42 research outputs found
Costa Rica Seismogenesis Project (CRISP): sampling and quantifying input to the seismogenic zone and fluid output
Recycled gabbro signature in hotspot magmas unveiled by plume–ridge interactions
Lavas erupted within plate interiors above upwelling mantle
plumes have chemical signatures that are distinct from midocean
ridge lavas. When a plume interacts with a mid-ocean
ridge, the compositions of both their lavas changes, but there
is no consensus as to how this interaction occurs1–3. For the
past 15 Myr, the Pacific–Antarctic mid-ocean ridge has been
approaching the Foundation hotspot4 and erupted lavas have
formed seamounts. Here we analyse the noble gas isotope
and trace element signature of lava samples collected from
the seamounts. We find that both intraplate and on-axis
lavas have noble gas isotope signatures consistent with the
contribution from a primitive plume source. In contrast, nearaxis
lavas show no primitive noble gas isotope signatures, but
are enriched in strontium and lead, indicative of subducted
former oceanic lower crust melting within the plume source5–7.
We propose that, in a near-ridge setting, primitive, plumesourced
magmas formed deep in the plume are preferentially
channelled to and erupted at the ridge-axis. The remaining
residue continues to rise and melt, forming the near-axis
seamounts. With the deep melts removed, the geochemical
signature of subduction contained within the residue becomes
apparent. Lavas with strontium and lead enrichments are found
worldwide where plumes meet mid-ocean ridges6–8, suggesting
that subducted lower crust is an important but previously
unrecognised plume component
IODP Expedition 334: An Investigation of the Sedimentary Record, Fluid Flow and State of Stress on Top of the Seismogenic Zone of an Erosive Subduction Margin
The Costa Rica Seismogenesis Project (CRISP) is an
experiment to understand the processes that control nucleation
and seismic rupture of large earthquakes at erosional
subduction zones. Integrated Ocean Drililng Program
(IODP) Expedition 334 by R/V JOIDES Resolution is the first
step toward deep drilling through the aseismic and seismic
plate boundary at the Costa Rica subduction zone offshore
the Osa Peninsula where the Cocos Ridge is subducting
beneath the Caribbean plate. Drilling operations included
logging while drilling (LWD) at two slope sites (Sites U1378
and U1379) and coring at three slope sites (Sites U1378–1380)
and at one site on the Cocos plate (Site U1381). For the first
time the lithology, stratigraphy, and age of the slope and
incoming sediments as well as the petrology of the subducting
Cocos Ridge have been characterized at this margin.
The slope sites recorded a high sediment accumulation rate
of 160–1035m m.y.-1 possibly caused by on-land uplift triggered
by the subduction of the Cocos Ridge. The geochemical
data as well as the in situ temperature data obtained at
the slope sites suggest that fluids are transported from
greater depths. The geochemical profiles at Site U1381 reflect
diffusional communication of a fluid with seawater-like
chemistry and the igneous basement of the Cocos plate
(Solomon et al., 2011; Vannucchi et al., 2012a). The
present-day in situ stress orientation determined by borehole
breakouts at Site U1378 in the middle slope and Site
U1379 in the upper slope shows a marked change in stress
state within ~12 km along the CRISP transect; that may
correspond to a change from compression (middle slope) to
extension (upper slope)
Ice-confined construction of a large basaltic volcano—Austurfjöll massif, Askja, Iceland
Austurfjöll is the largest basaltic glaciovolcanic massif at Askja volcano (Central Iceland), and through detailed studies of its volcanological and geochemical characteristics, we provide a detailed account of the sequence and structure of the ice-confined construction of a large Icelandic basaltic volcano. In particular, Austurfjöll represents a geometry of vents, and resulting glaciovolcanic morphology, not previously documented in ice-confined basaltic volcanoes. Austurfjöll was constructed during two major phases of basaltic volcanism, via seven eruptive episodes through disperse fissure-dominated eruptions. The earliest episode involved a rare and poorly exposed example of subaerial activity, and this was succeeded by six episodes involving the eruption of ice-confined pillow lavas and numerous overlapping fissure eruptions of phreatomagmatic tephra. Evidence of local subaerial lavas and tephras indicates the local growth of eruptive centers above englacial lake levels, and subsequent flooding, but no prolonged subaerial activity. Localized ice-contact facies, paleowater levels, and diamictons indicate the position and thickness of the ice was variable during the construction of Austurfjöll, and eruptive activity likely occurred in multiple and variable level meltwater lakes during the last glacial period. Lithofacies evidence including gradational transitions from effusive to explosive deposits, superposition of fragmental facies above coherent facies, and drainage channels suggest that changes in eruptive style were driven largely by external factors such as drainage and the increasing elevation of the massif. This study emphasizes the unique character of Austurfjöll, being composed of large pillow lava sheets, numerous (> 40) overlapping glaciovolcanic tindars, and only localized emergent deposits, as a product of its prolonged ice-confined eruptive history, contrasts with previous descriptions of tuyas and tindars
Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODP Expedition 340
IODP Expedition 340 successfully drilled a series of sites offshore Montserrat, Martinique and Dominica in the Lesser Antilles from March to April 2012. These are among the few drill sites gathered around volcanic islands, and the first scientific drilling of large and likely tsunamigenic volcanic island-arc landslide deposits. These cores provide evidence and tests of previous hypotheses for the composition and origin of those deposits. Sites U1394, U1399, and U1400 that penetrated landslide deposits recovered exclusively seafloor-sediment, comprising mainly turbidites and hemipelagic deposits, and lacked debris avalanche deposits. This supports the concepts that i/ volcanic debris avalanches tend to stop at the slope break, and ii/ widespread and voluminous failures of pre-existing low-gradient seafloor sediment can be triggered by initial emplacement of material from the volcano. Offshore Martinique (U1399 and 1400), the landslide deposits comprised blocks of parallel strata that were tilted or micro-faulted, sometimes separated by intervals of homogenized sediment (intense shearing), while Site U1394 offshore Montserrat penetrated a flat-lying block of intact strata. The most likely mechanism for generating these large-scale seafloor-sediment failures appears to be propagation of a decollement from proximal areas loaded and incised by a volcanic debris avalanche. These results have implications for the magnitude of tsunami generation. Under some conditions, volcanic island landslide deposits comprised of mainly seafloor sediment will tend to form smaller magnitude tsunamis than equivalent volumes of subaerial block-rich mass flows rapidly entering water. Expedition 340 also successfully drilled sites to access the undisturbed record of eruption fallout layers intercalated with marine sediment which provide an outstanding high-resolution dataset to analyze eruption and landslides cycles, improve understanding of magmatic evolution as well as offshore sedimentation processes. This article is protected by copyright. All rights reserved
IODP expedition 334: An investigation of the sedimentary record, fluid flow and state of stress on top of the seismogenic zone of an erosive subduction margin
金沢大学理工研究域地球社会基盤学
IODP Expedition 334: An Investigation of the Sedimentary Record, Fluid Flow and State of Stress on Top of the Seismogenic Zone of an Erosive Subduction Margin
Hotspot-Ridge Interaction
The exchange of material (magma, mantle rock) between an intraplate mantle melting anomaly (hotspot, thought to be caused in places by the presence of a mantle plume) and the global spreading ridge system. Evidence for the interaction is found in the depth of the spreading axis, its morphology, the chemistry of the lavas (both on the spreading axis and possibly at the hotspot), and sometimes by the presence of linear volcanic ridges between spreading axis and hotspot. These linear volcanic ridges generally do not show clear age-progressive volcanism, in contrast to the volcanoes of the hotspot itself