OREGON STATE UNIVERSITY

Stop 3: Dacite Disks

Dacite Disks  22°10'32.27"S  67°42'11.48"W

Disks are flattened like pancakes

 

One of the most unusual features about the Laguna Colorada ignimbrite shield is a layer of dacite disks found associated with the ignimbrite.  These disks are crystalline and have been flattened, forming round, pancake-like shapes.  Their emplacement mechanism is unknown.  In the APVC these disks appear to be unique to Laguna Colorada.  They are found in abundance on the western and southeastern sides of the ignimbrite but are not found near welded material.  The best places to observe these disks are off the northern and western roads at 22°10'32.27"S  67°42'11.48"W and  22°16'59.23"S  67°43'17.18"W.

 

Disks litter the ground in many places

 

 

 

 

Wind scours away the matrix surrounding the ash, leaving broad surfaces littered with disks.

 

 

 

 

 

Disks outcropping in exposure

 

 

 

 

 

Many of the disks are up to 1/2 meter long.  All are flattened to some extent, although aspect ratios can vary in an outcrop such as this.  Many of the disks appear to have flowed like viscous lavas during emplacement.  In outcrops, the disks are encased in a fine ash. 

 

 

 

 

 

 

 

Disks make good frisbees

 

 

 

 

The disks can even be used as frisbees, although we wouldn't recommend a game of ultimate at this elevation!