Download NEVADAN ROCKS

CGnevadan
NEVADAN ROCKS
I. Granitic Rocks
a. Sierra Nevada Batholith
Batholith:
igneous Pluton (intrusion) that has a surface area of greater 40 sq miles (100 sq km)
Formed and cooled deep in the Lithosphere
Extent--Sierra Nevada Mts, around southern end of Great valley, across Transverse
Range into Peninular Ranges
country (host) rock
b. Formation (A la Plate Tectanics)
(1) Batholith--has roots about 30 miles deep (50km)
(2) Paleozoic Strata dip from both east and west towards center (axis of mountain
Range)
Huge Synclinorium > 100 miles across
Syncline has been intruded by Granite batholith
CGnevadan
c. History
(1) 150 My ago ocean crust was thrusted under American Continent (Lava flow and
volcanism along an island arc system)
(2) 140 my pressures great between colliding plates
(a) older rock formed were folded and thrust faulted and elevated during
Nevadan Orogeny (most intense in Sierra Nevada)
(b) Initial thrusting on Great Coast Range Thrust (dips eastward along East flank
of Coast Range)
(3) Sierra Nevada Block result of 140 my of uplift, westward tilting and erosion
(4) Coast Range Thrust inactive surface expression of
subduction zone (observed on west side of Great Valley)
II. Franciscan Rocks and Building of Coast Ranges and
Continental Margin
a. Franciscan--Eugeosynclinal Sedimentary and Volcanic Rocks massive bedded graywacke
within interbedded dark shale, minor chert and Limestone and altered Volcanic Rock
(greenstone) and Metamorphic rocks--green Chlorite Actinolite schists and blue glaucophane
schists
Rocks intruded by masses of peridotite (mostly serpentinized)--origin from upper mantle
b. 50,000 ft thick
c. glaucophane, Lawsonite, jadeite
(1) Low temperature (<300degrees C)
(2) high pressure (5,000 to 9,000 Atm)
(3) reached depth of >70,000 ft
(4) rapid uplift
III. Granite Rocks--contemporaneous with Sierra Nevada Granite
IV. Coast Ranges
a. 30,000 ft of unmetamorphosed shelf facies to deep sea fan sandstone, shale, siltstone and
minor conglomerate and Limestone
Late Jurassic.-Late Cretaceous
b. Thrust faulted over Franciscan and Granite rocks
c. Most continuous section lies on eastern flanks of Diable and Mendocino Range above the
coast Ranges
CGnevadan
Transition to the Cenozoic Period
V. Mountain Building and Westward Extension of Continental platform
a. Profound faulting--in subduction zone--Great Valley series in the Continental block were thrust
many miles westward over oceanic plate rocks of the Franciscan in mid Jurassic.--early Cenozoic
b. Subsequent folding uplift and erosion--left only remnants of Coast Range Thrust (except along
east side of Coast Ranges)
c. Mid Eocene to Oligocene-regime profoundly changes subduction and thrusting ceased and
great right lateral strike slip San Andreas fault system began to develop
d. Opinions differ but displacement totals 160-310 miles since middle Eocene time
e. along with stike slip-intermittent uplifting has occurred culminating in major coast range
orogeny in late Pliocene-Pleistocene time