| Autor: |
T.J. Worthington, Peter Stoffers, Roger Hekinian, Richard Mühe |
| Rok vydání: |
2008 |
| Předmět: |
|
| Zdroj: |
Journal of Volcanology and Geothermal Research. 176:571-582 |
| ISSN: |
0377-0273 |
| DOI: |
10.1016/j.jvolgeores.2008.05.007 |
| Popis: |
A submersible dive conducted on Volcano #1 located near 21 degrees 09'S-175 degrees 45'W on the Tonga Arc showed that the volcanic edifice with a caldera floor area of 30 km(2) located at and 450 m deep (b.s.l.=below sea level) was constructed recently during episodic volcanism. The sequential volcanic events are recorded along a faulted terrain formed in response to the collapse of the caldera wall. The post-caldera events are marked by occasional eruptions that have built scoriaceous cones associated with low-temperature hydrothermal venting and localized small-scale collapse features. The stratigraphy of the caldera wall indicates that the volcano was built by explosive volcanism alternating with quieter eruptive events. The repeated, violent explosive events formed 8 m in diameter) conduits and extruded onto the sea floor. In addition, massive lava flows forming sill-like complexes were observed underneath and near the giant radial-jointed columnar flows. Also, an intermittent quiet type of eruption produced vesicular lava flows, which are interbedded within the pyroclastic layered deposits. The massive and vesicular lavas consist of andesites and dacites with Ca-depleted (pigeonite) and Ca-enriched (salite) pyroxene, and intermediate (andesine-labradorite) to calcic (bytownite) plagioclase. They are depleted in total alkalis (Na2O+K2O |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
|
Full Text from ScienceDirect