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通过对塔里木盆地中、北部地区寒武系—奥陶系碳酸盐岩的研究,发现鞍形白云石胶结物发育比较普遍,常见于孔洞或裂缝之中,乳白色,晶体粗大,晶面弯曲或呈阶梯状,镜下波状消光,晶体内部常见微裂缝,常与热液矿物共生。本文对28个鞍形白云石样品进行了碳、氧、锶同位素测试,结果显示鞍形白云石的δ~(13)C和δ~(18)O值分别介于-2.446‰～0.686‰和-9.101‰～-5.117‰之间,~(87)Sr/~(86)Sr值介于0.708 6～0.710 2之间;流体包裹体测温分析表明,鞍形白云石中气—液两相包裹体的均一温度(T_h)介于121～159.5℃之间,但集中分布在135～145℃之间;根据最后冰融点温度(T_m)求得的白云岩化流体盐度介于21.3%～23.1%之间。这些数据表明,该类型白云石形成于热卤水(盐度是海水的5～8倍)之中。塔里木盆地鞍形白云石与世界范围内其它盆地的鞍形白云石的碳、氧同位素特征基本相似,但其~(87)Sr/~(86)Sr值相对偏低。导致这一现象的原因可能是鞍形白云石形成于来自深部的岩浆热液流体之中,这些流体伴随岩浆侵位或通过切穿基底的深大断裂及其与之相连的次级断裂系统从深部直接进入碳酸盐岩地层中,未经过碎屑岩输导层的长时间运移,所以导致其中形成的鞍形白云石~(87)Sr/~(86)Sr值偏低。
Through the study of the Cambrian-Ordovician carbonate rocks in the central and northern Tarim Basin, it is found that the development of saddle-shaped dolomite cements is relatively common and often found in holes or fissures, milky white, coarse crystals, curved facets or Was stepped, wavy underglaze microscopy, the common micro-cracks within the crystal, often with hydrothermal minerals symbiosis. In this paper, 28 saddle-shaped dolomite samples were tested for carbon, oxygen and strontium isotopes. The results show that δ ~ (13) C and δ ~ (18) O values of saddle dolomite range from -2.446 ‰ to 0.686 ‰ and -9.101 ‰ -5.117 ‰, and the 87 Sr / 86 Sr values ranged from 0.708 6 to 0.710 2. The temperature measurements of fluid inclusions show that the gas-liquid two-phase The homogenization temperature (T_h) of inclusions ranged from 121 ℃ to 159.5 ℃, but concentrated between 135 ℃ and 145 ℃. The salinity of dolomitization fluid obtained from the final ice melting temperature (T_m) ranged from 21.3% 23.1% between. These data show that this type of dolomite is formed in hot brine (salinity 5 to 8 times that of seawater). The saddle-shaped dolomites in the Tarim Basin have similar carbon and oxygen isotopic characteristics to saddle-shaped dolomites in other basins in the world, but their 87 Sr / 86 Sr values are relatively low. The reason for this may be the formation of saddle-shaped dolomites in magmatic hydrothermal fluids from the deep with either magmatic emplacement or through deep faults that cut through the substrate and their associated secondary fracture systems Deep into the carbonate rock formation directly, without long-term migration of the clastic rock transport layer, resulting in the formation of saddle-shaped dolomite ~ (87) Sr / ~ (86) Sr value is low.