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Volcanology and Petrology of Mathews Tuya, Northern British Columbia, Canada: Glaciovolcanic Constraints on Interpretations of the 0.730 Ma Cordilleran Paleoclimate

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Volcanology and Petrology of Mathews Tuya, Northern British Columbia, Canada: Glaciovolcanic Constraints on Interpretations of the 0.730 Ma Cordilleran Paleoclimate Bull Volcanol (2011) 73:479–496 DOI 10.1007/s00445-010-0418-z RESEARCH ARTICLE Volcanology and petrology of Mathews Tuya, northern British Columbia, Canada: glaciovolcanic constraints on interpretations of the 0.730 Ma Cordilleran paleoclimate Benjamin R. Edwards & James K. Russell & Kirstie Simpson Received: 12 June 2009 /Accepted: 5 October 2010 /Published online: 11 November 2010 # Springer-Verlag 2010 Abstract Petrological, volcanological and geochronological (e.g., Ash Mountain, South Tuya, Tuya Butte) as well as the data collected at Mathews Tuya together provide constraints on dominant NCVP rock type. Crystallization scenarios calculat- paleoclimate conditions during formation of the edifice. The ed with MELTS account for variations between whole rock and basaltic tuya was produced via Pleistocene glaciovolcanism in glass compositions via low pressure fractionation. The northern British Columbia, Canada, and is located within the presence of olivine microphenocrysts and the absence of Tuya volcanic field (59.195°N/130.434°W), which is part of pyroxene phenocrysts constrain initial crystallization pressures the northern Cordilleran volcanic province (NCVP). The to less than 0.6 GPa. The eruption of Mathews Tuya occurred edifice comprises a variety of lithofacies, including columnar- between 0.718±0.054 Ma and 0.742±0.081 Ma based on jointed lava, pillow lava, massive dikes, and volcaniclastic 40Ar/39Ar geochronology (weighted mean age of 0.730 Ma). rocks. Collectively these deposits record the transition from an The age determinations provide the first firm documentation explosive subaqueous to an effusive subaerial eruption for large (>700 m thick), pre-Fraser/Wisconsin glaciers in environment dominated by Pleistocene ice. As is typical for north-central British Columbia ~0.730 Ma, and correlate in tuyas, the volcaniclastic facies record multiple fragmentation age with glaciovolcanic deposits in Russia (e.g., Komatsu et processes including explosive, quench and mechanical al. Geomorph 88: 352-366, 2007) and with marine isotopic fragmentation. All samples from Mathews Tuya are olivine- evidence for large global ice volumes ~0.730 Ma. plagioclase porphyritic alkali olivine basalts. They are minera- logically and geochemically similar to nearby glaciovolcanic Keywords Mathews . Tuya . Cordilleran . Glaciation . centers from the southeastern part of the Tuya volcanic field Pleistocene . NCVP. AOB Editorial responsibility: M.A. Clynne Introduction Electronic supplementary material The online version of this article (doi:10.1007/s00445-010-0418-z) contains supplementary material, which is available to authorized users. Volcanoes that erupt in glacial environments produce unique features that can be used to constrain paleo-environmental * B. R. Edwards ( ) conditions at the time of eruption. Such glaciovolcanic Department of Earth Sciences, Dickinson College, Carlisle, PA 17013, USA products have been documented worldwide, but are especially e-mail: [email protected] prevalent in Iceland (e.g., Kjartsansson 1943; van Bemmelen and Rutten 1955; Sigvaldason 1968;Jones1969; Tuffen et J. K. Russell al. 2002; Hoskuldsson et al. 2006; Schopka et al. 2006; Volcanology and Petrology Laboratory, Earth & Ocean Sciences, University of British Columbia, Jakobsson and Guðmundsson 2008; Skilling 2009), western Vancouver, BC, Canada North America (e.g., Mathews 1947;HoareandCoonrad 1978; Allen et al. 1982; Moore et al. 1995;Hickson2000; K. Simpson Lescinsky and Fink 2000; Dixon et al. 2002; Edwards et al. Geoscience BC, #440-890 West Pender Street, 2002, 2006, 2009;Kelmanetal.2002; Bacon and Lanphere Vancouver, BC V6C 1J9, Canada 2006), and Antarctica (e.g., Skilling 1994; Smellie and 480 Bull Volcanol (2011) 73:479–496 Skilling 1994; Wilch and McIntosh 2007; Smellie et al. compositions of whole rock and glass samples. Most of the 2008; Smellie 2009). Tuyas, also referred to as ‘table field-based observations were made in July/Aug 1995, with a mountains’ (e.g. Mathews 1947; van Bemmelen and Rutten brief reconnaissance visit in 2009. Secondly, we present a 1955), represent one of two uniquely distinctive glaciovol- model for the physical and chemical evolution of the volcano canic landforms. The term ‘tuya’ was coined 60 years ago by that integrates the observed stratigraphic relationships and W.H. Mathews, based on his landmark work describing the the petrological character of the volcanic rocks. Lastly, we stratigraphy and morphology of basaltic volcanoes in the use new 40Ar/39Ar geochronometry to constrain the regional Tuya-Teslin region of northwestern British Columbia paleoclimatic conditions in the area surrounding Mathews (Mathews 1947). There, he encountered numerous, small, Tuya and, in conjunction with previously published data, to apparently young, volcanic edifices hosting a variety of provide a preliminary view from glaciovolcanic constraints enigmatic features. Most of the volcanoes are basaltic in for the distribution of Pleistocene glaciers in the Canadian composition, are steep-sided and many have “flat” tops. Cordillera. Mathews recognized that these volcanic edifices shared common stratigraphic elements, including: pillow lavas and breccias, massive to bedded deposits of fragmented glassy Geological setting basalt (‘hyaloclastite’), and capping, massive basaltic lava. He proposed the term ‘tuya’ for these volcanoes and The Tuya volcanic field of the northern Cordilleran volcanic interpreted their morphology and attendant volcanic lithofa- province (NCVP) is an extensive area of Neogene to Recent cies as indicative of volcanic eruptions from beneath and alkaline volcanism formed from transtensional stresses con- within Pleistocene ice sheets. He also recognized that the centrated within the western Canadian Cordillera after transition from pillow lava and volcanic breccia to subaerial subduction of the Farallon and Nazca plates (Fig. 1; Edwards lava flows was an intrinsically important marker horizon for and Russell 1999, 2000;Madsenetal.2006). Due to the establishing the minimum thickness of the confining ice, thus spatial and temporal coincidence of NCVP volcanism and providing critical information about paleo-environmental Pleistocene glaciations, including the Cordilleran Ice Sheet conditions extant during the eruptions. Jones (1969)named (CIS), a diverse range of glaciovolcanic landforms and these transitions ‘passage zones’, which have recently been deposits have been documented within the NCVP (e.g., described in detail by Smellie (2006). Allen et al. 1982;Souther1992; Moore et al. 1995;Hickson Relatively few studies subsequent to Mathews (1947) 2000; Dixon et al. 2002; Edwards et al. 2002, 2006,2008). have examined the formation of basaltic tuyas in detail (e. More than 30 individual volcanic centers/deposits are g., Smellie and Skilling 1994; Moore et al. 1995; Werner mapped as part of the Tuya Formation in the Jennings River and Schmincke 1999; Skilling 2009), and even fewer have 1:250,000 map sheet (Fig. 1b; Watson and Mathews 1944; attempted to integrate stratigraphic, petrological, and Gabrielse 1970); at least 20 of those deposits show evidence geochronologic data (Werner and Schmincke 1999). Strati- for glaciovolcanism. Mathews (1947) gave brief descriptions graphic studies of flat-topped volcanoes formed by glacio- of the petrology and volcanology of six tuyas, including volcanism derive mainly from work in Iceland (van what has been informally referred to as ‘Mathews Tuya’. Bemmelen and Rutten 1955; Sigvaldason 1968; Jones Several studies have subsequently been published on the 1969; Werner and Schmincke 1999; Tuffen et al. 2002; volcanology, petrology and geochemistry of the volcanic Skilling 2009), Antarctica (e.g., Smellie and Skilling 1994; centers that form part of the Tuya Formation (Allen et al. Skilling 1994; Smellie et al. 2008), and British Columbia, 1982; Moore et al. 1995; Simpson 1996; Dixon et al. 2002; Canada (e.g., Mathews 1947; Allen et al. 1982; Moore et al. Wetherell et al. 2006; Simpson et al. 2006), but none have 1995; Dixon et al. 2002). Tuyas likely formed in other done more than briefly mention ‘Mathews Tuya’. Work by glacially covered, volcanically active regions of Earth in the Allen et al. (1982) and Moore et al. (1995) gave brief field past (e.g. Russia; Komatsu et al. 2007), and are also and geochemical descriptions of Tuya Butte, Ash Mountain thought to be present on Mars (e.g., Allen 1979; Chapman and South Tuya (Fig. 1c; Table 1). Dixon et al. (2002) et al. 2000); their presence and stratigraphy can be used to presented data on volatile behavior and geochemistry of constrain planetary paleoclimates (e.g., Smellie 2009). Tanzilla Butte, a glaciovolcanic edifice immediately south- Here we present an integrated study of the formation of east of Tuya Lake; they concluded that ice was up 1 km thick Mathews Tuya, which is located in the Tuya volcanic field of at the onset of eruption. Wetherell et al. (2006)andSimpson northern British Columbia (59.195°N/130.434°W; Fig. 1; et al. (2006) documented subaerial components of the Tuya Mathews 1947; Allen et al. 1982; Moore et al. 1995). The Formation, which appear to be less common than glacio- purpose of this paper is threefold. First, we describe the volcanic deposits. geology and petrology of Mathews Tuya, including descrip- Gabrielse (1970) inferred that the area underlying the tions of the critical lithofacies and measurements of chemical Tuya Formation had been affected by regional ice sheets, Bull Volcanol (2011) 73:479–496
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