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Orogenies
CONTINENTS migrate over the Earth’s surface because they are integral parts of the moving lithospheric plates; they simply ride piggyback on the plates. Measurements of these migrations show that North America is now moving away from Europe at about 2.5 centimetres per year, as the mid-Atlantic ridge continues to separate.
South America is drawing away from Africa at a rate of about 3.5 centimetres per year. The Atlantic Ocean is widening, but the Pacific is shrinking at the same rate. Thus, as continents move, ocean basins open and close over geologic time.
The geological features of Guyana were caused by events originating deep in the bowels (interior) of the earth. The surface and the interior of the planet have been divided into layers, namely: The crust, the upper and inner mantle, the outer core, and the inner core.
The crust is the thin shell of rock that covers the Earth. It is separated into two types: Continental crust, which underlies the continents; and oceanic crust, which underlies the oceans. The thickness of this crust varies from three to 31 miles, being thickest below land and thinnest below the oceans.
The mantle under the crust extends downwards for roughly 1,800 miles. The mantle itself is separated into two distinct layers: The uppermost layer, which is cold and rigid. Geologists combine this uppermost layer with the overlying crust, calling it the lithosphere. The lithosphere is roughly 60 miles thick. That part of the mantle immediately beneath the lithosphere is called the asthenosphere. It is composed of partially melted rock, and extends to a depth of about 155 miles.
Beginning some 1,800 miles beneath the surface and extending to a depth of 3,960 miles — the very centre of the planet — is Earth’s core. Composed of iron and nickel, Earth’s core has a solid inner portion, and a liquid outer portion. Scientists estimate that temperatures in the core exceed 5,482°C (almost 175 times the heat of a sunny day in Guyana), creating extreme heat energy.
Convection currents form in the planet’s interior when rock surrounding the core heats up. Expanding and becoming less dense, the heated rock slowly rises through cooler, denser rock that surrounds it in the mantle. Circulating currents, called convection currents, carry the energy to the surface of the planet, where it is released.
The slowly moving convection currents are able to release their heat energy near the surface of the planet because the lithosphere, as has previously been stated, is not solid, but is broken into many large slabs, or plates, that literally “float” on the soft asthenosphere.
Being in constant contact with each other, these plates (tectonic plates) fit together like a giant jigsaw puzzle.
Convection is the driving force behind the motion of Earth’s interior. The pressure exerted by the convection currents underneath the lithosphere causes the plates to move towards or away from each other, or to slide against each other. When one plate moves, other plates move in response.
The word “orogeny” comes from Greek (oros for “mountain”, plus genesis for “creation” or “origin”), and it is the primary mechanism by which mountains are built on continents.
Circulating convection currents under the asthenosphere literally push tectonic plates.
Mountains and mountain ranges are typically formed by the movement and/or interaction of these plates. When two continental (land) plates converge, they crumple and compress like cars in a head-on collision.
Some of the mountain ranges in Guyana were created when convergent tectonic plates crashed into each other during the Trans-Amazonian Orogeny, also referred to as the Trans- Amazonian Tectonothermal Episode, some 2.4 billion years ago.
Many of these ranges have long since disappeared, having been worn down to flat land by the forces of weathering and erosion.
CONTINENTS migrate over the Earth’s surface because they are integral parts of the moving lithospheric plates; they simply ride piggyback on the plates. Measurements of these migrations show that North America is now moving away from Europe at about 2.5 centimetres per year, as the mid-Atlantic ridge continues to separate.
South America is drawing away from Africa at a rate of about 3.5 centimetres per year. The Atlantic Ocean is widening, but the Pacific is shrinking at the same rate. Thus, as continents move, ocean basins open and close over geologic time.
The geological features of Guyana were caused by events originating deep in the bowels (interior) of the earth. The surface and the interior of the planet have been divided into layers, namely: The crust, the upper and inner mantle, the outer core, and the inner core.
The crust is the thin shell of rock that covers the Earth. It is separated into two types: Continental crust, which underlies the continents; and oceanic crust, which underlies the oceans. The thickness of this crust varies from three to 31 miles, being thickest below land and thinnest below the oceans.The mantle under the crust extends downwards for roughly 1,800 miles. The mantle itself is separated into two distinct layers: The uppermost layer, which is cold and rigid. Geologists combine this uppermost layer with the overlying crust, calling it the lithosphere. The lithosphere is roughly 60 miles thick. That part of the mantle immediately beneath the lithosphere is called the asthenosphere. It is composed of partially melted rock, and extends to a depth of about 155 miles.
Beginning some 1,800 miles beneath the surface and extending to a depth of 3,960 miles — the very centre of the planet — is Earth’s core. Composed of iron and nickel, Earth’s core has a solid inner portion, and a liquid outer portion. Scientists estimate that temperatures in the core exceed 5,482°C (almost 175 times the heat of a sunny day in Guyana), creating extreme heat energy.
Convection currents form in the planet’s interior when rock surrounding the core heats up. Expanding and becoming less dense, the heated rock slowly rises through cooler, denser rock that surrounds it in the mantle. Circulating currents, called convection currents, carry the energy to the surface of the planet, where it is released.
The slowly moving convection currents are able to release their heat energy near the surface of the planet because the lithosphere, as has previously been stated, is not solid, but is broken into many large slabs, or plates, that literally “float” on the soft asthenosphere.
Being in constant contact with each other, these plates (tectonic plates) fit together like a giant jigsaw puzzle.
Convection is the driving force behind the motion of Earth’s interior. The pressure exerted by the convection currents underneath the lithosphere causes the plates to move towards or away from each other, or to slide against each other. When one plate moves, other plates move in response.
Orogenies
Orogenies refer to forces and events leading to a severe structural deformation of the Earth’s lithosphere (crust and uppermost mantle) due to the engagement of tectonic plates.
The word “orogeny” comes from Greek (oros for “mountain”, plus genesis for “creation” or “origin”), and it is the primary mechanism by which mountains are built on continents.
Circulating convection currents under the asthenosphere literally push tectonic plates.
Mountains and mountain ranges are typically formed by the movement and/or interaction of these plates. When two continental (land) plates converge, they crumple and compress like cars in a head-on collision.
Some of the mountain ranges in Guyana were created when convergent tectonic plates crashed into each other during the Trans-Amazonian Orogeny, also referred to as the Trans- Amazonian Tectonothermal Episode, some 2.4 billion years ago.
Many of these ranges have long since disappeared, having been worn down to flat land by the forces of weathering and erosion.
Next week: The three geologic provinces
