Victoria University Antarctic Research Expedition Science and Logistics Reports 1985-86: VUWAE 30
Introduction and Background
Introduction and Background
This was the last year of a Ph.D. study to determine the uplift history of the Transantarctic Mountains using fission track dating. The study of mountain uplift using this technique requires sampling at regular intervals over significant elevation ranges in order to gain information representing the greatest possible time period. Previous seasons have concentrated in southern Victoria Land but all field work this season was conducted out of the U.S. deep-field camp in the Beardmore Glacier area (84° 00′ 13.897″S, 164° 24′ 42.226″E). Two areas were visited from here; the coastal region around the mouth of the Beardmore Glacier and further inland In the Miller and Queen Elizabeth Ranges. The main field objective was the collection of samples to determine uplift rates and measure vertical displacement across faults. Sampling for fission track studies is limited to those rocks which contain uranium-enriched minerals. This study is looking mainly at apatite which is common in granitic rocks which in the Beardmore Glacier area outcrop mainly along the coast but make up a large proportion of the Miller Range and also occur as isolated plutons elsewhere.
Figure 3. Model for the uplift history of the Transantarctic Mountains based on a vertical sampling profile from the eastern end of the Kukri Hills, southern Victoria Land, and including a sample of basement gneiss from the CIROS 2 drillhole. The 'break in slope' in the graph at about 50 Ma marks the start of uplift of the mountains, giving an average uplift rate since that time of approximately 100 m/Ma. Errors plotted for the apatite ages are two standard deviations, for the elevations ±10 m.
DVDP 8 and 10, two holes drilled in New Harbour near the Transantarctic Mountain Front have geothermal gradients of 60°C/km (Decker and Bucher, 1982). This higher gradient is considered to be a result of the higher heat flow present in the Dry Valleys. - Ross Island area due to the present day extensional regime that is manifested by the presence of the McMurdo Volcanics.
It is also worth noting that the position of the vertical sample profile used to determine an uplift rate on the mountain front in relation to the point of maximum uplift is important. Profiles lying to the east of the point of maximum uplift in southern Victoria Land have been down faulted relative to it. Hence any uplift rate calculated from these will be a slight underestimate but still well within any error limits, given the assumptions made to calculate the uplift rate. Errors for ages less than 50 Ma are large compared to the change in elevation (Fig. 3) between successive page 15 samples. Errors in ages elder than 50 Ma are small compared to a change in elevation, a difference of a few hundred metres producing a significant age difference. This is an important point when generating artificial reference planes using apatite fission track ages as it is necessary to take samples from higher elevations to guarantee an age of over 50 Ma. In southern Victoria Land, near horizontal sills of dolerite within the basement can be used as reference surfaces to determine the amount of displacement across faults at the Transantarctic Mountain Front. The dolerite sills in the Beardmore Glacier area do not outcrop at the coast, hence the need for horizontal sampling traverses to confirm the position of faults suspected from analogy with other parts of the Transantarctic Mountains and from topographic evidence. To the south of the Beardmore Glacier at Cape Surprise a fault with 5 km of displacement downthrown to the east has been recorded (Barrett, 1965).