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Vast and geochemically diverse volcanic rocks from the western Alborz Magmatic Assemblage (AMA) represent the back-arc of the central Iran Neotethyan arc (Urumieh–Dokhtar Magmatic Assemblage; UDMA). Volcanic rocks of the west AMA record valuable information on the timing, source region(s) and geodynamic setting of magmatism. Over 30 days of field study and sampling, investigation of 170 thin sections, 30 whole-rock geochemical analyses, 13 whole-rock Sr–Nd isotopic ratios and U–Pb age dating of zircon separates from 7 samples furnished the present study data. Eocene (38.5 Ma) OIB-type volcanic rocks from South Kaleybar indicate an anorogenic (extensional) setting. This lithospheric-scale extensional event induced influx of asthenospheric mantle into the sub-arc wedge, of which the partial melts differentiated to produce OIB-type melts. The OIB-type melts incorporated some inherited zircons in their ascent through the Cadomian crust. A continued extensional regime led to asthenospheric upwelling and produced mafic melts that produced 27.5-Ma-old subalkaline series volcanics. The LILE-depleted signature of the South Kaleybar subalkaline volcanic rocks implies that their mantle source region experienced previous partial melting event(s), probably during OIB-type magmatism in the Eocene. Alkaline volcanism (24.4 Ma) and concurrent high-silica adakitic volcanism (24.3 Ma–23.4 Ma) followed subalkaline magmatism. The alkaline rock signature in the study area range from 'Nb–Ta depleted' to 'plume-type'. This is consistent with lithosphere–asthenosphere interaction in an arc-related setting. Simultaneous partial melts of delaminated lower crustal rocks reacted with the asthenosphere and produced adakitic melts. Asthenospheric, lithospheric and crustal contribution to the magmatism in South Kaleybar express the back-arc signature of magmatism in Eocene to Late Oligocene times. [ABSTRACT FROM AUTHOR]

This paper discusses the petrological and geochemical characteristics of the acid plutonic rocks (mainly granites of different colors) exposed in Khanak and Devsar areas of Neoproterozoic Malani Igneous Suite (MIS) to understand their magmatic evolution processes, petrogenetic history and tectonic regimes. Petrographically, granites of both areas show porphyritic, hypidiomorphic, granophyric, perthitic and micro-granophyric textures. Geochemically, these acidic rocks having peraluminous nature are enriched in SiO2, Na2O + K2O, Fe/Mg, Rb, Zr, Y, Th, U, REE and depleted in MgO, CaO, Sr, P, Ti, Ni, Cr, V & Eu abundances, which have affinity with A-type granites in extensional environment. The enrichment of trace elements and negative anomalies of Sr, Eu, P & Eu in the multi-element spider diagrams suggest that the emplacement of these granites were controlled by fractional crystallization and crustal contamination of protolith magma. Elemental geochemistry also attests that they are of rare-metal bearing with high heat production (HHP) nature and represent a genetically related post-collisional A2-type granitic intrusions. Petrogenetic modeling (batch melt related) suggests that the early phase (grey and grayish green colored granites) might have been generated from a gabbroic source by partial melting (5%) leaving a residue with 25% alkali feldspar, 20% quartz, 35% plagioclase, 10% biotite, 8% hornblende, 1% orthopyroxene and 1% clinopyroxene whereas late phase (pink colored granites) might have been generated from a metavolcanic source by partial melting of 2% leaving a residue with 30% alkali feldspar, 15% quartz, 45% plagioclase, 2% biotite, 2% hornblende, 3% orthopyroxene and 3% clinopyroxene. Hence, the petrology and geochemistry of these acid plutonic rocks are consistent with their formation in a plume related rift-magmatic tectonic setting and exhibit complex post magmatic chemical variations. [ABSTRACT FROM AUTHOR]

This paper reports new mineral and whole-rock geochemical data on the acid volcano-plutonic rocks of the Tusham Ring Complex (TRC) from the Neoproterozoic Malani Igneous Suite (MIS), northwestern Peninsular India and discusses their magmatic evolution, tectonic implication, and geodynamic history. Geochemically, the investigated rocks have the characteristics of hypersolvus, high-K calc-alkaline to shoshonitic, peraluminous and A-type granitoids and they are enriched in SiO2, (Na2O + K2O), Fe/ Mg, Ga/Al, Th, U, REE (except Eu), LILE + HFSE, halogens (F and Cl) and depleted in CaO, MgO, Sr, Cr, Ni, P, Ti and Eu abundances. They also show high heat production (HHP) affinity and high mineralization potential. The high abundances of fluorine (0.80–7.11 wt %) and chlorine (0.44–1.56 wt %) in biotite and the geochemistry of the studied rock types indicate that the acid volcanics and granite massifs of TRC were derived from a halogen-enriched magmatic source under low degree partial melting of crustal protolith. The field, petrography, mineral chemistry, whole-rock geochemistry of the rocks under study, in combination with their tectonic and petrogenetic signatures have proposed that the rift-related Neoproterozoic magmatism of MIS has close linkage with geodynamic evolution of Nagarparkar, Seychelles and Madagascar A-type granitoids during Rodinia breakup. [ABSTRACT FROM AUTHOR]

The present study is carried out to probe geodynamic evolution and tectonic history of A-type granitoids from the Riwasa and Nigana areas in the Tusham Ring Complex (TRC), western Peninsular India on the basis of petrological and geochemical aspects. The investigated rocks have the characteristics of hypersolvus, calc-alkaline, peraluminous and A-type granitoids. They are enriched in SiO2, Na2O+K2O, Fe/Mg, Th, U, REE (except Eu), LILE+HFSE, elevated in Fe/Mg, Ga/Al, Th/U, A/CNK ratios, and depleted in CaO, MgO, Sr, Cr, Ni, P, and Ti, and having Eu abundances. They also show high heat production (HHP) affinity and high mineralization potential. Elemental geochemistry in conjunction with mineralogical variants attested that they were formed by limited fractional crystallization of a parental magma derived from partial melting of crustal protolith accreted during the Neoproterozoic magmatic event. Physicochemical features i.e. F and Cl-rich biotite, pegmatite rim, substantial model content of albite, high mineralized veins and altered mineralogy indicate rock-fluid interactions which are caused by magmatic origin or secondary metasomatic alteration superimposed on the host rock. The magmatism occurred in the TRC is interpreted to represent the Malani Igneous Suite (MIS) and their linkage with Rodinia Supercontinent and Pan-African thermal event. [ABSTRACT FROM AUTHOR]