Variations in Structure on the Southern Hikurangi Subduction Zone
Abstract
The structure and morphology of the upper plate across the Hikurangi subduction margin, New Zealand, varies significantly along- and across-strike. We use several multichannel seismic reflection profiles, including the SHIRE profile MGL1708-044, to characterise and compare the morphological and structural variation within the outer forearc and the incoming section in the southern part of the margin (between ~41°S and ~42°S). The nature of the Hikurangi subduction margin is known to change along strike in terms of input materials and input sediment thickness, width of the forearc, forearc structure including structural vergence, degree of obliquity and partitioning, and slip behaviour along the plate boundary fault. Around 41°S, the margin exhibits a thick (~1.5 km) incoming sedimentary section, including a high-amplitude reflection near the base of the sequence overlaying the smooth basement of the Hikurangi Plateau. The prism is broad (~60 km wide), with a well-developed proto-thrust system and prism structures that include back-thrusts and predominantly seaward-verging structures. There is a significant decrease in the thickness of sediment on the incoming plate at the southern end of the subduction zone as the Chatham Rise impinges on the subduction zone. At 42°S, the margin is characterised by a thin (<1 km), chaotic sedimentary sequence overlying the northern flank of the irregular Chatham Rise basement. Here there is a narrow (25 km) and steep accretionary wedge with a much less well developed frontal thrusting sequence, with evidence for landward vergence. We integrate our seismic data with existing fault maps and published stratigraphic correlations to map fault geometries and interpret the stratigraphy of the incoming section. We then compare the results with sediment thickness, subduction obliquity and patterns of seismicity to identify the possible causes for variation in the styles of fault development within the southern Hikurangi forearc.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T51F0359S
- Keywords:
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- 8045 Role of fluids;
- STRUCTURAL GEOLOGY;
- 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS;
- 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS;
- 8170 Subduction zone processes;
- TECTONOPHYSICS