comparison of the compositions of clinopyroxenes, garnets, and spinels from mantle and “crustal”...

ISSN 1028�334X, Doklady Earth Sciences, 2011, Vol. 441, Part 2, pp. 1695–1702. © Pleiades Publishing, Ltd., 2011.Original Russian Text © A.Yu. Selyatitskii, V.V. Reverdatto, 2011, published in Doklady Akademii Nauk, 2011, Vol. 441, No. 5, pp. 674–681.

1695

Ultrabasic rocks in collisional belts of high andultrahigh pressures may provide important petrologi�cal information. Among these rocks in Phanerozoicorogenic zones there are peridotites, which may bedivided into mantle and “crustal” by the genetic sign[1]. The first ones were intruded as tectonic fragmentsof restite mantle to the deeply subducted lithosphere.They preserved all geochemical signs of rocks of man�tle origin being characterized by high concentrationsof MgO, low concentrations of FeO, MnO, and Al2O3,and relatively enriched in rare elements such as Cr andNi and depleted in REE, Zr, Y, and Nb [2]. This is typ�ical for practically all mantle peridotites worldwide.They are called Alpine�type or orogenic as well. Peri�dotites of the second type (“crustal”) originate frompre�collisional ultrabasic and basic predecessors oflow pressures, which primarily occurred in the Earth’scrust and then subducted to the mantle along withcrust. Protoliths of “crustal” peridotites underwentsignificant changes of the chemical compositionbefore high/ultrahigh�pressure metamorphism [3–5].In contrast to mantle rocks, they are relativelyenriched in FeO, MnO, TiO2, Al2O3, Zr, Y, Nb, REE,and depleted in MgO, Cr, and Ni [2]. Later, mantleand “crustal” peridotites appeared on the Earth’ sur�face as a result of exhumation. They are considered aresult of crustal/mantle interaction and provide dataon the character of subduction and exhumation, prop�erties, and material composition of the upper mantleand the lower crust [6, 7].

Because of the chemical composition not typicalfor ultrabasic rocks, scarcity, and complex geologicalhistory, “crustal” peridotites are unique. Such peridot�ites were originally discovered by D. Carswell [8] dur�ing the study of rocks of the collisional zone of WesternNorway. According to peculiarities of the petrochemi�cal composition, he divided garnet peridotites of Nor�

way into two types: Mg–Cr type and Fe–Ti type. Laterperidotites of the Fe–Ti type were called “crustal” [1],whereas peridotites of the Mg–Cr type are related totypical mantle formations. After the study of D. Car�swell, rocks with such an unusual composition werefound in the Dabie–Sulu Terrane (Eastern China) [5]and in the Kokchetav massif (Northern Kazakhstan)[2–4, 9]. In [5] Chinese peridotites were subdividedinto “A�type peridotites” (mantle) and “B�type peri�dotites” (“crustal”).

Since minerals of typical peridotites reflecting thebulk composition of rocks have a high magnesiumnumber, and the compositions of two types of peridot�ites differ significantly, whereas their phases are thesame (olivine, pyroxenes, garnet, spinel), it was inter�esting to compare the peculiarities of mineral compo�sitions in “crustal” and mantle peridotites.

The differences in the composition of olivines andorthopyroxenes from the above�mentioned types ofultrabasic rocks were studied in [10]. In this paper weconsider the results of comparison of the compositionsof clinopyroxenes, garnets, and spinels. The analyticaldatabase used in this study is given in Table 1. Mostrocks are represented by lherzolites and, to a lesserextent, harzburgites. Almost all rocks are garnet�bear�ing, some of them contain spinel as well. Our own ana�lytical data on the Kokchetav massif (Table 2)obtained for minerals from titanium clinohumite gar�net�bearing ultrabasic rocks of the Kumdy�Kol’ Lakearea in the western part of the massif (garnets and cli�nopyroxenes) and spinel harzburgites in the Enbek�Berlyk Village area in the eastern part (spinels) wereapplied. The concentrations of FeO, MgO, MnO,TiO2, Cr2O3, NiO, Na2O, and Al2O3 were investigatedin minerals. The results of comparison are shown inFigs. 1–4.

Clinopyroxenes. In contrast to the compositions ofolivines and orthopyroxenes from mantle and crustalultrabasic rocks forming separate fields (except for sin�gle points) by iron, magnesium, chromium, and nickel[10], the compositional fields of clinopyroxenes fromdifferent types of peridotites partly overlap by these

Comparison of the Compositions of Clinopyroxenes, Garnets, and Spinels from Mantle and “Crustal” Peridotites

of Collisional High�Pressure/Ultrahigh�Pressure ZonesA. Yu. Selyatitskii and Academician V. V. Reverdatto

Received August 24, 2011

DOI: 10.1134/S1028334X11120191

Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russiae�mail: [email protected]

GEOCHEMISTRY

1696

DOKLADY EARTH SCIENCES Vol. 441 Part 2 2011

SELYATITSKII, REVERDATTO

components (Fig. 1). The average values (Xav) of theiron number (f = Fe/(Fe + Mg), data from Table 1) are0.07 (from 0.03 to 0.12) for mantle clinopyroxenes and0.12 (from 0.07 to 0.20) for “crustal” clinopyroxenes.The lowest iron number among “crustal” clinopy�roxenes is typical for pyroxenes from Kokchetav (f =0.07–0.08); points of their compositions on the Mg–Fe diagram (Fig. 1) are entirely located in the field ofmantle clinopyroxenes. The highest iron numbersamong “crustal” clinopyroxenes are typical for thosefrom the Dabie–Sulu Terrane (China) (f = 0.19–0.20); however, they have quite high Cr2O3 concentra�tions (0.43–0.90 wt %) comparable with the Cr2O3concentrations in mantle clinopyroxenes (0.19–2.98wt %, Xav for the whole set is 1.15 wt %). Clinopy�roxenes from “crustal” peridotites of the Kokchetavmassif and Western Gneiss Region (Norway) are char�acterized by the almost complete absence of chro�mium (from 0.00 to 0.0n wt %, i.e., below the micro�probe detection limit). The average Cr2O3 value for thewhole set of “crustal” clinopyroxenes is 0.17, which ismuch lower than the average value for mantle clinopy�roxenes (see above). In addition, “crustal” clinopy�roxenes are depleted in NiO. The concentration of thiscomponent in them ranges from 0.00 to 0.03 wt % (Xav= 0.004 wt %), whereas the concentration of NiO inmantle clinopyroxenes ranges from 0.00 to 0.53 wt %(Xav = 0.05 wt %).

Note that such components as MnO and TiO2 inclinopyroxenes from mantle peridotites (Mg–Cr type)are characterized by higher maximal and average val�

ues than clinopyroxenes from “crustal” peridotites(Fe–Ti type) (Fig. 1). The concentration of MnOranges from 0.01 to 0.23 wt % (Xav = 0.05 wt %) in“crustal” clinopyroxenes, and from 0.00 to 0.33 wt %(Xav = 0.08 wt %) in mantle clinopyroxenes. The con�centration of TiO2 is 0.01–0.11 wt % (Xav = 0.05 wt %)in “crustal” peridotites, and 0.00–0.97 wt % (Xav =0.21 wt %) in mantle peridotites.

There are no differences in the concentration ofsodium between clinopyroxenes of two genetic types;both sets demonstrate a wide range of values. Therange of Na2O concentrations is 0.07–2.43 wt %(Xav = 1.25 wt %) in mantle clinopyroxenes, and 0.16–3.61 wt % (Xav = 0.12 wt %) in crustal clinopyroxenes.Note that the concentrations of sodium in the mantleand “crustal” clinopyroxenes of the Dabie–Sulu (China)and Western Gneiss Region (Norway) demonstrate theopposite tendency: “crustal” clinopyroxenes of Chinaare richer in Na2O than mantle clinopyroxenes of China,whereas by contrast “crustal” clinopyroxenes of Norwayare depleted in sodium in comparison with mantle cli�nopyroxenes from the same region (Fig. 1).

Garnets. Garnets of “crustal” peridotites are char�acterized by a much higher concentration of iron anda much lower concentration of chromium in compar�ison with the mantle set (Figs. 2, 4a). According to theconcentration of iron and magnesium, garnets fromvarious genetic types occupy almost individual fields,except for two analyses of Norway mantle garnets fromSample E38 [8], which are similar to the “crustal”compositions. The iron number of “crustal” garnetsranges from 0.29–0.57 (Xav = 0.37), that of mantle gar�nets ranges from 0.12 to 0.33 (Xav = 0.21). The concen�tration of Cr2O3 is 0.00–1.33 wt % (Xav = 0.12 wt %) in“crustal” garnets, and 0.34–4.84 wt % (Xav = 2.12 wt %)in mantle garnets. Similarly to clinopyroxenes, theconcentration of Cr2O3 in garnets from “crustal” peri�dotites of the Dabie–Sulu Terrane is significantlyhigher than that in garnets from “crustal” peridotitesof Kokchetav and Norway and overlaps with the com�positions of mantle garnets. “Crustal” garnets ofKokchetav and Norway almost do not contain Cr2O3,whereas the concentration of Cr2O3 in “crustal” gar�nets from China is 0.32–1.33 wt %.

The concentrations of manganese and calcium ingarnets of different types almost completely overlap.The concentration of MnO is 0.15–0.90 wt % (Xav =0.36 wt %) in “crustal” garnets, and 0.01–0.87 wt %(Xav = 0.47 wt %) in mantle garnets. The concentrationof CaO is 2.67–6.78 wt % (Xav = 4.78 wt %) in “crustal”garnets, and 3.51–6.40 wt % (Xav = 4.73 wt %) in mantlegarnets.

Spinels. The “crustal” set is represented by thecompositions of spinels only from harzburgites of theKokchetav massif (Table 2). The main difference ofthe Kokchetav spinels from the mantle set is the verylow concentration of Cr2O3, as well as significantenrichment in the hercynite end�member and alu�mina (Figs. 3, 4b). The concentration of Cr2O3 in

Table 1. Applied analytical database on the compositions ofclinopyroxenes, garnets, and spinels from mantle and“crustal” peridotites

“Crustal” peridotites(Cpx 22; Grt 46; Spl 16)

Mantle peridotites(Cpx 94; Grt 72; Spl 40)

Kazakhstan, Kokchetav massif(Cpx 11; Grt 30; Spl 16)(our data)

Norway, Western Gneiss Region[Carswell et al., 1983;van Roermund et al., 2000](Cpx 8; Grt 12)

Norway, Western Gneiss Region[Carswell et al., 1983] (Cpx 6; Grt 11)

China, Dabie–Sulu Terrane[Zheng et al., 2005, 2006, 2008; Malaspina et al., 2009; Ye et al., 2009] (Cpx 31; Grt 38; Spl 5)

China, Dabie–Sulu Terrane[Zheng et al., 2008](Cpx 5; Grt 5)

Indonesia, Sulawesi Island[Helmers et al., 1990; Kadarus�man, Parcinson, 2000](Cpx 13; Grt 13; Spl 5)

Europe, Blansk les massif, Czech Republic [Naemura, 2009],West�ern Alps [Ernst, 1978; Ernst et al., 1979], Central Alps [Paquin and Al�therr, 2001] (Cpx 42; Grt 9; Spl 30)

Note: Cpx, clinopyroxene; Grt, garnet; Spl, spinel. Numeralsdenote the number of applied analyses. Full references on theinformation sources are given in [10].

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COMPARISON OF THE COMPOSITIONS 1697

0.20

0 0.2 1.2Mg

Fe

0.16

0.12

0.08

0.04

1.00.80.60.4

0.35

0 0.21Fe/(Fe + Mg)

MnO

0.140.07

0.30

0.25

0.20

0.15

0.10

0.05

3.0

0 0.21Fe/(Fe + Mg)

Cr2O3

0.140.07

0.10

0 0.15Fe/(Fe + Mg)

NiO

0.100.05

0.08

0.06

0.04

0.02

2.5

2.0

1.5

1.0

0.5

0.98

0 0.21Fe/(Fe + Mg)

TiO2

0.140.07

4.0

0 0.21Fe/(Fe + Mg)

Na2O

0.140.07

0.84

0.70

0.56

0.42

0.28

0.14

3.5

3.0

2.5

2.0

1.5

1.0

0.5

1 2 3 4 5 6 7

0.53 0.29

Fig. 1. Results of comparison of the compositions of clinopyroxenes from mantle and “crustal” peridotites. Here and in Fig. 2:(1–3) “Crustal” peridotites: (1) Western Gneiss Region (Norway), (2) Dabie–Sulu Terrane (Eastern China), (3) Kokchetav mas�sif (Northern Kazakhstan); (4–7) mantle peridotites: (4) Western Gneiss Region (Norway), (5) peridotites of Europe (Westernand Central Alps, Ligurian peridotites of Italy, Blansk les massif in Czech Republic), (6) Dabi–Sulu terrain (Eastern China),(7) Sulawesi Island (Indonesia). Dotted lines indicate the fields of “crustal” compositions; filled areas denote the fields of “man�tle” compositions. Fe, Mg, Ca, and Cr concentrations are given in formula units; MnO, TiO2, NiO, and Cr2O3, in wt %.

y'

1698



them ranges from 0.00 to 0.25 wt % at an average valueof 0.07 wt %, whereas the concentration of chromiumin spinels from mantle peridotites varies from ~4 to55 wt % at an average value of ~26 wt %. The concen�tration of Al2O3 is 60–67 wt % (Xav = 64 wt %) inspinels from the crustal set, and 4–64 wt % (Xav =40 wt %) in spinels from the mantle set. The ratioCr/(Cr + Al) is 0.000–0.003 (Xav = 0.001) in the first,and 0.04–0.88 (Xav = 0.37) in the second.

In addition to chromium, mantle spinels areenriched in nickel and titanium. The concentration ofNiO ranges from 0.00 to 0.78 wt % (Xav = 0.17 wt %)in the mantle set, and from 0.00 to 0.04 (Xav = 0.01 wt %)in the crustal set. The range of TiO2 concentrations is0.00–0.73 wt % (Xav = 0.16 wt %) in the mantle set,and 0.00–0.03 wt % (Xav = 0.01 wt %) in the crustal

set. The sets do not differ by the manganese concen�tration: the range of MnO concentrations is 0.00–0.45 wt % (Xav = 0.18 wt %) in the mantle set and0.05–0.25 wt % (Xav = 0.12 wt %) in the crustal set.

Thus, the genetic type of “crustal” peridotites rep�resented by garnet and spinel ultrabasic rocks of theKokchetav massif (Northern Kazakhstan), Dabie–Sulu Terrane (Eastern China), and the Western GneissRegion (Norway) is characterized by a number ofmineral peculiarities, which distinguish it from mantle(Alpine�type, orogenic) peridotites. First of all, theseare the high iron number and low concentrations ofchromium and nickel in the studied garnets, clinopy�roxenes, and spinels (Figs. 1–4), as well as in olivinesand orthopyroxenes [10]. These peculiarities radically

1.6

0 2.5Mg

Fe

1.50.5

1.2

0.8

0.4

2.01.0

5

0 0.6Fe/(Fe + Mg)

Cr2O3

0.40.1

4

2

1

0.50.2 0.3

3

0.10

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NiO

0.30.1

0.08

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0.40.2

1.0

0Fe/(Fe + Mg)

MnO

0.40.1

0.8

0.4

0.2

0.50.2 0.3

0.6

0.04

0.02

Fig. 2. Results of comparison of the compositions of garnets from mantle and “crustal” peridotites. See Fig. 1 for symbols.



50

0 0.9Fe/(Fe + Mg)

Cr2O3

45

40

35

30

25

20

15

10

5

0.80.60.50.30.2

70

0 0.9Fe/(Fe + Mg)

Al2O3

60

50

40

30

20

10

0.80.60.50.30.2

50

0 68Al2O3

Cr2O3

45

40

35

30

25

20

15

10

5

514326179

0.35

0TiO2

NiO

0.30

0.25

0.20

0.15

0.10

0.05

0.30.134 60 0.2

0.78

0.73

0.61

0.5

0 0.8TiO2

MnO

0.4

0.3

0.2

0.1

0.60.2 0.4

1

2

3

4

5

Fig. 3. Results of comparison of the compositions of spinels from mantle and “crustal” peridotites. (1) “Crustal” peridotites ofthe Kokchetav massif (Northern Kazakhstan); (2–5) mantle peridotites: (2) Blansk les massif (Czech Republic), (3) peridotitecomplexes of Western Alps (Alps Arami in Switzerland and Finero, Balmuccia, Baldissero, and Lanzo in Italy), (4) Dabie–SuluTerrane (Eastern China), (5) Sulawesi Island (Indonesia). See Fig. 1 for other symbols.

y'

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0.75

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1.00

Ca

Mg0.25 0.50 0.75 1.000

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01.00

0.50

0.25

0Cr

Mg0 0.25 0.50 1.00Fe

12345

0.75

0.75

(a)

(b)

1.00

Fig. 4. Ca–Fe–Mg diagram of the compositions of garnets (a). (1–3) “Crustal” peridotites: (1) Kokchetav massif (Northern Ka�zakhstan), (2) Western Gneiss Region (Norway), (3) Dabie–Sulu Terrane (Eastern China); (4–7) mantle peridotites: (4) Europe(Blansk les massif, Czech Republic, and peridotite complexes of Western Apls; see symbols to Fig. 3), (5) Western Gneiss Region(Norway), (6) Dabie–Sulu Terrane (Eastern China), (7) Sulawesi Island (Indonesia). Cr–Fe–Mg diagram of the compositionsof spinels (b). (1) “Crustal” peridotites of the Kokchetav massif (Northern Kazakhstan); (2–5) mantle peridotites: (2) Blanskles massif, Czech Republic, (3) peridotite complexes of Western Alps, (4) Dabie–Sulu Terrane (Eastern China), (5) Sulawesi Is�land (Indonesia). See Fig. 1 for other symbols.

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1702



distinguish them from minerals of ultrabasic rocks ofthe typical mantle origin.

The different concentrations of FeO, MgO, Cr2O3,and NiO in minerals from the mantle and “crustal”sets provide evidence for the differences in the bulkcomposition of peridotites of different genetic types.The higher concentrations of titanium in mantle cli�nopyroxenes, spinels, and orthopyroxenes [10] incomparison with the “crustal” ones are most likelyexplained by the fact that these minerals in mantleperidotites may be practically the only concentratorsof the TiO2 admixture, whereas the high bulk concen�tration of titanium and iron in “crustal” peridotitesresults in appearance of significant portions (n%) of anindividual titanium�bearing phase (ilmenite). Thisalso explains the similar concentrations of manganesein pyroxenes, olivines, spinels, and possibly garnets.

In addition to the bulk chemical compositions ofrocks, the revealed differences in the chemical compo�sitions of minerals from mantle and “crustal” peridot�ites may be applied for diagnostics of ultrabasic rocksin Precambrian cratons and collisional zones ofhigh/ultrahigh pressures with respect to the origin ofrocks and establishment of the nature of their pro�toliths.

ACKNOWLEDGMENTS

This study was supported by the Russian Founda�tion for Basic Research (project no. 10�05�00217) andan Integration Project of the Siberian Branch, RussianAcademy of Sciences (no. 2).

REFERENCES

1. H. K. Brueckner and L. G. Medaris, J. Metam. Geol.18, 123 (2000).

2. V. V. Reverdatto, A. Yu. Selyatitskii, and D. Carswell,Geol. Geofiz. 49 (2), 99 (2008).

3. V. V. Reverdatto and A. Yu. Selyatitskii, Dokl. EarthSci. 394, 130 (2004).

4. V. V. Reverdatto and A. Yu. Selyatitskii, Petrology 13,514 (2005).

5. R. Y. Zhang and J. G. Liou, Episodes 21, 229 (1998).6. R. G. Coleman and X. Wang, in Ultrahigh Pressure

Metamorphism, Cambridge Univ. Press, Cambridge,1995, pp. 1–32.

7. J. G. Liou and D. A. Carswell, J. Metam. Geol. 18, 121(2000).

8. D. A. Carswell, M. A. Harvey, and A. Al�Samman,Bull. Mineral. 106, 727 (1983).

9. A. Yu. Selyatitskii, Geol. Geofiz. 48 (5), 511 (2007).10. A. Yu. Selyatitskii and V. V. Reverdatto, Dokl. Earth

Sci. 438 (1), 705 (2011).

comparison of the compositions of clinopyroxenes, garnets, and spinels from mantle and “crustal”...

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