Jade Star Lackey, assistant professor of geology, is part of a research team proposing a new theory behind Earth's past oscillations between greenhouse and icehouse states. The study, published in this month's issue of GeoSphere, proposes that these climate swings over the past 500 million years were the result of plate tectonics causing episodic flare-ups of continental arc volcanoes, especially at times when supercontinents are breaking apart.
Led by Cin-Ty Lee, of Rice University, the team found that the continental arc volcanoes that arose during the late Cretaceous, when dinosaurs roamed, to early Paleogene, were "as much as 200% longer than in the late Paleogene to present, when a cooler climate prevailed."
When oceanic crust is thrust under the continental crust, it melts. The magma then travels upward through layers of carbonate-rich rocks found in continental crust before eruption. The more extensive continental arc volcanoes "could have increased global production of CO2 by at least 3.7 to 5.5 times that of present time," noted the study.
"We found that Earth's continents serve as enormous ‘carbonate capacitors,'" said Lee. "Continents store massive amounts of carbon dioxide in sedimentary carbonates like limestone and marble, and it appears these reservoirs are tapped from time to time by volcanoes, which release large amounts of carbon dioxide into the atmosphere." Today, most active volcanoes are located on island arcs, tectonic plates that don't contain continental crust.
Lackey role in the study focused on his knowledge of the metamorphic history of the Sierra Nevada and other areas of California, as well as expertise in stable isotope geochemistry, which is commonly used to trace the passage of fluids, including water and CO2 through rocks.
According to Lackey, "Because California and the western U.S. are on the edge of North America, these areas were on the volcanic ‘front lines' in the Cretaceous, with the subducting Farallon oceanic plate causing abundant magmatism beneath the western edge of the continent. This makes Pomona the perfect place to study the processes we discuss in this paper because it's within easy striking distance to do field studies of skarns, which are formed at the contact zones between intrusions of granitic magma and carbonate sedimentary rocks, in both the Peninsular Ranges and the Sierra Nevada. These give us different snapshots of the CO2 liberation processes when the California magmatic arcs were young, middle-aged, and mature, and they also allow us to see how depth in the Earth's crust controlled the efficiency of this process."
Among Lackey's students who have worked are related projects are Adam Kinnard '12, Callie Sendek SC '12, Ben Murphy '13 and James Muller '13. Support for the student field studies has come from a Hirsch Research Initiation Grant and the Keck Geology Consortium.
- Stories on the paper can be found in SpaceDaily.com and on ClimateCentral.org
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