Heterogeneous Zircon Cargo in Voluminous Late Paleozoic Rhyolites: Hf, O Isotope and Zr/Hf Records of Plutonic to Volcanic Magma Evolution

A. Pietranik*, E. Slodczyk, C. J. Hawkesworth, C. Breitkreuz, C. D. Storey, M. Whitehouse, R. Milke

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    20 Citations (Scopus)

    Abstract

    Voluminous rhyolitic lavas and ignimbrites (c. 34 000 km(3)) were formed in the NE German Basin in a post-collisional setting at c. 295 Ma. Trace elements, epsilon Hf and delta O-18 have been measured in dated magmatic and inherited rhyolitic zircons from three drill cores across the basin. Magmatic zircons crystallized in two stages: the first stage in less differentiated and isotopically heterogeneous magmas and the second stage in more differentiated and isotopically homogeneous magmas. The first and second stages can be related to the crystallization of zircons within a heterogeneous pluton and in an evolved, silicic magma that was later erupted. Some zircons crystallized entirely during the evolved magma stage and provide good resolution for identifying and characterizing processes happening shortly before eruption. The isotopic compositions of the magmatic zircons constrain the proportions of juvenile and reworked materials involved in the formation of voluminous silicic magmas in a post-collisional tectonic setting. The advantage of studying the volcanic rocks from the NE German Basin is that their petrogenesis involved a relatively simple, two-source interaction during magma production, which permits quantitative estimation of the amount of each source component. AFC modelling shows that the first stage zircons crystallized from magmas containing 5-80% of the juvenile component, whereas the final rhyolitic magmas contained 30-40% of this material. The inherited zircons have Hf model ages of 1 center dot 9-2 center dot 2 Ga, suggesting that much of the local basement was initially derived from the mantle at that time and that it was subsequently reworked at around 1 center dot 5 Ga. Similar model ages are a feature of Baltica-derived sediments and the implication is that such sediments underlie large areas of the NE German Basin. The lack of any record of Avalonian basement in the NE German Basin may indicate that both the sedimentary cover and the underlying basement are part of Baltica.

    Original languageEnglish
    Pages (from-to)1483-1501
    Number of pages19
    JournalJournal of Petrology
    Volume54
    Issue number8
    DOIs
    Publication statusPublished - Aug 2013

    Keywords

    • rhyolite
    • zircon
    • Baltica
    • Hf and O isotopes
    • NE German Basin
    • S-TYPE GRANITES
    • U-PB
    • TRACE-ELEMENT
    • CONTINENTAL-CRUST
    • DETRITAL ZIRCONS
    • NEW-BRUNSWICK
    • GERMAN BASIN
    • DRILL CORES
    • LU-HF
    • CONSTRAINTS

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