نشریه پترولوژی
پیاپی 15 (پاییز 1392)

Mafic alkaline lavas in Hormack area، North of Zahedan، SE Iran، are the host of zeolites and secondary minerals. Zeolites have been formed in three forms: amygdaloidal، vein-type and as replacement of both primary phases and groundmass. Based on field، petrographic، X-Ray diffraction (XRD) and backscattered secondary electron (BSE) studies and electron microprobe analyses، the studied zeolites were identified as natrolite (the most abundant)، thomsonite (in three blocky، bladded and waxy-growth habits)، analcime (as amygdaloidal and direct alteration of glass)، mesolite and trivial stellerite. The average chemical formulae، calculated for the zeolite minerals are as follow: [Na14. 967Ca0. 331K0. 062Ba0. 025Mg0. 013] [Al15. 893Si24. 098O80]. nH2O (natrolite) [Ca6. 008Na4. 731Sr1. 208K0. 066Ba0. 035Mg0. 023] [Al18. 453Si21. 292O80]. nH2O (thomsonite) [Na18. 256Ca14. 98K0. 103Mg0. 082Ba0. 046] [Al46. 413Si72. 964O240]. nH2O (mesolite) [Na13. 755Ca0. 362K0. 262Ba0. 105Mg0. 026] [Al15. 118Si32. 732O96]. nH2O (analcime) The mean Si/Al ratios calculated for natrolite، thomsonite، mesolite and analcime are 1. 52، 1. 16، 1. 57 and 2. 17، respectively. The zeolites most probably have formed after cooling of the host lava flows and as the result of precipitation of saline، alkaline fluids along fissures and in cavities of porous lavas at low temperatures.

Kuh-e-Siah is located in the north of Gavkhuni lagoon and east of the Varzaneh (SE of Isfahan) and is a part of Urumieh-Dokhtar magmatic arc (UDMA). The volcanic rocks of this area are vesicular basalt and basaltic andesite with Late Miocene age. The most common textures of these rocks are porphyry، microlitic porphyritic، hyaloporphyric and vesicular. Plagioclase، olivine and clinopyroxene are the main rocks forming minerals of basalts. Orthopyroxene and Cr-spinel are the accessory phases. The major minerals of the basaltic andesites are plagioclase، olivine and orthopyroxene. Clinopyroxene and Cr-spinel are present as accessory minerals. The secondary minerals of all studied rocks are chlorite، calcite and magnetite. In these rocks plagioclases are labradorite and bytownite، olivines are chrysolite (mainly changed into chlorite)، orthopyroxenes are enstatite (some of them have a rim of pigeonite)، clinopyroxenes are augite and chlorites are corundophilite in composition. Olivine-spinel geothermometry yielded 1 to 10 Kbar، and the temperature varies from 914 to 1201 oC. Also، orthopyroxene thermometery presents temperature of 1248 to 1304 oC for pressures of 1 to 10 Kbar. The whole rocks geochemical data and the chemistry of minerals indicate that the studied rocks are calc-alkaline in composition and geotectonically belong to the volcanic arc setting.

The Nash''s Tertiary volcanic rocks in the Alborz Mountains in the east of Roudbar (North of Iran) show a compositional range from olivine basalt، basaltic andesite، pyroxene-andesite to andesite. From petrographical point of view، the diversity of xenoliths and xenocrysts are evidences for crustal contamination. The positive correlation of CaO/Al2O3 vs. MgO and Al2O3/CaO vs. SiO2 are signatures of differentiation of olivine and clinopyroxene in magmatic evolution. The positive correlations of K2O/P2O5 vs. SiO2 and La/Sm vs. K2O/P2O5 indicate the contamination of magma with continental crust. The incompatible elements patterns and their comparison with those of continental crust point to the contamination of volcanic rocks with lower and upper continental crust. The linear trends on Zr/Y vs. Nb/Y diagram، indicate two different sources for the studied rocks. The MORB-mantle source and the continental crust. The variations of Zr/Nb vs. Y/Nb and Rb/Y vs. Nb/Y display the crustal contamination of magmas which are derived from MORB-mantle source. Geochemical studies show that the studied rocks were originated from 15% melting of a MORB source in spinel facies in continental within-plate.

The Darreh Bagh granitoid pluton (DGP)، with middle Jurassic age (178 Ma)، located in the northwest of Aligudarz city. The pluton is mainly granodioritic composition which emplaced in metapelitic rocks of Sanandaj-Sirjan structural zone. For the first time، the emplacement mechanism of this pluton، investigated by anisotropy of magnetic susceptibility (AMS) method. Based on the present investigations، the mean magnetic susceptibility، in terms of µSI for the studied rock groups are as follow: granodiorites (257)، leucogranites (47)، high tourmaline leucogranites (148)، low tourmaline leucogranites (48)، migmatites (437)، surmicaceous enclaves (386). Considering the obtained values، the felsic part of the DGP belongs to the paramagnetic granitoids (500>km>0 in µSI) (equal to ilmenite series or S-type). Based on the magnetic parameters and their interpretations it is possible to divide DGP into the A and B domains and A1، A2 subdomains. The magnetic lineations in the subdomains oriented to the north. Whereas in the middle part of the pluton (B domain) it oriented dominantly to the east and southeast. Based on distribution patterns of magnetic lineations these domains were emplaced with a short delay compared to each other. Meanwhile، A domain was emplaced prior to B domain. With attention to distribution patterns of magnetic lineations and foliations، the principles of interpretation of magnetic parameters and regional geological characteristics، the Darreh Bagh granitoid pluton was emplaced in the form of a relatively large sill in a dextral shear zone (related to a transpression regime).

The Roud Gaz area is located 25 km southeast of Gonabad city، Khorasan Razavi province. During Middle Jurassic، shale and sandstone was regionally metamorphosed to slate، schist and quartzite. The Tertiary subvolcanic rocks are mainly monzodiorite to monzonite. These rocks are mostly altered to: argillic، carbonisation، sericitic and silicification- tourmalinisation. Mineralization in the area is mostly as vein type and controlled by fault zones which are trending NW-SE and 85º to 90º dip. The primary minerals are quartz، tourmaline، chalcopyrite، pyrite and the secondary minerals are malachite، azurite and goethite. Lithogeochemical exploration (chip composite method) revealed Cu، Sn، Pb، As (up to 10000 ppm)، Zn (up to 5527 ppm) and Au (up to 325 ppb) anomalies. The least altered rocks are chemically meta-aluminous and medium-potassium. They were formed in a subduction magmatic arc and are strongly enriched in LREE and depleted in HREE and also LILE (K، Rb، Ba، Sr and Th) enriched rather than HFSE (Ti، Nb and Ta)، all features indicate that the magma formed in subduction zone. The positive Eu anomaly، high Sr (411 to 684 ppm) and high (La/Yb) N ratio (more than 21. 55) in all the samples can be attributed to the presence of residual garnet in mantle source. Based on high Sr/Y ratio (more than 67)، Y<8 ppm، Yb<0. 61 ppm and high (La/Yb) N ratio، the parent magma is adakitic type. The magma formed as the result of medium degree of partial melting (25%) from a garnet-amphibolite source. Apparently، these rocks have been only the veins host and have no effect on mineralization. The mineralization of the area is polymetal vein type and related to reduced intrusions in deeper zone.

The Ghohroud granitoid body is located 116 km of north-west of Isfahan on the magmatic strip of Urumieh-Dokhtar belt. The body of granodiorite and tonalite with middle Miocene age intruded into the Jurassic shale and sandstones as well as the Cretaceous and Eocene limestone and marls in the north and the south of Ghohroud village caused the contact metamorphic of surrounding rocks lead to formation of skarns. On the basis of the petrographic and geochemical data the Ghohroud body is granodiorite and tonalite in nature and calc-alkaline and meta-aluminous composition which point to I-type granite forms in the tectonomagmatic environment related to continental arc.

The study area is located in the Southeast of Fariman and it is considered as a part of the central Iranian zone. According to field and petrographic studies the composition of volcanic rocks a range from basalt andesite-basalt andesite، trachyandesite to dacite with Paleocene-Eocene age. The dominant textures of the volcanic rocks are microlitic porphyric and glomeroporphyric and the major minerals are plagioclase، olivine، pyroxene، hornblende، alkali feldspar and quartz. Biotite، apatite، sphene and magnetite are as minor minerals. Microscopic studies reveal the presence of disequilibrium textures in plagioclases (eg. zoning and corrosion). The occurrence of xenolites indicates magma contamination. Based on geochemistry of major and minor elements، the studied rocks belong to calc-alkaline series with moderate to high potassium type and meta-aluminous nature. The geochemical behavior of major and trace elements reveals the normal trend of differentiation in the magma. According to geochemical data، garnet-lerzolite may be the principal source rock for the studied volcanic rocks which experienced 1 to 10% partial melting in a depth of around 90 to 100 km. Based on petrographic studies، some evidences of magmatic contamination can be distinguished which can be also supported by Nb and Ti negative anomalies and Pb positive anomaly on spider diagrams and Ce/Pb and Nb/U ratios. Enrichment in LILE and depletion of HFSE in the studied rocks as well as various petrologic diagrams point to magmatism in arc of an active continental margin.