Finnmark Caledonides

Written Discussion of paper taken as read

R. H. FINDLAY

The Editor,

Dear Sir,

In their paper on the Finnmark Caledonides Gayer and Roberts (1973) do not discuss in detail therelationship between the Laksefjord Nappe and the basement. At the southern end of Lakseljordthe contact between the Laksefjord Nappe and the granitic basement is complexly faulted so thatit is not possible to determine whether or not the original contact was unconformable. NearStorernasvandet, to the south-east, granitic basement rocks are faulted up through the LakseljordNappe (FI/Jyn, 1960). Nearby, rocks of the Laksefjord Nappe rest unconformably on basic base­ment rocks (Feyn, 1960; Laird, 1972). These observations do not affect the reconstruction byGayer & Roberts to any extent, although the 'chiselling-off of the Finnmark Ridge by theLaksefjord Nappe is perhaps less dramatic than they suggest.

I am inclined to the view that the granitic basement material at the southern end of Lakseljordand at Storemasvandet was thrust into place after the Laksefjord and Gaissa Nappes arrived intheir present position. Two models can be postulated:

(i) The granitic basement is an intrinsic part of the Laksefjord Nappe and the metasedimentsrest unconformably on this basement, as suggested by Gayer & Roberts (1973, 416).

(ii) The granitic basement is part of the autochthon underlying both the Gaissa and Laksel­jord Nappes and was subsequently upfaulted into the Laksefjord Nappe.

If the second alternative is adopted we then must account for the presence of carbonates in thebasement complex at Landersfjord. These carbonates are caught up in fault planes which dipfairly steeply north-west and divide the complex into a number of imbricate slices. There are twoalternative interpretations of the relationship between the carbonates and the basement.

(a) Both the granitic basement and the carbonates are autochthonous. If the carbonates arecorrelated with the Porsanger Dolomite it follows that the area of sedimentation of the sedimentsin the Gaissa Nappe extended much farther south than proposed by Gayer & Roberts. TheLaksefjord Nappe was then thrust over this 'Gaissa Basin'. Subsequently the granitic basementwas thrust up through the overlying carbonates into the Laksefjord Nappe.

(b) A simpler hypothesis would be that the carbonates at Landersfjord formed part of theGaissa Nappe, and that the granitic basement at Landersfjord and Storemasvandet was upfaultedthrough both the Gaissa and the Laksefjord Nappes.

I would favour the second alternative.

REFERENCES

F0YN, SYEN. 1960. Tanafjord to Laksefjord. Guide 10

Excursion A3 (ed. J. A. Dons), Int. geol. Congr., 21,45-55. (Reprinted as Norg, geo/. Unders .. 212.)

GAYER, R. A. & J. D. ROBERTS. 1973. StratigraphicReview of the Finnmark Caledonides with PossibleTectonic Implications. Proc. Geol. Ass., 84 (4),405-28.

R. H. FindlayThe University of AucklandAucklandNew Zealand

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LAIRD, M. G. 1972. The stratigraphy and sedimen­tology of the Laksefjord Group, Finnmark. Norg,geo/. Unders.. 278, 13--41.