A Mixed Up Mantle Beneath Ocean Islands?

GSTDTAP

项目编号	1918322
	A Mixed Up Mantle Beneath Ocean Islands?
	James Day (Principal Investigator)
主持机构	University of California-San Diego Scripps Inst of Oceanography
项目开始年	2019
	2019-07-15
项目结束日期	2022-06-30
资助机构	US-NSF
项目类别	Standard Grant
项目经费	244097(USD)
国家	美国
语种	英语
英文摘要	Basaltic volcanic islands, which occur in all major ocean basins, do not fit particularly well in plate tectonic theory. The lavas from these islands have distinct compositions from basaltic rocks erupted at mid-ocean ridges, indicating the presence of subducted oceanic crust in some of their mantle sources. Current models for the generation of ocean island basalts favor either partial melting of mantle sources with two different rock-types, pyroxenite and peridotite, or sources with only "fertile" peridotite that can readily partially melt. The models are driven by the observation that direct partial melting of recycled oceanic crust cannot generate basaltic compositions. Both source types are therefore thought to form by melting and melding of subducted crust with peridotite in Earth's mantle. How these sources form and melt, in detail, are quite different, with pyroxenite indicating large-scale mantle heterogeneity. An accepted means for detecting pyroxenite is through precise measurement of olivine compositions in basalts. Precious metals such as osmium can also be used to examine between peridotite versus pyroxenite-dominated melting, and the most sensitive method for detecting recycled crustal contributions is from long-lived radiogenic isotopes, like strontium. This work will combine these methods to test whether pyroxenite exists in oceanic island sources through study of two locations where significant recycled crust components are known to exist; Mangaia in the Cook Islands, and the Canary Islands archipelago. New results, which will be partially generated by undergraduate students engaged in research and in the Scripps Undergraduate Research Fellowships (SURF) program, and who will also help publicly communicate the work, will enhance understanding of the fundamental process of basaltic melt generation, and enhance understanding of how ocean islands fit in plate tectonic theory. This project will examine the role of pyroxenite-peridotite or fertile peridotite melting in the generation of ocean island basalts (OIB) through examination of two key OIB localities. The first locality is Mangaia (Cook Islands), where long-lived radiogenic isotope (Sr-Nd-Os-Pb) variations will be coupled with olivine compositions to examine a location without a strong pyroxenite melting signature but that does have a strong recycled crustal signature (HIMU). The goal of this task is to quantify mantle source composition for an extreme recycled endmember composition in OIB petrogenesis. The second task is to evaluate pyroxenite-peridotite contributions to Canary Islands that also have a HIMU signature. Studies have argued for pyroxenite contributions, but with different endmember compositions. Here, new high-precision electron microprobe data will be collected for olivine grains in lavas from the islands to combine with Sr-Nd-Os-Pb isotope variations and highly siderophile element abundances. With these data, it will be possible to discriminate between depleted or enriched pyroxenite sources and to investigate if high pressure-temperature melting of fertile peridotite might offer an alternative. Research will include integration of undergraduates and underrepresented minorities who will also be engaged, along with the PI and graduate student, in outreach events that will take place in the San Diego region and in the Canary Islands, and through participation in organized STEM events. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/213777
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	James Day .A Mixed Up Mantle Beneath Ocean Islands?.2019.