Paleomagnetic and Structural Analysis of Geothermal Drill Core from Akutan, Alaska

Author

Molly Kathleen Johnson, Western Washington UniversityFollow

Date Permissions Signed

5-3-2020

Date of Award

Spring 2020

Document Type

Masters Thesis

Department or Program Affiliation

Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Housen, Bernard Arthur

Second Advisor

Stelling, Peter L.

Third Advisor

Schermer, Elizabeth, 1959-

Abstract

Hot Springs Bay Valley (HSBV) geothermal resource area on Akutan Island, Alaska, has increased fluid output and temperature by almost a magnitude, between 1981 and 2012 (Bergfeld et al., 2014). These increases have been attributed to increased permeability along NW-SE trending faults that may have been activated during a seismic swarm in 1996. In 2010 two unoriented drill cores were collected in Hot Springs Bay geothermal resource area. In this study I reorient sections from one of the highly fractured cores with paleomagnetic data to test this model of geothermal reservoir evolution at Akutan. The core is composed of interlayered island arc volcanic rocks, volcaniclastic rocks, and shallow marine mudstones. Paleomagnetic samples were collected from the volcanic rocks. Continuous sections of the core were reoriented using the declination of the remanent magnetization (RM) as an indication of geographic north. Structure from motion software was used to create digital reconstructions of the core from photographs. The resulting core images were then flattened with a cylindrical projection into a 2D depiction of the outside of the core. The orientation of structural features and the relationships between them were measured from these projections, while the mineralogy and rake of slickenlines were determined in hand sample. Veins with slickenfibers were separated by mineralogy and the Multiple Inverse Method (MIM) (Yamaji, 2000) was employed to calculate the stress regime that produced each set of shear veins. Results suggest that NNE dipping transtensional calcite filled shear veins are the result of periodic rupture possibly caused by inflation of the volcano due to dike emplacement and represent recharge of the reservoir. NNW trending chlorite filled shear veins are the result of normal overburden pressure alternating with NNW horizontal compression and likely represent the northward migration of heated fluids to the reservoir. Cross cutting relations indicate that NE and SW dipping, NW-SE normal faults are conjugate and have ruptured repeatedly. Therefore, events like the 1996 seismic swarm, which produced NW trending surface ground cracks, have likely acted to maintain permeability throughout the lifetime of the geothermal system at Akutan. I propose that the increased fluid flow and heat output recorded by Bergfeld et al. (2014) is the result of a recharge event initiated by the rupture of NE and SW dipping structures.

Type

Text

Keywords

Geothermal, Hot Strings Bay Valley, Aleutians, Structure From Motion, Agisoft Photoscane, Paleomagnetics, Core Reorintation, Core Log Creation, Paleostress

Publisher

Western Washington University

OCLC Number

1159899496

Subject – LCSH

Paleomagnetism--Alaska--Akutan Island; Faults (Geology)--Alaska--Akutan Island; Geology, Structural

Geographic Coverage

Akutan Island (Alaska)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

Rights Statement

http://rightsstatements.org/vocab/NKC/1.0/

Recommended Citation

Johnson, Molly Kathleen, "Paleomagnetic and Structural Analysis of Geothermal Drill Core from Akutan, Alaska" (2020). WWU Graduate School Collection. 964.
https://cedar.wwu.edu/wwuet/964