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¹⁸O-depleted igneous rocks from the Tertiary complex of the Isle of Mull, Scotland

Forester, Richard W. and Taylor, Hugh P., Jr. (1976) ¹⁸O-depleted igneous rocks from the Tertiary complex of the Isle of Mull, Scotland. Earth and Planetary Science Letters, 32 (1). pp. 11-17. ISSN 0012-821X. doi:10.1016/0012-821x(76)90178-3.

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New oxygen isotope analyses have been obtained on 31 rocks and minerals from the Tertiary ring-dike complex on the Isle of Mull, Scotland. Whole-rock δ18O values (SMOW) of basalts range from +9.1 to −6.5, and systematically decrease toward the central plutonic complex. The δ18O values of the intrusive igneous rocks systematically increase with successively younger ages of emplacement, presumably because the meteoric-hydrothermal systems decreased in intensity with time, as a result of waning igneous activity and mineral deposition within the conduit fractures. Whole-rock δ18O values of intrusions around the Beinn Chaisgidle center show a narrow range from −3.9 to −1.5, whereas those about the later Loch Ba center can be divided into two groups, the earliest with δ18O = −3.3 to +0.5, and the latest with δ18O = +1.0to+3.4. All of the rocks within the “limit of pneumatolysis”, a zone of hydrothermal contact metamorphism that lies 4–6 km outward from the central intrusions, are depleted in18O, some by as much as 13‰. These effects are observed over an area of 500 km2, and were produced by meteoric-hydrothermal convective circulation of early Tertiary ground waters, which apparently had initial δ18O values of about −11 to −12.

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Alternate Title:18O-depleted igneous rocks from the Tertiary complex of the Isle of Mull, Scotland
Additional Information:We thank Sam Epstein for the use of some of his laboratory facilities. This research was supported by National Science Foundation Grants GA-12945 and GA-30997X, and by the Phelps Dodge Fund and National Research Council of Canada Grant A8698.
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Phelps Dodge FundUNSPECIFIED
National Research Council of CanadaA8698
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Caltech Division of Geological and Planetary Sciences2721
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ID Code:116439
Deposited By: Tony Diaz
Deposited On:30 Aug 2022 20:25
Last Modified:31 Aug 2022 17:08

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