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The following gives an overview of the
geology, and North Carolina's geologic history, as one
travels the Interstate highway system in North Carolina. This is
written as if one were to travel each of the major interstate
routes in North Carolina (
With county boundaries and major population centers shown, travelers, citizens and educators can also have a good idea about the geology of individual counties using the two geology maps which follow. The geologic "belt map" gives the traveler an overall sense of the state's geology. The "generalized geologic map" provides somewhat more detailed information about the state's geology.
North Carolina is divided into three physiographic provinces, the Coastal Plain, the Piedmont and the Blue Ridge. Three major classes of rocks common to North Carolina are igneous, metamorphic and sedimentary. North Carolina has a long and complex geologic history. The state is best described in terms of geological belts; that is, areas with similar rock types and geologic history.
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I-40 Rocks between the TN-NC State Line and Old Fort along I-40 can be grouped into two broad subdivisions: Late Precambrian metamorphosed sedimentary rocks collectively referred to as "cover rocks," and Middle Proterozoic gneisses and schists known as "basement rocks." Basement rocks in North Carolina are among 1.1 and 1.8 billion years old, and represent an exposed remnant of some of the oldest continental crust in the eastern United States. About 700 million years ago, these ancient basement rocks were "covered" by younger sediments that became rock. Between 500 and 250 million years ago, several Paleozoic mountain-building events metamorphosed (changed the sediments and rocks through heat and pressure), folded, and faulted both basement and cover rocks. Two major ancient thrust sheets telescope the entire rock sequence. The Hayesville fault juxtaposes basement rocks over cover rocks near the Waynesville exit. The Holland Mountain fault separates basement rocks from metasedimentary cover rocks just beyond the Canton exit. Just west of Old Fort is a third major fault known as the Brevard fault zone. The Brevard fault separates these basement and cover rocks of the Blue Ridge Geologic Province from rocks of the Inner Piedmont Geologic Province. I-40 crosses rugged terrain in the Great Smoky Mountains through Pigeon River Gorge from the Tennessee border into North Carolina. The Pigeon River cuts across the "grain" of the mountains and the steep mountain sides and high road cuts combine to make numerous unstable slopes. Rock fall, rock slides and debris flows require nearly continual maintenance to keep the road clear – especially during heavy rainfall. On July 1, 1998, less than a half a mile from the state line, a major rock slide closed both lanes for ten weeks. A major rock fall damaged and closed the eastern tunnel portals at Mile Post 4 (MP4) in early 1985, and a slide blocked the eastbound lanes near MP16 in May 1978. Asheville lies in a broad, bowl-shaped valley shaped and smoothed by erosion and the flood plain of the north-flowing French Broad River. I-40 crosses the Blue Ridge Front between MP67 (top) and MP72 (bottom). The grade’s top is the eastern continental divide that separates streams that flow west to the Mississippi River from streams that flow east into the Atlantic Ocean. At the grade’s base the ancient Brevard fault separates the metamorphic rocks and more gentle and rolling topography of the Piedmont from the metamorphic rocks and mountainous terrain of the Blue Ridge. Between Marion and Mocksville, I-40 crosses the rolling terrain of the Inner Piedmont geologic province. Rocks include 500 million to 1 billion year old metamorphic rocks and igneous intrusive bodies. Between Mocksville and Greensboro, I-40 crosses the northern end of the Charlotte belt composed mostly of igneous intrusive bodies. Between Winston-Salem and Burlington, I-40 crosses igneous intrusive rocks of the Carolina slate belt. These rocks are quarried and crushed for highway aggregate and building construction. Between Burlington and Chapel Hill, I-40 crosses the Carolina slate belt. Resistant metamorphosed volcanic rocks underlie the hills. Between Chapel Hill (MP270) and Raleigh (MP 286) I-40 crosses low-lying topography of the Triassic age "redbeds." Deposited during the time of the dinosaurs in rift valleys formed as the Atlantic Ocean opened, the Triassic mudstones and claystones are the mainstay of North Carolina’s brick industry. Research Triangle Park and RDU Airport lie within the Durham Triassic Basin. The ancient Jonesboro Fault near MP286 forms the eastern basin boundary. From Wilmington to Benson the route crosses progressively older sediments ranging from Quaternary to Cretacous in age. This segment crosses the Coastal Plain. I-26 Traveling along I-26 from the SC-NC State Line to Asheville, there are two major geologic provinces. South of the Asheville Regional Airport, metamorphosed igneous and sedimentary rocks belong to the Inner Piedmont Geologic Province. North of the airport, metamorphosed sedimentary and igneous rocks lie in the Blue Ridge Geologic Province. The boundary is a major fault in the southern Appalachian Mountains known as the Brevard Fault Zone. I-26 ascends the Blue Ridge Front at MP31-35. Landslides disrupted construction from Howard Gap to the base of the Blue Ridge. Engineering stabilized slopes. Many underground drains control water in the soil and weathered rock. At MP22.5 I-26 crosses the eastern continental divide (elevation 2,130 feet) separating streams that flow west to the Mississippi River from streams that flow east into the Atlantic Ocean. I-95 -- North of Benson to the Virginia border This segment crosses the edge of the Coastal Plain and Piedmont boundary and parallels the Fall Zone. The Fall Zone was an old shore line during the Pliocene about three million years ago. The old shoreline is about 300 feet above present sea level. I-95 -- South of Benson to the South Carolina border This segment is wholly within the Coastal Plain. The route crosses fluvial (river) and deltaic sediments. I-85 Between the Virginia-North Carolina State line, I-85 crosses the northern Piedmont physiographic province including portions of the Raleigh belt and the Carolina slate belt. Between Greensboro and China Grove are metamorphosed volcanic and sedimentary rocks of the Carolina slate belt – the site of America’s first gold rush. Between China Grove and Gstonia, I-85 crosses igneous intrusive rocks of the Charlotte belt. These rocks are quarried for crushed stone and dimension stone. Between MP173 (about 1.5 miles east of the Orange-Durham county line) and MP198 (south of the Tar River), I-85 crosses low-lying topography characteristic of the Triassic "red beds." Deposited during the time of the dinosaurs in rift valleys formed as the Atlantic Ocean opened, the Triassic mudstones and claystones are the mainstay of North Carolina’s brick industry. The City of Durham is the namesake of the Durham Triassic Basin. Between Gastonia and the South Carolina-North Carolina State line, I-85 passes through the Kings Mountain belt. Hard resistant quartzites form Kings Mountain and Crowders Mountain, the tallest peaks to the south. I-77 Between Elkin and Charlotte, I-77 crosses the Inner Piedmont province. These metamorphic rocks (gneisses and schists) are between 500 million and 1 billion years old. Between Statesville and the South Carolina-North Carolina State line, I-77 crosses the Charlotte belt. Igneous intrusive rocks are quarried for use as crushed stone and dimension stone. MINERAL INDUSTRY North Carolina has important deposits of many minerals and annually leads the nation in the production of feldspar, lithium minerals, scrap mica, olivine and pyrophylitte. The state produces essential quantities of ultrapure quartz used for the fabrication of computer chips. The state ranks second in phosphate rock production and ranks in the top five state in clay and crushed granite production. North Carolina does not produce significant quantities of metallic minerals. EMERALD -- "The State Precious Stone"
GRANITE -- "The State Rock"
The following brief descriptions summarize the geology of each of the previously described geologic belts and provides additional information. For additional information about geology, mineral resources, geologic hazards, earth science education, and topographic maps visit the North Carolina Geological Survey web site at www.geology.enr.state.nc.us
This mountainous region is composed of rocks from over one billion to about one-half billion years old. This complex mixture of igneous, sedimentary and metamorphic rock has repeatedly been squeezed, fractured, faulted and twisted into folds. The Grandfather Mountain Window was formed when younger rocks eroded exposing older rocks below -- as a "window." The Blue Ridge belt is well known for its deposits of feldspar, mica and quartz-basic materials used in the ceramic, paint and electronic industries. Olivine is mined for use as refactory and foundry molding sand.
The Inner Piedmont belt is the most intensely deformed and metamorphosed segment of the Piedmont. The metamorphic rocks range from 500 to 750 million years in age. They include gneiss and schist that have been intruded by younger granitic rocks. The northeast-trending Brevard fault zone forms much of the boundary between the Blue Ridge and Inner Piedmont belts. Although this zone of strongly deformed rocks is one of the major structural features in the southern Appalachians, its origin is poorly understood. Crushed stone for aggregate and building construction is the principal commodity produced.
The belt consists of moderately deformed and metamorphosed volcanic and sedimentary rocks. The rocks are about 400-500 million years old. Lithium deposits here provided raw materials for chemical compunds, ceramics, glass, greases, batteries and televison glasses.
This belt consists of gneiss, schist and metamorphosed intrusive rocks. The principle mineral resource is crushed stone for road aggregate and for building construction.
This belt consists mostly of igneous rocks such as granite, diorite and gabbro. These are 300-500 million years old. The igneous rocks are good sources for crushed and dimension stone for road aggregate and buildings.
This belt consists of heated and deformed volcanic sedimentary rocks. It was the site of oceanic valcanic islands about 550-650 million years ago. This belt is known for its numerous abandoned gold mines and prospects. North Carolina led the nation in gold production before the California Gold Rush of 1849. In recent decades, only minor gold mining has taken place, but mining companies continue to show intereste in this area. Mineral production is crushed stone for road aggregate and pyrophyllite for refractories, ceramics, filler, paint and insecticide carriers.
The basins are filled with sedimentary rocks that formed about 200-190 million years ago. Streams carried mud, silt, sand and gravel from adjacent highlands into rift valleys similar to those of Africa today. The mudstones are mined and processed to make brick, sewer pipe, structural tile and drain tile.
The Raleigh belt contains granite, gneiss and schist. In the 19th century, there were a number of small building stone quarries in this region, but today the main mineral product is crushed stone for construction and road aggregate.
This belt contains slightly metamorphosed volcanic and sedimentary rocks similar to those of the Carolin slate belt. The rocks are poorly exposed and partly covered by Coastal Plain sediments. The metamorphic rocks, 500-600 million years old, are intruded by younger, approximately 300 million year old, granite bodies. Gold was once mined in the belt, and small occurrences of molybdenite, an ore of molybdenum, have been prospected here. Crushed stone, clay, sand and gravel are currently mined in the belt.
The Coastal Plain is a wedge of mostly marine sedimentary rocks that gradually thickens to the east. The Coastal Plain is the largest geologic belt in the state, covering about fourty-five percent of the state's land area. The most common sediment types are sand and clay, although a significant amount of limestone occurs in the sourthern part of the Coastal Plain. In the Coastal Plain, geology is best understood from studying data gathered from well drilling. The state's most important mineral resource in terms of dollar value is phosphate, an important fertilizer component, mined near the coast at Aurora, Beufort County. Industrial sand for making container and flat glass and ferrosilicon and used for filtration and sandblasting is mined in the Sand Hills area. FOR FURTHER INFORMATION For further information about the geology and mineral resources, or to obtain topographic maps of North Carolina, contact the North Carolina Geological Survey (NCGS) at: 1612 Mail Service Center, Raleigh, NC 27699-1612. The NCGS can be contacted by telephone at: (919) 733-2423, or by facsimile at (919) 733-0900. The NCGS’ street address is 512 North Salisbury Street, Raleigh, NC 27604-1148. The NCGS’ Internet site is: www.geology.enr.state.nc.us |
