| Summary: | The Hadean is the most mysterious period because no rocks and geologic bodies are preserved except for only the zircons in Western Australia, Canada, China and Greenland (Froude et al., 1983, Nature; Nelson et al., 2000, EPSL; Mojzsis & Harrison, 2002 EPSL; Iizuka et al., 2006, Geology;Wang et al., 2007, CSB). But, it is the most important period because the early evolution possibly clinched the history of the earth. We try to find the earliest supracrustal rocks in the world to investigate the Hadean tectonics and decode surface environments. As far, the oldest supracrustal rocks are found in Akilia association in West Greenland, Nuvvuagittuq in Quebec, and Nain Complex in Labrador (Nutman et al., 1996, Precamb. Res.; O’Neil et al., 2008, Science; Schiotte et al., 1989, Can Jour Earth Sci.). Because the Akilia association suffers from severe metamorphism and alteration, the precursors are highly in debate (e.g. Fedo & Whitehouse, 2002, Science). Recent geological works in the Nuvvuagittuq, Quebec showed the sequence contains amphibolite with a pyroclastic rocks affinity, ultramafic sills, felsic sediment, BIF and conglomerate. Although a pseudoisochron age of 147Sm/144Nd-142Nd/144Nd implies the Hadean age (O’Neil et al., 2008, Science), the supracrustal belt possesses 3811 Ma by conventional U-Pb zircon ages (David et al., 2009, GSAB). We made geological survey in the Nain Complex, and reinvestigated the occurrence of the supracrustal rocks and their relationship with the ambient orthogneisses. Previous works focused on distribution of the supracrustal belts within the orthogneisses (e.g. Bridgwater et al., 1974 Geol Surv Canada, Paper), but the detailed field occurrence of the supracrustal rocks within the belts is still ambiguous. Therefore, we focus on their internal structures. The supracrustal belts are repeatedly intruded by granitic intrusions with some ages and their original structures are obscured, but their lithostratigraphies are relatively well preserved in Nulliak, Big and Shuldham islands ...
|
|---|