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Tucson Geologic History: Cenozoic (65.5 – 0 Ma (million years ago))
Dr. Jan C. Rasmussen www.janrasmussen.com
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Temp. & Geologic
Time Scale
4.6 Ga
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Tertiary – 65-0 Ma
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Orogenies (mountain building)
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Cenozoic Formations near Tucson
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Cenozoic
outcrops
around
Tucson
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Early Cenozoic – porphyry Cu
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Early Tertiary paleogeography
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Tertiary (65-1.8 Ma)
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Early Cenozoic - Middle Laramide
(65-53 Ma) porphyry copper mines
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Early Cenozoic
- 65-54 Ma –
porphyry copper
deposits around
Tucson
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Early Cenozoic – porphyry Cu
Sierrita Mts. – Pima min. dist.
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Porphyry copper deposits –
Sierrita Mine
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Minerals from Pima mining district
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Ore Minerals from Mission mine
Chalcopyrite – copper fools gold Copper-iron-sulfide
Bornite – peacock copper – copper iron sulfide
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Reclamation at Mission mine
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Processing at Mission mine
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Early Cenozoic – porphyry copper Santa Rita Mts. – intrusive granitics
Rosemont/Helvetia
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Early Cenozoic –
(54 Ma Ma)
Santa Rita Mts. –
quartz monzonite
porphyry
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Geologic Map of Rosemont area
Near vertical Paleozoic (blue) Limestones near crest
Fault-bounded Paleozoics on west
Mineralized Paleozoics buried under Cretaceous and Tertiary sedimentary rocks
Cretaceous (green)bedding trends northeast
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Cross section of Rosemont area
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Early Cenozoic – porphyry Cu
Catalina Mts. - San Manuel mine
1987
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Santa Catalina Mts. - San
Manuel mine - 1998
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Santa Catalina Mts. - San
Manuel mine
2008
1999
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Santa Catalina Mts. - San
Manuel mine
1999 Tailings impoundments
2008- tailings impoundments covered
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San Manuel minerals
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Oracle Ridge mine – N. Catalinas
Leatherwood Quartz Diorite
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Oracle Ridge mine – N. Catalinas
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Early Cenozoic – Laramide
intrusions Tucson Mts.
Saginaw Hill
Sedimentary Hills
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Latest Laramide Orogeny 53-43 Ma
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Early Cenozoic
Wilderness
Granite suites
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Wilderness Granite
Looking west from ~ Sabino Looking east from west of Oro Valley
Bands of Wilderness granite in dark Oracle Granite
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Santa Catalina Mts. -
Wilderness Granite 43 Ma
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Garnets in Wilderness Granite
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Santa Catalina Mts. -
Wilderness Granite 43 Ma
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Texas Canyon granite – ~45 Ma
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Mid-Cenozoic mountain building -
volcanoes – like Cascades
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Mid-Cenozoic
outcrops
around
Tucson
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Mid-Cenozoic volcanics
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Mid-Tertiary volcanics – rhyolite
at Tiger, northern Catalinas
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Mid-Tertiary – Santa Catalinas -
Tiger – Mammoth-St. Anthony mine
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Mid-Tertiary – Santa Catalinas -
Tiger – Mammoth-St. Anthony mine
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Tucson Mts. mid-Tertiary volcanics
West of Contzen Pass, northern Tucson Mts.
Tumamoc Hill & A Mountain
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Is A Mountain a volanic cone or is it an erosional remnant?
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Sequence of Rocks, A Mountain
Map Rock type texture Special
features
name formation age
Ttb Basalt Fine-
grained
Some vesicles Tumamoc
basalt
Lava flow 19.8
Ttt Tuff Pyroclastic Pink tuff,
Tan tuff, pumice
fragments
Tumamoc
tuff
Ash fall 25.8
Tal Agglomerat
e
Pyroclastic Basalt (<
1inch)
fragments, tuff
matrix
Agglomer
ate
Cinder fall 27
Tab basalt Fine-
grained
Vesicular basalt Lava flow 28
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Base of A Mountain – Mission Road
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Andesite Porphyry at base of A
Mountain
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Caliche = natural concrete
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Midway up = A Mountain basalt
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Tan Tuff overlain by Pink Tuff
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Pumice in Pink Tuff
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Tumamoc Hill and A Mountain,
viewed from the south (Ajo Rd)
Black Mountain, view to south from top of A Mountain
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Age Dates,
southern
Tucson
Mountains
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Rincon Mts – mid-Tertiary
Turkey Track Andesite – 27 Ma
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Late Cenozoic mountain building
Basin & Range fault blocks
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San Andreas
fault cutting
off
subducting
eastward
moving plate
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Current San
Andreas
fault
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Basin and Range Valleys filled
with sand, gravel, clay,
gypsum, & salt
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Late Tertiary sedimentary rocks
Pantano Fm. - ~25 Ma
Rillito II - ~ 21 Ma
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Basin fill at Sonoita
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Basin fill – sand, gravel, & clay
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Basin and
Range
Disturbance
– current
basins
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Industrial minerals in Late
Cenozoic sediments
Sand & gravel Kalamazoo Clay - 1987
Pantano Clay - 1987 Gypsum rose
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Late Cenozoic volcanics
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San Francisco Peaks volcanism 5-0 Ma
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LaBrea tarpits, Los Angeles – Pleistocene 1 Ma
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Pleistocene maximum
glaciation – 18,000
years ago
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Pleistocene glaciation
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Carbon dioxide, last 100,000,000 years
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1,000,000 years of
temperature change
Glacial and Interglacial stages, last 2 million years
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500,000 years - Pleistocene temperatures
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800,000 years – astronomical
variations
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Climate Change, last 160,000 years
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Sea Level curve – last 20,000 years
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Temperature, last 10,000 years
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Temperature change, last 5,500 years
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Glaciation through Geologic time
• Depends on plate tectonics through geologic history
• Continental collisions = ice ages
• Big environmental changes through geologic time
• Warm periods vs. ice ages ~ every 250 million years