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The patterns of enrichment in felsic pegmatites ultimately depend on tectonic setting

R. F. Martin and C. De Vito
The patterns of enrichment in felsic pegmatites ultimately depend on tectonic setting (in The Mineralogical Association of Canada 50th anniversary symposium volume, F. C. Hawthorne (prefacer))
The Canadian Mineralogist (December 2005) 43, Part 6: 2027-2048

Abstract

A classification scheme is proposed for granitic pegmatites focused, not on an offshoot of the depth zone classification, but on petrogenetic processes at work, with an extension to pegmatites in silica-saturated and under-saturated systems. Small-scale pegmatites are encountered also in metamorphic systems undergoing anatexis, as temperature is rising regionally. A newly recognized category of corundum-bearing anatectic felsic pegmatite formed in mantle peridotite earlier subjected to a metasomatic overprint by a mixed H (sub 2) O + CO (sub 2) fluid is included. The bulk of pegmatite bodies encountered are not of anatectic origin, but are derived by fractionation of pluton-scale batches of felsic magma. The LCT (Li-Cs-Ta-enriched) pegmatites are considered to be members of orogenic (calc-alkaline suites) formed in a subduction setting; in contrast, NYF (Nb-Y-F-enriched) pegmatites are affiliated with anorogenic suites, formed in an extensional setting, and not really fundamentally different in petrogenetic lineage from suites in silica-undersaturated systems, including carbonatites. Both LCT and NYF types involve magmas containing crust and mantle components, but in the case of anorogenic magmatism, a metasomatic ground-preparation by a mantle-derived H (sub 2) O + CO (sub 2) fluid phase precedes large-scale melting, to assure a product having alkaline tendencies. A primary NYF-LCT signature may occur in shoshonitic suites. Hybrid pegmatites in which an NYF pegmatitic system takes on an LCT-like overprint owing to contamination from local sources are also discussed. The possibility of an LCT pegmatite also being affected by an LCT-like overprint, to form a 'super-LCT pegmatite' is explored briefly. Proper documentation of the petrogenetic processes at work is essential when assessing the economic potential of pegmatite occurrences.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 43, Part 6
Title: The patterns of enrichment in felsic pegmatites ultimately depend on tectonic setting
Title: The Mineralogical Association of Canada 50th anniversary symposium volume
Author(s): Martin, R. F.De Vito, C.
Author(s): Hawthorne, F. C.prefacer
Affiliation: McGill University, Department of Earth and Planetary Sciences, Montreal, QC, Canada
Affiliation: University of Manitoba, Winnipeg, MB, United States
Pages: 2027-2048
Published: 200512
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
Meeting name: The Mineralogical Association of Canada 50th anniversary symposium
Meeting location: Halifax, NS, USA, United States
Meeting date: 20050515May 15-18, 2005
References: 120
Accession Number: 2007-018181
Categories: Geochemistry of rocks, soils, and sedimentsIgneous and metamorphic petrology
Document Type: Serial Conference document
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
S17°25'00" - S17°25'00", E47°30'00" - E47°30'00"
Secondary Affiliation: Universita di Roma "La Sapienza", ITA, Italy
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
Update Code: 200706
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