Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust

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Tibetan tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism

[1] While conventional interferometric synthetic aperture radar (InSAR) is a very effective technique for measuring crustal deformation, almost any interferogram includes large areas where the signals decorrelate and no measurement is possible. Persistent scatterer (PS) InSAR overcomes the decorrelation problem by identifying resolution elements whose echo is dominated by a single scatterer in a series of interferograms. Existing PS methods have been very successful in analysis of urban areas, where stable angular structures produce efficient reflectors that dominate background scattering. However, man-made structures are absent from most of the Earth's surface. Furthermore, existing methods identify PS pixels based on the similarity of their phase history to an assumed model for how deformation varies with time, whereas characterizing the temporal pattern of deformation is commonly one of the aims of any deformation study. We describe here a method for PS analysis, StaMPS, that uses spatial correlation of interferogram phase to find pixels with low-phase variance in all terrains, with or without buildings. Prior knowledge of temporal variations in the deformation rate is not required for their identification. We apply StaMPS to Volcan Alcedo, where conventional InSAR fails because of dense vegetation on the upper volcano flanks that causes most pixels to decorrelate with time. We detect two sources of deformation. The first we model as a contracting pipe-like body, which we interpret to be a crystallizing magma chamber. The second is downward and lateral motion on the inner slopes of the caldera, which we interpret as landsliding.

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Persistent scatterer interferometric synthetic aperture radar for crustal deformation analysis, with application to Volcán Alcedo, Galápagos

SUMMARY Plate motions relative to the hotspots over the past 4 to 7 Myr are investigated with a goal of determining the shortest time interval over which reliable volcanic propagation rates and segment trends can be estimated. The rate and trend uncertainties are objectively determined from the dispersion of volcano age and of volcano location and are used to test the mutual consistency of the trends and rates. Ten hotspot data sets are constructed from overlapping time intervals with various durations and starting times. Our preferred hotspot data set, HS3, consists of two volcanic propagation rates and eleven segment trends from four plates. It averages plate motion over the past ≈5.8 Myr, which is almost twice the length of time (3.2 Myr) over which the NUVEL-1A global set of relative plate angular velocities is estimated. HS3-NUVEL1A, our preferred set of angular velocities of 15 plates relative to the hotspots, was constructed from the HS3 data set while constraining the relative plate angular velocities to consistency with NUVEL-1A. No hotspots are in significant relative motion, but the 95 per cent confidence limit on motion is typically ±20 to ±40 km Myr −1 and ranges up to ±145 km Myr −1 . The uncertainties of the new angular velocities of plates relative to the hotspots are smaller than those of previously published HS2-NUVEL1 (Gripp & Gordon 1990), while being averaged over a shorter and much more uniform time interval. Nine of the fourteen HS2-NUVEL1 angular velocities lie outside the 95 per cent confidence region of the corresponding HS3NUVEL1A angular velocity, while all fourteen of the HS3-NUVEL1A angular velocities lie inside the 95 per cent confidence region of the corresponding HS2-NUVEL1 angular velocity. The HS2-NUVEL1 Pacific Plate angular velocity lies inside the 95 per cent confidence region of the HS3-NUVEL1A Pacific Plate angular velocity, but the 0 to 3 Ma Pacific Plate angular velocity of Wessel & Kroenke (1997) lies far outside the confidence region. We show that the change in trend of the Hawaiian hotspot over the past 2 to 3 Myr has no counterpart on other chains and therefore provides no basis for inferring a change in Pacific Plate motion relative to global hotspots. The current angular velocity of the Pacific Plate can be shown to differ from the average over the past 47 Myr in rate but not in orientation, with the current rotation being about 50 per cent faster (1.06 ± 0.10 deg Myr −1 ) than the average (0.70 deg Myr −1 ) since the 47-Myr-old bend in the Hawaiian‐Emperor chain.

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Young tracks of hotspots and current plate velocities

Heterogeneous mantle domains: signatures, genesis and mixing chronologies

Dynamics of the Galapagos hotspot from helium isotope geochemistry

The Generation of Oceanic Rhyolites by Crystal Fractionation: the Basalt-Rhyolite Association at Volcán Alcedo, Galápagos Archipelago

Previous models relating the Snake River plain and Columbia River Basalt (northwest United States) to the Yellowstone plume have not taken into account the effects of the subducted Farallon and Juan de Fuca plates. Not only did subduction shield the surface from mantle plume activity, but it deflected the plume in the direction of plate motion. A variety of geophysical and geologic evidence suggests that the plume penetrated the subducted slab at ∼17.5 Ma, causing eruption of the Columbia River Basalt. The plate boundary then migrated over the plume, and the Yellowstone plume has recovered to a more nearly vertical conduit, forming the Snake River plain and Yellowstone plateau.

Origin of the Columbia Plateau and Snake River plain: Deflection of the Yellowstone plume

Although the Galapagos Islands have long been cited as an example of intraplate volcanism resulting from a mantle plume1,2, a number of features of the Galapagos appeared to conflict with a simple mantle-plume model. These include the non-linear arrangement of volcanoes, the non-time-transgressive nature of volcanism, and a tendency for the lavas to have more depleted trace-element and isotopic signatures towards the centre of the archipelago. The toroidal diapir model of Griffiths3,4, in which depleted asthenosphere is drawn into the centre of the rising diapir with the original diapir material preserved in a torus, appears to resolve these conflicts and provides an explanation for many of the enigmatic aspects of Galapagos volcanism.

Dennis Geist

Papers

Dynamics of the Galapagos hotspot from helium isotope geochemistry

The Generation of Oceanic Rhyolites by Crystal Fractionation: the Basalt-Rhyolite Association at Volcán Alcedo, Galápagos Archipelago

Origin of the Columbia Plateau and Snake River plain: Deflection of the Yellowstone plume

Plume-asthenosphere mixing beneath the Galapagos archipelago

Primitive neon from the center of the Galápagos hotspot