Geology and petrology of the Campbell‐Aviator divide, Northern Victoria Land, Antarctica

Abstract The pre‐Mesozoic rocks within the Campbell‐Aviator Divide consist of metasediments of the Ross Supergroup that have been intruded by granitic rocks of the Granite Harbour Intrusive Complex. Erosion has largely removed the Ross Supergroup, and this unit is now represented only by small areas of metasediment within and between large granite plutons. Two formations of the Ross Supergroup are recognised. The Priestley Formation consists of biotite and biotite‐hornblende schist containing scattered calcareous and metavolcanic bands. The Retreat Hills Schist consists of uniform biotite schist which is thought to be the metamorphosed equivalent of the Robertson Bay Group. A date of 461 ± 6 m.y. suggests that the Retreat Hills Schist was metamorphosed in the Ross Orogeny during the emplacement of granitic rocks. The Granite Harbour Intrusive Complex contains four major units—Aviator Granodiorite, Cosmonaut Granite, Northern Granite Complex, and Southern Granite Complex. The latter two are informal composite units containing a number of intrusive phases which are too small to be mapped separately. All the granitic rocks are undeformed and discordant to the structure of the country rock, which suggests that they are wholly post‐tectonic. A date of 454 ± 6 m.y. was obtained from the Cosmonaut Granite, but this can be regarded only as a minimum age. The mineralogy and chemistry of the post‐tectonic part of the Granite Harbour Intrusive Complex in northern Victoria Land and the younger Admiralty Intrusive Group are briefly compared. The Admiralty Intrusive Group is the more basic of the two suites, which probably accounts for the presence of abundant hornblende which is generally absent in the Granite Harbour Intrusive Complex.