Conditioned duality between supercontinental ‘assembly’ and ‘breakup’ LIPs

Abstract

A compilation of 178 more precise ages on 10 potential Large Igneous Provinces (LIPs) across southern Africa, is compared to Earth’s supercontinental cycles, where 5 more prominent LIP-events all formed during the assembly of supercontinents, rather than during breakup. This temporal bias is confirmed by a focused review of field relationships, where these syn-assembly LIPs formed behind active continental arcs; whereas, the remaining post-assembly – and likely breakup-related – LIPs never share such associations. Exploring the possibility of two radically different LIP-types, only the two younger breakup events (the Karoo LIP and Gannakouriep Suite) produced basalts with more enriched asthenospheric OIB-signatures; whereas, all assembly LIPs produced basalts with stronger lithospheric, as well as more or less primitive asthenospheric, signatures. A counterintuitive observation of Precambrian breakup LIPs outcropping as smaller fragments that are more peripherally located along craton margins, compared to assembly LIPs as well as the Phanerozoic Karoo breakup LIP, is explained by different preservation potentials during subsequent supercontinental cycles. Thus, further accentuating radical differences between (1) breakup LIPs, preferentially intruding along what evolves to become volcanic rifted margins that are more susceptible to deformation within subsequent orogens, and (2) assembly LIPs, typically emplaced along back-arc rifts within more protected cratonic interiors. A conditioned duality is proposed, where assembly LIPs are primarily sustained by thermal blanketing (as well as local arc hydration and rifting) below assembling supercontinents and breakup LIPs more typically form above impinging mantle plumes. Such a duality is further related to an overall dynamic Earth model whereby predominantly supercontinent-orientated ocean lithospheric subduction establishes/revitalizes large low shear velocity provinces (LLSVPs) during assembly LIP-activity, and heating of such LLSVPs by the Earth’s core subsequently leads to a derivation of mantle plumes during supercontinental breakup.