Fissures within sedimentary rocks of Permian to Tertiary age of the East Alpine realm, the Helveticum, the Flysch-zone and of the Molasse-zone contain three types of blocky calcites. These cements formed during the uplift of the Alps in the Tertiary, when metamorphic fluids migrated from the crystalline basement to the overlying sedimentary cover (Walter et al. 1995). Trace element contents (Sr, Mn, Fe) of the blocky calcites increases from the bottom to the top of the investigated rock sequence. The 18O-content of the carbonate cements increases in the same direction, but their formation temperature decreases. The geochemical trends are sometimes inverted in the uppermost level of the investigated rock sequence. 13C of the carbonate cements always remains constant. Further statistic analysis reveal different regional trends. Blocky calcites from the East Alpine (Northern Calcareous Alps) show a co-variance of Sr2+ with Mn2+ and with Fe2+ and of Mn2+ with Fe2+. Blocky calcites from another part of the East Alpine (Drau Range), the Helveticum, the Flysch-zone and the Molasse-zone show non co-variant trends of Sr2+ with Mn2+, i.e. the Sr-content increases with decreasing Mn-content. The other trace elements show here still co-variant trends.
Experimental studies (cf. Heydari and Moore, 1993) reveal that the trace element content of calcite mostly depends on the trace element/Ca ratio of the solution, the temperature, and the precipitation rate. With increasing temperature the Mn-, Sr-, and Fe-content of calcite increases, but our data show the opposite and the observed trends seem to be independent of temperature. A high precipitation rate of the blocky calcites in the lower part of the rock pile combined with a general low trace element/Ca ratio could explain the low trace element contents, because Mn- and Fe are deriched at these conditions. Sr is enriched at a high precipitation rates, but this could be compensated by a very low Sr/Ca ratio. The increase of the trace element content of the blocky calcites towards the top of the rock pile could be explained by an increase of the trace element/Ca ratio caused by the continuing precipitation of calcite and the resulting consumption of Ca. As mentioned above, the trend to higher trace elements contents towards the top of the rock pile is sometimes inverted at its uppermost levels. This might be due to a mixing of the fluids from which the carbonate cements precipitated with meteoric or marine waters, which were certainly present in these uppermost levels during
the Tertiary. Those mixing-processes would have caused a dilution of the fluid and a decrease of the trace element/Ca ratios.
The regional trends could be explained by a decrease of the Mn2+ distribution coefficient at very high Mn/Ca ratios (Dromgoole and Walter,1990). This regional trend reflects also the different geotectonic situation during the late Tertiary. The Northern Calcareous Alps were uplifted, while the other areas were partly flooded by marine waters.
Dromgoole, E.L. & Walter, L.M., Chem. Geol. 81, 311-336 (1990).
Heydari, E. & Moore, C.H., J. Sedim. Petrol. 63, 44-60 (1993).
Walter, U., Zeeh, S. & Bechstädt, T., Terra abstracts 1, 107 (1995).