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New Mexico Geochronology Research Laboratory

Evolution of a geologist cartoon

Introduction

The New Mexico Geochronology Research Laboratory (NMGRL) in Socorro is a state-of-the-art 40Ar/39Ar dating facility administered by the New Mexico Bureau of Geology at the New Mexico Institute of Mining and Technology. 40Ar/39Ar research at NMGRL is directed by Drs. Bill McIntosh and Matt Heizler who have over 60 years combined experience in the field of argon geochronology and thermochronology. The lab also employs a part-time technician, Lisa Peters who supervises mineral separation, sample irradiation and analyses, and data reduction.

Since its christening in the winter of 1992, the NMGRL laboratory has performed over 400,000 individual analyses. Necessary in this regard is the software developed in house by Dr. Jake Ross, which allows for full automation of extraction line and mass spectrometer functions. The software controls the three laser systems, the resistance furnace, and all crucial extraction line and mass spectrometer valves which are operated via pneumatic air drivers. Additional automation comes from laser and furnace sample "packages" which can contain up to 221 and 17 individual samples per load, respectively. Once under vacuum, sample analyses do not require the physical presence of laboratory personnel for extended periods of time.

Lab panorama
The argon geochronolgy lab in 2017

Argon gas extraction at NMGRL is accomplished either by resistance furnace, CO2 laser, Diode (810nm) laser heating, or UV Excimer 193 laser ablation.

NMGRL's resistance furnace is a double vacuum “Heine”-type resistance furnace with molybdenum crucible and crucible liner. Temperatures accuracy is ±10°C; precision is ±1°C; maximum temperature is 1750°C. Argon blanks for the entire furnace extraction line (dual stage) are on the order of 5x10-16 moles of 40Ar. The addition of a gate valve between the crucible and sample holder in the near future will likely decrease system blank as well as reduce turn around time for sample changes.

NMGRL uses a 75 watt Photon Machines Fusions CO2 laser for single crystal laser fusion. The CO2 laser provides many of the advantages of other lasers used in argon extraction (e.g. Ar-ion and Nd-Yag) but requires only a fraction of the cost to set up. The CO2 laser at NMGRL is used mainly for the total-fusion of sanidine crystals which include J-value determinations from Fish Canyon Tuff (FC-2) sanidine monitors. System blanks for the laser (single stage) are on the order of 2xE-19 moles of 40Ar.