40Ar-39Ar dating and isotopic composition of groundmass and felspar samples from core AND-2A

The AND-2A drillcore (Antarctic Drilling Program-ANDRILL) was successfully completed in late 2007 on the Antarctic continental margin (Southern McMurdo Sound, Ross Sea) with the aim of tracking ice proximal to shallow marine environmental fluctuations and to document the 20-Ma evolution of the Erebus Volcanic Province. Lava clasts and tephra layers from the AND-2A drillcore were investigated from a petrographic and stratigraphic point of view and analyzed by the 40Ar-39Ar laser technique in order to constrain the age model of the core and to gain information on the style and nature of sediment deposition in the Victoria Land Basin since Early Miocene. Ten out of 17 samples yielded statistically robust 40Ar-39Ar ages, indicating that the AND-2A drillcore recovered <230 m of Middle Miocene (~128-358 m below sea floor, ~11.5-16.0 Ma) and >780 m of Early Miocene (~358-1093 m below sea floor, ~16.0-20.1 Ma). Results also highlight a nearly continuous stratigraphic record from at least 358 m below sea floor down hole, characterized by a mean sedimentation rate of ~19 cm/ka, possible oscillations of no more than a few hundreds of ka and a break within ~17.5-18.1 Ma. Comparison with available data from volcanic deposits on land, suggests that volcanic rocks within the AND-2A core were supplied from the south, possibly with source areas closer to the drill site for the upper core levels, and from 358 m below sea floor down hole, with the 'proto-Mount Morning' as the main source.

AND-2A钻孔（Antarctic Drilling Program-ANDRILL）于2007年末在南极大陆边缘（罗斯海麦克默多湾南部）顺利完工，其研究目标为追踪近冰浅海环境的波动变化，并记录埃里伯斯火山省（Erebus Volcanic Province）2000万年的演化历程。研究人员从岩石学与地层学视角，对AND-2A钻孔中的熔岩碎屑及火山灰层开展了系统分析，并采用40Ar-39Ar激光定年技术（40Ar-39Ar laser technique）进行测试，以此约束钻孔的年龄模型，同时获取早中新世（Early Miocene）以来维多利亚地盆地（Victoria Land Basin）内沉积物的沉积样式与沉积性质相关信息。17个待测样品中有10个获得了统计意义上可靠的40Ar-39Ar定年结果，表明AND-2A钻孔获取了深度小于230米的中中新世（Middle Miocene）沉积物（海底以下约128~358米，对应年龄约11.5~16.0 Ma），以及深度大于780米的早中新世沉积物（海底以下约358~1093米，对应年龄约16.0~20.1 Ma）。研究结果同时显示，自海底以下至少358米的钻孔深度处起，存在近乎连续的地层记录，其平均沉积速率约为19厘米/千年，沉积波动幅度不超过数百千年，且在约17.5~18.1 Ma处存在沉积间断。将该结果与陆上火山沉积的已有公开数据对比后可知，AND-2A钻孔内的火山岩物质主要来自南侧；对于钻孔上部层位，其物源可能更靠近钻孔点位；而自海底以下358米至钻孔底部的层位，其主要物源为“原芒廷山（proto-Mount Morning）”。