Major and Trace Element and Sr, Nd, Hf, and Pb Isotope Compositions of the Karoo Large Igneous Province, Botswana–Zimbabwe: Lithosphere vs Mantle Plume Contribution

Enriched continental flood basalts from depleted mantle melts: modeling the lithospheric contamination of Karoo lavas from Antarctica

“…3b) generally ascribed to significant contribution from the underlying Precambrian basement and SCLM (e.g., Ellam 2006;Ellam andCox 1989, 1991;Harris et al 1990;Hawkesworth et al 1984;Jourdan et al 2007a;Luttinen and Furnes 2000;Luttinen et al 1998;Sweeney et al 1991Sweeney et al , 1994Neumann et al 2011). They have traditionally been divided into low-Ti and high-Ti provinces (e.g., Cox 1988;Sweeney et al 1994), but the geochemical and geochronological data are more compatible with a division into (1) ~182 Ma plateau-assemblage CFBs composed of relatively monotonous and widespread low-Ti tholeiites and (2) ~190-174 Ma rift-assemblage CFBs composed of diverse low-Ti and high-Ti basalts and picrites sandwiched between nephelinites and felsic volcanic rocks in the main triple rift ( Fig.…”

“…b Initial Sr and Nd isotopic characteristics of the Vestfjella lavas and Low-Nb dikes (Luttinen et al 1998(Luttinen et al , 2015Luttinen and Furnes 2000). "Lithospheresignatured" Karoo rift-and plateau-assemblage CFBs (Hawkesworth et al 1984;Ellam andCox 1989, 1991;Harris et al 1990;Sweeney et al 1994;Riley et al 2005Riley et al , 2006Jourdan et al 2007a;Luttinen et al 2010;Neumann et al 2011), SWIR MORB (le Roex et al 1983, 1992Mahoney et al 1992), and depleted MORB mantle (DMM; Workman and Hart 2005) also presented. The isotopic compositions of SWIR MORB sources and DMM were back-calculated at 180 Ma using DMM isotopic ratios after Workman and Hart (2005).…”

“…Most CFBs do not represent primary melts, but have differentiated in large magma chambers within the lithosphere (e.g., Cox 1980;Farnetani et al 1996). They generally exhibit strong geochemical affinities to continental rock types and many studies favor significant contributions from geochemically enriched subcontinental lithospheric mantle (SCLM; e.g., Lightfoot et al 1993;Gibson et al 1995;Jourdan et al 2007a;Xu et al 2007). In addition, the widely used assimilation-fractional crystallization (AFC; e.g., DePaolo 1981b) models typically require high degrees (up to 60 wt%) of (subsequent) crustal contamination to explain the most extreme enrichments in incompatible trace element and isotopic compositions (e.g., Carlson et al 1981;Arndt et al 1993;Molzahn et al 1996;Ewart et al 1998;Larsen and Pedersen 2009).…”

“…In the case of contamination with SCLM, the poor knowledge of its bulk composition and thermodynamic parameters (e.g., solidus temperature) limits the applicability of EC-AFC equations. Partial melting of fertile SCLM can be mimicked, however, by using alkaline and ultrapotassic rocks (i.e., low-degree melts of metasomatized SCLM) as contaminants using traditional binary mixing or AFC equations (e.g., Ellam and Cox 1991;Hergt et al 1991;Riley et al 2005;Jourdan et al 2007a).…”

Subduction-modified oceanic crust mixed with a depleted mantle reservoir in the sources of the Karoo continental flood basalt province

“…We therefore suggest that the purported recycled components rather resided in the upper mantle and were entrained into a rising mantle plume (cf. Richards et al, 1989;Riley et al, 2005; scenario 2 of Jourdan et al, 2007) …”