The Sedimentology of Detrital Thermochronology

Abstract

Detrital thermochronology is based on the radiometric dating of apatite, zircon and other minerals in sediments and sedimentary rocks. The objective of detrital thermochronology is to obtain quantitative information on sediment provenance and on the geologic evolution of the area from whence the sediment was generated. This chapter describes how the full potential of the detrital thermochronology approach can be exploited by applying simple sedimentology principles, in order to obtain provenance information that is largely independent from the physical and chemical modifications affecting sediment during transport, deposition and burial diagenesis. Simple strategies can be used to detect the effects of selective entrainment, which form placer and antiplacer deposits, and test the vulnerability of grain-age distributions to hydraulic sorting effects. The mineral fertility of eroded bedrock, which varies over orders of magnitude thus representing the largest source of potential bias in detrital thermochronology, can be readily measured by simple modifications to the standard procedures of mineral concentration. Multi-method studies are potentially biased by grain rounding and abrasion, as the removal of grain rims may lead to an incorrect interpretation of grain ages yielded by low-temperature thermochronometers. Bedload and suspended load have different transport time, and the instantaneous-transport-time assumption of exhumation studies based on the lag-time approach is not necessarily met.