New insights from field observations of the Younger giant dyke complex and mafic lamprophyres of the Gardar Province on Tuttutooq island, South Greenland

• Published in: GEUS Bulletin
• Main Authors: Lot Koopmans, Robert A. Webster, Rory Changleng, Lucy Mathieson, Alasdair J. Murphy, Adrian A. Finch, William McCarthy
• Format: Article in Journal/Newspaper
• Language: English
• Published: Geological Survey of Denmark and Greenland 2021
• Subjects: gardar province; rift magmatism; younger giant dyke complex; magma chamber; lamprophyre; Geology; QE1-996.5; Geophysics. Cosmic physics; QC801-809; Greenland; Tuttutooq
• Online Access: https://doi.org/10.34194/geusb.v47.6526; https://doaj.org/article/889e534ac23d412c9d8e3ebe353834be

The Gardar Province of south Greenland is defined by the products of alkaline igneous magmatism during the Mesoproterozoic. The most laterally extensive Gardar intrusions are a series of giant dyke complexes best exposed on the Tuttutooq archipelago. We present new field observations and a geological map of north-east Tuttutooq island that provide fresh insights into the temporal evolution of the Younger giant dyke complex and two associated ultramafic lamprophyres. Our data demonstrate that distinctive crystallisation regimes occurred in different sectors of the dyke complex, leading to the formation of marginal gabbros and ovoid pod-like domains displaying lamination, modal layering and/or more evolved differentiates. We infer that at least two pulses of magma contributed to the formation of the Younger giant dyke complex. In addition, the relative ages of two ultramafic lamprophyre diatremes are constrained and attributed to two distinct phases of rifting in the Gardar Province.