18O/16O and chemical relationships in K-rich volcanic rocks from Australia, East Africa, Antarctica, and San Venanzo-Cupaello, Italy

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doi: 10.1016/0012-821X(84)90186-9
Authors:Taylor, Hugh P., Jr.; Turi, Bruno; Cundari, Aldo
Author Affiliations:Primary:
Calif. Inst. Technol., Div. Geol. and Planet. Sci., Pasadena, CA, United States
Univ. Roma, Ist. Geochim., Italy
Univ. Melbourne, Dep. Geol., Australia
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 69(2), p.263-276. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:1984
Note:In English. 44 refs.; illus. incl. 1 table
Summary:18O/16O analyses were made on a set of leucite-bearing igneous rocks from five localities around the world. The samples chosen for study all have primitive characteristics, such as low SiO2 contents (42-52 wt.%). Whole-rock delta 18O values from the 10-15 m.y. old Australian leucitites range +7.1 - +11.0per mille, but none represents the original delta 10O of the erupted lavas, because every sample has undergone some subsolidus 18O enrichment. The delta 18O values of the primary magmas can be accurately calculated. The leucite mineral separates (pure, stoichiometric KAlSi2O6) have clearly not retained the primary igneous O isotopic compositions. The whole-rock delta 18O values show a positive correlation with H2O+ contents, and extrapolation to a plausible water content for such a subaerially erupted lava (<0.5 wt.% H2O) gives a range of primary delta 18O values of +5.8 - +6.8per mille. The much less hydrated Bufumbria, Africa, and Gaussberg, Antarctica, samples have delta 18O +6.7 - +7.9 and +6.1 - +7.0 respectively. The San Venanzo, Italy, samples are even less hydrated, so their extremely high delta 18O values of +10.8 - +12.0 are definitely magmatic values. The leucite-bearing magmas erupted in north-central Italy are unique in having much higher delta 18O values than potassic rocks from southern Italy or anywhere else in the world. The northward increase in delta 18O is thus clearly a manifestation of progressively greater interaction between mantle-derived magmas and the high-18O sedimentary and metasedimentary rocks of the Italian continental crust, which were strongly heated during the episode of Tuscan anatectic granitic magmatism. [P.Br.]
Subjects:Alkali metals; Alkaline earth metals; Framework silicates; Genesis; Geochemistry; Igneous rocks; Isotopes; Leucite; Leucitite; Magmas; Metals; Nd-144/Nd-143; Neodymium; O-18/O-16; Oxygen; Potassium; Rare earths; Silicates; Sr-87/Sr-86; Stable isotopes; Strontium; Volcanic rocks; Africa; Antarctica; Australasia; Australia; Central Africa; Congo Democratic Republic; East Africa; East African Lakes; Europe; Italy; Lake Kivu; New South Wales Australia; Rwanda; Southern Europe; Uganda; Bufumbira; Cupaello; Gaussberg; San Venanzo; Zaire
Abstract Numbers:85M/1653
Record ID:1985016319
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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