Pumice embedded in vitrified volcanic volcanic tuff
Pumice (whitish) embedded in vitrophyre. Looks like the embedded pumice has been subjected to pressure from the overlying ash and also shearing from the flowing solidifying vitrophyre resulting in cylindrical inclusions with tapered ends, all oriented in the same direction (perpendicular to the direction of shearing). It is just like a ball of cookie dough being rolled out with the pressure of a hand. Sample is from a float in the Lauder Pond area of Brian Head Utah. Sample is either from the Isom formation (26Ma) or the Leach Creek formation (24.05Ma). Size of specimen is 15cm top to bottom.
Left panel: Oblique view with cross section turned about 45° to the left, depicting the flat side (left) and the cross section of the specimen. The left side shows round wholes, some empty, some filled with pumice (whitish), the cross section shows the cylindrical deformation (most cavities have the pumice eroded out).
Center panel: Cross section of the specimen showing the cylindrical pumice cavities in the same parallel orientation, with pumice is filling or partially filling some of the cavities.
Right panel: Back side of the specimen, only small round cavities are visible, mostly are filled with pumice.This side has been misused to label the specimen (it really is indelible).
Small crystals appear throughout the specimen and are visible by their light reflection.
Tantalizing is the question on how the pumice got into this ash flow, either taking a ride with the pyroclastic flow, or being eject into the stratosphere and dropping down into the moving ash flow?? Likely the former.
These ash deposits are about 50-60 miles away from the site of eruption at the Utah-Nevada border(Caliente-Indian Peak ignimbrites), taking into account the Basin and Range expansion and the dislocation as part of the Markagunt landslide that transported the ash layers at least 20 miles to the south.
Pumice embedded in vitrified volcanic volcanic tuff
Pumice (whitish) embedded in vitrophyre. Looks like the embedded pumice has been subjected to pressure from the overlying ash and also shearing from the flowing solidifying vitrophyre resulting in cylindrical inclusions with tapered ends, all oriented in the same direction (perpendicular to the direction of shearing). It is just like a ball of cookie dough being rolled out with the pressure of a hand. Sample is from a float in the Lauder Pond area of Brian Head Utah. Sample is either from the Isom formation (26Ma) or the Leach Creek formation (24.05Ma). Size of specimen is 15cm top to bottom.
Left panel: Oblique view with cross section turned about 45° to the left, depicting the flat side (left) and the cross section of the specimen. The left side shows round wholes, some empty, some filled with pumice (whitish), the cross section shows the cylindrical deformation (most cavities have the pumice eroded out).
Center panel: Cross section of the specimen showing the cylindrical pumice cavities in the same parallel orientation, with pumice is filling or partially filling some of the cavities.
Right panel: Back side of the specimen, only small round cavities are visible, mostly are filled with pumice.This side has been misused to label the specimen (it really is indelible).
Small crystals appear throughout the specimen and are visible by their light reflection.
Tantalizing is the question on how the pumice got into this ash flow, either taking a ride with the pyroclastic flow, or being eject into the stratosphere and dropping down into the moving ash flow?? Likely the former.
These ash deposits are about 50-60 miles away from the site of eruption at the Utah-Nevada border(Caliente-Indian Peak ignimbrites), taking into account the Basin and Range expansion and the dislocation as part of the Markagunt landslide that transported the ash layers at least 20 miles to the south.