SE Asia is renowned as a region of complex plate tectonic interactions, both in the present day and throughout its Mesozoic and Cenozoic history. The study of subduction processes in SE Asia has been instrumental in our understanding of how complex subduction systems develop and evolve, including understanding double subduction zones, areas of subduction polarity reversal, and the interaction of subduction and strike-slip systems. This complexity in subduction style makes SE Asia an ideal natural laboratory for studying forearc development in a range of subduction styles across a relatively small area still exposed in the rock record. Here we present a recently studied example of forearc development in a Mesozoic double subduction zone exposed on Natuna Island in the South China Sea, as well as highlighting two other examples of forearc development in SE Asia. These include a Cenozoic subduction polarity reversal event and transform plate boundary in western New Guinea and forearc sedimentation along the Sunda Trench. All three scenarios chronicle histories of forearc accretion, either of deep-water cherts or continental-derived turbidites, whilst also recording the impacts of case-specific tectonic processes (such as ophiolite obduction, arc-continent collision, or strike-slip movement) that have fundamentally impacted their respective forearcs. Comparing these contrasting examples shows that studying forearc development of these complex subduction systems (including their structural styles, geochemistry and timing of associated magmatism, and sedimentation) in SE Asia can be a powerful tool for improving understanding of forearc evolution in other ancient and complex subduction systems.

We report palaeomagnetic and K-Ar geochronologic results of two volcanic sections from Ethiopia. One section, dated around 29-30 Ma and spanning ~1 km in thickness, is related to the Oligocene Afro-Arabian traps. The second ~700-m-thick section was emplaced during the Miocene in two pulses around 10-11 and 14-15 Ma. We sampled 67 flows (550 cores) of predominantly basaltic rocks at the Oligocene section and 59 rhyolitic to trachybasaltic flows (500 cores) at the Miocene section. The Oligocene section was correlated to subchrons C11r to C11n.1n, with an average emplacement rate of 1m/kyr and instantaneous rates increasing with time from ~0.5 m/kyr near the base to ~1.36 m/kyr towards the top. We combined our results to the available paleomagnetic studies for the Early Oligocene (N = 4; 167 sites), Middle Miocene (N = 2; 125 sites) and Plio-Pleistocene (N = 8; 249 sites) to better understand how geomagnetic secular variation changed through time in the Afro-Arabian region. Recentred directional distributions for all three periods are elongated in the meridian plane (e = 2.7 ± 0.4, 1.8 ± 0.6, 2.3 ± 0.4, respectively), in coherence with field models for a dipole-dominated field. The angular dispersion S of the virtual geomagnetic poles, representative of the vigour of the palaeosecular variation, was higher during the Early Oligocene (S=14.2°|13.2°15.4°) and the Middle Miocene (S=15.0°|13.8°16.5°) than during the Plio-Pleistocene (S=9.7°|9.0°10.5°). As the reversal frequency f during the Early Oligocene is half that for the Plio-Pleistocene, it appears that S and f are uncorrelated in this near-equatorial region.

The leading paradigm for rift initiation suggests “magma-assisted (wet)” rifting is required to weaken strong lithosphere such that only small tectonic stresses are needed for rupture to occur. However, there is no surface expression of magma along the 300 km long Albertine-Rhino Graben (except at its southernmost tip within the Tore Ankole Volcanic Field), which is the northernmost rift in the Western Branch of the East African Rift System. The two prevailing models explaining magma-poor rifting are: 1) Melt is present at depth weakening the lithosphere, but it has not reached the surface or 2) far-field forces driving extension are accommodated along weak pre-existing structures without melt at depth. The goal of this study is to test the hypothesis that melt is generated below the Albertine-Rhino Graben from Lithospheric Modulated Convection (LMC) using the 3D finite element code ASPECT. We develop a regional model of a rigid lithosphere and an underlying convecting sublithospheric mantle that has dimensions 1000 by 1000 by 660 km along latitude, longitude, and depth, respectively. We solve the Stokes equations using the extended Boussinesq approximation for an incompressible fluid which considers the effects of adiabatic heating and frictional heating. We include latent heating such that we can test for melt generation in the sublithospheric mantle from LMC. Using LITHO1.0 as the base of our lithosphere, our preliminary results suggest melt could be generated beneath the Albertine-Rhino graben given a mantle potential temperature of 1800 K. These early results indicate LMC can generate melt beneath the northernmost Western branch of the East African Rift System.

The coal fires that started over a century ago in Jharia Coal Fields constitute a significant threat to the coal reserves, infrastructure, and residents’ lives. The fires burn underground coal leaving the surface with no support, leading to land subsidence and roof collapse. This will have a multiplier effect as it creates cracks and crevices that pump in more oxygen to aggravate the coal fires further. Despite the various measures taken by authorities, coal fires and land subsidence still have an increasing presence. In this study, we investigated the two hazards and their impact on the coal mines and surrounding settlements. We observed the subsidence and coal fires in the study area with the help of Persistent Scatterer Interferometry analysis of Sentinel-1 images and Temperature anomaly mapping of Thermal Infrared Imagery from Landsat-8, respectively. The subsidence velocity results and the coal fire zones are analysed, and a significant spatial overlap of both hazards is noticed. A few key locations severely affected by both the hazards are identified and examined to understand the mutual effect of coal fires and land subsidence. The subsidence of up to 20 cm/yr is observed in the study area. The results show that nearly 80% of the subsiding area is also affected by coal fires. Kusunda, Bararee and Keshalpur collieries are critically affected by both the hazards and need immediate intervention. Subsidence and coal fires extending towards the residential zones in several collieries is a matter of concern. In conclusion, the study presents an efficient methodology for multi-hazard monitoring, and the findings assist the authorities in enforcing appropriate disaster management strategies.

Automatically extracting buildings from remotely sensed imagery has always been a challenging task, given the spectral homogeneity of buildings with the non-building features as well as the complex structural diversity within the image. Traditional machine learning (ML) based methods deeply rely on a huge number of samples and are best suited for medium resolution images. Unmanned aerial vehicle (UAV) imagery offers the distinct advantage of very high spatial resolution, which is helpful in improving building extraction by characterizing patterns and structures. However, with increased finer details, the number of images also increase many fold in a UAV dataset, which require robust processing algorithms. Deep learning algorithms, specifically Fully Convolutional Networks (FCNs) have greatly improved the results of building extraction from such high resolution remotely sensed imagery, as compared to traditional methods. This study proposes a deep learning based segmentation approach to extract buildings by transferring the learning of a deep Residual Network (ResNet) to the segmentation based FCN U-Net. This combined dense architecture of ResNet and U-Net (Res-U-Net) is trained and tested for building extraction on the open source Inria Aerial Image Labelling (IAIL) dataset. This dataset contains 360 orthorectified images with a tile size of 1500m2 each, at 30cm spatial resolution with red, green and blue bands; while covering total area of 805km2 in select US and Austrian cities. Quantitative assessments show that the proposed methodology outperforms the current deep learning based building extraction methods. When compared with a singular U-Net model for building extraction for the IAIL dataset, the proposed Res-U-Net model improves the overall accuracy from 92.85% to 96.5%, the mean F1-score from 0.83 to 0.88 and the mean IoU metric from 0.71 to 0.80. Results show that such a combination of two deep learning architectures greatly improves the building extraction accuracy as compared to a singular architecture.

The nature of deep earthquakes with depths greater than 70 km is enigmatic because brittle failure at this high-temperature and the high-pressure regime should be inhibited. Three main hypotheses have been proposed to explain what causes deep earthquakes within the subducting slabs, dehydration embrittlement, phase transformational faulting, and thermal runaway instability. However, the existing seismological constraints can’t yet definitively distinguish between these hypotheses because the fine 3D slab structures are not well constrained in terms of slab upper interface, thickness, and internal fine layering. To better image the slabs in the Western Pacific subduction zones, this study employs a full waveform inversion (FWI) that minimizes waveform shape misfit between the synthetics and the observed waveforms from a large dataset, with 142 earthquakes recorded by about 2,400 broadband stations in East Asia. A 3-D initial model that combines two previous FWI models in East Asia (i.e., FWEA18 and EARA2014) are iteratively updated by minimizing the misfit measured from both body waves (8–40 s) and surface waves (30–120 s). Compared to the previous models, the new FWI model (EARA2020) shows much stronger wave speed perturbations within the imaged slabs with respect to the ambient mantle, with maximum perturbation of 8% for Vp and 13% for Vs. Furthermore, the slab thickness derived from EARA2020 exhibits significant downdip and along-strike variations at depths greater than 100 km. The large intra-slab deep earthquakes (Mw>6.0) appear to occur where significant slab thinning happens. This observation suggests that the significant deformation (or strain accumulation) of the slab is likely the first-order factor that controls the distribution of large deep earthquakes within the slab regardless of their triggering mechanism.

Rapid progress in investigation of zircon records for U-Th-Pb ages and O and Hf isotopes in igneous rocks require understanding how magma bodies are formed and evolve in the crust. We here present a 2D model of magma bodies formation in granitic crust by injection of rhyolitic or andesitic dikes and sills. We combine this model with our zircon crystallization/dissolution software and compute zircon survival histories in individual batches of magma and country rocks. Simulations reproduces incremental accumulation of intruded magma into magma chambers generating eruptible and interconnected magma batches with melt fraction >50 vol% that form in clusters. The rate of melt production is highly variable in space and time. The volume of eruptible melt strongly depends on the input rates of magma Q and the width W of the dike injection region. For example, dikes injection with Q=0.25 m3/s with W=500 m during 4 ka generate 20 km3 of melt while no significant melt forms if W=4 km. Injection of andesitic dikes produces only slightly more melt than rhyolite to granite injection despite of much larger thermal input. Due to rock melting most of zircons loose significant portion of their old cores and, thus, average age. Magmatic zircons in the periphery of the intrusion form very quickly while in its central part crystals contain old cores and young rims and can grow during several hundreds of ka. We observe diverse proportions of crustal melt/newly intruded magma, which translates into diverse O and Hf isotope distribution in zircons.

The Department of Earth & Environmental Sciences at the University of Michigan formed an Unlearning Racism in GEosciences (URGE) pod composed of six graduate students, three postdocs and eight faculty in the beginning of 2021. The department’s Diversity, Equity and Inclusion (DEI) efforts have been building in the preceding years. Our first DEI committee was formed in 2017 and increased its activity since initiation, hosting DEI discussions and initiatives with participation from students, postdocs, staff and faculty. Existing DEI activities include a Fall Preview event for prospective graduate students, DEI office hours and book discussions, adding DEI resources to the public-facing Department website, student grants for DEI related activities, and hosting workshops. The formation of an URGE pod provided new, focused energy to our DEI efforts and bolstered ongoing work by creating a bigger, critical mass of people who met regularly and were focused on action. The scope of URGE, the NSF support for it, and the interactions with other institutions that came from it, helped give our pod momentum, legitimacy, and contributed to broader departmental support for the recommendations that it produced. It also helped our department identify our most critical deficits on a DEI front and concrete ways that we will respond to them, which parallel needs articulated in a recent report from our college’s anti-racism task force, a major focus of our Dean. Actions emerging from the URGE pod include, but are not limited to, hiring a Wellness and Inclusion Advocate staff member, creation of field safety training and guidance, and building a workshop series to address issues centered on creating a culture of wellness and inclusion (anti-bias training, ally training, etc). The formation of our pod coincided with and complemented the finalization of our department’s self-study as part of a decadal strategic planning process. Many recommendations related to hiring, inclusive teaching, reporting, and deliberate mentoring practices that our URGE pod discussed were incorporated into our department’s strategic plan that was finalized in July 2021. We are eager to translate these recommendations for anti-racism work into actions, building on and contributing to the momentum and resources of the URGE community.

The thermal regime of continental lithosphere plays a fundamental role in controlling the behavior of tectonic plates. In this work, we assess the thermal state of the North American upper mantle by combining shear-wave velocity models calculated using data from the EarthScope facility with empirically-derived anelasticity models and basalt thermobarometry. We estimate the depth to the thermal lithosphere-asthenosphere boundary (LAB), defined as the intersection of a geotherm with the 1300° C adiabat. Results show lithospheric thicknesses across the contiguous US vary between ~40 km and > 200 km. The thinnest thermal lithosphere is observed in the tectonically active western US and the thickest lithosphere in the mid-continent. By combining geotherm estimates with solidus curves for peridotite, we show that a pervasive partial melt zone is common within the western US upper mantle and that partial melt is absent in the eastern and central US without significant metasomatism.

We analysed crystal-preferred orientation of c-axis and microstructure data from the Alpine ice core KCC at an unprecedented resolution and coverage of any Alpine ice core. We find that an anisotropic single-maximum fabric develops as early as 25 m depth in firn under vertical compression and strengthens under simple shear conditions towards the bedrock at 72 m depth. The analysis of continuously measured intervals with subsequent thin section samples from several depths of the ice core reveals a high spatial variability in the crystal orientation and crystal size on the 10 cm-scale as well as within a few centimeters. We quantify the variability and investigate the possible causes and links to other microstructural properties. Our findings support the hypothesis that the observed variability is a consequence of strain localisation on small spatial scales with influence on fabric and microstructure. From a methodological perspective, the results of this study lead us to challenge whether single thin sections from ice cores provide representative parameters for their depth to be used to infer the fabric development in a glacier on the large scale. Previously proposed uncertainty estimates for fabric and grain size parameters do not capture the observed variability. This might therefore demand a new scale-sensitive statistical approach.

This study investigates the mineralogical, elemental, and spatial variability from source (proximal) to sink (distal) of Merapi basalt-andesitic stratovolcano (Java, Indonesia) to better constrain volcaniclastic mineral sorting in fluvial, aeolian, and coastal environments. Merapi volcaniclastics are products of an active volcano with an ongoing quadrennial eruption, which can provide insights to constrain Mars’ older and more recent volcaniclastics by focusing on anorthite, albite, and pyroxenes found on Mars’ crust. We collected stream sediment samples across the Opak River that connects Merapi with the Indian Ocean and acquired Ground Penetrating Radar (GPR) surveys on Parangkusumo Shoreface and a parabolic coastal sand dune. In addition to grain size separation, all collected samples were subjected to X-Ray Diffractometer (XRD) and X-Ray Fluorescence (XRF) to quantify their mineralogical and elemental composition, respectively, like the techniques used by the Curiosity rover on Mars to investigate the geochemistry and mineralogy of geological units in the Gale crater. To interpret the geochemical analysis, we applied multivariate statistical analysis based on Principal Component Analysis (PCA) and Hierarchical Clustering of Principal Component (HCPC). The quantitative assessment shows that the provenance contains pyroclastic materials dominated by plagioclase feldspars (albite and anorthite), followed by pyroxenes (augite and enstatite), similar to the findings of basalt-andesitic minerals on Mars’ Gale and Gusev Crater. Mineral sorting from Merapi volcaniclastics shows a plagioclase feldspar sorting from proximal to the proximal-medial interface, fault-influenced pyroxene sorting from medial to distal, and pyroxene sorting in the aeolian-dominated sedimentary system.

The withdrawal of fluid from a reservoir results in a decline of the fluid pressure followed by a consequent change in stress state in porous rocks. Stress change may cause irreversible deformation and compaction. Such compaction is generally the result of pore collapse and shear-enhanced compaction caused by changes at a microscopic level in the porous rocks. Pore collapse and shear-enhanced compaction are considered as potential problems during reservoir production and drilling operations. The purpose of this paper is to analyze the pore collapse and shear-enhanced compaction in hydrocarbon reservoirs using coupled poro-elastoplasticity and permeability. This coupling is implemented using a sequentially coupled scheme with a fixed stress split. In this coupling, the poro-elastoplasticity analysis includes the linear component based on Biot’s theory and the nonlinear component based on a cap plasticity model. The fluid flow formulation is defined by Darcy’s law, including nonlinear permeability model. The numerical approximation is implemented using continuous finite element approximations for rock deformation and mixed finite element approximation for pore pressure and flux. Several numerical simulations are performed to indicate the onset of pore collapse and shear-enhanced compaction and evaluate their effects on reservoir performance.

Effective monitoring of groundwater withdrawals is necessary to help mitigate the negative impacts of aquifer depletion. In this study, we develop a holistic approach that combines water balance components with a machine learning model to estimate groundwater withdrawals. We use both multi-temporal satellite and modeled data from sensors that measure different components of the water balance at varying spatial and temporal resolutions. These remote sensing products include evapotranspiration, precipitation, and land cover. Due to the inherent complexity of integrating these data sets and subsequently relating them to groundwater withdrawals using physical models, we apply random forests- a state of the art machine learning algorithm- to overcome such limitations. Here, we predict groundwater withdrawals per unit area over a highly monitored portion of the High Plains aquifer in the central United States at 5 km resolution for the years 2002-2019. Our modeled withdrawals had high accuracy on both training and testing datasets (R≈ 0.99 and R≈ 0.93, respectively) during leave-one-out (year) cross-validation with low Mean Absolute Error (MAE) ≈ 4.26 mm and Root Mean Square Error (RMSE) ≈ 13.57 mm for the year 2014. Moreover, we found that even for the extreme drought year of 2012, we have a satisfactory test score (R≈ 0.79) with MAE ≈ 10.34 mm and RMSE ≈ 27.04 mm. Therefore, the proposed hybrid water balance and machine learning approach can be applied to similar regions for proactive water management practices.

Rockwall permafrost is extremely sensitive to climate change and its degradation is supposedly responsible for the recent increase in periglacial rock slope failures. Investigations of rockwall permafrost dynamics and mechanics have so far neglected possible hydrogeological processes acting in bedrock fractures. In this study, we propose the first numerical approach to couple thermal and hydrological processes in alpine rockwall permafrost and show that the latter have major effects on permafrost (thermal) dynamics and mechanics when the fractures and/or rock matrix are saturated. Water flows into fractures favor deep-reaching of the permafrost body by driving cold water top-down. Ice-filled fractures delay permafrost thawing in a first stage due to latent heat consumption but then accelerate it when the ice starts to melt. Thus, frozen fractures may subsist in thawed bedrock while thawing corridors may form in frozen bedrock. As a result, tmperature gradients are exacerbated. When connected fractures thaw, bottom-up permafrost degradation can occur through upwards propagation of thawing wedges delineated by these fractures. High hydraulic head values are associated to perched water table over or within the impermeable permafrost body, and correspond to hydrostatic pressures that can reach critical valus in trms of rockwall stability. These results bear strong implications to understand permafrost response to climate signals, periglacial geomorphology and hazards assessment as well as alpine hydrothermal processes.

Coastal saltwater intrusion (SWI) is one key factor affecting the hydrology, nutrient transport, and biogeochemistry of coastal marsh landscapes. Future climate change, especially intensified sea level rise (SLR), is expected to trigger SWI to encroach coastal freshwater aquifers more intensively. Numerous studies have investigated decadal/century scale SWI under SLR by assuming a static coastal landscape topography. However, coastal marshes are highly dynamic systems in response to SLR, and the impact of coastal marsh evolution on SWI has received very little attention. Thus, this study investigated how coastal marsh evolution affects future SWI with a physically-based coastal hydro-eco-geomorphologic model, ATS (Advanced Terrestrial Simulator). Our synthetic modeling experiments showed that it is very likely that the marsh elevation increases with future SLR, and a depression zone is formed due to the different marsh accretion rates between the ocean boundary and the inland. We found that, compared to the cases without marsh evolution, the marsh accretion may significantly reduce the surface saltwater inflow at the ocean boundary, and the evolved topographic depression zone may prolong the residence time of surface ponding saltwater, which causes distinct subsurface salinity distributions. We also found that the marshland may become more sensitive to the upland groundwater table that controls the freshwater flux to the marshes, compared with the cases without marsh evolution. This study demonstrates the importance of marsh evolution to the freshwater-saltwater interaction under sea level rise and can help improve our predictive understanding of the vulnerability of the coastal freshwater system to sea level rise.

Two recent supereruptions (magnitude (M) scale ≥ 8), the Young Toba Tuff (YTT), Sumatra, and the Los Chocoyos (LCY), Guatemala, are found to be statistically synchronous at ca. 74 ka and near antipodal. Such planetwide synchroneity of supereruptions is shown to be statistically non-random implying a causal link. We propose that the seismic energy release from the YTT supereruption may have initiated eruption from the contemporaneous “perched” LCY magma system. This near-equatorial supereruption “double-whammy” may be the more compelling source of the significant environmental impacts often attributed to a singular YTT eruption.

Iron is a key limiting nutrient for phytoplankton. Continental shelf and slope sediments are important sources of dissolved iron (DFe). Stable iron isotopes (d56Fe) are a particularly useful tool to quantify the DFe sources and sinks in the ocean. The isotopic signature of the sedimentary DFe source is controlled by environmental factors such as bottom water redox conditions, carbon oxidation and bioturbation by burrowing fauna, but the exact relation on a global scale is poorly understood. We developed a reaction-transport model capable of tracing dissolved iron isotope fractionation in marine sediments to quantify the isotopic signature of benthic DFe fluxes under a wide range of environmental conditions. We derived fractionation factors for iron reduction (-1.3 permille), iron oxidation (+0.4 permille), iron sulphide precipitation (+0.5 permille and dissolution (-0.5 permille and pyrite precipitation (-0.7 permille) that were in line with existing literature. At bottom-water oxygen concentrations >50 µM, bioturbation increased the benthic DFe flux and increased the d56Fe signature. In contrast, at bottom-water oxygen concentrations <50 µM, a reduction in bioturbation led to a decrease in the benthic DFe flux and its d56Fe value. On a global scale, a model simulation without bioturbation decreased the sedimentary DFe release from ~158 Gmol DFe yr-1 to ~70 Gmol DFe yr-1, and decreased the variability in the d56Fe signature of the DFe flux. Finally, we find that a decrease in ocean oxygen content by 40 µM can increase global sedimentary DFe release by up to 103 Gmol DFe yr-1.

Mudrocks serve as geological seals for carbon sequestration or hydrocarbon formation where mudrock capillary seals having high capillary entry pressure prevent leakage of underlying fluids. However, seal failure can occur if the trapped nonwetting fluid escapes by porous flow or by induced tensile fractures caused by elevated nonwetting phase pressures. Since mudrocks are mainly composed of silt and clay size grains, a silt bridging effect has been observed when there are sufficiently abundant silt size grains. This effect creates force chains across the rock to help preserve large pores and throats and can reduce the sealing capacity of a mudrock. We used network models and discrete element (DEM) models to determine the conditions under which silt abundance will cause a mudrock seal to fail and allow a non-wetting fluid like CO2 or natural gas to flow. We show that when larger grains in a grain pack become 40-60 % of total grain volume, the drainage capillary pressure curves display two percolation thresholds, and the percolation threshold transitions to a lower value allowing seal failure even below tensile fracture pressure. The DEM compaction simulations found that strong force chains are mostly formed across grain contacts between large grains and their neighbors and not between small grains, which decreases coordination numbers and shields pore space from compaction before reaching a stress limit. Thus, through better understanding of grain concentrations and sizes on fluid flow behavior, we can improve risk management efforts in anthropogenic storage and estimates of reserve capacity of reservoirs.

Oblique collision of buoyant provinces against subduction zones frequently results in individualizing and rotating regional-scale blocks. In contrast, the collision of the Bahamas Bank against the Northeastern Caribbean Plate increased the margin convexity triggering forearc fragmentation into small-scale blocks. This deformation results in a prominent >450-km-long sequence of V-shaped basins that widens trenchward separated by elevated spurs, in the Northern Lesser Antilles (NLA, i.e. Guadeloupe to Virgin Island). In absence of deep structure imaging, various competing models were proposed to account for this faults-bounded Basins-and-Spurs System. High-resolution bathymetric and deep multichannel seismic data acquired during cruises ANTITHESIS1-3, reveal a drastically different tectonic evolution of the NLA forearc. During Eocene-Oligocene time, the NLA margin accommodated the Bahamas Bank collision and the consecutive margin convex bending by trench-parallel extension along N40-90°-trending normal faults, opening V-shaped valleys in the forearc. Backarc spreading in the Kalinago Basin and block rotations went along with this tectonic phase, which ends up with tectonic uplifts and an earliest-middle Miocene regional emersion phase. Post middle Miocene, regional subsidence and tectonic extension in the forearc is partly accommodated along the newly-imaged N300°-trending, 200-km-long Tintamarre Normal Faults Zone. This drastic subsidence phase reveals vigorous margin basal erosion, which likely generated the synchronous westward migration of the volcanic arc. Thus, unlike widely-accepted previous theoretical models, the first deep seismic images in the NLA forearc show that the NE-SW faulting and the prominent V-Shaped valleys result from a past and sealed tectonic phase related to the margin bending and consecutive blocks rotation.

The martian surface is predominantly covered by FeO-rich basalts and their alteration products. Several samples, either analyzed in situ by rovers or recovered as meteorites, might represent primitive (i.e. near-primary) basaltic melts that can shed light on the mineralogy, the bulk composition, and the temperature of their mantle sources. We recently developed a new melting model, called MAGMARS, that can predict the melt compositions of FeO-rich mantles and the martian mantle in particular (Collinet et al., submitted to JGR:P). It represents a more accurate alternative to pMELTS (Ghiorso et al., 2002, G3), which systematically overestimates the FeO and MgO content of martian melts and underestimates the SiO2 content (by up to 8 wt.%). MAGMARS can simulate near-fractional and batch melting of various mantle compositions. For example, MAGMARS can produce melts identical to the Adirondack-class basalts by near-fractional melting, between 2.3 and 1.7 GPa, of a depleted mantle with a potential temperature (Tp) of 1390°C (~7 wt.% melt fraction). For this study, MAGMARS is applied to all other martian basalts from which the primary melt compositions can be inferred in order to constrain their mantle sources: the Columbia hills basalts, igneous rocks from Gale crater, shergottites, nakhlites and Northwest Africa (NWA) 7034/7533. We find that a few basaltic clasts in the pre-Noachian polymict regolith breccia NWA 7034/7533 are the only samples with bulk compositions that could represent melts derived from a primitive mantle. The Columbia hills basalts (Gusev crater), alkali-rich rocks from Gale crater, nakhlites and enriched shergottites are most easily reproduced by melting depleted mantle reservoirs that were re-fertilized to different degrees in alkalis by fluids or melts (i.e. metasomatized sources). Most martian basalts, with the exception of depleted shergottites, can be produced from martian mantle reservoirs with Mg# comprised between 75 and 81. From this sample set, the melting conditions of the martian mantle seem to remain relatively stable through time (Tp = 1400 ± 100 ºC and P = 2 ± 0.5 GPa) but the depleted nature of all mantle sources sampled after the pre-Noachian points towards an early crust-mantle differentiation.

Many aquatic environments are dominated by muddy sediments. These cohesive sediments, however, often contain a mixture of sand, mud and organic material, giving rise to complex interactional behaviour, the nature of which is often controlled by bio-physical attributes. An understanding of these complex interactions is paramount in the accurate prediction of sediment transport processes in numerical models, facilitating monitoring and management of marine environments. Calibration of such models relies on quantitative erodibility and depositional data. Muddy sediments flocculate; a process impacted by complex sedimentary and hydrodynamic interactions. The degree of sediment stability describes the degree of flocculation and depends on interactive forces (including bonding cohesion) between suspended particulate matter and turbulent shear stress, as well as mineralogy and biological composition. Erodibility and deposition properties rely greatly on the formation and break-up of these flocs, in turn impacting processes of sediment transport. This study examines, through the use and comparison of various data sets, aspects of both erodibility and deposition for several different sedimentary conditions. Collation of a range of quantitative field and laboratory-derived sedimentary and hydrodynamical data sets (e.g. sediment composition, floc properties, bed density, mass erosion rates, erosion thresholds, suspended particular matter concentration, turbulent shear stress) from a range of aquatic scenarios (including estuaries, intertidal areas, shelf seas, and lakes) are utilised to investigate the impacts of related controlling and influencing parameters on sediment transport, in particular to assess coastal erosion and sustainability. Case studies include: water quality monitoring, contaminated sediments, and dredging applications; these will be used to demonstrate / illustrate various applications of this sedimentary-hydrodynamic investigation. This research augments our understanding of the interactive processes within different cohesive sediments, providing quantitative analysis to inform and ultimately improve our mathematical representation of bio-physical sedimentary processes for implementation within predictive numerical modelling.

Mature faults with large cumulative slip often separate rocks with dissimilar elastic properties and show asymmetric damage distribution. Elastic contrast across such bimaterial faults can significantly modify various aspects of earthquake rupture dynamics, including normal stress variations, rupture propagation direction, distribution of ground motions, and evolution of off-fault damage. Thus, analyzing elastic contrasts of bimaterial faults is important for understanding earthquake physics and related hazard potential. The effect of elastic contrast between isotropic materials on rupture dynamics is relatively well studied. However, most fault rocks are elastically anisotropic, and little is known about how the anisotropy affects rupture dynamics. We examine microstructures of the Sandhill Corner shear zone, which separates quartzofeldspathic rock and micaceous schist with wider and narrower damage zones, respectively. This shear zone is part of the Norumbega fault system, a Paleozoic, large-displacement, seismogenic, strike-slip fault system exhumed from mid-crustal depths. We calculate elastic properties and seismic wave speeds of elastically anisotropic rocks from each unit having different proportions of mica grains aligned sub-parallel to the fault. Our findings show that the horizontally polarized shear wave propagating parallel to the bimaterial fault (with fault-normal particle motion) is the slowest owing to the fault-normal compliance and therefore may be important in determining the elastic contrast that affects rupture dynamics in anisotropic media. Following results from subshear rupture propagation models in isotropic media, our results are consistent with ruptures preferentially propagated in the slip direction of the schist, which has the slower horizontal shear wave and larger fault-normal compliance.

Determining the spatial relations between volcanic edifices and their underlying magma storage zones is fundamental for characterizing long-term evolution and short-term unrest. We compile centroid locations of upper crustal magma reservoirs at 56 arc volcanoes inferred from seismic, magnetotelluric, and geodetic studies. We show that magma reservoirs are often horizontally offset from their associated volcanic edifices by multiple kilometers, and the degree of offset broadly scales with reservoir depth. Approximately 20% of inferred magma reservoir centroids occur outside of the overlying volcano’s mean radius. Furthermore, reservoir offset is inversely correlated with edifice size. Taking edifice volume as a proxy for long-term magmatic flux, we suggest that high flux or prolonged magmatism leads to more centralized magma storage beneath arc volcanoes by overprinting upper crustal heterogeneities that would otherwise affect magma ascent. Edifice volumes therefore reflect the spatial distribution of underlying magma storage, which could help guide monitoring strategies at volcanoes.

Located at the northern tip of the Altiplano, the Abancay Deflection marks abruptly the latitudinal segmentation of the Central Andes spreading over the Altiplano to the south and the Eastern Cordillera northward. The striking contrast in terms of morphology between the low-relief Altiplano and the high-jagged Eastern Cordillera makes this area a privileged place to determine spatio-temporal variations in surface and/or rock uplift and discuss the latest phase of the formation of the Central Andes. Here, we aim to quantify exhumation and uplift patterns in the Abancay Deflection since 40 Ma, and present new apatite (U-Th)/He and fission-track data from five altitudinal profiles and additional individual samples. Age-Elevation relationships and thermal modeling both evidence that the Abancay Deflection experienced a moderate, spatially-uniform and steady exhumation at 0.2±0.1 km/m.y. between 40 Ma and ~5 Ma implying common large-scale exhumation mechanisms. From ~5 Ma, while the northern part of the Eastern Cordillera and the Altiplano registered similar ongoing slow exhumation, the southern part of the Eastern Cordillera experienced one order-of-magnitude of exhumation acceleration (1.2±0.4 km/m.y). This differential exhumation since ~5 Ma implies active tectonics, river capture and incision affecting the southern Eastern Cordillera. 3D thermo-kinematic modeling favors a tectonic decoupling between the Altiplano and the Eastern Cordillera through backthrusting activity of the Apurimac fault. We speculate that the Abancay Deflection, with its “bulls-eye” structure and significant exhumation rate since 5 Ma, may represent an Andean proto-syntaxis, similar to the syntaxes described in the Himalaya or Alaska.