The Gardar Geological Province - Geological Setting


Image from www.geus.dk

The Gardar province of SW Greenland is host to some of the world's finest examples of highly alkaline igneous rocks. These igneous intrusions are products of deep, small fraction melts of the mantle and crust in a  mid-continental geological setting similar to that of the East African Rift except exhumed to mid-crustal levels. These superbly exposed rocks provide an ideal means to study the mineralogy of a diverse suite of alkaline igneous rocks.

The majority of Greenland is underlain by metamorphic rocks (gneisses) of Archaean age. These rocks, once attached to the Canadian Shield, make up the core of the ancient continent of Laurentia on to which orogenic (mountain building) events accreted younger rocks of Proterozoic age. The Ketilidian Batholith of southern Greenland is one of these Proterozoic units thrust onto the craton and is composed predominantly of a relatively uniform granite accompanied by a volcano-sedimentary succession. Its age is early mesoproterozoic.

The Gardar period lasted from about 1400 Ma to 1000 Ma and commenced with a period of uplift and erosion of the Archaean and Proterozoic basement to form several kilometers thickness of  quartzites interbedded with basaltic lava flows and occasional carbonatitic flows. A long period (~1300-1000Ma) of highly alkaline magmatism ensued after the deposition of this volcano-sedimentary succession  to form the famous Gardar intrusive rock units such as Ilimaussaq, Ivigtut, Gronnedal-Ikka, Tugtutoq and Igaliko that puncture through all preceding rock types.

During the Gardar period widespread and voluminous intrusion by basic and evolved alkaline and acid dykes are indicative of a long period of relatively continuous lithospheric extension. Little geological activity for a period of 1 billion years after the Gardar period enabled the igneous minerals to escape potential alteration from their original form. Quaternary ice has sculpted the rocks into their current morphology and it's removal 10,000 years ago has allowed the land to rebound to generate the raised beaches and steep fjord sides visible today.

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