The mantle origins of Karoo picrites

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doi: 10.1016/0012-821X(91)90075-S
Authors:Sweeney, R. J.; Falloon, T. J.; Green, David H.; Tatsumi, Y.
Author Affiliations:Primary:
Univ. Tasmania, Geol. Dep., Hobart, Tasmania, Australia
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 107(2), p.256-271. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:1991
Note:In English. 55 refs.; illus. incl. 2 tables, geol. sketch map
Summary:These picrites are divided into a volumetrically high Ti-Zr (HTZ) group and a less abundant low Ti-Zr (LTZ) group. It is then possible to use the comparison of major element compositions with those of experimentally determined partial melts of mantle peridotites to constrain the depth of segregation for each magma type. This approach also identifies the nature of source and residual mantle materials from which such magma segregation may have occurred. The LTZ group show uniformly shallow P (10- >30 kbar) of segregation which are correlated with incompatible element abundance. The K2O, TiO2 and Zr contents are greater in those HTZ picrites which indicate greater segregation P (here called the high-NaKTZ group). The HTZ picrites segregated from sources as or more refractory than MORB or OIB sources, whereas the LTZ picrites segregated from sources more refractory than MORB or OIB. A model for Karoo magmatism can be constructed in which the high-NaKTZ group represents the first eruptions and may derive from a deep metasomatized source in the mantle lithosphere underlying cratonic regions. With the start of rifting and asthenospheric upwelling this magma extraction would move to shallower depths and reflect an increasing dominance of the asthenospheric component. The low-MgO LTZ basalts then represent the final and most voluminous basaltic eruption prior to or synchronous with the disruption of Gondwana. Their source is inferred to be shallow-level mantle lithosphere. [R.E.S.]
Subjects:Alkali metals; Classification; Differentiation; Genesis; Geochemistry; Igneous rocks; Karoo Supergroup; Magmas; Major elements; Mantle; Metals; Mineral composition; Picrite; Segregation; Titanium; Trace elements; Ultramafic composition; Volatiles; Zirconium; Africa; East Africa; Mozambique; South Africa; Southern Africa; Transvaal region; Zimbabwe; Transvaal South Africa
Abstract Numbers:92M/3019
Record ID:1992005166
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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