The Lithofacies Local Structure And Its Genesis Of The Holocene Airborne Plagioclase In Tianchi Volcano, Changbai Mountain

Vesicles in pyroclasts directly recorded volatile exsolution, expansion and coalescence in the process of explosive eruptions. The size, shape, number density, spatial distribution of localized structure-as important reference-can infer conditions of eruption dynamics. On the basis of nonlinear dynamics and complexity science, through a series of geological fieldwork, SEM and XRD analysis on the Holocene pumice erupted from Tianchi volcano, we do some quantitative researches on typical pumice structure.1. The balance between viscous force and surface tension of magma significantly reveal the magma decompression and bubble growth. Through fluid dynamics and conduit dynamics during bubble growth, we get pumice capillary number(Ca) about102and bubble irregular shape parameter(1-Ω) about10-1, these indicate Tianchi volcano Holocene eruption is Plinian.2. Lorenz curves show pore size distribution represents heterogeneity and vesicle structure of the pumice fits power-law distribution. Results indicate that the Lorenz curve on grey pumice from millennium eruption is very close to that on black pumice erupted in1668, and the yellow pumice from5,000a B.P. eruption has the obvious difference. The power-law index of the yellow pumice is0.48. In contrast, the power-law index of the gray pumice is0.40and that of the black pumice is0.41. All features explain self-organized criticality during explosive eruptions.3. The values of fractal dimension about three eruptions from big to small are yellow pumice, gray pumice and black pumice. By using single-hole box dimension statistical analysis, we can see that box dimension of the yellow pumice on average is far less than fractal dimension, unlike black or grey pumice. The phenomenon indicates that shear effect is far greater than surface tension, and a few big pores with complex boundary shape of the yellow pumice restrict volcanic explosion criticality and brittle magma fragmentation.4. For localized structure of the Holocene pumice, Lorenz curves, power law and fractal dimension analysis not only imply the possible relationship between the white and black pumice, but also especially indicate that the yellow pumice from5,000a B.P. explosive eruption may keep relative independence.