Major element chemistry of Precambrian dolerite dikes of tholeiitic composition from RogalandNest Agder, SW Norway

The Egersund dike swarm was emplaced in the Precambrian terrain of Rogaland/Vest Agder about 790 Ma. The dikes resulted from crystallization of magma of broadly tholeiitic composition. The main
penocrystal and microphenocrystal phases are olivine, plagioclase, augite and magnetite. On the basis of petrography and whole-rock chemistry, three main types of dolerite are recognized: olivine dolerites (abundant olivine phenocrysts, > 6% normative 01), dolerites (abundant augite, 2.1% normative 01-0.6% normative Q) and trachydolerites (presence of K-feldspar and apatite). The dolerites
were derived from the olivine dolerites by fractional crystallization but the trachydolerites cannot be related to the other types by this process. The dikes crystallized at 1210-1196°C and P= 1 atm-1 kb,
and they contained 1 wt.% H20 on intrusion. This pressure estimate, together with pressure estimates for M3 metamorphism (4.5 kb) allow uplift rates of 0.004-0.022 cm yr-1 to be calculated for the metamorphic complex.