Tectonics
Mohammad Amir Alimi
Abstract
This paper presents the results of a field study aiming to describe and to interpret origin of the vein network in the south of Birjand. Adjacent to Birjand ophiolite in eastern Iran, the Paleocene-Eocene flysch facies was deposited in the Birjand foreland area concomitant with the Alpine orogeny (Laramide). ...
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This paper presents the results of a field study aiming to describe and to interpret origin of the vein network in the south of Birjand. Adjacent to Birjand ophiolite in eastern Iran, the Paleocene-Eocene flysch facies was deposited in the Birjand foreland area concomitant with the Alpine orogeny (Laramide). The sandstone unit of this facies contain two orthogonal sets of quartzite veins. The N310-340 striking veins (set 1) are arranged parallel to the Bagheran Kuh range front and perpendicular to the vein set 2 (N215-240). The paleostress reconstruction in the Paleocene-Eocene shows that the regional compression direction N240 is perpendicular to the Bagheran Kuh range front. Structurally, to create orthogonal veins, σ1 should be perpendicular to the layering and σ2 and σ3 should be horizontal. This situation was created in the middle Eocene-Oligocene. The post-collision extensions of this period caused a decrease in regional pressure in the region. As a resault, the maximum principal stress (σ1), was changed to a vertical state and intermediate stress (σ2) was parallel to the orogenic pressure. In these conditions, orthogonal tensile openings (state I) were formed as a result of the local inversion of stress and fluid pressure in the flysch facies.
A. A. Baharifar
Abstract
Chloritoid as one of the common metamorphic mineral in low to medium grade metapelites, is absent in metapelitic rocks of Hamedan area. Comparing with geochemical limitations for Chloritoid appearance in metapelites, whole rock composition of the area is suitable for Chloritoid formation. Since P, T ...
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Chloritoid as one of the common metamorphic mineral in low to medium grade metapelites, is absent in metapelitic rocks of Hamedan area. Comparing with geochemical limitations for Chloritoid appearance in metapelites, whole rock composition of the area is suitable for Chloritoid formation. Since P, T and X are in appropriate range for Chloritoid, the role of fluid could be important. Microscopic investigations show that all metapelitic rocks are in equilibrium with graphite and fluid composition is combination of CO2 and H2O. Based on estimated P and T, highest portion of H2O in the fluid, could be 0.9. Although this is highest approximation, it can conclude that for Chloritoid appearance, XH2O in fluid must be more than 0.9. Since in the Hamedan area staurolite is widespread and Chloritoid is absent - considering almost same composition between chloritoid and staurolite - the composition of fluid is more important. There are many doubts in geochemical limitations for Chloritoid appearance. Considering the results of this study and in the case of attention to fluid composition, geochemical limitations will change and Chloritoid could appear in many rocks, as its higher temperature equivalent, staurolite.
