Mineral reactions at a peridotite-gneiss contact, Jotunheimen, Norway

Abstract

Summary: The assemblage aluminous pyroxenes+ spinel forms reaction zones between olivine-rich and plagioclase-rich layers in the Jotunheimen complex. These zones have probably formed by cooling from high T at moderate P, passing through the ol + plag → pyroxenes + spinel reaction. The absence of garnet, which would be expected to form upon further cooling, is attributed to interruption of the cooling history by rapid uplift. This uplift is demonstrated by symplectitic breakdown of aluminous pyroxenes, with expulsion of Ts and Acm, to yield low-Al pyroxenes, spinel, and plagioclase. The uplift must be Precambrian, and suggests that the Jotun rocks were involved in rapid vertical movements long before the Caledonian thrusting took place.