Grant: $214,053 - National Science Foundation - Jul. 19, 2009
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Award Description: This proposal seeks funding to study the evolution of the lithospheric mantle beneath the central Rio Grande Rift and Colorado Plateau margin. The project will provide insights into a variety of questions related to the tectonic and volcanic evolution of this province, including the role of Farallon plate subduction and dehydration in generation of 'enriched' mantle sources of Rio Grande Rift lavas. However, this proposal seeks primarily to answer one simple question: Has the original Proterozoic-age lithospheric mantle beneath the central Rio Grande Rift and Colorado Plateau margin been actively removed by delamination or convective erosion, as suggested by several recent geophysical studies? If correct, these studies suggest that lithosphere delamination, previously recorded beneath the Sierra Nevada, may be more prevalent than currently recognized and may be triggered by extensional as well as compressional tectonic regimes. Correlation of Hf- and Os-isotope variations in peridotite xenoliths with mineralogic constraints on degree of melt depletion will allow constraints on the timing of melt depletion recorded in xenoliths from the Rio Grande Rift and Colorado Plateau. Also, peridotite clinopyroxene trace element abundances combined with Sm-Nd isotope compositions will constrain the age of metasomatic overprints observed in portions of the Colorado Plateau and Rio Grande Rift. Together, these data will allow us to distinguish between Proterozoic, melt-depleted and possibly metasomatized lithospheric mantle and young, fertile asthenosphere. This study will thus provide a direct test of the lithosphere delamination model proposed by Gao et al. (2004) and Song & Helmberger (2007) to explain the presence of anomalously low seismic velocities in the shallow mantle beneath the central rift and plateau margin and complementary, anomalously high velocities within a slab-like structure dipping beneath the Central Plains lithosphere. Identification of asthenosphere-derived peridotite at the relatively shallow depths (~40-60 km) represented by peridotite xenolith suites throughout the region would support the proposed delamination models, and would be inconsistent with simple passive thinning of the lithosphere in response to extension. In contrast, identification of ancient lithosphere at these depths would suggest significantly less lithosphere removal and would require reevaluation of current interpretations of the available seismic tomographic data. Insights gained from this study on the chemical and physical evolution of lithospheric mantle prior to and during continental rifting will expand our understanding of the triggers and mechanisms involved in continental rifting and continental break-up. This remains a fundamental question in plate tectonics.
Project Description: This project involves a geochemical investigation of mantle xenoliths contained in volcanic rocks from the eastern Colorado Plateau and central Rio Grande Rift. The goal of the project is to investigate the chemical and physical investigation of the mantle under this tectonically and volcanically active area. In particular, Hf-and Os-isotope study of the xenoliths will constrain the timing of mantle melting recorded in the xenoliths. This will allow us to test the hypothesis that the continental lithospheric mantle beneath the Rio Grande Rift was delaminated or mechanically eroded during opening of the tectonic rift, as suggested by recent seismic studies. The project is providing funding for the training of one PhD graduate student, who is currently measuring trace element and mineral compositions of xenoliths from two localities from the Colorado Plateau and Rio Grande Rift. This student has also initiated Os-isotope measurement of his samples, and has prepared an abstract for presentation at a national conference in December, 2009.
Jobs Summary: The following were appointed to this project: GRAD RES ASST (0.09 FTE) and RESEARCH ENGR/SCI ASST (0.04 FTE). Calculations of Number of Jobs were made using OMB guidance. (Total jobs reported: 0)
Project Status: Less Than 50% Completed
This award's data was last updated on Jul. 19, 2009. Help expand these official descriptions using the wiki below.