Chaotic three-dimensional distribution of Ba,Rb, and Sr in feldspar megacrysts grown in an open magmatic system |
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| Authors: | Ewa S?aby Micha? ?migielski Tomasz ?migielski Andrzej Domonik Klaus Simon Andreas Kronz |
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| Institution: | 1.Institute of Geological Sciences, Polish Academy of Sciences,Research Centre in Warsaw,Warsaw,Poland;2.Institute of Geology,University of Warsaw,Warsaw,Poland;3.‘Sofrecom Polska’,Warsaw,Poland;4.Institute of Hydrogeology and Engineering Geology,University of Warsaw,Warsaw,Poland;5.Department of Geochemistry,GZG of Georg-August-University,G?ttingen,Germany |
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| Abstract: | As has been demonstrated in recent years, the heterogeneities of coeval magmas can be more successfully revealed by zoned
megacrysts rather than by analysis of the whole rocks hosting them. Here, the geochemical heterogeneities of feldspar megacrysts
from the Karkonosze granite, Poland, are investigated by LA-ICP-MS. The crystals are the product of migration and growth in
regions of poorly mixed magmas. 3D-modeling of the Ba, Sr, and Rb distributions emphasizes the importance of micro-domain
growth morphologies. Two models of element behavior—a relative concentration model and a composition gradient model—provide
a potentially effective tool for tracking the mixing process on a microscale. Measured concentrations of elements of different
mobilities do not agree with what might be expected from the mixing of two end-member magmas. If mixing was the only process
occurring, linear correlations between the concentrations of any two elements should be observed; this, however, is not the
case. For combinations of any two of the three elements, modeling reveals differing non-linear correlations between concentrations.
The megacryst heterogeneities provide an insight into how mixing magmas are chaotically advected to growing crystals and the
degree of inter-magma element exchange between the magmas. |
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