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Magmatic Evolution during the Cretaceous Transition from Subduction to Continental Break-up of the Eastern Gondwana Margin (New Zealand) documented by in-situ Zircon O and €“Hf Isotopes and Bulk-rock Sr and €“Nd Isotopes
Swedish Museum of Natural History, Department of Geology. (Nordsim)ORCID iD: 0000-0003-2227-577X
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2018 (English)In: Journal of Petrology, Vol. 59, no 5, p. 849-880Article in journal (Refereed) Published
Abstract [en]

Major changes in tectonic style can lead to tapping of highly variable magma sources and potentially result in significant episodes of crustal growth. Here we focus on magmatism associated with a transition from arc magmatism to subsequent over-thickening and eventual orogenic collapse. This transition is associated with cessation of subduction and was followed by continental extension and finally continental break-up as recorded in the Cretaceous magmatic record of Zealandia. Orogenic collapse peaked at 110 Ma and is expressed through core complex formation and the intrusion of I- to evolved I/S-type Rahu Suite plutons that have widely varying chemical compositions but homogeneous whole-rock and zircon isotopic signatures that are intermediate between mantle and local upper crust values. The Rahu Suite is interpreted to be derived from differing degrees of melt extraction from a pre-existing lower crustal source and lacks a demonstrable juvenile component. This lower crustal source was likely formed by magmatic underplating and melt–crust hybridization during preceding arc volcanism (Separation Point and Darran suites), effectively smearing out a pulsed event of crust formation in the zircon record. Therefore, late orogenic I- and I/S-type suites do not have to equate to crustal growth and can be an expression of crustal re-melting. An abrupt change in magma sources in Zealandia occurred after 100 Ma during the onset of progressive crustal extension. A juvenile alkaline component (presumably derived from the lithospheric mantle) is suggested to have been present from >97 Ma. This component became more pronounced with time until the emplacement of granites and trachytes with isotopic signatures overlapping with coeval mafic mantle-derived dikes during bimodal rift-related magmatism. The juvenile alkaline component dictated the composition of the felsic magmas but did not represent a significant crustal growth event due to small total volumes.

Place, publisher, year, edition, pages
2018. Vol. 59, no 5, p. 849-880
National Category
Earth and Related Environmental Sciences
Research subject
The changing Earth
Identifiers
URN: urn:nbn:se:nrm:diva-3189DOI: 10.1093/petrology/egy047OAI: oai:DiVA.org:nrm-3189DiVA, id: diva2:1273385
Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2019-01-14Bibliographically approved

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Publisher's full texthttp://dx.doi.org/10.1093/petrology/egy047

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