Subduction-related strain in a calcareous-pelagic shear zone: insights on deformation at the hikurangi margin plate interface from the input sequence at site U1520 and the Llanddwyn island shear zone, Anglesey, U.K

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Author(s): Leah, Harold Robert; Fagereng, Ake; Meneghini, Francesca; Morgan, Julia; Savage, Heather M.; Wang Maomao; Saffer, Demian M.; Wallace, Laura M.; Petronotis, Katerina E.
International Ocean Discovery Program (IODP), Expedition 372 Scientists
Author Affiliation(s): Primary:
Cardiff University, Cardiff, United Kingdom
University of Pisa, Italy
Rice University, United States
Lamont-Doherty Earth Observatory, United States
Hohai University, China
Pennsylvania State University, United States
GNS Science, New Zealand
International Ocean Discovery Program, United States
Volume Title: AGU 2018 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2018; American Geophysical Union 2018 fall meeting, Washington, DC, Dec. 10-14, 2018. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The rheology of the subduction thrust interface is significantly affected by the nature of the incoming sedimentary sequence. Core recovered from Site U1520, drilled by International Ocean Discovery Program Expedition 375, sampled the sedimentary input sequence for the Hikurangi subduction megathrust. The samples reveal calcareous sediments at depths of ∼500-850 mbsf, overlying volcaniclastic sediments and volumetrically minor mudstones down to 1015 mbsf. Faults and dissolution features are common within the calcareous sediments, whereas volcaniclastic sediments below host frequent carbonate veins and calcite and zeolite cements. These lithologies likely host a significant component of megathrust deformation. The Llanddwyn Island Shear Zone (LISZ) preserves material accreted to the upper plate during Ordovician subduction of dominantly oceanic material, and represents a possible exhumed analogue to northern Hikurangi. The LISZ is a moderate-to-low temperature shear zone that reached upper prehnite-pumpellyite facies conditions (<300°C) within the Gwna Melange of Anglesey, Wales, UK. It comprises repeating units of pillow basalts, mudstones and fine sandstones, massive and brecciated carbonates, and carbonate-cemented hyaloclastites. Deformation within the LISZ occurred dominantly by pressure-solution creep within carbonate and clay-rich rocks, as also observed in the Hikurangi input sequence. Strain across the LISZ is dominantly macroscopically ductile, and heterogeneously distributed between weaker (mudstones, hyaloclastites) and stronger lithologies (pillow basalts, carbonates). To quantitatively assess the strain distribution across this shear zone, normalised aspect ratios were determined from pillow basalt and clast aspect ratio measurements. These data provide a lower bound for finite strain throughout the shear zone, indicate the distribution of deformation throughout the LISZ, and provide an analogue of deformation processes which may be occurring at shallow to moderate depths at the Hikurangi plate interface. The onset of pressure solution-mediated slip in the LISZ was promoted at low temperature by its calcareous-pelagic composition. Comparable compositions cored near the Hikurangi trench may deform similarly at low temperatures during subduction.
Year of Publication: 2018
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 18 Geophysics, Solid-Earth; Anglesey; Anglesey Wales; Crust; Europe; Faults; Great Britain; Hikurangi Margin; Hikurangi Trough; IODP Site U1520; International Ocean Discovery Program; Lithosphere; Llanddwyn Island; Oceanic crust; Oceanic lithosphere; Pacific Ocean; Plate tectonics; Shear zones; South Pacific; Southwest Pacific; Subduction; Subduction zones; United Kingdom; Wales; West Pacific; Western Europe
Coordinates: S385810 S385810 E1790756 E1790756
Record ID: 2019050435
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States