Ninety degrees east ridge

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The Ninety Degree East Ridge is an inactive volcanic ridge in the Indian Ocean that extends roughly from the Nicobar Islands in the north to about thirty degrees south. The ridge got its name thanks to the fact that it follows the ninetieth east longitude in its course from north to south.

Origin and morphology

The emergence of the back is now generally the Kerguelen - hotspot assigned. The drift of the Indian plate over the stationary hotspot gradually created the elongated structure of the back due to the large amounts of ejected basalt , with the help of which the drift of the Indian plate can also be traced over the last 80 million years. About forty million years ago the spreading axis was formed, which today allows the Indian and Antarctic plates to drift apart. The Broken Ridge Plateau separated from the Kerguelen Plateau, and the drift direction of the Indian Plate changed, which can be traced back to a kink in the orientation of the 90-degree east ridge towards the south-southwest.

The ridge also played a crucial role in the development of the Bengal deep-sea fan . Due to the subduction of the ocean floor in the Sunda Trench , it came closer and closer to the Nicobar Islands and finally closed the gap in the early Quaternary , so that the part of the Bengal fan behind was cut off from the sediment supply. The part of the fan, also known today as the Nikobar fan, therefore has significantly less sediment thicknesses than the main fan located to the east.

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