Seismic gap beneath Logachev Seamount: Indicator for melt focusing at an ultraslow mid-ocean ridge?

摘要

Ultraslow spreadingmid-ocean ridges have a low magma\udbudget and melt is distributed unevenly along the ridge axis.\udThere is little or no basaltic crust between isolated magmatic\udcenters. The processes that focus melts to segments of robust\udmagmatism are not yet understood. During a seismic\udsurvey of the ultraslow spreading Knipovich Ridge in the\udNorwegian-Greenland Sea with ocean bottom seismometers,\udwe discovered a seismic gap in the upper mantle beneath\udLogachev Seamount, where micro-earthquakes clearly\uddelineate a shallowing of the maximum depth of faulting.\udA topography of the lithosphere that allows melts to travel\udlaterally along its base and rise in areas of thin lithosphere\udhas been proposed as a possible mechanism to explain the\udfocusing of melts at volcanic centers, but has never been\udconfirmed observationally. Our results are the first\udgeophysical evidence for an along-axis variation of the\udlithospheric thickness at an ultraslow spreading ridge.