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.
J Ghalamghash; S. Houshmand Manavi; M. Vousoughi Abedini
Abstract
Oshnavieh Plutonic Complex (OPC), hosted within the northernmost part of the Sanandaj- Sirjan zone, allows distinguishing three suites including diorite, granite and alkalisyenite-alkaligranite (AS-AG). Dioritic rocks formed from partial melting of enriched lithospheric mantle sources on base of minerlogical ...
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Oshnavieh Plutonic Complex (OPC), hosted within the northernmost part of the Sanandaj- Sirjan zone, allows distinguishing three suites including diorite, granite and alkalisyenite-alkaligranite (AS-AG). Dioritic rocks formed from partial melting of enriched lithospheric mantle sources on base of minerlogical and geochemistry. The granite suite is S type that formed from partial melting of metapelitic-greywacke source. The peraluminous A-type granite of AS-AG suite are generated by partial melting of quartzo-feldspatic source at high temperatures. According to the negative Nb, Ta and Ti anomaly in spider diagrams, and tectonic discrimination diagram of Rb-(Y+Nb), the diorite suite formed in active continental margin (VAG) environment. According to the diorite’s formed environment and simultaneously formed granite in 100 M.a., OPC seems to have formed by northeastward subduction of Neo-tethyan oceanic crust under the Iranian continental crust. Following intrusion and setting of mafic magma into the crust, partial melting of pelitic-greywacke, resulted from heating by intrusion of the mafic magma, produced the granitic magma. After 20 Ma the AS-AG suite formed from melting of quartzo-feldspatic rocks of lower crust, probably by heating of mafic magma and/or in relaxation period of subduction and emplaced in the continental volcanic arc.
R. Mohamadi; M.H., Emami; M. Vosoghiabedi
Abstract
The area is located about 230 km of southwest of Tehran. Based of geological observations, the plutonic rocks in the area consist of Neogene (Miocene) alkaline gabbro , gabbrodiorite, locogabbro and diabase . The Oligo - Miocene calc-alkaline extrusive rocks are dacite - ryodacite , andesite trachyandesite ...
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The area is located about 230 km of southwest of Tehran. Based of geological observations, the plutonic rocks in the area consist of Neogene (Miocene) alkaline gabbro , gabbrodiorite, locogabbro and diabase . The Oligo - Miocene calc-alkaline extrusive rocks are dacite - ryodacite , andesite trachyandesite , hornblendandesite , basaltic andesite and trachybasalt .Studing on isotopic analyses of Nd and Sr indicate that surveyed area were contaminated with crustal rocks of Sialic composition . In isotopy geochemical studies, The Andesite samples are plotted in the limit of BSE; however, it seems that mantling rocks besides being settled in crust (esp. the upper continental crust) have been contaminated with in. The combination of BSE towards enrichment, from the proportion of 87Sr/86Sr has shifted; a sample of rocks shows this position. Spider diagrams related to trace elements of plutonic samples which are used for identifying the tectonic setting show intrusives are in the extensive regime; while the lavas don’t have a steady trend and are similar to subduction zones. This shows that the intrusives of the the investigated area are different genesis from the southern volcanic rocks.
