TEM AND AEM STUDY OF PERVASIVE, MULTISTEP DOLOMITIZATION OF THE UPPERTRIASSIC DOLOMIA PRINCIPALE (NORTHERN ITALY)

Authors
Citation
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
Citations number
50
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geology
Journal title
ISSN journal
0022-4472
Volume
63
Issue
6
Year of publication
1993
Pages
1049 - 1058
Database
ISI
SICI code
0022-4472(1993)63:6<1049:TAASOP>2.0.ZU;2-8
Abstract
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.