The ridge divides the Indian Ocean into the West and East Indian Ocean. The northeastern side is named the
Wharton Basin and ceases at the western end of the
Diamantina fracture zone which passes to the east and almost to the Australian continent. The ridge is primarily composed of
ocean island tholeiites (OIT), a subset of
basalt which were shown to increase in age from approximately in the south to in the north. A more recent analysis using modern
Ar–Ar techniques gives an age progression from at 5°N to at 31°S. Even more recent work with more samples gives a range of This age progression has led geologists to theorize that a
hotspot in the
mantle beneath the
Indo-Australian plate created the ridge as the plate has moved northward in the late
Mesozoic and
Cenozoic. This theory was supported by analysis of the chemistry of the
Kerguelen Plateau and
Rajmahal Traps, which were believed to represent the
flood basalts erupted at the initiation of volcanism at the
Kerguelen hotspot which was then sheared in two as the Indian subcontinent moved northward. This has led to modifications of understanding. Some maintain close to the original view. The Ninety East Ridge has no systematic isotopic variation observed along the ridge and this is inconsistent with the hypothesis of an ageing mantle plume origin for all of the ridge.
Surveying The ridge has been surveyed several times in the past, including several times by the
Deep Sea Drilling Program (DSDP). In 2007, the
RV Roger Revelle collected bathymetric, magnetic and seismic data together with dredge samples from nine sites along the ridge as part of an
Integrated Ocean Drilling Program (IODP) site survey intended to examine the hotspot hypothesis for the ridge. ==Origins==