Isotopic evidence for rapid continental growth in an extensional accretionary orogen: The Tasmanides, eastern Australia

AIS Kemp, Christopher John Hawkesworth, WJ Collins, CM Gray, PL Blevin, EIMF

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    416 Citations (Scopus)

    Abstract

    The trace element signature of Earth's continental crust resembles that of arc lavas, but the continents may have formed during ancient igneous pulses that are hard to reconcile with supra-subduction zone magmatism. We explore the role of coupled arc-back-arc accretionary processes in crust generation by considering the tectonic context of whole rock Nd isotope and zircon Hf-O isotope data from igneous rocks of the Australian Tasmanides (515-230 Ma), which is thought to have evolved by the repeated opening and closure of sediment-filled back-arc basins behind a long-lived subduction zone. The significance of this process for continental crust formation has yet to be evaluated from an isotopic perspective. Granitic rocks in this area define striking secular epsilon(Nd)-epsilon(Hf)-delta O-18 trends that correlate with the pattern of deformational events and register changes in magma source during tectonic activity. These trends reveal that juvenile magmatic input was enhanced during extensional, back-arc rifting episodes that immediately followed crustal thickening. suggesting a relationship between stab rollback and continental growth. Interaction between juvenile magma and sedimentary units deposited during a preceding back-arc rifting cycle was integral to the formation of stable continental material. This highlights the importance of back-arc environments for both the generation and differentiation of continental crust. The juvenile component within the Tasmanide igneous rocks increased from the Cambrian to the Triassic, consistent with a diminished input from craton-derived metasedimentary material as the subduction zone migrated outboard of the Gondwana margin. Subduction zone retreat formed large tracts of new crust in eastern Australia at comparable rates to crust generation at modern island arcs, providing a mechanism for rapid continental growth at convergent margins. Using isotopic tracers to link tectonic evolution and crust generation in modem and ancient orogens can lead to a better understanding of the geodynamic controls on planetary differentiation. (C) 2009 Elsevier B.V. All rights reserved.

    Original languageEnglish
    Pages (from-to)455-466
    Number of pages12
    JournalEarth and Planetary Science Letters
    Volume284
    Issue number3-4
    DOIs
    Publication statusPublished - 15 Jul 2009

    Keywords

    • continental growth
    • Nd isotopes
    • Hf isotopes
    • tectonics
    • Tasmanides
    • granite
    • LACHLAN FOLD BELT
    • NEW-ENGLAND-BATHOLITH
    • TRANS-HUDSON OROGEN
    • A-TYPE GRANITES
    • S-TYPE GRANITES
    • NEW-SOUTH-WALES
    • SOUTHEASTERN AUSTRALIA
    • CRUSTAL GROWTH
    • TECTONIC EVOLUTION
    • DELAMERIAN OROGEN

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