U-Pb Dating

Highly accurate and precise in-situ ages using a laser ablation system (Teledyne Photon MachinesTM Analyte G2 Laser) connected to an inductively coupled plasma mass spectrometer (Thermo ScientificTM iCAPTM RQ-ICP-MS).

Prior to analysis samples can be inspected for zoning, evidence of dissolution-reprecipitation, or other factors that can affect the interpretation of the age data, using cathodoluminescence (CL) and back scattered electron (BSE) imaging with a field emission-scanning electron microscope (Hitachi SU5000 FE-SEM).

Depending on the sample we can obtain U-Pb ages by analysing minerals directly from a thin section, from a polished puck, or from mineral separates mounted on polished pucks.

Our Mineral Separation Laboratory has the facilities for separating out almost any mineral phase using a combination of gravity separation with a Wilfley table, heavy liquids and magnetic methods.

For further information on geochronological services contact:

Dr Huiqing (Jeffrey) Huang (laboratory specialist)
Phone: 07 4781 4691, Email: huiqing.huang@jcu.edu.au

Information about other EGRU geochemical services can be found here.

Zircon

The U-Pb system in zircon is very stable over a wide range of temperature and alteration conditions therefore it is the mineral of choice for obtaining highly precise emplacement ages for volcanic and plutonic rocks, for provenance analyses and maximum depositional ages for sedimentary rocks. Less commonly it is used for dating metamorphic and alteration events. However, in certain cases through careful petrographic analysis zircon grains can be identified to have formed during a metamorphic or hydrothermal event and, in these conditions, it is a suitable candidate for dating metamorphic and alteration events.

Monazite

Monazite is suitable for a wide range of geochronological applications including emplacement ages for igneous rocks, provenance analyses and maximum depositional ages, dating metamorphism and hydrothermal events. However, as monazite is less stable than zircon during geological processes, and the U-Pb system in monazite is less robust, we recommend a thorough petrographic analysis before dating monazite grains to identify the conditions under which the monazite grains formed.

Titanite

The constraints on U-Pb dating of titanite grains are similar to those for monazite.  However, titanite presents an advantage because it can form in mafic rocks as a primary mineral therefore, if the U-Pb system was not disturbed by metamorphic or hydrothermal events, it can be used to date the emplacement of mafic igneous rocks.

Allanite

The constraints on U-Pb dating of allanite are similar to those for monazite.  Allanite is common in many hydrothermal systems and can be used to date alteration. However, because it can react with hydrothermal fluids and can undergo dissolution-reprecipitation, we recommend a through petrographic investigation before dating.

Apatite

The constraints on U-Pb dating of apatite grains are like those for monazite.  Like titanite, apatite can form as a primary mineral in mafic magmas and therefore can be used to obtain emplacement ages for magmas where zircon is absent. However, thermal, metamorphic, and hydrothermal events can disturb the U-Pb system in apatite and ages must be interpreted carefully and in conjunction with a thorough petrographic analysis.

Garnet

Andradite and grossular garnet commonly contain ppm levels of U and Pb and are suitable for U-Pb dating. Care must be taken with the interpretation of ages because the U-Pb system can be disturbed by metamorphic and hydrothermal events. However, because garnets can be very large often the U-Pb system is reset in only parts of the grains and a multistage age history can be reconstructed.

Cassiterite

Cassiterite can be used to directly date the timing of tin mineralization and, because cassiterite grains are robust during erosion and weathering, they can be used for provenance analysis and to obtain maximum depositional ages for sediments. We recommend that the cassiterite ages be accompanied by a detailed petrographic analysis and the dating results interpreted within the geological context.

Rutile

Rutile can be used to date a variety of geological process including the emplacement age of igneous rocks, metamorphic events, detrital studies to assess maximum depositional ages and provenance of sediments, alteration, and mineralization events. The U-Pb system in rutile can be reset by metamorphism, fluids and thermal events and we recommend detailed petrographic and geological context analyses for the most robust interpretation of the age dates.

Wolframite

U-Pb dating of wolframite is a newly developed method.  The factors that affect the behaviour of the U-Pb system in wolframite are not well understood therefore the age results must be interpreted in context and through rigorous petrographic analysis.