642 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



may be taken to be of the order of 5-10 million years. The fact that the sedi- 

 ments immediately underlying and overlying the thick Plateau Basalt Series 

 are both of shallow water marine origin shows that during or soon after the 

 extrusion of the basalts there must have been sinking of the basalt pile com- 

 parable in amount with its thickness. 



Some basic intrusions, e.g., the Skaergaard and Kap Edvard Holm complexes 

 were formed during or soon after the main period of basalt outpouring. This 

 also seems to have been the chief period of sill intrusion although this phase 

 never reached large proportions. 



The chief tectonic event affecting the area, namely, the elevation of what is 

 now the coastal mountain belt of East Greenland and the sinking of the area 

 which is now the Denmark Strait, took place subsequendy to the formation of 

 the main plateau basalts. The junction between the two areas of differential 

 epeirogenic movement is marked in Middle East Greenland by a flexure of the 

 crust. Where the flexure is intense with dips of more than 10°, a dike swarm 

 is developed which follows the convex part of the flexure. The intensive flexur- 

 ing and associated dike swarm occur along much of the Middle East Greenland 

 coast and, as it is likely that all the flexuring took place during the same limited 

 period of time, we are provided with a useful method of dating certain local 

 events. The coastal flexure and dike swarm almost certainly came after the 

 formation of the Kap Dalton sediments, which are Middle or Lower Eocene. 

 The main part of the inland doming of Knud Rasmussens Land is considered 

 to have been incidental to the general epeirogenic uplift and to have developed 

 at that time. 



Not all of this impressive differential vertical movement is to be ascribed to 

 the coastal flexure stage and it is suggested that the total movement as now de- 

 termined by the lie of the rocks can be analysed into the following parts: 



1. Early slight flexuring due to differential sinking of the lava pile as it ac- 

 cumulated. 



2. The main epeirogenic movement and associated flexuring, with a dike 

 swarm where flexuring was sufficiently intense. 



3. Possible later up-warping of the edge of the uplifted area as a result of 

 isostatic adjustments to erosion and to the development of the ice cap. 



Faults have been recognized on both the west and east coasts of Green- 

 land. The Cape York district of northwest Greenland is especially broken 

 by high-angle faults (Koch, 1929), and the fiords of the west coast about 

 Disko and Umnak bays generally take their courses parallel to faults 

 (Hobbs, 1932). It is not clear, however, that these faults are to be 

 associated with Tertiary land movements. Koch ( 1935) believes that 

 strong faulting in Tertiary time may be recognized in many places 

 along the eastern coast, and that it is associated with the great vol- 

 canic activity just described. The faults have tilted a plane to the west on 



Molne Land, and may be seen cutting the sediments there. Along the east 

 side of Hurry Inlet are Tertiary faults, and Liverpool Land was doubtless 

 strongly raised in Tertiary time. Although the basalts with their great 

 flexure are not present north and south of the middle east Greenland area, 

 the topography along the coast in the absence of the basalts suggest com- 

 parable crustal movement (Wager, 1947). The volcanics of east Green- 

 land, as a number of writers have proposed, must be continuous with the 

 basalt fields of Iceland, the Faeroes, and Scotland; but Wager does not 

 believe that they extend under the ice of Greenland and connect with the 

 basalts of the west coast. 



Precambrian 



An outline of the Precambrian rocks and history of east Greenland is 

 given below. It is after Koch ( 1961 ) . 



East-Central Green/and 



Eleonore Bay group 

 (Proterozoic) 



Archean basement 

 Northeast Greenland 



Upper 



Tillite and varved strata, 200-1000 m 



Dolomite and Is, 1100 m 



Psammite, pelite, 3000 m 

 Lower 



Tillite, Is, phyllite, 2600-7400 m. 



Proterozoic 



Hagens Fiord group, derived from Carolinidian belt 

 Faulting and eruption of basalts 



Folding and magmatic activity (Carolinidian orogenic belt) 

 Basalt dikes and sills 

 Thule group (psammites), 3000 m 



Greenlandian (semipellites), 3000 -f- m 

 Archean basement 



ARCTIC OCEAN BASIN 



Surrounding Shelves 



The floor of the Arctic Ocean is about half shelf and half deep basin. 

 See Fig. 40.6. Off Alaska and the Canadian Arctic Archipelago the shelf 



