Petrology
Niloofar Nayebi; Dariush Esmaeily; Soroush Modabberi; Ryuichi Shinjo
Abstract
Anomaly 21A, as a part of Bafq iron-apatite ore metallogenic district, is located in Central Iran, and encompasses wide spectrume of igneous, sedimentary and metamorphic rocks. The igneous rocks that show narrow geochemical variations and dominantly plot in the monzonite to monzodiorite fields, are ...
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Anomaly 21A, as a part of Bafq iron-apatite ore metallogenic district, is located in Central Iran, and encompasses wide spectrume of igneous, sedimentary and metamorphic rocks. The igneous rocks that show narrow geochemical variations and dominantly plot in the monzonite to monzodiorite fields, are plotted in the calc-alkaline and high-K calc-alkaline affinities. Geochemical data are characterized by enrichment LILE and LREE as compare to HFSE and HREE, respectively, and depletions in Nb-Ta-Ti imply the mantle-derived melts modified by subduction components. The isotopic signatures of Anomaly 21A samples, e.g., (87Sr/86Sr)i, εNd(t)=, imply the dominant mantle signature. Their initial Pb isotopic composition of study rocks are 18.87 to 20.32 for (206Pb/204Pb), 15.72 to 15.84 for (207Pb/204Pb), and 40.74 to 42.32 for (208Pb/204Pb). The isotopic modellings show less than 4% incorporation of melt-derived subducted sediment into the mantle wedge or variable degrees of contamination by upper continental crust. We suggest partial melting of a sub-arc mantle melt that has been metasomatized by slab-derived sediments and interacted with continental crust en-route the shallower surface as the premise of the geodynamic of Central Iran.
Petrology
Niloofar Nayebi; Dariush Esmaeily; Sourosh Modabberi; Ryuichi Shinjo; Reza Deevsalar; Bernd Lehmann
Abstract
Sr-Nd-Pb isotopes and whole-rock geochemical analyses were carried out on plutonic rocks of the Chadormalu district to constrain the magmatic history of the Cadomian orogeny of the northern Gondwana margin during Late Precambrian–Early Paleozoic times. Despite the similarities in the geochemical ...
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Sr-Nd-Pb isotopes and whole-rock geochemical analyses were carried out on plutonic rocks of the Chadormalu district to constrain the magmatic history of the Cadomian orogeny of the northern Gondwana margin during Late Precambrian–Early Paleozoic times. Despite the similarities in the geochemical data, i.e., calc-alkaline affinity, enrichment in large ion lithophile elements (e.g., Rb, Ba, K, and Cs), and depletion in high field strength elements, e.g., Nb, Ta, P, Ti, and rare earth element patterns, bulk rock Sr-Nd isotope data rull out the co-magmatic nature of investigated basic (gabbro) and felsic (granite) magmas. Sr-Nd isotopic data (e.g., ɛNd(t)= -3.6 to +1.8) along with rather high (207Pb/206Pb)t attest to the crust-dominant, and mantle-derived melts for the granitoids and gabbros, respectively. The investigated zircons yielded the older ages for the gabbroic samples. The extensional tectonic regime is followed by slab retreat or delamination brought flare-up of the oldest arc-related igneous rocks and interacted with Cadomian basement to form the investigated granitoid melts. The gabbroic rocks show geochemical and isotopic disruption and elevation of L-MREE/HREE ratios on the chondrite-normalized rare earth element (REE) patterns; interpreting the evidences of mantle heterogeneity and interaction with Paleoproterozoic basement.
E Mohammadi; Gh Ghorbani; H Shafaii Moghadam
Abstract
The studied volcanic rocks are situated in NW of the Sabzevar, mainly at southern domains of the Northern Sabzevar ophiolitic belt. Abundant rhyolitic domes (e.g., Sarough, Zard-Kuhi, Kuh-e-Sefid Mehr and Nahr domes) in the southern margin of the Davarzan-Sabzevar ophiolitic belt crosscut the above-mentioned ...
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The studied volcanic rocks are situated in NW of the Sabzevar, mainly at southern domains of the Northern Sabzevar ophiolitic belt. Abundant rhyolitic domes (e.g., Sarough, Zard-Kuhi, Kuh-e-Sefid Mehr and Nahr domes) in the southern margin of the Davarzan-Sabzevar ophiolitic belt crosscut the above-mentioned ophiolitic rocks. The Geochemical signatures of these volcanic rocks including enrichment in LREEs and LILEs relative to HREEs and HFSEs, depletion in TNT (Ta-Nb-Ti) elements, metaluminous to peraluminous and medium to high K-calc-alkaline characteristics, and their positions in discrimination tectonomagmatic diagrams, displayed that these rocks derived from a subduction-related environment. These adakitic domes are characterized by adakitic signatures (e.g., 69.2 wt.% < SiO2، 14.7 wt.% < Al2O3، MgO < 0.35 wt.% ، Sr > 273 ppm, enrichment in LREEs and LILEs, depletion in Y and HREE (Y < 9.7 and Yb < 0.86( and high ratio of Sr/Y > 58 and La/Yb > 12.1 and belong to high silica adakites (SiO2 ≥ 69.2 wt.%, MgO = 0.19-0.31 wt.% ، CaO+Na2O < 7.62 wt.% and Sr = 273-936). Nd-Sr-Pb isotopes characteristics of the adakitic rocks show similarities to a MORB-type and/or PREMA mantle source, highlighting that their magma (s) is originated from a depleted MORB-type mantle source associated with minor contamination with crustal materials. The geochemical and isotopes characteristics of the Sabzevar adakitic rocks display derivation from partial melting of subducted oceanic crust (garnet amphibolite) associated with subsequent fractional crystallization.
