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Age dependent porosity of young upper oceanic crust: Insights from seafloor gravity studies of recent volcanic eruptions
Author(s) -
Pruis Matthew J.,
Johnson H. Paul
Publication year - 2002
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2001gl013977
Subject(s) - geology , seafloor spreading , crust , volcano , ridge , oceanic crust , mid ocean ridge , seismology , porosity , petrology , geophysics , paleontology , tectonics , subduction , geotechnical engineering
An October 1997 ALVIN program collected a series of seafloor gravity stations over the February, 1996, volcanic eruption site on the northern Gorda Ridge (46°41′N, 126°47′W). These measurements yielded estimates of the density and porosity of mid‐ocean ridge crust in the first few decades following formation. The estimated crustal density for this pillow eruption of 2270 ± 260 kg/m 3 is very low, but in good agreement with the estimated densities of other recent seafloor volcanic flows. Rock matrix densities, measured from hand samples retrieved from the study area, give a bulk porosity for this flow of 34% ± 16%. This data, when included with similar estimates of upper crustal porosity, argue for a rapid evolution of upper crustal porosities from very high values (≥30%) for recent eruptions to much lower values (∼10–15%) where the seafloor is older than 0.5 million years. These variations of density and porosity are of a magnitude consistent with previously observed changes in seismic compressional wave velocity and permeability of ocean crust.