Tobin Mesa

Ferrar Supergroup (Jurassic) Kirkpatrick basalt lava flows and Ferrar Dolerite sills 

The map identifies the location of Mt. Masley on Pain Mesa and of Solo Nunatak which are described in the text (Reproduced from Mensing 1987) 

The flow Stratigraphy, petrography, and chemical composition of the basalt flows on Tobin Mesa in Fig. 12.9 were described by Siders (1983), Haban (1984), Siders and Elliot (1985), Elliot et al. (1986b), and Fleming et al. (1995). This mesa is composed of about 40 flows that have a total stratigraphic thickness of about 900 m. 

The thickness of the flows ranges from less than 1 m to more than 120 m. All flows have amygdaloidal zones at their bases and tops and the vesicles are filled with zeolites, quartz, and calcite. The thickest flows are coarse grained and have diabasic texture. Tobin Mesa is capped by a black flow composed of aphanatic to glassy basalt. 

The basalt flows on Tobin Mesa are interbedded with thin layers of sedimentary rocks most of which 

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The Exposure Hill Formation occurs at the base of the sheet-like lava flows of Kirkpatrick Basalt that form the Mesa Range of northern Victoria Land and on nearby nunataks most of which are located in the Rennick graben in Fig. 12.6. The deposits of breccia and related pyroclastic rocks occur at Exposure Hill at the southern end of Gair Mesa and at Mt. Fazio and Scarab Peak on Tobin Mesa as well as on Mt. Carson adjacent to the Aeronaut Glacier in Fig. 12.7. hi addition, Elliot et al. (1986a) described a deposit of breccia on Agate Peak located about 26 km east of the northern tip of Pain Mesa (Fig. 12.6). 

Siders and Elliot (1985) published chemical analyses of 18 basalt specimens most of which originated from Siders Bluff on the northwest corner of Tobin Mesa. The rocks are silica-rich but alkali-poor such that most specimens from Tobin Mesa analyzed by Siders and Elliot (1985) are classifiable in Fig. 12.10 as basaltic andesite and even andesites. However,... 

Tobin Mesa, Mesa Range, Northern Victoria Land ... 

Fig. 12.10 The lava flows on Tobin Mesa are subalkaline basaltic andesites and even stray into the andesite field in this alkali-silica diagram (Wilson 1989). The phenocryst assemblage of plagioclase, pyroxene, and magnetite identifies these rocks as tholeiitic basalt in spite of their high silica concentrations (Data from Siders and Elliot 1985)...

The first measurements of the isotopic composition of strontium in the Kirkpatrick Basalt flows on Tobin Mesa were made by L.M. Jones and interpreted by Hill (1969). The samples were collected by H.S. Gair and included three specimens of the high-Ti flow that eaps Scarab Peak, one sample of low-Ti basalt taken about... 

Table 12.3 Analytical data for Kirkpatrick Basalt on Scarab Peak, Tobin Mesa, NVL (Collected by H.S. Gair, analyzed by L.M. Jones, and interpreted by HiU 1969)...

Scarab Peak, top of dark flow (61 m) that forms the top of Tobin Mesa (Gair s sample 1) "Scarab Peak, 2.50 m below sample 296 (Gair s sample 5)... 

Scarab Peak, 640 m below the top of Tobin Mesa (Gair s sample 17)... 

Pain Mesa in Fig. 12.11 is composed of flat-lying layers of Kirkpatrick Basalt much like Tobin Mesa described in the previons section. These basalt flows were investigated by Mensing (1987) and by Mensing et al. (1991). Mount Masley on Pain Mesa is composed... 

Fig. 12.18 On the alkali-silica diagram of Cox et al. (1979) and Wilson (1989) the flows of Kirkpatrick Basalt of Solo Nunatak extend from basalt to basaltic andesite much like the lava flows on Pain Mesa (Fig. 12.14) and on Tobin Mesa (Fig. 12.10). However, the mineral composition of the phenocrysts cause all of the flows to be classified as subalkalic tholeiite basalt. In addition, all of the flows are composed of low-Ti basalt because the high-Ti basalt flows that cap Tobin and Pain mesas of the Mesa Range are not present and may have been eroded (Mensing 1987)...

The high-Ti flows appear to be conformable to the underlying low-Ti flows on Pain Mesa and there is no evidence for an extended hiatus between the eruption of the two sets of flows. In addition, the ArPAr plateau dates of plagioclase in the high-Ti flow on Tobin Mesa demonstrate that the age of this flow is Middle Jurassic and not Cretaceous. The loss of Ar and the homogeni-... 

The break-away of Australia from East Antarctica between 100 and 65 Ma (Lawver et al. 1991) was initiated by a rift that subsequently evolved into the Southeast-Indian Ridge (Fig. 15.9). Transform faults associated with this spreading ridge may have caused crustal blocks from the Campbell Plateau adjacent to the South Island of New Zealand or from the Tasman Plateau located near Tasmania to be transported south into juxtaposition with the Wilson terrane of northern Victoria Land. The age of accretion of the Bowers and Robertson Bay terranes may have been recorded by the alteration of the Rb-Sr systematics of the high-Ti basalt flows that cap the Pain and Tobin mesas in the Mesa Range of northern Victoria Land (Sections 12.4-12.6). 

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