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。现有对80多个玄武岩的锶、钕和铅同位素研究表明，在西南极裂谷系统(WARS)约4500公里处，普遍存在类HIMU(高U/Pb)的同位素特征(低87/86Sr，高206/204Pb)。在该地区已经确定了三个海洋热点；巴勒尼和斯科特群岛显示出与裂谷火山相同的HIMU特征。彼得一号岛显示了这一成分的暗示，尽管这些岩石总体上表明有更丰富的地幔热点来源(被称为类似EM-2的热点)。许多战争火山岩也显示存在富集组分，但它来自大陆岩石圈(低Rb/Cs和Th/Pb)。在维多利亚陆地上，是否存在富集组分与罗斯海裂谷和横贯北极山脉前缘之间的边界的位置直接相关。它在马里伯德岛的极少存在表明，相对于横跨北极的山区，地壳更薄和/或更年轻。裂谷本身实际上缺乏富集组分，这表明地壳高度减薄，可能没有明显的下伏岩石圈。在这一较长期项目的第二阶段，这项工作将侧重于对三座战争火山(锡德利火山、霸王火山、普莱德斯火山)进行详细的地球化学研究，以限制地壳与地幔岩石圈来源的浓缩成分。将研究一些同源和地幔包体，作为对这一来源歧视问题的进一步帮助。HIMU-WARS标志的地理范围将通过分析坎贝尔高原南极以下岛屿的新生代玄武岩(包括同源和地幔包体)来检验。在所有这项工作中，我们将第一次使用臭氧和氧同位素的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.