Documentation of a Holocene Volcanic Cone in the Tuya-Teslin Volcanic Field, Northern British Columbia

K. Simpson,B.Edwards,andWetherell Columbia northern British field, volcanic Tuya-Teslin the cone in volcanic Holocene a of Documentation 2006 2006-A1 CURRENT RESEARCH C Resources Natural anada Geological SurveyofCanada C naturelles Ressources anada

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Authors’ addresses K. Simpson ([email protected]) Geological Survey of Canada 605 Robson Street, Suite 101, Vancouver, British Columbia V6B 5J3

B.Edwards ([email protected]) K. Wetherell ([email protected]) Department of Geology, Dickinson College, P.O. Box 1773, Carlisle, Pennsylvania 17013 U.S.A.

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K. Simpson, B. Edwards, and K. Wetherell

Simpson, K., Edwards, B., and Wetherell, K., 2006: Documentation of a Holocene volcanic cone in the Tuya-Teslin volcanic field, northern British Columbia; Geological Survey of Canada, Current Research 2006-A1, 7 p.

Abstract: A previously unnamed Holocene volcanic cone is herein informally named Gabrielse cone. Gabrielse cone is a subaerial basaltic scoria cone that is one of the few subaerial volcanic features in the Tuya-Teslin area. The cone is approximately 400 m in diameter with a central crater approximately 30 m deep. It consists largely of unconsolidated basaltic scoria some of which show preserved fluidal shapes typical of subaerial bombs. To the northeast the scoria cone appears to be breached and remnants of a lava flow were observed. Mineral compositions as determined by scanning electron microscope–energy dispersive spectometer are consistent with other occurrences of alkali olivine basalts in the area.

Résumé : Un cône volcanique auparavant innommé est ci-après désigné de manière informelle «cône Gabrielse». Le cône Gabrielse est un cône de scories basaltiques subaérien et l’une des rares entités volcaniques subaériennes dans la région de Tuya-Teslin. Il a un diamètre approximatif de 400 m et présente un cratère central d’une profondeur d’environ 30 m. Il se compose en grande partie de scories basaltiques non consolidées, dont certaines présentent des formes d’écoulement caractéristiques de bombes subaériennes. Au nord-est, le cône de scories semble égueulé et on a observé des vestiges d’une coulée de lave. Les compositions minérales telles que déterminées au moyen d’un microscope électronique à balayage muni d’un spectromètre dispersif en énergie sont compatibles avec celles d’autres occurrences de basaltes alcalins à olivine dans la région.

Current Research 2006-A1 1 K. Simpson et al. INTRODUCTION GABRIELSE CONE

Holocene volcanic activity has occurred at a number of Gabrielse (1969) identified an unnamed volcanic cone in volcanic centres in Canada (Fig. 1) including: Fort Selkirk the northern part of the Jennings River 1:125 000 map area. volcanic complex (Volcano Mountain; e.g. Jackson and The cone was described as “a remarkably fresh, clearly Stevens (1992); Trupia and Nicholls (1996)), Hoodoo volca- postglacial volcanic vent” and was mapped as part of the Tuya nic complex (e.g. Edwards and Russell, 2002), Iskut River formation (Gabrielse, 1969, p. 30). The volcanic vent erupted volcanic field (Iskut River lava field, Lava Fork; e.g. through Carboniferous metasedimentary and metavolcanic Hauksdottir et al. (1994)), Nass volcanic field (Tseax cone; rocks of the Oblique Creek Formation (Fig. 2; Gabrielse e.g. Symons (1975); Wuorinen (1978)), Nazko cone (e.g. (1969)). This report of a Holocene volcanic vent prompted Souther et al., 1987), Mount Edziza volcanic complex (e.g. the present authors to visit the cone in August 2003 to make Souther, 1992), Wells Gray–Clearwater volcanic field (e.g. observations and collect samples. The cone is herein named Hickson and Souther, 1984; Hickson, 1986), Mount Meager ‘Gabrielse cone’ after Hu Gabrielse who first identified it. volcanic complex (e.g. Clague et al., 1995), Garibaldi volca- Gabrielse cone is located in the Tuya-Teslin volcanic field nic complex (e.g. Green et al., 1988) and the Tuya-Teslin vol- (Fig. 2; UTM zone 9: 6590072 m N 421835 m E, 1605 m canic field (e.g. Gabrielse, 1969). These volcanic centres a.s.l.). The cone is approximately 400 m in diameter with a represent a diverse range of activity from monogenetic cinder central crater approximately 30 m deep (Fig. 3, 4). It has an cones with associated lava flows to stratovolcanoes and unusually low profile (Fig. 4d) and sits on a side hill near the shield volcanoes. Compositions are predominantly mafic, but base of a glacial valley. The cone consists of unconsolidated, include phonolite (e.g. Hoodoo volcanic complex; Edwards aphyric, basaltic scoria that weathers to a distinctive red et al. (2002)) and dacite (e.g. Mt. Meager volcanic complex; colour (Fig. 4). Clasts range from less than 1 cm to 7 cm and Stasiuk et al. (1996)). clast shapes vary from fluidal, typical of volcanic bombs, to This paper documents the occurrence of a Holocene vol- broken angular shapes. canic vent in the Tuya-Teslin volcanic field reported by To the northeast the crater appears to have been breached Gabrielse (1969). and a basaltic lava flow can be traced for more than 400 m (Fig. 3, 4c). Basalt from the lava flow is olivine- and plagioclase-phyric (<1 cm in long dimension) with rare PREVIOUS WORK IN THE troctolitic (plagiclase+olivine) glomerocrysts (Fig. 5). The TUYA-TESLIN AREA groundmass is fine grained (generally >50 µm) and consists of olivine, plagioclase, clinopyroxene, magnetite, and Previous work in the Tuya-Teslin area includes regional ilmenite. Olivine phenocrysts range between Fo83 and Fo59, mapping by Watson and Mathews (1944) and Gabrielse and olivine in the groundmass range between Fo59 and Fo63. (1969), and detailed stratigraphic analysis of specific volca- Plagioclase phenocrysts range between An60 and An70 and nic centres (Mathews, 1947; Allen et al., 1982; Moore et al., plagioclase in the groundmass range between An45 and 1995; Simpson, 1996; Dixon et al., 2002). Watson and An50. Olivine and plagioclase phenocryst compositions fall Mathews (1944) informally defined the Tuya formation to within the range for porphyritic alkali olivine basalt include basaltic lava, tuff, and agglomerate in the Tuya-Teslin (Fo50-80, An50-70) from the West Tuya lava field (Fig. 2; area. Subsequently, a number of flat-topped, steep-sided Wetherell (2005)). Zoning in olivine and variation between volcanoes within the Tuya formation were interpreted by plagioclase phenocrysts and groundmass is consistent with Mathews (1947) to have formed by eruption of lava into lakes some fractionation at depth and possibly magma storage. thawed through an ice sheet. Mathews (1947) proposed that There is no evidence that Gabrielse cone has been glaci- these subglacial volcanoes be called “tuyas”. Since 1947, the ated, whereas the surrounding terrain has been glaciated. The Tuya formation has been mapped across the Dease Lake, cone is therefore interpreted to have formed postglacially Jennings River, and Cry Lake map areas (Gabrielse, 1969, (<11 000 a). Gabrielse cone and the West Tuya lava field 1998) and includes more than thirty individual volcanic (Wetherell et al., 2005) are the only nonglacial volcanic features of both subaerial and subglacial origin. features in the Tuya-Teslin volcanic field. The term ‘Tuya-Teslin volcanic field’ is used in this paper to describe an area of monogentic volcanic centres of similar age and composition. It includes the ‘tuyas’ around High SUMMARY Tuya and Tuya lakes, the West Tuya lava field (Wetherell et al., 2005), and centres on the Kawdy Plateau (Fig. 2). It does Gabrielse cone is a subaerial basaltic scoria cone in the not include the Level Mountain volcanic complex (Hamilton, Tuya-Teslin volcanic field and is one of the few subaerial vol- 1981) as it is a long-lived volcanic centre that is distinct from canic features in the area. The cone consists of angular to the monogentic centres of the Tuya-Teslin volcanic field. fluidal shaped scoriaceous basalt. A lava flow appears to have breached the northeast side of the cone and can be traced for at

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Figure 1. Distribution of Holocene volcanic centres in British Columbia and Yukon Territory.

Current Research 2006-A1 3 K. Simpson et al. 18 km mbia u ntain u GS RIVER e Creek Formation u N Units ndenberry Batholith Terranes I ya Formation ya esnellia u ya and Parallel Creek and Parallel ya LEGEND u u u T Gl T Batholith Klinkit Batholith Cassiar Batholith Christmas Creek Batholith Obliq Q Cache Creek Dorsey Slide Mo Cassiar NN British Col N Generalized geology Generalized 0 km JE 30' 59°00 15' 130°00 W etherell et al., 2005). W 15' ’ modified from a y u T

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Current Research 2006-A1 4 K. Simpson et al. Figure 3. Stereopair of Gabrielse cone. Scale 1:40 000. NAPL A11373-129 and 130.

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Figure 4. Gabrielse cone. Cone diameter is approximately 400 m. a) View looking towards the north-northeast. b) View looking towards the west. c) View looking towards the northeast. The distinctive red weathering of the volcanic rocks outlines the distribution of the lava flow in the distance. d) View to the west-southwest illustrating the low profile of the cone.

Current Research 2006-A1 5 K. Simpson et al. P15-10 a)a) P15-11 REFERENCES

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015_1 Clague, J.J., Evans, S.G., Rampton, V.N., and Woodsworth, G.J. P15-3 1995: Improved age estimates for White River and Bridge River 015-6 P15-5a 015-2 tephras, western Canada; Canadian Journal of Earth P15-5b 015-9 015-3 015-5 P15-2 Ap-PI Sciences, v. 32, p. 1172–1179. 015-7 Mt5-2 Dixon, J.E., Filiberto, J.R., Moore, J.G., and Hickson, C.J. P15-7 015-4 015-8 Mt5-1 2002: Volatiles in basaltic glasses form a subglacial volcano in Mt5-3 northern British Columbia (Canada): implications for ice sheet thickness and mantle volatiles; in Volcano-ice

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Current Research 2006-A1 7 K. Simpson et al.