October 18, 2013
Unraveling The Origins Of Antarctic Seamounts
April Flowers for redOrbit.com - Your Universe Online
When you think of the Antarctic, images of snow, ice and glaciers are the usual associations. We forget that it is also a region of fire, dotted with volcanoes on the mainland and the surrounding islands. Some of these volcanoes are extinct and some are still active, such as the Marie Byrd Seamounts in the Amundsen Sea. Today, their summit plateaus are at depths of 7,800 - 5,200 feet, making them difficult to reach with conventional research vessels. This means they have barely been explored, despite having fascinating formations that do not fit any of the usual models for the formation of volcanoes.
Two types of volcanoes exist according to classical volcanologists. The first is created where tectonic plates meet, so the planet's crust is already cracked to begin with. The second type is formed within the Earth's plates.
"The latter are called intraplate volcanoes. They are often found above a so-called mantle plume. Hot material rises from the deep mantle, collects under the earth's crust, makes its way to the surface and forms a volcano," said Dr. Reinhard Werner. An example of this is the Hawaiian Islands.
Neither of these traditional models fits the Marie Byrd Seamounts, however. "There are no plate boundaries in the vicinity and no plumes underground," says graduate geologist Andrea Kipf from GEOMAR.
Scientists from Kiel participated in an expedition of the research vessel POLARSTERN in 2006, to clarify the origins of the Marie Byrd Seamounts. Rock samples were collected from the seamounts. The samples were subjected to thorough geological, volcanological and geochemical investigations after the scientists returned to their home labs.
"Interestingly enough, we found chemical signatures that are typical of plume volcanoes. And they are very similar to volcanoes in New Zealand and the Antarctic continent," says geochemist Dr. Folkmar Hauff.
This finding sent the scientific team searching for explanations. The history of the southern hemisphere tectonic plates provided an answer. Approximately 100 million years ago, what was left the supercontinent Gondwana was located in the current region of Antarctica. The continental plate was cracked open when a mantle plume melted through, creating two new continents: Antarctica and "Zealandia." New Zealand is the present day remains of Zealandia.
Large quantities of plume material attached to the underside of these young continents as they drifted apart, forming reservoirs for future volcanic eruptions on the two continents.
"This process explains why we find signatures of plume material at volcanoes that are not on top of plumes," says Dr. Hauff.
This still doesn't completely explain the Marie Byrd Seamounts, however, as they did not form on the Antarctica continent, but on the adjacent oceanic crust.
"Continental tectonic plates are thicker than the oceanic ones. This ensures, among other things, differences in temperature in the underground," says volcanologist Dr. Werner. The temperature differences beneath the Earth's crust generate flows and movements, just as air masses of different temperatures create winds. This allowed the plume material from the continent to shift under the oceanic plate. Cracks and crevices formed because of other tectonic plate disruptions, allowing hot material to rise, turn into magma and then- about 60 million years ago - allowed the Marie Byrd Seamounts to grow.
"This created islands that are comparable to the Canary Islands today," explains Andrea Kipf. "Someday the volcanoes became extinct again, wind and weather eroded the cone down to sea level, and other geological processes further eroded the seamounts. Finally, the summit plateaus arrived at the level that we know today."
The scientists were able to show another example of how diverse and complex the volcanic formation processes can be with these results. "We are still far from understanding all of these processes. But with the current study, we can contribute a small piece to the overall picture," says Dr. Werner.