Figure from:Petrology of the eclogites from western Tasmania: Insights to the Cambro-Ordovician evolution of the paleo-Pacific margin of Gondwana. Lithos

See full PDF downloadDownload figure

Fig. 7. Variation in composition of amphibole in terms of 100xNa/(Na+Ca) versus 100 Al/(A+Si). Plotted data are amphiboles from the Collingwood River eclogite samples (squares) and grey areas refer to Northern Victoria Land (Antartica) (Di Vincenzo and Palmeri, 2001). Compositional fields of amphiboles from different metamorphic series are from (Laird and Albee, 1981). — Figure 7 Variation in composition of amphibole in terms of 100xNa/(Na+Ca) versus 100 Al/(A+Si). Plotted data are amphiboles from the Collingwood River eclogite samples (squares) and grey areas refer to Northern Victoria Land (Antartica) (Di Vincenzo and Palmeri, 2001). Compositional fields of amphiboles from different metamorphic series are from (Laird and Albee, 1981).

Related Figures (16)

ana In Tasmania, the Neoproterozoic-Cambrian metamorphic rocks involved in the Tyennan Orogeny are confined to the western and northern areas (Fig. 1C). In western Tasmania, the Neoproterozoic-early Tasmania is a key region located between the Cambro-Ordovician rocks of the Ross Orogen in Northern Victoria Land and the Lachlan Fold Belt in southern mainland Australia (Fig. 1A, B, C). In addition, these three Fig. 1. (A) Configuration of Antarctica, Australia, and Tasmania during Cambro-Ordovician times (modified after Foden et al., 2006); (B) tectonic sketch map showing the different structural zones of Northern Victoria Land (Antarctica), Tasmania, and southeast Australia (after Fl6ttmann et al., 1993, Foden et al., 2006); (C) geological map of western Tasmania (modified after Meffre et al., 2000).

Fig. 2. Geological sketch map of the Collingwood River-Lyell Highway area of the Franklin Metamorphic Complex showing sample locations. A-B: Location of the geological sectio Map adapted from (Brown et al., 2005). (Crawford & Berry, 1992; Foster et al., 2005; Foden et al., 2006). The collision generated a Tethyan-style ophiolite complex containing abundant mafic-ultramafic rocks including boninities. High-pressure metamorphic rocks in this complex formed from fragments of the continental margin (Berry and Crawford, 1988; Crawford and Berry, 1992; Turner et al., 1998; Meffre et al., 2000; Foster et al., 2005). This Cambrian passive margin consists of continental-derived turbidite intercalated with basalt and intruded by dolerite dykes and sills, and it overlies early Neoproterozoic shallow-water sedimentary rocks (Fig. 2C; Meffre et al., 2000). The passive margin of Tasmania was involved in a collision with an island arc system at the beginning of the convergent stage of the Delamerian-Tyennan-Ross Orogeny (520 to 505 Ma)

Fig. 3. Photomicrographs of microstructures in eclogite from the Collingwood River (Tasmania). Mineral symbols after Kretz (1983) and Phe for phengite. (A) Euhedral porphyroblastic garnet with abundant inclusions in a partly retrogressed matrix. Crossed nicols, sample RCOG11. (B) Fine-grained layer showing textural equilibrium among Grt, Omp. Cam, and Ep. Crossed nicols, sample RO380. (C) Backscattered scanning electron microscope (BSE-SEM) image showing the good textural equilibrium among the mineral phases defining the eclogite facies stage III. Sample RO380. (D) Porphyroblastic garnet and the Di+Pl symplectite after omphacite. Crossed nicols, sample RCO611. (E) BSE-SEM image of a phengite relic surrounded by its destabilization products (Bt +P symplectite). Sample RO380. (F) Anhedral garnet relics, together with abundant porphyroblastic amphiboles. Crossed nicols, sample RO289. (G) BSE image of a porphyroblastic amphibole with a garnet relic as inclusion. Sample RO380. (H) BSE image of a late vein cross-cutting a porphyroblastic amphibole. The vein consists of an association of chlorite, tremolite, and calcite. Sample RO380.

Representative garnet analyses for eclogite r: rim; m: mantle; c: core; Fe** calculated after Ryburn et al. (1976).

r: rim; c: core; sy: symplectite; Fe** calculated after Ryburn et al. (1976). Representative pyroxene analyses for eclogite

sy: symplectite; kel: kelyphite; porphyr: porphyroblastic; cleav: cleavage; Fe>* calculated after Holland and Blundy (1994). Representative amphibole analyses for eclogite Table 3

Representative garnet, white mica, biotite, plagioclase and tourmaline analyses for host pelitic schist Table 5

sy: symplectite. Representative white mica, biotite, plagioclase and epidote analyses for eclogite

Fig. 4. Garnet ternary diagram after Coleman et al. (1965). Plotted data refer to garnets from the Collingwood River eclogite samples. Garnet compositions from Northern Victoria Land (Antarctica) (Di Vincenzo et al., 1997) are shown for comparison (grey area). End members are almandine + spessartine (Alm+Sps), grossular (Grs), and pyrope (Prp). Fields A, B, and C represent the compositional variations of garnets in eclogites associated with kimberlites and peridotites (A), gneiss (B), and blueschist (C). Garnets from Antarctica partly overlap with those of Tasmania. However, the core compositions of garnet from Tasmania lie in the C field, whereas the rims are mainly in the B field. The opposite is reported for garnets from Antarctica.

Fig. 5. Chemical zonation of different types of garnet in terms of the almandine (100*Xre), pyrope (100*Xyg), grossular (100*Xc,), and spessartine (100Xn) end members. Note the different profiles for pyrope, grossular, and spessartine in the different microtextural occurrences of garnet. Profile (A) refers to large porphyroblastic garnet, profile (B) refers to small recrystallized garnet, and profile (C) refers to relics in mylonitized portions of the rock. For comparison, in Figs. 4, 6, and 7 the mineral composition of arnet, omphacite, and amphibole of eclogites from the Lanterman