Writers : Helmi.F
Refference : Geosciences Scientific Quarterly Journal,No.:13,P.:48
Publishing Year : 1373

Abstract :

Potassic and Ultrapotassic rocks cover a wide range of compositions and ate found as volcanic,
hypabyssal and plutonic bodies in a variety of geologic environments. On the basis of petrologlcal parameters, they can be classified Into several main groups that include the Shoshonitic Series, the Roman-type series, lamproites, and kamafugites. All of these are characterized by high to extreme enrichment in incompatible elements. Strontium, neodymium, lead, and oxygen isotopic ratios are also variable, a fact that gives evidence of complex genetic and evolutionary histories.
Petrological and geochemical data suggest that potassic and ultrapotassic magmas are generated in a heterogeneous, anomalous, phiogopite- bearing upper mantle at different pressures and under the effects of volatile phases. Together these factors, produce a wide spectrum of petrologically and geochemically distinct magmas. Geochemical anomalies in the sources are believed to result from metasomatic processes related to the addition of small melt fractions and (or) gaseous fluids that are rich in potassium and incompatible elements. Geochemical and Isotopic evidence Indicates that these metasomatic agents may be derived either from sublithospheric mantle or from the dehydration and melting of oceanic slab as well as upper crustal material brought into the mantle by the subduction process. Subduction- related material can be recycled through the mantle for long times before being involved in the genesis of potassic magma.
Potassic and ultrapotassic rocks are mainly occurred in Shoshonitic series in Iran, where as, some occurs in Roman- Type series, only one istance is found as lamproite but no Kamafugite is encountered.
In Tertiary times and less quantities from the Quaternary, potassic rocks have been reported from
several places in central Iran and the Alborz. Since then, only in the eastern coast of Urumieh Lake, and one locality in Kerman area, ultrapotassic rocks accompanied with potassic rocks crop out. Available data from these rocks are often limited to chemical analysis of major elements and their normative minerals. Thus research about the manner in which their magmas are formed and related conditions will be encountered with several difficulties.

Subject List : Potassic rocks