CORDILLERAN METAMORPHIC CORE COMPLEXES—HISTORICAL PERSPECTIVES ON EVOLUTION OF CONCEPTS IN THE BASIN AND RANGE

The Basin and Range province seeded many early concepts about metamorphic core complexes and their significance. This presentation offers a personal perspective on the early history of core-complex research. Enigmatic metamorphic complexes in the Basin and Range began to be recognized as somehow important to Cordilleran architecture in the 1950s and 1960s. Seperately, some examples of low-angle normal faults were found and they began to be recognized as a record of large-scale extension. A 1977 Penrose Conference on metamorphic core complexes helped crystallize a growing awareness that metamorphic complexes in the Basin and Range province display evidence of ductile flattening and Tertiary low-angle normal faults. The metamorphic core complexes began to be recognized as windows of deep crust unroofed by large tectonic extension. As extensional denudation more firmly established itself as a major tectonic process, geochronologic and thermochronologic research in the Basin and Range advanced the study of heating, cooling, uplift, and fault denudation rates. Research on core complexes and extensional tectonics drove many advancements in low-temperature thermochronology since the 1980s, and much of that work was done in the Basin and Range. Seismic and heat-flow evidence confirmed that isostatic uplift of denuded middle crust was rooted in the Basin and Range crust and involved deep crustal return flow. The Basin and Range core complexes have continued to yield fietile new insights into large-magnitude tectonic extension, which has now been recognized on continents worldwide and on oceanic crust as well.