南秦岭十里坪锑矿床成矿时代及成因的初步研究

十里坪锑矿床受赵川陆缘隆_滑构造的主滑脱拆离带的控制。矿体呈脉状赋存于韧_脆性主滑脱带上部的脆性次级断层_节理中,矿石类型主要为萤石石英辉锑矿型。围岩为太古宙_元古宙变质岩系,围岩蚀变弱。成矿流体属H2O_CO2_NaCl体系,流体包裹体盐度w(NaCleq)为3.6%～11.3%,均一温度为109～232℃,形成压力大致为800×105Pa。硫、铅同位素研究表明,矿质主要来源于变火山岩围岩;氢、氧同位素显示,成矿流体以大气降水为主,初步将该矿床定为变质岩源就地式大气降水热液矿床。矿石中萤石Sm_Nd等时线年龄为(392±24)Ma,与南秦岭北部晚古生代拗陷区热水喷流_沉积成矿时代相一致,它们都形成于秦岭微板块泥盆纪非造山裂解阶段。     

Dislocating modernity: Identity, space and representations of street trade in Durban, South Africa

South Africa’s cities have experienced dramatic changes over the past decade. Cities are now home to a multiracial population, and have been transformed by new forms of economic and social interaction. For some, these changes have become a significant source of fear and anxiety. In this paper, we examine reactions to urban spatial change in the city of Durban, as expressed in local newspapers and interviews with suburban residents. We describe how the discourses of urban change in Durban have centred on the increased presence of street traders within the city’s public spaces, and the various ways in which the activity of street trade has disrupted long-established modernist norms governing the occupation and use of the urban space. Specifically, we offer a detailed reading of three prominent narratives within the discussion of street traders in Durban--chaos, congestion and pollution. We argue that street traders have come to embody a wide range of more deeply seated cultural anxieties, which have been brought to the fore in the context of South Africa’s transition. These anxieties arise from the ways in which modern understandings of order, agency and subjectivity have been called into question by material changes in the city, and have implications for the nature of citizenship and civic engagement in post-apartheid South Africa.     

Geochemical Correlation Between Metasediments of the Mfongosi Group of the Natal Sector of the Namaqua-Natal Metamorphic Province, South Africa and the Ahlmannryggen Group of the Grunehogna Province, Antarctica

The whole-rock geochemistry of metamorphosed greywackes, arenites and arkoses within the Mesoproterozoic Namaqua-Natal-Maudheim Province is interpreted with the aim of establishing geochemical correlations and defining common sediment source terrains. Metasediments of the Mfongosi Group of the Natal Sector of the Namaqua-Natal Metamorphic Province were sampled from their type area in the Mfongosi Valley. Metagreywackes from the northern limits of the Mfongosi Valley, directly adjacent to the Kaapvaal Craton, show ocean island arc signatures while metagreywackes from the southern limits of the Mfongosi Valley, near the contact with the Madidima Thrust of the Natal nappe zone, show mainly active continental margin signatures. Interleaved, geochemically distinct low-Ca+Na, high-K metamorphosed arkoses to lithic arkoses indicate a minor passive margin sediment component. Geochemical classification of low-grade Ahlmannryggen Group greywackes, arenites and arkoses of the Grunehogna Province, Antarctica, indicates both active and passive continental margin sediment sources. An oceanic island arc signature is not evident in Ahlmannryggen Group data. The active continental margin signature in both Natal Sector and Grunehogna Province metasediments potentially provides for a common link between these terranes. Discriminant Function Analysis, using three pre-defined provenance sub-sets within the Mfongosi Group and two pre-defined provenance sub-sets within the Ahlmannryggen Group, indicate that metasediments with active continental margin signatures from both groups are geochemically identical, implying that the active continental margin of the Grunehogna Province shed immature sediments westwards (African azimuths) into the developing, narrow or restricted Mesoproterozoic ‘Mfongosi Basin.’ This was accompanied by minor sediment influx from a stable continental platform, potentially the Kaapvaal Craton. Oblique and diachronous collision, initiated in the southwestern portions of the combined Natal Sector/Grunehogna Province system produced a laterally variable Mfongosi Group, which formed in the ‘Mfongosi Basin’. Coarse-grained sediments dominated in its eastern portions while basalts with thin sapropelite units dominated in its western portions.     

Temnospondyls from the Beaufort Group (Karoo Basin) of South Africa and Their Biostratigraphy

The Permo-Triassic Beaufort Group (Karoo Basin) of South Africa is biostratigraphically subdivided into eight, temporally successive assemblage zones based on therapsids (‘mammal-like reptiles’). The Temnospondyli, fossil tetrapods usually regarded as extinct amphibians, are second only to therapsids in terms of diversity and abundance in these strata, with nine higher-level taxa (‘families’) known. Temnospondyls are also playing an increasingly important role in biostratigraphy and correlation of the Beaufort strata. The lower Beaufort Group (Late Permian) contains six of the eight biozones, but only one temnospondyl ‘family’, the Rhinesuchidae, whose record in the Karoo is the richest in the world. However, rhinesuchid taxonomy remains in flux and the group is thus of limited biostratigraphic utility. The Early Triassic Lystrosaurus Assemblage Zone (middle Beaufort Group) contains the Rhinesuchidae, Amphibamidae, Lydekkerinidae, Tupilakosauridae, Rhytidosteidae, Mastodonsauridae and Trematosauridae, although the biostratigraphy of temnospondyls within this biozone is poorly constrained. The uppermost reaches of the Lystrosaurus biozone contain a paucity of fossils but includes ‘Kestrosaurus’ (Mastodonsauridae) and ?Trematosuchus (Trematosauridae), taxa previously thought to pertain to the lower part of the overlying Cynognathus biozone. The late Early to Middle Triassic Cynognathus Assemblage Zone (upper Beaufort Group) hosts the Mastodonsauridae, Trematosauridae, Brachyopidae, Laidleriidae and, possibly, the Rhytidosteidae. Based largely on the spatial and temporal distribution of mastodonsaurids, this biozone has been biostratigraphically subdivided into a lower A, middle B and upper C subzones, characterised by differing ages and faunas.     

Late Pleistocene-Holocene Paleoclimatic History of the Southern Kerala Basin, Southwest India

The South Kerala Sedimentary Basin (SKSB) constitutes one of the most significant landward extensions of the southwest offshore sedimentary basins of India, and is situated between 8^o45^' and 10^o15^' N latitudes. With a maximum width of about 20 km and incorporating a 700 m thick sedimentary succession ranging in age from Early Miocene to Holocene, this belt lies almost entirely under water or alluvium-covered coastal plains. In this study, we use two continuously cored bore holes at Eruva (7.25m deep) and Muthukulam (3m deep) separated by a distance of about 7km to investigate the depositional environment as well as paleo ecology of the depocentre and climatic aspects during the Late Pleistocene and Holocene. Results from C¹⁴ dating of shell fragments from Eruva (depth zone: 2.10–6.64m) yielded ages in the range of 36.2 to 42.5 kyBP corresponding to the late Pleistocene. Wood fragments in the Muthukulam core sample (depth zone: 1.27–3.00m) gave C¹⁴ ages in the range of 3.7 to 7.2 kyBP indicating a Holocene history. The lower half of the Eruva bore hole indicates a marginal marine environment with an abundant supply of terrestrial carbonaceous debris probably corresponding to a period of abnormally high rainfall recorded in many parts of the globe covered by the Asian summer monsoon. The sediments in the upper part of this bore hole indicate a continuation of this environment but with much less input of terrestrial organic carbon. The lower part of the bore hole from this locality, corresponding to the Holocene transgression, is similar to the lower part of Eruva bore hole in the case of TOC. Deposition took place in water bodies with considerable marine influence but receiving high amounts of terrestrial plant debris-mostly in the form of finely divided particles mixed with mud. This transgressive sequence was also deposited during a time when the Asian summer monsoon was abnormally high in intensity as indicated by many examples in India, Africa, Madagascar and elsewhere. It is significant that during the deposition of this part, the sea level was probably the same as present or higher suggesting possible lowering of the stream velocities and resultant deposition of only muddy sediments laden with terrestrial organic material along the coast. The upper part of the section shows a progressively reduced rainfall pattern culminating in a period of very low precipitation with the development of a paleosol, which is traceable all over the SKSB where Late Holocene sediments are available. This period also witnessed aeolian activity modifying the sand ridges in the ridge-runnel systems formed by the Holocene regression.     

Researching the South African tourism and development nexus

Under apartheid, tourism was essentially anti-developmental in focus and tourism research largely centred on the recreation of white South Africans. Since the 1994 democratic transition tourism has become recognised as an increasingly important sector for South Africa's economy and for achieving the government's goals for reconstruction and development. In this paper a review and critical analysis is presented of the changing directions and foci of tourism scholarship in South Africa. It is shown that South African scholars are beginning to respond to the challenges posed by tourism as a developmental focus. This revised version was published online in August 2006 with corrections to the Cover Date.     

Time-Frequency Variations of Plio-Pleistocene Foraminiferal Isotopes： A Case Study from Southern South China Sea

The continuous wavelet transform (CWT) analysis reveals the instantaneous variability of the foraminiferal δ18O and δ13C of Site 1143 for the past 5 Ma at the eccentricity, obliquity and precession bands. The cross CWT analysis further demonstrates nonstationary phases of the benthic -δ18O relative to ETP at the three primary Milankovitch bands in the last 5 Ma. The instantaneous phases between benthic -δ18O and δ13C at the precession band display a prominent 128 ka period, probably the cyclicity of the nonstationary climate close to the eccentricity. To explain these nonstationary phases, it is desirable to introduce a nonlinear response model to the global climate system, in which the output has a prominent cycle around 100 ka to match the 128 ka cycle of the instantaneous phase of the δ13C and -δ18O on the precession band.     

Seismic studies of the Brasília fold belt at the western border of the São Francisco Craton, Central Brazil, using receiver function, surface-wave dispersion and teleseismic tomography

The Tocantins Province in Central Brazil is composed of a series of SSW–NNE trending terranes of mainly Proterozoic ages, which stabilized in the Neoproterozoic in the final collision between the Amazon and São Francisco cratons. No previous information on crustal seismic properties was available for this region. Several broadband stations were used to study the regional patterns of crustal and upper mantle structure, extending the results of a recent E–W seismic refraction profile. Receiver functions and surface wave dispersion showed a thin crust (33–37 km) in the Neoproterozoic Magmatic Arc terrane. High average crustal Vp/Vs ratios (1.74–1.76) were consistently observed in this unit. The foreland domain of the Brasília foldbelt, on the other hand, is characterized by thicker crust (42–43 km). Low Vp/Vs ratios (1.70–1.72) were observed in the low-grade foreland fold and thrust zone of the Brasília belt adjacent to the São Francisco craton. Teleseismic P-wave tomography shows that the lithospheric upper mantle has lower velocities beneath the Magmatic Arc and Goiás Massif compared with the foreland zone of the belt and São Francisco craton. The variations in crustal thickness and upper mantle velocities observed with the broadband stations correlate well with the measurements along the seismic refraction profile. The integration of all seismic observations and gravity data indicates a strong lithospheric contrast between the Goiás Massif and the foreland domain of the Brasília belt, whereas little variation was found across the foldbelt/craton surface boundary. These results support the hypothesis that the Brasília foreland domain and the São Francisco craton were part of a larger São Francisco-Congo continental plate in the final collision with the Amazon plate.     

南方NGS200应用实践中的若干问题

对南方NGS200在工程控制测量领域应用实践中的一些问题作了阐述，提出了一些见解和措施。