Writers : Helmi.F
Refference : Geosciences Scientific Quarterly Journal,No.:17-18,P.:40
Publishing Year : 1374

Abstract :

Very low- grade metamorphism Is an ubiquitious process In the upper portion of the earth's crust. limit
of recrystallization that has occurred in this stage of metmorphism does not cause structural and textural changing in rocks. Depending on the tectonic setting and physico- chemical conditions, various types of low temperature metamorphism ar, hence produced In both basaltic- andesitic volcanic rocks with different thickness and shapes: Ocean ridge + ocean- floor, burial, subduction- zone metamorphism, thermal and hydrothermal metamorphism. Thos. generally have slightly .ffect on th. chemical composition of rocks. Mineral assemblages of low- T metamorphism of basaltic and andesitic rocks commonly consist of one or two Ca-Al hydrosilicates together with albite, white mica, quartz, chlorite (or smectite), sphene, carbonates, pyrite, haematite and/or magnetit.. Zeolite, prehnite- pumpellyite, prehnite- actionolite, pumpellyite- actinolite and blueschist are facies kinds in very Iow.grade- metamorphism. Zeolite Fades all those assemblages produced under physical conditions in which the following are commonly formed: guartz- analcime, quartz- heulandite, and quartz- laumontite. Low and high T zeolite facies have different assemblages.
Prehnlte- pumpellyite fades metabasites are common in all tectonic settings and characterized by the stable association of Pumpellyite + Epidote Prehnite and the absenc of laumontite and actinolite. In many regionally metamorphosed terranes, Pumpellyite commonly coexists with actinolite. The assemblage pumpellyite + actinolite + epidote (4- chlorite + albite + quartz)occurs in deeply buried volcanics with considerable thickness.
C02 has an important role in diagenesis and metamorphism. The most significant effects of C02 on
very low- grade metamorphic parageneses indlude (i) decreasing the dehydration temperatures of Ca-Al and other hydrosilicates; and (ii) stabilizing carbonates at the expense of Ca- Al silicates.
Phenomena related to alteration or very low- grade metamorphism are visible in the most Tertiary volcanic rocks of Saveh region. Hydrothermal and fumerolle alterations, burial and thermal metamorphismes have produced in the temporal order in Saveh.

Subject List : , Metabasite