USING A PRECAMBRIAN TERRANE BOUNDARY TO ESTIMATE SLIP ON THE WEGENER FAULT, NARES STRAIT

The Wegener fault is a sinistral transform in Nares Strait, which lies between Greenland and Ellesmere Island; the fault facilitated opening of the Arctic Ocean by connecting Paleogene spreading ridges in the Eurasian basin (Arctic Ocean) and Baffin Bay after ≈56 Ma (i.e. magnetic anomaly 24) and before 36 Ma (magnetic anomaly 13). The existence of the Wegener fault has been questioned by some scientists, but it is generally accepted based on: 1) the presence of left-lateral strike slip faults and pull-apart basins of Paleocene age on Judge Daly Promontory on eastern Ellesmere Island, 2) seismic studies in Smith Sound and Kane Basin that indicate possible flower structures with a steep boundary between North America and Greenland and 3) fault population analysis of Precambrian gneisses in the Inglefield uplift, along the southeast coast of Ellesmere Island, showing three stages of development – the first of which correlates with sinistral displacement. The Wegener fault is probably best thought of as a complex fault system with both offshore and onshore elements. The amount of horizontal slip on the Wegener fault system can potentially be estimated from the offset of the boundary between the Archean Rae craton to the south and a Paleoproterozoic gneiss terrane to the north, because this boundary is at a moderately high angle to the NE-striking Wegener fault. This boundary is best defined on the Greenland side due to recent U-Pb geochronology of zircon in the gneisses, but is less well known on the Ellesmere Island side. We have dated zircon in five samples of Precambrian quartzofeldspathic gneiss from the Inglefield uplift on Ellesmere Island using the sensitive high resolution ion microprobe – reverse geometry (SHRIMP-RG) at Stanford University. U/Pb analyses from oscillatory zoned domains with REE patterns typical of igneous zircon define Paleoproterozoic intrusive ages that range from 2016±12 to 1942±12 Ma. The new ages corroborate previous placement of the boundary to the south near Devon Island. We suggest that the boundary between Archean and Paleoproterozoic gneisses is offset by a minimum of 200 km across Nares Strait, and this corresponds to the minimum offset on the Wegener fault.