Timing of gold mineralisation in the Ballarat goldfields,central Victoria: Constraints from 40Ar/39Ar results     

F. P. Bierlein  D. A. Foster  S. McKnight  D. C. Arne 《Australian Journal of Earth Sciences》2013,60(2):301-309

⁴⁰Ar/³⁹Ar data for muscovite separates and hydrothermally altered whole‐rock samples from the Ballarat West and the Ballarat East goldfields indicate that mesothermal gold mineralisation at Ballarat occurred during several episodic pulses, ranging in age from the Late Ordovician to the Early Devonian. Initial formation of auriferous structures in the Ballarat goldfields coincided with folding and thrusting associated with the development of the western Lachlan Fold Belt between 460 and 440 Ma. Subsequent fault reactivation and magmatism resulted in remobilisation and additional mineralisation between 410 and 380 Ma, and around 370 Ma. The results presented herein are in agreement with findings for other major gold deposits in central Victoria and further constrain the history of deformation, metamorphism and mineralisation in the western subprovince of the Lachlan Fold Belt.  相似文献   

Detection of land subsidence in Semarang,Indonesia, using stable points network (SPN) technique   总被引：2，自引：0，他引：2  

Friedrich Kuehn  David Albiol  Geraint Cooksley  Javier Duro  Johanna Granda  Susanne Haas  Arne Hoffmann-Rothe  Dodid Murdohardono 《Environmental Earth Sciences》2010,60(5):909-921

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Geological observations in high‐grade mid‐Proterozoic rocks from Else Platform,northern Prince Charles mountains region,east Antarctica     

M. Hand  C. J. L. Wilson  I. Scrimgeour  Kurt Stüwe  D. Arne 《Australian Journal of Earth Sciences》2013,60(4):311-329

Granulite facies rocks on Else Platform in the northern Prince Charles Mountains, east Antarctica, consist of metasedimentary gneiss extensively intruded by granitic rocks. The dominant rock type is a layered garnetbiotite‐bearing gneiss intercalated with minor garnet‐cordierite‐sillimanite gneiss and calc‐silicate. Voluminous megacrystic granite intruded early during a mid‐Proterozoic (ca 1000 Ma) granulite event, M₁, widely recognized in east Antarctica. Peak metamorphic conditions for M₁ are in the range of 650–750 MPa at ～800°C and were associated with the development of a gneissic foliation, S₁ and steep east‐plunging lineation, L₁. Strain partitioning during progressive non‐coaxial deformation formed large D₂ granulite facies south‐dipping thrusts, with a steep, east‐plunging lineation. In areas of lower D₂ strain, large‐scale upright, steep east‐plunging fold structures formed synchronously with the D₂ high‐strain zones. Voluminous garnet‐bearing leucogneiss intruded at 940 ±20 Ma and was deformed in the D₂ high‐strain zones. Textural relationships in pelitic rocks show that peak‐M2 assemblages formed during increasing temperatures via reactions such as biotite + sillimanite + quartz ± plagioclase = spinel + cordierite + ilmenite + K‐feldspar + melt. In biotite‐absent rocks, re‐equilibration of deformed M₁ garnet‐sillimanite‐ilmenite assemblages occurred through decompressive reactions of the form, garnet + sillimanite + ilmenite = cordierite + spinel + quartz. Pressure/temperature estimates indicate that peak‐M₂ conditions were 500–600 MPa and 700±50°C. At about 500 Ma, north‐trending granitic dykes intruded and were deformed during D₃‐M₃ at probable upper amphibolite facies conditions. Cooling from peak D₃‐M₃ conditions was associated with the formation of narrow greenschist facies shear zones, and the intrusion of pegmatite. Cross‐cutting all features are abundant north‐south trending alkaline mafic dykes that were emplaced over the interval ca 310–145 Ma, reflecting prolonged intrusive activity. Some of the dykes are associated with steeply dipping faults that may be related to basin formation during Permian times and later extension, synchronous with the formation of the Lambert Graben in the Cretaceous.  相似文献   

Asynchronous responses of East Asian and Indian summer monsoons to mountain uplift shown by regional climate modelling experiments   总被引：1，自引：1，他引：0  

Hui Tang  Arne Micheels  Jussi T. Eronen  Bodo Ahrens  Mikael Fortelius 《Climate Dynamics》2013,40(5-6):1531-1549

It has been demonstrated in climate models that both the Indian and East Asian summer monsoons (ISM and EASM) are strengthened by the uplift of the entire Asian orography or Tibetan Plateau (TP) (i.e. bulk mountain uplift). Such an effect is widely perceived as the major mechanism contributing to the evolution of Asian summer monsoons in the Neogene. However, geological evidence suggests more diachronous growth of the Asian orography (i.e. regional mountain uplift) than bulk mountain uplift. This demands a re-evaluation of the relation between mountain uplift and the Asian monsoon in the geological periods. In this study, sensitivity experiments considering the diachronous growth of different parts of the Asian orography are performed using the regional climate model COSMO-CLM to investigate their effects on the Asian summer monsoons. The results show that, different from the bulk mountain uplift, the regional mountain uplift can lead to an asynchronous development of the ISM and EASM. While the ISM is primarily intensified by the thermal insulation (mechanical blocking) effect of the southern TP (Zagros Mountains), the EASM is mainly enhanced by the surface sensible heating of the central, northern and eastern TP. Such elevated surface heating can induce a low-level cyclonic anomaly around the TP that reduces the ISM by suppressing the lower tropospheric monsoon vorticity, but promotes the EASM by strengthening the warm advection from the south of the TP that sustains the monsoon convection. Our findings provide new insights to the evolution of the Asian summer monsoons and their interaction with the tectonic changes in the Neogene.  相似文献   

Innovation by co-evolution in natural resource industries: The Norwegian experience     

Bjørnar Sæther  Arne Isaksen 《Geoforum》2011,42(3):373-381

Some resource-based economies become wealthy while others stay poor and Norway belongs to the first category. This paper argues that part of the answer to why Norway has managed to benefit from its rich natural resources is found in the formation of a well-functioning national innovation system. The paper integrates the innovation system approach with a historical approach through the concept of co-evolution. The empirical study investigates how innovation systems evolve in natural resource industries through analysing the co-evolution between industry, knowledge organisations and national policy in the Norwegian aluminium and petroleum sectors. Parallels are found in the development of these two sectors, which are: (i) the deliberate use of concession laws to seize value creation and technological development from foreign direct investments, (ii) the establishment and prioritisation of state-owned companies and (iii) the more or less intentional formation of a national innovation system. The paper points to the relevance of analysing the historical evolution of national innovation systems to understand the creation of their specific path-dependent characteristics, to analyse how policy influences the creation and working of innovation systems, to use a multilevel approach in studies of innovation systems and to consider how innovation processes in different industries are linked in value chains and through knowledge flows.  相似文献   

Regional thermal history of the Lennard shelf,Canning Basin,from apatite fission track analysis: Implications for the formation of Pb‐Zn ore deposits     

D. C. Arne  P. F. Green  I. R. Duddy  A. J. W. Gleadow  I. B. Lambert  J. F. Lovering 《Australian Journal of Earth Sciences》2013,60(4):495-513

Zinc mineralization in Devonian carbonates of the Lennard Shelf, northern Canning Basin is similar in many respects to that of the Mississippi Valley‐type including estimated minimum temperatures of sulphide precipitation between 70 and 110°C. Apparent apatite fission track ages for Precambrian granitic basement and for detrital apatites in Devonian carbonates in and near Pb‐Zn mineralization generally range between 260 and 340 Ma, with Precambrian samples tending to have slightly older apatite fission track ages than the Devonian carbonates. These apparent ages are younger than the stratigraphic age of the material analysed, indicating that appreciable annealing of fission tracks in apatite has occurred in post‐Devonian times. Mean horizontal confined track lengths are 12–13 μm for most samples and preclude attaching any ‘event’ significance to the fission track ages. Studies of well sequences (Grevillea 1 and Kennedia 1) indicate a period of rapid uplift in the area during the Late Triassic/Early Jurassic. Assuming a constant geothermal gradient of 30°C/km, approximately 1.5 km of uplift and erosion is estimated. Immediate thermal effects related to Miocene lamproite intrusion into Precambrian basement appear to be restricted to within 200 m of the contact zone.

For outcropping Devonian carbonates, a thermal history is proposed involving burial in the Late Palaeozoic/Early Mesozoic, followed by uplift and cooling from peak temperatures around 70–80°C in mid‐Mesozoic times. With reference to this period of burial, Pb‐Zn occurrences represent thermal anomalies when reported fluid inclusion homogenization temperatures are compared with the estimated peak temperatures. However the possibility of a phase of higher temperatures during the Late Devonian/ Early Carboniferous is suggested by the apatite fission track results, in which case sulphide mineralization may reflect ambient regional temperatures if it formed at that time. The absence of enhanced annealing effects in detrital apatites proximal to Pb‐Zn deposits suggests that either sulphide mineralization preceded or accompanied peak regional temperatures suspected during the Late Devonian/Early Carboniferous, or that the mineralizing episodes were of too short a duration to significantly anneal fission tracks in apatite.  相似文献   

A new early Holocene shoreline displacement record for Blekinge,southern Sweden,and implications for underwater archaeology     

Anton Hansson  Dan Hammarlund  Giacomo Landeschi  Arne Sjstrm  Bjrn Nilsson 《Boreas: An International Journal of Quaternary Research》2019,48(1):57-71

We present evidence of a submerged early Holocene landscape off the Blekinge coastline in the Baltic Sea, dating to the Yoldia Sea and Initial Littorina Sea Stages when the water level was lower than at present. ¹⁴C dated wood remains obtained by surveillance diving and new archaeological findings in combination with bathymetric analyses and interpolations between other sites across the Baltic Sea were used for refinement of the shoreline displacement history of the region. The new results reveal a Yoldia Sea lowstand level at 20 m b.s.l., a subsequent Ancylus Lake highstand at 3 m a.s.l., and then a period of relatively stable water level at about 4 m b.s.l. during the Initial Littorina Sea Stage, several metres lower than previously concluded. The refined shoreline displacement record was used for palaeo‐reconstructions of the study area during four key periods, the Yoldia Sea lowstand phase, the Ancylus Lake transgression phase, the Ancylus Lake highstand phase and the Initial Littorina Sea lowstand phase, using elevation data and map algebra functions. A flow accumulation algorithm was used for reconstruction of the now submerged prehistoric river network in order to identify areas of high archaeological potential. Our revised shoreline displacement record, and especially its lowstand period during the Initial Littorina Sea Stage around 9500–8500 cal. a BP, raises future demands not only for specific archaeological shallow‐water surveys down to 4 m b.s.l. in the area, but also for a renewed cultural heritage management strategy. The results of this study fill an important gap in the early Holocene part of the shoreline displacement history of Blekinge, contributing to its completion since the deglaciation, which is unique for the Baltic Sea.  相似文献   

Disturbance,geomorphic processes and recovery of wildfire slopes in North Tyrol     

Oliver Sass  Michael Heel  Karl‐Friedrich Wetzel  Arne Friedmann 《地球表面变化过程与地形》2012,37(8):883-894

Wildfires in the sub‐alpine belt of the Austrian Limestone Alps sometimes cause severe vegetation and soil destruction with increased danger of secondary natural hazards such as avalanches and debris flows. Some of the affected areas remain degraded to rocky slopes even decades after the fire, raising the question as to whether the ecosystems will ever be able to recover. The mean fire interval, the duration of recovery and the role of geomorphic processes for vegetation regeneration are so far unknown. These questions were tackled in a broad research approach including investigation of historical archives to determine the frequency of historical wildfires, mapping vegetation regeneration on 20 slopes of different post‐fire ages, and soil erosion measurements on two slopes. To date, > 450 historical wildfires have been located in the study area. The mean fire interval per square kilometre is c. 750 years, but can be as low as 200–500 years on south‐facing slopes. Vegetation regeneration takes an extremely long time under unfavourable conditions; the typical window of disturbance is between 50 and 500 years, which is far longer than in any other wildfire study known to us. Soil erosion constantly increases in the years after the fires and the elevated intensity can be maintained for decades. A two‐part vegetation regeneration model is proposed depending upon the degree of soil loss. In the case of moderate soil erosion, spreading grassland communities can slow down shrub re‐colonization. In contrast, after severe soil destruction the slopes may remain degraded for a century or longer, before rather rapid regeneration occurs. The reasons are not fully understood but are probably governed by geomorphic process intensity. The interdependence of vegetation regeneration and geomorphic processes is a paradigm of ecology–geomorphology interaction, and is a unique example of a very long‐lasting disturbance response caused by wildfire in a non‐resilient ecosystem. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

An integrated study of economic effects of and vulnerabilities to global warming on the Barents Sea cod fisheries     

Arne Eide 《Climatic change》2008,87(1-2):251-262

The Barents Sea area is characterised by a highly fluctuating physical environment causing substantial variations in the ecosystems and fisheries depending upon this. Simulations assuming different management regimes have been carried out to study how physical and biological effects of global warming influence the Barents Sea cod fisheries. A regional, high-resolution representation of the B2 world region (OECD90) scenario from the Intergovernmental Panel on Climate Change was used to calculate water temperatures and plankton biomasses by hydrodynamic modelling. These results were included in simulations performed by a multi-fleet, multi-species model, by which a fully integrated model linking to the global circulation model to the Barents Sea fisheries through a regional downscaling to the Barents Sea area is constructed. One factor of particular importance for the natural annual biological variations is the occasional inflow of young herring into the Barents Sea area. The herring inflow is difficult to predict and links to dynamical systems outside the Barents Sea area, complex recruitment mechanisms and oceanographic conditions. These processes are in the study represented by a stochastic representation of herring inflow based on historical observations. According to the performed simulations the biomass fluctuations may slightly increase over the next 25 years, possibly caused by changes in temperature patterns. Six different management regimes have been included in the study and the results support earlier studies claiming that the choice of management regime potentially has a greater importance for biological and economic performance in the Barents Sea fisheries than impacts which derive from global warming over the next 25 years. A basic assumption for this conclusion is however that the Barents Sea ecosystem essentially preserves its structure and composition of today. Possible, unpredictable significant shifts in the ecosystem structure are not considered.  相似文献   

Composition and properties of glacigenic sediments in the southwestern Barents Sea     

Joar Sættem  Leif Rise  Dag Arne Westgaard 《Marine Georesources & Geotechnology》2013,31(3-4):229-255

Abstract

The composition and properties of glacigenic sediments in the southwestern Barents Sea are described based on data from 33 shallow boreholes (< 143 m below seabed) and 11 seabed cores (<4.2m below seabed). The cores are tied into a regional seismostratigraphic framework, illustrating the relationships between different boreholes.

A massive, muddy diamicton (silty, sandy clay with scattered gravel) is found in nearly all cores. Average clay content (<2 pm) of this lithology is about 38%, but varies between about 25% and 50%. Short intervals of finely laminated, waterlain sediments or gravelly sand are cored in a few occasions. A high content of sand and gravel in the cores from near the Norwegian coast shows an influence of sediment input from the mainland, while material eroded from sedimentary rocks dominates farther offshore.

The data presented on physical properties include undisturbed and remolded undrained shear strength, natural water content, bulk density, compressional sound velocity (P waves), Atterberg consistency limits, effective preconsolidation pressure, and consolidation coefficient.

Prediction of overconsolidation from seismic mapping of erosional surfaces is confirmed by the borehole cores. High compaction is found both in Weichselian and older deposits, with a general increase in compaction toward the east as well as toward shallower water. Cores that are “underconsolidated” at their present burial depth are also reported.

The average compressional sound velocity is about 1780 m/s for the borehole cores, 1550 m/s for the seabed cores, and increases with increasing shear strength and consolidation. Both horizontal and vertical sound velocities are measured in several cores, and although the data have a considerable scatter, a slightly aniso‐tropic sound velocity is indicated.  相似文献