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DESCRIPTION:Professor Ali Polar\n\n2024 Howard Street Robinson Medalist \n
 \nUniversity of Windsor \n\nFriday\, November 29 \n\n11- 12pm \n\nFDA 232
 \n\nThe Mechanism of Archean Continental Growth: Evidence from Field Relat
 ionships\, and Volcanic Rock and TTG Geochemistry\n\nAbstract: \n\nArchean
  terrains consist predominantly (>90%) of contemporaneous tonalite-trondhj
 emitegranodiorite suites (TTGs) and greenstone belts\, representing relict
  fragments of early continental crust. One of the most contentious areas o
 f Earth Science today is the tectonic mechanism by which Archean continent
 al crust was generated. Although studies on Archean terrains over the past
  four decades have enhanced our understanding of how these terrains formed
 \, the nature of large-scale tectonic processes that produced Archean cont
 inental crust still remains highly controversial. This controversy and ong
 oing substantial debate have centered around opposing uniformitarian and n
 on-uniformitarian tectonic models. The uniformitarian models propose that 
 modern-style plate tectonic processes (e.g.\, subduction\, accretion\, col
 lision) operated in the Archean\, whereas the non-uniformitarian models po
 stulate that vertical tectonics or other unknown processes (e.g.\, sagduct
 ion\, catalytic delamination\, heat pipe\, mantle upwelling\, stagnant lid
 ) operated in the Archean. The question is which of these models is suppor
 ted by the Archean rock record?\n\nA review of the main lithological\, str
 uctural\, and geochemical data from 4.0 to 2.5 Ga Archean terrains reveals
  that they were generated at convergent plate boundaries by accretion of o
 ceanic arcs\, continental arcs\, oceanic crust\, and trench turbidites. Ex
 tensive geochemical data (>8\,200 samples) from Eoarchean to Neoarchean vo
 lcanic rocks plot mostly in the oceanic arc\, continental arc\, and back-a
 rc fields in tectonic setting discrimination diagrams\, which suggest that
  subduction-related geodynamic processes operated throughout the Archean. 
 Similarly\, a comparison of large trace element data (>3500 samples) from 
 Eoarchean to Neoarchean TTGs with those from Phanerozoic arc TTGs (4100 sa
 mples) suggests that most Archean TTGs also formed in arc environments. Th
 e positive Pb and negative Nb anomalies of most Archean volcanic rocks and
  TTGs are fully consistent with subduction-related settings. The temporal 
 variations in the incompatible trace element ratios of Archean volcanic ro
 cks and TTGs\, coupled with their lithological associations\, demonstrate 
 that intra-oceanic arc magmatism was prominent in the Eoarchean. The trace
  element systematics of Paleoarchean volcanic rocks and TTGs signify the b
 eginning of Andeanstyle continental arc magmatism between 3.5 and 3.2 Ga. 
 From ~ 3.2 Ga there was a gradual transition in intra-oceanic arc magmatis
 m to more abundant Andean-type continental margin magmatism in the form of
  voluminous TTGs and sanukitoids. From 3.2 to 2.5 Ga juvenile oceanic crus
 t and arcs continued to form\, accompanied by more active continental marg
 in magmatism until 2.7-2.5 Ga\, by which time there were sufficient crusta
 l rocks to amalgamate into incipient large continents\, the fragmentation 
 of which started the first complete classical Wilson Cycle Plate Tectonics
  of breaking apart and re-assembling large continental masses. Field evide
 nce for uniformitarian tectonic processes in the Archean rock record is ex
 uberant\, whereas field evidence to support the non-uniformitarian models 
 is lacking. 2024 Howard Street Rob\n\n \n
DTSTART:20241129T160000Z
DTEND:20241129T170000Z
SUMMARY:EPS Seminar Series: Professor Ali Polat
URL:https://www.mcgill.ca/eps/channels/event/eps-seminar-series-professor-a
 li-polat-360192
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