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Document Type

Open Access

Degree Program

Geosciences

Degree Type

Master of Science (M.S.)

Year Degree Awarded

2013

Month Degree Awarded

February

Keywords

mylonite, Cora Lake, lower crust, monazite

Abstract

Interpreting the tectonic significance of high strain zones requires detailed knowledge of the P-T-t-D history of rocks on either side and of tectonized rocks within the shear zone. In-situ monazite geochronology is particularly useful because it generates a time-integrated framework of metamorphism and fabric development. This can be achieved by correlating monazite compositional domains with the growth and consumption of major phases. Furthermore, monazite can be a fabric forming mineral, and can be directly linked to structural fabrics and kinematics. The Cora Lake shear zone (CLsz) represents a major lithotectonic discontinuity within the deep crustal Athabasca Granulite terrain, and preserves intense mylonitic to ultramylonitic fabrics. The 3-5 km wide CLsz strikes ~231°, and dips ~62° to the Northwest, has a moderately plunging stretching lineation (SW trend) with abundant sinistral kinematic indicators. These data indicate oblique extension with NW hanging wall down and to the SW relative to the SE footwall. The NW hangingwall is dominated by the ca. 2.6 Ga charnockitic Mary batholith. The southeastern footwall is primarily underlain by the heterogeneous ca. 3.3-3.0 Ga Chipman tonaite straight gneiss. Although both share common Archean (ca. 2.55 Ga) and Paleoproterozoic (ca. 1.9 Ga) deformation events, the style and P-T conditions of deformation are different. The earliest phase of deformation within the NW hangingwall consists of a penetrative subhorizontal flow fabric at 0.9 GPa and ~725°C (2.56 Ga), but folding in the SE footwall associated with the development of a strong upright axially planar fabric at 1.35 GPa and 850°C. Deformation at ca 1.9 Ga was characterized by upright folding, similar in orientation, in both hangingwall (0.9 GPa; 725°C) and footwall (1.17 GPa; 825°C). Deformation related to the CLsz occurred at 1880 Ma (0.9-1.06 GPa; ~775°C), and is responsible for juxtaposing two levels of lower crust. The Cora Lake shear zone is interpreted to be the culmination of a trend of increased strength, localization, strain partitioning, and vertical coupling. Furthermore, the CLsz overprints fabrics from each wall, marks the development of a major lateral lithotectonic discontinuity, and an introduction of major structural and compositional heterogeneity within the lower continental crust.

First Advisor

Michael L Williams

Second Advisor

Michael J. Jercinovic

Mahan_Fig1_draft1.png (1286 kB)
Figure 1

clsz map.pdf (452 kB)
Figure 2

Fig 3.pdf (123472 kB)
Figure 3

fig 4.pdf (91791 kB)
Figure 4

fig 5.pdf (125585 kB)
Figure 5

Fig 6.pdf (273 kB)
Figure 6

fig 7.pdf (99988 kB)
Figure 7

NW domain.pdf (906 kB)
Figure 8

chip dike.pdf (601 kB)
Figure 9

10W-112.pdf (2175 kB)
Figure 10

10W-100a.pdf (819 kB)
Figure 11

10W-099.pdf (1846 kB)
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10W-099 PT.pdf (100 kB)
Figure 13

table of events with T.pdf (276 kB)
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Figure 15.docx (198 kB)
Figure 15

all portrait.docx (22 kB)
tables 1-5

all landscape.docx (17 kB)
tables 6-7

first pages.docx (24 kB)
First pages to thesis

captions.docx (15 kB)
Figure captions

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