THE MECHANISM OF MAGMA ASCENT THROUGH THE В«SOLID» LITHOSPHERE AND RELATION BETWEEN MANTLE AND CRUSTAL DIAPIRISM: NUMERICAL MODELING AND NATURAL EXAMPLES
O.P. Polyansky1,2, V.V. Reverdatto1, A.V. Babichev1, V.G. Sverdlova1
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
pol@igm.nsc.ru
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Diapirs, magma, lithosphere, viscosity, rheology, numerical modeling, continental crust, melting, intrusion
Abstract
Diapirism can be regarded as the main mechanism of transport through the lithosphere for both felsic and mafic/ultramafic magmas. However, the lack of field observations makes it difficult to identify the key mechanism responsible for the formation of dome-shaped structures. In this study, emplacement of natural diapirs is reconstructed by numerical experiments handling realistic rheological and petrological models for the crust and mantle lithosphere. Three different regimes of diapiric ascent were established depending on the chosen model rheology: (1) single-stage diapir ascent; (2) pulsating ascent of successive batches of mantle-derived magma to the base of the crust with a periodicity of 2-3 Myr; (3) emplacement of extensive magma bodies in the form of sills either beneath the base of the crust (underplating) or to deeper mantle levels. The timescale of 30 Myr for a heat source at the base of the lithosphere is sufficient to initiate the ascent of a diapir through the mantle and crust. The study provides the estimates of rheological properties of the lithosphere and partially molten material at which diapiric ascent through the mantle and crust can occur.
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