Petrogenesis of greenstones from the Mino–Tamba belt, SW Japan: Evidence for an accreted Permian oceanic plateau
Petrogenesis of greenstones from the Mino–Tamba belt, SW Japan: Evidence for an accreted Permian oceanic plateau
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DOI：
10.1016/j.lithos.2007.06.014
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发表时间：
2008
期刊：
影响因子：
3.5
通讯作者：
Y. Ichiyama;A. Ishiwatari;K. Koizumi
中科院分区：
文献类型：
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作者：
Y. Ichiyama;A. Ishiwatari;K. Koizumi
根据地质产状、矿物学和地球化学特征，将日本西南部侏罗纪美浓-丹波增生杂岩中的二叠纪绿岩划分为三个不同的系列。低钛系列（LTS）与下二叠统硅质岩和石灰岩有关，是三个系列中体积最大的。LTS的地球化学和同位素特征略高于MORB。过渡系列（TS）主要与下二叠统硅质岩有关，比MORB具有更丰富的地球化学特征。其同位素特征可分为富集型和亏损型。高钛系列（HTS）以中二叠世硅质岩中的岩床和透明碎屑岩以及侵入TS的岩脉形式出现。某些高温超导岩石具有高MgO含量。HTS的特点是富集不相容的微量元素和同位素组成的HIMU型玄武岩。大量的LTS的地球化学是类似的大洋玄武岩系列的Kerguelen高原，建议生产的浅地幔柱头下厚的大洋岩石圈在早二叠世时间的部分熔融。我们推断，TS同时形成于地幔柱头的边缘。相反，高温超导可能是中二叠世深部地幔柱尾部部分熔融的结果。因此，米诺-坦巴带的二叠纪绿岩可能是由洋内环境中的超级地幔柱活动形成的。由于存在两个已知的当代大陆溢流玄武岩省（西伯利亚和峨眉山）和一些增生的海洋高原玄武岩，巨大的岩浆活动的米诺-坦巴海洋高原建议在二叠纪的时间大规模的超级羽脉冲。在日本和环太平洋区域其他地方，海洋高原的增生可能在大陆边和岛弧的增长中发挥了重要作用。
Permian greenstones in the Jurassic Mino–Tamba accretionary complex, southwest Japan, are divided into three distinct series on the basis of their geological occurrence, mineralogy, and geochemistry. A low-Ti series (LTS) is associated with Lower Permian chert and limestone, and is the most voluminous of the three series. The LTS shows slightly more enriched geochemical and isotopic characteristics than MORB. A transition series (TS) is mainly associated with Lower Permian chert, and has more enriched geochemical signatures than MORB. Its isotopic characteristics are divided into enriched and depleted types. A high-Ti series (HTS) occurs as sills and hyaloclastites within Middle Permian chert and as dikes intruding the TS. Some HTS rocks have high MgO contents. The HTS is characterized by enrichment in incompatible trace elements and an isotopic composition comparable to HIMU-type basalt. The geochemistry of the voluminous LTS is similar to that of the oceanic basalt series of the Kerguelen plateau, suggesting production by partial melting of a shallow mantle plume head below thick oceanic lithosphere in Early Permian time. We infer that the TS formed simultaneously at the margins of the mantle plume head. In contrast, the HTS may have resulted from partial melting of a deep mantle plume tail in Middle Permian time. Permian greenstones in the Mino–Tamba belt may have thus formed by superplume activity in an intra-oceanic setting. Given the presence of two known contemporary continental flood basalt provinces (Siberia and Emeishan) and some accreted oceanic plateau basalts, the vast magmatism of the Mino–Tamba oceanic plateau suggests a large-scale superplume pulse in Permian time. Accretion of oceanic plateaux may have played an important role in the growth of continental margins and island arcs in Japan and elsewhere in the circum-Pacific region.