Nilsen Plateau

Granite Harbor Intrusives (Southern Nilsen Plateau)... 

The basement of the southern part of the Nilsen plateau in Fig. 6.5, mapped by McLelland (1967), consists of the Granite Harbor Intrusives which are... 

Fig. 6.5 The western edge of the southern part of the Nilsen Plateau along the Amundsen Glacier contains small outcrops of metavolcanic and metasedimentary rocks of the basement complex that were intruded by the Granite Harbor suite. McLelland (1967) divided the granitic basement rocks into the Cougar Canyon Quartz Monzonite, the Lonely Ridge Granodiorite, the North Quartz Monzonite, and the South Quartz Monzonite which are not differentiated on this map. The basement rocks are unconformably overlain by sandstones of the Beacon Supergroup and sdUs of Ferrar Dolerite (Adapted from McLelland 1967)...

The northern part of the Nilsen Plateau in Fig. 6.6, where the Amundsen Glacier turns east around the Olsen Crags, is dissected by the Epler Glacier and by the Blackwall Glacier which McLelland (1967) called the Black Rock Glacier in Fig. 6.5 and which is not identified at all on the topographic map of the Nilsen Plateau published by the US Geological Survey. 

Fig. 6.6 The northwestern margin of the Nilsen Plateau at 86°20 S and 158°00 W of the Queen Maud Mountains is dissected by cirques and alpine vaUey glaciers that drain ice which has accumulated on the top of the plateau. Rock outcrops in the cirques and valleys of the northern Nilsen Plateau expose metasedimentary rocks of the La Gorce Formation and metavolcamc rocks of the...

The valley of the Blackwall Glacier in Fig. 6.7 also contains several small outcrops of cross-bedded quartzite and shale which were described by Stump (1985). The relation of these rocks to the La Gorce and Wyatt formations is uncertain. All of the basanent rocks of the Nilsen Plateau are unconformably overlain by the sedimentary rocks of the Beacon Supergroup (Devonian to Triassic) described by Long (1965). The Beacon rocks were intruded by sills of Ferrar Dolerite which are not shown in Fig. 6.5 and 6.7. 

The Wyatt Formation occurs in conjunction with the La Gorce Formation not only in the northern part of the Nilsen Plateau but also on the west side of the... 

Table 6.2 Stratigraphy of the basement rocks in the Duncan Mountains and the Nilsen Plateau of the Queen Maud Mountains (Stump 1985)...

Fig. 6.7 The basement complex of the northern part of the Nilsen Plateau consists of the La Gorce and Wyatt formations and of the Granite Harbor Intrusives. The volcano-sedimentary rocks predominate in the northern part of the Nilsen Plateau, whereas Granite Harbor Intrusives dominate the basement rocks of the southern part in Fig. 6.5. The Blackwall Glacier was referred to as the Black Rock Glacier by McLelland (1967). The Kukri Peneplain that divides the basement from the overlying Beacon Supergroup is not flat in this area but has elevation differences of about 34 m (Adapted from Stump 1985, 1995)...

The basement rocks of the Nilsen Plateau were dated by Eastin (1970) who used the whole-rock Rb-Sr isochron method. The resulting dates in Table 6.3 have been recalculated to A, = 1.42 x 10 year". All of the rock specimens dated by Eastin (1970) were collected by Douglas McLelland or other members of the group that mapped the Nilsen Plateau during the 1963/64 field season and were provided to Eastin by M.J. Hibbard, University of Nevada in Reno. The dates were calculated by the method of York (1966, 1969). The analytical data are tabulated in Appendix 6.7.1 and are interpreted there in Figs. 6.8-6.11. 

The metavolcanic rocks of the Wyatt Formation in the Nilsen Plateau were extruded or intruded into the rocks of the La Gorce Formation after the sedimentary... 

Table 6.3 Whole-rock Rb-Sr dates of the basement rocks exposed in the Nilsen Plateau at the head of the Amundsen Glacier (Data from Eastin 1970 are listed in Appendix 6.7.1 with Rb-Sr isochron diagrams in Figs. 6.8, 6.9, 6.10, and 6.11) ...

Fig. 6.8 Rb-Sr age determinations of metasedimentary rocks of the LaGorce Formation from the valley of the Blackwall Glacier, Nilsen Plateau (Fig. 6.7). The dates and initial Sr/ Sr ratios were calculated by Eastin (1970) by the methods of York (1966, 1969) and have been adjusted to = 1.42 x 10" year" Isochron A is based on four colinear data points (472, 474, 475. and 476). Line B is defined by samples 471 and 473 which have the highest Rb/ Sr ratios and have lost some in situ produced radiogenic Sr. Plotted from data by Eastin (1970)...

The rocks of the La Gorce and of the Wyatt formations of the Nilsen Plateau were intruded by syntec-tonic plutons of the Granite Harbor Intrusives represented here by the Lonely Ridge Granodiorite which crystallized at about 598 17 Ma with an ratio of 0.7116 0.0003 (Table 6.3 and Appendix 6.7.1.3, Fig. 6.10). This date may be more uncertain than indicated by the error limits ( 17 Ma) because only four of seven samples analyzed by Eastin (1970) satisfy the assumptions required for dating by... 

We now move east from the Nilsen Plateau into the drainage of the Scott Glacier in Fig. 6.12 formerly known as the Thome Glacier. Virtually the entire area drained by the Scott Glacier and its tributaries exposes rocks of the basement complex consisting of the La Gorce Formation, the Wyatt Formation, the Ackerman Formation, and the... 

South Ridge, Nilsen Plateau 6.7.1.3 Lonely-Ridge Granodiorite, Lonely Ridge ... 

Lonely Ridge, Nilsen Plateau Biotite 472 10 McLelland (1967)... 

These insights concerning the history of magmatic activity in the Wisconsin Hills remind us that McLelland (1967) divided the Granite Harbor Intrusives in the southern part of the Nilsen Plateau into four distinctive facies (Section 6.3.1). Three of these facies are cata-clastically deformed (i.e., syntectonic), whereas the North Quartz Monzonite is not foliated (i.e., post-tectonic) and may be younger than the other facies. 

McLeUand D (1967) Geology of the basement complex, Nilsen Plateau, Antarctica. MSc thesis. University of Nevada, Reno, NV... 

The Fremouw Formation of the Beardmore Glacier area extends north as far as the Mackay Glacier of southern Victoria Land where it is correlated with the Lashly Formation. It also extends southeast to the Nilsen Plateau (Barrett et al. 1972 Elliot 1975 Collinson et al. 1994). However, sedimentary rocks of Triassic age do not occur in the Scott Glacier area (Doumani and Minshew 1965 Minshew 1966, 1967), in the Ohio Range (Long 1962, 1965), and in the Pensocola Mountains (Schmidt et al. 1965 Schmidt and Eord 1969). 

---