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.