Abstract
The Southern Andes are regarded as a typical subduction orogen formed by oblique plate convergence. However, there is considerable uncertainty as to how deformation is kinematically partitioned in the upper plate. Here we use analogue experiments conducted in the MultiBox (Multifunctional analogue Box) apparatus to investigate dextral transpression in the Southern Andes between 34 °S and 42 °S. We find that transpression in our models is caused mainly by two prominent fault sets; transpression zone-parallel dextral oblique-slip thrust faults and sinistral oblique-slip reverse faults. The latter of these sets may be equivalent to northwest-striking faults which were believed to be pre-Andean in origin. We also model variable crustal strength in our experiments and find that stronger crust north of 37 °S and weaker crust to the south best reproduces the observed GPS velocity field. We propose that transpression in the Southern Andes is accommodated by distributed deformation rather than localized displacements on few margin-parallel faults.
Highlights
The Southern Andes are regarded as a typical subduction orogen formed by oblique plate convergence
Structural studies of the northern Liquiñe-Ofqui Fault Zone (LOFZ) identified a rather wide zone of faults with diverse orientations and kinematically associated with the LOFZ10–12 (Fig. 1b). These observations call into question the popular hypothesis of kinematic partitioning, by which northward displacement of the crust is accomplished on a few margin-parallel faults, notably those of the LOFZ
Scaled analogue experiments simulating crustal transpression using the MultiBox prompt us to reconsider the simple concept of kinematic partitioning at the obliquely convergent Southern Andean plate margin between 34 °S to 42 °S
Summary
The Southern Andes are regarded as a typical subduction orogen formed by oblique plate convergence. Structural studies of the northern LOFZ identified a rather wide zone of faults with diverse orientations and kinematically associated with the LOFZ10–12 (Fig. 1b) These observations call into question the popular hypothesis of kinematic partitioning, by which northward displacement of the crust is accomplished on a few margin-parallel faults, notably those of the LOFZ. We test to what extent the observed GPS velocity field and first-order fault zones in the SVZ are caused by kinematic partitioning associated with dextral transpression and the orogen-parallel variation in crustal strength. The experiments explore the extent to which the GPS velocity pattern of the SVZ is kinematically related to the LOFZ and changes in margin-parallel thickness, and strength, of crust in the upper plate. Our study pertains to better understanding the significance of prominent NW-striking faults in the Southern Andes, which have been considered to be pre-Andean in origin[11,29]
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