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

南极裂谷边缘的火山活动：同位素和微量元素研究

• 批准号: 0003702
• 负责人: Kurt Panter
• 金额: $ 7万
• 依托单位: Bowling Green State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-08-01 至 2003-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0003702&HistoricalAwards=false
• 关键词: Volcanism; Antarctic; Rift; Margin; Isotopic

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.

该奖项由极地方案办公室南极地质和地球物理方案提供，支持对西南极裂谷系统西侧的新生代火山岩进行调查。南极洲西部的新生代(3500万年前到现在是活跃的)火山活动归因于：1)‘被动’裂谷作用使地壳和地幔岩石圈变薄，2)‘主动’裂谷作用导致地幔熔融，伴随着热的上涌地幔热柱；3)‘主动-被动’结合的情景，包括通过被动裂谷作用熔化古老的地幔热柱来源。弄清南极洲裂谷和火山活动的根本原因，对我们理解大陆解体具有重要意义。在这方面，拟议的工作将利用新西兰与西南极的裂谷和分离模型。该项目将进行新的地球化学研究，试图利用南维多利亚土地皇家学会山脉山脚下的一套玄武岩火山岩来揭示地幔融化和大陆解体的过程。由于玄武岩代表了地幔的近原始熔融，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作用提供了一个独特的机会，可以沿着分隔西南极裂谷系统和东南极大陆盾的主要构造边界研究1400万年来的地幔演化。该项目的主要目标是首次对该地区的玄武岩进行详细的同位素和微量元素调查。新的结果将被整合到地区性研究中，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，在这部分裂谷之下，熔融的程度和深度发生了变化。以前对裂谷其他地区的玄武岩的研究表明，熔融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得的同位素提供了地幔中长期存在的化学储集层的“指纹”，这种变化肯定表明不同储集层的熔融正在产生玄武岩。更好地了解不同的地幔储集层的类型和成因对于裂谷作用和火山作用的模型至关重要。例如，以前的研究表明，许多西南极玄武岩以及来自新西兰的一些玄武岩的同位素特征具有共同的地幔成分；其组成具有地幔热柱来源的特征。这导致了一种羽流辅助破碎模型的开发。皇家学会山脉玄武岩的完整高质量地球化学数据集将使该项目能够测试地幔热柱活动和热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矿业与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。