Satellite Maps Reveal Small Tectonic Plate, Help Answer Big Questions
SAN FRANCISCO — Using satellite maps, a team of Australian and U.S. researchers has found a small tectonic plate or microplate in the Indian Ocean and used that discovery to settle a long-running debate on the timing of India’s impact with Eurasia.
India smashed into Eurasia, prompting the Himalayan Mountains to form, 47 million years ago, according to a paper published Nov. 9 in Earth and Planetary Science Letters by researchers from the University of Sydney’s School of Geosciences and the Scripps Institution of Oceanography at the University of California, San Diego.
“Knowing this age is particularly important for understanding the link between the growth of mountain belts and major climate change,” Kara Matthews, lead author and a University of Sydney postdoctoral research associate, said in a statement. Mountain belt formation has major implications for climate change because new peaks can change the path of prevailing winds, alter precipitation patterns and decrease air temperatures.
The researchers discovered the Indian Ocean microplate, called Mammerickx Microplate and measuring roughly the size of West Virginia, using seafloor maps that combine data drawn from radar altimeters onboard the Jason-1 ocean surveying spacecraft launched in 2001 by NASA and the French space agency, CNES, and CryoSat-2, a European Space Agency environmental research satellite launched in 2010.
In 2014, a Scripps team led by geophysicist David Sandwell used the satellite data to produce a comprehensive set of seafloor maps showing thousands of underwater mountains and other tectonic features never before detected. Those maps have since been folded into Google Earth’s ocean maps.
The new Indian Ocean discovery is noteworthy because researchers have identified seven microplates in the Pacific Ocean but never before found one in the Indian Ocean. “Normal seafloor spreading does not produce microplates, but if you have a collision of one continent with another continent, it causes the whole plate to change direction,” said Sandwell, co-author of the paper. “As it changes direction, it creates things like microplates.”
Researchers were able to determine the age of the new microplate using magnetic surveys that reveal distinct patterns near mid-ocean ridges. Minerals pushed to the surface when Earth’s crust forms those ridges become magnetized in the direction of Earth’s magnetic field. Because the magnetic field periodically changes direction, scientists use that knowledge coupled with observations of seafloor spreading rates to estimate the age of geologic features.
With the space-based altimeters on Jason-1 and CryoSat-2, researchers can detect features on the ocean floor that measure 6 kilometers or more. Scientists obtain far more accurate maps using data drawn from multibeam echosounders, ship-based sonars that can pinpoint features as small as 200 meters. However, multibeam echosounders have only been used to map about 15 percent of the ocean floor, producing “a very incomplete picture,” Sandwell said. To fill in the picture, Scripps researchers use space-based radar altimeters to obtain detailed observations of the ocean surface and use the data to determine the shape of the seafloor below.
The Indian Ocean discovery is the latest application of Scripps’ seafloor maps. Researchers and educators use the maps to explain active tectonic processes taking place deep under water. Although Earth is 4 billion years old, the seafloor has an average age of 70 million years. The seafloor exhibits far more active plate tectonic processes, including spreading ridges, transform faults and 90 percent of the planet’s volcanic activity, Sandwell said.
Oil companies use seafloor maps to aid exploration. High-resolution maps can offer clues to the location of sedimentary basins. “When continents rift apart, they leave behind scars in seafloor,” Sandwell said. “If you find oil in Africa, you can use those scars to look for oil in the same basin in South America.”
In addition, military agencies rely on seafloor maps for submarine navigation as well as gravity field mapping. Those gravity maps are used to correct inertial navigation and guidance systems by distinguishing a vehicle’s acceleration from a variation in the pull of gravity resulting from massive ocean trenches or seamounts.
Because of that utility, the first comprehensive seafloor maps were produced in from the U.S. Navy’s Earth observing Geodetic Satellite launched in 1985, although the observations remained classified until 1995.