Browsing by Author "Barnes, Philip M."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Compactive deformation of incoming calcareous pelagic sediments, northern Hikurangi subduction margin, New Zealand: Implications for subduction processes(Elsevier, 2023) Wang, Maomao; Barnes, Philip M.; Morgan, Julia K.; Bell, Rebecca E.; Moore, Gregory F.; Wang, Ming; Fagereng, Ake; Savage, Heather; Gamboa, Davide; Harris, Robert N.; Henrys, Stuart; Mountjoy, Joshu; Tréhu, Anne M.; Saffer, Demian; Wallace, Laura; Petronotis, KaterinaCalcareous rocks are commonly found in subduction zones, but few studies have investigated the consolidation and compactive deformation of these rocks prior to subduction, and their potential effects on subduction and accretionary processes are thus poorly understood. Using drilling data obtained during International Ocean Discovery Program (IODP) Expeditions 372 and 375 combined with 2D and 3D seismic reflection data, the structure, growth history, and slip rates of normal faults identified in the incoming pelagic sedimentary sequences of the Hikurangi Margin were investigated. A seismic coherence depth slice and vertical profiles show that these faults exhibit polygonal structure that has rarely been documented at subduction margins. The polygonal faults are closely spaced and layer-bound within sequences dominated by pelagic carbonate and calcareous mudstone of Paleocene-Pliocene age. Kinematic modeling and 2D displacement analysis reveal that fault throws decrease toward the upper and lower tipline. In detail, two groups of throw profiles are defined by locations of displacement maxima, possibly reflecting lateral variations in physical properties. The polygonal fault system (PFS) likely formed by syneresis processes that involve diagenetically induced shear failure and volumetric contraction of the pelagic unit associated with fluid escape. Fault growth sequences reveal multiple, weakly correlated intervals of contemporaneous seafloor deformation and sedimentation and allow estimates of fault slip rates. We find evidence for a significant increase in typical slip rates from 0.5-3 m/Ma during pelagic sedimentation to >20 m/Ma following the onset of terrigenous sedimentation. These observations suggest that rapid loading of the pelagic sediments by the trench-wedge facies was associated with renewed and faster growth of the PFS. The PFS will eventually be transported into the base of the accretionary wedge, enhancing geometric roughness and heterogeneity of materials along the megathrust, and providing inherited zones of weakness. Selective fault reactivation may facilitate deformation and episodic vertical fluid migration in the lower wedge associated with microearthquakes, tremor, and slow slip events.Item The role of protothrusts in frontal accretion and accommodation of plate convergence, Hikurangi subduction margin, New Zealand(The Geological Society of America, 2018) Barnes, Philip M.; Ghisetti, Francesca C.; Ellis, Susan; Morgan, Julia K.Protothrusts mark the onset of deformation at the toe of large subduction accretionary wedges. They are recognized in seismic reflection sections as small-displacement (tens of meters) faults seaward of the primary frontal thrust fault. Although assumed to reflect incipient accretionary deformation and to mark the location of future thrusts, few studies discuss their displacement properties, evolution, and kinematic role during frontal accretion and propagation of the subduction décollement. We analyze high-quality geophysical and bathymetric images of the spectacular 25-km-wide Hikurangi margin protothrust zone (PTZ), the structure of which varies along strike north and south of the colliding Bennett Knoll seamount. We provide a quantitative data set on protothrust scaling relationships and fractal fault population characteristics. Our analyses lead us to speculate on the importance of stratigraphic heterogeneity in structural development, and highlight the role of protothrust arrays in the formation of the frontal thrust. We document a migrating wave of protothrust activity in association with forward advancement of the décollement and deformation front. Shortening east of the present frontal thrust, calculated from displacements on seismically imaged faults and from subseismic faulting derived from power law relationships, reveal the significant role of the PTZ in accommodating shortening. There is possibly as much as ∼7.4 km and ∼4.0 km of shortening accommodated by the PTZ south and north, respectively, of Bennett Knoll seamount. As much as ∼90% of the total shortening may be accommodated at subseismic scale. These data indicate that the active PTZ, together with older accreted PTZs, may accommodate ∼10%–50% of the total margin-normal convergence rate at the Hikurangi margin.