S. Frisia et Hr. Wenk, TEM AND AEM STUDY OF PERVASIVE, MULTISTEP DOLOMITIZATION OF THE UPPERTRIASSIC DOLOMIA PRINCIPALE (NORTHERN ITALY), Journal of sedimentary petrology, 63(6), 1993, pp. 1049-1058
Microstructures, textures, and composition of dolomites from different
facies and stratigraphic level of a carbonate platform sequence 1000-
2000 m thick in the Brenta Dolomites and Eastern Lombardy (Italy) are
interrelated. Mimetic, unimodal (4 mu m), planar-e dolomite and polymo
dal (20-200 mu m), planar-s to nonplanar matrix dolomite show calcian
and stoichiometric areas in the same crystals. Ca-rich areas (53-56 mo
le % Ca) have pervasive modulated microstructure. As stoichiometric co
mposition is approached (51-52 mole % Ca), modulations are coarser and
less pervasive. Stoichiometric zones show few dislocations. Dolomites
with excess calcium and modulated microstructures appear to have posi
tive delta(18)O values. Matrix dolomite crystals with more abundant sl
ightly calcian and stoichiometric areas have negative delta(18)O value
s. Void-filling dolomites are stoichiometric and contain only a few di
slocations. The onset of solid-state diffusion is recorded in some voi
d-filling dolomites formed at temperatures above 60 degrees C. Regiona
lly extensive dolomitization was almost completed by the end of the Tr
iassic. Late hydrothermal dolomitization did not cause neomorphism of
early replacive dolomites.