Plateau volcanism in the African-Southern Ocean gateway

南大洋门户的打开使南极绕极流（ACC）的出现成为可能，这对全球新生代冷却的开始至关重要。在非洲南部，这个开口与几个大火成岩省（LIP）的形成有关，包括莫桑比克海岭、厄古拉斯高原和较小的东北格鲁吉亚海隆和莫德海隆。板块构造重建意味着后三个曾经是一个更大的“大厄古拉斯高原”（或“超级LIP”）的一部分，并被随后的裂谷分开。这是有争议的，以及在何种程度上，这些大型火山特征的就位阻碍了大西洋和印度洋之间的新生海道中的水团的交换，从而推迟了ACC. The海底Agulhas高原的发病钻在最近的IODP远征392。在高原南部的两个地点（地点U1579，U1580）和靠近其北方边缘的一个地点（U1582）发现了火成岩。初步（船上）数据表明，所有站点采样拉斑玄武岩，形成的低压（浅岩浆房）分馏主要是橄榄石和斜长石（是典型的海洋LIP熔岩）。正在进行的40 Ar/39 Ar定年将有助于回答高原侵位时代及其时空演化的问题。在之前的ODP考察（分别为第114和113航段）中，还对东北格鲁吉亚海隆和莫德海隆的火成岩样品进行了取芯。对三个高原的岩石进行地球化学研究，将有助于揭示岩浆活动的性质、构造背景和岩浆来源。拟议的项目将侧重于放射成因（Sr，Nd，Hf，Pb）同位素组成的测定，以限制岩浆源成分与其他区域和全球LIP岩浆活动进行比较。特别是，我们想解决一个悬而未决的问题，即厄古拉斯高原、东北格鲁吉亚隆起和莫德隆起岩浆活动是否都可以归因于相同的岩浆来源和构造背景（即，柱脊相互作用），以测试以前的板块构造重建模型。其他问题包括（深层来源？）地幔柱是岩浆活动的起源，它与区域大陆裂解、洋盆开启和深部地幔结构有着潜在的因果关系。同位素数据结合年龄测定和主要/微量元素地球化学的结果将有助于限制该区域LIP岩浆活动的起源和对构造配置，海洋环流和全球气候的影响，在中晚白垩世。

The opening of the Southern Ocean gateways allowed for the emergence of the Antarctic Circumpolar Current (ACC), crucial to the onset of global Cenozoic cooling. South of Africa, the opening was associated with the formation of several large igneous provinces (LIPs) including the Mozambique Ridge, Agulhas Plateau and the smaller Northeast Georgia Rise and Maud Rise. Plate tectonic reconstructions imply that the latter three were once part of a much larger "Greater Agulhas Plateau" (or "super-LIP") and were separated by subsequent rifting. It is debated whether and to what extent the emplacement of these large volcanic features obstructed the exchange of water masses in the nascent seaway between the Atlantic and the Indian Oceans thereby delaying the onset of the ACC. The submarine Agulhas Plateau was drilled during recent IODP Expedition 392. Igneous rocks were recovered at two sites on the southern part of the plateau (Sites U1579, U1580) and at one site near ist northern edge (U1582). Preliminary (shipboard) data indicate that all sites sampled tholeiitic basalts, formed by low pressure (shallow magma chamber) fractionation of mainly olivine and plagioclase (as is typical for marine LIP lavas). Ongoing 40Ar/39Ar dating will help to answer questions regarding the emplacement age of the plateau and ist spatial-temporal evolution. Igneous rock samples from Northeast Georgia Rise and Maud Rise have also been cored during previous ODP expeditions (Legs 114 and 113, respectively). Geochemical investigations of the recovered rocks from all three plateaus will help to reveal the nature, tectonic setting and source of the magmatism. The proposed project will focus on the determination of radiogenic (Sr, Nd, Hf, Pb) isotope compositions to constrain the magma source composition for comparison with other regional and global LIP magmatism. In particular, we want to address the open question whether the Agulhas Plateau, Northeast Georgia Rise and Maud Rise magmatism can all be attributed to the same magma source and tectonic setting (i.e., plume-ridge interaction) to test the previous plate tectonic reconstruction models. Additional questions include whether a (deeply-sourced?) mantle plume initiated the magmatism and ist potential causal relationship to regional continental breakup, the opening of ocean basins, and the structure of the deep mantle. The isotope data in combination with the results from age dating and major/trace element geochemistry will help to constrain the origin and impact of this regional LIP magmatism on tectonic configuration, ocean circulation, and global climate during the mid to late Cretaceous.