Columbia River Basalt Plateau—An integrated approach to interpretation of basalt‐covered areas

Abstract

An interpretation is presented of a 219 km regional profile which traverses the eastern Columbia River Plateau in Washington State. Aeromagnetic, magnetotelluric (MT), and gravity data were first interpreted separately. All three data sets then were satisfied by a single geologic model. The objective of this case study is to illustrate the individual contributions derived from these three geophysical data sets to a final integrated interpretation. The aeromagnetic interpretation has produced regional structural information and data from which rock compositions can be inferred. The MT interpretation shows that the basalt/sediment interface can be determined, and thus a relative sediment thickness can be inferred. The gravity interpretation is dependent upon an additional method to determine either the basalt or basement horizon. In order for the gravity interpretation to approximate depth to basement or sedimentary thickness, the base of the basalt must be determined from another scientific method. From comparison of the regional structural results of the three geophysical techniques we conclude that aeromagnetic or MT data can be used to determine major structural trends. Reasonable rock compositions are also determined from the combined data sets. The interpreter must be aware of the different rock properties measured by each tool when performing an integrated interpretation; comparisons between the various techniques must be based upon similar assumptions. We recommend that detailed, integrated models be included for a thorough evaluation of any basalt‐covered area. The analysis of rock composition and regional structural information thus derived provides a sound basis for a regional tectonic interpretation and subsequent prospect evaluation.