Luenha picrites, Central Mozambique – Messengers from a mantle plume source of Karoo continental flood basalts?

• Published in: Lithos
• Main Authors: Turunen, Sanni T., Luttinen, Arto V., Heinonen, Jussi S., Jamal, Daúd L.
• Other Authors: Natural Sciences Unit, Finnish Museum of Natural History, University Management, Department of Geosciences and Geography, Staff Services
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier Scientific Publ. Co 2019
• Subjects: Geosciences; Picrite; Flood basalt; Mantle source; Large igneous province; Mantle plume; DRONNING-MAUD-LAND; TRACE-ELEMENT COMPOSITION; PERIDOTITE SOURCES; MELT INCLUSIONS; DEPLETED MORB; OLIVINE; ANTARCTICA; MAGMAS; LITHOSPHERE; Dronning Maud Land; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/10138/306192

We present geochemical and isotopic (Nd, Sr) data for a picrite lava suite from the Luenha River and adjacent areas in Mozambique. The Luenha picrites represent a previously unknown type of picrites related to the Karoo large igneous province (LIP) and are distinguished by their notably low TiO2 contents (0.3-1.0 wt%) and coupling of high Nb/Y with low Zr/Y and Sm/Yb. Relatively high CaO and low Zn/Fe point to a peridotitic mantle source. Contamination-sensitive incompatible element ratios show that one lava flow is likely to be uncontaminated by the crust and its composition suggests a mantle source with primitive mantle-like incompatible element ratios and mildly depleted isotopic ratios (initial Sr-87/Sr-86 = 0.7041 and epsilon(Nd) = +1.4 at 180 Ma). The primary melts of the Luenha picrites had MgO contents in the range of 13-21 wt%. Our preferred estimate for a primary melt composition (MgO = 18 wt%) resembles experimental melts of fertile mantle peridotite at 3-4 GPa and indicates liquidus temperature of 1445-1582 degrees C. Geochemical similarities suggest the Luenha picrites were generated from the same overall primitive mantle-like reservoir that produced the main volume of Karoo flood basalts in the Karoo, Kalahari, and Zambezi basins, whereas the previously identified enriched and depleted (upper) mantle sources of Karoo picrite suites (Mwenezi, Antarctica) were subordinate sources for flood basalts. We propose that the Luenha picrites record melting of a hot, chemically primitive mantle plume source that may have been rooted in the sub-African large low shear velocity province boundary and that such a source might have been the most significant magma source in the Karoo LIP. (C) 2019 The Author(s). Published by Elsevier B.V. Peer reviewed