April 27, 2002 A Sense of Place
Santa
Catalina
Mtns
Tucson
Mtns
Tucson
Basin
Rincon
Mtns
These mountains are at your front door.
They don’t have to remain a mystery.
Annual Precipitation
Sky Islands of SE Arizona
Vegetation change tells a Sky Island story.
•Altitude mimics latitude.
•To pines
and aspen.
•To manzanita.
•From desert floor.
Even dead trees can tell a story…
… of climate change and fire history.
Messengers from deep in Earth’s crust tell a
story about Tucson’s evolving landscape.
Learn to read the metamorphic rocks at Babad Do’ag overlook.
Metamorphic Rocks
Recrystallization in the solid state
(heat and pressure but little to no
melting) modifies the minerals and
texture of a prexisting rock.
Heat and
Pressure
transform
igneous and
sedimentary
rocks to
metamorphic
rocks.
Key minerals (e.g. garnet) can provide
information about pressure and
temperature of metamorphism.
Increasing Pressure and Temperature >>>>
Textures indicate direction of tectonic forces.
Reading deformation from metamorphic fabric.
Example: Development of foliation.
Undeformed granite
Foliated gneiss
Metamorphic
rocks formed in
zones of
convergence
between plates.
Colliding
continents
produce
metamorphic
rocks.
India – Asia collision produced Himalaya
Tortured rocks that were once on the
sea floor between India and Asia
Metamorphic rocks formed in Appalachians
by collision of North America & Africa.
Cenozoic
crustal
extension
in
western
North
America.
The
Basin
and
Range
Province.
The Geopuzzle of
Saguaro National Park East
Low pressure rocks
High pressure rocks
How did rocks from ~10 km deep in Earth’s
crust get placed adjacent to rocks that were
never buried by more than 2 km?
Operation of a Detachment Fault
New mechanism for extending the crust.
Occurred in western US between
30 and 15 million years ago.
Operation of a Detachment Fault
Upper crust is brittle.
Lower crust is “ductile” (capable
of plastic deformation).
Operation of a Detachment Fault
Tucson Mountains in upper plate of
Catalina Detachment Fault while
Catalina Mountains were in lower plate.
Catalina Detachment Fault is NOT
flat. It has huge corrugations.
Why do the Catalina Mountains look like an
arrowhead pointed at the Tucson Mountains?
Santa
Catalina
Mtns
Tucson
Mtns
Why are Pusch Ridge and
Tanque Verde Ridge parallel?
Did the Tucson Mountains get
pusched off of the Catalinas?