Miocene to Present

High Cascade Range Late Tertiary Volcanism Columbia River Mid-Miocene to present Plateau Snake River Plain Reading: Basin and Range Southwestern DNAG volume G3, Ch. 7 California Sierra Madre Trans Mexican Volcanic Belt

High Cascades North Washington

Volcanic centers define Individual andesitic High Cascades volcanoes and intrusive systems with regular Active volcanoes extend spacing between Mt. from northern Garibaldi, Mt. Baker, & California to southern Glacier Peak British Columbia NW trending alignment Distribution of volcanoes perpendicular to subduction related to segmented arc Between Glacier Peak and Mount St. Helens there is Different dips and a nearly right angle seismicity change in direction

Other Andesite Southern Washington Volcanoes • Subduction here is steeper Located at spacings of 60 • Additional numerous short-lived volcanic to 130 km in this zone systems Mount Rainier, Goat Rocks, – Mafic andesite and basaltic shields Mount St. Helens, Mount Adams, Mount • Tectonic system changes southerly Hood, Mount Jefferson, – Uplift and contraction in the north Three Sisters, Crater Lake, Mount McLaughlin, – Extension within and adjacent to the arc in Mount Shasta, Mount the south Lassen

1 Columbia Intermontane Area Columbia Plateau tholeiitic flood basalts Extreme extrusion rate of 2 x 105 km3 between 17 to 15 Ma Isolated small volcanic fields e.g. Modoc Plateau

Southwest Oregon

Eastward decreasing ages

Bimodal (basalt-rhyolite) compositions

Domes and lavas

South Rocky Mountains, South Rocky Mountains, Sierra to Wasatch Range Rio Grande, Mojave

Mainly basaltic magmatism Scoria cones and lava flows Central volcanoes Basaltic volcanism Peaks, White Mountains, Ash-flow tuffs Mount Taylor Local high-F - Valles magmas Diatremes - Buttes Topaz- bearing magmas

2 Drastic Change in Tectonic High Plateaus Pattern • Occurred in mid-Miocene (18 to 10 Ma) • Earlier extension related to degrading of Laramide highlands • Formed depositional or volcanic plains Northern Nevada to Snake • Later extension related to regional linear block River Plain faulting Bimodal rhyolite (calderas) & • Features are manifest in present day morphology flood basalts Eastward younger ages = hot spot trace

Late Cenozoic Extension Tectonic and Uplift Extension • Southern Rocky Mountains and Rio Grande-Mojave region • Entire region • Salton Trough broadly uplifted in mid-Miocene • Sierra-Wasatch high plateaus region • Columbia intermontane region and • Colorado northern Rocky Mountains Plateau – Mid-Miocene Columbia volcanic episode – Later Miocene to Quaternary volcanism •Great Basin of the Columbia and Oregon Plateaus

Rocky Mountains and Great Rocky Mountains and Great Plains Uplifted Plains Uplifted • Late Cenozoic uplift of Rocky Mountains • Middle and southern Rockies • Fixed position of present continental divide – Undergone Basin and Range faulting • Much of earlier basin deposits removed and redeposited – Deeper erosion – Ogallala Fm of great plains of eastern Colorado • Highest elevations are in the southern • Northern Rockies Rockies – Continuous with Canadian Rockies • Epeirogenic uplift • Undergone little late Cenozoic tectonism

3 Rio Grande Rift Gila-Sonora-Mojave System

Early rift system • Southern Basin and Range & Mogollon Developed in late Oligocene (30 Ma) Plateau Followed zone of Laramide uplifts • Regional Basin and Range extension and Reflects Basin and Range extension block faulting (12 Ma to present) Later faulting Along zone of grabens and half • Widespread extension and basin formation grabens • Mafic to intermediate calc-alkaline volcanism Related to regional uplift Broad integrated system of widely distributed extension

Sierra-Wasatch • Mid-Miocene was a period of transition (21 to 14 Ma) • Widespread welded ash-flow sheets – Broken by late Miocene and younger faults • Distributed extension – Broad subsiding basins – Some rotational fault blocks • Local mafic to intermediate volcanism • Parallel linear fault block ranges – Began to form 14 to 10 Ma

Mexico • •Tertiary ash flow plateau & calderas

–Basaltic fields and isolated diatremes

•Baja California

•Trans Mexican Volcanic Belt

–Composite andesite volcanoes

–Scoria cones and basalt fields

4 Summary:

• Laramide paleogeography and physiography • Post-Laramide, Eocene to mid- Miocene (55 to 21 Ma) • Mid-Miocene to Quaternary (14 to 0 Ma)

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