Open AccessEvolution of the Southwest Indian Ridge from 55°45′E to 62°E: Changes in plate‐boundary geometry since 26 Ma
Author(s) -
Baines A. Graham,
Cheadle Michael J.,
Dick Henry J. B.,
Scheirer Allegra Hosford,
John Barbara E.,
Kusznir Nick J.,
Matsumoto Takeshi
Publication year - 2007
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2006gc001559
Subject(s) - geology , transform fault , classification of discontinuities , seafloor spreading , mid ocean ridge , ridge , seismology , echelon formation , magnetic anomaly , bathymetry , clockwise , plate tectonics , geometry , mantle (geology) , lineation , offset (computer science) , geodesy , upwelling , oblique case , rotation (mathematics) , fault (geology) , geophysics , tectonics , paleontology , mathematical analysis , mathematics , oceanography , linguistics , philosophy , computer science , programming language
From 55°45′E to 58°45′E and from 60°30′E to 62°00′E, the ultraslow‐spreading Southwest Indian Ridge (SWIR) consists of magmatic spreading segments separated by oblique amagmatic spreading segments, transform faults, and nontransform discontinuities. Off‐axis magnetic and multibeam bathymetric data permit investigation of the evolution of this part of the SWIR. Individual magmatic segments show varying magnitudes and directions of asymmetric spreading, which requires that the shape of the plate boundary has changed significantly over time. In particular, since 26 Ma the Atlantis II transform fault grew by 90 km to reach 199 km, while a 45‐km‐long transform fault at 56°30′E shrank to become an 11 km offset nontransform discontinuity. Conversely, an oblique amagmatic segment at the center of a first‐order spreading segment shows little change in orientation with time. These changes are consistent with the clockwise rotation of two ∼450‐km‐wide first‐order spreading segments between the Gallieni and Melville transform faults (52–60°E) to become more orthogonal to spreading. We suggest that suborthogonal first‐order spreading segments reflect a stable configuration for mid‐ocean ridges that maximizes upwelling rates in the asthenospheric mantle and results in a hotter and weaker ridge‐axis that can more easily accommodate seafloor spreading.