Showing 2 results for Lower Cretaceous
E Moradian Teshnizi, Mostafa Ghomashi, Ali Ahmadi, Hadi Aminrasoli,
Volume 13, Issue 4 (2-2014)
Abstract
The study area is located to the south, west and north Esfahan province. this research is geochemical and petrographic study of Lower cretaceous dolomites. Five dolomite type have been identified.
The first type is very fine-fine crystalline dolomite formed in near surface conditions and in early stages of diagenesis, in tidal flat to lagoonal environments. The Sr content is high (2537ppm) and Fe (8861ppm) and Mn (852ppm) is low.
The second type is fine-medium-grained, subhedral to euhedral, crystalline dolomites. Compared to the first type, Sr content is lower and Fe and Mn content is higher. This type of dolomites is most likely formed in early burial diagenesis.
The third type is medium-coarse-grained, euhedral and subhedral, crystalline dolomite and show clear rim and cloudy center. Compared to the type1 and type2, this type of dolomite contains higher Fe and Mn and lower Sr. They are likely formed in deeper burial diagenesis and by dolomitization of earlier calcareous deposits or recrystalization of first- and second- type dolomites.
The medium-coarse-grained, crystalline dolomite fill in pores and fractures, and are called "four-type" in this study. This type of dolomite is likely formed during late diagenesis and under conditions of medium pressure and temperatures less than 60-80 °C. In this dolomite values of Fe and Mn increase from the fringes of pores and fractures to the center.
The fifth dolomite type is coarse, crystalline, saddle dolomite filling pores and fractures. This dolomite
Volume 18, Issue 57 (1-2004)
Abstract
Ab-e-garm village situated 85km to sw of Ghazvin, and the studied area located somewhere around. From geographical point of view this area is the Soltanieh mountains continuation in Kabudar Ahang geological quadrangle. Lower Cretaceous igneous rocks in this area consist of: spilitic basalt, alkali olivine basalt, basalt, mugearite and trachy-basalt, which would be seen as lava and tuff, and their intrusives are mostly, microgabbro, pyroxene hornblende gabbro and mela gabbro. These igneous rocks are of alkaline series. Good correlations and continuous trends of main element oxides vs. silica in chemical variation diagrams, confirm genetic relationship between different facies. Comparison of geochemical data and petrography of these rocks shows that seperation of OL, PX and magnetite caused parent magma differentiation, ended into formation of different terms from it. With respect to continental rifts abundances between small continent boundaries in Iran in lower Cretaceous time, it is possible that the lower Cretaceous igneous rocks of Ab-e-garm area be related to these rifts or back arc zone of oceanic crust subduction between these small continents, however,to distinguish exact history of Ab-e-garm area we do need much more data at this time.
