Abstract
AbstractStrain partitioning onto margin‐parallel thrust and strike‐slip faults is a common process at obliquely convergent plate margins, leading to the formation and migration of crustal slivers. The degree of strain partitioning and rate of sliver migration can be linked to several factors including the angle of convergence obliquity, the dip angle of subduction, frictional coupling between the plates and the strength of the upper plate, among others. Although these factors are known to be important, their relative influence on strain partitioning is unclear, particularly at natural margins where the factors often vary along strike. Here we use a 3‐D mechanical finite‐element model to investigate the relationship between continental crustal strength, the convergence obliquity angle, the subduction angle, and strain partitioning in the Northern Volcanic Zone (NVZ) of the Andes (5°N–3°S). In the NVZ the subduction dip and obliquity angles both vary along strike, weaknesses in the continental crust may be present in suture zones or regions of arc volcanism, and strain partitioning is only observed in some regions. Thus, it is an ideal location to gain insight in which of the factors have the largest influence on deformation and sliver formation in the upper plate. Our numerical experiments confirm that a moderately high obliquity angle is needed for partitioning and that a continental crustal weakness is also required for movement of a coherent continental sliver at rates similar to geodetic observations from the NVZ. In contrast, the subduction dip angle is only of secondary importance in controlling strain partitioning behavior.
Highlights
Subduction is the fundamental tectonic process recycling lithospheric material into the Earth's interior, and one that causes shortening, extension, and lateral shearing in the upper plate depending on the relative sense of motion of the plates and their interface
In regions of oblique subduction, upper‐plate deformation can be understood in the context of two end‐member models: oblique thrusting, where the dip‐slip and strike‐slip components of the plate movement are accommodated by the plate‐bounding fault, and partitioned strain, where convergence occurs on the plate‐bounding fault and a separate strike‐slip fault accommodates the margin‐parallel residual movement (Figure 1; e.g., Fitch, 1972; McCaffrey, 1992)
To investigate the conditions under which strain is partitioned in an oblique subduction zone and its implications for sliver movement in the Northern Andes, we focus on the influence of three factors: the strength of the continental crust, the plate convergence obliquity angle, and the subduction dip angle
Summary
Subduction is the fundamental tectonic process recycling lithospheric material into the Earth's interior, and one that causes shortening, extension, and lateral shearing in the upper (overriding) plate depending on the relative sense of motion of the plates and their interface. In regions of oblique subduction, upper‐plate deformation can be understood in the context of two end‐member models: oblique thrusting, where the dip‐slip and strike‐slip components of the plate movement are accommodated by the plate‐bounding fault, and partitioned strain, where convergence occurs on the plate‐bounding fault and a separate strike‐slip fault (or fault system) accommodates the margin‐parallel residual movement (Figure 1; e.g., Fitch, 1972; McCaffrey, 1992). The partitioned strain end‐member model results in separation of upper plate material proximal to the plate margin from the rest of the upper plate, and translation of a forearc, orogenic wedge, or continental sliver along strike (e.g., Fitch, 1972). Understanding the partitioning of strain onto various faults in the upper plate and the motion of continental slivers requires consideration of all these components
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