Crustal Imaging and Characterization Team

Argon Geochronology

Task Objectives

Argon geochronology provides fundamental isotopic age constraints for a wide range of earth-science studies. This technology is fundamental research that clearly maintains the USGS premier science role in Earth-science studies. The Denver argon geochronology laboratory is currently participating in studies that span ages from the over 3.0 billion years ago to less than 30,000 years. Because of this robustness and versatility, argon geochronologic results are in much demand from USGS programmatic projects currently mostly funded by the National Cooperative Geologic Mapping Program and the Mineral Resources Program. Although the data are critical, operation of the laboratory and associated sample preparation facilities requires high maintenance and several qualified technicians and scientists. This task within the Core Operations project is designed to ensure that adequate funds for operation, development, and upgrade of the argon laboratory and associated sample preparation laboratories.

Statement of Work

The personnel of this laboratory will continue to ensure the production of top-quality argon geochronologic data that meets USGS scientific goals. This task ensures that the argon laboratories receive minimal basis operating expenses to accomplish this goal.

Highlights & Key Findings

Argon geochronological work on Archean gold deposits in Western Australia is providing important temporal constraints on host rock thermal histories and age of gold formation. This work has established the credibility of argon termochronology on old mineral deposits. An offshoot of the work is cross calibration of geochronologic methods and the establishment of "best" age for one of the argon mineral standards--MMhb1; this age is 523.1 Ma, which is consistent with new calibration work recently completed by Berkeley University investigators.

Argon and noble gas studies of Precambrian alunite from high-sulfidation gold deposits in the Amazon, in conjunction with University of Sao Paulo and University of Para geologist have confirmed the preservation of this ancient pristine volcanic terrane despite nearly 2 billion years of exposure to earth processes.

Design and acquisition of an Excimer-laser system during 2004 has completed the acquisition process for major components for a new argon laboratory. The new MAP215-50 argon mass spectrometer with unique automated sample chamber, extraction line, CO2-laser system, and Excimer laser will be the world's foremost argon system. The automated sample chamber is designed to rotate any of 60 samples to the loading port over a low-blank double vacuum furnace. CO2 laser system will be a routine single crystal heating laser. The Excimer laser system is an exciting new approach to ablation laser studies of small intergrown or zoned minerals. The Labview-based software that has already been put into operation in the noble-gas laboratory has been shown to be far more effective than any other automation language and has been modified to meet the special requirements of a two-electron multiplier collector system. A new upright extraction table has been built and is ready for assembly of furnace and laser extraction systems.

References to non-USGS products and services are provided for information only and do not constitute endorsement or warranty, express or implied, by the USGS, USDOI, or U.S. Government, as to their suitability, content, usefulness, functions, completeness, or accuracy.

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