Термодинамический анализ устойчивости первичных и вторичных минералов в мелилит-нефелинитовых туфах с отпечатками Australopithecus Afarensis, Лаетоли, северная Танзания

Elena Perova; Anatoly Zaitsev; John Spratt; Nataliya  Vlasenko; Nataliya Vladimirovna Platonova; Olga  Bubnova

doi:10.21638/spbu07.2022.202

Authors

Elena Perova St Petersburg State University, 7–9, Universitetskaya nab., St Petersburg, 199034, Russian Federation https://orcid.org/0000-0002-4762-8853
Anatoly Zaitsev St Petersburg State University, 7–9, Universitetskaya nab., St Petersburg, 199034, Russian Federation
John Spratt Imaging and Analysis Centre, Department of Earth Sciences, The Natural History Museum, Cromwell Road, London, SW 7 5BD, UK https://orcid.org/0000-0002-6395-8895
Nataliya Vlasenko St Petersburg State University, 7–9, Universitetskaya nab., St Petersburg, 199034, Russian Federation
Nataliya Vladimirovna Platonova St Petersburg State University, 7–9, Universitetskaya nab., St Petersburg, 199034, Russian Federation
Olga Bubnova St Petersburg State University, 7–9, Universitetskaya nab., St Petersburg, 199034, Russian Federation

DOI:

https://doi.org/10.21638/spbu07.2022.202

Abstract

The Laetoli area in northern Tanzania is an important palaeo-anthropological site, where the oldest footprints of Australopithecus afarensis reside. Aeolian tuffs are the major rock type at Laetoli and they are divided into Lower and Upper Laetolil Beds that were deposited at an interval of 4.36 and 3.63 million years. The Upper Laetolil Beds contain eight layers of air-fall tuffs known as marker tuffs. The Australopithecus afarensis footprints are observed on the surface of the white tuff, which is a part of the Upper Laetolil marker tuff 7, also known as the “Footprint Tuff.” The interpolated age of the marker tuff 7 is 3.66 million years. Two mineral assemblages are distinguished in the Upper Laetolil marker tuffs. The first assemblage consists of primary tuff minerals and includes clinopyroxene (diopside, augite, aegirine-augite), nepheline, melilite (åkermanite and alumoåkermanite), garnet (andradite and schorlomite), magnetite, and others. The second mineral assemblage consists of secondary minerals, montmorillonite, calcite, and phillipsite. They were formed during replacement of the primary minerals, volcanic glass, and ash cementation. Thermodynamic calculations show that the major primary tuff minerals (melilite and nepheline) are stable at variable sodium activity and pH values. Replacement of melilite and nepheline by montmorillonite is caused by a decrease of sodium activity in slightly alkaline, neutral and acidic conditions (рН < 10). Montmorillonite is not present in the altered nephelinitic tuff of the Sadiman volcano (which is considered as a source of the Laetolil Beds) where kaolinite is the major secondary mineral. This is explained by the difference in H₂O fugacity with higher lgfH₂O values in Sadiman and lower values in Laetoli. Relationships between primary and secondary tuffs minerals on the lgaHCO₃ vs pH plot suggest mineral transformation within the Laetolil Beds in slightly acid and neutral con- ditions (рН = 5–7) compared with more alkaline conditions at Sadiman (рН > 10).

Keywords:

melilite, nepheline, montmorillonite, calcite, tuff, Laetoli, Tanzania

Downloads

Download data is not yet available.

References

Balagizi, C.M., Kasereka, M.M., Cuoco, E., Liotta, M., (2017). Rain-plume interactions at Nyiragongo and Nyamulagira volcanoes and associated rainwater hazards, East Africa. Applied Geochemistry, 81, 76-89.

Barker, D.D., Milliken, K.L., (2008). Cementation of the footprint tuff, Laetoli, Tanzania. Canadian Mineralogist, 46, 831–841.

Dawson, J.B., (2008). The Gregory Rift Valley and Neogene-Revent Volcanoes of Northern Tanzania. Geological Society, London Geological Society Memoir No. 33.

Deino, A. L. (2011). 40Ar/39Ar dating of Laetoli, Tanzania. In: T. Harrison, ed., Paleontology and Geology of Laetoli: Human Evolution in Context. Volume 1: Geology, Geochronology, Paleoecology and Paleoenvironment. Dordrecht: Springer, 77–97.

Deino, A. L. (2012). 40Ar/39Ar dating of Bed I, Olduvai Gorge, Tanzania, and the chronology of early Pleistocene climate change. Journal of Human Evolution, 63, 251–273.

Frank-Kamenetsky, V. A. (1975). Instructions to the X-ray investigation of minerals. Leningrad: Nedra Publ. (In Russian)

Frank-Kamenetsky, V. A. (1983). X-ray analysis of most important types of rock-forming minerals (layer and framework silicates). Leningrad: Nedra Publ. (In Russian)

Gailhanou, H., Blanc P., Rogez, J., Mikaelian, G., Kawaji, H., Olives, J., Amouric, M., Denoyel, R., Bourrelly, S., Montouillout, V., Vieillard, P., Fialips, C. I., Michau, N. and Gaucher, E. C. (2012). Thermodynamic properties of illite, smectite and beidellite by calorimetric methods: Enthalpies of formation, heat capacities, entropies and Gibbs free energies of formation. Geochimica et Cosmochimica Acta, 89, 279–301.

Getty Conservation Institute (2001). Laetoli Hominid Trackway, Site G: Condition Records, G1 and G2/3 Footprints. [online] Los Angeles: Getty Conservation Institute. Available at: http://hdl.handle.net/10020/gci_pubs/laetoli_condition_records [Accessed Oct. 18, 2021].

Getty Conservation Institute (2011). Report on the Partial Re-Excavation of the Laetoli Hominid Trackway, Site G. [online] Los Angeles: Getty Conservation Institute. Available at: http://hdl.handle.net/10020/gci_pubs/laetoli_re-excavation [Accessed Oct. 18, 2021].

Harrison, T., ed. (2011). Paleontology and Geology of Laetoli: Human Evolution in Context. Vol. 1: Geology, Geochronology, Paleoecology and Paleoenvironment. Dordrecht, Heidelberg, London, New York: Springer.

Hay, R. L. (1976). Geology of the Olduvai Gorge. Berkeley: University of California Press.

Hay, R. L. (1978). Melilitite-carbonatite tuffs in the Laetoli beds of Tanzania. Contributions to Mineralogy and Petrology, 67, 357–367.

Hay, R. L. (1987). Geology of the Laetoli area. In: M. D. Leakey, J. M. Harris, eds, Laetoli, a Pliocene Site in Northern Tanzania, Oxford: Clarendon Press, 23–47.

Keller, J. and Zaitsev, A. N. (2012). Geochemistry and petrogenetic significance of natrocarbonatites at Oldoinyo Lengai, Tanzania: Composition of lavas from 1988 to 2007. Lithos, 148, 45–53.

Langmuir, D. (1997). Aqueous Environmental Geochemistry. Prentice Hall, Englewood Cliffs, New Jersey.

Leakey, L. S. B. (1959). A new fossil skull from Olduvai. Nature, 184, 491–493.

Leakey, M. D. and Hay, R. L. (1979). Pliocene footprints in the Laetolil beds at Laetoli, northern Tanzania. Nature, 278, 317–323.

Leakey, L. S. B., Tobias, P. V. and Napier, J. R. (1964). A new species of the genus Homo from Olduvai Gorge. Nature, 202, 7–9.

Mana, S., Furman, T., Carr, M. J., Mollel, G. F., Mortlock, R. A., Feigenson, M. D., Turrin, B. D. and Swisher III, C. C. (2012). Geochronology and geochemistry of the Essimingor volcano: melting of metasomatized lithospheric mantle beneath the North Tanzanian Divergence zone (East African Rift). Lithos, 155, 310–325.

McHenry, L. J. (2011). Geochemistry and mineralogy of Laetoli area tuffs: lower Laetolil through Naibadad beds. In: T. Harrison, ed., Paleontology and Geology of Laetoli: Human Evolution in Context Volume 1: Geology, Geochronology, Paleoecology and Paleoenvironment. Dordrecht: Springer, 121–141.

Mitchell, R. H. and Dawson, J. B. (2007). The 24th September 2007 ash eruption of the carbonatite volcano Oldoinyo Lengai, Tanzania: mineralogy of the ash and implications for formation of a new hybrid magma type. Mineralogical Magazine, 71, 483–492.

Mollel, G. F. (2007). Petrochemistry and Geochronology of Ngorongoro Volcanic Highland Complex (NVHC) and its Relationship to Laetoli and Olduvai Gorge, Tanzania. PhD thesis, Rutgers University, USA.

Mollel, G. F., Swisher III, C. C., Feigenson, M. D. and Carr, M. J. (2008). Geochemical evolution of Ngorongoro Caldera, Tanzania: implications for crust-magma interaction. Earth and Planetary Science Letters, 271, 337–347.

Moore, D. N. and Reynold, R. C. (1997). X-ray Diffraction and the Identification and Analysis of Clay Minerals. Oxford University Press.

Musiba, C. M., Mabula, A., Selvaggio, M. and Magori, C. C. (2008). Pliocene animal trackways at Laetoli: research and conservation potential. Ichnos, 15, 166–178.

Musiba, C. M., Mwambungu, M. M., Mwankunda, J., Zaitsev, A. N., Savchenok, A. I., Mabulla, A. Z., Magori, C. C., Bergstrom, K., Pelissero, A. and Assefa, S. (2020). Balancing research, education, conservation and sustainable use of the 3.6 million years old hominin footprint Site G and S at Laetoli in northern Tanzania. American Journal of Physical Anthropology, 171 (S69), 194.

Ogorodova, L. P., Gritsenko, Yu. D., Vigasina, M. F., Bychkov, A. Y., Ksenofontov, D. A. and Melchakova, L. V. (2018). Thermodynamic properties of natural melilites. American Mineralogist, 103, 1945–1952.

de la Villa, R. V., Cuevas, J., Ramírez, S. and Leguey, S. (2201). Zeolite formation during the alkaline reaction of bentonite. European Journal of Mineralogy, 13, 653–644.

Scoon, R. N. (2018). Geology of National Parks of Central/Southern Kenya and Northern Tanzania. Springer International Publishing AG.

Su, D. F. and Harrison, T. (2015). The paleoecology of the upper Laetolil beds, Laetoli Tanzania: a review and synthesis. Journal of African Earth Sciences, 101, 405–419.

Zaitsev, A. N., Wenzel, T., Spratt, J., Williams, T. C., Strekopytov, S., Sharygin, V. V., Petrov, S. V., Golovina, T. A., Zaitseva, E. O. and Markl, G. (2011). Was Sadiman volcano a source for the Laetoli footprint tuff? Journal of Human Evolution, 61, 121–124.

Zaitsev, A. N., Marks, M. A. W., Wenzel, T., Spratt, J., Sharygin, V. V., Strekopytov, S. and Markl, G. (2012). Mineralogy, geochemistry and petrology of the phonolitic to nephelinitic Sadiman volcano, Crater Highlands, Tanzania. Lithos, 152, 66–83.

Zaitsev, A. N., Spratt, J., Sharygin, V. V., Wenzel, T., Zaitseva, O. A. and Markl, G. (2015). Mineralogy of the Laetolil footprint tuff: a comparison with possible volcanic sources from the Crater Highlands and Gregory rift. Journal of African Earth Sciences, 111, 214–221.

Zaitsev, A. N., McHenry, L., Savchenok, A. I., Strekopytov, S., Spratt, J., Humphreys-Williams, E., Sharygin, V. V., Bogomolov, E. S., Chakhmouradian, A. R., Zaitseva, O. A., Arzamastsev, A. A., Reguir, E. P., Leach, L., Leach, M. and Mwankunda, J. (2019). Stratigraphy, mineralogy and geochemistry of the Upper Laetolil tuffs including a new tuff 7 site with footprints of Australopithecus afarensis, Laetolil, Tanzania. Journal of African Earth Sciences, 158, 103561.

Zaitsev, A. N., Vlasov, D. Y., Zelenskaya, M. S., Zaitseva, O. A., Pavlova, O. A., Chakhmouradian, A. R., Savchenok, A. I., Leach, L., Leach, M. and Mwankunda, J. (2020). Microbiology of the Laetolil Tuff 7 with 3.66 Ma Australopithecus Afarensis footprints, Ngorongoro Conservation Area, Tanzania. In: O. V. Frank-Kamenetskaya, D. Yu. Vlasov, E. G. Panova, S. N. Lessovaia, eds, Processes and Phenomena on the Boundary Between Biogenic and Abiogenic Nature, Lecture Notes in Earth System Sciences. Springer Nature Switzerland AG, 669–692.

Zaitsev, A. N., Arzamastsev, A. A., Marks, M. A. W., Braunger, S., Wenzel, T., Spratt, J., Salge, T. and Markl, G. (2021). Hybridisation of alkali basaltic magmas: a case study of the Ogol lavas from the Laetoli area, Crater Highlands (Tanzania). Journal of Petrology, 62 (8), egab035.