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Recent advances in the understanding of mid-ocean ridge tectonics and volcanism using swath-mapping tools

Universitat de Barcelona
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  • Earth Science


ACTA GEOLOGICA HISPANICA, v. 27 (1992). nv-4, pags. 13-32 Recent advances in the understanding of mid-ocean ridge tectonics and volcanism using swath-mapping tools K.C. MACDONALD('), D.S. SCHEIRER('), S. CARBOTTE(') and P.J. FOX(2) (1) Department of Geological Sciences and Marine Sciences 1nstitute.University of California. Santa Barbara, CA 03106, USA. (2) Graduate School of Oceanography. University of Rhode Island. Narragansett, RI 02882, USA. ABSTRACT RESUMEN New swath mapping sonar systems have revealed the structure of the mid-ocean ridge (MOR) and sunounding deep ocean floor with unprecedent clarity. These images show that the MOR is partitioned into segments by a variety of offsets such as transform faults, overlap- ping spreading centers and very fine scale discontinuities which are barely detectable. The smallest scale segments are the fundamental building blocks for creation of new oceanic crust. They are only 2-20 km long and are active, distinct units for only =100-10,000 years. At fast spreading centers, the axial neovolcanic zone is a persistent 300- 400 m high elevation produced by the bouyancy of hot rock and mag- ma; it is not a volcanic construction (most of the time and in most pla- c e ~ ) so there is almost no vestige of it off-axis. Along ~ 6 0 % of its length, the spreading center is characterized by an axial summit calde- ra produced by volcanic inflation and collapse. The size and shape of the axial high are very sensitive indicators of a relatively steady and robust magma supply at fast-spreading ndges, and have been used successfuliy to predict the location of magma chambers and to fore- cast recent volcanic emptions including one witnessed from ALVIN in March-Apnl 1991. At intermediate spreading rates, the axial region cools sufficiently for a volcanic constructional edifice to develop epi- sodically and for normal faulting to occur along an axial graben. Un- der these conditions axial volcanoes are split in two by the axial gr

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