Download Geología Norteamerica

Phanerozoic History
of North America
Tectonic Context of NA: Part 4
Last Topics


CM of Eastern
North America
CM of the Southern
North America
ENACM-Tectonic Regimes
SNACM – Tectonic Regimes
Western North America

The western margin
of the North
American continent
extends from the
southern California to
central part of Alaska
and from the Pacific
Coast to the craton
below the Great
Plains.
Tectonostructural Feature

Western North
America
Continental
Margin consists
of a series of
margin parallel
tectonic belts.
Tectonostructural Feature



The most landward
of these belts is
composed of
deformed Proterozoic
North America.
Seaward, the belts
consist of a set of
terranes, each of
them being
differentiated mainly
by the age of
attachment to North
America.
Generally, younger
terranes are to be
found seaward.
Belt Features


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The total width of the belts is highly variable.
Some belts seem to be continuous along the
strike and extremely short on strike.
Some of them consist of a single terrane but in
some others several discrete segments have been
identified along the strike.
These terranes have undergone synattachment
and postattachment deformations.
Moreover, the structural arrangement varies
significantly on strike.
Belt Features

In California and British Columbia it includes the surfaces that
accommodate the maximum rate of slip between the plates (San
Andreas and Queen Charlotte faults respectively).
Sucession of the Tectonic Regimes
Pacific Basin Lithosphere


An oceanic basin has probably existed along the
western margin of North America throughout
the Phanerozoic.
Its evolution can be viewed in three phases
(i) end-Proterozoic breakup of Rodinia and sea-floor
spreading;
 (ii) Cambrian-Jurassic intrabasinal tectonic phase
from which no plate survives;
 (iii) a Cretaceous-Cenozoic phase for which plates
exists for which their position and kinematics can be
reasonably well restored.

Phase 1: End Proterozoic


Breakup of Rodinia caused the development of
the Proto-Pacific oceanic basin and the growth
of the Paleozoic oceanic lithosphere against the
newly generated passive margin of the western
North America.
By Permian times, the sea floor spreading
produced a huge ocean and the Proto-Pacific
was only a part of it. The name of the huge
ocean that surrounded the Pangea
supercontinent is Panthalassa.
Phase 2:Cambrian-Jurassic



Plate boundaries have been created within the
Proto-Pacific lithosphere, dividing it into plates.
Moreover, convergent motions relative to the
Proto-Pacific plates developed at various times
and places along the western margin of North
America.
The convergence may not have occurred
completely along the western continental
margin until the Middle Cretaceous times.
Phase 2: Characteristics


In this phase, the continent started to expand
basinward (westward) by accretion. All the
events are recorded in the rock and structural
features of the terranes and by continental arcs.
Glimpses of the pre-Cretaceous plate tectonics
within the Proto-Pacific Ocean come the
tectonostratigraphic records of certain terranes
transferred from the Proto-Pacific plates to
North America at active and collisional margins.
Phase 2: Examples

Oceanic Spreading is documented by the age
of crystallization of the ophiolites and oceanic
basalt in the terranes.
Ex: Trinity Terrane of the Klamath Mts. (California)
includes Lower Cambrian ophiolites that can document
the early magmatism at the western edge of the newly
formed North America.
 Middle and and Late Paleozoic ophiolites of Sierra
Nevada (Feather River & Keweah ultramafic rocks)
indicate Paleozoic spreading in the Proto-Pacific Ocean.

Phase 2: Record Nature

For these events, we can infer the nature of
the events but the real position and
orientation of the plate boundaries at which
they developed remain utterly unknown.
Phase 3: Cretaceous Cenozoic


There is a huge amount of data for the
Cretaceous-Cenozoic tectonics (magnetic
anomalies, fracture zones, hotspot tracks,
paleomagnetic data, structure and fossil
provinciality).
These data indicate the presence of three major
oceanic plates: Pacific, Farallon and Kula with
divergent boundaries among themselves that
migrated towards and intersected the convergent
boundaries of the North America plate at
various times and places.
Farallon Plate
Collisional Margins
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
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The first collision is dated Late Devonian and
the last one in the Middle Cretaceous times.
Therefore, by the end of the Cretaceous the
whole western margin of North America was an
active one.
The main criterion to document an active
margin is the existence of a continental
magmatic arc. Collisional margins have no
continental arc, although arc magmatic rocks can
be thrust on them during collision.
Devonian Collision - Antler

The main effect of the
Antler Orogeny
(Uppermost DevonianMississippian) was the
destruction of the
Cordilleran passive
margin that has been
formed with the block
up of Rodinia.
Devonian Collision - Antler
Mississippian
Pennsylvanian
Active Margins

At such margins there is a subduction of the
pacific plates below the North American
continent. Such margins have been classed
as Andean, employing western South
America as the global example.
Active Margins
Active Margins
Associated Magmatism
Sevier Orogeny
Laramide Orogeny