Abstract The identification and real‐time monitoring of geofluids during drilling is crucial for safe drilling operations and can provide valuable insights into reservoir properties and fluid migration. While mud gas logging is well established in oil and gas exploration, recent interest in natural hydrogen (H 2 ) and helium (He) exploration has prompted the need for improved mud gas logging techniques for continuous wireline coring in crystalline bedrock. The detection of both H 2 and He is particularly useful when exploring these two commodities but also for identifying deep fluid migration notably in crystalline bedrock. This study presents the results of mud gas logging of O 2 , N 2 , 40 Ar, 38 Ar, 36 Ar, CO 2 , CH 4 , H 2 , He, and 222 Rn from two boreholes (909.5 and 578.5 m deep) drilled in the Ivrea‐Verbano Zone (Northern Italy) as part of the DIVE‐ICDP project. Comparison with data from geophysical logging showed that gas peaks correlate well with variations in the physical characteristics of the well fluid, indicating zones of fluid inflow. Real‐time gas monitoring proved to be valuable for identifying deep gas migration and aiding decision‐making. Despite its potential, this technique faces challenges, such as distinguishing between formation‐derived and drilling‐induced gases. Complementary analyses, including isotopic studies, are recommended to refine source identification. Nevertheless, the correlation of He and H 2 with CH 4 and CO 2 provides initial insights into their possible origins, making this method a promising tool for exploring H 2 and He gases in deep geological formations.
Abstract Micro‐diamonds and moissanite (SiC) have been identified in ophiolitic mantle harzburgites and chromitites of the New Caledonian Peridotite Nappe. The pale yellow (100–250 μm) micro‐diamonds and light blue moissanite (mean −26.5‰, range −33.5‰ to −23.8‰ and mean −26.9‰, range −31.8‰ to −25.6‰ respectively) exhibit consistently strong negative δ 13 C values consistent with vegetal (C3) photosynthesis. Preservation of U‐Pb ages amongst co‐occurring rutile xenocrysts, with a closure temperature of 620 ± 20°C, constrains the maximum thermal conditions experienced by these rocks. These temperatures indicate that the New Caledonian diamonds did not form under the deep mantle conditions typical of conventional diamond genesis but instead within a distinct supra‐subduction zone (SSZ) forearc setting. The association with moissanite suggests formation within anoxic, organic carbon‐rich sediments at the top of the subducting slab or within the subduction channel under localized super‐reducing conditions. In light of mantle heterogeneity, extension of the known distribution of ophiolitic diamonds to the Southern Hemisphere supports interpretation of their formation in relation to an SSZ process rather than a deep mantle source. It also highlights a previously unrecognized aspect of the global carbon cycle, underscoring the significance of SSZ forearc ophiolites in deep carbon transport and transformation.
Abstract Continental intraplate magmatism remains a fundamental challenge in Plate Tectonics. Triassic magmatism represents a critical phase in the evolution of the Central Asian Orogenic Belt and continues to provoke debate about its tectonic setting. This study presents an integrated analysis of field, petrographic, geochronologic, geochemical, and isotopic data from two newly identified Triassic granitoids in the Bogda Range: an adakitic porphyry and a low‐Sr/Y granite porphyry. Zircon U‐Pb dating yields nearly coeval crystallization ages of 221–220 Ma and 219–217 Ma, respectively. Both granitoids are characterized by high SiO 2 and K 2 O content, low MgO (Mg # ) and Ni content, and elevated K 2 O/Na 2 O and Th/Nb ratios. They have also depleted whole‐rock Sr‐Nd and zircon Hf isotopic compositions, indicative of juvenile crustal sources. The adakitic porphyry exhibits high Sr/Y and (La/Yb) N ratios, low Rb/Sr ratios, and weak Eu anomalies, suggesting derivation from garnet‐stable mafic lower crust. In contrast, the granite porphyry displays low Sr/Y and (La/Yb) N ratios, consistent with a plagioclase‐stable source. By integrating these results with regional data, we propose that the diversity of Triassic magmatism in the Eastern Tianshan is due to the reworking of juvenile and ancient crust at different depths and temperatures, resulting in arc‐like geochemical signatures. This process was associated with transcurrent tectonics and variable mantle contributions in a continental intraplate setting.
Abstract Provenance of pre‐obduction Eocene turbidites from New Caledonia is used to better constrain their geodynamic context and inform debate on subduction polarity. Chemical compositions of detrital clinopyroxenes in arenites are compared against potential sources. Basaltic source modeling using cpx/rock partition coefficients confirms E‐MORB origins from the allochthonous Poya Terrane. Detrital zircon populations in the Bourail Flysch are similar to those of the autochthonous Upper Cretaceous sedimentary cover. In contrast, a predominance of early Eocene zircons in the Nepoui‐Koumac Flysch suggests derivation from the supra‐subduction dyke system of the Peridotite Nappe. Results were compared with other arenite components (bioclasts, oxides, sulfides, zircon) and whole‐rock compositions of rock fragments and blocks of the breccia/olistostrome in the upper part of the turbidites. Together, the data set allows identification of multiple successive sources and processes. A syntectonic character for the flysch basins is inferred from the pre‐turbidite unconformity and provenance evolution. An abundance of shallow‐water bioclasts throughout the succession indicates the formation and continuous destruction of a rimming carbonate platform. The existence of two previously identified types of turbidite basins is confirmed by the characteristics of the Bourail (foreland) and the Nepoui‐Koumac (wedge‐top) flysch successions. These basins were located on the northern Norfolk Ridge (lower plate) and ultramafic allochthon (accretionary wedge), respectively, representing elements of a foreland basin. These observations are inconsistent with a hypothesized connection between New Caledonia and a continent‐directed Pacific subduction zone. Together with all available geologic data, the results of this investigation confirm the model of northeast‐ or east‐dipping pre‐obduction subduction.
Abstract This study investigates the influence of surface roughness, current intensity, and direction on tidal flows over asymmetric low‐angle dunes using high‐resolution particle image velocimetry in a laboratory flume. Experimental measurements reveal that, consistent with previous studies, low‐angle dunes generate substantial turbulence through flow expansion and shear, despite inducing only intermittent flow separation. Enhanced surface roughness and current intensity significantly increase turbulence, leading to permanent flow separation, akin to that observed over angle‐of‐repose dunes. When the flow direction opposes the dune's morphological orientation, weaker turbulent stresses are observed; however, flow expansion at the crest generates sufficient turbulence that persists downstream, impacting the flow field over the next dune. Hydraulic roughness parameters estimated from single and double log‐law velocity profiles offer a quantitative assessment of the variability of form roughness along the dunes during both ebb and flood tides. Ejection‐sweep cycles dominate turbulent flow in both aligned and opposing flow conditions, albeit with distinct spatial distributions. This study highlights crucial aspects of the interaction between dune morphology and reversing tidal currents, demonstrating that asymmetric low‐angle dunes can induce significant form roughness across the different tidal phases. These findings have important implications for flow resistance and sediment transport in tidal environments.