<< School of Environment & Technology - University of Brighton.

Dr Conor J Ryan - BAAE

The association between the British Army Antarctic Expedition series and the University of Brighton (in collaboration with other UK and international institutions) has already yielded important constraints on the geological evolution of the Antarctic Peninsula. The 2007-2008 expedition offers a unique opportunity to further our understanding of the geological evolution of West Antarctica. The geological fieldwork to be carried out as part of the scientific programmes of the 2007-2008 British Army Antarctic Expedition fall into two main sub-programmes;

A. Testing the thermo-chronological response to the opening of the Drake Passage.

BAAE - Team

This project aims to quantify the timing of exhumation on the northern tip of the Antarctic Peninsula using multiple low temperature thermochronometers (40Ar/39Ar K-feldspar, zircon fission track, apatite fission track and (U-Th)/He apatite). These data will be assessed to determine if pulses of rapid exhumation-related cooling can be temporally linked to either the opening of the Drake Passage, the oceanic gateway which separates the Antarctic Peninsula from Tierra del Fuego, or the onset of glaciation in western Antarctica. Opening of the Drake Passage is controversial but important, because gateway opening probably had a profound effect on global circulation and climate. The timing of uplift of the highly mountainous Antarctic Peninsula is not known. It is proposed to determine the timing of uplift of this mountain belt by isotopic dating. Combining different isotope-mineral systems will create a thermal history for the peninsula. Periods of rapid cooling (exhumation events) will be compared to important regional geological events, including the rifting of South America from Antarctica which formed the Drake Passage oceanic gateway. This may have led to the onset of the Antarctic Circumpolar Current, whose development has been implicated in the formation of permanent ice sheets on Antarctica 34 million years ago.

The opening of the Drake Passage gateway is thought to have been an important event in the history of global oceanic and atmospheric circulation, because it allowed the free transfer of water masses between the Pacific and Atlantic oceans at mid to high southerly latitudes for the first time since the breakup of Gondwana. This circulation may have led to the onset of the Antarctic Circumpolar Current, the world's largest current, by removing the final barrier to deep circumpolar circulation. The development of the Antarctic Circumpolar Current has been implicated in the formation of permanent ice sheets on Antarctica near the Eocene–Oligocene transition (34 Ma).

However the Cenozoic uplift history of the Drake Passage - Scotia Sea region is poorly constrained. Most of the continental fragments inferred to have acted as barriers to deep water flow (e.g. the Davis Bank and Aurora Bank of the North Scotia Ridge; the Terror Rise, Pirie Bank and Bruce Bank of the South Scotia Sea) are in deep water and are poorly studied, and even their affinity (crustal versus oceanic) is debated. In contrast, the neighbouring Antarctic Peninsula is well exposed, and offers to the potential to quantify the timing of rift-related exhumation. A detailed low temperature thermochronological record from the Antarctic Peninsula region could resolve many fundamental problems in western Antarctic geology, because temporal relations are often keys to causality arguments in the Earth Sciences. In addition to integrating exhumation data from the Antarctic Peninsula region with temporal constraints on the initiation of extension in the Drake Passage region, it will be tested if there is a link between uplift of the Antarctic Peninsula, and the onset of glaciation. Some have suggested that the creation of a > 2 km-high ridge of mountains would have affected precipitation and local climate sufficiently to have caused the development of an ice sheet. Recent field-based studies in the James Ross Basin have demonstrated that the onset of glaciation on the Antarctic Peninsula occurs at the Eocene – Oligocene boundary, contemporaneous with the onset of glaciation in Eastern Antarctica.

The bid to carry out this work has been prepared jointly with Dr David Chew, Trinity College Dublin.

B. Detrital zircon characteristics of the Trinity Peninsula Group of northern Graham Land.

This project will aim to study the detrital zircon characteristics of an enigmatic group of sedimentary rocks that are exposed in northern Graham Land. The results of these studies could have extremely important consequences on current ideas regarding the more ancient tectonic evolution of the Antarctic Peninsula. These sedimentary rocks are well exposed along the Danco Coast. Zircon is a robust mineral that survives erosion from existing rocks and incorporation into sedimentary rocks. The usefulness of this detrital mineral lies in the fact that it is easily dated via geochronological techniques. If we can find out how old the populations of zircon contained in the Trinity Peninsula Group sediments are, we can place constraints on the age of the source region of these zircons.

Interestingly, limited previous studies of the Trinity Peninsula Group in other parts of the Antarctic Peninsula have hinted at a zircon age population of about 300 Ma. Petrographical constraints tell us that the Trinity Peninsula Group sediments were eroded from a continental magmatic arc (like the Antarctic Peninsula). No such 300 million year old arc is present in the area under study. This begs the question as to where these rocks were originally formed; it is possible that they were tectonically transported to their present position via terrane accretion processes. This project hopes to describe the zircon population characteristics of the poorly studied western tracts of the Trinity Peninsula Group of the Danco Coast region.