Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Chonashu (Irtashskii)


Occurrence number: 
Longitude: 79.07, Latitude: 42.37

Situated within the deep fracture zone which divides the north and central Tyan-Shan, the Chonashu intrusion extends over 10 km in a northeasterly direction but has a width of only 1-3 km. The country rocks to the south are Precambrian granitoids and to the north phyllites, schists and andesitic tuffs. The complex includes gabbros, diorites and pyroxenites with alkaline and nepheline syenites forming a series of vein-shaped bodies. The nepheline syenites are unevenly grained, gneiss-like rocks, with a pegmatitic facies, composed of albite, microcline, nepheline, associated with which are sodalite and cancrinite, and biotite. Sometimes the nepheline syenites pass into nepheline-bearing or alkaline syenites 80-90% of which may comprise large crystals of albite, biotite and actinolite. Similar accessories occur in all the peralkaline rocks of the complex, namely titanite, garnet, zircon, fluorite, catapleite, corundum and apatite.

K-Ar on biotite gave 324 Ma.

BORODIN, L.S. 1974. The principle provinces and formations of alkaline rocks. Izdatel'stvo, Nauka, Moscow. 376 pp.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith