Collaborative Research: Timescales of Magmatic Differentiation and Crustal Assimilation Beneath Iceland: Combined U-Series and Oxygen Isotope Studies

本研究将测量冰岛Krafla火山近期熔岩的全岩样品、地块分离物和斜长石分离物中的226Ra-230Th不平衡和氧同位素组成。这种方法既可以应用于不同喷发之间整体岩石(226Ra)/(230Th)和d18O的相对广泛的变化，也可以通过分离和分析从同一熔岩中分离出的斜长石的多个尺寸部分来详细分析。由于共存的斜长石和硅酸盐液体之间氧同位素的分馏是比较众所周知的，所以晶体中测量的d18O可以直接与它们结晶的液体的d18O变化有关。因此，早期形成晶体的d18O可以保存岩浆混合或地壳同化发生之前液体成分的记录。克拉弗拉熔岩中斜长石在不同喷发之间和同一熔岩内氧同位素组成的多样性，将提供有关地幔源物质和地壳源物质的相对影响以及产生中间熔岩过程的信息。通过对相同的晶体种群定年，可以确定混合/同化的时间，从而提供有关这些岩浆过程速率的前所未有的信息。知识价值：本项目的结果将通过将岩浆分异和地壳同化过程发生的时间尺度信息与地壳和地幔物质的质量平衡联系起来，增强我们对岩浆分异和地壳同化过程的理解。这些结果将对地壳储层系统的质量和热平衡产生重要影响，并将与冰岛在地壳结构、储层体积和地热活动的地球物理观测方面的大量工作进行比较。这些结果将为今后冰岛其他地区和其他构造环境下岩浆混合和地壳同化的研究提供背景和基础。更广泛的影响：该项目将通过支持女性PI的早期职业发展，扩大代表性不足的群体对地球科学的参与。此外，我们预计研究生将广泛参与这个项目，作为他或她的论文项目的一部分或全部，本科生将参与这个项目的技术方面；因此，这个项目的资金将支持下一代科学家的教育和培训。最后，这次合作的一个明确目标是，PI Cooper将与研究生一起前往WHOI，以获得专门由PIMMS进行的u系列分析的经验。她将把这些专业知识转移到西澳大学的新分析设施中，这些技术随后将应用于各种固体地球和海洋学问题。

EAR-0307123SimsThis study will measure 226Ra-230Th disequilibria and oxygen isotope compositions in whole-rock samples, groundmass separates and plagioclase separates from recent lavas of Krafla volcano in Iceland. This approach will be applied both on the relatively broad scale of variations in whole-rock (226Ra)/(230Th) and d18O between different eruptions, and also in detail by separating and analyzing more than one size fraction of plagioclase separates from the same lava. Because the fractionation of oxygen isotopes between coexisting plagioclase and silicate liquid is relatively well-known, d18O measured in crystals can be related directly to variations in d18O of the liquids from which they crystallized. Thus, d18O of early-formed crystals can preserve a record of the compositions of liquids before magma mixing or crustal assimilation occurred. The diversity of oxygen-isotope composition of plagioclase in Krafla lavas, both between different eruptions and within a single lava, will provide information on the relative influence of mantle-derived and crustally-derived material and the process of producing intermediate lavas. By dating the same crystal populations, the timing of mixing/assimilation can be established, providing unprecedented information about the rates of these magmatic processes.Intellectual Merit: The results of this project will enhance our understanding of the processes of magmatic differentiation and crustal assimilation by linking information about the timescales over which such processes occur to mass balance of crustally-derived and mantle-derived material. These results will have important implications in terms of the mass and heat balance of crustal reservoir systems, and will be compared to the extensive body of work in Iceland on geophysical observations of crustal structure, reservoir volume, and geothermal activity. These results will provide background and groundwork for future studies of magma mixing and crustal assimilation in other areas of Iceland and in other tectonic settings. Broader Impacts: This project will serve to broaden the participation of underrepresented groups in the geosciences by supporting the early career development of a female PI. Furthermore, we anticipate that a graduate student will be extensively involved in this project as part or all of his or her thesis project, and that an undergraduate will be involved in the technical aspects of this project; funding for this project would therefore support the education and training of the next generation of scientists. Finally, an explicit goal of this collaboration is that the PI Cooper will travel to WHOI with the graduate student in order to gain experience in U-series analyses specifically by PIMMS. She will transfer this expertise to the new analytical facilities at UW, and these techniques will subsequently be applied to a variety of solid earth and oceanographic problems.