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 Mark Harrison, Professor of Geology

GE 70, ESS 1, ESS 8, ESS 137, ESS 209, ESS 210, ESS 252, ESS 298

I'm currently working on two fronts - understanding the very early Earth as seen through the record of 4.0-4.4 billion year old zircons (e.g., Harrison et al., Science 310, 1947-1950, 2005) and learning how orogens work by studying active deformation in the Tibetan-Himalayan mountain system (e.g., Yin and Harrison, Ann. Revs. Earth Planet. Sci. 28, 211-80, 2000).  There are field and laboratory-based projects for graduate study in both areas.

STUDIES OF THE HADEAN WORLD

In terms of fundamental discovery, I can’t think of many studies that have more potential than shedding light on Earth's "dark ages". There is no known rock record from the Hadean Eon (4.5-4.0 Ga), but detrital zircons as old as nearly 4.4 Ga from Western Australia offer unprecedented insights into this formative phase of Earth history. We're beginning to discover that the early Earth may have much more in common with the present than previously thought, such as a hydrosphere and continental crust, but many questions remain including:

• Does the evidence of Hadean continental recycling suggest pre-4 billion year plate boundary interactions?
• Are Nd and Hf isotope variations indicative of massive Hadean mantle differentiation and continental crust formation?
• Why does plutonium/uranium vary substantially in Hadean zircons?
• Is the heavy oxygen isotope signature in Hadean zircons indicative of Hadean oceans?
• Are Hadean zircons of extra-terrestrial origin?
• Is the apparent absence of >4 billion-year-old rocks consistent with massive early continent formation coupled with continuous recycling?

INVESTIGATIONS OF TIBET AND THE HIMALAYA

Although long recognized as the best example of an active continental collision orogen, the Indo-Asian collision zone remains one of the most extraordinary and puzzling tectonic features on Earth. Heightened interest in the evolution of this region developed over the past 25 years as its key role in documenting the failure of plate tectonics to describe the diffuse intraplate deformation characteristic of continental tectonics became clear. As a consequence, the region has become the principal natural laboratory in which approaches for estimating the thickening and uplift histories of the continental lithosphere are tested.

Our work is directed towards developing new field and laboratory tools to quantify the evolution of crustal structure and thickness over the past 60 million years. We are currently involved in field-based programs in various locations in the Himalaya, southern Tibet, and Indo-China. A major focus is establishment of a new geotransect across the Himalayan and Tibetan suture zone at 92°E to test models for the origin and evolution of the mountain system, such as the channel flow model (e.g., Harrison, 2006).

B.S., 1977, University of British Columbia
Ph.D., 1981, Australian National University

A. Yin and T.M. Harrison (2000) Geologic evolution of the Himalayan-Tibetan Orogen. Ann. Revs. Earth Planet. Sci. 28, 211-80.

T.M. Harrison, A. Yin, M. Grove, O.M. Lovera and F.J. Ryerson (2000) The Zedong Window: A record of superposed Tertiary convergence in southeastern Tibet. Jour. Geophys. Res. 105, 19,211-19,230.

S.J. Mojzsis, T.M. Harrison, and R.T. Pidgeon (2001) Oxygen-isotope evidence from ancient zircons for liquid water at the Earth’s surface 4300 Myr ago. Nature 409, 178-181.

O.M. Lovera, M. Grove, and T.M. Harrison (2002) Systematic analysis of K-feldspar 40Ar/ 39Ar step-heating experiments II: Relevance of laboratory K-feldspar argon diffusion properties to Nature. Geochim. Cosmochim. Acta 66, 1237-1255.

G. Turner, T.M. Harrison, G. Holland, S.J. Mojzsis, and J. Gilmour (2004) Xenon from extinct 244Pu in ancient terrestrial zircons. Science 306, 89-91.

E.B. Watson and T.M. Harrison (2005) Zircon thermometer reveals minimum melting conditions on earliest Earth. Science 308, 841-844.

J.L.D. Kapp, T.M. Harrison, P.A. Kapp, M. Grove, O.M. Lovera, and D. Lin (2005) The Nyainqentanglha Shan: A window into the tectonic, thermal and geochemical evolution of the Lhasa block, southern Tibet. Jour. Geophys. Res. 110, doi:10.1029/2004JB003330.

T.M. Harrison, J. Blichert-Toft, W. Müller, F. Albarede, P. Holden, and S.J. Mojzsis (2005) Heterogeneous Hadean hafnium: Evidence of continental crust by 4.4–4.5 Ga. Science 310, 1947-1950.

T.M. Harrison (2006) Did the Himalayan crystallines extrude from beneath the Tibetan plateau? In Channel Flow, Ductile Extrusion and Exhumation in Continental Collision Zones. R.D. Law, M.P. Searle, and L. Godin (eds). Geological Society, London, Special Publications, 268, 237-254.