Meso- and Neoarchaean geological history of the Bjørnesund and Ravns Storø Supracrustal Belts, southern West Greenland: Settings for gold enrichment and corundum formation

Nynke Keulen*, John C. Schumacher, Tomas Næraa, Thomas F. Kokfelt, Anders Scherstén, Kristoffer Szilas, Vincent J. van Hinsberg, Denis M. Schlatter, Brian F. Windley

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

19 Citations (Scopus)

Abstract

To understand the Meso- and Neoarchaean geological history of the Bjørnesund region, southern West Greenland (ca. 62-63° N), we have undertaken an integrated study combining field observations with U-Pb zircon geochronology by LA-ICP-MS, metamorphic petrology, and microstructural analyses. The Bjørnesund region links the southern part of the Fiskenæsset anorthosite complex to the well-preserved metavolcanic rocks of the Ravn Storø Supracrustal Belt and the Bjørnesund Supracrustal Belt, so the development of this region is of key interest to unravelling the Archaean geology of the entire region. In this study, we couple the observed phases of gold-enrichment and corundum formation to the geological history.The leucogabbroic rocks of the Bjørnesund region, which are part of the Fiskenæsset complex, intruded at ca. 2.95. Ga into the tholeiitic and calc-alkaline metavolcanic rocks of the two studied belts. Following isoclinal folding, the rocks were intruded by diorite (2.92. Ga) and granodiorite (2.91 and 2.88. Ga), which are now texturally orthogneisses. The area was affected by three major phases of folding; F1 (undated), F2 at 2.85-2.83. Ga, and F3 at 2.71-2.70. Ga. The former deformation event is associated with the gold-enrichment in alteration zones in shear folds in metavolcanic amphibolite near the contact with the orthogneiss. Intrusion of granitic sheets during the F3 deformation triggered the formation of corundum, which is locally of gem quality, at the contact between leucogabbroic and ultramafic rocks. Peak metamorphic conditions were calculated as 580-630. °C and 6-4. kbar at 2.85-2.83. Ga. Later retrogression in the southern part of the area at ca. 500-450. °C and 4.5-3. kbar, and extensional fault reactivation overprinted some of the older structures.

Original languageEnglish
Pages (from-to)36-58
Number of pages23
JournalPrecambrian Research
Volume254
DOIs
Publication statusPublished - 2014

Keywords

  • Fiskenæsset complex
  • Gold
  • Metamorphic petrology
  • Ravns storø (Ikattoq Nunaa) and bjørnesund supracrustal belt
  • Ruby and pink sapphire corundum
  • Zircon U-Pb LA-ICP-MS geochronology

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