| Mid-ocean ridge segmentation which persists for tens of millions of years is defined by observable along-axis changes in geophysical parameters such as subsidence rate of the oceanic crust, asymmetry in crustal subsidence, zero-age depth of the ridge, and geoid height decrease with age (geoid rate). The long-lived segmentation of the mid-ocean ridge results in tectonic corridors, within which geophysical characteristics are relatively uniform. Corridor boundaries are identified where several geophysical parameters change abruptly and are consistent with the premise that their loci are parallel to flowlines. The South Atlantic Ridge, the Pacific - Antarctic Ridge and the Southeast Indian Ridge, which cover a wide range of spreading rates, have been studied. The total length of ridge crest examined is approximately 15,000 km.;Conspicuous long-lived segmentation is observed along the South Atlantic and Southeast Indian Ridges with an along-strike wavelength of about 500-1000 km. In contrast, for the Pacific - Antarctic Ridge, only differences in the geoid rate provide evidence of long-lived segmentation processes. Independent geochemical and seismic tomographic data are entirely compatible with the existence of the segmentation boundaries proposed. Linear relationships between subsidence rate and zero-age depth regression statistics are observed in all three study areas. These relationships have not yet been explained.;Several models commonly used to explain subsidence rate, geoid rate and zero-age depth are re-examined. Even when the thermal parameters (mantle temperature, density, thermal diffusivity, thermal expansion coefficient) are allowed to vary by as much as 20%, these models are inconsistent with many of the observations in the three study areas. The zero-age depth variations, however, can be reasonably explained by a geochemistry-based model. A qualitative composite model of local and regional temperature variations is developed that can explain all of the major observations. This model implies different quantitative relationships between the geophysical parameters (subsidence rate and geoid rate) and the dependent mantle variables (temperature, mantle density, thermal diffusivity, thermal expansion coefficient) from the commonly applied thermal conduction model. |
