Ignimbrite

Classification：Igneous Rock

A pyroclastic rock containing plastic glass dust, crystalline debris, debris and slurry. Other translations are volcanic ash flow, pyroclastic flow and welding tuff.

It is also called "thawing rock". It is a volcanic clastic rock formed by the cause of melting. The rock is relatively dense and looks like lava but has pyroclastic structure. It contains cuttings, crystal chips, plastic chips, chips and so on. Plastic detritus is often compressed and elongated, bypassing the rigid debris in parallel arrangement to form a "pseudo rhyme structure". The cause of the formation is different. The more popular is the volcano ash flow theory, that is, the high viscosity of the acid, acid and alkaline melts rich in volatile matter, up to the near surface, as the external pressure drops suddenly, as if the expansion is bubbling. The milk is boiling. The wall of the bubble is thinner and thinner, eventually the explosion, the rupture of the bubble wall, the pulverization of the melt, and a large number of gushing out of the fire, which is suspended in the gas in a hot state, forming a volcanic ash flow along the slope. Then ash deposition rapidly accumulated. Under the influence of heat and load, glass dust was extruded and fused to form fused tuff. In foreign literature, ignimbrite word also represents cold (or non welded) volcanic ash flow deposits.

Cause:
The product of the ash flow after the consolidation of the volcanic ash. The high viscosity of the volatile acid, acid and alkaline melts, rising to the near surface, due to the sudden drop of external pressure, swelling and foaming, like milk boiling. The wall of the bubble is thinner and thinner, eventually exploding, the bubble wall breaks, the melts are smashed, and the lava is poured out of the crater, which is suspended in the gas in a hot state, forming rock formed by the volcanic ash flow or volcanic debris flow along the slope. Then the volcano ash flow in rapid accumulation, and under the influence of thermal load, vitric by extrusion deformation, melting into each other. Some hollow debris (ashfall) will also fuse to form molten tuff if they keep the high temperature at the time of eruption.

Distribution:
The melted tuff is often formed within a few hours to a few weeks, so they are a reliable, precise dating geological body. In the late Paleozoic Early Devonian, more than 200 km of volcanic sedimentary rocks were distributed in the southern margin of Altai. These tuff deposits are distributed all over the world.
In the Kron and mate basins, the volcanic sedimentary rocks of the Lower Devonian conbursburger formation are more than 4000 meters in thickness. These volcanic rocks are dominated by acid (RIS) volcanic clastic rocks, accompanied by massive rhylitic tuff eruptions, and a large number of volcanic ash flows. At the same time, in the crowns and in Maizi basin but also the distribution of small amount of basalt - andesite mainly calc alkaline volcano rock.

Characteristic：
1) volcaniclastic rocks form large or huge rock mats.
2) chemical composition of high silicon and high potassium;
3) enrichment of large ion affinity elements, low field strength elements and depleted Sr, Nb and Ti elements.

Eruption:
The melted tuff erupted on a large scale along a large fracture. The fused tuff is different from the general pyroclastic flow in terms of depositional mode, spatial distribution, type and compaction or degree of soldering. The distribution of molten tuff from the fissure is very large. Nevada in the western part of the United States, the early Oligocene to late Miocene fused tuff covers an area of 200 thousand square kilometers, with a volume of 50 thousand cubic kilometers. Western Utah, Southern Arizona, New Mexico, the snack River Plain, 40 million years ago - 25 million years ago, large-scale silicic acid volcano erupted, the fusion tuff volume up to 500 thousand cubic kilometers. The New Zealand pottery volcanic belt is 25 thousand square kilometers, and the pottery volcano erupted 254 thousand years ago to produce more than 1000 cubic kilometers of IgG Nimes rock. In 233, the pottery volcano erupted in 30 cubic kilometers of IgG Nimes rock. The Yellowstone National Park is 15000 square kilometers. 4000 years ago on the border between China and North Korea, 4000 years ago and 800 years ago, the formation of IgG Nimes rock (fusible tuff) erupted, and two large IgG Nimes rocks erupted, with a volume of more than 20 cubic kilometers. The accumulation thickness of fused tuff is also commonly used to identify complex crater structures.
The content of grit in tuff is coarsely than that in tuff. The content of phenocryst is up to 50%, but due to blasting collision, the phenocrysts are more ruptured. The eruption of the eruption of the Jess type volcanic debris flow and St. Vincent type volcaniclastic flow began, but only a few spouts were higher than the nozzle, but the multi bubble magma poured into the ground like a dense blanket consisting of incandescent clots and gases. The upper part of the volcaniclastic flow is vortex, while the lower part is laminar flow.