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Title: Petrogenesis of the sapphirine-bearing rocks at Fiskenaesset Harbour, west Greenland

Abstract

Discontinuous horizons of sapphirine-bearing gneiss, characterized by various combinations of Sap-Opx-Ged-Hbl-Spn-Co-Bio-Plag-Hog, occur near the upper contact of the anorthositic Fiskenaesset Complex with supra-crustal amphibolite. At Fiskenaesset Harbour, the Sap rocks occur in a approx. 10m wide zone containing thin concordant lenses of ultramafic rock (Hbl+Spn+/-Cpx+/-Opx). The Sap rocks have high Al/sub 2/O/sub 3/ (26-56 wt%) and MgO (15-30), modest SiO/sub 2/ (21-43), and low FeO (1.7-7.1), K/sub 2/O (.1-4.5), CaO (.1-7.4) and Na/sub 2/O (.1-1.7). Unexpectedly, the assemblage Sap-Ged-Hbl is most common, whereas bimineralic, granular Sap-Bio and bladed Sap-Opx or Sap-Ged types are visually spectacular. The affinity of Sap for such high variance assemblages, which are arranged in dm-sized layers parallel to the contact with anorthosite, suggests control by metasomatic processes. The fact that Sap rocks have negative Eu-anomalies (Eu/Eu*=.3-.9), and may have enriched and strongly fractionated light REE ((La/Sm)/sub N/ approx. 5), suggests involvement of a crustal sedimentary component. Thus, incorporation of supracrustal sillimanitic gneisses (source of Al, K) into the Fiskenaesset Complex, and subsequent metasomatic interaction with anorthosite (source of Ca) and periodotite (source of Mg) is preferred as a mechanism which can reconcile field, petrographic and geochemical features. Sap compositions span virtually the entire range reported previouslymore » for natural samples, which raises concern regarding proposed use of Sap as a single mineral P-T indicator. Nevertheless, Mg-Fe partitioning among phases is highly regular, suggesting preservation of equilibration at high-grade conditions .« less

Authors:
;
Publication Date:
Research Org.:
Washington Univ., St.Louis, MO (USA)
OSTI Identifier:
6610667
Report Number(s):
CONF-8510489-
Journal ID: CODEN: GAAPB
Resource Type:
Conference
Journal Name:
Geol. Soc. Am., Abstr. Programs; (United States)
Additional Journal Information:
Journal Volume: 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; GNEISSES; CHEMICAL COMPOSITION; PETROGENESIS; GREENLAND; GEOCHEMISTRY; GEOLOGIC HISTORY; MAGMATISM; METAMORPHISM; SAPPHIRE; ALUMINIUM COMPOUNDS; ALUMINIUM OXIDES; CHALCOGENIDES; CHEMISTRY; CORUNDUM; METAMORPHIC ROCKS; MINERALS; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; ROCKS; 580400* - Geochemistry- (-1989)

Citation Formats

Dymek, R F, and Stocking, R. Petrogenesis of the sapphirine-bearing rocks at Fiskenaesset Harbour, west Greenland. United States: N. p., 1985. Web.
Dymek, R F, & Stocking, R. Petrogenesis of the sapphirine-bearing rocks at Fiskenaesset Harbour, west Greenland. United States.
Dymek, R F, and Stocking, R. 1985. "Petrogenesis of the sapphirine-bearing rocks at Fiskenaesset Harbour, west Greenland". United States.
@article{osti_6610667,
title = {Petrogenesis of the sapphirine-bearing rocks at Fiskenaesset Harbour, west Greenland},
author = {Dymek, R F and Stocking, R},
abstractNote = {Discontinuous horizons of sapphirine-bearing gneiss, characterized by various combinations of Sap-Opx-Ged-Hbl-Spn-Co-Bio-Plag-Hog, occur near the upper contact of the anorthositic Fiskenaesset Complex with supra-crustal amphibolite. At Fiskenaesset Harbour, the Sap rocks occur in a approx. 10m wide zone containing thin concordant lenses of ultramafic rock (Hbl+Spn+/-Cpx+/-Opx). The Sap rocks have high Al/sub 2/O/sub 3/ (26-56 wt%) and MgO (15-30), modest SiO/sub 2/ (21-43), and low FeO (1.7-7.1), K/sub 2/O (.1-4.5), CaO (.1-7.4) and Na/sub 2/O (.1-1.7). Unexpectedly, the assemblage Sap-Ged-Hbl is most common, whereas bimineralic, granular Sap-Bio and bladed Sap-Opx or Sap-Ged types are visually spectacular. The affinity of Sap for such high variance assemblages, which are arranged in dm-sized layers parallel to the contact with anorthosite, suggests control by metasomatic processes. The fact that Sap rocks have negative Eu-anomalies (Eu/Eu*=.3-.9), and may have enriched and strongly fractionated light REE ((La/Sm)/sub N/ approx. 5), suggests involvement of a crustal sedimentary component. Thus, incorporation of supracrustal sillimanitic gneisses (source of Al, K) into the Fiskenaesset Complex, and subsequent metasomatic interaction with anorthosite (source of Ca) and periodotite (source of Mg) is preferred as a mechanism which can reconcile field, petrographic and geochemical features. Sap compositions span virtually the entire range reported previously for natural samples, which raises concern regarding proposed use of Sap as a single mineral P-T indicator. Nevertheless, Mg-Fe partitioning among phases is highly regular, suggesting preservation of equilibration at high-grade conditions .},
doi = {},
url = {https://www.osti.gov/biblio/6610667}, journal = {Geol. Soc. Am., Abstr. Programs; (United States)},
number = ,
volume = 17,
place = {United States},
year = {Tue Jan 01 00:00:00 EST 1985},
month = {Tue Jan 01 00:00:00 EST 1985}
}

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