Subsurface tectonic structure between overlapping mid-ocean ridge segments

Our results from seismic anisotropy analyses reveal for the first time the complex spatial variability of the characteristics of subsurface tectonic structures associated with ridge propagation. The significance lies in the fact that these variations are found at a locality with few lineaments or fissures at seafloor level. The overlap region between mid-ocean ridge segments at 98N on the East Pacific Rise is characterized by aligned cracks that are structurally more closely related to the propagating-ridge segment. These aligned cracks, which are approximately parallel to the ridge segments, provide conclusive observational evidence for establishing the nontransform nature of overlapping spreading centers, especially those with overlap basins covered by volcanic edifices. The aligned cracks of the 98039N overlapping spreading center are more similar to the ridge-parallel lineaments observed between overlapping axial-summit collapse troughs than those found at larger overlapping spreading centers. Our results therefore suggest that the lithospheric deformation between overlapping ridge segments depends on ridge offset and that this dependency may be thermally related.

[1]  D. Toomey,et al.  Shear wave splitting and crustal anisotropy at the Mid‐Atlantic Ridge, 35°N , 2003 .

[2]  Matthew C. Smith,et al.  Magmatic processes and segmentation at a fast spreading mid‐ocean ridge: Detailed investigation of an axial discontinuity on the East Pacific Rise crest at 9°37′N , 2001 .

[3]  P. Barton,et al.  Three‐dimensional shallow crustal emplacement at the 9°03′N overlapping spreading center on the East Pacific Rise: Correlations between magnetization and tomographic images , 2001 .

[4]  D. Toomey,et al.  Crack-induced seismic anisotropy in the oceanic crust across the East Pacific Rise (9°30′N) , 2001 .

[5]  D. Pollard,et al.  Fault linkage: Three‐dimensional mechanical interaction between echelon normal faults , 1998 .

[6]  S. Solomon,et al.  Seismic structure and crustal magmatism at the Mid‐Atlantic Ridge, 35°N , 1998 .

[7]  B. Cornuelle,et al.  Three‐dimensional tomographic velocity structure of upper crust, Coaxial segment, Juan de Fuca Ridge: Implications for on‐axis evolution and hydrothermal circulation , 1997 .

[8]  Dawn J. Wright,et al.  Crustal fissuring and its relationship to magmatic and hydrothermal processes on the East Pacific Rise crest (9°12′ to 54′N) , 1995 .

[9]  M. Cormier,et al.  Magnetic and tectonic studies of the dueling propagating spreading centers at 20°40′S on the East Pacific Rise: Evidence for crustal rotations , 1993 .

[10]  D. Wiens,et al.  Evidence from earthquakes for bookshelf faulting at large non-transform ridge offsets , 1993, Nature.

[11]  S. Carbotte,et al.  East Pacific Rise 8°–10°30′N: Evolution of ridge segments and discontinuities from SeaMARC II and three‐dimensional magnetic studies , 1992 .

[12]  S. Carbotte,et al.  Mid-Ocean Ridges: Discontinuities, Segments and Giant Cracks , 1991, Science.

[13]  P. Lonsdale.  The rise flank trails left by migrating offsets of the equatorial East Pacific Rise axis , 1989 .

[14]  P. J. Fox,et al.  Tectonic evolution of ridge-axis discontinuities by the meeting, linking, or self-decapitation of neighboring ridge segments , 1987 .

[15]  K. Macdonald,et al.  Deep‐tow studies of the overlapping spreading centers at 9°03′N on the East Pacific Rise , 1986 .

[16]  R. Stephen.  Seismic anisotropy in the upper oceanic crust , 1985 .

[17]  P. Lonsdale.  Nontransform offsets of the Pacific-Cocos plate boundary and their traces on the rise flank , 1985 .

[18]  R. S. White,et al.  An investigation of seismic anisotropy due to cracks in the upper oceanic crust at 45°N, Mid-Atlantic Ridge , 1984 .

[19]  P. J. Fox,et al.  East Pacific Rise from Siqueiros to Orozco Fracture Zones: Along‐strike continuity of axial neovolcanic zone and structure and evolution of overlapping spreading centers , 1984 .

[20]  R. White,et al.  Effects of tectonism and magmatism on crack structure in oceanic crust: A seismic anisotropy study , 2004 .

[21]  J. Hudson,et al.  The mechanical properties of materials with interconnected cracks and pores , 1996 .