Magmatic enclaves from the Rudolfov quarry near Liberec (Czech Republic)
are interpreted to represent remnants of lamprophyric melt that intruded
the Karkonosze granite at a stage at which the granite was not fully
solidified. Based on the observation that larger enclaves are generally
more circular than the smaller ones, we conclude that bigger blobs of
mafic magma became more spherical during flow in the gravity field (sink
or float). This flow is also interpreted to be responsible for the
incorporation of mineral grains into the enclaves and may have
facilitated the assimilation of granitic melt. Linear mixing trends on
Harker diagrams for most network-forming and mainly slow-diffusing or
fluid-immobile elements indicate such an assimilation process between
granite and lamprophyre. In contrast, all fast-diffusing or fluid-mobile
elements display scattered element distributions, implying that chemical
diffusion also played a role. Pressure and temperature for this late
magmatic stage are estimated at around 1 kbar and 500A degrees C. These
results suggest that two processes modified the composition of the
enclaves in the Karkonosze granite: (1) assimilation (mechanical mixing)
of granitic melt during the injection of the lamprophyric melt and the
subsequent flow of the forming enclaves in the gravity field
(responsible for the linear mixing trends) and (2) diffusion-controlled
redistribution of elements between both solidifying rock types at the
magmatic stage and/or due to late-stage magmatic fluids (responsible for
the scattering and deviation from the linear mixing trends).