Marie Tharp

Tectonic fabric of the Atlantic and Indian oceans and continental drift

The floor of the Indian Ocean is dominated by (1) the seismically active Mid-Oceanic Ridge, (2) scattered linear micro-continents (mostly meridional), and (3) fracture zones (some displace the axis of the Mid-Oceanic Ridge and others parallel the micro-continents). The pattern suggests that movement along the Diamantina Fracture Zone has displaced Australia to the east relative to Broken Ridge. In the Arabian Sea north-northeast trending fracture zones have displaced the axis of the Carlsberg Ridge. The complex tectonic fabric of the Indian Ocean is difficult to explain in terms of a simple pattern of convection currents. The location and origin of the Mid-Oceanic Ridge, of oceanic rises, aseismic ridges and transcurrent fault systems must be accounted for in any hypothesis of continental displacement despite unique or exotic assumptions as to strength, viscosity or composition of the oceanic crust and mantle.

Chain and romanche fracture zones

Abstract A series of left-lateral faults displace the axis of the Mid-Atlantic Ridge in the equatorial Atlantic. Two of the most prominent of these faults are the Romanche and Chain Fracture Zones. The ridge crest is offset 180 miles by the Chain Fracture Zone. The Vema Depth of 4106 fm is the maximum depth observed in the Romanche Trench. The floor of the trench is locally smoothed by sediments gravity transported from adjacent areas. Allochthonous fossils occur in cores from the trench floor. Scour by bottom currents is apparent in photographs and in the character of the sediments obtained by coring.

Cretaceous Drowning of Reefs on Mid-Pacific and Japanese Guyots

Reefs dredged on guyots of the Mid-Pacific Mountains and the Japanese Seamounts yield middle Cretaceous fossils, indicating that submergence killed off the fauna of the reefs sometime during the Albian-Cenomanian. Eustatic rise of sea level is probably responsible.

PHYSIOGRAPHY OF THE INDIAN OCEAN

As a result of the International Indian Ocean Expedition, the bottom of the Indian Ocean is now one of the best known areas of the ocean floor. The Mid-Indian Ocean Ridge, a rugged mountain range, lies in the centre of the Indian Ocean. North-northeast trending fractures offset the axis of the ridge. In the Arabian Sea these fractures are right lateral; in the southwest Indian Ocean they are left lateral. Displacements range from a few miles* to over 200 miles. The northeast Arabian Sea and the Bay of Bengal are occupied by huge abyssal cones built by sediments discharged from the Indo-Gangetic plain. Extensive abyssal plains lie seaward of the abyssal cones. In low latitudes smooth topography is characteristic of the continental rise, the abyssal cones, and the oceanic rises. However, near the polar front smooth c swale9 topography laps over the normally rugged Mid-Oceanic Ridge. This c swale5 smoothing appears the result of the higher organic productivity of the Antarctic seas. Microcontinents, mostly linear meridional ridges, are unique features of the Indian Ocean. These massive but smooth-surfaced blocks contrast markedly with the broad rugged Mid-Oceanic Ridge.