Continental evolution from detrital mineral petrochronology

Abstract

Clastic sedimentary rocks capture a spatially and temporally integrated record of the age and composition of the exposed continental crust. Modern microanalytical techniques have given rise to the field of detrital mineral petrochronology in which time-integrated geochemical and isotopic proxies of rock-forming processes are reconstructed from individual detrital mineral grains, offering our most detailed view of continental evolution from the clastic sedimentary record. This chapter outlines the progress and potential for using detrital mineral petrochronology to study continental evolution. We review the petrogenesis, geochronology, geochemistry, and isotopic systematics of the five most established detrital mineral petrochronometers: zircon, rutile, apatite, titanite, and monazite. For each mineral, we present global compilations of single-grain U-Pb ages tied to geochemical and isotopic proxies to track secular changes in the composition, thickness, and thermal character of the continental crust. The global age distributions of each detrital mineral petrochronometer are characterized by an increasing number of single-mineral ages from the Archean to the Phanerozoic with a series of prominent age ‘peaks’ coinciding with assembly of supercontinents. Geochemical and isotopic proxies preserved in different detrital minerals suggest that the continental crust sampled by clastic sedimentary rocks has mostly comprised metaluminous, felsic igneous rocks throughout most of Earth history. The production of peraluminous igneous rocks and the contamination of igneous sources by pre-existing continental crust appears to have generally increased from the Archean to the Phanerozoic with both processes being particularly important during phases of supercontinent assembly. Metamorphic temperatures estimated from detrital rutile and monazite grains document predominantly granulite and amphibolite facies conditions during the Archean and early Proterozoic with greenschist and/or blueschist facies conditions becoming more common from the Neoproterozoic onwards. We also review the progress toward recognizing and mitigating the biases inherent to studying continental evolution from the detrital mineral record. The clastic fill of modern sedimentary basins is strongly skewed toward sampling of topographically elevated crust in active orogenic belts. This natural sampling bias essentially limits detrital mineral petrochronology to qualitative, rather than quantitative, reconstructions of the volume and composition of different source rocks exposed in the catchment of a sedimentary basin. The uneven fertility of detrital mineral petrochronometers can be remedied by integrating information from multiple different detrital minerals to capture a more diverse range of rock types in the source region. Similarly, pairing labile and robust detrital minerals with comparable fertility (e.g., zircon and K-feldspar) can distinguish between first- and poly-cycle detritus in clastic sedimentary basins, helping to account for the variable stability of different detrital minerals within the sedimentary cycle.