The Astaneh granitoid massif is located about 40 km to Arak city, central Iran, is a part of Sanandaj-Sirjan structural Zone. These intrusive rocks which are mainly composed of grnodioritic rocks, widely affected under hydrothermal alteration. The alteration zones, on the basis of field studies and mineralogy as well as the study of the REE behavior, are investigated in this paper. Eight alteration zones including phyllic (sericitic) with quartz, sericite and pyrite; chloritic with quartz, sericite and chlorite; propylitic with chlorite, epidot, calcite and albite; argillic with clay minerals (chlorite and illite); silicic with abundant quartz; albitic with albite, chlorite and quartz; hematitisation with hematite, Fe-carbonates (ankerite and siderite) and tourmalinisation with tourmaline (dravite) are identified. The results demonstrate notable differences in the REE behavior in the different alteration zones. Accordingly, comparison with the fresh rocks, in the phyllic (sericitic) alteration, LREE are enriched, but HREE, except Yb which enriched, unchanged. Also in chloritic alteration zone, LREEs are depleted, but HREEs represent different behaviors. In the argillic and propylitic alteration zones, all REE are depleted, but compared with HREE, the LREE represent more depletion. In the silicic and hematitisation alteration zones, compared with HREE, the LREE are enriched. Finally, in the albitic and tourmalinisation alteration zones all REE are depleted. These features indicate that the behavior of REE in the hydrothermal alteration zones of the Astaneh granitoid rocks is mainly controlled by PH, availability of complexing ions in the fluid as well as the presence of secondary phases as host REE minerals.
Abstract The Zargoli granite, which extends in a northeast–southwest direction, intrudes into the Eocene–Oligocene regional metamorphic flysch‐type sediments in the northwest of Zahedan. This pluton, based on modal and geochemical classification, is composed of biotite granite and biotite granodiorite, was contaminated by country rocks during its emplacement, and is slightly changed to more aluminous. The SiO 2 content of these rocks range from 62.4 to 66 wt% with an alumina saturation index of Shand [molar Al 2 O 3 /(CaO + Na 2 O + K 2 O)] ∼ 1.1. Most of its chemical variations could be explained by fractionation or heterogeneous distribution of biotite. The features of the rocks resemble those which are typical to post‐collisional granitoids. Chondrite‐normalized rare‐earth element patterns of these rocks are fractionated at (La/Lu) N = 2.25–11.82 with a pronounced negative Eu anomaly (Eu/Eu* = 3.25–5.26). Zircon saturation thermometry provides a good estimation of magma temperatures (767.4–789.3°C) for zircon crystallization. These characteristics together with the moderate Mg# [100Mg/(Mg + Fe)] values (44–55), Fe + Mg + Ti (millications) = 130–175, and Al–(Na + K + 2Ca) (millications) = 5–50 may suggest that these rocks have been derived from the dehydration partial melting of quartz–feldspathic meta‐igneous lower crust.
Abstract The Khalkhab–Neshveh (KN) pluton is a part of Urumieh–Dokhtar Magmatic Arc and was intruded into a covering of basalt and andesite of Eocene to early Miocene age. It is a medium to high‐K, metaluminous and I‐type pluton ranging in composition from quartz monzogabbro, through quartz monzodiorite, granodiorite, and granite. The KN rocks show subtle differentiation trends strongly controlled by clinopyroxene, plagioclase, hornblende, apatite, and titanite, where most major elements (except K 2 O) are negatively correlated with SiO 2 ; and Al 2 O 3 , Na 2 O, Sr, Eu, and Y define curvilinear trends. Considering three processes of magmatic differentiation including mixing and/or mingling between basaltic and dacitic magmas, gravitational fractional crystallization and in situ crystallization revealed that the latter is the most likely process for the evolution of KN magma. This is supported by the occurrence of all rock types at the same level, the lack of mafic enclaves in the granitoid rocks, the curvilinear trends of Na 2 O, Sr, and Eu, and the constant ratios of ( 87 Sr/ 86 Sr) i from quartz monzodiorite to granite (0.70475 and 0.70471, respectively). In situ crystallization took place via accumulation of plagioclase and clinopyroxene phenocrysts and concentration of these phases in the quartz monzogabbro and quartz monzodiorite at the margins of the intrusion at T ≥ 1050°C, and by filter pressing and fractionation of hornblende, plagioclase, and later biotite in the granitoids at T = ∼880°C.
Biotite samples from different units of Boroujerd Granitoid Complex (BGC) of the Sanandaj-Sirjan Zone, western Iran, have beenanalyzed by electron microprobe for major elements. Biotite analyses from three units of quartzdiorite, granodiorite and monzograniteof BGC have their own distinct non-overlapping compositional fields in the annite – siderophyllite – phlogopite – eastonitequadrilateral (ASPE), reflecting their host rock compositions. Biotite from each rock unit has an increasing trend of Al contents atalmost fixed Fe/(Fe+Mg) values. In quartzdiorite it shows an approximately constant range of Fe/(Fe+Mg) with a low to moderate Alcontent from 2.5 to 3 atoms per formula unit (apfu). Biotite from granodiorite exhibits a fairly wide range of Al values reaching up to3.32 apfu, at Fe/(Fe+Mg) from 0.6 to 0.7, whereas biotite from monzogranite have a relatively narrow range of Fe/(Fe+Mg) and totalAl values of limited range of 3.1 to 3.3 apfu. Biotite compositions from these two latter units considered to be derived entirely fromcrustal material, characterized by a remarkable increase in total Al at relatively high Fe contents. Biotite samples of quartzdioritesdefine a distinct and non-overlapping trend from those of granidiorites and monzogranites and hence interpreted to be derived from aparental magma with different composition. Calculation of log(XMg/XFe) ranges from -0.09 to -0.02 and most of samples fromquartzdiorite fall within weakly and moderately contaminated I-type field of log(XF/XOH) versus log(XMg/XFe) diagram, whereasthe other two units, containing biotites with log(XMg/ XFe)< -0.21, classified as strongly contaminated reduced I-type. Oxygenfugacity (log ƒO2) of -15.4 to -17.5 bars and ƒH2O of 200 to 560 bars were calculated for quartzdiorite. Likewise, log (ƒO2) of –17.66bars and water fugacity (ƒH2O) of 400 and 700 bars were also calculated for granodiorite and monzogranites respectively. In theFeO*–MgO–Al2O3 biotite discrimination diagram, biotite compositions from BGC are distributed between the calc-alkaline andperaluminous fields, i.e., biotite from the qaurtzdioritic rocks fall principally in the calc-alkaline field, whereas those from thegranodioritic and monzogranitic units plot almost exclusively in the peraluminous field consistent with their host rock nature
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