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Genesis of the Khaluta Alkaline-Basic Ba-Sr Carbonatite Complex (West Transbaikala, Russia)

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Genesis of the Khaluta Alkaline-Basic Ba-Sr Carbonatite Complex (West Transbaikala, Russia) See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/226169877 Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex (West Transbaikala, Russia) Article in Mineralogy and Petrology · March 2009 DOI: 10.1007/s00710-009-0063-4 CITATIONS READS 12 73 3 authors, including: Anna Doroshkevich G. S. Ripp Sobolev Institute of Geology and Mineralogy Russian Academy of Sciences 52 PUBLICATIONS 239 CITATIONS 71 PUBLICATIONS 332 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Petrological, geochemical, and physico-chemical factors of metal-bearing capacity of carbonate melts and magmatic fluids as criteria of estimation of ore productivity (REE, Au, Pt) of alkaline massifs View project Petrological, geochemical, and physico-chemical factors of metal-bearing capacity of carbonate melts and magmatic fluids as criteria of estimation of ore productivity (REE, Au, Pt) of alkaline massifs View project All content following this page was uploaded by Anna Doroshkevich on 03 July 2016. The user has requested enhancement of the downloaded file. Miner Petrol (2010) 98:245–268 DOI 10.1007/s00710-009-0063-4 ORIGINAL PAPER Genesis of the Khaluta alkaline-basic Ba-Sr carbonatite complex (West Transbaikala, Russia) Anna G. Doroshkevich & German S. Ripp & Kathryn R. Moore Received: 18 November 2008 /Accepted: 11 June 2009 /Published online: 29 June 2009 # Springer-Verlag 2009 Abstract The Khaluta carbonatite complex comprizes Introduction fenites, alkaline syenites and shonkinites, and calcite and dolomite carbonatites. Textural and compositional criteria, One of the key questions regarding the petrogenesis of melt inclusions, geochemical and isotopic data, and carbonatite is whether they form directly by partial melting comparisons with relevant experimental systems show that of a carbonated peridotite mantle (e.g. Wallace and Green the complex formed by liquid immiscibility of a carbonate- 1988; Dalton and Wood 1993; Harmer and Gittins 1998), saturated parental silicate melt. Mineral and stable isotope by fractional crystallization (e.g. Otto and Wyllie 1993), or geothermometers and melt inclusion measurements for the by liquid immiscibility of a silicate parental melt (e.g. silicate rocks and carbonatite all give temperatures of Kjarsgaard and Hamilton 1989; Lee and Wyllie 1998). crystallization of 915–1,000°C and 890–470°C, respective- Both fractional crystallization and liquid immiscibility ly. Melt inclusions containing sulphate minerals, and may be important processes in carbonatite magma evolu- sulphate-rich minerals, most notably apatite and monazite, tion in subvolcanic and volcanic environments, and the occur in all of the lithologies in the Khaluta complex. All aim of this research is to define the most probable path lithologies, from fenites through shonkinites and syenites to from a source with identified characteristics to emplaced calcite and dolomite carbonatites, and to hydrothermal rock compositions for a particular occurrence (Khaluta) mineralisation are further characterized by high Ba and Sr based on integrated evidence from field, geochemical and activity, as well as that of SO3 with formation of the experimental studies. The hypothesis of liquid immisci- sulphate minerals baryte, celestine and baryte-celestine. bility has been favoured by many authors for alkali-rich as Thus, the characteristic features of the Khaluta parental well as alkali-poor carbonatites and is supported by field melt were elevated concentrations of SO3, Ba and Sr. In evidence, experimental data and melt inclusion studies addition to the presence of SO3, calculated fO2 for (e.g. Romanchev and Sokolov 1980; Panina 2005). Asso- magnetites indicate a high oxygen fugacity and that ciation with silicate rocks is one of the important criterion Fe+3>Fe+2 in the Khaluta parental melt. Our findings for the hypothesis of carbonatite formation by immiscible suggest that the mantle source for Khaluta carbonatite and separation. Carbonatites are often associated with alkaline associated rocks, as well as for other carbonatites of the igneous rocks such as ijolites and nepheline syenites, and West Transbaikalia carbonatite province, were SO3-rich and only 10% of carbonatite occurrences have been found in characterized by high oxygen fugacity. association with mafic rocks (Woolley 2003). Examples of the latter are Mountain-Pass, USA (Olson et al. 1954), Mushugai-Khuduk, Mongolia (Samoilov and Kovalenko 1983), Kaiserstuhl, Germany (Hay and O’Neil 1983) and Editorial handling: L.G. Gwalani Khaluta, Russia (Yarmolyuk et al. 1997; Ripp et al. 2000). However, most of these occurrences do not have a well- * : : A. G. Doroshkevich ( ) G. S. Ripp K. R. Moore supported genetic model of formation. Some authors (e.g. Geological Institute SB RAS, Ulan Ude, Russia Yarmolyuk et al. 1997; Ripp et al. 2000; Mariano 1989) e-mail: [email protected] suggest that these carbonatites are magmatic, while others 246 A.G. Doroshkevich et al. regards these rocks as carbothermal residua (Mitchell 2005; carbonates. δ34S values were also measured in inclusions Rass et al. 2006). Therefore, the Khaluta carbonatite within minerals, where it had been shown that inclusions complex is now rigorously examined in order to also usually contain water-soluble K, Na sulphates, as found in establish the nature of the relationship between carbonatite previous investigations (Doroshkevich and Ripp 2004). The and associated mafic rocks. The petrogenetic association of samples of minerals containing the inclusions were crushed carbonatites with alkaline igneous rocks of the Khaluta to a powder and then processed using distilled water. K, Na complex has been previously ascertained on the grounds of sulphates from inclusions were dissolved during this geological, geochronological and petrographic data and the process, and then were precipitated by addition of BaCl2. 34 similarity of isotopic composition of carbonatites and the The resulting BaSO4 precipitate was analyzed for δ S carbonate component of alkaline rocks (Ripp et al. 1998, isotope values. 2000; Nikiforov et al. 1998, 2000; Bulnaev and Posokhov Inclusions were studied in polished wafers up to 0.3 mm 1995; Bulnaev 1996). In this paper, we present new results thick, using optical and thermometric methods. Primary and combined with previously reported mineralogical and secondary inclusions were distinguished using textural geochemical data on Khaluta carbonatites (Ripp et al. criteria formulated by Roedder (1983). Inclusions that 1998, 2000; Nikiforov et al. 1998, 2000). Specifically, the clustered along randomly orientated surfaces tracing healed results of melt inclusion studies, experimental phase microcracks were considered secondary. Random, solitary equilibrium studies, calculated trace element partition inclusions were considered to be primary. A heating stage coefficients between silicate and carbonate pairs, and for temperatures up to 400°C with a silicon carbide heating detailed mineralogical, geochemical and stable isotope element was used (Sobolev and Kostyuk 1975). Tempera- characteristics are examined, which collectively provide ture was measured using a Pt\Pt-Rh thermocouple (type S) important insights into the source characteristics of magmas calibrated against the melting points of S, NaNO3, and the petrogenesis of the Khaluta complex. K2Cr2O7, NaCl and two standard fluid inclusions synthe- sized at controlled temperature and pressure. The power- law best fit of these data yielded a standard error for Analytical methods temperature measurements of ± 5°C. Heating of inclusions under confining argon pressure was carried out using an Whole-rock chemistry was determined by atomic absorp- internally heated pressure vessel at the Institute of Exper- tion (Perkin-Elmer) and conventional chemical methods. imental Mineralogy (IEM RAS), Chernogolovka, for 24 h CO2 was determined by titrametric chemical decomposi- at pressures up to 0.5 GPa and 1,000°C. tion. ICP-MS (Finnigan MAT, Bremen, Germany) was used Chemical analysis of daughter crystals was carried out for measuring trace and REE elements in a sample under using a MAR-3 WDS microprobe (accelerating voltage of standard operating conditions for these devices. All the 20 kV, a beam current of 40 nA, a beam size of 3–4 µm and above-mentioned investigations were carried out in the 20 s counting time) and scanning electron microscope Vinogradov Institute of Geochemistry and Analytical (LEO-1430) with energy-dispersive spectrometer (Inca Chemistry, SB RAS, Irkutsk, Russia. Energy-300) (SEM-EDS). Strontium isotope values in rubidium-free minerals were measured using an МI-1201 Т mass-spectrometer. The minerals were analyzed using electron probe micro-analysis Geology (EPMA): a MAR-3 WDS microprobe with an accelerating voltage of 20 kV, beam current of 40 nA, beam size of The Khaluta carbonatite complex is a part of a Late 3 μmto4μm and a 20 s counting time, and a LEO-1430 Mesozoic West Transbaikalia carbonatite province (Ripp scanning electron microscope with an IncaEnergy-300 et al. 2002) within an intracontinental rift (volcanic) zone energy-dispersive system (SEM-EDS) operated at 20 kV represented by a large (200–1,000 km) system of grabens and 0.5 nA. All the above analyses were carried out in the and associated fields of Late Mesozoic to Cenozoic laboratories of the Geological Institute SB RAS (Ulan-Ude, volcanic rocks (Yarmolyuk et al. 1995, 2001). The magmat- Russia).
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