Tibet became the world’s roof in stagesMarch 25th, 2008 - 1:18 pm ICT by admin
New York, March 25 (IANS) It has long been known that the Himalayas rose, and the Tibetan plateau became the “roof of the world”, thanks to the collision of tectonic plates as India ploughed northward into Asia. Now we know a little more about how exactly this happened. New evidence from an eight-year study by researchers in University of California, Santa Cruz (UCSC), indicates that the plateau rose in stages, with the uplift occurring first in the central plateau and later in the north and south.
These findings have been published in the Proceedings of the National Academy of Sciences.
“Our work shows that the central part of the plateau was uplifted first 40 million yeas ago, while Everest and much of the Himalayas was resting deep on the ocean basin and it seems to fit pretty well with other studies,” said co-author Robert Coe.
The rise of the plateau led to dramatic changes in the climate, both regionally and globally. For climate researchers trying to unravel major episodes of global climate change, the timing of the uplift is a crucial piece of information.
The discovery narrows the window of time during which the Himalayas could have been uplifted.
The area’s geologic history is recorded in layers of sedimentary rock 5,000 metres thick. Now a part of the high plateau, it was once a basin on the northern edge of the central plateau, Lippert said.
Several lines of evidence support the team’s conclusions. In addition to field studies, the researchers used a variety of laboratory techniques to analyse and date the rocks.
Past changes in the earth’s magnetic field, recorded in the magnetisation of the rocks, provide one method of dating. Called magnetostratigraphy, this analysis was performed in Coe’s laboratory at UCSC.
Another dating technique used in the study, called apatite fission-track analysis, is based on the damage trails left in apatite crystals by the decay of radiogenic isotopes.
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