The Pounamu terrane, a new Cretaceous exotic terrane within the Alpine Schist, New Zealand; tectonically emplaced, deformed and metamorphosed during collision of the LIP Hikurangi Plateau with Zealandia

Cooper, Alan F.; Ireland, Trevor

doi:10.1016/j.gr.2013.11.011

Cited by 19 publications

(7 citation statements)

References 57 publications

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“…Additionally, the WC14-38 garnet age is consistent with the timing of high-temperature (HT) to ultrahigh-temperature (UHT) metamorphism of the lower crust beneath the Otago Schist, dated at 91.7 AE 2 Ma using zircon from granulite xenoliths contained within the Kakanui Mineral Breccia (Jacob, Scott, Turnbull, Tarling, & Sagar, 2017). Although these xenoliths are located 200 km from the location of WC14-38, it is possible that high-grade metamorphism in these regions was driven by the same regional heating event, such as conductive heating of the lower crust by hot upper mantle, as suggested by Jacob et al (Scott et al, 2015) (Cooper and Ireland, 2013) (Vry et al, 2004) (Mortimer and Cooper, 2004) Thrust faulting A-type magmatism Lu-Hf Garnet, this study (Mortimer and Cooper, 2004;Cooper and Ireland, 2015) Zircon Monazite (Vry et al, 2004)…”

Section: Comparison To Previous Workmentioning

confidence: 63%

“…The Lu–Hf garnet ages reported here are consistently older than existing zircon rim and monazite ages from the PUB and the Mataketake Range regions (Figure ; Cooper & Ireland, , ; Mortimer & Cooper, ). A clear link between these zircon and monazite age data and the metamorphic conditions which they record has not been established, therefore the significance of these dates with respect to garnet growth remains unclear.…”

Section: Discussionmentioning

confidence: 99%

“…A cluster of Lu–Hf and Rb–Sr ages at 87–86 Ma (Vry et al., ) suggests that metamorphism persisted until the late Cretaceous. However, younger dates of 72–64 Ma from zircon rims (Cooper & Ireland, , ) and 83–71 Ma from monazite (Mortimer & Cooper, ; Scott et al., ) have also been reported; these are not yet reliably linked to any metamorphic stage, and their significance is yet unclear.…”

Section: Geological Backgroundmentioning

confidence: 99%

“…In addition, both Vry et al (2004) and Cooper and Ireland (2015) suggested that a potentially prolonged late Cretaceous convergent tectonic regime in the Alpine Schist region of the Pacific-Gondwana accretionary complex was caused by collision and partial subduction of the Hikurangi Plateau large igneous province (Figure 1; Reyners, Eberhart-Phillips, & Bannister, 2011). The exact timing of Hikurangi Plateau collision and duration of partial subduction is unclear, but must be younger than c. 122 Ma when the plateau was formed (Neal, Mahoney, Kroenke, Duncan, & Petterson, 1997).…”

Section: Tectonic Implicationsmentioning

confidence: 99%

“…Existing ages for the growth of prograde major and accessory metamorphic minerals in Alpine Schist have been obtained using a variety of methods and mineral chronometers (Sm–Nd and Lu–Hf garnet dating, U–Pb dating of monazite and zircon). The data cover a large range from 100 to 70 Ma for which interpretations differ (Cooper & Ireland, , ; Mortimer & Cooper, ; Scott et al., ; Vry et al., ). The continental arc regions of this subduction margin record extensional orogenic collapse from c .…”

Section: Introductionmentioning

confidence: 99%

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Record of plate boundary metamorphism during Gondwana breakup from Lu–Hf garnet geochronology of the Alpine Schist, New Zealand

Briggs

Cottle

Smit

2018

Journal Metamorphic Geology

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The Zealandia portion of the Pacific–Gondwana margin underwent widespread extension, fragmentation, separation and subsidence during the final stages in the breakup of Gondwana. Although these processes shaped the geology of New Zealand, their timing and the timing of subduction cessation in the region remain unclear. To investigate the timing of these processes, we used Lu–Hf garnet geochronology to date six samples of the Alpine Schist, which represents the metamorphic section of the former Zealandia margin. The garnet dates range from 97.3 ± 0.3 to 75.4 ± 1.3 Ma. Compositional zoning in garnet indicates that the spread in ages results from diachronous metamorphism in the upper plate at the Pacific–Gondwana margin, occurring concurrently with rifting of Zealandia from East Gondwana via opening of the Tasman Sea. Clear spatial trends in the timing of garnet growth throughout the Alpine Schist are absent, indicating that either regional age trends were offset by post‐metamorphic deformation, or that metamorphism did not result from a single regional heat source, and was instead driven by short‐duration, spatially dispersed processes such as episodic fluid‐fluxing or mechanical heating. Diachronous metamorphism of the Alpine Schist can be attributed to heat conduction from the rising upper mantle during widespread extension, progressive burial and heating of accretionary wedge sediments during ongoing horizontal shortening, or fluid‐fluxing sourced from a subducting and dehydrating Hikurangi Plateau. These results indicate that during separation of Zealandia from East Gondwana in the late Cretaceous, the crust at the Pacific–Gondwana margin remained hot, potentially facilitating the extensive thinning of the Zealandia lithosphere during this time.

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