Homogenization temperatures (HTs) of fluid inclusion, carbon, oxygen and strontium isotopes and rare earth elements (REEs) werenanlyzed for calcites filled in vugs and fractures in Ordovician limestones in the North and Central Tarim Basin. Most of the calcite samples in the North Tarim Basin are related to meteoric water, indicated by relatively low HT, light oxygen isotope composition and high 87Sr/86Sr values. Their average HTs range from 66.6 to 105.8℃,δ18OPDB from–18.9‰to–10.8‰, and 87Sr/86Sr from 0.709190 to 0.709989. Five of the other calcite samples in the North Tarim Basin are related to formation water, and two related to hydrothermal water. The calcite samples in Central Tarim Basin are related to hydrothermal water, with higher HTs than burial temperature of the surround rocks, light oxygen isotope composition, high 87Sr/86Sr values, REE distribution pattern remarkably different from surround limestone and considerable positive Eu anomaly. Their average HTs range from 139.2 to 180.0℃,δ18OPDB from–7.9‰to–14.3‰, 87Sr/86Sr from 709049 to 0.719503, andδEu from 1.39 to 76.03. It can be summarized from the above that fluids in the Ordovician limestone are mainly meteoric water with minor formation and hydrothermal waters in the North Tarim Basin, whereas fluids are dominantly hydrothermal in the Central Tarim Basin. The differences in fluid activities in the North and Central Tarim Basin can be attributed to the difference in geological environments such as tectonic evolution, magma-volcano activities and so on. The Ordovician limestone in the North Tarim Basin had suffered strong meteoric alteration for several times because of multiple-stage tectonic uplifts. In contrast, The dominant fluids are hydrothermal in the Central Tarim Basin due to intensive and extensive magma-volcano activities in the Permian.% 对塔里木盆地塔北和塔中地区奥陶系灰岩孔洞和裂缝中的方解石进行了系统的流体包裹体测温、碳氧锶同位素以及稀土元素方面的分析测试.塔北地区多数方解石样品具有较低的流体包裹体均一温度、较轻的氧同位素组成和较高的87Sr/86Sr 值,其均一温度平均值范围为66.6~105.8℃,δ18OPDB值为–18.9‰~–10.8‰,87Sr/86Sr比值为0.709190~0.709989,为大气降水成因；此外,还有5个方解石样品认为是地层水成因,2个样品认为是热液流体成因.塔中地区方解石样品多数具有高于围岩埋藏温度的流体包裹体均一温度、较轻的氧同位素组成和较高的87Sr/86Sr值,其均一温度平均值范围为139.2~180.0℃,δ18OPDB值为–7.9‰~–14.3‰,87Sr/86Sr比值为0.709049~0.719503；与灰岩围岩差别明显的稀土元素分布模式及显著的Eu正异常,其δEu变化范围为1.39~76.03；这些方解石认为是以热液流体成因为主.由上可见,塔北奥陶系灰岩中的流体作用类型主要为大气降水；塔中地区奥陶系灰岩中主要的流体作用类型是热液流体.流体作用的差异主要是由两个地区构造演化、岩浆火山活动等地质环境的差异造成的.塔北奥陶系灰岩因多次强烈构造抬升作用导致遭受多次大气降水地表岩溶改造,塔中则因二叠纪强烈而广泛的岩浆火山作用而经历以热液为主的流体改造作用.
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