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Abstract

A succession of deep burial carbonate cements with two types of saddle dolomite and three types of blocky calcite was investigated in Permian to Tertiary sedimentary rocks in different nappes of the Eastern Alps. The first generation of saddle dolomite occurs only in rocks of Permian to Late Triassic/Early Jurassic age. All otlier carbonate cements occur within rocks of Permian to Early Tertiary age.

Carbon and oxygen isotopic compositions of the carbonate cements and of the Triassic to Tertiary host rocks exhibit regional trends as well as trends to more negative δ18O with increasing burial. Fluid inclusion data show homogenization temperatures between 90° and 250°C for the carbonate cements. Temperatures decrease from the bottom to the top of the stratigraphic column, and regional trends are also exhibited. Calculated oxygen isotopic compositions of fluids precipitating the carbonate cements suggest strong positive 8’“0 values, which are characteristic of saline formation waters or metamorphic waters.

The first generation of saddle dolomite is inferred to have formed in the same paleo-fluid system as Late Triassic/Early Jurassic Pb-Zn ores by fluid flow directed from the hinterland in the north (Vindelician high, Bohemian massif) to the East Alpine area. The fluids ascended and precipitated saddle dolomite and, under certain conditions, Pb-Zn ores. All other carbonate cements formed post-Oligocene time after the peak of metamorphism in the Central Eastern Alps and during uplift of this area. Results suggest that meteoric fluids descended and equilibrated with metamorphic rocks subsequently mixed with metamorphic waters in this uplifted area and flowed northwards and southwards, ascending through the rock pile. Fluid mixing with a second, near surface, meteoric groundwater system could explain a renewed decrease in carbonate cement δ18O values at the top of the sedimentary succession and in northern parts of the Alpine realm.

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