Journal of the Virtual Explorer

In eclogites, AmpII and AmpIII were analysed (Fig. 6). AmpII is a Na-Ca amphibole while AmpIII are mainly actinolites (Fig. 6 and Table 2); the Natot content in AmpII is 0.702 a.p.f.u., while it varies from 0.153 to 0.341 a.p.f.u. in AmpIII. The AlVI and NaB contents are higher in AmpII than AmpIII, respectively 0.782 and 0.552 a.p.f.u. in AmpII, from 0.262 to 0.439 a.p.f.u. (AlVI) and from 0.134 to 0.244 a.p.f.u. (NaB) in AmpIII.

Figure 6. Compositional variations

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Compositional variations in the amphiboles (A) and clinopyroxene (B) from eclogites, ultramafics, serpentinites and schists. Pyroxene compositions plotted into the Na-pyroxene triangular representation, after Morimoto (1988). C) Compositions of Grt from eclogites. A, B and C are the fields in which plot garnet from different eclogite types according to Coleman (1965). Large ellipses correspond to the composition of Grt synthesised during experiment on basaltic system at 650°C and 2.0-2.2-2.6 GPa from Poli (1993). D) Epidote compositions from eclogites and schists.

In Amp-Chl schists AmpII are mainly magnesio-hornblendes; Natot contents vary from 0.26 to 0.67 a.p.f.u., while CaB varies from 1.70 to 1.78 a.p.f.u.. The differences in Amp composition shown in Fig. 6 most likely correspond to original chemical differences within the wider group of Amp-Chl schists.

In ultramafites Amp are tremolites; Natot content is 0.10 a.p.f.u. CaB content from 1.82 to 1.93 a.p.f.u. and Mg from 4.51 to 4.68 a.p.f.u.

OmpI within eclogites show different X^Jd content with respect to the microstructural site and to the Fe³⁺ content (Fig. 6) from 0.18 to 0.44 and Fe³⁺ 0.06 a.p.f.u.. The large OmpI porphyroblasts in eclogites show the highest X^Jd values, corresponding to lowest Fe³⁺ content; OmpI porphyroblasts within Lws-bearing eclogites show the highest Fe³⁺ contents where OmpI is in contact with Grt and Ep (Fig. 6). OmpI of the Lws-eclogites show the highest Mg contents, ranging from 0.3 to 0.94 a.p.f.u., and the lowest Ca and Na contents (Table 2) with respect to other omphacites in eclogites.

In Amp-Chl schists, Cpx are Ca-rich pyroxenes, with the Na content varying from 0.02 to 0.18 a.p.f.u., Ca from 0.81 to 0.94 a.p.f.u. and Altot from 0.06 to 0.10 a.p.f.u..

In ultramafites and serpentinites Cpx are Di with Ca content from 0.94 to 0.96, Na 0.01 a.p.f.u. and Altot always below 0.01 a.p.f.u..

Garnets were analyzed only in eclogites. They show an XCa content varying from 0.19 to 0.23, X_Mg (where X_Mg =Mg/(Ca+Fe²⁺ Mg+Mn)) from 0.28 to 0.41, X_Fe from 0.40 to 0.51 and X_Mn 0.04. Grt from Lws-bearing eclogite show compositional variations with an increase of the Fe²⁺ and Ca content from core to rims (Fig. 6).

Chlorites in ultramafics (Table 2) are characterized by Mg content ranging from 9.14 to 9.72 a.p.f.u., Fetot from 1.07 to 1.61 a.p.f.u., Al from 2.63 to 2.99 a.p.f.u. and Cr from 0.28 to 0.30 a.p.f.u. In serpentinites Mg content varies from 9.78 to 10.09 a.p.f.u., Fetot from 0.79 to 0.81 a.p.f.u., Al from 2.99 to 3.11 a.p.f.u and Cr from 0.08 to 0.10 a.p.f.u. In Amp-Chl schists the Mg content in Chl varies from 6.40 to 8.33 a.p.f.u., Fetot from 1.55 to 3.30 a.p.f.u, Al 3.94 to 4.64 a.p.f.u. and Cr from 0.04 to 0.23 a.p.f.u.

Serpentine shows an Mg content varying from 9.40 to 9.61 a.p.f.u. Fetot from 1.87 to 2.01 a.p.f.u.; the Cr content is always negligible. White micas in eclogites are paragonites: Pg (=Na/(Na+K)) content is higher than 0.93. Fetot and Mg contents are below 0.04 a.p.f.u.. In serpentinites carbonates are characterized by Mg content from 2.69 to 2.88 a.p.f.u. and Fetot from 0.22 to 0.25 a.p.f.u.. In serpentinites the composition are similar to those of serpentinites: Mg content varies from 2.69 to 2.78 a.p.f.u. and Fetot from 0.24 to 0.29 a.p.f.u. Chemical compositions of Wm, Ep, Ky, Oxides, Ttn and Pl are also reported in Table 2.