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Stable isotopic signatures of authigenic minerals in a Holocene ophiolitic debris flow, Southland, New Zealand

Published online by Cambridge University Press:  09 July 2018

D. Craw
Affiliation:
Geology Department, University of Otago, PO Box 56, Dunedin, New Zealand
P. Blattner
Affiliation:
Institute of Geological and Nuclear Sciences Ltd, PO Box 31312, Lower Hutt, New Zealand
C. A. Landis
Affiliation:
Geology Department, University of Otago, PO Box 56, Dunedin, New Zealand

Abstract

Authigenic chrysotile, stevensite, calcite, aragonite and pectolite have formed together in a Holocene ophiolitic debris flow in Southland, New Zealand. Mineral growth occurred about 4700-5700 years ago. The temperature of formation of these minerals is estimated from climatological data to be 5–10°C Surface water and groundwater δ180 is currently about –10‰, and was estimated to be about –9.5±1‰ during mineralization. Coexisting calcite (δ180 = +23‰) and aragonite (δl8O = +24‰) were in equilibrium with each other and with the groundwater at 5–10°C Stevensite δ180 is +14 to +16‰, chrysotile has δ180 = +5.5‰, and authigenic pectolite has δ180 near +10‰. Carbon isotope ratios for calcite and aragonite are strongly depleted (δ13C = –13 to –18) which suggests that dissolved CO2 had δ13C below -27. This isotopically light carbon probably resulted from a high organic component of carbon dissolved in the groundwater.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1995

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