Abstract

The Kandik area of east-central Alaska provides an excellent example of how thermal-maturity data can be used in the analysis of tectonostratigraphic terranes. The northeast-trending Glenn Creek fault zone is a fundamental structural feature in the region; nonetheless, previous workers extended stratigraphic correlations across the fault zone. Our analyses, however, prove that the thermal histories of the respective fault blocks (terranes) are completely different. Northwest of the fault zone (Kandik terrane), strata are mostly Early Cretaceous in age, and these rocks yield values of mean vitrinite reflectance (R_m%) ranging from 1.6 to 4.2%. In contrast, all but one of the Devonian shales analyzed from the southeast side of the fault zone (Tatonduk terrane) range from 0.6 to 1.2% R_m. Analyses of illite crystallinity also show that the older Tatonduk terrane is within the zone of diagenesis, whereas much of the younger Kandik terrane is within the anchimetamorphic zone. We infer that 7-10 km overburden were eroded from the Kandik terrane; rapid denudation and paleothermal inversion across the terrane boundary probably were accomplished through southeast-directed overthrusting along the Glenn Creek fault zone. The precise geographic setting, thermal source, tectonic regime, and overburden required for metamorphism of the Kandik terrane, all remain enigmatic, but volcanic activity to the northwest of the study area may have played a contributing role.