PROTO-BASEMENT IN SVALBARD

Candidates for possible Precambrian proto-basement throughout Svalbard are considered and evaluated. The paper provides a tectono-stratigrap hic framework for consideration of new data. Proto-basement, in the se nse of basement in Proterozoic time, implies the occurrence of a Preca mbrian tectonic event. Vendian rocks are widespread in Svalbard and, b ecause there is no known Vendian major tectonic event, the search is n arrowed to pre-Vendian rocks. The approach is primarily tectono-strati graphic, to identify a signiificant break by unconformity, contrast in metamorphic facies and isotopic age determinations. The paper conclud es that the following rock units are proto-basement: Isbjornbamna and (newly defined) Eimfjellet groups, Nordbukta Group, Magnethogda Group, the Richarddalen Complex; the Atomfjella Complex, the Brennevinsfjord en Group and the granitoids related to the Kapp Hansteen Group and the Duvefjorden Complex. While considered unlikely to be proto-basement t he following cannot be ruled out: the Mefonntoppane and Kistefjellet r ocks and the Sigfredbogen unit, the blue-schist Vestgotabreen rocks, t he Pinkie Formation and parts of the Kongsvegen Group. Terrane implica tions are consistent with the three terrane model of Harland & Wright (1979), modified by Harland et al. (1993); but the data presented here hardly constrain such a model. In so far as the conclusions here are valid the effect is to subtract from, rather than add to, the outcrops commonly mapped as likely proto-basement.