درزه‌شدگی سنگ‌های سازند کرج در ورقه راندگی پورکان-وردیج، شمال تهران

The present research is aimed at investigation of geometry and kinematics of joints, relationships and temporal and spatial distribution of the ‎joints regarding the two deformational events within the purkan-vardij thrust sheet. we also studied the relationships between development ‎of different joint sets and the lithological characteristics of layers of the karaj formation. considering outcrops of volcaniclastic and igneous ‎rocks of variable lithology, we have divided them into five different rock units including thick-bedded to massive tuffs, thin- to medium-‎bedded tuffs, tuff-shale-sandstone sequence, shale, and igneous units. joint study was carried out using selection method, and in part using ‎listing method, which are useful for quick survey and statistical purposes. joint classification was carried out using concentrations of pole to ‎joint planes. we have used the fracture spacing index (fsi), which is an important parameter in controlling morphology and erodibility of the ‎rock units; it is also useful for prediction of joint spacing in other layers and in surrounding areas. these characteristics are useful in road ‎construction, tunneling and other engineering projects. a comparison of the fsi in different rock units indicates that the intrusive bodies and ‎thick-bedded units develop a highly variable fsi with a wide range of spacings, which in most cases due to lower concentration of the joints ‎show lower erodibility as compared to the other rock units, and therefore have more relief in their outcrops. two major joint sets, j1 and j2, ‎show the highest frequency within the classified joint sets. both of these sets are of extension joint type, and their strikes indicate the ?1 ‎direction during their development. our study in this research confirms that amount of the strain produced by the joints is very small. ‎