Geochemistry and magmatic properties of eruption episodes from Haroharo linear vent zone, Okataina Volcanic Centre, New Zealand during the last 10 kyr

Abstract

Post-10 ka rhyolitic eruptions from the Haroharo linear vent zone, Okataina Volcanic Centre, have occurred from several simultaneously active vents spread over 12 km. Two of the three eruption episodes have tapped multiple compositionally distinct homogeneous magma batches. Three magmas totalling~8 km 3 were erupted during the 9.5 ka Rotoma episode. The most evolved Rotoma magma (SiO 2 =76.5-77.9 wt%, Sr=96-112 ppm) erupted from a southeastern vent, and is characterised by a cummingtonite-dominant mineralogy, a temperature of 739±14°C, and f O 2 of NNO+0.52±0.11. The least evolved (SiO 2 =75.0-76.4 wt%, Sr=128-138 ppm, orthopyroxene+ hornblende-dominant) Rotoma magma erupted from several vents, and was hotter (764±18°C) and more reduced (NNO+0.40±0.13). The~11 km 3 Whakatane episode occurred at 5.6 ka and also erupted three magmas, each from a separate vent. The most evolved (SiO 2 = 73.3-76.2 wt%, Sr=88-100 ppm) Whakatane magma erupted from the southwestern (Makatiti) vent and is cummingtonite-dominant, cool (745±11°C), and reduced (NNO+0.34±0.08). The least evolved (SiO 2 =72.8-74.1 wt%, Sr=132-134 ppm) magma was erupted from the northeastern (Pararoa) vent and is characterised by an orthopyroxene+ hornblende-dominant mineralogy, temperature of 764±18°C, and f O 2 of NNO+0.40±0.13. Compositionally intermediate magmas were erupted during the Rotoma and Whakatane episodes are likely to be hybrids. A single~13 km 3 magma erupted during the intervening 8.1 ka Mamaku episode was relatively homogeneous in composition (SiO 2 =76.1-76.8 wt%, Sr= 104-112 ppm), temperature (736±18°C), and oxygen fugacity (NNO+0.19±0.12). Some of the vents tapped a single magma while others tapped several. Deposit stratigraphy suggests that the eruptions alternated between magmas, which were often simultaneously erupted from separate vents. Both effusive and explosive activity alternated, but was predominantly effusive (>75% erupted as lava domes and flows). The plumbing systems which fed the vents are inferred to be complex, with magma experiencing different conditions in the conduits. As the eruption of several magmas was essentially concurrent, the episodes were likely triggered by a common event such as magmatic intrusion or seismic disturbance.

Degassing of the H2O-rich rhyolites of the Okataina Volcanic Center, Taupo Volcanic Zone, New Zealand

“…The OVC eruptions are geochemically complex; most eruptions involved multiple batches of rhyolite magma, and some involved injection of basaltic magma (e.g., Nairn et al, 2004;Schmitz and Smith, 2004;Smith et al, 2004Smith et al, , 2006Shane et al, 2007Shane et al, , 2008aShane et al, , 2008bSaunders et al, 2010). Our melt inclusion and pumice glass major and trace element data reveal variations in melt composition ( Fig.…”

“…The TVZ rhyolites have been the subject of many petrological and geochemical studies (e.g., Nairn et al, 2004;Schmitz and Smith, 2004;Smith et al, 2004Smith et al, , 2006Wilson et al, 2006;Shane et al, 2007Shane et al, , 2008aShane et al, , 2008b; however, few have focused on the volatile contents and degassing of the melts, which have a great infl uence on eruption style and volcanic hazards. Here we constrain the preeruptive volatile contents (H 2 O, Cl, CO 2 ) and degassing behavior of rhyolitic magmas erupted from the Okataina Volcanic Center (OVC), in the northern end of the central TVZ.…”

Tephrochronology and its application: A review

“…As well as providing isochrons for palaeoenvironmental research, tephras provide a comprehensive record or dossier of explosive volcanism and recurrence rates in the Quaternary or earlier and can therefore be used to establish time-space relationships of volcanism and insight into petrogenesis (e.g., Kohn and Topping, 1978;Wilson and Hildreth, 1997;Nakagawa et al, 1999;Smith et al, 2002Smith et al, , 2005Smith et al, , 2006Óladóttir et al, 2008;Turner et al, 2008b), and for volcanic hazard prediction and risk management (e.g., Shane and Hoverd, 2002;Smith, 2004, 2010;Jenkins et al, 2007;Turner et al, 2008aTurner et al, , 2009Lindsay et al, 2009). Tephra sequences preserved in peat or lake or marine sediments, or in ice, at medial or distal sites paradoxically may provide records potentially more comprehensive, or more assessable, than those proximal to volcanoes where the stratigraphy can be compromised by deep burial or erosion or other factors Alloway et al, 2005;Narcisi et al, 2005Narcisi et al, , 2010Lowe et al, 2007;Allan et al, 2008;Paterne et al, 2008;Turner et al, 2008b;Davies et al, 2010b).…”

Stress Field Control during Large Caldera-Forming Eruptions

“…Dykes feeding these eruptions have to be long enough and remain open over much of their length throughout the entire explosive activity. The mechanics of feeding explosive silicic ignimbrite eruptions through a linear fissure (Korringa, 1973;Aguirre-Díaz and Labarthe-Hernañdez, 2003) or from multiple vents along a fissure (Suzuki-Kamata et al, 1993;Wilson, 2001;Smith et al, 2005Smith et al, , 2006Folch and Martí, 2009) are largely unexplored.…”

“…In order to erupt, magmas stored in relatively shallow chambers (3-8 km; e.g., Smith et al, 2005Smith et al, , 2006Matthews et al, 2011;Chesner, 2012) normally have to overcome critical overpressures up to ∼50 MPa for nucleating new fractures and up to ∼10 MPa for propagating magma up to the surface (Rubin, 1995;Jellinek and De Paolo, 2003). Whereas for small magma chambers such overpressures can be easily achieved, for very large chamber volumes it is more problematic to reach such overpressures, and dyke formation and propagation are, as a consequence, inhibited (Jellinek and De Paolo, 2003).…”