foraminiferal stratigraphy, we correlated the Danian sediments directly overlying the Chicxulub impact-related Cretaceous/Paleogene boundary deposits (K/Pg deposits) at localities across the Gulf of Mexico, the Caribbean, and the Colombian Pacific. The aim of this study was to apply recently developed planktic foraminiferal biochronological scales to determine whether these American K/Pg sections record continuous stratigraphic succession or show evidence of a hiatus between the K/Pg deposits and the first Danian sediments deposited under normal conditions (K/Pg-Danian hiatus). To accomplish this, we reviewed, completed, and updated biostratigraphic information generated over the last three decades, incorporating new data from thirty K/Pg sections. This effort resulted in a highly comprehensive biostratigraphic database for the lower to upper Danian across the studied regions. Leveraging this database, we developed two biochronological scales with a higher resolution than the more standardized scale by extending the Dan-achrozonation and the DanAZ-acmezonation of Arenillas et al. (2021)into the middle-upper Danian. These new planktic foraminiferal scales enable the estimation of stratigraphic continuity in the K/Pg sections or, where applicable, the temporal duration of the K/Pg-Danian hiatuses. We conclude that, among the sections studied, only Bochil and Guayal (Mexico), Moncada (Cuba), Beloc HA, Nan Pak and Roche à Pierre (Haiti), and probably Isla Gorgonilla (Colombia) exhibit stratigraphic continuity between the K/Pg deposits and the first normal Danian sediments.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"173 ","pages":"Article 105959"},"PeriodicalIF":1.5,"publicationDate":"2026-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146080255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New findings of pseudotachylytes and their paleoseismic significance, Sierras Pampeanas of San Juan, Argentina","authors":"Gladis N. Palacio Balderramo ,&nbsp;Brígida Castro de Machuca ,&nbsp;Ana C. Mugas Lobos ,&nbsp;Gustavo F. Ortíz ,&nbsp;Gimena M. Bazán ,&nbsp;Cristian E. Robledo","doi":"10.1016/j.jsames.2026.105956","DOIUrl":"10.1016/j.jsames.2026.105956","url":null,"abstract":"<div><div>In this contribution, the first occurrence of pseudotachylyte veins in the crystalline basement of the Sierras Pampeanas of San Juan province, Argentina, is presented.</div><div>The Pan de Azúcar and El Retamo pseudotachylyte veins were found closely related to the NNW-SSE trending Valle Fértil and Portezuelos fault zones, two major ductile-brittle shear zones that were tectonically active since the early Paleozoic.</div><div>Macro- and microstructures observed in both pseudotachylytes suggest that they are the product of rapid cooling of silicate melts along paleoseismic zones during faulting. This inference is supported by the presence of distinctive features like intrusive margins, flow banding and melt-corroded rims in clasts. Acicular and globular microlites, as much as lesser quantities of spherulites, were identified in the matrix of these rocks are considered as a product of direct crystallization from the melt. The presence of vesicles and amygdules indicates a possible formation depth of less than 7 km.</div><div>The chemical composition of pseudotachylyte veins closely resembles that of their host rocks, greenschist facies mylonitic rocks and mylonitized granitoid rocks, indicating that they were formed by frictional melting.</div><div>The pseudotachylytes described from the Pan de Azúcar and El Retamo fault zones were found occurring in veins, which is interpreted as an “in situ” origin. These pseudotachylytes were formed long after host rocks mylonitization. Well preserved microstructures and absence of subsequent overprinting suggest that they were formed in the late stages of faulting.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"173 ","pages":"Article 105956"},"PeriodicalIF":1.5,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146039671","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geology, U-Pb geochronology, and petrological affinity of peraluminous granitoids in Carajás Province, SE Amazonian Craton","authors":"Heron Silva Bezerra da Costa ,&nbsp;Davis Carvalho de Oliveira ,&nbsp;Bhrenno Marangoanha ,&nbsp;Marco Antônio Galarza ,&nbsp;Williamy Queiroz Felix ,&nbsp;Yury Harrison da Costa Reis ,&nbsp;Ana Carolina Mendes da Silva ,&nbsp;Elizangela de Jesus Vasconcelos","doi":"10.1016/j.jsames.2026.105961","DOIUrl":"10.1016/j.jsames.2026.105961","url":null,"abstract":"<div><div>Peraluminous magmatism records crustal reworking processes and provides important information about the evolution of continental crust. Peraluminous granitoids are uncommon in Archean geology, reflecting the unusual nature of processes at the time. In this context, the Vila Minerasul area in central-western Carajás Province contains a complex geological framework comprised of multiple granitoid plutons with distinct petrogenetic affinities. The main pluton has biotite as its main ferromagnesian mineral and is distinguished by the presence of primary muscovite as a varietal phase. This pluton is elongated in an E-W direction, covering an area of approximately 75 km² and delineated by shear zones. It comprises three lithological facies: muscovite-biotite granodiorite, biotite-muscovite granodiorite, and muscovite-biotite monzogranite. Deformational microstructures reveal the syntectonic character of this pluton, which has zones of low and high strain and deformation temperatures ranging from 300 to 600 °C. The rocks are magnesian, calc-alkaline, and highly peraluminous (A/CNK &gt;1.1). They present low HFSE and high LILE contents and a slight negative Eu anomaly. Compared to the main granitoid units of the Carajás Province, the peraluminous pluton of Vila Minerasul has a stronger affinity for potassic granites, differing by its higher A/CNK values. The crystallization age of this pluton is 2918.5 ± 5.1 Ma, although zircon populations between 2.94 Ga and 3.17 Ga are thought to be inherited. Two younger populations (2888.2 ± 6.7 Ma, 2839 ± 10 Ma) are thought to be rejuvenated metamict ages or regional metamorphic overprints. These rocks are considered to have formed in a collisional environment, with petrogenesis involving partial melting of TTG crust and the incorporation of metasedimentary components.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"173 ","pages":"Article 105961"},"PeriodicalIF":1.5,"publicationDate":"2026-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146001838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Seismotectonic analysis of the 2017 earthquakes in the Cordón del Plata, Mendoza (33°S): active strike-slip faults oblique to the Andean orogen","authors":"Araceli Tamara Diaz Zapata ,&nbsp;Silvana Liz Spagnotto ,&nbsp;José Francisco Mescua","doi":"10.1016/j.jsames.2026.105952","DOIUrl":"10.1016/j.jsames.2026.105952","url":null,"abstract":"<div><div>We present a seismotectonic study of a sequence of seismic events produced in 2017 in the Frontal Cordillera in Mendoza province, Argentina. The sequence consists of a M_L 5.6 main event that took place on February 3, 2017, west of the Cordón del Plata range and the major aftershocks occurred during February and March. Using seismological data from INPRES and IRIS, we reprocessed the events to obtain improved earthquake locations and to calculate focal mechanisms. Our results indicate that this seismicity was generated by a fault system that we name the Santa Clara fault, a NW-trending sinistral strike-slip structure. Our findings suggest that this fault is capable of producing earthquakes of magnitude greater than 6, with the potential to cause significant damage to populations and infrastructure in northern Mendoza. We also recognize that some of the aftershocks are localized along the ENE-trending nodal plane of this structure, indicating that it was also active during the seismic sequence. This structure can be associated with a fault system inherited from the Triassic extensional event in the region. Field data show that minor faults of this ENE-trending fault system affect Quaternary deposits, documenting its recent activity. We interpret that both fault systems are structures inherited from the pre-Andean history that reactivate in the current stress field as strike-slip faults. The Santa Clara fault is a hazardous structure that should be incorporated in analysis of the seismic hazard and risk in the region. More studies are needed to determine if the ENE-trending fault system is also capable of major earthquakes.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"173 ","pages":"Article 105952"},"PeriodicalIF":1.5,"publicationDate":"2026-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146080257","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evidence of Ediacaran transitional arc magmatism in the pelotas terrane, southernmost Brazil: Insights into the source and magmatic processes of the Pinheiro Machado Complex","authors":"Vivianne Andrade Bastos ,&nbsp;Edinei Koester ,&nbsp;Cristine Lenz ,&nbsp;Carla Cristine Porcher ,&nbsp;Daniel Triboli Vieira ,&nbsp;Rodrigo Chaves Ramos","doi":"10.1016/j.jsames.2026.105962","DOIUrl":"10.1016/j.jsames.2026.105962","url":null,"abstract":"<div><div>The Dom Feliciano Belt in southern Brazil records successive accretionary processes of the Brasiliano/Pan-African cycle that contributed to the assembly of Western Gondwana. This study investigates the Pinheiro Machado Complex (PMC), the main Neoproterozoic unit of the Pelotas Terrane, through whole-rock geochemistry and Sr–Nd isotope analyses. PMC lithotypes range from diorites to granites, with SiO₂ contents of 53.9–73.9 wt% and MgO of 0.6–6.1 wt%, reflecting compositional diversity from mantle-to crust-dominated sources. Trace-element spidergrams show enrichment in LILE (K, Th, Ce) and negative Nb–Ta–Ti anomalies, consistent with subduction-related arc magmatism. Chondrite-normalized REE patterns indicate LREE (Ce/Yb_N = 2.5–55.73) enrichment and subtle negative Eu anomalies. Sr–Nd isotope ratios define a mixed mantle–crustal signature, with ⁸⁷Sr/⁸⁶Sr_(i) = 0.7087–0.7104, εNd_(t) = −6.7 to −4.5, and T_DM ages of 1.4–1.7 Ga, suggesting significant assimilation of Paleoproterozoic orthogneiss basement. Geochemical modeling indicates that PMC magmas evolved predominantly through decoupled assimilation-fractional crystallization (AFC), involving ∼20 % assimilation of gneissic crust. In comparison, the mafic members were generated by 5–10 % partial melting of a spinel lherzolite mantle. These results, discussed in the context of the Pelotas Terrane, demonstrate that PMC magmatism formed in an oblique continental-arc environment during the closure of a V-shaped oceanic basin. The geodynamic model involves subduction, slab failure, and subsequent collision, recorded in the multiple intrusive pulses and structural associations of PMC rocks. This study refines the petrogenetic framework of the Pelotas Terrane and contributes to understanding the Neoproterozoic evolution of Western Gondwana.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"173 ","pages":"Article 105962"},"PeriodicalIF":1.5,"publicationDate":"2026-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146039663","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ichnological and chemostratigraphic analysis from the K-Pg transition in well 1-PO-01-PE, Paraíba Basin, Northeast Brazil","authors":"Sonia Agostinho ,&nbsp;Carlos Alves Moreira Júnior ,&nbsp;José Antônio Barbosa ,&nbsp;Wilson Rodrigues de Andrade Freitas ,&nbsp;Emmanuel Franco Neto ,&nbsp;Alcides da Nóbrega Sial","doi":"10.1016/j.jsames.2026.105958","DOIUrl":"10.1016/j.jsames.2026.105958","url":null,"abstract":"<div><div>We present an analysis of the ichnofossiliferous content from the Upper Campanian to the Lower Danian, obtained from well 1-PO-01-PE, Paraíba Basin, NE Brazil. The investigation integrated the bioturbation record and lithofaciological changes with δ¹³C and δ¹⁸O isotopic data to understand how variations in depositional environments and climatic conditions affected the benthic community. The analysis of core samples revealed a low diversity ichnological suite, dominated by the generalist ichnogenera <em>Palaeophycus</em> and <em>Planolites</em>, suggesting an ecosystem under ecological stress. The results suggest an intrinsic relationship between the intensity of bioturbation on the carbonate platform and sea-level changes, which controlled substrate oxygenation and energy levels. Reduced bioturbation is observed in periods associated with shallower waters and increased environmental energy (Danian), and also during the high sea-level period which may have reduced substrate oxygenation. The reduction of bioturbation during the Danian was influenced by marine regressive effects and occurred during colder climatic conditions.</div></div>","PeriodicalId":50047,"journal":{"name":"Journal of South American Earth Sciences","volume":"172 ","pages":"Article 105958"},"PeriodicalIF":1.5,"publicationDate":"2026-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145978414","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}