Transcript Mesozoic - Cordilleran

Earth History
GEOL 2110
The Mesozoic Era
Geologic and Tectonic History of the
North American Cordilleran
Major Concepts
• The geologic history of Cordilleran Orogen of North
America during the Mesozoic Era was dominated
compressional tectonics that accreted exotic terranes in
the early Mesozoic (Triassic and early Jurassic periods)
and then became Andean-type volcanic arc in the mid- to
late Mesozoic (Jurassic and Cretaceous periods).
• A flattening out of subduction in the Cretaceous is
thought to squelch volcanism in the central part of the
western US and bring about a basin and range-type
tectonism called the Laramide Orogeny
• A major transgression in the Cretaceous created a Great
Interior Seaway where great accumulation of marine and
non-marine sediment were deposited in the Great Plains
Events of the Mesozoic Era
Accumulation of Thick Cambrian
Sediments on the Rifted Western
Margin of Laurentia
Belt Supergroup
sediments preserved in
rift grabens (aulocogens)
Late Devonian-Mississippian Antler Orogeny
Accretion of a Volcanic Island Arc
Sediments Shed off the Antler Orogen
The Ancestral Rocky Mountains
Pennsylvanian-Permian Cratonic Warping
Penn-Perm Ouchita Orogen
Extension of the Appalacian Orogen
Tectonic
Grain of
Vergence
shifts in
the
Mesozoic
Triassic Accretion of Suspect Terranes
Collage Tectonics
Six Major Suspect Terranes
2 mostly Paleozoic
3 Late PaleozoicEarly Mesozoic
1 mostly Mesozoic
Wrangellia – oceanic ridge
system
Sonoma/Stikinia – volcanic
arcs
Evidence for Suspect Terranes
Paleomagnetic Latitudes Reconstructions and
Tethyan Fossil Assemblages
Many terranes contain fossils that
suggest a source from the Tethys Sea
Timing of Suspect Terranes Vergence
Cont, TerA and TerB all
have unique
paleopole orienations
Cover Sed I contains
pebbles from Cont
and Ter B only
Cover Sed II contains
pebbles from all
terranes and late
intrusions
Age of granites sets
upper age of vergence
of TerA and TerB
Late Triassic Transition to Andean-type Margin
Antler Orogeny
Accretion of
Suspect/Exotic
Terranes and
Volcanic Arcs
Sonoman Orogeny
Navajo Sandstone
Sierran Orogeny
Continental Volcanic Arc
Forearc Environment
Accretionary Wedge - material scraped
off descending slab
Melange – complex mix of rock types –
ophiolites and deep water sediments
Forearc basin – filled with immature
graywacke turbidites
Forearc Rock Types
Franciscan Melange
Pillowed Basalts
Blueschist (Hi-P metamorphic rx)
Great Valley Greywackes
Magmatic Arc Environment
Granite Batholiths – Feeders to Stratovolcanoes
Mt Jefferson
Foreland Basin
Environment
Clastic Wedge Sedimentation
Alluvial Fan
Conglomerates
= Molasse
Deep water muds
= Flysche
Sevier Orogeny
Intense Compression in the Late Cretaceous (~80 Ma)
results in Crustal Thickening by Overthrusting
Devonian
Sentinal Mtns,
British Columbia
Triassic
Laramide Orogeny
Uplifted Blocks of Precambrian Crust
Latest Cretaceous – Eocene (65-35 Ma)
Laramide Orogeny
Magmatic Null Zone – Shallow Slab Subduction
Magmatic Nulls in
the Andean
Continental Arc
Gaps in volcanic activity
• shallow subduction
• overthickened slab
Winter (2011)
Next Lecture
Cretaceous Trangression
And Mesozoic Life