各位老师和同学：
应王强研究员邀请，国际著名地球化学家和岩石学家Chris J. Hawkesworth教授访问我所，并将于今天上午做“同位素室学术报告”2019年第26次报告。欢迎大家参加并积极参与讨论！
Topic: The Onset of Plate Tectonics on Earth
Speaker: Prof. Chris J. Hawkesworth (Univ. of Bristol)
Time: 10:30 AM, October. 8th (Tuesday)
Place:
Conference Room 108 of Sample Building
报告人简介:
Chris J. Hawkesworth教授是国际著名地球化学家和岩石学家。他的研究兴趣非常广泛，主要包括同位素地球化学、大陆地壳形成与演化、沉积和构造过程的地质记录、大火成岩省和地幔柱、造山带热演化以及气候变化的地球化学记录等等，并在这些领域均做出了具有重要国际影响力的突出成果。他已经出版学术专著6本，发表论文逾316篇，且主要发表在国际重要刊物上，其中在《Nature》和《Science》上就发表论文37篇（第一作者11篇），论文引用逾38000次。他先后荣获英国皇家学会院士和苏格兰皇家学会院士、美国地球物理联合会和欧洲地球化学协会Fellow、伦敦地质学会Wollaston和Major John Coke奖、英国皇家学会Wolfson Merit奖、欧洲地质协会Robert Wilhelm Bunsen奖、英国矿物学会Schlumberger奖、中国科学院“国际杰出学者（原爱因斯坦讲座教授）”（2015和2018年）、以及丹麦哥本哈根大学荣誉博士学位等，也曾任《Science》、《EPSL》和《Geology》等刊物编委和英国圣安德鲁斯大学副校长等。
Abstract:
Plate tectonics is a globally linked system of lateral motion of rigid surface plates. Estimates of its onset range from the Hadean to the Neoproterozoic; over three-quarters of Earth history. This contribution considers the spatial and temporal distribution of a range of geological constraints as to when plate tectonics began. It explores ways in which the results of detailed case studies carried out in different locations can be put into a more global context.
Tectonic styles, and the degree of seismic anisotropy, are different in different Archaean terranes. Those with dome and basin geometries, associated with vertical tectonics, characterise the Australian Pilbara and southern Africa cratons. They tend to be associated with within-plate magmatism. Linear Archaean orogenic systems with pronounced regional deformation fabrics appear to be characterised by lithosphere of greater seismic anisotropy, as in North America. These in turn tend to be characterised by fluid flux melting in the mantle, as in subduction zones at the present day, and in some areas terrains with stronger regional fabrics are younger than those in which such fabrics are less well developed. Magma types similar to those from recent within-plate and subduction-related settings were generated in different areas at broadly similar times in the period 3.8-2.7 Ga. It may be that subduction took place locally, but that is not necessarily evidence that plate tectonics was active globally.
The end of the Archaean is marked by the development of passive margins and of supercontinents, the preservation of major dyke swarms, an increase in the degree of crustal reworking, and a shift in the composition of both juvenile and upper crust from mafic to more intermediate compositions accompanied by an increase in the thickness of the crust at the sites of crust generation. Critically it marks a ~70% reduction in the rates of crustal growth which is attributed to an increase in the rates of crustal recycling. It is argued that these global signals reflect the transition to plate tectonics as a sustainable global tectonic system on Earth.
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