Mixed pyroxenite-peridotite sources for mafic and ultramafic dikes from the Antarctic segment of the Karoo continental flood basalt province

Heinonen, Jussi S.; Luttinen, Arto V.; Riley, Teal R.; Michallik, Radoslaw M.. 2013 Mixed pyroxenite-peridotite sources for mafic and ultramafic dikes from the Antarctic segment of the Karoo continental flood basalt province. Lithos, 177. 366-380. 10.1016/j.lithos.2013.05.015

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Primitive rocks that are related to continental flood basalts are rare, but often reveal crucial information on the ultimate sources of these huge outpourings of mantle-derived magma. Here we present mineral chemical data for mafic and ultramafic dikes from the Antarctic extension of the Jurassic (~ 180 Ma) Karoo continental flood basalt province that was emplaced during the initial stages of the breakup of the Gondwana supercontinent. We concentrate on two previously recognized high-Ti dike rock suites (Group 3 and Group 4) that exhibit high MgO contents (up to 22 wt. %). Both groups are characterized by Mg-rich olivine phenocrysts (up to Fo90) that are not mantle xenocrysts and indicate derivation from relatively Mg-rich parental magmas. Orthopyroxene is a common phenocryst and groundmass phase indicating emplacement at mid-crustal pressures (2–5 kbar; depth of ~ 10–20 km). The parental magmas of Group 3 and Group 4 dikes can be associated with pyroxenite sources on the basis of high olivine NiO, high whole-rock Zn/Fe, and low whole-rock CaO. In the case of Group 3 dikes, however, the samples that contain the most Mg-rich olivine also exhibit the mildest pyroxenite fingerprint and indications of an additional olivine-bearing (peridotitic) source component. We propose that the pyroxenite fingerprint of Group 3 and Group 4 dikes reflects relatively low-degree melting of fertile mantle at high pressures beneath the thick and cold Gondwanan lithosphere. Such conditions limited high-degree melting of peridotite sources which may have been predominant in the generation of the Karoo low-Ti basalts within lithospheric thinning zones.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.lithos.2013.05.015
Programmes: BAS Programmes > Polar Science for Planet Earth (2009 - ) > Environmental Change and Evolution
ISSN: 00244937
Additional Keywords: Large igneous province; Continental flood basalt; Karoo; Picrite; Pyroxenite; Mantle source
NORA Subject Terms: Earth Sciences
Date made live: 14 Jun 2013 12:39 +0 (UTC)

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