Everything about Tholeiitic Basalt totally explained
Tholeiitic basalt is an
igneous rock, a type of
basalt. Like all basalt, the rock type is dominated by
clinopyroxene plus
plagioclase, with minor iron-titanium oxides.
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) Orthopyroxene or
pigeonite may also be present in tholeiitic basalt, and
olivine, if present, may be rimmed by either of these calcium-poor pyroxenes.
Tridymite or
quartz may be present in the fine-grained groundmass of tholeiitic basalt, and
feldspathoids are absent. Tholeiitic rocks may have a fine, glassy
groundmass(AGI, 41), as may other types of basalt.
Chemically, these rocks have been described as subalkaline basalts, that is, they contain less (Na
2O plus K
2O) at similar SiO
2 than alkali basalt; the field for basalts plotted with these chemical variables is shown in the
TAS classification, and the distinction between basalt types is discussed by Le Maitre and others (2002).
The International Union of Geological Sciences recommends that "
tholeiitic basalt" be used in preference to the term "tholeiite" (Le Maitre and others, 2002).
Basalt magmas are partial melts of
peridotite produced by decompression melting in the
Earth's mantle, a process described for
igneous rocks. Tholeiitic basalts are the most common
volcanic rocks on
Earth, as they're produced by
submarine volcanism at
mid-ocean ridges and make up much of the ocean crust.
MORB, the acronym for typical
mid-
ocean-
ridge
basalt, is a type of tholeiitic basalt particularly low in
incompatible elements. In contrast, alkali basalt isn't typical at ocean ridges, but is erupted on some oceanic islands and on continents, as also is tholeiitic basalt. (AGI, 41),
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