The transition from subduction to transform motion along horizontal terminations of trenches is associated with tearing of the subducting slab and strike-slip tectonics in the overriding plate. One prominent example is the northern Tonga subduction zone, where abundant strike-slip faulting in the NE Lau back-arc basin is associated with transform motion along the northern plate boundary and asymmetric slab rollback. Here, we address the fundamental question: how does this subduction-transform motion influence the structural and magmatic evolution of the back-arc region? To answer this, we undertake the first comprehensive study of the geology and geodynamics of this region through analyses of morphotectonics (remote-predictive geologic mapping) and fault kinematics interpreted from ship-based multibeam bathymetry and Centroid-Moment Tensor data. Our results highlight two unique features of the NE Lau Basin: (1) the occurrence of widely distributed off-axis volcanism, in contrast to typical ridge-centered back-arc volcanism, and (2) fault kinematics dominated by shallow-crustal strike slip-faulting (rather than normal faulting) extending over ~120 km from the transform boundary. The orientations of these strike-slip faults are consistent with reactivation of earlier-formed normal faults in a sinistral megashear zone. Notably, two distinct sets of Riedel megashears are identified, indicating a recent counter-clockwise rotation of part of the stress field in the back-arc region closest to the arc. Importantly, these structures directly control the development of complex volcanic-compositional provinces, which are characterized by variably-oriented spreading centers, off-axis volcanic ridges, extensive lava flows, and point-source rear-arc volcanoes that sample a heterogenous mantle wedge, with sharp gradients and contrasts in composition and magmatic affinity. This study adds to our understanding of the geologic and structural evolution of modern backarc systems, including the association between subduction-transform motions and the siting and style of seafloor volcanism.
Using active ultrasonic source survey data, Coda-wave Decorrelation (CWD) time-lapse imaging during the triaxial compression of Whitby Mudstone cores provides a 3-D description of the evolution and redistribution of inelastic strain concentrations. Acoustic Emissions (AEs) monitoring is also performed between any two consecutive surveys. From these data, we investigate the impact of initial water saturation $S_w$ on the onset, growth, and reactivation of inelastic deformation, compared to the post-deformation fracture network extracted from X-ray tomography scans. Our results indicate for the applied strain-rate and degree of initial water saturation, and within the frequency range of our ultrasonic transducers (0.1 to 1 MHz), that inelastic strain localisation and propagation in the Whitby Mudstone does not radiate AEs of sufficient magnitude to be detected above the average noise level. This is true for both the initial onset of inelasticity (strain localisation), and during macroscopic failure. In contrast, the CWD results indicate the onset of what is interpreted as localised regions of inelastic strain at less than fifty percent of the peak differential stress the Whitby Mudstone can sustain. The seemingly aseismic nature of these clay-rich rocks suggests the gradual development of inelastic strain, from the microscopic diffuse damage, up until the macroscopic shear failure.
The hazardous impact and erosive potential of slow-moving landslides depends on landslide properties including velocity, size, and frequency of occurrence. However, constraints on size, in particular, subsurface geometry, are lacking because these types of landslides rarely fully evacuate material to create measurable hillslope scars. Here we use pixel offset tracking with data from the NASA/JPL Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) to measure the three-dimensional surface deformation of 134 slow-moving landslides in the northern California Coast Ranges. We apply volume conservation to infer the actively deforming thickness, volume, geometric scaling, and frictional strength of each landslide. These landslides move at average rates between ~0.1–3 m/yr and have areas of ~6.1 x 10^3–2.35 x 10^6 m^2, inferred mean thicknesses of ~1.1–25 m, and volumes of ~7.01 x 103–9.75 x 10^6 m^3. The best-fit volume-area geometric scaling exponent is γ ~ 1.2–1.5, indicating that these landslides fall between typical soil and bedrock landslide scaling. A rollover in the scaling relationship suggests that the largest landslide complexes in our dataset become large primarily by increasing in area rather than thickness. In addition, the slow-moving landslides display scale-dependent frictional strength, such that large landslide tend to be weaker than small landslides. This decrease in frictional strength with landslide size is likely because larger landslides are composed of higher proportions of weak material. Our work shows how state-of-the-art remote sensing techniques can be used to better understand landslide processes and quantify their contribution to landscape evolution and hazards to human safety.
Serpentinite subduction and the associated formation of dehydration veins is important for subduction zone dynamics and water cycling. Field observations suggest that en-échelon olivine veins in serpentinite mylonites formed by dehydration during simultaneous shearing of ductile serpentinite. Here, we test a hypothesis of shear-driven formation of dehydration veins with a two-dimensional hydro-mechanical-chemical numerical model. We consider the reaction antigorite + brucite = forsterite + water. Shearing is viscous and the shear viscosity decreases exponentially with porosity. The total and fluid pressures are initially homogeneous and in the antigorite stability field. Initial perturbations in porosity, and hence viscosity, cause fluid pressure perturbations. Dehydration nucleates where the fluid pressure decreases locally below the thermodynamic pressure defining the reaction boundary. Dehydration veins grow during progressive simple-shearing in a direction parallel to the maximum principal stress, without involving fracturing. The porosity evolution associated with dehydration reactions is controlled to approximately equal parts by three mechanisms: volumetric deformation, solid density variation and reactive mass transfer. The temporal evolution of dehydration veins is controlled by three characteristic time scales for shearing, mineral-reaction kinetics and fluid-pressure diffusion. The modelled vein formation is self-limiting and slows down due to fluid flow decreasing fluid pressure gradients. Mineral-reaction kinetics must be significantly faster than fluid-pressure diffusion to generate forsterite during vein formation. The self-limiting feature can explain the natural observation of many, small olivine veins and the absence of few, large veins. We further discuss implications for transient weakening during metamorphism and episodic tremor and slow-slip in subduction zones.
The Dead Sea Fault (DSF) is a plate-boundary where large earthquakes are expected and largely overdue due to the lack of such events in the instrumental era. Sequences of earthquakes along the DSF are documented by historical evidence, one of the most devastating occurred in the mid-8th century CE. Here we describe site-specific archaeoseismological observations at the ancient Tiberias city, on the western shore of the Sea of Galilee. We map Roman and Byzantine relics faulted in the mid-8th century CE by a pure normal fault. We use geophysical, geomorphological and structural analyses integrated with published data, to assess the seismic hazard of the Jordan Valley Western Boundary Fault (JVWB). We propose that the normal JVWB can rupture the surface along its ~45 km trace running from Tiberias toward the S crossing Bet Shean, Tel Rehov and Tel Teomim. The JVWB, parallel to the main strike-slip Jordan Valley Fault segment, might be regarded as a major earthquake source in this region. We test the hypotheses of both single fault and multi-faults rupture scenarios, which result in an expected range of Mw from 6.9 (single rupture of the JVWB) to 7.6 (multiple rupture of the JVWB and Jordan Valley Fault). Our results suggest that seismic source characterization in the Sea of Galilee region must include normal faults capable of surface rupturing, despite the absence of such events in the instrumental catalogue.
Fault slip is controlled by the normal and shear tractions on a fault plane. A full understanding of the factors influencing induced seismicity requires quantitative knowledge of the in-situ stress tensor and fluid pressure. We analyze these variables for a 200 km × 200 km region with active hydraulic fracturing near the city of Red Deer, Canada. The levels of induced seismicity in the area were generally low before Mar 04, 2019, MW 3.8/ML 4.2 event that local residents felt. We use geophysical logs and pressure tests within the targeted Duvernay Formation to construct maps of ambient pore pressure, vertical and minimum horizontal stresses. Maximum horizontal stress is constrained from the focal mechanism inversion and borehole-based estimation method. We find a broad range of orientations are susceptible to slip and small perturbations of fluid pressure would promote displacement. This suggests that the differential variations in pore fluid pressure in the target formation may provide a metric of slip susceptibility; a map for the study area is developed. Areas of high susceptibility correlate with those experiencing higher levels of induced seismicity except for the Willesden Green oil field that has similarly elevated susceptibility and active hydraulic fracturing operations. The methods and results demonstrate how more quantitively constrained in-situ stresses developed from an ensemble of real field measurements can assist in assessing fault stability and in developing metrics for slip susceptibility.
Cumulate rocks record the magmatic and cooling processes during formation of Earth’s igneous crust. Extracting the information of these two processes from mineral records, however, is often convoluted by various extents of diffusive resetting during cooling subsequent to main stages of crystallization. Accordingly, for cumulate rocks at diffusive closure, the apparent “equilibrium” temperatures derived from geothermometers are generally lower than the crystallization temperatures. Using analytical or numerical models, geospeedometers can extract cooling rates from the closure temperatures (or profiles) but only if the initial temperatures are determined independently. Here I summarize the general framework of geothermometry and geospeedometry from a trace element perspective. The Mg and REE-based exchange geothermometers for mafic cumulate rocks are reviewed as examples of the geothermometer design. Based on the observed differential diffusive closures of Mg and REE in oceanic gabbros, I outline a general resolution to uniquely determine the initial crystallization temperature and cooling rate of a cumulate rock. The basic idea is further demonstrated using the recently developed Mg-REE coupled geospeedometer for mafic cumulate rocks. Finally, I use the Hess Deep gabbros as a case study to show that this two-element coupled geospeedometer is particularly useful to delineate the igneous accretion and cooling styles during crust formation. This two-element (or multi-element) coupled approach outlined here can also be readily extended for decoding comprehensive thermal histories of other petrological systems at various geological settings or other rocky planetary bodies.
Studying diffusion of hydrogen in nominally anhydrous minerals (NAMs), like clinopyroxene, at low temperatures is a challenging task due to experimental and analytical difficulties. We applied a combination of hydrogen implantation to produce concentration gradients in natural diopside crystals with Nuclear Resonance Reaction Analysis (NRRA) measurements of nanoscale diffusion profiles. Thereby, we were able to conduct experiments at temperatures between 195 – 400 °C. Obtained diffusion rates show a consistent Arrhenius relation Ｄн = 5.47 (± 13.98) ·10⁻⁸ · exp (-115.64 (±11.5) kJ mol⁻¹/RT) m²s⁻¹. Notably, our results lie well within the range of extrapolations from high temperature experiments (≥ 600 °C) of previous studies. This implies that fast diffusion of hydrogen (compared to other elements) extends to low temperatures. We used these results in a non-isothermal diffusion model that simulates the ascent of crystals (0.5, 1.0, and 2.0 mm) along two representative geotherms (oceanic and continental) from 600 to 100 °C, to assess potential re-equilibration of H contents in clinopyroxene at low temperatures. Our model highlights the need to carefully consider boundary conditions, which are a function of P-T-𝘧O₂, that control the concentration gradient at the crystal’s rim. The results from this model allow an assessment when re-equilibration in dependence of crystal size and cooling rate must be considered. Fast ascent (e.g., kimberlitic melt) preserves initial hydrogen contents even in 0.5 mm size clinopyroxene crystals. However, dwelling at low temperatures (e.g., 300 °C) for several thousands of years (e.g., serpentinization) leads to extensive re-equilibration in 2 mm crystals.
The increasing use of the seasonally frozen and permafrost regions for civil engineering constructions and the effects of global warming on these regions have stimulated research on the behaviors of frozen soils. In the present study, the frost heave characteristics of a coarse-grained soil with volcanic nature was experimentally investigated. A large soil tank model was established in laboratory for this purpose. The effects of temperature boundary, external water supply, and water transfer type on the frost heave characteristics of the volcanic soil were studied, through a series of frost heave tests. The particle image velocimetry (PIV) technique was used to quantify the full field deformation of the soil specimen. The results suggest that temperature gradient inside the soil specimen is the driving force for the migration of pore water and vapor. The largest increment in water content generally agrees well with the frost penetration depth. The contribution of vapor to the frost heave of the Komaoka soil specimen is typically small. The applied seeding method, selected subset size, image-object space calibration, and calculation processes ensured accurate PIV results. Discussions regarding the presented experimental investigation and the employment of PIV technique for quantifying frozen soil deformation are summarized. These findings and discussions can provide valuable insights into the frost heave behavior of the studied soil in particular, as well as promote the application of PIV for frozen soil engineering.
The relative roles of parameters governing relative permeability, a crucial property for two-phase fluid flows, are incompletely known. To characterize the influence of viscosity ratio (M) and capillary number (Ca), we calculated relative permeabilities of nonwetting fluids (knw) and wetting fluids (kw) in a 3D model of Berea sandstone under steady-state condition using the lattice Boltzmann method. We show that knw increases and kw decreases as M increases due to the lubricating effect, locally occurred pore-filling behavior, and instability at fluid interfaces. We also show that knw decreases markedly at low Ca (log Ca < −1.25), whereas kw undergoes negligible change with changing Ca. An M–Ca–knw correlation diagram, displaying the simultaneous effects of M and Ca, shows that they cause knw to vary by an order of magnitude. The color map produced is useful to provide accurate estimates of knw in reservoir-scale simulations and to help identify the optimum properties of the immiscible fluids to be used in a geologic reservoir.
The flow of organic matter (OM) along rivers and its retention within floodplains are fundamental to the function of aquatic and riparian ecosystems and are significant components of terrestrial carbon storage and budgets. Carbon storage and ecosystem processing of OM largely depends upon hydrogeomorphic characteristics of streams and valleys. To examine the role of channel complexity on carbon dynamics in mountain streams, we (1) quantify organic carbon (OC) storage in sediment and wood along 24 forested stream reaches in the Rocky Mountains of CO, U.S.A., (2) employ six years of logjam surveys and examine related morphological factors that regulate sediment and carbon storage, and (3) utilize fluorescence spectroscopy to examine how the composition of OM in surface water and floodplain soil leachates is influenced by valley and channel morphology. We find that lower-gradient stream reaches in unconfined valley segments at high elevations store more OC per area than higher-gradient reaches in more confined valleys, and those at lower elevations. We find that limited storage of fine sediment and increased mineralization of OC in multithread channel reaches decrease storage per area compared to simpler single-thread channel reaches. Results suggest that the positive feedbacks between channel complexity and persistent channel-spanning logjams that force multiple channels to flow across valley bottoms limit the aggradation of floodplain fine sediment, and promote hotspots for the transformation of OM. These multithread hotspots likely increase ecosystem productivity and ecosystem services by filtering dissolved organic carbon with potential to decrease contaminants associated with organic matter from surface water.
Dislocation recovery experiments were conducted on predeformed olivine single crystals at temperatures of 1,450 to 1,760 K, room pressure, and oxygen partial pressures near the Ni-NiO buffer to determine the annihilation rate constants for (010) edge dislocations. The obtained rate constants were found to be comparable to those of previously determined  screw dislocations. The activation energies for the motion of both dislocations are identical. This result suggests that the motion of screw dislocations in olivine is not controlled by cross-slip but by the same rate-limiting process of the motion of edge dislocations, i.e., climb, under low-stress, high-temperature conditions. The diffusivity derived from dislocation climb indicates that dislocation recovery is controlled by Si pipe diffusion, rather than Si lattice diffusion. Our results suggest that the conventional climb-controlled model for olivine can be applied to motions of not only edge but also screw dislocations. Therefore, the previous proposed cross-slip model cannot explain the softness of asthenosphere.
Microcosm experiments using microbial mats can be useful at times to understand mineral precipitation induced by microorganisms and their extracellular polymeric substances (EPS). Currently, the existing knowledge limits our ability to elucidate the interactions between microbes, which form communities as microbial mats, and minerals that precipitate in natural environments (e.g., lagoons, rivers, springs, soils). Much of the prior research did not consider entire microbial communities, despite recent evidence that microorganisms interact in a community-based way. This is especially relevant in extreme environments where the entire microbial communities are not yet known despite their relevance to biosignatures exploration on other planets. Here, we grew microbial mats on natural substrates in the laboratory to monitor changes in mat texture and mineral paragenesis. Several analytical techniques were used to compare mineral paragenesis in association with and without microbes. This paragenesis included major phases of chemical sedimentary deposits, such as gypsum, calcium carbonate, and some silicates, whose formation is traditionally linked to evaporative processes but was not in these experiments. In addition, some of the phases only precipitated within microbial mat samples and there were differences in mineral fabrics between mat samples and abiotic controls.
The Greater Caucasus (GC) Mountains within the central Arabia-Eurasia collision zone, are an archetypal example of a young collisional orogen. However, the mechanisms driving rock uplift and forming the topography of the range are controversial, with recent provocative suggestions that uplift of the western GC is strongly influenced by an isostatic response to slab detachment, whereas the eastern half has grown through shortening and crustal thickening. Testing this hypothesis is challenging because records of exhumation rates mostly come from the western GC, where slab detachment may have occurred. To address this data gap, we report 623 new, paired zircon U-Pb and (U-Th)/He ages from 7 different modern river sediments, spanning a ~400 km long gap in bedrock thermochronometer data. We synthesize these with prior bedrock thermochronometer data, recent catchment averaged 10Be cosmogenic exhumation rates, topographic analyses, structural observations, and plate reconstructions to evaluate the mechanisms growing the GC topography. We find no evidence of major differences in rates, timing of onset of cooling, or total amounts of exhumation across the possible slab edge, inconsistent with previous suggestions of heterogeneous drivers for exhumation along-strike. Comparison of exhumation across timescales highlight a potential acceleration, but one that appears to suggest a consistent northward shift of the locus of more rapid exhumation. Integration of these new datasets with simple models of orogenic growth suggest that the gross topography of the GC is explainable with traditional models of accretion, thickening, and uplift and does not require any additional slab-related mechanisms.
Rockwall slope erosion is an important component of alpine landscape evolution, yet the role of climate and tectonics in driving this erosion remains unclear. We define the distribution and magnitude of periglacial rockwall slope erosion across 12 catchments in Himachal Pradesh and Jammu and Kashmir in the Himalaya of northern India using cosmogenic 10Be concentrations in sediment from medial moraines. Beryllium-10 concentrations range from 0.5±0.04x104 to 260.0±12.5x104 at/g SiO2, which yield erosion rates between 7.6±1.0 and 0.02±0.04 mm/a. Between ~0.02 and ~8 m of rockwall slope erosion would be possible in this setting across a single millennium, and >2 km when extrapolated for the Quaternary period. This erosion affects catchment sediment flux and glacier dynamics, and helps to establish the pace of topographic change at the headwaters of catchments. We combine rockwall erosion records from the Himalaya of Himachal Pradesh, Jammu and Kashmir and Uttarakhand in India and Baltistan in Pakistan to create a regional erosion dataset. Rockwall slope erosion rates progressively decrease with distance north from the Main Central Thrust and into the interior of the orogen. The distribution and magnitude of this erosion is most closely associated with records of Himalayan denudation and rock uplift, where the highest rates of change are recorded in the Greater Himalaya sequences. This suggests that tectonically driven uplift, rather than climate, is a first order control on patterns of rockwall slope erosion in the northwestern Himalaya. Precipitation and temperature would therefore come as secondary controls.
Minerals are information-rich materials that offer researchers a glimpse into the evolution of planetary bodies. Thus it is important to extract, analyze, and interpret this abundance of information in order to improve our understanding of the planetary bodies in our solar system and the role our planet’s geosphere played in the origin and evolution of life. Over the past decades, data-driven efforts in mineralogy have seen a gradual increase. The development and application of data science and analytics methods to mineralogy, while extremely promising, has also been somewhat ad-hoc in nature. In order to systematize and synthesize the direction of these efforts, we introduce the concept of “Mineral Informatics”. Mineral Informatics is the next frontier for researchers working with mineral data. In this paper, we present our vision for Mineral Informatics, the X-Informatics underpinnings that led to its conception, the needs, challenges, opportunities, and future directions. The intention of this paper is not to create a new specific field or a sub-field as a separate silo, but to document the needs of researchers studying minerals in various contexts and fields of study, to demonstrate how the systemization and increased access to mineralogical data will increase cross- and interdisciplinary studies, and how data science and informatics methods are a key next step in integrative mineralogical studies.
The different olivine fabrics in ultramafic rocks have been widely used to discuss past tectonic settings, given that the olivine fabrics vary with pressure, temperature and water content. However, there are no researches that whether and how the olivine fabrics transform at different metamorphic stages in a natural rock during the process of deep subduction and exhumation. Yinggelisayi garnet lherzolites from South Altyn have experienced deep continental subduction and exhumation. The garnet lherzolites contain well-preserved residual protolith minerals, and near-peak (M1), granulite-facies retrograde (M2), and amphibolite-facies retrograde (M3) metamorphic mineral assemblages. Olivine grains in M1 formed at P–T conditions of 2.52–3.08 GPa, 1095–1136°C and low water contents (183–213 ppm H/Si), and showed  axes sub-normal to the foliation and  axes subparallel to the lineation, which is characteristic of B-type fabric ((010)). Olivine grains in M2 formed at P–T conditions of 1.31–1.80 GPa, 851–893°C and also low water contents (93–139 ppm H/Si), and exhibited  axes sub-normal to the foliation and  axes subparallel to the lineation, which is characteristic of A-type fabric ((010)). These observations suggest that olivine fabrics in HP-UHP metamorphosed ultramafic rocks are different in the near-peak and retrograde metamorphic stages, and also that the olivine fabrics can be transformed during deep continental subduction and exhumation. Therefore, the dispersed or no clear olivine fabric probably caused by multi-stage deformation and metamorphism, and the distinct olivine fabrics can be used as a clue to identify geological processes and better understand metamorphism and deformation during subduction and exhumation.
Yamato and Brun (Nature Geoscience 10, 46-50, 2017) claimed that metamorphic data from global (ultra)high-pressure ((U)HP) rocks exhibit an unusual linear relation, between peak pressure and pressure drop, which challenges current interpretation of P-T-t paths but supports their model invoking excessive overpressures. If their model holds, most research on (U)HP rocks since their discovery would require serious reconsideration. Here, I demonstrate that their model requires critical assumptions that are neither justified by the principles of rock mechanics in the context of realistic geologic settings nor consistent with microstructures of (U)HP rocks. Furthermore, contrary to their claim, the global (U)HP data can be readily explained in the current framework but are inconsistent with their model prediction.