Permian Radiolarians, Chert and Basalt from the Nan Suture Zone, Northern Thailand
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摘要: 在泰国北部难河构造带Pha Som变质杂岩中发现保存很好的放射虫硅质岩、玄武岩地层层序.层状硅质岩含放射虫化石Follicucullus porrectus, 地质时代为中二叠世晚期至晚二叠世早期.其硅质岩SiO2含量均在92.5%以上, Al/ (Al+Fe+Mn) 平均比值为0.51, Ce/Ce*比值为1.14, 为大陆边缘型硅质岩.玄武岩具有富集大离子亲石元素与高场强元素以及轻稀土富集等洋岛玄武岩的特点.说明难河构造带中-晚二叠世之交存在洋岛型火山岩和靠近大陆边缘的深海盆地硅质岩, 代表了小洋盆的沉积组合.该构造带闭合时间应在晚二叠世与晚三叠世之间.Abstract: Well-preserved stratigraphic sequences composed of radiolarian chert and basalt were found in Pha Som metamorphic complex in Nan suture zone, northern Thailand.Bedded chert contains Follicucullus porrectus, fossils from late Middle Permian to early Late Permian.These cherts have high SiO2 (> 92.5%), low Al/ (Al+Fe+Mn) ratio (0.51 on average), and high Ce/Ce ratio (1.14 on average).These geochemical characteristics mentioned above indicate that the cherts deposited on continental margins.The basalt has high abundances of large ion lithophile elements (LILE), high field strength elements (HFSE), and light rare earth lements (LREE), suggesting characteristics of oceanic island basalt (OIB).The OIB characteristics of basalts and deep-sea-basin chert imply that the Nan suture zone was a small oceanic basin, which is similar to modern Southwest Pacific.The Nan Ocean presumably closed during the period from Late Permian to Late Triassic.
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Key words:
- Permian /
- radiolaria /
- chert /
- oceanic island basalt /
- Nan suture zone
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图 1 研究区大地构造位置(a) 及地理位置图(b) (Hada et al., 1999; Mantajit, 1999)
Fig. 1. Tectonic location (a) and geographical map (b) of study area
图 2 研究区地质简图及采样位置(Hess and Koch, 1975)
Fig. 2. Geological sketch map of study area and sampling sites
图 4 难河构造带硅质岩Al-Fe-Mn图解(Adachi et al., 1986)
Fig. 4. Al-Fe-Mn discrimination diagram for chert in the Nan suture zone
图 5 难河构造带硅质岩形成环境判别图(据Murray, 1994)
Fig. 5. Tectonic setting discrimination diagram for cherts in the Nan suture zone
图 6 难河构造带硅质岩北美页岩(NASC) 标准化的REE分布形式(北美页岩REE值引自Gromet, 1984)
Fig. 6. NASC-normalized REE distribution patterns for cherts in the Nan suture zone
图 7 难河构造带火山岩Zr/TiO2-Nb/Y图解(a) (据Winchester et al., 1977) 和难河构造带火山岩TAS图解(b) (据Le Bas et al., 1986)
S-B.亚碱性玄武岩; A-B.碱性玄武岩; B/A.玄武岩-玄武质安山岩; A.安山岩; D.英安岩; R.流纹岩; Ta.粗安岩; Bn.碧玄岩; Ne.霞石岩; Pc.苦橄玄武岩; B.玄武岩; O1.玄武安山岩; O2.安山岩; O3.英安岩; S1.夏威夷岩(Na质)、钾质粗面玄武岩(K质); S2.橄榄粗面岩(Na质)、钾玄岩(K质); S3.长粗面岩(Na质)、安粗岩(K质); T.粗面岩(Na质)、粗面英安岩
Fig. 7. Zr/TiO2-Nb/Y (a) and TAS (b) diagrams for the basalt in the Nan suture zone
图 9 难河构造带洋中脊玄武岩(MORB)标准化的微量元素丰度型式(a)图(MORB数据引自Pearce, 1982) 和难河构造带球粒陨石标准化的稀土元素配分模式图(b)(球粒陨石REE值引自Boynton, 1984)
Fig. 9. MORB normalized trace element (a) and chondrite normalized REE distribution (b) patterns for basalts in Nan suture zone
表 1 泰国北部难河构造带硅质岩和玄武岩的主量元素(%) 和微量元素(μg/g) 分析结果a
Table 1. Major element (%) and trace element (μg/g) contents in cherts and basalts from the Nan suture zone, northern Thailand
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