Magnetic fabric and rheology of co-mingled magmas in the Nasavrky PlutonicComplex (E Bohemia): implications for intrusive strain regime and emplacement mechanism

The fabrics of mafic microgranular enclaves (MME) and of the host granodior ite of the old granodiorite intrusion of the Nasavrky Plutonic Complex (E B ohemia) were investigated by means of magnetic anisotropy. The magnetic fab ric in MME is oriented coaxially with the magnetic fabric of the host grano diorite which is undoubtedly magmatic (intrusive) in origin. Consequently, the magnetic fabric in MME originated during the same process as the magnet ic fabric in granodiorite, i.e. during the granodiorite emplacement. In add ition, also the degree of anisotropy and the shapes of susceptibility ellip soids are very similar in MME and in granodiorite, which probably indicates that the MME had probably a similar viscosity to that of granodiorite and behaved as passive markers whose shapes resembled those of the intrusive st rain ellipsoids. Petrological and geochemical approaches coupled with rheol ogical modelling allow the prediction of the physical states of magmas and of the development of their internal fabrics. Observed fabrics were compare d to the results of numerical modelling of multiparticle systems slowly mov ing in viscous fluid. The steep magnetic foliations and almost vertical mag netic lineations suggest that today's erosion level represents a relatively deep intrusive level where magma flowed vertically and its intrusion was c ontrolled by the shape of the feeder zone used for magma ascension. (C) 199 9 Elsevier Science B.V. All rights reserved.