Postsedimentation transformation of triassic terrigenous rocks in West Chukotka as an indicator of folding conditions |
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Authors: | M I Tuchkova S M Katkov I O Galuskina I M Simanovich |
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Institution: | 1.Geological Institute,Russian Academy of Sciences,Moscow,Russia;2.Faculty of Earth Sciences,University of Silesia,Katowice,Poland |
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Abstract: | Postsedimentation alteration and structural assemblies of the Triassic sedimentary complexes of West Chukotka are discussed.
Zoning of the alteration is based on examination of newly formed structural and mineral assemblages, the chemical composition,
and the polytypes of clay minerals. Three zones of postsedimentation transformation of sandstones are distinguished: (1) the
zone of chlorite, illite, and mixed-layer disordered chlorite-smectite; (2) the zone of illite and chlorite; and (3) the zone
of phengite and ferroan chlorite. The grade of postsedimentation transformation and the composition of the newly formed micas
are correlated with the cleavage type. The development of two-three types of cleavage leads to the highest degree of rock
transformation. The assemblages of clay minerals and the crystal chemistry of the authigenic phengite show that the grade
of postsedimentation transformation of the Triassic rocks attains the stage of greenschistfacies metamorphism in the zone
of development of two cleavage types. Where the second cleavage is not documented or poorly developed, the rocks remain unmetamorphosed.
Evidence is given that postsedimentation transformation of terrigenous rocks in the foldbelt is controlled largely by deformation. |
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