SYNDEFORMATIONAL EMPLACEMENT OF A TONALITIC SHEET-COMPLEX IN A LATE-VARISCAN THRUST REGIME: FABRICS AND MECHANISM OF INTRUSION, MONTE'E SENES, NORTHEASTERN SARDINIA, ITALY

摘要

The Monte'e Senes intrusive complex in northeastern Sardinia represents a good example of a syntectonic tonalitic sheet-complex. Its history consists of at least three intrusive events involving tonalitic magma and one subsequent intrusive event involving leucogranitic magma. The tonalites form numerous cm-to m-thick layers subparallel to the main foliation and layering of the country rocks. Emplacement occurred under greenschist-facies conditions of the country rocks. Deformation fabrics and fabrics of the contact aureole provide information on kinematics and P-T conditions during intrusion, as well as the relationship to the regional deformation. High-T deformation fabrics of quartz and plagioclase in the intrusive bodies, together with magmatic and high-T foliations and lineations parallel to foliations and lineations of the country rocks, indicate syntectonic intrusion. The deformation of cordierite, andalusite and sillimanite in the contact aureole, as well as the high-T deformation of quartz, point to a long-lasting history of partly synchronous deformation and intrusion. A relatively shallow intrusive body is indicated by the occurrence of andalusite and cordierite in the contact aureole and by granophyric microstructures. Greenschist-facies deformation fabrics in all of the igneous rocks indicate that the intrusion was outlasted by the regional deformation. The Monte'e Senes complex was emplaced during retrograde metamorphism associated with west-directed thrusting of the late Variscan continent-continent collision between Gondwana and Armorica.