Mesozoic Mountain Building
- Tr Results of Sonoma Orogeny
- Two belts of rock existed:
- Western belt of thick volcanics and siliceous rocks (800 m in SE California & SW Nevada);
- Wide eastern tract adjacent to the craton.
- Golconda Arc
- Latest Perm or earliest Tr
- Eastward- moving volcanic island arc collided with pacific margin of craton.
- Island arc welded onto western edge adding 300 km to east-west dimension.
- Emplacement of Golconda Arc
- Ocean rocks thrust eastward onto site of Antler orogenic belt
- Thick volcanics and graywackes
- Eastern cordillera (SE Idaho) 1000 m of sandstones and limestones of shallow water origin that interfinger
with terrestrial red beds.
- Why A Painted Desert?
- Regression of the Absaroka Sequence results in extensive vivid-colored terrestrial deposits (Chinle [painted
desert] & Kayenta Fm)
- Erosion & Deposition in the Early Jurassic
- Alluvial plain deposits alternate with eolian & nearshore clean sandstones
- Erosion & Terrestrial Sedimentation
- Zion National Park - Utah
- Navajo & Wingate SS
- >220 meters with basal sediments deposited in water; upper sediments eolian
- Nevadan Orogeny I
- Variable subduction (rate, inclination, and direction) continues resulting in eastward-shifing phases of
deformation.
- Deformation of graywacke, mudstone, chert, volcanics accumulated in the subduction zone.
- Nevadan Orogeny II
- Subducted sediments folded, faulted, & metamorphosed
- Termed mélange, such as the Franciscan Fold Belt (Jr deep water sediments and volcanics)
- Nevadan Orogeny
- Granodiorite generated above the subduction zone
- Intruded into Jr & K rocks as batholiths (Sierra Nevada [K], Idaho, Coast Range).
- Sevier Orogeny
- Early K tectonic activity east of Sierra Nevada (Nevada- Utah) affecting shallow water carbonates and
terrigenous clastics
- Sevier Orogeny II
- Paleozoic strata sheared from underlying Precambrian rocks, broken along parallel planes of weakness
forming multiple imbricated low-angle thrust faults (décollement).
- Crustal shortening of > 100 km.
- Similar deformation north of Montana, British Columbia & Alberta.
- Laramide Orogeny I
- Late Cretaceous to early Cenozoic tectonic activity in the Cordillera involving the folding, tilting, and
faulting of the Cretaceous seaway deposits.
- Compressional forces continued in the west as divergence occurred in the east.
- Laramide Orogeny II
- Development of a steeply dipping subduction zone along western margin
- Subducting ocean crust carried allochthonous terranes: sections of volcanic island arcs, fragments of
microcontinents, and pieces of oceanic plateaus.
- Accretionary Tectonics
- More than 50 displaced terranes identified in the Cordillera and may comprise more than 70% of the rock.
- North America has grown by accretionary tectonics where tectonic collage (crashing of one unit after
another) has occurred.