tholeiite
/ˈθəʊlɪʌɪt
/noun [mass noun] Geology
A basaltic rock containing augite and a calcium-poor pyroxene (pigeonite or hypersthene), and with a higher silica content than an alkali basalt.Trace element data and isotopic analysis demonstrate that the arc is composed of islandarc tholeiite and ocean-island basalts and calc-alkaline arc-type extrusive rocks....
- Except for its lower degree of partial melting (hence, a higher content of volatile matter), alkali basalt is thought to have an origin similar to that of tholeiite.
- In the Pechenga-Varzuga volcanosedimentary belt, alkali basalts eruptions about 2.2 Ga in age gradually gave way to tholeiite pillow lavas, Fe-picrite flows and Ti-rich basalts with ages around 1.98 Ga.
Derivatives
tholeiitic
- In the Canaries, the lavas are much more compositionally varied in each of these stages, ranging from tholeiitic basalts to phonolites and trachytes.
- A tholeiitic suite of dolerite dykes in the southwestern Borrowdale Volcanic Group is a separate, later magmatic event.
- The Whin Sill complex is a large tholeiitic quartz dolerite intrusion in northern England.
Origin
Mid 19th century: from Tholei, the name of a village (now Tholey) in the Saarland, Germany, + -ite1.