Paleozoic and Mesozoic rocks of Stikinia exposed in northwestern British Columbia: Implications for correlations in the northern Cordillera: Discussion and reply Discussion Stephen T. Johnston*
Department of Geology, University of Durban–Westville, Private Bag X54001, Durban 4000, South Africa
Mitchell G. Mihalynuk†
British Columbia Geological Survey Branch, P.O. Box 9320, Station Provincial Government, Victoria, British Columbia V8W 9N3, Canada
David A. Brew
U.S. Geological Survey, Alaskan Geology Section, 345 Middlefield Road, M.S. 901, Menlo Park, California 94025
Craig J. R. Hart
Yukon Geology Program, Box 2703 (F-3), Whitehorse, Yukon Y1A 2C6, Canada
Philippe Erdmer
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
George E. Gehrels
Department of Geosciences, University of Arizona, Tucson, Arizona 85721
INTRODUCTION Currie and Parrish (1997) presented new rock descriptions, stratigraphic relationships, and isotopic data for metamorphic and plutonic rocks in the Tagish Lake area, northwestern British Columbia. They used these data to reinterpret terrane and assemblage relationships in a large area of the northern Cordillera. Their welcomed goal was to simplify the admittedly complex terrane nomenclature of the region. However, through the application of inconsistent and contradictory methods of terrane analysis, they have, at best, revealed some of the failings of terrane analysis as a paradigm for study of the northern Cordillera. We assess two of the criteria employed to distinguish between terranes and address their suggested correlations for the Stikinia and Nisling terranes. THE TAGISH LAKE AND RELATED PLUTONIC SUITES: ARE THEY DIAGNOSTIC IN THEIR ABSENCE? In the Tagish Lake area, one of the characteristics used by Currie and Parrish to distinguish be*Present address: School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3055, STN CSC, Victoria, British Columbia V8W 3P6, Canada. †Corresponding author; e-mail: mitch.mihalynuk @gems5.gov.bc.ca.
tween the Stikinia and Tracy Arm terranes is the presence of Early Jurassic plutons of the Tagish Lake plutonic suite. The Tracy Arm terrane is referred to by most recent workers as either the lower unit of the Yukon-Tanana terrane (cf. Gehrels et al., 1991) or the Nisling terrane; we use the latter name here. Rocks of the Stikinia terrane are intruded by the Early Jurassic Hale Mountain granodiorite (part of the Tagish Lake plutonic suite) whereas those of the Nisling terrane are not. Currie and Parrish concluded that Early Jurassic magmatism distinguishes Stikinia from the Nisling terrane and inferred that amalgamation of these terranes postdates Tagish Lake plutonism. They extrapolated this relationship north to the Aishihik Lake area, Yukon, where the Aishihik batholith, an Early Jurassic pluton correlative with the Tagish Lake plutonic suite, intrudes the Aishihik metamorphic suite. The latter includes a lower metapelitic assemblage and an upper heterogeneous assemblage of graphitic quartzite, marble, and meta-igneous rocks (Johnston and Timmerman, 1994; Johnston et al., 1996). The Aishihik batholith intrudes rocks of the upper assemblage. Its contact with the lower assemblage is not exposed, but metamorphic mineral isograds concentric to the batholith define a hotside-up aureole and are continuous across the boundary between the lower and upper assem-
GSA Bulletin; July 1999; v. 111; no. 7; p. 1103–1106.
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blages (Johnston and Erdmer, 1995; Johnston and Timmerman, 1994; S. Johnston, written communication to L. Currie, 1995). The batholith clearly invaded and metamorphosed the entire Aishihik metamorphic suite. Currie and Parrish assumed that the lower assemblage lacks any Early Jurassic plutons considered diagnostic of Stikinia and correlated it with the Nisling terrane. They correlated the upper assemblage with Stikinia and concluded that a major terrane boundary separates the two assemblages within the Aishihik metamorphic suite. In contending that there is a lack of “diagnostic” Early Jurassic plutons in the lower assemblage, Currie and Parrish have ignored documented field relationships that invalidate their terrane correlations. The suggestion that Early Jurassic plutons may be diagnostic of the Stikinia terrane is further undermined in the discussion of the Taku terrane and of the Whitewater assemblage. Currie and Parrish correlated parts of the Taku terrane, southeast Alaska, with the Stikinia terrane although recognizing that these rocks lack “documented Lower Jurassic plutons (Tagish Lake suite equivalents).” In the Taku River area, the Whitewater assemblage underlies the Boundary Ranges suite along a gradational contact. Currie and Parrish included the assemblage in the Stikinia terrane, despite the lack of plutons dated as Early Jurassic and despite
DISCUSSION AND REPLY
the fact that the assemblage is correlative with the Nisling terrane (Mihalynuk et al., 1994). Thus, in the Aishihik and Tagish lake areas, Currie and Parrish relied upon “diagnostic” Early Jurassic plutons to distinguish Stikinia, whereas in the southeast Alaska and Taku River areas, they disregarded this criterion. In itself, the presence or absence of a diagnostic unit or suite is rarely a suitable means for terrane analysis, particularly when dealing with plutonic suites (Johnston et al., 1994). Once out of sight of a pluton deemed diagnostic of a specific terrane, one is left to ponder whether or not one has passed into another terrane. The discovery of a previously unmapped pluton is capable of instantly changing the terrane affiliation of the intruded rocks, no matter what other evidence exists. Therefore, the absence of diagnostic rocks needs to be approached with caution in terrane analysis. THE WANN RIVER SHEAR ZONE: IS IT A TERRANE-BOUNDING FAULT? In the Tagish Lake area, amphibolite-grade rocks of the Nisling terrane (the Florence Range suite) are juxtaposed over greenschist-grade rocks of the Stikinia terrane (the Boundary Ranges suite) along the Wann River shear zone (Currie and Parrish, 1993, 1997). Currie and Parrish inferred that the shear zone is a terrane-bounding fault along which two previously separate terranes were juxtaposed at about 184 Ma. Implicit in this conclusion is that the Nisling and Stikinia terranes are everywhere in fault contact. If the upper assemblage of the Aishihik Lake metamorphic suite correlates with the Stikinia terrane, and the lower assemblage with the Nisling terrane, then Stikinia-equivalent rocks would indeed overlie Nisling rocks along a sheared contact. However, there is no increase in strain toward the contact between the two assemblages within the Aishihik metamorphic suite, and previous studies (Tempelman-Kluit, 1974; Johnston, 1993; Johnston and Timmerman, 1994) have found no evidence of significant displacement across the contact. The interpretation proposed by Currie and Parrish requires that the Nisling terrane rocks (the lower assemblage) are the basement to Stikinia (the upper assemblage).
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Similar relationships, with similar implications, are observed to the south. The type section of the Tracy Arm assemblage, from which the Tracy Arm terrane (Nisling here) derives its name, is well exposed in southeast Alaska. On the basis of lithological similarities with coeval Stikinia rocks in the Tagish Lake area, the structurally overlying Paleozoic Endicott Arm and Port Houghton assemblages were included in Stikinia by Currie and Parrish. However, the Endicott Arm assemblage unconformably overlies the Tracy Arm assemblage along a depositional contact (Gehrels et al., 1992). A conglomerate in the Port Houghton assemblage is in depositional contact with metavolcanic rocks of the Endicott Arm assemblage. The conglomerate contains porphyritic quartz rhyolite clasts, interpreted to be derived from porphyritic quartz rhyolite of the Endicott Arm assemblage, and metaclastic quartzite clasts that may have been derived from the Tracy Arm assemblage (Gehrels et al., 1991). Terrane correlations by Currie and Parrish would require that the Nisling terrane is the basement on which Stikinia rocks were deposited. Currie and Parrish proposed that the Nisling terrane structurally overlies the Stikinia terrane along the Wann River shear zone in the Tagish Lake area. Thus, Nisling would stratigraphically underlie Stikinia in some places (Aishihik Lake, southeast Alaska, Taku River area) and structurally overlie it elsewhere (Tagish Lake). Therefore, these correlations would serve to establish the Nisling terrane as the basement of part of the Stikinia terrane; the Wann River shear zone would be an intraterrane thrust responsible for the exhumation of Stikinia’s higher-grade basement. Before a fault can be considered to be terrane bounding, it must first be demonstrated to be part of a continuous, terrane-confining system. No such demonstration has been made for the Wann River shear zone. CONCLUSIONS Terrane analysis has been rightly criticized because it emphasizes differences in rock character “at the expense of equally or more compelling similarities” (Dover, 1990). Currie and Parrish have reported useful data from the Tagish Lake
Geological Society of America Bulletin, July 1999
area and drawn attention to the likelihood that the Boundary Ranges suite may be metamorphosed Stikine assemblage (cf. Mihalynuk, 1994). However, they have employed inconsistent methods of terrane analysis and, in doing so, have overemphasized differences between the Stikinia and Nisling terranes at the expense of compelling data linking the two. REFERENCES CITED Currie, L. D., and Parrish, R. R., 1993, Jurassic accretion of Nisling terrane along the western margin of Stikinia, Coast Mountains, northwestern British Columbia: Geology, v. 21, p. 235–238. Currie, L. D., and Parrish, R. R., 1997, Paleozoic and Mesozoic rocks of Stikinia exposed in northwestern British Columbia: Implications for correlations in the northern Cordillera: Geological Society of America Bulletin, v. 109, p. 1402–1420. Dover, J. H., 1990, Opinion: Problems of terrane terminology—Causes and effects: Geology, v. 18, p. 487–488. Gehrels, G. E., McClelland, W. C., Samson, S. D., and Patchett, P. J., 1991, U-Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska: Canadian Journal of Earth Sciences, v. 28, p. 1285–1300. Gehrels, G. E., McClelland, W. C., Samson, S. D., Patchett, P. J., and Orchard, M. J., 1992, Geology of the western flank of the Coast Mountains between Cape Fanshaw and Taku inlet, southeastern Alaska: Tectonics, v. 11, p. 567–585. Johnston, S. T., 1993, The geological evolution of Nisling assemblage and Stikine terrane in the Aishihik Lake area, southwest Yukon [Ph.D. thesis]: Edmonton, University of Alberta, 270 p. Johnston, S. T., and Erdmer, P., 1995, A hot-side-up aureole in SW Yukon and limits on terrane assembly of the northern Canadian Cordillera: Geology, v. 23, p. 419–422. Johnston, S. T., and Timmerman, J., 1994, Preliminary results of 1:50 000 scale geological mapping in Aishihik Lake (115H/6) and Hopkins Lake (115H/7) map areas, Yukon, in Yukon exploration and geology, 1993: Yukon, Indian and Northern Affairs Canada, Exploration and Geological Services Division, p. 93–110. Johnston, S. T., Hart, C. J. R., and Mihalynuk, M. G., 1994, The Northern Intermontane superterrane—A NUNA Conference summary: Geoscience Canada, v. 21, p. 27–30. Johnston, S. T., Mortensen, J. K., and Erdmer, P., 1996, Igneous and metaigneous age constraints on the Aishihik metamorphic suite, southwest Yukon: Canadian Journal of Earth Sciences, v. 33, 1543–1555. Mihalynuk, M. G., Smith, M. T., Hancock, K. D., and Dudka, S., 1994, Regional and economic geology of the Tulsequah River and Glacier areas (104K/12 and 13), in Geological fieldwork 1993: British Columbia Ministry of Energy, Mines and Petroleum Resources Paper 1994-1, p. 171–197. Tempelman-Kluit, D. J., 1974, Reconnaissance geology of Aishihik Lake, Snag and part of Stewart River map-areas, west-central Yukon: Geological Survey of Canada Paper 73-41, 93 p. MANUSCRIPT RECEIVED BY THE SOCIETY MARCH 27, 1998 MANUSCRIPT ACCEPTED OCTOBER 5, 1998
Reply Lisel D. Currie*
Geological Survey of Canada, 3303 33rd Street N.W., Calgary, Alberta T2L 2A7, Canada
Randy R. Parrish Department of Geology, Leicester University, University Road, Leicester, LE1 7RH, United Kingdom
INTRODUCTION Johnston et al. (1999) have eloquently questioned terrane interpretations we made in Currie and Parrish (1997) by implying that our terrane assignments were made solely on the basis of the presence or absence of Early Jurassic plutons. If their allegations were correct, they would have been justified in accusing us of applying “inconsistent and contradictory methods of terrane analysis.” However, our terrane assignments were primarily based on the recognition of suites of characteristic rock types (mostly metasedimentary and metavolcanic rocks) and, wherever possible, on age and isotopic constraints. In fact, as Johnston et al. (1999) have correctly pointed out, we included the Whitewater assemblage in Stikinia, despite its lack of Jurassic plutons. The same is true for the Endicott Arm and Ruth assemblages (Currie and Parrish, 1997). CRITERIA USED TO DISTINGUISH BETWEEN NISLING AND STIKINIA TERRANE ASSEMBLAGES We will briefly review the lithologic characteristics that we use to distinguish between assemblages we consider part of Stikinia and those we include in the Nisling terrane (referred to as the Tracy Arm terrane in Currie and Parrish, 1997). Because Currie and Parrish (1997) focused on Stikinia, references (e.g., Currie and Parrish, 1993; Currie, 1994) were provided rather than detailed descriptions of Nisling terrane rocks. Bona fide Nisling terrane rocks are best exposed, with the least structural complication, in the Tagish Lake area of northwestern British Columbia. There, they are referred to as the Florence Range metamorphic suite (Currie, 1990; Mihalynuk et al., 1990) and comprise schist, quartzofeldspathic schist, thick, continuous marble layers, and minor quartzite, calc-silicate, and amphibolite (Currie, 1994). The rocks that have been analyzed have isotopically evolved signatures (R. L. Armstrong, 1991, personal commun., documented in Currie, 1994), and quartzites contain Precambrian detrital zircons (Currie, 1994). We consider this lithologic assemblage to be indicative of deposition in a con*E-mail:
[email protected].
tinental-margin setting. Note that this assemblage lacks a significant igneous component. In contrast, the Boundary Ranges suite, which we consider part of Stikinia, is dominated by metaigneous rocks. It exhibits an upward progression from well-layered felsic gneiss with pelitic rocks (biotite schist, biotite-muscovite schist), quartzrich graphitic schist, and graphite schist, to actinolite schist, pyroxene- and/or hornblende-phyric actinolite schist, hornblende-plagioclase gneiss, and felsic gneiss, with minor marble. U-Pb age dating indicates that felsic gneisses in the Boundary Ranges suite are 325 to 375 Ma (Currie and Parrish, 1997), and a hornblende-plagioclase gneiss is 270 ± 5 Ma (Currie, 1992). On the basis of the very limited available data (four samples), the Boundary Ranges suite appears, at least in part, to have been derived from an isotopically unevolved source. The Boundary Ranges suite is thought to have formed in an arc environment with a juvenile magmatic source. This interpretation and the available age and isotopic constraints are consistent with a Stikinia origin. Clearly, we have taken into consideration a suite of characteristics that distinguish Stikinia from the Nisling terrane, and Johnston et al. (1999) have incorrectly stated that we “concluded that Early Jurassic magmatism distinguishes Stikinia from the Nisling terrane” (p. 2). THE STIKINIA-NISLING TERRANE BOUNDARY In the Tagish Lake area, we concluded that the amalgamation of the Nisling terrane and Stikinia postdated Early Jurassic plutonism on the basis of the lack of Early Jurassic plutons in the Nisling terrane, which contrasts strongly with their abundance in adjacent Stikinia (Currie and Parrish, 1993; Currie, 1994). The oldest link that the Boundary Ranges suite shares with the overlying Florence Range suite is the post–184 Ma shear fabric that is associated with the sheared and imbricated contact that separates these two suites (referred to as the Wann River shear zone; Currie and Parrish, 1993). Johnston et al. (1999) have provided an alternate interpretation for the Wann River shear zone; they have suggested that it formed an intraterrane boundary along which the basement to Stikinia Geological Society of America Bulletin, July 1999
(Nisling terrane) was thrust over Stikinia. We consider this interpretation less likely than our terrane boundary interpretation because it seems improbable that any “basement to Stikinia” would have escaped the extensive and long-lived igneous activity (Devonian, Mississippian, Permian, Triassic, and Jurassic) that is characteristic of Stikinia (e.g., Anderson, 1993). Johnston et al. (1999) questioned whether or not the Wann River shear zone could be considered a terrane boundary because of its limited extent, and they challenged the potential extensions of the Nisling-Stikinia terrane boundary that we suggested might exist in the Aishihik Lake area and southeastern Alaska. Their concerns are discussed in the following sections. AISHIHIK LAKE AREA, SOUTH-CENTRAL YUKON Johnston et al. (1999) have taken issue with two of our correlations: (1) between the lower metapelitic assemblage of the Aishihik metamorphic suite (referred to as the “lower package” in Johnston and Timmerman, 1994a) and the Florence Range suite and (2) between the upper heterogeneous assemblage of the Aishihik metamorphic suite (referred to as the “upper package” in Johnston and Timmerman, 1994a) and the Boundary Ranges suite. They have argued that both assemblages belong to the same terrane on the basis of metamorphic isograds, which cross the boundary between the lower and upper assemblages and which are considered by Johnston and Erdmer (1995) to have formed as part of an aureole around the Early Jurassic Aishihik batholith. Here, we review the reasoning behind our correlations and then evaluate the evidence for the intrusion of the Aishihik batholith into Nisling terrane rocks. The lower assemblage of the Aishihik metamorphic suite comprises feldspathic quartz-mica schist, quartzite, metachert and marble, and hornblende metabasite (Johnston and Timmerman, 1994b, 1994c). The same rock types are characteristic of the Florence Range suite and other assemblages that we have identified as potential components of the Nisling terrane (Currie, 1994; Currie and Parrish, 1997). The lower assemblage lacks the meta-igneous rocks characteristic of Stikinia and, like the Florence 1105
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Range suite, is interpreted as a passive continental-margin assemblage (Johnston et al., 1996). The upper assemblage of the Aishihik metamorphic suite comprises graphitic quartzite, marble, and meta-igneous rocks, including metabasite, metagabbro, metafelsite, hornblende diorite gneiss, and Early Mississippian two-mica granite gneiss (Johnston et al., 1996); all rock types occur in the Boundary Ranges suite. The upper package is clearly intruded by the Early Jurassic Aishihik batholith, but our correlations do not require the presence of Early Jurassic plutons. If the Aishihik batholith did intrude both the upper and lower packages of the Aishihik metamorphic suite, its presence does not preclude the possibility that these two assemblages were separate entities before its intrusion at 186.0 ± 2.8 Ma (Johnston et al., 1996). Data from the Tagish Lake area indicate that Nisling and Stikinia were amalgamated between 184 and 176 Ma (Currie, 1994). Furthermore, it is clearly possible that amalgamation did not take place simultaneously along the entire NislingStikinia terrane boundary. An alternative interpretation of previous observations (Johnston and Erdmer, 1995; Johnston and Timmerman, 1994a, 1994b, 1994c) is that the upper package of the Aishihik metamorphic suite, along with the Aishihik batholith (Stikinia), was thrust over the lower package of the Aishihik metamorphic suite (Nisling terrane) soon after the intrusion of the Aishihik batholith. Thrusting of hot rocks (Stikinia) over cooler rocks (Nisling terrane) could have resulted in the isograd pattern observed today. This collisional interpretation is consistent with the conclusion of Johnston et al. (1996) that the age difference between the shallowly intruded Long Lake suite (185.6 ± 2 Ma) and the more deeply intruded (~30 km depth) Aishihik batholith requires denudation rates of 4.2–12.5 mm/yr. These denudation rates are considered reasonable for a collisional orogen (see references in Johnston et al., 1996). Johnston et al. (1999) have also argued that there cannot be a terrane boundary between the lower and upper packages of the Aishihik metamorphic suite because there is “no evidence of significant displacement across the contact” and because “there is no increase in strain toward the contact between the two assemblages within the Aishihik metamorphic suite.” It is not clear how one would document pre–189 Ma displacement, significant or otherwise, across a contact that separates two assemblages that share nothing in common until after 189 Ma (i.e., metamorphic isograds). Outcrop-scale boudins of metabasite surrounded by finely layered quartzite at the upper assemblage–lower assemblage contact may suggest that the contact is tectonic (S. T. Johnston,
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1994, personal commun.). In addition, the degree of strain clearly increases from within Aishihik batholith, where original igneous textures are preserved, to its margins and the rocks below. SOUTHEAST ALASKA Johnston et al. (1999) have dismissed the possibility that the contact between the Tracy Arm assemblage (Nisling terrane) and the Endicott Arm assemblage (Stikinia?) is a terrane boundary because Gehrels et al. (1991) interpreted it as “gradational” and stated that the quartzite clasts in the Endicott Arm assemblage “may have come from the Tracy Arm assemblage” (Gehrels et al., 1991, p. 1287). We have offered an alternate interpretation by suggesting that the ~1-km-wide zone within which metaclastic rocks, marble, and meta-igneous rocks occur correlates with the lower part of the Boundary Ranges suite, whereas the volcanic rock–dominated part of the Endicott Arm assemblage correlates with the upper part of the Boundary Ranges suite. Our interpretation places the contact east of the conglomerates and assumes that quartzite cobbles found in the Endicott Arm assemblage conglomerate were derived from within the Endicott Arm assemblage (Stikinia). Consequently, our correlations do not establish that Nisling terrane rocks are the basement to Stikinia, and we do not believe that we have ignored any documented field relationships. Compelling data linking Stikinia and Nisling terrane are still lacking. CONCLUSIONS We agree that the presence or absence of a plutonic suite is not a suitable means for terrane analysis. The criticism by Johnston et al. (1999) of our alleged use of such a criterion is surprising considering that Johnston and Erdmer (1995) stated that “the Aishihik plutonic suite is characteristic of Nisling” (p. 241) and used the absence of significant Early Jurassic igneous rocks in North America to distinguish it from the Nisling terrane. Early Jurassic plutonism is well documented throughout universally accepted parts of Stikinia (e.g., Anderson, 1993). Its presence cannot be used on its own to identify Stikinia rocks, but can be used in conjunction with other characteristics to make correlations between disparate components of Stikinia. Thus, when used judiciously, terrane analysis remains a useful paradigm for the study of the northern Cordillera. ACKNOWLEDGMENTS This is Geological Survey of Canada contribution number 1998139.
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REFERENCES CITED Anderson, R. G., 1993, A Mesozoic stratigraphic and plutonic framework for northwestern Stikinia (Iskut River area), northwestern British Columbia, in Dunne, G., and McDougall, K., eds., Mesozoic paleogeography of the western United States, Volume II: Society of Economic Paleontologists and Mineralogists, Pacific Section, v. 71, p. 477–494. Currie, L. D., 1990, Metamorphic rocks in the Florence Range, Coast Mountains, northwestern British Columbia, in Geological fieldwork 1989: British Columbia Ministry of Energy, Mines and Petroleum Resources Paper 1990-1, p. 197–203. Currie, L. D., 1992, Metamorphic rocks in the Tagish Lake area, northern Coast Mountains, British Columbia: A possible link between Stikinia and parts of the Yukon-Tanana terrane, in Current research, Part E: Geological Survey of Canada Paper 92-IE, p. 199–208. Currie, L. D., 1994, The geology and mid-Jurassic amalgamation of Tracy Arm terrane and Stikinia of northwestern British Columbia [Ph.D. thesis]: Ottawa, Ontario, Canada, Carleton University, 385 p. Currie, L. D., and Parrish, R. R., 1993, Jurassic accretion of Nisling terrane along the western margin of Stikinia, Coast Mountains, northwestern British Columbia: Geology, v. 21, p. 235–238. Currie, L. D., and Parrish, R. R, 1997, Paleozoic and Mesozoic rocks of Stikinia exposed in northwestern British Columbia: Implications for correlations in the northern Cordillera: Geological Society of America Bulletin, v. 109, p. 1402–1420. Gehrels, G. E., McClelland, W. C., Samson, S. D., and Patchett, P. J., 1991, U-Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska: Canadian Journal of Earth Sciences, v. 28, p. 1285–1300. Johnston, S. T., and Erdmer, P., 1995, Magmatic flow and emplacement foliations in the Early Jurassic Aishihik batholith, southwest Yukon: Implications for northern Stikinia, in Miller, D. M., and Busby, C., eds., Jurassic magmatism and tectonics of the North American Cordillera: Geological Society of America Special Paper 299, p. 65–82. Johnston, S. T., and Timmerman, J. R., 1994a, Geology of the Aishihik Lake and Hopkins Lake map areas (115 H/6,7), southwestern Yukon, in Yukon Exploration and Geology, 1993: Yukon, Indian and Northern Affairs Canada, Exploration and Geological Services Division, p. 93–110. Johnston, S. T., and Timmerman, J. R., 1994b, Geological map of the Aishihik Lake area, southwest Yukon (1 1511/6 E&W): Yukon, Indian and Northern Affairs Canada, Exploration and Geological Services Division, Open File 1994-1(g), scale 1:50 000. Johnston, S. T., and Timmerman, J. R., 1994c, Geological map of the Hopkins Lake area, southwest Yukon (11511/7 E&W): Yukon, Indian and Northern Affairs Canada, Exploration and Geological Services Division, Open File 1994-2(g), scale 1:50 000. Johnston, S. T., Mortensen, J. K., and Erdmer, P., 1996, Igneous and metaigneous age constraints on the Aishihik metamorphic suite, southwest Yukon: Canadian Journal of Earth Sciences, v. 33, p. 1543–1555. Johnston, S. T., Mihalynuk, M. G., Brew, D. A., Hart, C. J. R., Erdmer, P., and Gehrels, G. E., 1999, Paleozoic and Mesozoic rocks of Stikinia exposed in northwestern British Columbia: Implications for correlations in the northern Cordillera: Comment: Geological Society of America Bulletin, v. 111, p. 1103–1104. Mihalynuk, M. G., Mountjoy, K. J., Currie, L. D., Lofihouse, D. L., and Winder, N., 1990, Geology and geochemistry of the Edgar Lake and Fantail Lake map area (104M/8,9E): British Columbia Ministry of Energy, Mines and Petroleum Resources, Open-File Map 1990-4, scale 1:50 000.
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