Title: Zeolitic alteration of Eocene volcaniclastic sediments at Metaxades, Thrace, Greece
Abstract: The conditions of alteration of the upper Eocene zeolite-bearing volcaniclastic sediments at Metaxades, Thrace, Greece, were examined using a variety of petrographic and mineralogical techniques. A fine silt- to clay-size matrix, containing abundant altered glass shards, predominates. The primary minerals include quartz, K-feldspar, plagioclase, micas (especially biotite) and some opaque minerals. The diagenetic phases, clinoptilolite, smectite and cristobalite, occur as microcrystalline aggregates within the matrix or as replacements of glass shards. The abundances of cristobalite and clinoptilolite are related chiefly to the original composition of the rocks. The abundance of cristobalite increases and that of clinoptilolite + smectite decreases as the abundance of the matrix increases. The formation of clinoptilolite and cristobalite took place either at near-surface temperatures or at slightly elevated temperatures (lower than 70°C). The smectite content of the altered volcaniclastics decreases with increasing depth in the 15 m thick exposed section. No other systematic variation in mineral assemblages with depth was observed. However, the ratio clinoptilolite/smectite increases systematically with depth suggesting to us that smectite may have formed subsequent to the formation of clinoptilolite and as an alteration product of clinoptilolite. The initial composition of the volcanic material and to a less extent the interstitial fluids, greatly affected the diagenetic mineral assemblages of the final alteration products.
Publication Year: 1993
Publication Date: 1993-03-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 28
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