Date of Award

6-2022

Degree Type

Honors College Thesis

Academic Program

Geology BS

Department

Geography and Geology

First Advisor

Jeremy Deans, Ph.D.

Second Advisor

Jake Schaefer, Ph.D.,

Third Advisor

Sabine Heinhorst, Ph.D.

Advisor Department

Geography and Geology

Abstract

The Tonga-Kermadec Arc is an active volcanic arc located between New Zealand and Fiji. The arc expands over an approximate distance of 2530 km. The Kermadec Arc is currently host to over 30 volcanoes, the majority of which are submarine. The magmatic activity along the arc is characterized by the convergence between the Pacific and Australian plates. Brothers volcano is the most active hydrothermal system along the Kermadec arc and hosts two distinct hydrothermal systems, one magmatic fluid dominated, and the other seawater dominated, making the site perfect for studying nascent volcanogenic massive sulfide formation and fluid pathways. The International Ocean Discovery Program (IODP) drilled five sites at Brothers volcano to understand the process of mineral deposit formation from hydrothermal activity and the relationship between discharge of magmatic fluids and the deep biosphere. This project focused on the data acquired from Site U1528, a resurgent cone hosting the magmatic fluid dominated hydrothermal system. Micro computed X-ray tomography (μCT) was used to determine the three-dimensional (3D) pore and secondary mineral structure of seven mini cores from Hole U1528D with varying depth (66.42-297.95 mbsf) and lithology (dacite lapilli tuff to lava flows). The pore characteristics were consistent at this site irrespective of volcanic lithology and depth except for sample 44Z. The total pore volume ranges between 10× 3 and 31× 3. The average pore volume is approximately 1× μm3. The variances observed in sample 44Z may be explained by the presence of a vug along a vein in the sample. The data obtained for total number of pores, distribution and volume indicates all rock types in this system have similar characteristics, which may suggest similar eruptive styles and volatile abundance through time. Secondary mineral phase volume and number have a general increase with depth despite alternating alteration intensity and rock types with depth. A general increase in secondary mineral phases with depth is thought to correlate with increased proximity to the magmatic-derived fluid source and therefore solutes that precipitated out of the fluid. These results indicate the resurgent cone hosts a robust hydrothermal system capable of carrying and precipitating heavy metals. At the Upper Cone, the fluid pathways of magmatic fluids are likely through the bulk rock given the pervasive nature of secondary minerals in all mini cores analyzed. However, outflow at the seafloor suggests there are faster and more voluminous pathways other than pores, like fractures, not studied here.

Keywords: Fluid pathways, magmatic fluids, pores, secondary minerals, alteration, lithology

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