72 research outputs found
Cretaceous alkaline volcanism in south Marzanabad, northern central Alborz, Iran: Geochemistry and petrogenesis.
No full textThe alkali-basalt and basaltic trachy-andesites volcanic rocks of south Marzanabad were erupted during Cretaceous in central Alborz, which is regarded as the northern part of the Alpine-Himalayan orogenic belt. Based on petrography and geochemistry, en route fractional crystallization of ascending magma was an important process in the evolution of the volcanic rocks. Geochemical characteristics imply that the south Marzanabad alkaline basaltic magma was originated from the asthenospheric mantle source, whereas the high ratios of (La/Yb)N and (Dy/Yb)N are related to the low degree of partial melting from the garnet bearing mantle source. Enrichment pattern of Nb and depletion of Rb, K and Y, are similar to the OIB pattern and intraplate alkaline magmatic rocks. The K/Nb and Zr/Nb ratios of volcanic rocks range from 62 to 588 and from 4.27 to 9 respectively, that are some higher in more evolved samples which may reflect minor crustal contamination. The isotopic ratios of Sr and Nd respectively vary from 0.70370 to 0.704387 and from 0.51266 to 0.51281 that suggest the depleted mantle as a magma source. The development of south Marzanabad volcanic rocks could be related to the presence of extensional phase, upwelling and decompressional melting of asthenospheric mantle in the rift basin which made the alkaline magmatism in Cretaceous, in northern central Alborz of Iran
Rhönite in undersaturated alkaline gabbroic rocks, Central Alborz, North Iran: petrography and mineral chemistry
No full textThe Kamarbon alkaline gabbroic intrusion crops out in Central Alborz, north Iran, along the northern margin of the Alpine-Himalayan belt. The gabbroic intrusion includes theralites at marginswhich replace with teschenites toward the center. In teschenitic rocks, the main minerals are diopside, clinopyroxene, and rhnite. In this research, the occurrence of rhnite is reported in Kamarbon teschenitic gabbros, and also its mineralogical properties, paragenesis, and source magma are investigated. Based on whole rock and microprobe analysis data, we try to clarify the formation of Kamarbon gabbro and the crystallization condition of rhnite. In teschenitic gabbros, rhnite reveals the composition (Na, Ca)(1.97)(Ti, Al-VI, Fe+3, Fe+2, Mn, Mg)(5.99)(Si, Al-IV)(6.02)O-20. On the basis of petrographical observations and mineral chemistry, we suggest that the teschenites were formed in distinctive lower pressures and temperatures than theralites, below 1.9 kbar and 1075 degrees C. Rhnite was crystallized (at the mentioned P-T condition) as a primary phase, in the late stage of crystallization at shallow depth corresponding with 6-10 km, in teschenites. Important factors of the rhnite crystallization in undersaturated magmas can be regardarded as Al and Ti enrichment and Si depletion; the same enrichment and depletion are also observed in the associated clinopyroxenes
Mesozoic alkaline plutonism: Evidence for extensional phase in Alpine-Himalayan orogenic belt in Central Alborz, north Iran
No full textThe Kamarbon Jurassic alkaline basic intrusion crops out in Central Alborz, north Iran, along the northern margin of the Alpine-Himalayan belt. The intrusion includes foid gabbros at the margins and foid monzodiorites towards the center. The foid monzodiorites are considered as the evolved melts after the fractional crystallization mostly of olivine and clinopyroxene from a foid gabbro parental magma. Based on mass balance calculation the evolution of the Kamarbon alkaline gabbro could be explained by 19.2% fractionation of clinopyroxene, 13.8% of olivine, 3% of plagioclase and 1.0% Ti-Magnetite, with 63% of residual liquid. REE inversion modeling indicates that the Kamarbon intrusion magma was generated by low degrees (<3%) of partial melting from a garnet-bearing mantle source. In primitive mantle-normalized incompatible element diagrams, the Kamarbon rocks show enrichment in LILE elements (Ba, Rb, Sr and Th), HFSE elements (Nb, Ta, Ti, Zr and Hf) and P and depletion in K, Y and HREE (Yb, Lu) which are similar to patterns of HIMU-OIBs or intraplate alkaline magmas. According to the existence of extensional phases and occurrence of different rifting during late Triassic to middle Jurassic in Central Alborz, the formation of Kamarbon intrusion could be related to an intracontinental rifting
Petrogenesis and mantle source characteristics of Triassic alkaline basaltic rocks of North Kamarbon, Northern Central Alborz, Iran
No full textThe Triassic alkaline basaltic rocks (TABR) of North Kamarbon are located in Central Alborz, which is regarded as the northern part of the Alpine-Himalayan orogenic belt. Fractional crystallization does not appear as a major process in the genesis of TABR while different degree of partial melting may be regarded as the mail process, based on petrography and geochemistry studies. The geochemical characteristics of TABR are in conflict with a substantial involvement of continental crust or crustal contamination. High (La/Yb)N and (Dy/Yb)N ratios, along with other geochemical features, in the TABR magma, suggest an asthenospheric origin, with low degree of partial melting of a garnet-bearing mantle sources. Enrichment patterns of LILE (Ba, Sr and Th), HFSE (Nb, Ta and Zr) and P, and the depletion at HREE (Yb, Lu) are similar to what observed for OIB or intraplate alkaline magmatic rocks. The Sr and Nd isotopic ratios range from 0.70448 to 0.70522 and from 0.51269 and 0.51280, respectively, suggesting time-integrated slightly depleted magma sources. The data indicate that the evolution of TABR could be related to the rifting basin, in Late Triassic, which caused their development by upwelling and decompressional melting of an asthenospheric mantle, without a major involvement of subcontinental lithospheric mantle or crustal contaminatio
Neogene ultrabasic volcanic rocks in central Urumieh-Dohktar Magmatic Arc (NW Iran): melilitites and nephelinites in subduction setting
No full textAbout 180 km SW Tehran (central-northern Iran) young (likely <1 Myr old) and small volume lava flows are emitted
from volcanic chains close to Nowbaran town. These volcanoes belong to the so-called Urumieh-Dokthar Magmatic
Arc (UDMA), running from NW to SE along the western margin of Iran. The volcanism of the UDMA is related to the
NE-ward Neotethys Ocean subduction beneath the Iranian plate since Early Cretaceous time, evolved into Arabia-Iran
continental collision during early Cenozoic. The lava flows consist of strongly ultrabasic magmas, represented by
melilitites and nephelinites. Clinopyroxene is the most abundant microphenocryst, followed by olivine, calcite and
biotite. Diopside is always twinned or shows normal zoning, and olivine is Mg-rich, with Fo content ~86. Primary
calcite largely occurs as large plagues (often including opaque minerals and diopside); Mg-rich (Mg# ~0.87) and Tirich
(TiO2 up to ~7.3 wt%) phlogopite-eastonite is also frequent. Cancrinite-sodalite group minerals are the main
groundmass foids, together with nepheline and minor Ti-magnetite.
The investigated rocks show anomalous mineral paragenesis and whole-rock chemical compositions compared to the
other Cenozoic volcanic rocks occurring in Iran. SiO2 content is extremely low (down to 36.0 wt%), with CaO reaching
contents as high as ~19.2 wt%, coupled with generally high MgO (~9.1-13.9 wt%). Alkalis range between ~2.2 and 6.2
wt%, with Na2O/K2O varying from ~0.9 to 8.5. Primitive mantle-normalized patterns show marked troughs at K, Rb
and Pb and enrichment in Nb and Ta, resembling typical HIMU-OIB compositions.
The presence of these compositions imply a carbonatitic component in the mantle source, which is uncommon in
subduction-related settings, and certainly unique within the entire Cenozoic volcanic rocks of UDMA. Experimental
petrology studies in the last decades have demonstrated that carbonated peridotite is able to produce melts characterized
by extremely low content of silica but high amount of CaO and MgO (e.g. Presnall and Gudfinnsson, 2005; Hammouda
and Keshav, 2015). It is therefore necessary to understand these peculiar rock compositions in order to constrain their
mantle source, the role of carbonates and their origin in a subduction-related setting
Quaternary Melanephelinites and Melilitites from Nowbaran (NW Urumieh-Dokhtar Magmatic Arc, Iran). Origin of ultrabasic-ultracalcic melts in a post-collisional setting
No full textThe small Quaternary volcanic district of Nowbaran (NW Iran) belongs to the Urumieh-Dokhtar Magmatic Arc, a ∼1800-km long NW–SE striking Cenozoic belt characterized by the irregular but abundant presence of subduction-related igneous products. Nowbaran rocks are characterized by absence of feldspars coupled with abundance of clinopyroxene and olivine plus nepheline, melilite and other rarer phases. All the rocks show extremely low SiO2 (35.4–41.4 wt%), very high CaO (13.1–18.3 wt%) and low Al2O3 (8.6–11.6 wt%), leading to ultracalcic compositions (i.e. CaO/Al2O3 > 1). Other less peculiar, but still noteworthy, characteristics are the high MgO (8.7–13.3 wt%) and Mg# (0.70–0.75), coupled with a variable alkali content with sodic affinity (Na2O = 1.8–5.4 wt%; K2O = 0.2–2.3 wt%) and variably high LOI (1.9–10.4 wt%; average 4.4 wt%). Measured isotopic ratios (87Sr/86Sr = 0.7052–0.7056; 143Nd/144Nd = 0.51263–0.51266; 206Pb/204Pb = 18.54–18.66; 207Pb/204Pb = 15.66–15.68; 208Pb/204Pb = 38.66–38.79) show small variations and plot within the literature field for the Cenozoic volcanic rocks of western Iran but tend to be displaced towards slightly higher 207Pb/204Pb. Primitive mantle-normalized multielemental patterns are intermediate between typical subduction-related melts and nephelinitic/melilititic melts emplaced in intraplate tectonic settings. The enrichment in Th, coupled with high Ba/Nb and La/Nb, troughs at Ti in primitive mantle-normalized patterns, radiogenic 87Sr/86Sr and positive Δ7/4 anomalies (from +15.2 to +17.0) are consistent with the presence of (old) recycled crustal lithologies in the sources.
The origin of Nowbaran magmas cannot be related to partial melting of C–H-free peridotitic mantle, nor to digestion of limestones and marls by ‘normal’ basaltic melts. Rather, we favour an origin from carbonated lithologies. Carbonated eclogite-derived melts or supercritical fluids, derived from a subducted slab, reacting with peridotite matrix, could have produced peritectic orthopyroxene- and garnet-rich metasomes at the expenses of mantle olivine and clinopyroxene. The residual melt compositions could evolve towards SiO2-undersaturated, CaO- and MgO-rich and Al2O3-poor alkaline melts. During their percolation upwards, these melts can partially freeze reacting chromatographically with portions of the upper mantle wedge, but can also mix with melts from shallower carbonated peridotite. The T–P equilibration estimates for Nowbaran magmas based on recent models on ultrabasic melt compositions are compatible with provenance from the lithosphere-asthenosphere boundary at average temperature (∼1200°C ± 50°C). Mixing of melts derived from subduction-modified mantle sources with liquids devoid of any subduction imprint, passively upwelling from slab break-off tears could generate magmas with compositions recorded in Nowbaran
A showcase of igneous processes in the Urumieh-Dokhtar Magmatic Arc: the Miocene-Quaternary collisional magmatism of the Bijar-Qorveh area, northwest Iran
No full textThe Cenozoic Arabia-Iran continental collision was associated with emplacement of a large variety of magmatic rock types. This aspect is particularly evident in the Bijar-Qorveh area of NW Iran, where Miocene andesitic to rhyolitic rocks and Quaternary basic alkaline rocks crop out. The Miocene intermediate to acid compositions show radiogenic Sr and Pb isotopic compositions (87Sr/86Sri 0.70531-0.71109, 206Pb/204Pb 18.71-19.01, 207Pb/204Pb 15.66-15.73, 208Pb/204Pb 38.76-39.14), coupled with unradiogenic Nd isotopic ratios (143Nd/144Ndi 0.51223-0.51265). These characteristics, together with primitive mantle-normalized multielemental patterns resembling “subduction-related” geochemical fingerprints, are considered ultimately derived from the Iranian plate mantle wedge, metasomatised during previous NE-directed Neothetyan Ocean subduction. The alkali-rich andesitic and dacitic rocks evidence both closed- and open-system differentiation, as typically observed for collisional settings in general. Both rock types display a high Sr/Y (37-100) and La/Yb (29-74) “adakitic” signature that it is interpreted here with plagioclase (± amphibole) accumulation or melting of local mafic crustal rocks. Open-system processes involve recycling of crustal cumulates for pyroxene-rich andesite and biotite-rich dacite varieties, and low-degree partial melting of the local crust for leuco-rhyolites.
A radical change occurred during the Quaternary, when SiO2-understaturated to SiO2-saturated poorly evolved rocks (basanites, tephrites, alkaline and subalkaline basalts) were emplaced. The complete change of mantle sources suggests a phase of local extensional tectonics related with WNW-ESE right-transcurrent faults. The major oxide, as well as incompatible trace element and Sr-Nd-Pb isotopic fingerprint of these younger rocks is more akin to that of intraplate magmas, but still bearing some evidences for a variable contribution from a “subduction-modified” mantle source. The NW-trend of increasing involvement of this subduction component, is indicative of the strong tectonic control on magmatism. Additional lithotypes indicate the presence of open-system differentiation and remelting processes in the youngest phase of magmatic activity
Correction to: Relationship Between Care Burden and Religious Beliefs Among Family Caregivers of Mentally Ill Patients
No full textThe original version of this article unfortunately contained a mistake in the author name. The co-author name should be Reza Masoudi instead of Reza Masoodi
Mineralogical evidence for regional metamorphism overprinted by contact metamorphism
No full textThe Soursat metamorphic complex (SMC) in northwestern Iran is part of the Sanandaj–Sirjan metamorphic belt. The complex is composed of different metamorphic and plutonic rocks, but is dominated by metapelites composed of garnet, staurolite, kyanite, fibrolite, cordierite, and andalusite. Porphyroblasts in schists have the same fabric, and three stages of schistosity are present. The internal schistosity (Sn) inclusion trails are also offset by conjugate sets of extensional schistosity (Sn+1) and a second (Sn+2) that crenulates (Sn+1). Polyphase metamorphisms are present in the complex. Garnet, staurolite, kyanite, and fibrolite assemblage preserves conditions during the M1 metamorphic event. This assemblage yields a P–t estimate of 645±11°C and 6.5±0.5 kbar. Other samples of the central part of SMC contain cordierite and andalusite (M2) overgrowth that yields a P–t estimate of 532±33°C and 2.1±1.1 kbar.Mahboobeh Jamshidi Badr, Fariborz Masoudi, Alan S. Collins and Ali Sorb
WEATHERING OF VOLCANIC BASIC ROCKS IN NORTH OF IRAN AND RELATED DEVELOPED SOILS
No full textThe rocks are regarded as the most important factor for developing soils in the different areas. The chemical composition and properties of the source rocks play so important role in definition the properties of the soil. The aim of this research is surveying the geochemical and mineralogical characteristics of basic volcanic rocks in the south of Marzanabad (north of Iran) and its influence on the characteristics of soils on the studied area
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