W.W. Hutchison Medal
The W.W. Hutchison Medal is named after Dr. William W. Hutchison in recognition of his many contributions to the Geological Association of Canada and to Canadian and international geoscience. The medal is awarded to a young individual for recent exceptional advances in Canadian earth science research. It was awarded for the first time in 2004, replacing the Past-Presidents’ Medal.
The 2014-2015 W. W. Hutchison Lecturer is Dr. Ali Polat, Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario.
Dr. Polat will offer a choice between two lectures during his tour:
1. Convergent Plate Boundary Processes in the Early Earth: Evidence from West Greenland (Abstract)
If you are interested in having Ali Polat come to visit your area, contact:
Hutchison and H.S. Robinson Lecture Tours (2014-2015)
The Archean craton of West Greenland is composed of fault-bounded tectonic blocks (terranes) characterized mainly by 3800 to 2800 Ma supracrustal (greenstone) belts and TTG (tonalite, trondhjemite and granodiorite) gneisses. In addition to supracrustal rocks and TTG gneisses, there are layered anorthositic complexes consisting of anorthosite, leucogabbro, gabbro, hornblendite, pyroxenite, peridotite, and dunite in several tectonic blocks. Despite polyphase deformation and amphibolite to granulite facies metamorphism, pillow structures, and cumulate textures and igneous layering are locally well preserved in supracrustal rocks and anorthositic complexes, respectively. The anorthositic complexes were derived from hydrous mantle sources and emplaced into oceanic crust as multiple sills and dykes of magma and crystal mush. The style of deformation and fold interference patterns in 1 to 10 m wide shear zones are comparable to those occur on regional scales. The structural, magmatic and metamorphic characteristics of the tectonic blocks are comparable to those of Phanerozoic convergent plate margins, suggesting that Archean supracrustal-TTG terranes can be viewed as relic convergent margin fragments and that Archean continents grew at subduction zones. The supracrustal belts are composed mainly of tectonically-juxtaposed fragments of juvenile mafic to ultramafic volcanic rocks, peridotites, gabbros, and minor sedimentary and volcaniclastic rocks. Volcanic rocks consist mainly of island arc tholeiitic basalts, picrites, boninites, with minor MORB and andesites. These supracrustal belts are interpreted as accretionary prisms and dismembered oceanic island complexes. Field observations and trace element data suggest that the protoliths of the TTG gneisses were derived mainly from partial melting of amphibolites in thickened arcs and emplaced along thrust faults during multiple tectonothermal events.
Among many Archean rock associations, anorthositic layered intrusions have unique mineralogical and lithological characteristics in that they range from calcic-plagioclase-dominated anorthosite cumulates to olivine-dominated dunite cumulates, providing a unique opportunity to study petrogenetic and geodynamic processes in the early Earth. The Fiskenæsset Complex, southwestern Greenland, is the best-known example of Archean anorthositic layered intrusions in the world. Despite multiple phases of deformation and metamorphism, the Fiskenæsset Complex contains well-preserved cumulate layers consisting of olivine, pyroxene, hornblende, plagioclase and chromite. Petrographic observations indicate that the order of crystallization was olivine, orthopyroxene, hornblende/clinopyroxene and plagioclase. Formation of abundant orthopyroxene-magnetite symplectitic (vermicular) intergrowths, mainly at the expense of olivine, is attributed to chemical reactions between late stage, residual hydrous melts and olivine. Whole-rock and mineral trace element and oxygen isotope data indicate that the complex has preserved its primary igneous chemistry. Large negative Nb anomalies in all major rock types and hornblendes suggest that the magmas of the Fiskenæsset Complex were derived from a hydrous sub-arc mantle peridotite, consistent with the formation of the complex in a supra-subduction zone geodynamic setting. The whole-rock samples from the complex yielded a Sm-Nd regression age of 2973±28 Ma, with an average initial eNd=+3.3, consistent with a long-term depleted mantle source. The complex is characterized by a modern mantle-like whole-rock O-isotope composition (d18O=+5.8±0.5‰; n=36). Average d18O values in olivine (d18O=+4.9‰), hornblende (d18O=+5.7‰), clinopyroxene (d18O=+6.5‰) and plagioclase (d18O=+6.4‰) are consistent with the fractionation of these minerals in magma chamber(s).