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

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6610667

Dymek, R F; Stocking, R

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 .

• Research Organization: Washington Univ., St.Louis, MO (USA)
• OSTI ID: 6610667
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580400* -- Geochemistry-- (-1989)
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMISTRY
CORUNDUM
GEOCHEMISTRY
GEOLOGIC HISTORY
GNEISSES
GREENLAND
MAGMATISM
METAMORPHIC ROCKS
METAMORPHISM
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PETROGENESIS
ROCKS
SAPPHIRE