Paleomagnetic evidence for vertical‐axis rotations of crustal blocks in the Woodlark Rift, SEPapua New Guinea: Miocene to present‐day kinematics in one of the world's most rapidly extending plate boundary zones

Abstract

The continental Woodlark Rift, in SE Papua New Guinea lies west of a propagating oceanic spreading center in the Woodlark Basin and is currently one of few places on Earth where active continental breakup is thought to be occurring. Here north-south extension is localized on a few major normal faults. We determined characteristic remanent magnetization (ChRM) components from demagnetization profiles of >300 individual specimens. From these, 157 components contribute to paleomagnetic directions for six formations. We compare Early Miocene (20 Ma) to Late Pliocene (3.0 6 0.5) ChRM mean directions, at four localities, with contemporaneous expected field directions corresponding to the Australian Plate. Timevarying finite rotations from Cape Vogel Peninsula (28-128) suggest anticlockwise rotation had begun by 15 Ma. This rotation may have been accompanied by rifting, 7 Ma earlier than previously inferred. Furthermore, that early extension may have occurred south of the present rift, and that deformation later migrated north of the Peninsula. Pliocene vertical-axis rotations are consistent with GPS-determined plate motions, suggesting that contemporary rift kinematics were established by 3 Ma. Finite anticlockwise rotation (10.1 6 7.68) in the Amphlett Islands is accordant with seafloor spreading in the Woodlark Basin, suggesting this locality has seen the full Woodlark plate motion since 3 Ma. Clockwise rotation of the Goodenough Bay Block (26.5 6 11.28) since the Late Miocene has accomplished transfer of deformation between major extensional corridors, and an especially rapid local rotation (216.3 6 9.58) in NW Normanby Island may suggest an incipient dextral transfer fault.

Continental breakup and UHP rock exhumation in action: GPS results from the Woodlark Rift, Papua New Guinea

“…It is possible that some portion of the current GPS extension budget was accommodated on these more southerly features earlier in the rifting history (Option 2), and that deformation has become progressively localized northward into the Goodenough Bay and D'Entrecasteaux Islands regions as rifting has progressed. Recent paleomagnetic data [ Cairns et al ., ] supports this model—with data recording an anticlockwise rotation of Miocene rocks on the southern side of the SE Papuan Peninsula relative to the Australian Plate, requiring extensional deformation south of the Papuan Peninsula since the Miocene. However, we also note that Fitz and Mann [] reconstruct ∼3–4 km of extension on the Mai'iu Fault (referred to as the Owen Stanley Fault in that paper), largely based on seismic reflection data from the hanging wall that does not extend far enough south to image the fault itself or the footwall.…”

Slow‐to‐Fast Deformation in Mafic Fault Rocks on an Active Low‐Angle Normal Fault, Woodlark Rift, SE Papua New Guinea

“…In the active eastern Woodlark Basin, this rotation has resulted in north‐south seafloor spreading (Eilon et al., 2015; Wallace et al., 2004). Farther west, the spreading center transitions into a zone of active continental rifting―the Woodlark Rift―which is thought to have initiated at 3.6–8.4 Ma (Figure 1a; Taylor & Huchon, 2002; Wallace et al., 2014; Cairns et al., 2015).…”

Southeast Papuan crustal tectonics: Imaging extension and buoyancy of an active rift

“…Rather, we suspect that this sharp truncation in seismicity marks a rheological boundary as a brittle-ductile transition, similar to that seen beneath the Gulf of Corinth [Hatzfeld et al, 2000]. The southeast Papuan Peninsula also experienced pre-late Miocene counterclockwise rotation of 12-28° [ Cairns et al, 2015], so some inactive deformational structures should be present.…”