塔里木盆地下古生界碳酸盐岩中硅化作用成因

塔里木盆地下古生界碳酸盐岩局部发生了显著的硅化作用。塔北的沙15井、沙5井、沙13井、塔深1井,塔中的中3井、塔中1井等的下古生界岩心上可以看到晶簇状石英充填或半充填于碳酸盐岩溶蚀孔洞中。石英中的流体包裹体具有较高的均一温度,其主峰区间为150~190℃。石英氧同位素δ18OV-SMOW值位于18.6‰和24.14‰之间,流体包裹体水氢同位素δDV-SMOW值位于-118.36‰和-83.39‰之间。石英在稀土元素组成上具有轻稀土富集和显著的Eu负异常的特征。流体包裹体均一温度、氢氧同位素和稀土元素组成表明下古生界碳酸盐岩中的石英形成于岩浆热液流体。岩浆热液在沉淀石英的同时会对碳酸盐岩储层产生显著的溶蚀改造作用,在实际油气勘探中应该给予足够的重视。

THE GENESIS OF SILICIFICATION IN THE LOWER PALEOZOIC CARBONATE IN THE TARIM BASIN

Remarkable silicification was found locally in the Lower Paleozoic carbonate in the Tarim Basin.Euhedral drusy quartz were frequently observed filled or half-filled in the dissolution pores in the carbonate cores of some wells,such as S₁5,S5,S₁3 and TS₁ wells in the north of Tarim Basin and Zhong 3 and Tazhong 1 wells in the central of Tarim Basin.The homogenization temperature of the fluid inclusions in the quartz is generally high,and the maximum frequency of the homogenization temperature is between 150℃ and 190℃.The δ18OV-SMOW values of the quartz and the δDV-SMOW values of the water in the fluid inclusions in the quartz are between 18.6‰ and 24.14‰,-118.36‰ and-83.39‰,respectively.The rare earth elements of the quartz have features of relatively high content of heavy rare earth elements and considerable negative Eu anomaly.The characteristics of homogenization temperature,hydrogen and oxygen isotope compositions and rare earth elements indicate that the quartz in the Lower Paleozoic carbonate were precipitated from hydrothermal fluid associated with volcanic activity.When precipitating quartz,the hydrothermal dissolved the carbonate remarkably.So that,more attention should be paid to the hydrothermal alteration of the carbonate during the exploration.