PRIMITIVE LAVAS, CHEMOSTRATIGRAPHIC VARIATION AND MAGMATIC EVOLUTION IN THE KEWEENAWAN MID-CONTINENT RIFT

基韦纳湾中大陆裂谷的原始熔岩、化学地层变化和岩浆演化

• 批准号: 8709257
• 负责人: Jonathan Berg
• 金额: $ 7.9万
• 依托单位: Northern Illinois University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1987
• 资助国家: 美国
• 起止时间: 1987-07-01 至 1989-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8709257&HistoricalAwards=false
• 关键词: PRIMITIVE; LAVAS; CHEMOSTRATIGRAPHIC; VARIATION; MAGMATIC

The Keweenawan rocks of the Lake Superior region afford an excellent opportunity to study contemporaneous volcanic and plutonic activity associated with continental rifting in the Proterozoic. By comparing genetically related volcanic sequences and plutons on a regional basis, a range of basic problems can be addressed. In a pilot study the PI has discovered very primitive basaltic and picritic lavas near the base o the Mamainse Point Formation (MPF) in Ontario. These lavas display spectacular quench-olivine textures and systematic chemical variations with stratigraphy. This project will sample the remaining four-fifths of the MPF and analyze for major and trace elements by XRF and DC plasma spectrometry. Mineral chemistry will be determined by electron microprobe, and geochemical modeling will be attempted in order to delineate the processes responsible for the origin and compositional evolution of this important volcanic sequence. Results will be used to evaluate the hypotheses derived from previous work, and to determine the relationship between the plutonic and volcanic rocks. An attempt will be made to characterize the nature of the subcontinental mantle source and to evaluate possible relationships between these lavas and plutonic anorthosite complexes.

苏必利尔湖地区的Keweenawan岩石为研究元古代与大陆裂陷有关的同生火山和深成活动提供了极好的机会。通过在区域基础上比较与遗传相关的火山序列和岩体，可以解决一系列基本问题。在一项初步研究中，PI在安大略省马曼斯点地层（MPF）底部附近发现了非常原始的玄武岩和苦质熔岩。这些熔岩显示出壮观的淬硬橄榄石结构和系统的化学变化。该项目将对剩余的五分之四的MPF进行采样，并通过XRF和直流等离子光谱分析主要和微量元素。将利用电子探针测定矿物化学成分，并尝试建立地球化学模型，以描绘这一重要火山层序的起源和成分演化过程。研究结果将用于评估从以前的工作中得出的假设，并确定深成岩和火山岩之间的关系。将尝试描述次大陆地幔源的性质，并评价这些熔岩与深深斜长岩复合体之间的可能关系。