What is dacite composed of?
Like andesite, dacite consists mostly of plagioclase feldspar with biotite, hornblende, augite, or enstatite and generally has a porphyritic structure (scattered larger crystals in a fine-grained groundmass); additionally, however, it contains quartz as rounded, corroded crystals or grains, or as a constituent of the …
What type of rocks are at the Teton Mountains?
A 2.7 billion-year old metamorphic rock called gneiss makes up much of the Teton Range. These rocks were formed when sea floor sediments and volcanic debris were buried up to 18 miles deep as two tectonic plates collided – similar to the collision of India and Asia today forming the Himalayas.
What is rhyolite rock made of?
Rhyolite is extrusive equivalent of granite magma. It is composed predominantly of quartz, K–feldspar and biotite. It may have any texture from glassy, aphanitic, porphyritic, and by the orientation of small crystals reflecting the lava flow.
What is the composition of a basaltic igneous rock?
Basalt is a dark-colored, fine-grained, igneous rock composed mainly of plagioclase and pyroxene minerals. It most commonly forms as an extrusive rock, such as a lava flow, but can also form in small intrusive bodies, such as an igneous dike or a thin sill. It has a composition similar to gabbro.
How do you identify dacite?
Dacites consisting mostly of plagioclase and quartz are usually light in color, often white to light gray. Those with abundant hornblende and biotite can be light gray to light brown. The darkest dacites usually contain abundant augite or enstatite.
What is an explosive dacite volcano?
Dacite lavas are viscous and tend to form thick blocky lava flows or steep-sided piles of lava called lava domes. Dacitic magmas tend to erupt explosively, thus also ejecting abundant ash and pumice.
What made the Grand Tetons?
About 10 million years ago, Earth’s crust started to stretch and thin, forming faults and causing earthquakes. Over time, the block of earth west of the Teton fault shot upward, forming the Tetons, and the block of earth east of the fault dropped more than 6,000 meters (20,000 feet) forming the valley.
Are the Grand Tetons made of granite?
Main mass of the mountain is layered gneiss and streaky granite gneiss. White lines are dikes of granite and pegmatite; light-gray mound on the summit is about 50 feet of Cambrian sedimentary rock (Flathead Sandstone).
Is dacite mafic or felsic?
Dacite is a felsic extrusive rock, intermediate in composition between andesite and rhyolite. It is often found associated with andesite, and forms lava flows, dikes, and, in some cases, massive intrusions in the centres of old volcanoes.
What is the chemical composition of basalt rock?
Basalt generally has a composition of 45–52 wt% SiO2, 2–5 wt% total alkalis, 0.5–2.0 wt% TiO2, 5–14 wt% FeO and 14 wt% or more Al2O3.
What kind of rock is a dacite rock?
Dacite is a felsic extrusive rock, intermediate in composition between andesite and rhyolite. It is often found associated with andesite, and forms lava flows, dikes, and, in some cases, massive intrusions in the centres of old volcanoes.
What kind of rock is the andesite made of?
Weakly to strongly metamorphosed volcanic rocks. Protoliths include basalt, andesite, dacite, and rhyolite deposited as lava or tuff, related sedimentary rock, and shallow intrusive rock. These rocks, widely exposed in several belts in central Arizona, include metavolcanic rocks in the Yavapai and Tonto Basin supergroups. (1650 to 1800 Ma)
Where can you find dacite in a volcano?
It is often found associated with andesite, and forms lava flows, dikes, and, in some cases, massive intrusions in the centres of old volcanoes. Dacite is the volcanic equivalent of granodiorite. Group – volcanic. Colour – variable, but generally bluish-grey or pale grey. Texture – generally porphyritic.
What kind of phenocrysts are found in dacite?
Dacite consists mostly of plagioclase feldspar with biotite, hornblende, and pyroxene ( augite and/or enstatite ). It has quartz as rounded, corroded phenocrysts, or as an element of the ground-mass. The plagioclase ranges from oligoclase to andesine and labradorite.