Writers : N. S. Mahdavi; M. Arvin
Refference : Geosciences Scientific Quarterly Journal,No.:53,P.:88
Publishing Year : 1383

Abstract :

The upper Jurassic to lower Cretaceous volcano-sedimentary rocks of Deh-Sard are located in southern part of Sanandaj-Sirjan zone in the south of Kerman. They consist of intermittent lava flows (mainly basalt, basaltic-andesite and trachy-basaltic-andesite), pyroclastics (various types of tuffs and bereccias) and sedimentary rocks (limestones and shales).
The Deh-Sard basalts composed essentially of plagioclase and clinopyroxene microphenocrysts, set in a matrix of the same mineralogy associated with opaque minerals and apatite as accessory phases. The existence of disequilibrium textures in Deh-Sard basalts reveals the rapid changes in the pressure of rising magma.
The pyroclastic rocks are less common in the area and consist mainly of crystal litic tuffs, in which crystals are mainly plagioclases and lithic fragments mainly basaltic-andesites and trachy-basalt-andesites. The sedimentary rocks were formed in a shallow marine environment.
The Deh-sard basalts shows a selective enrichment of elements with low ionic potential (eg., K, Rb, Sr, Ba,+ Th) and a depletion in elements having high ionic potential (eg., Nb, Ce, P. Y, Cr)compared to N-type MORB. Based on the geochemical data, trace and REE element diagrams, the Deh-Sard basalts show characteristics of transitional tholeiitic basalt MORB and chonderitic normalized trace element patterns are believed to reflect that the Deh-Sard basalts have affinities toward subduction and within-plate basalts. A rift environment formed on transitional continental-oceanic crust "off-axis" from the spreading center is suggested for the formation of Deh-Sard basaltic rocks. In this case, off-axis magmas do not represent the same range of chemical variation as magmas delivered to the axial system, but they show similarity with seamount-type volcanism. The occurrence of intermittent limestones and lava flows may suggest that Deh-Sard basalts might have formed in a rift environment on transitional continental-oceanic crust "off-axis" from the spreading center.

Subject List : Off axis