Antarctic Rift and Hot Spot Volcanism

该奖项支持对南极洲罗斯海地区火山岩的研究。现有的80多块玄武岩的锶（Sr）、钕（Nd）和铅（Pb）同位素研究表明，在南极西部裂谷系（WARS）约4500公里的范围内普遍存在高U/Pb同位素特征（低87/86Sr，高206/204Pb）。该地区已经确定了三个海洋热点；巴莱尼岛和斯科特岛显示出与裂谷火山相同的类似himu的特征。彼得一号岛显示了这种成分的暗示，尽管这些岩石表明，一般来说，一个更丰富的地幔热点来源（被称为em -2类热点）。许多战争火山也显示出富集成分的存在，但这种成分来源于大陆岩石圈（低Rb/Cs和Th/Pb）。在维多利亚地，富集成分的存在与否与罗斯海裂谷和横贯南极山锋之间边界的位置直接相关。相对于横贯南极山区，它在玛丽伯德地的最小存在表明地壳更薄和/或更年轻。裂谷中几乎没有富集成分，这表明地壳非常薄，可能没有明显的底层岩石圈。在这个长期项目的第二阶段，工作将集中在三个战争火山（Sidley, Overlord, Pleides）的详细地球化学研究上，以限制地壳和地幔岩石圈对富集成分的来源。本文还将研究一些同源和地幔捕虏体，以进一步帮助解决这一问题。HIMU-WARS特征的地理范围将通过分析坎贝尔高原亚南极岛屿上的新生代玄武岩（包括同源和地幔捕虏体）进行测试。在所有这些工作中，我们将首次使用锇和氧同位素组合作为区分地壳和地幔岩石圈特征的工具。

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 signatupe 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.