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- Singh, S., et al.
(författare)
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2.0 Ga Granite of the Lower Package of the Higher Himalayan Crystallines, Maglad Khad, Sutlej Valley, Himachal Pradesh
- 2006
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Ingår i: Journal of the Geological Society of India. - 0016-7622 .- 0974-6889. ; 67:3, s. 295-300
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Tidskriftsartikel (refereegranskat)abstract
- Along the Sutlej valley, the lower package of the Higher Himalayan Crystallines (HHC) exposes a small concordant to discordant intrusive grey granite-The Maglad Khad Granite, within garnet mica schist/banded gneiss of the Jeori Formation. This body is fine grained and foliated along the margins, whereas the central part is relatively undeformed. This body along with aplites and pegmatites intrudes the country rock during early to syn-D-1 deformation. This is later affected by the most pervasive D-2-deformation producing gneissosity within the granite. U-Pb dating of zircons by conventional isotopic dilution technique yield an upper intercept age of 2068 +/- 5 Ma (2 sigma) from 6 zircon-fractions with MSWD=0.93, constraining the age of crystallization in the basal parts of the HHC during Early Proterozoic as well as the constraining pre-Himalayan fabric development.
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- Hode Vuorinen, Jaana, 1974-
(författare)
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The Alnö alkaline and carbonatitic complex, east central Sweden - a petrogenetic study
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Alnö complex on the central Swedish east coast is composed of a main composite intrusion (the main intrusion) and four smaller satellite intrusions (Söråker, Sälskär, Långharsholmen and Båräng) distributed around the main intrusion on Alnö Island and on the mainland north of the island. The major rock types exposed within the complex are melilitolite, pyroxenite, ijolite series (melteigite-ijolite-urtite), nepheline syenite, carbonatite and alnöite dykes. Melilitolite is only exposed within the Söråker intrusion. The intrusive sequence is melilitolite → pyroxenite → ijolite series → nepheline syenite → carbonatite → alnöite.Mineralogical, whole rock geochemical and radiogenic isotope (Nd-Sr-Pb) studies of exposed rocks from the Alnö alkaline complex, east central Sweden, were performed in order to investigate the genetic relationships between the diverse rock-types, and to evaluate the contributions from mantle and crustal components in the genesis of the complex. Most analysed samples fall within the depleted quadrant in a eNd-eSr diagram, similar to carbonatites and alkaline silicate rocks from other complexes, indicating derivation of parental magma(s) from a source that had experienced time-integrated depletion in LIL elements. Contamination by local crust is indicated by Sr and Pb isotope data, but is geographically restricted to samples collected from the outer parts of the main intrusion and from satellite intrusions. This localized contamination is attributed to selective hydrothermal element leaching of surrounding bedrock during fenitization. Nd- and Sr-isotope data separates the carbonatites into two groups (group I and II), each related to a specific set of silicate rock types. The overlap of group II carbonatites with ijolite and nepheline syenite could indicate a common origin through liquid immiscibility but this hypothesis cannot be confirmed by trace element data because initial concentrations are obscured by fractionation processes. Interestingly, results from AFC-modelling suggest that production of ijolite residual magma requires addition of a small volume (2.4 %) of carbonatite component to the parental magma, whereas formation of nepheline syenite residuals requires removal of an almost equal amount of carbonatite (1.5 %) to yield a statistically significant result. AFC-modelling further suggests that the various silicate rock types exposed within the complex are related to the same parental olivine-melilitite magma through crystal fractionation of olivine, melilite, clinopyroxene, nepheline, Ti-andradite and minor phases. These results agree with compositional trends exhibited by clinopyroxene and Ti-andradite from the silicate rocks of the main intrusion, which suggests co-genesis of pyroxenite, ijolite series rocks and nepheline syenite. Production of ijolite-like residual liquids can be achieved by <40% fractionation whereas production of nepheline syenite residuals requires >80% fractionation.An investigation of the origin of silicate minerals in carbonatites suggest that most silicate minerals observed in the carbonatites on Alnö Island are derived from surrounding wall-rock and/or produced through corrosive interaction between carbonatite liquid and assimilated phases. This leads to ambiguities when addressing the possible genetic link between carbonatites and associated silicate rocks as occurrences of identical “liquidus” phases in inferred immiscible liquids may not actually be such.
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- Sultan, Lena, et al.
(författare)
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Proterozoic and Archaean ages of detrital zircon from the Palaeoproterozoic Västervik Basin, SE Sweden: Implications for provenance and timing of deposition
- 2005
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Ingår i: Gff. - 1103-5897. ; 127:Part 1, s. 17-24
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Tidskriftsartikel (refereegranskat)abstract
- Ages of detrital zircons, derived from Palaeoproterozoic metasedimentary rocks from Finland and Sweden are poorly represented in the presently exposed crust in the Baltic Shield. This study reports U-Pb ages of detrital zircons from the Svecofennian Vastervik Basin. 41 spots from 31 zircon crystals were dated using U-Pb geochronology at the NORDSIM ion microprobe in Stockholm. Most analyses are concordant and the zircon grains commonly display well-developed magmatic oscillatory zoning. The ages documented are: &SIM; 3.64 Ga, 3.03-2.95 Ga, 2.72-2.69 Ga, 2.12-1.87 Ga and 1.84 Ga. 75% of the grains are Palaeoproterozoic and 25% are Archaean. Ages gained from Proterozoic metasediments in Sweden, Finland, Svalbard, Greenland and Great Britain also report a large proportion of &SIM; 2.1-1.9 Ga and a smaller proportion of Archaean zircons with ages around 2.7 and 3 Ga. These age groups probably represent major crust forming events. The here presented results provide an estimate of the time of deposition in the Vastervik Basin for the time interval of 1882-1850 Ma, constrained by two concordant zircon analyses of 1872 &PLUSMN; 24 and 1870 &PLUSMN; 12 Ma, and the newly presented 1859 &PLUSMN; 9 Ma age for the Loftahammar granite that intrudes the metasedimentary succession in the north. The young detrital zircon age of 1837 &PLUSMN; 22 Ma might suggest that parts of the basin may be younger. As input of detrital grains may occur from several sources simultaneously (e.g. by rivers and by tidal currents from a marine source), the detrital grains were sampled from different depositional environments. Main fluvial sediment transport in the Vastervik Basin was from present north whereas the tidal sediment transport was from the present south. The age groups documented in the Vastervik Basin are poorly represented in the presently exposed crust in the Baltic Shield, but are represented in Sarmatia.
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