Clays and Clay Minerals, Vol. 56, No. 1, 66–81, 2008.
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Authors
Van De Kamp, Peter C.
Issue Date
2008
Type
Article
Language
Keywords
Periodicals , Geology , Anchizone , Clay Transformation , Diagenesis , Epizone , Illite , Muscovite , Quartz , Silica , Smectite
Alternative Title
Smectite-illite-muscovite Transformations, Quartz Dissolution, And Silica Release In Shales
Abstract
Quantitative analysis of the smectite-to-illite and illite-to-muscovite transformations indicates that 17-28 wt.% SiO2 and 17-23 wt.% SiO2, respectively, are liberated during these reactions, assuming that Al is conserved. Dissolutionof quartz silt inshale s yields up to 6-9% SiO2 inthe range up to 200ºC and a further 10-15% SiO2 inthe 200-500ºC range. For muds altered to shales at 200ºC, 14-20 wt.% silica is evolved. From 200 to 500ºC, a further 18-28 wt.% silica is evolved. Additional small amounts of silica may be released int he alterationof feldspar to clay and by stylolitizationof quartz silt. Thus, inthe burial and temperature range of diagenesis into the epizone, major quantities of silica are released from clays and by quartz dissolution in shales. Within this range of alteration, concomitant decline of wholerock Si/Al (SiO2/Al2O3) inthe transformation of smectite to illite to muscovite suggests the liberated silica migrates from the source shale. As a result, the metamorphosed shales are more micaceous and less quartzose than their progenitor muds. In the diagenetic zone and anchizone, the evolved silica is probably a major source of quartz cement in sandstones. In the epizone, evolved silica is commonly present in quartz veins in the parent rocks. Fluid-inclusion temperatures in quartz overgrowths and fracture fillings in some sandstones suggest that some cements may have been derived from downdip basinal shales and pressure solutioninsan dstones.
Description
Clays and Clay Minerals, Vol. 56, No. 1, 66–81, 2008. Smectite-illite-muscovite Transformations, Quartz Dissolution, And Silica Release In Shales. Peter C. Van De Kamp. DOI: 10.1346/CCMN.2008.0560106. Copyright © 2008, The Clay Minerals Society.
Citation
Clays and Clay Minerals, Vol. 56, No. 1, 66–81, 2008.
Publisher
The Clay Minerals Society
License
Copyright © 2006-2018, The Clay Minerals Society