Yosuke Kawachi

Pumpellyite-actinolite and contiguous facies metamorphism in part of Upper Wakatipu District, South Island, New Zealand

Abstract Metamorphic minerals from pumpellyite-actinolite and contiguous facies in the Upper Wakatipu district, South Island, New Zealand, have been studied using optical and X-ray diffraction methods, and electron microprobe analyser. Analyses are given for chlorite, garnet, prehnite, stilpnomelane, alkali-amphibole, actinolite, pumpellyite, epidote, and muscovite. The area is divided into four progressive metamorphic zones. Mineralogical change is summarised. Plagioclase feldspars are all low albite. Muscovite is ubiquitous in all zones except for a few mafic rocks. Analysed muscovites are mildly phengitic. The composition is not related to grade, but is related to host rock composition. Refractive indices of muscovites are rather low and indicate a lower celadonite content than those of eastern Otago and the Sambagawa zone. Basal spacing of muscovites do not differ much between zones or rock types. Epidote is common throughout the area, especially in mafic rocks. The compositional range is fairly narro...

Geology and petrochemistry of weakly metamorphosed rocks in the upper Wakatipu district, southern New Zealand

Abstract The area near the head of Lake Wakatipu lies between the Livingstone Fault to the west, and the Otago Schist terrane to the east. The area is divided into three major tectonic slices or subareas by north-striking faults. A eastward-younging sequence of Caples Group strata in the western-subarea is subdivided into four informal units consisting predominantly of volcanogenic sediments, feldspathic sandstone, tuff and tuffaceous sandstone, and grey sandstone and slate respectively. The Greenstone Ultramafite Belt, which separates the western subarea from the middle subarea, is interpreted as a tectonic melange of serpentinite, metagabbro, mafic volcanic and meta-sedimentary rocks. The synclinal Bold Peak unit, predominantly rhythmically alternating green sandstone and slate, occupies the middle subarea and is separated by an important inferred fault, the West Wakatipu Fault, from the eastern subarea which represents the western limit of the Haast Schist of Central Otago. Five metamorphic zones are r...

Andradite and andradite-grossular solid solutions in very low-grade regionally metamorphosed rocks in Southern New Zealand

AbstractAlmost pure andradite and intermediate members of the andradite-grossular series (gros40–49, and 47–54, py0–3, alm0–3, spess0–2, hydrogarnet0–3), often framboidal in habit, are widespread in metabasites including lavas, minor intrusions, and volcanic sandstones and breccias metamorphosed under prehnite-pumpellyite and pumpellyite-actinolite facies conditions, possibly extending into the zeolite facies. Coexisting phases include iron-rich epidotes (100 Fe*/Fe*+Al=22–34), pumpellyite, prehnite, actinolite, and chlorite, electron microprobe analyses of which are given, as well as quartz, albite, and calcite. Zoisite (100 Fe*/Fe*+Al=1–5) and iron-poor epidote (100 Fe*/Fe*+Al=11–18) occur in 2 rocks in pseudomorphs after plagioclase together with more iron-rich epidote, but not in close association with the garnets. Coexisting pumpellyite is iron-rich (FeO* 9–14%) in the prehnite-pumpellyite facies and iron-poor (FeO* 5%) in the pumpellyiteactinolite facies. Chlorites and actinolites vary widely and sympathetically in FeO/MgO+FeO ratio. Andradite is also described from a stilpnomelane-actinolite-hematite-bearing andradite quartzite of the pumpellyite-actinolite facies.Conditions of formation involved temperatures of 300 to 400 ° or less, at pressures up to a few kilobars. A wide range of oxygen fugacities is possible, but

Geochemistry and origin of piemontite-bearing and associated manganiferous schists from Arrow Junction, western Otago, New Zealand

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Multiple-rind structure in pillow lava as an indicator of shallow water

in the fluid phase was low. Grandite and chlorite are incompatible in the pumpellyite-actinolite and greenschist facies in the presence of quartz but the 2 minerals occur together in some pumpellyite-actinolite facies assemblages as a result of incomplete reaction and/or local deficiency in silica. In the greenschist facies the association is replaced by epidote-actinolite±hematite and sodic amphibole.Whereas at medium to high grades of metamorphism andradite and grandite are characteristic of skarns irrespective of

Geochemistry of dike rocks in Dun Mountain Ophiolite, Nelson, New Zealand

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