Petrology
Z. Gharamohammadi; A. Kananian; M. Eliassi
Abstract
The Dehe Bala pluton is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This pluton includes several mafic microgranular enclaves (MMES) with ellipsoidal and rounded shapes and varying sizes (from a few centimeters up to 30 cm). The MMEs are composed of diorite, monzodiorite ...
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The Dehe Bala pluton is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This pluton includes several mafic microgranular enclaves (MMES) with ellipsoidal and rounded shapes and varying sizes (from a few centimeters up to 30 cm). The MMEs are composed of diorite, monzodiorite and diorite-gabbro while the host rocks comprise mainly granodiorite. The presence of disequilibrium textures in enclaves, such as plagioclase phenocrysts with repeated resorption surfaces and sieve texture, quartz ocelli and acicular apatite, suggest a varity of magma mixing processes affecting the Dehe Bala pluton. The distribution of major, trace and rare earth elements apparently reflect exchange between the MMEs and the felsic host rocks. Unusual REE enrichment of the enclaves compared to the country rocks can be attributed to significant differences in their parent magma compositions. The complexity of the morphology of the enclaves (fractal dimension) caused by magma mixing processes. Fractal dimensions of the enclaves vary between 1.14 to 1.29. The frequencies of Dbox = 1.29 is the highest frequency in histogram. According to the fractal dimensions of enclaves, the logarithm of the viscosity ratio between the host granodiorite and the enclave ranges between 0.56 to0.96 with most values clustering around 0.96. The most of enclaves in the Dehe Bala pluton characterized by silica content around 56 w% and a high fractal dimension. These evidence confirmed the occurrence of slight hybridization between the mafic enclave magma and surrounding felsic magma, causing increasing of viscosity difference between the host granodiorite and the enclave magmas.
F. Zaeimnia; A. Kananian; M. Salavaty
Abstract
South Amlash alkaline rocks, located in south of Caspian Sea, occur like small and discrete bodies within the Cretaceous igneous rock association which is a small part of Gorgan-Rasht tectonic zone. These rocks crop out as large-volume pillow lavas and homogeneous fine- to coarse- grained gabbros and ...
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South Amlash alkaline rocks, located in south of Caspian Sea, occur like small and discrete bodies within the Cretaceous igneous rock association which is a small part of Gorgan-Rasht tectonic zone. These rocks crop out as large-volume pillow lavas and homogeneous fine- to coarse- grained gabbros and are essentially composed of Clinopyroxene (augite), plagioclase and relatively abundant small apatite needles. Geochemical data clearly identifies an enrichment of LREE and positive anomalies of Nb and Ti suggesting an intra-plate ocean island (OIB) tectonic setting. Considering the LREE/HREE ratio and some of other incompatible element contents, it seems that the alkaline rocks are probably derived from a garnet lehrzolitic mantle.
A. Kananian; F. Sarjoughian; J. Ahmadian
Abstract
The Kuh-e Dom intrusion is a small section of Upper Eocene Urumieh- Dokhtar magmatic belt in the Central Iran tectonic zone. This intrusion is composed of two separate phases which include an acidic and intermediate- mafic units. The acidic rocks consist of monzogranite, granodiorite, quartz monzonite ...
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The Kuh-e Dom intrusion is a small section of Upper Eocene Urumieh- Dokhtar magmatic belt in the Central Iran tectonic zone. This intrusion is composed of two separate phases which include an acidic and intermediate- mafic units. The acidic rocks consist of monzogranite, granodiorite, quartz monzonite and quartz monzodiorite whereas the intermediate-mafic rocks comprise gabbro, diorite, quartz diorite, monzodiorite and monzonite. Mafic microgranular enclaves of dioritic, quartz dioritic, monzodioritic and quartz monzodioritic composition are common in the acidic rocks. Based on geochemical data, magma mixing along with fractional crystallization has important role in evolution of the plutonic rocks. Also, Kuh-e Dom intrusive rocks have low TiO2, P2O5 and Nb/Zr ratio which are characteristics of active continental margin. The isotopic signature of plutonic rocks is not exactly like those of mantle- or crustal-derived magma, but these rocks have some features commonly found both in the crustal and mantlic sources so that the enclaves tend to illustrate mantlic composition and the acidic rocks tend to show crustal composition, but the intermediate- mafic rocks are in the range from acidic rocks to enclaves. This result along with field and petrographical studies indicate that magma mixing/magma or mingling processes may play an important role in evolution of the intrusion. The upper mantle magma forming the microgranular enclaves, after emplacement in the crust may lead to partial melting of lower crust and because of magma mixing between crustal and mantlic melts, the mafic to intermediate rocks may form.
