东南极内陆格罗夫山和外缘拉斯曼丘陵地区基岩暴露年龄及其古气候含义

This paper is concerned of the I0Be and 26A1 exposure ages of bedrocks in the Grove Mountains (GMs), inland of East Antarctica, and in the Larsemann Hills, peripheral alongshore of East Antarctica, respectively. The results of our study indicate that the higher bedrock samples in two profiles in the GMs have minimum exposure ages of-2 Ma, and their 26Al/10Be can be projected into the erosion island, which means they only have simple exposure history. The actual exposure ages may be mid-late Pliocene because the bedrocks should have erosion. The relationship between the altitudes and cosmogenic nuclide concentrations of those higher samples suggests that they have not reached secular equilibrium, means that a higher than -2300m East Antarctic Ice Sheet (EAIS) existed in the GMs before mid-Pliocene, and decreased monotonously for a period since mid-Pliocene. Lower samples of the two profiles have much younger exposure ages, and had been covered at least once obviously implicated by that their 26Al/10Be are projected down to the erosion island. Using a 10Be-26Al project figure to determine the history of the GMs samples shows that the lower samples have minimum total initial exposure and cover time of 1.7-2.8Ma, suggesting that those samples were exposed initially since about late Pliocene too, and the interior EAIS fluctuated after late Plicoene obviously. The altitudes and exposure ages of all the GMs samples indicate that the ice surface level of the interior EAIS in the GMs was >2300m during or before mid Pliocene (more than 200m higher than present ice surface level), and only rose to -2200m during the fluctuation occurred after late Pliocene, thus the elevation of the interior EAIS in the GMs after mid-Pliocene was never higher than during or before mid Pliocene even during the Quaternary Glacial Maximum. According to data from the GMs and other parts of East Antarctica, a larger East Antarctic Ice Sheet existed before mid-Pliocene, thus the elevation decrease of interior EAIS in the GMs after mid Pliocene may be a director of volume decrease of the EAIS. Since the Antarctic climate has a cooling trend since ~3Ma, similar to the global climate change, the volume decrease of the EAIS since mid-Pliocene may beause of moisture supply decrease directly rather than atmosphere temperature change. As for the Larsemann Hills, samples farther to the glacier have exposure age of 40~50ka, means they exposed in the early time of Last Glacier Cycle, obviously earlier than the Last Glacial Maximum (LGM). Samples nearer to the glacier have exposure ages younger than LGM. Thus, different to the GMs, exposure ages of the Larsemann Hills samples have more obvious relationship to their distance from the glacier margin rather than to the altitudes of the samples.