ABSTRACT Knickpoints, or topographic perturbations within river profiles, are often attributed to uplift, climate or sea‐level change. However, knickpoint dynamics along continental shelves are poorly understood. Here, we use a landscape evolution model to simulate the response of an artificial passive margin to multiple sea‐level fluctuations in order to understand how knickpoints form and propagate inland. We demonstrate that, while it may be difficult for knickpoints to traverse an entire 100–200 km wide shelf within one lowstand, this is not necessary for preservation. The erodibility contrast between a soft coastal plain and a relatively resistant hinterland allows knickpoints to develop at the contact during eustatic lows. These knickpoints accumulate over multiple sea‐level cycles and generate a broad zone of rapid incision, which we relate to dated fluvial terrace incision along the US mid‐Atlantic margin.
ABSTRACT Oceanic rises in the Indian Ocean are generally interpreted as products of mantle plume magmatism that developed on the oceanic lithosphere; however, evidence suggests the presence of inherited continental materials beneath select oceanic plateaus and rises. We report zircon and titanite petrochronological data from Eocene intraplate basalt dredged from the Conrad Rise in the southern Indian Ocean. Zircon cores yielded concordant Mesoproterozoic U–Pb ages, with a weighted mean 206 Pb/ 238 U age of 1052 ± 26 Ma, and exhibited oscillatory zoning, heavy rare earth element (HREE)‐enriched REE patterns, and high Th/U ratios (> 0.1), whereas the thin zircon rims yielded younger ages of ca. 550 Ma and low Th/U ratios (< 0.1). Titanite yielded concordant Eocene ages (39–44 Ma) overlapping the previously reported 40 Ar– 39 Ar age of the host volcanic rock. These data suggest the preservation of continental crustal materials beneath or within the Conrad Rise during Eocene intraplate volcanism.
ABSTRACT The Southern Brasília Orogen formed during Western Gondwana's final assembly and comprises nappe systems piled against the São Francisco Craton. We present new rutile U–Pb ages from the lowermost Canastra Group (> 2.2 Ga) and the uppermost Carrancas Group (~560 Ma), integrated with published zircon, monazite, garnet, and mica ages from the Araxá and Andrelândia Groups. The dataset reveals a progressive increase in metamorphic resetting toward structurally higher nappes, from preserved Paleoproterozoic ages to partial and complete Ediacaran ca. 560 Ma resetting (late‐stage retrogression/exhumation potentially influenced by the Ribeira Orogen tectonothermal activity). This pattern supports the inverted metamorphic gradient, influenced by mineral closure temperatures and structural position. The results define crustal‐scale thermal architecture, indicating deeper burial and higher‐temperature metamorphism in the upper nappes, while the lower Canastra Group remained relatively cool and was later incorporated into the thrust system.
ABSTRACT Eocene dolomites of Saudi Arabia host silica and calcite concretions. Diagenetic processes that lead to their formation are investigated using petrography, stable isotopes, U/Pb geochronology and clumped isotopes. Early dolomitization and possible shallow burial recrystallization are inferred from U/Pb Palaeocene‐Eocene crystallization age (54.6 ± 70 Ma), very close to depositional age, and precipitation temperature around 51°C from Δ 47 data. Four generations of quartz replaced synsedimentary anhydrite nodules, including megaquartz, chalcedony, radial drusy quartz and euhedral hexagonal megaquartz. These results support an early replacement of the anhydrite nodules by silica under limited burial and temperature conditions. Calcites dated from Pliocene to Holocene (< 5 Ma) are the last diagenetic phase observed within concretions and fractures, precipitated while the Rus Formation was subaerially exposed. Δ 47 data and very negative δ 18 O calcite (reaching −14‰ V‐PDB) suggest precipitation from meteoric fluids (δ 18 O water −8.0 to −5.4‰ V‐SMOW) percolating through fractures, probably under a wet monsoonal context.
ABSTRACT Geothermal energy is central to the global green energy transition, but its development has long focused on regions with positive thermal anomalies. Through a semi‐quantitative global‐scale review and spatial analysis of 361 geothermal sites, we show that 56.2% of global geothermal electricity production occurs in regions with thermal conditions typical of average continental crust, challenging conventional models that prioritize heat flow as the main exploration criterion. Our results indicate that crustal permeability, especially fault‐related permeability linked to active seismicity, is a major control on geothermal viability and remains underestimated in resource assessments. In these geothermal contexts, permeable structural networks can sustain deep fluid circulation, even without recent magmatic activity. Rather than replacing thermal criteria, we propose that permeability should be considered as a complementary and, in many cases, decisive parameter in geothermal exploration. This perspective provides a refined framework for identifying underexplored regions and improving global geothermal resource assessment.
