M Sadeghian; S Shekari
Abstract
Darreh-Bagh granitoidic pluton in the northwest of Aligoodarz composed of two felsic and mafic parts, with lithological composition range from diorite to quartzdiorite, and granodiorite to leucogranite respectively. Felsic rocks have calc-alkaline and peraluminous affinity and belong to S-type and continental ...
Read More
Darreh-Bagh granitoidic pluton in the northwest of Aligoodarz composed of two felsic and mafic parts, with lithological composition range from diorite to quartzdiorite, and granodiorite to leucogranite respectively. Felsic rocks have calc-alkaline and peraluminous affinity and belong to S-type and continental arc granitoids (CAG). The most significant characterizes of felsic part are as follows: presence of the metapelitic andalusite bearing enclaves, silica (quartz fragments which inherited from quartz vein with metamorphic origin), surmicaceous and metapasamitic enclaves and also andalusitic xenocrysts through out of the felsic part. Mafic rocks have calc-alkaline and metaluminous affinity and belong to I-type and continental arc granitoids (CAG). Based on the field observations, petrographical and geochemical characterictics, penetration of basic-intermediate magmas into late Triassic - lower Jurassic metapelites and metagraywackes caused to rise temperature up to produce a large scale contact metamorphism including andalusite hornfels and sillimanite hornfels. Intersecting the temperature of melting point of metapelites and metagraywackes resulted in producing melts with suitable composition for forming of S – type granitoid plutons. Then, the produced magma ascended to the higher levels in the upper crust and emplaced in it. Granitoid magmas emplacement are associated with low-extent contact metamorphism up to cordierite hornfels facies.
H Ghasemi; M Rostami Hossuri; M Sadeghian; F Kadkhodaye Arab
Abstract
Subduction of the Neo–Tethyan oceanic lithosphere beneath the southern edge of the Central Iran caused development of extensional back-arc basins behind the Urumieh–Dokhtar magmatic belt during Mesozoic and Cenozoic. Some researchers have noted formation of the oceanic back-arc basins in ...
Read More
Subduction of the Neo–Tethyan oceanic lithosphere beneath the southern edge of the Central Iran caused development of extensional back-arc basins behind the Urumieh–Dokhtar magmatic belt during Mesozoic and Cenozoic. Some researchers have noted formation of the oceanic back-arc basins in Nain, Sabzevar and Sistan in Central Iran during Mesozoic, but little is known about generation of such basins in Cenozoic. The depressed extensional back-arc basin of Central Iran contains sedimentary successions of intracontinental extensional environments associated with alkaline basic magmatic rocks. These magmatic rocks are outcropped in the Oligo-Miocene gypsiferous red marls (red formations), as both intrusive (gabbro) and extrusive (basalt) forms. The present study has focused on the basaltic lava flows in the Oligo-Miocene siliciclastic-evaporitic sedimentary succession extending for about 300 kilometers from Sabzevar to Shahroud along the northern edge of Central Iran. These lava flows are observed as interbedded with the Oligo-Miocene sedimentary units. In the Kalate-Sadat area, located SW of Sabzevar, there are at least five intermittent basaltic lava flows in the red marls. These basaltic rocks (with a composition of olivine-basalt to basalt) show porphyritic, glomeroporphyritic and trachytic textures and are composed of olivine, clinopyroxene and plagioclase phenocrysts in a glassy to microlitic ground mass. On the basis of geochemical data, the parent magma of these rocks had a sodic-alkaline affinity, enriched in LILEs and LREEs and depleted in HREEs, without negative anomalies in HFSEs. The basalts show the geochemical characteristics of the basaltic magmas originated from partial melting of adjusted enriched garnet lherzolite mantle source beneath the continental areas of extensional back-arc basins.
S Saki; H Ghasemi; M Sadeghian
Abstract
Bouin- Miandashtgranitoid pluton with an area of 40 Km2, outcropped in the north of Bouin Miandasht- Aligoudarz road, was emplaced into Triassic to early Jurassic low to medium grade metapelitic rocks of Sanandaj - Sirjan structural zone. This pluton composed of alkali feldspar granite to leucogranite. ...
Read More
Bouin- Miandashtgranitoid pluton with an area of 40 Km2, outcropped in the north of Bouin Miandasht- Aligoudarz road, was emplaced into Triassic to early Jurassic low to medium grade metapelitic rocks of Sanandaj - Sirjan structural zone. This pluton composed of alkali feldspar granite to leucogranite. For the first time, variation of anisotropy of magnetic susceptibility (AMS) is applied to investigate magnetic fabric of this pluton. The Mean magnetic susceptibility values (Km in µSI) of the different rock groups of Bouin- Miandasht pluton are as follows: alkali feldspar granites (158), fine granites (120), coarse granites (166), and leucogranites (34). The lower Km values for the main compositions of this pluton (< 500 µSI) suggesting the paramagnetic nature of these granites. Biotite is the main carrier of magnetic properties in the studied rocks. The magnetic anisotropy (P %) varies from 1 to 15. Aalkali feldspar granites have the highest P value and show positive correlation with degree of deformation. Shape parameter of magnetic ellipsoid (T) values varies from -0.43 to 0.85 and most of the magnetic ellipsoids are oblate. Seventy five percent of specimens have positive T value. This subject indicates that magnetic ellipsoids are oblate and then foliation is prevailing, and also field evidence confirms this conclusion.
