Improved resolution of thermal history reconstruction at low temperatures Geotrack International, in association with CSIRO Division of Petroleum Resources, Sydney, is pleased to announce this new addition to our range of thermal history reconstruction THR services.
Reliable reconstruction of thermal histories in sedimentary basins is a key aspect of reducing exploration risk, e. Particularly when integrated with information from AFTA and other thermal indicators e.
Technical details Instrumentation The CSIRO He extraction and analysis facility comprises an all-metal He extraction and gas-handling line connected to a dedicated on-line Balzers Prisma quadrupole mass spectrometer. Active gases, particularly hydrogen, are removed using SAES getters.
Helium measurement 4He abundances are determined by isotope dilution using a pure 3He spike, which is calibrated on a regular basis against an independent 4He standard tank. After the heating and purification procedures, the extracted gas is handled and measured via the fully automated computer controlled system.
Blanks are prepared by adding an equivalent amount of nitric acid to washed, empty capsules. Sample selection and grain size measurement Apatite grains are carefully handpicked in order to avoid U- and Th-rich mineral inclusions that may produce excess He eg. Images of selected grains are captured by a CCD video camera mounted on the microscope and measured using image analysis techniques for the purposes of alpha ejection correction calculation.
This correction is mathematically calculated using the estimated dimensions of each grain and is applied directly to the final age discussed in more detail below. Data interpretation Software provided by Prof. By modelling ages through a variety of different thermal history scenarios, it is possible to define the range of histories giving predictions which are consistent with measured ages.
The thermal history framework provided by AFTA forms a solid basis for this procedure. For an example of this procedure, check our website at www. Selected references Farley, K. Helium diffusion from apatite: Journal of Geophysical Research, B2 , Geochimica et Cosmochimica Acta, 60, An empirical test of helium diffusion in apatite: Earth and Planetary Science Letters, , Chemical Geology Isotope Geoscience Section , , Chemical Geology, , Helium diffusion and low-temperature thermochronometry of apatite.