On Palaeozoic–Mesozoic brittle normal faults along the SW Barents Sea margin: fault processes and implications for basement permeability and margin evolution

摘要

Palaeozoic–Mesozoic brittle normal faults onshore along the SW Barents Sea passive margin off northern Norway give valuable insight into fault and fluid flow processes from the lower brittle crust. Microstructural evidence suggests that Late Permian–Early Triassic faulting took place during multiple phases, with initial fault movement at minimum P–T conditions of c. 300 °C and c. 240 MPa (c. 10 km depth), followed by later fault movement at minimum P–T conditions of c. 275 °C and c. 220 MPa (c. 8.5 km depth). The study shows that pore pressures locally reached lithostatic levels (240 MPa) during faulting and that faulting came to a halt during early (deep) stages of rifting along the margin. Fault permeability has been controlled by healing and precipitation processes through time, which have sealed off the core zone and eventually the damage zones after faulting. A minimum average exhumation rate of c. 40 m Ma?1 since the Late Permian is estimated. It implies that the debated Late Cenozoic uplift of the margin may be explained by increased erosion rates in the coastal regions owing to climate detoriation, which caused subsequent isostatic recalibration and uplift of the marginal crust. The studied faults may be used as analogues of basement-involved fault complexes offshore, revealing details about the offshore nature of faulting, including past and present basement and fault zone permeability.