U-Pb laser ablation geochronology has become the most commonly applied tool for dating zircons. Despite the widespread application of this tool to a host of geological problems, there is little consensus with regard to analytical strategies and data reduction protocols. The result is inter-laboratory bias and both under- and over-estimation of errors on calculated dates. This limits our ability to compare results from different labs and limits rigorous compilations from databases such as EarthChem. This project will remedy this situation by developing cyber infrastructure tools in support of Laser-Ablation ICP-Mass Spectrometry (LA-ICP-MS). The project will develop open-source, free, software in consultation with the international community to treat with statistical rigor all aspects of data reduction, from calculation of ratios to correction for interferences and drift. Our approach will follow that used in developing similar software as part of the EARTHTIME project and requires the integration of the fields of software engineering and geochemistry. The resulting software will eliminate large sources of interlaboratory bias and serve as a teaching tool showing clearly how raw ratios are converted into dates and uncertainties.
Creating the software for connecting the LA-ICP-MS community with the developing EarthChem database for geochronology and thermochronology will provide the integration of data from this important technique into the larger data structure of geochemistry and geology. These data will play an important role in far-ranging fields such as understanding the growth of continents, chronology of evolutionary changes, timing of early hominid evolution, and linkages between climate and tectonics. During all phases of the planned work, we will involve a broad cross section of the community from undergraduates to post-doctoral scientists to help develop the next generation of analysts and software engineers. In particular, the systematic evolution of the collaboration between software engineers and earth scientists will be advanced as it produces robust and reliable workflow tools.
When rocks form from the cooling of a magma or lava they crystalize a variety of minerals. Some of these minerals contain radioactive parent elements such as Uranium that decays to the daughter element Lead (U goes to Pb, in chemical symbols). Determining the concentration of both elements and using a radioactive decay equation can give the age at which the rock formed. One of the most common ways for determining such ages is by using a technique called Laser Ablation, Inductively Couple Plasma Mass Spectrometry (LA-ICPMS). The laser is used to vaporize a small portion of a U and Pb-bearing mineral, perhaps on a spot 30 microns in diameter. The vapor is put into the mass spectrometer that allows the scientist to determine the concentrations of parent (U) and daughter (Pb) elements and thus the age of the mineral and host rock. A study of the age of such materials is called Geochronology (earth time) in the Geosciences. This technique is used by 10’s of labs in the United States producing 100’s of analyses per day. Part of the work on this project was to create a website (really a project management system) where data could be uploaded, archived, and discovered by any host of users. This was accomplished during this study, and can be viewed at http://geochron.org. Of particular interest is that not only can the scientist determine the age of a rock by sampling it (the cooled magma or lava), but erosion of existing rocks produces sediment that carries the age signature of the rock in the form of mineral deposited in sedimentary rocks (call detrital). This detrital signature can be analyzed to determine where and what ages were present in the sediment source. This has the power to reveal past drainage patterns and where ancient mountain sources were present. In this project we created a home for both the age and detrital data. There are a variety of visualization methods that users can employ. Lastly, the system provides long term archiving for results so that data generated are available to geoscientists, commercial firms, and the general public for the foreseeable future.
