Argon Geochronology

Science Issue and Relevance

The ⁴⁰Ar/³⁹Ar Method: ⁴⁰Ar/³⁹Ar geochronology is an experimentally robust and versatile method for constraining the age and thermal history of rocks. Such information is extremely valuable for understanding a variety of geological processes including the formation of ore deposits, mountain building and history of volcanic events, paleo-seismic events, and paleo-climate. The ⁴⁰Ar/³⁹Ar isotopic dating method has evolved into the most commonly applied geochronological method, and can be applied to many geological problems that require precise and accurate time and temperature control.

Methodology to Address Issue

This project provides partial support for the USGS argon geochronology laboratory in Denver. The USGS ⁴⁰Ar/³⁹Ar geochronology laboratory is a state-of-the-art research facility for determining absolute ages of minerals and rocks. The ⁴⁰Ar/³⁹Ar laboratory contributes critical geochronology to individual USGS research projects and to partners in academia and other Federal agencies. This facility houses necessary equipment for sample preparation and analysis, including high-sensitivity noble gas mass spectrometers and ultraviolet (UV) and infrared (IR) lasers. The versatility of the ⁴⁰Ar/³⁹Ar method permits determining the timing of processes and events such as igneous intrusions and extrusions, ore mineralization and hydrothermal fluid circulation, metamorphic cooling and exhumation, mineral formation and recrystallization, and shallow crustal faulting. Scientists are dependent on the geochronologist for data and interpretations to determine these parameters. This laboratory develops methodology for small and difficult sample analysis often at the limits of existing mass spectrometer technology.