Fault tectonics in the Rapid depression of the Yukon North Slope (Canadian Arctic) - Summary of preliminary results W. von Gosen1 Geozentrum Nordbayern, Krustendynamik, Friedrich-Alexander-Universität Erlangen-Nürnberg K. Piepjohn Bundesanstalt fur Geowissenschaften und Rohstoffe (BGR), Geologie der Energierohstoffe, Polargeologie D.C. Murphy Yukon Geological Survey C. Brandes Institut für Geologie, Leibniz Universität Hannover W.C. McClelland Department of Earth and Environmental Sciences, University of Iowa M. Colpron Yukon Geological Survey von Gosen, W., Piepjohn, K., Murphy, D.C., Brandes, C., McClelland, W.C. and Colpron, M., 2015. Fault tectonics in the Rapid depression of the Yukon North Slope (Canadian Arctic) – Summary of preliminary results. In: Yukon Exploration and Geology 2014, K.E. MacFarlane, M.G. Nordling and P.J. Sack (eds.), Yukon Geological Survey, p. 157-165. ABSTRACT Mesozoic to Tertiary rocks in the Rapid depression on the Yukon North Slope are dissected by a N-NNE striking fault array. Two phases of Tertiary deformation are recorded from the Barn uplift eastwardly across the Rapid depression. D1 is characterized by strike-slip faults with either sinistral or dextral displacement in the depression and reverse-dextral oblique displacement on the southern Barn fault, indicating broadly E-W regional contraction. In contrast, D2 deformation is somewhat more complex with first-order faults in the Rapid depression inferred to be primarily sinistral, while the southern Barn fault maintained its reverse-dextral oblique displacement. The structural style is inconsistent with the propagation of a large-scale strike-slip fault zone such as the Kaltag fault through the Rapid depression, as previously suggested, but rather may indicate reactivation of older structural heterogeneity in the subsurface. [email protected] YUKON EXPLORATION AND GEOLOGY 2014 157 YUKON GEOLOGICAL RESEARCH INTRODUCTION predominantly underlain by Mesozoic sedimentary rocks. It is flanked to the west by structural culminations of the In northernmost Yukon (Canadian Arctic), south of the Barn and Romanzof uplifts and to the east by the Aklavik Beaufort Sea, there is a wide area known as the Yukon arch complex (including Rat, Scho, White and Cache North Slope. The Rapid depression (Fig. 1), in the Creek uplifts; Fig. 1; Norris, 1997); Paleozoic and locally eastern part of the Yukon North Slope, is a broad trough older rocks are exposed in both regions. Mesozoic rocks of the Rapid depression 70°N 70°N 141°W 132°W straddle the boundary between the Paleozoic B e a u f o r t S e a North American continental Kugmallit margin in the east and Arctic Bay ELFZ 1 Alaska terrane in the west. Mackenzie 21 Tuktoyaktuk Alaska Yukon Bay Mesozoic and locally Tertiary British 2Mountains rocks in the depression are cut by a swarm of N-~NNE BF striking faults which occur ELFZ 13 in a north-south corridor 1 Mackenzie BeF BF Delta ~60 km wide (Rapid fault 4 GF EF CI F Inuvik array; see Norris and BuF 8 HF YSF Yorath, 1981; Norris, 1997). 3 CnF 12 1 CCF 11 CCF Mackenzie BuF 7 FCF 9 11 U. S.A. KF Canada Old Crow 10 Richardson Mountains TF YF DLF Arctic Red River River 5 6 Northwest Territories Yukon DF TF 20 16 17 YF KnF PorcupineEagle River Arctic Circle DIF Plain YF Highway TF Ogilvie Mountains Dempster 14 DF Nahoni Range 18 15 TF 19 YF 15 DIF Figure 1. Tectonic elements 100 km KnF 141°W 132°W and main faults in northern 65°N 65°N Yukon and adjacent Boundary between Strike-slip fault Contraction fault Extension fault tectonic elements Northwest Territories, Canada (map modified from Norris, Tectonic Elements: Faults: 1 - Rapid depression 12 - Campbell uplift BF - Barn fault FCF - Fish Creek fault 1997). Frame with yellow fill 2 - Romanzof uplift 13 - Eskimo Lakes block BeF - Beaver fault GF - Gilbert fault shows location of the map of 3 - Old Crow-Babbage depression 14 - Kandik basin BuF - Buckland fault HF - Hoidahl fault 4 - Barn uplift 15 - Taiga-Nahoni foldbelt CCF - Cache Creek fault KF - Kaltag fault the study area 5 - Keele block 16 - Eagle foldbelt CnF - Canoe fault KnF - Knorr fault (Fig. 3). Note that the 6 - Dave Lord uplift 17 - Richardson anticlinorium CIF - Castle fault TF - Trevor fault 7 - White uplift 18 - Bonnet Plume basin DLF - Dave Lord fault YT - Yukon fault extension of the Tertiary, 8 - Cache Creek uplift 19 - Mackenzie foldbelt DF - Deception fault YSF - Yukon (Skull) fault strike-slip Kaltag fault into 9 - Scho uplift 20 - Interior platform DIF - Deslauriers fault 10 - Rat uplift 21 - Beaufort-Mackenzie basin EF - Eagle fault Yukon is called into question 11 - Canoe depression ELFZ - Eskimo Lakes fault zone here and in Lane (1992). 158 YUKON EXPLORATION AND GEOLOGY 2014 VON GOSEN ET AL. - FAULT TECTONICS IN THE RAPID DEPRESSION OF THE YUKON NORTH SLOPE Structural information from the depression is critical to reconstructions of the Arctic (e.g., Jones, 1980; McWhae, reconstructing the nature of interactions between Arctic 1986), it appears restricted to the western and central Alaska and the northwestern North American margin in parts of Alaska (e.g., Grantz, 1966; Patton and Hoare, late Mesozoic and Tertiary. Furthermore, these data might 1968; Patton 1973; Fig. 2). Lane (1992) argued against its give insight into the plate tectonic significance of the faults along-strike continuation into northern Yukon. and related structures and answer the question of whether Deformation in the Rapid depression has been the tectonic development in the Rapid depression can characterized as a Paleocene-Eocene fold-and-thrust belt, be geometrically and kinematically linked to the Eurekan lacking regionally important strike-slip faults (Lane, 1988). deformation in the Canadian Arctic Archipelago, North This belt continues northward into major fold structures Greenland and Svalbard (compare, for example, Balkwill, of the arcuate Beaufort fold-and-thrust belt offshore in the 1978; Kerr, 1981; Tessensohn and Piepjohn, 2000). southern Beaufort Sea (e.g., Lane, 1998; Fig. 2). Several interpretations of seismic lines from these offshore areas PREVIOUS WORK have shown that the arcuate belt was mainly formed during the Paleocene-Eocene but youngs towards its The Rapid depression has been inferred to be the locus outboard northern and eastern parts (compare, for of the continuation of the Kaltag fault, a major ENE-WSW example, Dietrich et al., 1989; Lane and Dietrich, 1991; dextral strike-slip fault defined in western and central Lane, 1998, 2002; Dixon et al., 2001; Dinkelman et al., Alaska (cf., Norris, 1976, 1981, 1997; Fig. 1). Although the 2008; Helwig et al., 2011). Kaltag fault has been included in Cenozoic plate tectonic 135° Anticline 150° 145° 140° Syncline 100 km Thrust Fault Beaufort Sea 70° Normal Fault Strike-Slip Fault, dextral Fault, type not defined 69° 69° Alaska Yukon 68° Eskimo Lakes Fault 68° Old Crow Basin 67° 67° Fault Kobuk Fault Yukon Knorr Fault 66° Yukon Flats 66° Bonnet Plume 65° Basin 65° Kaltag Fault Tintina Fault 155° U. S. A. S. U. Canada 135° 150° 140° Pre-mid Cretaceous to Holocene deformations: 145° Campanian and Pre-mid Cretaceous Post-mid Cretaceous Paleocene - Mid-Eocene - Late Oligocene - younger Early Eocene Oligocene Holocene Figure 2. Simplified tectonic map of northeastern Alaska, northern Yukon, and adjacent Northwest Territories (Canada) showing the trends of major Late Cretaceous-Tertiary structures and approximate ages of pre-mid Cretaceous to Holocene deformations (modified from Lane, 1998, 2002). Frame with yellow fill shows location of map in Figure 3. YUKON EXPLORATION AND GEOLOGY 2014 159 YUKON GEOLOGICAL RESEARCH GEOLOGIC SETTING OF THE RAPID (Cecile, 1988) or Middle-Late Devonian (Dyke, 1997); it is inferred to be related either to the Ellesmerian Orogeny DEPRESSION or to the Romanzof Orogeny (Lane, 2007). The Barn uplift The Barn uplift, partly bounding the western edge is bounded on the east by the Barn fault. In the north, of the Rapid depression (Figs. 1 and 3), consists of west, and south, the rocks in the uplift are unconformably Neoproterozoic to lower Paleozoic (meta-)clastic and overlain by Carboniferous and younger clastic deposits carbonate rocks intruded by granitic plutons of Late (Fig. 3). Devonian age (Lane, 2007), all part of the Arctic Alaska The Rapid depression and areas surrounding the Barn terrane. The pre-Carboniferous succession is folded and uplift are underlain by Jurassic to Upper Cretaceous, and dissected by several east-directed thrust faults (Cecile, locally Tertiary clastic deposits (Fig. 3). The eastern margin 1988; Cecile and Lane, 1991; Dyke, 1997). The first phase of the Rapid depression, in the Richardson Mountains, of deformation in the core of the Barn uplift has been consists of upper Paleozoic deposits overlain by Mesozoic interpreted as post-Late Silurian to pre-Early Carboniferous rocks in the White and Cache Creek uplifts (Figs. 1 and 3). 139° W 138° W 137° W M a c k e n z i e B a y 68° 40' N 68° 40' N Barn fault Gilbert fault Blow fault B a r n U p l i f t f i l p U n r a B Buckland fault 68° 20' N 68° 20' N Gilbert anticline Hoidahl fault 139° W Anticline Strike-slip fault Skull (Yukon) fault Gilbert fault Syncline Fault, inferred Contraction fault Fault 20 km 138° W 137° W Quaternary Upper Cretaceous and lower Tertiary Jurassic and Lower Cretaceous Jurassic Permian Late Devonian, Granite Tertiary (Paleocene) Lower and Upper Cretaceous Jurassic and Lower Cretaceous Triassic Carboniferous Proterozoic - lower Paleozoic (Porcupine River Formation) Figure 3. Simplified geological map of the Rapid depression and adjacent areas (north Yukon, Canada) modified from Norris (1981). For location see Figures 1 and 2. 160 YUKON EXPLORATION AND GEOLOGY 2014 VON GOSEN ET AL. - FAULT TECTONICS IN THE RAPID DEPRESSION OF THE YUKON NORTH SLOPE FAULTING IN THE RAPID DEPRESSION STRUCTURAL OBSERVATIONS From west to east the major faults in the Rapid depression RELEVANT TO FAULT KINEMATICS are as follows (Norris, 1981, 1997; Fig.