Structural and Geomorphic Evidence for Rolling‐Hinge Style Deformation of an Active Continental Low‐Angle Normal Fault, SE Papua New Guinea

Abstract

To what degree low‐angle normal faults (LANFs) deform by a “rolling‐hinge” mechanism is still debated for continental metamorphic core complexes (MCCs). The Mai'iu fault in SE Papua New Guinea is one of the best preserved and fastest slipping active continental LANFs on Earth, providing an ideal setting in which to evaluate footwall deformation and doming in MCCs. We analyzed structural field data from the exhumed slip surface and subjacent footwall of the Mai'iu fault, together with geomorphic data interpreted from aerial photographs and GeoSAR‐derived digital terrain models. The exhumed part of the Mai'iu fault forms a smooth, continuous surface, traced at least 28 km in the slip direction. The fault emerges from the ground near sea level with a northward dip of ≤22°N and flattens southward over the crest of the Suckling‐Dayman Dome. Its most southern mapped portion dips ~12°S. Geomorphic and structural evidence indicates updip tectonic transport of the footwall and progressive back‐tilting of the exposed part of the fault and the underlying foliation through >26°. We infer that antithetic (northside‐up) dip slip on an array of steep‐dipping faults striking parallel to the Mai'iu fault accommodated some of the exhumation‐related inelastic bending of the footwall. The exhuming footwall was subject to late‐stage slip‐parallel contractional strain as recorded by a postmetamorphic crenulation foliation that strikes parallel to the curved Mai'iu fault trace, by folds of bedding in a large rider block that is stranded on the current footwall and by strike‐parallel warps in the exhumed fault surface. Geodynamic modeling predicts the observed footwall strain.

Tectonic Inheritance Following Failed Continental Subduction: A Model for Core Complex Formation in Cold, Strong Lithosphere

“…Modeled exhumation is mainly due to continued fault offset; however, isostatic footwall uplift aids the rapid vertical exhumation. Rocks at the main divide of the modeled dome structure at 3.4 Myr were originally adjacent to the trace of the inherited shear zone, as is consistent with exhumed remnants of the Mai'iu fault surface being found 30‐km updip of the fault trace (Mizera et al, , in press). The modeled footwall exhumes through a rolling‐hinge process as indicated by the progressively increasing upward convexity of the detachment, as suggested by topographic and geological field observations (Spencer, ; Webber, ; Mizera et al, , in press; Little et al, ).…”

“…The DSM includes three high peaks in the Owen‐Stanley Ranges: Mount Dayman, Mount Suckling, and Mount Masasoru (Figure ). The exposed culminations range from 1,700‐ to 3,576‐m elevation and vary in their degree of erosion (Mizera et al, , in press). The actively uplifting DSM (Miller et al, ; Ollier & Pain, ) is bounded to the North by the Mai'iu fault, an active LANF that dips NNE on average ~21° to the surface (Mizera et al, , in press) and accommodates 7–9 mm/year of horizontal extension (Wallace et al, ) with long‐term along‐dip slip rates (1,000 year timescales) of 8.2–15.2 mm/year (Webber et al, ).…”

“…The actively uplifting DSM (Miller et al, ; Ollier & Pain, ) is bounded to the North by the Mai'iu fault, an active LANF that dips NNE on average ~21° to the surface (Mizera et al, , in press) and accommodates 7–9 mm/year of horizontal extension (Wallace et al, ) with long‐term along‐dip slip rates (1,000 year timescales) of 8.2–15.2 mm/year (Webber et al, ). Near the 2,950‐m tall Mount Dayman exhumed remnants of the Mai'iu fault are found 30‐km updip from the fault trace in the slip direction, recording accumulated slip of similar magnitude (Mizera et al, , in press). Normal slip initiated by at least 3.3 Mya as evidenced by the age of the synextensionally intruded Suckling Granite (Daczko et al, ).…”

“…Normal slip initiated by at least 3.3 Mya as evidenced by the age of the synextensionally intruded Suckling Granite (Daczko et al, ). Rapid exhumation of footwall rocks from original depths of ~25 km along the Mai'iu fault from circa 3 Mya is inferred to have occurred by the rolling‐hinge mechanism based on a host of tectonically tilted geomorphic features, progressive back‐arching of foliation in the footwall, the convex‐up shape of the exposed Mai'iu fault surface, the 30°–40° alignment of microseismicity downdip of the Mai'iu fault trace and bedding‐fault cutoff angles of up to 40°–50° in former hanging wall sediments that have been uplifted and eroded as part of an abandoned rider block (Spencer, ; Abers et al, ; Webber, ; Mizera et al, , in press; Little et al, ).…”

“…(a) Simplified map showing spatial relationship between Woodlark spreading centers and the Dayman‐Suckling MCC (DSM). (b) Hillshade DTM (Digital Terrain Model) of Mount Dayman area from Figure a showing mapped antithetic and locally synthetic faults cutting the footwall of the DSM, adapted from Mizera et al (, in press); (c) Elevation profile of transect A′‐A from Figure b with representative mapped footwall faults and back‐warped footwall foliations; (d) Oblique view of the DSM and Mai'iu fault, from 90‐m SRTM (Shuttle Radar Topography Mission) data and GeoMappApp ( http://www.geomappapp.org).…”