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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract



Journal of Sedimentary Research, Section A: Sedimentary Petrology and Processes
Vol. 66 (1996)No. 1. (January), Pages 139-146

Authigenic Feldspar as an Indicator of Paleo-Previous HitRockNext Hit/Previous HitWaterTop Interactions in Permian Carbonates of the Northern Calcareous Alps, Austria

Christoph Spotl (1), Martin Kralik (2), Michael J. Kunk (3)

ABSTRACT

Dolostones interbedded with Upper Permian evaporites at the base of the Northern Calcareous Alps contain abundant authigenic K-feldspar. Two petrographically, structurally, and isotopically distinct generations of K-feldspar can be distinguished: crystals composed of an inclusion. rich core and a clear rim, and optically unzoned, transparent crystals. Both feldspar types have essentially identical K-feldspar end-member compositions with >= 99.5 mole % Or component. Low oxygen isotope ratios (+16.1^pmil to +18.1^pmil SMOW) suggest precipitation from 18O-enriched, saline fluids at temperatures in excess of ^sim 140°C. 40 r/39Ar plateau-age spectra of five samples range from 145 ± 1 to 144 ±1 Ma (Early Berriasian) and suggest that both types of feldspar were formed within an interval that did not exceed ^sim 2 m.y. Rb/Sr model ages range from 152 to 140 Ma, assuming that the burial diagenetic regime was buffered with respect to strontium by the associated marine Permian evaporites. Authigenic K-feldspar records two distinct events of hot brine flow, most likely triggered by tectonic movements (detachment) and by an increase in the subsurface temperature in response to thrust loading.

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