Early results from SISIE--South Island Subduction Initiation Experiment--in the context of recent drilling and geodynamic models

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http://abstractsearch.agu.org/meetings/2018/FM/T44A-04.html
Author(s): Gurnis, Michael; Van Avendonk, Harm J.; Gulick, Sean P. S.; Stock, Joann M.; Sutherland, Rupert; Hightower, Erin; Shuck, Brandon; Patel, Jiten
South Island Subduction Initiation Experiment (SISIE) Shipboard Science Party
Author Affiliation(s): Primary:
California Institute of Technology, Pasadena, CA, United States
Other:
University of Texas at Austin, United States
Victoria University of Wellington, New Zealand
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: Our understanding of subduction initiation, a vital but poorly constrained phase of plate tectonics, is rapidly unfolding in light of recent marine geophysical surveys, ocean drilling and geodynamic modeling. Theoretical studies, and interpretation of the Mesozoic and later plate tectonic history of the Pacific, suggest that subduction initiation alters the force balance on plates. Several recently completed IODP expeditions have focused on the incipient and subsequent history of Izu-Bonin-Mariana and Tonga-Kermadec subduction zones (Expeditions 351, 352 and 371). These expeditions provide a wealth of information on the evolution of these subduction zones and suggest an important role of pre-existing subduction zones, including relic arcs, in defining conditions that lead to subduction initiation. Some of the key unknowns in subduction initiation can be answered through study of a subduction zone that has partially proceeded through the nucleation stage, as this setting would provide plate motions along with knowledge of antecedent tectonics and subsequent history to constrain the process. The Puysegur incipient subduction zone south of New Zealand is precisely in this state and so we undertook an active source seismic survey in the region during February-March 2018 aboard the R/V Marcus G. Langseth, using 28 University of Texas Institute of Geophysics OBSs for 43 deployments on two refraction lines and a single, towed hydrophone streamer either 4.05 or 12.6 km in length. We also collected multibeam bathymetry, gravimetry and magnetometer data. Early analysis of the results shows that the tectonic conditions that exist along the Puysegur system are substantially different than inferred from prior work. The decollement between subducting and the over-riding plates is clearly evident in seismic lines that cross the plate boundary; along a northern profile, where plate convergence is greater, MCS images reveal an accretionary structure. Block-faulted thinned continental crust is found on the over-riding plate. We advance a novel model for the initiation of subduction involving the juxtaposition of thin, block-faulted continental crust adjacent to oceanic crust which may have wide applicability which we place in the context of recent drilling and geodynamic modeling.
Year of Publication: 2018
Research Program: IODP2 International Ocean Discovery Program
Key Words: 18 Geophysics, Solid-Earth; Australasia; Expedition 351; Expedition 352; Expedition 371; International Ocean Discovery Program; New Zealand; North Pacific; Northwest Pacific; Pacific Ocean; Plate tectonics; South Island; South Pacific; Southwest Pacific; Subduction; Subduction zones; West Pacific
Coordinates: N272300 N272301 E1341907 E1341905
N282425 N282705 E1424600 E1423600
S373400 S262900 E1712100 E1601800
Record ID: 2019050424
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