HIGH RESOLUTION ZIRCON PROVENANCE ANALYSIS COMPILED FROM RECENT RIVER SANDS

Geochronological investigations of zircons from recent river sands are a common method in provenance analysis. Thus, it has been used for this study and was supplemented by morphological investigations, which allow to precise the source area of zircons with similar ages.

Beneath others, we investigated the Elbe River within a length of 500 km. The geological setting of its catchment area is multifaceted and well known. Accordingly it is suitable to trace back most of the zircon populations.

Up to now ca. 2.000 zircon grains of four samples have been analysed. EDX measurements of inclusions, BSE and CL pictures required a SEM. Crystal morphology was determined referring to the diagram of Pupin (1980). Elongation, rounding and grain surface microtexture have also been investigated and classified. U-Pb and Th-U ratio measurements were performed by LA-SF-ICP-MS. Received data allowed the calculation of absolute ages and gave hints to the source of the magma the zircon formation took place (Wang et al. 2011).

Combining these methods we are now able to narrow down the source area of some special zircon populations to one locality and to a defined region for frequently occurring populations. Further observations show variations in the percentage of different crystal morphologies between Baltica and Gondwana. Finally we found different surface microtextures of grains from areas influenced by pleistocene glaciations compared to those which are unaffected.

Literature:

Pupin, J. P. (1980): Zircon and granite petrology. - Contrib. Mineral. Petrol., 73: 207-220.

Wang, X., Williams, L. G., Chen, J., Huang, P. & Li, X. (2011): U and Th Contents of Zircon in Felsic and Mafic Rocks: Improved Zircon-Melt Distribution Coefficients. – Acta Geologica Sinica, 85: 164-174.