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SUMMARY:Impact-driven tectonism during the Hadean - Craig O'Neill\,\, Dire
 ctor of the Macquarie Planetary Research Centre\, Macquarie University\, S
 ydney\, Australia.
DTSTART:20180321T120000Z
DTEND:20180321T130000Z
UID:TALK103225@talks.cam.ac.uk
CONTACT:Andy Buckley
DESCRIPTION:Impacting was one of the dominant processes in shaping planeta
 ry surfaces in the early solar system evolution. While its effects on volc
 anism and crustal evolution of  other planetary bodies has been well docum
 ented\, its effects on early Earth dynamics remain poorly constrained\, la
 rgely due to dearth of data from the Hadean. It has speculated that impact
 s may have contributed to the development of active tectonics and subducti
 on\, but the physical interactions between large impacts and mantle dynami
 cs are poorly understood. Here we introduce a model of mantle convecting i
 ncorporating the thermo-physical response of large impacts on the mantle. 
 Our simulations track the tectonic evolution of an evolving early Earth\, 
 beginning immediately post-magma ocean\, through the Hadean.  Our simulati
 ons show that giant impacts in the Hadean both weaken the lithosphere\, an
 d create a large thermal anomaly in the mantle. These factors may be capab
 le of driving transient tectonic activity and subduction. Our preferred mo
 dels demonstrate waning tectonic activity with diminishing impact flux fro
 m 4.5-4.3Ga\, a lull in tectonic activity from ~4.3-4.1Ga\, and a resurgen
 ce of activity at ca. 4.1Ga due to the effect of a thick\, negatively dens
 e subductable lithosphere\, and increased impact flux at this time.  We ha
 ve simulation a parameterised evolution of the core in these models\, and 
 track the magnetic field strength\, as well as the evolution of mantle and
  crustal melting. We compare the predictions of our models with existing z
 ircon\, paleointensity\, and geochemical datasets.\n
LOCATION:Tilley Lecture Theatre\, Department of Earth Sciences\, Downing S
 treet
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