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California Rock Stories Linking tectonics to rock formation Ellen Metzger BAESI – October 8, 2011

California Rock Stories Linking tectonics to rock formation Ellen Metzger BAESI – October 8, 2011. California’s Rocks. California, including the Bay Area, has a greater variety of rocks than do other regions of the United States. This reflects the state’s complex tectonic/geologic history.

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California Rock Stories Linking tectonics to rock formation Ellen Metzger BAESI – October 8, 2011

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  1. California Rock Stories Linking tectonics to rock formation Ellen Metzger BAESI – October 8, 2011

  2. California’s Rocks • California, including the Bay Area, has a greater variety of rocks than do other regions of the United States. • This reflects the state’s complex tectonic/geologic history.

  3. Mineral Hazards • Serpentinite • California state rock • Metamorphosed ultramafic rocks from the mantle (can you find these rocks on your California geologic map?) • There are several minerals in the serpentine group • Chrysotile is asbestiform

  4. California’s Mineral Resources

  5. Mineral Hazards: Mercury in the Environment • Mercury is a neurotoxin – principal source for humans: consumption of mercury-contaminated fish • Sources of mercury in the environment • Natural sources: • Volcanoes, hot springs, and natural mercury deposits (the mineral cinnabar (HgS)is an ore of mercury • Sources related to human activities: coal combustion, incineration of waste, industrial activities, mining Source: BLM Source: California Geological Survey

  6. Bay Area Rocks • Young sedimentary and volcanic rocks • Mesozoic rocks • Franciscan Complex • Coast Range Ophiolite • Great Valley Group • Salinian basement

  7. Bay Area Rocks • Do your students bring you grungy, fine-grained, black and green rocks?

  8. California Tectonics: Present Source: USGS

  9. California tectonics in the past: a subduction zone Cross section of western North America at about 100 million years ago /www.nps.gov/prsf/naturescience/images/Subduction-animation_1.gif

  10. The Rock Cycle Source: USGS

  11. Rock Description • Color • Texture • Weathering/resistance to erosion

  12. Unique Bay Area Rocks • Igneous • Sea floor basalt Pillow lavas Greenstone (altered basalt) • Sedimentary • Graywacke (“dirty” sandstone) • Radiolarian Chert Radiolarians: Tiny ocean animals that make their skeletons of silica (SiO2) http://www.mdia.org/images/Radiolaria.jpg

  13. Unique Bay Area Rocks • Metamorphic • Glaucophane schist (“blueschist”) formed under high P-low T in a subduction zone. • Serpentinite - hydrated mantle rocks Mantle rock = ultramafic (Si02-poor), dense, dark • Serpentinite = rock (CA State Rock) • Serpentine = mineral • Should serpentinite be “demoted” as our state rock?

  14. Formation of Blueschist in a Subduction Zone http://openlearn.open.ac.uk/file.php/3512/SXR260_1_007i.jpg Unique conditions: High pressure combined with low temperature Note depressed isotherms. Due to slow heating of cold, down-going oceanic plate

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