Alkaline magmatism and rare metallic ore-beareness
|Location||International Geological Congress,oslo 2008|
|Author||Bekzhanov, Murat۱; Abdrakhmanov, Kaidar۲|
|Holding Date||08 September 2008|
There could be distinguished four types of alkaline magmatism within Kazakhstan folded area.
The first type is represented by the comendite - alkali-granite formation of folded areas which has spatial-and-temporal and petrogenetic connection with potassium-granite of the granitization cycle late stage.
Development of the comendite - alkali-granite magmatism is possible in mature continental crust under the influence of highly alkaline fluids. Same conditions could be realized at the late stage of orogenic-collision cycle of folded areas. Alkali-granites and leukogranite - alaskites synchronically formed in the different parts of continental area could be interpreted as agpaite and plumasite branches of genetically united series of potassium-granites.
Based on the depth facies of their formation alkaline-granites are distributed in volcanic, hypo- and mezobyssal facies. On the basis of alkali-granites of Kazakhstan there were developed petro-geochemical criteria of the evaluation of their formation depth.
The most ore-bearing granites are hypo abyssal ribekito-alkali-granites characterised by apogranite type of evolution, fluorine - albite -metasomatites and enriched with zirconium, niobium, heavy lanthanides, rare zonation and variety of accessories.
The second type is represented by leucite - tephrite - bazanite, alkali-gabbro-shonkinite-leucitophire, alkali syenite - nepheline syenite, trachyandesite, gabbro-monzonite-cienite sub formations of a single leucite-tephrite-shonkinite-syenite formation.
This type of alkali basaltoide magmatism of the potassium profile is known in Talas Alatau (Irisu-Daubaba complex of the late perm-early-triasse age) and Ishim strata volcano (late-Devonian Ishim).
Alkali basaltoide - gabbro - shonkinite magmatism is laid over the orogenic-granitization cycle and connected with deep zones of tectonic-magmatic activisation.
The third type of the alkali magmatism is fixed with alkali-ultra basic formation (Krasnomay complex of the mid-late Cambrian) and is typical for pre-Cambrian middle massives bedding in the form of disconnected blocks. The forth type of the alkali magmatism is represented by essexite-monzonite-cienite and monzonite-granocinite formations known in the Kastek ridge of the North Tien-Shan and Kokshetau massive.