Auxiliary Material Submission for Paper 2013JB010864
Three-dimensional mantle circulations and lateral slab deformation
in the southern Chilean subduction zone
Shu-Chuan Lin
(institute of Earth Sciences, Academia Sinica, Taipei, Taiwan)
J. Geophys. Res., doi:10.1029/2013JB010864, 2014
Auxiliary Material
S1. Model setup
We assume that the flat subduction zone at ~ 30-34 S acts as a boundary for flow in
regions south of ~ 33 S. The free-slip southern boundary is used to minimize the
influence of the lateral flow in the southern boundary. Lateral flow may exist in both
boundaries, but it would only enhance the trench-parallel components and not change
the flow patterns for regions away from the boundaries in general. Particularly the
model domain should be large enough to allow the minimum boundary effects on the
overall flow patterns. Influence of the wedge flow is roughly confined within several
hundred kilometers from the slab, while the distances from the eastern boundary to
the trench are ~ 1000-2000 km (Figure A1).
Tests show that variation in depth of the low-viscosity layer for a few tens of
kilometers does not substantially change the flow field. A variable grid spacing
increasing from < 1 km to > 100 km is used. The grid contains ~ 15 million grid
points. The grids are refined with highest resolutions of 1.875, 1, and ~0.375 km in
the x-, y- and z-directions, respectively, for the wedge corner and regions adjacent to
the plate surfaces, plate boundaries and the boundaries of the model domain, to
resolve the large gradients in velocity and viscosity.
S2. Initial thermal structure
Ridge segments west of ~ 78 W with small lateral offsets (a few tens of kilometers
apart) are merged as one longer segment in the numerical models (Figure 2). The
thermal structures of the plates in advance of the trench are determined according to
the half-space cooling model by increasing the plate age with distance from the ridge
based on half-spreading rates of 70 cm yr-1 for the Nazca plate. Each thermal profile is
derived from an approach that resembles high-resolution thermal models using
kinematical-dynamical models [e.g., van Keken et al. 2008, Lin et al., 2010, 2013],
except that the age for each segment of the subducting plate at the trench varies with
time. The ages of the Nazca plate increase with slab depth and the ages of the
Antarctic plate decreases with slab depth at the trench in the time-dependent 2D
models.
Figure A1. Maps for contours at 50 km intervals showing slab geometry for each
models (a-g), and depth profiles showing variations in slab base along the y-direction.
Numbers mark in (g) show plate ages in the vicinity of the trench in the models.
Figure A2. Location map showing the relationship between the vertical cross sections
(text: solid lines, Figure A3: dashed lines) and the recent Patagonian basalts (yellow).
(b)
Figure A3. Vertical cross sections in roughly the trench-perpendicular directions
showing thermal and flow fields for model XII and XIII. Model parameters in both
models are same as those in model I, except for the slab geometry (initial thermal
structure). The initial thermal structure of model XII is obtained from results of
time-dependent model for a model with the perturbation within a deep slab. The initial
slab dips of the slab segments with different plate age along the strike are the same for
the time-dependent experiments. The slab dip becomes steep at greater depths for
young segments after ~ 1.4 Myr (model XII). The thermal field of model XIII is
obtained from perturbation of thermal field of model XII. The locations are marked in
Figure A2 (model XII: dashed blue line, model XIII: dashed green line).