Magmatism controls global oceanic transform fault topography.

Oceanic transform faults play an essential role in plate tectonics. Yet to date, there is no unifying explanation for the global trend in broad-scale transform fault topography, ranging from deep valleys to shallow topographic highs. Using three-dimensional numerical models, we find that spreading-rate dependent magmatism within the transform domain exerts a first-order control on the observed spectrum of transform fault depths.

Deglaciation-enhanced mantle CO fluxes at Yellowstone imply positive climate feedback.

Mantle melt generation in response to glacial unloading has been linked to enhanced magmatic volatile release in Iceland and global eruptive records. It is unclear whether this process is important in systems lacking evidence of enhanced eruptions. The deglaciation of the Yellowstone ice cap did not observably enhance volcanism, yet Yellowstone emits large volumes of CO due to melt crystallization at depth.

How transform fault shear influences where detachment faults form near mid-ocean ridges.

Oceanic detachment faults represent an end-member form of seafloor creation, associated with relatively weak magmatism at slow-spreading mid-ocean ridges. We use 3-D numerical models to investigate the underlying mechanisms for why detachment faults predominantly form on the transform side (inside corner) of a ridge-transform intersection as opposed to the fracture zone side (outside corner). One hypothesis for this behavior is that the slipping, and hence weaker, transform fault allows for the detachment fault to form on the inside corner, and a stronger fracture zone prevents the detachment fault from forming on the outside corner.

Sensitivity of rift tectonics to global variability in the efficiency of river erosion.

SignificanceThe efficiency of erosion in leveling relief mainly depends on climate and strength of exposed rocks. However, whether erosion is sufficiently efficient to influence the architecture of a tectonic plate boundary remains a topic of debate. Here, we analyze continental rift landscapes reworked by river incision to assess a globally representative range of fluvial erosion efficiency.

High He/He in central Panama reveals a distal connection to the Galápagos plume.

It is well established that mantle plumes are the main conduits for upwelling geochemically enriched material from Earth's deep interior. The fashion and extent to which lateral flow processes at shallow depths may disperse enriched mantle material far (>1,000 km) from vertical plume conduits, however, remain poorly constrained. Here, we report He and C isotope data from 65 hydrothermal fluids from the southern Central America Margin (CAM) which reveal strikingly high He/He (up to 8.

Hydraulic transmissivity inferred from ice-sheet relaxation following Greenland supraglacial lake drainages.

Surface meltwater reaching the base of the Greenland Ice Sheet transits through drainage networks, modulating the flow of the ice sheet. Dye and gas-tracing studies conducted in the western margin sector of the ice sheet have directly observed drainage efficiency to evolve seasonally along the drainage pathway. However, the local evolution of drainage systems further inland, where ice thicknesses exceed 1000 m, remains largely unknown.

Aseismic transient slip on the Gofar transform fault, East Pacific Rise.

Oceanic transform faults display a unique combination of seismic and aseismic slip behavior, including a large globally averaged seismic deficit, and the local occurrence of repeating magnitude (M) [Formula: see text] earthquakes with abundant foreshocks and seismic swarms, as on the Gofar transform of the East Pacific Rise and the Blanco Ridge in the northeast Pacific Ocean. However, the underlying mechanisms that govern the partitioning between seismic and aseismic slip and their interaction remain unclear. Here we present a numerical modeling study of earthquake sequences and aseismic transient slip on oceanic transform faults.

Grain-size dynamics beneath mid-ocean ridges: Implications for permeability and melt extraction.

Unlabelled: Grain size is an important control on mantle viscosity and permeability, but is difficult or impossible to measure in situ. We construct a two-dimensional, single phase model for the steady state mean grain size beneath a mid-ocean ridge. The mantle rheology is modeled as a composite of diffusion creep, dislocation creep, dislocation accommodated grain boundary sliding, and a plastic stress limiter.

Greenland supraglacial lake drainages triggered by hydrologically induced basal slip.

Water-driven fracture propagation beneath supraglacial lakes rapidly transports large volumes of surface meltwater to the base of the Greenland Ice Sheet. These drainage events drive transient ice-sheet acceleration and establish conduits for additional surface-to-bed meltwater transport for the remainder of the melt season. Although it is well established that cracks must remain water-filled to propagate to the bed, the precise mechanisms that initiate hydro-fracture events beneath lakes are unknown.

Foundering of lower island-arc crust as an explanation for the origin of the continental Moho.

A long-standing theory for the genesis of continental crust is that it is formed in subduction zones. However, the observed seismic properties of lower crust and upper mantle in oceanic island arcs differ significantly from those in the continental crust. Accordingly, significant modifications of lower arc crust must occur, if continental crust is indeed formed from island arcs.

Fracture propagation to the base of the Greenland Ice Sheet during supraglacial lake drainage.

Surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change. The process whereby such a pathway is created through thick, cold ice has not, however, been previously observed. We describe the rapid (<2 hours) drainage of a large supraglacial lake down 980 meters through to the bed of the Greenland Ice Sheet initiated by water-driven fracture propagation evolving into moulin flow.

Intermittent plate tectonics?

Although it is commonly assumed that subduction has operated continuously on Earth without interruption, subduction zones are routinely terminated by ocean closure and supercontinent assembly. Under certain circumstances, this could lead to a dramatic loss of subduction, globally. Closure of a Pacific-type basin, for example, would eliminate most subduction, unless this loss were compensated for by comparable subduction initiation elsewhere.

Spreading rate dependence of gravity anomalies along oceanic transform faults.

Mid-ocean ridge morphology and crustal accretion are known to depend on the spreading rate of the ridge. Slow-spreading mid-ocean-ridge segments exhibit significant crustal thinning towards transform and non-transform offsets, which is thought to arise from a three-dimensional process of buoyant mantle upwelling and melt migration focused beneath the centres of ridge segments. In contrast, fast-spreading mid-ocean ridges are characterized by smaller, segment-scale variations in crustal thickness, which reflect more uniform mantle upwelling beneath the ridge axis.

Trench-parallel anisotropy produced by foundering of arc lower crust.

Many volcanic arcs display fast seismic shear-wave velocities parallel to the strike of the trench. This pattern of anisotropy is inconsistent with simple models of corner flow in the mantle wedge. Although several models, including slab rollback, oblique subduction, and deformation of water-rich olivine, have been proposed to explain trench-parallel anisotropy, none of these mechanisms are consistent with all observations.

Automated analysis of electrospray ionization fourier transform ion cyclotron resonance mass spectra of natural organic matter.

The advent of ultra-high-resolution mass spectrometry has revolutionized the ability of aquatic biogeochemists to examine molecular-level components of complex mixtures of organic matter. The ability to accurately assess the chemical composition, elemental formulas, or both of detected compounds is critical to these studies. Here we build on previous work that uses functional group relationships between compounds to extend elemental formulas of low molecular weight compounds to those of higher molecular weight.