An investigation on flow field partitioning related to the rheological heterogeneities and its application to geological examples
Abstract
Earth’s lithosphere is heterogeneous and composed of rheologically distinct elements at various scales of observations. This causes the flow of rocks to vary with space and time, which may influence the formation of various kinds of geological rock records. This thesis provides quantitative solutions to some first-order problems in structural geology regarding this heterogeneous flow variation and thereby the development of various geological rock records at different scales of observations.
Pressure in a rheologically heterogeneous element may deviate from its ambient value and if significant, may influence the metamorphic assemblages. This might cause problems in the routine use of geothermobarometry-based pressure estimates from mineral assemblages as a proxy for depth in geodynamic models of geological processes. A micromechanics-based multiscale model called Multi Order Power Law Approach (MOPLA) is applied to simulate pressure deviation in and around a rheologically distinct rock element embedded in a rock medium of a non-linear viscous anisotropic rheology. The results show that the pressure deviations are in the same order as the deviatoric stress levels and hence limited by the strength of rocks.
Flow variation can influence c-axis fabrics from quartz aggregate within feldspar-mica matrix in the natural high strain zones. If such effect is not accounted for, crucial geological information such as deformation temperature, deformation history and shear sense obtained using c-axis fabrics can be seriously misinterpreted. A multiscale approach coupling MOPLA with Viscoplastic Self-consistent (VPSC) model is used to simulate c-axis fabrics under partitioned flow. The results show that the quartz c-axis fabric variation showing apparent opposite senses of shear within a single thin section, can be explained by partitioned flow within the quartz domains and reflect finite strain gradient rather than a reversal of vorticity sense as previously thought.
Flow variation can form flanking structures around a cross-cutting element like a vein or a dyke that may provide kinematic information such as ‘shear sense’ and ‘finite strain’. Their correct interpretations are critical for understanding regional tectonics. A micromechanics-based modeling approach is used to simulate 3-D flanking structures and demonstrate how the flanking structure may vary with the cutting element’s shape, orientation, and rheological contrast to the ambient medium. A reverse-dynamic modeling approach is applied to quantitatively estimate kinematic vorticity number, viscosity contrast of the cutting element to the ambient medium, and finite strain from natural flanking structures.