Timing of Late Neoproterozoic glaciation on Baltica constrained by detrital zircon geochronology in the Hedmark Group, south-east Norway

The Moelv Tillite is the Late Neoproterozoic Varanger glacial deposit recorded in the Hedmark Group, SE Norway. Paired U–Pb and Lu–Hf data collected on detrital zircons in the Rendalen Formation underlying the Moelv Tillite have identified an uncommon 677 ± 15 to 620 ± 14 Ma population, that constrain the deposition of the Moelv Tillite to be younger than 620 ± 14 Ma. The youngest detrital zircons may be derived from granite magmatism related to the 616 ± 3 Ma Egersund dolerite magmatism, situated in the western part of the Sveconorwegian orogen. The Moelv Tillite, which is not overlain by a cap carbonate, possibly correlates with the c. 580 Ma Squantum-Gaskiers glacial deposits of Avalonia. Available palaeomagnetic data for the Late Neoproterozoic suggest that Baltica was located at intermediate to high latitude between 620 and 555 Ma.     

Crustal zircons and mantle sulfides: Archean to Triassic events in the lithosphere beneath south-eastern Sicily

Three types of zircon coexist in an unusual lower crustal xenolith from the Valle Guffari diatreme (Hyblean Plateau, Sicily): igneous Type 1 (near-euhedral, weakly zoned; Ce/Ce > 1); partially recrystallised Type 2 (ovoid, structureless; weak Ce anomaly); hydrothermal Type 3 (sugary, spongy-textured, probably related to F-rich aqueous fluids). U–Pb dating by LAM-ICPMS, supported by in situ Hf-isotope analysis, suggests that both Type 1 and Type 2 zircons were originally Archean (ca 2.7 Ga), though many of these grains have experienced severe Pb loss. The U–Pb ages of the hydrothermal zircons cluster around 246 Ma, interpreted as the timing of the hydrothermal event. Their ε_Hf (+ 8.5 to − 1.2) indicates the mixing of old crustal components and material from a juvenile source.

In situ Os-isotope analyses of sulfides hosted in peridotite xenoliths from Valle Guffari show Paleoproterozoic–Archean T_RD minimum ages, corresponding to the age of the oldest zircon grains in the crustal xenolith. Other peaks of T_RD ages suggest that multiple metasomatic events have affected the lithospheric mantle.

These observations suggest that the lower crust and the upper part of the lithospheric mantle beneath the Hyblean Plateau represent the northernmost portion of the African Plate. These two units have coexisted since at least late Archean time, and have remained linked through several episodes of crustal modification, including the Permo-Triassic hydrothermal event, which was probably related to the onset of rifting in the Ionian Basin.     

Discussion of “Geology and diamond distribution of the 140/141 kimberlite, Fort à la Corne, central Saskatchewan, Canada”, by A. Berryman, B.H. Scott-Smith and B.C. Jellicoe (Lithos v. 76, p. 99–114)

A wide variety of geological data and geological observations by numerous geoscientists do not support a two-stage crater excavation and in-fill model, or a champagne glass-shaped geometry for the 169 or 140/141 kimberlite bodies in the Fort à la Corne kimberlite field, Saskatchewan as described by Berryman, A., Scott Smith, B.H., Jellicoe, B., (2004). Rather, these kimberlite bodies are best described as polygenetic kimberlite tephra cones and tuff rings with associated feeder vents of variable geometry as shown by previous workers for the 169 kimberlite, the 140/141 kimberlite and the Star kimberlite. The domal tephra cone geometry is preserved due to burial by conformable Cretaceous marine mudstones and siltstones and is not an artifact of Quaternary glacial processes.     

Origin and evolution of topaz-bearing granites from the Nanling Range, South China: a geochemical and Sr–Nd–Hf isotopic study

Summary The F-rich Hongshan pluton in the eastern Nanling Range, southern China, is a topaz-bearing albite leucogranite. It is distinctive from other topaz-bearing felsic rocks in South China with respect to age, size, geochemical evolution and topaz mode and morphology. The Hongshan granites are highly peraluminous and characterized by high K₂O/Na₂O, Si, Rb, Cs, Nb, Ta and F, and low Ca, Ba, Sr, Zr, Hf, P, K/Rb, Zr/Hf and Eu/Eu^*. The granites show significant trace-element variations with magma evolution, with increasing Rb, Cs, Nb, Ta, Sn, W and decreasing Sr, Ba, Zr, Hf, Y, REE, Pb, Th, K/Rb, Zr/Hf, Th/U and Eu/Eu^*. These changes dominantly reflect fractional crystallization of plagioclase, biotite and accessory minerals such as zircon and monazite. The granites also exhibit a decrease in ɛNd(t = 225 Ma) from −7.9 to −11.7 with magma evolution. Modeling shows that the Nd isotopic variation could result from assimilation of the Taoxi Group wall rocks during fractional crystallization. The Hongshan pluton also shows spatial geochemical variations; the most evolved parts are located in the southeastern part of the pluton, which would be the most likely target area for rare-metal mineralization commonly associated with other topaz-bearing granites. Zircon grains from two rock types in the Hongshan body were analyzed in situ for U–Pb ages and Hf isotopic values. The concordant zircon grains mostly range from 218 to 230 Ma with an average of 224.6 ± 2.3 Ma (Indosinian). Some zircons with different internal structures and Hf isotope compositions, as well as monazite fragments, yield U–Pb ages of ca. 280 to 240 Ma, suggesting older thermal events in the studied area. The ɛHf(t) of these older zircons is strongly negative (−12.3), implying a crustal source with a Paleoproterozoic model age, similar to that for the Proterozoic Zhoutan Group. The main (∼225 Ma) zircon population exhibits less negative ɛHf(t) (−3.0 to −7.6) and Mesoproterozoic model ages, suggesting that the original magma of the Hongshan granite was generated from deeper Mesoproterozoic crust.     

Natural hazard impacts in small island developing states: A review of current knowledge and future research needs

Small island developing states (or SIDS) are exposed to a large number of natural hazards and many characteristics of small island developing states make them particularly vulnerable to the impacts of natural hazards. In spite of this acknowledged vulnerability, there are relatively few studies which focus on the impacts of natural hazards in these countries. This paper presents a review of our current state of knowledge of impacts in small island developing states and highlights a number of research needs. Central to these is the need to integrate natural hazards research within a sustainable development context and the need to exploit existing procedures such as government coordinated disaster impact assessments to generate a detailed understanding of natural hazards impacts.     

Contrasting Peridotite Types in the Dabie UHP Belt, Eastern China: the Raobazhai and Bixiling Ultramafic-mafic Complex

The Dabie UHP metamorphic belt, central China,contains two contrasting types of mafic-ultramafic complex. The Bixiling peridotite in the southern Dabie terrane contains abundant garnet (21.1-32.2 vol% )and thus has high CaO + Al2O3 (9.81-15.9 wt% ).     

Spectroscopic binaries near the north Galactic pole paper 24: HD 106104, 109281, 109463 and 110743

The four stars treated in this paper have been under observation with photoelectric radial-velocity spectrometers for many years. They have proved to be binaries with periods of 30, 1828, 1514 and 822 days respectively; the orbits are of modest eccentricity apart from that of HD 110743 which is indistinguishable from a circle. The mass functions are small, and no companion has been observed for any of the stars. HD 110743, a K dwarf, is much the nearest of the four, and its orbit is of short enough period for the photocentric motion to have been recognized byHipparcos. An eleventh-magnitude star rather more than 1≈ away from HD 106104 is shown to be a genuine physical companion, with practically identical radial velocity, proper motion and distance modulus, although the projected separation is about 13,000 AU.     

Measurement of stratospheric aerosol on Saturn using an eclipse of Titan

An eclipse of Titan by Saturn was observed on December 20, 1979, to measure the aerosol content in the atmosphere of Saturn. The measurements were made with the 74-in. telescope of the Helwan Observatory, Egypt, in the bandpass 6300–7300 Å and extend to ～5 magnitudes of eclipse darkening. The faint portion of the lightcurve unambiguously requires the presence of aerosol in the lower stratosphere of Saturn. The aerosol extends to at least 20 km above the tropopause and has a one-way stratospheric vertical optical depth of 0.4_?0.02^+0.04 at 6700 Å. The results apply to the sunset terminator at a cronographic latitude of 23°S.     

A spectroscopic orbit for HD 115968

Photoelectric radial-velocity measurements show that the eighth-magnitude star HD 115968 is a spectroscopic binary with a period of 16.195 days. The star has a large proper motion, and is unlikely to have the luminosity corresponding to the spectral type of G8 III favoured by Zaitseva. It is most probably a late-G dwarf.