Origin of some bedded welded tuffs |
| |
| Authors: | R J Suthren H Furnes |
| |
| Institution: | 1. Geologisk Institutt, Avd. A, Allégt. 41, 5014, Bergen, Norway
|
| |
| Abstract: | Well defined, laterally continuous welded tuff beds from <1 cm to 2 m thick are more common than has previously been recognized. Examples ranging in composition from rhyolitic to basaltic are described from Ordovician volcanic areas in Britain and Norway, and from the Miocene of the Canary Islands. Bedded welded tuffs are most common in areas of alkaline and peralkaline acidic pyroclastics. They generally occur within successions of massive, welded ash-flow tuff, or within non-welded air-fall tuff successions. Sequences consisting entirely of bedded welded tuff range from <1 m up to 75 m thick. Bedded welded tuffs are thought to originate in three ways. Poorly sorted, thick-bedded welded tuffs are interpreted as the deposits of pyroclastic flows, in which case the beds represent either individual flows units or the layers within flow units. Better sorted, thin-bedded welded tuffs are thought to be of air-fall origin. Thirdly, welding may be produced by the effects of an external heat source on non-welded bedded tuffs. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
