S13—Cobb: A review of the new map and the structural interpretation of the Central Belt rocks of S13 and S8

Emplacement depths of 33 rocks from 27 Paleozoic and Mesozoic plutons from western New Zealand have been estimated utilising the hornblende-AI barometer of Anderson and Smith. Emplacement depths for plutons from the Median Batholith/Median Tectonic Zone (Median and Separation Point Suites) plutons range from 8 to 27 km. The greatest emplacement depths are found along the western edge of the batholith, in areas dominated by plutons of the Separation Point Suite; together with geochronological data they suggest significant uplift in the interval 118 to c. 110 Ma. Emplacement depths of c. 8-10 km are typical along the eastern side of the batholith in mainly Triassic plutons. No trend along the length of the batholith is apparent. Plutons associated within the lower plates of metamorphic core complexes were emplaced in the range 19-23 km, and were uplifted over a similar, but possibly slightly later, time interval. No significant consistent difference in amphibole type or chemistry was observed between the suites. Epidote believed to be of magmatic origin occurs in 11 plutons which record emplacement pressures of 3.1 kbar or greater, in conflict with the notion that such epidote indicates pluton emplacement pressures 6-8 kbar.

Section: Median Batholithsupporting

confidence: 68%

Section: Median Batholithmentioning

confidence: 99%

Section: Median Batholithmentioning

confidence: 99%

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Emplacement depths of Paleozoic‐Mesozoic plutons from western New Zealand estimated by hornblende‐AI geobarometry

Tulloch

Challis

2000

“…The faults are interpreted to be part of an east-west-directed listric system with duplexing that formed during latest Silurian to Early Devonian tectonism (Cooper & Tulloch 1992), but they are likely to have had a complex history over a long period of time. Grindley 1961Grindley , 1971Grindley , 1980Bishop 1971) The Takaka Terrane which includes the gersdorffite and related sulphide localities described in this paper, consists of a variable assemblage of Cambrian volcanics, volcaniclastics, carbonates, quartzites, and quartzofeldspathic sediments (Grindley 1971(Grindley , 1980Coleman 1981;Powell 1986), and Ordovician/Silurian quartz-rich elastics, carbonates, and minor basic volcanics (Grindley 1971;Bishop 1971;Wodzicki 1972). Middle-late Cambrian rocks are associated with an ophiolitic ultramafic-mafic association (Cobb Igneous Complex) of mid-Cambrian age (Hunter 1977).…”

Section: Geologic Settingmentioning

confidence: 99%

Gersdorffite with pentlandite, violarite, pyrrhotite, and pyrite, northwest Nelson, New Zealand

Grapes

Challis

1999

Gersdorffite (NiAsS), only reported in New Zealand in 1887 from the Richmond Hill area, has been found in two further localities in northwest Nelson. Gersdorffite has been relocated in a quartz-veined ophicarbonate at Parapara River near Richmond Hill, and has average compositions of (Fe 0.21 , and minor pyrite. The Ni-As-Fe sulphides at Parapara River and Calphurnia Creek are products of talccarbonate facies alteration of ultramafic rock during early Paleozoic (Pre-Baton Event) regional greenschist facies metamorphism, with temperatures of sulphidation ranging between c. 300 and <100°C (below that of associated silicate/carbonate assemblages of 320-490°C), -33 to -30 logƒO 2 , c. -1 to -1.3 logΣS, and between c. -0.9 and -0.11 logƒS in the fluid phase; the presence of gersdorffite requires the introduction of As ± Bi from a carbonate-bearing fluid. At Contact Creek, arsenic was introduced into the fuchsite quartzite by hydrothermal fluids from the nearby Early Cretaceous Onahau Granite that also transported nickel and cobalt scavenged from a lens of antigorite-talc-magnesite within the pluton. Temperatures of gersdorffite and an initial metal solid solution (mss) formation at Contact Creek were between c. 500 and >380°C, the mss subsequently exsolving G98001

“…Arthur Marble (Ordovician) is extensively exposed on the Pikikiruna Range and is faulted against the main part of the Separation Point Batholith. Onekaka Schist was derived by metamorphism of predominantly siliceous sedimentary rocks of Silurian age (Grindley 1980) and is cut in the area south of Holyoake Stream by intrusive basic sheets of the Riwaka Igneous Complex (Upper Devonian to Carboniferous). These three formations are cut by several tongue-like intrusions of Canaan Granodiorite; radiometric dating of this rock at Canaan gives a late Early Cretaceous age, similar to dates determined elsewhere in the Separation Point Batholith (Grindley 1980;Muir et al 1994).…”

Section: Introductionmentioning

confidence: 99%

Petrography and genesis of a wollastonite body and its associated rocks at Holyoake Valley, Nelson, New Zealand

Watters¹

1995

Samples from a wollastonite-rich lens, up to 55 m long and 10 m wide, within the contact aureole of the Canaan Granodiorite at Holyoake Valley, include a variety of calc-silicate rocks which locally contain abundant titanite. The mineralogy of the contact rocks indicates hornblendehornfels facies conditions during metamorphism. Within the wollastonite body, an intrusive vein of monzonitic composition, up to 2 m across, probably resulted from crystallisation of granodioritic magma modified by partial desilication and contamination from adjacent calcium-rich rocks. Zoned calc-silicate rocks, apparently formed by reaction between wollastonite and basic hornfels that had been produced by recrystallisation of a dike of probable basaltic composition, are also present. Late intrusion of small amounts of quartzofeldspathic magma took place along discontinuities, including the dike boundaries, within and adjacent to the wollastonite body. Iron and titanium metasomatism was probably associated with intrusion of the quartzofeldspathic magma, while diffusion of calcium towards it led to the formation of heterogeneous contaminated rocks interpreted as endoskarns.Available evidence is insufficient to allow a decision to be made between formation of the wollastonite by reaction between marble and enclosed quartz-rich layers or lenses, or by introduction of silica into marble from the adjacent granodiorite magma. Formation of the contact rocks probably took place with low values of XCO 2 relative to XH 2 O in the fluid phase. Late changes accompanying cooling of the contact rocks in the presence of a fluid with high XH 2 O resulted in the crystallisation of small amounts of retrograde vesuvianite, prehnite, and apophyllite.