Литосфера (May 2020)
Plume-related granite-rhyolite magmatism
Abstract
Plume-related magmatism is widespread and its existence is well-founded. Mostly, plume-related magmatism is represented by trap rocks, oceanic island basalts (OIB) and oceanic plateau basalts (OPB), although the composition of plume-related igneous products is very diverse. Among others, silicic igneous rocks – rhyolites and granites – play a prominent role. Two main types of plume magmatism are recognised. The former comprises Large Igneous Provinces (LIP) and is thought to be born at the core-mantle boundary within structures called superswells, which produce giant, short-lived mantle upwellings resulting in abundant magmatism on the earth’s surface. The latter is represented by time-progressive linear volcanic chains formed by single plumes – thin upward mantle flows being continuously active during longer periods of time. It is shown that the relative volume of silicic magmatism strongly depends on the type of the earth’s crust. Among continental trap basalts, silicic magmatism is usually present, being subordinate to the basalts in volume, and belongs to the bimodal type. However, in some cases, continental LIPs are formed predominantly by silicic rocks (silicic LIPS, or SLIPS). Oceanic LIPs are mainly basaltic comprising an insignificant or no amount of silicic rocks. Time-progressive volcanic chains are rarely found on the continents and, as a rule, include a significant silicic component. Oceanic chains are comprised mostly of basalts (OIB), although at the top of volcanoes there are more acid and alkaline differentiates, which, howe ver, usually lack rhyolites and granites, except for the cases when the relics of the continental crust or anomalously thick mafic crust are present. The analysis suggests that the melting of continental crust plays an important role in the formation of plume-related rhyolite-granite magmatism. As for the Urals, the presence of plume-related magmatism in its history has been pro ven relatively recently. Plume events characterised by the presence of (rhyolite)-granite components include mashak (1380–1385 Ma), Igonino (707–732 Ma), Mankhambo (mainly Cambrian), Ordovician Kidryasovo, Stepninsky (Permian) and Urals-Siberian (Triassic).
