The Ketilidian orogeny ca. 1855 - 1725 Ma

1850-1800 Ma Emplacement of Julianehåb batholith in a calc-alkaline magmatic (island) arc.

What is North and South today was respectively East and West at around 1.8 Ga, when a supercontinent probably got assembled. (Columbia or Hudsonland or Hudsonia supercontinent).

Photo of Julianehåb granite.

Erosion of the Julianehåb batholith and transport of the erosion products to the fore arc basin at the south as sediments - sand (yellow on sketch) and mud (brown on the sketch).

Metamorphism and deformation started ca. 1792 Ma, i.e. only a few million years after the sedimentation began. The sandstones were metamorphosed to psammites (mainly in the northerly psammite zone) and the mudstones to pelites (mainly in the more southerly pelite zone).

Photo of (pelitic to semipelitic) gneiss from Nanortalik.

Some time after three deformation phases and under a fourth and probably fifth deformation phase Rapakivi granite (or rather a rapakivi suite of noritic to syenitic plutons) was intruded in the south/south-eastern part of the Ketilidians. (1755–1723 Ma)

The Rapakivi granite pictured to the left is NOT from Greenland, but from Finland. Typical of Rapakivi granites (rapakivi textures) are round to oval balls with a core of kali feldspar (orthoclase) overgrown with (a rim of) plagioclase. The largest "ball" on the picture has a diameter of about 5 cm.

Most of the peaks (such as the "Church Steeple" and nanutaks in this area of South Greenland are made up of Rapakivi granite, which is more resistant to erosion than the softer metamorphic rocks (psammites and pelites).

1300-1120 Ma (Failed) continental rifting in the Gardar province with alkaline to peralkaline intrusions, maybe due to decompression melting (rift-related intraplate alkaline magmatism).

Photo of naujaite from the Ilímaussaq Complex.

Before and at the beginning of the Gardar period (ca. 1600-1310) the Eriksfjord formation was deposited in the central part of the Gardar graben system. The Eriksfjord formation rests unconformably on denuded Julianehåb granite and consists mainly of (continental, i.e. fluvial and aeolian) sandstones, and basalts/basalt lavas. Photo of Igaliko sandstone used in stairs.

Sketch geology of Southern Greenland

The timing of the ketilidian orogeny seems to coincide with the assembly of a suggested Hudsonia supercontinent (Dubbed "Columbia" by Professor John J.W. Rogers according to the news from Space Daily of 18 March 2002 and BBC News of 25 march 2002 later (2003) referred to as Hudsonland and most recently Hudsonia). Note that Baltica was rotating during the Paleoproterozoic — and in this drawing turned anticlockwise relative to the reconstruction drawn by prof. Rogers.

 
(Above reconstruction is based on an oral presentation by R. Lahtinen at the 26^th Nordic Geological Winter Meeting at Uppsala, Sweden, January 6^th-9^th 2004. – R.Lahtinen et al. Paleoproterozoic orogenic evolution of the Fennoscandian Shield at 1.92-1.77 Ga – the formation of a supercontinent).

Ole Nielsen

Note: I made the drawings of the Ketilidian evolution to help myself to get a better grip of the events. They are my personal extremely simplified interpretation of the papers I have read, and no more than that. I hope however they may help the reader like they helped me. If they have wetted your appetite there is reference to more reading at our page with links and references.