Lineament Analysis of Potential-Field Data in the Studies of Basin Structure
Darran J. Edwards, Henry V. Lyatsky, and R. James Brown
The horizontal gradient of magnetic and gravity data is a two-component vector quantity with magnitude and direction. We map the horizontal-gradient magnitude and direction by vector-arrow length and azimuth. The arrows originate at grid nodes and point away from local maxima. Scaled vector arrows are longest, and the shading density due to arrows greatest, in zones of maximum gradient. Coupled with geological information, this technique offers a tool for mapping fault networks and rock-composition variations in the basement and sedimentary cover.
In the Western Canada Basin, correlations with local geological data show that potential-field lineaments follow faults in the Precambrian basement. Regionally, magnetic horizontal-gradient vector (HGV) maps reveal a basin-wide NW/NE rectilinear fracture grid. Tilted basement blocks are identified from gravity HGV domains. Correlations with stratigraphy suggest these faults influenced growth of Paleozoic reefs and dissolution of Devonian salt. Mesozoic units contain lithofacies variations and structures that mimic the basement fracture grid and the salt dissolution pattern.
In the Tertiary Queen Charlotte Basin in the western Canadian Cordillera, potential-field HGV maps and shadowgrams help map regional networks of dip-slip faults. Local geological and seismic data show these networks, inherited from Mesozoic time, bound Cenozoic depocenters.
Magnetic and gravity HGV maps of these basins outline faults in the basement that controlled basin evolution. The HGV method can be similarly applied in other exploration provinces.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California