MATCHING MAGNETIC TRENDS AND PATTERNS ACROSS THE TINTINA FAULT, ALASKA AND CANADA – IMPLICATIONS FOR ESTIMATES OF TOTAL FAULT OFFSET

The Tintina fault zone in eastern Alaska and western Canada is a major tectonic boundary between cratonic North America and peri-cratonic rocks of the Yukon-Tanana and related terranes. Numerous estimates have been made of the amount and timing of offset on this fault system. Several of the latest estimates, based on matching geologic elements across the fault, indicate probable offset of at least 400 km. Some paleomagnetic studies infer offset as high as 1,100 – 2,400 km.

Regional geophysical data, such as magnetic and gravity field maps, display patterns and trends that represent the composition of the crust. The amount of offset on crustal faults can be investigated by “cutting and sliding” the geophysical maps to evaluate pattern and trend alignment under various slip scenarios. In particular, the compiled aeromagnetic data portrayed on the 2002 Magnetic Anomaly Map of North America provides an excellent base map for this endeavor.

I have investigated several back-slip scenarios that produce alignments of magnetic anomalies across the fault. The most compelling configuration yields about 550 km of apparent slip and produces several interesting geologic juxtapositions. For example, several eclogite/blueschist occurrences on opposite sides of the fault are brought in close proximity under the preferred slip scenario. Also, several major Devonian-Mississippian mineral districts cluster into domains across the fault after restoration. Some geological juxtapositions are difficult to evaluate, however, because of contrasting styles and scales of geologic mapping available across the fault.