Monday, 13 April 2009

Himalayas are twice older than believed

By Syed Akbar

How old are the Himalayas, the snow-covered mountains that wall the northern India? Existing scientific records and evidence show that the Himalayas are less than eight million years old. But a group of scientists from India and the United Kingdom has negated this widely held belief and established with latest scientific evidence that the mountains are twice as older. In short, the Himalayas took their birth about 15 million years ago.

The Indo-British team has found evidence for early uplift of Himalayas within the central Indian Ocean. "The discovery that the earth’s strong outer shell — the ‘lithosphere’ — within the central Indian Ocean began to deform and fracture 15.4-13.9 million years ago, much earlier than previously thought, impacts our understanding of the birth of the Himalayas and the strengthening of the Indian-Asian monsoon," says Dr K.S. Krishna of the Goa-based National Institute of Oceanography.

According to an official release from the National Institute of Oceanography, India and Asia collided around 50 million years ago as a result of plate tectonics — the large-scale movements of the lithosphere, which continue to this day. The study was published in Geology, a scientific magazine published by the Geological Society of America.

"The ocean floor has been systematically transformed into folds 100-300 kilometres long and 2,000-3,000 metres high, and there are also regularly spaced faults or cracks that are evident from seismic surveys and ocean drilling," points out Dr Krishna in the research study.

The onset of this deformation marks the start of major geological uplift of the Himalayas and the Tibetan Plateau, some 4,000 km further to the north, due to stresses within the wider India-Asia area. Some studies indicate that it began around 8.0-7.5 million years ago, while others have indicated that it started before 8.0 million years ago, and perhaps much earlier.

This controversy has now been addressed by Dr Krishna and his British colleagues Prof. Jon Bull of the University of Southampton, and Prof. Roger Scrutton of Edinburgh University. They have analysed seismic profiles of 293 faults (vertical cracks in the ocean floor) in the accumulated sediments of the Bengal Fan. This is the world’s largest submarine fan, a delta-shaped accumulation of land-derived sediments covering the floor of the Bay of Bengal.

The NIO statement points out that the team demonstrated that deformation of the lithosphere within the central Indian Ocean started around 15.4-13.9 million years ago, much earlier than most previous estimates. This implies considerable Himalayan uplift before 8.0 million years ago, which is when many geologists believe that the strong seasonal winds of the India-Asia monsoon first started.

"However," says Dr Krishna, "the realisation that the onset of lithospheric deformation within the central Indian Ocean occurred much earlier fits in well with more recent evidence that the strengthening of the monsoon was linked to the early geological uplift of the Himalayas and Tibetan plateau up to 15-20 million years ago."

Scientists believe that intensive deep-sea drilling within the Bengal Fan would provide better age estimates for the onset of deformation of the lithosphere in the central Indian Ocean and concretise the recent findings. There are more weighty geological questions related to the geodynamics of the Indian Plate yet to be understood.

Principal among these being the issue of how exactly did the ocean floor buckle and crack in space and time, and what will be the future course of this compressional activity in the central Indian Ocean.

The NIO statement said further scientists would like to gather new evidences for understanding of 1) why and how the central Indian Ocean region has now become site where mountains are rising up from the ocean floor and cracks are propagating within the crust; and 2) whether the present process could be a pre-cursor to the formation of a subduction zone in the central Indian Ocean.

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