The Pacific-Antarctic and the Southeast Indian ridges are examined for evidence of long-lived (tens of millions of years) tectonic segmentation of the mid-ocean ridge by examining a variety of geophysical parameters similar to those previously documented in the South Atlantic (Kane and Hayes, 1992). These parameters include subsidence rate of the oceanic crust (individual flanks and asymmetry), zero-age depth, and geoid height decrease with age (geoid rate). The variability in these parameters along-strike of the mid-ocean ridge is systematic and serves to define a large scale ridge segmentation of the order of hundreds of kilometers. The Southeast Indian ridge exhibits long-lived segmentation in all parameters examined and is subdivided into five flow line corridors with boundaries between corridors occurring at or near major fracture zones. While the Pacific-Antarctic ridge exhibits conspicuous asymmetric crustal subsidence, evidence of segmentation exists primarily in the along-strike geoid rate. The observations in these two areas are found to be internally inconsistent with simple thermal conduction models for oceanic crust, strongly suggesting that factors other than cooling and isostasy are influencing the creation and subsequent modification of the oceanic crust and lithosphere.
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