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: California Geological Survey Source: BLM

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

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