Textural features of some contrasted igneous cumulates from South Greenland

Abstract

Five particular occurrences of layered plutonic rocks within the south Greenland alkaline province are discussed. These five examples are of gabbro, anorthosite, syenite of larvikite-nordmarkite type, foyaite and eudialyte nepheline syenite, respectively. Each is thought to consist of cumulate rocks formed by bottom accumulation of the early mineral phases and the subsequent crystallization of the trapped interstitial liquid. The possible causes of banding and feldspar lamination are considered in each case. The presence or absence of feldspar lamination is used as one criterion for deciding whether the settling of the early (cumulus) phases occurred through moving or still magma. Magmatic flow during the accumulation of the cumulus mush was important in controlling the degree of packing within the latter and hence was influential in determining the ultimate bulk composition of the solidified rock.