Garnets - Rare Earth Elements in Ultramafic and Mafic Rocks and their Minerals - page 37

Roberts Victor pipe (1) Roberts Victor pipe (2) Bobbejaan pipe

Koidu pipe

Figure 1.5 Chondrite-normalized REE patterns for garnets from eclogite xenoliths from kimberlites
(data Table 1.4).

considered by the example of the samples from Norway, Switzerland, Kazakhstan and
Kyrgyzstan metamorphic complexes (Table 1.5). Garnets from eclogites presented in
Norwegian metamorphic complexes are notable for a much lower total REE con-
tent (6.5-18.2 ppm) compared with the samples from Soazza complex (Switzerland)
(34-148 ppm). Garnets from eclogites represented in Kazakhstan (22-44 ppm) and
Kyrgyzstan (16.4-31.6 ppm) metamorphic complexes occupy an intermediate posi-
tion on this basis. The samples of Soazza complex demonstrate the most intense frac-
tionation of REE, which is due to its depletion by LREE and enrichment with heavy
elements, as it is shown on the configuration of REE pattern (Figure 1.6). Due to
the relative enrichment with LREE, patterns of garnets from Kazakhstan complexes
(Kumdy-Kol', Sulu Tube, Chiglinka, Kulet), as well as from Atbashi complex in South
Tien Shan (Kyrgyzstan) [Shatsky, 1990], have a more gentle positive slope. In some
patterns we can observe negative Eu anomalies (Sulu Tube complex), or Nd and Sm
anomalies (Norwegian complexes). Let us consider in detail the collected data on
the geochemistry of REE in garnets from eclogites of Atbashi metamorphic complex.
Eclogites from Atbashi metamorphic complex are denuded in a series of small tectonic
blocks in the valley of Kembel' river, draining the western spurs of Atbashi ridge.
Their first structural-geological description was given by Bakirov [1964], and then a
detailed petrographic, petrochemical, mineralogical and geochemical study of eclog-
ites was carried out from this, as well as from some other eclogite-bearing complexes
of Tien Shan [Shatsky, 1990]. Recently, the additional data on the chemical composi-
tion of garnets, omphacites and glaucophanes from eclogites of Atbashi complex as
well as estimates of PT- parameters of their formation have been published [Lesnov
et al ., 2004b]; by LA ICP-MS method we determined REE contents in these garnets
and coexisting minerals [Lesnov et al ., 2005a].