Precambrian rocks of the Ross Sea region

Publisher Website
Google Scholar
Abstract
Precambrian rocks of at least two orogenic cycles form the basement of the Transantarctic Mountains between the Ross and Weddell Seas. Precambrian basement rocks also outcrop in Marie Byrd Land and in the intervening Ross Sea depression. In the central Transantarctic Mountains, the Beardmore Group comprises folded metagreywackes overlying shallow-water calcareous and quartzitic metasediments. In the Queen Maud and Thiel Mountains, similar metagreywacke terrains underlie and are intruded by silicic ignimbrite and quartz porphyry. Folded metagreywacke associations in northern Victoria Land and in Marie Byrd Land are tentatively correlated on the basis of late Proterozoic acritarch assemblages. The Beardmore Group and southern equivalents were deformed, metamorphosed and intruded by granites before the deposition of shallow-water Lower Cambrian carbonate and clastic sequences. Precambrian metamorphic complexes in the Transantarctic Mountains have undergone polyphase deformation and metamorphism. Migmatization is widespread and has given rise to late Precambrian - Ordovician anatectic granitoids. Both Rb/Sr and K/Ar radiogenic systems have remained open during the latest Precambrian and Cambro-Ordovician orogenic episodes, giving rise to numerous reset radiometric ages in the 700 - 450 m.y. interval. An earlier Precambrian history is recognised in the Nimrod Group of the central Transantarctic Mountains, where an Archaean (c. 2800 m.y.) source terrain provided detritus to an early Proterozoic sedimentary suite. The apparent eastward displacement of late Precambrian - Cambrian? metasediments from the McMurdo Sound region to the central Ross Sea has been interpreted as a result of transform faulting and spreading in the Byrd Basin during the separation of the Marie Byrd Land block of West Antarctica from East Antarctica.