Geochemical Evolution of the Lithospheric Mantle Beneath East Antarctica: Connections to the Plate Tectonic Development of Eastern Gondwanaland

9615274来自东南极洲Jetty半岛的Mukasa超镁铁质包体套件，提供了一个无与伦比的机会来研究和描述在侏罗纪末和白垩纪初分裂东冈瓦纳大陆的岩石圈扩张期间，在次大陆地幔温度和压力下岩浆/岩石反应平衡的后果。本研究中使用的样本是由苏联/俄罗斯在1982-83年、1983-84年和1986-87年期间的探险队收集的，由俄罗斯圣彼得堡VNII okeeologia南极地质系的亚历克斯·安德罗尼科夫博士（目前在德国哥廷根大学休假）完全交给我们使用。该奖励将支持分析工作，以确定从石榴石和尖晶石橄榄岩捕虏体中提取的斜辉石（cpx）和玻璃的Nd， Sr和Pb同位素组成以及Rb/Sr， Sm/Nd和U/Pb元素比例，并对来自主岩浆岩的整体岩石样本进行相同的测量，这些岩浆岩的成分是碱性硬辉石，alalite和钠辉石。此外，分析程序将包括浓度测量，使用二次电离质谱（SIMS），稀土元素（REE）和Ba， Cs, Cr， K, Nb, Rb, Sr, Ti， V， Y和Zr（以不同的组合）在cpx，石榴石和各种玻璃存在于一些捕虏体。Andronikov博士最近获得了亚历山大·冯·洪堡基金会（Alexander von Humboldt Foundation）的奖学金，他将在德国哥廷根大学（University of G ttingen）对相同的材料进行补充研究，重点研究由电子显微探针确定的包体矿物化学，以及分别由x射线荧光光谱法和电感耦合等离子体质谱法测量的宿主岩石的主要和微量元素组成。这些综合数据将使捕虏体的一个子集能够评估来自上地幔不同深度的热橄榄岩部分熔融的程度和影响，并使含玻璃的子集能够描述侵入地幔岩石圈并通过渗透改变其成分的熔体的成分特征。通过对这些结果的分析，这项工作将有助于更好地了解地球地幔深处熔体与邻近围岩之间化学相互作用的规模。本工作的主要目的是模拟裂谷期影响次大陆地幔岩石圈的岩浆过程，重建裂谷期岩石圈的热演化过程，确定岩石圈演化过程中不同时期侵入岩石圈的岩浆的来源，并确定岩石圈的模式年龄。建立东南极洲岩石圈地幔演化与冈瓦纳大陆东部板块构造史之间的联系。除了这项工作对区域地质模型的重要性外，了解在伸展过程中控制岩石圈演化的过程将为裂谷的热力学模型和大陆下地幔的化学演化提供重要的一般约束。

9615274 Mukasa Ultramafic xenolith suites from Jetty Peninsula, East Antarctica, provide an unparalleled opportunity to examine and describe the consequences of magma/rock reactions equilibrated at subcontinental mantle temperatures and pressures during the lithospheric extension that fragmented eastern Gondwanaland at the end of the Jurassic and beginning of the Cretaceous. The samples to be used in this study were collected by Soviet/Russian expeditions during 1982-83, 1983-84 and 1986-87 and have been put entirely at our disposal by Dr. Alex Andronikov of the Department of Antarctic Geology, VNII Okeangeologia, St. Petersburg, Russia (now on leave at the University of G ttingen, Germany). This award will support analytical work to determine the Nd, Sr, and Pb isotopic compositions and Rb/Sr, Sm/Nd, and U/Pb elemental ratios for clinopyroxene (cpx) and glass taken from garnet lherzolite and spinel lherzolite xenoliths, and to perform the same measurements on whole-rock samples from the host magmatic rocks which are alkaline picrite, aln ite, and nephelinite in composition. In addition, the analytical program will include concentration measurements, using secondary ionization mass spectrometry (SIMS), of the rare earth elements (REE) and Ba, Cs, Cr, K, Nb, Rb, Sr, Ti, V, Y and Zr (in different combinations) in cpx, garnet and the various glasses present in some of the xenoliths. With his recent award of a fellowship by the Alexander von Humboldt Foundation, Dr. Andronikov will carry out complementary studies on the same materials at the University of G ttingen, Germany, focusing on xenolith mineral chemistry determined by electron microprobe, and the major and trace element compositions of the host rocks measured by X-ray fluorescence spectrometry and Inductively Coupled Plasma-mass spectrometry, respectively. The combined data will allow, for a subset of the xenoliths, assessment of the degree and effects of partial melting in lherzolites derived from different depths in the upper mantle, and, for a glass-bearing subset, characterization of the compositions of the melts which intruded the mantle lithosphere and altered its composition by infiltration. Through analysis of these results, this work will lead to better understanding of the scale of chemical interactions between melts and adjacent wall rocks at mantle depths in the Earth. The principal objectives of this work are to model the magmatic processes which affect subcontinental mantle lithosphere during rifting, reconstruct the thermal evolution of the lithosphere during such deformation, determine the provenance of magmas which intrude the lithosphere at various times during its evolution, and with model ages, establish a connection between the evolution of the lithospheric mantle beneath East Antarctica and the plate tectonic history of eastern Gondwanaland. In addition to the importance of this work to regional geologic models, understanding the processes that control lithospheric evolution during extension will provide important general constraints on thermo-mechanical models of rifting, and on chemical evolution of the mantle beneath continents.