ON THE KINEMATICS OF ZIRCON GROWTH AND ITS PETROGENETIC SIGNIFICANCE - A CATHODOLUMINESCENCE STUDY

The relative growth rates of zircon crystal faces are recorded by growth zoning, which is recognizable in cathodoluminescence photographs of oriented crystal sections. The kinematics of zircon growth is graphically presented by the slopes of "Grabahnen" between crystal sectors. The relative velocities of advance of crystal faces correlate to the pattern of growth zoning. Widely spaced zoning, interrupted by surfaces of dissolution, on the one hand, and narrowly spaced uninterrupted oscillatory zoning, on the other hand, are interpreted as markers of low and high zircon-supersaturation of the melt, respectively. The following model is deduced from this correlation. The prism {110} is that crystal form, the growth rate of which reacts most sensitively to the zircon-supersaturation of the melt. The growthrate of the steep pyramid {211} is not primarily controlled by zircon-supersaturation. Instead, the growth of {211} is delayed by the adsorption of foreign atoms on its faces. The kinematics of zircon growth in anatectic, plutonic and meta-rhyolitic host rocks in the pre-Mesozoic basement of the Tauern Window (Eastern Alps) is explained by this model. Results show that the kinematics of zircon growth carry a much greater petrogenetic significance than has been previously suggested for the final shape of crystals alone. © 1990 Springer-Verlag.