March 27, 2012
Scientists Examine Peculiar Underwater Mountain
Scientists have recently finalized an expedition in an effort to learn more about an undersea mountain they say may have formed in a very different way than the rest of the seafloor.
Aboard the JOIDES (Joint Oceanographic Institutions for Deep Earth Sampling) research ship, these scientists studied the formations and makeup of Atlantis Massif. This undersea mountain has been found to be made up of rocks typically found much deeper in the oceans crust. Other volcanic seamounts are usually made up of a black rock called basalt, which is typical of the majority of the seafloor.
Atlantis Massif lies about 3,000 miles east of the United States and measures nearly 10 miles across and rises 14,000 feet from the seafloor. By comparison, Atlantis Massif is roughly the same size as Mount Rainier in Washington State.
Embarking on Integrated Ocean Drilling Program (IODP) 340T, the scientists measured the geophysical properties of gabbroic rocks in place for the first time. Previously, these sort of measurements had to be taken remotely via techniques such as seismic surveying.
These researchers and scientists now hope to make mapping out geophysical structures beneath the seafloor easier.
“This is exciting because it means that we may be able to use seismic survey data to infer the pattern of seawater circulation within the deeper crust,” says Donna Blackman of the Scripps Institution of Oceanography in La Jolla, California.
“This would be a key step for quantifying rates and volumes of chemical, possibly biological, exchange between the oceans and the crust.”
Atlantis Massif lies on a fault that runs down the middle of the Atlantic ocean. As the tectonic plates at the fault shift and separate from one another, new crust is formed. The combination of this stretching, spreading, and intrusion of magma work together to shape the new seafloor.
When this process takes place, an oceanic core complex (OCC) is formed.
“Recent discoveries from scientific ocean drilling have underlined that the process of creating new oceanic crust at seafloor spreading centers is complex,” says Jamie Allan, IODP program director at the US National Science Foundation (NSF), which co-funds the program. “This work significantly adds to our ability to infer ocean crust structure and composition, including predicting how ocean crust has ℠aged´ in an area,” says Allan, “thereby giving us new tools for understanding ocean crust creation from Earth´s mantle.”
These scientists are looking to Atlantis Massif as a prime example of this kind of oceanic core complex.
As it is young, relatively speaking, scientists say it is an ideal place to research how faulting, magmatism, and seawater circulation effects the evolution of an OCC.
“Vast ocean basins cover most of the Earth, yet their crust is formed in a narrow zone,” says Blackman. “We´re studying that source zone to understand how rifting and magmatism work together to form a new plate.”
While the JOIDES research team first visited Atlantis Massif 7 years ago, they only focused on shallower parts of the seamount, gathering information on gabbro, the type of rock that makes up most of Atlantis Massif. Rather than drill new holes as they had during the previous expedition, the scientists aboard the JOIDES Resolution lowered instruments into existing holes to take their measurements.
As for the results of their newest expedition, Alistair Harding, also from the Scripps Institution of Oceanography and a co-chief scientist for Expedition 340T had this to say: “The expedition was a great opportunity to ground-truth our recent seismic analysis. It also provides vital baseline data for further seismic work aimed at understanding the formation and alteration of the massif.”
Image 1: The JOIDES Resolution. Credit: William Crawford, IODP/TAMU
Image 2: Map of IODP expedition undersea sampling sites at Atlantis Massif. Credit: IODP