Radiogenic isotopes decay at known rates and can be used to interpret ages for minerals, rocks and geologic processes. Different isotopic systems provide information related to different time periods and geologic processes, systems include: U-Pb and Ar/Ar, Sm-Nd, Pb-Pb, Lu-Hf, Rb-Sr and Re-Os isotopes. The GEOCHRON database stores full analytical U-Pb age data from Geoscience Australia's (GA) Sensitive High Resolution Ion Micro-Probe (SHRIMP) program. The ISOTOPE database is designed to expand GA's ability to deliver isotopic datasets, and stores compiled age and isotopic data from a range of published and unpublished (GA and non-GA) sources. OZCHRON is a depreciated predecessor to GEOCHRON and ISOTOPE, the information once available in OZCHRON is in the process of migration to the two current databases.
The ISOTOPE compilation includes sample and bibliographic links through the A, FGDM, and GEOREF databases. The data structure currently supports summary ages (e.g., U-Pb and Ar/Ar) through the INTERPRETED_AGES tables, as well as extended system-specific tables for Sm-Nd, Pb-Pb, Lu-Hf and O- isotopes. The data structure is designed to be extensible to adapt to evolving requirements for the storage of isotopic data. ISOTOPE and the data holdings were initially developed as part of the Exploring for the Future (EFTF) program - particularly to support the delivery of an Isotopic Atlas of Australia.
During development of ISOTOPE, some key considerations in compiling and storing diverse, multi-purpose isotopic datasets were developed:
1) Improved sample characterisation and bibliographic links. Often, the usefulness of an isotopic dataset is limited by the metadata available for the parent sample. Better harvesting of fundamental sample data (and better integration with related national datasets such as Australian Geological Provinces and the Australian Stratigraphic Units Database) simplifies the process of filtering an isotopic data compilation using spatial, geological and bibliographic criteria, as well as facilitating 'audits' targeting missing isotopic data.
2) Generalised, extensible structures for isotopic data. The need for system-specific tables for isotopic analyses does not preclude the development of generalised data-structures that reflect universal relationships. GA has modelled relational tables linking system-specific Sessions, Analyses, and interpreted data-Groups, which has proven adequate for all of the Isotopic Atlas layers developed thus far.
3) Dual delivery of 'derived' isotopic data. In some systems, it is critical to capture the published data (i.e. isotopic measurements and derived values, as presented by the original author) and generate an additional set of derived values from the same measurements, calculated using a single set of reference parameters (e.g. decay constant, depleted-mantle values, etc.) that permit 'normalised' portrayal of the data compilation-wide.
4) Flexibility in data delivery mode. In radiogenic isotope geochronology (e.g. U-Pb, Ar-Ar), careful compilation and attribution of 'interpreted ages' can meet the needs of much of the user-base, even without an explicit link to the constituent analyses. In contrast, isotope geochemistry (especially microbeam-based methods such as Lu-Hf via laser ablation) is usually focused on the individual measurements, without which interpreted 'sample-averages' have limited value. Data delivery should reflect key differences of this kind.
Value: Used to provide ages and isotope geochemistry data for minerals, rocks and geologic processes.
Scope: Australian jurisdictions and international collaborative programs involving Geoscience Australia
