Tectonic setting of the Balaram-Kui-Surpagla-Kengora granulites of the South Delhi Terrane of the Aravalli Mobile Belt,NW India and its implication on correlation with the East African Orogen in the Gondwana assembly     

Yengkhom Kesorjit Singh  Bert De Waele  Subrata Karmakar  Sunayana Sarkar  Tapas Kumar Biswal 《Precambrian Research》2010

Granulites are developed in various tectonic settings and during different geological periods, and have been used for continental correlation within supercontinent models. In this context the Balaram-Kui-Surpagla-Kengora granulites of the South Delhi Terrane of the Aravalli Mobile Belt of northwestern India are significant. The granulites occur as shear zone bounded lensoidal bodies within low-grade rocks of the South Delhi Terrane and comprise pelitic and calcareous granulites, a gabbro-norite-basic granulite suite and multiple phases of granites of the Ambaji suite. The granulites have undergone three major phases of folding and shearing. The F₁ and F₂ folds are coaxial along NE-SW axis, and F₃ folds are developed across the former along NW-SE axis. Thus, various types of interference patterns are produced. The granulite facies metamorphism is marked by a spinel–cordierite–garnet–sillimanite–quartz assemblage with melt phase and is synkinematic to the F₁ phase of folding. The peak thermobarometric condition is set at ≥850 °C and 5.5–6.8 kb. The granulites have been exhumed through thrusting along multiple ductile shear zones during syn- to post-F₂ folding. Late-stage shearing has produced cataclasites and pseudotachylites. Sensitive High Resolution Ion MicroProbe (SHRIMP) U–Pb dating of zircon from pelitic granulites and synkinematically emplaced granites indicate that: (1) the sedimentary succession of the South Delhi Terrane was deposited between 1240 and 860 Ma with detritus derived from magmatic sources with ages between 1620 and 1240 Ma; (2) folding and granulite metamorphism have taken place between ca. 860 and 800 Ma, and exhumation at around ca. 800–760 Ma; and (3) the last phase of granitic activity occurred at ca. 759 Ma. This shows, for the first time, that the granulites of the South Delhi Terrane are much younger than those of the Sandmata Granulite Complex of the northern part of the Aravalli Mobile Belt, the Saussar granulites of the Central India Mobile Belt and the Eastern Ghats Mobile Belt. Instead, they show similarities to the Neoproterozoic granulites of the Circum Indian Orogens that include the East African Orogen (East Africa and Madagascar), the Southern Granulite Terrane of India and much of Sri Lanka. We suggest that the South Delhi Basin probably marks a trace of the proto-Mozambique Ocean in NW India within Gondwana, that closed when the Marwar Craton, arc fragments (Bemarivo Belt in Madagascar and the Seychelles) and components of the Arabian-Nubian Shield collided with the Aravalli-Bundelkhand Protocontinent at ca. 850–750 Ma.  相似文献   

Interferometric studies of spectral lines in the solar corona     

Joseph G. Hirschberg  Alain Wouters  Lyman Hazelton Jr. 《Solar physics》1971,21(2):448-451

A photographic Fabry-Perot interferometer was used to measure the breadth and wavelength of the Fexiv spectral line at 5303 Å in the solar corona, during the eclipse of 7 March, 1970, in Mexico. The observations were consistent with a possible large-scale vortex structure in a bright streamer, in which cooler gases revolved about a hotter core.Work supported by the United States National Science Foundation and by the Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force, under Grant AF-AFOSR-68-1496.  相似文献   

Petrography, geochemistry, and geochronology of granitoid rocks in the Neoproterozoic-Paleozoic Lufilian–Zambezi belt, Zambia: Implications for tectonic setting and regional correlation     

Crispin Katongo  Friedrich Koller  Urs Kloetzli  Christian Koeberl  Francis Tembo  Bert De Waele 《Journal of African Earth Sciences》2004,40(5):219

There are several pre-orogenic Neoproterozoic granitoid and metavolcanic rocks in the Lufilian–Zambezi belt in Zambia and Zimbabwe that are interpreted to have been emplaced in a continental-rift setting that is linked to the break-up of the Rodinia supercontinent. However, no geochemical data were previously available for these rocks in the Zambian part of the belt to support this model. We conducted petrographic and whole-rock chemical analyses of the Neoproterozoic Nchanga Granite, Lusaka Granite, Ngoma Gneiss and felsic metavolcanic rocks from the Lufilian–Zambezi belt in Zambian, in order to evaluate their chemical characteristics and tectonic settings. Other magmatic rocks of importance for understanding the evolution of the belt in Zambia, included in this study, are the Mesoproterozoic Munali Hills Granite and associated amphibolites and the Mpande Gneiss. The Neoproterozoic rocks have monzogranitic compositions, aluminum-saturation indices (ASI) < 1.1, and high contents of high field strength elements (HFSE) and rare earth elements (REE). The chondrite-normalised spider diagrams are similar to those of A-type granites from the Lachlan fold belt and show negative Sr, P, and Ti anomalies. On various tectonic discrimination diagrams the Neoproterozoic rocks plot mainly in A-type granite fields. These petrographic and trace element compositions indicate that these rocks are A-type felsic rocks, but they do not have features of granites and rhyolites emplaced in true continental-rift settings, as previously suggested. On the basis of the A-type features and independent regional geological and geochronological data, we suggest that the Neoproterozoic granitoid and felsic metavolcanic rocks were emplaced during the earliest extensional stages of continental rifting in the Lufilian–Zambezi belt. The apparent continental-arc like chemistry of the granitoid and felsic metavolcanic rocks is thus inferred to be inherited from calcalkaline sources. The Mesoproterozoic Munali Hills Granite and Mpande Gneiss have trace element features e.g., Nb–Ta depletions, which indicate that that these gneisses were emplaced in a convergent-margin setting. The MORB-normalised spider diagram of co-magmatic amphibolites exhibit a fractionated LILE/HFSE pattern recognized in subduction zones. This inference is consistent with remnants of ocean crust, juvenile Island arcs and ophiolites elsewhere in the Mesoproterozoic Irumide belt in Zambia and Zimbabwe. In addition, we report the first U–Pb zircon age of 1090.1 ± 1.3 Ma for the Munali Hills Granite. The age for the Munali Hills Granite provides new constraints on correlation and tectono-thermal activity in the Lufilian–Zambezi belt. The age of the Munali Hills Granite indicates that some supracrustal rocks in the Zambezi belt of Zambia, which were previously thought to be Neoproterozoic and correlated with the Katanga Supergroup in the Lufilian belt, are Mesoproterozoic or older. Consequently, previous regional lithostratigraphic correlations in the Lufilian–Zambezi belt would require revision.  相似文献   

Book reviews     

Bert Bolin  G. Shaw  Michel M. Verstraete  M. J. Salinger 《Climatic change》1986,9(3):363-366

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Coastal morphometry as regulator of water exchange—a Swedish example     

Lars Hkanson  Hans Kvarns  Bert Karlsson 《Estuarine, Coastal and Shelf Science》1986,23(6)

This is a paper from the Swedish research project ‘The coastal zone—scientific criteria for planners’. The goal has been to establish simple, general scientific methods for management of Swedish coastal waters. In this paper the focus is on a set of empirical data from 21 so-called type areas and on the exchange of surface water. The working hypothesis has been that the water retention (or residence) time is regulated by the morphometry. The theory has been verified. It has been shown that the water retention time can be determined from a formula based on only two key morphometric parameters, the exposure and the mean coastal width. It provides an 86% degree of explanation (r²=0·86) of the variation in empirically determined retention times and can be physically linked to the basic mass balance equation. The formula is valid for the bioproductive season (May–Oct.) and for small (1–100 km²) Swedish coastal areas. It cannot be directly applied to areas affected by heavy tides.  相似文献   

Beta diversity of tropical marine benthic assemblages in the Spermonde Archipelago, Indonesia     

Leontine E. Becking  Daniel F. R. Cleary  Nicole J. de  Voogd  Willem Renema  Manon de  Beer  Rob W. M. van  Soest & Bert W. Hoeksema 《Marine Ecology》2006,27(1):76-88

In order to preserve diversity it is essential to understand how assemblages change across space. Despite this fact, we still know very little about how marine diversity is spatially distributed, especially among lesser‐studied invertebrate taxa. In the present study beta‐diversity patterns of sea urchins, sponges, mushroom corals and larger foraminifera were assessed in the Spermonde Archipelago (Indonesia). Using ordinations we showed that the inshore zone (<5 km offshore), midshore zone (5 < x < 30 km offshore) and distance offshore zone (>30 km offshore) all contained distinct assemblages of sponges and corals, while only foraminifera assemblages from the inshore (<5 km offshore) zone were distinct. There was a significant spatial pattern of community similarity for all taxa surveyed, but this pattern proved to be wholly related to environmental variables for sponges and foraminifera, and primarily for mushroom corals and sea urchins. The lack of a pure spatial component suggests that these taxa may not be dispersal limited within the spatial scales of this study (c. 1600 km²). The analyses of the corals and foraminifera were additionally tested at two spatial scales of sampling. Both taxa were primarily associated with local‐scale environmental variables at the local scale and larger‐scale variables at the larger scale. Mean inter‐plot similarity was also higher and variation lower at the larger scale. The results suggest that substantial variation in similarity can be predicted using simple locally assessed environmental variables combined with remotely sensed parameters.  相似文献   

Exploring the hydrological effects of normal faults at the boundary of the Roer Valley Graben in Belgium using a catchment-scale groundwater flow model     

Casillas-Trasvina  Alberto  Rogiers  Bart  Beerten  Koen  Wouters  Laurent  Walraevens  Kristine 《Hydrogeology Journal》2022,30(1):133-149

Hydrogeology Journal - Faults may impact regional groundwater flow and transport, so it is important to include them during aquifer-system conceptualization and while constructing groundwater flow...  相似文献   

Science and User Needs for Observing Global Mass Transport to Understand Global Change and to Benefit Society     

Roland Pail  Rory Bingham  Carla Braitenberg  Henryk Dobslaw  Annette Eicker  Andreas Güntner  Martin Horwath  Eric Ivins  Laurent Longuevergne  Isabelle Panet  Bert Wouters  IUGG Expert Panel 《Surveys in Geophysics》2015,36(6):743-772

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Climate Change Policy Targets and the Role of Technological Change     

Marco A. Janssen  Bert de Vries 《Climatic change》2000,46(1-2):1-28

In this paper, we present results of simulationexperiments with the TIME-model on the issue ofmitigation strategies with regard to greenhouse gases.The TIME-model is an integrated system dynamics worldenergy model that takes into account the fact that the systemhas an inbuilt inertia and endogenouslearning-by-doing dynamics, besides the more commonelements of price-induced demand response and fuelsubstitution. First, we present four scenarios tohighlight the importance of assumptions on innovationsin energy technology in assessing the extent to whichCO₂ emissions have to be reduced. The inertia ofthe energy system seems to make a rise ofCO₂ emissions in the short term almostunavoidable. It is concluded that for the populationand economic growth assumptions of the IPCC IS92ascenario, only a combination of supply- anddemand-side oriented technological innovations incombination with policy measures can bring the targetof CO₂-concentration stabilization at 550 ppmv bythe year 2100 within reach. This will probably beassociated with a temporary increase in the overallenergy expenditures in the world economy. Postponingthe policy measures will be more disadvantageous,and less innovation in energy technology willhappen.  相似文献   

A multi-model comparison of Atlantic multidecadal variability     

Jin Ba  Noel S. Keenlyside  Mojib Latif  Wonsun Park  Hui Ding  Katja Lohmann  Juliette Mignot  Matthew Menary  Odd Helge Otterå  Bert Wouters  David Salas y Melia  Akira Oka  Alessio Bellucci  Evgeny Volodin 《Climate Dynamics》2014,43(9-10):2333-2348

A multi-model analysis of Atlantic multidecadal variability is performed with the following aims: to investigate the similarities to observations; to assess the strength and relative importance of the different elements of the mechanism proposed by Delworth et al. (J Clim 6:1993–2011, 1993) (hereafter D93) among coupled general circulation models (CGCMs); and to relate model differences to mean systematic error. The analysis is performed with long control simulations from ten CGCMs, with lengths ranging between 500 and 3600 years. In most models the variations of sea surface temperature (SST) averaged over North Atlantic show considerable power on multidecadal time scales, but with different periodicity. The SST variations are largest in the mid-latitude region, consistent with the short instrumental record. Despite large differences in model configurations, we find quite some consistency among the models in terms of processes. In eight of the ten models the mid-latitude SST variations are significantly correlated with fluctuations in the Atlantic meridional overturning circulation (AMOC), suggesting a link to northward heat transport changes. Consistent with this link, the three models with the weakest AMOC have the largest cold SST bias in the North Atlantic. There is no linear relationship on decadal timescales between AMOC and North Atlantic Oscillation in the models. Analysis of the key elements of the D93 mechanisms revealed the following: Most models present strong evidence that high-latitude winter mixing precede AMOC changes. However, the regions of wintertime convection differ among models. In most models salinity-induced density anomalies in the convective region tend to lead AMOC, while temperature-induced density anomalies lead AMOC only in one model. However, analysis shows that salinity may play an overly important role in most models, because of cold temperature biases in their relevant convective regions. In most models subpolar gyre variations tend to lead AMOC changes, and this relation is strong in more than half of the models.  相似文献