Eclogite petrography

A set of thin section images, all at the same scale (1.5 x 1 cm) showing the range of textures to be found in metabasic eclogites from several different terranes, plus a few other associated high-pressure rock types.
Monviso, Western Alps, metagabbro  Ophiolitic metagabbro. Little deformation; large igneous augite at left is transformed to clouded omphacite. Right-hand half is former plagioclase, now dominated by garnet with clear interstitial omphacite. Monviso, Western Alps, metagabbro  Ophiolitic metagabbro. Little deformation; large green (chromian) omphacite takes the place of augite, plagioclase mostly replaced by garnet, large igneous Fe-Ti oxide grains are now aggregates of rutile. Monviso, Western Alps, metagabbro  Deformed ophiolitic metagabbro. Large omphacites still present (but many will be partly recrystallised), garnets are coarser, rutile aggregates strung out in fabric. Monviso, Western Alps, metabasite  Mylonitic fabric with greatly strung-out rutile aggregates; a sheared metabasite whose precursor was probably a gabbro. Monviso, Western Alps, metabasite  Coarser-grained heterogeneous eclogite with metamorphic fabric. Greyish lozenge-shaped domains in lower half are pseudomorphs of clinozoisite and white mica after large lawsonite porphyroblasts.
Monviso, Western Alps, metabasite  Eclogite, with some coarse omphacite and rutile clusters, so probably a metagabbro, but rich in phengitic white mica, as a result either of pre-metamorphic alteration or later fluid influx. Monviso, Western Alps, metabasite  Very fine-grained and finely banded eclogite, probably a highly strained metabasalt or metagabbro. Pillow basalts in which the pillow margins develop a different composition from pillow cores (by seawater interaction, for example) can form banded rocks like these when deformed. Monviso, Western Alps, metabasite  Another fine-grained eclogite, but this sample underwent a fluid-rich recrystallisation and contains chlorite among the dominant well-formed prismatic omphacite Monviso, Western Alps, blueschist-facies metabasite  At Monviso the overlying tectonic slice contains lower-grade assemblages like this metabasic blueschist with glaucophane, epidote and chlorite. Zermatt-Saas zone, W Alps, metabasic eclogite  Eclogite from the Lago di Cignana UHP unit. Garnets zoned in colour and inclusion density. A little green retrogression around some grain boundaries.
Zermatt-Saas zone, W Alps, metabasic eclogite  Eclogite from the Lago di Cignana UHP unit. Crossed polars. Zermatt-Saas zone, W Alps, metabasic eclogite  Eclogite from the Lago di Cignana UHP unit. Prismatic omphacite in central domain. Above and below, scruffy buff-coloured clinozoisite aggregates replace former lawsonite. Zermatt-Saas zone, W Alps, metabasic eclogite  Eclogite from the Lago di Cignana UHP unit. Crossed polars. Anomalous blue-grey colours are shown by clinozoisite aggregates replacing former lawsonite. Zermatt-Saas zone, W Alps, metabasic eclogite  Eclogite from the Lago di Cignana UHP unit. The large garnet is zoned in colour and inclusion density. Some pale glaucophane is also present, but hard to distinguish from omphacite. Zermatt-Saas zone, W Alps, metabasic eclogite  Eclogite from the Lago di Cignana UHP unit. The large garnet contains rectangular and lozenge-shaped pseudomorphs after lawsonite in its outer zones.
Zermatt-Saas zone, W Alps, metabasite  Garnet-glaucophane rock from Zermatt, with porphyroblasts of bluish high-relief (Mg-)chloritoid near top of image, and patches of pale green chlorite. Garnets have complex arrangements of imclusions. Zermatt-Saas zone, W Alps, metabasite  Garnet-glaucophane rock from Zermatt, with porphyroblasts of chloritoid (grey) near top of image. Other grey patches are mostly chlorite, and glaucophane mostly shows yellow to orange colours. Zermatt-Saas zone, W Alps, metabasite  Eclogite from Zermatt, with cross-cutting prisms of glaucophane and flakes of white mica, probably representing a hydrous blueschist-facies overprint. Zermatt-Saas zone, W Alps, metabasite  Garnet-glaucophane-white-mica rock from Taschtal, near Zermatt; high-relief cluster of omphacite grains visible in centre of image, and in top right corner. Zermatt-Saas zone, W Alps, metabasite  Garnet-glaucophane-white-mica rock from Taschtal, near Zermatt; cluster of omphacite grains visible in centre of image.
Zermatt-Saas zone, W Alps, manganiferous schist  Manganese nodule in mica schist (Mn-oxide, Mn-garnet, piemontite). This is the lithology in which coesite was first found in the Lago di Cignana unit, as an inclusion in garnet. Dora Maira massif, W Alps, pyrope schist  This is the rock unit in which coesite was first discovered in the Alps (Chopin, 1984). The garnet contains more than 90% of the pyrope end member. Other minerals visible are phengite (with very high Si content) and minor kyanite. Dora Maira massif, W Alps, pyrope schist  This is the rock unit in which coesite was first discovered in the Alps (Chopin, 1984). The Mg-rich garnet is partly altered to talc around its rim. The quartz domain on the left shows a columnar structure ("palisade texture") which probably formed as a result of the inversion from coesite. Norway, Western Gneiss Complex  Coarse-grained eclogite with garnet, pale green omphacite, minor quartz and rutile. This was a UHP eclogite and coesite relics occur elsewhere in this section as inclusions in garnet and omphacite. Green amphibole and pyroxene-feldspar symplectite formed at omphacite grain boundaries during exhumation. Norway, Western Gneiss Complex  Coarse-grained eclogite with a hydrous overprint: large blue-green amphibole and phengite plates form between garnet grains and many garnets are now atoll structures with phengite replacing the garnet cores.
Oman, As Sifah eclogite  Garnet and omphacite, with glaucophane, phengite and epidote defining a strong fabric. Coarser-grained pale green omphacite occurs in local clusters, typically in low-strain pockets near garnet. Oman, As Sifah eclogite  Garnet and omphacite, with glaucophane, phengite and epidote defining a strong fabric. Coarser-grained omphacite occurs in local clusters, typically in low-strain pockets near garnet. Oman, As Sifah glaucophane eclogite  Garnet, omphacite, phengite, glaucophane and epidote. Glaucophane and epidote overprint the folded eclogite-facies fabric. Himalaya, Kaghan eclogite  Fine-grained garnet, omphacite of variable grain size, coarse amphibole plates (slightly darker colour, later overprint), colourless phengite, rutile grains in trails and clusters. Coesite has been recorded as inclusions in garnet at this locality. Himalaya, Kaghan eclogite  Fine garnet, larger green omphacite, very large blue-green amphibole (later overprint), rutile clusters. Vein at upper left has quartz and phengite.
Himalaya, Tso Morari complex  Garnets with inclusion-packed cores. Matrix contains omphacite, Na-Ca-amphibole and phengite. Coesite has been recorded as inclusions in garnet at this locality. Himalaya, Tso Morari complex  Garnets with inclusion-packed cores. Matrix contains omphacite with symplectite on grain boundaries, Na-Ca-amphibole and phengite. Tibet, Sumdo eclogite  Roughly equal proportions of garnet and omphacite, with some phengite and secondary amphibole. Large rutile aggregates. This eclogite occurs in a PermoTriassic suture zone complex in the Lhasa Terrane of southern Tibet.