Thursday, November 19, 2015 - 2:00pm
Dr. Jade Star Lackey, of Pomona College, will give a talk entitled Rates and Residues of CO2 Liberation in Continental Arcs. Dr. Lackey's talk will begin at 2:00 PM on Thursday, November 19 in Webb Hall 1100.
Greenhouse gasses, particularly CO2 are the dominant control on Earth’s long-term (>1 My) climate variability. Continental magmatic arcs have high potential for interaction of magmas with carbonate wallrocks and thus should be a major contributor to atmospheric CO2; nevertheless, episodic magmatism, variable thermal and fluid activity regimes, and irregular distribution of carbonate wallrocks in continental arcs make for a murky picture of metamorphic CO2 fluxes. Ongoing studies of calc-silicate skarns and marbles in the Sierra Nevada and Mojave Desert show considerable variability of decarbonation efficiency in California’s Mesozoic arc section. Contact metamorphic aureoles in upper crustal exposures show some of the greatest proportions of skarn vs. carbonate. These greater levels of decarbonation are attributed to the availability of copious surface waters that promote reaction progress. U-Pb dating of skarn garnets helps decipher the timing of contact metamorphism in a number of locations and shows high CO2fluxes in the Late Jurassic and Early Cretaceous during extension in the arc. This extension promoted ascent of hot mafic magmas to high levels in the arc crust, enhancing CO2 liberation. Oxygen isotope and trace element variations in oscillatory-zoned skarn garnets contain rich records of the evolution of individual hydrothermal systems. These single-crystal records indicate a mixture of fluid flow regimes during skarn formation, ranging from simple, single-pass magmatic water sources in deeper skarns, to highly variable meteoric sources in upper crustal skarns. As a whole, our findings indicate that CO2 flux from continental arcs is episodic but not necessarily correlated with large magmatic fluxes.
November 10, 2015 - 8:49pm