James M. Scott

Aarhus University

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Petrus le Roux

University of Cape Town

Tod E. Waight

University of Copenhagen

Quinten H. A. Van Der Meer

University of Cape Town

J. Michael Palin

University of Otago

Jingao Liu

China University of Geosciences (Beijing)

Steven A. Smith

University of Otago

D. Graham Pearson

University of Alberta

Marshall C. Palmer

University of Otago

Alan F. Cooper

University of Otago

Malcolm Reid

University of Otago

Cooperative Institutions

University of Otago

191

University of Auckland

Chinese Academy of Sciences

Centre National de la Recherche Scientifique

Australian National University

China University of Geosciences (Beijing)

China University of Geosciences

University of Alberta

Search for Extraterrestrial Intelligence

University of Sydney

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Abrupt spatial and geochemical changes in lamprophyre magmatism related to Gondwana fragmentation prior, during and after opening of the Tasman Sea

Gondwana Research (2016)

Quinten H. A. Van Der Meer Michael Storey James M. Scott Tod E. Waight

Dike

Continental Margin

10.1016/j.gr.2016.04.004

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Citations (51)

Emplacement and Paleozoic and Cretaceous recrystallisation of the Broughton Arm Peridotite in Western Fiordland, New Zealand

Figshare (2018)

T. Dwight James M. Scott Joshua Schwartz

Ultramafic rocks are rare on Earth’s surface but can provide important insights into crust and mantle evolution. The recently discovered Broughton Arm Peridotite in the mountains of central Fiordland is exposed as two 75–150 m wide by several hundred metres-long harzburgite-dunite lobes encased sequentially in hornblendite, amphibolite and then quartzofeldspathic gneiss. On the basis of the refractory harzburgitic-dunitic composition and the bulk rock Mg# (86–87) lower than most mantle peridotites, the peridotite is interpreted to have an igneous cumulate rather than an exhumed mantle peridotite origin. The marginal hornblendite and amphibolite and internal pods of edenite-diopside rock may represent metasomatised peridotite. The Broughton Arm Peridotite has been metamorphosed twice. The first event generated an anhydrous assemblage comprising olivine (Mg# = 79.4–92.8), enstatite and Cr-magnetite. This assemblage has been overprinted by an anastomosing weak to pervasive mylonitic foliation of Mg-chlorite, tremolite ± serpentinite ± talc. The age of the anhydrous assemblage is unknown but suspected from regional data to be Early Carboniferous. A titanite ²⁰⁸Pb/²³⁸U lower intercept age of 105.6 ± 6.8 Ma in the host Deep Cove Gneiss is correlated with the peridotite hydration-deformation event. The proximity of the Early Cretaceous (≥ 114 Ma) Western Fiordland Orthogneiss to the east, west and north means that the Broughton Arm Peridotite and surrounding rocks may have recrystallised within the extensional Doubtful Sound Shear Zone, which elsewhere is an up to several hundred meter-wide shear zone active at c. 110–100 Ma separating Western Fiordland Orthogneiss from Deep Cove Gneiss. The Broughton Arm Peridotite therefore preserves a history that involves emplacement in the Early Paleozoic, penetrative anhydrous metamorphism in the Early Carboniferous, and hydration and recrystallisation during regional extensional tectonism in the Early Cretaceous.

Peridotite

10.6084/m9.figshare.7181180

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Rapid characterisation of Mars' mantle reservoirs by in situ laser ablation 87Sr/86Sr analysis of shocked feldspar (maskelynite)

Geochimica et Cosmochimica Acta (2022)

Daniel L. Burgin James M. Scott Petrus le Roux Geoffrey H. Howarth Marshall C. Palmer

Trace element

10.1016/j.gca.2022.11.011

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Carboniferous metamorphism and partial melting of the Greenland Group in the Jackson River valley, south Westland

Figshare (2015)

MC Palmer James M. Scott Janet R. Muhling AK Kennedy

The peak conditions and timing of metamorphism have been determined for the early Paleozoic Greenland Group in south Westland, New Zealand. The Greenland Group, which is the most extensive pre-Cenozoic unit west of the Alpine Fault in Westland, is dominated by greenschist facies greywacke and argillite. However, in the Jackson River valley this unit comprises amphibolite facies pelitic and psammitic gneisses. Psammitic horizons are dominated by biotite, plagioclase and quartz. Pelitic horizons have similar mineralogy but also contain sillimanite and K–feldspar, as well as boudinaged K–feldspar-bearing leucosomes. Conventional geothermometry and thermodynamic modelling indicate that peak metamorphism occurred between 660 and 700 °C and 3.5 and 6.0 kbar. The timing of this moderately high–T/low–P event is constrained to be mid-Paleozoic by U–Th–Pb dating of overgrowths on detrital zircon (334 ± 18 Ma) and confirmed to be Carboniferous by a single population of monazite grains (343 ± 3 Ma). Greenland Group metamorphism in the Jackson River valley may represent Carboniferous high crustal heat flow in the Gondwana margin hinterland while crustal thickening was occurring closer to the subduction zone.

10.6084/m9.figshare.1286795

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Cretaceous metamorphism, magmatism and shearing in the Waipuna Valley, directly south of the Reefton Goldfield

Figshare (2015)

TW Ritchie James M. Scott Janet R. Muhling AK Kennedy

Rocks in the Waipuna Valley in Westland show that the area immediately south of the Reefton Goldfield has been dramatically affected by Cretaceous tectonism. The main lithology in the Waipuna Valley is metasedimentary Greenland Group that is here subdivided into four types (I, II, III and IV). Type I contains abundant detrital grains with a weak Palaeozoic greenschist facies overprint and is compositionally indistinguishable from unmineralised Greenland Group within the goldfield. Type II contains detrital grains, but also a weak amphibolite facies foliation or, where proximal to granitoid intrusions, a hornfelsic texture. Type III contains no detrital components and records polyphase recrystallisation. U–Th–Pb monazite dating indicates that metamorphism in the Type III rocks occurred, at least in part, at 108.1 ± 1.2 Ma. Type IV Greenland Group has partially melted. Zircon from granitoids intruding Greenland Group in the Waipuna Valley indicate Cretaceous (c. 111 Ma) emplacement. Greenland Group Types III and IV, and the granitic plutons, have been variably sheared with quartz textures indicating progressive cooling during deformation. A mylonite zone occurs just above outcrop of the Type IV rocks. Field and age relationships are interpreted to show that the Waipuna Valley exposes portions of an upper plate and lower plate to a Cretaceous ductile shear zone that is here named the Waipuna Shear Zone. The overall structure is similar to the nearby Cretaceous extensional Paparoa Metamorphic Core Complex. The Reefton Goldfield lies in the upper plate to the Waipuna Shear Zone, not far above the mylonite zone. Cretaceous metamorphism and shearing of Greenland Group could have aided formation and then transport of gold-bearing fluids into structurally higher rocks.

Shearing (physics)

10.6084/m9.figshare.1290943

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Cretaceous igneous-related mineralisation in the Reefton Goldfield, New Zealand

New Zealand Journal of Geology and Geophysics (2018)

Jim E. Dickie James M. Scott Matthew W. Sagar Hamish Blakemore

The Reefton Goldfield is well known for its orogenic style of Au mineralisation although the timing remains largely unconstrained. Here, a first unequivocal occurrence of igneous-related mineralisation is documented and it is suggested to place a lower age constraint on when orogenic Au mineralisation occurred. Emplacement of the 118.5 ± 1.3 Ma (U-Pb zircon) Blackwater granitoid dike into Early Paleozoic Greenland Group caused contact metamorphism up to hornblende hornfels facies temperatures (>500°C) at low pressures (<3.75 kbar). A hydrothermal convective system that developed during cooling led to propylitic and phyllic alteration associated with the precipitation in order of decreasing abundance of: pyrite, chalcopyrite, molybdenite, arsenopyrite-galena-sphalerite-millerite. Quartz veins and stockworks containing combinations of pyrite, chalcopyrite and molybdenite are common within several hundred metres of the dike. This igneous-related mineralisation overprints Greenland Group metasedimentary rocks displaying evidence for a phase of ductile deformation and associated with the occurrence of pyrite and ankerite-cored siderite porphyroclasts, chalcopyrite and cobaltite. Au-in-pyrite trace element data indicate that these pyrite porphyroclasts are more enriched in Au than the pyrite associated with dike emplacement. Quartz lodes containing Au occur within zones of ductile deformation elsewhere in the goldfield, and therefore Early Cretaceous emplacement of the Blackwater dike provides a lower age constraint for the ductile mineralisation event.

Hornblende

10.1080/00288306.2018.1529684

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The subantarctic lithospheric mantle

Geological Society London Memoirs (2021)

Guillaume Delpech James M. Scott Michel Grégoire Bertrand Moine Dongxu Li

Abstract We present a summary of peridotite in the Subantarctic (46–60° S) surrounding the Antarctic Plate. Peridotite xenoliths occur on the Kerguelen Islands and Auckland Islands. The Kerguelen Islands are underlain by a plume, whereas the Auckland Islands are part of continental Zealandia, which is a Gondwana-rifted fragment. Small amounts of serpentinized peridotite has been dredged from fracture zones on the Southeast Indian Ridge, Southwest Indian Ridge and Pacific Antarctic Ridge, and represent upwelled asthenosphere accreted to form lithosphere. Suprasubduction-zone peridotite was collected from two locations on the Sandwich Plate. Peridotites from most subantarctic occurrences are moderately to highly depleted, and many show signs of subsequent metasomatic enrichment. Os isotopes indicate that subantarctic continental and oceanic lithospheric mantle contains ancient fragments that underwent depletion long before formation of the overlying crust.

Peridotite

Asthenosphere

Mantle plume

10.1144/m56-2020-13

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Citations (8)

A possible Late Oligocene–Early Miocene rocky shoreline on Otago Schist

New Zealand Journal of Geology and Geophysics (2013)

James M. Scott De Lee R. Ewan Fordyce JM Palin

Duntroonian–Waitakian limestone at Kokonga in the Maniototo district, Central Otago, New Zealand is interpreted to be a rocky shoreline facies formed near the time of maximum Cenozoic marine transgression across Zealandia. The limestone, which is correlated with the Otekaike Limestone of North Otago, contains shallow and warm water indicators such as coralline algae, oysters, echinoderms, bryozoa and a foraminiferal assemblage composed almost entirely of Amphistegina. Textural zone 2B Otago Schist cobbles, pebbles and sand within the limestone, often adjacent to invertebrate fossil and coralline algal fragments, were sourced from proximal schist exposures and may be indirect evidence of the limestone having formed near to a low-lying Otago Schist coastline. However, because the precise age of limestone deposition cannot be constrained by fossil assemblages or Sr isotopes and the timing of peak marine transgression is imprecisely known, it is not possible to state whether Otekaike Limestone at Kokonga formed before, during or after the peak of maximum Cenozoic marine transgression.

Marine transgression

Coralline algae

Rocky shore

10.1080/00288306.2013.814575

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Citations (12)

Chemical reactions trigger fluid overpressure and shear failure in plate boundary-scale serpentinite shear zones

AGUFM (2018)

Matthew S. Tarling Steven A. Smith James M. Scott

Overpressure

Source

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Late Devonian contact metamorphism and a possible upper age to gold mineralisation in the northernmost portion of the Reefton Goldfield

New Zealand Journal of Geology and Geophysics (2018)

Bryce A. Robinson James M. Scott

The 378–370 Ma Dunphy Granite has contact metamorphosed Greenland Group metasedimentary rocks in the Awarau/Larry River valley in the northernmost portion of the Reefton Goldfield in Westland. Hornblende hornfels facies Greenland Group occurs up to ∼1300 m of the granite contact, followed by albite-epidote hornfels facies assemblages between ∼1300 and 2000 m from the granite, after which the rocks retain Early Paleozoic greenschist facies assemblages. The historic Caledonian goldmine is located on a fault zone within hornfels facies rocks. There is a complex mineralisation paragenesis in samples obtained from the mine area in which quartz, gold, arsenopyrite, pyrite with minor galena and chalcopyrite formed in quartz veins and brecciated Greenland Group. Fractures in the early-formed minerals and rocks contain quartz, minor galena and molybdenite and oligoclase and biotite. Although the poor exposure and collapsed mine workings prohibit firmly establishing the relationship of mineralisation to the contact aureole, hand specimen and optically observed textures indicate that mineralisation is hosted in a brittle fault zone that most likely cuts across the hornfels facies rocks. Mineralisation is therefore interpreted to post-date formation of the Late Devonian contact aureole at 378–370 Ma.

Hornfels

Greenschist

Batholith

Paragenesis

Arsenopyrite

Hornblende

10.1080/00288306.2018.1534745

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Citations (4)