DEFINITION OF TECTOSPHERE

Cratons are large areas of thick continental

lithosphere that have been stable for long periods of geological

time, generally since the Archean. Most cratons are characterized

by low heat flow and no or few earthquakes. Many

have a thick mantle root or tectosphere, characterized seismologically

and from xenolith studies to be cold and refractory,

having had basaltic melt extracted from it during the Archean.

Seismological studies have shown that many parts of the tectosphere

are strongly deformed with most of the minerals oriented

in planar or linear fabrics. Current understanding about

the origin of stable continental cratons and their roots hinges

upon recognizing which processes change the volume and

composition of continental lithosphere with time, and how

and when juvenile crust evolved into stable continental crust.

Despite decades of study, several major unresolved questions

remain concerning Archean tectosphere: (1) how is it formed?

Large quantities of melt extraction (komatiite in composition,

if melting occurred in a single event) are required from petrological

observations, yet little of this melt is preserved in

Archean cratons, which are characterized by highly evolved

crust compositions. (2) In what tectonic settings is it formed?

Hypotheses range from intraplate, plume-generated settings to

convergent margin environments. (3) Finally, once formed,

does the chemical buoyancy and inferred rheological strength

of the tectosphere preserve it from disruption? Until recently,

most scientists would argue that cratonic roots last forever—

isotopic investigations of mantle xenoliths from the Kaapvaal,

Siberian, Tanzanian, and Slave cratons document the longevity

of the tectosphere in these regions. However, the roots of

some cratons are now known to have been lost, including the

North China craton, and the processes of the loss of the tectosphere

are as enigmatic as the processes that form the roots.

See also ARCHEAN; CRATONS; PLATE TECTONICS.

Title Post:
Rating: 100% based on 99998 ratings. 99 user reviews.
Author:

Terimakasih sudah berkunjung di blog SELAPUTS, Jika ada kritik dan saran silahkan tinggalkan komentar