Geologic History of Tahoe Basin, Walker Lane Belt and the Long Valley Caldera by Allison Whybrew

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Geologic History of Tahoe Basin, Walker Lane Belt
and the Long Valley Calderaby Allison Whybrew
Lin Vana
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• Precambrian- ended 540 m.y.a.
• Eastern part of Nevada was the continental
  margin. The areas studied in this class were
  covered by ocean.

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• Paleozoic- 540 m.y.a. to 250 m.y.a.
• Trilobites and other ocean animals are the
  primary life forms. Sediments deposit, forming
  varying types of rock layers. Undersea volcanoes
  contribute volcanic debris. Earth movements-
  possibly earthquakes- shake sea bottom. Early
  subduction and two main episodes of mountain
  building occur, the Antler and the Sonoma.

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• Mesozoic- 250 m.y.a. to 65 m.y.a.
• Subduction of the Farallon plate continues, then
  formation of the Sierra batholith occurs 200 to
  80 million years ago. Dinosaurs roam Earth.
  Pangaea splits up. Sevier thrust sheets occur in
  eastern Nevada. Formation of the Rocky Mountains
  occurs because of low angle subduction into the
  continent.

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• Tertiary Cenozoic-
• A. Subduction of the Farallon plate continues
  into Miocene epoch. 30 mya Pacific plate
  intersects North American plate, initiating San
  Andreas transform plate boundary. Faulting
  begins in the southern Walker Lane Belt. Great
  Basin changes from compressional tectonics to
  extensional tectonics as a result of the
  subduction zone moving northward. Uplift of
  Sierra batholith begins about 5 million years
  ago.

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• IV. Tertiary Cenozoic-
• B. 15 million years ago to 3 million years ago
  Normal faulting series begins in the east and
  moves westward, forming the ranges from the
  Wassuk (in the east) to the Tahoe Basin (in the
  west). Strike-slip faulting begins in the
  Southern Walker Lane and moves northward. In the
  Southern Sierra, normal faulting forms the White
  Mountains 10 to 12 million years ago and the
  Owens Valley 6 million years ago. This is due to
  the northward propagating San Andreas transform
  fault (50mm/yr).

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• Tertiary Cenozoic-
• C. The Walker Lane Belt is thought to be an
  insipient plate boundary and may become the
  western edge of the North American plate in the
  future. Faults in the southern Walker Lane Belt
  have a cumulative offset of about 75 km. Faults
  include White Mtns, Fish Lake Valley, Owens
  Valley, and Furnace Creek. Central Walker Lane
  40-50 km of offset Northern 20-30 km.

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• Late Cenozoic-
• A. Tahoe Basin
• 1. Volcanic eruptions block north end of
  basin, forming lake, 5 mya.
• 2. Tioga (20kya) and Tahoe (100kya)
  glaciation create moraines.
• 3. Continued movement along normal faults
  (.5mm/yr) offset moraines and landslides such as
  McKinney Bay form tsunamis.
• 4. Sierra Nevada's move northward at rate of
  10-14mm/yr.

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• B. Walker Lane Belt
• 1. Continued volcanism and movement along
  strike-slip and normal faults.
• 2. Ancient Lake Lahontan disappears creating
  stadials (shoreline features) 10kya.
• 3. Walker Lane is divided up into 7 zones based
  on different fault characteristics.
• 4. 25 of San Andreas plate boundary shear is
  accommodated in the Walker Lane Belt.

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• C. Long Valley Caldera
• 1. Two million year old volcanic activity
  occurs.
• 2. Eruption of caldera occurs 760,000 years
  ago, forming Bishop Tuff.
• 3. Continued volcanic activity forms Mammoth
  Mountain about 160,000 years ago.
• 4. Rhyolitic volcanism continues along the
  Mono-Inyo chain, 20kya to 600ya.