西南大别榴辉岩和麻粒岩的氧同位素地球化学

An oxygen isotope study of eclogite and granulite from Southwest Dabie Mountains in Hubei Province

报道了大别造山带西南部湖北红安榴辉岩和罗田麻粒岩的氧同位素组成，并讨论了氧扩散作用对矿物氧同位素平衡的影响。结果得到， 红安榴辉岩的全岩δ 18O值为 6.4‰～ 7.3‰， 罗田黄土岭麻粒岩的全岩δ 18O值为 7.6‰～ 7.8‰，罗田惠兰山麻粒岩的全岩δ 18O值为 3.9‰。这些榴辉岩和麻粒岩全岩的氧同位素组成保持了峰期变质条件下的平衡分馏特征，得到的氧同位素温度对于红安榴辉岩为 425～ 620℃，对于罗田麻粒岩为 740～ 945℃。根据快速颗粒边界扩散模型计算的矿物对氧同位素温度不仅与大多数实测氧同位素温度一致，而且与岩石学测温结果相吻合。因此，这些岩石与东大别榴辉岩一样在形成后经历了快速冷却过程，退变质反应过程中没有外来流体加入。

The oxygen isotope composition of single minerals from eclogite at Hong an and granulite at Luotian in the Southwest Dabie Mountains of Hubei Province were measured, respectively. The results were discussed in view of the effect of oxygen diffusion on oxygen isotope equilibrium between minerals. The Gaoqiao eclogite at Hong an has whole- rockδ 18O values of 6.4‰ to 7.3‰ , Huangtuling felsic granulite at Luotian has whole- rockδ 18O values of 7.6‰ to 7.8‰ , and Huilanshan mafic granulite at Luotian has whole- rockδ 18O values of 3.9‰ . Oxygen isotope equilibrium fractionations have been preserved between the minerals at peak metamorphic conditions, yielding oxygen isotope temperatures of 425℃ to 620℃ for the eclogite and 740℃ to 945℃ for the granulites. The fast boundary diffusion model was applied to the minerals and corresponding oxygen isotope temperatures were calculated, which are not only in agreement with most of the oxygen isotope temperatures measured for the mineral- pairs, but also concordant with petrological temperatures. Therefore, both eclogite and granulite in Southwest Dabie Mountains experienced a fast cooling process like the eclogites in East Dabie Mountains subsequent to their formation, and there was no the significant introduction of exotic fluid to the high- pressure rocks in the process of retrograde metamorphism.