Date of Award

Fall 2019

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

School

Biological, Environmental, and Earth Sciences

Committee Chair

Jeremy Deans

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Franklin Heitmuller

Committee Member 2 School

Biological, Environmental, and Earth Sciences

Committee Member 3

Mark Puckett

Committee Member 3 School

Biological, Environmental, and Earth Sciences

Abstract

Atlantis Bank (AB) is an oceanic core complex (OCC), formed at the slow-spreading (spreading rate/yr) Southwest Indian Ridge (SWIR)-Atlantis II transform junction. AB is a domal massif composed of lower crustal and upper mantle rocks exhumed along a normal-sense detachment shear zone/fault. OCCs are of high interest since oceanic crust comprises the majority of Earth’s crust and OCCs form up to 15% of the crust that is formed at slow-spreading ridges. Brittle deformation, such as faults and fractures provide pathways for fluids to interact with the crust, which increases heat and mass exchange between the crust and hydrosphere, and is related to the redistribution of nutrients supporting the deep biosphere. However, little has been done to understand the brittle history of OCCs especially in their footwall. AB is one of the best studied OCCs in the world, which makes it an ideal location for this study providing insight into the brittle evolution of OCCs. AB has one moderate and two deep drilled holes distributed around the massif. Each hole was cored and logged by the Ocean Drilling Program (ODP) or International Ocean Discovery Program (IODP). This study analyzed core and downhole petrophysical logs (Ultrasonic Borehole Imager and Formation Microscanner) in order to locate and determine the orientation of fractures and joints throughout the three holes. The use of petrophysical tools is essential since they provide a near-continuous record of the borehole wall and record geographic orientation information, which are lost in core samples. By completing a dynamic and kinematic analysis using fracture and fault slickenline orientation across all holes, the paleo-stress field(s) responsible for the brittle evolution of AB were estimated and then compared with potential local and regional causes for fracturing. Brittle deformation is thought to be potentially caused by 1) a flexure of the footwall during exhumation, 2) detachment shear zone/fault zone deformation, 3) horizontal rotation of the spreading direction of SWIR causing transtension along the Atlantis II transform and/or, 4) late-stage, high-angle, ridge parallel and ridge perpendicular normal faults.

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