Tectonic Plates

What is a horst?

A block that has been relatively uplifted between two normal faults that dip away from each other is called a horst.

What is graben?

A block that has dropped relatively downward between two normal faults dipping toward each other is called a graben.

Name a continental plate

A continental plate is exemplified by the North American Plate, which includes North America as well as the oceanic crust between it and a portion of the Mid-Atlantic Ridge.

What is a tilted fault block?

A tilted block that lies between two normal faults dipping in the same direction is a tilted fault block.

How much does the earth's crust or the hard layer extend below?

Analysis of seismic waves within Earth's interior, show that the crust extends about 50 km (30 miles) beneath the continents but only 5-10 km (3-6 miles) beneath the ocean floors.

What creates new crusts

As plates move apart at a divergent plate boundary, the release of pressure produces partial melting of the underlying mantle. This molten material, known as magma, is basaltic in composition and is buoyant. As a result, it wells up from below and cools close to the surface to generate new crust. Because new crust is formed, divergent margins are also called constructive margins.

What is asthenosphere?

Asthenosphere, zone of Earth's mantle lying beneath the lithosphere and believed to be much hotter and more fluid than the lithosphere. The asthenosphere extends from about 100 km (60 miles) to about 700 km (450 miles) below Earth's surface.

What is mantle?

At the base of the crust, a sharp change in the observed behaviour of seismic waves marks the interface with the mantle. The mantle is composed of denser rocks, on which the rocks of the crust float. The mantle behaves as a very viscous fluid and responds to stress by flowing.

What is the third type of plate boundary

At the third type of plate boundary, the transform variety, two plates slide parallel to one another in opposite directions. These areas are often associated with high seismicity, as stresses that build up in the sliding crustal slabs are released at intervals to generate earthquakes.

Are the Himalayas still rising?

Because of the continued subduction of the Indian peninsula against the Eurasian Plate, the Himalayas and the associated eastern ranges remain tectonically active. As a result, the mountains are still rising, and earthquakes—often accompanied by landslides—are common.

What is the composition of continental crust?

Continental crust (sial from silicon and aluminium) consists principally of lower density granitic rocks ("felsic").

What is earth's crust?

Earth's outermost, rigid, rocky layer is called the crust. It is composed of low-density, easily melted rocks;

What is a fault?

Fault, in geology, a planar or gently curved fracture in the rocks of the Earth's crust, where compressional or tensional forces cause relative displacement of the rocks on the opposite sides of the fracture. Faults range in length from a few centimetres to many hundreds of kilometres, and displacement likewise may range from less than a centimetre to several hundred kilometres along the fracture surface (the fault plane).

What is divergence?

In areas of divergence, two plates move away from each other. Buoyant upwelling motions in the mantle force the plates apart at rift zones (such as along the middle of the Atlantic Ocean floor), where magmas from the underlying mantle rise to form new oceanic crustal rocks.

What is convergence?

Lithospheric plates move toward each other along convergent boundaries. This can either result in new mountain ranges or subduction zones.

Examples of strike slip faults

Many are found at the boundary between obliquely converging oceanic and continental tectonic plates. A well-known terrestrial example is the San Andreas Fault, which, during the San Francisco earthquake of 1906, had a maximum movement of 6 metres (20 feet).

Explain normal dip-slip fault

Normal dip-slip faults are produced by vertical compression as the Earth's crust lengthens. The hanging wall slides down relative to the footwall. Ex-Rift valleys are formed by the sliding of the hanging walls downward many thousands of metres, where they then become the valley floors.

Give an example of ocenanic plate

Pacific Plate which extends from the East Pacific Rise to the deep-sea trenches bordering the western part of the Pacific basin.

What is the theory of plate tectonics?

Plate tectonics is the theory that Earth's outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to Earth's mantle. This strong outer layer is called the lithosphere.

How many plates are there in the world?

Plate tectonics on Earth, at present, consists of 12 large semirigid plates of irregular shapes and sizes that move over the surface, separated by boundaries that meet at triple junctions. There are also many broad zones of deformation. The seven major plates account for 94% of the surface area of Earth.

What are reverse dip slip faults?

Reverse dip-slip faults result from horizontal compressional forces caused by a shortening, or contraction, of the Earth's crust. The hanging wall moves up and over the footwall.

What is Rift valley?

Rift valley, any elongated trough formed by the subsidence of a segment of the Earth's crust between dip-slip, or normal, faults. Such a fault is a fracture in the terrestrial surface in which the rock material on the upper side of the fault plane has been displaced downward relative to the rock below the fault. A rift valley constitutes a type of tectonic valley and, as such, differs from river and glacial valleys, which are produced by erosional forces.

How does a rift valley form?

Rift valleys are found both on the continents and on the floor of ocean basins. In terms of the theory of plate tectonics, they occur in divergence zones, belts where two of the various lithospheric plates that make up the Earth's surface are separating.

What is Strike -slip

Strike-slip (also called transcurrent, wrench, or lateral) faults are similarly caused by horizontal compression, but they release their energy by rock displacement in a horizontal direction almost parallel to the compressional force. The fault plane is essentially vertical, and the relative slip is lateral along the plane.

Give an example of transform activity of plate boundaries

The San Andreas Fault in California is an example of this type of boundary, which is also known as a fault or fracture zone (see submarine fracture zone).

What is fault strike?

The fault strike is the direction of the line of intersection between the fault plane and the surface of the Earth. The dip of a fault plane is its angle of inclination measured from the horizontal.

What are Tectonic plates?

The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken up , like a cracked eggshell into dozen rigid blocks called tectonic plates. The Earth's lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates.

How do tectonic plates move in respect to each other at convergent plate boundaries?

The movement of the plates creates three types of tectonic boundaries: convergent, where plates move into one another; divergent, where plates move apart; and transform, where plates move sideways in relation to each other.

List of Tectonic plates

The plates are around 100 km (62 mi) thick and consist of two principal types of material: oceanic crust (also called sima from silicon and magnesium) and continental crust (sial from silicon and aluminium).

What are Thrust faults

Thrust faults are reverse faults that dip less than 45°. Thrust faults with a very low angle of dip and a very large total displacement are called overthrusts or detachments; these are often found in intensely deformed mountain belts. Large thrust faults are characteristic of compressive tectonic plate boundaries, such as those that have created the Himalayas and the subduction zones along the west coast of South America.

What is lithosphere?

Together the uppermost mantle and the crust act mechanically as a single rigid layer, called the lithosphere.

What is subduction?

When a continental plate and an oceanic plate come together, the leading edge of the oceanic plate is forced beneath the continental plate and down into the asthenosphere—a process called subduction. Only the thinner, denser slabs of oceanic crust will subduct, however.

What are hanging wall? foot wall?

When rocks slip past each other in faulting, the upper or overlying block along the fault plane is called the hanging wall, or headwall; the block below is called the footwall.

What produces mountain ranges?

When two thicker, more buoyant continents come together at convergent zones, they resist subduction and tend to buckle, producing great mountain ranges. The Himalayas, along with the adjacent Plateau of Tibet, were formed during such a continent-continent collision, when India was carried into the Eurasian Plate by relative motion of the Indian-Australian Plate.

What is the composition of oceanic crust?

oceanic crust (also called sima from silicon and magnesium) has basaltic rocks ("mafic") and gabbro dominating its crust