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Kinematic Evolution and Mechanisms of Strike-Slip Faulting in the Solar System: Insight from Analogue Experiments

  • Author(s): Curren, Ivy Savannah
  • Advisor(s): Yin, An
  • et al.
Abstract

Identifying the ways in which faults initiate and propagate in disparate tectonic environments is fundamental for understanding regional and global deformation on rocky and icy bodies throughout the solar system. Furthermore, the kinematics and mechanisms of faulting provide a framework for understanding the range of dynamic processes that operate (or have previously operated) on planetary surfaces. To provide insight into these processes, my research focuses on strike-slip fault formation on Earth, Venus, and tidally deformed satellites (e.g., Europa, Enceladus, Phobos). Strike-slip faults are widespread across tectonic environments and their geometry, morphology, and kinematics are easily identifiable through remote sensing techniques, making this class of structures ideal for reconstructing the histories of planetary crusts. In this work, I integrate geologic observations and interpretations with experimental analogues to investigate the tectonic development of strike-slip faults in response to (1) pre-existing heterogeneous crust structure and/or composition, and (2) cyclic “tidal” stresses.

The geometry and morphology of strike-slip faults can be used to test competing models of structural deformation and geodynamic properties of solar system bodies. The current understanding for strike-slip fault initiation, geometry, and morphology, derived from field and experimental studies in homogenous material by unidirectional simple shear, suggests a sequence of deformation variable only by the shape of an underlying fault. Strike-slip fault zones are defined as having a primary throughgoing fault that accommodates the majority of regional strain and flanking offset folds and fractures that form at characteristic angles away from the applied stress direction. However, along-strike variations in morphology and lateral offsets, pervasive off-fault deformation, and the absence of throughgoing faults do not adhere to anticipated outcomes of traditional strike-slip fault formation models. Instead, I propose that the sequence, geometry, and morphology of strike-slip faults are highly dependent on the tectonic environment in which they were formed. Using experimental analogues I show that (1) strike-slip faults that initiate in structurally heterogeneous (i.e. previously deformed or compositionally disparate) crust fit a distributed deformation pattern that results in widening of the fault zone, fracture deflection, and regional strain accommodation across many faults exhibiting small or no lateral offsets (as opposed to a single throughgoing fault), and (2) the process of cyclic bidirectional horizontal shearing results in strike-slip fault morphologies that resemble commonly observed features on the surfaces of tidally deformed objects that are not observed elsewhere in the solar system in association with strike-slip faulting. In addition, I employ a scaling model to estimate crust strength on Europa and evaluate geodynamic processes for Europa, Enceladus, Phobos, Earth, and Venus.

A more complete understanding of strike-slip faulting in response to diverse tectonic environments allows for improved tectonic reconstructions and interpretations of planetary surfaces and histories, respectively. By evaluating several planetary surfaces through the use of tectonic models, experimental analogues, and remote sensing observations, I propose and test that brittle strike-slip deformation is more complex than previously supposed, and highly dependent on the environment in which formation occurred. The implications for the results presented here span topics from earthquake hazard analysis to astrobiology, and broadly suggest that care must be taken when interpreting stress states, histories, and geodynamic processes based solely on fault structure.

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