Terrane

A Terran (from Latin terra " earth ") is a crustal block of regional expansion, which has attached by large tectonic shifts to a different continent to which he has a different geological career.

Properties

The crustal portion of a Terran is characterized by uniform petrography and him closing line structure of mostly inactive geological faults. A Terran has a closed geological overall picture, which is determined by stratigraphy, fauna / flora, structures, age and type of metamorphism, igneous rocks, metallogeny, Paleomagnetism and geophysical properties. It is bounded on all sides by faults or thrust faults, which may contain rocks a Subduktionsgrabens as blends or ophiolite. It may consist solely of a ceiling unit without crustal roots.

Formation

Terrane are primarily found within a mountain belt ( orogen ) of active continental margins ( subduction zones ) and are distinguished by their different lithology and mineral paragenesis of adjacent areas. Therefore, It is assumed that there is at terranes welded to the plate tectonic movement allochthonous ( non-local ) fragments of other continents ( microplates ), island arcs or seamounts. The crustal portions will not be subducted, but sheared off from their support and pushed to the continent ( autopsy ). At sea facing Terra edge is evident in such cases, often a narrow hem autopsied, so deferred seabed. A Terran can travel a great distance to its accretion. The North American cordilleras consist to a large extent from such exotic crustal blocks in the Canadian Cordillera terranes were first observed and studied scientifically.

Types of terranes

A distinction is overgrowing Terrane ( Akkretionsterrane ) and group-forming Superterrane (English: composite terranes ), the surrounding areas are characterized by different tectonic evolution.

Other distinguishing opportunities exist in the geological history of terranes:

• Exotic Terran: drifted by an oceanic basin and contains a geological overall picture that is different from the region to which the Terran was accreted. These differences can not be explained by facies. Examples are micro - continents and island arcs.
• Proximal Terran: Redeemed from a continental margin and was moved along the same continental margin over 100 km. The limiting lateral displacement zone can be changed by subsequent collision (eg, covered by blankets complexes; rotates during the collision, the original movement sense is inverted, and the lateral displacement has partially transformed into an up - or thrust ). A proximal Terran can show a geological overall picture that is similar to the region, in addition to which it was added.

A particular problem is the detection of proximal terranes, for a minimum displacement of 100 km is specified, the extent of the shift is quite elusive.

Occurrence

Well-known examples are the Canadian Cordillera, the East Siberian Primorsky region and smaller microplates in Western and Central Europe, such as the Hebrides Terran. Large parts of Western Europe consisting of terranes that were moved during the Late Devonian and Lower Carboniferous at the northern edge of Gondwana over distances of 1000-4000 km. These terranes were welded on the collision of Gondwana with Laurussia in the Carboniferous to Laurussia, as the supercontinent Pangaea formed. They are therefore proximally with respect to Gondwana (eg North West Africa) and exotic in terms of Laurussia (eg British Isles - Northern Germany - North and East Poland ).