Residual liquid from deep magma ocean crystallization in the source of komatiites from the ICDP drill core in the Barberton Greenstone Belt

Komatiites and sedimentary rocks sampled during the International Continental Drilling Program (BARB1-2-3-4-5) in the Barberton greenstone belt, South Africa, were analyzed for Sm-146-Nd-142 systematics. Resolved negative mu Nd-142 values (down to -7.7 +/- 2.8) were identified in komatiites from the 3.48 Ga Komati Formation and this signature correlates with low Hf/Sm ratios measured in these samples. The negative mu Nd-142 point to a source with subchondritic Sm/Nd ratio which formed during the Hadean. No analytically resolvable Nd-142 anomalies were measured in crustal detritus-rich, Si-rich, Ca-Fe-rich sediments and cherts from the Buck Reef (3.42 Ga) and the Fig Tree Group (3.23-3.28 Ga). Our new measurements are incorporated into a larger set of Sm-147-Nd-143 and Lu-176-Hf-176 data to better understand the Nd-142,Nd-143-Hf-176 isotope signatures in the mantle source at the time of komatiite crystallization. Our calculations show that the Nd-142,Nd-143-Hf-176 isotope signatures and Hf/Sm ratios cannot be produced by recycling into the komatiite source of detrital sediments like those sampled in the Barberton area. Only cherts have the required trace element characteristics - low Hf/Sm, radiogenic epsilon Hf-176 -but the trace element concentrations in the cherts are so low that unrealistic amounts of chert would need to be added.