California Through Geologic Time
Geologic Time: Basically, it is unfathomable to recent inhabitants of this Planet, Earth. The Earth is 4.6 billion years old. Rocks older than about 600 million years old are very rare in California, and most of the tectonic development of California has occurred in the last 300 million years.
So really, California is an extremely young geologic feature on this Planet.
California has only existed for about 6.5% of Planet Earth’s Geologic History. And the uplift of the Sierra Nevada, Coast Ranges, and Big Bend on the San Andreas (5 Ma) is only a mere 0.00000012% of Geologic Time (1.2e-7%).
Let’s discuss the Geotectonic Evolution of California with emphasis on the TECTONIC SETTING of California through Geologic Time.
Oldest Rocks in California
There are very few and occur primarily in southeastern California:
Basin and Range Province
Southern Panamint Range
Mojave Desert Province
San Gabriel Mountains
San Bernardino Mountains
These rocks are primarily crystalline plutonic rocks and metamorphic gneiss, schist, and marble.
They form part of a Proterozoic margin that borders the Archean core of nuclear North America (Laurentia).
Proterozoic = 570 Ma to 2.5 Ga
Archean = 2.5 Ga to 4.6 Ga
Overhead, Harden, Fig. 18-1
Discuss the Proterozoic (1.0 Ga) margin of Western North America.
Rift Tectonic Setting: Not much is known about what the western margin of North America was like, it may have been a rift based on 900 Ma sedimentary deposits found in Death Valley (Kingston Peak Formation). This unit contains crystalline cobbles and boulders that presumably had their origin somewhere to the east (present day) of Precambrian California, nuclear North America.
Overhead, ES130, Rodinia
At this time North America is considered to have been part of a supercontinent known as Rodinia. The portion of North America closest to where California will be was not involved in any orogenic events (mountain building).
When the supercontinent of Rodinia broke apart, a rift margin developed.
"TCM" Tectonic Setting: After the rift development, separating the landmasses, California’s tectonic setting is a stable "Trailing Continental Margin".
On this "Trailing Continental Margin" we formed the carbonates, quartz sandstones, and shales typical of this stable, non-California-like environment. The tectonic setting here is that of a stable continental shelf, which continued from Latest Proterozoic to Early Paleozoic (about 650 Ma to about 350 Ma).
Again, many of these stable "Trailing Continental Margin" sedimentary rocks are exposed in the Mojave and Basin and Range Province as well as in the Roof Pendant metamorphic rocks of the Sierra Nevada.
Island Arc Tectonic Setting: Beginning in Devonian time (360 Ma), island arc volcanic rocks began forming off of the Paleozoic California coast.
These island arc rocks would eventually crash onto Paleozoic California forming the first major tectonic event in California.
And this orogeny is known as the? Antler orogeny.
These rocks are exposed in the northern Sierra Terrane up in Plumas and Sierra counties. The rocks here are the Sierra Buttes Formation island arc volcanic lavas.
Transition, Island Arc to Continental Arc Tectonic Setting: During the Late Paleozoic and early part of the Mesozoic (280 to 150 Ma), numerous island arcs collided with California forming the Sonoma Orogeny and the Nevadan Orogeny.
Overhead, field guide cartoons (show Sonoma arcs, Nevadan arcs).
Note Island arc collisions during Sonoma orogeny: Sierra Nevada and Klamath Mountains.
Note that right before Nevadan Orogeny, Continental Arc magmatism is occurring. Granites in Eastern Sierra and White Mountains are these.
Mesozoic California – Franciscan Fm., Sierra Batholith, GVS
Globally, California and North America were part of a second supercontinent. This one was known as Pangea.
Overhead, ES130 Pangea and current World
So during the time of the Antler and Sonoma, the world’s continents were regrouping to form this supercontinent of Pangea.
By about 200 Ma, Pangea started to break up, opening of the Atlantic ocean and the formation of the North America plate.
After Nevadan Orogeny, subduction moved west from the Melones fault zone to the current position of Coast Ranges.
Overhead, KLC, Mesozoic California
Tectonic Setting – Continental Arc
Continental Arc – Sierra Nevada batholith, Ritter Range, Minarets
Subduction zone – Franciscan Complex
Subducting Plate – Farallon Plate
Arc-Trench gap – Great Valley sequence
Trapped Ocean floor – Coast Range Ophiolite
Cenozoic California – Transform Boundary
At about 28 Ma, the Pacific Plate makes first contact with the North American Plate resulting in the birth of the San Andreas Transform.
Overhead, Harden, Fig. 12-1
Note: Farllon Plate split into Juan de Fuca and Rivera plates
Continental arc activity ceases east of the new transform
As much as 180 mi right lateral offset, Pinnacles and Neenach
Multiple activities at 5 Ma
Sierra Nevada uplift – evidence is in Table Mountain lava flows.
14,000 ft. of displacement on the Eastern Sierra Range Front fault in last 4 Ma.
Uplift of Coast Ranges and Transverse Ranges – movement of the San Andreas Transform onshore and east of Los Angeles, Baja breaks away from mainland Mexico.
Young Volcanism in California
The San Andreas may be growing in length, but there are still remnants of the Farallon plate, now the Juan de Fuca and Gorda plates that are actively subducting beneath northern California to form the Cascade volcanoes, Mt. Shasta and Lassen Peak.
Other types of recent volcanism include the activity at Long Valley Caldera and the Mono-Inyo volcanic chain in the eastern Sierra Nevada.
Volcanic activity along range front faults in the Basin and Range Province – Big Pine, Coso, Ubehebe, and in the Mojave province, Amboy and Pisgah craters.
Tectonic Future of California?
1) Basin and Range faulting will continue to the west, perhaps making the Central Valley the last basin in the Basin and Range.
2) The Cascade volcanoes will be turned off as the San Andreas fault grows to the north and cuts off the subduction zone.
3) With increased extension in the Basin and Range, magmatism will continue in the eastern Sierra Nevada, and Long Valley and the Mono-Inyo chain will continue to erupt, perhaps in another catastrophic caldera forming event, like the Bishop tuff and Long Valley caldera.
4) In the Bay Area, the San Andreas Fault will step to the east and have the most amount of movement along the Calaveras-Hayward faults. Los Gatos, Saratoga, San Jose, and San Francisco will become part of the Pacific plate.
5) A M7 earthquake will strike on the Hayward fault within the next 30 years. A M7 earthquake will strike on the San Andreas Fault between Portola Valley and San Francisco. Parkfield will eventually rupture. More M7 or greater subduction zone earthquakes are imminent north of the Mendocino Triple junction. Blind Thrust earthquakes will strike the San Fernando Valley again as well as the Los Angeles Basin.
6) More offshore oilrigs will be developed (go back to 70’s mentality of using smaller cars).
7) The Gulf of California will extend northward along the East Pacific Rise and consume the Imperial Valley and Salton Trough.