Tholeiitic basaltic magmas are initially generated as partial melts of peridotite (olivine and pyroxene) produced by decompression melting of the Earth's mantle.

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.

The ridge tholeiite has the following characteristics: (1) the phenocrysts are olivine or (and) plagioclase and the matrix minerals are olivine, plagioclase, klinaugite, and iron minerals, which often contain the vitreous and crystallographic mineral crystallite, (2) low potassium (K2 O less than 0.4%), high titanium (TiO 2 is 0.7-2.3%), low P ...

Jul 31, 2014 · When the parent magmas of basalts crystallize, they preferentially crystallize the more magnesium-rich and iron-poor forms of the silicate minerals olivine and pyroxene, causing the iron content of tholeiitic magmas to increase as the melt is depleted of iron-poor crystals.

Olivine phenocrysts of Hawaiian tholeiites display a variety of textures and a variation in composition which is due to supercooled crystallization. The highest forsterite content measured is 91%, and the highest magnesia content estimated for a tholeiitic liquid is 17%, using the olivine geothermometer.

Basalt in the generic sense = plagioclase + clinopyroxene +/- (olivine, nepheline, hypersthene, quartz, melilite, magnetite). The basalt tetrahedron is a useful tool for classifying basalts. The tetrahedron is constructed using the normative components olivine, quartz, clinopyroxene, and …

Field, petrographic, chemical, and geochronologic information has led to the identification and characterization of a widespread low-K, high-alumina olivine tholeiite (HAOT) magma type in the northwestern Great Basin.

Tholeiite has very less or no olivine content but more calcic plagioclase i.e. Anorthite.

Jun 20, 2007 · Nd- and Sr-isotopic compositions overlap with coeval olivine tholeiites (ɛ Nd = −4 to −6; 87 Sr/ 86 Sr i = 0.7080–0.7102) and contrast markedly with isotopically evolved Archean country rocks. In at least two cases, the rhyolite lavas occur as cogenetic parts of compositionally zoned (~55–75% SiO 2) shield volcanoes.

The Tertiary to Recent basalts of Victoria and Tasmania have mineralogical and major element characteristics of magmas encompassing the range from quartz tholeiites to olivine melilitites.