• Issue
    Volume 21, Issue 9
    September 2020

Issue Information

Free Access

Issue Information

  • First Published: 25 August 2020

Research Articles

Open Access

The Impact of Life on Climate Stabilization Over Different Timescales

  • First Published: 12 September 2020
Key Points

  • The impact of marine calcification and biological enhancement of weathering on climate oscillations of periods from 0.1–10 Myr is explored
  • A combination of both biologically driven feedbacks reduces surface temperature oscillations of periods between 0.5 and 2 Myr by approximately 1/3
  • The high pH of an ocean dominated by inorganic precipitation reduces high-frequency oscillations but amplifies low-frequency oscillations

Open Access

Seismological and Geophysical Signatures of the Deep Crustal Magma Systems of the Cenozoic Volcanic Fields Beneath the Eifel, Germany

  • First Published: 30 July 2020
Key Points

  • Melts below volcanic fields are narrow zones in the lower crust and upper mantle, identified by low velocities and transparent lower crust
  • Deep low-frequency earthquakes can originate from zones of high melt concentration in the upper mantle
  • The location of Tertiary and Quaternary volcanic fields can be controlled by preexisting lithospheric structures and terrane boundaries

Free Access

Distribution of Earthquakes on a Branching Fault System Using Integer Programming and Greedy-Sequential Methods

  • First Published: 15 July 2020
Key Points

  • An integer programming method is developed to determine the optimal distribution of earthquakes on a fault system with branching faults
  • Results are compared to the greedy-sequential method—a local optimization algorithm previously developed for complex fault systems
  • Application of these methods to San Francisco Bay Area faults indicate which branching faults are involved in multifault ruptures

Open Access

Quantification of Eruption Dynamics on the North Rift at Axial Seamount, Juan de Fuca Ridge

  • First Published: 02 August 2020
Key Points

  • AUV mapping along the north rift identifies hummocky mounds with pillows, channelized, and inflated flows formed during the 2015 eruption
  • Impulsive sounds formed by lava/seawater interaction track mound growth over a 28-day period with an average extrusion rate of 22–45 m3 s−1
  • The sounds record the history of flow advancement and inflation from multiple eruptive centers and are used to infer volcanic activity style

Free Access

Paleomagnetism of the Middle Cenozoic Mula Basin (East Tibet): Evidence for km-Scale Crustal Blocks Rotated by Midlower Crust Drag

  • First Published: 18 August 2020
Key Points

  • We report on the paleomagnetism of middle Cenozoic red beds from the Mula basin (East Tibet)
  • The basin is fragmented in 2–5 km wide crustal blocks showing irregular rotation pattern
  • We suggest that post-20 Ma SE-ward directed midlower crust flow drag and rotated randomly upper crust blocks

Free Access

MATE: An Analysis Tool for the Interpretation of Magnetotelluric Models of the Mantle

  • First Published: 06 August 2020
Key Points

  • A new software that creates a conductivity distribution of the lithospheric mantle for given composition and thermal state is introduced
  • It is crucial while interpreting MT data to consider the correct mantle composition with realistic water distribution and geometric models
  • In the cratonic lower lithospheric mantle, combination of hydration and well-connected minor mineral phases can explain the conductivities

Free Access

Insights Into the Origins and Compositions of Mantle Plumes: A Comparison of Galápagos and Hawai'i

  • First Published: 23 June 2020
Key Points

  • The Galápagos and Hawai'i plumes are bilaterally asymmetric in composition, sourced at the LLSVP-lower mantle interface
  • The Galápagos and Hawai'i plumes share a common mantle source, the Pacific lower mantle
  • The Pacific large low shear velocity province is heterogeneous, with a variety of ancient recycled material (HIMU- and EM1-type)

Free Access

Spatiotemporal Correlation Analysis of Noise-Derived Seismic Body Waves With Ocean Wave Climate and Microseism Sources

  • First Published: 24 August 2020
Key Points

  • Time variations of a noise-derived P-type phase are compared with those of the ocean wave heights and microseism sources
  • Do not equate a positive correlation with a causal relation when studying the links between noise sources and noise-derived signals
  • The derivation of seismic signals from ambient noise relies on the competition between the effective and ineffective sources

Open Access

Structural Control, Evolution, and Accumulation Rates of Massive Sulfides in the TAG Hydrothermal Field

  • First Published: 24 August 2020
Key Points

  • Intersecting fault and fissure populations dominate the structural control of seafloor massive sulfide mineralization
  • Ninety percent of the sulfide material is contained in the inactive and weakly active mounds (26 Mt) compared to the high-temperature mound (3 Mt)
  • The structural complexity in the TAG area has lead to a large accumulation of sulfide material in a confined area

Free Access

No Cretaceous-Paleogene Boundary in Exposed Rajahmundry Traps: A Refined Chronology of the Longest Deccan Lava Flows From 40Ar/39Ar Dates, Magnetostratigraphy, and Biostratigraphy

  • First Published: 06 August 2020
Key Points

  • Exposed Rajahmundry Traps lava flows were all erupted after the Cretaceous-Paleogene boundary, between 65.92 and 65.27 million years ago
  • Rajahmundry Traps consistent with Deccan Traps chronostratigraphy and chemostratigraphy thus are very long flows from main Deccan eruptive vents
  • Model and climate records show that eruptive CO2 release from large individual Deccan eruptions is insufficient to cause significant warming

Free Access

Large Silicic Eruptions, Episodic Recharge, and the Transcrustal Magmatic System

  • First Published: 24 August 2020
Key Points

  • New thermal model suggests that the temperature of the magma reservoir is controlled by the replenishment rate and the heat loss
  • The growth of silicic reservoir requires decaying replenishment with a peak rate coincident with the previous eruption
  • Episodic pulse of mafic magma may cause the rapid expulsion of melt from the mush, triggering the eruption

Free Access

Hydrothermal Alteration on Composite Volcanoes: Mineralogy, Hyperspectral Imaging, and Aeromagnetic Study of Mt Ruapehu, New Zealand

  • First Published: 24 August 2020
Key Points

  • Surface weathering and hydrothermal mineralogy were constrained using VNIR and SWIR reflectance spectroscopy and SEM-EDS analysis
  • Combination of airborne hyperspectral image analysis and aeromagnetic data inversion mapped surface and buried hydrothermal alteration on Mt Ruapehu volcano
  • Complex spatial and temporal hydrothermal evolution of Mt Ruapehu is revealed

Open Access

Evolution of the Oceanic Lithosphere in the Equatorial Atlantic From Rayleigh Wave Tomography, Evidence for Small-Scale Convection From the PI-LAB Experiment

  • First Published: 29 August 2020
Key Points

  • We image a lithosphere that increases from 20–30 to 50 km thick beneath 0–40 My old seafloor
  • We image punctuated slow velocity zones beneath the ridge and up to 400 km off-axis in the asthenosphere that likely require melt
  • The pattern of anomalies suggests small-scale convection may occur beneath a range of seafloor ages

Free Access

A Lithosphere-Asthenosphere Boundary and Partial Melt Estimated Using Marine Magnetotelluric Data at the Central Middle Atlantic Ridge

  • First Published: 20 August 2020
Key Points

  • Marine magnetotelluric data are used to better understand the lithosphere-asthenosphere boundary at the central Middle Atlantic Ridge
  • A dynamic lithosphere-asthenosphere boundary is observed and compatible with geodynamic modeling
  • Partial melt fraction, 1–7%, is estimated based on the inverted resistivity models and consistent with previous studies

Technical Reports: Methods

Free Access

A User-Friendly Workbook to Facilitate Rapid and Accurate Rare Earth Element Analyses by ICP-MS for Multispiked Samples

  • First Published: 04 September 2020
Key Points

  • A workbook deconvolves raw ICP-MS data to calculate concentrations of all the rare earth elements for multispiked samples
  • Values of some common REE reference standards are evaluated
  • Data quality using this approach is evaluated with seawater as an example

Research Articles

Free Access

Slow Stick-Slip Failure in Halite Gouge Caused by Brittle-Plastic Fault Heterogeneity

  • First Published: 07 August 2020
Key Points

  • Stick-slip failure events occurred within a 16-cm-long halite gouge layer
  • Increasing the ratio of semibrittle to plastic deformation led to a transition from fast dynamic slip to slow quasi-static slip
  • Brittle-plastic heterogeneity in fault zones contributes to the emergence of slow earthquakes

Technical Reports: Methods

Open Access

Intercomparison of XRF Core Scanning Results From Seven Labs and Approaches to Practical Calibration

  • First Published: 09 September 2020
Key Points

  • Seven international labs X-ray fluorescence (XRF) scanned the same seven sections from Integrated Ocean Drilling Program sediment cores
  • XRF scans are compared as element counts per second and ratios and calibrated with ICP
  • Log-ratio calibrations are recommended to achieve the most quantitative outcomes

Research Articles

Free Access

Evidence for an Active, Transcrustal Magma System in the Last 60 ka and Eruptive Degassing Budget (H2O, CO2, S, F, Cl, Br): The Case of Dominica

  • First Published: 03 August 2020
Key Points

  • The storage system beneath Dominica includes the entire crust width, with two main storage depths
  • Volatile degassing budget highlights significant halogen emissions toward the atmosphere
  • An exsolved fluid phase traps S and Cl, so calculated degassing budgets are minimum values

Open Access

The Probability of Mantle Plumes in Global Tomographic Models

  • First Published: 09 September 2020
Key Points

  • This is a new technique for interpreting tomographic models numerically and objectively based on a wavelet transform and noise simulations
  • The most likely plumes are at the Tahiti, Macdonald, East Africa, Pitcairn, Marquesas, and Canary Islands hotspots
  • The Amsterdam-St Paul hotspot is likely to have a deep plume in many models, whereas Yellowstone is unlikely

Open Access

Evolution of Magmatism in the New Hebrides Island Arc and in Initial Back-Arc Rifting, SW Pacific

  • First Published: 04 September 2020
Key Points

  • Back-arc rifting is initiated by tectonic rather than magmatic processes
  • Back-arc magmas form by decompression melting with little influence of a slab component
  • Arc front magmas form from flux melting containing variable slab components reflecting different input from the slab

Free Access

Combined Seismic and Geodetic Analysis Before, During, and After the 2018 Mount Etna Eruption

  • First Published: 31 August 2020
Key Points

  • We show a model of the inflation phase preceding the 2018 eruption
  • A time-space evolution analysis, based on seismic and geodetic data, of the intrusive process of 24–25 December 2018 at Mount Etna is also proposed
  • We also show a model of the posteruptive phase and its meaning for the evaluation of future volcanic hazards at Mt. Etna

Free Access

Bidirectional Loading of the Subduction Interface: Evidence From the Kinematics of Slow Slip Events

  • First Published: 04 September 2020
Key Points

  • Slip on the plate interface during slow slip events in Cascadia is perpendicular to strike
  • Strain accumulation across the locked patch in oblique subduction zones may be spatially variable
  • Slab pull is the dominant force acting on the slab downdip of the locked patch

Open Access

What Controls Maximum Magnitudes of Giant Subduction Earthquakes?

  • First Published: 07 September 2020
Key Points

  • We use numerical modeling to investigate effects of slab geometry, friction, and subduction rate on magnitude of giant subduction earthquakes
  • Maximum magnitudes are controlled by the size of the rupture zones, which are the largest for the low-angle subductions with thick sediments
  • Neutral upper plate strain of low-angle subduction zones hosting giant earthquakes results from low friction in the subduction channels

Free Access

Advanced Newton Methods for Geodynamical Models of Stokes Flow With Viscoplastic Rheologies

  • First Published: 29 July 2020
Key Points

  • Stokes equations with nonsmooth von Mises rheology are derived from an optimization formulation
  • Proposed velocity-stress Newtonlinearization has favorable convergence properties
  • 2-D and 3-D viscoplastic problems with strain localization and 7 orders of viscosity variation are solved