Geologic History of Arizona

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Geologic History of Arizona
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Overview

• Arizona has it all.
• PreCambrian to Quaternary deposits
• Ancient to recent volcanics
• Folded and faulted sed. rocks
• Metamorphics
• Mountains to playas

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Geologic Time Scale
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Proterozoic Continental Growth- Craton Forms

• Mid-Proterozoic (1.6-1.8 BA) accretionary belts
• Metamorphosed igneous, sedimentary, and
  metamorphic rocks formed during orogenic
  (mountain building) events.

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Late Proterozoic-Early Paleozoic Platform
Development

• After orogenisis, extended period of erosion
• First deposition of shallow marine and coastal
  plain sediments (platform)

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Cambrian Sedimentation

• Super-continent breakup
• Oceans inundate craton, marine sediments
  deposited on passive margin

Marine sedimentary environments
Grand Canyon stratigraphy
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Late Cambrian Geography

• Continents near equator, ice free

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Early-Mid Paleozoic

• Continued platform marine sedimentation.
• Arizona still drifting near equator.

Ordovician
Devonian
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Geologic Time Scale
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Late Paleozoic

• Continued sedimentation, orogenisis to the east
  and west.

Pennsylvanian
Permian
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West Coast Orogeny

• Mid-Paleozoic, volcanic arc forms off west coast
• Subduction occurs
• Overthrusting inland
• More land added to coastline

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North American Cordillera

• Series of orogenies
• Laramide, Late Cretaceous to mid Tertiary was
  different
• Affects rocks farther inland
• Igneous rocks not as common
• Many rocks lifted vertically

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Pre-Laramide Events

• Typical orogeny subduction angle of 50
• Volcanoes 150-200 km inland
• Thrust belts further inland

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Laramide Orogeny

• Shallow subduction in early Tertiary
• Igneous activity moves inland (and stops)
• Brittle fractures, vertical uplifts

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Late Cretaceous Arizona

• Volcanism in the south, uplift in the north

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Late Cenozoic Extension

• Overthickened, hot crust begins to stretch and
  collapse
• Basin and Range Province forms

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Basin and Range Province

• Parallel series of mountain ranges with flat
  floored valleys between
• Today, extension inactive to the south, active to
  the north

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Caldera Formation

• Laramide volcanics
• Large volcanoes collapse, creating calderas
• Rock types present include lava (rhyolite,
  andesite, dacite), tuff (pyrocalstics), breccia,
  country rock blocks

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Caldera Formation

• Stratovolcano builds from ash/lava layers
• Magma chamber empties, volcano collapses into the
  void
• Later eruptions may partially fill caldera

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Tucson Mountain Caldera

• Intruded through Paleozoic rocks.
• Chaotic assemblage of rocks tilted by BR
  faulting.
• Intrusions around edges through caldera faults.

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Porphyry Copper Deposits

• Mineralization associated with porphyritic
  intrusions.
• Hot water circulates through rocks surrounding
  intrusion.
• Hot water dissolves minerals, metals concentrated
  as new minerals deposited.

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Porphyry Copper Deposits

• Major metals include Cu, Ag, Mo, Au, Pb

Morenci, AZ