Isotopic evidence for continental growth during accretionary orogenesis in the Tasmanides, eastern Australia

Kemp, Tony (2008) Isotopic evidence for continental growth during accretionary orogenesis in the Tasmanides, eastern Australia. In: Australian Earth Sciences Convention. p. 152. From: Australian Earth Sciences Convention 2008, 20-24 July 2008, Perth, WA, Australia.

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The trace element signature of Earth's continental crust resembles that of modern arc lavas, but much of the continental mass apparently formed during ancient igneous pulses that may be difficult to reconcile with subduction zone magmatism. We explore the role of plate subduction in crust generation by considering the tectonic context of whole-rock Nd isotope and zircon Hf-O isotope data from granites of the Australian Tasmanides (515-230 Ma), an accretionary orogen that evolved by alternating back-arc basin opening and closure. Crustal growth in this area is manifest by the emplacement of granitic suites with a sizeable, but latent, basaltic component (30-90%). Nd-Hf-O isotope-time patterns reveal that juvenile input into the granites was enhanced during extensional cycles that followed crustal thickening, cementing a link between slab rollback and continental growth. Interaction between juvenile magmas and supracrustal material deposited during prior back-arc rifting masked the bulk-rock isotope evidence for crust generation, but was integral to the formation of stable felsic crust. Metasedimentary reworking peaked at the inception of slab rollback episodes with the emplacement of peraluminous 'S-type' plutons, but magmatism becoming increasingly juvenile and 'I-type' thereafter as extension and crustal thinning continued. Subduction zone retreat added large tracts of new crust to eastern Australia in <300 Ma, providing an additional perspective on the conundrum of rapid continental growth.

Item ID: 27802
Item Type: Conference Item (Abstract / Summary)
ISSN: 0729-011X
Date Deposited: 30 Jul 2013 04:59
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040313 Tectonics @ 50%
04 EARTH SCIENCES > 0402 Geochemistry > 040203 Isotope Geochemistry @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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