Ancient Volcanic Cataclysms Discovered in the Indian Ocean
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Scientists from the largely National Science Foundation (NSF) supported Ocean Drilling Program (ODP) have completed an expedition to one of the most remote places on Earth, the Kerguelen Plateau. The results of their expedition will shed new light on how and when continents formed and broke apart millions of years ago.
The international team of 45 scientists conducted their research aboard the world's largest scientific drilling vessel, the JOIDES Resolution. The drillship departed Fremantle, Australia, on December 13, 1998, and returned to Fremantle on February 11, 1999.
Kerguelen Plateau is located in the southern Indian Ocean, is one-third the size of the United States, and is described as a large igneous province (LIP). LIPs are areas where magma wells up from deep beneath Earth's surface and forms molten rock. The major objectives of the ODP expedition, explains Bruce Malfait, director of ODP at NSF, were to determine through drilling when volcanism was active; how much of the plateau formed above sea level and how long portions of the feature remained above sea level; and if continental fragments form part of the plateau.
Using evidence from fossils as well as terrestrial plant remains, the scientific team constrained the time period during which the Kerguelen LIP formed. They found that the southern Kerguelen Plateau, only hundreds of kilometers from Antarctica, formed approximately 110 million years ago. To the north, the central Kerguelen Plateau and the once-contiguous Broken Ridge formed between 85 and 95 million years ago. In contrast, the northern Kerguelen Plateau is much younger, having formed less than 35 million years ago. These results indicate that several intense episodes of volcanism formed this large plateau over a long time period, rather than from a single massive volcanic event.
"We found abundant evidence that much of the Kerguelen LIP formed above sea level," states co-chief scientist Mike Coffin of the University of Texas Institute of Geophysics. "Wood fragments, a seed, spores and pollen recovered in 90-million-year- old sediment from the central Kerguelen Plateau, just southeast of Heard Island, unambiguously indicates that this region was above sea level."
A spectacular result was finding uniquely continental rocks in a conglomerate that was probably deposited in a river on Elan Bank near the central and southern Kerguelen Plateau, explains co chief scientist Fred Frey of the Massachusetts Institute of Technology. "Knowing how pieces of an ancient continent were incorporated into the oceanic environment of Elan Bank will have significant impact on our understanding of the approximately 130- million-year-old break-up of Australia, India and Antarctica."
A surprising finding at three drill sites was evidence for large-scale explosive volcanism, apparently a common phenomenon as volcanic construction of the plateau came to an end. Explosive volcanism can perturb the earth-atmosphere system significantly by injecting material into the stratosphere where, depending on the magnitude and altitude of the material, it may persist for several years. This can cause considerable short- term environmental effects, such as those resulting from the recent eruption of Mount Pinatubo in the Philippines.
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