Temperature conditions in soils as an ecological factor of ecosystem evolution

Criteria of ecological estimation of temperature conditions for functioning of land ecosystems are examined in this work. It has been shown that soil climate has a key influence on the spatial distribution of phytocenosises of the East European Plain. To characterize the temperature regime of soils, it is proposed, together with active temperatures (>10°C), to use ecologically sufficient (5–10°C) and ecologically optimal (10–22°C) temperatures. Some parameters concerning the different depths of the root layer (20 cm, 40 cm, 80 cm, 160 cm, and 320 cm) are proposed for use as the criteria of ecological estimation of the temperature regime. On the basis of the mentioned criteria, the main regularities of the temperature regime of East European Plain soils have been examined.     

Double transformation at the eastern border of the EU: the case of the Euroregion pro Europa Viadrina

One of the major means to foster European integration is the establishment of border spanning regions (‘Euroregions’). This is particularly important on the Eastern borders of the EU, e.g. in Eastern Germany. There, however, a double transformation to post-socialist society is taking place, both inside and outside the EU. Tensions arise between objectives on local and higher political levels, intensified by totally different economic structures and access to EU funds on both sides of the border. This is particularly true for the case of the emerging Euroregion Viadrina. Problems in preserving old industrialised localities in East Germany (e.g. steel) and attempts to resurrect the urban fair place Frankfurt/Oder, clash with transition in agriculture and consumer industries and with new concepts in tourism development and environmental protection in the Polish border zone. In region building, political, economic and ideological goals compete with each other. Local initiatives and higher political governance may both support and hamper each other. The same holds true for the interdependence of cultural integration and economic development. The paper concludes that regional economic development can only be expected if, via the building of the Euroregion, the interplay of these factors leads to compromise and harmonization between the different parties involved. This revised version was published online in August 2006 with corrections to the Cover Date.     

The binational cities of Dover and Calais and their region

This paper analyses the question of cities that are localised at each part of an international border. We take as an example the two cities of Dover and Calais and look at if they can be considered as binational cities, because they have been recently connected by a tunnel, the ‘fixed link’, and because since 1993, the inner state borders of the European Union have disappeared. It determines firstly if these two towns have been brought closer by the construction of the Channel tunnel and if specific ties are linking these two towns. The article scrutinizes actions taken under INTERREG funds under the general framework of the creation of the ‘Transmanche Region’ and its extension towards a Euroregion to sort out these two cities joint involvement. Finally, it checks if this new area could lead to cross-border activity either for work or tourism and leisure purposes that could conduct the cities of Dover and Calais toward a new type of relationship, premises of a binational city. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characteristics of post-socialist urban transformation in East Central Europe

The development of the post-socialist city has already been characterised by substantial restructuring processes. Particular emphasis should be drawn to the take-off of the tertiary sector and the comprehensive blight phenomena in the previously industrial areas. The urban housing sector has witnessed increasing housing affordability problems, a marginalisation of communal housing stock, an increase of segregation and an intensification of the decay in the old housing stock. In all East Central European states the spatial development processes of industry and services within the cities basically show clear parallels to the pattern of urban development in continental Europe. In Hungary housing policy, tenure structure and the level of segregation already show relatively closer similarities to the neoliberal, Anglo–American pattern of development. The other ECE states show closer similarities to the corporatist welfare states of continental Europe. As far as medium-term urban development in East Central Europe is concerned, it is to be assumed that – regardless of the specific path of further development – overall solutions shall not be found for the fundamental problems which are the legacy of the socialist era – the decay of old housing stock, large scale derelict industrial areas and the extent and deficiencies of high-rise housing estates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Age paradoxes of Devonian magmatism of the northeastern part of the Kola Peninsula

A structural-geochemical study has been conducted on the dikes of presumably Devonian mafic rocks confined to a small graben filled in with Riphean sedimentary rocks hosted by Early Precambrian granite-gneiss of the Murmansk block. It has been demonstrated that the dolerite dikes of this region can be considered as manifestations of trap magmatism whose products fill in the foundation of the East Barents riftogenic downfold. In turn, manifestations of alkaline and kimberlite rocks of the White Sea region are confined to the peripheral portion of the trap magnetism area. Zircons from dolerite transecting Late Riphean sediments examined in two laboratories have a concordant age of 2.74–2.72 Ba, while zircons from a similar dike located in granite-gneiss of the basement are characterized by an age range of 2700–155 Ma, and the concordant age based on 4 points is 790 Ma. All these factors indicate that the age determinations of the mafic rocks are ambiguous, particularly in the zone of transition from the center of the trap province to its periphery, where alkaline magmatism is observed.     

Sulfur isotopic zonation in the Cadia district,southeastern Australia: exploration significance and implications for the genesis of alkalic porphyry gold–copper deposits

The alkalic porphyry gold–copper deposits of the Cadia district occur in the eastern Lachlan Fold Belt of New South Wales, Australia. The district comprises four porphyry deposits (Ridgeway, Cadia Quarry, Cadia Hill, and Cadia East) and two iron–copper–gold skarn deposits (Big Cadia and Little Cadia). Almost 1,000 tonnes of contained gold and more than four million tonnes of copper have been discovered in these systems, making Cadia the world’s largest known alkalic porphyry district, in terms of contained gold. Porphyry gold–copper ore at Cadia is associated with quartz monzonite intrusive complexes, and is hosted by central stockwork and sheeted quartz–sulfide–(carbonate) vein systems. The Cadia porphyry deposits are characterized by cores of potassic and/or calc–potassic alteration assemblages, and peripheral halos of propylitic alteration, with late-stage phyllic alteration mostly restricted to fault zones. Hematite dusting is an important component of the propylitic alteration assemblage, and has produced a distinctive reddening of feldspar minerals in the volcanic wall rocks around the mineralized centers. Sulfide mineralization is strongly zoned at Ridgeway and Cadia East, with bornite-rich cores surrounded by chalcopyrite-rich halos and peripheral zones of pyrite mineralization. The Cadia Hill and Cadia Quarry deposits have chalcopyrite-rich cores and pyrite-rich halos, and Cadia Hill contains a high-level bornite-rich zone. Distinctive sulfur isotopic zonation patterns have been identified at Ridgeway, Cadia Hill, and Cadia East. The deposit cores are characterized by low δ³⁴S_sulfide values (−10 to −4‰), consistent with sulfide precipitation from an oxidized (sulfate-predominant) magmatic fluid at 450 to 400°C. Pyrite grains that occur in the propylitic alteration halos typically have δ³⁴S_sulfide values near 0‰. There is a gradual increase in δ³⁴S_sulfide values outwards from the deposit cores through the propylitic halos. Water–rock interaction during propylitic alteration caused magmatic sulfate reduction and concomitant oxidation of ferrous iron-bearing minerals, resulting in enrichment of ³⁴S in pyrite and also producing the distinctive reddened, hematite-rich alteration halos to the Cadia deposits. These results show that sulfur isotope analyses have potential applications in the exploration of alkalic porphyry-style deposits, with zones of depleted δ³⁴S_sulfide values most prospective for high-grade mineralization.     

Changing poverty distribution in Bolivia: the role of rural–urban migration and urban services

Bolivia is a country with high levels of poverty and inequality among its peoples and regions. For the nation and its urban and rural areas, trends in the social and spatial distribution of poverty (and extreme poverty) are identified from 1976 to 2003 using UBN data with minor support where appropriate from poverty lines. The main survey between 1992 and 2001 uses composite and selected UBN to track detailed poverty change for the country’s nine departments, its ten largest cities and a selection of other smaller urban and rural municipalities. Because of rising background increases in population in the various surveyed administrative units, many instances of relative reductions in poverty are accompanied by rising absolute increases. Marked spatial variations in poverty and development in the country over the last several decades are identified as the main driver for the country’s quickening pace of rural–urban migration. As a result, the paper concludes by assessing two different but closely related views. One investigation tests the notion that because more poor people have been living in Bolivia’s cities than in its rural areas since the mid to late 1990s, rapid rural–urban migration has simply shifted the locus of poverty from the countryside to the cities in a process called, the ‘urbanisation of poverty.’ A second, more challenging, investigation assesses the view that the flow of poor rural people to the better serviced urban areas of Bolivia has actually acted to alleviate national poverty levels.     

Inequality and development in rural West Africa

Inequality seems to be a feature of all societies, but some are probably more equal than others. It is in Third World countries however where inequalities between particular areas, groups and individuals are most marked. The paper first traces the growing interest in both the study of inequality and the rural household as a focus of analysis. Some of the problems of measuring inequality are then considered and various indicators of inequality are examined with reference to empirical evidence from rural W Africa. The paper concludes that recent development strategies have often directly or indirectly led to greater rural inequality and makes suggestions as to how future projects might achieve greater impact in reducing the gap between rich and poor. Paper presented at Commonwealth Geographical Bureau, Workshop on Spatial Inequalities in the Developing World, Kano, Nigeria 16–20 September 1985     

U–Pb zircon dating of the Gruf Complex: disclosing the late Variscan granulitic lower crust of Europe stranded in the Central Alps

Permian granulites associated with noritic intrusions and websterites are a common feature of the post-Variscan European crust. Such granulites are common in the Southern Alps (e.g. Ivrea Zone), but occur only in the Gruf Complex in the Central Alps. To understand the geotectonic significance of these granulites, in particular in the context of Alpine migmatisation, zircons from 15 high-grade samples have been U–Pb dated by SHRIMP II analysis. Oscillatory zoned zircons from charnockite sheets, interpreted as melts generated through granulite facies fluid-absent biotite melting at 920–940°C, yield ages of 282–260 Ma. Some of these zircons contain inclusions of opx, unequivocally attributable to the granulite facies, thus confirming a Permian age for the charnockites and associated granulites. Two samples from an enclave-rich orthogneiss sheet yield Cambrian and Ordovician zircon cores. Two deformed leucogranites and six ortho- and augengneisses, which compose two-thirds of the Gruf Complex, give zircon ages of 290–260 Ma. Most zircons have milky rims with ages of 34–29 Ma. These rims date the Alpine amphibolite facies migmatisation, an interpretation confirmed by directly dating a leucosome pocket from upper amphibolite facies metapelites. The Gruf charnockites associated with metre-scale schlieren and boudins of opx–sapphirine–garnet–granulites, websterites and gabbronorites can thus be identified as part of the post-Variscan European lower crust. A geotectonic reconstruction reveals that this piece of lower crust stranded in the (European) North upon rifting of the Neotethys, such contrasting the widespread granulite units in the Southern Alps. Emplacement of the Gruf lower crust into its present-day position occurred during migmatisation and formation of the Bergell Pluton in the aftermath of the breakoff of the European slab.     

Cross-border conservation in East Central Europe: The Danube-Carpathian complex and the contribution of the World Wide Fund for Nature

Cross-border cooperation in environmental matters has become much more evident since 1989 because open frontiers facilitate contact while common tasks emerge as protected areas in frontier zones lose their isolation. Pollution hazards have been discussed more openly since 1989 while further stimuli arise from the harmonisation process in the run-up to EU enlargement and the finance available from Brussels and other international donors to solve pollution problems and create international ecological networks. The paper examines the progress made in the Danube Valley and the Carpathians which together constitute the core of East Central Europe. Particular attention is paid to the role of environmental non-governmental organisations (ENGOs) – and especially the World Wide Fund for Nature (WWF) – in the progress of conservation. Along with the World Conservation Union (IUCN), WWF has demonstrated the value of floodplain wetlands and ensured that wetland restoration is an important part of the Strategic Action Plan for the Danube. And by involving local ENGOs in specific projects the role of the non-governmental sector in environment matters is enhanced. Also, with momentum growing for a pan-European ecological network ('Natura 2000'), WWF has attracted the support of international donors for a ecoregion-based conservation (ERBC) in the Carpathians where priority areas have now been identified. Ecological and diplomatic capacities are thus deployed to maximise the scope for biodiversity conservation commensurate with sustainable socio-economic development. This revised version was published online in July 2006 with corrections to the Cover Date.     

U–Pb geochronology of gneisses and granitoids from the Danish island of Bornholm: new evidence for 1.47–1.45 Ga magmatism at the southwestern margin of the East European Craton

The Danish island of Bornholm is located at the southwestern margin of the Fennoscandian Shield, and features exposed Precambrian basement in its northern and central parts. In this paper, we present new U–Pb zircon and titanite ages for granites and orthogneisses from 13 different localities on Bornholm. The crystallization ages of the protolith rocks all fall within the range 1,475–1,445 Ma (weighted average ²⁰⁷Pb/²⁰⁶Pb ages of zircon). Minor age differences, however, may imply a multi-phase emplacement history of the granitoid complex. The presence of occasional inherited zircons (with ages of 1,700–1,800 Ma) indicates that the Bornholm granitoids were influenced by older crustal material. The east–west fabric observed in most of the studied granites and gneisses, presumably originated by deformation in close connection with the magmatism at 1,470–1,450 Ma. Most titanite U–Pb ages fall between 1,450 and 1,430 Ma, reflecting post-magmatic or post-metamorphic cooling. Granitoid magmatism at ca. 1.45 Ga along the southwestern margin of the East European Craton has previously been reported from southern Sweden and Lithuania. The ages obtained in this study indicate that the Bornholm magmatism also was part of this Mesoproterozoic event.     

Case studies of seasonal rainfall forecasts for Hong Kong and its vicinity using a regional climate model

Seasonal climate forecasts are one of the most promising tools for providing early warnings for natural hazards such as floods and droughts. Using two case studies, this paper documents the skill of a regional climate model in the seasonal forecasting of below normal rainfall in southern China during the rainy seasons of July–August–September 2003 and April–May–June 2004. The regional model is based on the Regional Spectral Model of the National Centers for Environmental Prediction of the United States. It is the first time that the model has been applied to a region dominated by the East Asian Monsoon. The article shows that the regional climate model, when being forced by reasonably good forecasts from a global model, can generate useful seasonal rainfall forecasts for the region, where it is dominated by the East Asia monsoon. The spatial details of the dry conditions obtained from the regional climate model forecast are also found to be comparable with the observed distribution.     

New age constraints for Grenville-age metamorphism in western central Dronning Maud Land (East Antarctica), and implications for the palaeogeography of Kalahari in Rodinia

New SHRIMP zircon data from Gjelsvikfjella and Mühlig–Hofmann–Gebirge (East Antarctica) indicate that the metamorphic basement is composed of Grenville-age rocks that are most likely part of the north-eastern continuation of the Namaqua–Natal–Maud Belt. Crystallisation ages of meta-igneous rocks range between ca. 1,150 to 1,100 Ma, with little inheritance recorded. Metamorphic zircon overgrowth during high-grade metamorphism is dated between ca. 1,090 to 1,050 Ma. Both, the crystallisation ages and the metamorphic overprint are similar to U–Pb data from a number of areas along a ca. 2,000-km stretch from Natal in South Africa to central Dronning Maud Land. The basement underwent in part strong high-grade reworking during the collision of East and West Gondwana at ca. 550 Ma. The timing of Grenville-age metamorphism has important implications for the position of Kalahari in Rodinia. It also questions that Coats Land is part of the Maud Belt because the undeformed volcanic rocks of Coats Land are older than the main metamorphism within the Maud Belt and, therefore, must rest on older basement. This interpretation explains why the pole of Coats Land at ca. 1,110 Ma differs from the Kalahari poles by 30°, i.e. Coats Land had not yet amalgamated to Kalahari. On the other hand, the palaeopoles from Coats Land and Laurentia at 1,110 Ma are identical within error. Thus, Coats Land could have been part of Laurentia prior to the final amalgamation of Rodinia, the Namaqua–Natal–Maud Belt could have been a part of the Grenville Belt and the entire Kalahari Craton could indeed have opposed Laurentia on its eastern side.     

Medium-scale maps after survey from space—The “Metric-Camera”—Experiment

Airphotos have been used for topographic survey since the Twenties. The “European Space Agency” (ESA), the “Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt” (DFVLR) and “Carl Zeiss” have modified this successful technique for spacecraft and recently have tested the system over four continents. Each of these satellite photos covers a region of 189×189 km to the scale of 1∶800000 and may be enlarged to 1∶250000 or 1∶100000. Between the altitudes of 200 and 300 km, mapmaking or-revision seems to be economic in zones or in countries, where existing maps are of minor quality or outdated. In this paper, examples from deserts and semideserts in the Sudan are presented.     

Imprint of meteoric water on the stable isotope compositions of igneous and secondary minerals,Kap Edvard Holm Complex,East Greenland

 Hydrogen and oxygen isotope analyses have been made of hydrous minerals in gabbros and basaltic xenoliths from the Eocene Kap Edvard Holm intrusive complex of East Greenland. The analyzed samples are of three types: (1) primary igneous hornblendes and phlogopites that crystallized from partial melts of hydrothermally altered basaltic xenoliths, (2) primary igneous hornblendes that formed during late–magmatic recrystallization of layered gabbroic cumulates, and (3) secondary actinolite, epidote and chlorite that formed during subsolidus alteration of both xenoliths and gabbros. Secondary actinolite has a δ¹⁸O value of −5.8‰ and a δD value of −158‰. These low values reflect subsolidus alteration by low–δ¹⁸O, low–δD hydrothermal fluids of meteoric origin. The δD value is lower than the −146 to −112‰ values previously reported for amphiboles from other early Tertiary meteoric–hydrothermal systems in East Greenland and Scotland, indicating that the meteoric waters at Kap Edvard Holm were isotopically lighter than typical early Tertiary meteoric waters in the North Atlantic region. This probably reflects local climatic variations caused by formation of a major topographic dome at about the time of plutonism and hydrothermal activity. The calculated isotopic composition of the meteoric water is δD=−110 ± 10‰, δ¹⁸O ≈−15‰. Igneous hornblendes and phlogopites from pegmatitic pods in hornfelsed basaltic xenoliths have δ¹⁸O values between −6.0 and −3.8‰ and δD values between −155 and −140‰. These are both much lower than typical values of fresh basalts. The oxygen isotope fractionations between pegmatitic hornblendes and surrounding hornfelsic minerals are close to equilibrium fractionations for magmatic temperatures, indicating that the pegmatites crystallized from low–δ¹⁸O partial melts of xenoliths that had been hydrothermally altered and depleted in ¹⁸O prior to stoping. The pegmatitic minerals may have crystallized with low primary δD values inherited from the altered country rocks, but these values were probably overprinted extensively by subsolidus isotopic exchange with low–δD meteoric–hydrothermal fluids. This exchange was facilitated by rapid self–diffusion of hydrogen through the crystal structures. Primary igneous hornblendes from the plutonic rocks have δ¹⁸O values between +2.0 and +3.2‰ and δD values between −166 and −146‰. The ¹⁸O fractionations between hornblendes and coexisting augites are close to equilibrium fractionations for magmatic temperatures, indicating that the hornblendes crystallized directly from the magma and subsequently underwent little or no oxygen exchange. The hornblendes may have crystallized with low primary δD values, due to contamination of the magma with altered xenolithic material, but the final δD values were probably controlled largely by subsolidus isotopic exchange. This inference is based partly on the observation that coexisting plagioclase has been extensively depleted in ¹⁸O via a mineral–fluid exchange reaction that is much slower than the hydrogen exchange reaction in hornblende. It is concluded that all hydrous minerals in the study area, whether igneous or secondary, have δD values that reflect extensive subsolidus isotopic equilibration with meteoric–hydrothermal fluids. Received: 22 March 1994 / Accepted: 26 January 1995     

Business and Bludgeon at the Border: A transnational political economy of human displacement in Thailand and Burma

Transnational economic integration between Thailand and Burma is intimately linked to protection for Burmese refugees in Thailand. In the case of Burmese nationals who seek safety in Thailand, their protection becomes more negotiable as economic integration with Thailand proceeds. Since 1988, hundreds of thousands of Burmese citizens have fled beyond the borders of their state, fearing both human rights abuses and successive offensives by a military junta intent on its own survival. Critical analysis of the dynamic of human displacement and bi-national economic cooperation between the governments of Thailand Burma grounds this study. The story is one of transnational trade across one border, where people's labour, homes, and passports are exchanged – in an obscured fashion – for investment, natural resources, and economic cooperation. The Thai-Burmese border proves to be a flexible concept that can be invoked to produce refugees or blurred to promote binational economic infrastructure and trade. Despite economic booms and busts in Southeast Asia, economic integration in the region is on-going. At the same time, Burma's government – the State Peace and Development Council – and its military force more and more citizens into neighbouring countries. Their reception in Thailand, however, is increasingly chilly. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sedimentary characteristics of terrigenous debris at site MD05-2905 in the northeastern part of the South China Sea since 36 ka and evolution of the East Asian monsoon

Sediments with high sedimentation rate at site MD05-2905 in the Northeastern slope of the South China Sea provide unique materials for a high-resolution study on the paleoenvironment. Based on precise dating of AMS ¹⁴C, grain size analysis of terrigenous debris at core MD05-2905 was conducted after organic matter, biological carbonate and biogenic opal were removed. The results show that 15.5–63.5 μm coarse grain size ingredients may indicate East Asian winter monsoon changes and that 2–9 μm fine grain size ingredients may be used as a proxy of evolution of the East Asian summer monsoon. The results of grain size analysis, which suggest East Asian monsoon intensity, reveal that a winter monsoon dominated the glacial regime and a summer monsoon dominated the Holocene regime. It was also shown that the summer monsoon increased gradually, experienced several abrupt changes and reached a culmination in the early Holocene (11200–8500 a B.P.) since 36 ka. Controlled by precession periodicity, it may be related with the amount of solar radiation at the highest stage, which needs further study. __________ Translated from Advances in Earth Science, 2007, 22(10): 1012–1018 [译自: 地球科学进展]     

Vertical velocity of mantle flow of East Asia and adjacent areas

Based on the high-resolution body wave tomographic image and relevant geophysical data, we calculated the form and the vertical and tangential velocities of mantle flow. We obtained the pattern of mantle convection for East Asia and the West Pacific. Some important results and understandings are gained from the images of the vertical velocity of mantle flow for East Asia and the West Pacific. There is an upwelling plume beneath East Asia and West Pacific, which is the earth’s deep origin for the huge rift valley there. We have especially outlined the tectonic features of the South China Sea, which is of the “工” type in the upper mantle shield type in the middle and divergent in the lower; the Siberian clod downwelling dives from the surface to near Core and mantle bounary (CMB), which is convergent in the upper mantle and divergent in the lower mantle; the Tethyan subduction region, centered in the Qinghai-Tibet plateau, is visible from 300 to 2 000 km, which is also convergent in the upper mantle and divergent in the lower mantle. The three regions of mantle convection beneath East Asia and the West Pacific are in accordance with the West Pacific, Ancient Asia and the Tethyan structure regions. The mantle upwelling originates from the core-mantle boundary and mostly occurs in the middle mantle and the lower part of the upper mantle. The velocities of the vertical mantle flow are about 1–4 cm per year and the tangential velocities are 1–10 cm per year. The mantle flow has an effect on controlling the movement of plates and the distributions of ocean ridges, subduction zones and collision zones. The mantle upwelling regions are clearly related with the locations of hotspots on the earth’s surface. Translated from Geology in China, 2006, 33(4): 896–905 [译自: 中国地质]     

Trace elements in sub-alpine forest soils on the eastern edge of the Tibetan Plateau,China

Industrial development has increased fast in China during the last decades. This has led to a range of environmental problems. Deposition of trace elements to forest ecosystems via the atmosphere is one potential problem. In this paper, we report the results from a pilot study where the trace element levels of the sub-alpine forest soils on the eastern edge of the Tibetan Plateau have been measured. Possible relationships between soil properties and trace element concentrations have also been investigated. The obtained concentrations (mg kg⁻¹) were boron (B) 48.06–53.70, molybdenum (Mo) 1.53–2.26, zinc (Zn) 68.18–79.53, copper (Cu) 36.81–42.44, selenium (Se) 0.33–0.49, cadmium (Cd) 0.16–0.29, lead (Pb) 25.80–30.71, chromium (Cr) 96.10–110.08, nickel (Ni) 30.16–45.60, mercury (Hg) 0.05–0.11, and arsenic (As) 3.09–4.17. With a few exceptions, the element concentration can be characterized as low in the investigated sub-alpine forest soils. No clear differences in trace element levels were found between topsoil and subsoil samples, indicating that the atmospheric deposition of trace element has been low. The soil parent material plays a key role to determine trace element levels. Soil properties, including pH_w, organic carbon (OC), clay fraction, cation-exchange capacity (CEC), total iron (Fe), and total aluminum (Al) concentrations were related to trace element concentration using correlation analysis. Total Fe and Al showed the strongest relationships with concentrations of most trace elements in the sub-alpine forest soils. PCA analyses indicated that a significant increase in the number of cars with the fast development of local tourism may result in higher Pb concentration in the future.     

The application of single zircon evaporation and model Nd ages to the interpretation of polymetamorphic terrains: an example from the Proterozoic mobile belt of south India

The technique of single zircon dating from the thermal evaporation of ²⁰⁷Pb/²⁰⁶Pb (Kober 1986, 1987) provides a means of dating successive periods of growth and nucleation of zircons in polymetamorphic assemblages. In contrast Nd model ages may provide a measure of the period of crustal residency for the sample or its protolith. These two techniques have been combined to elucidate the tectonic history of the Proterozoic mobile belt of southern India, exposed south of the Palghat-Cauvery Shear Zone that marks the southern boundary of the Archaean craton of Karnataka. The two main tectonic units of this mobile belt comprise the Madurai and Trivandrum Blocks, both of which are characterised by massive charnockite uplands and low-lying polymetamorphic metasedimentary belts that have undergone a complex tectonic history throughout the Proterozoic. Evidence for early Palaeoproterozoic magmatism is restricted to the Madurai Block where single zircon evaporation ages from a metagranite (2436 ± 4 Ma) are similar to model Nd ages from a range of lithologies suggesting crustal growth at that time. The Trivandrum Block, to the south of the Achankovil shear zone, is comprised of the Kerala Khondalite Belt, the Nagercoil charnockites and the Achankovil metasediments. Single zircon evaporation ages, together with conventional zircon and garnet chronometry, suggest that all three units underwent upper-amphibolite facies metamorphism at ∼1800 Ma, an event unrecorded in the metagranite from the Madurai Block. This implies that the Madurai and Trivandrum blocks represent distinct terrains throughout the Palaeoproterozoic. Model Nd ages from the Achankovil metasediments are much younger (1500–1200 Ma) than those from the adjacent Kerala Khondalite Belt and Madurai Blocks (3000–2100 Ma), but there is no evidence for zircon growth in these metasediments during the Mesoproterozoic. Hence the comparatively young model Nd ages of the metasediments are indicative of a mixed provenance rather than a discrete period of crustal growth. Zircon overgrowths from the Madurai Block (547 ± 17 Ma) and Achankovil metasediments (530 ± 21 Ma) suggest that all tectonic units of the Proterozoic mobile belt of South India shared the same metamorphic history from the early Palaeozoic. This event has been recognised in the basement lithologies of Sri Lanka and East Antarctica, confirming that the constituent terrains of East Gondwana had assembled by this time. Received: 10 October 1995 / Accepted: 27 October 1997