Active fault traces along Bhuj Fault and Katrol Hill Fault, and trenching survey at Wandhay, Kachchh, Gujarat, India

Several new active fault traces were identified along Katrol Hill Fault (KHF). A new fault (named as Bhuj Fault, BF) that extends into the Bhuj Plain was also identified. These fault traces were identified based on satellite photo interpretation and field survey. Trenches were excavated to identify the paleoseismic events, pattern of faulting and the nature of deformation. New active fault traces were recognized about 1km north of the topographic boundary between the Katrol Hill and the plain area. The fault exposure along the left bank of Khari River with 10m wide shear zone in the Mesozoic rocks and showing displacement of the overlying Quaternary deposits is indicative of continued tectonic activity along the ancient fault. The E-W trending active fault traces along the KHF in the western part changes to NE-SW or ENE-WSW near Wandhay village. Trenching survey across a low scarp near Wandhay village reveals three major fault strands F1, F2, and F3. These fault strands displaced the older terrace deposits comprising Sand, Silt and Gravel units along with overlying younger deposits from units 1 to 5 made of gravel, sand and silt. Stratigraphic relationship indicates at least three large magnitude earthquakes along KHF during Late Holocene or recent historic past.     

Groundwater arsenic contamination in Manipur,one of the seven North-Eastern Hill states of India: a future danger

Manipur State, with a population of 2.29 million, is one of the seven North-Eastern Hill states in India, and is severely affected by groundwater arsenic contamination. Manipur has nine districts out of which four are in Manipur Valley where 59% of the people live on 10% of the land. These four districts are all arsenic contaminated. We analysed water samples from 628 tubewells for arsenic out of an expected total 2,014 tubewells in the Manipur Valley. Analyzed samples, 63.3%, contained >10 μg/l of arsenic, 23.2% between 10 and 50 μg/l, and 40% >50 μg/l. The percentages of contaminated wells above 10 and 50 μg/l are higher than in other arsenic affected states and countries of the Ganga–Meghna–Brahmaputra (GMB) Plain. Unlike on the GMB plains, in Manipur there is no systematic relation between arsenic concentration and the depth of tubewells. The source of arsenic in GMB Plain is sediments derived from the Himalaya and surrounding mountains. North-Eastern Hill states were formed at late phase of Himalaya orogeny, and so it will be found in the future that groundwater arsenic contamination in the valleys of other North-Eastern Hill states. Arsenic contaminated aquifers in Manipur Valley are mainly located within the Newer Alluvium. In Manipur, the high rainfall and abundant surface water resources can be exploited to avoid repeating the mass arsenic poisoning that has occurred on the GMB plains.     

滇西北藏族神山传统与持续农牧生产研究

从区域和村寨两个层次,讨论了滇西北藏族地区的神山与农牧生产的关系.藏族神山,分布广泛,形成等级体系,有佛教和原始宗教内涵.以人们定居的低洼盆地为中心,人们通过轮歇放牧获得维持基本生活的畜牧产品,同时种植粮食,采集森林产品,维持着持续的农牧生产.神山理念从精神上控制着人的行为,并渗入到农牧生产实践之中,促成了人与自然和谐相处的人居生态系统.     

Evidence for multiple Palaeoproterozoic thermal events and magmatism adjacent to the Broken Hill Pb---Zn---Ag orebody, Australia

Thermal events at 1690-1680, 1660-1640 and 1600-1570 Ma have been resolved by SHRIMP U---Pb geochronological study on zircons and monazites from seven localities near to the Broken Hill Pb---Zn---Ag orebody, Australia. The earliest-recognized thermal event included intrusion of now deformed granites such as Rasp Ridge Gneiss and Alma Gneiss and intrusion of gabbro at Round Hill. Previously these have been interpreted as volcanic in origin, and have been assigned to different stratigraphic units of the Palaeoproterozoic Willyama Supergroup. Because these rocks are intrusions, they should be removed from the Supergroup stratigraphic sequence. The 1640–1660 Ma thermal event reached upper amphibolite to granulite conditions and produced melt segregations in parts of the Rasp Ridge Gneiss. Granites of this age are the Purnamoota Road Gneiss, previously correlated with 1690-1680 Ma rocks assigned to the Hores Gneiss stratigraphic unit, and granitic veins within Sundown Group metapelites. The 1600-1570 Ma thermal event also reached upper amphibolite to granulite conditions. The only possible 1600-1570 Ma intrusive rock reported in this study is ‘Lf-leucogneiss’ (granite) at the Purnamoota Road locality. Melt segregations of this age have been found in the Round Hill gabbro and metamorphic segregations have been found in the Purnamoota Road Gneiss. The granite intrusions and segregations are absolute time markers for fabric development and therefore can be used to re-evaluate tectonothermal evolution of rocks close to the Broken Hill Pb---Zn orebody. Within the studied rocks several discrete high grade deformation phases have been observed. The earliest detected deformation is older than 1640–1660 Ma, but syn- or post 1690 Ma. A later deformation phase can be constrained to be pre-or syn 1640–1660 Ma and a yet later deformation phase to be syn- or post- 1600-1570 Ma. The current consensus classifies the Broken Hill Pb---Zn---Ag orebody as the metamorphosed equivalent of classic SEDEX (sedimentary-exhalative) deposits, deposited at ca 1690 Ma. This interpretation heavily relies on the Hores Gneiss being a volcanic marker horizon, because the orebody is situated, apparently conformably, within the Hores Gneiss. However, results of this study show that rocks assigned to the Hores Gneiss are of different age, thus do not form a reliable marker horizon. The present results suggest that in the Thackaringa and Broken Hill Groups in the vicinity of Broken Hill, true supracrustal rocks are ≥ 1690 Ma, rather than ca 1690 Ma as previously suggested. Large parts of rocks surrounding the orebody are intrusions and together with their host supracrustal rocks were metamorphosed and locally remelted at 1660-1640 and 1600-1570 Ma.     

Influence of non-linearities on the limits of stability of ships rolling in head seas

The present paper describes an investigation on parametric resonance in head seas in which a new third-order coupled mathematical model is considered. The restored modes of heave, roll and pitch are contemplated. The discussion is illustrated for the case of a transom stern fishing vessel at different speeds. It is pointed out that numerical simulations employing the new model are successfully compared to experimental results previously obtained for the vessel.Considering that analyticity is an important tool when handling complex stability issues, some theoretical dynamic characteristics of the equations are discussed. By means of the analysis of the coupled linear variational equation derived from an extended third-order model, the appearance of super-harmonics and increased rigidity proportional to wave amplitude squared due to third-order terms is demonstrated.In the present paper, an important tool is explored, that is the analysis of the limits of stability obtained from the new model. Limits of stability are a well-known and practical way of looking into the problem of parametric resonance. New limits of stability are derived and compared to the more conventional Strut diagram. Dynamic characteristics associated with the new limits of stability are discussed. The influence of different parameters is investigated, including vessel speed, damping and tuning. Consistent and revealing results are obtained through the analysis of the new limits of stability for different speeds and damping.     

Asymmetric periodic solutions of the averaged Hill problem with allowance for a planet’s oblateness

We consider asymmetric periodic solutions of the double-averaged Hill problem by taking into account oblateness of the central planet. They are generated by steady-state solutions, which are stable in the linear approximation and correspond to satellite orbits orthogonal to the line of intersection of the planet’s equatorial plane with the orbital plane of a disturbing point. For two model systems [(Sun+Moon)-Earth-satellite] and [Sun-Uranus-satellite], these periodic solutions are numerically continued from a small vicinity of the equilibrium position. The results are illustrated by projecting the solutions onto the (pericenter argument-eccentricity) and (longitude-inclination) planes.     

Large-eddy Simulations of Flow Over Forested Ridges

Large-eddy simulations (LES) of flow over a series of small forested ridges are performed, and compared with numerical simulations using a one-and-a-half order mixing length closure scheme. The qualitative and quantitative similarity between these results provides some confidence in the results of recent analytical and numerical studies of flow over forested hills using first-order mixing length schemes. Time series of model velocities at various locations within the canopy allow the application of various experimental techniques to study the turbulence in the LES. The application of conditional analysis shows that the structure of the turbulence over a forested hill is broadly similar to that over flat ground, with sweeps and ejections dominating. Differences are seen across the hill, particularly associated with regions of mean flow separation and recirculation near the summit and in the lee of the hill. Detailed comparison of derived mixing lengths from the LES with the assumed values used in mixing-length closure schemes show that the mixing length varies with location across the hill and with height in the canopy. This is consistent with previous wind-tunnel measurements, and demonstrates that a constant mixing-length assumption is not strictly valid within the canopy. Despite this, the first-order mixing-length schemes do give similar results both for the mean flow and the turbulence in such situations.     

Stratiform and stratabound tungsten mineralisation in the Broken Hill Block,N.S.W.

The Early‐Middle Proterozoic Broken Hill Block contains three types of W occurrences, which show close stratigraphic control. All three types occur within a relatively narrow stratigraphic interval (the ‘Mine Sequence’ Suite of Stevens et al., 1980) comprising a highly variable group of metamorphosed silicic and mafic volcanics, clastic sediments, and exhalative and chemical sediments containing base metals. The first type includes occurrences of W and base metals in bedded calc‐silicate rocks. In the second type, W occurs in layered to non‐layered calcsilicate rocks associated with amphibolite; these are intimately associated in a narrow stratigraphic interval containing abundant, small, Broken Hill type deposits. The third type comprises stratabound, W‐bearing pegmatites, which have been remobilised from quartz‐feldspar‐biotite gneiss and bedded quartz‐tourmaline rocks. Tungsten has been mined only from the third type and only in small quantities. The three types of tungsten deposits show a close spatial relationship with stratiform and stratabound Pb‐Zn mineralisation, including the Broken Hill type. The Pb‐Zn and W deposits are inferred to be genetically related.     

Mixed deposits of complex magmatic and phreatomagmatic volcanism: an example from Crater Hill,Auckland, New Zealand

 A series of alternating phreatomagmatic ("wet") and magmatic ("dry") basaltic pyroclastic deposits forming the Crater Hill tuff ring in New Zealand contains one unit (M1) which can only be interpreted as the products of mixing of ejecta from simultaneous wet and dry explosions at different portions of a multiple vent system. The principal characteristics of M1 are (a) rapid lateral changes in the thicknesses of, and proportions in juvenile components in individual beds, and (b) wide ranges of juvenile clast densities in every sample. M1 appears to have been associated with an elongate source of highly variable and fluctuating magma : water ratios and magma discharge rates. This contrasts with the only other documented mixed (wet and dry) basaltic pyroclastic deposits where mixing from two point sources of quite different but stable character has been inferred. Received: July 11, 1995 / Accepted: February 13, 1996     

The seismicity of the Gunning and surrounding areas, 1958–1961

Between October 1958 and August 1961, 98 tremors were located within 100 km. of Yass, New South Wales, of which 52 were in the vicinity of Gunning. Many of the epicentres appear to be closely associated with granite boundaries and with known faults in the area. The Gunning epicentres form two arms of a wedge, and activity oscillates between these arms. Temporary cessation of activity at Gunning is often accompanied by an increase in the frequency of events in the surrounding areas, which suggests that the wedge acts as a “safety valve” for the region.

Only one tremor was observed in the vicinity of Lake George. Fault plane analysis of the tremor gave a solution consistent with movement on a meridional high angle fault. It is inferred that recent movement on the Lake George Fault has been largely eliminated by the formation of the Gunning wedge.