Geology of the Nain Complex, Labrador, Canada: Occurrence of the Early Archean Supracrustals

• Main Authors: 小宮剛, Tsuyoshi Komiya, 下條将徳, Masanori Shimojo, 山本伸次, shinji yamamoto, 澤木佑介, Yusuke Sawaki, 石川晃, Akira Ishikawa, 青木一勝, Kazumasa Aoki, ケン コラーソン, Kenneth D. Collerson
• Format: Conference Object
• Language: English
• Published: 2013
• Subjects: Canada; Greenland; Nain; Shuldham Island
• Online Access: http://t2r2.star.titech.ac.jp/cgi-bin/publicationinfo.cgi?q_publication_content_number=CTT100647896

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 [1]. But, it is the most important period because the early evolution possibly clinched the earth’s history. We try to find the earliest supracrustal rocks in the world to investigate the Hadean tectonics. As far, the oldest supracrustal rocks are found in Akilia association in West Greenland, Nuvvuagittuq in Quebec, and Nain Complex in Labrador [2,3]. 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. 4], 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 and St Jones Harbor. The supracrustal belts in Nulliak and Big islands comprise ultramafic rocks, mafic rocks and mafic sediments intercalated with feldspathic sediments and banded iron formations in ascending order. In the St Jones Harbor, it is composed of ultramafic rocks, mafic rocks, banded iron formation, and clastic sediments, intercalated with chert in the middle and with bedded carbonate rocks in the upper part, respectively, in ascending order. In the Shuldham Island, it consists of ultramafic rocks, layered gabbro with precursors of plagioclase and pyroxene accumulation layers, mafic rocks and terrigenous sediments in ascending order. The lithostratigraphies are very similar to oceanic plate stratigraphy. The fact that some supracrustal belts are intruded by Uivak I orthogneisses and presence of >3.86 Ga zircons in the supracrustal rocks [e.g. 3] suggest that ...