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WORK IN PROGRESS!

For continued discussion of related geochemical analytical data modelling, see here

-- OliverRaymond - 2009-10-28

Geochronology Data Model

Geology is a four-dimensional science: When did this volcano last erupt? What is the rate of crustal uplift in this area? Are the deformation and mineralising events at gold prospect Alpha the same age as documented at gold mine Beta? Does the age of this coral fit the known climate record?

Because geochronology is a vital component of understanding geology and geological processes it is equally vital that means be developed to freely and easily exchange data.

The following is the tentative first step in building a geochronology information model in the GeoSciML mileau, particularly for exchanging absolute radiogenic isotopic geochronology data at first, but there are already clearly potential overlap with stable isotope and other geo/chemical domains.

Geochronology 101

Providing an absolute age of geological material (or, more accurately, the geological event represented by that material) is based on the decay of a radiogenic parent isotope into a daughter isotope (or series of daughter isotopes) occurring at a known, unchangeable rate. There are several parent-daughter isotopic systems that are routinely analysed including: uranium-238/lead-206, uranium-235/lead-207, thorium-238/lead-208, potassium-40/argon-40, rubidium-87/strontium-87, lutetium-176/hafnium-176, etc. Some methods are little more complex such as argon-argon which involves irradiating a sample prior to analysis or fisson-track which measures the damage done to a crystal lattice when uranium isotopes fission. Because of differences in geochemical behaviour between isotopes and elements some of these systems also provide important geochemical information about processes such as crustal and mantle evolution.

Each isotopic system has particular properties that lend itself to be used in different circumstances, e.g. the uranium-lead system will provide the age a granite was intruded into the crust in billions of years whereas carbon-dating will provide the age of an animal just before it became someones dinner in thousands of years. It is critical that any geochronology data model be generic enough to describe as many of these systems as possible.

Analyses are made on suitable earth material, usually single mineral grains or parts thereof that incorporate the parent/daughter system in their mineralogy. Typical minerals include zircon, monazite, apatite, muscovite although the list is ever expanding. The ratio of a daughter isotope to the original parent isotope is measured along with associated analyses that provide for necessary method and/or instrument related corrections. Given those values and a known rate of decay, an absolute age can be calculated from a raw measurement.

There are now dozens of instrument techniques for making these measurements, but all involve some form of mass spectrometer where the sample is ionised and a selected range of ions are separated and measured by controlled electrical and/or magnetic fields. It is critical that the geochronology data model is generic enough to encompass as many of these techniques as possible.

In the beginning...

The work presented here has been driven by Geoscience Australia Geochronology Laboratory (GAGL) to date. Geoscience Australia holds a large repository of geochronological data comprised largely of isotopic data collected over 30 years of regional projects around Australia. Many of these projects have involved partnerships with various State and Territory geological surveys, mineral exploration companies and university researchers, so the 'clients' reading our data are very varied with a wide range of requirements. In the last 15 years this has focussed particularly on U-Pb zircon dating using the SHRIMP (Sensitive High Resolution Ion Microprobe) technique. Although we have a readily apparent bias in our world-view, recent project requirements are taking us increasingly into other systems and methods that we are keen to incorporate into our information systems Geoscience Australia is also heavily involved in the emerging GeoSciML and associated standards with a view toward a seamless interoperable data environment. Geochronology is obviously an important part of that.

Thus our interest in developing a geochronology information model is three-fold:
  1. We want a standard data format we can provide to our clients.
  2. We want a model that can aid the redevelopment of our internal systems.
  3. We want to contribute to the develop of national and international standards.

What happens now

An example of geochronological data is provide below. This is a typical data set from a series of single zircon grain analyses made on the SHRIMP measuring the U-Pb system. The data include an analytical ID, some pertinent chemical composition values, a series of isotopic ratios and their measurement uncertainities and a calculated age for each analysis. The analyses are also grouped according to an interpretation for that group. A group may also provide the data that is combined, typically an average or weighted mean, to form a single 'determined age'. A series of analyses may have zero, one or several determined ages derived from various and frequently overlapping groups.

Such data tables are typically accompanied by metadata regarding the analytical session/s and/or data processing (such as information about coeval standards measurements, calibrations etc.)

ExampleGeochronDataTable.jpg

The Prototype Two model

This is the Prototype Two model. (Prototype One was released in January 2007 as simply a very ugly strawperson to get discussion going). The main purpose of this version is to continue discussion and to focuss on the patterns and details that need to developed to describe our geochronological data. The more feedback the better! Note that this version has linked the model to the relevant parts of external models such as GeoSciML and HollowWorld.

  • NOTE: The following class diagrams are taken from the Geochronology UML model. To see the detailed content of the current model download a copy of GeochronML-doc.zip below, extract to a local folder and open index.html in a web browser.

  • Overview of main geochronology package:
    geochron-mainview.gif

Comparing this with the Observations and Measurements (OM) standard model:

  1. AnalysisInstrument is a kind of Process - SensorML provides a model and syntax in this area
  2. GeochronAnalysis appears to be a kind of Observation - it is time-tagged so relates to the procedure-application-event
  3. MolecularMeasurement captures a component of the result of the Observation

Some of the complexity in the model shown here relates to information that is re-used by many observations or relates to many results (instrument, observation-time). The strategy used in the model here is that these elements are associated with a standard aggregation class (e.g. AnalysisSession) and inherited by the members. This contrasts with the OM pattern, which has no aggregations that imply property inheritance at the instance level. "Normalization" in the OM case is managed, instead, by explicit references.

The Interpretation classes are another part of the process chain. The complete "Observation Procedure" is the chain that combines the Instrument + Interpretation.

The model could be re-formulated by specialization of OM, perhaps also with some constraints and patterns.

-- SimonCox - 05 Jul 2007
  • Overview of microAnalysis package:
    microanalysis.gif

Comparing this with the Sampling Features standard model:
  1. AnalyticalMaterial could probably be implemented as a specialization of Specimen
  2. maybe the "analysis location" should be modelled as a separate specialization of SamplingFeature, and associated with its Specimen using the relatedSamplingFeature association?
  3. SpecimenContainer appears to be related to some implementation details that are probably only of internal interest, so maybe wouldn't appear in the implementation of the model for transfer.

N.B. AnalysisSession appears to be a collection of Specimens, the Observations on them, and the Instruments and Procedures associated with them. In the Assay Data world this is called a "batch".

-- SimonCox - 05 Jul 2007

Comments and discussion

 
Topic attachments
I Attachment Action Size Date Who Comment
Demo_xml_instance_for_AGU.xmlxml Demo_xml_instance_for_AGU.xml manage 225.4 K 17 Dec 2007 - 08:53 NickArdlie Sample XML document instance
ExampleGeochronDataTable.jpgjpg ExampleGeochronDataTable.jpg manage 127.9 K 07 Mar 2007 - 13:00 KeithSircombe An example of some published geochronological data.
Geochron-workflow-detail-2.jpgjpg Geochron-workflow-detail-2.jpg manage 150.3 K 07 Mar 2007 - 13:01 KeithSircombe Overview of data requirements in geochronology workflow.
GeochronML-doc.zipzip GeochronML-doc.zip manage 151.6 K 17 Dec 2007 - 09:08 NickArdlie HTML documentation set for the GeochronML model
GeochronPrototype.jpgjpg GeochronPrototype.jpg manage 139.9 K 07 Mar 2007 - 13:00 KeithSircombe UML prototype version of proposed geochronology data model
atwork.gifgif atwork.gif manage 3.6 K 07 Mar 2007 - 12:59 KeithSircombe Work in progress...
geochron-mainview.gifgif geochron-mainview.gif manage 62.7 K 17 Dec 2007 - 08:49 NickArdlie Geochron main package class diagram.
microanalysis.gifgif microanalysis.gif manage 16.4 K 15 Jun 2007 - 13:16 NickArdlie Geochron microanalysis package class diagram
Topic revision: r7 - 15 Oct 2010, UnknownUser
 

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