Stress-induced comenditic trachyte effusion triggered by trachybasalt intrusion: multidisciplinary study of the AD 1761 eruption at Terceira Island (Azores)

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• 作者：A. Pimentel ; V. Zanon ; L. V. de Groot ; A. Hipólito ; A. Di Chiara…
• 关键词：Bimodal volcanism ; Paleomagnetic dating ; Stress changes ; Fissure zone ; Dyke intrusion ; Terceira (Azores)
• 刊名：Bulletin of Volcanology
• 出版年：2016
• 出版时间：March 2016
• 年：2016
• 卷：78
• 期：3
• 全文大小：15,591 KB
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• 作者单位：A. Pimentel (1) (2)
  V. Zanon (2) (3)
  L. V. de Groot (4)
  A. Hipólito (2)
  A. Di Chiara (5)
  S. Self (6)
  
  1. Centro de Informação e Vigilância Sismovulcânica dos Açores, 9501-801, Ponta Delgada, Azores, Portugal
  2. Centro de Vulcanologia e Avaliação de Riscos Geológicos, University of the Azores, 9501-801, Ponta Delgada, Azores, Portugal
  3. Institut de Physique du Globe de Paris, 1, Rue Jussieu, 75005, Paris, France
  4. Paleomagnetic Laboratory Fort Hoofddijk, Department of Earth Sciences, Utrecht University, 3584 CD, Utrecht, The Netherlands
  5. School of Geography, Earth and Environment, Plymouth University, PL4 2NJ, Plymouth, UK
  6. Department of Earth and Planetary Science, University of California, Berkeley, CA, 94720-9980, USA
  
• 刊物主题：Geology; Geophysics/Geodesy; Mineralogy; Sedimentology;
• 出版者：Springer Berlin Heidelberg
• ISSN：1432-0819

文摘

The AD 1761 eruption on Terceira was the only historical subaerial event on the island and one of the last recorded in the Azores. The eruption occurred along the fissure zone that crosses the island and produced a trachybasalt lava flow and scoria cones. Small comenditic trachyte lava domes (known as Mistérios Negros) were also thought by some to have formed simultaneously on the eastern flank of Santa Bárbara Volcano. Following a multidisciplinary approach, we combined geological mapping, paleomagnetic, petrographic, mineral and whole-rock geochemical and structural analyses to study this eruption. The paleomagnetic dating method compared geomagnetic vectors (directions and intensities) recorded by both the AD 1761 lava flow and Mistérios Negros domes and revealed that the two events were indeed coeval. Based on new data and interpretation of historical records, we have accordingly reconstructed the AD 1761 eruptive dynamics and distinguished three phases: (1) a precursory phase characterized by decreased degassing in the fumarolic field of Pico Alto Volcano and a gradual increase of seismic activity, which marked the intrusion of trachybasalt magma; (2) a first eruptive phase that started with phreatic explosions on the eastern flank of Santa Bárbara Volcano, followed by the inconspicuous effusion of comenditic trachyte (66 wt% SiO₂), forming a WNW-ESE-oriented chain of lava domes; and (3) a second eruptive phase on the central part of the fissure zone, where a Hawaiian to Strombolian-style eruption formed small scoria cones (E-W to ENE-WSW-oriented) and a trachybasalt lava flow (50 wt% SiO₂) which buried 27 houses in Biscoitos village. Petrological analyses show that the two batches of magma were emitted independently without evidence of interaction. We envisage that the dome-forming event was triggered by local stress changes induced by intrusion of the trachybasalt dyke along the fissure zone, which created tensile stress conditions that promoted ascent of comenditic trachyte magma stored beneath Santa Bárbara Volcano.