A ~2.051 Ga anatectic event and peraluminous leucogranite from the Mahalapye Complex, northern edge of the Kaapvaal Craton: Record of an effect of Bushveld mafic magmatism

Rajesh, H.M.; Safonov, O.G.; Belyanin, G.A.; Vorster, C.

Авторы: Rajesh H.M., Safonov O.G., Belyanin G.A., Vorster C.
Журнал: Lithos
Том: 378
Год издания: 2020
Издательство: Elsevier BV
Местоположение издательства: Netherlands
Номер статьи: 105805
DOI: 10.1016/j.lithos.2020.105805
Аннотация: Anatectic events and related leucogranites are rarely reported from Precambrian large igneous provinces (LIPs). However, their appearance is possible in relation to the intrusion of later pulses of maficmagmas into the earlierrocks. Silicic intrusive rocks associated with the ~2.06–2.05 Ga Bushveld LIP within the Kaapvaal Craton include granites, syenites or granophyres. This study reports syn-Bushveld partial melting of ~2.061 Ga diorite gneiss producing leucogranite from theMahalapye Complex high-grade terrane, at the northern edge of the Kaapvaal Craton. Both the migmatitic diorite gneiss and associated leucogranite are crosscut by the ~2.039 Ga granodiorite. The different stages of melting of the biotite-bearing diorite gneiss – from onset of melting to melt segregation – are well preserved. Petrographic continuity between the leucosomes, and concordant and discordantleucogranite bodies point to a melt flow-accumulation network. Garnet formed after biotite during partial melting. Phase equilibriamodelling and conventional thermobarometry indicate conditions of ~730 °C and ~7.2–7.5-kbar for the anatectic event. The predictedmelt composition is peraluminous,magnesian and alkali-calcic, that is comparable to the chemistry of leucogranites. The low content of anatectic melt for the estimated P-T conditioncorresponds to the occurrence of leucogranites as thin veins to dykes. LA-MC-ICPMS U–Pb zircon age of 2051.3±6.8Ma is interpreted to date the anatectic event. The leucogranite exhibits co-mingling structures with dyke-like and sill-like syn-Bushveld norite intrusions associated with diorite gneiss. Preferential accumulation of the leucocraticmaterial along the contact of diorite gneiss and norite, and the liquid-liquid interfacewith the norite,indicate the close age of leucogranite and norite. This is supported by the LA-Q-ICPMS U–Pb zircon age of 2054±7.9Ma fromthe norite. Thus, the partial melting of the diorite gneiss and formation of the leucogranites is arguedas a response to Bushveld mafic magmatism. The present study shows that one of the causative agents of overprint event(s) in high-grade terranes along Archean cratonic margins can be mafic magmatism of similar age within the craton. However, in the case of LIP-related magmatismthe footprints are restricted to terranes immediately adjacent to the cratonic margins.
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A ~2.051 Ga anatectic event and peraluminous leucogranite from the Mahalapye Complex, northern edge of the Kaapvaal Craton: Record of an effect of Bushveld mafic magmatismстатья

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