Petrology of eclogites and surrounding schists from the Lyell highway—Collingwood river area
Titel:
Petrology of eclogites and surrounding schists from the Lyell highway—Collingwood river area
Auteur:
Råheim, Arne
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 23 (1976) nr. 3 pagina's 313-327
Jaar:
1976-09
Inhoud:
The metasedimentary rocks of the Lyell Highway-Collingwood River area are characteristically garnet-mica-quartzite, garnet-mica schist and mica schist, all very low in CaO content. Included in the metasedimentary sequence are eclogite and garnet amphibolite, interpreted as derived from original dolerite. The conditions of metamorphism of the eclogite are the same as those of the country rocks. The PT conditions at the peak of metamorphism are exceptionally well determined by four different PT indicators: KD =(FeO/MgO)epx/(FeO/MgO)gar, Si4+ content of phengitic micas, minimum melting curve of quartz + albite and a talc + garnet + kyanite + quartz mineral association. The PT conditions at the metamorphic maximum were 670 ± 20°C, 11 ± 1 kb. Zoned minerals (garnet and coexisting ferromagnesian phases) failed to re-equilibrate during prograde metamorphism. This makes it possible to estimate an earlier PT stage (520°C, 7 kb) and to evaluate the PT path to the metamorphic maximum. The Si4+ content of phengite mica is the same for the metamorphic maximum in all the rock types and is considered to be an important PT indicator. A superimposed deformational event caused retrogressive effects to varying extents in most, but not all, of the rocks. The secondary minerals created mainly during this deformation are amphiboles, chlorites, biotite and plagioclase (albite).
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