Heterogeneous distribution of water in the mantle beneath the central Siberian Craton: Implications from the Udachnaya Kimberlite Pipe |
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| Institution: | 1. Sobolev Institute of Geology and Mineralogy, SB RAS, Koptyuga ave. 3, Novosibirsk 630090, Russia;2. Novosibirsk State University, Pirogova st. 2, Novosibirsk 630090, Russia;1. ISTO, 7327 Université d''Orléans-CNRS-BRGM, 1A rue de la Férollerie, 45071 Orléans cedex 2, France;2. Université de Nantes, Nantes Atlantique Universités, Laboratoire de Planétologie et Géodynamique de Nantes (LPGN), UMR CNRS 6112, France;3. Bayerisches Geoinstitut, University of Bayreuth, 95440 Bayreuth, Germany;1. Geocycles Research Centre and Institute of Geosciences, University of Mainz, Becherweg 21, 55099 Mainz, Germany;2. Department of Earth and Atmospheric Sciences, University of Alberta, 126 ESB, Edmonton, AB T6G 2E3, Canada;3. ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) & Department of Earth and Planetary Sciences, Macquarie University, North Ryde, New South Wales 2109, Australia;1. KiDs (Kimberlites and Diamonds), School of Earth Sciences, The University of Melbourne, Parkville, 3010, Victoria, Australia;2. ARC Centre of Excellence for Core to Crust Fluid Systems and GEMOC, Department of Earth and Planetary Sciences, Macquarie University, North Ryde, 2019, NSW, Australia;3. School of Physical Sciences, University of Tasmania, Hobart, 7001, Tasmania, Australia;4. Melbourne Isotope Geoscience, School of Earth Sciences, The University of Melbourne, Parkville, 3010, Victoria, Australia;5. Central Science Laboratory, University of Tasmania, Hobart, 7001, Tasmania, Australia |
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| Abstract: | The paper presents new petrographic, major element and Fourier transform infrared (FTIR) spectroscopy data and PT-estimates of whole-rock samples and minerals of a collection of 19 relatively fresh peridotite xenoliths from the Udachnaya kimberlite pipe, which were recovered from its deeper levels. The xenoliths are non-deformed (granular), medium-deformed and highly deformed (porphyroclastic, mosaic-porphyroclastic, mylonitic) lherzolites, harzburgite and dunite. The lherzolites yielded equilibration temperatures (T) and pressures (P) ranging from 913 to 1324 °C and from 4.6 to 6.3 GPa, respectively. The non-deformed and medium-deformed peridotites match the 35 mW/m2 conductive continental geotherm, whereas the highly deformed varieties match the 45 mW/m2 geotherm. The content of water spans 2 ± 1–95 ± 52 ppm in olivine, 1 ± 0.5–61 ± 9 ppm in orthopyroxene, and 7 ± 2–71 ± 30 ppm in clinopyroxene. The amount of water in garnets is negligible. Based on the modal proportions of mineral phases in the xenoliths, the water contents in peridotites were estimated to vary over a wide range from < 1 to 64 ppm. The amount of water in the mantle xenoliths is well correlated with the deformation degree: highly deformed peridotites show highest water contents (64 ppm) and those medium-deformed and non-deformed contain ca. 1 ppm of H2O. The high water contents in the deformed peridotites could be linked to metasomatism of relatively dry diamondiferous cratonic roots by hydrous and carbonatitic agents (fluids/melts), which may cause hydration and carbonation of peridotite and oxidation and dissolution of diamonds. The heterogeneous distribution of water in the cratonic mantle beneath the Udachnaya pipe is consistent with the models of mantle plume or veined mantle structures proposed based on a trace element study of similar xenolithic suits. Mantle metasomatism beneath the Siberian Craton and its triggered kimberlite magmatism could be induced by mantle enrichment in volatiles (H2O, CO2) supplied by numerous subduction zones which surrounded the Siberian continent in Neoproterozoic-Cambrian time. |
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