Petrology
Sakine Moradi; Muhammad Reza Ghorbani; Shao- Yang Jing
Abstract
The Kahak mafic volcanic rocks in the central part of the Urumieh-Dokhtar Magmatic Arc are composed of basalts and basaltic andesite and show sub alkaline to transitional affinity. They are calc-alkaline based on the tholeiitic index (THL). U-Pb zircon dating yields ...
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The Kahak mafic volcanic rocks in the central part of the Urumieh-Dokhtar Magmatic Arc are composed of basalts and basaltic andesite and show sub alkaline to transitional affinity. They are calc-alkaline based on the tholeiitic index (THL). U-Pb zircon dating yields almost 60 (Middle Paleocene) and 24 to 19 Ma (Late Oligocene–Early Miocene) for andesitic basalt and basaltic rocks respectively. These rocks are identified by LREE and LILE enrichment and HFSE depletion with relatively negative or without Eu anomalies and E-MORB like pattern in multiple spider diagrams that.attributed to the subduction of the Neotethyan oceanic slab beneath the central Iranian microcontinent. Based on petrography, trace and rare earth elements, and isotopic features, fractional crystallization played a significant role during magma evolution in these rocks. Trace element modeling suggests that the studied mafic rocks were derived by partial melting within the spinel lherzolite mantle. Isotopic ratios also show that they resulted from lithospheric mantle metasomatized by released fluids from subducted slab sediments. The studied samples might have formed in the extensional regime followed by slab rollback and undergone a continental arc to back-arc basin transition during the Paleocene to Miocene. This basin might have been closed in the middle Miocene.
FARHAD ZALL; Zahra Tahmasbi; ahmad ahmadi khalaji; Shao Yang Jing; Leonid Danyushevsky3; chris harris
Abstract
Several distinct morphologies of tourmaline have been identified in Mashhad biotite-muscovite granite: nodule, pegmatite, aplite, quartz-tourmaline veins, tourmaline-rich veins and radial tourmalines. The δ18O and δD values in solar tourmaline (12.4 and -69 ‰), nodule tourmaline (11.8 ...
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Several distinct morphologies of tourmaline have been identified in Mashhad biotite-muscovite granite: nodule, pegmatite, aplite, quartz-tourmaline veins, tourmaline-rich veins and radial tourmalines. The δ18O and δD values in solar tourmaline (12.4 and -69 ‰), nodule tourmaline (11.8 and -63), quartz-tourmaline vein (11.7 and -57), pegmatite tourmaline (11.62-11.67 and -59 to -73), aplite tourmaline (11.39 and -57), tourmaline-rich vein (11.82 and -62) and mica schist tourmaline (11.06 and -77) with low changes are similar together. These values show same origin for tourmalines fluid source in biotite-muscovite granite. The difference in δ18O values between quartz and tourmaline (Δqtz-tur) are positive (between+2.0 and+2.2‰), and this show quartz and tourmaline are in equilibrium. The δ18O thermometry of tourmaline - quartz minerals show a range between 492°C and 579 °C for tourmaline crystallization. The calculated δ18O, and δD values of the initial fluid in equilibrium with tourmaline suggest a magmatic and primitive magmatic water of peraluminous granite source. All tourmalines show similar δ11B values (with a narrow range between −7.4 and −10.8‰). This indicates a same boron source for them that resulting during highly evolved magmatic differentiation. Based on the 11B values of tourmalines in Mashhad fall within the range reported for granite-related tourmaline and similar to the S-type source granites that derived by Continental crust. The δ11B values of tourmalines show the δ11B values of the magma of the biotite-muscovite granite.
