Chemical and mineralogical compositions of silicic, mafic, and alkali tonsteins in the late Permian coals from the Songzao Coalfield, Chongqing, Southwest China
Chemical and mineralogical compositions of silicic, mafic, and alkali tonsteins in the late Permian coals from the Songzao Coalfield, Chongqing, Southwest China
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DOI：
10.1016/j.chemgeo.2011.01.006
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发表时间：
2011-03-07
期刊：
影响因子：
3.9
通讯作者：
Zou, Jianhua
中科院分区：
文献类型：
--
作者：
Dai, Shifeng;Wang, Xibo;Zou, Jianhua
我国西南地区硅质、碱性层内夹矸岩发现较早。本文报道了重庆松藻煤田煤岩的地球化学和矿物学组成的新资料，并对煤岩中矿物和元素的来源和分布提供了新的认识。三种类型的tonsteins（镁铁质，镁铁质，碱性）的基础上，他们的横向相关性在一个大的煤田面积和相应的矿物和化学成分的整体相似性。晚二叠世下部的镁铁质凝灰岩和不同来源的绝大多数灰岩中的粘土矿物以高岭石为主或以伊利石和蒙皂石混层为主。镁铁质灰岩和镁铁质凝灰岩中石英含量较高。所有的灰岩和凝灰岩都含有黄铁矿，这归因于海水的影响。镁铁质灰岩和凝灰岩中黄铁矿含量较高，可能是由于镁铁质火山灰中的铁含量较高。镁铁质灰岩和凝灰岩富含Sc、V、Cr、Co、Ni等元素，与西南地区正常粘土沉积物相似，表明其来源相似。碱性高变石的特征是Nb、Ta、Zr、Hf、RE（稀土元素）和Ga含量高。碱岩的TiO（2）/Al（2）O（3）值为0.02-0.08，镁铁质灰岩< 0.02，镁铁质灰岩和镁铁质凝灰岩> 0.10，表明岩浆来源不同。镁铁质凝灰岩和碱性钙华富稀土元素，钙华钙华的稀土元素含量最低，但轻重稀土元素分馏最高。在峨眉山大火成岩省的外围可能有凝灰岩和灰岩，它们可能是地幔柱活动减弱的结果。它们可能来自不同的地幔源区，这些源区不仅经历了低程度的部分熔融，而且还经历了流体分馏和岩石圈地幔的混染。其源区岩浆具有碱性玄武岩成分，与洋岛玄武岩相似。(C)2011 Elsevier B. V.保留所有权利。
Silicic and alkali intra-seam tonsteins were discovered earlier in southwestern China. This paper reports new data on the geochemical and mineralogical compositions of tonsteins from the Songzao Coalfield, Chongqing, southwestern China, and provides new insights into the origin and distribution of the minerals and elements present. Three types of tonsteins (silicic, mafic, and alkali) were identified based on their lateral correlation over a large coalfield area and the overall similarity of corresponding mineralogical and chemical compositions. The clay minerals in most tonsteins of different sources and the mafic tuffs in the lower portion of the late Permian are dominated by kaolinite or are mainly composed of mixed layers of illite and smectite. The silicic tonsteins contain high quartz while the mafic tonsteins and mafic tuffs have high contents of anatase. All the tonsteins and tuffs contain pyrite, attributed to the seawater influences. The mafic tonsteins and tuffs have higher pyrite contents, probably due to the higher Fe derived from mafic volcanic ashes. The mafic tonsteins and tuffs are enriched in Sc, V, Cr, Co, and Ni, similar to the normal clay sediments in the southwestern China, indicating similar sources. The alkali tonsteins are characterized by high contents of Nb, Ta, Zr, Hf, REEs (rare earth elements), and Ga. The TiO(2)/Al(2)O(3) values are 0.02-0.08 for alkali, < 0.02 for silicic, and > 0.10 for mafic tonsteins and mafic tuffs, indicating different magma sources. Mafic tuffs and alkali tonsteins are enriched in rare earth elements, and silicic tonsteins contain a lowest REE but have the highest fractionation between light REE and heavy REE. Tonsteins and tuffs may be at the periphery of the Emeishan Large Igneous Province and probably resulted from a waning activity of the plume. They were probably derived from different mantle sources that were underwent not only low-degree partial melting but also fluid fractionation and contamination by lithospheric mantle. Their source magmas had an alkali-basalt composition and were similar to that of ocean island basalt. (C) 2011 Elsevier B.V. All rights reserved.