Volcanism at the Antarctic Rift Margin: An Isotopic and Trace-Element Study

0003702 Panter该奖项由极地计划办公室的南极地质和地球物理计划提供，支持对西南极裂谷系西侧新生代火山岩的调查。南极洲西部新生代（3500万年前到目前活跃）的火山活动被归因于：1）地幔熔融的“被动”裂谷，使地壳和地幔岩石圈变薄，2）地幔熔融的“主动”裂谷与热，上涌地幔柱，和3）一个组合的“主动-被动”的情况下，涉及熔融的被动裂谷的古老地幔柱源。理解南极洲裂谷和火山活动的根本原因对我们理解大陆分裂具有重要意义。在这方面，拟议的工作将采用新西兰从西南极洲断裂和分离的模型，该项目将进行新的地球化学研究，试图利用南维多利亚地皇家学会山脉山麓小丘的一套玄武质火山岩，揭示地幔熔融和大陆分裂的过程。由于玄武岩代表了地幔的近原生熔体，它们将被用作地球内部的地球化学示踪剂。皇家学会山脉的玄武岩火山活动为研究沿着分离西南极裂谷系统和东南极大陆盾的主要构造边界的1400万年地幔演化提供了一个独特的机会。 该项目的主要目标是首次对该地区玄武岩进行详细的同位素和微量元素调查。新的研究结果将被纳入区域研究，以建立更好的西南极火山活动和裂谷模型。对地球化学数据的初步调查表明，在裂谷的这一部分下面，融化的程度和深度都发生了变化。以前对裂谷其他地区玄武岩的研究表明，融化程度和深度的变化与同位素组成的变化有关。 由于在原生玄武岩中测量的同位素提供了地球地幔内长寿化学储层的“指纹”，这些变化必须表明不同储层的熔融正在产生玄武岩。更好地理解不同地幔储层的类型和起源对裂谷和火山作用模型至关重要。例如，以前的研究表明，许多西南极玄武岩以及新西兰的一些玄武岩的同位素特征具有共同的地幔成分;其成分具有地幔柱来源的特征。这导致了一个模型的发展羽辅助分裂。 皇家学会山脉玄武岩的一套完整的高质量地球化学数据将使该项目能够检验地幔柱活动和地幔柱参与新西兰从南极洲分裂的理论。这项工作是与新墨西哥州采矿和技术研究所和伦敦大学皇家霍洛威的研究人员合作进行的。

0003702PanterThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports an investigation of Cenozoic volcanic rocks from the western flank of the West Antarctic Rift System. Cenozoic (35 million years ago to presently active) volcanism in West Antarctica has been attributed to: 1) mantle melting by 'passive' rifting that has thinned the crust and mantle lithosphere, 2) mantle melting by 'active' rifting associated with a hot, upwelling mantle plume, and 3) a combined 'active-passive' scenario that involves the melting of an ancient mantle plume source by passive rifting. Making sense of the underlying causes of rifting and volcanism in Antarctica has important implications to our understanding of continental breakup. In this regard the proposed work will engage models of rifting and separation of New Zealand from West Antarctica.This project will undertake new geochemical research in an attempt to unravel processes of mantle melting and continental breakup using a suite of basaltic volcanic rocks from the foothills of the Royal Society Range, South Victoria Land. Because the basalts represent near-primary melts of the mantle, they will be used as geochemical tracers of the Earth's interior. Basaltic volcanism in the Royal Society Range offers a unique opportunity to study 14 million years of mantle evolution along a major tectonic boundary separating the West Antarctic rift system from the East Antarctic continental shield. The principal objective of this project is to provide the first detailed isotopic and trace-element investigation of basalts in this area. The new results will be integrated into regional studies to build better models for West Antarctic volcanism and rifting. A preliminary survey of the geochemical data suggests that there has been a change in the degree and depth of melting beneath this portion of the rift. Previous work on basalts in other areas of the rift has shown that variations in the degree and depth of melting correlate with changes in isotopic composition. Because isotopes measured in primary basalts provide a 'fingerprint' of long-lived chemical reservoirs within the Earth's mantle, the variations must indicate that melting of different reservoirs is producing the basalt. A better understanding of the type and origin of distinct mantle reservoirs is critical to models of rifting and volcanism. For instance, previous studies have shown that the isotopic signature of many West Antarctic basalts, as well as some basalts from New Zealand, have a common mantle component; one whose composition is characteristic of a mantle plume source. This has led development of a model for plume-assisted breakup. A complete high-quality geochemical data set for Royal Society Range basalts will allow this project to test theories of mantle plume activity and plume involvement in the breakup of New Zealand from Antarctica. This work is collaborative with investigators at the New Mexico Institute of Mining and Technology and at Royal Holloway, University of London.