山东蒙阴金刚石的形成时代及地质环境

对山东蒙阴胜利1号岩管的金刚石样品进行了CL、FTIR、RAMAN等测试。结果表明,除部分样品阴极发光显示平直的生长色带外,多数金刚石显示均一的CL颜色,说明金刚石生长过程连续,未遭受明显的溶(熔)蚀,不同于复县的多数金刚石。依据金刚石中N的聚集状态,估算了蒙阴金刚石主要形成于三个时期:1·8~1·7 ,1·3 ~1·1和0·9 ~0·6 Ga。有意义的是,这三个时期与华北克拉通三次伸展事件时间相吻合。通过金刚石中橄榄石包裹体拉曼漂移,计算出源区压力为4·6 ,5和5·5 GPa ,得出蒙阴金刚石形成的深度分别为:152 ,165和181 km,靠近岩石圈底部。上述成果为蒙阴金刚石的形成提供了时间、空间、压力等重要地质信息。

Ages and environments of formation of diamonds in Mengyin County,Shandong Province

CL (cathodoluminescence), FTIR (Fourier Transform Infrared) and Raman spectroscopy techniques have been used to study the characteristics of intergrowth texture, N concentration and aggregation state and internal pressure in olivine inclusions of diamonds from kimberlite pipe Shengli No.1, Mengyin County, Shandong Province. CL results show that most of diamond samples have homogeneous CL color and single growth zone implying the continuous processes of crystallization and no breakage and erosion have been developed. They are different from diamonds of kimberlite pipe No.50 Fuxian county which exhibit multi-stage of complex structure and discontinuous growth histories. According to N concentration and aggregate states of 15 diamonds obtained from FTIR, the t_(MR) (time of mantle residency) estimates of each diamond has been made for T_(NA)=1 184 ℃. Three formation age (t_(MR) + emplacement age of kimberlite from Mengyin) populations of diamonds also can be obtained which are : 1.8～1.7 Ga, 1.3～1.1 Ga and 0.9～0.6 Ga. It is very interesting that these three periods coincide with three lithospheric extensional events that affected the North China Craton. Using a new Raman barometry of diamond formation, the internal pressure in olivine inclusions and the stresses in the surrounding diamond have been studied. We calculated diamond source pressures of 4.6, 5.0 and 5.5 GPa. Therefore, the diamonds formed at depths of 152, 165 and 181 km, respectively, located at the lower part of lithosphere in North China Craton.