- The Washington Times - Wednesday, July 6, 2005

George Washington University geology professor Richard Tollo and three of his undergraduate students are detectives of the Blue Ridge Mountains, looking for clues about rocks, their composition and how the Earth formed.

“The whole idea is to fully characterize very complicated rocks and to train students at the same time to become professional geologists,” says Mr. Tollo, who holds a doctorate in geology.

The geology students, hired by the U.S. Geologic Survey (USGS), are studying pyroxene-bearing rocks that are about 1 billion to 1.2 billion years old. The students observe and note the location of the rocks, the oldest in the metro area, making measurements and collecting samples for microscopic and geochemical analysis.

They are participating in the Educational Geologic Mapping Program, a research project under the Appalachian Blue Ridge Project that aims to provide background geological information for the region’s environmental and developmental issues.

“The mineralogy of rocks tells you a great deal about their origin,” says Mr. Tollo, who conducts most of his research in the Blue Ridge and the Culpeper Basin, a lowland area east of the Blue Ridge.



The Blue Ridge has two major types of rocks identified through mineralogy, the study of the properties and distribution of minerals, Mr. Tollo says.

Pyroxene-bearing rocks, including gneisses (banded with layers of dark and light minerals) and granites, were crystallized under high-pressure conditions from magma, a molten material below the Earth’s surface, he explains.

The rocks, which have other minerals, including quartz and feldspar, were lifted to the Earth’s surface when an ancient mountain belt, or range of mountains called Grenville, developed 1 billion years ago. At the time, a giant landmass, or supercontinent, called Rodinia formed with the mountain chain in the middle.

The second type of rock identified in the Blue Ridge is a bit younger, formed about 700 million to 730 million years ago, and can be found west of Gainesville and Warrenton. The rock is a granite with amphibole, a black-colored mineral, and fluorite, a mostly purple-colored trace mineral, among other minerals.

Pyroxene-bearing rocks are metamorphic, altered in material content and appearance by heat and pressure, says James Reger, principal geologist at the Maryland Geologic Survey in Baltimore.

Igneous rocks, such as granite, are formed from molten material from deep within the Earth that solidifies underground or on the surface, Mr. Reger says. Underground or intrusive rocks are dark in color and high in certain substances, such as iron and magnesium, and do not make it to the Earth’s surface, he says. Extrusives are lighter in color, often rich in silicon and aluminum, and do make it to the surface, he says.

Sedimentary rocks, such as shale and limestone, are loose weathered rock debris that can have organic material deposited by wind, water or glaciers, says Alex Speer, executive director of the Geologic Society of Washington, a nonprofit organization in Northwest focused on communicating research results.

“It really is a material world,” says Mr. Speer, who holds a doctorate in geology. “If there weren’t rocks and minerals, there isn’t much left.”

The forming of that world comes, in part, from platectonics. Platectonics occurs when continents collide and move apart, the movement driven by the heat flow within the Earth.

“Platectonics work at the rate fingernails grow … over tens to hundreds of millions of years,” says Diane Noserale, spokeswoman for USGS in Reston.

Rodinia split apart about 570 million years ago, forming an ocean called Iapetus where the Atlantic Ocean is today, says Rick Diecchio, professor of geology at George Mason University in Fairfax. (The continents came back together 250 million years ago as the supercontinent Pangea.)

The coastal area on the ancient continent Laurentia included most of what is Virginia today, along with Maryland and the District, says Mr. Diecchio, who holds a doctorate in geology.

The Iapetus Ocean started to close about 500 million years ago, causing the Earth’s crust to be pushed into the Earth, Mr. Diecchio explains. The crust melted and formed a volcano and eventually a volcanic arc or belt, or chain of volcanos. The volcanic arc pushed against the North American coast, extending the land area.

“The volcanic arc today is the Piedmont, a lowland, hilly area between the coastal plain and the Blue Ridge,” Mr. Diecchio says.

The Blue Ridge is in the Piedmont province and, with the Shenandoah Valley, is part of the Appalachians, the set of mountains that formed about 300 million years ago when the ancient continent Laurentia collided with Africa, Mr. Tollo says.

Rocks in the Piedmont include metamorphic rocks that originally were volcanics, granites or sedimentary rocks; limestones, which are made up of seashells and lime; and diabase, also called basalt, formed after lava cooled at the time Rodinia broke apart, he says.

Several quarries in the Culpeper Basin, located in the Piedmont, dig for diabase, which is a dark-colored, fine-grained igneous rock that weathers to an orange color.

Luck Stone Corp., which operates nearly 20 crushed-stone and sand-and-gravel plants in Virginia and North Carolina, quarries diabase that is used to produce asphalt and concrete and in road, airport runway and building construction.

“It formed better stone than anything else,” says Bruce Faison, geologist at Luck Stone Corp. “When it cooled, it became very dense.”

The Culpeper Basin also is home to red sandstone and shale. The red color in the rocks results from oxygen oxidizing the iron to iron oxide.

Sandstone and shale also are found on the coastal plain, a relatively flat area made up of weathered sediment from the Appalachians. Sandstone is primarily composed of sand-size grains and of quartz and other minerals. Shale is fine-grained.

Other sediments in the coastal plain include gravel, silt and clay. Clay, used in brick production, is formed from weathering, the process by which rocks decompose from exposure to the atmosphere. It is accumulated by erosion and deposition.

The types of rocks change from the coastal plain to the Piedmont. The line between the two provinces in the District is along 16th Street, Ms. Noserale says.

“The eastern part of the city is underlain by a fairly thin part of the coastal plain,” Mr. Speer says. “The western part is underlain by harder rocks.”

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