LUOMUS

Finnish Museum of Natural History

The largest lava eruptions on Earth

(c) Teppo MäkeläPlate tectonic theory explains most of Earth's geological processes, including the growth and drift of continents, rise of mountain belts, and occurrence of earthquakes and volcanic chains along the plate tectonic margins.

On the other hand, geological strata bears evidence on large-scale cataclysms that are not explained by the plate tectonic theory. The most dramatic of these are the breakup of continents and eruption of enormous lava field that have taken place in approximately 15 million year intervals.

The remnants of these supereruptions are called continental flood basalts and they are the largest known subaerial volcanic deposits. Flood basalts can be found on all continents and their eruptions have had notable effects on the evolution of life and climate throughout the history of the Earth. In spite of their importance, the ultimate origins of flood basalts are still a matter of debate.

Flood basalt research at Luomus

A four-year research project MARZ (Magmatism in the Africa-Antarctica Rift Zone), funded by the Academy of Finland, was launched at Luomus in September 2011. The project focuses on studying the geocehmistry of the Karoo continental flood basalt province.

The Karoo continental flood basalts were emplaced on the juxtaposed land masses of Africa and Antarctica during the early stages of the breakup of the Gondwana supercontinent at Jurassic times (~180 million years ago). About 2,000,000 km3 (~100 times the volume of the Baltic Sea) of basaltic magma was emplaced in and on to the crust in a time scale of a few million years

Remnants of the Mesozoic flood basalts on the reconstructed Gondwana supercontinent. In the case of Karoo province, intrusive rocks (formed when the feeding channels and magma chambers crystallized) also shown. Main research areas marked with red. Image: Luomus / Jussi Heinonen


Guidelines of the research

Flood basalts of the Karoo province have been studied in the University of Helsinki since the early 1990’s and, for example, three PhD theses focus on the topic (Luttinen 2000, Vuori 2004, Heinonen 2011). The MARZ project is based on our recent results on Karoo magmatism in the Antarctic subprovince (e.g. Heinonen et al. 2010, Luttinen et al. 2010). We concentrate on recently discovered Mg-rich rocks from Antarctica and relatively little-studied Karoo flood basalts from RSA and Mozambique. The former represent rare, highly primitive magmas that were derived from deep sublithospheric mantle below Antarctica (Riley et al. 2005; Heinonen 2011). Field trip to Mozambique was successfully conducted in August 2012 and the analysis of ~200 previously unexplored lava flows is on the way.

These and previously collected flood basalt samples will be analysed for major and trace element compositions, mineral chemistry, and radiogenic and stable isotope (Sr, Nd, Pb, Os, Li, B, He) compositions. These analyses shed light on the origin and evolution of Karoo magmas and provide crucial information on the composition and evolution of the mantle sources involved. Our results from Africa and Antarctica may also provide new general insights into the causes of catastrophic flood basalt eruptions that have shaped our planet.

Flood basalt samples are collected dirty from the field... and analyzed cleanly in the laboratory. Image: Luomus / Arto Luttinen and Mary Horan

One of key obstacles in resolving the origin of flood basalts stems from the fact that flood basalt magmas generally have been strongly modified by crystal fractionation and contamination during ascent. Specifically, strong interaction with crust adjacent to magma conduits hinders characterization of the original magma compositions derived from deep mantle sources. Understanding of deep subcontinental mantle is fundamentally important for resolving the mysteries of flood basalt magmatism, however. Was the mantle source of flood basalts compositionally exceptional? Was the mantle exceptionally hot?

Schematic cross-section of the Karoo continental flood basalt province c. 180 million years ago. 1) Mantle melts extensively and the 2) melts intrude the lithosphere (=crust + brittle upper mantle), where they form large magma chambers and mix with it. 3) The contaminated melts proceed upwards and 4) erupt from shield volcanoes or fissures. 5) Some rare melts do not assimilate lithosphere and preserve the original mantle-derived geochemical signature. Image: Luomus / Jussi Heinonen


Latest results!

Our latest findings indicate that the enromous melt generation was caused by at least two processes: 1) Gondwana supercontinent functioned like a "lid on a cooking pot" and prevented the cooling of the sublithospheric mantle. High amount of accumulated heat caused more efficient melting of the mantle (Heinonen et al., 2010, 2015; Heinonen and Kurz, 2015; Luttinen et al., 2015). 2) Some portions of the sublithospheric mantle were relatively Fe-rich and melted more efficiently than ambient mantle materials. Such portions were formed by mixing with ancient parts of oceanic crust that sank in to the mantle at subduction zones (Heinonen et al., 2013, 2014).

Basalt-hosted olivine crystals in a polarized light microscope (width of the image ~2 mm). Image: Luomus / Jussi Heinonen


Our collaborators:


MARZ team of LUOMUS:On the field in Mozambique: Arto Luttinen, Estêvão Sumburane, Jussi Heinonen, Teofilo Gove. Image: Luomus / Arto Luttinen

Arto Luttinen (PhD), principal investigator

Jussi Heinonen (PhD), postdoctoral researcher

Matti Kurhila (PhD), postdoctoral researcher

Sanni Turunen (BSc), graduate student

Riina Puttonen (BSc), graudate student

 

 

 

 

 

References:

Heinonen, J.S. 2011. Geochemistry and petrology of the ferropicrite dikes and associated rocks of Vestfjella, western Dronning Maud Land, Antarctica. Academic Dissertation, Department of Geosciences and Geography A9, Unigrafia, Helsinki, 50 s. https://helda.helsinki.fi/handle/10138/26267

Heinonen, J.S., Kurz, M.D. 2015. Low-3He/4He sublithospheric mantle source for the most magnesian magmas of the Karoo large igneous province. Earth and Planetary Science Letters 426:305–315. http://dx.doi.org/10.1016/j.epsl.2015.06.030

Heinonen, J.S., Carlson, R.W., Luttinen, A.V. 2010. Isotopic (Sr, Nd, Pb, and Os) composition of highly magnesian dikes of Vestfjella, western Dronning Maud Land, Antarctica: A key to the origins of the Jurassic Karoo large igneous province? Chemical Geology 277:227–244. http://dx.doi.org/10.1016/j.chemgeo.2010.08.004

Heinonen, J.S., Luttinen, A.V., Riley, T.R., Michallik, R.M. 2013. Mixed pyroxenite–peridotite sources for mafic and ultramafic dikes from the Antarctic segment of the Karoo continental flood basalt province. Lithos 177, 366-380. http://dx.doi.org/10.1016/j.lithos.2013.05.015

Heinonen, J.S., Carlson, R.W., Riley, T.R., Luttinen, A.V., Horan, M.F. 2014. Subduction-modified oceanic crust mixed with a depleted mantle reservoir in the sources of the Karoo continental flood basalt province. Earth and Planetary Science Letters 394, 229-241. http://dx.doi.org/10.1016/j.epsl.2014.03.012

Heinonen, J.S., Jennings, E.S., Riley, T.R. 2015. Crystallisation temperatures of the most Mg-rich magmas of the Karoo LIP on the basis of Al-in-olivine thermometry. Chemical Geology 411, 26-35. http://dx.doi.org/10.1016/j.chemgeo.2015.06.015

Luttinen, A. 2000. Origin of Jurassic Vestfjella flood basalts, Dronning Maud Land, Antarctica. Academic Dissertation, University of Helsinki, Yliopistopaino, Helsinki, 106 s.

Luttinen, A.V., Leat, P.T., Furnes, H. 2010. Björnnutane and Sembberget basalt lavas and the geochemical provinciality of Karoo magmatism in western Dronning Maud Land, Antarctica. Journal of Volcanology and Geothermal Research 198:1–18. http://dx.doi.org/10.1016/j.jvolgeores.2010.07.011

Luttinen, A.V., Heinonen, J.S., Kurhila, M., Jourdan, F., Mänttäri, I., Vuori, S.K., Huhma, H. 2015. Depleted Mantle-sourced CFB Magmatism in the Jurassic Africa–Antarctica Rift: Petrology and 40Ar/39Ar and U/Pb Chronology of the Vestfjella Dyke Swarm, Dronning Maud Land, Antarctica. Journal of Petrology 56, 919-952. http://dx.doi.org/10.1093/petrology/egv022

Riley, T.R., Leat, P.T., Curtis, M.L., Millar, I.L., Duncan, R.A., Fazel, A. 2005. Early-Middle Jurassic dolerite dykes from Western Dronning Maud Land (Antarctica): Identifying mantle sources in the Karoo Large Igneous Province. Journal of Petrology 46:1489–1524. http://petrology.oxfordjournals.org/content/46/7/1489.abstract

Vuori, S.K. 2004. Petrogenesis of the Jurassic gabbroic intrusions of Vestfjella, Dronning Maud Land, Antarctica. Academic Dissertation, University of Helsinki, Gummerus Kirjapaino Oy, Saarijärvi, 25 s.

 

Remnants of Karoo flood basalts in Antarctica. Image: Luomus / Jussi HeinonenRemnants of Karoo flood basalts in Mozambique. Image: Luomus / Jussi Heinonen
 
 

 

Person in charge of the page: 
Heinonen, J.S. and Luttinen, A.V.
31.8.2015