Ca Geology Chp 18 Geologic Time

Front 1

By the __, the nature & approximate age of many of the rock formations, faults, folds, were established in CA maps. Gold rush spurred preparation of accurate & detailed geologic maps of CA.

Back 1

1960s

Front 2

Rocks older than ___ million years are rare in CA. Only found in ___ CA. Thought to be old terranes accreted early in history of ancient continents that are preserved in today's North American Plate.

Back 2

600 million years old;

southeastern CA;

Front 3

Oldest rocks in SE CA are called the ___ & consist of metasedimentary rocks, mainly gneiss, schist, & marble, & granitic plutonic rocks. The granitic rocks are about 1.4 to 1.7 billion years old & because they are intruded into the metasedimentary rocks, those rocks are even older. Some places, metamorphic rocks are as old as 2.4 billion years old.

Back 3

crystalline basement;

Front 4

Geologists believe the west coast of North America was next to the future __ and ___ continents.

Back 4

Australia & Antarctica;

Front 5

About 900 million years ago, sediments were deposited on the crystalline basement rocks of the Rodinia supercontinent. Today these sediments are represented by the ___ in the Death Valley region. It as coarse-grained gravels & some striated by glaciers provides evidence that Rodinia was located in polar latitudes. In other regions, sedimentary rocks of this age are associated with volcanic rocks.

Back 5

Kingston Peak Formation

Front 6

By 700-800 mya Rodinia broke & rift developed within continent. Sediments began to accumulate along west margin of North America in response to sinking of the continental edge. Sedimentary rocks in SE formed in shallow marine waters during subsidence. Quartz sandstone & shale.

Back 6

OKAY

Front 7

By early __ time, a stable continental shelf had developed along Continental margin of west North America. In next 350 million years, thousands of meters of sedimentary rocks mainly carbonates accumulate on the platform. This sedimentary environment found along a tectonically quiet or passive margin is known as a ___. Can be seen in Basin & Range Province. Also preserved as a metamorphic roof pendant.

Back 7

Paleozoic;

miogeocline;

Front 8

Generally, Paleozoic sedimentary rocks in SE CA increase in thickness from __east to __west. Paleozoic continental margin faced toward the __ in most areas.

Back 8

southeast to northeast (northwest is thickest).

Northwest;

Front 9

Beyond continental margin other oceanic rocks were forming west of North America. Later they would be accreted to North America in Mesozoic. Some were subduction zone complexes, others remnants of volcanic terranes. During Mississipiian & Permian, belt of volcanic island arcs lay west of continent. Today can be seen in Sierra Nevada & Klamath mountains.

Back 9

Although quiet in west, tectonic upheaval in the east North America. Collisions produced complex rocks in Appalachian mountains. Pangaea formed.

Front 10

Early in ___, 225 million years ago, Pangaea broke and Atlantic ocean began to form from rift. West North American had north-south subduction zone. Belts of oceanic rock were added to CA by a series of collisions & accretions. Earliest rocks add were Paleozoic sedimentary & volcanic rocks. Subduction zone shifted westward each episode & accretion of younger terrane began. Andesitic volcano chain formed.

Back 10

Mesozoic

Front 11

Between the trench & the Sierran volcanic arc, a marine ___ extended along most of CA's length. The Cretaceous ____, including marine sedimentary rocks found today in Transverse Ranges, accumulated in this linear basin. Have fragments of old volcanoes that used to be above Sierra Nevada granitic rocks. The sedimentary rocks of the [last answer] accumulated on Coast Range ophiolite (crust & upper crust mantle beneath the ocean floor).

Back 11

forearc basin;

Great Valley Sequence;

Great Valley Sequence;

Front 12

Major tectonic events of Mesozoic had dramatic effect on rocks already there. They faulted, folded, metamorphosed during intrusions of magma & episodic compressional events. Hard to determine pre-Mesozoic history.

Back 12

YO FACE IS HARD TO DETERMINE

Front 13

__ million years ago Pacific & North American Plate touched for the first time. Created the ___. Influenced a lot of stuff. Large blocks shifted 315 km. Ex. Salinian Black moved from south to northwest to central CA. Right lateral movement brought crystalline basement rocks from SE CA to present positions in San Gabriel Mountains.

Back 13

27 million years ago;

San Andreas Fault;

Front 14

In early history of SAF, large volumes of sediment accumulated in marine basins along continental margin by ___ basins meaning through extension. In south Great Valley, San Joaquin basin was a very deep marine basin between 35-15 million years ago & a shallow marine embayment persisted there until 2.5-3 million years ago.

Back 14

pull-apart basins;

Front 15

Extension of crust along north-south zone of what is now the Mojave Desert & Basin & Range. Large crustal blocks were pulled apart along detachment faults with some removing the overlying rocks to expose the metamorphic rocks of the lower plate. These ___ can be seen in belt form dome-shaped ranges of SE CA.

Back 15

metamorphic core complexes;

Front 16

West Transverse Range & Mojave Desert have rotated in a clockwise direction during Miocene due to right-lateral motion along the edge of North American Plate. Southern end of west Transverse Ranges broke free of North America, but eastern end remained attached to the continent which rotated it. This created a region of ___ to the south where LA basin & offshore islands are. Believe this caused uplift & unroofing of metamorphic rocks from lower levels of the crust.

Back 16

extension;

Front 17

One major consequence of the development of the transform margin was the shutting off of magmatic activity beneath North America. In areas east of the growing transform margin, no oceanic plate was being subducted so no magma was generated. Crust extension in the east is what causes only magmatic activity. Also, the boundary between the Farallon & Pacific Plates, the ____ was an oceanic spreading ridge. After Farallon completely subducted, ___ encountered the subduction zone. Geologists believe this may have triggered a period of volcanic activity close to the plate boundary & that these volcanic rocks can be seen today.

Back 17

East Pacific Ridge;

East Pacific Ridge;

Front 18

5 million years ago, Gulf of CA began to open, Baja CA became part of Pacific Plate. Transform boundary shifted in south. Now transpression instead of transtension. Created greater convergence between North American & Pacific plate & formed Big Bend.

Back 18

During past few million years, transform boundary still growing in length. Pacific going northwest & North American going southeast.

Front 19

Most of CA's major mountain ranges were elevated about 4-5 million years ago in response to increased compression along the plate boundary. Present Sierra Nevada range rose in same way as Mesozoic chain of volcanoes in past 9 million years, but not as high. Lots of uplifting from compressional fores. Crust extension still happening in Mojave Desert & Basin & Range Province.

Back 19

OKAY