Magma Genesis Beneath Continents

大陆之下的岩浆起源

• 批准号: 0338385
• 负责人: Julia Bryce
• 金额: $ 2.88万
• 依托单位: University of New Hampshire
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-05-01 至 2004-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0338385&HistoricalAwards=false
• 关键词: Magma; Genesis; Beneath; Continents

BryceEAR-0207939Continental basalts provide the broadest insights into the nature and origin of the continental lithosphere but, because they may represent a mixture of contributions acquired during melt formation, transport from the source region, evolution in a magma chamber, and eruption, the chemical identities and the relative roles of these processes are topics of debate. Isotopic and chemical studies of melt inclusions in phenocrysts of mafic lavas provide a means to examine and quantify contributions from these processes before exotic melts have been mixed away during melt aggregation and magma storage. The focus of the proposed work is to investigate these contributions in the 0-8 Ma alkali basalts of the Cima volcanic field of eastern California. Mantle xenoliths contained within the lavas demonstrate that the mantle at shallow levels beneath Cima is compositionally heterogeneous and that the lavas had a limited residence time in crustal chambers. Accordingly, the large variations in Pb isotopic compositions observed in magmas of the Cima suite most likely reflect signatures acquired during their formation and transport through the mantle, rather than from assimilation of continental crust. The proposed study will combine in situ techniques (e.g., electron and ion microprobe) to characterize the major, trace, and Pb isotopic compositions of melt and mineral inclusions in olivine and other phases from mafic (MgO 6 wt. %) Cima lavas. Our results will address whether the compositional and Pb isotopic variety of melt inclusions trapped in continental lavas is even greater than that observed in the suite of lavas that contain them, from which we can better delimit the nature and origin of compositional domains in the mantle at levels deeper than those sampled by xenoliths. The results from this project can be combined with ongoing studies of the isotopic and compositional variability of melt inclusions trapped in oceanic basaltic phenocrysts to improve our understanding of the processes significant in the generation of basaltic magmas.

Bryceear-0207939-continental玄武岩提供了对大陆岩石圈的性质和起源的最广泛的见解，但由于它们可能代表了熔体形成过程中获得的贡献的混合，因此从源区域运输，来自源区域的进化，在Magma室内的进化，以及这些过程的化学身份以及这些过程的相对角色是辩论的顶部。 粉碎熔岩熔岩中熔体夹杂物的同位素和化学研究提供了一种手段，可以在熔体聚集和岩浆储存过程中混合外来熔体之前检查和量化这些过程的贡献。拟议的工作的重点是调查加利福尼亚州CIMA火山田的0-8 Ma碱中的这些贡献。 熔岩中包含的地幔Xenoliths表明，CIMA下面的浅层地幔在组成上是异质的，并且熔岩在地壳室的停留时间有限。 因此，在CIMA套件的岩浆中观察到的PB同位素组合物的大变化很可能反映出在其形成和通过地幔运输过程中获得的特征，而不是来自大陆壳的同化。 拟议的研究将结合原位技术（例如电子和离子微探针），以表征橄榄石中熔体和矿物质的主要，痕量和PB同位素组成，以及来自Mafic（MGO 6wt。％）CIMA lavas的其他阶段。 我们的结果将解决捕获在大陆熔岩中的融合物的成分和Pb同位素种类是否比包含它们的熔岩套件中观察到的融合体是否要大，我们可以从中可以更好地划定地幔中覆盖物的性质和起源，而比Xenoliths Sampleliths更深的水平。该项目的结果可以与对海洋基底层中融合体的同位素和组成变异性的持续研究相结合，以提高我们对玄武岩岩浆产生的过程重要的理解。