Presentation is loading. Please wait.

Presentation is loading. Please wait.

The Cordilleran Orogen of western North Americais part of the circum-Pacific orogenic belt. 1% 10%/m.y. At any time, geology is made over only a small.

Similar presentations


Presentation on theme: "The Cordilleran Orogen of western North Americais part of the circum-Pacific orogenic belt. 1% 10%/m.y. At any time, geology is made over only a small."— Presentation transcript:

1 The Cordilleran Orogen of western North Americais part of the circum-Pacific orogenic belt. 1% 10%/m.y. At any time, geology is made over only a small fraction of the Earth’s surface. The colored area in the map above show current-day strain rate, i.e., where geology currently is happening. This occurs at spreading centers, subduction zones, and in areas of continental orogeny. The western U.S. is such a place. Mercator map projection about pole at 25° N 15 ° E now USA Island arc assemblage Oceanic subduction complex Rift S wUS_Intro.ppt

2 Mexico Canada Pacific Plate North American Plate Surface Velocity 1/ mm/yr km S-wave velocity ± 5.0% The western U.S. Cordilleran Orogen is defined by broad zones of uplift, deformation and magmatism km The area of uplift (which is unusually wide in the western U.S.) is where the Farallon slab is thought to have been flat against North America lithosphere during the Laramide orogeny. Currently, the upper mantle is very slow to seismic waves beneath the uplifted area (the mantle is hot or partially molten). Also, the uplifted area has high amounts of gPE (gravitational potential energy), which acts to drive extension. Cordilleran uplift Cordilleran interior compression tension gPE and resulting stress The area of active deformation (which is unusually wide in the western U.S.) occurs both at the plate margin and where intense magmatism occurred recently (in the Basin and Range). Only the western portion of the high gPE area is extending, which argues that the deforming area is relatively weak. This is consistent with its history of recent, intense magmatism. Interior deformation is mostly extension, whereas near the transform plate margin deformation is dominated by right- lateral shearing. deformation Stress field created by combination of gPE and plate interaction. Light gray areas are weak. Velocity of points relative to stable North America. Projection s such that the Pacific plate moves toward the top of the page. Plate interactions Figure to left shows stresses caused by plate interaction alone; figure at top right shows stresses created by gPE alone. Yellow arrows show plate interaction forces Summary > Plate interaction > Grav. PE > Plate weakness Inheritance } Present

3 Simplified Geologic Maps. Precambrian (pink and orange in top map) forms stable continental cores. North America (above). Archean craton blocks were assembled at mobile belts; a series of Proterozoic arcs accreted to the south side of the Archean continent. Proterozoic rifts emplaced intrusions (mid-continent rift, 1.1 Ga) and made basins (diagonal dashes below), but it wasn’t until the end of the Precambrian that rifting split away the western continent. The continent margin (west of the gray line at above) formed an Atlantic-type “miogeoclonal’ margin, with a normal sedimentary shelf (see cross section to right). Precambrian Lund (2008)

4 Blakey (web site) Dickinson (2006) Cambrian (~510 Ma) paeogeography. The passive margin setting is established. Carbonate rocks, fluvial and shallow marine sandstone and mudstone grade westward into the paleo- Pacific. Deposits were thin on the continental platform east of the hingeline, and thicken rapidly to the west of the hingeline. hingeline sediment Precambrian lithosphere post-rift lithosphere miogeocline ocean crust crust Latest Precambrian rifting stretched the margin of North America (the area between the hingeline and the western edge of purple crust in the tilted figure below). Post-rift lithospheric cooling caused subsidence and creation of a passive “Atlantic-type” margin that received a thick accumulation of sediment in the “miogeocline” west of the hingeline. This state of affairs continued through much of the Paleozoic. Passive Margin and the Miogeocline Dickinson (2006) Main Geologic Events of the Southwest U.S. (for the area shown in the Blakey figure at bottom left) core complexes Rift Nevadan Laramide Sonoma Antler Sevier Ancestral Rockies Rift Tectonic Event Paleozoic

5 Dickinson (2002) and magmatic arc accretion and growth Paleozoic Mesozoic

6 Dickinson (2002) ignimbrite flareup. (SMO, Paleogene Ma Ma Laramide Post-Laramide Northern core complexes Southern core complexes Cascade Arc Challis-trend magmatism Ma Siletzia accretion and the Ignimbrite flareup 43 Cenozoic


Download ppt "The Cordilleran Orogen of western North Americais part of the circum-Pacific orogenic belt. 1% 10%/m.y. At any time, geology is made over only a small."

Similar presentations


Ads by Google