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

EAR-0307691Coper本研究将测量冰岛克拉夫拉火山近期熔岩中的全岩样品、基质分离和斜长石的226Ra-230Th不平衡和氧同位素组成。这一方法将应用于不同喷发之间全岩(226Ra/(230th)和d18O的相对较大范围的变化，也将通过分离和分析从同一熔岩中分离出的一种以上粒度的斜长石来详细地应用。因为共存的斜长石和硅酸盐液体之间的氧同位素分馏是相对众所周知的，所以在晶体中测量的d18O可以直接与它们结晶的液体的d18O的变化有关。因此，早期形成的晶体d18O可以在岩浆混合或地壳同化发生之前保存液体成分的记录。Krafla熔岩中斜长石氧同位素组成的多样性，无论是在不同喷发之间还是在单一熔岩中，都将提供关于地幔和地壳来源的物质的相对影响以及产生中间熔岩的过程的信息。通过对相同的晶体群体进行测年，可以确定混合/同化的时间，从而提供有关这些岩浆作用速率的前所未有的信息。智力上的好处：该项目的结果将加强我们对岩浆分异和地壳同化过程的理解，将这些过程发生的时间尺度的信息与地壳和地幔来源的物质的质量平衡联系起来。这些结果将对地壳储藏系统的质量和热量平衡产生重要影响，并将与冰岛在地壳结构、储集层体积和地热活动的地球物理观测方面的广泛工作相比较。这些结果将为今后研究冰岛其他地区和其他构造环境中的岩浆混合和地壳同化作用提供背景和基础。更广泛的影响：该项目将通过支持女性专业人员的早期职业发展，扩大未被充分代表的群体在地球科学领域的参与。此外，我们预计，研究生将广泛参与该项目，作为其论文项目的一部分或全部，本科生将参与该项目的技术方面；因此，为该项目提供资金将支持对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，以便获得由PIMMS专门进行的U系列分析的经验。她将把这些专业知识转移到威斯康星大学的新分析设施，这些技术随后将应用于各种固体地球和海洋问题。

EAR-0307691CooperThis 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.