Recognition of an Early Triassic accretionary complex in the Nedamo Belt of the Kitakami Massif, Northeast Japan: New evidence for correlation with Southwest Japan
Recognition of an Early Triassic accretionary complex in the Nedamo Belt of the Kitakami Massif, Northeast Japan: New evidence for correlation with Southwest Japan
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日本东北部北上地块内达莫带中早三叠世增生杂岩的识别：与日本西南部相关的新证据
DOI：
10.1111/iar.12397
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发表时间：
2021
期刊：
影响因子：
1.5
通讯作者：
Takayuki Uchino
中科院分区：
文献类型：
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作者：
Takayuki Uchino
日本东北地区的北上地块主要由南北上带（志留纪-白垩纪弧前浅海沉积物、花岗岩类和弧前蛇绿岩）和北北上带（侏罗纪增生杂岩）组成。内达莫带（石炭纪增生杂岩）作为一个小单元出现在这两个带之间。根达摩带的增生单元在岩性上分为早石炭世纲取单元和年龄未知的泷泽单元。为了确定泷泽单元的增生时代，进行了碎屑锆石U-Pb定年。新的数据表明，砂岩和凝灰质岩石的最年轻年龄分别为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缘强烈的岩浆活动时期。砂岩和凝灰质岩石的最年轻的簇年龄之间的30-40米的间隔可以解释为凝灰质岩石中没有同沉积锆石。新的碎屑锆石数据表明，泷泽单位可以区分为早三叠世增生杂岩不同于早石炭世纲取单位。这一认识确立了北方北上地块从石炭纪到早白垩世的增生单元的长期东北向极性。岩石学特征和碎屑锆石光谱表明，根达摩带早三叠世竹泽单元与四国黑濑川带的Hisone和Shingai单元具有可比性。早三叠世增生杂岩的存在有力地支持了日本西南部和东北部之间的前侏罗纪大地构造相关性和相似性。
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.