Helium Isotopic Ratios in Volcanic Crystals and Hot Spring Bubbles in Lutao Island, SE offshore Taiwan
Date Issued
2009
Date
2009
Author(s)
Wu, Nian-Ru
Abstract
Noble gas isotopes have several important applications in geochemistry, such as petrogenesis, volcanism, tectonics and mineral dating. In this study, I focus on the helium isotopic ratios (3He/4He) in volcanic mineral crystals and hot spring bubbles. elium is not able to be recycled by plate tectonics into the Earth’s interior, making the 3He/4He ratio unique among isotopic tracers of mantle sources involved in volcanism. As magma ascends it may suffer He exchange with crust material which with lower He isotopic values. Even minor amounts of crustal interaction with the ascending magma through the process of crust contamination can be easily recognized through the helium isotopic ratios. Therefore, He isotopes have been proven as a powerful tool for assessing crustal contributions to the magmatic systems in subduction-related settings.ases exist in two different positions inside a mineral grain: fluid inclusion and crystal lattice. There are two major ways to extract gases from minerals or rocks. One is vacuum crushing, the other is total fusion. Using vacuum crusher, the gases in fluid inclusions may be separated from those in mineral matrix (lattice). Together with the total fusion method, we can measure the gas composition of fluid inclusions and mineral matrix respectively.here is a long-standing debate in the petrogenetic processes of Lutao volcanic rocks, surrounding a main issue that is: if it is source contamination or crust contamination for the magma genesis?revious studies have reported 87Sr/86Sr, εNd and δ18O results on this issue. In this study, helium isotopes have unique properties that enable them to provide crucial information regarding this debate. In our results, we did not find significant crustal signal in helium isotopes ratios of crystals. It is consistent with the results of hot spring bubbles. Therefore, we can conclude the crustal contamination is not the major process for the genesis of Lutao magmatism.
Subjects
North Luzon arc
Helium isotopes
Magma genesis
Type
thesis
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