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      報告題目：Geological Cycles and the Evolution of the Continental Crust
      
										
      
											撰稿：       
											    
											發(fā)布時(shí)間：2015-05-30 

										
      
										
      各位老師、同學(xué)：您們好！
      應王強研究員的邀請，英國圣安德魯斯大學(xué)教授Chris Hawkesworth近期將訪(fǎng)問(wèn)我所，并將于7月8日（周三）上午 10：00做學(xué)術(shù)報告，歡迎大家參加。
      報告題目：Geological Cycles and the Evolution of the Continental Crust
      報告專(zhuān)家:Prof. Chris Hawkesworth
      英國圣安德魯斯大學(xué)教授
      英國皇家學(xué)會(huì )院士
      蘇格蘭皇家學(xué)會(huì )院士
      中國科學(xué)院“國際杰出學(xué)者”
      報告時(shí)間: 7月8日（周三）上午 10：00
      報告地點(diǎn): 標本樓1樓階梯會(huì )議室
       
       
      報告摘要：
      Geological Cycles and the Evolution of the Continental Crust

      The continental crust is the archive of Earth history, and the apparently cyclical nature of geological evolution is a feature of the geological record. The advent of radiometric ages has highlighted that the continental crust is characterised by distinctive peaks and troughs in the distribution of ages of igneous crystallization, metamorphism, continental margins and mineralization. It is argued that the temporal distribution largely reflects the different preservation potential of rocks generated in different tectonic settings, rather than fundamental pulses of activity, and the peaks of ages are linked to the timing of supercontinent assembly.

      Less than 5% of the geological record consists of rocks older than 3 Ga, and there no known rocks older than 4 Ga. The sedimentary record is biased by preferential sampling of relatively young material in their source terrains. The implication is that there were greater volumes of continental crust in the Archaean than might be inferred from the compositions of detrital zircons and sediments. Recent studies based on the U-Pb, Hf and O isotope ratios of detrital zircons suggest that at least ~60-70% of the present volume of the continental crust had been generated by 3 Ga. The growth of continental crust was a continuous process, but there was a decrease in the rate of crustal growth at ~3 Ga. Before 3 Ga the rates of continental growth were high (~3.0 km3.yr-1), broadly similar to the rates at which new crust is generated and destroyed at the present time. Since 3 Ga the net growth rate was much lower (~0.8 km3.yr-1), perhaps because of higher rates of destruction of crustal materials. It is inferred that subduction-driven plate tectonics and discrete subduction zones have been dominant since ~3 Ga.
      
									
      
								
      
								
      
												
					
      
						
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