Longevity of a small shield volcano revealed by crypto-tephra studies (Rangitoto volcano, New Zealand): Change in eruptive behavior of a basaltic field

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• 作者：Phil Shane^a ; ^{pa.shane@auckland.ac.nz} ; Maria Gehrels^b ; Aleksandra Zawalna-Geer^a ; Paul Augustinus^a ; Jan Lindsay^a ; Isabelle Chaillou^a
• 关键词：Shield ; Monogenetic ; Basaltic volcano ; Crypto-tephra ; Auckland Volcanic Field
• 刊名：Journal of Volcanology and Geothermal Research
• 出版年：2013
• 出版时间：1 May, 2013
• 年：2013
• 卷：257
• 期：Complete
• 页码：174-183
• 全文大小：644 K

文摘

The life-span of small volcanoes in terrestrial basaltic fields, commonly considered ¡®monogenetic¡¯, can be difficult to assess due to a paucity of datable materials capable of providing a 10²-10³-year age resolution. We have used microscopic tephra layers (crypto-tephra) in lake sediments to determine the longevity of Rangitoto volcano, a small shield that represents the most recent volcanism in the Auckland Volcanic Field (AVF), New Zealand. Previous studies suggested construction in a relatively short interval at ~ 550-500 cal yrs BP. In contrast, the tephra record shows evidence of intermittent activity from 1498 ¡À 140 to (at least) 504 ¡À 6 cal yrs BP, a longevity of ~ 1000 years. Rangitoto volcano is thought to represent about half the magma erupted in the 250-ka-history of AVF. Thus, the AVF has experienced a dramatic shift to prolonged and voluminous central-vent volcanism in its most recent history. This demonstrates the difficulty in determining time-erupted volume relationships in such fields. Previous AVF hazard-risk modeling based on isolated, short-lived (< 1 year) phenomena at sites that have not experienced activity needs to be revisited in light of the new Rangitoto chronology.