Mesozoic and Cenozoic tectonics of the More Trondelag Fault Complex, central Norway: constraints from new apatite fission track data

摘要

The More Trondelag Fault Complex (MTFC) of central Norway is a long-lived structural zone whose tectonic history included dextral strike slip, sinistral strike slip, and vertical offset. Determination of an offset history for the MTFC is complicated by the lack of well preserved stratigraphic markers. However, low temperature apatite fission track (AFT) thermochronology offers important new clues by allowing the determination of exhumation histories for individual fault blocks presently exposed within the MTFC area. Previously published AFT data from crystalline basement in and near the MTFC suggest the region has a complicated pattern of exhumation. We present new AFT data from a NW–SE transect perpendicular to the principal structural grain of the MTFC. FT analyses of 15 apatite samples yielded apparent ages between 90 and 300 Ma, with mean FT length ranging from 11.8 to 13.5 μm. Thermal models based upon the age and track length data show the MTFC is comprised by multiple structural blocks with individual exhumation histories that are discrete at the 2σ confidence level. Thermal modeling of the AFT data indicates exhumation progressed from west to east, and that the final juxtaposition and exhumation of the innermost blocks took place during Cretaceous or Tertiary (possibly Neogene) time. We suggest that least some of the fracture lineaments of central Norway were re-activated during Mesozoic extension and the opening of the Norwegian sea, and may have remained active into the Cenozoic.