Strength and Stress Evolution of an Actively Exhuming Low-Angle Normal Fault, Woodlark Rift, SE Papua New Guinea

Abstract

 The active Mai'iu low-angle normal fault dips ~20° at the surface, but is steeper at depth.  A differential stress peak of 140-185 MPa at 6-12 km depth was identified in a zone of mixed-mode seismic-and aseismic slip.  High differential stresses drive slip on a ~35° dipping part of this fault and cause new brittle yielding of strong mafic footwall rocks.  The Mai'iu fault is frictionally weak near the surface (µ≈0.15-0.38), but strong in the middle crust (µ>0.25-0.62).  Reconstructed principal stresses are constrictional and consistent with rolling-hinge style flexure of the footwall.

Regional‐Scale Low‐Angle Normal Fault Friction and Cohesion Constrained From Mohr‐Coulomb Models of Active and Abandoned Range‐Front Faults in Papua New Guinea

“…Their kinematics indicate an NNE extension direction (Little et al., 2019), which is consistent with the NNE‐trending slickenlines and corrugations on the exhumed Mai'iu fault surface (Daczko et al., 2011). Stress inversions based on these late‐stage mesoscopic faults indicate subvertical σ 1 ‐and sub‐horizontal σ 3 ‐stresses parallel to the extension direction, with σ 1 ≈ σ 2 (constriction; Mizera et al., 2021). It is not immediately obvious why such Andersonian faults ( sensu lato ) might cut the metabasaltic footwall of the active LANF; or why the Mai'iu fault, a highly misoriented structure, continued to slip despite yielding taking place in its footwall (Little et al., 2019; Mizera et al., 2019).…”

“…Such small faults that cut the footwall would have steep original dips (assuming Andersonian stresses), in contrast to the shallow dip of the LANF at that depth. Another possible explanation is that the minor faults formed as a result of exhumation-related bending/unbending stresses in the footwall cause new brittle yielding of strong, formerly intact mafic footwall rocks (Mizera et al, 2021). Such bending stresses might not be transmitted across the weak, creeping shallow portion of the fault the hanging-wall (Biemiller, Boulton, et al, 2020).…”

Using Syntectonic Calcite Veins to Reconstruct the Strength Evolution of an Active Low‐Angle Normal Fault, Woodlark Rift, SE Papua New Guinea

“…All structural data from the Suckling‐Dayman Metamorphic Core Complex, raw EBSD data of analyzed calcite veins and MATLAB codes used in this study can be obtained from the Data Repository (Mizera et al., 2021: https://dx.doi.org/10.17632/mkpgbs4hf3.4). Additional information on fault rocks analyzed in this study can be found in the research archive of Victoria University of Wellington (http://hdl.handle.net/10063/8666, Mizera, 2019).…”