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Ch 2 geologic history and processes
 

Ch 2 geologic history and processes

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    Ch 2 geologic history and processes Ch 2 geologic history and processes Presentation Transcript

    • Chapter Two Geologic History and Processes
    • Plate Tectonics
        • Divergent Boundary
          • East Pacific Rise
          • Salton Trough
          • Cape Mendocino
        • Convergent Boundary
          • Cascades: Mt Shasta and Mt Lassen
          • Historically: Sierra Nevada, Coast Ranges, Klamath Mtns.
        • Transform Boundary (“Sliding”)
          • San Andreas
    • California Through the Ages
        • Precambrian Era ends 540 mya
        • California’s oldest rocks 1.8 billion years old
          • Crust under us 1.8 billion years old
            • Basin and Range, Transverse Range, and deserts
          • Many younger intrusions
      A nearly 3,000 meter-thick section of Paleozoic-age sedimentary rocks are exposed in the mountain ranges of the eastern Mojave Desert region. This view shows Paleozoic-age rocks exposed on the eastern flank of the Panamint Mountains in Death Valley National Park. http://geomaps.wr.usgs.gov/socal/geology/geologic_history/index.html
    • California Through the Ages
        • San Gabriel Mountains
          • Metamorphic and igneous rocks
          • Complex geologic past
    • California Through the Ages
        • Proterozoic (late precambrian)
          • A sea covered California
          • Sediments were deposited
            • Later igneous material intrudes
    • California Through the Ages
        • Roof Pendants abundant in California
          • Sierra Nevada’s, Inyo-White Mtns.
            • Hornfels, cherts, marbles, slates, and quartzites
    • California Through the Ages
        • Northern California
          • More volcanic material mixed with ocean sediments
          • Continental crust crushed together with ocean crust
    • California Through the Ages
        • Southern California
          • Paleozoic rocks not as common
          • Some in the Ord Mountains, Eastern Transverse Range, Peninsular Ranges
            • Some gneiss and schist, Riverside limestone quarried for cement
      http:// www.desertmuseum.org/programs/flw_mohave.php
    • California Through the Ages
        • Mesozoic Period
          • Lots of subduction going on
          • Results in mountain building
          • Nevadan Orogeny
          • When the sea began to disappear
    • California Through the Ages
        • Mesozoic Rocks Important
          • Pre-Nevadan roof pendants
          • Limestone, slate
        • Cenozoic Basins
          • Filled with sediments and eroded mesozoic rocks
    • California Through the Ages
        • Mesozoic period
          • Granite plutons: Sierra Nevadas and Cascades
          • Franciscan Complex (Coast Ranges)
            • When sedimentary material was brought to and crushed against the continent
            • Chert, serpentine, sandstone, shale
          • Klamath Mountains:
            • both plutons and schist from being pushed against and onto the continental plate
    • California Through the Ages
        • California: 1.8 billion years of rocks
          • Impressive quantities of valuable minerals, ores, and other earth resources.
            • Shaped history and still an import part of the economy
    • Gold, Silver, and Other Ores
        • In and near subduction zones, ocean and continental crust materials incorporate into magmas.
        • This magma becomes granitic plutons.
        • As the magma is pushed towards the surface it comes in contact with older sedimentary or metamorphic rocks.
        • As the magma cools, it squeezes into cracks and joints forming veins.
        • Often it is the most felsic magma with the most minerals that forms the veins.
        • High feldspar veins then cool and crystallize with precious mineral deposits.
    • Gold
        • Placer Deposits
          • Where veins have eroded into streams, rivers, lakes, etc.
        • Mother Lode
          • Principal zone of veins of gold or silver
          • Usually refers to California’s Sierra Nevada .7 mi wide, 120 mile long zone
        • Hydraulic Placer Mining
          • Way of mining with high powered water spray
    • Mix of Valuable Resources in the North
        • Klamaths
          • Chromium, cobalt, nickel, zinc, copper, gravel, clay, limestone
        • Shasta
          • Pyrite, chalcopyrite, sphalerite, magnetite, mercury
    • Mines in Transmontane California
        • Basin and Range
          • Today: talc, saline minerals
          • Cerro Gordo
            • Silver, lead, zinc
          • Bodie
            • gold
    • Mining in the Mojave and Southern Deserts
        • Rand Mining District
          • Gold, silver, tungsten, boron
        • Further South
          • Gold, rare earth minerals, iron, limestone, magnetite, hematite, boron