羌塘地块南缘新近系唢呐湖组湖相喷流岩岩石学特征及沉积模式

LITHOLOGICAL CHARACTERISTICS AND SEDIMENTARY MODELS OF THE LACUSTRINE HYDROTHERMAL SEDIMENTARY ROCKS OF THE NEOGENE SUONAHU FORMATION ON THE SOUTHERN EDGE OF QIANGTANG

针对改则地区新近系唢呐湖组湖相喷流岩的岩石学研究,认为总体上新近系唢呐湖组喷流岩以硅质岩-碳酸盐岩为组合特征,识别出热液通道、皮壳状构造等热液沉积构造及4种热水矿物。喷流岩7件样品δ^(18)O平均值为-15.2‰,δ^(13)C平均值为-3.79‰,所得喷流岩成岩温度平均值为92.10℃;微量元素中Ba,U,Sr,Zr,Sm的富集,U/Th平均值为19.35,Co/Ni为0.23;稀土元素的总量ΣREE变化在6.90×10^(-6)~19.28×10^(-6)之间,稀土元素的页岩标准化配分形式具有中组稀土富集的特点,中等偏强正铕异常,地球化学特征整体上符合热水沉积岩特征,属于中低温热液沉积成因。根据热水沉积岩结构构造特征,将新近系唢呐湖组喷流岩角砾型喷流岩、脉状充填型喷流岩、喷流口附近盆地沉积型喷流岩和远端区域扩散型喷流岩,并建立其沉积模式。

The lithology of the lacustrine hydrothermal sedimentary rocks in Neogene Suonahu Formation on thesouthern edge of Qiangtang terrance is studied. Hydrothermal sedimentary rock of Suonahu Formation is composed of the siliceous rocks and carbonate rocks assemblages, with characteristics of sedimentary structures of hydrothermal channel and crustification as well as 4 types of hot-water minerals. It reveals that the hydrothermal sedimentary rocks are enriched in Ba,U,Sr,Zr and Sm,U/Th is 19.35,Co/Ni is 0. 23. The shale-normalized REE patterns display middle REE enrichments and moderately strong positive Eu anomalies,indicating its medium-low hot-water sedimentary origin. On the basis of structural characteristics, 3 types of hydrothermal sedimentary rocks can be divided, they are brecciate type, filling rode type and region diffusing type far from the mouth, respectively. Accordingly, the sedimentary model of the sublacustrine hydrothermal sedimentary rocks is established.