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SOME CRITICAL DIFFERENCES BETWEEN ALPINE-TYPE AND STRATIFORM PERIDOTITE-GABBRO COMPLEXES

T. P. THAYER
 

 

 

 

ABSTRACT

 

A close association between gabbro and peridotite; along alpine mountain chains has become apparent in recent years, and a gradational series between alpine-type peridotites and stratiform gabbro-pcridotite complexes has been suggested. Comparison of the features of alpine-type and truly stratiform complexes, however, reveals difference in form, structure, composition, and texture which are believed to be more important genetically than their similarities.

In the stratiform complexes, such as the Bushveld and Stillwater, crystallization of a molten magma in place with little or no disturbance is indicated by features attributable to crystal settling and reaction of settled crystals with entrapped magma, great lateral persistence of compositional layers, cryptic layering, and systematic upward progression from peridotitie to gabbroic rocks. In alpine-type gabbroperidotite complexes, strong deformation of semisolid rocks is implied by irregular form and internal, structure, lack of cryptic layering, prominent lincation and foliation crossing the boundaries between major rock units, and cataclastic textures.
 

 

 

 

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