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The tholeiitic magma series (/ ˌθoʊliˈaɪtɪk /) is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma into a more evolved, silica rich end member. Rock types of the tholeiitic ...
Rocks in the alkaline magma series are distinguished from rocks in the subalkaline tholeiitic and calc-alkaline magma series by their high content of alkali metal oxides (K 2 O plus Na 2 O) relative to silica (SiO 2). They are distinct from the rare peralkaline magmas, which have excess alkali oxides relative to alumina (Na 2 O + K 2 O > Al 2 O 3).
The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it fractionally crystallizes to become a felsic magma, which is low in ...
[4] [5] The overall composition of this rock places it among the slightly alkaline andesites and dacites of the subalkaline igneous magma series, typical of subduction zones. [6] The most visible crystals are numerous andesine-type plagioclases, often zoned (because they are more calcic in the centre), but also biotite and hornblende crystals.
Trachyandesite. A cut block of trachyandesite lava from a volcano in Auvergne, France, used as building stone, forming part of the walls of Clermont-Ferrand Cathedral, France. Trachyandesite is field S3 in the TAS diagram. Trachyandesite is an extrusive igneous rock with a composition between trachyte and andesite.
In geology, igneous differentiation, or magmatic differentiation, is an umbrella term for the various processes by which magmas undergo bulk chemical change during the partial melting process, cooling, emplacement, or eruption. The sequence of (usually increasingly silicic) magmas produced by igneous differentiation is known as a magma series.
Hawaiite is sodic trachybasalt. Hawaiite is an aphanitic (fine-grained) volcanic rock produced by rapid cooling of lava moderately poor in silica and enriched in alkali metal oxides (potassium oxide plus sodium oxide). It is often impractical to determine the mineral composition of such a fine-grained rock, and so hawaiite is defined chemically.
Trachyte is the usual silica-rich end member of the alkaline magma series, in which alkaline basaltic magma experiences fractional crystallization while still underground. This process removes calcium, magnesium, and iron from the magma to give it a composition close to that of alkali feldspar.