Dataset Title: 2D thermo-mechanical simulations of flat subduction - supporting data for research manuscript

Name and contact information of PI:
Name:        Anthony R. Lowry
Institution: Utah State University
Address:     Dept. of Geosciences, 4505 Old Main Hill, Logan UT 84322-4505
Email:       tony.lowry@usu.edu

Name and contact information of Co-PI:
Name:        Ravi V. S. Kanda
Institution: Utah State University
Address:     Dept. of Geosciences, 4505 Old Main Hill, Logan UT 84322-4505
Email:       kanda.vs.ravi@gmail.com

Name and contact information of Co-PI:
Name:        Susanne J. H. Buiter
Institution: RWTH Aachen University
Address:     Tectonics and Geodynamics, Lochnerstrasse 4-20, 52064 Aachen, Germany
Email:       susanne.buiter@tag.rwth-aachen.de

Funding source: 
Agency, Grant: USGS Earthquake Hazards Program, grant #G17AP00104
Project Title: Toward Earthquake System Science: Western U.S. Lithospheric Stress/Strain Partitioning of Mantle Dynamics

Manuscript Title:
"Localized viscous coupling of slab and wedge corner driven by long-lasting lower mantle resistance triggers flattening of subducting slabs", 
 by Ravi V. S. Kanda, Anthony R. Lowry, Susanne J. H. Buiter
Abstract: 
In < 10% of global subduction zones, the downgoing oceanic plate “flattens” just beneath the overriding plate, attaining near-horizontality for hundreds of km before diving steeply into the mantle. Despite decades of inquiry, the rarity of flat subduction and its causes are not fully understood. Previous studies established a need for oceanward retreat of the trench caused by an advancing overriding plate but combined that with distinct causative factors for each flat slab occurrence, such as subducting slab buoyancy, a cratonic root in the overriding plate, large plate convergence rate, or mantle wedge suction. Here we propose a more universal mechanism for slab flattening based on the evolution of lithosphere and mantle rheology common to all long-lived subduction zones. Using thermomechanical models, we show that the necessary and sufficient conditions for slab flattening are long-lasting resistance to slab penetration into the lower mantle beneath an advancing continental plate, strong lithospheric cores, and viscous coupling restricted to the wedge corner. The advancing overriding plate advects cooler basal-lithospheric mantle into the mantle wedge. Resistance to subduction into the lower mantle hinders the equilibration of pressure between the top and bottom slab surfaces at the wedge corner. Together, these processes increase the slab-wedge viscous coupling within a compact, <30 km region around the corner, overcoming the slab's local bending strength and flatten it. It is this interaction between lower mantle resistance to flow and the evolution of trench proximal viscous coupling, rather than site-specific anomalies, that determines the global occurrence of flat subduction.

Data summary:
    Supporting Data for manuscript titled "Localized viscous coupling of slab and wedge corner driven by long-lasting lower mantle resistance triggers flattening of subducting slabs", by Ravi V. S. Kanda, Anthony R. Lowry, Susanne J. H. Buiter, submitted to J. Geoph. Res. - Solid Earth for review (November, 2021). 

Brief description of collection and processing of data:
    We solve the equations for conservation of mass, momentum and energy using the arbitrary Lagrangian-Eulerian finite-element viscous-plastic code SULEC (v3.4). The code can achieve large deformations with a true free surface(Crameri et al., 2012; Fullsack, 1995; Ghazian & Buiter, 2013; Grigull et al., 2012; Quinquis et al., 2011; Tetreault & Buiter, 2012). SULEC output – including temperature, pressure, strain-rate, viscosity, stresses, velocities, principal stress orientations, etc – was generated in VTK structured grid format (*.vts files), with tracer points tracking the free surface in ASCII format. Detailed multi-panel dashboards were developed for simultaneously visualizing the 2D fields for many of these parameters at each time-step, along with depth (e.g., temperature, differential stress) and free surface profiles (e.g., heat-flow), in order to pin down the mechanics of deformation. All 2D cross-sections presented in the manuscript were generated from subsets of these dashboard visualizations using an open-source data analysis and visualization package, Paraview (Ahrens et al., 2005; Henderson, 2007; available for Linux, OS-X, and Microsoft Windows at https://www.paraview.org/download/). ASCII data (e.g., time at each time-step, free surface marker data), were extracted and processed using scripts written in the Linux Bash-shell, and/or the free open-source programming language Python (Python-Software-Foundation, n.d.) and associated open-source scientific computing packages (Numpy (Oliphant, 2010), Scipy (E. Jones et al., 2015), and Matplotlib (Hunter, 2007)). Manuscript figures were further processed where necessary with the open source image editing package GIMP (Kimball et al., n.d.), and all figures were assembled in an open-source vector graphics package, Inkscape (Inkscape Project, 2019).

Description of Data/files:
    Data consists of 44 archives, each containing the following ASCII data: annotated input file(s), screen/std-output (raw & parsed), simulation output (2D VTK structured grid files at each output time-step) for the entire model domain, and surface topography XY-coordinates for all model output times (in a separate sub-folder).  All input files are commented to identify the modeling parameters used.  The simulation output structured grid VTS files can be viewed with several open-source visualization packages. VTS file data structure is documented here: https://kitware.github.io/vtk-examples/site/VTKFileFormats/#structuredgrid

Descriptions of parameters/variables
a. Temporal (beginning and end dates of data collection): Simulations were performed between 2016 and 2019
b. Instruments used and units of measurements: Simulations were performed on a hexcore Ubuntu Linux workstation, and took roughly 1 week of run-time per simulation.

Special software required to use data: Software that can visualize VTK datasets: Paraview, MayaVi, OpenDX, etc.

Publications that cite or use this data:
    Localized viscous coupling of slab and wedge corner driven by long-lasting lower mantle resistance triggers flattening of subducting slabs", by Ravi V. S. Kanda, Anthony R. Lowry, Susanne J. H. Buiter, submitted to J. Geoph. Res. - Solid Earth for review (November, 2021). 

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