U-Pb Geochronology

High-precision U-Pb dating of accessory minerals to resolve timescales of geological processes

News

30.10.2017

Successful upgrade of our 13 years old TRITON with 1E13 Ohm feedback resistors

Urs Schaltegger

Or Triton TIMS was purchased from Thermo Scientific in 2005 and has been reliably serving for precise isotope ratio determination since then. The amplifiers of the 10 faraday cups were initially equipped with 5 1E12 Ohm, and 5 1E12 Ohm resistors. The 5 aplifiers with 1E12 Ohm resistors have now been replaced by 1E13 Ohm resistors, together with the respective gain calibration board and new software to allow for the tau correction. Noise values are slightly worse than predicted by the equation for the Johnson-Nyquist noise. The plot shows a comparison of noise values of currently available amplifiers on Triton (Thermo Scientific) and Phoenix (IsotopX) platforms

20.07.2017

End-Triassic mass extinction started by intrusive CAMP activity

Davies J.H.F.L., Marzoli A., Bertrand A., Youbi H., Ernesto N. & Schaltegger U.

Read the article on the website of Nature

Ongoing Research

Scientific Infrastructure

infra_lowest-blank_clear_room.jpeg

Lowest-blank clean room facility for isotope analysis of accessory mineral grains

The class 100 clean-air facility is used for the chemical preparation of mineral grains for high-precision U-Pb geochronology, and trace element and Hf isotope analysis. Lowest levels of procedural Pb blanks allow precise isotope analysis of 1 pg of Pb from a variety of minerals (zircon, baddeleyite, monazite, xenotime, titanite, rutile, apatite) that have been dissolved previously in acids using Parr digestion vessels. All acids employed for U-Pb chemistry are distilled in-house and have blank levels of 100 fg Pb/ml or less. The laboratory is using Earthtime 205Pb-233U-235U and 202Pb-205Pb-233U-235U tracer solutions. Quality assessment is carried out by repeated analysis of Earthtime synthetic solutions (ET100, ET500, ET2000) as well as zircon reference materials, such as Plesovice, Temora, R33, GJ-1 and others.

Mineral separation and preparation facility

Samples are crushed manually or in a jaw-crusher, milled to <350µm size, washed and separated using a Wilfely shaking table, methylene iodide heavy liquids and Frantz magnetic separators. Final selection is done under binoculars ; most of analyzed grains are imaged by cathodo-luminescence or back-scattered electrons using the scanning electron microscope in-house, and undergo chemical abrasion prior to dissolution.

Thermal ionization mass spectrometry

The mass spectrometry lab features two pieces of equipment :

  1. A TRITON thermal ionisation mass spectrometer from Thermo Scientific, purchased in 2005. It is equipped with 1011 and 1112 Ohm resistance faraday cups and a MasCom discrete-dynode secondary electron multiplier used in pulse-counting mode, which is demonstrated to be linear up to 1.3 Mcps.
  2. A PHOENIX thermal ionisation mass spectrometer from IsotopX, purchased in 2016. It is equipped with 1112 Ohm resistance faraday cups and a Daly-based ion-counting system using a Hamamatsu photo-multiplier, demonstrated to be linear up to 2.5 Mcps. The equipment allows measurement of low levels of radiogenic lead via a multidynamic procedure using the high-resistance faraday cups or, alternatively, the Daly ion counting system.

The two mass spectrometers are intercalibrated at the level of 0.01% for 206Pb/238U dates.

Funded Research Projects

200020_156424 Establishing globally valid tie points for intercalibration of biochronologic and radioisotopic timescales between the latest Permian and middle Jurassic using high-precision U-Pb dating of volcanic ash beds
Swiss National Science Foundation http://p3.snf.ch/project-156424

2000020_162341 Temporal calibration of eruption dynamics of Large Igneous Provinces and correlation to global environmental disturbance with high-precision U-Pb dating of micro-zircon and -baddeleyite
Swiss National Science Foundation http://p3.snf.ch/project-162341

200021_169086 Direct determination of early Earth's orbital parameters through high-precision age determination of sedimentary cycles in Archean and Proterozoic sedimentary deposits
Swiss National Science Foundation http://p3.snf.ch/project-169086

200020_182007 Temporal coupling of environmental change, volcanism and evolution in the geological past through high-precision geochronology
Swiss National Science Foundation (from 1/1/2019)

CRSII5_180253 Quantifying decamillenial changes in carbon cycling, climatic and biotic responses to Late Permian-Early Triassic volcanism. Interdisciplinary Sinergia program with University of Zürich leading house.
Swiss National Science Foundation, http://p3.snf.ch/project-180253

IZSEZ0_180188 Developing new isotope techniques to study magmatic and paleoenvironmental processes.
Swiss National Science Foundation (from 1/1/2019)

 

top