Warren B. Hamilton

Warren Hamilton in Colorado, 2007

Warren B. Hamilton (born May 13, 1925) is an American structural geologist[1] known for developing fieldwork into planetary-scale syntheses describing the evolution of Earth’s crust and mantle. In 1989 he was elected to the National Academy of Sciences,[2] and also that year was awarded the Penrose Medal,[3] highest honor of the Geological Society of America (GSA). In 2007 he received the GSA’s Structural Geology and Tectonics Career Contribution Award.[4]

A native of southern California, Hamilton served with the US Navy from 1943 to 1946. He completed a Bachelor’s degree at the University of California, Los Angeles (UCLA) in 1945, becoming a commissioned officer on the aircraft carrier USS Tarawa. After returning to civilian life he earned an M.Sc. in Geology from the University of Southern California in 1949, and a Ph.D. in Geology from UCLA in 1951. He married Alicita V. Hamilton (née Koenig, 1926–2015) in 1947.

Early career

Following a brief stint as Assistant Professor at the University of Oklahoma (1951–1952), Hamilton moved to Denver where he began his principal career as research scientist with the US Geological Survey (USGS, 1952–1995). Early publications include reports based on his fieldwork in granite batholiths of the Sierra Nevada and Idaho. As his career progressed he traveled more widely, notably to lead a two-man field party in Antarctica (October 1958–January 1959) for the International Geophysical Year. The 600-meter Hamilton Cliff in Antarctica’s Thiel Mountains was named by a subsequent party of geologists in honor of Hamilton’s 1958–1959 exploration.

Antarctic Insights

Warren Hamilton in Antarctica, 1958-59

Based on his Antarctic fieldwork, Hamilton launched a new understanding of the continent. His 1960 paper “New interpretation of Antarctic tectonics” (Geological Survey Research) was the first to apply the name trans-Antarctic Mountains (two years later, formalized as Transantarctic Mountains) to that 3,500 km range.[5] He discovered that these mountains contained distinctive granitic rocks also found in Australia’s Adelaide Geosyncline, thus establishing a clear link between formations now separated by thousands of kilometers of ocean. Finding similar fossils in Antarctica and Australia, and similar rocks in southernmost Africa, also linked these continents in ways Hamilton recognized as supporting then-radical hypotheses of continental drift. Before traveling to Antarctica, Hamilton was what he later described as a “closet drifter,” who suspected that continental mobility had likely occurred but saw no evidence in his North American data that required it.[6] His Antarctic fieldwork supplied overwhelming evidence, however, which then led him to reinterpret North American and global data as well. Antarctica, Australia, South Africa, and South America had each been found to contain pieces of the Precambrian–Paleozoic supercontinent of Gondwana.

Continental Drift to Plate Tectonics

Continental mobility became central to Hamilton’s post-IGY research, including return trips to Antarctica in 1963 and 1964, and fieldwork in the western US. Hamilton recognized that the Gulf of California, formerly thought to be a sunken continental block, was instead a product of movement along the San Andreas Fault (“Origin of the Gulf of California” in GSA Bulletin 1961). He applied this new perspective to understanding the “Cenozoic tectonics of the western United States” (Reviews of Geophysics 1966) and “Formation of the Scotia and Caribbean Arcs” (Canada Geological Survey 1966). At that time continental mobility was still widely rejected by orthodox geologists, however. Science historian Henry Frankel writes that Hamilton “was the most active North American mobilist who developed his ideas independently of contemporaneous advances in paleomagnetism and oceanography.”[7]

New concepts from the plate tectonics revolution informed “Mesozoic California and the underflow of Pacific mantle” (GSA Bulletin 1969) and subsequent work. Although Hamilton’s research met with contemporary resistance, he was later credited with having “paved new paths for the structure and tectonics community to integrate plate-tectonic concepts and on-land geology.”[8] Interpretations that were initially radical, but confirmed by later research, include a 100 percent Cenozoic extension of the Basin and Range province, integration of Mesozoic California geology into subduction models, and 100:1 tectonic attenuation of the Grand Canyon’s Paleozoic formations.[9]

Top-Down Plate Tectonics

Hamilton’s most-cited publication is a book-length study with geological map, Tectonics of the Indonesian Region (1979). William Dickinson, introducing Hamilton's 1989 Penrose Medal award, wrote that this "magnificent monograph on Indonesian tectonics includes the first regional tectonic map to depict the whole of a classic orogenic region in the framework of plate tectonics."[10] Keith Howard described it in 2007 as “a standard of comparison for countless newer studies of subduction belts worldwide.”[11]

The Indonesian synthesis brought further insights. Having quickly embraced plate tectonics, Hamilton subsequently found his own interpretations once again diverging from orthodoxy—this time, from mainstream views about what drives plate tectonics. Many geologists envision plate motions driven by upwelling of hot plumes from the mantle. Hamilton argued from Indonesian and other evidence for a top-down process driven by cooling and sinking of oceanic crust.[12][13]

An Alternative Earth

After retiring from USGS in 1995, Hamilton embarked on a second career teaching geophysics and continuing his research as a Distinguished Senior Scientist in the Department of Geophysics at Colorado School of Mines (1995–present). Through papers such as “Archean magmatism and deformation were not products of plate tectonics” (Precambrian Research 1998) and “The closed upper-mantle circulation of plate tectonics” (Plate Boundary Zones 2002) he continued to challenge conventional wisdom, proposing an alternative framework that looked back billions of years, before the startup of modern plate tectonics. This framework was summarized in the 2003 GSA Today paper, “An alternative Earth.” He developed the ideas further in papers such as “Driving mechanism and 3-D circulation of plate tectonics” (GSA Special Papers 2007), “Plate tectonics began in Neoproterozoic time, and plumes from deep mantle have never operated” (Lithos 2011), and “Evolution of the Archean Mohorovicic discontinuity from a synaccretionary 4.5 Ga protocrust” (Tectonophysics 2013).

Hotspots or Weak Crust?

The mid-plate volcanoes of the Emperor–Hawaii chain, presented in textbooks as paradigmatic manifestations of a hotspot or mantle plume, received a different interpretation in “An alternative Earth” (1993) and Hamilton’s subsequent papers. From his top-down tectonic perspective, Emperor–Hawaii is understood as a propagating crustal weakness, reflecting extensional stress caused by the migrating Boso triple junction where North American, Philippine and Pacific tectonic plates meet trench to trench to trench. The diversity of compositions in magma erupted from Hawaiian volcanoes, long a challenge for mantle-plume hypotheses that assume a common deep origin, is readily explained if they have local sources instead, coming from relatively shallow depths where rocks nevertheless are hot enough to liquefy when overhead pressure is released.

An Alternative Venus

One element of the alternative Earth framework is the non-existence of deep mantle plumes. While mantle plume hypotheses for the Earth became increasingly complex to accommodate observed anomalies,[14] some planetary scientists applied the general concept, with contrasting assumptions, to Venus and Mars. On Venus, huge upwelling or downwelling phenomena and a geologically recent planet-wide resurfacing event, both unlike anything known elsewhere, were conjectured to explain hundreds of circular and quasi-circular overlapping surface structures with rim diameters up to 2,000 kilometers. Hamilton argued instead that most or all of these structures represent ancient, variably distorted impact features, formed by bombardments similar to those recorded by the surfaces of other rocky planets, and collectively with other Venusian craters exhibiting a similar distribution of sizes. In Venus’ case the ancient projectiles (sometimes icy themselves) passed through a thick atmosphere and often struck wet ground or seas, creating features with some differences from impacts on dry rock. Subsequent erosion, deposition and dessication further modified terrain.

In “Plumeless Venus preserves an ancient impact-accretionary surface” (GSA Special Papers 2005) and “An alternative Venus” (GSA Special Papers 2007), Hamilton presented detailed analyses of radar-backscatter and nadir-radar altimetry images from the Magellan spacecraft. The imagery reveals that, rather than a dichotomy, there exists a continuum of surface features with characteristics intermediate between the conventionally-acknowledged “pristine” impact craters (not always pristine but often showing modifications themselves) and more heavily modified features that are conventionally assigned to unique endogenous processes.

Terrestrial Planets

Hamilton’s paper “Terrestrial planets fractionated synchronously with accretion, but Earth progressed through subsequent internally dynamic stages whereas Venus and Mars have been inert for more than 4 billion years”[15] (The Interdisciplinary Earth, 2015) synthesizes plate tectonics, early Earth, and planetary studies into a unified view of crustal evolution on Earth, Venus, Mars and the Moon. Physical calculations suggest that most of Earth’s current internal heat could not have been retained through the 4.65 billion years since planetary accretion, but instead results from ongoing radioactive decay. Similar calculations of primordial heat loss apply to Venus, slightly smaller and with less radioactivity; and to much smaller Mars and the Moon. Weak or absent magnetic fields, and long-lived elevation anomalies that could only be sustained by a cold, rigid crust, add to evidence that other terrestrial planets now are internally cool and inert. In keeping with this view, and the accepted lack of plate tectonics, Hamilton’s Martian topographic analysis led him to re-interpret Olympus Mons and other vast, low-angle and roughly circular Martian domes as resulting from impacts instead of endogenous volcanoes.

Lunar Oceans

Another novel inference of the 2015 paper is that the Moon may have received enough water to form oceans through bombardment by icy material from then-outer parts of the asteroid belt at roughly the same time as Earth, Mars, and Venus, around 4 to 4.1 billion years ago. Evidence for past oceans and aqueous erosion on Mars is well known. Venus has canyons and indications of former oceans as well.[16][17] The only images we have from Venus’ surface, taken by four Soviet landers, show smooth horizontally plated rocks that resemble undeformed sedimentary strata rather than the lava or basalt predicted for those locations by volcanic hypotheses.[18]

In the Moon’s case most topographical evidence of water would have been obliterated by later impacts, although we can see thick strata on some mountainsides including the central uplift of Tycho crater, and the southeast rim of Mare Imbrium. Lunar rocks sampled from Mare Imbrium ejecta by Apollo 14 astronauts contain fragments that could have been finely-sorted sediments, if those were washed in from impact-comminuted mafic rocks. The possibility of transient lunar seas suggested to Hamilton that “Perhaps a landscape analogous to the sedimented one of much of Mars is hidden beneath the space-weathered rubbly and impact-recycled surface of the Moon.”[19]

Selected Publications

Honors and Awards

External links

Wikimedia Commons has media related to Warren B. Hamilton (geologist).

References

  1. ↑ Warren B. Hamilton, Colorado School of Mines http://inside.mines.edu/~whamilto/
  2. ↑ http://www.nasonline.org/member-directory/members/4683.html
  3. ↑ http://www.geosociety.org/awards/past.htm
  4. ↑ http://www.geosociety.org/awards/07speeches/divisions.htm
  5. ↑ Hamilton, W.B. 1960. “New interpretation of Antarctic tectonics.” Geological Survey Research 1960 — Short Papers in the Geological Sciences, pp. B379–380. Washington DC: US Geological Survey. https://books.google.com/books?id=iGpXAAAAMAAJ&pg=SL2-PA379&lpg=SL2-PA379
  6. ↑ Frankel, H.R. 2012. The Continental Drift Controversy: Wegener and the Early Debate. Cambridge, UK: Cambridge University Press. ISBN 9780521875042
  7. ↑ Frankel, H.R. 2012. The Continental Drift Controversy: Wegener and the Early Debate. Cambridge, UK: Cambridge University Press. ISBN 9780521875042
  8. ↑ Keith Howard, 2007, citation for the Structural Geology and Tectonics Career Contribution Award presented to Warren B. Hamilton. http://www.geosociety.org/awards/07speeches/sgt.htm
  9. ↑ Keith Howard, 2007, citation for the Structural Geology and Tectonics Career Contribution Award presented to Warren B. Hamilton. http://www.geosociety.org/awards/07speeches/sgt.ht
  10. ↑ Dickinson, W.R. 1990. Citation for Penrose Medal award to Warren B. Hamilton. GSA Bulletin 102, 1139
  11. ↑ Keith Howard, 2007, citation for the Structural Geology and Tectonics Career Contribution Award presented to Warren B. Hamilton. http://www.geosociety.org/awards/07speeches/sgt.htm
  12. ↑ Hamilton, W.B. 1993. “Convergent-plate tectonics viewed from the Indonesian region.” Pp. 655–698 in A.M.C. Sengör (ed.) Tectonic Evolution of the Tethyan Region. NATO ASI Series Volume 259. ISBN 978-94-009-2253-2
  13. ↑ Hamilton, W.B. 1994. “Subduction systems and magmatism.” Geological Society, London, Special Publications 81 (1), 3–28.
  14. ↑ Foulger, G.R., J.H. Natland, D.C. Presnall and D.L. Anderson (eds.). 2005. Plates, Plumes, and Paradigms. Geological Society of America Special Volume 388. ISBN 0813723884
  15. ↑ Hamilton, W.B. 2015. “Terrestrial planets fractionated synchronously with accretion, but Earth progressed through subsequent internally dynamic stages whereas Venus and Mars have been inert for more than 4 billion years.” Pp. 123–156 in G.R. Foulger, M. Lustrino and S.D. King (eds.) The Interdisciplinary Earth: A Volume in Honor of Don L. Anderson. Co-published by the American Geophysical Union and the Geological Society of America. ISBN 978-0-8137-2514-7. http://specialpapers.gsapubs.org/content/514
  16. ↑ Grinspoon, D.H. and M.A. Bullock. 2007. “Searching for evidence of past oceans on Venus.” Bulletin of the American Astronomical Society 39, 540.
  17. ↑ Kulikov, Y.N., H. Lammer, H.I.M. Lichtenegger, N. Terada, I. Ribas, C. Kolb, D. Langmayr, R. Lundin, E.F. Guinan, S. Barabash, and H.K. Biernat. 2006. “Atmospheric and water loss from early Venus.” Planetary and Space Science 54, 1425–1444. doi:10.1016/j.pss.2006.04.021.
  18. ↑ Hamilton, W.B. 2005. “Plumeless Venus preserves an ancient impact-accretionary surface.” Geological Society of America Special Papers 388, 781–814.
  19. ↑ Hamilton, W.B. 2015. “Terrestrial planets fractionated synchronously with accretion, but Earth progressed through subsequent internally dynamic stages whereas Venus and Mars have been inert for more than 4 billion years.” Pp. 123–156 in G.R. Foulger, M. Lustrino and S.D. King (eds.) The Interdisciplinary Earth: A Volume in Honor of Don L. Anderson. Co-published by the American Geophysical Union and the Geological Society of America. ISBN 978-0-8137-2514-7. http://specialpapers.gsapubs.org/content/514
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