Chemical and thermal evolution of the upper mantle; implications for Earth's climate and biosphere and the nature of mantle convection
Final Report Abstract
This research project has resulted in the development of a large new dataset for the chemistry of the ancient oceanic crust underlying the ocean basins, and show for the first time that the composition of magmatism at spreading ridges has changed systematically since the Jurassic (170 million years age) in the Atlantic Ocean, but not the Pacific Ocean. The chemical variations in Atlantic basalts result record a decrease in the temperature of the upper mantle beneath the Atlantic, and result from the effects of 'continental insulation', whereby the upper mantle cools once the insulating effect of overlying continental crust is removed by continental rifting and breakup. Although continental insulation effects had been predicted to be important on the basis of geophysical modelling, our data can be used to estimate the magnitude of the effect for the first time. Our results were published in the prestigious journal Nature Geoscience, and highlighted by a accompanying News and Views article in the same journal. Other related work carried out by funding from this project aimed to investigate the effects of mantle heterogeneity and the melting process on the chemical composition of oceanic basats. The results of a related project, to investigate the chemical stratigraphy of the oceanic crust, and determine whether ophiolites are representative of oceanic crust are currently under review.
Publications
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(2011). Insights into mantle composition and mantle melting beneath mid-ocean ridges from postspreading volcanism on the fossil Galapagos Rise. Geochemistry Geophysics Geosystems 12, Q0AC11
Haase, K.M., Regelous, M., Duncan, R.A., Brandl, P.A., Stroncik, N., Grevemeyer, I.
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(2012): Volcanism on the flanks of the East Pacific Rise: quantitative constraints on mantle heterogeneity and melting processes. Chemical Geology 298, 41-56
Brandl, P.A., Beier, C., Regelous, M., Abouchami, W., Haase, K.M., Garbe- Schonberg, D., Galer, S.J.G.
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(2013): High mantle temperatures following rifting caused by continental insulation. Nature Geoscience 6, 391-394
Brandl, P.A., Regelous, M., Beier, C., Haase, K.M.
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(2013): The geochemistry of oceanic basalts: constraints on melting and composition of the Earth's mantle (Die Geochemie ozeanischer Basalte: Einblicke in Schmelzprozesse und Zusammensetzung des Erdmantels). PhD thesis, Universität Erlangen-Nürnberg
Brandl, P.A.
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Formation of the Troodos Ophiolite at a triple junction: Evidence from trace elements in volcanic glass. Chemical Geology Volume 386, 29 October 2014, Pages 66-79
Regelous, M., Haase, K.M., Freund, S., Keith, M., Weinzierl, C., Beier, C., Brandl, P.A., Endres, T., Schmidt, H.
