Metals in tuffisite veins
Kim Berlo 1, Hugh Tuffen 2
Affiliations: 1 Geotop Research Centre, McGill University, Canada 2 Lancaster Environment Centre, Lancaster University, United Kingdom
Presentation type: Talk
Presentation time: Thursday 15:00 - 15:15, Room R290
Programme No: 3.8.8
Abstract
Fractures are the main outgassing pathway of shallow felsic magma. Diffusion profiles of hydrogen around tuffisite veins, hydrofractures occluded with sintered pyroclastic material, suggest lifespans of such pathways of minutes to hours. Diffusion of other elements, e.g. Li, Na, Rb, has also been observed. This mobility of elements, particularly H, affects crystallisation, which in turn promotes further element redistribution. Tuffisite veins are not only sites of outgassing, but form transient, permeable networks in the shallow conduit through which the MVP and particulates are transported from deeper magma. Elements are redistributed between MVP, host and vein-filling material. This study takes a look at this redistribution of elements during MVP advection and clast-MVP interaction. Three tuffisite veins from the 2008-2011 eruption of Chaitén volcano in Chile with similar appearance were selected for tandem LIBS-ICP-MS analysis and element mapping. In each vein, similar components were identified: host, angular clasts, vesicular clasts, microcrystalline clasts, and the matrix of sintered ash. The matrix and the microcrystalline clasts in all three veins are consistently depleted in major- and incompatible trace-elements. They are however enriched in volatile metals, which can be traced to individual phases, though the degree of enrichment and the specific metals involved differ between the veins. These differences between the veins may result from their formation at different depths as they have different H and Cl concentrations. Multivariate analysis suggests that the depletion in most and enrichment in some elements are the result of a single process of mobilization and redistribution of elements.