Early proterozoic basement in Ny Friesland—implications for the Caledonian tectonics of Svalbard

Proto-basement in Svalbard

“…Using much the same sequence and nomenclature, the map by Johansson et al (1995) adds new data partly to show the outcrops of the newly defined InstrumentbergetFlaten granitic gneiss, and partly far the improved outcrop pattern of the Harkerbreen Group formations in the remote interior, presumably based on unpublished mapping by Abakumov. All candidate rocks were certainly tectonised in midPaleozoic, mainly Silurian time, Gee & Page 1994) and the methods of dating were not sufficient, until recently, to demonstrate basement material within the sequence (Gee et al 1992;Balashov et al 1993). Since Harland (1941) it was known that thrust and nappe structure was dominant, that many layers could be thrust slices and that this structure was imparted during the Caledonian Ny Friesland Orogeny (Harland 1959).…”

“…However, repeated attempts to identify protobasement rocks have borne fruit (Gee, 1991;Gee et al 1992;Johansson 1994;Johansson et al 1995). Manby & Lyberis (1991) indicated a preliminary age of 1757 f 90Ma by Sm-Nd and Rb-Sr methods from cross-cutting amphibolites.…”

“…As these rocks would appear to belong to the Harkerbreen Group the evidence would support Candidate (b) though not be inconsistent with Candidate (a). U-Pb results from zircon analyses, have given ages of granitoids around 1750Ma (Gee, 1991); 1670 Ma and 1778 Ma (Gee et al 1992). Gavrilenko & Kamensky (1992) in Balashov et al (1993) investigated an ultrabasic dyke in the north (Mosselhalv#ya) approximately between the Planetfjella Group and the Polhem Formation of the Bleikfjellet Subgroup by K-Ar analysis of N 1.8 Ga for the ultrabasic rocks and -500 Ma for the adjacent strata.…”

“…Some authors have speculated on terrane implications in papers detailing new data (e.g. Peucat et al 1989;Dallmayer 1989;Gee et al 1992;Gee et al 1995;Gee & Page 1994). Other papers, without detailing new data, have treated terranes, their boundaries and pre-existing relationships, from the newly emerging evidence of Precambrian thermal events (Gee 1986;Gee 1989;Ohta & Dallmayer 1986;Ohta et al 1989;Ohta et al 1991;Gee et al 1993;Ohta 1994;Gee 1994;Manby & Lyberis 1995).…”

“…Gee 1989;Gee et al 1992) it would be sub-parallel to the Caledonian belt and so would not necessarily overlap it to the east. Indeed, a lack of 950Ma determinations in Greenland is irrelevant to the palinspastic position of Svalbard terranes which is best argued on post-Grenvillian evidence and may then elucidate the Grenvillian story.…”