California Geology California Geology Science Content Standards for California Public Schools 6 th Grade Focus on Earth Sciences Students know how to explain major features of California geology (including mountains, faults, volcanoes) in terms of plate tectonics. From: Geologic Map of California California Geological Survey, California Department of Conservation For free copy, go to: http://geology.about.com/library/bl/maps/blcaliforniamap.htm or: www.consrv.ca.gov/cgs/information/publications/cgs_notes/note_17/note_17.pdf Throughout its history, California has been, at times, the site of all three types of plate boundaries (divergent, convergent, transform) Before 2 billion years -?? no rocks preserved Before 2 billion years -?? no rocks preserved 1.5-1.8 billion years -?? intensely metamorphosed rocks only 1.2 billion years-900 million years - DIVERGENT BOUNDARY 800-~300 million years - passive margin ~300-30 million years - CONVERGENT BOUNDARY 30 million years to present - TRANSFORM BOUNDARY added on later *Also, Fig. 6.22 in EST 1.5-1.8 billion years -?? intensely metamorphosed rocks only 1.2 billion years-900 million years - divergent boundary DeLand (2003) added on later Pahrump Group sediments were deposited in a restricted, fault-bounded basin similar to those found today where continents are breaking up (e.g., Africa). 1
Death Valley Death Valley Death Valley Geology at a divergent plate margin Today. Sedimentation in fault-bounded basins 1.2 billion years-900 million years - Divergent boundary in CA Deposition of Pahrump Group sediments during breakup of Rodinia super-continent ~1.1 Byr From: R. Blakey, Northern Arizona University, Paleogeography of the Southwestern United States Pahrump Group: ~billion-year-old deposits in fault-bounded rift basin Pahrump Group: ~billion-year-old deposits in failed rift arm Pahrump Group: ~billion-year-old deposits in failed rift arm (aka, aulacogen) X-section view of Pahrump Group sediments in Amargosa rift basin N S Death Valley Site of new ocean Death Valley Site of new ocean N S 2
4 formation in Pahrump Group 4 formation in Pahrump Group Kingston Range Kingston Range Crystal Springs Formation Beck Springs Dolomite Beck Springs Dolomite Kingston Peak Formation Noonday Dolomite Saddle Peak and Ibex Hills Saddle Peak and Ibex Hills 5 formations in Pahrump Group Crystal Springs and Becks Springs Formations Kingston Range Crystal Springs Formation Beck Springs Dolomite Beck Springs Dolomite Kingston Peak Formation Noonday Dolomite talc rkopp rkopp Saddle Peak and Ibex Hills Kingston Peak and Noonday Formations rkopp Kingston Peak Glacial Deposit rkopp rkopp 3
Crystal Springs stromatolites and Kingston Peak diamictite 800-~300 million years - passive margin Deposition of thick sequence (10s of thousands of ft) of widespread sediment layers all along the west coast of North America Development of a Passive Margin after Divergent Plate Margin leaves the scene Passive Margin Today: North Carolina CA Paleogeography of California s passive margin sediments Passive Margin ~900-300 mya: California underlying Pahrump Group extensive passive margin sediments deposition in extensive layers parallel to continental margin R. Blakey, Northern Arizona University 4
California s passive margin sediments California s passive margin sediments Kingston Range Kingston Range Johnnie Formation California s passive margin sediments Northern Salt Spring Hills Paleozoic Life: Trilobites Johnnie Formation Stirling Formation Wood Canyon Formation Zabriskie Quartzite Trilobite track and head from Wood Canyon Formation, Salt Spring Hills Paleozoic Life: Graptolites and Archaeocyathids 5
Graptolites from Inyo Range, California Archeocyathids from Inyo Range, California Archeocyathids from Inyo Range, California Archeocyathids from Inyo Range, California Paleozoic Life: Molluscs (Bivalves) and Brachiopods Brachiopods from Bird Springs Formation, Salt Spring Hills, California 6
Paleozoic Life: Echinoderms and Foraminifera Echinoderms from Bird Springs Formation, Salt Spring Hills, California Paleozoic Life: Molluscs (Cephalopods) and Brachiopods Rugose Corals from Salt Spring Hills, California Belemnites from Salt Spring Hills, California Metamorphic Roof Pendants In the Sierra Nevada 7
Passive margin sediments as Roof Pendants in Sierra Nevada Passive margin sediments as Roof Pendants in Sierra Nevada From: Geologic Map of California California Geological Survey, California Department of Conservation For free copy, go to: http://geology.about.com/library/bl/maps/blcaliforniamap.htm or: www.consrv.ca.gov/cgs/information/publications/cgs_notes/note_17/note_17.pdf ~300-30 million years - CONVERGENT BOUNDARY Generation of magma chamber/volcano complexes, sedimentary basins associated with subduction zones plus accretion of continental fragments onto western margin of North America Mesozoic Subduction with Accretion and Collisions Formation of Sierra Nevada batholith 300-30 mya Remains of 100 my old volcano above Sierra batholith, Ritter Range 8
Mesozoic Subduction with Accretion and Collisions Mesozoic Accretion of Terranes Accreted Terranes in western North America and California (USGS) 9
30 million years to present - TRANSFORM BOUNDARY Onset of strike-slip faulting (SAF) on western margin of California. Northward translation of subduction zone. Present-Day Plate Boundaries Continuing convergence north of Mendocino triple junction Strike-slip faulting on boundary Mt. Shasta Mt. Lassen 10
Strike-slip faulting on boundary Strike-slip faulting on boundary: transtension Strike-slip faulting on boundary: transtension Strike-slip faulting on boundary: transtension Figure 7-7 Harden Wright and Troxel Death Valley Turtleback Strike-slip faulting on boundary: transpression 11
Transverse Ranges associated with the Big Bend in the San Andreas Fault Strike-slip faulting on boundary: transpression Glacial Polish and Striations near Bishop Pass Pleistocene Ice Sheet in Sierra Harden (2004) Convict Lake Moraines Faulted glacial moraines near Crowley Lake, CA J. Shelton 12