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Geochronology of the Precambrian crust in the Mozambique belt in NE Mozambique, and implications for Gondwana assembly 总被引：2，自引：0，他引：2
B. Bingen J. Jacobs G. Viola I.H.C. Henderson
. Skr R. Boyd R.J. Thomas A. Solli R.M. Key E.X.F. Daudi 《Precambrian Research》2009,170(3-4):231-255
Zircon and monazite U–Pb data document the geochronology of the felsic crust in the Mozambique Belt in NE Mozambique. Immediately E of Lake Niassa and NW of the Karoo-aged Maniamba Graben, the Ponta Messuli Complex preserves Paleoproterozoic gneisses with granulite-facies metamorphism dated at 1950 ± 15 Ma, and intruded by granite at 1056 ± 11 Ma. This complex has only weak evidence for a Pan-African metamorphism. Between the Maniamba Graben and the WSW–ENE-trending Lurio (shear) Belt, the Unango and Marrupa Complexes consist mainly of felsic orthogneisses dated between 1062 ± 13 and 946 ± 11 Ma, and interlayered with minor paragneisses. In these complexes, an amphibolite- to granulite-facies metamorphism is dated at 953 ± 8 Ma and a nepheline syenite pluton is dated at 799 ± 8 Ma. Pan-African deformation and high-grade metamorphism are more intense and penetrative southwards, towards the Lurio Belt. Amphibolite-facies metamorphism is dated at 555 ± 11 Ma in the Marrupa Complex and amphibolite- to granulite-facies metamorphism between 569 ± 9 and 527 ± 8 Ma in the Unango Complex. Post-collisional felsic plutonism, dated between 549 ± 13 and 486 ± 27 Ma, is uncommon in the Marrupa Complex but common in the Unango Complex. To the south of the Lurio Belt, the Nampula Complex consists of felsic orthogneisses which gave ages ranging from 1123 ± 9 to 1042 ± 9 Ma, interlayered with paragneisses. The Nampula Complex underwent amphibolite-facies metamorphism in the period between 543 ± 23 to 493 ± 8 Ma, and was intruded by voluminous post-collisional granitoid plutons between 511 ± 12 and 508 ± 3 Ma. In a larger context, the Ponta Messuli Complex is regarded as part of the Palaeoproterozoic, Usagaran, Congo-Tanzania Craton foreland of the Pan-African orogen. The Unango, Marrupa and Nampula Complexes were probably formed in an active margin setting during the Mesoproterozoic. The Unango and Marrupa Complexes were assembled on the margin of the Congo-Tanzania Craton during the Irumidian orogeny (ca. 1020–950 Ma), together with terranes in the Southern Irumide Belt. The distinctly older Nampula Complex was more probably linked to the Maud Belt of Antarctica, and peripheral to the Kalahari Craton during the Neoproterozoic. During the Pan-African orogeny, the Marrupa Complex was overlain by NW-directed nappes of the Cabo Delgado Nappe Complex before peak metamorphism at ca. 555 Ma. The nappes include evidence for early Pan-African orogenic events older than 610 Ma, typical for the Eastern Granulites in Tanzania. Crustal thickening at 555 ± 11 Ma is coeval with high-pressure granulite-facies metamorphism along the Lurio Belt at 557 ± 16 Ma. Crustal thickening in NE Mozambique is part of the main Pan-African, Kuunga, orogeny peaking between 570 and 530 Ma, during which the Congo-Tanzania, Kalahari, East Antarctica and India Cratons welded to form Gondwana. Voluminous post-collisional magmatism and metamorphism younger than 530 Ma in the Lurio Belt and the Nampula Complex are taken as evidence of gravitational collapse of the extensive orogenic domain south of the Lurio Belt after ca. 530 Ma. The Lurio Belt may represent a Pan-African suture zone between the Kalahari and Congo-Tanzania Craton. 相似文献
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K. Solli B. Kuvaas Y. Kristoffersen G. Leitchenkov J. Guseva V. Gandjukhin 《Marine Geophysical Researches》2008,29(1):51-69
A set of multi-channel seismic profiles (∼15,000 km) is used to study the depositional evolution of the Cosmonaut Sea margin
of East Antarctica. We recognize a regional sediment wedge, below the upper parts of the continental rise, herein termed the
Cosmonaut Sea Wedge. The wedge is situated stratigraphically below the inferred glaciomarine section and extends for at least
1,200 km along the continental margin with a width that ranges from 80 to about 250 km. The morphology of the wedge and its
associated depositional features indicate a complex depositional history, where the deep marine depositional sites were influenced
by both downslope and alongslope processes. This interaction resulted in the formation of several proximal depocentres, which
at their distal northern end are flanked by elongated mounded drifts and contourite sheets. The internal stratification of
the mounded drift deposits indicates that westward flowing bottom currents reworked the marginal deposits. The action of these
currents together with sea-level changes is considered to have controlled the growth of the wedge. We interpret the Cosmonaut
Sea Wedge as a composite feature comprising several bottom current reworked fan systems. The wide spectrum of depositional
geometries in the stratigraphic column reflects dramatic variations in sediment supply from the continental margin as well
as varying interaction between downslope and alongslope processes. 相似文献
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This paper investigates how transportation sector managers perceive and utilize climate science, and subsequently, how they appropriate the climate change problem. The analysis focuses on which devices they qualify as useful for translating between knowledge, policy and practice concluding with a discussion of what this suggests in the development of efficient climate adaptation strategies. The paper demonstrates that although transportation sector managers accept the findings of climate science knowledge presented to them, their understanding of the climate change problem and the range of qualifying anchoring devices used in the development of climate adaption strategies are differentiated according to where they are located in the institutional context. For transportation sector managers on the regional and district level, the climate problem is largely perceived through the occurrence of extreme weather rather than through climate science. However, this knowledge basis is not considered sufficient to support ‘knowing how to act’ and has resulted in waiting for the authorities to make standards and regulations that would translate climate change knowledge into methods of practice. We argue that the development of standards and regulations might be underestimated in relation to user demands in climate adaptation work that involves reconciling scientific information. 相似文献
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K. Solli B. Kuvaas Y. Kristoffersen G. Leitchenkov J. Guseva V. Gandjukhin 《Marine Geophysical Researches》2007,28(1):43-57
Multichannel seismic data from the eastern parts of the Riiser-Larsen Sea have been analyzed with a sequence stratigraphic
approach. The data set covers a wide bathymetric range from the lower continental slope to the abyssal plain. Four different
sequences (termed RLS-A to RLS-D, from deepest to shallowest) are recognized within the sedimentary section. The RLS-A sequence
encompasses the inferred pre-glacial part of the deposits. Initial phases of ice sheet arrival at the eastern Riiser-Larsen
Sea margin resulted in the deposition of multiple debris flow units and/or slumps on the upper part of the continental rise
(RLS-B). The nature and distribution of these deposits indicate sediment supply from a line or a multi-point source. The subsequent
stage of downslope sediment transport activity was dominated by turbidity currents, depositing mainly as distal turbidite
sheets on the lower rise/abyssal plain (RLS-C). We attribute this to margin progradation and/or a more focussed sediment delivery
to the continental shelf edge. As the accommodation space on the lower rise/abyssal plain declined and the base level was
raised, the turbidite channels started to backstep and develop large channel–levee complexes on the upper parts of the continental
rise (RLS-D). The deposition of various drift deposits on the lower rise/abyssal plain and along the western margin of the
Gunnerus Ridge indicates that the RLS-D sequence is also associated with increased activity of contour currents. The drift
deposits overlie a distinct regional unconformity which is considered to reflect a major paleoceanographic event, probably
related to a Middle Miocene intensification of the Antarctic Circumpolar Current. 相似文献
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