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-Hf Isotopes and Bulk Rock Sr-Nd Isotopes

TY - JOUR

T1 - 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-Hf Isotopes and Bulk Rock Sr-Nd Isotopes

AU - van der Meer, Quinten

AU - Waight, Tod Earle

AU - Tulloch, AJ

AU - Whitehouse, Martin

AU - Andersen, T.

PY - 2018

Y1 - 2018

N2 - 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.

AB - 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.

U2 - 10.1093/petrology/egy047

DO - 10.1093/petrology/egy047

M3 - Journal article

SN - 0022-3530

VL - 56

SP - 849

EP - 880

JO - Journal of Petrology

JF - Journal of Petrology

IS - 5

ER -