Crustal Structure of the Northern Hikurangi Margin, New Zealand: Variable Accretion and Overthrusting Plate Strength Influenced by Rough Subduction

Gase, Andrew; Avendonk, H. J. Van; Bangs, N. L.; Bassett, Dan; Henrys, S. A.; Barker, D. H. N.; Kodaira, Shuichi; Jacobs, Katrina; Luckie, Thomas W.; Okaya, D. A.; Fujie, Gou; Yamamoto, Yojiro; Arnulf, A. F.; Arai, Ryuta

doi:10.1029/2020jb021176

Cited by 18 publications

(47 citation statements)

References 115 publications

(296 reference statements)

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“…The Moho of the Hikurangi Plateau is 18-19 km deep along the southern half of Line 4, but gradually shallows by 4 km between the northern flanks of Unnamed Seamount 2 (Model km 280-Figure 3b) and Mahia Seamount (Model km 380-Figure 3b), reaching a depth of 14 km at the northern end of the transect. These Moho depths are consistent with the results of margin-normal wide-angle seismic profiles traversing the Hikurangi Plateau in North (SHIRE Line 1) and South Hikurangi (SAHKE) respectively (Gase et al, 2021;Mochizuki et al, 2019).…”

Section: Hikurangi Plateau Structure From Wide-angle Seismic Datasupporting

confidence: 87%

“…Through the crust, Unnamed Seamounts 1 and 2, and Te Kurī‐a‐Paoa Seamount appear associated with reductions in seismic velocities in the upper crust, and we note that regions where the lower‐crust does exhibit higher velocities appear to be between, rather than beneath, the seamounts imaged at shallow depth. High‐resolution geophysical imaging of subducting and unsubducted seamounts offshore Gisborne show their internal structure to be heterogeneous with high‐velocity and resistive cores embedded within a larger, lower‐velocity and more conductive matrix (Arai et al., 2020; Chesley et al., 2021; Gase et al., 2021). We therefore suggest that differences in the seismic velocity structure of seamounts imaged along Line 4 reflect their three‐dimensionality and position in relation to our 2D transect, rather than any overall differences in internal structure or composition.…”

Section: Resultsmentioning

confidence: 99%

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Heterogeneous Crustal Structure of the Hikurangi Plateau Revealed by SHIRE Seismic Data: Origin and Implications for Plate Boundary Tectonics

Bassett,

Fujie,

Kodaira

et al. 2023

Geophysical Research Letters

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Marine multichannel and wide‐angle seismic data constrain the distribution of seamounts, sediment cover sequence and crustal structure along a 460 km margin‐parallel transect of the Hikurangi Plateau. Seismic reflection data reveals five seamount up‐to 4.5 km high and 35–75 km wide, with heterogeneous internal velocity structure. Sediment cover decreases south‐to‐north from ∼4.5 km to ∼1–2 km. The Hikurangi Plateau crust (VP 5.5–7.5 km/s) is 11 ± 1 km thick in the south, but thins by 3–4 km further north (∼7–8 km). Gravity models constructed along two seismic lines show the reduction in crustal thickness persists further east, coinciding with a bathymetric scarp. Gravity data suggest the transition in crustal thickness may reflect spatial variability in deformation and lithospheric extension associated with plateau breakup. Variability in the thickness of subducting crust may contribute to differences in megathrust geometry, upper‐plate stress state and high‐rates of contraction and uplift along the southern Hikurangi margin.

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Section: Hikurangi Plateau Structure From Wide-angle Seismic Datasupporting

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Heterogeneous Crustal Structure of the Hikurangi Plateau Revealed by SHIRE Seismic Data: Origin and Implications for Plate Boundary Tectonics

Bassett,

Fujie,

Kodaira

et al. 2023

Geophysical Research Letters

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“…6). Past seamount subduction has also been identified at the Hikurangi margin, where tremors occur in front of the actively colliding seamount (Gase et al 2021). Thus, understanding the variety of earthquakes associated with BTH subduction requires consideration of not only the actively colliding BTH, but also of previous BTHs.…”

Section: Effects Of Multiple Bth Collisions On Earthquakesmentioning

confidence: 99%

Evolution of the geological structure and mechanical properties due to the collision of multiple basement topographic highs in a forearc accretionary wedge: insights from numerical simulations

Miyakawa

Noda

Koge

2022

Prog Earth Planet Sci

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We propose a conceptual geological model for the collision of multiple basement topographic highs (BTHs; e.g., seamounts, ridges, and horsts) with a forearc accretionary wedge. Even though there are many BTHs on an oceanic plate, there are few examples of modeling the collision of multiple BTHs. We conducted numerical simulations using the discrete element method to examine the effects of three BTH collisions with forearcs. The typical geological structure associated with a BTH collision was reproduced during the collision of the first BTH, and multiple BTH collisions create a cycle of formation of BTH collisional structures. Each BTH forces the basal décollement to move up to the roof décollement, and the roof décollement becomes inactive after the passage of the BTH, and then the décollement moves down to the base. As the active décollement position changes, the sequences of underthrust sediments and uplifted imbricate thrusts are sandwiched between the décollements and incorporated into the wedge. At a low horizontal compressive stress, a “shadow zone” is formed behind (i.e., seaward of) the BTH. When the next BTH collides, the horizontal compressive stress increases and tectonic compaction progresses, which reduce the porosity in the underthrust sediments. Heterogeneous evolution of the geological and porosity structure can generate a distinctive pore pressure pattern. The underthrust sediments retain fluid in the “shadow” of the BTH. Under the strong horizontal compressive stresses associated with the next BTH collision, pore pressure increases along with a rapid reduction of porosity in the underthrust sediments. The distinctive structural features observed in our model are comparable to the large faults in the Kumano transect of the Nankai Trough, Japan, where a splay fault branches from the plate boundary and there are old and active décollements. A low-velocity and high-pore-pressure zone is located at the bottom of the accretionary wedge and in front (i.e., landward) of the subducting ridge in the Kumano transect. This suggests that strong horizontal compressive stresses associated with the current BTH collision has increased the pore pressure within the underthrust sediments associated with previous BTHs.

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“…6). Past seamount subduction has also been identi ed at the Hikurangi margin, where tremors occur in front of the actively colliding seamount (Gase et al, 2021). Thus, understanding the variety of earthquakes associated with BTH subduction requires consideration of not only the actively colliding BTH, but also of previous BTHs.…”

Section: Effects Of Multiple Bth Collisions On Earthquakesmentioning

confidence: 99%

Evolution of the geological structure and mechanical properties due to the collision of multiple basement topographic highs in a forearc accretionary wedge: Insights from numerical simulations

Miyakawa

Noda

Koge

2021

Preprint

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We propose a conceptual geological model for the collision of multiple basement topographic highs (BTHs; e.g., seamounts, ridges, and horsts) with a forearc accretionary wedge. Even though there are many BTHs on an oceanic plate, there are few examples of modeling the collision of multiple BTHs. We conducted numerical simulations using the discrete element method to examine the effects of three BTH collisions with forearcs. The typical geological structure associated with a BTH collision was reproduced during the collision of the first BTH, and multiple BTH collisions create a cycle of formation of BTH collisional structures. Each BTH forces the basal décollement to move up to the roof décollement, and the roof décollement becomes inactive after the passage of the BTH, and then the décollement moves down to the base. As the active décollement position changes, the sequences of underthrust sediments and uplifted imbricate thrusts are sandwiched between the décollements and incorporated into the wedge. At a low horizontal compressive stress, a “shadow zone” is formed behind (i.e., seaward of) the BTH. When the next BTH collides, the horizontal compressive stress increases and tectonic compaction progresses, which reduce the porosity in the underthrust sediments. Heterogeneous evolution of the geological and porosity structure can generate a distinctive pore pressure pattern. The underthrust sediments retain fluid in the “shadow” of the BTH. Under the strong horizontal compressive stresses associated with the next BTH collision, pore pressure increases along with a rapid reduction of porosity in the underthrust sediments. The distinctive structural features observed in our model are comparable to the large faults in the Kumano transect of the Nankai Trough, Japan, where a splay fault branches from the plate boundary and there are old and active décollements. A low-velocity and high-pore-pressure zone are located at the bottom of the accretionary wedge and in front (i.e., landward) of the subducting ridge in the Kumano transect. This suggests that strong horizontal compressive stresses associated with the current BTH collision has increased the pore pressure within the underthrust sediments associated with previous BTHs.

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Crustal Structure of the Northern Hikurangi Margin, New Zealand: Variable Accretion and Overthrusting Plate Strength Influenced by Rough Subduction

Abstract: At convergent margins, the overriding plate responds to processes ranging from accretion to erosion in its rock record. Thus, the structural configurations of overthrusting plates are the products of long-term processes, for example frontal accretion,

Cited by 18 publications

References 115 publications

Heterogeneous Crustal Structure of the Hikurangi Plateau Revealed by SHIRE Seismic Data: Origin and Implications for Plate Boundary Tectonics

Heterogeneous Crustal Structure of the Hikurangi Plateau Revealed by SHIRE Seismic Data: Origin and Implications for Plate Boundary Tectonics

Evolution of the geological structure and mechanical properties due to the collision of multiple basement topographic highs in a forearc accretionary wedge: insights from numerical simulations

Evolution of the geological structure and mechanical properties due to the collision of multiple basement topographic highs in a forearc accretionary wedge: Insights from numerical simulations

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