TY - JOUR
T1 - Re-initiation of plutonism at the Gondwana margin after a magmatic hiatus
T2 - The bimodal Permian-Triassic Longwood Suite, New Zealand
AU - McCoy-West, A. J.
AU - Mortimer, N.
AU - Burton, K. W.
AU - Ireland, T. R.
AU - Cawood, P. A.
N1 - Funding Information:
We thank the University of Otago, Department of Geology for permission to use Ruapuke Island material from its rock collection. Geoff Nowell, Chris Ottley and Peter Holden are thanked for analytical assistance. Ben Durrant, John Simes and Belinda Smith-Lyttle are acknowledged for thin section and mineral separation work. We thank Hamish Campbell and Gideon Rosenbaum for discussions about Permian Gondwana, and Priyadarshi Chowdhury for discussion of trondhjemite genesis. An earlier version of the manuscript was improved by comments from Matt Sagar. Josh Schwartz and an anonymous referee are thanked for thought-provoking journal reviews. NM's contribution was supported by core funding to GNS Science from the New Zealand Ministry of Business, Innovation and Employment contract C05X1103. This project was also funded by NERC grant NE/N003926/1 and ARC grant FL160100168.
Funding Information:
We thank the University of Otago, Department of Geology for permission to use Ruapuke Island material from its rock collection. Geoff Nowell, Chris Ottley and Peter Holden are thanked for analytical assistance. Ben Durrant, John Simes and Belinda Smith-Lyttle are acknowledged for thin section and mineral separation work. We thank Hamish Campbell and Gideon Rosenbaum for discussions about Permian Gondwana, and Priyadarshi Chowdhury for discussion of trondhjemite genesis. An earlier version of the manuscript was improved by comments from Matt Sagar. Josh Schwartz and an anonymous referee are thanked for thought-provoking journal reviews. NM’s contribution was supported by core funding to GNS Science from the New Zealand Ministry of Business, Innovation and Employment contract C05X1103. This project was also funded by NERC grant NE/N003926/1 and ARC grant FL160100168.
Publisher Copyright:
© 2021
Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.
PY - 2022/5
Y1 - 2022/5
N2 - 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.
AB - 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.
KW - Brook street terrane
KW - Darran suite
KW - Longwood suite
KW - Radiogenic Sr-Nd
KW - Separation point suite
KW - Stable Nd
KW - Trondhjemite
KW - U-Pb geochronology
UR - http://www.scopus.com/inward/record.url?scp=85117097283&partnerID=8YFLogxK
U2 - 10.1016/j.gr.2021.09.021
DO - 10.1016/j.gr.2021.09.021
M3 - Article
AN - SCOPUS:85117097283
SN - 1342-937X
VL - 105
SP - 432
EP - 449
JO - Gondwana Research
JF - Gondwana Research
ER -