| Popis: |
Miocene Kareki-nada arcuate dikes occur intermittently along the southern coast of Kii Peninsula. They consist of pyroclastic rocks with lithic fragments. We described field occurrence of the Ebisu-Jima pyroclastic dike in Susami, one of the arcuate dikes, and inferred its emplacement process. The dike shows two lithofacies A and B in the field. The facies A has tuffaceous breccia to crystal coarse tuff including blocky lithic fragments derived from host rock, indicating that pyroclastics intruded into consolidated sedimentary rocks. The facies B is of vitric fine tuff with multiple lamination with pumice, banding and welding structures with pumice lense, and bubble-wall type volcanic glass, all indicative of repeatedly explosive volcanism. Based on these observations, we inferred that the Ebisu-Jima pyroclastic dike was emplaced as follows: At the first stage, pyroclasts intruded into consolidated host rock through fracturing and fragmentation, and then at the second stage, vitric pyroclasts with pumice intruded into semi-consolidated pyroclasts of the first stage repeatedly and explosively to form banding or welding structures. |
