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- Title
Titanium-rich metasomatism in the lithospheric mantle beneath the Arkhangelsk Diamond Province, Russia: insights from ilmenite-bearing xenoliths and HP–HT reaction experiments.
- Authors
Kargin, Alexey; Bussweiler, Yannick; Nosova, Anna; Sazonova, Lyudmila; Berndt, Jasper; Klemme, Stephan
- Abstract
To provide new insights into the interaction of ultramafic alkaline melts with the subcontinental lithospheric mantle, we present results of a petrographical-mineralogical study of ilmenite-bearing mantle xenoliths from the Grib kimberlite, Archangelsk, Russia along with results from reaction experiments between harzburgite and Fe–Ti bearing carbonate–silicate melts similar to aillikite. The compositions of orthopyroxene, ilmenite and garnet from our mantle xenoliths are similar to compositions of minerals of the low-Cr megacryst suite from different kimberlite occurrences worldwide including the Grib kimberlite as well as minerals from sheared lherzolite xenoliths captured by the Grib kimberlite. This suggests that ilmenite-bearing xenoliths, megacrysts, and sheared lherzolite xenoliths could have a common origin and/or formed under similar conditions. The reaction experiments were performed at 4 GPa and 1200 °C with varying proportions of aillikite (0, 10, and 50 wt%) that reacted with harzburgite. The experimental runs with 10% and 50% aillikite resulted in two layers within the capsule, with an ilmenite-bearing reaction zone at the contact between aillikite and harzburgite, and an ilmenite-free zone characterized by higher garnet and clinopyroxene abundances. An increase of aillikite melt is directly correlated with increasing TiO2 and decreasing Cr2O3 contents and Mg# values in the mineral phases, most significantly for pyroxenes. Overall, the experiments produce a chemical gradation of minerals from Cr-rich (Fe–Ti-poor) to Cr-poor (Fe–Ti-rich) which is strikingly similar to the chemical gradation observed in minerals from natural mantle-derived xenoliths from kimberlites. In summary, comparison of our experimental data with natural samples indicates possible links between the generation of megacrysts and Ti-rich metasomatism of the lithospheric mantle by ultramafic alkaline (aillikite-related) melts and their possible evolution towards kimberlites. Our results illustrate the importance of melt-rock ratios in generating the mineralogical and chemical diversity in mantle xenolith suites.
- Subjects
ARKHANGELSK (Russia); RUSSIA; INCLUSIONS in igneous rocks; METASOMATISM; KIMBERLITE; ORTHOPYROXENE; LHERZOLITE; DIAMONDS
- Publication
Contributions to Mineralogy & Petrology, 2021, Vol 176, Issue 12, p1
- ISSN
0010-7999
- Publication type
Article
- DOI
10.1007/s00410-021-01863-9