Thermal Histories of Chondrules: Petrologic Observations and Experimental Constraints

Rhian Jones, Guy Libourel, Johan Villeneuve

    Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

    Abstract

    Thermal histories of chondrules can be deduced by studying the petrology and mineral chemistry of natural chondrules and their experimental analogues. Dynamic crystallization experiments have successfully reproduced chondrule textures, and provide general but broad constraints on peak temperatures and cooling rates. Porphyritic textures result when a chondrule is heated to a maximum temperature close to, but below, its liquidus, and cooled at initial rates between about 10 and 1000 °C/h. Typical liquidus temperatures for chondrules range from about 1400 – 1700 °C. Non-porphyritic chondrules are produced when peak temperatures exceed the liquidus slightly (for barred / dendritic textures) and significantly (radiating textures) and chondrules cool at rates around 500 – 3000 °C/h. More quantitative constraints on cooling rates can be determined by considering growth and diffusion-related zoning in chondrule minerals. Results of such modelling are consistent with dynamic crystallization experiments. Rapid dissolution rates for relict olivine grains also indicate a limited time at high temperatures, and indicate fast cooling rates of hundreds to thousands of °C/h, close to peak temperatures. Other cooling rate indicators include disequilibrium partition coefficients between minerals and chondrule glass, and consideration of chemical and isotopic diffusion between relict grains and their overgrowths. Interpretation of both these features is currently ambiguous. Several lines of evidence suggest that cooling rates decreased at lower temperatures, as the chondrule approached the solidus, to <50 °C/h. These include slow cooling required to nucleate plagioclase, cooling rates inferred from trace element diffusion profiles in metal grains, and exsolution microstructures in clinopyroxene. In contrast, clinoenstatite microstructures, the presence of chondrule glass, and dislocation densities in chondrule olivine appear to argue for rapid cooling (103 to 104 °C/h) through the lower temperature regime, and textures in opaque (metal / sulfide) assemblages indicate cooling rates of hundreds of degrees per hour at subsolidus temperatures. Overall, thermal histories of chondrules can provide fundamental constraints for chondrule formation models. Whilst high-temperature thermal histories are reasonably well constrained, there are currently some open questions about the nature of the cooling curve at lower temperatures. A better understanding of chondrule cooling rates at lower temperatures would help to discriminate between chondrule formation models that make quantitative predictions for thermal histories. Within a single chondrite, cooling rates may vary widely. It is also possible that the nature of cooling histories varies within a given population of chondrules. A statistical treatment of chondrule populations in which individual chondrules show distinct thermal histories would help to make predictions about chondrule formation environments, and the diversity of processes that might be represented in a single chondrule-forming region.
    Original languageEnglish
    Title of host publicationChondrules and the Protoplanetary Disk
    EditorsSara Russell, Alexander Krot, Harold Connolly
    PublisherCambridge University Press
    Chapter3
    Pages57-90
    ISBN (Print)9781108418010
    Publication statusPublished - 2018

    Keywords

    • Chondrules
    • Chondrites
    • Protoplanetary disks

    Fingerprint

    Dive into the research topics of 'Thermal Histories of Chondrules: Petrologic Observations and Experimental Constraints'. Together they form a unique fingerprint.

    Cite this