The ultrabasic rocks at Tovqussaq, West Greenland A contribution to the peridotite problem

Abstract

Ultrabasic rocks of bahiaitic type occur as bands in amphibolite at Tovqussaq. It is concluded that the ultrabasics are form ed in situ in the amphibolite in zones of s tress con centration.

Stress of high order in connection with chemically, and mechanically generated heat is regarded to be the cause of the metamorphic differentiation that was responsible for the formation of the ultrabasic rocks.

From the results of the examination of the hypersthenes of the Tovqussaq region it seems reasonable to assume that the hypersthene may be used as a geological thermometer.

Ultrabasic rocks are described from other pre-Cambrian areas and the peridotites of orogenic zones are discussed. The interpretation of the ultrabasic rocks as being the products of metamorphic rather than magmatic processes seems to have general validity.

Finally, the peridotites are compared with eclogites which were probably formed in a similar way.