Stop 3
Flanking the
Volcanic Dome
---Superposition---
Southwest of the Volcanic Dome
(Google Earth)
Stop
3
Green
Valley Tonalite beneath the volcanic unit. The tonalite seen in the road cut is
deeply weathered, coarse grained, it has an orangish hue and round internal
structures in it. The volcanic unit is heavily weathered and may be mixed in
with a paleosol near the contact. Using
the principle of superposition what does this tell you about the
relative ages of the rocks at this location?
Photo 1 Green
Valley Tonalite overlain by the volcanic unit. Photo 2 The volcanic unit
closeup
The
Adit
This
is at the end of Stop 3. Notice the
small opening in the outcrop, this is called an “adit”.
It's an exploratory excavation looking for valuable minerals. It’s common for
prospectors to look for mineralization and ore deposits when warm rocks contact
cooler surfaces. These pictures were taken years ago
and it has since been plugged with cement.
Note
the contact between the Green Valley Tonalite and the overlying volcanic unit.
The volcanic unit is heavily weathered and may be mixed in with a paleosol near
the contact.
Walking
to Stop 4
You
will begin to notice more purple hues in the path which are
common in volcanic rocks. This is from the hydrothermal fluids and dissolved minerals which alter the coloring.
