Regional Tectonic Evolution Processes Revealed From The Electrical Anisotropic Structure Of Major Shear Zone

In this thesis, the studies of using magnetotelluric souding data imaging the lithothpheric structure of the major fault/shear zones are reviewed. From these studies, electrical anisotropy can be supposed to be one of the key breakthroughs and hotspots in this field. Thus, several problems as follow have been studied for the purpose of using electrical anisotropy to study the structure of fault zones. Firstly, a Matlab codes package named MT-DimAnisTools was developed to analyze the anisotropic feature of MT data with various dimentionality indicators. Then, based on the analysis results, isotropic and anisotrpic inversion and interpretation can be done. Finaly, according to the above procedure, MT data collected from GSLsz was analyzed and modeled. Regional tectonic processes had been revealed from the along-strike variations of the electrical anisotropic structure the GSLsz.Three magnetotelluric (MT) profiles in northwestern Canada cross the central and western segments of Great Slave Lake shear zone (GSLsz), a continental scale structure active during the Slave-Rae collision in the Proterozoic. Dimensionality analysis indicates that the conductivity structure is approximately2-D with a geoelectric strike direction consistent with the dominant geological strike of N60°E and that electrical anisotropic structure can be inferred beneath the two southernmost profiles. Isotropic and anisotropic2-D inversion and isotropic3-D inversions show different resistivity structures on different segments of the shear zone. The GSLsz is imaged as a high resistivity zone (>5000Ω·m) on all three profiles that is10-20km wide and extends to a depth of at least50km on the northern profile. On the southern two profiles, the resistive zone is confined to the upper crust and pierces a crustal, east-dipping, conductor. Inversions show that this dipping conductor is anisotropic, likely caused by conductive materials filling in a network of fractures with a preferred spatial orientation. These conductive regions would have been disrupted by strike-slip, ductile deformation on the GSLsz accommodated by granulite to greenschist facies mylonite belts. The predominantly granulite facies mylonites are resistive and explain why the GSLsz appears as a resistive structure piercing the east-dipping anisotropic layer. The absence of a dipping anisotropic/conductive layer on the northern MT profile, located on the central segment of the GSLsz, is consistent with the lack of subduction or accretion at this location as predicted by geological and tectonic models.