Thermal thickness of the lithosphere of the Yakutian DIAMOND province based on clinopyroxene composition data from kimberlites
N.S. Tychkov1, A.M. Dymshits2,3, E.A. Muraveva1, A.M. Logvinova1, N.P. Pokhilenko1,4
1Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia (tych@igm.nsc.ru)
2Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
3Geological Institute KSC RAS, Apatity,Russia
4Geology and Geophysics Department of Novosibirsk State University, Novosibirsk, Russia
Keywords: Siberian platform, kimberlite, clinopyroxene, geotherm, lithosphere, diamond
Abstract
As a result of data processing for more than 3000 clinopyroxene xenocrysts from kimberlites of different ages in the Siberian Platform, a generalized model of the lithospheric mantle thickness evolution within the Yakutian diamond province has been obtained. New data on surface heat flow (SHF) and thermal lithospheric thickness (TLT) have been obtained for seven localities on the Siberian Platform, including Paleozoic and Mesozoic kimberlites from different regions with different diamond potential, as well as Late Triassic sedimentary rocks from the northeastern margin of the platform. The composition of clinopyroxenes from the Late Triassic sedimentary rocks corresponds to the Devonian–Carboniferous type of lithospheric mantle of the Siberian Platform. New data on kimberlites from the northeastern part of the platform (Ivushka and Zaoblachnaya pipes) yield results that contradict previous interpretations. The Ivushka pipe (Toluopka field) exhibits a TLT thickness closer to that of Jurassic kimberlites, but the sampling depth of clinopyroxene-bearing rocks is typical of Devonian–Carboniferous kimberlites. The geotherm of the Zaoblachnaya pipe (Khorbusuon field) corresponds to Devonian–Carboniferous and Triassic kimberlites, which contradicts the absence of diamonds in the pipe and its tectonic setting. The SHF and TLT values separating the Jurassic lithosphere of the northeastern part of the platform from the older lithosphere are 36.9 mW/m² and 230 km, respectively. Based on the TLT and the depth of lithospheric section sampled by kimberlite magmas of different ages, it is shown that the lower diamond potential of Triassic kimberlites may be related not to lithospheric thinning, but to a shallower depth of onset of mantle material entrainment, caused by increased permeability of the lithospheric mantle resulting from the preceding influence of the Permo–Triassic plume.
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