As an igneous petrologist, I am is interested in the evolution of cratonic regions through the study of kimberlites, mantle xenoliths, diamonds, and continental flood basalts (CFBs). This is achieved through a multidisciplinary approach involving field work, petrography, mineral chemistry, X-ray computed tomography, geochemistry, and thermodynamic modeling. I have also developed a new line of research applying my knowledge as a terrestrial petrologist to the study of Mars through the use of meteorites. In this combined terrestrial and martian research, I aim at approaching big-picture questions involving plume volcanism and the evolution of the mantles of Earth and Mars in collaboration with American and international scientists.
- Post-doctoral research associate, University of Cape Town. 2015-2017.
- Post-doctoral research associate, University of Tennessee, Knoxville. 2013-2015.
- PhD, Rhodes University, South Africa. 2013. Geology.
- MSc, Rhodes University, South Africa. 2010. Geology.
- BSc (Honours), Rhodes University, South Africa. 2007. Geology
- BSc, Rhodes University, South Africa, 2006. Geology and Environmental Sciences.
Kimberlites and mantle xenoliths
Kimberlites are rare magmas that originate at great depth (~200 km) beneath the Earth’s surface in the lithospheric mantle. These magmas entrain and transport a variety of solid components (xenoliths) from the mantle, including diamonds. My research focuses on both the petrogenesis of the kimberlite magmas as well as the entrained mantle xenoliths, including the formation of diamonds. This research has focused on kimberlites and mantle xenoliths from Siberia and South Africa. My research aims at understanding the modification of the lithospheric mantle through metasomatism by subduction derived fluids. Metasomatism at the base of the lithospheric mantle produces geochemically enriched lithologies that are more prone to melt in later plume-related volcanism, such as Continental Flood basalts (CFBs). In this regard, this area of research is linked with that of his research into the petrogenesis of Large Igneous Provinces (LIPs).
Graduate level project available: Petrogenesis of ultra-fresh kimberlites from Sierra Leone, West Africa. I have recently acquired a particularly interesting and extremely fresh suite of kimberlite samples from Sierra Leone (West Africa). Very little is known about kimberlites from this region with only a handful of previous studies being conducted. This project will represent the first detailed look into the origin of these rare magmas in Sierra Leone.
Martian meteorites and the evolution of Mars
The only available material from the surface of Mars is that of meteorites that have been ejected from the martian surface and subsequently intersect Earth’s orbit. They are collected in regions such as Antarctica by NASA funded missions as well as by private dealers in Northwest Africa. These meteorites are extremely rare with only ~100 now in existence. My research in this area focuses on the petrology and geochemistry of these meteorites to understand the origin and evolution of magmatic systems at the surface of Mars as well as the evolution of the martian mantle over billions of years.
Graduate level project available: Olivine chemistry in shergottite meteorites and implications for mantle mineralogy on Mars. Currently, the main research theme is understanding the mantle source chemistry and mineralogy on Mars by analyzing the minor and trace element chemistry of olivine in martian shergottite meteorites. A graduate project is available as part of this larger project making use of Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to analyze the olivine trace element chemistry, and possibly the Mg and Fe isotopes. This projects aims at identifying peridotitic versus pyroxenitic components in the martian mantle.
Large Igneous Provinces
More recently, I have become interested in understanding the mantle source chemistry and mineralogy of Large Igneous Provinces (LIPs) on Earth, in particular, LIPs that erupted in regions of Earth with very thick lithospheric mantle. Current research has focused on the Karoo and Etendeka Continental Flood Basalts (CFBs) of southern Africa. My current research is aimed at identifying geochemically enriched mantle components in the source for these magmas. Specifically, the proportion of recycled crustal material and whether this component is located within the asthenospheric or lithospheric mantle.
Graduate level project available: Osmium isotope systematic in Karoo Continental Flood Basalts (CFBs). A project is available making use of existing samples as well as collecting new samples from the Karoo CFB in southern Africa. The projects aims to use osmium isotopes and highly siderophile elements (HSEs) to constrain the mantle source components for these rocks. This will be the first study making use of the highly informative osmium isotope system to constrain to proportion of recycled crustal material in the source for these basalts.
- Howarth, G. H., Day, J. M., Pernet-Fisher, J. F., Goodrich, C. A., Pearson, D. G., Luo, Y., Ryabov, V. V., & Taylor, L. A. 2017. Precious metal enrichment at low-redox in terrestrial native Fe-bearing basalts investigated using laser-ablation ICP-MS. Geochimica et Cosmochimica Acta, 203, 343-363.
- Pernet-Fisher, J. F., Day, J. M., Howarth, G. H., Ryabov, V. V., & Taylor, L. A. 2017. Atmospheric outgassing and native-iron formation during carbonaceous sediment–basalt melt interactions. Earth and Planetary Science Letters, 460, 201-212.
- Udry, A., Howarth, G. H., Lapen, T. J., & Righter, M. 2017. Petrogenesis of the NWA 7320 enriched martian gabbroic shergottite: Insight into the martian crust. Geochimica et Cosmochimica Acta, 204, 1-18.
- Howarth, G.H. & Udry, A. 2017. Trace elements and the petrogenesis of the intermediate, olivine-phyric shergottite NWA 10170. Meteoritics and Planetary Science DOI: 10.1111/maps.12799.
- Howarth, G. H. & Taylor, L. A. 2016. Multi-stage kimberlite evolution tracked in zoned olivine from the Benfontein sill, South Africa. Lithos, 262, 384-397.
- Jean, M. M., Taylor, L. A., Howarth, G. H., Peslier, A. H., Fedele, L., Bodnar, R. J., Y Guan, LS Doucet, DA Ionov, AM Logvinova, AV Golovin, & Sobolev, N.V. 2016. Olivine inclusions in Siberian diamonds and mantle xenoliths: Contrasting water and trace-element contents. Lithos 265, 31-41.
- Howarth, G. H., Liu, Y., Chen, Y., Pernet‐Fisher, J. F., & Taylor, L. A. 2016. Postcrystallization metasomatism in shergottites: Evidence from the paired meteorites LAR 06319 and LAR 12011. Meteoritics & Planetary Science. DOI: 10.1111/maps.12576
- Taylor, L. A., Logvinova, A. M., Howarth, G. H., Liu, Y., Peslier, A. H., Rossman, G. R., Guan, Y., Chen, Y., & Sobolev, N. V. 2016. Low water contents in diamond mineral inclusions: Proto-genetic origin in a dry cratonic lithosphere. Earth and Planetary Science Letters, 433, 125-132.
- Howarth, G. H., Pernet-Fisher, J. F., Bodnar, R. J., & Taylor, L. A. 2015b. Evidence for the exsolution of Cl-rich fluids in Martian magmas: Apatite petrogenesis in the enriched lherzolitic shergottite Northwest Africa 7755. Geochimica et Cosmochimica Acta, 166, 234-248.
- Howarth, G. H., Sobolev, N. V., Pernet-Fisher, J. F., Ketcham, R. A., Maisano, J. A., Pokhilenko, L. N., Taylor, D., & Taylor, L. A. 2015a. 3-D X-ray tomography of diamondiferous mantle eclogite xenoliths, Siberia: A review. Journal of Asian Earth Sciences, 101, 39-67.
- Logvinova, A. M., Taylor, L. A., Fedorova, E. N., Yelisseyev, A. P., Wirth, R., Howarth, G.H, Reutsky, V.N., & Sobolev, N. V. 2015. A unique diamondiferous peridotite xenolith from the Udachnaya kimberlite pipe, Yakutia: role of subduction in diamond formation. Russian Geology and Geophysics, 56(1), 306-320.
- Pernet-Fisher, J. F., Howarth, G. H., Pearson, D. G., Woodland, S., Barry, P. H., Pokhilenko, N. P., Pokhilenko, L.N. , Agashev, A.M., & Taylor, L. A. 2015. Plume impingement on the Siberian SCLM: Evidence from Re–Os isotope systematics. Lithos, 218, 141-154.
- Barry, P. H., Hilton, D. R., Day, J. M., Pernet-Fisher, J. F., Howarth, G. H., Magna, T., & Taylor, L. A. 2015. Helium isotopic evidence for modification of the cratonic lithosphere during the Permo-Triassic Siberian flood basalt event. Lithos, 216, 73-80.
- Howarth, G.H., Pernet-Fisher, J.F., Balta, J.B., Barry, P.H., Bodnar, R.J., & Taylor, L.A. 2014c. Two-stage polybaric formation of the new enriched, pyroxene-oikocrystic, lherzolitic shergottite, NWA 7397. Meteoritics and Planetary Science, 49, 1812-1830.
- Pernet-Fisher, J.F., Howarth, G.H., Liu, Y., Chen, Y., & Taylor, L.A. 2014. Estimating the lunar mantle water budget from phosphates: Complications associated with silicate-liquid-immiscibility. Geochimica et Cosmochimica Acta, 144, 326-341.
- Howarth, G.H., Sobolev, N.V., Pernet-Fisher, J.F., Barry, P.H., Penumadu, D., Puplampu, S., Ketcham, R.A., Maisano, J.A., Taylor, D., & Taylor, L.A. 2014b. The secondary origin of diamonds: multi-modal radiation tomography of diamondiferous mantle eclogites. International Geology Reviews, 56(9), 1172-1180.
- Pernet-Fisher, J.F., Howarth, G.H., Liu, Y., Barry, P.H., Carmody, L., Valley, J.W., Bodnar, R.J., Spetsius, Z.V., & Taylor, L.A. 2014. Komsomolskaya diamondiferous eclogites: Evidence for oceanic crustal protoliths. Contributions to Mineralogy and Petrology, 167, 981-998.
- Howarth, G.H., Barry, P.H., Pernet-Fisher, J.F., Baziotis, I., Pokhilenko, N.P., Pokhilenko, L.N., Bodnar, R.J., Taylor, L.A., & Agashev, A.V. 2014a. Superplume metasomatism: Evidence from Siberian mantle xenoliths. Lithos, 184-187, 209-224.
- Howarth, G.H. & Skinner, E.M.W. 2013. Coherent Kimberlite at the Lace and Voorspoed (Group II) Kimberlite Pipes, Kroonstad Cluster, South Africa: Implications for root zone processes in the development of kimberlite pipes. Journal of Volcanology and Geothermal Research, 268, 1-16.
- Howarth, G.H. & Prevec, S.A. 2013b. Trace element, PGE, and Sr-Nd isotope geochemistry of the Panzhihua mafic layered intrusion, SW China: Constraints on ore-forming processes and evolution of parent magma at depth in a plumbing-system. Geochimica et Cosmochimica Acta, 120, 459-478.
- Howarth, G.H., Prevec, S.A., & Zhou, M-F. 2013. Timing of Ti-magnetite crystallization and silicate disequilibrium in the Panzhihua mafic layered intrusion: Implications for ore-forming processes. Lithos, 170-171, 73-89.
- Howarth, G.H. & Prevec, S.A. 2013a. Hydration vs. oxidation: Modelling implications for Fe-Ti oxide crystallization in mafic intrusions, with specific reference to the Panzhihua intrusion, SW China. Geoscience Frontiers (Special Edition on the Panzhihua Intrusion), 4, 555-569.
- Ganino, C., Harris, C., Arndt, N.T., Prevec, S.A., & Howarth, G.H. 2013. Assimilation of carbonate country rock by the parent magma of the Panzhihua Fe-Ti-V deposit (SW China): Evidence from stable isotopes. Geoscience Frontiers (Special Edition on the Panzhihua Intrusion), 4, 547-554.
- Zhou, M-F., Chen, W.T., Wang, C.Y., Prevec, S.A., Liu, P.P., & Howarth, G.H. 2013. Two stages of immiscible liquid separation in the formation of Panzhihua-type Fe-Ti-V oxide deposits, SW China. Geoscience Frontiers (Special edition on the Panzhihua Intrusion), 4, 481-502.
- Howarth, G.H. & Skinner, E.M.W. 2012. The geology and emplacement of the volcaniclastic infill at the Voorspoed Group II kimberlite (orangeite) pipe, Kroonstad cluster, South Africa. Journal of Volcanology and Geothermal Research, 231-232, 24-38.
- Howarth, G.H. & Skinner, E.M.W. 2011. Petrology of the hypabyssal kimberlite of the Kroonstad Group II kimberlite (orangeite) cluster, South Africa: Evolution of the magma within the cluster. Lithos, 125, 795-808.
- Hanson, E.K., Moore, J.M., Bordy, E.M. Marsh, J.S., Howarth, G., & Robey, J.V.A. 2009. Cretaceous erosion in central South Africa: Evidence from upper-crustal xenoliths in kimberlite diatremes. South African Journal of Geology, 112, 125-140.