Dolerite-pegmatites from the Whin Sill near Barrasford, Northumberland

摘要: SUMMARY Four varieties of dolerite-pegmatite occurring in the Whin Sill at Barrasford are described. They (1) normal pegmatite (NP) which is similar to dolerite-pegmatites Teesdale as concordant lenticular lenses parallel sill’s upper surface and confined portion sill; (2) intrusive (IP) a discordant vein containing autoliths dolerite; (3) (QP) below partially filled vesicles quartz calcite (4) (PP) amygdales completely with pectolite. QP PP only occur have form basal layers about 10mm thick. The pegmatites developed an early stage consolidation sill had vesicular space above them. filling took place later lower temperature two separate hydrothermal episodes yet there invarient relationship between composition amygdale fill. A chemical study four pegmatites, dolerite (ND), basalt (IB) aplite veins (IA) their component minerals shows that all rocks except lie on differentiation trend Sill. Final temperatures indicated by feldspar geothermometry are:- ND 1025°C; NP 713°C; IP 748°C; 572°C 590°C. equilibration 460°C for supports conclusion metasomatic product QP, altered solutions deposited Some pectolite has been subsequently replaced stevensite X-ray characteristics heat treated (400°C) stevensite.