Structural control of strontium concentrations in stream sediments: an example from major fault zones in central Norway

Abstract

A distinct linear Sr anomaly traceable over a distance of >120 km in central Norway can be linked directly to the ENE–WSW-trending Møre-Trøndelag Fault Complex. Another less prominent linear anomaly is associated with a major extensional detachment fault. Although the Sr values are not unusually high, those above the 90th percentile define a distinct subpopulation indicative of the effects of a secondary process. This is considered to relate to accessory and secondary mineral phases that precipated in dense vein networks (calcite, zeolites, epidote) within the hydrothermally and metasomatically altered cataclasites and breccias of this major, multiply reactivated, fault complex. Along and adjacent to the Møre-Trøndelag Fault Complex and the detachment fault, a likely primary source of the enhanced Sr concentrations is that of Ordovician, calc-alkaline granitoid plutons with up to 1400 mg/kg Sr. In one area along the fault complex, an extensively exposed Ordovician limestone with high Sr contents (up to 950 mg/kg) may represent a second primary source. In a third area, Vikna, a more diffuse positive Sr anomaly may relate to the widespread occurrence of shell-rich marine deposits, but this area is also intensely faulted. Thus, although there are three likely primary sources for the Sr anomalies, the single unifying feature and underlying cause of the exceptional anomaly linearity has to be the intensely hydrothermally altered, multiply deformed, Møre-Trøndelag Fault Complex with its dense network of mineral veins and, to a slightly lesser extent, the major, extensional detachment fault. These observations stress the overall significance of structural control in defining these unusually prominent Sr anomalies.