Morning, looking south toward the mouth of the Kangerdlugssuaq Fjord. The weather change overnight has shifted the ice around, some back into our sheltered fjord where we spent the night avoiding a storm.
Traveling to the drop-off point outside Uttental Sund. Lots of small bergs and ice bits around.
The lowered gangplank, with a Zodiac moving into position to take on passengers.
View of the stern of the ship, with the second Zodiac loading up and the third still empty.
Traveling into Uttental Sund, leaving the ship behind in open water.
Photo from the Zodiac, looking northeast. Right peak is Pukugagryggen, left is Wager’s Top. Pukugagryggen has the Triple Group exposed about 2/3 of the way up the cliff, and below the Triple Group is a large gabbroic anorthosite autolith. A giant autolith is also barely discernable below Wager’s Top.
Disembarking from the Zodiacs just west of the contact between Archean gneiss and the Skaergaard, just south of Uttental Plateau. View is to the south, across Uttental Sund.
Discussion near the Skaergaard contact, which is approximately at the position of the distant people.
Photo of the Marginal Boarder Series near the contact, showing ultramafic xenoliths (cumulate wherlite with interstitial plagioclase). The olivine in the xenoliths is Fo80 to 85, which is too Mg-rich for the visible Skaergaard. It seems likely that this wherlite is from ultramafic cumulates in a somewhat older Tertiary pluton cut by the Skaergaard. Such bodies are found in the area.
Closer view of a fresh surface, showing densely packed wherlite xenoliths, larger grains visible are pyroxene, with plagioclase in between.
Close-up of one of the wherlite xenoliths, the larger crystals being pyroxene, with smaller olivine crystals and interstitial plagioclase. The olivine appears dark because they contain cracks where the olivine has been partially converted to serpentine and magnetite.
Looking south across Uttental Sund, down the contact on this side of the water, and up the contact on Kramer Island on the other side. Ice in the water is mostly sea ice.
This photo was taken from an elevation of ~150 m in the “Tranquil Zone”, in a section with relatively featureless gabbro having 2 to 3 cm augite oikocrysts enclosing cumulus olivine and plagioclase.
Cross bedded gabbro in the cross bedded belt of LZa.
View to the south across Uttental Sund to Skaergaard Bay and the open Greenland Strait. Foreground is LZa gabbro on Uttental Plateau, Kramer Island is in the midground, and the Homestead area is in the middle distance. The highest full peak on the far left is Pilespidsen, 768 m.
Looking NE from the summit of Uttental Plateau toward Watkins Fjord. Much of the ice in this and in Kangerlussuaq Fjord comes from glaciers in Watkins Fjord.
Crossbeds in the crossbedded belt on Uttental Plateau, in LZa. View is looking east toward Wager’s Top.
Channel fill and crossbeds in the crossbedded belt on Uttental Plateau, in LZa. Notice the small white autoliths near the base of the scoured surface.
Perpendicular feldspars growing inward from the base of the scoured surface in the photo above.
Replacement gabbroic anorthosite body, with a thin mafic layer at its base. This body has abundant mafic oikocrysts, which is typical of this kind of rock. Stratigraphic tops are toward the top of this photo.
Small mafic pegmatite in LZa, stratigraphic top is toward the top of the photo.
Small mafic pegmatite in LZa, connected to a replacement gabbroic anorthosite at its top. Mafic pegmatite and replacement anorthosite appear to be related in many places, probably related to the availability of water and its control on the residual liquid phase relations.
A large replacement gabbroic anorthosite body, just northeast of the summit region of Uttental Plateau.
Graded layers and crossbeds near the margin of the crossbedded belt, LZa, with several bodies of replacement anorthositic gabbro above a large dark-brown-weathering erosional scour structure.
View to the north from the north rim of Uttental Plateau, toward one of the glaciers at the end of Watkins Fjord. The blue ice calving front of the glacier, visible in the distance, has glacial streams extending back toward the distant Greenland interior ice sheet. The ice sheet is not visible from here, but this is the closest we got to it.
Another small replacement anorthositic gabbro, this one sub-parallel to some layering, but crosscutting others. It has a mafic layer on the bottom, which is typical. Notice the truncated layers just in front of the hammer.
Close-up view of the replacement anorthosite in the photo immediately above, showing abundant oikocrystic pyroxene.
Photo of the gabbroic anorthosite “diapir”, west side of Wager’s Peak in LZb. This is a complex structure that is not fully understood. It has a flat base and a mushrooming top, with upturned beds on the right, and less steeply upturned beds on the left. Just to the right of the top of the structure, the beds are disturbed (see photo below). One idea is that this is a real diapir, that pushed aside and broke the overlying layers. The resulting bump then caused turbulence in the magma, that deposited in the disturbed bed. Unless the rising magma or mush body was fed from deeper down, to give the anorthositic material sufficient hydrostatic head to raise the 2 or 3 m of semiconsolidated crystal mush, it is difficult to see how diapirism would succeed.
Another idea is that this body was precipitated in situ from water-rich, plagioclase-rich liquids fed from below. In this scheme the structure grew into a mushroom as the migrating plagioclase-rich liquid reached the magma-gabbro interface. There, the rising hydrous, plagioclase-rich liquid would lose water to the adjacent water-poor magma, and freeze. More liquid from below would eventually construct a growing mushroom. In this model the upturned beds are primary depositional features, like the upturned beds on the flanks of autoliths.
Photo from slightly to the south of the mushroom, showing another body of gabbroic anorthosite slightly lower in the section, and the strikingly disturbed bed to the right of the mushroom top.
Photo of the rock that makes up the body of replacement anorthosite to the right of the mushroom, seen in the photo immediately above.
Photo of typical LZb gabbro, 20 m south of the mushroom.
View looking southwest from the mushroom locality on the west flank of Wagers Top. Uttental Sund is the water far below. The nearby body of water to the lower right is a small pond at 141 m elevation, on the southern flank of Uttental Plateau. The Skaergaard-Archean gneiss contact is beautifully exposed on the other side of Uttental Sund, on Kramer Island.
View west to the Uttental Plateau, from just south of the gabbroic anorthosite mushroom locality, shown above. Note people, on the top of the plateau at the far right. Most of this view shows LZa which, inside of the crossbedded belt, is rather featureless with little in the way of long-distance-visible layering. In contrast, LZb does have long-distance layering.
Looking uphill near the pickup place on Uttental Sund, showing layers in LZb. Note the presence of both regular and irregular layering, and truncations.
View from the Zodiac toward Basistoppen (885 m), looking up Forbindelses Glacier.
Blue iceberg just outside of Skaergaard Bay.
Another blue iceberg just outside of Skaergaard Bay.
