THESIS PROPOSAL. DEGREE PROGRAMME: M. Sc. SUPERVISOR and COMMITTEE: Supervisors - Isabelle Coutand Committee Members - Richard Cox Mladen Nedimovic

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1 THESIS PROPOSAL DEGREE PROGRAMME: M. Sc. SUPERVISOR and COMMITTEE: Supervisors - Isabelle Coutand Committee Members - Richard Cox Mladen Nedimovic TITLE OF PROPOSAL: Tertiary cooling history of the Mackenzie Mountains and Corridor region using apatite fissiontrack thermochronology KEY WORDS Mackenzie Mountains, apatite, apatite fission-track, thermochronology, upper crustal cooling history, thermal modeling, spontaneous fission, uranium LIST INNOVATIONS or EXPECTED SIGNIFICANT OUTCOMES: 1. Delineate the thermal history of the Mackenzie Mountains to determine the timing of mountain building. 2. Determine whether the Miocene collision of the Yakutat terrane along southeastern Alaska was responsible for the formation of the Mackenzie Mountains. 3. Determine whether strain can be transferred over 800 km from a collisional boundary. 4. Increase exploration success in a region with significant oil and gas potential by determining the thermal evolution of the foreland basin and the timing of hydrocarbon thermal maturation. 5. Increase Canada's use of thermochronology to explore for natural resources. SUMMARY OF PROPOSED RESEARCH: This project will investigate whether uplift and exhumation of the Mackenzie Mountains has resulted from contractional strain transferred from the collision of the Yakutat terrane with the western margin of North America during the Miocene-Pliocene. Mazzotti and Hyndman (2002) suggest that the Mackenzie Mountains would be at least Miocene in age if they formed as a result of the Yakutat collision. Gabrielse (1991) previously established that the Mackenzie Mountains formed during the Late Cretaceous-Paleocene. Therefore, the major question to be addressed by this study is to determine the timing of the low-temperature thermal history of the Mackenzie Mountains and Corridor region as a proxy for mountain building. Constraints on the thermal history of the Mackenzie Mountains will aid in determining the thermal evolution of the foreland basin which would in turn help to determine timing of hydrocarbon thermal maturation. Determining the timing of maximum hydrocarbon generation will help to increase exploration success in a region with significant oil and gas potential.

2 The main objectives of this project are (1) to determine the upper crustal cooling history of the Mackenzie Mountains and (2) compare this cooling history with the timing of the collision of the Yakutat terrane. To solve this problem, I will use apatite fission-track (AFT) thermochronology (closure temperature ~120 o C) to constrain the cooling history of the 5-6 upper km of the crust in the Mackenzie Mountains and surrounding Mackenzie Corridor region. There is currently very limited use of lowtemperature thermochronology in the study area. Once the data is collected, inverse modeling TIMETABLE Activity Start Date End Date Mineral separation and Fission-track training September 2011 October 2011 Sample reception/collection November 2011 February 2012 July 2012 Sample preparation and irradiation November 2011 September 2012 Fission-track calibration and sample dating September 2011 March 2013 Thermal modeling April 2013 June 2013 Prepare final thesis July 2013 September 2013 Defend thesis September Statement of Problem The collision of the Yakutat terrane with the North American continent began in the Miocene (Perry et al., 2009). The terrane, attached to the Pacific Plate, migrated northeastward to its current position along the southern Alaska margin by the Pliocene (Perry et al., 2009). The collision and subsequent underthrusting and accretion of the terrane to the North American plate margin resulted in crustal thickening and uplift of the adjacent Saint Elias and Chugach Mountains in Southeastern Alaska and northwest Canada (Mazotti and Hyndman, 2002, Fig. 1). Mazzotti and Hyndman (2002) further suggest that a portion of contractional strain from the collision was transferred far inland, approximately 700 km to the northeast across the northern Canadian Cordillera, inducing uplift and exhumation of the Mackenzie and Richardson Mountains on the eastern mountain front. Gabrielse (1991) previously suggested that deformation in the northern Canadian Cordillera progressed from west to east and led to uplift of the Mackenzie Mountains between the Mid Cretaceous and Paleocene. The question to be answered by this project is whether the Mackenzie Mountains were formed as late as the Miocene or as early as the Mid to Late Cretaceous. I will test this hypothesis by using apatite fission track dating techniques on samples collected along a roughly 50-kilometer long transect cross-cutting the Mackenzie Mountains to delineate and model the cooling history of the upper crust in that region. I will use this information to assess whether a temporal correlation exists between the cooling of the Mackenzie Mountains and the collision of the Yakutat block.

3 Background The study region is located in the Northern Canadian Cordillera in the Mackenzie Mountains and Mackenzie Plain, around the region of Norman Wells (approximately 65o W, 126o N) (Fig. 1). The project will use apatite fission-track thermochronology (AFT) to determine upper cooling history of Mackenzie Mountains and Plain in order to determine temporal correlations between cooling history and key structural events. Figure 1 Geodynamic setting of the northern Canadian Cordillera (Mazzotti and Hyndman, 2005). The blue arrows indicate overall plate tectonic movements while the red arrows show strain transfer across the northern Canadian Cordillera. Geodynamic setting The western Canadian cordillera developed from a system of island arcs in the Late Triassic and Early Jurassic to a continental cordillera in the Late Mesozoic and Early Tertiary (Monger et al., 1972). In the Jurassic, the North American continent began to converge with offshore subduction zones resulting in the accretion of rocks from back arc basins and offshore arcs to the continental margin. New continental arcs continued to form and were built on both the accreted margin and parts of the ancient continental margin (Monger and Price, 2002). Far-travelled terranes were also colliding and accreting to North America (Price, 2008). The upper crust of these accreted terranes became detached from their lower crustal and upper mantle lithosphere and became juxtapositioned over North America and ultimately stacked on top of each other (Price, 2008). Subduction of the oceanic lithosphere beneath the North American craton was primarily near orthogonal and left-lateral oblique before the Mid Cretaceous but became dominated by rightlateral oblique convergence during the Late Cretaceous and Tertiary (Price, 2008).

4 Collision and accretion of terranes to the western margin of the North American craton led to lateral growth of approximately 500 km of western North America (since the early Jurassic) (Price, 2008) and also to the deformation observed in the Northern Canadian Cordillera (Lane, 2002). The Yakutat terrane, positioned on the leading edge of Pacific Plate, started moving in a northwesterly direction from the Miocene and has been colliding since then with the northwestern margin of North America (Mazzotti and Hyndman, 2002). The collision has resulted in crustal thickening, uplift, and seismicity in the Canadian Cordillera which is recorded in the region as far as the Mackenzie and Richardson Mountains (Mazzotti and Hyndman, 2002, Fig. 1). Regional geology The structure of the Mackenzie Mountains is marked by easterly and westerly verging concentric folds and thrust faults (Fig. 2) (Gabrielse, 1991). In the north, the Mackenzie Mountains are characterized by broad anticlines and narrow synclines. Broad anticlines (up to 20 km across, 50 km long) expose Cambrian to Devonian carbonates (such as Franklin Mountain and Mount Kindle formations, Fig. 3) that unconformably overly Proterozoic clastics and minor carbonates; the narrow synclines are underlain by Upper Devonian shale (such as the Hare Indian formation, Fig. 3) and sandstone (Gabrielse, 1991). Reactivated Precambrian faults cause minor northtrending offset of Proterozoic and Paleozoic strata in the anticline cores. In the south of the Mackenzie Mountains, Paleozoic and Mesozoic strata are folded into narrow anticlines and broad synclines that are cut by late stage north-northeast-trending right lateral wrench faults (Gabrielse, 1991). The anticlines are locally en echelon, doubly plunging, and faulted and expose Paleozoic carbonate (Mid Devonian and older) and some Mid Proterozoic quartzites are seen at the surface. The synclines are broad and flat-bottomed and generally expose Devonian shales (Gabrielse, 1991). The main structural feature in the central Mackenzie Mountain region is the east-vergent Plateau Fault (Fig. 2), approximately 270 km in length, which has emplaced mostly undeformed Mid Proterozoic and younger strata (hanging-wall) over Late Devonian flat lying to gently dipping strata in the footwall (Fig. 2) (Gordey et al., 2009; Gabrielse, 1991). Figure 2 Cross-section of study area (Gordey et al., 2009). Strata age codes (first letter/symbol) are as follows: K: Cretaceous; C: Carboniferous; D: Devonian, SD: Silurian-Devonian; OS: Ordovician-Silurian; ЄO: Cambrian-Ordovician; Є: Cambrian; P: Neoproterozoic. Several levels of detachment explain the concentric folding patterns of the Mackenzie Mountains (Gordey et al., 2009; Gabrielse, 1991); deep detachment of Proterozoic strata (Fig. 2) occurred in the north while much shallower detachment was inferred to occur in the south. In the central region, shallow detachment was observed, represented by the Plateau Fault (Fig. 2). Overall, shortening across the Mackenzie Mountains has been estimated at approximately 45 to 55

5 kilometers (Gabrielse, 1991). Previous low-temperature thermochronology in the Canadian Cordillera There is a limited amount of thermochronological data for the Mackenzie Mountains and corridor region. There have been several thermochronological studies conducted for the Mackenzie delta and Beaufort Sea region, approximately 900 km north of the study region (Fig. 1). O'Sullivan and Lane (1997) provide AFT data for rocks (9 samples) exposed in the Big Fish River (Northwest Territories), with ages ranging from 107 ± 31 to 47 ± 10 Ma. Figure 3 Regional stratigraphic chart (Issler et al, 2005) Thermal modeling indicates that these rocks cooled rapidly from paleotemperatures of o C to < 60 o C at about 56 ± 2 Ma in response to kilometerscale denudation. In the Barn Mountains and Blough Trough regions (second region of their study area), there were seven AFT ages ranging between 59 ± 5 to 53 ± 5. Approximately 3.8 km of denudation occurred since cooling

6 began. Overall, these results indicate that there was rapid regional denudation in the early Eocene across the onshore Beaufort - Mackenzie region followed by rapid cooling in the Early Eocene which was attributed to kilometer-scale denudation resulting from Early Tertiary folding and thrusting. Lane and Issler (2011) have recently published apatite fission track thermochronology data for samples from the British and northern Richardson Mountains as well as the Keele Range, hundreds of kilometers away from my study area. The study involved one sample from the northernmost Mackenzie Mountains (Fig. 1). This sample yielded an apparent age of 34.8 ± 3 Ma which, with the presence of a plurimodal track-length distribution, suggesting a complex thermal history. There is no published information on thermal modeling results available for this study. In 2005, Issler et al. reported data to thermally constrain the Keele Tectonic Zone in the Tulita area, 80 km southwest of Norman Wells (Fig. 1). The study utilised detrital material from the East Mackay I-77 petroleum exploration well. The study used a combination of thermal maturity data (including %Ro and Rock-Eval pyrolysis), shale compaction, and apatite fission-track thermochronology. Apatite fission-track thermochronology samples were collected over the depth interval of 1730 to 1780 m from a single sandstone sample from the Devonian Imperial Formation, a predominantly carbonate and shale succession. Two grain-age populations were identified: 90.4 ± 6.1 Ma and ± 22.5 Ma (Issler et al., 2005). The authors modeled the thermal history using an inverse multi-kinetic fission-track annealing model which indicated that one major heating event in the sedimentary basin occurred in the Early Triassic to Mid Jurassic ( Ma) with a peak temperature of 124 ± 10 o C. The maximum thickness of the rocks overlying the analyzed sample is estimated to be between km with a thermal gradient estimated as o C / km during this period. A smaller heating event occurred in the Albian ( Ma) where average temperatures are estimated to be < 75 o C. Maximum burial is estimated to have occurred in the Paleocene to Early Eocene (65-50 Ma), where average temperature was 97 ± 9 o C. From Cretaceous to Tertiary times, the average geothermal gradient is estimated to be 32 o C / km, comparable to today's geothermal gradient. These studies emphasize that there has been very limited use of thermochronometers in the investigation of the thermal history of the study region. The variety of ages reported and the thermal histories described above suggest that there is room for this project to contribute to the overall understanding of the thermal events that occurred since the Cretaceous. OBJECTIVES The overriding objective of this project is to investigate whether uplift and exhumation of the Mackenzie Mountains has resulted from contractional strain transferred from the collision of the Yakutat terrane, to the western margin of North America. If the Mackenzie Mountains were formed by the Yakutat collision then the mountain range would be at most Miocene in age. The alternative or default view is that the Mackenzie Mountains formed sometime during the Mid Cretaceous to Paleocene. To test this hypothesis, the project will use two short-term objectives, (1) to determine the upper crustal cooling history of Mackenzie Mountains and (2) to use this information to determine whether a temporal correlation exists between cooling history and the collision of the Yakutat block. Apatite fission-track (AFT) thermochronology is the tool that will be used to determine the upper crustal cooling history of Mackenzie Mountains and surrounding

7 Mackenzie Corridor region. As described in the previous section, there is no low-temperature thermochronology data for the study area. Once the data has been collected from apatite crystals found in rock samples, inverse modeling using the HeFTY program will help to delineate a detailed thermal history of the region. METHODS The Mackenzie Mountains-corridor region resides in a compressional or thrust tectonic setting (Fig. 4) where advective heat transfer is a prominent process (Ehlers, 2005). Erosion and tectonics lead to crustal particle displacement from high temperatures at depth (open circle) to surface temperatures in the modern landscape (closed circle) (Fig. 4). The hanging-wall of thrust faults are marked by erosion due to slope steepening, subsequent landslides, and river incision, as well as by enhanced geothermal gradient through isotherm compaction and upward advection of "hot" material in the vicinity of the fault (Ehlers, 2005). In the footwall, the foreland basin receives the erosional products of the uplifting range and is thermally marked by depressed isotherms due to downward advection of "cold" material lowering the geothermal gradient. This results in curved isotherms that produce a lateral variation in crustal geothermal gradients across the fault. In the range, each exhumed sample passes through the closure temperature of a given thermochronometric system at variable depths (according to its position with respect to the fault) and travels different distances before becoming exposed (or exhumed) at the surface. Figure 4 Processes that may influence thermochronometry interpretation in thrust tectonic settings (modified from Ehlers 2005) Sampling strategy A northeast-oriented transect perpendicular to the Mackenzie Mountains structures (such as the crosssection in Fig. 2), was selected in order to reconstruct the rock cooling along their shortest exhumation path, assuming displacement on the thrust faults is dip-slip and that deformation is plane. As a result, samples were (and will be) collected perpendicularly to the range front. Sample collection A key part of this project is finding samples that contain apatite crystals. The study area is very inaccessible with all sites being reached only by helicopter. Being unable to participate in the GSC's 2011 field season, samples were collected from their repository for 2010 and 2011 field seasons. Mineral separation

8 I will process bedrock samples here at Dalhousie University's Geochronolgy lab. First, the rock sample (4-5 kg in weight) is crushed using a jaw crusher and disk mill and sieved to collect the 400 µm fraction then further processed through a density separator (Wilfley table) to concentrate heavy minerals. The heavy fraction is placed in a solution of Lithium Metatungstate (LMT) with a density of approximately 2.9 g/cm 3 in which apatites (density of ~2.1 g/cm 3 ) and other heavy minerals (zircon, sphene) sink while the other lighter minerals such as quartz, feldspar, and calcite float. The heavy fraction is then isolated and run through the Frantz isodynamic separator to remove magnetic minerals and isolate non-magnetic minerals such as apatite and zircon. The remaining non-magnetic fraction is placed in Diiodomethane (density of ~3.32 g/cm 3 ) where apatite float and zircon sink. The used LMT and DI are collected and recycled for future use. The sample is inspected under the microscope to determine the quality of the apatite yield. Apatite Fission-track thermochronology (AFT) Apatite fission track (AFT) analysis is a powerful quantitative method used to determine the low temperature thermal history of rocks (Donelick et al. 2005). AFT analysis is a form of radiometric dating based on the spontaneous fission of 238U that occurs in uranium-rich minerals such as apatite. Fission creates damage trails or "fission tracks" in the crystal lattice. The key characteristics that make apatite very suitable for fission track analysis has been summarized by Donelick et al. (2005) as follow:1) it is a ubiquitous accessory mineral found in many common crustal rock types; 2) its physical properties, such as crystal shape, specific gravity and hardness; 3) its major and minor element chemistries; 4) its trace element chemistry, such as the presence of uranium and thorium; 5) its ability to retain fi ssion tracks in the geological environment, and 6) the ability to model apatite spontaneous fi ssion tracks in the geological environment using laboratory analogues. To determine the age of a rock sample, AFT analysis utilizes the following age equations (derived from the basic age equation for radiometric dating): The known values are: λd: total decay constant of 238 U (y -1 ); ζ : zeta (calibration factor of the operator); g: geometry factor. The values that need to be determined are: ρd : Induced track density for a uranium standard (dosimetry glass); ρs: Spontaneous fission-track density (daughter products); ρi: Induced fission-track density (parents). External Detector Method (EDM) This project will use the External Detector Method (EDM) (Fig. 5) which uses a Uranium-free external detector (muscovite slab) to indirectly measure the concentration of parent element in a nondestructive way. After mounting the apatite grains in epoxy on a glass thin-section, the grains are ground and polished to expose their internal surface (Dumitru, 1993). Fission tracks need to be chemically etched in order to become optically observable under the microscope. Etching involves immersing the polished grain mount in 5.5M HNO<sub>3 at 21 o C for 20 seconds to enlarge the damage in the crystal lattice (Donelick et al, 2005). The grain mount is then sealed in

9 contact with the external detector, then irradiated with thermal neutrons to induce the fission of 235 U in apatite crystals (the value of the ratio 238 U/ 235 U being known and constant, this allows to subsequently retrieve the concentration of the parent 238 U). Irradiation will take place at the Oregon State University reactor. After irradiation, the mica (only) will be etched in 40% HF at 21 o C for 45 minutes to reveal the induced fission tracks. Induced fission tracks from the mica are used to determine the fission track density of the parent 235 U (ρi ) while the spontaneous fission track density, or the density of the daughter product ( ρs:), is determined by counting the spontaneous fission tracks revealed on the grains after chemical etching. In addition, a uranium-doped glass (such as CN-5 glass) is attached to a sheet of mica and placed in three locations (top, middle, bottom) in the tube sent for irradiation in order to monitor the variability in intensity of the neutron flux in the reactor and its potential variation across the can containing the samples. Induced tracks from the glass will be used to determine the value of (ρd) described in the age equation. Figure 5 External Detector Method (EDM) (modified after Gallagher et al., 1998) Computer-automated microscope stage system The computer automated system facilitates easy matching of grain to mica which allows values of ρd and ρs to be determined for a given grain and the matching location on the mica (Dumitru 1993). Each pair of values is entered into the age equation. To determine both spontaneous and induced track density, tracks are counting over a constant area materialized by a grid attached to the eyepiece of the microscope. About 20 single-grain ages are determined for each sample in order to obtain a statistically representative mean age.

10 Track lengths Surface fission tracks that have been etched for counting provide information on the apparent age of a rock sample. Sometimes the age number is not sufficient to interpret the geological meaning of a sample; this is because of the annealing characteristics of fission tracks (Donelick et al. 2005). Tracks are formed at an approxmate length of ~ 16 µm. If a fission track is exposed to temperatures greater than approximately 120 o C, the crystals in the zone of complete annealing and all tracks will be instantaneously erased by fast atomic diffusion. However, as soon as apatite crystals are cooled below the closure temperature (120 o ± 20 o C) the clock starts and the tracks are preserved. If the sample is rapidly cooled to surface temperatures, the tracks contained in apatite crystals will have uniform lengths. However, if the apatite resides for a prolonged period of time in a temperature zone between about 60 and 110 o C (the partial annealing zone or PAZ), while new tracks continue to form and accumulate, the first tracks formed will start to anneal and become shorter. In that case of slow cooling, which indicate a more complex thermal history, the crystals will contain long tracks that have newly formed, old tracks that have been severely annealed, and other tracks of intermediate lengths. As a result of track shortening in the PAZ, the probability for the spontaneous tracks (daughter products) to intersect the crystal's surface and be counted for age determination is reduced, and the fission-track age obtained is then considered an apparent age, younger than the time at which the sample effectively cooled below the closure temperature; it has limited geological meaning. In that case, both the apparent age and the track length distribution can be used together to interpret the complex thermal history of the sample. This is made possible by using annealing models for fission-tracks in apatite crystals, calibrated by laboratory experiments (Donelick et al., 2005). AFT is the only thermochronologic techniques that can quantify the partial loss of daughter products, making it a powerful and unique tool to reconstruct complex thermal histories. Inverse modeling with HeFTY Ages obtained from the age equation and the confined track lengths distribution are input into a thermal modeling program (HeFTy) used to determine the thermal history of the region (Ketcham, 2005). The model uses inverse modeling and defines the time-temperature (t-t) path of a particle through specific t-t constraints defined by the user and based on independent geological information

11 Figure 6 Example of time-temperature constraints from HeFTy (Ketchum, 2005). In this case, the sample is a detrital sediment that was eroded from the source region prior to 70 Ma, was deposited in a sedimentary basin at surface temperature conditions between Ma, then buried by overlying strata between Ma and then finally cooled to surface temperature where it was collected (black boxes in Fig. 6). Constraints mark the regions in t-t space where thermal history must pass and will be generated from the data collected by this study. Time constraints include a hightemperature initial condition (temperature above total annealing of most robust / heat resistant apatite grain), present-day surface temperature and in case of more complicated geological setting, time-temperature of deposition and reburial of the sample. SIGNIFICANCE AND PRELIMINARY RESULTS This project will contribute to current research undertaken in Mackenzie Mountains-Beaufort Sea region by the Thermochronologic Approaches for Fundamental Energy Exploration (TAFFEE) project, which is a collaboration between academia, oil industry, and GSC. The project currently has adequate funding to meet its objectives and is expected to be completed on time (by September 2013). The AFT method described above provides a step-by-step procedure to go from exposed bedrock to its thermal history across the upper 5-6 km of the continental crust and is a uniquely powerful tool to unravel the timing and magnitude of mountain building processes in the Mackenzie Mountains region. To date, yields in apatite have been very low, which is one of the risks identified previously for this project. To mitigate this risk, additional samples obtained from the GSC are currently being processed.

12 REFRENCES Donelick, R.A., O'Sullivan, P.B., and Ketcham, R. A Apatite fission track analysis. Reviews in Min & Geochem. 58: Dumitru, T Fission-track geochronology. Quat. Geochron.: Methods and applications. Dumitru, T A new computer-automated microscope stage system for fission-track analysis. Nucl. Tracks Radiat. Meas., 21(4): Ehlers, T. A Crustal thermal processes and the interpretation of thermochronometer data. Rev. in Min. & Geochem. 58: Fallas, K M; MacLean, B C., MacNaughton, R B; Hadlari, T New bedrock map compilations for the central Mackenzie Corridor, NWT. GSC, Scientific Presentation 11, 2012, 1 sheet. Gabrielse, H. (Comp) Structural styles, Chapter 17 in Geology of the Cordilleran Orogen in Canada, H. Gabrielse and C.J. Yorath (ed.); GSC, Geol. of Canada, no. 4, p (also GSA, The Geology of N. American, v. G-2). Gordey, S.P., MacDonald, J.D., Roots, C.F., Fallas, K.M., and Martel, E Regional cross-sections, detachment levels, and origin of the Plateau Fault: Central Mackenzie Mountains, Northwest Territories. GSC Open File Scale 1: Issler, D.R., Grist, A.M., Stasiuk, L.D Post-Early Devonian thermal constraints on hydrocarbon source rock maturation in the Keele Tectonic Zone, Tulita area, NWT, Canada, from multi-kinetic apatite fission track thermochronology, vitrinite reflectance and shale compaction. Bull. of Can. Petroleum Geol. 53: Ketcham, R. A Forward and inverse modeling of lowtemperature thermochronometry data. Rev. in Min. & Geochem. 58: Lane, L.S Latest Cretaceous-Tertiary tectonic evolution of Northern Yukon and adjacent Arctic Alaska. AAPG Bull., 82(7): Lane, L.S. and Issler, D.R Overview of the Tertiary cooling-uplift history of the northernmost Yukon adjacent to the Beaufort Basin, based on apatite fission track studies. Recovery CSPG CSEG CWLS Convention abstract.

13 Mazzotti, S. and Hyndman, R.D Yakutat collision and strain transfer across the northern Canadian Cordillera. Geology. 30 (6): Monger, J. W. H., and R. A. Price (2002), The Canadian Cordillera: Geology and tectonic evolution, CSEG Rec. Feb 2002, 17-36, Can. Soc. of Explor. Geophys., Calgary, AB. O'Sulivan, P.B., and Lane, L.S Early Tertiary thermotectonic history of the nnorthern Yukon and adjacent Northwest Territories, Arctic Canada. Can. J. Earth Sci. 34: Monger, J.W.H., Souther, J.G., and Gabrielse, H Evolution of the Canadian Cordillera: a plate tectonic model. American J. of Science, 272: Perry, S.E., Garver, J.I., and Ridgway, K.D Transport of the Yakutat Terrane, Southern Alaska: evidence from sediment petrology and detrital zircon fision-track and U/Pb double dating. Geol. 17(2), pp