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PHREATO-MAGMATIC MAARS: THE ORIGIN OF EXPLOSIVE
BRECCIA PIPES

John A. Wolfe
 

 

 

 

ABSTRACT


Taal, a phreato-magmatic volcano on Luzon Island, Philippines illustrates the origin of maars which are the surface expression of explosive breccia pipes or diatremes. The maar clusters near Mt. Makiling, a solfataric stratovolcano, represent breccia pipe clusters which could be
mineralized in the solfataric stage.

Pebble dikes and intrusive breccias are formed by the explosive emplacement of a "slug" of breccia, blasted out of the pipe along fractures which open at the time of resurgent phreato-magmatic eruption.

Collapse breccia pipes form by the withdrawal of magma from a cupola as a result of loss of head when a nearby cupola explodes into a maar. The collapse pipe may pump and eventually tap a water source and also explode into a maar, then losing all characteristics of collapse.

Another class of diatreme which also forms as a maar is the mantle maar or kimberlite pipe which contains a signfcant percentage of ultra basic fragments in the tephra ring. Being in the youthful stage, it may be difficult to distinguish it from the intrusive-extrusive maars.

 

 

 

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