T. Mark Harrison
University of California, Los Angeles
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Primary Section: 15, Geology Secondary Section: 16, Geophysics Membership Type:
Member
(elected 2011)
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Research Interests
Since virtually all important geophysical processes involve significant changes to crustal heat flow (e.g., thrusting, rifting, magmatism), understanding the thermal history of the lithosphere is akin to understanding its geologic evolution. My research is characterized by efforts to develop and apply thermochronometry to understand previously hidden aspects of Earth history. Our initial approach was to use isotopic variations in radioactive mineral systems to empirically calibrate closure temperatures using laboratory-based diffusion laws. This led to the recognition that continuous, high-accuracy thermal histories could be extracted via intragrain isotopic gradients and the multidiffusion domain model was born. With the progressive refinement of this method, the need arose for field testing under extreme geologic conditions requiring the highest attainable resolution. Thus we turned our attention to the Himalayan-Tibetan mountains revealing hitherto unrecognized tectonic activity. More recently, my attention turned to a unique resource -- zircons as old as nearly 4.4 billion years -- to probe the first 500 million years of Earth history, a period for which no rock record is known. As a consequence of this on-going work, the perception of earliest Earth has changed from the certainty of a hellish world hostile to life to perhaps something more akin to the modern planet.
