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take place. Suitable marginal country rocks might get dragged
downward. In the case of kimberlites the impressive volume in-
crease due to hydration of olivine to serpentine leads frequently
to an overall volume increase of the diatreme fill that ultimate-
ly results in some upward movement of the diatreme fill. Suit-
able country rocks at the diatreme wall, Such as Nama shales
in the Gibeon kimberlite province of Namibia, get dragged up-
wards (Kurszlaukis et al. 1998).
Diagenesis of diatreme fill in soft-rock environment. In
soft-rock environments, both the country rock material and
the diatreme fill are unconsolidated and water-saturated, the lat-
ter at least shortly after the eruptions ended. Compaction and
initial diagenetic processes will have started in the unconso-
lidated country rock sediments much earlier than in the dia-
treme; its fill formed with the latter having become emplaced
rather suddenly and in an appreciable volume. Compaction of
the diatreme fill causes differential subsidence and marginal
dragdown of suitable country-rock sediments (Francis 1962,
1970, Lorenz 1971). At Argyle, unconsolidated country rocks
(mostly quartz sands) transformed into silica-cemented quartz-
ites, and unconsolidated pyroclastic material rich in individual
quartz grains in the diatreme also transformed into hard rocks
via silica-precipitation in the pore space (Boxer et al. 1989).
In the two graben structures of synsedimentary volcanism of
the Carboniferous-Permian Saar-Nahe Basin in southwestern
Germany and the Carboniferous Midland Valley basin in Scot-
land, oxidizing and respectively reducing conditions in the
graben sedimentary sequence (red beds and drab beds) influ-
enced Eh and pH in the diatreme fill and resulted in reddish or
greenish colours of pyroclastic rocks in the diatremes (Fig. 5;
Lorenz 1972).
Acknowledgements
I acknowledge the request of Jaromir Ulrych, the Convenor of
the Symposium Hibsch 2002 in the Ohre (Eger) Rift region,
Czech Republic, to write this paper following the author’s at-
tending this symposium.
This manuscript reviews the results of various studies of
the present author over more than 35 years and of course also
the results of studies of a number of other authors. Fruitful dis-
cussions and support by many colleagues and friends as well
as financial support by many institutions and companies were
therefore too numerous to be named individually, and are grate-
fully acknowledged. The manuscript was critically reviewed by
Felicity E. Lloyd, Reading, Georg Buechel, Jena, and Stephan
Kurszlaukis, Johannesburg. Felicity E. Lloyd also considerably
improved the English. Their helpful reviews are also gratefully
acknowledged.
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