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SUMMARY: Crust formation and deformation on the rapidly rotating early Ear
 th  - Simon Lock\, University of Bristol
DTSTART:20220524T110000Z
DTEND:20220524T120000Z
UID:TALK174032@talks.cam.ac.uk
CONTACT:Oscar Branson
DESCRIPTION: The last event in the main stage of Earth’s accretion is th
 ought to be the Moon-forming giant impact. A planet-sized body slammed int
 o the proto-Earth\, injecting material into orbit out of which the Moon fo
 rmed. The huge torques exerted during the impact meant that the early Eart
 h was rapidly rotating\, with a day between ~ 5 and 2.5 hrs. As a result\,
  Earth was significantly oblate\, with a ratio of polar to equatorial radi
 i between 0.9 and 0.5\, with a very different physical structure (e.g.\, i
 nternal pressure\, surface gravity) than at present. As the Moon receded f
 rom Earth\, the planet’s spin period increased and its shape changed dra
 matically\, becoming roughly spherical within a few 10s Myrs. This is a ke
 y period of Earth’s history in which the first crust formed\, the initia
 l atmospheric composition was set\, and the conditions for Earth’s subse
 quent evolution established. However\, little work has been done to unders
 tand the role that Earth’s rapid rotation played during this epoch. \n\n
  \n\nWe used petrological\, tidal evolution\, and planetary structure calc
 ulations to determine the effect of Earth’s distorted and changing shape
  on the early crust. We find that the composition and thickness of a terre
 strial crust formed by decompression melting of the primitive mantle varie
 d with latitude due to the varying surface gravity. We demonstrate that th
 e change in shape of Earth caused by lunar tidal recession drove extensive
  deformation of this early crust during the first few 10s Myr after the gi
 ant impact. There would have been extension in polar regions and convergen
 t tectonics in the equatorial regions at rates potentially higher than tho
 se forming the Himalayas today. Such substantial deformation could have fo
 rced hydrated crust to depth\, driving secondary melting and the productio
 n of more evolved magmas. A tectonically active early Earth could explain 
 the diversity of lithologies recorded in the early zircon and rock records
 .  
LOCATION:Department of Earth Sciences\, Tilley Lecture Theatre
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