Constraints on the structure of the Border Ranges fault system, south-central Alaska from integrated 3D inversion of gravity/magnetic data

Niti Mankhemthong, University of Texas at El Paso

Abstract

I use updated gravity data, available aeromagnetic data, and other geophysical information as constraints to develop 2D and 3D structural models of density and magnetic susceptibility to better locate and determine the shape of the Border Ranges fault system (BRFS), the Border Range ultramafic and mafic assemblages and other forearc-arc boundary structures in south-central Alaska, that have previously been studied in only limited detail. There are three geophysical research projects that form the chapters of the dissertation. First, I estimated near-surface density variations in the central Kenai Peninsula based on the adaptation of the Nettleton (1939)-Parasnis (1952) method using Tarantola and Valette's (1982) inversion formulations. Results from computations showed reasonable densities and density uncertainties for regions along both sides of the fault trace. These density estimations were then used as one of several available datasets used for surface density constraints, along with other data, for the next study that performed 2D integrated gravity and magnetic modeling. In the second study, I constructed four 2D integrated density-magnetic models to determine the shape of the BRFS and other major geological structures using the GM-SYS software packages. The results helped define the extent of a serpentinized body and underplated sediments and I hypothesized about how these structures were formed. Lastly, I tested and constructed a 3D block model of density over the region of the Border Ranges fault system and the Border Range ultramafic and mafic assemblage (BRUMA). This simple 3D model was inverted and used to further examine the geometry of the BRFS and BRUMA. These results show a reasonable fit of observed and calculated free air gravity based on simple density model. The next step will be to construct more realistic complex geometrical bodies to better explore plausible subsurface geometries for the region.^

Subject Area

Physical Geography|Geology

Recommended Citation

Mankhemthong, Niti, "Constraints on the structure of the Border Ranges fault system, south-central Alaska from integrated 3D inversion of gravity/magnetic data" (2012). ETD Collection for University of Texas, El Paso. AAI3552251.
http://digitalcommons.utep.edu/dissertations/AAI3552251

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