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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]

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]

The southern Sinai Peninsula, underlain by the northernmost extension of the Arabian-Nubian Shield, exposes post-collisional calc-alkaline and alkaline granites that represent the youngest phase of late Neoproterozoic igneous activity. We report a petrographic, mineralogical and geochemical investigation of post-collisional plutons of alkaline and, in some cases, peralkaline granite. These granites intrude metamorphosed country rocks as well as syn- and post-collisional calc-alkaline granitoids. The alkaline and peralkaline granites of the southern tip of Sinai divide into three subgroups: syenogranite, alkali feldspar granite and riebeckite granite. The rocks of these subgroups essentially consist of alkali feldspar and quartz with variable amounts of plagioclase and mafic minerals. The syenogranite and alkali feldspar granite contain small amounts of calcic amphibole and biotite, often less than 3%, while the riebeckite granite is distinguished by sodic amphibole (5-10%). These plutons have geochemical signatures typical of post-collisional A-type granites and were most likely emplaced during a transition between orogenic and anorogenic settings. The parental mafic magma may be linked to lithospheric delamination and upwelling of asthenospheric mantle material. Differentiation of the underplated basaltic magma with contributions from the juvenile crust eventually yielded the post-collisional alkaline granites. Petrogenetic modelling of the studied granitic suite shows that pure fractional crystallization cannot quantitatively explain chemical variations with the observed suite, with both major oxides and several trace elements displaying trends opposite to those required by the equilibrium phase assemblage. Instead, we show that compositional variation from syenogranite through alkali feldspar granite to riebeckite granite is dominated by mixing between a low-SiO2 liquid as primitive or more primitive than the lowest-SiO2 syenogranite and an evolved, high-SiO2 liquid that might be a high-degree partial melt of lower crust. [ABSTRACT FROM AUTHOR]

Abstract: Age populations of detrital zircons in sand or sandstone preserve a reliable record of the ages of granitoid source rocks from which most of the zircon grains were ultimately derived, and this provenance signal can be used to infer sediment sources from independent knowledge of the areal distribution of granitoids of different ages provided allowance is made for sedimentary recycling of durable zircon sand grains. A compilation of 1386 whole-rock Zr analyses (ppm) from 72 North American suites of granitoid rock implies that the mean zircon fertility of different types and ages of granitoids ranges over nearly half an order of magnitude. Although Zr enters the lattices of some other igneous minerals sparingly, zircon contents of granitic rocks are inferred to vary with Zr contents. Subduction-related granitoid suites of varying ages (Archean, Paleoproterozoic, accreted peri-Gondwanan Neoproterozoic, Appalachian Paleozoic, Cordilleran Mesozoic) have a mean Zr content of 150 ppm and are assigned an arbitrary zircon fertility factor (ZFF) of 1.0. Mesoproterozoic Grenville granitoid suites associated with collisional orogeny have a mean Zr content of ~520 ppm (ZFF~3.5). Anorogenic plutons of a transcontinental Mesoproterozoic igneous belt and of Appalachian pre-Iapetan Neoproterozoic and pre-Atlantic Mesozoic rift belts have a mean Zr content of ~375 ppm (ZFF~2.5). Variations in the content of other high field strength elements (HFSE) parallel variations in Zr content. The differential zircon fertility of granitoid basement rocks should be taken into account for estimates of relative contributions of zircon populations from multiple bedrock sources to sediment of mixed provenance, and variations in ZFF suggest that subduction-related, collision-related, and anorogenic granitoid assemblages reflect different modes of crust–mantle evolution. [Copyright &y& Elsevier]

The 1·43 Ga Sherman batholith, southeastern Wyoming, USA, shows extreme A-type petrochemical characteristics compared with other Mid-Proterozoic granite batholiths of North America. It consists of: (1) the Sherman granite, a coarse-grained biotite hornblende granite that locally contains fayalite and pyroxenes; (2) the Lincoln granite, a medium-grained biotite granite; (3) a porphyritic biotite hornblende granite that probably formed by interaction of granitic and mafic magmas; and (4) iron-enriched mafic dikes and pods. The ilmenite-series, metaluminous Sherman granite exhibits extreme values of FeOt/(FeOt + MgO) and is rich in K, REE, Nb and Y. It crystallized at temperatures exceeding 900°C and a pressure of ~2·5 kbar, with water activity of 0·7 and [Delta]log fO2 of -0·1 to -0·5. The Lincoln granite, which is peraluminous and has less extreme A-type geochemical characteristics, crystallized at temperatures as low as 750°C and [Delta]log fO2 of around 0·5 units above FMQ (fayalite-magnetite-quartz). The rocks of the Sherman batholith are chemically equivalent to lavas from the Yellowstone hotspot. Like the Yellowstone magmas, the Sherman batholith probably originated by partial melting of underplated, mantle-derived mafic rocks. [ABSTRACT FROM PUBLISHER]

Abstract: This introductory article of the IGCP-510 Special Issue of Lithos presents the goals of IGCP Project 510 (A-type Granites and Related Rocks through Time), activities in the first two years (2005–2006) of the project, and plans for the years 2007–2009. The 11 research papers in this issue are based on papers presented at the inaugural meeting of IGCP-510 in conjunction with the 15th Goldschmidt Conference in Moscow, Idaho, USA in 2005. [Copyright &y& Elsevier]