Low-temperature geothermal reserves in New Zealand

SummaryEarlier palaeomagnetic studies on the Dunedin volcano showed that a portion of the sequence is reversely or anomalously magnetized. Some of the rocks used for palaeomagnetic study were subsequently classified into groups according to their thermomagnetic behaviour (unpublished work).Cell dimensions and Curie-point curves have been measured for oxides separated from representative rocks of each group. The oxides are mostly homogeneous titanomagnetites containing between 40 and 55 mol. % of ulvöspinel, with a generally small degree of late low-temperature alteration. X-ray and thermomagnetic data also suggest that there was some early oxidation to titanomaghemite, probably during cooling.The thermomagnetic behaviour of rocks classified in the different groups is attributed to variable oxidation of the titanomagnetite during thermomagnetic treatment. The high Curie points of rocks used for palaeomagnetic studies may often be due merely to oxidation of titaniferous magnetite and not to nearly pure primary Fe3O4. Since there is insufficient oxidation in the lavas examined for any currently accepted self-reversal process to have been operative, the reversely magnetized part of the Dunedin sequence was probably erupted during a reversed polarity epoch, possibly between about 13 and 11 million years ago.The basanitic lavas contain minor amounts of chromiferous spinel, as inclusions in silicate phenocrysts and as cores to separate microphyric titanomagnetite; its significance is briefly discussed.

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Screening the New Zealand potato germplasm collection for resistance to sugar accumulation during low temperature storage

New Zealand Journal of Crop and Horticultural Science ◽

10.1080/01140671.1998.9514045 ◽

1998 ◽

Vol 26 (2) ◽

pp. 89-93 ◽

Cited By ~ 2

Author(s):

W. J. Harvey ◽

R. A. Genet ◽

J. P. Lammerink ◽

J. D. Mann

Keyword(s):

New Zealand ◽

Low Temperature ◽

Germplasm Collection ◽

Sugar Accumulation ◽

Low Temperature Storage ◽

Potato Germplasm ◽

Temperature Storage

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Voluminous low temperature rhyolitic magmas in New Zealand

Contributions to Mineralogy and Petrology ◽

10.1007/bf00386111 ◽

1971 ◽

Vol 33 (2) ◽

pp. 128-144 ◽

Cited By ~ 45

Author(s):

A. Ewart ◽

D. C. Green ◽

I. S. E. Carmichael ◽

F. H. Brown

Keyword(s):

New Zealand ◽

Low Temperature

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Electron spin resonance studies of halloysites

Clay Minerals ◽

10.1180/claymin.1987.022.3.03 ◽

1987 ◽

Vol 22 (3) ◽

pp. 287-296 ◽

Cited By ~ 12

Author(s):

N. Chaikum ◽

R. M. Carr

Keyword(s):

Electron Spin Resonance ◽

New Zealand ◽

Low Temperature ◽

Esr Spectra ◽

Octahedral Sheet ◽

Clay Surface ◽

Spin Resonance ◽

Line Resonance ◽

Positive Hole ◽

Paramagnetic Centres

AbstractAbsorption lines in the g ∼ 4 region of ESR spectra of three New Zealand halloysites were found to originate from similar paramagnetic centres as in kaolinites. Resonances in the g ∼ 4 region were not common to all the halloysites, although the signal at g = 2·0 for the Matauri Bay halloysite is probably due to a trapped positive hole or trapped ion. A 6-line resonance produced by Te Puke halloysite and removable by Na-saturation is attributed to exchangeable Mn on the clay surface. Low-temperature lines exhibited by all samples are due to V4+ or VO2+ replacing Al3+ in the octahedral sheet.

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Alkali Metasomatism and the Petrology of Some Keratophyres

Geological Magazine ◽

10.1017/s001675680006341x ◽

1955 ◽

Vol 92 (2) ◽

pp. 104-126 ◽

Cited By ~ 22

Author(s):

M. H. Battey

Keyword(s):

High Temperature ◽

New Zealand ◽

Low Temperature ◽

Mineral Assemblage ◽

Chemical Study ◽

Rhyolite Magma ◽

Textural Evidence

AbstractPetrographic and chemical study of New Zealand keratophyres, occurring in a typical spilite-keratophyre association, shows that they were originally partly glassy flow-rocks and breccias comparable with rhyolites of young volcanic areas. They are now composed of a low temperature mineral assemblage inconsistent with textural evidence of high temperature extrusive origin, and alkali metasomatism has enriched some rocks in soda and others in potash, so that their compositions are symmetrically disposed about that of a primary rhyolite magma with roughly equal amounts of the two alkalis.Data from other occurrences suggest that this condition is common amongst described keratophyres.Though the rocks do not originate from any special magma, the term keratophyre should be retained, with appropriate qualifiers, for old rhyolites with low-temperature mineralogy, which, incidentally, will often be found to have been affected by alkali metasomatism.

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