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Tectonics of an Early Carboniferous forearc inferred from a high‐ P / T schist‐bearing conglomerate in the Nedamo Terrane, Northeast Japan
Author(s) -
Uchino Takayuki,
Kawamura Makoto
Publication year - 2010
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/j.1440-1738.2009.00691.x
Subject(s) - schist , geology , forearc , ultramafic rock , terrane , conglomerate , clastic rock , carboniferous , geochemistry , metamorphic rock , petrology , paleontology , tectonics , subduction , sedimentary rock , structural basin
The Nedamo Terrane, an Early Carboniferous accretionary complex, is the oldest biostratigraphically dated accretionary complex in Japan. The purpose of this study is to describe and interpret a conglomerate from the Nedamo Terrane that contains clasts of high‐pressure/low‐temperature (high‐ P/T ) schist (mainly garnet‐bearing phengite schist) and ultramafic rock, and to infer the tectonics of an Early Carboniferous arc–trench system at the eastern margin of the paleo‐Asian continent. Clasts of high‐ P/T schist and ultramafic rock within the conglomerate make up 8.4 and 6.7% of the total clasts, respectively, based on modal counts. These clasts are subangular to subrounded, whereas volcanic clasts are well rounded. The source of the schist clasts, which yield a radiometric age of 347–317 Ma, is considered to be the Renge Metamorphic Rocks of Southwest Japan or equivalent rocks. Based on the chemical composition of chromian spinel, the source of ultramafic clasts is inferred to be the island‐arc‐type Ordovician Miyamori and Hayachine ultramafic complexes in the Kitakami Massif. The conglomerate records multiple provenance regions, including an island arc (South Kitakami Terrane) and a forearc ridge; the high P/T schist and ultramafic rocks were exhumed in the forearc region. The duration of the interval from the early stages of exhumation of the schist to its deposition in the trench as clasts is estimated to have been less than 30 my.