Cape Crozier, Ross Island

Mafic phonolite occurs in the form of small plugs and flows throughout Ross Island and elsewhere within the Erebus volcanic province. For examples. Post Office Hill at Cape Crozier and Observation Hill at McMurdo Station are composed of this rock type. Their chemical compositions are quite variable. Normative nepheline can be as high as 30%. Most samples contain more augite and kaersutite than the anorthoclase phonolites. 

Fig. 16.7 The ultramafic inclusions that were erupted with the Cenozoic alkali-rich lavas at Cape Crozier (CC-82) and Cape Bird (CB-64) on Ross Island and at Brandau vent (BV-5g) in the Royal Society Range define a straight line that yields a date of 1140 Ma. This date is largely based on the sample of trachyte (CC-82) which contains only 3.01 ppm of strontium and is susceptible to contanunation by radiogenic Sr. Therefore, the geological significance of the Rb-Sr date is questionable (Data from Stuckless and Ericksen (1976))...

The inclusions of crustal rocks in the lava flows of the Erebus volcanic province consist of lower-crustal granulites, upper-crustal basement rocks, and supra-crustal rocks. Berg (1991) described inclusions from 17 sites in the Erebus volcanic province, 7 of which are located in the Royal Society Range (Brandau Vent, Roaring Valley, Foster Crater, Ward Valley, The Bulwark, Lower and Upper Radian Glacier) and five on Ross Island (Cape Crozier, Cape Bame, and at three places on the Hut Point Peninsula). 

Fig. 16.11 Ross Island consists of volcanic rocks that were erupted by the three principal volcanoes Mt. Erebus, Mt. Bird, and Mt. Terror. The island is separated from the mainland of Antarctica by McMurdo Sound where the sea ice breaks up in late December allowing cargo ships to dock at McMurdo Station on the southern tip of the Hut Point Peninsula. The south side of the island from Scott Base at the tip of the peninsula to Cape Crozier is in direct contact with the Ross Ice Shelf. Ross Island contains rookeries of Adelie penguins at...

---