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The mafic rocks also typically have a higher density than felsic rocks. The term roughly corresponds to the older basic rock class. [9] Mafic lava, before cooling, has a low viscosity, in comparison with felsic lava, due to the lower silica content in mafic magma. Water and other volatiles can more easily and gradually escape from mafic lava.
Some of the minerals found in the region are mafic (high Ca pyroxenes, e.g., augite)—these suggest volcanic material. The volcano is located at 7.40°S, 94.60°W. The authors of the paper consider the volcano to be an eroded shield volcano. Sub-circular depressions near the top are interpreted as caldera remnants. [36]
A rock with over 90% mafic mineral content will be classified instead as an ultramafic rock. A gabbroic rock with less than 10% mafic mineral content will be classified as an anorthosite. [8] [13] A more detailed classification is based on the relative percentages of plagioclase, pyroxene, hornblende, and olivine. The end members are: [8] [13]
The youngest mafic volcano in the Lassen volcanic center, [53] it is surrounded by unvegetated block lava and has concentric craters at its summit. [52] Cinder Cone is comprised by five basaltic andesite and andesite lava flows, and it also has two cinder cone volcanoes, with two scoria cones, the first of which was mostly destroyed by lava ...
In 1992, Coffin and Eldholm initially defined the term "large igneous province" as representing a variety of mafic igneous provinces with areal extent greater than 100,000 km 2 that represented "massive crustal emplacements of predominantly mafic (magnesium- and iron-rich) extrusive and intrusive rock, and originated via processes other than 'normal' seafloor spreading."
Belknap was the last volcano to erupt in the Three Sisters area. [21] Basaltic andesite dominates the eruptive material in the local mafic volcanoes, which range from early Pleistocene to Holocene age. [22] Belknap is one of the larger mafic volcanoes in the Sisters Reach, more than 30 of which run continuously along the segment. [22]
Eruptions of volcanoes into air are termed subaerial, whereas those occurring underneath the ocean are termed submarine. Black smokers and mid-ocean ridge basalt are examples of submarine volcanic activity. [13] The volume of extrusive rock erupted annually by volcanoes varies with plate tectonic setting.
Most examples come from areas of active continental rifting such as the Basin and Range Province. Bimodal volcanism has also been described from areas of transtension, [2] the early phases of back-arc basin formation [3] and in the products of both continental and oceanic hotspots (e.g. Yellowstone, Anahim and the Canary Islands). [4] [5] [6]