What is the difference between a tholeiitic basalt and an alkali basalt?

A tholeiitic basalt contains more conspicuous plagioclase and pyroxene crystals. An alkali basalt contains potassium feldspar. An alkali basalt contains more conspicuous plagioclase and pyroxene crystals.

Is tholeiitic basalt mafic?

Tholeiitic basaltic lavas are characterized by calcic plagioclase with augite, pigeonite or hypersthene, and olivine (rarely) as the dominant mafic minerals; basalts without olivine are also well represented. Tholeiitic basalts, which contain 45 to 63 percent silica, are rich in iron and include the tholeiites…

What is tholeiitic in geology?

tholeiite, fine-grained extrusive igneous rock, a basalt that contains plagioclase feldspar (labradorite), clinopyroxene (augite with pigeonite), and iron ore (magnetite and ilmenite). Tholeiitic lavas often contain glass, but little or no olivine.

What is the calc alkaline trend?

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 magnesium and iron and produces rhyolite or granite. …

What is tholeiitic basalt composed of?

The tholeiitic magma is relatively rich in silica and poor in sodium. The rock is composed of clinopyroxene, hypersthenes and plagioclase with minor iron–titanium oxide, and ±olivine. Tholeiitic basalt often represents a fine, glassy groundmass consisting of fine-grained quartz and other main constituent minerals.

How does tholeiitic basalt differ from most volcanic rocks?

Rocks in the tholeiitic magma series are classified as subalkaline (they contain less sodium than some other basalts) and are distinguished from rocks in the calc-alkaline magma series by the redox state of the magma they crystallized from (tholeiitic magmas are reduced; calc-alkaline magmas are oxidized).

Does basalt have a consistent chemical composition?

Geochemistry. Relative to most common igneous rocks, basalt compositions are rich in MgO and CaO and low in SiO2 and the alkali oxides, i.e., Na2O + K2O, consistent with their TAS classification.

What is the difference between dolerite and basalt?

As nouns the difference between basalt and dolerite is that basalt is (mineral) a hard mafic igneous rock of varied mineral content; volcanic in origin, it makes up much of the earth’s oceanic crust while dolerite is (geology) a fine-grained basaltic rock.

What is the composition of dacite?

Dacite (/ˈdeɪsaɪt/) is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. It is composed predominantly of plagioclase feldspar and quartz.

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 is the difference between calc-alkaline and tholeiitic rocks?

Rocks in the tholeiitic magma series are classified as subalkaline (they contain less sodium than some other basalts) and are distinguished from rocks in the calc-alkaline magma series by the redox state of the magma they crystallized from ( tholeiitic magmas are reduced;

What are the characteristics of tholeiitic basalt?

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, as may other types of basalt.

What is the tholeiitic magma series?

The tholeiitic magma series 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.

What is the meaning of calc-alkaline basalts?

To my understand, the name of calc-alkaline or tholeiitic basalts are used to express the implication of what path its corresponding magma will evolve along, towards Fe-depleted ,Al-rich or towards Fe-rich, Al-depleted.