Abstract
Examination of mineral phases in metabasalts and metadolerites from lava flows and intrusions exposed in the Hellefiskefjord - G. B. Sehley Fjord area of North Greenland shows that the metamorphie grade in this region is generally within the greensehist facies, with the development of assemblages eontaining aetinolite-epidote-albite-ehlorite-sphene±biotite±stilpnomelane. However, eertain flows eontain pumpellyite, whieh is indieative of a slightly lower grade of metamorphism. The reason for this variation is thought to be loeal permeability-eontrolled alteration within the flows. The lateral equivalents of these metabasites in the area south of Independenee Fjord show lower grades of metamorphism, within either the prehnite-pumpellyite or the zeolite facies. This is probably related to thinner Lower Palaeozoic sequences and/or the absence of Carboniferous to Tertiary Wandel Sea Basin sediments in the area to the south.
Highlights
This paper describes the mineralogy, mineral assemblages and metamorphic grade of Proterozoic metabasalts and metadolerites exposed in the Hellefiskefjord - G
It appears that the metabasites of the Hellefiskefjord area have suffered greenschist facies metamorphism, characterized by the diagnostic mineral assemblage actinolite-epidote-albite-chlorite-sphene±biotite±stilpnomelane
The Proterozoic metabasic rocks of the Hellefiskefjord area have generally recrystallized within the greenschist facies, with the production of assemblages including actinoliteepidote-albite-chlorite-sphene±biotite±stilpnomelane
Summary
This paper describes the mineralogy, mineral assemblages and metamorphic grade of Proterozoic metabasalts and metadolerites exposed in the Hellefiskefjord - G. Actinolite is widely developed, occurring in both intrusive and extrusive metabasites and most typically occurs as randomly distributed needle-like crystals overprinting or replacing earlier phases, such as chlorite It forms both epitaxial overgrowths on clinopyroxene and discrete, well-formed crystals in rocks where the primary igneous textures have been almost entirely obliterated by recrystallization. Epidote is widely developed in the Hellefiskefjord metabasites and occurs in a number of forms, which include small, well-formed crystals in feldspar, thin irregular veins, vesicle infillings, idioblastic crystals in association with chlorite and granular aggregates in association with chlorite overprinting original igneous textures. It has been suggested that stilpnomelane may occur as an additional phase in rocks with low MglFe (Zen, 1974) Such a control has recently been emphasized by Bevins & Rowbotham (1983) from Wales, and it is supported here by the fact that the analysed stilpnomelane-bearing Hellefiskefjord sample (233922) possesses a relatively low Mg/Fe stilpnomelane. Biotite analyses plotted on an AI:Fe:Mg diagram (fig. 10) reveallittie compositional variation and are of similar eomposition to biotites in metabasites from the Haast Schist Group of New Zealand, reported by Cooper (1972)
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