Uranium Series Constraints on Rates of CO2 Production by Skarnification at Merapi Volcano, Indonesia
[Thesis]
Hansen, Sarah
Reagan, Mark
The University of Iowa
2020
55
M.S.
The University of Iowa
2020
Merapi volcano is the most active volcano in Indonesia and has had three large eruptions in the past 20 years (2006, 2010, and 2018- ongoing). A common feature of Merapi's lavas is the presence of calc-silicate xenoliths, which result from magma-carbonate interaction. There are three distinct xenolith types: magmatic skarn xenoliths, formed within the magma from a limestone protolith; exoskarn xenoliths, fragments of metamorphosed limestone wall-rocks; and buchite, a quartz-rich skarn assemblage. This study presents the first 238U-230Th-226Ra-210Pb data on these xenoliths, with a goal of constraining rates of CO2 production by decarbonation reactions at Merapi. The magmatic skarns have (238U/230Th) and (230Th/232Th) values indicating mixing and element transfer between Merapi magmas and the local carbonate crust. The presence of 226Ra and 210Pb excesses in the 2006 samples indicate that the element transfer from carbonates to magma must have happened within several decades before eruption. These excesses result from skarnification and decarbonation reactions, which add CO2 from the limestone to the magma, and thus the volatile budget of Merapi.