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ORACLE STATE PARK
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Granite Inselberg
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Oracle State Park
Coronado National Forest
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San Pedro Valley - Galiuro Mountains
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ORACLE STATE PARK
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Oldest Rock - 1.65 Billion Years
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1.65 BYA
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Pinal Schist Origins
Pinal Schist Origins
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Undersea Avalanches - Turbidity Flows
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ORACLE STATE PARK
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Thousands of feet thick
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Metamorphosed from Turbidite
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Oracle Granite - Basement Rock of the Park
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1.4BYA - Crystallized from magma, miles below the surface
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While still buried, joints formed from extreme pressure
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Percolated groundwater, reacting with feldspar, created clay
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More than 25 MYA, faults lifted Oracle Granite towards the surface
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Erosion removed thousands of feet overlying rock, exposing the fractured bedrock
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Delamination - Exfoliation
After millions of years of winds and erosion, exposed the underlying basement
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Pinal Schist Xenoliths in Oracle Granite
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1.4 BYA magma rose from earth's crust as Oracle Granite
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As it rose, it broke through a roof of Pinal Schist
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The fragments, carried by the magma, became a part of the cooling rock
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Aplite dikes
Tourmaline
Diabase in Mescal Limestone
Encased Diabase
Granodiorite Porphyry
Laramide Orogeny
- 60 - 70 mya
- North America collided with the ocean crust
- Magmatic activity produced Laramide Granitic Porphyry
- This time, hydrothermal solutions were rich in copper
- Smaller amounts of silver, gold and molybdenum were also present
Sources
Azstateparks.com, Oracle State Park - Special thanks to Tom Buckley, geologist, Oracle State Park volunteer
Bezy, J.V., 2016, A Guide to the Geology of the Santa Catalina Mountains, Arizona: The Geology and Life Zones of a Madrean Sky Island. Arizona Geological Survey Down-to-Earth #22 , 83p.
Johnson, Chris, Affolter, Matthew D., Inkenbrandt, Paul, Mosher, Cam, 2017, An Introduction to Geology, Salt Lake City Community College
Copy of Oracle State Park v.2
By Anne Martin
