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Oligocene Igneous Center in Stillwater Range, Nevada

Explore the Tertiary ash-flow calderas and granitic plutons in southern Stillwater Range, Nevada, showcasing unique features like extreme thickness deposits and compositional zoning. Discover the Oligocene caldera complex and Miocene extension's impact.

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Oligocene Igneous Center in Stillwater Range, Nevada

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  1. Tilted middle Tertiary ash-flow calderas and subjacent granitic plutons, southern Stillwater Range, Nevada : Cross sections of an Oligocene igneous center By David A. John

  2. Introduction • Steeply tilted late Oligocene caldera system • record a number of unusual features • Extremely thick (>4-5.5 km) caldera related deposits • Lack of evidence of structural doming • Preservation of compositional zoning • Cogenetic plutonic rocks are exposed over depth range of~10 km

  3. Stillwater Caldera Complex • Job Canyon (29-28 Ma) • Poco Canyon (25-23 Ma) • Eleven Mile Canyon (25-23 Ma) • Composite Freeman Creek pluton

  4. Unusual features • Extreme thickness caldera related deposits (>4-5.5 km)

  5. Unusual features continued • Preservation of compositional zoning

  6. Caldera collapse • Miocene extension • Basement rocks tilted 40°-90° • Subvertical ring-fracture faults (>3-5 km) depth • Piston like blocks • Lack of evidence of structural doming

  7. Conclusions • Oligocene caldera complex in the southern Stillwater Range • Extremely thick caldera related deposits due to extreme subsidence • Cogenetic plutonic rocks over a depth range of ~10 km due to tilting during Miocene extension

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