6:15 PM - 7:30 PM
[SVC47-P07] Magma mingling of the Kagusa lava in the Kusatsu-Shirane volcano: preliminary results from analyses of a boring core
Keywords:magma mingling, magma mixing, Kusatsu-Shirane volcano
Core samples were cut into homogeneous fractions which had no banded texture and each fractions were powdered. Some core samples which had complex mingling texture were powdered as a whole. Eleven times diluted glass beads were prepared for each sample using Li2B4O7. Major elements of whole-rock compositions were analyzed using XRF (RIGAKU RIX2100) which was installed at Tokyo Tech. In the results, two groups were recognized in the compositions of most samples; group (1) corresponded to 〜60 wt.% SiO2 (andesite) and group (2) corresponded to 〜65 wt.% SiO2 (dacite). In view of the whole trend, intermediate samples which compositions corresponded to 62-63 wt.% SiO2 lay along mixing trend between group (1) and (2). Core samples above 〜35 m in depth were dominated by dacite and those below 〜35 m in depth were dominated by andesite. This profile was consistent with core description of NE observation well (Uto et al. 2004). Some lower core samples which was collected below 〜50 m in depth sometimes displayed banded texture of andesite and dacite. Judging from this results, regarding compositions, magmas of group (1) and (2) were mingled together immediately before eruption and mingled magma had no time to homogenize. In order to discuss mingling time scale in detail, I will carried out petrological study; phenocryst assemblage, composition, and zoning profile of phenocryst in the regions of contact will be researched.