The genesis and formation of fluvial features at the mouth of the Amazon River (Northern Brazil) have been commonly associated only with changes in the mean sea level that occurred in the Quaternary. In this sense, the objective of this study was to understand the dynamics of the Breves-Boiuçu Delta and its Quaternary evolution, according to its progradation/erosion and Neotectonic controls. Structural lineaments were automatically detected using SRTM data by the SID3 software, and statically analyzed to identify the main lineament domains. In addition, drainage anomalies were mapped and the coastline changes (1986 to 2019) were evaluated using Landsat 5 and 8 satellite images. The lineament domain analysis point to the existence of a regional dextral shear zone NE-SW oriented. The ENE-WSW structures correspond to T fractures, whereas the N-S structures are dextral P, and NW-SE are sinistral faults (R’). The drainage patterns are tectonically controlled, and there is a long paleochannel between the Pará and Amazon Rivers, suggesting the existence of an ancient connection between these rivers. Finally, the changes in the coastline data indicate progradations in the delta frontal part and erosion in the distributary zone. In this context, through an evolutionary model we infer that there was a paleodelta between the Pará and Amazon rivers, which was abandoned due to river captures, resulting from the reactivation of the NE-SW dextral shear corridor and the Gurupá Arch. After the abandonment of the paleodelta, the Breves-Boiuçu Delta developed on the north of the Melgaço Bay.
The Salado Basin is a Late Mesozoic–Cenozoic intracratonic sedimentary basin developed over the Río de la Plata craton in eastern Argentina, with sedimentary fill exceeding 6 km in its main depocentral areas. Despite its regional significance, subsurface information across the onshore basin remains sparse, and no systematic ambient-noise study has previously been conducted within its limits. This work presents the first HVSR dataset within the Salado Basin, based on 19 sites distributed across a broadly NNW–SSE-oriented regional sampling framework extending from the shallower-basement domain north of the basin into the depocentral sector. The reference fundamental frequency decreases from approximately 0.3–0.5 Hz at the shallower-basement sites to ∼0.1–0.2 Hz in the depocentre, accompanied by a transition from simple, single-peak curves to broader, multi-peak responses. Exploratory full-curve clustering identifies two coherent families of HVSR morphology that align spatially with this pattern and with the regional gradient in compiled basement depth. At S01, where independent constraints indicate a basement depth of approximately 280–300 m, a first-order analysis yields an effective shear-wave velocity of ∼540–580 m/s, which is geologically plausible for the partially consolidated cover overlying the crystalline basement. In the depocentral sector, however, a sensitivity analysis shows that reproducing the compiled basement depths would require average shear-wave velocities that are difficult to reconcile with a plausible sedimentary fill. The lowest-frequency peak is therefore interpreted as more likely to reflect a major intra-basin impedance contrast, with the sediment–basement interface probably lying below the analysed frequency band. Secondary peaks are tentatively associated with shallower intra-basin contrasts. The dataset extends previous HVSR applications from the Río de la Plata coastal plain into the basin interior and provides a regional framework for future calibrated investigations.
Contrary to classical paradigms in the Geosciences, recent studies indicate that Neotectonics plays an important role in the landscape evolution of intraplate regions. In this context, this study evaluates possible neotectonic activity and its influence on the relief of the Itacaré region, an intraplate area in northeastern Brazil. To this end, structural lineaments were mapped using SRTM data and automatically extracted with SID3 software to identify the main lineament domains, which were then compared with seismicity data. Morphometric analyses (AF, Bs, SL index, and geomorphological anomaly degree) of the main drainage basins were also performed. A total of 1,077 tectonic features were surveyed in 55 outcrops and used as the basis for paleostress calculations. The main lineament trends are N–S and NNE–SSW, corresponding to the orientation of SHmax. Field evidence of neotectonic deformation was identified in outcrops of the Barreiras Group (Miocene), as well as in Podzols and Quaternary coral reefs. These recent deformations occur in the northeastern sector of the study area, coinciding with the occurrence of low-magnitude earthquakes and higher values of the SLsector/SLtotal ratio. The measured structures are related to three paleostress fields: NW–SE extension (Neogene), N–S extension (Pleistocene), and NW–SE extension (Holocene). These results confirm that Neotectonics is active in the study area, although its influence on landforms is either limited or concentrated in specific zones, such as the Maraú Peninsula, since most of the lithostructural control over the drainage network is most likely inherited from pre-existing basement structures.
A finite-fault model of the Mw 7.6 Limón earthquake (Costa Rica, 1991) was integrated with Coulomb static stress transfer (CFS), focal-mechanism stress inversion and slip/dilation-tendency analysis to assess fault reactivation, seismic-hazard and exploration implications in the Limón back-arc. Sixty-four focal mechanisms were grouped into five sub-areas, yielding six stress tensors (WSM qualities A-D) that define a strongly partitioned field ranging from radial extension to radial compression. SHmax trends NE–SW in the southern Limón Basin and rotates approximately 37° counterclockwise to NNE–SSW across the Moín paleo-high, interpreted here as a mechanical barrier separating contraction-dominated deformation in the south from coexisting contraction and distension in the northern basin. Although the regional regime is dominantly compressive, the CFS scenario for optimally oriented strike-slip receiver faults best reproduces the 1991 aftershock distribution, indicating preferential reactivation of inherited oblique faults aligned with the rotated SHmax. Slip-Ts (τ/σn) and Td dilation-tendency (σ1-σn/σ1-σ3) calculations for 40 regional faults and all nodal planes identify critically stressed structures where positive CFS lobes overlap intermediate to high Ts values and revealing that faults with low to intermediate dips and NW-SE or NE-SW strikes yield the highest reactivation potential. The 1993 Pejibaye sequence is interpreted as CFS-induced. The results refine seismic-source characterization east and south of the Moín paleo-high and provide a geomechanical framework for evaluating seismic hazard, fault-controlled fluid circulation, top-seal integrity and exploration risk in the Limón basins.
Aquifers exploited in the Riobamba area, located in the southeastern sector of the Chimborazo volcano (Andean Ecuador), are essential in the drinking-water supply, which is strongly affected by climate change. Unconfined and semiconfined volcano-sedimentary aquifers are exploited through springs and wells in both rural and urban areas.The aim of this study is to identify the recharge areas of aquifers through an isotopic approach (δ2H and δ18O) in relation to the geological and hydrogeological context. 49 monitoring points including precipitation, surface waters, wells, springs and glacier ice from the Chimborazo glacier were analyzed over four different sampling campaigns (2020-2022 period), collecting 143 samples. Main physicochemical parameters were analyzed to better understand the recharge processes.Results highlight that precipitation and plausibly glacier ice melting of the Chimborazo glacier recharge groundwater. Differences in recharge areas between the aquifer groups (Chimborazo springs, Guano springs, Llio wells, Riobamba wells) were highlighted, with potential shallow and deep groundwater circuits in the study area.The probable Average Recharge Area Elevation (ARAE) of the aquifers extends broadly between 3,020 and 4,530 m a.s.l. Nevertheless, the main ARAE is potentially situated between 3,400 and 4,000 m a.s.l., based on the prevailing isotopic compositions and the dominant fracture permeability. Specifically, the Riobamba urban area aquifer is also recharged at lower altitudes, suggested by the presence of an anthropogenic footprint in the groundwater.This study clarified the groundwater recharge areas and processes, providing valuable knowledge for starting actions aimed at safeguarding these areas in a context particularly vulnerable to climate change and contamination.
In previous studies, Lages et al. (2025) and Andrade et al. (2026) identified tooth marks on the holotype of Procaroloameghinia pricei (MCT.M.805+924) based on the presence of a fracture and a polished/sanded surface associated with the observed punctures. However, experimental studies plus micro-CT analyses reidentified these marks as bioerosions attributed to necrophagous invertebrates. We discussed the presence of ‘sanded’/‘polished’ surfaces as diagnostic features of tooth marks and made a brief comment about the association of fractures with punctures to identify Nihilichnus fissuratus.
The Martin Vaz Archipelago, located in the South Atlantic Ocean, approximately 1,200 km east of the Brazilian coastline, at the eastern end of the Vitória-Trindade Ridge (VTR), comprises three small islands (Martin Vaz, Norte, and Sul) and one islet (Agulha). Martin Vaz Island rocks are alkaline, silica-undersaturated, and range from ultrabasic to intermediate in composition. This study presents new petrographic, geochemical, and Sr–Nd–Pb–Hf isotopic data from Martin Vaz Island rocks to investigate their petrogenesis and tectonic setting within the VTR. Based on analyses of major and trace elements, the evolution of these rocks was influenced by processes such as fractional crystallization and melt mixing. The geochemical characteristics suggest a low degree of partial melting (< 2%) of a predominantly garnet lherzolite mantle source. To account for the Sr, Nd, Pb, and Hf isotopic characteristics, we propose a model involving the mixing of a dominant asthenospheric end-member (DMM; depleted MORB mantle), hybridized by the addition of two enriched end-members: enriched mantle I (EMI) and high-μ (HIMU, where μ = 238U/204Pb). The ternary mixing model suggests contributions of approximately 20% EMI and 19% HIMU to a DMM component (62%). The enriched components are interpreted to derive from recycled fragments of detached South American subcontinental lithospheric mantle incorporated into the mantle during the breakup of Gondwana. This process may have involved lithospheric delamination of the South American Plate beneath subducted slabs, facilitating mantle contamination beneath the South Atlantic Ocean and generating heterogeneities associated with the Brasiliano Orogeny.
This study examines the association between secondary lahar occurrence and rainfall conditions by comparing the timing of three events reported in the aftermath of the June 2011 Cordón Caulle eruption with precipitation records. The analysis focuses on proximal and mid-volcaniclastic settings, represented by the Nilahue and Maderera Misiones watersheds, respectively. The Maderera Misiones upper catchment comprises steep (up to 35°) slopes capped by very fine- to fine-grained ashfall deposits, whereas Nilahue upper catchments feature gentler slopes mantled by coarser tephra.For the 22 January Maderera Misiones and 3 February Nilahue lahars, a consistent association with moderate same-day rainfall totals is observed (ca 20 mm), whereas the 17 February Nilahue event is associated with exceptionally high same-day rainfall (>100 mm). Rainfall occurred in the days preceding the Nilahue lahars, whereas no precipitation was recorded before the Maderera Misiones-triggering storm.The analysis suggests that concentrated episodes of moderate rainfall may result in limited-volume lahars. At more distal downwind sites, fine-grained ashfall deposits on steep slopes may reduce infiltration, favouring surface runoff and rapid lahar generation from intense, isolated rainstorms. In contrast, in proximal upper catchments with gentler slopes, the higher infiltration capacity through coarser tephra may increase the importance of antecedent rainfall in promoting deposit instability.Despite the lack of a robust event dataset for the region, this evaluation provides a preliminary contribution to lahar modelling and hazard assessment associated with explosive volcanism in the Southern Volcanic Zone.
Gully fan depositional processes are not yet fully understood. This study investigated the stratigraphy of a gully fan connected to a fluvial channel network in the Amazon, focusing on microstratigraphy to identify flow types and depositional processes, and to determine if they resemble those generated by sheet flow. The macrostratigraphy shows very thin to medium beds (<0.03 to ≤ 30 cm) that are heterogeneously laminated, primarily consisting of soil aggregates (pedosediments). The microstratigraphy revealed a variety of textures, including sand, gravelly sand, sandy gravel, muddy sand, gravel, and sandy mud, with various primary structures, predominantly massive. The lithofacies indicate the following flow types: high-density flow (non-Newtonian rheology, dominant), high to low transitional density flow (non-Newtonian and/or Newtonian rheology), and low-density flow (Newtonian rheology, rare occurrence). This suggests a decreasing frequency of depositional processes: frictional freezing en masse deposition, traction carpet, suspended-load settling, ‘gradual aggradation in non-uniform flow’, and cohesive freezing (‘mud flow’). A comparison between the stratigraphic and sedimentological characteristics of the gully fan and sheet flow deposits showed total or partial similarities in hydraulic controls, stratigraphic attributes, and flow-deposition types. These similarities can be explained by the hydraulic controls of (i) slope type transport/accommodation and (ii) stream morphology. We believe our findings can serve as a facies model for both modern and ancient gully fans in various geomorphic settings worldwide.
Globally, low-δ18O (<5.7‰) magmas are rare, especially in subduction zone settings. Here we report the variation in oxygen isotope composition of 0 to 12 Ma magmatic rocks across the Central Volcanic Zone (CVZ) of the Andes. The analysed samples range from andesite to dacite lavas (SiO2 62 to 72 wt%), ignimbrite sheet deposits, and lava domes. The δ18O value of quartz phenocrysts range between 7.1 and 10.7‰ (n = 83) and reflect those of the magma and give an average estimated magma δ18O value of 9.33‰. Biotite and quartz phenocryst pairs have δ18O values that are consistent with oxygen isotope equilibrium at magmatic temperatures. In this study, we actively sought hydrothermally altered rocks for bulk rock analysis. Bulk rock δ18O values (n = 74) range from 5.0 to 22.3‰, with the majority of visibly altered samples having high δ18O values. The δD values of biotite phenocrysts are similar to those of bulk rock (−71 to −138‰). We, therefore, find little evidence for either low-δ18O magmas or low-δ18O rocks in the CVZ; even in zones of hydrothermally alteration.Previous explanations why low-δ18O rocks and magmas are not present in the CVZ highlight the low precipitation combined with high evaporation rates, which limited the influx of meteoric water to hydrothermal systems. Our data show that even when hydrothermal alteration occurred it did not generate low-δ18O rocks, without which, low-δ18O magmas could not be generated. The CVZ and other subduction-related volcanoes in the Caribbean and Indonesia share similar ranges of whole-rock δ18O and δD values. This is consistent with a common alteration fluid dominated by subduction-related magmatic fluid that limits the influx of 18O-depleted surface water into sub-volcanic hydrothermal systems.
Petrography, geochemical and isotopic analysis and new radiometric ages of the Tunnel Tonalite (TT) a small stock made up of epidote bearing amphibole-biotite quartz diorite and biotite-amphibole tonalite which intrude the medium grade metamorphic rocks of the Devonian Cushamen Formation are presented. A mainly pervasive magmatic-submagmatic foliation overprinted by a more localized planar fabric associated with high solid state deformational features are partially reworked and overprinted by a lower temperature deformation event. New whole-rock chemical analyses and Sr isotope data together with published data indicate that TT (SiO2 50.3-63.70%) is metaluminous (A/CNK. 0.85) to mildly peraluminous (A/CNK:1.07) and belong to a medium-K calc-alkaline series. Relative to primitive mantle samples show selective enrichments in large ion lithophile elements and to a lesser extent in La and Ce, but depletions in some high field-strength elements. Nb-Ta troughs are typical for arc-related rocks. REE patterns indicate both a marked increase in LREE and a decrease in HREE. Eu/Eu∗ varies from 0.85 to 0.94. Tectonic diagrams based on trace elements indicate arc magmatism. Rb-Sr data that were recalculated at 295 Ma indicate a narrow range of 87Sr/86Sr295, 0.70670 for the quartz diorite and 0.70634 to 0.70761 for the tonalite of TT. A new LA ICPMS zircon age of 291.76 ± 0.89 Ma for a biotite hornblende tonalite and 40Ar/39Ar age of 279.6 ± 04 Ma on hornblende from a quartz diorite allowed to constrain the regional D3 event. Textural evidence of magmatic epidote before plagioclase suggests P above 10 kbar for the crystallization. Modelling of fractional crystallization indicates that the tonalite derive from the quartz diorite by plagioclase and amphibole fractionation. The comparison with the available chemical and isotopic data for mafic to intermediate rock that cover the time span from 325 to 290 Ma, i.e. the Mid-Late Pennsylvanian-early Permian mafic to intermediate rocks from Laguna del Toro, Paso del Sapo and Sierra de Pichiñanes and the Upper Mississipian to Lower Pennsylvanian from Bariloche to El Bolson area in the foothills of the Patagonian Andes would constrain an across arc change in crustal thickness at ca. 315 Ma that is mainly accompanied by the metasomatism of the mafic source of the Cisularian magmatism by subduction related fluids and probably some sediment melts.
