Geochemistry Geophysics Geosystems最新文献

Mantle metasomatism is a common phenomenon in convergent margins; however, metasomatism by subducted sediments and their role in alkaline magma generation remain poorly understood. Alkaline rocks from the Tangra-YumCo rift (TYR) in southern Tibet show a unique geochemical composition among post-collisional volcanic rocks of the Lhasa terrane. These rocks exhibit high potassium (up to 10.59 wt. %) and silica (up to 70.01 wt. %) contents, very light boron (B) isotopic ratios (δ¹¹B = −14.85‰ to −29.72‰), and negative mass-independent fractionation in mercury (Hg) isotopes (Δ¹⁹⁹Hg = 0 to −0.54‰). We propose that these magmas were derived from a mantle source that was metasomatized by continental sediments, which underwent extensive dehydration during subduction. Slab tearing beneath southern Tibet triggered partial melting of this metasomatized domain around 13.0 ± 0.2 Ma (U-Pb). The resulting magmas record the reactivation of a sediment-enriched mantle source previously modified by continental subduction. These results demonstrate that deeply recycled continental sediments, like their oceanic counterparts, can contribute to mantle metasomatism and ultimately to the genesis of compositionally extreme magmas. The combined application of B-Hg-O-Hf isotopes provides new constraints on sediment recycling and the thermal reactivation of enriched mantle domains in post-collisional orogenic settings.

Pressure and temperature estimates of metamorphic terranes are increasingly retrieved from forward thermodynamic modeling coupled with isopleth thermobarometry. Although geodynamic reconstructions are mathematically derived, thermobarometric estimates are limited by a lack of quantitative constraints, especially on their uncertainties. This work explores the application of the statistically based approach of Bingo-Antidote on a chloritoid-garnet-bearing micaschist from a high-pressure unit in the continental Western Alps, Italy. Calculations highlighted a good match between the observation and the model at conditions that overlay the quartz-coesite polymorphic reaction. This result called for targeted investigations, which ultimately led to the recognition of coesite inclusions in the garnet domain modeled to be equilibrated at such conditions, pinpointing the pressure peak at ultra-high-pressure conditions. Our results show a so-far unexplored application of Bingo-Antidote as a straightforward and fast tool for guiding targeted investigations, such as the search for potential occurrences of otherwise elusive phases like coesite, which might be time-consuming if randomly applied. In addition, this contribution infers a possible architecture of the Dora-Maira Massif paleomargin, discussing it in the framework of existing geodynamic simulations.

Metamorphic transformations in subduction lithosphere are triggered by pressure and temperature changes occurring under stress. This anisotropic stress field can in turn be locally altered by the transformation pattern, as reactions induce significant changes of the material properties of the rocks. The granulite to eclogite transformation constitutes a striking example of a pressure-driven transformation potentially able to generate significant volume forces due to densification and known to be associated with transient weakening. However, the feedback mechanisms between pressure variations and the evolution of the physical properties of rocks during eclogitization remain poorly constrained. Formalizing these interactions is thus required to understand how eclogitization initiates and propagates under stress. In this study, mechanical numerical models are used to explore the evolution of eclogitization in a matrix-inclusion system subjected to shear boundary conditions, where pressure variations control the physical properties of the materials. Our results show that the initiation of the transformation is controlled by both the strength of the protolith and by the degree of overstepping of the transformation. Eclogite structures then systematically propagate in the direction normal to the principal shortening direction. In contrast, other parameters such as the density variations involved in the transformation, the initial difference in strength between the protolith and the inclusion, and the shape and orientation of the inclusion do not play a major role on the transformation initiation itself but enhance or inhibit its propagation.

Hydrothermal activity during continental breakup and early oceanic spreading is poorly understood due to limited samples. A basalt-hosted hydrothermal mineralization, drilled during IODP Expedition 367/368 at the northern South China Sea at the continent-ocean transition provides a unique opportunity to investigate this phenomenon. Detailed petrological and geochemical analyses, including pyrite trace elements reveal a diverse paragenetic sequence consisting of two main generations of hydrothermal alteration and veining. The first generation is marked by chloritization and disseminated pyrite mineralization, followed by quartz-epidote-pyrite veining with minor chalcopyrite and sphalerite precipitation. The second generation consists of early, sulfide-free siderite-ankerite veins, followed by the formation of ankerite-dolomite veins containing pyrite, chalcopyrite, and rare calcite. These variations highlight the spatiotemporal complexity of this hydrothermal system. Pyrite trace element chemistry, particularly Co, Ni, and Cu enrichments, suggests peak fluid temperatures exceeding 250°C for all sulfide-bearing generations. Pyrite trace elements further contribute to a better understanding of the nature of the underlying crust at this continent-ocean transition. They infer a reaction of hydrothermal fluids with underlying basalt and syn-rift sediments with no indication for interaction with continental or mantle material. The early silicate-rich generation of chlorite-quartz-sulfide mineralization shows characteristics similar to other drilled hydrothermal systems, for example, TAG on the Mid-Atlantic Ridge. However, abundant epidote and siderite, as observed here, have not been documented for modern seafloor stockwork zones. This indicates potentially important differences in the characteristics and formation conditions of hydrothermal mineralization formed during the onset of oceanic spreading and those formed at mature mid-ocean ridges.

The Lepontine dome (European Central Alps) is constituted by basement nappes under Alpine regional Barrovian metamorphism, yet the duration and pattern of its post-peak amphibolite-facies cooling remain uncertain. We examine garnet-rim compositional re-adjustment and employ inverse multicomponent diffusion modeling to estimate apparent cooling rates. We selected six garnet paragneisses at different tectonic levels within the Lepontine nappe pile. Garnet crystal rims are syn-kinematic with respect to the amphibolite-facies metamorphic foliation and display coupled Mn increase and Mg decrease, indicative of retrograde reactions. Using geothermobarometry, we estimate re-equilibration post-peak temperatures between 577 and 661°C at pressures between 0.5 and 1.3 GPa. Our inferred cooling rates reveal a spatial trend: the shear zone below the main nappe (Maggia-Adula) records rapid cooling with rates between 100 and 400°C/Myr, the footwall cools slower with a rate of 2°C/Myr, and the migmatitic belt in the southern Lepontine dome shows intermediate cooling rates between 20 and 50°C/Myr. We perform one-dimensional (1D) thermal and two-dimensional (2D) thermo-kinematic models. The observed cooling rate distribution, characterized by high rates along the shear zone and significantly lower rates in the footwall, matches the predictions of 2D models where a hotter nappe is emplaced onto a colder one. Both 1D and 2D models suggest that high cooling rates above 600°C and above 0.5 GPa observed along the main shear zone are likely not caused solely by heat advection and diffusion associated with nappe stacking and exhumation. Local heat sources, such as the percolation of hot fluids or shear heating, may have contributed to high cooling rates.

Subsurface geometries, such as faults and subducting slab interfaces, are often poorly constrained, yet they exert first-order control on key geophysical processes, including subduction zone thermal structure and earthquake rupture dynamics. Quantifying model sensitivity to geometric variability remains challenging for high-fidelity simulations that require generated meshes, due to the manual effort of mesh generation and the computational cost of exploring high-dimensional parameter spaces. We present a mesh morphing approach that deforms a reference mesh into geometrically varying configurations while preserving mesh connectivity. This enables the automated generation of large ensembles of geometrically variable meshes with minimal user input. Importantly, the preserved connectivity allows for the application of data-driven, non-intrusive reduced-order models (ROMs) to perform robust sensitivity analysis and uncertainty quantification. We demonstrate mesh morphing in two geophysical applications: (a) 3D dynamic rupture simulations with fault dip angles varying across a 40° range, and (b) 2D thermal models of subduction zones incorporating realistic slab interface curvature and depth uncertainties. The morphed meshes retain high quality and lead to accurate simulation results that closely match those obtained using generated meshes. For the dynamic rupture case, we construct ROMs that efficiently predict surface displacement and velocity time series as functions of fault geometry, achieving speedups of up to $��1�0^9�$ times relative to full simulations. Our results show that mesh morphing can be a powerful and generalizable tool for incorporating geometric uncertainty into physics-based modeling. The method supports efficient ensemble modeling for rigorous sensitivity studies applicable across a range of problems in computational geophysics.

The evolution of the Isthmus of Panama during the Miocene resulted in climatic shifts leading to global cooling, reorganization of ocean currents, and regional mass extinctions. The causes of this change in ocean circulation between ∼15 and 5 Ma have been debated, with various tectonic scenarios being proposed as explanations for this event. However, few geophysical imaging investigations have been carried out beneath Panama to probe the tectonic structure of this region. Here we investigate the crust and upper mantle of the Isthmus of Panama, directly beneath the Panama Canal, using seismic receiver function analysis. We focus on back-azimuthal harmonic regression to isolate directionally dependent signals. We report evidence for clearly defined southernly dipping anisotropic layers at depths between ∼38 and 49 km, coincident with relocated seismicity beneath the Panama landmass. Our tectonic interpretation is informed by a synthetic modeling exercise incorporating a Bayesian inversion framework to investigate the harmonic regression terms. We interpret our results as evidence for Caribbean Plate subduction beneath the Isthmus of Panama. Considering our results, the depths of relocated seismicity, and present-day plate motion, we estimate that Caribbean Plate subduction initiated ∼14–10 Ma, broadly coincident with changes in deep ocean circulation through what is today the Panama landmass. We propose that incipient subduction caused progressive uplift of the overriding plate, leading to the cessation of deepwater flow ∼7.5 Ma and of shallow water flow ∼5 Ma, and culminating in the formation of the isthmus of Panama and the Great American Biotic Interchange by ∼2.7 Ma.

The drift history of the Tethyan Himalaya provides key constraints on the India-Asia collision, Himalayan-Tibetan orogenesis, and associated global climate change. Here we present rock magnetic, petrographic, geochronologic, and paleomagnetic results of the Bolinxiala Formation limestones in the western Tethyan Himalaya. In situ calcite U-Pb dating and biostratigraphy indicate that the Bolinxiala Formation limestones were formed during the Early Cretaceous (∼125–100 Ma), not Middle Jurassic as previously thought. The site-mean direction for the 23 sites is D_g = 23.3°, I_g = +10.0°, k_g = 40.1 and α₉₅ = 4.8° in situ and D_s = 20.8°, I_s = +19.0°, k_s = 67.2 and α₉₅ = 3.7° after tilt-correction, yielding a paleomagnetic pole position at 61.6°N, 212.9°E with A₉₅ = 2.7°, corresponding to a paleolatitude of 10.3° ± 2.7°N. A positive fold test indicates a prefolding origin. When compared with reliable Cretaceous–Eocene paleopoles from the western Tethyan Himalaya, we suggest that the Bolinxiala Formation limestones likely underwent remagnetization during ∼54–49 Ma. Petrologic evidence, including the presence of framboidal oxides derived from sulfides (primarily pyrite) and calcite veins, supports chemical remanent magnetization as the primary mechanism responsible for the remagnetization. Our new results, combined with reliable Cretaceous paleomagnetic data from the western Lhasa terrane, indicate that the western part of the India-Asia collision occurred no later than ∼54–49 Ma.

Olivine-hosted melt inclusions give unique information about primary melt differentiation, magma storage conditions, and their volatile contents, but their compositions are typically affected by post-entrapment processes. Corrections for post-entrapment crystallization (PEC) are often done numerically and their results shape interpretations of deep magmatic processes. Importantly, calculated PEC extents (PEC%) depend on how these algorithms internally model key parameters like mineral-melt partition coefficients, melt Fe³⁺/Fe²⁺ ratios, and liquidus temperatures. However, current PEC correction algorithms offer no or limited flexibility in model selection for these parameters. To investigate the impact of PEC correction algorithms and associated uncertainties on corrected melt compositions and petrological interpretations, we developed MagmaPEC. MagmaPEC is a Python-based software that supports a wide range of models and includes error propagation of analytical and model calibration errors. Results indicate variations of up to 25 PEC%, depending on model choice for the various parameters. Crucially, total propagated errors are generally smaller, highlighting the importance of flexible model selection. Examples of melt inclusions from oceanic intraplate and rift volcanism show variations of up to 6.7 wt.% MgO in corrected melts calculated with different model setups. Associated inclusion entrapment temperature estimates vary by 140°C and applying this temperature range to olivine Fe-Mg diffusion models produces timescales varying by a factor of seven, while modeled melt viscosities vary by one log unit. Combined, our results highlight the impact PEC corrections have on our understanding of magmatic processes and emphasize the need for flexible correction tools.