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Siberian Traps Volcaniclastic Rocks and the Role of Magma-Water Interactions Siberian Traps Volcaniclastic Rocks and the Role of Magma-Water Interactions

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Siberian Traps Volcaniclastic Rocks and the Role of Magma-Water Interactions Siberian Traps Volcaniclastic Rocks and the Role of Magma-Water Interactions Siberian Traps volcaniclastic rocks and the role of magma-water interactions Siberian Traps volcaniclastic rocks and the role of magma-water interactions Benjamin A. Black1,†, Benjamin P. Weiss2,†, Linda T. Elkins-Tanton3,†, Roman V. Veselovskiy4,5,†, and Anton Latyshev4,5,† 1Department of Earth and Planetary Science, University of California, Berkeley, California 94720, USA 2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 3School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287, USA 4Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, 123995 Moscow, Russia 5Faculty of Geology, Lomonosov Moscow State University, 119991 Moscow, Russia ABSTRACT et al., 2000; Fedorenko and Czamanske, 1997). et al., 2014; Self et al., 1997; Thordarson and The total volume of mafic volcaniclastic mate- Self, 1998). Similarly, the historic Laki fissure The Siberian Traps are one of the largest rial has been estimated at >200,000 km3 (Ross eruption in Iceland was characterized by epi- known continental flood basalt provinces and et al., 2005), or >5% of the total volume of the sodic explosive pulses accompanied by ash fall may be causally related to the end-Permian Siberian Traps (Malich et al., 1974; Reichow and often followed by a pulse of lava emplace- mass extinction. In some areas, a large frac- et al., 2009). ment (Thordarson et al., 2003; Thordarson and tion of the Siberian Traps vol canic sequence The eruption of the Siberian Traps over- Self, 1993). In a further example that may be consists of mafic volcaniclastic rocks. Here, laps within geochronologic uncertainty with particularly relevant to the genesis of Siberian we synthesize paleomagnetic, petrographic, the catastrophic end-Permian mass extinction Traps mafic volcaniclastic rocks, similar rocks and field data to assess the likely origins of (Kamo et al., 2003; Reichow et al., 2009; Bur- in the Transantarctic Mountains associated with these volcaniclastic rocks and their signifi- gess et al., 2014). Consequently, Siberian Traps the Jurassic Ferrar large igneous province have cance for the overall environmental impact magmatism has been widely invoked as a direct been interpreted as the products of an extraordi- of the eruptions. We argue that magma- or indirect trigger for the extinction, which narily large phreatomagmatic vent complex in water interactions, including both lava-water began at 251.941 ± 0.037 Ma and lasted 60 ± the Coombs Hills (McClintock and White, inter actions and phreatomagmatic explo- 48 k.y. (Burgess et al., 2014). However, the pre- 2006; White and McClintock, 2001; Ross and sions in vents, were important components cise causal mechanisms linking magmatism to White, 2006). Volcaniclastic rocks from some of Siberian Traps magmatism. Phreato- extinction remain poorly understood. Carbon Siberian localities distinctly resemble descrip- magmatic episodes may have generated tall release from the Siberian Traps has been cited tions from the Coombs Hills and may represent water-rich eruption columns, simultaneously to explain global warming across the Permian- periods of similar phreatomagmatic activity promoting removal of highly soluble volcanic Triassic boundary (Joachimski et al., 2012; Sun during the early phases of eruption of the Sibe- gases such as HCl and potentially delivering et al., 2012); the climate effects of volcanic CO2 rian Traps. additional sulfur to the upper atmosphere. do not depend on injection altitude (Williams The extent and style of explosive volcanism et al., 1992; Wignall, 2001). While the enor- during the emplacement of the Siberian Traps INTRODUCTION mous volume and rich volatile budget of the could have far-reaching consequences. If a Siberian Traps could also produce large fluxes large fraction of the mafic volcaniclastic rocks Volcaniclastic rocks within the Siberian Traps of sulfur and halogen gases (Black et al., 2012, were originally fragmented through explosive large igneous province (Ross et al., 2005) are 2014a), explosive delivery of those gases to the processes, they could represent one of the widely recognized but poorly understood and stratosphere is a prerequisite for lasting global largest mafic pyroclastic assemblages known documented. Detailed accounts of these volcani- environmental effects (e.g., White, 2002; Wig- in the rock record. Perhaps more importantly, clastic rocks vary considerably. The thickness of nall, 2001; Black et al., 2012). the type and intensity of explosive activity volcaniclastic material ranges from intercalated Recent work suggests that flood basalt vol- influence plume heights and the fate of vol- layers less than a meter thick on the Putorana canism may span the spectrum from effusive to canic gases. Plateau (Büchl and Gier, 2003) to hundreds of explosive. During episodes of particularly high The nomenclature of fragmented volcanic meters near the base of the volcanic sections mass flux, fire fountaining may result in erup- rocks is complex and occasionally contradictory. in Angara (Naumov and Ankudimova, 1995) tion columns tall enough to breach the high-lati- Throughout this article, we follow the nomen- and in the Maymecha-Kotuy area (Fedorenko tude tropopause (Glaze et al., 2015). Proximal clature of White and Houghton (2006). Among scoria falls, clastogenic lava flows, and welded volcaniclastic rocks the terms tuff, lapilli tuff, †E-mails: bblack@ berkeley .edu, bpweiss@ mit .edu, spatter near the Roza vent system of the 16 Ma tuff breccia, and breccia refer to grain size in ltelkins@ asu .edu, roman .veselovskiy@ ya .ru, anton Columbia River flood basalts in Washington ascending order, from ash to lapilli to blocks .latyshev@ gmail .com. denote episodes of pyroclastic activity (Brown and bombs. Volcaniclastic rocks are lithified GSA Bulletin; September/October 2015; v. 127; no. 9/10; p. 1437–1452; doi: 10.1130/B31108.1; 8 figures; 2 tables; Data Repository item 2015161; published online 30 April 2015. For permission to copy, contact [email protected] Geological Society of America Bulletin, v. 127, no. 9/10 1437 © 2015 Geological Society of America Black et al. deposits of fragments produced and/or trans- Druitt, 1989; McClelland et al., 2004; Paterson METHODS AND GEOLOGIC ported during the course of a volcanic eruption, et al., 2010). The emplacement temperatures BACKGROUND including everything from fallout to pyroclastic of phreatomagmatic pyroclastic density cur- density current deposits to fluvially transported rents are expected to be slightly cooler due to Field work is challenging in north-central syneruptive volcanic materials (White and incorporation of external water (Koyaguchi and Siberia. Siberian Traps sections are exposed pri- Houghton, 2006). In contrast, epiclastic depos- Woods, 1996; McClelland et al., 2004) and span marily along river valleys, making inter regional its include the transported weathering products a range from ~100 °C to >300 °C (Cioni et al., correlations difficult. Our sample names reflect of volcanic rocks that have been reshaped and 2004; Porreca et al., 2008). the locality of the sample, followed by the resized relative to the original volcanic frag- In this paper, we classify the Siberian Traps year of collection, followed by the section and ments (White and Houghton, 2006). volcaniclastic rocks into six preliminary litho- sample number. For example, sample K08–11.6 Emplacement temperatures should differ facies. Among these lithofacies, the massive was collected in 2008 on the Kotuy River, from depending on the origins of volcaniclastic rocks. rocks are the most difficult to interpret on the section number 11. As shown in Figure 1A, we Epiclastic rocks should be emplaced at ambi- basis of textural features alone. We apply paleo- visited volcaniclastic sections on the Kotuy (K), ent surface temperatures. Lahars can emplace magnetic measurements to help distinguish Maymecha (M), Angara (A), and Nizhnyaya warmer material, but temperatures will none- pyroclastic rocks emplaced at high temperatures Tunguska (NT) rivers, as well as at Noril’sk theless be less than 100 °C (e.g., Pierson et al., from other fragmental rocks. We find paleomag- (N), in the summers of 2006, 2008, 2009, 2010, 1996). In contrast, the emplacement tempera- netic and volcanological evidence for a range of and 2012. Table 1 contains a summary of our tures of pyroclastic rocks can reach near-mag- magma-water interactions and occasional pyro- lithofacies classifications and interpretations, matic temperatures. Emplacement temperatures clastic episodes. The extent to which such erup- and Table 2 contains descriptions of all samples of pyroclastic density currents with little exter- tions increased global environmental stresses discussed in this paper. To allow labeling of nal water should significantly exceed 100 °C, depends on the frequency with which eruption individual samples in Figure 2, we have cre- ranging up to >580 °C (e.g., McClelland and columns reached the stratosphere. ated alphabetical sample signifiers that are also 85°E 90° 95° 100° 105° 110° 85°E 90 95° 100° 105° 110° 71°N 71°N Noril'sk **Kotuy Ma*ymecha Putorana Plateau 67° Severnaya * 67° Nizhnyaya Tunguska * Present-day Siberian Traps 62° 62° Lavas Volcaniclastic rocks 1700 m Intrusives enisey Y m m 1700 2000 Section shown in Fig. 2 Angara 57° * Paleomag samples 57° * Field area Krasnoyarsk Ust-Ilimsk 1700 m Thickness of Cambrian Late Permian paleogeography 2000 sedimentary rocks
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