The Kitakami Massif of the Tohoku district, Northeast Japan, consists mainly of the South Kitakami Belt (Silurian–Cretaceous forearc shallow‐marine sediments, granitoids, and forearc ophiolite) and the North Kitakami Belt (a Jurassic accretionary complex). The Nedamo Belt (a Carboniferous accretionary complex) occurs as a small unit between those two belts. An accretionary unit in the Nedamo Belt is lithologically divided into the Early Carboniferous Tsunatori Unit and the age‐unknown Takinosawa Unit. In order to constrain the accretionary age of the Takinosawa Unit, detrital zircon U–Pb dating was conducted. The new data revealed that the youngest cluster ages from sandstone and tuffaceous rock are 257–248 Ma and 288–281 Ma, respectively. The Early Triassic depositional age of the sandstone may correspond to a period of intense magmatic activity in the eastern margin of the paleo‐Asian continent. A 30–40 my interval between the youngest cluster ages of the sandstone and the tuffaceous rock can be explained by the absence of syn‐sedimentary zircon in the tuffaceous rock. The new detrital zircon data suggest that the Takinosawa Unit can be distinguished as an Early Triassic accretionary complex distinct from the Early Carboniferous Tsunatori Unit. This recognition establishes a long‐duration northeastward younging polarity of accretionary units, from the Carboniferous to Early Cretaceous, in the northern Kitakami Massif. Lithological features and detrital zircon spectra suggest that the Early Triassic Takinosawa Unit in the Nedamo Belt is comparable with the Hisone and Shingai units in the Kurosegawa Belt in Shikoku. The existence of this Early Triassic accretionary complex strongly supports a pre‐Jurassic geotectonic correlation and similarity between Southwest and Northeast Japan.

中文翻译：

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在日本东北的北上地块的内达摩地带，认识到一个早期的三叠纪增生复合体：与日本西南部相关的新证据

日本东北部东北地区的北上市地块主要由南北上市地带（西陆－白垩纪前陆浅海沉积物，花岗岩和前陆蛇绿岩）和北北上市地带（侏罗纪增生复合体）组成。Nedamo带（石炭纪增生复合体）在这两个带之间是一个很小的单元。Nedamo带中的增生单元在岩性上分为早期石炭纪的Tsunatori单元和不知名的Takinosawa单元。为了限制Takinosawa部队的增生年龄，进行了碎屑锆石U–Pb测年。新数据表明，来自砂岩和凝灰岩的最年轻团簇年龄分别为257-248 Ma和288-281 Ma。砂岩的早三叠世沉积时代可能对应于古亚洲大陆东部边缘的强烈岩浆活动时期。砂岩和凝灰岩的最小团簇年龄之间存在30-40 my的间隔，这可以解释为：凝灰岩中不存在沉积沉积锆石。新的碎屑锆石数据表明，可以将Takinosawa单位区别于早期的三叠纪增生复合体，而不同于早期的石炭纪Tsunatori单元。这种认识建立了北上北地块从石炭纪到白垩纪早期的增生单元向东北的长期年轻化极性。岩性特征和碎屑锆石光谱表明，内达摩地带的早期三叠纪冲绳泽单位与四国黑濑川地带的Hisone和Shingai单位相当。这种早三叠世增生复合体的存在强烈支持侏罗纪前大地构造的相关性和日本西南部与东北部之间的相似性。