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> Forsiden > Data og kort > Grønland > Proterzoic units developed after formation of the Precambrian S.

Proterzoic units developed after formation of the Precambrian shield

 
Independence Fjord Group, North Greenland, Zig-Zag Dal Basalt Formation, North Greenland, Mesoprpterozoic,


The Greenland Precambrian shield is mainly composed of crystalline gneisses and plutonic rocks older than 1600 Ma. Younger rock units, nearly all middle Proterozoic to Phanerozoic in age, are in part related to the formation of sedimentary basins and fold belts along the margins of the stable shield. Two major Palaeozoic fold belts – the Ellesmerian fold belt of Ellesmere Island (Canada) and North Greenland and the Caledonian fold belt of East Greenland – developed along the north and east margins of the shield respectively.

Independence Fjord Group, North Greenland
The earliest recorded major depositional basin developed on the Greenland shield is represented by the Independence Fjord Group [31] which is found over large areas of eastern North Greenland and North East Greenland between north-eastern Peary Land (83oN) and westernmost Dronning Louise Land (77oN). The group is more than 2 km thick, with its base only exposed in western Dronning Louise Land. Strongly deformed units are found within the Caledonian fold belt in Kronprins Christian Land and areas to the south. Radiometric dating indicated a middle Proterozoic age (about 1380 Ma) for the deposition, but more recent SHRIMP U-Pb dates from intercalated volcanics in equivalent sandstones occurring within the Caledonian fold belt suggest that some of the sandstones were deposited before 1740 Ma ago. The new data post-date compilation of the map, where a middle Proterozoic age is indicated for the Independence Fjord Group.
The succession has primarily been studied in the type area around Independence Fjord in North Greenland, where deposition took place in an intracratonic sag basin. The Independence Fjord Group is dominated by alluvial clastic deposits, mainly sandstones that form three 300–900 m thick, laterally correlatable units. These are separated by two laterally extensive, much thinner (4–90 m) silt-dominated units that represent deposition in ephemeral lakes.

Zig-Zag Dal Basalt Formation, North Greenland
This middle Proterozoic formation [30] of up to 1350 m of well-preserved tholeiitic flood basalts is among the oldest well-preserved basalt sequences known; the main outcrops are south of Independence Fjord in eastern North Greenland. The Zig-Zag Dal Basalt Formation comformably overlies the Independence Fjord Group and is itself disconformably overlain by the Hagen Fjord Group. South of Independence Fjord the basalt sequence outcrops over an area of 10 000 km2, but the local occurrence of similar basalts in eastern Peary Land indicates that the formation once covered a very large part of North Greenland.

Gardar Province, South Greenland
The Mesoproterozoic Gardar Province is characterised by faulting, deposition of sediments and volcanic rocks, and alkaline igneous activity. An approximately 3400 m thick succession of sandstones and lavas described as the Eriksfjord Formation accumulated within an ENE–WSW trending continental rift, preserved at about 61oN. Within and outside the rift major central intrusions and numerous dykes were emplaced.
The Gardar intrusive complexes range in age from c. 1300 to c. 1120 Ma and have been divided into three age groups. These comprise central ring intrusions, complexes with several individual intrusive centres and giant dykes. Petrologically the intrusive complexes are dominated by differentiated salic rocks including syenites, nepheline syenites, quartz syenites, and granites; mildly alkaline gabbros and syenogabbros are subordinate but are dominant in the giant dykes. The intrusions were emplaced in the middle part of the Gardar rift as well as in the areas both to the north and south. Major swarms of basic dykes of Gardar age occur throughout South and South-West Greenland.

Mesoproterozoic orogenic units in the Caledonian fold belt
A Mesoproterozoic 'Grenvillian- event has been recorded in the crystalline rocks of the Caledonian fold belt between Scoresby Sund (70o N) and Grandjean Fjord (76o N). A thick sequence of middle Proterozoic metasediments, the Krummedal supracrustal sequence, rests on early Proterozoic and Archaean basement gneisses. During a tectonometamorphic event around 950 Ma ago the supracrustal rocks and the underlying basement rocks were apparently reworked to form a migmatite and paragneiss complex containing granite and augen granite intrusions. Zircon and Rb-Sr whole rock studies indicated some of the granites were c. 1000 Ma old, and SHRIMP studies on zircons from a major granite body (74o19´N) yielding an age of c. 930 Ma have recently confirmed the Grenvillian age.

Meso – Neoproterozoic sedimentary basin in North-West Greenland

Thule Supergroup
The Thule Basin in North-West Greenland is one of several middle–late Proterozoic depocentres fringing the northern margin of the Canadian–Greenland shield. The basin fill consists of undeformed sediments and basaltic rocks assigned to the Thule Supergroup. The rocks are widely exposed in the region between Inglefield Land (79oN) and Thule Air Base/Pituffik (76oN) in Greenland and also crop out in the coastal regions of Ellesmere Island in Canada. The lower part of the basin-fill shows many similarities with the Independence Fjord Group and overlying volcanic rocks.

The Thule Supergroup has a cumulative thickness of at least 6 km comprising continental to shallow marine sediments, basaltic volcanic rocks and a conspicuous number of doleritic sills; it accumulated between c. 1270 Ma and c. 650 Ma ago. The sediments rest with profound unconformity on peneplained early Proterozoic crystalline basement throughout the region. Lup

The Thule Supergroup has a cumulative thickness of at least 6 km comprising continental to shallow marine sediments, basaltic volcanic rocks and a conspicuous number of doleritic sills; it accumulated between c. 1270 Ma and c. 650 Ma ago. The sediments rest with profound unconformity on peneplained early Proterozoic crystalline basement throughout the region.

Neoproterozoic sedimentary basins in North, North-East and East Greenland

Hagen Fjord Group, North Greenland
Deposits of a late Proterozoic basin laid down between 800 and 590 Ma ago occur extensively in eastern North Greenland, where they crop out over an area of 10 000 km2 west of Danmark Fjord. These deposits, assigned to the Hagen Fjord Group, overlie sandstones of the lower Proterozoic Independence Fjord Group and basalts of middle Proterozoic Zig-Zag Dal Basalt Formation. The easternmost occurrences of the succession are found in Caledonian thrust sheets with substantial westward displacement in Kronprins Christian Land, indicating that the basin originally had a wider eastwards extent.
The Hagen Fjord Group is an up to 1000 m thick succession of siliciclastic and carbonate sediments deposited on a shallow water shelf.
Deposits of a late Proterozoic basin laid down between 800 and 590 Ma ago occur extensively in eastern North Greenland, where they crop out over an area of 10 000 km2 west of Danmark Fjord. Lup

Eleonore Bay Supergroup, East and North-East Greenland
The Eleonore Bay Supergroup comprises an up to 16 km succession of shallow water sediments which accumulated in a major sedimentary basin extending between latitudes 71o 40´ and 76o 00´ N in East and North-East Greenland. Exposures occur within the present Caledonian fold belt, and in general are moderately deformed and weakly to moderately metamorphosed. The contact with the underlying basement is structural, variously described as an extensional detachment preceded or post-dated by thrusting. Sedimentation is constrained to the interval between c. 950 Ma and 610 Ma on the basis of Grenvillian ages on underlying basement rocks and the Varangian age of the overlying Tillite Group. Acritarchs from the three youngest groups of the Eleonore Bay Supergroup indicate a Sturtian age.

Lup

The Eleonore Bay Supergroup comprises an up to 16 km succession of shallow water sediments which accumulated in a major sedimentary basin extending between latitudes 71° 40´ and 76° 00´ N in East and North-East Greenland.

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Proterzoic units developed after formation of the Precambrian S.