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Showing 3 results for Geothermobarometery

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Volume 20, Issue 1 (3-2012)
Abstract

The amphibolitic xenoliths are the most aboundant xenoliths in the Markouh dacitic dome northeast of Birjand. The Markouh dacite is composed of plagioclase, quartz, green hornblende, biotite, magnetite and amphibolitic xenoliths that are contaning brown- green hornblende, plagioclase ± biotite ± quartz ± pyroxene. Determination of temperature and pressure of these rocks, based on Al content in amphibole, indicate that green hornblende of host rock  are formed in 784-804 ˚C temperature and 5-6 Kbar pressure equivalent to 20.44-23.52 Km depths and  xenoliths are formed in 777-845 ˚C temperature and 5-7.5 Kbar pressure equivalent to 20-30 Km depths. The more extensive P-T domains for amphibolitic xenoliths to host rocks show that they are formed at first stage during a regional metamorphism from ophiolitic basement in the amphibolite facies. Then with increasing of P-T in the late amphibolite and early granulite facies, green hornblende changed to brown hornblende plagioclase riching in Ca and clinopyroxene is formed. At last, the pyroxene amphibolites falling into magma where condition was suitable for the formation of green hornblende and occured at retrograde contact metamorphism. Thus brown hornblende is changed to green hornblende again. The results of microprobe analysis and microscopic evidence confirmed this matter. The plagioclases in xenoliths are the more rich in Ca to compare with the host rock.


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Volume 22, Issue 1 (4-2014)
Abstract

Zoisite and clinozoisite are coexistent in the Salmas epidote- amphibolites, NW Iran. The frequency of zoisite is higher than clinozoisite in the studied epidote- amphibolites. The pistacite content of zoisite is lower than clinozoisite. XPs in zoisite is about 6.46-10.65% while for clinozoisite it is about 16.72-18.73%. Al-Fe3+ substitution was effective to create the mineral compositional changes in the Salmas epidote group minerals. Composition of coexisting zoisite and clinozoisite is a function of pressure, temperature and whole rock composition. According to zoisite and clinozoisite phase relations and compositions, epidote- amphibolite metamorphism in the Salmas area occurred at temperature of 500±20 C and pressure of 6.5-7 Kbar conditions.


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Volume 22, Issue 4 (1-2015)
Abstract

More than 20 tonalitic to granodioritic plutons with Oligo-Miocene age had intruded the Eocene volcanic rocks, in south-east of Urumieh- Dokhtar magmatic belt, north-west of Shahre-Babak. These rocks show granoporphyritic texture and consist of phenocrysts of plagioclases (An21-An44), with normal to reverse zoning, magnesio hornblende and tshermakite and biotites. The matrix consists of fine-grained plagioclase and potash-feldspars, amphibole, biotite, quartz and opaque minerals. K-feldspars compositions vary between (Ab26.6-An0.07-Or73.4) to (Ab73.3-An15.8-Or11). Thermometry and barometry, based on Al content in amphibole, suggest that hornblendes are formed in 2-5.5Kb pressure (8.3 to 22 km depths) and 707-793˚C temperature. Results also imply that amphiboles formed at different depths and temperatures. Geochemical data suggest that the calc-alkaline plutons formed in an active continental margin.  



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