Geochronology

Geochronology is the science of age dating, whether it involves determining the age of rocks, mineral, fossils, sediments, or other materials. There are two age dating techniques, absolute and relative. Absolute age determination is performed using numeric dating methods, while relative age determination uses paleomagnetism and stable isotope ratio calculation.


Accessing Earth’s history using isotope dating methods

Geologists can establish the absolute age of a parent material (rock, mineral, or fossil) by looking at a radioactive isotope with a known half-life (i.e., the time it takes for half of the original isotope to decay) that is present in the sample and measuring its radioactive decay. Various radioactive isotopes may be used for different geological periods depending on their rate of decay. Isotopes that decay more slowly are used to date things within longer time periods (older material), whereas isotopes with shorter half-lives are ideal for shorter time periods (younger material). Commonly used techniques are U-Pb, U-Th, K-Ar and Ar-Ar dating.

The U-Pb technique measures the amount of 206Pb and 207Pb relative to the amount of uranium in a mineral or rock. This technique is commonly applied to minerals from igneous and metamorphic rocks, such as zircons and monazites, and is used to date materials of up to 4.5 billion years old.

The U-Th technique uses the short half-lives of uranium and thorium isotopes to date geologically young material, such as fossils, speleothems, carbonates and volcanic rocks. This dating technique is applied to samples of just a few years, up to about 700,000 years old.

The K-Ar dating technique is based on measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar) and is used for samples a few thousands years and older such as igneous, volcanic and metamorphic rocks. Ar-Ar dating is similar to K-Ar dating, but provides greater accuracy. In addition to the previously mentioned isotope-based techniques, other isotope systems used for radiometric dating include Re-Os, Rb-Sr, Sm-Nd, Lu-Hf and Hf-W.

Geologists use different mass spectrometric instruments for the dating techniques mentioned above: Thermal Ionization Mass Spectrometry (TIMS), Multicollector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS), and Noble Gas Mass Spectrometry. These instruments, in combination with micromill and laser ablation sample preparation systems, provide high-precision, whole-grain bulk and high-spatial in situ analyses.

The innovative mass spectrometer portfolio from Thermo Fisher Scientific helps geoscientists to provide insights into the age of their valuable rocks, minerals, sediments and fossils, enabling them to make exciting pioneering discoveries.


Popular products

Triton Plus Multicollector Thermal Ionization Mass Spectrometer

Triton XT Multicollector Thermal Ionization Mass Spectrometer

The Thermo Scientific Triton XT Multicollector Thermal Ionization Mass Spectrometer (TIMS), equipped with 1013 Ω amplifier technology, provides the ultimate precision for U-Pb geochronology. Beyond U-Pb, the Triton XT TIMS is the workhorse for obtaining high-quality age data from other radiogenic isotopic systems such as Rb-Sr, Sm-Nd and Re-Os.

Neptune XT High Resolution Multicollector ICP-MS

Neptune XT High Resolution Multicollector ICP-MS

If in situ information is required, the Thermo Scientific Neptune XT MC-ICP-MS or Thermo Scientific Element 2 and Thermo Scientific Element XR High-Resolution ICP-MS, combined with a laser ablation system, enables simultaneous in situ analysis of Pb-U and Hf isotope ratios of very small minerals, such as zircons. For highly precise U-Th age dating, the MC-ICP-MS is the method of choice. Combined with new 1013 Ω amplifier technology, the Neptune XT MC-ICP-MS delivers highly accurate age information for the smallest samples.

Argus VI Static Vacuum Noble Gas Mass Spectrometer

Argus VI Static Vacuum Noble Gas Mass Spectrometer

Our noble gas mass spectrometers are the ultimate choice for obtaining high-precision Ar-Ar, cosmogenic exposure neon and low temperature thermochronology data. A major step forward in Ar-Ar age dating precision comes from the new 1013 Ω amplifiers, available for the Thermo Scientific Argus VI static vacuum noble gas mass spectrometer and Thermo Scientific Helix MC Plus multicollector noble gas mass spectrometer.

Element 2/XR High Resolution ICP-MS

Element 2/XR High Resolution ICP-MS

If in situ information is required, the Element 2 and Element XR HR-ICP-MS systems, combined with a laser ablation system, enable in situ analysis of Pb-U isotope ratios of very small minerals, such as zircons. The high sensitivity of the Element 2 HR-ICP-MS system in dry plasma maximizes the number of analyzable zircons in a sample leading to increased confidence in the U-Pb age obtained. Its fast scanning capabilities enable the high throughput required for the analysis of large numbers of detrital zircons in provenance studies.


U-Pb dating by ID-TIMS

U-Pb geochronology by isotope dilution thermal ionization mass spectrometry (ID-TIMS) requires precise and accurate determinations of parent-daughter isotope ratios. The small sample size, particularly with respect to radiogenic Pb, demands highly sensitive ion detection systems. Most studies, therefore, employ either secondary electron multipliers (SEMs) or Daly photomultipliers that provide low background noise and high sensitivity. However, they also have limited linear range and require dynamic peak hopping. Such sequential single collector ion counting measurements have several drawbacks, including reduced sample utilization, ion current fluctuations, and mass-dependent detection inefficiency. Also, ion counting measurement requires an accurate deadtime calibration.

Multicollection analysis helps optimize sample usage and allow precision to be independent of signal fluctuation. Until recently, the Faraday detection system was limited by the noise of the current amplifiers. New amplifier technology, using 1013 Ω resistors in the Faraday cup amplifier feedback loop, enables up to 4-5 times better precision for small samples.

Triton Plus Multicollector Thermal Ionization Mass Spectrometer
Triton Plus Multicollector Thermal Ionization Mass Spectrometer

New amplifier technology for ID-TIMS U-Pb analysis

The application of 1013 Ω resistors for the static collection of all Pb isotopes measured on Faraday cups and 204Pb measured in the axial SEM of a Thermo Scientific TRITON Plus TIMS instrument permits both sensitive detection and an extended linear range. Both single and multicollector detector systems show excellent agreement, suggesting that a static measurement routine with 1013 Ω resistors produces accurate and precise U-Pb isotopic data with superior external reproducibility. The new amplifier technique has the potential to push the frontiers of high-precision U-Pb geochronology and may represent a crucial advance in the quest towards inter- and intra-laboratory reproducibility at the 0.01% level.

The large dynamic range and high signal-to-noise ratio of our 1013 Ω resistors allow static Faraday collection of all relevant UO2 molecules, including the minor 272(UO2) molecule during analyses of typical U-Pb sample loads (which are comparable to single zircons). This allows for online determination of the 18O/16O ratio from 272(UO2)/ 270(UO2) and accurate line-by-line isobaric interference correction, eliminating the dominant source of uncertainty in these analytical set-ups.

U-Pb dating by laser ablation ICP-MS

Neptune XT High Resolution Multicollector ICP-MS
Neptune XT High Resolution Multicollector ICP-MS
Element XR ICP-MS
Element XR ICP-MS

Either single- or multicollector ICP-MS, combined with laser ablation, offers a powerful technique to obtain unique information on the age and formation of a variety of geological samples. Combining two or even three mass spectrometers has become a very powerful way for studying zircon and monazite petrochronology because it enables simultaneous analysis of U-Pb, Lu-Hf, and rare Earth elements (REE) within a single crater. High sensitivity is critical for enabling analysis of samples as small as a few microns. With a high-sensitivity jet pump and the ability to analyze with multiple ion counters, the Neptune Plus MC-ICP-MS and Element XR HR-ICP-MS instruments are able to provide highly-precise in situ U-Pb and Lu-Hf isotope data in zircons, monazites, and other minerals.

Further reading

Re-Os dating

Neptune Plus MC-ICP-MS
Neptune Plus MC-ICP-MS
Triton Plus Multicollector Thermal Ionization Mass Spectrometer
Triton Plus Multicollector Thermal Ionization Mass Spectrometer

The application of Re-Os mainly evolved around the analysis of molybdenite and sulfides. This dating technique uses the decay of 187Re to 187Os and is applied to study the geochemical evolution of the Earth’s interior (mantle), as well as to determine origin and age of ore deposits. The rhenium-osmium chronometer requires highly sensitive techniques to precisely measure isotopic abundances in small osmium samples.

Negative TIMS (N-TIMS) is a powerful ionization technique for a broad range of elements. Many of the transition metals form negatively charged oxide ions and high ion yields can be obtained for those elements that have high electron affinities.

Using N-TIMS, geologists are able to analyze samples with ppt-level precision. This precision enables the analysis of as little as 1 ng of Os, allowing the chronometer to be applied to very small samples. Successful dating using isotope dilution techniques relies on careful preparation of the mineral and the appropriate choice of spiking concentrations. Multicollector ICP-MS is ideal for in situ Re-Os isotope analysis and analysis of larger samples.

Hf-W dating

Neptune Plus MC-ICP-MS
Neptune Plus MC-ICP-MS

The Hf-W dating technique, based on the decay of 182Hf to 182W, is used to study the early solar system. Extraterrestrial samples are rare and the elemental concentrations of Hf and W in those samples is limited, so sensitivity critical for obtaining high-precision isotopic information from chondritic grains. Multicollector ICP-MS combines the advantages of magnetic sector instruments with the superior ionization of an ICP source, enabling the measurement elements with ionization potential, such as Hf and W. Applying the Hf-W chronometer to material from meteorites, geologists can study the timing and other details of planetary formation processes.

Ar-Ar dating

Argus VI Static Vacuum Noble Gas Mass Spectrometer
Argus VI Static Vacuum Noble Gas Mass Spectrometer

Isotopes of the noble gases are powerful tools in geochronology, cosmochemistry and thermochronology. The Ar-Ar dating technique can be used to date any mineral or rock that contains measurable amounts of potassium. These samples include sanidine and micas, but also plagioclase and pyroxene, which have ages from a few thousand years to as old as the solar system itself. As a result of its broad analysis range, the technique is utilized in all areas of geosciences, including volcanology, weathering processes, tectonics, structural and planetary geology, but also in archaeology, evolution of flora and fauna, provenance studies, ore and petroleum genesis, and climate research.

The Ar-Ar dating technique relies on neutron irradiation from a nuclear reactor to convert 39K (stable form of potassium) into 39Ar (radioactive argon). When a standard of known age is co-irradiated with the unknown samples, a single measurement of argon isotopes can be used to calculate the 40K/ 40Ar* ratio (i.e., ratio of radiogenic Ar versus 40Ar from radioactive decay of 40K), and thus to calculate the age of the unknown sample.

Thermo Fisher Scientific developed the Thermo Scientific Argus IV Noble Gas Mass Spectrometer especially for high-precision Ar-Ar dating. This instrument enables simultaneous analysis of all five Ar isotopes on a mixed Faraday-ion counting detection system. For large sample sizes, a Faraday cup array employing standard 1011 Ω amplifiers is the preferred detector. For medium-sized samples, the Faraday cups used to detect the minor isotopes can be equipped with a higher gain 1013 Ω amplifier, which improves the signal-to-noise ratio and results in excellent precision. For smaller samples, the minor isotopes are measured on an ion counting detector.

Further reading

U-Pb dating by ID-TIMS

U-Pb geochronology by isotope dilution thermal ionization mass spectrometry (ID-TIMS) requires precise and accurate determinations of parent-daughter isotope ratios. The small sample size, particularly with respect to radiogenic Pb, demands highly sensitive ion detection systems. Most studies, therefore, employ either secondary electron multipliers (SEMs) or Daly photomultipliers that provide low background noise and high sensitivity. However, they also have limited linear range and require dynamic peak hopping. Such sequential single collector ion counting measurements have several drawbacks, including reduced sample utilization, ion current fluctuations, and mass-dependent detection inefficiency. Also, ion counting measurement requires an accurate deadtime calibration.

Multicollection analysis helps optimize sample usage and allow precision to be independent of signal fluctuation. Until recently, the Faraday detection system was limited by the noise of the current amplifiers. New amplifier technology, using 1013 Ω resistors in the Faraday cup amplifier feedback loop, enables up to 4-5 times better precision for small samples.

Triton Plus Multicollector Thermal Ionization Mass Spectrometer
Triton Plus Multicollector Thermal Ionization Mass Spectrometer

New amplifier technology for ID-TIMS U-Pb analysis

The application of 1013 Ω resistors for the static collection of all Pb isotopes measured on Faraday cups and 204Pb measured in the axial SEM of a Thermo Scientific TRITON Plus TIMS instrument permits both sensitive detection and an extended linear range. Both single and multicollector detector systems show excellent agreement, suggesting that a static measurement routine with 1013 Ω resistors produces accurate and precise U-Pb isotopic data with superior external reproducibility. The new amplifier technique has the potential to push the frontiers of high-precision U-Pb geochronology and may represent a crucial advance in the quest towards inter- and intra-laboratory reproducibility at the 0.01% level.

The large dynamic range and high signal-to-noise ratio of our 1013 Ω resistors allow static Faraday collection of all relevant UO2 molecules, including the minor 272(UO2) molecule during analyses of typical U-Pb sample loads (which are comparable to single zircons). This allows for online determination of the 18O/16O ratio from 272(UO2)/ 270(UO2) and accurate line-by-line isobaric interference correction, eliminating the dominant source of uncertainty in these analytical set-ups.

U-Pb dating by laser ablation ICP-MS

Neptune XT High Resolution Multicollector ICP-MS
Neptune XT High Resolution Multicollector ICP-MS
Element XR ICP-MS
Element XR ICP-MS

Either single- or multicollector ICP-MS, combined with laser ablation, offers a powerful technique to obtain unique information on the age and formation of a variety of geological samples. Combining two or even three mass spectrometers has become a very powerful way for studying zircon and monazite petrochronology because it enables simultaneous analysis of U-Pb, Lu-Hf, and rare Earth elements (REE) within a single crater. High sensitivity is critical for enabling analysis of samples as small as a few microns. With a high-sensitivity jet pump and the ability to analyze with multiple ion counters, the Neptune Plus MC-ICP-MS and Element XR HR-ICP-MS instruments are able to provide highly-precise in situ U-Pb and Lu-Hf isotope data in zircons, monazites, and other minerals.

Further reading

Re-Os dating

Neptune Plus MC-ICP-MS
Neptune Plus MC-ICP-MS
Triton Plus Multicollector Thermal Ionization Mass Spectrometer
Triton Plus Multicollector Thermal Ionization Mass Spectrometer

The application of Re-Os mainly evolved around the analysis of molybdenite and sulfides. This dating technique uses the decay of 187Re to 187Os and is applied to study the geochemical evolution of the Earth’s interior (mantle), as well as to determine origin and age of ore deposits. The rhenium-osmium chronometer requires highly sensitive techniques to precisely measure isotopic abundances in small osmium samples.

Negative TIMS (N-TIMS) is a powerful ionization technique for a broad range of elements. Many of the transition metals form negatively charged oxide ions and high ion yields can be obtained for those elements that have high electron affinities.

Using N-TIMS, geologists are able to analyze samples with ppt-level precision. This precision enables the analysis of as little as 1 ng of Os, allowing the chronometer to be applied to very small samples. Successful dating using isotope dilution techniques relies on careful preparation of the mineral and the appropriate choice of spiking concentrations. Multicollector ICP-MS is ideal for in situ Re-Os isotope analysis and analysis of larger samples.

Hf-W dating

Neptune Plus MC-ICP-MS
Neptune Plus MC-ICP-MS

The Hf-W dating technique, based on the decay of 182Hf to 182W, is used to study the early solar system. Extraterrestrial samples are rare and the elemental concentrations of Hf and W in those samples is limited, so sensitivity critical for obtaining high-precision isotopic information from chondritic grains. Multicollector ICP-MS combines the advantages of magnetic sector instruments with the superior ionization of an ICP source, enabling the measurement elements with ionization potential, such as Hf and W. Applying the Hf-W chronometer to material from meteorites, geologists can study the timing and other details of planetary formation processes.

Ar-Ar dating

Argus VI Static Vacuum Noble Gas Mass Spectrometer
Argus VI Static Vacuum Noble Gas Mass Spectrometer

Isotopes of the noble gases are powerful tools in geochronology, cosmochemistry and thermochronology. The Ar-Ar dating technique can be used to date any mineral or rock that contains measurable amounts of potassium. These samples include sanidine and micas, but also plagioclase and pyroxene, which have ages from a few thousand years to as old as the solar system itself. As a result of its broad analysis range, the technique is utilized in all areas of geosciences, including volcanology, weathering processes, tectonics, structural and planetary geology, but also in archaeology, evolution of flora and fauna, provenance studies, ore and petroleum genesis, and climate research.

The Ar-Ar dating technique relies on neutron irradiation from a nuclear reactor to convert 39K (stable form of potassium) into 39Ar (radioactive argon). When a standard of known age is co-irradiated with the unknown samples, a single measurement of argon isotopes can be used to calculate the 40K/ 40Ar* ratio (i.e., ratio of radiogenic Ar versus 40Ar from radioactive decay of 40K), and thus to calculate the age of the unknown sample.

Thermo Fisher Scientific developed the Thermo Scientific Argus IV Noble Gas Mass Spectrometer especially for high-precision Ar-Ar dating. This instrument enables simultaneous analysis of all five Ar isotopes on a mixed Faraday-ion counting detection system. For large sample sizes, a Faraday cup array employing standard 1011 Ω amplifiers is the preferred detector. For medium-sized samples, the Faraday cups used to detect the minor isotopes can be equipped with a higher gain 1013 Ω amplifier, which improves the signal-to-noise ratio and results in excellent precision. For smaller samples, the minor isotopes are measured on an ion counting detector.

Further reading

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