Antarctic Rift and Hot Spot Volcanism

摘要 该奖项支持对南极罗斯海地区火山岩的研究。 现有的锶（Sr），钕（Nd），铅（Pb）同位素的工作超过80玄武岩表明，HIMU（高U/Pb）的同位素特征（低87/86 Sr，高206/204 Pb）是无处不在的沿着约4500公里的西南极裂谷系（WARS）。 在该地区已经确定了三个海洋热点; Balleny和Scott群岛显示出与裂谷火山岩相同的HIMU样特征。 彼得一世岛显示了这种成分的暗示，尽管这些岩石表明，在一般情况下，一个更丰富的地幔热点来源（称为EM-2样热点）。 许多WARS火山岩也显示出富集成分的存在，但其中一个是来自大陆岩石圈（低Rb/Cs和Th/Pb）。 在维多利亚地，富集组分的存在或不存在与罗斯海裂谷和横贯南极山脉前缘之间边界的位置直接相关。 它在玛丽伯德地的最小存在表明相对于跨南极山脉地区，地壳更薄和/或更年轻。 裂谷中几乎没有富集的成分，这表明地壳非常薄，可能没有重要的岩石圈。 在一个长期项目的第二阶段，工作将集中在地球化学研究的三个WARS火山（西德利，霸王，Pleides）详细，以限制地壳与地幔岩石圈来源的富集成分。 一些同源和地幔捕虏体将被研究作为进一步的援助，在这个源歧视问题。 将通过分析坎贝尔高原上亚南极岛屿的新生代玄武岩（包括同源和地幔捕虏体）来测试HIMU-WARS特征的地理范围。 在所有这些工作中，我们将首次采用锇和氧同位素组合作为区分地壳与地幔岩石圈特征的工具。

Abstract This award supports a study of volcanic rocks in the Ross Sea area of Antarctica. Existing strontium (Sr), neodymium (Nd), and lead (Pb) isotopic work on more than 80 basalts shows that a HIMU (High U/Pb)-like isotopic signature (low 87/86Sr, high 206/204Pb) is ubiquitous along some 4500 km of the West Antarctic Rift System (WARS). Three oceanic hotspots have been defined in the region; Balleny and Scott Islands show the same HIMU-like signature as the rift volcanics. Peter I Island shows a hint of this component, though these rocks indicate, in general, a more enriched mantle hotspot source (refered to as an EM-2-like hotspot). Many of the WARS volcanics also show the presence of an enriched component, but one which is derived from the continental lithosphere (low Rb/Cs and Th/Pb). In Victoria Land, the presence or absence of the enriched component is directly related to location with respect to the boundary between the Ross Sea rift and the Transantarctic Mountain Front. Its minimal presence in Marie Byrd Land suggests a thinner and/or younger crust, relative to the Transantarctic Mountain area. The virtual absence of enriched component in the rift proper suggests a highly thinned crust, perhaps without significant underlying lithosphere. In this second phase of a longer term project, the work will focus on geochemical study three WARS volcanoes (Sidley, Overlord, Pleides) in detail, to constrain a crustal versus mantle lithospheric source for the enriched component. A number of cognate and mantle xenoliths will be studied as a further aid in this source discrimination issue. The geographic extent of the HIMU-WARS signature will be tested by analyzing Cenozoic basalts from sub-Antarctic islands on the Campbell Plateau (including cognate and mantle xenoliths). In all of this work we will, for the first time, employ osmium and oxygen isotopes in combination as a tool to discriminate crustal versus mantle lithosphere signatures.