2 (g.a.) Rock Cycle
The Rock Cycle and Plate Tectonics: The changes of the rock cycle are closely related to plate tectonics. Plate
movements start the rock cycle by helping to form magma, the source of
igneous rocks.
Igneous Rocks: Where oceanic plates move apart, magma formed from melted mantle rock moves upward and fills the gap with new igneous rock. Where an oceanic plate is subducted beneath a continental plate, magma forms and rises. The result is a volcano made of igneous rock. A collision of continental plates may push rocks so deep that they melt and form magma. This magma slowly cools and hardens to form igneous rock.
Sedimentary and Metamorphic Rocks: The collision of continental plates produces faults, folds, and uplift of the crust. Eventually, the collision could push up a mountain range. Then, erosion begins. The mountains eventually are worn away, leading to the formation of sedimentary rock.
A collision between continental plates can also push rocks down deep into the mantle. There, heat and pressure could change the rocks to metamorphic rock. And so the rock cycle continues.
Here’s one possible pathway through the rock cycle. The igneous rock granite formed beneath the surface. Then, the forces of mountain building slowly pushed the granite upward, forming a mountain. Slowly, water and wind wore away the granite. These granite particles became sand, carried by streams to the ocean. Over millions of years, layers of sandy sediment piled up on the ocean floor. Slowly, the sediment changed to sandstone, a sedimentary rock. Over time, the sandstone became deeply buried. Heat and pressure changed the rock’s texture from gritty to smooth. The sandstone changed into the metamorphic rock quartzite. But metamorphic rock does not end the rock cycle, which continues for millions of years.
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Igneous Rocks: Where oceanic plates move apart, magma formed from melted mantle rock moves upward and fills the gap with new igneous rock. Where an oceanic plate is subducted beneath a continental plate, magma forms and rises. The result is a volcano made of igneous rock. A collision of continental plates may push rocks so deep that they melt and form magma. This magma slowly cools and hardens to form igneous rock.
Sedimentary and Metamorphic Rocks: The collision of continental plates produces faults, folds, and uplift of the crust. Eventually, the collision could push up a mountain range. Then, erosion begins. The mountains eventually are worn away, leading to the formation of sedimentary rock.
A collision between continental plates can also push rocks down deep into the mantle. There, heat and pressure could change the rocks to metamorphic rock. And so the rock cycle continues.
Here’s one possible pathway through the rock cycle. The igneous rock granite formed beneath the surface. Then, the forces of mountain building slowly pushed the granite upward, forming a mountain. Slowly, water and wind wore away the granite. These granite particles became sand, carried by streams to the ocean. Over millions of years, layers of sandy sediment piled up on the ocean floor. Slowly, the sediment changed to sandstone, a sedimentary rock. Over time, the sandstone became deeply buried. Heat and pressure changed the rock’s texture from gritty to smooth. The sandstone changed into the metamorphic rock quartzite. But metamorphic rock does not end the rock cycle, which continues for millions of years.
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