Faulting and volcanism in the axial valley of the slow-spreading center of the Mariana back arc basin from Wadatsumi side-scan sonar images
Montesi, Laurent G. J.
MetadataShow full item record
We analyzed in detail the geology of the median valley floor of the Mariana Basin slow-spreading ridge using sea surface geophysical data and a high-resolution deep-tow side-scan sonar survey over one spreading segment. Analysis of surface magnetic data indicates highly asymmetric accretion, with the half-spreading rate on the western side of the basin being two to three times larger than on the eastern side. Surface magnetic and reflectivity data together suggest that asymmetric spreading is accomplished through eastward ridge jumps of ∼10 km of amplitude. Deep-tow backscatter data indicate along-axis variations of the volcanic processes with the emplacement of smooth and hummocky flows at the segment center and end, respectively. This variation likely relates to changes in the effusion rate due to the deepening or even disappearance of the magma chamber toward the segment end. Concerning tectonic processes, we find a power law distribution of the fractures, with an exponent of 1.74. This suggests that within the inner valley floor, fracture growth prevails over fracture nucleation and coalescence and that fractures accommodate less than 8% of the strain. According to our calculation based on a ratio of 0.02 to 0.03 between the vertical displacement and the length of faults, the amount of tectonic strain accommodated in the inner valley floor would consistently be ∼1.1–3.4%. Data also show two distinct sets of fractures. One trend is parallel to the rift direction at the segment center (∼N160°E) and perpendicular to the plate separation direction. Another set trends ∼17° oblique to this direction (∼N175°E) and is located over the eastern part of the valley, in the vicinity of a major bounding fault also trending ∼N175°E, that is, obliquely to the direction of plate motion. We modeled the stress field near a major fault that is oblique to the regional stress field associated with plate separation using a three-dimensional boundary element approach. We found that the orientation of the predicted fissuring near the oblique fault is locally rotated by ∼15° due to a flexure of the bending plate close to this fault.
Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 6 (2005): Q05006, doi:10.1029/2004GC000881.
Showing items related by title, author, creator and subject.
Submarine volcanic morphology of the western Galapagos based on EM300 bathymetry and MR1 side-scan sonar Glass, Jennifer B.; Fornari, Daniel J.; Hall, Hillary F.; Cougan, Allison A.; Berkenbosch, Heidi A.; Holmes, Mark L.; White, Scott M.; De La Torre, Giorgio (American Geophysical Union, 2007-03-21)A compilation of high-resolution EM300 multibeam bathymetric and existing MR1 side-scan sonar data was used to investigate the volcanic morphology of the flanks of the western Galápagos Islands. The data portray an assortment ...
Lucky Strike seamount : implications for the emplacement and rifting of segment-centered volcanoes at slow spreading mid-ocean ridges Escartin, Javier E.; Soule, Samuel A.; Cannat, Mathilde; Fornari, Daniel J.; Dusunur, D.; Garcia, Rafael (John Wiley & Sons, 2014-11-07)The history of emplacement, tectonic evolution, and dismemberment of a central volcano within the rift valley of the slow spreading Mid-Atlantic Ridge at the Lucky Strike Segment is deduced using near-bottom sidescan sonar ...
Interplay between faults and lava flows in construction of the upper oceanic crust : the East Pacific Rise crest 9°25′–9°58′N Escartin, Javier E.; Soule, Samuel A.; Fornari, Daniel J.; Tivey, Maurice A.; Schouten, Hans A.; Perfit, Michael R. (American Geophysical Union, 2007-06-07)The distribution of faults and fault characteristics along the East Pacific Rise (EPR) crest between 9°25′N and 9°58′N were studied using high-resolution side-scan sonar data and near-bottom bathymetric profiles. The ...