The ocean of the planet Earth, which is as thin as a cicada's wings, play a role of catalyst to

As a particularly common minerals in granites, the presence of feldspar and altered feldspar-chlorite gouges at hydrothermal conditions have important implications in fault strength and reactivation. We present laboratory observations of frictional strength and stability of feldspar (K-feldspar and albite) and altered feldspar-chlorite gouges under conditions representative of deep geothermal reservoirs to evaluate the impact on fault stability. Velocity‐ stepping experiments are performed at a confining stress of 95 MPa, pore pressures of 35-90 MPa and temperatures of 120-400°C representative of in situ conditions for such reservoirs. Our experiment results show that the feldspar gouge is frictionally strong (μ~0.71) at all experimental temperatures (~120-400℃) but transits from velocity-strengthening to velocity-weakening at T>120°C. Increasing the pore pressure increases the friction coefficient (~0.70-0.87) and the gouge remains velocity weakening, but this weakening decreases as pore pressures increase. The presence of alteration-sourced chlorite leads to a transition from velocity weakening to velocity strengthening in the mixed gouge at experimental temperatures and pore pressures. As a ubiquitous mineral in reservoir rocks, feldspar is shown to potentially contribute to unstable sliding over ranges in temperature and pressure typical in deep hydrothermal reservoirs. These findings emphasize that feldspar minerals may increase the potential for injection-induced seismicity on pre-existing faults if devoid of chlorite alteration.

Mantle convection plays a fundamental role in driving evolution of oceanic and continental lithosphere. In turn it impacts a broad suite of processes operating at or close to Earth’s surface including landscape evolution, glacio-eustasy, magmatism and climate. A variety of theoretical approaches now exist to simulate mantle convection. Outputs from such simulations are being used to parameterise models of landscape evolution and basin formation. However, the substantial body of existing simulations has generated a variety of conflicting views on the history of dynamic topography, its evolution and key parameters for modelling mantle flow. The focus of this study is on developing strategies to use large-scale quantitative stratigraphic observations to asses model predictions and identify simulation parameters that generate realistic predictions of Earth surface evolution. Spot measurements of uplift or subsidence provide useful target observations but are often controlled by tectonic processes, yet avoiding areas where tectonics have influenced vertical motions is challenging. To address this issue, we use large inventories of stratigraphic data from across North America with contextual geophysical and geodetic data to constrain the regional uplift and subsidence history. We demonstrate that a suite of fairly typical simulations struggle to match the amplitude, polarity and timing of observed vertical motions. Building on recent seismological advances, we then explore strategies for understanding patterns of continental uplift and subsidence that incorporate (and test) predicted evolution of the lithosphere, asthenosphere and deep mantle. Our results demonstrate the importance of contributions from the uppermost mantle in driving vertical motions of continental interiors.

A document by Wen-Pin Hsieh. Click on the document to view its contents.

In Southeast Asia, emerging subduction zones often appear to begin at the corners of small oceanic basins, which have a triangular-indenter continent–ocean boundary geometry. To investigate the influence of a triangular indenter on subduction initiation, we performed a series of three-dimensional numerical simulations with varying indenter angles and base lengths. The results show that the apex of the indenter constitutes the initial location of subduction, irrespective of the angle or the extent of the indenter. Smaller angle indenters are more likely to facilitate subduction initiation. At the same time, wide acute angle indenters are difficult to form. Our findings suggest that triangular indenter structures may facilitate subduction initiation in smaller basins; however, the role such indenters in subduction initiation is limited in larger basins. Our results emphasize the importance of accounting for the three-dimensional geometry of a subduction zone when examining its subduction dynamics and geological features.

In this study, we measure velocity variations during two cycles of crustal inflation and deflation in 2020 on the Reykjanes peninsula (SW Iceland) by applying coda wave interferometry to ambient noise recorded by distributed dynamic strain sensing (also called DAS). We present a new workflow based on spatial stacking of raw data prior to cross-correlation which substantially improves the spatial coherency and the time resolution of measurements. Using this approach, a strong correlation between velocity changes and ground deformation (in the vertical and horizontal direction) is revealed. Our findings may be related to the infiltration of volcanic fluids at shallow depths, even though the concurrent presence of various processes complicates the reliable attribution of observations to specific geological phenomena. Our work demonstrates how the spatial resolution of DAS can be exploited to enhance existing methodologies and overcome limitations inherent in conventional seismological datasets.

The Neoproterozoic tectonics of South China is crucial for understanding its evolution history throughout the assembly and disintegration of Rodinia. Herein, we employ integrally tectono-magmatic records over the period of ~1.0-0.6 Ga from the northern Yangtze block, combining with available geochemical and geological data, to investigate the secular tectonic evolution of the craton. Early Neoproterozoic intra-oceanic subduction may have initiated at ~1.0-0.9 Ga after a long-period of late Mesoproterozoic passive margin. A flare-up of magmatism at ~900 Ma attributed to continental arc magmatism that led to increased crustal reworking during episodes of arc compression and lithospheric thickening, and subsequently enhanced juvenile mantle input during the transition to extensional back-arc rift modes. The isotope–time pattern displays cyclic trends shifting towards less radiogenic values and then progression to more radiogenic, near-depleted mantle isotope compositions, indicating alternation regimes of contractional and extensional tectonics due to repeatedly slab advancing and rollback. The occurrence of volumetrically-large radiogenic isotope-depleted calc-alkaline rocks associations, low-δ18O and bimodal rocks along the Yangtze-block continental margin likely indicates rapid reworking of juvenile crust within a composite tectonic setting involving both arcs and rifts, which may maintain until the end of calc-alkaline arc magmatism at ~730-720 Ma and ultimately evolved into an anorogenic rifted passive margin setting, as revealed by the deposition of massive ~720-620 Ma syn-rift Yaolinghe-group volcanic-sedimentary sequence and intraplate-like magmatism. Collectively, prolonged (~1.0-0.7 Ga) suprasubduction-related magmatism traces accretion to the Yangtze-block margin, and thus likely indicates a paleogeographically peripheral position of South China in Rodinia.

A document by Nathaniel Forbes Inskip. Click on the document to view its contents.

A document by Erik van der Wiel. Click on the document to view its contents.

The 0–2.5 Ma volcanism in Easter Island (Rapa Nui) emerges just east of the East Pacific Rise on young (Pliocene, 3–4.8 Ma) ocean floor. Here, we report the finding of mantle-derived zircon grains retrieved from Easter Island beach sands and red soils that are much older than the Easter Island volcanism and its underlying lithosphere. A large population of 0–165 Myr old zircons have coherent oxygen (δ18O(zircon) 3.8– 5.9‰) and hafnium mantle isotopic signatures (εHf(t) +3.5–+12.5). These results are consistent with the crystallization of zircon from plume-related melts. In addition, a chemically diverse population with ages as old as Precambrian was also found. We thus suggest that the Easter hotspot started at least ~165 Ma ago. A large population of ~160-164 Ma zircons could signal an intense initial massive melting phase associated with the formation of a Large Igneous Province (LIP) upon the first arrival of the plume. We use plate reconstructions to show that such a LIP would have formed on the Phoenix Plate. It would have subducted below the Antarctic Peninsula around 100-105 Ma, offering a solution for the enigmatic Palmer Land deformation event, previously proposed to result from a collision with an unknown indenter. Our findings show that asthenospheric mantle-derived xenocryst zircon cargo, as recently reported from Galápagos, may not be an exception. The here-reported “ghost” of a prolonged hotspot activity suggests that the Easter hotspot and the sub-lithospheric mantle in which it is entrained remained mantle-stationary for at least 165 Ma.

The Cuo E (CE) core contains the entire Quaternary stratigraphy of the Cuo E Lake (31°24′ - 31°.32′ N, 91°28′ - 91°33′E, Tibetan Plateau, China). Here, we study the magnetic properties of 1748 samples from the CE core, combined with scanning electron microscopy and X-ray energy dispersive spectrometer analysis on selected samples. The main magnetic minerals appear to be magnetite and greigite. To further quantify the presence of greigite in CE core, 84 samples were rock magnetically analyzed in more detail including: susceptibility (χ) vs. temperature, coercivity component analysis of acquisition curves of the isothermal remanent magnetization (IRM), and Principal component analysis (PCA) of the first-order reversal curve (FORC) diagrams. The greigite content and saturation IRM over susceptibility (SIRM/χ) appear to be exponentially related. SIRM/χ can be used as greigite concentration indicator. We also propose a rapid way to identify greigite in the CE core: When the SIRM/χ value increases and anhysteretic remanent susceptibility (χARM) increases only slowly, the sample contains greigite. Samples with SIRM/χ < 15kAm-1 also obey this relation. This method has a lower limit of detection than the traditionally used SIRM/χ parameter for greigite detection. It is also faster than FORC analysis and thus particularly suitable for analysis of large sample collections. Twenty greigite-bearing layers were identified in the CE core using this method. The location of the Jaramillo subchron in the CE core is controversial in the currently available magnetostratigraphy, possibly related to the presence of greigite in this core interval.

Volcanic eruptions generate continuous or episodic tremor, which can provide unique information about activity changes during eruption. However, the wealth of information in episodic tremor patterns is often not harvested and transitions between patterns remain obscure. The 2021 Geldingadalir eruption of the Fagradalsfjall Fires, Iceland, is an exceptional case, where the lava effusion caused continuous tremor, and 8696 tremor episodes spanning two orders of magnitude in duration and repose. Based on seismometer and video camera data, we associate several-minute-long, symmetrical episodes with an open vent system, where lava remains in the crater bowl during repose, connected to a shallow magma compartment. Ramp-shaped episodes, lasting several hours, are associated with a temporary closure of the vent system, where no lava remains in the crater bowl during repose and more time is required to resume effusion. The transition from continuous to episodic effusion is related to the cumulative time spent in effusion and repose, and to external factors like crater wall collapses.

A document by Hongcheng Guo. Click on the document to view its contents.

Venus boasts an abundance of volcano and volcano-like structures. Synthetic aperture radar images of the surface have revealed extensive evidence of volcanism, including lava flows and edifices. Volcanic activity is further supported by crater statistics, and analysis of topography and gravity data. Unique to Venus, coronae are quasi-circular, volcano-tectonic features exhibiting diverse volcanic characteristics. Despite this, volcanism is often under-represented in formation models. We identify a new subset of coronae that display topographic change subsequent to the emplacement of lava flows within their fracture annuli, pointing to the critical role of volcanism in the formation of these coronae. Through spherical-harmonic distribution analysis, we find that this new subset is spatially related to the full coronae database, pointing to an intrinsic process of coronae formation. Furthermore, coronae exhibit strong correlations and similar spectral shapes at low spherical harmonic degrees with large volcanoes, suggesting a shared geodynamic origin. Our findings underscore the pivotal role of volcanism in coronae formation and highlight the need for future research that integrates magmatic processes into geophysical models.

A document by Noor Ahmad Akhundzadah. Click on the document to view its contents.

A document by Harsh Kumar. Click on the document to view its contents.

Rich Briggs1, Robert C. Witter2, Jeffrey T. Freymueller3, Peter M. Powers1, Peter J. Haeussler2, Stephanie L. Ross4, Tina Dura5, Simon E. Engelhart6, Richard D. Koehler7, Hong Kie Thio81 U.S. Geological Survey, Geological Hazards Science Center, Golden, CO, USA2 U.S. Geological Survey, Alaska Science Center, Anchorage, AK, USA3 Department of Earth and Environmental Sciences, Michigan State University, East Lansing, MI, USA4 Pacific Coastal and Marine Science Center, US Geological Survey, Moffett Field, CA, USA5Department of Geosciences, Virginia Tech, Blacksburg, VA, USA6Department of Geography, Durham University, Durham, UK7Nevada Bureau of Mines and Geology, University of Nevada, Reno, Reno, NV, USA8 AECOM, Los Angeles, CA, USACorresponding author: Rich Briggs (rbriggs@usgs.gov)Key Points:We present earthquake recurrence estimates from geologic and geodetic data for the Alaska-Aleutian subduction zoneRecurrence estimates provide constraints for seismic hazard modelsThe recurrence estimates indicate that the rates of Mw≥ 8 ruptures are higher than previously inferred west of Kodiak Island

Shore-oblique bathymetric features occur around the world and have been statistically correlated with enhanced shoreline retreat on sandy beaches. However, the physical mechanisms that explain a causal relationship are not well understood. In this study, radar remote sensing observations and results from a phase-resolved numerical model explore how complex morphology alters nearshore hydrodynamics. Observations at selected times during high-energy storm events as well as a suite of idealized simulations indicate that shore-oblique features induce strong spatial variations in the water surface elevation and wave breaking patterns. Re-emergent offshore flows and longshore current accelerations occur near the apex of the oblique nearshore features. The results suggest that complex bathymetric morphology exerts a powerful control on nearshore hydrodynamics and increases the potential for enhanced cross-shore and alongshore sediment transport, thus contributing to localized erosional zones.

Kumar et al. (2023) in their article discuss and highlight the complexities involved in the comparison of long-term and short-term ongoing deformation in the Northwest Himalaya and their influence over the topographic evolution of the region. Their observations that rely largely on the GNSS geodetic results (Kumar et al., 2023) have also been the basis of conclusions presented in a companion paper by Malik et al., 2023a. The conclusions presented in the latter-mentioned paper have been questioned in a rejoinder by Singh and Rajendran (2023) and defended by Malik et al. (2023b). Below we present pointwise inconsistencies in the present study (Kumar et al., 2023) and the conclusions presented therein. We present our differing observations of the two segments of the fault system called the ‘Khetpurali-Taksal’ Fault (KTF-1 and KTF-2), as discussed in the paper by Kumar et al. (2023)

A document by Anouk Beniest. Click on the document to view its contents.

We have studied the properties of the Nili Fossae olivine lithology from orbital data and in situ by the Mars 2020 rover at the Séítah unit in Jezero crater. We used the geochemistry collected by the rover’s instruments to calculate the viscosity and relative flow distance of the Séítah unit. Based on the low viscosity and distribution of the unit we postulate a ponded lava flow origin for the olivine rich unit at Séítah. We calculate an approximate depth for the cumulate layer of the lava pond based on the viscosity of the unit and model of Worster et al. (1993). We show that the resolution of orbital data is inadequate to map the phyllosilicate 2.38 μm band and demonstrate that it can be supplemented by in situ data from Mars 2020 SuperCam Laser Induced Breakdown Spectroscopy (LIBS) and reflectance observations to show that the low Al phyllosilicate in the olivine cumulate in the Séítah formation is either talc, serpentine, hectorite, Fe/Mg smectite, saponite or stevensite. We discuss two intertwining aspects of the history of the lithology: 1) the potential emplacement and properties of the cumulate layer within a ponded lava flow, using previously published models of ponded lava flows and lava lakes, and 2) the limited extent of post emplacement alteration, including phyllosilicate and carbonate alteration.

Intraslab earthquakes do not produce primary paleoseismic evidence at the Earth’s surface, making efforts to develop an event chronology challenging. However, the strong ground motion from intraslab events may initiate gravity-driven turbidity flows in subaqueous basins; the resulting deposits (turbidites) can provide a paleoseismic proxy if the conditions that initiate these flows are known. To better constrain the initiating conditions, we use two recent intraslab earthquakes in southcentral Alaska, the Mw 7.1 November 30, 2018, Anchorage and the Mw 7.1 January 24, 2016, Iniskin earthquakes, as calibration events. Through a multi-lake investigation spanning a range of shaking intensities and based on a combined geological and geophysical dataset, we document the occurrence, or absence, of earthquake-generated turbidity flows from these two earthquakes. The 2018 and 2016 earthquakes are recorded by centimeter-scale turbidites that can be differentiated from climatically generated deposits, as well as other seismic sources (i.e., the 1964 Alaska megathrust earthquake) based on deposit thickness, sedimentological properties, and deposit age. We show that a Modified Mercalli Intensity (MMI) of ~V-V1/2 is the minimum shaking intensity required to generate localized sediment remobilization from deltaic slopes, and a MMI of ~V1/2 is required to produce a deposit of sufficient thickness that a seismic origin can be confidently assigned. Deltaic slopes are the major source of remobilized sediment that record the 2018 and 2016 events, however sediment from non-tributary sourced basin slopes may become remobilized in steep-sloped, high sedimentation areas, and under elevated shaking intensity. The documentation of seismically generated deposits in quick succession (~2 years) with diagnostic features that can be assigned to the seismic source highlights the utility of using recent earthquakes as calibration events to investigate the subaqueous response to strong ground motion. 

Erosional perturbations from changes in climate or tectonics are recorded in the profiles of bedrock rivers, but these signals can be challenging to unravel in settings with non-uniform lithology. In horizontally layered rocks, the surface lithology at a given location varies through time as different layers of rock are exposed. Recent modeling studies have used the Stream Power Model (SPM) to highlight complex variations in erosion rates that arise in bedrock rivers incising through layered rocks. However, these studies do not capture the effects of coarse sediment load on channel evolution. We use the “Stream Power with Alluvium Conservation and Entrainment” (SPACE) model to explore how sediment cover influences landscape evolution and modulates the topographic expression of erodibility contrasts in horizontally layered rocks. We simulate river evolution through alternating layers of hard and soft rock over million-year timescales, with a constant uplift rate of 1 mm/year. Compared to the SPM, model runs with sediment cover have systematically higher channel steepness values in soft rock layers and lower channel steepness values in hard rock layers. As sediment cover effects increase, the contrast in steepness between the two rock types decreases. Effective bedrock erodibilities back-calculated assuming the SPM are strongly influenced by sediment cover. We also find that sediment cover can significantly increase total relief and timescales of adjustment towards landscape-averaged steady-state topography and erosion rates.

In mountain rivers, sediment from landslides or debris flows can alluviate portions or even full reaches of bedrock channel beds, influencing bedrock river incision rates. Various landscape evolution models have been developed to account for the coevolution of alluvial cover and sediment-flux-dependent bedrock incision. Despite the commonality of their aims, one major difference between these models is the way they account for and conserve sediment. We combine two of the most widely used sediment conservation schemes, an Exner-type scheme and an erosion-deposition scheme, with the saltation-abrasion model for bedrock incision to simulate the coevolution of sediment transport and bedrock incision in a mixed bedrock-alluvial river. We compare models incorporating each of these schemes and perform numerical simulations to explore the transient evolution of bedrock incision rates in response to changes in sediment input. Our results show that the time required for bedrock incision rates to reach a time-invariant value in response to changes in sediment supply is over an order of magnitude faster using the Exner-type scheme than the erosion-deposition scheme. These different response times lead to significantly different time-averaged bedrock incision rates, particularly when the sediment supply is periodic. We explore the implications of different model predictions for modeling mixed bedrock-alluvial rivers where sediment is inevitably delivered to rivers episodically during specific tectonic and climatic events.