Prof. A. W. Hofmann gave a talk in ESE

At the invitation of Prof. Li-Hui Chen, the famous geochemist Prof. Albrecht W. Hofmann visited School of Earth Science and Engineering (ESE), NJU and gave a speech titled “Where did all the subducted sediments go?”on October 11, 2016. The report started at 2:00 p.m. in Room A125, Zhugongshan Building and attracted many teachers and students from ESE.

Prof. Albrecht W. Hofmann is recognized as one of the most famous geochemists and the foreign associate of the US National Academy of Sciences. During his academic career, he has ever held the leadership of European Geosciences Union (EUG), European Association of Geochemistry, The Association of Geochemists and American Geophysical Union (AGU) and received many awards such as Harry H. Hess Medal ofthe American Geophysical Union (2001), V.M. Goldschmidt Medal of the Geochemical Society (1996) and Franco-German Humboldt Award (1996). After his retirement from Max-Planck-Institut für Chemie, Mainz, he continued his research upon geochemistry with the posts of the senior visiting scholar in Columbia University and the part-time professor in Nanjing University.

Prof. AlbrechtW. Hofmann ’s contributions to geochemistry are numerous, and the major parts are the hypothesis about the important role of recycled oceanic crust inmantle plumes, which is widely accepted by academic community, and the relative abundance of some elements, especially the ones of Nb and Pb, which could beused to distinguish the recycles oceanic crust and continental crust. Another major contribution could be described as the retrieval method of using the compositions of igneous rocks to rebuild the composition of mantle sources. The current research projects are mainly located in the Hawaiian mantle plumes, the volcanic rocks with the research in highest degree.

Here follows the abstract of the report:

Several linesof reasoning have revived the idea that subduction has recycled continent-derived sediments into the mantle on a massive scale. If these ideas are correct, then recycled sedimentary components should be present in MORB and OIB sources. As previously established, Nb/U and ⁸⁷Sr/⁸⁶Sr are negatively correlated in all EM2-type OIBs, clearly indicating continental / sedimentary input. However, the MORB source reservoir, being depleted in incompatible elements, is particularly susceptible to “pollution” by subducted sediments. Chauvel et al. modeled the Hf-Nd isotopic array of MORBs+OIBs and concluded that it requires the addition of up to 6 % subducted sediment. We revisit this issue and show that global MORBs show no decrease in Nb/U with increasing ⁸⁷Sr/⁸⁶Sr, ruling out extensive addition of recycled sediment into global MORB sources. Instead, the Hf-Nd array can be obtained by recycled alkali basalts derived from subducted seamounts and ocean islands, rather than sediments. These results imply that continental recycling is subordinate and the growth of the continental crust has been largely irreversible.

Prof. Hofmann was giving his report

A heated discussion arised after the report