Cleavage microstructures and stretching indicators in black-slate rocks of the northern part of the Ulakhan-Sis antiform (Kularsky district, Yakutia)

The varieties of cleavage in the black-shale rocks of the northern part of the Ulakhan-Sis antiform (in the Tuoguchan and Tarbagannakh suites of the Upper Permian age) and some rocks stretching indicators in this part of the antiform are considered. In the reconstruction of the deformation processes, along with the ordinary geological methods, systematic microstructural observations of rocks in the thin sections under a microscope were used. The main sub-conformable cleavage S₁ and the role of pressure solution in its formation are characterized. The cleavage S₁ formation sometimes accompanied by the formation of a stretching lineation. In metasandstones the of quartz and plagioclase grains and sericitequartz «beards» adjacent to the ends of these grains are elongated along lineation. Based on the orientation of this lineation, the rocks during the formation of the cleavage S₁ were subjected to stretching in the northnorth-western direction. The carbonaceous shales of the Tuoguchan suite often contain the sedimentarydiagenetic carbon-quartz nodules and later pyrite crystals. Both are often surrounded by fibrous strain fringers (SF) composed of quartz and chlorite. The fibers in SF is rectilinear and parallel to S₁, which indicates the formation of SF during the coaxial deformation of rocks with stretching parallel to S₁. Based on the fiber directions in SF on pyrite crystals, the stretching during these SF formation was oriented mainly in the north-north-eastern direction, close to the axis of the Ulakhan-Sis antiform. The article also considers the crenulation cleavage S₂ (described in this area for the first time), locally superimposed on S₁. The S₂ cleavage zones correspond to the microfolds limbs into which the cleavage S₁ is bended. The cleavage S₂ has a north-eastern strike, close to the antiform axis, and a predominantly steep south-eastern fall. The cleavage S₁ formation may be associated with the first (thrust-fold) stage of the early collisional thrust phase of the Late Mesozoic deformations of the Verkhoyano-Kolyma orogenic region, and the crenulation cleavage S₂ – with the second (fold) stage of the same deformation phase.

1. Seyferth M., Henk A. Syn-convergent exhumation and lateral extrusion in continental collision zones – insights from three-dimensional numerical models // Tectonophysics. 2004. Vol. 382. P. 1–29.

2. Vernon R.H. A practical guide to rock microstructure. Cambridge University Press, 2018. 431 p. https://doi.org/10.1017/9781108654609

3. Passchier C.W., Trouw R.A. J. Microtectonics. Berlin; Heidelberg; New York: Springer, 2005. 366 p.

4. Kirmasov A.B. Osnovy strukturnogo analiza. M.: Nauchnyj mir, 2011. 368 p.

5. Polufuntikova E.I., Fridovskij V.Ju. Mikrodeformacii rudonosnyh terrigennyh tolshh // Razvedka i ohrana nedr. 2013. No. 12. P. 16–19.

6. Fridovskij V.Ju. Kularskaja metallogenicheskaja zona: metamorfogennye Au kvarcevye mestorozhdenija // Tektonika, geodinamika i metallogenija territorii Respubliki Saha (Jakutija) / Pod red. L.M. Parfenova i M.I. Kuz’mina. M.: MAIK «Nauka/Interperiodika», 2001. P. 350–353.

7. Sustavov O.A. Deformacii zhil’nogo kvarca pri formirovanii zolotogo orudenenija v chernoslancevyh tolshhah (Kularskij rajon, Vostochnaja Jakutija) // Geol. i geof. 1995. No. 4. P. 81–87.

8. Atlas of Deformational and Metamorphic Rock Fabrics / Edited by G.J. Borradaile, M.B. Bayly, C. McA. Powell. Berlin; Heidelberg: Springer-Verlag 1982. 551 р.

9. Parfenov L.M., Oksman B.C., Prokoi’ev A.V., Timofeev V.F., Tret’jakov F.F., Trunilina V.A., Dejkunenko A.V. Kollazh terrejnov Verhojano-Kolymskoj orogennoj oblasti // Tektonika, geodinamika i metallogenija territorii Respubliki Saha (Jakutija) / Pod red. L.M. Parfenova i M.I. Kuz’mina. M.: MAIK «Nauka/Interperiodika», 2001. P. 199–254.

10. Powell C. MсA. Conjugate cleavage in quartzose sandstone // Atlas of Deformational and Metamorphic Rock Fabrics. Edited by G. J. Borradaile M. B. Bayly C. McA. Powell. Berlin; Heidelberg: Springer-Verlag, 1982. P. 266–267.

11. Bushmakin A.F. Unasledovannoe stroenie kristallov pirita iz porod s uglerodistym veshhestvom // Problemy ontogenii mineralov. L.: Nauka, 1985. P. 73–82.

12. Schieber J. Early diagenetic silica deposition in algal cysts and spores: a sourse of sand in black shales? // Jour. Sedim. Res. 1996. Vol. 66. P. 175–183.

13. Ramsay J.G., Huber M.I. The Techniques of Modern Structural Geology. London: Academic press, 1983. Vol. 1. 307 p.

14. Fоssen H. Structural Geology. Cambridge University Press, 2010. 463 p.

15. Tret’jakov F.F. Stadii nadvigovogo jetapa pozdnemezozojskih deformacij Verhojano-Kolymskoj orogennoj oblasti // Otech. geol. 2015. No. 5. P. 89–95.

16. Poyatos D.M., Nieto F., Azor A. Relationships between very low-grade metamorphism and tectonic deformation: examples from the southern Central Iberian Zone (Iberian Massif, Variscan belt) // Jour. Geol. Soc. London. 2001. Vol. 158. P. 953–968.

17. Chen C.T., Chan Y.C., Lo C.H., Malavieille J., Lu C.Y., Tang J.T., Lee Y.H. Basal accretion, a major mechanism for mountain building in Taiwan revealed in rock thermal history // Jour. Asian Earth Sci. 2018. Vol. 152. P. 80–90. https://doi.org/10.1016/j.jseaes.2017.11.030.

18. Friedel C.H., Huckriede H., Leis B., Zweig M. Large-scale Variscan shearing at the southeastern margin of the eastern Rhenohercynian belt: a reinterpretation of chaotic rock fabrics in the Harz Mountains, Germany // Intern. Jour. Earth Sci. (Geol Rundsch). 2019. Vol. 108. P. 2295–2323. https://doi.org/10.1007/s00531-019-01763-1

19. Tillman K.S., Byrne T.B. Kinematic analysis of the Taiwan Slate Belt // Tectonics. 1995. Vol. 14, No. 2. P. 322–341.

20. Fridovskij V.Ju. Deformacii i orudenenie Kularskogo segmenta Kular-Nerskogo slancevogo pojasa (Vostochnaja Jakutija) // Izv. vuzov. Geol. i razv. 1996. No. 4. P. 64–71.

21. Aerden D.G.A.M. Porphyroblast non-rotation during crustal extension in the Variscan Lys-Caillaouas Massif, Pyrenees // Jour. Struct. Geol. 1995. Vol. 17, No. 5. P. 709–725,

22. Miller Ju.V. Tektono-metamorficheskie cikly. L.: Nauka, 1982. 159 p.

23. Lačný A., Plašienka D., Vojtko R. Structural evolution of the Turňa Unit constrained by fold and cleavage analyses and its consequences for the regional tectonic models of the Western Carpathians // Geol. Carpathica. 2016. Vol. 67, No. 2. P. 177–193. https://doi.org/10.1515/geoca-2016-0012