Oceanic plateau accretion inferred from Late Paleozoic greenstones in the Jurassic Tamba accretionary complex, southwest Japan

Abstract

The Jurassic Tamba accretionary complex is divided into two tectonostratigraphic suites (Type I and II nappe groups), which are further divided into six complexes (nappes) each of which is characterized by a rock sequence of Late Paleozoic greenstone/limestone, Permian to Jurassic chert and Jurassic terrigenous clastic rocks. The mode of occurrence of the greenstone is divided into two types. The major basal type occurs as a large coherent slab associated with Permian chert and limestone, constituting the basal part of each complex, and the minor mixed type occurs as fragmented allochthonous greenstone blocks and lenses mixed with chert, limestone and sandstone in the Jurassic mudstone matrix. Most of the basal greenstones have uniform geochemical characteristics, which indicate enriched-mid-oceanic ridge basalt (MORB) affinity. Their geochemical compositions are akin to the reported Permo-Carboniferous and Triassic oceanic plateau basalts. Mixed greenstones are divided into two petrochemical types: (i) tholeiitic basalt with normal-MORB affinity, which is predominant in the uppermost complex of the Type II suite (upper nappe group); and (ii) tholeiitic and alkalic basalts of oceanic island or seamount origin, which are common in all complexes of the Tamba Belt. Geochemical characteristics of the greenstones thus vary in accordance with their occurrences and the structural units to which they belong. This relationship reflects the difference in topographic relief and crustal thickness of the accreted oceanic edifices -the remnants of thick oceanic plateau crust tended to accrete to the continental margin as a large basal greenstone body, whereas thin normal oceanic crust with small seamounts or oceanic islands accreted as mixed greenstones because of their mechanical weakness. The Type II suite (upper nappe group) contains the basal and mixed greenstones, whereas the Type I suite (lower nappe group) includes only mixed greenstones. This distinction may reflect the temporal change of subducting edifices from a thick oceanic plateau to a thin normal oceanic crust, and suggests that the accretion of a large oceanic plateau may be responsible for building accretionary complexes with thick basal greenstones slabs.

Chrome spinel in normal MORB‐type greenstones from the Paleozoic–Mesozoic Mino terrane, East Takayama area, central Japan: Crystallization course with a U‐turn

“…Bryan & Moore ). Similar chrome spinel has been reported in some late‐Paleozoic greenstones in the Tamba terrane adjoining the Mino terrane (Koizumi & Ishiwatari ), but spinel in most greenstones in the Mino‐Tamba belt is higher in Cr/(Cr+Al) and richer in Fe 3+ and Ti (Agata & Hattori ; Ichiyama et al . ).…”

Recognizing OIB and MORB in accretionary complexes: A new approach based on ocean plate stratigraphy, petrology and geochemistry

“…the crystallization from olivine to clinopyroxene (Ti-augite) plus plagioclase and then amphibole (kaersutite) ( Table 2; Fig. 10A-C; Koizumi and Ishiwatari, 2006;Safonova et al, 2015a), fit the geological and geochemical data. However, the first reported compositions of the Inuyama and Toba samples disagree with the geological and, partly, petrologic data.…”

“…Triangle tectonic discrimination diagrams, MnO-TiO 2 -P 2 O 5 (Mullen, 1983); B, Zr/4-2Nb-Y (Meschede, 1986); C, Zr-Ti/100-3Y (Pearce and Cann, 1973), for basalts from accretionary complexes of Japan (upper row) and for the Archean, Paleozoic and Meso-Cenozoic MORBs (middle row) and OIBs (lower row). The lower two rows show differences between Archean and Phanerozoic MORBs and OIBs and thus imply uncertainties in their application (based on data from Dong et al, 2008;Gordienko et al, 2012;Guo et al, 2007;Ichiyama et al, 2014;Jian et al, 2010;Koizumi and Ishiwatari, 2006;Komiya et al, 2002Komiya et al, , 2004Kuzmichev et al, 2005;Mahoney et al, 2005;Miao et al, 2008;Miyake, 1985;Mizoguchi et al, 2009;Mongush et al, 2011;Regelous et al, 1999;Safonova et al, 2008Safonova et al, , 2009Safonova et al, , 2011aSafonova et al, ,b, 2012Safonova et al, , 2015aTatsumi et al, 1998Tatsumi et al, , 2000Tejada et al, 1996;Ueda and Miyashita, 2005;Volkova and Budanov, 1999;Zhang et al,2009 shown in Suppl. Electr.…”

“…Based on the previous data from geology (association with massive and brecciated carbonates and slope facies; e.g., Kanmera and Sano, 1991;Maruyama et al, 1997;Onoue et al, 2004) and geochemistry (enrichment in Ti, Nb, LREE; Koizumi and Ishiwatari, 2006;Safonova et al, 2009Safonova et al, , 2015a it was suggested that the dominating OIB-type alkaline lavas of the Akiyoshi, Mino-Tamba and Southern Chichibu ACs erupted in seamounts of the Farallon (Akiyoshi AC) and Izanagi (Mino-Tamba, Chichibu ACs) oceanic plates (Safonova et al, 2015a). Our present study showed that the petrological features of these lavas,…”

Jurassic synorogenic basin filling in western Korea: sedimentary response to inception of the western Circum‐Pacific orogeny

“…Jurassic subduction of the paleo‐Pacific plate beneath the East Asian continent resulted in formation of a several‐thousand kilometers‐long accretionary complex along the continental margin (e.g. Takami & Itaya, 1996; Maruyama et al , 1997; Koizumi & Ishiwatari, 2006). The Jurassic trench, represented by the Tanba–Mino–Ashio Belt (a constituent of the Japanese Jurassic accretionary complex) in Fig.…”