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Photomicrographs of the granulite-facies rocks. A-C – Felsic granultes. a) Antiperthitic porphyroclastic plagioclase with garnet inclusion, besides perthitic orthoclase of biotite ± garnet-bearing felsic granulite; b) Mineral assemblage of the orthopyroxene-bearing felsic granulite; c) Coronitic texture defined by symplectitic garnet around plagioclase in orthopyroxene-bearing felsic granulite; D-F – Mafic granulites . d) Granoblastic fabric. e) Cummingtonite pseudomorph after orthopyroxene. f) Corona of garnet around plagioclase; G-I – Aluminous granulites. g) Biotite and hercinite spinel inclusions in porphyroblastic garnet; h) Corona of symplectitic garnet around earlier garnet and ilmenite; i) Kink band in orthopyroxene. Abbreviations: Kfs-alkali-feldspar; Pl-plagioclase; Or-orthoclase; Grt-garnet; Qz-quartz; Ilm-ilmenite; Hbl-hornblende; Bt-biotite; Opx-orthopyroxene; Cpx-clinopyroxene; Cum-cummingtonite; Hc-hercynite.
Source publication
The Pedra Dourada Granulite (PDG) occurs at the southeastern portion of the Araçuaí Belt, north of the town of Ponte Nova. It comprises bodies up to 45 km2 inserted into amphibolite-facies gneisses of the Mantiqueira Complex. Motivated by the discrepancy of metamorphic grade with surrounding rocks, this paper presents results of the petrographic an...
Contexts in source publication
Context 1
... consist of anhedral to subhedral grains with interlobate or ameboid boundaries, suggesting grain boundary migration recrystallisa- tion. They commonly exhibit perthitic (alkali-feldspar) and antiperthitic (pla- gioclase) exsolutions ( Figure 4a) and also show evidences for intracrystalline deformation, like undulose extinction and deformation twins (plagioclase). Matrix grains exhibit anhedral crystal shape and often define core-and-mantle structures in porphyroclasts. ...
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... felsic granu- lites display inequigranular granoblastic fabric ( Figure 4b). This lithotype compris- es coarse-grained feldspar porphyroclasts surrounded by a fine to medium-grained matrix. ...
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... (0 -12%) is usually better preserved than orthopyroxene but also exhibits replace- ment by symplectitic intergrowths of quartz + amphiboles. Garnet (0-10%) is alm 65,4 grs 18,5 prp 12,0 sps 4,0 uv 0,1 and may compose symplectitic intergrowth with ilmenite or forms coronas around pla- gioclase ( Figure 4c). Hornblende (0 -8%) occurs both as individual brownish-green crystals of ferropargasite (15eNK esti- mate, Leake et al., 1997) as in aggregates replacing pyroxenes. ...
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... have a gabbroic compo- sition and display inequigranular grano- blastic fabric. This lithotype is composed by the mineral assemblage plagioclase + biotite ± orthopyroxene ± clinopyroxene ± hornblende ± quartz ± garnet ( Figure 4d). Zircon, titanite, apatite, allanite and opaque minerals are the common acces- sory minerals, plus secondary minerals like actinolite, cummingtonite, epidote, scapolite and sericite. ...
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... main deformation microstructures are undulose extinction, deformation twins, subgrains and core-and-mantle struc- tures. Orthopyroxene (0 -35%) is hy- persthene (En 56-57 ) and shows anhedral to subhedral crystal shape and is partially or totally replaced by fibrous aggregates of biotite and/or cummingtonite ( Figure 4e). Clinopyroxene (0 -30%) is diopside (Wo 47 En 39 Fe 14 ) and occurs both in granu- lar aggregates with orthopyroxene or as coronas around this mineral. ...
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... (<1 -15%) usually forms monominer- alic aggregates and displays deforma- tion microstructures like undulose extinction and chessboard subgrains. Garnet (0 -8%) has a composition alm 58,5 prp 19,5 grs 18,5 sps 3,4 uv 0,1 and may constitute symplectitic intergrowth with ilmenite or coronitic textures at pyrox- ene-plagioclase contacts (Figure 4f). ...
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