Krogh Air Abrasion Chamber for U-Pb Dating

IHPST

Accession Number: 2019.ihpst.103

Description:

A white-coloured cardboard box, marked with hand-written lettering in black ink, contains the following items:

1 metal artifact marked “abrader.” This has a shiny iron alloy cap, and a copper alloy. The base has a tube-like attachment for an air hose. This artifact is wrapped in bubble wrap.

1 square piece of mesh (~10.8 x 10.3 cm). The mesh has a small label at the top left corner that is marked with “70 mesh” in black ink.

1 tapering plastic disposable dropper (10.4 cm long).

1 glass sample tube (~11.5 cm long). This is tapered at the closed end and has a flared rim at the open end.

1 pair of white disposable gloves.

Primary Materials: Metal, Cardboard, Glass,

Markings:

The box lid is marked “Sample Preparation” in black ink at the top left corner.

Both the lid and the base of the metal artifact are marked with the letter “A”, which is scratched into a side surface.

Dimensions (cm):

(Box) Height = 5.3, Width = 10.2, Length = 13.2; (Metal artifact) Max Width = 6, Length = 9.5

Function:

The Krogh abrasion chamber is used to polish zircons as part of the process of uranium-lead (U-Pb) dating. Pressurized air blown into the chamber is used to remove chemically altered or cracked parts of the zircon crystal through impact with the wall of the steel abrasion chamber, or through polishing with pyrite. First published in 1982, the polishing technique greatly improved the accuracy of the U-Pb dating process.

Condition:

Very good: The artifact has light signs of wear, but no major damage.

Manufacturer: Royal Ontario Museum

Date of Manufacture: Early-to-mid 1980s

Provenance:

This these artifacts were acquired from Dr. Sandra Kamo, Director of the Jack Satterly Geochronology Laboratory, on January 15, 2019. It was among a small collection of artifacts prepared by technician Kim Kwok.

This technology was developed by Thomas Edvard “Tom” Krogh, (1936 – 2008) while working at his geochronology laboratory at the Royal Ontario Museum. It was likely created for that lab in the early-to-mid 1980s and brought to the University of Toronto Department of Earth Sciences when the lab relocated there in 2004.

Additional Information and References:

Krogh, Tom E. “A Low-Consumption Method for Hydrothermal Decomposition of Zircon and Extraction of U and Pb for Isotopic Age Determinations.” Geochimica et Cosmochimica Acto 46 (1973): 483 – 494.

Krogh, Tom E. “Improved Accuracy of U-Pb Zircon Ages by the Creation of More Concordant Systems using an Air Abrasion Technique.” Geochimica et Cosmochimica Aclo 46 (1982): 637 – 649.

Mattinson, James M. “Extending the Krogh Legacy: Development of the CA-TIMS Method for Zircon U-Pb Geochronology.” Canadian Journal of Earth Sciences 48, 2 ( 2011): 95-105.

Kamo, Sandra L. , Fernando Corfu, Larry M. Heaman, and Desmond E. Moser. “The Krogh Revolution: Advances in the Measurement of Time.” Canadian Journal of Earth Sciences 48, 2 (2011): 87-94.

Historical Notes:

Thomas Edvard (Tom) Krogh (1931-2008) received his PhD in 1964 from MIT. He did postgraduate work at the Geophysical Laboratory of the Carnegie Institution of Washington before receiving a position there. His early focused on the rubidium–strontium (Rb-Sr) and strontium-strontium method of radioisotope dating. He later turned his attention to uranium-lead (U-Pb) dating.

In 1973, Tom Krogh published a seminal paper that introduced a new sample preparation technique known as hydrothermal decomposition and chemical purification that greatly simplified the process of U-Pb dating while reducing lead contamination by an order of magnitude. (See Krogh 1973 and Kamo et al. 2011)

In 1975, Krogh accepted an offer to establish a new lab at the Royal Ontario Museum. The position was supported by the Geological Survey of Canada. In 1982, while working at the ROM, Krogh developed a superior method of preparing zircon crystals based on air abrasion (see Krogh 1982). This became a standard laboratory method. Air abrasion has been succeeded by the chemical abrasion (“CA-TIMS”) method of zircon preparation that was first published in 2005.

In 2004, Krogh’s ROM U-Pb lab was transferred to the University of Toronto Department of Earth Sciences, where it remains a leading laboratory for U-Pb dating.