Lyell Collection
Journal of the Geological Society
Lyell Centre  |   Lyell Collection  |   Subscriptions   |   Geological Society  |   Email alerts  |   Online bookshop  |   Help

Keywords:
Author:
Advanced search>>
This Article
Right arrow Figures Only
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (16)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Smith, V. C.
Right arrow Articles by Nairn, I. A.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation
Journal of the Geological Society; 2004; v. 161; issue.5; p. 757-772;
DOI: 10.1144/0016-764903-092
© 2004 Geological Society of London

Original Article

Reactivation of a rhyolitic magma body by new rhyolitic intrusion before the 15.8 ka Rotorua eruptive episode: implications for magma storage in the Okataina Volcanic Centre, New Zealand

Victoria C. Smith1, Phil Shane1 & Ian A. Nairn2

1 1Department of Geology, University of Auckland, Private Bag 92019, Auckland, New Zealand (e-mail: v.smith@auckland.ac.nz)
2 245 Summit Road, RD5, Rotorua, New Zealand

The 15.8 ka Rotorua rhyolite eruptive episode from the Okataina Volcanic Centre comprises a plinian pumice fall deposit followed by the extrusion of two rhyolitic lava domes or flows and their associated block-and-ash flows, with a total volume >1 km3 (dense rock equivalent). Variations in mineralogy, whole-rock, glass and mineral chemistry, and calculated magmatic properties suggest that two distinct rhyolitic magmas were sequentially tapped during the eruption. The first magma erupted (T1) is characterized by low SiO2 (c. 76.5 wt% in glass), calcic feldspars (An44), magnesian hornblendes (MgO c. 14.45 wt%), clinopyroxene, and high temperatures (c. 835 °C) and fO2 (1.8–2.1 {Delta}FMQ (where FMQ is the fayalite–magnetite–quartz buffer)). The second magma (T2) was more evolved and is characterized by higher SiO2 (c. 77.4 wt% in glass), Na-rich feldspars (An24), less magnesian hornblendes (MgO c. 11.8 wt%), biotite, and low temperatures (c. 750 °C) and fO2 (0.65–1.1 {Delta}FMQ). Both magmas are homogeneous, but evidence for some magma mingling indicates that they were in contact during eruption. However, there was only a minor degree of hybridization, perhaps reflecting the contrasting temperatures and viscosities of the two magmas. The crystal-rich, poorly vesicular nature of the T2 ejecta indicates that it originated from a cooling, high-level magma chamber that was reactivated by intrusion of hotter, volatile-rich T1 magma. The ponding of rhyolite magmas at shallow depth and their subsequent reactivation by later rhyolitic intrusion may be an important process in the compositional evolution and eruption dynamics of many Okataina Volcanic Centre rhyolite magma bodies.


Keywords: Taupo Volcanic Zone, Okataina, rhyolite, intrusion, magmas.




This article has been cited by other articles:


Home page
 J PetrologyHome page
G. Girard and J. Stix
Magma Recharge and Crystal Mush Rejuvenation Associated with Early Post-collapse Upper Basin Member Rhyolites, Yellowstone Caldera, Wyoming
J. Petrology, 2009; egp070v1.
[Abstract] [Full Text] [PDF]

Home page
 Mineral MagHome page
R. Macdonald and B. Baginski
The central Kenya peralkaline province: a unique assemblage of magmatic systems
Mineralogical Magazine, 2009; 73: 1 - 16.
[Abstract] [Full Text] [PDF]

Home page
 J PetrologyHome page
C. J. N. Wilson and B. L. A. Charlier
Rapid Rates of Magma Generation at Contemporaneous Magma Systems, Taupo Volcano, New Zealand: Insights from U-Th Model-age Spectra in Zircons
J. Petrology, 2009; egp023v1.
[Abstract] [Full Text] [PDF]

Home page
 J PetrologyHome page
C. D. Deering, J. W. Cole, and T. A. Vogel
A Rhyolite Compositional Continuum Governed by Lower Crustal Source Conditions in the Taupo Volcanic Zone, New Zealand
J. Petrology, 2008; egn067v1.
[Abstract] [Full Text] [PDF]

Home page
 J PetrologyHome page
R. Macdonald, H. E. Belkin, J. G. Fitton, N. W. Rogers, K. Nejbert, A. G. Tindle, and A. S. Marshall
The Roles of Fractional Crystallization, Magma Mixing, Crystal Mush Remobilization and Volatile-Melt Interactions in the Genesis of a Young Basalt-Peralkaline Rhyolite Suite, the Greater Olkaria Volcanic Complex, Kenya Rift Valley
J. Petrology, 2008; 49: 1515 - 1547.
[Abstract] [Full Text] [PDF]