The role of eclogites in the redistribution of water in the subcontinental mantle of the Siberian craton: results of determination of the water content in minerals from the Udachnaya pipe eclogites

Abstract

A comprehensive study of 26 mafic mantle xenoliths from the Udachnaya kimberlite pipe was carried out. The contents of major and trace elements, equilibrium temperature parameters, and water content in the rock-forming minerals were determined. The temperatures of formation of the studied rocks are estimated at 800–1300 °C. According to IR spectroscopy data, the water content in clinopyroxenes from the studied eclogites varies from values below the detection limit to 99 ppm. The IR spectra of garnets lack bands of water. The water content in clinopyroxene and orthopyroxene from garnet websterite is 72 and 8 ppm, respectively. The water content in the average rock, calculated from the ratio of the rock-forming minerals, varies from a few to 55 ppm. No relationship among the water content, equilibrium temperatures, and rock composition is established. The low water contents in the eclogites are close to the earlier determined water contents in peridotites from the same pipe and are, most likely, due to the re-equilibration of the eclogites with the rocks of the peridotitic lithospheric mantle. The dehydration of the protolith during its subduction and the partial melting of eclogites before their removal by kimberlitic magma to the surface might be an additional cause of the low water contents in the mantle eclogite xenoliths.

Origin of Water in Mantle Eclogites from the V. Grib Kimberlite Pipe, NW Russia

“…Figure 9 illustrates the range of water content in global eclogite clinopyroxenes and those of the V. Grib pipe. The water content in the clinopyroxene of the V. Grib pipe eclogites (39-111 ppm) was similar to or equal to those of the Udachnaya (61-152 ppm, [16]; 7-91 ppm, [17]) and Mir (31-61 ppm, [16]) kimberlites and was three to nine times lower than that of the eclogites from the Kaapvaal Craton (250-1840 ppm, [20]; 211-1496 ppm, [15]), the Obnazhennaya (448-466 ppm, [16]) and Zagadochnaya (504-510 ppm, [16]) kimberlites and the orogenic massifs (450-1650 ppm, [28]; 111-695 ppm, [35]; 400-820 ppm, [43]). However, the two garnets from the V. Grib pipe eclogites contained the highest concentrations of water (211 and 337 ppm) compared with all previously studied cratonic samples, including eclogites (1-120 ppm, [14,34,68]), peridotites (1-133 ppm, [1,3,14,34]), pyroxenites (1-47 ppm, [34]), and megacryst (1-135 ppm, [14,34,66]) associations.…”

“…The eclogites are minor components of the lithospheric mantle and their origin can be linked to several distinctively different processes: (1) metamorphism and the partial melting of various stratigraphic levels of the ancient oceanic crust during subduction (e.g., [5][6][7]), (2) crystallisation of the primary mantle melts at high pressure (e.g., [8,9]), and (3) the reaction between the peridotite and siliceous partial melts that are derived from the crustal rocks of the subducting plate (e.g., [10][11][12][13]). To date, the available data on the water content in the cratonic eclogite NAMs are sparse [14][15][16][17][18][19][20]. However, the juxtaposition and interpretation of the origin of eclogites with water content in their NAMs can provide additional information about water cycles in the lithospheric mantle and the factors that control their saturation with water.…”

Ultramafic Carbonated Melt‐ and Auto‐Metasomatism in Mantle Eclogites: Compositional Effects and Geophysical Consequences

“…Electrical conductivity, which can be extracted from regional magnetotelluric studies, is strongly temperature‐dependent, but also increases with increasing mineral H 2 O content (e.g., Jones et al, 2009; Yang et al, 2011; Zhao & Yoshino, 2016). With the exception of the Roberts Victor and Udachnaya (Siberia) eclogites studied by Huang et al (2014) and Kolesnichenko et al (2018), respectively, there are no comprehensive published studies on H 2 O content in mantle eclogite suites. Garnet in both studies has very low H 2 O contents, but whereas clinopyroxene in eclogite from Udachnaya has a low median content of ~40 ppm, that from Roberts Victor contains ~760 ppm H 2 O.…”

Micro-Raman Spectroscopy Assessment of Chemical Compounds of Mantle Clinopyroxenes

“…In total, 28 clinopyroxene grains were also selected from peridotite (n = 8) and eclogite (n = 20) xenoliths from Udachnaya kimberlite pipe. The characterization of the clinopyroxenes from these samples is provided in [12,13]. The discrimination of clinopyroxenes of different paragenesis: (a) Mg# vs. Cr# of clinopyroxenes-lherzolitic, websteritic, and eclogitic compositional fields and the transition from peridotite to eclogite clinopyroxenes at Cr# 0.07-0.10 (gray vertical stripe) are taken from [2]; (b) Na 2 O vs. MgO contents in clinopyroxenes (A, B, C are the groups of eclogites are shown according to [3]).…”

“…In total, 28 clinopyroxene grains were also selected from peridotite (n = 8) and eclogite (n = 20) xenoliths from Udachnaya kimberlite pipe. The characterization of the clinopyroxenes from these samples is provided in [12,13]. The chemical composition of the clinopyroxenes was determined on a JEOL JXA-8100 electron probe microanalyzer (EPMA), equipped with five wavelength-dispersive spectrometers and an energy-dispersive (EDX) spectrometer at an accelerating voltage of 20 kV and probe current of 100 nA.…”