Document Type

Thesis

Abstract

The Fork Church Fault is a major normal fault in the eastern Piedmont of Virginia that separates Proterozoic to Paleozoic metamorphic rocks of the Goochland Terrane from the Mesozoic Taylorsville basin, a large half-graben complex with strata that dip 10° to 30° northwest towards the Fork Church Fault. The Fork Church Fault bounds the western edge of the exposed part of the Taylorsville basin. To the west of the fault is the Hylas zone, a mylonitic shear zone that records dextral transpression during the Alleghanian orogeny. The Fork Church Fault formed during the early Mesozoic, alongside the development of the Taylorsville basin, when rifting of Pangaea began. Pseudotachylite occurs as 0.1-15 cm wide injection and fault veins in the footwall of the Fork Church Fault. The pseudotachylite does not appear in the hanging wall of the fault and is only visible for about 100 m from the contact with the Taylorsville basin. The pseudotachylite is surrounded by foliated and fractured mylonitic quartzofeldspathic gneiss and mafic hornblende-bearing gneiss. The pseudotachylite veins are typically northeast striking with variable dips. Microstructures within the pseudotachylite include abundant spherulites and microlites, flow structures and cataclasite along the margins of the veins. Xenocrysts of plagioclase, quartz and cataclasite range in size from 0.01 to 3 mm with inclusions of pseudotachylite that commonly form deeply embayed grains. These observations are consistent with a frictional melt origin, likely generated by large magnitude slip events along the Fork Church Fault. The pseudotachylite veins are cut by mineralized fractures composed of quartz, calcite, and zeolites. Basaltic dikes also crosscut the fault, although there is no evidence whether they cross-cut the pseudotachylite or not.

Date Awarded

2016

Department

Geology

Advisor 1

Christopher M. Bailey

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