Oxygen isotope evidence for large-scale hybridization of the lower crust during magmatic underplating

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doi: 10.1016/0016-7037(92)90041-G
Authors:Kempton, Pamela D.; Harmon, Russell S.
Author Affiliations:Primary:
NERC Isot. Geosci. Lab., Keyworth, United Kingdom
Aust. Natl. Univ., Australia
Volume Title:Taylor Colloquium; Origin and evolution of planetary crusts
Volume Authors:McLennan, Scott M., editor; Rudnick, Roberta L.
Source:Geochimica et Cosmochimica Acta, 56(3), p.971-986; The Taylor Colloquium; Origin and evolution of planetary crusts, Canberra, Australia, Oct. 1-2, 1990, edited by Scott M. McLennan and Roberta L. Rudnick. Publisher: Pergamon, Oxford, International. ISSN: 0016-7037
Publication Date:1992
Note:In English. 81 refs.; illus. incl. 2 tables
Summary:Oxygen-isotope data with summarized bulk compositions, mineralogy and radiogenic isotope analyses are presented for granulite xenoliths from an Archaean stable cratonic site (Bearpaw Mts, Montana, USA), and 7 Proterozoic crustal areas affected by folding and/or rifting (Geronimo, Arizona; Eifel, Germany; Massif Central, France; Tariat and Dariganga, Mongolia; Chudleigh and McBridge, Australia). Subduction, terrain accretion and/or continental collision have been involved in the development of the deep crust sampled at these sites. The large range in O isotope ratios (delta18O +5.4 to +13.5 per mille) for these granulite xenoliths indicates that the present lowermost crust is very heterogeneous in its O isotope composition. Mafic granulites with mg numbers > 0.7 show the smallest range and average delta18O value of all the granulites. Silicic meta-igneous granulites and metasediments are enriched in 18O relative to other granulite groups with the widest range of delta18O. Pervasive deep crustal fluid flow and isotopic homogenization is not significant regionally. Contamination (20-50%) by an 18O- enriched component is required to account for the 18O/16O ratios of most mafic granulites. Reasons for these ratios in other groups are discussed, and may explain the rarity of restites in lower crustal xenolith suites. [R.K.H.]
Subjects:Crust; Granulites; Hybridization; Inclusions; Isotopes; Lower crust; Metamorphic rocks; O-18/O-16; Oxygen; Stable isotopes; Xenoliths; Evolution; Ratios
Abstract Numbers:92M/4277
Record ID:1992012441
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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