Chrome-spinels - Rare Earth Elements in Ultramafic and Mafic Rocks and their Minerals - page 97

Cr # , %

Max.

C1

Aver.

Min.

Figure 2.3 Chondrite-normalized REE patterns
of average, maximum and minimum
contents of elements in the accessory
chrome-spinels from harzburgites
from Ergak massif (West Sayan, Rus-
sia) (data Table 2.2).

Figure 2.4 The graphs of relationship between
Cr # % parameter for accessory
chrome-spinels and degree of partial
melting of lherzolite (D melt , %) (data
Table 2.3).

Table 2.3 Relationship between Cr #
parameter values of accessory chrome-
spinels and the degree of partial melting
of lherzolites (D melt ) (experimental data
[Hirose, Kawamoto, 1995]).

Cr # D melt

11,5 7,0

17,5 12,4

34,5 13,4

42,6 17,8

55,7 29,6

56,8 21,8

58,8 20,1

69,5 38,0

Note: Cr # , % = Cr ⋅ 100/(Cr + Al).

data, during the formation of harzburgite of Ergak massif the degree of partial melting
of the mantle protolite should have changed in a fairly wide range - from 12 to 37%.
Almost the same range of values of D melt determined in the calculations based on the

general sample of 90 chemical analyses of chrome-spinels from ultramafic Ergak mas-
sif. In addition, the results of the same physical experiments have been previously used
to construct an appropriate scale which allows us to determine the degree of partial
melting of mantle source, based on the values of Cr # for the accessory chrome-spinels
[Page et al ., 2008]. Estimates obtained using the named scale, show that ultramafic
rocks from Ergak massif could be formed as restites for a very wide range of variations
in the degree of partial melting of the mantle protolite (Figure 2.5, a).