Ferrar dolerit intrusions at Terracotta Mountain, suothern Victoria Land, Antarctica.

Author:

Morrison, AD

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Abstract:

At Terra Cotta Mountain, in the Taylor Glacier region of southern Victoria Land, basement granitoids of the Granite Harbour Intrusives are overlain by approximately 1000 metres of Beacon Supergroup sediments. A thick (237 metre) Ferrar Dolerite sill is intruded along the unconformity between the basement and overlying sediments. Numerous other Ferrar Dolerite dikes intrude the Beacon Supergroup and represent later phases of intrusion.
In-situ differentiation in the sill has involved the removal of phenocrysts from the upper zone of the sill by crystal settling, and the migration of the differentiated liquid to form a granophyric zone approximately 40 m below the top of the sill. However, differences between the calculated bulk composition of the sill and the composition of the chilled margins indicate that the sill did not crystallize from a single, homogeneous intrusion of magma. The apparent inhomgeneity of the magma may be the result of flow differentiation, or the later intrusion of a more phenocryst-rich magma.
The sill is truncated by the intrusion of a large dike. The dike interior is distinguished from the margins by a relative depletion in Cr. A model is favoured whereby the large dike acted as a magma conduit to higher levels. The low Cr concentrations in the interior of the dike reflect a depletion of Cr in the magma with time.
Geochemistry indicates a trend towards a more basic composition from the oldest to youngest dolerite intrusion. Crystal fractionation may account for much of the geochemical variation between the intrusive events. However, the poor correlations between many trace elements are consistent with the additional involvement of open system processes. The "decoupling" of Cr and highly incompatible elements is similar to the theoretical behaviour predicted for the products of a periodically replenished, tapped and fractionating magma chamber.
The Ferrar Dolerite samples from Terra Cotta Mountain exhibit large ion lithophile element-enrichment and depletions in Nb, Sr, P and Ti. The similarity of the trace element characteristics of the dolerite from Terra Cotta Mountain with those of other Ferrar Group rocks from the central Transantarctic Mountains and northern Victoria Land, as well as with the Tasmanian Dolerites, supports current ideas that the trace element signature of the Ferrar Group is inherited from a uniformly enriched mantle source region.

Thesis description:

ix. 266 p., ill., maps (folded in pocket); 30 cm.

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OU geology Identifier:

1989Morrison

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Location (WKT, WGS84):

POLYGON ((161.301669644104408 -77.903250131472902,161.176623976081089 -77.903986808103056,161.175966465343151 -77.902143184156301,161.167108352889613 -77.877251309256465,161.308033053877068 -77.875251639617318,161.316036961821965 -77.875135909040566,161.385368619156054 -77.874123718749161,161.390151357286271 -77.884033168102974,161.357194941527723 -77.891201136751889,161.301669644104408 -77.903250131472902))

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http://download.otagogeology.org.nz/temp/Abstracts/1989Morrison.pdf

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Citation

Morrison, AD, “Ferrar dolerit intrusions at Terracotta Mountain, suothern Victoria Land, Antarctica.,” Otago Geology Theses, accessed March 29, 2024, http://theses.otagogeology.org.nz/items/show/233.

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