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Title: Low-temperature hydrothermal fluid flow using geochemical tracers, Juan de Fuca Ridge flank, N.E. Pacific Ocean
Author: Hunter, F. M. I.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2002
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Fluid flow through mid-ocean ridge axes has long been recognised by geophysical and geochemical methods as well as direct observations. However, hydrothermal circulation through mid-ocean ridge flanks is more difficult to study and quantify due to the lower temperatures and less extreme fluid chemistry. In this thesis, a region of low-temperature fluid flow (up to 65°C), on the eastern flank of the Juan de Fuca Ridge, N.E. Pacific Ocean, has been investigated using isotopic and geochemical tracers. Pore water samples contained within sediment cores were collected at outcrops and subcrops of igneous basement where over-pressurised basement fluid upwells through thin sediment cover into the overlying ocean. Strongly upwelling pore waters are representative of basement fluid and therefore may be geochemically and isotopically analysed to understand fluid flow within igneous basement. Initially, two methods were set up to analyse Li and its isotopes in seawater-derived fluids. Then, fluids from two areas of the Juan de Fuca Ridge flank (First and Second Ridge) were investigated using the methods developed and other standard techniques (geochemical analysis, radiocarbon dating, Sr isotopes and O isotopes). Geochemical profiles of Ca, Mg and for some sites, F, were modelled to constrain the vertical fluid flow at thinly sedimented basement outcrops and subcrops. This showed that upwelling of hydrothermal fluid from igneous basement is observed throughout the study area, while downwelling of seawater is less frequent and only occurs within Second Ridge Area. Radiocarbon age measurements show large variation across the study area suggesting that fluids sampled at different outcrops are not connected and may represent discrete systems.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available