Wyatt Formation

Wyatt Formation which was intruded by small plutons of Granite Harbor Intrusives (Fig. 6.7). A cache of food and miscellaneous equipment was left at the Amundsen Glacier camp that was occupied during the 1963/64 field season. Excerpt of the topographic map SVl-lQ/10 8-8600-15,000/1 x 15 (Nilsen Hateau, Antarctica) of the US Geological Survey, Washington, DC... 

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 rocks of the overlying Wyatt Formation are composed of quartz, albite, and biotite with phe-nocrysts of K-feldspar and albite (1-5 mm) in a finegrained matrix of quartz, albite, and K-feldspar. The albite phenocrysts and the groundmass are partially altered to chlorite and sericite, whereas the mattix also contains epidote, calcite, and magnetite (McLelland 1967 Eastin 1970). 

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... 

Beardmore Not present Dunan Formation Wyatt Formation LaGorce Formation... 

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 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... 

The whole-rock Rb-Sr date of the Wyatt Formation appear to have been reset by contact metamorphism caused by the North Quartz Monzonite (Eastin 1970)... 

Fig. 6.9 Rb-Sr age determination of metavolcanic rocks of the Wyatt Formation in the valley of the Blackwall Glacier, Nilsen Plateau (Fig. 6.7). The date and initial Sr/ Sr ratio were calculated by Eastin (1970) by the methods of York (1966,1969) and have been adjusted to = 1.42 x 10 year Samples 461 and 463 were excluded because they deviate significantly from the line fitted to the remaining data points. 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... 

Wyatt Formation near Mt. Wyatt on the west side of the Scott Glacier (Fig. 6.12). 

The mineral composition (mode) of the Wyatt Formation in the Scott-Glacier area was determined by Minshew (1967) and is listed in Appendix 6.7.3.1 followed by chemical analyses in Appendix 6.7.3.2. The rocks of the Wyatt Formation in the La Gorce Mountains were altered either by the original magmatic fluid or during later metamorphism. In extreme cases, plagioclase was completely altered to sericite or saussurite (Stump et al. 1986). Saussurite is a mineral aggregate composed of albite and zoisite or epidote with variable amounts of calcite, sericite, and prehnite (Jackson 1997). 

The Ackerman Formation of the La Gorce Mountains (Table 6.4) consists of a sequence of inter-bedded sedimentary and volcaniclastic rocks that crop out on the northern part of Ackerman Ridge in Fig. 6.13. Green shale at the base of the Ackerman Formation was deposited conformably on massive rocks of the Wyatt Formation. The top of the Ackerman Formation is faulted against the sedimentary rocks of the La Gorce Formation. The volcanic rocks of the Ackerman Formation resemble the Wyatt Formation in color, texture, phenocrysts content, and bulk chemical composition. The rocks were sericitized and mafic minerals were converted to chlorite, but the extent of... 

The chemical composition of the volcanic rocks of the Ackerman and Wyatt formations in Fig. 6.14 are similar but not identical. The high concentrations of silica and the reported presence of quartz indicate that the rocks of both formations are oversaturated with respect to silica according to the classification of Shand... 

Fig. 6.14 Silica-variation diagrams of the silicic porphyries of the Wyatt Formation and of the Ackerman Formation in the La Gorce Mountains and in the upper Scott Glacier area (Data by Stump et al. 1986 Minshew 1967)...

The igneous rocks of the Wyatt Formation occur at many locations within the Queen Maud Mountains, as well as in the Horlick and Thiel Mountains. In spite of these extensive exposures, the origin of the Wyatt Formation is still uncertain because in some places it clearly intruded folded metasedimentary rocks of the LaGorce Formation, whereas in other places it over-lies them conformably. In addition, hydrothermal alteration of the rocks and the effects of regional metamorphism described by Minshew (1967) have disturbed the isotopic composition of strontium of the rocks, which has caused data points to scatter on Rb-Sr isochron diagrams and caused large uncertainties in age determinations of the Wyatt Formation listed in Table 6.5. 

Faure et al. (1979) analyzed five samples of the Wyatt Formation collected by Minshew between Mt. Wyatt and Mt. Gardiner in the upper reaches of the Scott Glacier. The results in Appendix 6.7.3.3 were originally used only to state an upper limit of 788 Ma (Neoproterozoic) for the age of the Wyatt Formation. A least-squares linear regression of these data (plus one duplicate) defines line A in Fig. 6.15 which results in a calculated date of 524 13 Ma (Early Cambrian) with an initial Sr/ Sr ratio of 0.711919 0.000547 for X = 1.42 X 10" year Three of the samples in Fig. 6.15 precisely define line B which corresponds to... 

A more recent attempt to date rocks of the Wyatt Formation in the Scott Glacier area by Stump et al. (1986) was also frustrated by the scatter of data points. 

Fig. 6. 15 A suite of five whole-rock samples of the Wyatt Formation collected by V.H. Minshew from outcrops between Mt. Wyatt and Mt. Gardiner in the Scott Glacier area define two straight lines labeled A and B derived by least-squares linear regression. Line A which includes all five samples plus one duplicate analysis yields a date of 524 13 Ma and a high initial Sr/ Sr ratio of 0.711919 0.000547 (la). Line B is defined by three selected samples and corresponds to a precise date of 802 2 Ma but it has an impossibly low initial Sr/ Sr ratio of 0.69775. We conclude that the igneous rocks of the Wyatt Formation are older than 524 13 Ma but younger that 802 2 Ma. These previously unpublished data by G. Faure are presented in Appendix 6.133. In addition. Appendices 6.7.3.1 and 6.7.3.2 contain modal analyses and chemical compositions of rocks of the Wyatt Formation from Minshew (1967)...

Wyatt Formation, Scott Glacier Rb-Sr, whole rock 524 13... 

Nevertheless, the slope of a straight line defined by their data yielded a date of 545 59 Ma with and initial "Sr/ Sr ratio of 0.7114 0.0030. Stump et al. (1986) concluded that the date had been reset and therefore is an underestimate of the crystallization age of the Wyatt Formation. Even the U-Pb method of dating zircon failed to provide a reliable date of the Wyatt Formation because the data points derived from the zircon fractions analyzed by Van Schmus et al. (1997) did not define a discordia curve. Even so, Van Schmus et al. (1997) inferred Early Cambrian dates between 520 and 540 Ma for this formation. The most precise age determination for the Wyatt Formation is a U-Pb date of 526 2 Ma reported by Encamacidn and Grunow (1996). Therefore, the age of the Wyatt Formation appears to be Early Cambrian. 

Modal and Chemical Compositions and Rb-Sr Systematics of the Wyatt Formation, Scott-Glacier Area and Wisconsin Range, Transantarctic Mountains... 

Modal Analyses of the Wyatt Formation Collected by V.H. Minshew in the Scott Glacier Area (All Data in This Table Are from Minshew 1967 Fig. 6.12)... 

Chemical Compositions of Whole-Rock Samples of the Wyatt Formation from the Scott Giacier Area (Minshew, 1967) and from the Wisconsin Range of the Horiick Mountains in Percent by Weight (Analyst Sam Botts, US Geological Survey)... 

A 235, Wyatt Formation, Mt. Gardiner, Scott Glacier B F-64-61, Wyatt Formation, Metavolcanic Mountain, Wisconsin Range... 

C F-64-108, Wyatt Formation, Wisconsin Plateau, east of Olentangy Glacier... 

Rb-Sr Systematics, Wyatt Formation, Scott-Glacier Area, Queen Maud Mountains (Faure, Unpubiished)... 

The data listed below are previously unpublished because they scatter on the isochron diagram and were judged to be unsuitable for dating the Wyatt Formation by the whole-rock Rb-Sr method. Faure et al. (1979) used this data set only to set an upper limit of 788 Ma for the age of the Wyatt Formation. 

Blackburn QA (1937) The Thorne Glacier section of the Queen Maud Mountains. GeogrRev 27 598-614 Borg SG (1980) Petrology and geochemistry of the Wyatt Formation and the Queen Maud bathoUth, upper Scott Glacier area, Antarctica. Unpublished MS thesis, Arizona State University, Tempe, AZ... 

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