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 Paleozoic Vergence Tectonic Grain of Vergence shifts in the Mesozoic Mesozoic Vergence

Triassic Accretion of Suspect Terranes Collage Tectonics Six Major Suspect Terranes 2 mostly Paleozoic 3 Late Paleozoic- Early 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 Blueschist (Hi-P metamorphic rx) Franciscan Melange Pillowed Basalts 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 Thrust Fault 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)

Cretaceous Trangression Next Lecture Cretaceous Trangression And Mesozoic Life