DEFINITION OF DIAPIR

Intrusive bodies of relatively buoyant rocks that

produce an upwarp, a fold, or penetrate through surrounding

denser rocks. They may be made of sedimentary, igneous, or

even metamorphic rocks.

In sedimentary sequences, diapirs are typically made of

salt or shale that became mobilized and buoyant when buried

under thick piles of younger strata. Most salts and shales of

this category were initially formed as sedimentary layers but

intruded upward to form diapirs when the weight of overlying

rocks became sufficient to mobilize the salt and shale deposits.

The salts typically become buoyant relative to the surrounding

rocks when they reach a burial depth of about 1,450–3,250

feet (450–1,000 m), but it takes some triggering mechanism

(such as shaking on a fault) to initiate the movement of the

salt, referred to as diapirism. In a few places, such as the

Great Kavir in the Zagros Mountains of Iran, salt diapirs have

emerged at the surface and have formed great salt glaciers.

Salt diapirs move by ductile flow forming complex and

strongly attenuated folds. Externally, most salt diapirs form

mushroom shapes with thin necks and expanded heads. These

are referred to as salt domes. Some salt diapirs have moved

very far, even tens of kilometers from their area of deposition,

forming large sheets that are said to be allochthonous (far

traveled). Many other shapes of salt and shale diapirs are

known. Salt and shale diapirs typically form folds and make

permeability barriers that form economically significant

petroleum traps, so a great deal of seismic exploration for

hydrocarbons has been done around salt domes and diapirs.

Diapirs may also be composed of igneous rocks that

intrude surrounding country rocks. Igneous diapirs may be

isolated bodies or internal parts of plutons. Some form

shapes similar to salt and shale diapirs, but internal structures

are more difficult to recognize because they do not have as

many marker horizons as sedimentary salts and shales. Some

metamorphic gneiss domes may also rise diapirically,

although this is disputed because similar patterns can be

formed by fold interference patterns in gneiss terrains.

See also CONTINENTAL CRUST; PLUTON; STRUCTURAL

GEOLOGY; ZAGROS AND MAKRAN MOUNTAINS.

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