Date of Award:

Summer 5-12-2017

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geology

Department name when degree awarded

Geology

Advisor/Chair:

Dennis L. Newell

Abstract

The Hurricane Fault is a 250-km long, west dipping, Basin and Range-bounding normal fault in SW Utah and NW Arizona that initiated in the mid-Miocene to Pliocene. It has been primarily active in the Quaternary, with slip rates of 0.2 – 0.6 mm/yr. There are multiple hot springs along its 250-km length and multiple late Tertiary-Quaternary basaltic centers broadly parallel the fault. Possible sources of hot spring fluids include deeply-circulated meteoric water that experienced water-rock exchange at high temperatures (>100 °C) and deep-seated crustal fluids. Aside from the source of modern hot spring fluids and heat, questions about the spatio-temporal history of fluid flow along the Hurricane Fault remain unaddressed. Abundant damage zone veins, cements, and host rock alteration are present, indicative of past fluid flow. Carbonate veining and cementation is a key feature of the Hurricane Fault zone, and is the primary feature exploited to characterize the thermochemical history of fault-related paleofluids. A combination of macroscopic and microscopic carbonate observations, chemical composition, and precipitation temperature of calcite veins was used to determine past water-rock diagenetic interaction and vein evolution in the Hurricane Fault zone. Calcite iv in concretions and veins from the damage zone of the fault shows a wide range of carbon and oxygen stable isotope ratios, with δ13CPDB from -4.5 to 3.8 ‰ and δ18OPDB from -17.7 to -1.1‰. Fluid inclusion microthermometry homogenization temperatures range from 45 to 160 °C, with fluid salinities of 0 to 15 wt% NaCl calculated from melting temperatures. Combining the two datasets, two main fluids that interacted with the fault zone are inferred: (1) basin brines with a δ 18OSMOW of 9.2 ‰ and (2) altered meteoric fluids with a δ 18OSMOW of -11.9 to -8.3 ‰. Calculated dissolved CO2 δ 13CPDB (-8.5 to -1.3 ‰) indicates mixed marine carbonate and organic or magmatic sources. Fault zone diagenesis was caused by meteoric water infiltration and interaction with carbonate-rich rocks, mixed with upwelling basin brines. Fluid-rock interaction is concentrated in the damage zone, where fracture-related permeability was utilized for fluid flow. A distinct mineralization event punctuated this history, associated with basin brines that were chemically influenced by nearby basaltic magmatism. This implies a hydrologic connection between the fault and regional magmatism.

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