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êDmitriy S. Ashikhmin, Yi-Xiang Chen, Sergey G. Skublov, Aleksey E. Melnik
Geochemistry of Spinels from Xenoliths of Mantle Lherzolites...
Geology
UDC 550.42
GEOCHEMISTRY OF SPINELS FROM XENOLITHS OF MANTLE LHERZOLITES (SVERRE VOLCANO, SPITSBERGEN ARCHIPELAGO)
Dmitriy S. ASHIKHMIN \ Yi-Xiang CHEN 2, Sergey G. SKUBLOV 3, Aleksey E. MELNIK3
1 A.P.Karpinsky Russian Geological Research Institute, Saint-Petersburg, Russia
2 School of Earth and Space Sciences of University of Science and Technology of China, Hefei, China
3 Institute of Precambrian Geology and Geochronology Russian Academy of Sciences, Saint-Petersburg, Russia
The paper presents the results of a study (LA-ICP-MS method) of spinel from the collection of mantle xenoliths of lherzolites (seven xenoliths) selected in quaternary alkaline basalts of the Sverre volcano, the Spitsbergen archipelago. The study of two large (more than 15 cm in diameter) xenoliths made it possible to study changes in the composition of minerals in the central, intermediate, and marginal parts of the samples of chromium diopside spinel lherzolites. The sinusoidal character of the REE distribution in spinels, which indicates the manifestation of mantle metasomatism, is established.
The results obtained for the first time on the trace-element composition for spinels from mantle xenoliths in alkaline basalts of the Spitsbergen archipelago are supplemented by data on the geochemistry of spinels of mantle origin published in the world literature.
Key words: spinel, mantle xenoliths, mantle metasomatism, mineral geochemistry, LA-ICP-MS, Spitsbergen archipelago
How to cite the article: Ashikhmin D.S., Chen Y.-X., Skublov S.G., Melnik A.E. Geochemistry of Spinels from Xenoliths of Mantle Lherzolites (Sverre volcano, Spitsbergen archipelago). Zapiski Gornogo instituta. 2017. Vol. 227, p. 511-517. DOI: 10.25515/PMI.2017.5.511
Introduction. The study of mantle xenoliths is the only source of information on the deep structure of the Earth. Xenoliths are witnesses and participants in the processes occurring in the mantle, and carry information about the mineralogical and geochemical changes associated with migration and redistribution of matter.
The choice of spinel material for a detailed mineralogical and geochemical analysis of xenoliths and reconstruction of processes occurring in the mantle is not accidental. Spinel is the most stable and resistant to secondary changes in the mineral, which tends to retain its primary composition, which is important in studying the structure of the upper mantle of the Earth [6].
In this paper, we present the results of a spinel study from the collection of mantle xenoliths (seven xenoliths) selected in quaternary alkaline basalts of the Sverre volcano, the Spitsbergen archipelago. At our disposal were two large (more than 15 cm in diameter) xenoliths, which allowed investigating changes in the composition of minerals in the central, intermediate, and marginal parts of the samples of chromium diopside spinel lherzolites.
Mantle xenoliths were extracted on the surface by quaternary alkaline basaltic melts. According to already existing data, spinel lherzolites underwent at least two significant processes: depletion caused by partial melting, and then to the effects of mantle metasomatism [3]. At the mineral level, the latter process is characterized by the appearance of newly formed minerals developing in the primary minerals of xenoliths, in particular, the formation of a new spinel generation should be noted (Fig. 1).
Analytical methods. The chemical composition of the minerals at the level of the main elements is determined by the SEM-EDS method at the IPGG of the Russian Academy of Sciences using the scanning electron microscope JEOL JSM-6510LA with the energy dispersing attached device JED-2200. Thin polished plates of rocks were covered with a layer of carbon. Point samples were used to determine the composition of minerals with the help of an electron beam with an accelerating voltage of 20 kV and a current of 1 nA, the beam spot size was 3 p,m. The accumulation time of each spectrum is 35 s, natural minerals, pure oxides and metals were used as standards. To correct the matrix effect, the ZAF algorithm was used.
Rare earth and trace elements were measured by the LA-ICP-MS method at the Laboratory of mantle-crust substance and environment of the University of Science and Technology of China.
j "» Dmitriy S. Ashikhmin, Yi-Xiang Chen, Sergey G. Skublov, Aleksey E. Melnik
Geochemistry of Spinels from Xenoliths of Mantle Lherzolites...
Fig. 1. Image in BSE mode of spinels from mantle xenoliths: a - spinel of the first generation of Sp1 become cluttered with crystals of the second generation of Sp2; b - inclusion of olivine Ol in grain of spinel
The detailed conditions of the laser ablation system and the ICP-MS tool and data processing are given in [5]. The GeLAS 2005 laser was 193 nm ArF and the Agilent 7900 ICP-MS mass spectrometer. Helium was used as the carrier gas. Argon was used as an additive gas and mixed with the carrier gas through a T-connector before entering the ICP.
Each analysis consisted of measuring the background (~20-30 s) and analyzing the actual sample (50 s). The content of the elements was calibrated according to the widely accepted standards (BCR-2G, BIR-1G, BHVO-2G and GSE-1G), the NIST 610 standard was used to calibrate the drift of the signal during the analysis. The spot size of the analysis was 32-44 p,m. Processing of background and analytical signals, correction of time displacement and quantitative calibration was performed using the ICPMSDataCal program [4, 5]. A signal with a temporal resolution for each analysis was carefully checked for jumps in the content of each element, and in most cases only a «clean» part of the spectrum with a smooth signal intensity was selected. The accuracy and reproducibility of the analysis, based on the repeated analysis of standards, for most trace elements is not worse than ± 10% (2o).
Results and discussion. According to the petrographic composition, xenoliths are represented by spinel lherzolites of the following mineral composition typical of these rocks: olivine (80 %), clinopyroxene (13 %), orthopyroxene (5 %), spinel (2 %). Spinel is divided into two generations: the first - crystals that originated from the original melt, and the second, associated with the process of mantle metasomatism (Fig.1, a).
Spinel of the first generation is represented by xenomorphic crystals located in the intergranular space of olivine and clinopyroxene. The size of the spinel crystals varies from 50 p,m to the first millimeters. According to its chemical composition, the first generation of spinel refers to hercynite, the Al2O3 content averages 53 %, and Cr2O3 is 13 % by mass. Individual grains of spinel are not generally zonal in composition, however, when the composition of different spinel grains is compared, even within a single sample, the variations of the content of the main elements is observed.
Small crystals of the second generation, with an average size of 5 p,m, have a more idiomorphic appearance and are cluttered in the form of a fine grain brush of the spinel of the first generation (Fig.1, a). According to the content of the main elements, the spinel of the second generation differs from the first generation by a reduced content of alumina (up to 42 % by mass) and an increase in the Cr2O3 content by an average of 20 %. The small size of the crystals of the second generation does not allow us to investigate them by the laser ablation method, therefore, below is discussed the trace-element composition of the spinel of only the first generation.
Representative compositions of first-generation spinels according to LA-ICP-MS are given in the table. The content of oxides of the main elements according to LA-ICP-MS is in good agreement with the results of spinel analysis on an electronic microanalyzer - the average content of alumina according to laser ablation data is also 53.1 % by mass. It should be noted that in the
êDmitriy S. Ashikhmin, Yi-Xiang Chen, Sergey G. Skublov, Aleksey E. Melnik
Geochemistry of Spinels from Xenoliths of Mantle Lherzolites...
large xenoliths SH-1 and SH-2 there are noticeable strong fluctuations in the alumina content depending on the region of the sample from which the spinels were selected. Thus, in the central, intermediate and marginal zone, the content of alumina in spinels has the following average values: 55.5, 51.8 and 50.8 % by mass, respectively. The remaining xenoliths are characterized by consistent alumina content (on average 54 %), close to the spinel composition from the central part of the large xenoliths.
Spinel composition by LA-ICP-MS data
Sample MgO AI2O3 Cr2O3 FeO Ti V Mn Co Ni Cu Zn Sn Mg # Cr # Dmelt
wt % PPm
21.7 53.3 11.6 11.5 533 399 803 286 3275 2.58 1236 1.11 38.0 40.8 18.94
21.3 53.5 12.1 11.4 434 405 781 270 3296 2.72 1242 0.98 39.1 42.0 19.43
22.0 53.0 11.8 11.5 440 397 843 278 3258 3.00 1220 1.04 38.5 41.3 19.14
SH-1b-1b-15 (central part of the xenolith SH-1) 21.5 21.7 53.5 53.3 8 6 11.6 11.5 433 438 410 407 819 804 275 281 3297 3578 3.71 3.43 1266 1307 0.94 1.16 37.7 38.4 40.5 41.2 18.79 19.11
21.5 53.3 11.9 11.6 456 404 789 272 3225 3.14 1184 1.02 38.3 41.1 19.04
21.9 53.7 11.3 11.4 440 431 797 279 3284 2.67 1247 0.74 37.6 40.5 18.78
21.5 53.2 11.6 11.8 440 400 819 296 3214 3.50 1295 1.02 37.4 40.3 18.69
21.0 54.9 11.3 11.2 447 390 773 276 3063 3.10 1190 0.60 38.0 40.8 18.91
21.7 53.7 11.2 11.6 427 391 799 299 3375 2.90 1276 1.08 37.0 39.8 18.50
20.6 51.1 14.1 12.3 491 470 829 267 2950 2.48 1176 0.91 41.2 44.1 20.33
SH-1b-2b-15 20.6 51.5 13.8 12.4 494 458 811 253 2829 1.93 1080 0.79 40.4 43.3 19.98
(intermediate part 20.3 50.7 14.7 12.4 536 481 846 259 2864 2.54 1240 0.93 41.8 44.7 20.58
of the xenolith SH-1) 21.1 49.8 14.3 12.9 476 457 842 264 2967 2.38 1144 0.99 40.3 43.2 19.96
21.0 50.1 14.1 12.9 483 465 880 274 3015 2.60 1223 1.18 40.0 42.8 19.79
20.8 51.1 13.9 12.3 495 464 847 266 3063 2.04 1218 1.16 40.8 43.7 20.17
SH-1b-3b-15 20.4 51.6 14.0 12.1 507 511 841 266 2966 3.01 1151 0.98 41.2 44.1 20.31
(marginal part of 20.6 51.6 13.9 12.1 481 469 857 258 2994 2.89 1133 0.91 41.2 44.1 20.34
the xenolith SH-1) 20.4 51.9 13.8 12.1 495 467 831 261 2897 2.28 1183 0.95 41.0 43.9 20.24
20.8 51.1 13.9 12.2 486 461 834 261 2958 2.62 1192 1.22 40.8 43.7 20.16
21.4 55.0 10.1 11.2 390 360 790 276 3257 3.51 1309 1.10 35.5 38.2 17.83
21.2 56.0 10.1 11.1 401 363 798 280 3330 2.95 1290 1.14 35.7 38.5 17.92
21.5 55.6 10.0 11.4 352 359 804 285 3309 2.61 1384 0.90 34.9 37.7 17.59
SH-2b-1b-15 (central part of the xenolith SH-2) 21.5 21.1 55.9 56.4 10.0 10.3 11.1 10.8 352 439 354 367 798 766 277 264 3258 3097 2.61 3.12 1319 1210 0.77 0.91 35.4 36.6 38.1 39.3 17.78 18.30
21.9 55.2 10.4 11.1 417 371 791 278 3251 3.34 1278 0.85 36.3 39.0 18.17
21.5 55.6 10.4 11.1 423 369 786 279 3228 2.65 1263 0.78 36.2 38.9 18.13
21.6 55.0 10.4 11.4 440 371 813 288 3433 2.74 1302 1.09 35.8 38.6 17.99
21.5 55.2 10.3 11.5 445 368 800 281 3280 3.24 1248 0.90 35.3 38.1 17.75
21.7 54.8 10.7 11.3 440 364 811 286 3295 2.79 1241 1.02 36.5 39.3 18.27
20.7 52.0 14.3 11.6 442 443 762 248 2780 2.42 1073 0.41 42.7 45.7 20.99
21.1 51.3 14.4 11.9 440 442 776 250 2771 2.36 1075 0.25 42.3 45.3 20.82
21.0 51.1 14.7 11.8 453 448 780 257 2821 2.65 1068 0.45 43.1 46.0 21.15
21.3 50.4 15.2 11.8 482 455 796 261 2860 2.12 1111 0.44 43.9 46.8 21.47
21.0 51.5 14.6 11.5 468 441 791 260 2860 2.45 1096 0.44 43.5 46.4 21.31
SH-2b-2b-15 21.4 50.6 14.6 11.9 442 446 811 270 3012 2.04 1152 0.39 42.8 45.8 21.04
(intermediate part 21.1 50.9 14.7 11.9 441 442 807 269 3048 2.52 1140 0.24 42.7 45.6 20.98
of the xenolith 21.0 50.9 15.0 11.7 424 437 811 267 2974 2.46 1120 0.59 43.8 46.7 21.44
SH-2) 21.1 51.1 14.5 11.9 454 444 805 267 3001 2.36 1131 0.38 42.5 45.4 20.89
21.0 51.4 14.4 11.8 446 444 808 271 3009 2.45 1117 0.31 42.5 45.5 20.90
20.8 50.1 15.6 12.1 480 455 847 266 2898 2.64 1116 0.28 43.8 46.7 21.44
20.7 50.0 15.6 12.2 482 460 822 268 2944 2.67 1116 0.51 43.7 46.7 21.42
20.9 51.0 14.6 12.1 428 445 809 265 2979 2.17 1112 0.42 42.3 45.3 20.82
20.4 50.4 15.3 12.4 445 456 824 266 2889 2.52 1151 0.45 42.9 45.9 21.07
Dmitriy S. Ashikhmin, Yi-Xiang Chen, Sergey G. Skublov, Aleksey E. Melnik DOI: 10.25515/PMI.2017.5.511
Geochemistry of Spinels from Xenoliths of Mantle Lherzolites...
End of the table
Sample MgO AlA Cr2O3 FeO Ti V Mn Co Ni Cu Zn Sn Mg # Cr # Dmelt
wt % PPm
20.4 51.8 14.5 11.9 453 453 794 259 2925 2.38 1138 0.55 42.5 45.5 20.90
SH-2b-3b-15 (marginal part of the xenolith SH-2) 21.3 21.1 50.5 50.6 14.3 14.7 12.3 12.1 444 455 439 452 792 787 259 259 2891 2816 2.37 2.17 1103 1121 0.56 0.42 41.4 42.4 44.3 45.3 20.43 20.85
21.0 51.0 14.4 12.2 450 451 798 257 2876 2.42 1075 0.48 41.6 44.5 20.52
21.3 51.1 14.2 12.0 442 459 779 257 2849 2.19 1084 0.33 41.9 44.8 20.64
21.0 50.9 14.9 11.8 465 450 809 254 2810 2.19 1057 0.53 43.5 46.4 21.31
22.0 54.4 11.7 10.4 432 384 730 255 3096 4.23 1124 0.38 40.5 43.3 20.00
22.1 54.6 11.4 10.5 428 380 718 250 3018 3.10 1083 0.34 39.8 42.7 19.74
22.2 54.5 11.5 10.3 491 394 719 254 3158 3.02 1072 0.40 40.4 43.3 19.99
22.0 54.9 11.4 10.3 461 394 733 255 3141 3.50 1116 0.46 40.2 43.1 19.89
22.6 55.0 11.1 9.9 461 411 694 245 3004 3.26 1084 0.43 40.4 43.3 19.98
21.8 55.4 11.5 9.9 484 406 701 250 2998 3.54 1079 0.38 41.3 44.2 20.39
22.2 55.1 11.5 9.8 488 392 705 251 3125 3.16 1079 0.46 41.7 44.6 20.55
SH-4-15 22.1 54.2 12.0 10.1 514 417 735 269 3167 2.85 1118 0.48 41.8 44.7 20.59
22.0 54.2 12.2 10.2 429 397 746 256 3182 3.21 1089 0.36 42.2 45.1 20.74
22.0 55.2 11.5 9.8 450 386 728 262 3180 3.32 1128 0.37 41.7 44.6 20.53
21.5 55.3 11.8 10.0 456 388 737 260 3218 3.57 1116 0.39 41.7 44.6 20.55
21.8 54.8 11.8 10.1 511 413 736 261 3142 3.28 1114 0.38 41.4 44.3 20.41
22.5 54.1 12.0 9.9 446 415 746 269 3141 3.15 1130 0.33 42.4 45.4 20.87
22.0 54.4 11.7 10.6 479 410 736 265 3151 3.44 1130 0.37 40.2 43.0 19.87
21.7 55.3 11.9 9.7 415 387 731 263 3052 3.16 1140 0.23 42.6 45.6 20.94
21.0 53.1 11.9 12.4 471 444 799 266 2846 1.48 1181 0.55 36.7 39.5 18.38
20.3 54.4 11.8 11.8 484 395 768 259 2972 2.10 1127 0.50 37.9 40.7 18.88
19.9 52.3 14.2 12.0 442 398 826 255 2707 1.52 1147 0.47 41.8 44.7 20.60
20.1 52.4 13.6 12.1 418 444 824 262 2770 2.54 1121 0.72 40.5 43.4 20.01
21.0 53.7 10.9 12.6 464 399 789 260 2886 3.99 1178 0.63 34.5 37.2 17.40
20.6 52.5 11.5 13.6 468 404 843 296 2973 2.10 1177 0.64 34.0 36.7 17.18
21.3 52.0 13.4 11.6 427 425 762 263 2761 1.79 1114 0.38 41.2 44.1 20.32
SH-5-15 20.7 53.6 11.8 12.3 409 404 821 266 2895 1.69 1181 0.62 36.8 39.6 18.42
20.5 53.5 11.9 12.4 415 408 831 266 2952 1.50 1186 0.44 36.9 39.7 18.46
22.5 52.5 11.5 11.9 433 396 794 269 2904 1.99 1181 0.55 36.9 39.8 18.47
20.8 52.8 13.2 11.6 458 409 748 249 2841 1.63 1179 0.47 40.8 43.7 20.14
20.9 54.3 10.6 12.4 479 403 776 258 3038 1.60 1156 0.55 34.2 36.9 17.27
20.9 53.6 11.8 12.0 429 422 829 268 2871 1.86 1224 0.55 37.4 40.2 18.68
20.4 52.5 13.7 11.8 494 392 751 243 2835 1.67 1116 0.36 41.3 44.2 20.36
20.7 54.0 11.0 12.6 471 401 805 259 2965 2.26 1239 0.47 34.8 37.5 17.52
22.3 54.0 11.6 10.7 519 395 738 252 3050 3.11 1054 0.37 39.9 42.8 19.75
22.0 54.9 11.1 10.5 454 383 706 249 2954 2.92 1085 0.29 39.1 41.9 19.40
SH-6-15 21.7 55.2 11.1 10.6 499 391 707 249 3069 3.13 1076 0.29 38.9 41.7 19.31
21.6 55.5 11.2 10.3 466 390 703 255 3041 3.14 1042 0.38 39.7 42.5 19.66
21.6 54.7 11.9 10.5 522 407 736 247 2929 2.97 1091 0.43 40.8 43.6 20.13
21.0 52.7 11.7 12.6 476 409 848 282 3143 1.92 1247 0.45 36.2 38.9 18.13
20.7 53.7 11.5 12.2 467 434 825 274 3024 1.80 1270 0.56 36.4 39.1 18.21
SH-7-15 20.6 53.8 11.3 11.9 431 404 803 255 2833 5.51 828 0.61 36.7 39.5 18.35
20.6 53.4 12.5 11.8 480 397 774 260 3048 2.48 1193 0.50 39.1 42.0 19.41
21.1 54.3 10.8 12.0 509 411 793 335 3122 2.51 1185 0.43 35.3 38.1 17.76
Mg # = Mg / (Mg x Fetot) x 100 % in the studied samples of spinels varies, a difference is observed in this index even within one sample (see table). In large xenoliths, the magnesia of spinels is of a consistent variation, but only in its own zone. Thus, in the SH-1 and SH-2 xenoliths in the central part, the average magnesia value is 35.8, in the intermediate region - 40.7, and in the mar-
Dmitriy S. Ashikhmin, Yi-Xiang Chen, Sergey G. Skublov, Aleksey E. Melnik
Geochemistry of Spinels from Xenoliths of Mantle Lherzolites...
ginal zone - 38.0. This character of zoning can be explained by the presence in the intermediate part of large xenoliths of microinclusions of olivine in spinel according to electron microscopy. Further interaction of fluids with olivine microinclusions leads to a redistribution of part of magnesium to the host olivine spinel [3].
Cr# = Cr / (Cr x Fetot) x 100 % of studied spinel varies from 36.7 to 46.8 without certain regularities. So, in one sample this indicator can vary from 38.1 to 42.0 (see table). In large xenoliths there is a marked increase in chromium content from the center to the edge. Most likely, this is due to mantle metasomatism, manifested in the form of partial melting processes, which manifested itself in the investigated xenoliths [7]. The degree of partial melting can be estimated using the regression equation [1]:
Dwelt = 0.426 x Cr# + 1.538.
where Dmeit - degree of partial melting, %; Cr# - chromium content index for spinels, %.
The degree of partial melting averages about 20 %, not exceeding 21.5 % (see table). The degree of partial melting is most strongly represented in the intermediate part of the large xenoliths, and not in the marginal xenoliths. This pattern is most likely associated with a temperature gradient in large xenoliths during processes of mantle metasomatism, in which the fluid unevenly affects the entire volume of a large xenolith.
By the ratio of the principal elements, a regular inverse correlation of the content in spinels MgO and FeO (Fig.2, a) and Al2O3 and Cr2O3 is observed (Fig.2, b), due to isomorphous substitutions of these pairs of elements. With respect to the correlation of chromium with other elements, it is worth noting the dependences associated with manganese (Fig.2, c). The chart clearly shows two trends. fundamentally different in the nature of the correlation of the content in the spinels Q2O3
14 1
13
12
10
900
850
750
700
-i-i a
»« * i*T
■ ■
!
■ SH-2b-1b-15
• SH-2b-2b-15 A SH-2b-3b-15 V SH-1b-1b-15
SH-1b-2b-15 ► SH-1b-3b-15
• SH-4-15
• SH-5-15
• SH-6-15
• SH-7-15
♦ ♦
20 20.5
21 21.5 MgO
22 22.5
V
1 ^
. " *
\ #
* t
♦
10
11
12 13 &2O3
14 15 16
U
16 15 14 13 12 11 10
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ft s $
f
* ■
■ #
50 51 52
53 54
Al2O3
55 56 57
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* * * ♦
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10 11
12
13 Cr2O3
14 15
16
Fig.2. Composition of spinels from mantle xenoliths of Sverre volcano
b
a
9
d
c
Dmitriy S. Ashikhmin, Yi-Xiang Chen, Sergey G. Skublov, Aleksey E. Melnik
Geochemistry of Spinels from Xenoliths of Mantle Lherzolites...
0.1
0,01
0.001.
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
0.1
0.01
0.001
11 and Mn. For large xenoliths in the central and
intermediate parts, as well as in smaller xenoliths (SH-4-15, SH-6-15), there is a positive correlation of these elements, for marginal parts and xenoliths of smaller size (SH-5-15, SH-7-15) is a less significant negative correlation. Such an ambiguous distribution is difficult to interpret. We can note the direct dependence for all the samples of spinels between the contents of Cr2O3 and V (Fig.2, d). which is typical for xenoliths of the upper mantle.
The average iron content in the spinels under consideration is 11.5 %, with a minimum of 9.8 % and a maximum of 13.6 %. In large xenoliths, the FeO content is sufficiently sustained in each zone, while in small xenoliths variations in the iron content are rather significant (see table).
The distribution of rare-earth elements (REE) in spinels is a rather complex issue, since it has not been established to date exactly what position the REE ions occupy in the crystal lattice of the mineral. However, it is worth noting, that the work of F.P.Lesnov [2] suggests that the most likely candidates, the position of which in the spinels is occupied by trivalent HREE ions, are the ions VIIIFe2+ and VIIIMg2+. Data on the content of REE in spinels are very limited and mainly affect chrome spinels (reviewed in [2]).
We provide representative analyzes of the REE content in spinels. The average total content of rare-earth elements in the studied grains does not exceed 0.12 ppm, and the REE distribution spectra have a pronounced sinusoidal appearance with inflection points, corresponding to Dy and, in some cases, Ho (Fig.3). Such a distribution of rare-earth elements is atypical for spinels, since in the literature analysis (review in [2]) it was established that typical REE spectra in spinels show a gradual decrease from light to heavy REE. It was previously established that the sinusoidal character of the REE distribution spectra in minerals, in particular in mantle garnets, along with other features of the composition is an indicator of mantle metasomatism [8]. The normalized content of light REE in the entire representative sample of spinels increases from La to Eu and further to Gd. In some spinels, the content of La and Ce is below the sensitivity threshold of the LA-ICP-MS method. Eu-anomaly in a number of samples has an implicitly pronounced positive character (Fig.3). The content of heavy REE is sharply differentiated, from Gd to Dy, the normalized contents decrease, and the min-
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
0.1
0.01
0.001
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Fig.3. Distribution spectra normalized to chondrite composition CI, rare-earth elements in spinels from xenolith SH-1: a - central part, b - intermediate part, c - marginal part
êDmitriy S. Ashikhmin, Yi-Xiang Chen, Sergey G. Skublov, Aleksey E. Melnik
Geochemistry of Spinels from Xenoliths of Mantle Lherzolites...
imum value among the HREEs is Ho, which is the inflection point with the subsequent increase in the normalized contents of the elements from Er to Lu.
Thus, for the first time the results (method LA-ICP-MS) were obtained for the sparse composition of spinels from mantle xenoliths of lherzolites in alkaline basalts of the Spitsbergen archipelago, supplementing the data on the geochemistry of spinels of mantle origin published in the world literature.
Acknowledgments. The authors thank Doctor of Geological and Mineral Sciences, A.N.Sirotkin (PMGSE) for provided samples of xenoliths and Candidate of Geological and Mineral Sciences, O.L.Galankin (IPGG RAS) for conducting analytical work. The research was carried out with the financial support of the Ministry of Education and Science of Russia within the framework of the basic and design part of the state task in the sphere of scientific activity N 5.9248.2017/VUfor 2017-2019.
REFERENCES
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Authors: Dmitriy S. Ashikhmin, Geologist, Dmitry_Ashihmin@vsegei.ru (A.P.Karpinsky Russian Geological Research Institute, Saint-Petersburg, Russia), Yi-Xiang Chen, Doctor of Science, Associate Professor, yxchen07@ustc.edu.cn (School of Earth and Space Sciences of University of Science and Technology of China, Hefei, China), Sergey G. Skublov, Doctor of Geological and Mineral Sciences, Chief leading researcher, skublov@yandex.ru (Institute of Precambrian Geology and Geochronology Russian Academy of Sciences, Saint-Petersburg, Russia), Aleksey E. Melnik, Candidate of Geological and Mineral Sciences, Junior Researcher, aleks@melnik.me (Institute of Precambrian Geology and Geochronology Russian Academy of Sciences, Saint-Petersburg, Russia).
The paper was accepted for publication on 29 May, 2017.
