The Hadean time period - spanning the first 500 million years of the Earth's history - has no rock record and is the subject of intense debate. It has been recently demonstrated that during the Hadean magma extraction from Earth's primordial mantle created a depleted layer from which 3.8 billion year old rocks from Isua, Greenland were derived. One of the key issues arising from these observations is that of the fate the primordial crust or protocrust. Did the protocrust get isolated from the depleted mantle or did it not form in the first place? The former scenario would be possible if the protocrust either foundered into the deep mantle. The latter scenario would be possible if the early Earth's magma ocean was covered by a stagnant lid comprising dominantly of mafic-ultramafic lithologies. Using the isotopic effects in Nd-142 produced from the decay of short-lived Sm-146 (half life of 103 million years) this project will look for the evidence of protocrust and its location in modern mantle. If an enriched protocrust formed in the first 300 million years of Earth's history and has been preserved it would display a deficit in Nd-142. Two potential locations of the protocrust in the mantle are: the D" region of the lower mantle and the subcontinental lithospheric mantle below ancient continents. High precision neodymium isotopes in volcanic rocks from Iceland hotspot and Deccan flood basalt province will be examined; initial investigations of the latter have already revealed the presence of negative Nd-142 effects in some lava flows that have been inferred to have significant subcontinental lithospheric mantle component.
This project will constitute a major part of a Ph.D. and a senior thesis. It promotes teaching and training by encouraging graduate students and laboratory technicians to teach sophisticated laboratory skills to undergraduate students and provides graduate students an opportunity to present results in national conferences. The origin and evolution of continental crust is a fascinating topic for the general public and it is believed that the outcome of the project will be widely read and disseminated.
