Geology of the Appalachians

The geology of the Appalachians dates back to more than 480 million years ago. A look at rocks exposed in today's Appalachian mountains reveals elongate belts of folded and thrust faulted marine sedimentary rocks, volcanic rocks and slivers of ancient ocean floor - strong evidence that these rocks were deformed during plate collision. The birth of the Appalachian ranges marks the first of several mountain building plate collisions that culminated in the construction of the supercontinent Pangaea with the Appalachians and neighboring Anti-Atlas (now in Morocco) near the center. These mountain ranges were once higher than today's Himalaya mountain range, which was also formed by continental collision.

Paleozoic Era

During the earliest Paleozoic Era, the continent that would later become North America straddled the equator. The Appalachian region was a passive plate margin, not unlike today's Atlantic Coastal Plain Province. During this interval, the region was periodically submerged beneath shallow seas. Thick layers of sediment and carbonate rock was deposited on the shallow sea bottom when the region was submerged. When seas receded, terrestrial sedimentary deposits and erosion dominated.cite web|url=http://wrgis.wr.usgs.gov/docs/parks/province/appalach.html|title=Geologic Provinces of the United States: Appalachian Highlands Province|work=USGS Geology in the Parks|lastaccess=2007-09-02 (public domain source)]

During the middle Ordovician Period (about 480-440 million years ago), a change in plate motions set the stage for the first Paleozoic mountain building event (Taconic orogeny) in North America. The once quiet, Appalachian passive margin changed to a very active plate boundary when a neighboring oceanic plate, the Iapetus, collided with and began sinking beneath the North American craton. With the birth of this new subduction zone, the early Appalachians were born.

Along the continental margin, volcanoes grew, coincident with the initiation of subduction. Thrust faulting uplifted and warped older sedimentary rock laid down on the passive margin. As mountains rose, erosion began to wear them down. Streams carried rock debris downslope to be deposited in nearby lowlands.

This was just the first of a series of mountain building plate collisions that contributed to the formation of the Appalachians. Mountain building continued periodically throughout the next 250 million years (Caledonian, Acadian, Ouachita, Hercynian, and Allegheny orogenies). Continent after continent was thrust and sutured onto the North American craton as the Pangean supercontinent began to take shape. Microplates, smaller bits of crust, too small to be called continents, were swept in, one by one, to be welded to the growing mass.

By about 300 million years ago (Pennsylvanian Period) Africa was approaching North American craton. The collisional belt spread into the Ozark-Ouachita region and through the Marathon Mountains area of Texas. Continent vs. continent collision raised the Appalachian-Ouachita chain to lofty, Himalayan-scale ranges. The massive bulk of Pangea was completed near the end of the Paleozoic Era (Permian Period ) when Africa (Gondwana) plowed into the continental agglomeration, with the Appalachian-Ouachita mountains near the core.

Mesozoic Era and later

Pangea began to break up about 220 million years ago, in the Early Mesozoic Era (Late Triassic Period). As Pangea rifted apart a new passive tectonic margin was born and the forces that created the Appalachian, Ouachita, and Marathon Mountains were stilled. Weathering and erosion prevailed, and the mountains began to wear away.

By the end of the Mesozoic Era, the Appalachian Mountains had been eroded to an almost flat plain. It was not until the region was uplifted during the Cenozoic Era that the distinctive topography of the present formed. Uplift rejuvenated the streams, which rapidly responded by cutting downward into the ancient bedrock. Some streams flowed along weak layers that define the folds and faults created many millions of years earlier. Other streams downcut so rapidly that they cut right across the resistant folded rocks of the mountain core, carving canyons across rock layers and geologic structures.

References

External links

* http://tapestry.usgs.gov
* http://pubs.usgs.gov/dds/dds11/


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Geology of North America — The geology of North America, like most topics of scientific study, is undergoing progressive investigation by numerous public and private sector earth scientists, academicians, and students. In that regard, the detailed picture is subject to… …   Wikipedia

  • Geology of Tennessee — The geology of Tennessee is as diverse as its landscapes. Politically, Tennessee is broken up into three Grand Divisions: East, Middle, and West Tennessee. Physically, Tennessee is also separated into three main types of landforms: river valley… …   Wikipedia

  • Geology of Georgia (U.S. state) — The Geology of Georgia consists of four distinct geologic regions, beginning in the northwest corner of the state and moving through the state to the southeast: the Ridge and Valley, the Blue Ridge, the Piedmont, and the Coastal Plain.… …   Wikipedia

  • Geology of Alabama — The geology of Alabama is marked by abundant geologic resources and a variety of geologic structures from folded mountains in the north to sandy beaches along the Gulf of Mexico coast. Alabama spans three continental geologic provinces as defined …   Wikipedia

  • Geology — Oceanic crustContinental Crust] Geology (from Greek: γη, gê , earth ; and λόγος, logos , speech lit. to talk about the earth) is the science and study of the solid and liquid matter that constitute the Earth. The field of geology encompasses the… …   Wikipedia

  • Geology of Scotland — The geology of Scotland is unusually varied for a country of its size, with a large number of differing geological features. [Keay Keay (1994) op cit page 415.] There are three main geographical sub divisions: the Highlands and Islands is a… …   Wikipedia

  • The Ozarks — Ozark redirects here. For other uses, see Ozark (disambiguation). Ozark Mountain redirects here. For the wine region, see Ozark Mountain AVA. The Ozarks, Ouachitas, Black Hills, and Sawtooths …   Wikipedia

  • geology — /jee ol euh jee/, n., pl. geologies. 1. the science that deals with the dynamics and physical history of the earth, the rocks of which it is composed, and the physical, chemical, and biological changes that the earth has undergone or is… …   Universalium

  • Ridge-and-Valley Appalachians — The Ridge and Valley Appalachians, also called the Ridge and Valley Province or the Valley and Ridge Appalachians, are a physiographic province of the larger Appalachian division and are also a belt within the Appalachian Mountains extending from …   Wikipedia

  • East Coast of the United States — The East Coast of the United States, also known as the Eastern Seaboard or Atlantic Seaboard , refers to the easternmost coastal states in the central and northern United States, which touch the Atlantic Ocean and stretch up to Canada. While in a …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.