This document summarizes a study of surface salt deformation in the Kuqa fold-thrust belt of northwestern China using radar interferometry. The study finds: 1) The Quele salt nappe is subsiding at average rates of up to 1 cm/yr. 2) The Awate and Daxiagu namakiers show complex patterns of uplift and subsidence of up to 1 cm/yr and 9 mm/yr respectively. 3) Preliminary mechanical models simulate the evolution of the Quele salt structure over 100,000 years with height changes consistent with observed subsidence rates.

1. Surface salt kinematic models
Surface salt in Kuqa fold-thrust belt, northwestern China: time-
lapse surface deformation and mechanical modelling
Cindy Colón*, Marcello G. Teixeita, François Renard, A. Alexander G. Webb, Cécile Lasserre, Marie-
Pierre Doin, Rowena Lohman, Jianghai Li
Please email *CColon3@LSU.edu for
references and any questions.
GEOLOGIC SETTING
The Kuqa fold-thrust belt (KFTB), NW China, actively accommodates N-S shortening between the
Tian Shan and Tarim basin across a ~400 km long, ~20-65 km wide region. Salt tectonics
dominates the regional deformation patterns but surface salt exposures are restricted to the west
where the Paleocene-Eocene Kumugeliemu Group (dominated by gypsum, halite, anhydrite)
outcrops.
Figure 4. Average linear LOS (line-of-sight) velocity maps with the extent of surface salt
structures outlined by thin black lines. Surface movement toward and away from the satellite is
represented by warm (uplift) and cool (subsidence) colors, respectively.
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SURFACE SALT IN KUQA FOLD THRUST BELT
INSAR METHODS & RESULTS
PRELIMINARY MECHANICAL MODELS
Contact information:
Figure 1. Geologic map of
the western Kuqa fold-
thrust belt adapted from Li
et al., 2014. The black
boxes highlight particular
areas of interest: Bozidun
(A), Awate (B), Daxiagu
(C), Quele (D) and the
Dawanqi oil field (E).
Figure 2. Cross section from A-A’ (South to North –
see Figure 1) across Baicheng mini basin, Quele
salt thrust fault and Misikantage anticline. The inset
shows a schematic profile of the Quele salt thrust.
RESULTS SUMMARY
 Quele salt nappe: Dominated by negative average velocity rates, corresponding to subsidence.
 Awate namakier: Western segment approaches ~1 mm/yr of subsidence at the center of the structure. The eastern segment approaches ~1 cm/yr of
subsidence at the center and decreases radially.
 Daxiagu namakier: Uplift rates at the eastern portion of the namakier reach up to ~9 mm/yr. Subsidence, approaching -4 mm/yr, is dominant at the
southwestern segment of the namakier.
 Bozidun namakier: Observed displacements are coincident with background deformation signal indicating an inactive salt structure.
 No correlation is observed between surface salt deformation and temperature, humidity or rainfall.
Figure 6. Mesh and boundary conditions of Quele (A=2350m, B=580m, C=110m, D=150m,
E=500, F=1270m). Lighter brown represents the salt and the darker brown represents sediment.
Figure 7. Configuration of the salt structure after 100 time steps (100000 years). Red represents salt
layer. Green represents surrounding sedimentary layers. Inset: height and length evolution of the salt
structure over 0.1 Myear. The height velocity (0.8 mm/yr) is of the same magnitude as the InSAR
measurements.
A recent mathematical approach, called Successive Linear Approximation Method (SLA), was developed to simulate of the motion of the salt and
the surrounding sedimentary layers, in a unified manner, considering the rock salt as a viscoelastic solid. This method is a Lagrangian formulation
of mechanical problems in relative motion and it differs from other Eulerian or Lagragian methods because: (i) the linearization of the constitutive
equation and the boundary problem and (ii) the actualization of the reference configuration at each time step. Our goal is to apply SLA to
numerically simulate the active deformation of surface salt structures observed in the Kuqa region, northwestern China.
RADAR INTERFEROMETRY
 40 Envisat ASAR C-band radar images (Track 291) from June 2003 and October 2010 were combined into 85 interferograms (90m x 90m, 4 looks in
range, 20 looks in azimuth). Interferograms were processed and analyzed in time series using the NSBAS (New Small Baseline Algorithm Subset)
chain described by Doin et al. (2011), based on the Caltech/JPL Repeat Orbit Interferometry Package (ROI_PAC, Rosen et al, 2004).
 The time series analysis includes corrections of tropospheric delays based on the ERA-Interim Global Atmospheric Model from the European Centre
for Medium-Range Weather Forecasts (ECMWF) (Doin et al., 2011; Jolivet et al., 2011), and corrections of DEM errors (Ducret et al., 2014).
 We retrieve an average velocity map and the Line of Sight displacement evolution through time around the salt structures
PROJECT MOTIVATION
The present study at KFTB contributes to the knowledge of surface salt kinematics by
presenting a case study in a new region where the models of salt behavior developed
based on Iranian namakiers can be tested. Additionally, the active kinematics of
extrusive salt sheets, like the Quele namakier in the KFTB, is not well understood
because few, if any, examples exist at the surface today. We target the following
questions that are necessary to further understand surface salt kinematics at KFTB:
(1) How does active subaerial salt behave in KFTB?
(2) Do surface conditions control subaerial salt flow?
(3) Are surface salt flow rates the same over different temporal scales?
Figure 3. Models of surface salt kinematics
over short time scales with varying moisture.
Model 1 is based on work by Talbot & Pohjola,
[2009] which suggests dome deflation during
wet periods. Model 2, based on work by Aftabi
et al., [2010], suggests a
short-lived dome
deflation flowed by
dome inflation during
wet periods.
LOS Velocity Maps Time series analysis
Figure 5. Differential time series displacements (cm) across KFTB. Negative displacement
trend is observed at Quele, central Awate, the western flank of Daxiagu, and at the Dawanqi oil
field. Positive displacement trend is observed at the riverbed in between the two Awate
segments, the eastern flank of Daxiagu, and the Dawanqi oil field.