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Classification of melanges

Loren A. Raymond
Loren A. Raymond
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January 01, 1984

Melanges and related rock bodies have been defined, described, and classified in a variety of ways. Classifications, divisible into eight types, reflect specific definitions of the term melange. Although melanges were originally considered to be tectonic in origin, currently the term is used widely in a descriptive rather than a genetic sense. Melanges are here defined as bodies of rock mappable at a scale of 1:24000 or smaller and characterized both by the lack of internal continuity of contacts or strata and by the inclusion of fragments and blocks of all sizes, both exotic and native, in a fragmented matrix of finer-grained material. Matrix composition and fabric are rejected as definitive criteria. Progressive fragmentation and mixing of original sedimentary, igneous, and/or metamorphic protoliths give rise to broken formations, dismembered formations, and melanges—three classes of unit that, together with formations, represent a continuum of rock bodies ranging from coherent stratified units at one extreme to chaotically mixed masses at the other. Melanges may originate through sedimentary processes, diapiric processes, tectonic processes, or combinations of these processes, and are classified accordingly.

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GSA Special Papers

Melanges: Their Nature, Origin, and Significance

Loren A. Raymond
Loren A. Raymond
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Geological Society of America
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Publication date:
January 01, 1984



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