title of the thesis - Department of Geology - Queen's University

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$Fayek & Kyser 2000 uraninite fractionations.pdf - Queen's University$

View of the northern Karnali valley near the village of Chala. Dr. Borja Antolín is leading the way, followed by our trusted guide Dawa Tamang. The foreground is Tethyan sedimentary sequence and the distant peaks are Greater Himalayan sequence. The contact between these domains is roughly 200 meters towards the peaks from the photograph position. ii
Abstract Field mapping and, structural, microstructural, and chronological analyses confirm the existence of a segment of the Gurla-Mandhata-Humla fault, an orogen-parallel strike-slip dominated shear zone in the upper Karnali valley of northwestern Nepal. This shear zone forms the upper contact of, and cuts obliquely across the Greater Himalayan Sequence (GHS). Data from this study reveal two phases of GHS deformation. Phase 1 is characterized by U-Th-Pb monazite crystallization ages (~26–12 Ma, peak ~18–15 Ma), consistent with typical Neohimalayan metamorphic ages, and the final stages of south-directed extrusion of the GHS. Phase 2 is characterized by south-dipping high-strain foliations and intensely developed ESE-WNW trending, shallowly plunging mineral elongation lineations, indicating orogen-parallel extension. Thermochronology of muscovite defining these fabrics implies that the area was cooling and experiencing orogen-parallel extension by ~15–9 Ma. Mineral deformation mechanisms and quartz c-axis patterns of these fabrics record a rapid increase in temperature from ~350°C along the shear zone, to ~650°C at ~2.5 structural km below the shear zone. Such temperature gradients may be remnants of telescoped and/or flattened isotherms generated during south-directed extrusion of the GHS. Overprinting ESE-WNW fabrics record progressive deformation of the GHS at lower temperatures. Progressive deformation included a significant component of pure shear, as indicated by symmetric high-temperature quartz c-axis fabrics and a lower-temperature vorticity estimate (~59% pure shear). A transition in c-axis fabrics from type I to type II cross-girdles at ~ 1.2 km below the fault could indicate a transition from plane strain towards constriction. Together, these data suggest orogen-parallel extension was occurring as a result of transtension. This study reveals a transition from south-directed extrusion of the GHS to orogenparallel extension between ~15–13 Ma. Comparing these data with tectonic events across the iii
Page 1: FROM CESSATION OF SOUTH-DIRECTED MI
Page 5 and 6: Co-Authorship This thesis is my own
Page 7 and 8: Table of Contents Abstract ........
Page 9 and 10: 4.1 Introduction ..................
Page 11 and 12: Figure 4.3 Microscale CPO variabili
Page 13 and 14: Abbreviations Mineral Biotite Calci
Page 15 and 16: Figure 1.1 Color relief map of the
Page 17 and 18: 1.2 Evolution of the Himalayan-Tibe
Page 19 and 20: Figure 1.3 Structures in the Himala
Page 21 and 22: the various models. However, this a
Page 23 and 24: of shear (Murphy and Copeland, 2005
Page 25 and 26: Chapter 4 outlines proposed future
Page 27 and 28: indicated by symmetric high-tempera
Page 29 and 30: The second phase of middle Miocene
Page 31 and 32: 2.3 Geologic Setting 2.3.1 Himalaya
Page 33 and 34: 2.4 Geology of the upper Karnali Va
Page 36 and 37: Figure 2.3 Lithotectonic map and si
Page 38 and 39: the main shear zone fabric. The lit
Page 40 and 41: South of the interface, the TSS is
Page 42 and 43: WNW Figure 2.6 Representative struc
Page 44 and 45: Figure 2.7 Representative structure
Page 46 and 47: distribution of dextral and sinistr
Page 48 and 49: al., 1986; Mainprice et al., 1986).
Page 50 and 51: Figure 2.9 Summary of CPO post-acqu
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a c a c Figure 2.10 Summary of quar
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Sample HK131A is a high-strain quar
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constriction, where rhomb slip domi
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± 50°C (Law et al., 2004). Furthe
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Figure 2.14 (a) Photomicrograph of
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Figure 2.15 Summary of lithotectoni
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elationships, these data constrain
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primary reference material, “4409
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Figure 2.16 - continued. 57
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monazite grains are aligned paralle
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Analysis Position Pb U Th Th/U 207
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Analysis Position HK117A Pb U Th Th
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are derived from intensely deformed
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Samples KH10, HK102a, HK105, HK115,
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the intralaboratory standard (MAC-8
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Figure 2.18 - continued. 76
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espectively. Note that the plateaus
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Figure 2.19 Plots of muscovite cool
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Figure 2.20 Summary of results from
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(2) Previously published chronologi
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Figs. 2.7b,d, 2.15) is locally over
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Thermochronology of muscovite grain
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Figure 2.21 - continued - Box (3) r
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92 Figure 2.22 (a) Location of stud
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is little data to support both afor
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Figure 2.23 Numerical model of modi
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The second phase is associated with
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yr Figure 3.1 Numerical model of Co
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phenomena are consistent with ongoi
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towards the topographic front of th
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Chapter 4 Microstructural analyses:
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a c a c Figure 4.1 Summary of quart
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Figure 4.2 Results of study by Toy
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factors on the formation of differe
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1987; Simpson and De Paor, 1993, 19
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2009). Furthermore, there is rising
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Figure 4.5 Simplified set up of ana
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Appendix A Station locations and st
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Station Latitude Longitude Elevatio
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Station Latitude Longitude KH019 KH
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HK 140 - Non-processed EBSD data 12
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HK 131A - U-Stage data 128
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HK 131A - Non-processed EBSD data 1
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HK 139D - Non-processed EBSD data 1
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HK 105A - U-Stage data 134
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HK 105A - Processed EBSD data (e.g.
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HK 125 - Processed EBSD data (e.g.
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HK 124B2 - Processed EBSD data (e.g
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KH18a - Monazite 1 150
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HK109 - Thin section * For HK109_mo
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U Th 4 3 2 1 5 10 9 11 7 8 6 Nd Y 1
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HK109 - Monazite 3 170
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U SL CP 172
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U Th SL 174
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U Nd CP 178
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U Nd Th 180
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Y Nd U Th 184
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U Th SL 186
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CP Nd 2 3 4 6 5 1 Y P 190
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U Th SL 192
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CP Nd Y P 196
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U Th SL 198
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HK117a - Thin section 200
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9 8 7 10 6 5 4 3 2 1 206
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Holdsworth, R.E., McCaffrey, K.J.W.
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Cottle, J. M., Jessup, M. J., Newel
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Ghosh, S.K., and Ramberg, H. 1976.
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Hodges, K.V., and Silverberg, D.S.
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Kohn, M.J. 2008. P-T-t data from ce
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Means, W. D., Hobbs, B. E., Lister,
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Prior, D.J. 2009. EBSD in the earth
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Caledonides. In, S. Sengupta (Ed.),
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Yakymchuck, C., 2010. Tectonometamo
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