Magnetostratigraphy of the lower Triassic volcanics from deep drill SG6 in western Siberia: evidence for long-lasting Permo–Triassic volcanic activity

The deep drill hole SG6 in western Siberia (66°N, 78.5°E) penetrated 1.1  km of lower Triassic basalts, which are possibly an extension of the central Siberian Permo– Triassic flood basalt province. About 300 samples of these basalts were progressively demagnetized and measured. Principal component analysis often shows multiple magnetizations carried by haematite and magnetite. The corrected mean inclinations are +77° and −77° for the haematite component. A magnetostratigraphic scale was derived and showed a N–R–N–R–N succession. This is quite different from the Noril'sk and Taimyr typical polarity scale, R–N.
  The basalts found in the SG6 deep drill hole are slightly younger than those of central Siberia and Taimyr. They correspond to middle–upper Induan age, whereas the Noril'sk and Taimyr sections correspond to an uppermost Permian and lower Induan age. Altogether they indicate that, after a high output rate of volcanic material near the Permo–Triassic boundary, this activity slowed down drastically on the Siberian platform and Taimyr, but persisted for several million years in western Siberia.     

Uplift rates of the Loyalty Islands as determined by 230Th234U dating of raised coral terraces

Uplift rates of the Loyalty Islands (S.W. Pacific) have been determined from ${}^{230}\text{Th}{}^{234}\text{U}$ dating of raised coral terraces standing 2 to 7.5 m above sea level. The ages of the terraces on Ouvéa and Lifou correspond closely to previously documented periods of high sea levels at 120,000 and 180,000 yr BP. A +2-m terrace on Beautemps-Beaupré is considered to be beyond the range of the dating technique. The uplift rates of the various islands show a decrease toward the west. This lends support to the hypothesis of a lithospheric bulge of the leading edge of the Australian plate prior to its subduction at the level of the New Hebrides trench.     

The Néel transition and magnetic properties of terrestrial,synthetic, and lunar ilmenites

The magnetic susceptibility of a terrestrial, synthetic and lunar ilmenite specimen has been measured from 4 to 300 K. All specimens had a single Néel temperature transition which ranged from 56 to 57.7 K. In one case the powdered specimen was partially aligned in the magnetic field prior to the susceptibility measurements and the Néel transition was observed to shift to 60 K indicating magnetic anisotropy. A study of several magnetic parameters calculated from the experimental data showed gross impurities in the terrestrial specimen, single-domain to multi-domain metallic iron in the synthetic specimen, and a small amount of superparamagnetic metallic iron in the lunar sample. No multidomain iron was observed in the lunar ilmenite. The results of electron spin resonance measurements were also in general agreement with these findings. Because of the absence of Fe³⁺ compared to most terrestrial samples it is suggested that the anisotropic magnetic parameters be determined on lunar ilmenite when a large enough single crystal becomes available.     

87Rb-86Sr age of rocks from the Apollo 15 landing site and significance of internal isochrons

Internal isochrons for two Apollo 15 rocks give an age of(3.34 ± 0.09)and(3.46 ± 0.04) × 10⁹ years with an identical⁸⁷Sr/⁸⁶Sr initial ratio of 0.69928. Considering the possibility for the line obtained in a⁸⁷Sr/⁸⁶Sr,⁸⁷Rb/⁸⁶Sr diagram to be a mixing line, the significance of these results are discussed.     

From subduction to transform motion: a seabeam survey of the Hellenic trench system

Preliminary results of a multi-narrow beam survey of the Hellenic trench system, in the Eastern Mediterranean, are presented. The southwestern Ionian branch is divided in small basins, partly filled with Pleistocene sediments. The morphology suggests that the basins are deformed by a compressional stress acting roughly perpendicularly to the trench along N50°E. This direction is the direction of the regional slip vector of the shallow thrust-type earthquakes. The structure of the southeastern Pliny-Strabo branch is quite different. Narrow en-e´chelon slots, oriented N40°E, have been mapped within the main troughs oriented N60°E. The regional earthquake slip vector is also oriented along N40°E. We conclude that the Hellenic trench system is an active subduction system, dominated by thrust along the Ionian branch and by transform motion along the Pliny-Strabo branch.     

The fit of the continents around the North Atlantic Ocean

A new reassembly of the continents around the North Atlantic Ocean is presented. The first criterion used for this reassembly is the identification of the structural framework related to the opening which consists of marginal fracture zones generated by offsets of the Rift. The Africa—North America, Eurasia—Greenland, Greenland—North America and Eurasia—North America adjustments are successively discussed. It is argued that the adjustments are best made at the 3000-meters isobath between Africa and North America and at the 2000-meters isobath for the younger rifts. The difference is attributed to subsidence and modification of continental margins with time. The importance of the Late Paleozoic tectonic phase in determining the subsequent pattern of Mesozoic rifting is emphasized.     

Glacier mass balance of tropical Zongo glacier, Bolivia, comparing hydrological and glaciological methods

A glaciological program has been undertaken since 1991 on Zongo glacier in Bolivia (6000–4850 m asl, 2.4 km², 16°S). This program involves mass balance measurements, hydrological studies and energy balance investigations. On outer-tropical glaciers, melting and snow accumulation are both maximum in the wet season (austral summer), whereas the dry season (winter) is a period of low ablation. Errors on each term of the glaciological (stakes, snow-pits and integration method of the measurements) and hydrological (precipitation, discharge and runoff coefficient of free ice areas) methods are investigated to estimate the overall accuracy of the mass balance measurements. The hydrological budget is less than the glaciological one (mean difference: 60 cm w.e. per year), but both methods reproduce similar inter-annual variations. Errors in assessment of evaporation or water storage inside the glacier cannot explain the discrepancy. Errors using the glaciological method are large (around ± 40 cm w.e. per year), but no bias can explain the departure from the hydrological balance. Errors on discharge measurements are small and the uncertainty on the runoff coefficient has a minor effect on the mass balance. We concluded that hydrological budgets are too low due to the catch deficiency of rain gauges and absence of precipitation measurements at high altitudes, emphasizing the difficulty to assess snowfall distribution in high mountainous basins.     

The theory of the nutation for the rigid earth model at the second order

We perform a complete reconstruction of the series of the nutation for a rigid Earth model with the use of the very accurate theories ELP2000 and VSOP82 for the motion of the Moon and the planets respectively, in such a way that all the individual contributions up to 0.005 mas should be taken. This implies the introduction of the planetary effects, of the influence of second-order parts of the potential of the Earth (J3, triaxiality), and some improvements due to an extension of the theory at the second order. All this increase notably the number of coefficients to be taken in account, and modifies also in a significant way the value of some of them.     

The interaction between a manmade lake and groundwater: an example site in the Aurku area,Chiayi County,Taiwan

The objectives of this study are (1) to understand the subsurface hydrology in the Aurku area, Chiayi County, southern Taiwan, and (2) to determine the interaction between the manmade lake and groundwater level through the recharge produced by infiltration by on‐site investigation and laboratory sand tank simulation. The manmade lake was selected as the field site for groundwater recharge effect so as to assess the role of infiltration from the aquaculture ponds in this area. These results can be used as reference for future application of constructing a series of manmade lakes. The field experiment was performed to measure the infiltration rate of the manmade lake by using the water balance method and double‐ring infiltration test. The results demonstrated that the manmade lake had helped the recharge of the groundwater. Raising or maintaining a higher water level of the manmade lake can promote higher infiltration. When the groundwater level is equal to or higher than the bottom of the manmade lake, infiltration will slow or cease. The field experiment and laboratory sand tank simulation demonstrated that the infiltration rate increased with the higher storage depth of the manmade lake. The laboratory simulation also indicated that while the groundwater level was lower than the bottom of manmade lake (i.e. the reference level) and the initial water depth (3 cm) was equal to or greater than 50% of the full water storage depth, the infiltration depth increased with time. However, the infiltration depth would be very small or nearly zero when the groundwater level was higher than the bottom of the manmade lake. Copyright © 2006 John Wiley & Sons, Ltd.