The plume-dependent granite-rhyolite magmatism

Abstract

The plume-dependent magmatism is widespread and well justified. The bulk of it is represented by flood basalts, basalts of oceanic islands (OIB), and basalts of oceanic plateaus (OPB), though the whole scope of plume magmatism is very diverse. A noticeable role among them is played also by acid (silicic) magmatic rocks - rhyolites and granites. Two main types of plume magmatism are recognized. The first belongs to Large Igneous Provinces (LIP) and is thought to be born at the Core-Mantle boundary within structures, called superswells, that produce giant, short-living mantle upwellings, resulting in abundant volcanism on the Earth’s surface. The second type is represented by linear volcanic chains characterized by regular age progressions. They are formed by single plumes - thin ascending mantle flows, acting during longer periods of time. It is shown that the abundance of silicic magmatism strongly depends on the type of the earth’s crust. Among flood basalts of continents, silicic magmatism is usually present, subordinate in volume to basalts and belongs to a bimodal type of magmatism. But in some cases LIP in continents are formed predominantly by silicic rocks; they are given the name Silicic LIPS, or SLIPS. In oceans, LIP are fundamentally basaltic with no considerable volume of silicic volcanics, if any. The time-progressive volcanic chains in continents are rare and usually comprise a noticeable silicic component. In oceans, the chains are composed mostly of basalts (OIB type), though in the top parts of volcanoes more acid and alkaline differentiates are present; usually they lack rhyolites and granites, except the cases of a presence of some strips of continental crust or anomalously thick oceanic crust. This review can lead to a thought of an important role of melting of continental crust in formation of plume-dependent rhyolite-granite magmatism. As for the Urals, the proofs for a presence of plume-dependent magmatism in its history were presented only recently. Among the plume episodes, some are characterized by presence of silicic components, in particular: Mashak (1380-1385 Ma), Igonino (707-732 Ma), Man’khambo (mainly Cambrian), Ordovician Kidryasovo, Stepninsky (Permian) and Urals-Siberian (Triassic).