The Mineralogical and Geochemical Properties of Near-Crater Tephra from Erebus Volcano, Antarctica Based on the Ejecta o
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Mineralogical and Geochemical Properties of Near-Crater Tephra from Erebus Volcano, Antarctica Based on the Ejecta of the 2000 Eruption V. I. Silaeva, *, G. A. Karpovb, **, V. N. Filippova, B. A. Makeeva, S. N. Shaninaa, A. F. Khazova, and K. V. Tarasovb a
Institute of Geology, Komi Science Center, Ural Branch, Russian Academy of Sciences, ul. Pervomaiskaya, 54, Syktyvkar, 167982 Russia b Institute of Volcanology and Seismology, Far East Branch, Russian Academy of Sciences, bulvar Piipa, 9, Petropavlovsk-Kamchatsky, 683006 Russia *e-mail: [email protected] **e-mail: [email protected] Received November 12, 2019; revised February 5, 2020; accepted March 31, 2020
Abstract—Multidisciplinary petrologic, mineralogical, and geochemical studies have been carried out for the first time concerning near-crater tephra from the world-largest intraplate stratovolcano (Erebus). The volcano is characterized by a unique basanite–phonolite effusive lineage. We studied the grain-size and chemical compositions of the tephra and the concentration of trace elements in it, the mineral phase composition, lithogenic gases encapsulated in the tephra, an atomically dispersed carbonaceous substance, and the isotope composition of carbon in it. We came to the conclusion that the tephra studied here can be treated as an explosive analogue of anorthoclase lava phonolites that terminate the continuous series of magmatic differentiates known as the Erebus lineage. Keywords: Erebus, Erebus magmatic lineage, tephra, anorthoclase, fluochlorohydroxylapatite, monazite, barite, magnetite, native metals, chloride solid solutions DOI: 10.1134/S0742046320040053
INTRODUCTION Erebus (Fig. 1) is an active intraplate stratovolcano (standing on the volcanic Ross Island, 77°32′ S, 167°17′ E) on a thin (17–25 km) continental crust. It is confined to the edge of the West Antarctic Rift System (Kyle et al., 1992; Encyclopedia …, 1999). The volcano is 1.3 Ma old, with its recorded activity being known for the past 172 000 years (Late Pleistocene to the present). That period saw numerous, mostly effusive, eruptions, with the activity peaking in the time spans 95 ± 9… 76 ± 4 and 27 ± 3 … 21 ± 4 ka (Harpel et al., 2004; Esser et al., 2004; Kelly et al., 2008]. The associated lavas have a composition to make a nearly continuous sequence of magmatic differentiation (the so-called Erebus lineage) in the following sequence: basanites (olivine tephrite) → phonotephrite → tephrophonolite → anorthoclase phonolite (Iacovino et al., 2013; Iverson et al., 2014). The phonolite fraction in the sequence is 20–30%. The rock forming minerals of the lavas were found to be olivine ranging between Fa55–88 in basanite and Fa43–51 in the phonotephrite; aegirine-augite; Mn–Mg–Al–Cr-bearing ulvite-magnetite; hexagonal pyrrhotine of the Fe0.96–1S
composition concentrating in interstitial magnetite; feldspar ranging from orthoclase-albite-anorthite in basanites to anorthite-orthoclase-albite in phonolites; nepheline, whose concentration increases in the direction from basanite to phonote
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