Reaction textures in contact-metamorphosed xenoliths; implications for the tectonothermal evolution of the Seiland Igneous Province, Norwegian Caledonides
Elvevold, Synnøve; Reginiussen, Helge
European Journal of Mineralogy Volume 8 Number 4 (1996), p. 777 - 790
published: Jul 29, 1996
manuscript accepted: Feb 12, 1996
manuscript received: Jan 25, 1995
ArtNo. ESP147050804011, Price: 29.00 €
Abstract Contact metamorphosed pelitic xenoliths in metagabbro from the Seiland Igneous Province, North Norwegian Caledonides, contain high-T assemblages which include orthopyroxene, cordierite, spinel, garnet, quartz, ilmenite, corundum and feldspars. Re-equilibration of the contact metamorphic assemblages include the development of sillimanite coronas on spinel, ilmenite and corundum, the replacement of cordierite and spinel by garnet and sillimanite, and the partial replacement of cordierite by symplectites consisting of orthopyroxene + Al2SiO5 + quartz. The reaction textures are consistent with a substantial pressure increase after cooling from the peak conditions. Compositional zoning in garnet and adjacent cordierite is characterized by decreasing XFe where the minerals are in mutual contact, which is consistent with a P-T evolution involving compression. In nappe terranes such as the Caledonides, loading may be interpreted in terms of crustal thickening during overthrusting. The compression is interpreted as recrystallization in response to emplacement of structurally higher units on top of the Seiland rocks during the Caledonian orogeny.