These photomicrographs were taken of thin sections from samples I collected while on this trip. The photos here were generally taken to be representative, though doubtless my collection has gaps in mineralogy and textures.
UZc
Mineralogy: plagioclase, olivine (full of magnetite dust), primary augite (brown), augite inverted from ferrobustamite (green), oxides, apatite. Cumulate phases are plagioclase, olivine, augite, ferrobustamite(?), oxides, and apatite. Olivine has a dark, finely speckled appearance because of small, brown and black oxide plates, probably unmixed from the olivine during subsolidus oxidation. Notice that the green augite is generally in crystal cores, and the brown augite is on the rims. The two are optically continuous. No separate grains of relic ferrobustamite were identified by me.
6 mm width of field, plane polarized light.
UZc
Same as above. Note that augite of different colors, seen in the plane light view above, has somewhat different birefringence though similar extinction angles.
6 mm width of field, cross polarized light.
UZc
Detail of some of the augite, with strongly contrasting core and rim colors and sharp contacts.
3 mm width of field, plane polarized light.
UZc
Detail of some of the augite, with strongly contrasting cores and rims. Again, birefringence varies but the extinction angles of the brown and green augite are similar.
3 mm width of field, cross polarized light.
UZc
Interstitial quartz-bearing granophyre.
1.2 mm width of field, cross polarized light.
Mineralogy: plagioclase, augite, olivine, oxides, and apatite. Cumulus phases are plagioclase, olivine, augite, oxides, and apatite. This sample is somewhat altered. Though it contains no orthopyroxene or inverted pigeonite, the augite has abundant very thin pigeonite exsolution lamellae. Olivine crystals are visible at the left center and bottom left of the image.
6 mm width of field, plane polarized light.
UZb
Same as above.
6 mm width of field, cross polarized light.
Mineralogy: Plagioclase, augite, olivine, oxides. Cumulus phases are plagioclase, olivine, augite, and oxides. Augite is light brown, and olivines are slightly lighter in color and slightly greenish; several grains of each are visible here.
6 mm width of field, plane polarized light.
UZa
Same as above.
6 mm width of field, cross polarized light.
Mineralogy: Plagioclase, augite, and oxides. Cumulus phases are plagioclase, augite, and oxides. Parallel alignment of plagioclase crystals is prominent in this sample.
6 mm width of field, plane polarized light.
MZ
Same as above.
6 mm width of field, cross polarized light.
MZ
Grain of augite with exsolution lamellae of orthopyroxene on {100}. Pigeonite exsolution lamellae occur also at other orientations but are not easily seen here.
1.2 mm width of field, cross polarized light.
Mineralogy: Plagioclase, augite, olivine, inverted pigeonite, oxides. Cumulus phases are plagioclase, augite, olivine and oxides. Augite is light brown, olivine is lighter, as is the interstitial inverted pigeonite, which also has exsolution lamellae.
6 mm width of field, plane polarized light.
LZc
Same as above. Notice interstitial olivine rimming Fe-Ti oxides, optically continuous with cumulus olivine.
6 mm width of field, cross polarized light..
LZc
Detail showing olivine rimming Fe-Ti oxides. In this case the rim is optically continuous with an adjacent olivine crystal, but in some cases the rims are of polycrystalline olivine. This texture is usually found near inverted pigeonite, suggesting a partial subsolidus reaction, possibly: Pigeonite + Titanomagnetite = Olivine + Ilmenite + Augite. Interstitial inverted pigeonite is visible on the right.
3 mm width of field, cross polarized light.
LZc
Lovely inverted pigeonite showing high birefringence augite exsolution lamellae in a (now) orthopyroxene host. Blue and yellow crystals on the top left and lower center are augite, with thin pigeonite exsolution lamellae and twins.
1.2 mm width of field, cross polarized light.
Mineralogy: Plagioclase, augite, olivine, inverted pigeonite, and oxides (interstitial only). Cumulus minerals include plagioclase, olivine, and augite. Olivine is just above center, augite crystals are brownish, and inverted pigeonite (probably interstitial) is at the lower right.
6 mm width of field, plane polarized light.
LZb
Same as above.
6 mm width of field, cross polarized light.
LZb
Detail of the pigeonite grain in the image above. This was originally a twinned pigeonite crystal, now unmixed into an orthopyroxene host and augite exsolution lamellae close to {001} in orientation.
1.2 mm width of field, cross polarized light.
Mineralogy: Plagioclase, olivine, augite, inverted pigeonite, oxides. Cumulus phases are plagioclase and olivine. Augite crystals here are clearly interstitial, with lighter colored olivine crystals.
6 mm width of field, plane polarized light.
LZa
Same as above. The olivine crystals here are rather small, but are much larger elsewhere in this sample.
6 mm width of field, cross polarized light.
LZa
Detail of one of the interstitial inverted pigeonite crystals, showing how the augite exsolution lamellae are coalescing from thin lamellae into larger blobs.
1.2 mm width of field, cross polarized light.
Sandwich horizon candidate 1 from the southwest flank of Basistoppen. Mineralogy: Plagioclase, olivine, augite (in part inverted ferrobustamite), oxides, and apatite, with abundant interstitial granophyre and subsolidus alteration. Like the UZc sample shown above, the augite here includes brown and green color varieties. I think that the green augite, generally optically continuous with adjacent brown augite, is inverted ferrobustamite. No zircon was seen though the sandwich horizon is supposed to have up to 1500 ppm Zr..
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
Same as above showing detail of olivine (lower left) and the brown and green color green-brown color mottling in the augite.
3 mm width of field, plane polarized light.
Same as above.
3 mm width of field, cross polarized light.
Sandwich horizon candidate 2 taken from the east flank of Nunatak 1. Mineralogy: plagioclase, augite, olivine (mostly altered to a mass of serpentine, talc, and magnetite), oxides, apatite. The apatite is not particularly abundant, and no zircon was seen. Again, the sandwich horizon is supposed to have up to 1500 ppm Zr.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
Gabbro ~10 cm from the contact with the Archean gneisses on Mellemø Island. Mineralogy: Plagioclase augite, orthopyroxene, inverted pigeonite, oxides. Olivine was not found possibly because of contamination of the border zone by silica-rich liquids derived from the adjacent gneisses.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
Contact zone gabbro taken from between wherlite xenoliths at the base of Uttental Plateau, near Uttental Sund. Mineralogy: Plagioclase and olivine with interstitial orthopyroxene, augite, and oxides. This sample is remarkable in having large orthopyroxene crystals and no pigeonite, inverted or otherwise. The orthopyroxene is in the center and lower parts of this image and is pinkish, the augite is mostly at the upper right and is greenish, and the olivine crystals are all rather round and colorless.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, plane polarized light.
"Tranquil zone" sample from the margin of Uttental Plateau at ~150 m elevation. Mineralogy: Plagioclase and olivine with interstitial augite, orthopyroxene, and oxides. Orthopyroxene is the faintly pinkish mineral at the top center and right, augite is the mineral with exsolution lamellae in the center and bottom left, and olivine crystals are scattered throughout. No inverted pigeonite was found.
6 mm width of field, plane polarized light.
Same as above. Note that the large interstitial augite crystal is twinned.
6 mm width of field, cross polarized light.
Perpendicular feldspar rock from ~10 m inside the contact on Mellemø Island. Mineralogy: Plagioclase, olivine, interstitial augite, and oxides. The largest plagioclase crystal visible here, extending to the upper right corner, is one of the perpendicular feldspars. The scale of the perpendicular feldspars is difficult to see even on the scale of a whole thin section. For other examples, see Irvine et al. (2001), Figure 47.
6 mm width of field, plane polarized light.
Same as above, with the large perpendicular feldspar more clearly visible.
6 mm width of field, cross polarized light.
Replacement gabbroic anorthosite from the crossbedded belt, LZa, on Uttental Plateau. Mineralogy: Plagioclase appears to be cumulus like the plagioclase elsewhere in the pluton. All other phases (augite, minor inverted pigeonite, and oxides) are interstitial. I wonder if this replacement gabbroic anorthosite isn't basically a framework of the original rock with some mafic minerals dissolved out and more plagioclase precipitated in by migrating plagioclase-rich residual liquids.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
Gabbroic anorthosite from a small autolith block in the Homestead area, UZa. Mineralogy: Plagioclase with interstitial augite, olivine, oxides, and biotite.
6 mm width of field, plane polarized light.
Same as above. Interstitial olivine is on the right, augite is on the left.
6 mm width of field, cross polarized light.
Same as above, with interstitial quartz; possibly secondary.
3 mm width of field, cross polarized light.
Gabbroic anorthosite from a medium size autolith from the Homestead area, UZa. Mineralogy: cumulus plagioclase and olivine with interstitial augite, oxides, and biotite.
6 mm width of field, plane polarized light.
Same as above. Olivine is on the left, augite is on the bottom of the image.
6 mm width of field, cross polarized light.
Same as above. Interstitial quartz.
3 mm width of field, cross polarized light.
Gabbro autolith from the giant block on the east end of Kraemer Island on the shore of Uttental Sund, in the MZ. Mineralogy: Plagioclase, augite, inverted pigeonite, and oxides. No olivine was seen, so this rock is mineralogically equivalent to the MZ (roof facies called UBZβ).
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
Wherlite xenolith from the contact zone on the lower flanks of Uttental Plateau. Mineralogy: Olivine, augite, orthopyroxene, plagioclase, oxides. In this image the olivines are colorless with black magnetite-serpentine fractures running through them. Augite and orthopyroxene are both slightly brown and difficult to distinguish from one another.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
Olivine-free basalt xenolith from the MZ of southeastern Kraemer Island. Mineralogy: Plagioclase, augite, inverted pigeonite, and oxides. The texture has been annealed so that it is much more granulitic than is typical of basalts. No olivine was seen in this sample.
3 mm width of field, plane polarized light.
Same as above.
3 mm width of field, cross polarized light.
Olivine-rich basalt xenolith from the MZ of southeastern Kraemer Island. Mineralogy: Plagioclase, augite, olivine, and oxides. This sample also has a granulitic texture. Because this sample is so olivine-rich, it may be from the section of picrite flows into which the Skaergaard intruded. In this image olivine is slightly lighter in color than the augite. No pigeonite was seen in this sample.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
The plagioclase porphyry dike that is one of the oldest in the Skaergard Homestead area, based on crosscutting relationships. Mineralogy: Plagioclase, augite, oxides, and greenish altered material that was probably glass or fine-grained interstitial segregations. No olivine was seen in this rock, nor altered material that was obviously pseudomorphing olivine.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, plane polarized light.
Campsite composite dike chilled margin from the Homestead area, from which the xenolith sample below was taken. Mineralogy: Phenocrysts of plagioclase, olivine, and augite. The matrix is made of plagioclase, augite, and oxides without olivine.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
Gabbro xenolith in the Campsite composite dike. It was difficult to tell the size of the xenolith sampled, but it was at least 2 m across. Mineralogy: plagioclase with interstitial augite. No olivine was seen, nor oxides except those associated with patches of alteration. One interstitial pyroxene was unidentifiable because it was completely and selectively altered, and I suspect that it was an orthopyroxene.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
Transgressive granophyre dike taken from the northern end of the Homestead area, near Trough B. Mineralogy: Orthoclase perthite, plagioclase, quartz, brown hornblende, brown biotite, apatite, and oxides. There is no apparent flow foliation even though the dike is was only ~8 cm across. There is moderate alteration throughout.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
Granophyre in sandwich horizon candidate 1. This is interstitial granophyre that is completely unrelated to the transgressive granophyre. It represents the residual granitoid liquid produced by in situ fractional crystallization. Granophyre of this sort characteristically has graphic intergrowth patterns. Mineralogy: Quartz, orthoclase, plagioclase, olivine, augite, oxides, and apatite, with abundant interstitial granophyre and subsolidus alteration.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
This sample came from gray-weathering rock at the south end of Nunatak 1, mapped in McBirney (1989) as Basistoppen. Its gray color contrasts sharply with the mostly brown-weathering Skaergaard rocks. Mineralogy: Plagioclase, augite, olivine, oxides, and apatite. In several respects this rock looks much like the more evolved parts of the Skaergaard: Dark olivines are full of oxide inclusions. There is moderate alteration, rather dark greenish augites.
6 mm width of field, plane polarized light.
Same as above.
6 mm width of field, cross polarized light.
Interstitial granophyre in the Basistoppen sample with central quartz.
1.2 mm width of field, plane polarized light.
Same as above. The high birefringence grain just below and to the left of center looks like zircon to me. It is the only zircon grain I saw in any of the mafic rocks in my Skaergaard sample set.
1.2 mm width of field, cross polarized light.