Re-initiation of plutonism at the Gondwana margin after a magmatic hiatus: the bimodal Permian-Triassic Longwood Suite, New Zealand

McCoy-West, A.J., Mortimer, N., Burton, K.W., Ireland, T.R., and Cawood, P.A. (2022) Re-initiation of plutonism at the Gondwana margin after a magmatic hiatus: the bimodal Permian-Triassic Longwood Suite, New Zealand. Gondwana Research, 105. pp. 432-449.

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View at Publisher Website: https://doi.org/10.1016/j.gr.2021.09.021
 
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Abstract

The Cambrian to Cretaceous Tuhua Intrusives, New Zealand, preserve an igneous record of Phanerozoic subduction and crustal growth at the margin of Gondwana. Within the Tuhua Intrusives, the coeval gabbroic and trondhjemitic intrusions of the c. 261-243 Ma Longwood Suite stand out as being isotopically more primitive and chemically distinct from all other New Zealand plutonic suites. We present new U-Pb crystallization ages, trace element analyses and Sr-Nd isotope compositions of the Longwood Suite. U-Pb SHRIMP zircon ages of 258.5 ± 2.5 Ma, 256.0 ± 1.8 Ma, 247.8 ± 2.7 Ma and 243.2 ± 2.4 Ma obtained from plutons on Ruapuke Island, and a dike at Bluff, affirm the restricted time range and expand the known areal extent of the Longwood Suite. Longwood Suite granitoids are I-type and sodic (K/Na < 0.4), with distinctive low Rb and Nb/Ta, flat rare earth element patterns (La/YbN < 10), unradiogenic 87Sr/86Sr(t) (0.7029 to 0.7032) and radiogenic ε143Nd(t) (+6.3 to +8.2), compared to the nearby, calc-alkaline, Late Triassic Darran Suite I-type plutons of the Tuhua Intrusives. Stable Nd isotope ratios of Longwood Suite samples are highly variable (δ146/144Nd = 233 ppm) compared to global plutonic rocks (δ146/144Nd = 44 ppm) and reflect the removal of phosphate minerals. Collectively, these geochemical characteristics are consistent with generation of the granitoids by shallow (garnet-absent) melting of an amphibolitic residue, from which we infer relatively thin lithosphere. The Longwood Suite has a maximum areal addition rate of 43 km2/Ma, substantially less than the subsequent plutonic suites when the magmatic arc was fully established. We suggest a petrotectonic model whereby Gondwana continental margin crust was tectonically underplated by Permian intra-oceanic island arc crust and mantle lithosphere, which subsequently melted to generate the isotopically primitive gabbro and trondhjemite plutons of the Longwood Suite.

Item ID: 69723
Item Type: Article (Research - C1)
ISSN: 1342-937X
Copyright Information: Published Version: © 2021 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. Accepted Version: © 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
Funders: Australian Research Council (ARC)
Projects and Grants: ARC grant FL160100168
Date Deposited: 25 Oct 2021 23:21
FoR Codes: 37 EARTH SCIENCES > 3705 Geology > 370511 Structural geology and tectonics @ 20%
37 EARTH SCIENCES > 3703 Geochemistry > 370303 Isotope geochemistry @ 40%
37 EARTH SCIENCES > 3705 Geology > 370503 Igneous and metamorphic petrology @ 40%
SEO Codes: 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280107 Expanding knowledge in the earth sciences @ 100%
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