Orogenic Recycling of Detrital Zircons Characterizes Age Distributions of North American Cordilleran Strata

摘要

Detrital zircon (DZ) analysis has become the standard tool for source-to-sink sediment routing studies at many spatial and temporal scales. In North American source-to-sink studies, DZ distributions are commonly classified according to the presence/absence and proportions of DZ age groups associated with North American crustal provinces as well as peri-Gondwanan and Cordilleran terranes. Although such a classification scheme is descriptive, these age groups typically do not uniquely identify most recent DZ source areas. Using a compilation of 19,000 individual DZ ages for Mesoproterozoic-Paleogene strata of the northern Rocky Mountains, including 2,053 new analyses from the Paleogene Renova Formation and its equivalents in southwestern Montana, we demonstrate periodic derivation of first-cycle DZ from crystalline sources and widespread recycling of poly-cycle DZ from sedimentary sources over multimillion-year timescales. Results show that (1) DZ age distributions become increasingly complex between Mesoproterozoic and Paleogene time with the introduction of new DZ sources to the study area, but (2) once an age group appears in the northern Rocky Mountains stratigraphy, grains of that age persist up-section. These trends show that most DZ age groups are spatiotemporally ubiquitous and nonunique. We largely attribute this to periodic, tectonically induced recycling of DZ into progressively younger sedimentary systems, rather than prolonged derivation of DZ from crystalline basement sources, a trend that reflects the growth of increasingly complex topography associated with the North American Cordillera.