Science.gov

Sample records for african crust evidence

  1. Shear Wave Velocity Structure of Southern African Crust: Evidence for Compositional Heterogeneity within Archaean and Proterozoic Terrains

    SciTech Connect

    Kgaswane, E M; Nyblade, A A; Julia, J; Dirks, P H H M; Durrheim, R J; Pasyanos, M E

    2008-11-11

    Crustal structure in southern Africa has been investigated by jointly inverting receiver functions and Rayleigh wave group velocities for 89 broadband seismic stations spanning much of the Precambrian shield of southern Africa. 1-D shear wave velocity profiles obtained from the inversion yield Moho depths that are similar to those reported in previous studies and show considerable variability in the shear wave velocity structure of the lower part of the crust between some terrains. For many of the Archaean and Proterozoic terrains in the shield, S velocities reach 4.0 km/s or higher over a substantial part of the lower crust. However, for most of the Kimberley terrain and adjacent parts of the Kheis Province and Witwatersrand terrain, as well as for the western part of the Tokwe terrain, mean shear wave velocities of {le} 3.9 km/s characterize the lower part of the crust along with slightly ({approx}5 km) thinner crust. These findings indicate that the lower crust across much of the shield has a predominantly mafic composition, except for the southwest portion of the Kaapvaal Craton and western portion of the Zimbabwe Craton, where the lower crust is intermediate-to-felsic in composition. The parts of the Kaapvaal Craton underlain by intermediate-to-felsic lower crust coincide with regions where Ventersdorp rocks have been preserved, and thus we suggest that the intermediate-to-felsic composition of the lower crust and the shallower Moho may have resulted from crustal melting during the Ventersdorp tectonomagmatic event at c. 2.7 Ga and concomitant crustal thinning caused by rifting.

  2. The Mafic Lower Crust of Neoproterozoic age beneath Western Arabia: Implications for Understanding African Lower Crust

    NASA Astrophysics Data System (ADS)

    Stern, R. J.; Mooney, W. D.

    2011-12-01

    ) and Cr (435 vs. 117 ppm). Despite high Mg# in pyroxene-rich xenoliths, mineral compositions of labradoritic plagioclase (mean ~An64) and relatively Fe-rich pyroxenes (mean OPX ~En63; mean CPX~ WO48 En35 Fs17) indicate that these are somewhat fractionated. Trace element patterns are similar to those expected for convergent-margin magmatic suites. Nd-model ages define a mean of 0.76±0.08 Ga, similar to the age of exposed Arabian Shield upper crust. An isochron plot (147Sm/144Nd vs. 143Nd/144Nd) is consistent with formation in Neoproterozoic time. Lower crust of Arabia clearly formed during Neoproterozoic time, about the same time as its upper crust complement; a similar origin for the lower crust beneath the broad expanses of Neoproterozoic crust in N and E Africa is likely. There is no evidence that any of the mafic lower crust of Arabia formed due to underplating by Cenozoic magmas, which may also be true for NE Africa and perhaps mafic lower crust on the flanks of the East African Rift. Such an interpretation predicts a strong lower crust for those regions underlain by anhydrous mafic lower crust of Neoproterozoic age.

  3. Evolution of the earth's crust: Evidence from comparative planetology

    NASA Technical Reports Server (NTRS)

    Lowman, P. D., Jr.

    1973-01-01

    Geochemical data and orbital photography from Apollo, Mariner, and Venera missions were combined with terrestrial geologic evidence to study the problem of why the earth has two contrasting types of crust (oceanic and continental). The following outline of terrestrial crustal evolution is proposed. A global crust of intermediate to acidic composition, high in aluminum, was formed by igneous processes early in the earth's history; portions survive in some shield areas as granitic and anorthositic gneisses. This crust was fractured by major impacts and tectonic processes, followed by basaltic eruptions analogous to the lunar maria and the smooth plains of the north hemisphere of Mars. Seafloor spreading and subduction ensued, during which portions of the early continental crust and sediments derived therefrom were thrust under the remaining continental crust. The process is exemplified today in regions such as the Andes/Peru-Chile trench system. Underplating may have been roughly concentric, and the higher radioactive element content of the underplated sialic material could thus eventually cause concentric zones of regional metamorphism and magmatism.

  4. The African Plate: A history of oceanic crust accretion and subduction since the Jurassic

    NASA Astrophysics Data System (ADS)

    Gaina, C.; Torsvik, T. H.; Labails, C.; van Hinsbergen, D.; Werner, S.; Medvedev, S.

    2012-04-01

    Initially part of Gondwana and Pangea, and now surrounded almost entirely by spreading centres, the African plate moved relatively slowly for the last 200 million years. Yet both Africa's cratons and passive margins were affected by tectonic stresses developed at distant plate boundaries. Moreover, the African plate was partly underlain by hot mantle (at least for the last 300 Ma) - either a series of hotspots or a superswell, or both - that contributed to episodic volcanism, basin-swell topography, and consequent sediment deposition, erosion, and structural deformation. A systematic study of the African plate boundaries since the opening of surrounding oceanic basins is presently lacking. This is mainly because geophysical data are sparse and there are still controversies regarding the ages of oceanic crust. The publication of individual geophysical datasets and more recently, global Digital Map of Magnetic Anomalies (WDMAM, EMAG2) prompted us to systematically reconstruct the ages and extent of oceanic crust around Africa for the last 200 Ma. Location of Continent Ocean Boundary/Continent Ocean Transition and older oceanic crust (Jurassic and Cretaceous) are updates in the light of gravity, magnetic and seismic data and models of passive margin formation. Reconstructed NeoTethys oceanic crust is based on a new model of microcontinent and intr-oceanic subduction zone evolution in this area.The new set of oceanic palaeo-age grid models constitutes the basis for estimating the dynamics of oceanic crust through time and will be used as input for quantifying the paleo-ridge push and slab pull that contributed to the African plate palaeo-stresses and had the potential to influence the formation of sedimentary basins.

  5. Evidence for oceanic crust in the Herodotus Basin

    NASA Astrophysics Data System (ADS)

    Granot, Roi

    2016-04-01

    Some of the fundamental tectonic problems of the Eastern Mediterranean remain unresolved due to the extremely thick sedimentary cover (10 to 15 km) and the lack of accurate magnetic anomaly data. I have collected 7,000 km of marine magnetic profiles (2012-2014) across the Herodotus and Levant Basins, Eastern Mediterranean, to study the nature and age of the underlying igneous crust. The towed magnetometer array consisted of two Overhauser sensors recording the total magnetic anomaly field in a longitudinal gradiometer mode, and a fully oriented vector magnetometer. The total field data from the Herodotus Basin reveal a newly detected short sequence of long-wavelength NE-SW lineated anomalies that straddle the entire basin suggesting a deep two-dimensional magnetic source layer. The three components of the magnetic vector data indicate that an abrupt transition from a 2D to 3D magnetic structure occurs east of the Herodotus Basin, along where a prominent NE-SW gravity feature is found. Altogether, these new findings confirm that the Herodotus Basin preserves remnants of oceanic crust that formed along the Neotethyan mid-ocean ridge system. The continuous northward and counterclockwise motion of the African Plate during the Paleozoic and Mesozoic allow predicting the evolution of remanent magnetization directions, which in-turn dictate that shape of the anomalies. The shape of the Herodotus anomalies best fit Late Carboniferous to Early Permian (300±20 Myr old) magnetization directions. Finally, I will discuss the implications of these results on the tectonic architecture of the region as well as on various geodynamic processes.

  6. Eclogite xenoliths in west African kimberlites as residues from Archaean granitoid crust formation

    NASA Astrophysics Data System (ADS)

    Rollinson, Hugh

    1997-09-01

    Eclogites are a comparatively rare but petrologically important member of kimberlite xenolith suites. Their broadly basaltic chemistry has led many authors to propose that they represent ancient, subducted ocean crust. Recent studies, however, have suggested an alternative origin and propose that kimberlitic eclogites are residues from the process of Archaean granitoid crust formation. Geochemical arguments in support of this new model were previously based on the trace-element chemistry of eclogitic minerals. Here I report that the major-element chemistry of eclogite xenoliths also supports a crustal residue model. I examine eclogite xenoliths from kimberlite pipes at Koidu, Sierra Leone, which sample the lithospheric mantle underlying the Archaean (2.8Gyr) granitoid crust of the West African craton. Geochemical plots of major elements measured in unaltered, whole-rock samples of low-silica eclogite demonstrate that they are complementary to the granitoids of the West African craton and have compositions which indicate that both were derived from a common basaltic parent rock.

  7. African American Homeschooling Practices: Empirical Evidence

    ERIC Educational Resources Information Center

    Mazama, Ama

    2016-01-01

    Despite a significant increase in scholarly interest for homeschooling, some of its most critical aspects, such as instructional daily practices, remain grossly understudied. This essay thus seeks to fill that void by presenting empirical evidence regarding the homeschooling practices of a specific group, African Americans. Most specifically, the…

  8. Pb isotopic evidence for early Archaean crust in South Greenland

    NASA Astrophysics Data System (ADS)

    Taylor, P. N.; Kalsbeek, F.

    The results of an isotopic remote sensing study focussed on delineating the extent of Early Archean crust north and south of the Nuuk area and in south Greenland is presented. Contamination of the Late Archean Nuk gneisses and equivalents by unradiogenic Pb uniquely characteristic of Amitsoq gneiss was detected as far south as Sermilik about 70 km south of Nuuk and only as far north as the mouth of Godthabsfjord. This study was extended to the southern part of the Archean craton and the adjoining Early Proterozoic Ketilidian orogenic belt where the Pb isotopes suggest several episodes of reworking of older uranium depleted continental crust. The technique of using the Pb isotope character of younger felsic rocks, in this case Late Archean and Early Proterozoic gneisses and granites to sense the age and isotopic character of older components, is a particularly powerful tool for reconstructing the evolutionary growth and development of continental crust.

  9. Pb isotopic evidence for early Archaean crust in South Greenland

    NASA Technical Reports Server (NTRS)

    Taylor, P. N.; Kalsbeek, F.

    1986-01-01

    The results of an isotopic remote sensing study focussed on delineating the extent of Early Archean crust north and south of the Nuuk area and in south Greenland is presented. Contamination of the Late Archean Nuk gneisses and equivalents by unradiogenic Pb uniquely characteristic of Amitsoq gneiss was detected as far south as Sermilik about 70 km south of Nuuk and only as far north as the mouth of Godthabsfjord. This study was extended to the southern part of the Archean craton and the adjoining Early Proterozoic Ketilidian orogenic belt where the Pb isotopes suggest several episodes of reworking of older uranium depleted continental crust. The technique of using the Pb isotope character of younger felsic rocks, in this case Late Archean and Early Proterozoic gneisses and granites to sense the age and isotopic character of older components, is a particularly powerful tool for reconstructing the evolutionary growth and development of continental crust.

  10. In situ evidence for continental crust on early Mars

    NASA Astrophysics Data System (ADS)

    Sautter, V.; Toplis, M. J.; Wiens, R. C.; Cousin, A.; Fabre, C.; Gasnault, O.; Maurice, S.; Forni, O.; Lasue, J.; Ollila, A.; Bridges, J. C.; Mangold, N.; Le Mouélic, S.; Fisk, M.; Meslin, P.-Y.; Beck, P.; Pinet, P.; Le Deit, L.; Rapin, W.; Stolper, E. M.; Newsom, H.; Dyar, D.; Lanza, N.; Vaniman, D.; Clegg, S.; Wray, J. J.

    2015-08-01

    Understanding of the geologic evolution of Mars has been greatly improved by recent orbital, in situ and meteorite data, but insights into the earliest period of Martian magmatism (4.1 to 3.7 billion years ago) remain scarce. The landing site of NASA’s Curiosity rover, Gale crater, which formed 3.61 billion years ago within older terrain, provides a window into this earliest igneous history. Along its traverse, Curiosity has discovered light-toned rocks that contrast with basaltic samples found in younger regions. Here we present geochemical data and images of 22 specimens analysed by Curiosity that demonstrate that these light-toned materials are feldspar-rich magmatic rocks. The rocks belong to two distinct geochemical types: alkaline compositions containing up to 67 wt% SiO2 and 14 wt% total alkalis (Na2O + K2O) with fine-grained to porphyritic textures on the one hand, and coarser-grained textures consistent with quartz diorite and granodiorite on the other hand. Our analysis reveals unexpected magmatic diversity and the widespread presence of silica- and feldspar-rich materials in the vicinity of the landing site at Gale crater. Combined with the identification of feldspar-rich rocks elsewhere and the low average density of the crust in the Martian southern hemisphere, we conclude that silica-rich magmatic rocks may constitute a significant fraction of ancient Martian crust and may be analogous to the earliest continental crust on Earth.

  11. Magnetism of the oceanic crust: Evidence from ophiolite complexes

    SciTech Connect

    Banerjee, S.K.

    1980-07-10

    The magnetic properties of six ophiolite complexes from around the world, ranging in age from Jurassic to Miocene, are presented. An emphasis is placed in our study on the petrologic and isotopic data from these ophiolite complexes in order to determine first whether the rock samples presently available represent the pristine ocean crust or whether they have been altered subaerially since their formation. Five of the ophiolites are found to be acceptable, and the conclusion is overwhelmingly in favor of a marine magnetic source layer that includes not only the pillow lavas but also the underlying dikes and gabbro. At the moment, however, our observations do not suggest that the magnetic contributions of the basaltic dikes should be overlooked in favor of gabbro. A second important conclusion is that nearly pure magnetite could indeed be a magnetic carrier which contributes to marine magnetic anomanies. It only awaits discovery by deeper ocean crustal penetration by future Deep Sea Drilling Project legs.

  12. Thin crust as evidence for depleted mantle supporting the Marion Rise.

    PubMed

    Zhou, Huaiyang; Dick, Henry J B

    2013-02-14

    The global ridge system is dominated by oceanic rises reflecting large variations in axial depth associated with mantle hotspots. The little-studied Marion Rise is as large as the Icelandic Rise, considering both length and depth, but has an axial rift (rather than a high) nearly its entire length. Uniquely along the Southwest Indian Ridge systematic sampling allows direct examination of crustal architecture over its full length. Here we show that, unlike the Icelandic Rise, peridotites are extensively exposed high on the rise, revealing that the crust is generally thin, and often missing, over a rifted rise. Therefore the Marion Rise must be largely an isostatic response to ancient melting events that created low-density depleted mantle beneath the Southwest Indian Ridge rather than thickened crust or a large thermal anomaly. The origin of this depleted mantle is probably the mantle emplaced into the African asthenosphere during the Karoo and Madagascar flood basalt events. PMID:23389441

  13. Evidence for a thick oceanic crust adjacent to the Norwegian Margin

    NASA Astrophysics Data System (ADS)

    Mutter, John C.; Talwani, Manik; Stoffa, Paul L.

    1984-01-01

    The oceanic crust created during this first few million years of accretion in the Norwegian-Greenland Sea lies at an unusually shallow depth for its age, has a smooth upper surface, and in many places the results of multichannel seismic reflection profiling reveal that its upper layers comprise a remarkable sequence of arcuate, seaward-dipping reflectors. These have been attributed to lava flows generated during a brief period of subaerial seafloor spreading. We describe the results of inversions of digitally recorded sonobuoy measurements and two-ship expanded spread profiles collected over the oceanic crust adjacent to the Norwegian passive margin. We find that the crust of the deep Lofoten Basin is indistinguishable from normal oceanic crust in thickness and structure. Closer to the margin we observe up to a four times expansion in thickness of layers with velocities equal to those of oceanic layer 2, while the layer 3 region retains approximately the same thickness. The area over which the seaward-dipping reflectors can be observed on reflection profiles corresponds to the region of greatest expansion in "Layer 2" thickness. In the very oldest crust immediately adjacent to an escarpment that probably marks the continent-ocean boundary, we see evidence for a low velocity zone overlying an indistinct reflector that may mark the dyke-lava interface in the thick crust. Comparing the structure of the thick crust to that of eastern Iceland, we find a strong resemblance, especially in the expansion in thickness of material with layer 2 velocities. These results support the suggestion that during the earliest stages of spreading extrusive volcanism at the ridge crest was unusually voluminous, building a thick pile of lavas erupted from a subaerial spreading center.

  14. Petrochemical and petrophysical characterization of the lower crust and the Moho beneath the West African Craton, based on Xenoliths from Kimberlites

    NASA Technical Reports Server (NTRS)

    Haggerty, Stephen E.; Toft, Paul B.

    1988-01-01

    Additional evidence to the composition of the lower crust and uppermost mantle was presented in the form of xenolith data. Xenoliths from the 2.7-Ga West African Craton indicate that the Moho beneath this shield is a chemically and physically gradational boundary, with intercalations of garnet granulite and garnet eclogite. Inclusions in diamonds indicate a depleted upper mantle source, and zenolith barometry and thermometry data suggest a high mantle geotherm with a kink near the Moho. Metallic iron in the xenoliths indicates that the uppermost mantle has a significant magnetization, and that the depth to the Curie isotherm, which is usually considered to be at or above the Moho, may be deeper than the Moho.

  15. Sources of continental crust: neodymium isotope evidence from the sierra nevada and peninsular ranges.

    PubMed

    Depaolo, D J

    1980-08-01

    Granitic rocks from batholiths of the Sierra Nevada and Peninsular Ranges exhibit initial (143)Nd/(144)Nd ratios that vary over a large range and correlate with (87)Sr/(86)Sr ratios. The data suggest that the batholiths represent mixtures of materials derived from (i) chemically depleted mantle identical to the source of island arcs and (ii) old continental crust, probably sediments or metasediments with a provenance age of approximately 1.6 x 10(9) years. These conclusions are consistent with a model for continental growth whereby new crustal additions are repeatedly extracted from the same limited volume of the upper mantle, which has consequently become depleted in elements that are enriched in the crust. There is little evidence that hydrothermally altered, subducted oceanic crust is a primary source of the magmas. PMID:17821189

  16. Seawater osmium isotope evidence for a middle Miocene flood basalt event in ferromanganese crust records

    USGS Publications Warehouse

    Klemm, V.; Frank, M.; Levasseur, S.; Halliday, A.N.; Hein, J.R.

    2008-01-01

    Three ferromanganese crusts from the northeast, northwest and central Atlantic were re-dated using osmium (Os) isotope stratigraphy and yield ages from middle Miocene to the present. The three Os isotope records do not show evidence for growth hiatuses. The reconstructed Os isotope-based growth rates for the sections older than 10??Ma are higher than those determined previously by the combined beryllium isotope (10Be/9Be) and cobalt (Co) constant-flux methods, which results in a decrease in the maximum age of each crust. This re-dating does not lead to significant changes to the interpretation of previously determined radiogenic isotope neodymium, lead (Nd, Pb) time series because the variability of these isotopes was very small in the records of the three crusts prior to 10??Ma. The Os isotope record of the central Atlantic crust shows a pronounced minimum during the middle Miocene between 15 and 12??Ma, similar to a minimum previously observed in two ferromanganese crusts from the central Pacific. For the other two Atlantic crusts, the Os isotope records and their calibration to the global seawater curve for the middle Miocene are either more uncertain or too short and thus do not allow for a reliable identification of an isotopic minimum. Similar to pronounced minima reported previously for the Cretaceous/Tertiary and Eocene/Oligocene boundaries, possible interpretations for the newly identified middle Miocene Os isotope minimum include changes in weathering intensity and/or a meteorite impact coinciding with the formation of the No??rdlinger Ries Crater. It is suggested that the eruption and weathering of the Columbia River flood basalts provided a significant amount of the unradiogenic Os required to produce the middle Miocene minimum. ?? 2008 Elsevier B.V.

  17. Ancient oceanic crust in island arc lower crust: Evidence from oxygen isotopes in zircons from the Tanzawa Tonalitic Pluton

    NASA Astrophysics Data System (ADS)

    Suzuki, Kazue; Kitajima, Kouki; Sawaki, Yusuke; Hattori, Kentaro; Hirata, Takafumi; Maruyama, Shigenori

    2015-07-01

    Knowledge of the lithological variability and genesis of island arc crust is important for understanding continental growth. Although the volcanic architecture of island arcs is comparatively well known, the nature of island arc middle- and lower-crust remains uncertain owing to limited exposure. One of the best targets for deciphering the evolution of an island arc system is the Tanzawa Tonalites (4-9 Ma), in the intra-oceanic Izu-Bonin-Mariana arc. These tonalities which occupied a mid-crustal position were generated by partial melting of lower crust. To constrain protoliths of the plutonic rocks in the island arc lower crust, in-situ O-isotopic analysis using an IMS-1280 Secondary Ion Mass Spectrometer was carried out on 202 zircon grains separated from 4 plutons in the Tanzawa Tonalite. δ18O value of the zircons ranges from 4.1‰ to 5.5‰ and some zircons have δ18O slightly lower than the mantle range. The low zircon δ18O values from the Tanzawa Tonalite suggest that their protoliths involved materials with lower δ18O values than those of the mantle. Hydrothermally altered gabbros in the lower oceanic crust often have lower δ18O values than mantle and can be primary components of arc lower crust. The Tanzawa Tonalite is interpreted to have been formed by partial melting of island arc lower crust. Thus the low δ18O values in zircons from the Tanzawa Tonalites may originate by melting of the hydrothermally altered gabbro. Ancient oceanic crustal material was likely present in the Izu-Bonin-Mariana arc lower crust, at the time of formation of the Tanzawa Tonalites.

  18. Full seismic waveform inversion of the African crust and Mantle - Initial Results

    NASA Astrophysics Data System (ADS)

    Afanasiev, Michael; Ermert, Laura; Staring, Myrna; Trampert, Jeannot; Fichtner, Andreas

    2016-04-01

    We report on the progress of a continental-scale full-waveform inversion (FWI) of Africa. From a geodynamic perspective, Africa presents an especially interesting case. This interest stems from the presence of several anomalous features such as a triple junction in the Afar region, a broad region of high topography to the south, and several smaller surface expressions such as the Cameroon Volcanic Line and Congo Basin. The mechanisms behind these anomalies are not fully clear, and debate on their origin spans causative mechanisms from isostatic forcing, to the influence of localized asthenospheric upwelling, to the presence of deep mantle plumes. As well, the connection of these features to the African LLSVP is uncertain. Tomographic images of Africa present unique challenges due to uneven station coverage: while tectonically active areas such as the Afar rift are well sampled, much of the continent exhibits a severe dearth of seismic stations. As well, while mostly surrounded by tectonically active spreading plate boundaries (a fact which contributes to the difficulties in explaining the South's high topography), sizeable seismic events (M > 5) in the continent's interior are relatively rare. To deal with these issues, we present a combined earthquake and ambient noise full-waveform inversion of Africa. The noise component serves to boost near-surface sensitivity, and aids in mitigating issues related to the sparse source / station coverage. The earthquake component, which includes local and teleseismic sources, aims to better resolve deeper structure. This component also has the added benefit of being especially useful in the search for mantle plumes: synthetic tests have shown that the subtle scattering of elastic waves off mantle plumes makes the plumes an ideal target for FWI [1]. We hope that this new model presents a fresh high-resolution image of sub-African geodynamic structure, and helps advance the debate regarding the causative mechanisms of its surface

  19. Deep mantle cycling of oceanic crust: evidence from diamonds and their mineral inclusions.

    PubMed

    Walter, M J; Kohn, S C; Araujo, D; Bulanova, G P; Smith, C B; Gaillou, E; Wang, J; Steele, A; Shirey, S B

    2011-10-01

    A primary consequence of plate tectonics is that basaltic oceanic crust subducts with lithospheric slabs into the mantle. Seismological studies extend this process to the lower mantle, and geochemical observations indicate return of oceanic crust to the upper mantle in plumes. There has been no direct petrologic evidence, however, of the return of subducted oceanic crustal components from the lower mantle. We analyzed superdeep diamonds from Juina-5 kimberlite, Brazil, which host inclusions with compositions comprising the entire phase assemblage expected to crystallize from basalt under lower-mantle conditions. The inclusion mineralogies require exhumation from the lower to upper mantle. Because the diamond hosts have carbon isotope signatures consistent with surface-derived carbon, we conclude that the deep carbon cycle extends into the lower mantle. PMID:21921159

  20. Seismic structure of the crust and lithospheric mantle of the southern African cratonic region

    NASA Astrophysics Data System (ADS)

    Youssof, M.; Thybo, H.; Artemieva, I. M.; Levander, A.

    2013-12-01

    We present a new seismic model for the structure of the crust and lithospheric mantle in southern Africa constrained by a joint study of seismic receiver functions and finite-frequency tomography, using the high-quality data from the South Africa Seismic Experiment (SASE). A) The crust has a highly heterogeneous structure with short wavelength variations in (i) thickness, (ii) composition (reflected in Vp/Vs-ratio calculated for all SASE stations), and (iii) Moho sharpness (which is quantified and mapped for the entire region) (Youssof et al., Tectonophysics, in review). By mapping these three parameters, we distinguish ~20 crustal blocks that do not everywhere coincide with surface tectonic features. Our RFs also demonstrate strong azimuthal anisotropy in the crust, with a typical crustal contribution to the total S-wave splitting of at least 30%. Spatial correlation of the S-wave polarization directions of crustal and mantle anisotropy indicates (i) the presence of three distinct Archean lithospheric terranes and (ii) coupling between the crust and lithospheric mantle in most of the study area, with a strong decoupling in western Kaapvaal where the crustal anisotropy is strongest. The similarity of anisotropy directions in the crust and mantle beneath much of the Kaapvaal craton indicates that (a) the seismic anisotropy originates at the time of cratonization and (b) the observed correspondence between the present direction of absolute plate motion (APM) and lithosphere anisotropy is coincidental. B) A new 3D high-resolution seismic model of the lithospheric mantle has been determined from finite frequency tomographic inversions of teleseismic P- and S- body wave data. The two velocity models are very similar in structure, but differ in the relative P- and S-wave velocity anomalies. We find that: 1) the fast lithospheric keels extends very deep, perhaps to depths of 300-350 km and 250 km beneath the Kaapvaal and Zimbabwe cratons, respectively, and 2) the Archean

  1. Geochronologic and isotopic evidence for early Proterozoic crust in the eastern Arabian Shield

    SciTech Connect

    Stacey, J.S.; Hedge, C.E.

    1984-05-01

    The authors report zircon U-Pb, feldspar common Pb, whole-rock Sm-Nd, and Rb-Sr data from sample Z-103, a fine-grained granodiorite from the Jabal Khida region of the Saudi Arabian Shield (lat 21/sup 0/19'N; long 44/sup 0/50'W). The measurements yield conclusive evidence for continental crust of early Proterozoic age (approx.1630 Ma) at that locality. Furthermore, lead-isotope data indicate an even earlier, perhaps Archean, crustal history for the source of the lower Proterozoic rocks. 17 references, 4 figures, 1 table.

  2. Neodymium and lead isotope evidence for enriched early Archean crust in North America

    NASA Technical Reports Server (NTRS)

    Bowring, Samuel A.; Housh, Todd B.; Isachsen, Clark E.; Podosek, Frank A.; King, Janet E.

    1989-01-01

    Neodymium and lead isotope measurements and uranium-lead zircon geochronology from Archaean gneisses of the Slave Province in the Northwest Territories of Canada are reported. The gneisses contain zircons with cores older than 3.842 Gyr and an epsilon(Nd) (3.7 Gyr) of - 4.8. This is the oldest reported chondritic model age for a terrestrial sample and provides evidence for strongly enriched pre-3.8-Gyr crust, a reservoir complementary to the depleted mantle already in existence by 3.8 Gyr before the present.

  3. The Earth's crust deep structure of eastern Eurasia on evidence derived from deep seismic investigation

    NASA Astrophysics Data System (ADS)

    Salnikov, A.; Efimov, A.; Soloviev, V. M.

    2013-05-01

    Interest in investigations of the deep structure of the Earth's crust has quickened in the past few years. However, deep seismic sounding performed with the use of boreholes, big shots and less-than-conditioned spreads is connected with its technological inefficiency, high cost, risk and in many cases with impossibility of performance for reasons of ecology. We present an up-to-date DSS technology that is free from negative limitations, inherent in classical technologies, and so allows much room for its application under any conditions, including industrial estates, reserves, hydroelectric power stations, atomic power-stations, and so on. The technology is based on detailed deep seismic multiwave studies using multiple overlapping spreads and powerful seismic vibrators, which generate seismic waves of high radiation stability, and also remote self-contained recorders. Powerful 40-60 ton vibrators provide vibroseis records at 300 to 350 km that compare well with those of powerful 3 to 5 ton trotyl explosions in wells and basins. This technology is being profitably integrated into exploration practice. It was for the first time in the world that mobile powerful 40-60 t vibrators were used to measure four 300 km seismic lines and one 5 000 km lines in the Altai-Sayan fold area and Okhotsk-Kolyma region, respectively. In the Altai-Sayan area we measured the Novosibirsk-Novokuznetsk line more than 300 km in extent with 30 vibrators spaced at intervals of 5 to 10 km. We studied in details a wave field of the uphole vibrator at distances of 0 to 300 km, obtained fresh evidence on elastic P-wave and S-wave characteristics in the Earth's crust and upper mantle, and revealed the main structural elements of the region (Tom-Kolyvan folded zone, Salair Ridge, Kuznetsk trough). We also detected elastic anisotropy on the Moho and its almost complete absence in the upper Earth's crust. Eastern Eurasia remains worst studied as to deep seismic investigations. By the nature of

  4. Shear wave velocity structure of the lower crust in southern Africa: Evidence for compositional heterogeneity within Archaean and Proterozoic terrains

    NASA Astrophysics Data System (ADS)

    Kgaswane, Eldridge M.; Nyblade, Andrew A.; Juliã, Jordi; Dirks, Paul H. G. M.; Durrheim, Raymond J.; Pasyanos, Michael E.

    2009-12-01

    The nature of the lower crust across the southern African shield has been investigated by jointly inverting receiver functions and Rayleigh wave group velocities for 89 broadband seismic stations located in Botswana, South Africa and Zimbabwe. For large parts of both Archaean and Proterozoic terrains, the velocity models obtained from the inversions show shear wave velocities ≥4.0 km/s below ˜20-30 km depth, indicating a predominantly mafic lower crust. However, for much of the Kimberley terrain and adjacent parts of the Kheis Province and Witwatersrand terrain in South Africa, as well as for the western part of the Tokwe terrain in Zimbabwe, shear wave velocities of ≤3.9 km/s are found below ˜20-30 km depth, indicating an intermediate-to-felsic lower crust. The areas of intermediate-to-felsic lower crust in South Africa coincide with regions where Ventersdorp rocks have been preserved, suggesting that the more evolved composition of the lower crust may have resulted from crustal reworking and extension during the Ventersdorp tectonomagmatic event at c. 2.7 Ga.

  5. Blocks in the Europan Crust Provide More Evidence of Subterranean Ocean

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The image on the left shows a region of Europa's crust made up of blocks which are thought to have broken apart and 'rafted' into new positions. These features are the best geologic evidence to date that Europa may have had a subsurface ocean at some time in its past. Combined with the geologic data, the presence of a magnetic field leads scientists to believe an ocean is most likely present at Europa today. In this false color image, reddish-brown areas represent non-ice material resulting from geologic activity. White areas are rays of material ejected during the formation of the 25-km diameter impact crater Pwyll (see global view). Icy plains are shown in blue tones to distinguish possibly coarse-grained ice (dark blue) from fine-grained ice (light blue). Long, dark lines are ridges and fractures in the crust, some of which are more than 3,000 kilometers (1,850 miles) long. These images were obtained by NASA's Galileo spacecraft during September 7, 1996, December 1996, and February 1997 at a distance of 677,000 kilometers (417,489 miles).

  6. Seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing.

    PubMed

    Audet, Pascal; Bostock, Michael G; Christensen, Nikolas I; Peacock, Simon M

    2009-01-01

    Water and hydrous minerals play a key part in geodynamic processes at subduction zones by weakening the plate boundary, aiding slip and permitting subduction-and indeed plate tectonics-to occur. The seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization. However, seismological observations bearing on the presence of water within the subducting plate itself are less well documented. Here we use converted teleseismic waves to obtain observations of anomalously high Poisson's ratios within the subducted oceanic crust from the Cascadia continental margin to its intersection with forearc mantle. On the basis of pressure, temperature and compositional considerations, the elevated Poisson's ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values. Combined with observations of a strong negative velocity contrast at the top of the oceanic crust, our results imply that the megathrust is a low-permeability boundary. The transition from a low- to high-permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization. These results may have important implications for our understanding of seismogenesis, subduction zone structure and the mechanism of episodic tremor and slip. PMID:19122639

  7. Evolution of continental crust and mantle heterogeneity: Evidence from Hf isotopes

    USGS Publications Warehouse

    Jonathan, Patchett P.; Kouvo, O.; Hedge, C.E.; Tatsumoto, M.

    1982-01-01

    We present initial 176Hf/177 Hf ratios for many samples of continental crust 3.7-0.3 Gy old. Results are based chiefly on zircons (1% Hf) and whole rocks: zircons are shown to be reliable carriers of essentially the initial Hf itself when properly chosen on the basis of U-Pb studies. Pre-3.0 Gy gneisses were apparently derived from an unfractionated mantle, but both depleted and undepleted mantle are evident as magma sources from 2.9 Gy to present. This mantle was sampled mainly from major crustal growth episodes 2.8, 1.8 and 0.7 Gy ago, all of which show gross heterogeneity of 176Hf/177Hf in magma sources from ??Hf=0 to +14, or about 60% of the variability of the present mantle. The approximate ??Hf=2??Nd relationship in ancient and modern igneous rocks shows that 176Lu/177Hf fractionates in general twice as much as 147Sm/144Nd in mantle melting processes. This allows an estimation of the relative value of the unknown bulk solid/liquid distribution coefficient for Hf. DLu/DHf=??? 2.3 holds for most mantle source regions. For garnet to be an important residual mantle phase, it must hold Hf strongly in order to preserve Hf-Nd isotopic relationships. The ancient Hf initials are consistent with only a small proportion of recycled older cratons in new continental crust, and with quasi-continuous, episodic growth of the continental crust with time. However, recycling of crust less than 150 My old cannot realistically be detected using Hf initials. The mantle shows clearly the general positive ??Hf resulting from a residual geochemical state at least back to 2.9 Gy ago, and seems to have repeatedly possessed a similar degree of heterogeneity, rather than a continuously-developing depletion. This is consistent with a complex dynamic disequilibrium model for the creation, maintenance and destruction of heterogeneity in the mantle. ?? 1981 Springer-Verlag.

  8. Lithium in Jack Hills zircons: Evidence for extensive weathering of Earth's earliest crust

    NASA Astrophysics Data System (ADS)

    Ushikubo, Takayuki; Kita, Noriko T.; Cavosie, Aaron J.; Wilde, Simon A.; Rudnick, Roberta L.; Valley, John W.

    2008-08-01

    In situ Li analyses of 4348 to 3362 Ma detrital zircons from the Jack Hills, Western Australia by SIMS reveal that the Li abundances (typically 10 to 60 ppm) are commonly over 10,000 times higher than in zircons crystallized from mantle-derived magmas and in mantle-derived zircon megacrysts (typically < 2 ppb). High Li concentrations in zircons (10 to 250 ppm) have also been found in igneous zircons from three continental parent rocks: granites, Li-rich pegmatites, and migmatites in pelitic metasediment. The substitution of trivalent cations (REEs and Y) in zircon correlates with Li + 1 and P + 5 , suggesting that an interstitial site for Li, as well as the xenotime substitution for P, provides charge balance for REEs. Li is thus fixed in the zircon structure by coupled substitutions, and diffusive changes in [Li] composition are rate-limited by slow diffusion of REEs. The Jack Hills zircons also have fractionated lithium isotope ratios ( δ7Li = - 19 to + 13‰) about five times more variable than those recorded in primitive ocean floor basalts (2 to 8‰), but similar to continental crust and its weathering products. Values of δ7Li below - 10‰ are found in zircons that formed as early as 4300 Ma. The high Li compositions indicate that primitive magmas were not the source of Jack Hills zircons and the fractionated values of δ7Li suggest that highly weathered regolith was sampled by these early Archean magmas. These new Li data provide evidence that the parent magmas of ancient zircons from Jack Hills incorporated materials from the surface of the Earth that interacted at low temperature with liquid water. These data support the hypothesis that continental-type crust and oceans existed by 4300 Ma, within 250 million years of the formation of Earth and the low values of δ7Li suggest that weathering was extensive in the early Archean.

  9. Evolution of the African continental crust as recorded by U-Pb, Lu-Hf and O isotopes in detrital zircons from modern rivers

    NASA Astrophysics Data System (ADS)

    Iizuka, Tsuyoshi; Campbell, Ian H.; Allen, Charlotte M.; Gill, James B.; Maruyama, Shigenori; Makoka, Frédéric

    2013-04-01

    To better understand the evolutionary history of the African continental crust, a combined U-Pb, Lu-Hf and O isotopic study has been carried out by in situ analyses of approximately 450 detrital zircon grains from the Niger, Nile, Congo, Zambezi and Orange Rivers. The U-Pb isotopic data show age peaks at ca. 2.7, 2.1-1.8, 1.2-1.0, ca. 0.8, 0.7-0.5 and ca. 0.3 Ga. These peaks, with the exception of the one at ca. 0.8 Ga, correspond with the assembly of supercontinents. Furthermore, the detrital zircons that crystallized during these periods of supercontinent assembly have dominantly non-mantle-like O and Hf isotopic signatures, in contrast to the ca. 0.8 Ga detrital zircons which have juvenile characteristics. These data can be interpreted as showing that continental collisions during supercontinent assembly resulted in supermountain building accompanied by remelting of older continental crust, which in turn led to significant erosion of young igneous rocks with non-mantle-like isotopic signatures. Alternatively, the data may indicate that the major mode of crustal development changed during the supercontinent cycle: the generation of juvenile crust in extensional settings was dominant during supercontinent fragmentation, whereas the stabilization of the generated crust via crustal accretion and reworking was important during supercontinent assembly. The Lu-Hf and O isotope systematics indicate that terreigneous sediments could attain elevated 18O/16O via prolonged sediment-sediment recycling over long crustal residence time, and also that reworking of carbonate and chert which generally have elevated 18O/16O and low Hf contents is minor in granitoid magmatism. The highest 18O/16O in detrital zircon abruptly increased at ca. 2.1 Ga and became nearly constant thereafter. This indicates that reworking of mature sediments increased abruptly at that time, probably as a result of a transition in the dynamics of either granitoid crust formation or sedimentary evolution

  10. The Khida terrane - Geochronological and isotopic evidence for Paleoproterozoic and Archean crust in the eastern Arabian Shield of Saudi Arabia

    USGS Publications Warehouse

    Whitehouse, M.J.; Stoeser, D.B.; Stacey, J.S.

    2001-01-01

    The Khida terrane of the eastern Arabian Shield of Saudi Arabia has been proposed as being underlain by Paleoproterozoic to Archean continental crust (Stoeser and Stacey, 1988). Detailed geological aspects of the Khida terrane, particularly resulting from new fieldwork during 1999, are discussed in a companion abstract (Stoeser et al., this volume). We present conventional and ion- microprobe U-Pb zircon geoenronology, Nd whole-rock, and feldspar Pb isotopic data that further elucidate the pre-Pan-African evolution of the Khida terrane. Locations for the Muhayil samples described below are shown in figure 2 of Stoeser et al. (this volume). 

  11. The Origin of Andesite in the Deep Crust: Evidence from the West-Central Mexican Arc

    NASA Astrophysics Data System (ADS)

    Lange, R. A.; Ownby, S.; Delgado Granados, H.; Hall, C. M.

    2011-12-01

    by the crystal-poor examples, and (2) minimal plagioclase accumulation affects the bulk composition of the crystal-rich andesites, which is consistent with the absence of any Eu anomalies. No dacite or rhyolite has erupted, and there is thus no evidence of crystal fractionation of andesite, including segregation of interstitial liquid from crystal-rich andesites in the upper crustal chamber feeding V. Tancítaro. Magma mixing between dacite/rhyolite and basalt/basaltic andesite to make andesite can be ruled out on two counts: (1) the absence of any dacite or rhyolite as a requisite end-member for mixing, and (2) such mixing could not produce crystal-poor (1-5%) andesite. Although hornblende is absent from the phenocryst assemblage of the basalts and basaltic andesites, rare-earth element patterns among the andesites, basaltic andesites, and basalts show that crystal-liquid separation of up to 40% hornblende is required to form the andesites from the basalts. Therefore, the primary mechanism to form crystal-poor andesite in this arc segment appears to be partial melting of hornblende-rich (~40%) gabbronorite in the lowermost crust. No other mechanisms satisfy all the geochemical and petrological constraints.

  12. Evidence for Anisotropic Crust Within the Tibetan Plateau From Teleseismic Receiver Functions

    NASA Astrophysics Data System (ADS)

    Folsom, H.; Zandt, G.

    2001-12-01

    synthetics that provide a good match to observed data in many cases. The amount of anisotropy is expressed as a percent deviation of the fast axis velocity from the slow axis velocity; observed transverse component amplitudes can be mimicked with models having values of 10-15 percent, which are reasonable based on experimental studies of anisotropic rocks and common rock-forming minerals. Though the forward modeling discussed here is non-unique, even the simplistic nature of the anisotropy in these models fits more aspects of the data than any isotropic model. In addition, dipping layer models do not seem to adequately explain the observed high amplitudes of transverse receiver functions without unrealistically large velocity contrasts between steeply dipping layers. While reasonable models for many stations share the aforementioned anisotropy characteristics, the stations are too far apart to correlate individual layers, and velocities and thicknesses of layers in models for different stations vary slightly. In addition, stations in the southern portion of the Plateau seem to require more complex models, with more layers, than stations in the north. Despite some structural variations among stations, these basic observations provide strong evidence for anisotropic crust in the Tibetan Plateau. This anisotropy could be a result of past or present tectonic processes involved in the development of the Plateau, and further constraints on its orientation and spatial distribution could provide insight into deformational mechanisms currently or formerly active within the Plateau.

  13. Scattering beneath Western Pacific subduction zones: evidence for oceanic crust in the mid-mantle

    NASA Astrophysics Data System (ADS)

    Bentham, H. L. M.; Rost, S.

    2014-06-01

    Small-scale heterogeneities in the mantle can give important insight into the dynamics and composition of the Earth's interior. Here, we analyse seismic energy found as precursors to PP, which is scattered off small-scale heterogeneities related to subduction zones in the upper and mid-mantle. We use data from shallow earthquakes (less than 100 km depth) in the epicentral distance range of 90°-110° and use array methods to study a 100 s window prior to the PP arrival. Our analysis focuses on energy arriving off the great circle path between source and receiver. We select coherent arrivals automatically, based on a semblance weighted beampower spectrum, maximizing the selection of weak amplitude arrivals. Assuming single P-to-P scattering and using the directivity information from array processing, we locate the scattering origin by ray tracing through a 1-D velocity model. Using data from the small-aperture Eielson Array (ILAR) in Alaska, we are able to image structure related to heterogeneities in western Pacific subduction zones. We find evidence for ˜300 small-scale heterogeneities in the region around the present-day Japan, Izu-Bonin, Mariana and West Philippine subduction zones. Most of the detected heterogeneities are located in the crust and upper mantle, but 6 per cent of scatterers are located deeper than 600 km. Scatterers in the transition zone correlate well with edges of fast features in tomographic images and subducted slab contours derived from slab seismicity. We locate deeper scatterers beneath the Izu-Bonin/Mariana subduction zones, which outline a steeply dipping pseudo-planar feature to 1480 km depth, and beneath the ancient (84-144 Ma) Indonesian subduction trench down to 1880 km depth. We image the remnants of subducted crustal material, likely the underside reflection of the subducted Moho. The presence of deep scatterers related to past and present subduction provides evidence that the subducted crust does descend into the lower mantle at

  14. Andesite Magmas are Produced along Oceanic Arcs where the Crust is Thin: Evidence from Nishinoshima Volcano, Ogasawara Arc, Japan

    NASA Astrophysics Data System (ADS)

    Tamura, Y.; Ishizuka, O.; Sato, T.; Nichols, A. R.

    2015-12-01

    The incentive for this study is the ongoing explosive eruption of Nishinoshima volcano, located about 1,000 km south of Tokyo along the Ogasawara (Bonin) Arc. The straightforward but unexpected relationship presented here relates crustal thickness and magma type in the Izu-Ogasawara Oceanic Arc. Volcanoes along the Ogasawara segment of the arc, which include Nishinoshima, are underlain by thin crust (16-21 km)—in contrast to those along the Izu segment, where the crust is ~35 km thick. Interestingly, andesite magmas are dominant products from the former volcanoes and mostly basaltic lavas erupt from the latter. Why and how do volcanoes on the thin crust erupt andesite magmas? An introductory petrology textbook might answer this question by suggesting that, under decreasing pressure and hydrous conditions, the liquidus field of forsterite expands relative to that of enstatite, with the result that, at some point, enstatite melts incongruently to produce primary andesite melt. According to the hypothesis presented here, however, rising mantle diapirs stall near the base of the oceanic arc crust at depths controlled by the thickness of the overlying crust. Where the crust is thin, as along the Ogasawara segment of the arc, pressures are relatively low, and magmas produced in the mantle wedge tend to be andesitic. Where the crust is thick, as along the Izu segment, pressures are greater, and only basaltic magmas tend to be produced. To examine this hypothesis, JAMSTEC cruise NT15-E02 on the R/V Natsushima took place from 11 June to 21 June 2015 to Nishinoshima. It's present island has an elevation of only ~150 m, but its submarine flanks extend to ocean depths of 2,000-3,000 m, so the great bulk of the volcano is submarine and yet-to-be explored. We present the new hypothesis and its evidence from Nishinoshima based on the primitive lavas collected from the submarine parts of the volcano.

  15. Metamorphic record and Thermo-mechanical modelling of lower crust exhumation during the Palaeoproterozoic Eburnean orogeny, West African Craton

    NASA Astrophysics Data System (ADS)

    Gerbault, Muriel; Ganne, Jerome; Block, Sylvain

    2014-05-01

    A thermo-mechanical interpretation of the metamorphic evolution of moderate- to high-pressure volcano-sedimentary rocks (6-8 to >10 Kb) in the Birimian Province (2.2-2.0 Ga) of the West African Craton is explored in terms of burial and exhumation processes. Metamorphic data collected in Burkina Faso, southwest Ghana and eastern Senegal suggest that during the Eburnean orogeny (~2.1 Ga),this Palaeoproterozoic Birimian crust was dominated by moderate apparent geothermal gradients of 20-30°C/km (M2a), that produced greenschist- to amphibolite-facies metamorphic assemblages associated with regional shortening and granitoid intrusions. The M2a gradient is superimposed on a colder thermal regime (M1 : <10-15 °C/km) that produced high-P greenschist- to blueschist-facies metamorphic assemblages, and which most likely recorded the earlier formation of the protolith. The geodynamical origin of M1 is not directly addressed here. Thermo-mechanical two-dimensional numerical models were built in order to test whether late-stage compressional tectonics could generate the exhumation of meta-sediments, collected in Ca0-poor granitoids and which record elevated metamorphic pressures (P> 6-8 Kb). The poor data quality provide limited constraints on the appropriate initial setup conditions, and a number of tests have led us to conceptualize the spatial distribution of a hypothezised succession of volcanic island arcs emplaced on top of CaO rich TTG (Tonalite- Trondjhemite-Granodiorite suites) basement, tectonically paired with sedimentary basins. We postulated therefore the preexistence of wide (about 250 km) and thick flexural sedimentary basins (depth 15 km) in an orogenic mafic crust (about 20 km thick), underplated by a more felsic and lighter layer representing a TTG melange. The numerical results show that a mechanism of burial, heating and exhumation of meta-sediments can occur by simultaneous folding and gravitational instabilities within the broad extent of the basin

  16. Pervasive Layering in the Lunar Highland Crust: Evidence from Apollos 15, 16,and 17

    NASA Technical Reports Server (NTRS)

    Lowman, Paul D., Jr.; Yang, Tiffany

    2005-01-01

    This paper presents results of a photogeologic reconnaissance of 70 mm photographs taken on the lunar surface during the Apollo 15, 16, and 17 missions, whose primary objective was to investigate the lunar highland crust. Photographs at all three sites, notably the Apennine Front, show pervasive layered structure. These layers are easily distinguished from lighting artifacts, and are considered genuine crustal structures. Their number, thickness, and extent implies that they are lava flows, not ejecta blankets or intrusive features. They appear to be the upper part of the earliest lunar crust, possibly forming a layer tens of kilometers thick. Remote sensing studies (X-ray fluorescence and reflectance spectroscopy), indicate that the highland crust is dominantly a feldspathic basalt. It is concluded that the highland layers represent a global crust formed by eruptions of high-alumina basalt in the first few hundred million years of the Moon's history.

  17. Heterogeneous Hadean hafnium: evidence of continental crust at 4.4 to 4.5 ga.

    PubMed

    Harrison, T M; Blichert-Toft, J; Müller, W; Albarede, F; Holden, P; Mojzsis, S J

    2005-12-23

    The long-favored paradigm for the development of continental crust is one of progressive growth beginning at approximately 4 billion years ago (Ga). To test this hypothesis, we measured initial 176Hf/177Hf values of 4.01- to 4.37-Ga detrital zircons from Jack Hills, Western Australia. epsilonHf (deviations of 176Hf/177Hf from bulk Earth in parts per 10(4)) values show large positive and negative deviations from those of the bulk Earth. Negative values indicate the development of a Lu/Hf reservoir that is consistent with the formation of continental crust (Lu/Hf approximately 0.01), perhaps as early as 4.5 Ga. Positive epsilon(Hf) deviations require early and likely widespread depletion of the upper mantle. These results support the view that continental crust had formed by 4.4 to 4.5 Ga and was rapidly recycled into the mantle. PMID:16293721

  18. Evidence for biogenic processes during formation of ferromanganese crusts from the Pacific Ocean: implications of biologically induced mineralization.

    PubMed

    Wang, Xiao-Hong; Schlossmacher, Ute; Natalio, Filipe; Schröder, Heinz C; Wolf, Stephan E; Tremel, Wolfgang; Müller, Werner E G

    2009-01-01

    Ferromanganese [Fe/Mn] crusts formed on basaltic seamounts, gain considerable economic importance due to their high content of Co, Ni, Cu, Zn and Pt. The deposits are predominantly found in the Pacific Ocean in depths of over 1000m. They are formed in the mixing layer between the upper oxygen-minimum zone and the lower oxygen-rich bottom zone. At present an almost exclusive abiogenic origin of crust formation is considered. We present evidence that the upper layers of the crusts from the Magellan Seamount cluster are very rich in coccoliths/coccolithophores (calcareous phytoplankton) belonging to different taxa. Rarely intact skeletons of these unicellular algae are found, while most of them are disintegrated into their composing prisms or crystals. Studies on the chemical composition of crust samples by high resolution SEM combined with an electron probe microanalyzer (EPMA) revealed that they are built of distinct stacked piles of individual compartments. In the center of such piles Mn is the dominant element, while the rims of the piles are rich in Fe (mineralization aspect). The compartments contain coccospheres usually at the basal part. Energy dispersive X-ray spectroscopy (EDX) analyses showed that those coccospheres contain, as expected, CaCO3 but also Mn-oxide. Detailed analysis displayed on the surface of the coccolithophores a high level of CaCO3 while the concentration of Mn-oxide is relatively small. With increasing distance from the coccolithophores the concentration of Mn-oxide increases on the expense of residual CaCO3. We conclude that coccoliths/coccolithophores are crucial for the seed/nucleation phase of crust formation (biomineralization aspect). Subsequently, after the biologically induced mineralization phase Mn-oxide deposition proceeds "auto"catalytically. PMID:19443230

  19. Lead isotopic evidence for evolutionary changes in magma-crust interaction, Central Andes, southern Peru

    NASA Astrophysics Data System (ADS)

    Barreiro, Barbara A.; Clark, Alan H.

    1984-07-01

    Lead isotopic measurements were made on Andean igneous rocks of Jurassic to Recent age in Moquegua and Tacna Departments, southernmost Peru, to clarify the petrogenesis of the rocks and, in particular, to investigate the effect of crustal thickness on rock composition. This location in the Cordillera Occidental is ideal for such a study because the ca. 2 Ga Precambrian basement rocks (Arequipa massif) have a distinct Pb isotopic signature which is an excellent tracer of crustal interaction, and because geomorphological research has shown that the continental crust was here thickened drastically in the later Tertiary. Seven samples of quartz diorites and granodiorites from the Ilo and Toquepala intrusive complexes, and seven samples of Toquepala Group subaerial volcanics were analyzed for Pb isotopic compositions. The plutonic rocks range in age from Jurassic to Eocene; the volcanic rocks are all Late Cretaceous to Eocene. With one exception, the Pb isotopic ratios are in the ranges 206Pb/ 204Pb= 18.52-18.75, 207Pb/ 204Pb= 15.58-15.65, and 208Pb/ 204Pb= 38.53-38.74. The data reflect very little or no interaction with old continental material of the Arequipa massif type. Lead from four Miocene Huaylillas Formation ash-flow tuffs, two Pliocene Capillune Formation andesites and five Quaternary Barroso Group andesites has lower 206Pb/ 204Pb than that in the pre-Miocene rocks, but relatively high 207Pb/ 204Pb and 208Pb/ 204Pb ( 206Pb/ 204Pb= 18.16-18.30, 207Pb/ 204Pb= 15.55-15.63, 208Pb/ 204Pb= 38.45-38.90). Tilton and Barreiro [9] have shown that contamination by Arequipa massif granulites can explain the isotopic composition of the Barosso Group lavas, and the new data demonstrate that this effect is evident, to varying degrees, in all the analysed Neogene volcanic rocks. The initial incorporation of such basement material into the magma coincided with the Early Miocene uplift of this segment of the Cordillera Occidental [32], and thus with the creation of a thick

  20. Remote sensing evidence for an ancient carbon-bearing crust on Mercury

    NASA Astrophysics Data System (ADS)

    Peplowski, Patrick N.; Klima, Rachel L.; Lawrence, David J.; Ernst, Carolyn M.; Denevi, Brett W.; Frank, Elizabeth A.; Goldsten, John O.; Murchie, Scott L.; Nittler, Larry R.; Solomon, Sean C.

    2016-04-01

    Mercury’s global surface is markedly darker than predicted from its measured elemental composition. The darkening agent, which has not been previously identified, is most concentrated within Mercury’s lowest-reflectance spectral unit, the low-reflectance material. This low-reflectance material is generally found in large impact craters and their ejecta, which suggests a mid-to-lower crustal origin. Here we present neutron spectroscopy measurements of Mercury’s surface from the MESSENGER spacecraft that reveal increases in thermal-neutron count rates that correlate spatially with deposits of low-reflectance material. The only element consistent with both the neutron measurements and visible to near-infrared spectra of low-reflectance material is carbon, at an abundance that is 1-3 wt% greater than surrounding, higher-reflectance material. We infer that carbon is the primary darkening agent on Mercury and that the low-reflectance material samples carbon-bearing deposits within the planet’s crust. Our findings are consistent with the formation of a graphite flotation crust from an early magma ocean, and we propose that the heavily disrupted remnants of this ancient layer persist beneath the present upper crust. Under this scenario, Mercury’s globally low reflectance results from mixing of the ancient graphite-rich crust with overlying volcanic materials via impact processes or assimilation of carbon into rising magmas during secondary crustal formation.

  1. Crustal structure of Hubei Province of China from teleseismic receiver functions: Evidence for lower crust delamination

    NASA Astrophysics Data System (ADS)

    Huang, Rong; Zhu, Lupei; Xu, Yixian

    2014-12-01

    Western Hubei Province is at the southern end of the 3000-km-long north-south-oriented Xing'anling-Taihangshan-Wulingshan topographic step in China, which separates high-rising plateaus and mountain ranges in the west from low-elevation plains in the east. We calculated teleseismic P receiver functions of 32 permanent broadband seismic stations in Hubei Province and estimated crustal thicknesses under them using the H-κ method. We also obtained detailed crustal structural images along three profiles using the CCP stacking method. The results show an east-west crustal thickness increase in the study area from 30-35 km to 45-50 km in less than 20 km of horizontal distance, most likely in a step-wise fashion. The thin crust beneath the Nanxiang and Jianghan basins in eastern Hubei extends into the interior of the Wuling Uplift and the Huangling Massif in western Hubei. The lack of mirror symmetry between the Moho and surface topography suggests that part of the mountain ranges in western Hubei is either compensated by non-Airy-type isostasy models or is not in isostatic equilibrium but supported by the strength of the lithosphere. The brittle or localized ductile deformation in the lower crust/uppermost mantle as indicated by the abrupt Moho steps seems to be decoupled with brittle deformation in the upper crust. The CCP images also reveal an apparent double Moho beneath the Wudang Mts. which is interpreted to be due to a partially eclogitized lower crust after the original cratonic mantle lithosphere was replaced by warm and hydrated mantle materials in eastern China in the Late Mesozoic. The Moho steps were formed when a segment of eclogitized lower crust became gravitationally unstable and foundered into the mantle.

  2. Detrital zircon evidence for Hf isotopic evolution of granitoid crust and continental growth

    NASA Astrophysics Data System (ADS)

    Iizuka, Tsuyoshi; Komiya, Tsuyoshi; Rino, Shuji; Maruyama, Shigenori; Hirata, Takafumi

    2010-04-01

    We have determined U-Pb ages, trace element abundances and Hf isotopic compositions of approximately 1000 detrital zircon grains from the Mississippi, Congo, Yangtze and Amazon Rivers. The U-Pb isotopic data reveal the lack of >3.3 Ga zircons in the river sands, and distinct peaks at 2.7-2.5, 2.2-1.9, 1.7-1.6, 1.2-1.0, 0.9-0.4, and <0.3 Ga in the accumulated age distribution. These peaks correspond well with the timing of supercontinent assembly. The Hf isotopic data indicate that many zircons, even those having Archean U-Pb ages, crystallized from magmas involving an older crustal component, suggesting that granitoid magmatism has been the primary agent of differentiation of the continental crust since the Archean era. We calculated Hf isotopic model ages for the zircons to estimate the mean mantle-extraction ages of their source materials. The oldest zircon Hf model ages of about 3.7 Ga for the river sands suggest that some crust generation had taken place by 3.7 Ga, and that it was subsequently reworked into <3.3 Ga granitoid continental crust. The accumulated model age distribution shows peaks at 3.3-3.0, 2.9-2.4, and 2.0-0.9 Ga. The striking attribute of our new data set is the non-uniformitarian secular change in Hf isotopes of granitoid crusts; Hf isotopic compositions of granitoid crusts deviate from the mantle evolution line from about 3.3 to 2.0 Ga, the deviation declines between 2.0 and 1.3 Ga and again increases afterwards. Consideration of mantle-crust mixing models for granitoid genesis suggests that the noted isotopic trends are best explained if the rate of crust generation globally increased in two stages at around (or before) 3.3 and 1.3 Ga, whereas crustal differentiation was important in the evolution of the continental crust at 2.3-2.2 Ga and after 0.6 Ga. Reconciling the isotopic secular change in granitoid crust with that in sedimentary rocks suggests that sedimentary recycling has essentially taken place in continental settings rather than

  3. Seismic evidence of hyper-stretched crust and mantle exhumation offshore Vietnam

    NASA Astrophysics Data System (ADS)

    Savva, D.; Meresse, F.; Pubellier, M.; Chamot-Rooke, N.; Lavier, L.; Po, K. Wong; Franke, D.; Steuer, S.; Sapin, F.; Auxietre, J. L.; Lamy, G.

    2013-11-01

    We study the evolution of the Eocene-Recent Phu Khanh Basin opened during the rifting of the South China Sea (SCS). This sub-basin formed when continental crust ruptured along the East-Vietnam Boundary Fault (EVBF) at the western edge of the SCS. Using high quality long-streamer seismic lines we interpret structures that highlight the different phases of the SCS rifting and processes related to crustal boudinage. Extreme crustal thinning and mantle uplift that sometimes places sediments in contact with the Moho discontinuity mark the central part of the basin. The mantle is shallowest there and marks the final rupture of the continental crust during an intense phase of mantle upwelling. There, a low-angle detachment fault separates several crustal blocks from the Moho. The cylindrical axis of the Moho rise is roughly parallel to the trend of the South China Sea propagator. Above the mantle, the upper and lower crusts form large crustal boudins. The network of normal faults is dense in the upper crust and occasionally propagates into the lower crust. However, the lower crust is missing at some places. The seismic facies above the Moho rise is poorly stratified and might have been affected by a certain degree of metamorphism. At the apex of mantle uplift, there are frequent indications of fluid circulations, including volcanic edifices and gas escapes features. Three stages of extension are clearly identifiable, with ages of the two youngest constrained by well calibration: the first and oldest rift sequence is situated between the tilted pre-rift basement and the Oligocene horizons (32 Ma); the second is delimited by the Oligocene to the Mid Miocene (15.5 Ma) horizons, and the third is bound by the Mid Miocene and the Upper Miocene (before 10.5 Ma) horizons. These three rift episodes formed in at least two extension directions, the first N-S and the second NW-SE. The distinct Mid Miocene (15.5 Ma) horizon is tilted and the above layers show a diverging reflection

  4. Hydrological behaviour of microbiotic crusts on sand dunes of NW China: Experimental evidences and numerical simulations

    NASA Astrophysics Data System (ADS)

    Wang, Xin Ping; Tedeschi, Anna; Orefice, Nadia; de Mascellis, Roberto; Menenti, Massimo

    2010-05-01

    Large ecological engineering projects were established to reduce and combat the hazards of sandstorms and desertification in northern China. An experiment to evaluate the effects of dunes stabilization by vegetation was carried out at Shapotou in Ningxia Hui Autonomous Region at the southeast edge of the Tengger Desert using xerophyte shrubs (Caragana korshinskii, Hedysarum scoparium and Artemisia ordosica) planted in straw checkerboard plots in 1956, 1964, 1981, 1987, 1998, and 2002. The fixed sand surface led to the formation of biotic soil crusts. Biotic crusts formed at the soil surface in the interspaces between shrubs and contribute to stabilization of soil surfaces. Previous results on the area have showed that: i) straw checkerboards enhance the capacity of the dune system to trap dust, leading to the accumulation of soil organic matter and nutrients; ii) the longer the period of dune stabilization, the greater the soil clay content in the shallow soil profile (0-5 cm), and greater the fractal dimension of soil particle size distribution. Benefit apart, one should be aware that the formation of a crusted layer at the soil surface is generally characterized by an altered pore-size distribution, with a frequent decrease of hydraulic conductivity which can induce changes of the water regime of the whole soil profile. Accordingly, the main objective of the paper is to evaluate the equivalent (from a hydraulic point of view) geometry of the crusted layer and to verify if the specific characteristics of the crusted soil layer, although local by nature, affect the hydrological behaviour of the whole soil profile. In fact, it is expected that, due to the formation of an upper, impeding soil layer, the lower soil layers do not reach saturation. Such behaviour has important consequences on both water flow and storages in soils. The final aim will be to understand how the crust at the surface of the artificially stabilized sand dune affects the infiltration capacity

  5. Revisiting diagenesis on the Ontong Java Plateau: Evidence for authigenic crust precipitation in Globorotalia tumida

    NASA Astrophysics Data System (ADS)

    Branson, Oscar; Read, Elizabeth; Redfern, Simon A. T.; Rau, Christoph; Elderfield, Henry

    2015-11-01

    The calcite tests of foraminifera lie in marine sediments for thousands to millions of years, before being analyzed to generate trace element and isotope paleoproxy records. These sediments constitute a distinct physio-chemical environment from the conditions in which the tests formed. Storage in sediments can modify the trace element and isotopic content of foraminiferal calcite through diagenetic alteration, which has the potential to confound their paleoceanographic interpretation. A previous study of Globorotalia tumida from the Ontong Java Plateau, western equatorial Pacific, found that preferential dissolution of higher-Mg chamber calcite and the preservation of a low-Mg crust on the tests significantly reduced whole-test Mg/Ca and Sr/Ca. Here we revisit specimens with a combination of synchrotron X-ray computed tomography (sXCT) and electron probe microanalyses to reevaluate the nature of their diagenetic alteration. The dissolution of higher-Mg calcite with depth was directly observed in the sXCT data, confirming the inference of the previous study. The sXCT data further reveal a thickening of the chemically and structurally distinct calcite crust with depth. We propose that these crusts have a diagenetic origin, driven by the simultaneous dissolution of high-Mg chamber calcite and precipitation of low-Mg crust from the resulting modified pore water solution. While the breadth of the study is limited by the nature of the techniques, the observation of both dissolution and reprecipitation of foraminiferal calcite serves to demonstrate the action of two simultaneous diagenetic alteration processes, with significant impacts on the resulting paleoproxy signals.

  6. Late Permian Melt Percolation through the Crust of North-Central Africa and Its Possible Relationship to the African Large Low Shear Velocity Province

    NASA Astrophysics Data System (ADS)

    Shellnutt, J. G.; Lee, T. Y.; Yang, C. C.; Wu, J. C.; Wang, K. L.; Lo, C. H.

    2014-12-01

    The Doba gabbro was collected from an exploration well through the Cretaceous Doba Basin of Southern Chad. The gabbro is comprised mostly of plagioclase, clinopyroxene and Fe-Ti oxide minerals and displays cumulus mineral textures. Whole rock 40Ar/39Ar step-heating geochronology yielded a Late Permian plateau age of 257 ± 1 Ma. The major and trace elemental geochemistry shows that the gabbro is mildly alkalic to tholeiitic in composition and has trace element ratios (i.e. La/YbN > 7; Sm/YbPM > 3.4; Nb/Y > 1; Zr/Y > 5) indicative of a basaltic melt derived from a garnet-bearing sublithospheric mantle source. The moderately enriched Sr-Nd isotopes (i.e. ISr = 0.70495 to 0.70839; eNd(T) = -1.0 to -1.3) fall within the mantle array (i.e. OIB-like) and are similar to other Late Permian plutonic rocks of North-Central Africa (i.e. ISr = 0.7040 to 0.7070). The Late Permian plutonic igneous complexes of North-Central Africa are geologically associated with tectonic lineaments suggesting they acted as conduits for sublithospheric melts to migrate to middle/upper crustal levels. The source of the magmas may be related to the spatial-temporal association of North-Central Africa with the African large low shear velocity province (LLSVP). The African LLSVP has remained stable since the Late Carboniferous and was beneath the Doba basin during the Permian. We suggest that melts derived from deep seated sources related to the African LLSVP percolated through the North-Central African crust via older tectonic lineaments and form a discontiguous magmatic province.

  7. Seismic evidence for hyper-stretched crust and mantle exhumation offshore Vietnam.

    NASA Astrophysics Data System (ADS)

    Savva, D.; Meresse, F.; Pubellier, M.; Chamot-Rooke, N.; Franke, D.; Steuer, S.; Sapin, F.; Auxietre, J. L.

    2012-04-01

    The Phu Khan basin is one of the sub-basins opened during the rifting of the South China Sea during the Eocene. The basin is located against the East-Vietnam Boundary Fault (EVBF) to the west and the oceanic crust to the east. Good quality seismic lines allow us to observe structures which highlight the rifting history of the South China Sea margin and the processes of crustal boudinage. A Moho rise is the prominent feature of the Central part of the basin. The mantle is shallowest in the center of the basin and at places is directly in contact with the sediments, via a large low-angle detachment fault which separates several crustal blocks. The axis of the Moho rise is roughly parallel to the South China Sea propagator direction. As a consequence, the upper and lower crusts are strongly extended by large crustal boudins. The network of normal fault is dense in the upper crust and propagates into the lower crust occasionally. However, the lower crust seems to be missing at some places. At the apex of the Moho rise, several indicators of fluids circulations have been observed, including volcanic edifices and gas escapes features. The seismic facies just above this Moho rise looks poorly stratified and might be affected by a certain degree of metamorphism. Three stages of extension are clearly identifiable, with age constrained by wells calibration of the horizons: the oldest rift sequence is identified from basement to Oligocene horizons; a second from Oligocene to Mid Miocene (15.5 Ma), and a third from Mid-Miocene to Upper Miocene (10.5 Ma). These three rifts have been formed with at least two directions of extension, a first which is North-South and a second NW - SE The well imaged 15.5 Ma horizon is tilted, as well as part of the subsequent in-filling which is fan-shaped. These are in turn sealed by the 10.5Ma unconformity. Although tectonic activity appears diachronous from north to south, we suggest that cessation of rifting and opening did not occur before 12

  8. Evidence for the Buried "Pre-Noachian" Crust Pre-Dating the Oldest Observed Surface Units on Mars

    NASA Technical Reports Server (NTRS)

    Frey, H. V.; Frey, E. L.; Hartmann, W. K.; Tanaka, K. L. T.

    2003-01-01

    MOLA gridded data shows clear evidence for Quasi-Circular Depressions not visible on images in Early Noachian (EN) terrain units on Mars. We suggest these are buried impact basins that pre-date the superimposed craters whose high density makes these EN units the oldest visible at the surface of Mars. There is crust older than the oldest visible terrain units on Mars, and these EN units cannot date from 4.6 BYA. These and other Noa-chian units have similar total (visible + buried) crater retention ages, suggesting a common "pre-Noachian" crustal age OR crater saturation beyond which we cannot see.

  9. Recycled oceanic crust in the Hawaiian Plume: evidence from temporal geochemical variations within the Koolau Shield

    NASA Astrophysics Data System (ADS)

    Huang, Shichun; Frey, Frederick A.

    2005-07-01

    The subaerial surface of Koolau volcano is composed of lavas that define the distinctive endmember composition for Hawaiian shield lavas, known as the Koolau component, now designated as the Makapuu-stage. The geochemical characteristics of lavas recovered by the Koolau Scientific Drilling Project (KSDP) show that this distinctive composition forms a <300-m thick veneer. Below this veneer, from ~300m to 470 m below sea level, Koolau shield lavas transition to a composition similar to Mauna Loa lavas, now designated as the Kalihi-stage. This transition was gradual, occurring over >80 ka; therefore it was not caused by an abrupt event, such as a landslide. Among all Koolau shield lavas, there are correlations between radiogenic isotopic ratios of Sr, Nd and Pb and compositional characteristics, such as SiO2 content (adjusted to be in equilibrium with Fo90 olivine), Sr/Nb, La/Nb and Th/La. These long-term compositional and isotopic trends show that as the shield aged, there was an increasing role for an ancient recycled marine sediment component (<3% of the source) accompanied by up to 20% SiO2-rich dacitic melt. This melt was generated by partial melting of garnet pyroxenite, probably kilometers in size, that formed from recycled basaltic oceanic crust. In detail, time series analyses of depth profiles of Al2O3/CaO, Sr/Nb, La/Nb and Th/La in the KSDP drill core show correlations among these ratios indicating that recycled oceanic crust contributed episodically, ~29 ka period, to the magma source during the prolonged transition from Kalihi- to Makapuu-stage lava compositions. The long-term geochemical trends show that recycled oceanic crust was increasingly important as the Koolau shield moved away from the plume and encountered lower temperature.

  10. Pinch and swell structures: evidence for brittle-viscous behaviour in the middle crust

    NASA Astrophysics Data System (ADS)

    Gardner, R.; Piazolo, S.; Daczko, N.

    2015-04-01

    The flow properties of middle to lower crustal rocks are commonly represented by viscous flow. However, examples of pinch and swell structures found in a mid-crustal high strain zone at St. Anne Point (Fiordland, New Zealand) suggest pinch and swell structures are initiated by brittle failure of the more competent layer in conjunction with material softening. On this basis we develop a flexible numerical model using brittle-viscous flow where Mohr-Coulomb failure is utilised to initiate pinch and swell structure development. Results show that pinch and swell structures develop in a competent layer in both Newtonian and non-Newtonian flow provided the competent layer has enough viscosity contrast and initially fails brittlely. The degree of material softening after initial failure is shown to impact pinch and swell characteristics with high rates of material softening causing the formation of thick necks between swells by limiting the successful localisation of strain. The flow regime and yielding characteristics of the matrix do not impact pinch and swell structure formation itself, so long as the matrix is less competent. To aid analysis of the structures and help derive the flow properties of rocks in the field, we define three stages of pinch and swell development and offer suggestions for measurements to be made in the field. Our study suggests that Mohr-Coulomb behaviour combined with viscous flow is an appropriate way to represent the heterogeneous rocks of the middle to lower crust. This type of mid-crustal rheological behaviour has significant influence on the localization of strain at all scales. For example, inclusion of Mohr-Coulomb brittle failure with viscous flow in just some mid-crustal layers within a crustal scale model will result in strain localisation throughout the whole crustal section allowing the development of through-going high strain structures from the upper crust into the middle and lower crust. This localization then has a significant

  11. Deucalionis Regio, Mars: Evidence for a unique mineralogic endmember and a crusted surface

    NASA Astrophysics Data System (ADS)

    Merenyi, E.; Edgett, K. S.; Singer, R. B.

    1993-03-01

    A small equatorial region south of Sinus Meridiani, Deucalionis Regio, has been found spectrally distinct from other regions as seen in a high spectral resolution telescopic image of the meridian hemisphere of Mars. Analysis of Viking IRTM and other related data suggest that Deucalionis Regio has a crusted surface. The crust-bonding minerals may contribute to the spectral uniqueness of this region. Two independent analyses of spectral images, linear spectral mixing and supervised classification based on the spectral shapes, showed that in addition to the well-known spectral endmember regions in this image (western Arabia, south Acidalia, and Sinus Meridiani), Deucalionis Regio has spectral properties that are unique enough to make it a principle endmember unit. In those earlier works, Deucalionis Regio was referred to as 'Meridiani Border.' Analysis of thermal inertia, rock abundance, and albedo information derived from Viking images and Infrared Thermal Mapper (IRTM) data obtained 1977-80 also indicate that Deucalionis Regio has a surface of distinctly different physical properties when compared to Arabia, Sinus Meridiani, and Acidalia. Deucalionis Regio has a thermal inertia equivalent to the Martian average, a low rock abundance (less than 5 percent), and an intermediate albedo and color. Considerable effort by previous investigators has revealed a consistent model for the surface (upper few cm) properties of the endmember reigons Arabia, Sinus Meridiani, and Acidalia. Compared with these regions, we consider that Deucalionis Regio is not a region of either (1) unconsolidated, fine bright dust like Arabia, (2) considerable windblown unconsolidated sand like Sinus Meridiani, or (3) a rocky-and-sandy surface like Acidalia. Thus, we are forced to consider that either the surface of Deucalionis Regio is made of unconsolidated fine to medium sand (about 250 microns) of an unusual and previously unreported color and albedo, or that the surface is crusted, fine

  12. Evidence from the lamarck granodiorite for rapid late cretaceous crust formation in California

    USGS Publications Warehouse

    Coleman, D.S.; Frost, T.P.; Glazner, A.F.

    1992-01-01

    Strontium and neodymium isotopic data for rocks from the voluminous 90-million-year-old Lamarck intrusive suite in the Sierra Nevada batholith, California, show little variation across a compositional range from gabbro to granite. Data for three different gabbro intrusions within the suite are identical within analytical error and are consistent with derivation from an enriched mantle source. Recognition of local involvement of enriched mantle during generation of the Sierran batholith modifies estimates of crustal growth rates in the United States. These data indicate that parts of the Sierra Nevada batholith may consist almost entirely of juvenile crust added during Cretaceous magmatism.

  13. Evidence from the lamarck granodiorite for rapid late cretaceous crust formation in california.

    PubMed

    Coleman, D S; Glazner, A F; Frost, T P

    1992-12-18

    Strontium and neodymium isotopic data for rocks from the voluminous 90-million-year-old Lamarck intrusive suite in the Sierra Nevada batholith, California, show little variation across a compositional range from gabbro to granite. Data for three different gabbro intrusions within the suite are identical within analytical error and are consistent with derivation from an enriched mantle source. Recognition of local involvement of enriched mantle during generation of the Sierran batholith modifies estimates of crustal growth rates in the United States. These data indicate that parts of the Sierra Nevada batholith may consist almost entirely of juvenile crust added during Cretaceous magmatism. PMID:17836186

  14. Thorium isotope evidence for melting of the mafic oceanic crust beneath the Izu arc

    NASA Astrophysics Data System (ADS)

    Freymuth, Heye; Ivko, Ben; Gill, James B.; Tamura, Yoshihiko; Elliott, Tim

    2016-08-01

    We address the question of whether melting of the mafic oceanic crust occurs beneath ordinary volcanic arcs using constraints from U-Series (238U/232Th, 230Th/232Th and 226Ra/230Th) measurements. Alteration of the top few hundred meters of the mafic crust leads to strong U enrichment. Via decay of 238U to 230Th, this results in elevated (230Th/232Th) (where brackets indicate activity ratios) over time-scales of ∼350 ka. This process leads to the high (230Th/232Th), between 2.6 and 11.0 in the mafic altered oceanic crust (AOC) sampled at ODP Sites 801 and 1149 near the Izu-Bonin-Mariana arc. Th activity ratios in the Izu arc lavas range from (230Th/232Th) = 1.2-2.0. These values are substantially higher than those in bulk sediment subducting at the Izu trench and also extend to higher values than in mid-ocean ridge basalts and the Mariana arc. We show that the range in Th isotope ratios in the Izu arc lavas is consistent with the presence of a slab melt from a mixed source consisting of AOC and subducted sediments with an AOC mass fraction of up to approximately 80 wt.% in the component added to the arc lava source. The oceanic plate subducting at the Izu arc is comparatively cold which therefore indicates that temperatures high enough for fluid-saturated melting of the AOC are commonly achieved beneath volcanic arcs. The high ratio of AOC/sediments of the slab melt component suggested for the Izu arc lavas requires preferential melting of the AOC. This can be achieved when fluid-saturated melting of the slab is triggered by fluids derived from underlying subducted serpentinites. Dehydration of serpentinites and migration of the fluid into the overlying crust causes melting to start within the AOC. The absence of a significant sediment melt component suggests there was insufficient water to flux both AOC and overlying sediments.

  15. Evidence of heterogeneous crustal origin for the Pan-African Mbengwi granitoids and the associated mafic intrusions (northwestern Cameroon, central Africa)

    NASA Astrophysics Data System (ADS)

    Mbassa, Benoît Joseph; Kamgang, Pierre; Grégoire, Michel; Njonfang, Emmanuel; Benoit, Mathieu; Itiga, Zénon; Duchene, Stéphanie; Bessong, Moïse; Nguet, Pauline Wonkwenmendam; Nfomou, Ntepe

    2016-02-01

    The Mbengwi plutonics consist of intermediate to felsic granitoids forming a continuous magmatic series from monzonite to granite and mafic intrusions. Their mineralogical composition consists of quartz, plagioclases, K-feldspars, biotite, muscovite, and amphibole. The accessory phase includes opaque minerals + titanite ± apatite ± zircon, while secondary minerals are pyrite, phengite, chlorite, epidote, and rarely calcite. These plutonics are assigned high-K calc-alkaline to shoshonitic series, metaluminous to weakly peraluminous and mostly belong to an I-type suite (A/CNK = 0.63-1.2). They are typically post-collisional, with a subduction signature probably being inherited from their protoliths emplaced during the subduction phase. The Sr and Nd isotopic data evidence that these plutonics result from melting of the lower continental crust with variable contribution of the oceanic crust. Their geochemical features are similar to those of western Cameroon granitoids related to the Pan-African D1 event in Cameroon.

  16. Processes of lithosphere evolution: New evidence on the structure of the continental crust and uppermost mantle

    USGS Publications Warehouse

    Artemieva, I.M.; Mooney, W.D.; Perchuc, E.; Thybo, H.

    2002-01-01

    We discuss the structure of the continental lithosphere, its physical properties, and the mechanisms that formed and modified it since the early Archean. The structure of the upper mantle and the crust is derived primarily from global and regional seismic tomography studies of Eurasia and from global and regional data on seismic anisotropy. These data as documented in the papers of this special issue of Tectonophysics are used to illustrate the role of different tectonic processes in the lithospheric evolution since Archean to present. These include, but are not limited to, cratonization, terrane accretion and collision, continental rifting (both passive and active), subduction, and lithospheric basal erosion due to a relative motion of cratonic keels and the convective mantle. ?? 2002 Elsevier Science B.V. All rights reserved.

  17. Fiskenaesset Anorthosite Complex: Stable isotope evidence for shallow emplacement into Archean ocean crust

    SciTech Connect

    Peck, W.H.; Valley, J.W.

    1996-06-01

    Oxygen and hydrogen isotope ratios indicate that unusual rocks at the upper contact of the Archean Fiskenaesset Anorthosite Complex at Fiskenaesset Harbor (southwest Greenland) are the products of hydrothermal alteration by seawater at the time of anorthosite intrusion. Subsequent granulite-facies metamorphism of these Ca-poor and Al- and Mg-rich rocks produced sapphirine- and kornerupine-bearing assemblages. Because large amounts of surface waters cannot penetrate to depths of 30 km during granulite-facies metamorphism, the isotopic signature of the contact rocks must have been obtained prior to regional metamorphism. The stable isotope and geochemical characteristics of the contact rocks support a model of shallow emplacement into Archean ocean crust for the Fiskenaesset Anorthosite Complex. 45 refs., 3 figs., 2 tabs.

  18. Partial melting of the South Qinling orogenic crust, China: Evidence from Triassic migmatites and diorites of the Foping dome

    NASA Astrophysics Data System (ADS)

    Zhang, He; Ye, Ri-Sheng; Liu, Bing-Xiang; Wang, Yan; Zhang, Yuan-Shuo; Siebel, Wolfgang; Chen, Fukun

    2016-09-01

    The Qinling orogen was ultimately formed by suturing of the South Qinling and Yangtze blocks, but the exact timing of the final amalgamation of the two blocks has not been well established so far. Partial melting of the Qinling orogenic continental crust resulted in the generation of migmatites, and such rocks may help to decipher the chronology of such event. In this paper, we report U-Pb ages, trace element, and Hf isotopic compositions of zircons from migmatites and diorite gneisses of the Foping dome, South Qinling. Zircons from migmatites form anhedral grains of variable sizes that are characterized by complex trace element compositions. Based on zircon U-Pb ages, the migmatites can be subdivided into two groups: Group 1 migmatites mainly retain Triassic zircons with U-Pb ages of 214-211 Ma and Hf model ages of ~ 1.46 Ga in core and rim domains; zircons from Group 2 migmatites record both Triassic (~ 210 Ma) and Neoproterozoic U-Pb ages, analogous to igneous rocks of the Wudang and Yaolinghe Groups exposed in South Qinling. Zircons from the diorite gneisses yield U-Pb ages of 216-210 Ma with Hf isotopic composition (TDM2 ages of ~ 1.46 Ga) similar to the migmatites. Evidence from whole-rock Nd isotopic analyses also points to a similar genesis between migmatites and diorite gneisses. It is proposed that Group 1 migmatites were derived by melting of Triassic diorites, while Group 2 migmatites were derived from Neoproterozoic igneous rocks, a major basement lithology of South Qinling. Partial melting of the orogenic crust took place at ~ 214-210 Ma, approximately consistent with the retrograde metamorphism of granulites exposed along the suture zone between the South Qinling and Yangtze blocks. We suggest that the collision of these two blocks occurred prior to ~ 215 Ma and that the Foping dome resulted from rapid collapse of an overthickened crust followed by partial melting enhanced by asthenospheric influx.

  19. Crust-mantle interaction beneath the Luxi Block, eastern North China Craton: Evidence from coexisting mantle- and crust-derived enclaves in a quartz monzonite pluton

    NASA Astrophysics Data System (ADS)

    Lan, Ting-Guang; Fan, Hong-Rui; Santosh, M.; Hu, Fang-Fang; Yang, Kui-Feng; Yang, Yue-Heng; Liu, Yongsheng

    2013-09-01

    The Laiwu quartz monzonite in the Luxi Block of eastern North China Craton (NCC) is characterized by the presence of abundant plagioclase amphibolite and gabbro-diorite enclaves. Here we present LA-ICPMS zircon U-Pb ages which show that the host quartz monzonite was emplaced at 129.8 ± 1.0 Ma, whereas the protolith of the plagioclase amphibolite enclaves formed during early Paleoproterozoic. The gabbro-diorite enclaves were produced simultaneously with or slightly earlier than the formation of the host quartz monzonite. Combined with the Archean and Paleoproterozoic zircons as well as the low εNd(0) values (- 18.4 to - 18.0) in the plagioclase amphibolite enclaves, the equilibrium temperature and pressure conditions (645-670 °C and 4.8-6.5 Kb) suggest that the plagioclase amphibolite enclaves are fragments of the middle crust. The gabbro-diorite enclaves mainly originated from an enriched lithospheric mantle metasomatized by melts/fluids derived from the continental crust, as indicated by their low SiO2 (54.4-54.7 wt.%) and high MgO (10.9-11.1 wt.%) contents as well as the negative εNd(t) values (- 13.5 to - 10.7) and enrichment of LILEs (e.g., Ba and Sr) and depletion of HFSEs (e.g., Nb, Ta, P and Ti). Compared with the ancient crustal rocks and the mafic plutons considered to have been derived from lithospheric mantle in the Luxi Block, the moderate εNd(t) (- 15.7 to - 15.1) and εHf(t) (- 20.7 to - 13.0) values of the quartz monzonite in our study suggest that both mantle- and crust-derived melts were involved in the magma generation. Thus we propose a model involving magma mixing between mantle- and crust-derived melts for the formation of the quartz monzonite. Since significant crust-mantle interaction is recorded not only in the quartz monzonite and its enclaves in the Luxi Block but also in the other granitoids widespread in the NCC, it is considered that large-scale crust-mantle interaction and magmatic underplating were associated with the Mesozoic

  20. Experimental and geochemical evidence for derivation of the El Capitan Granite, California, by partial melting of hydrous gabbroic lower crust

    USGS Publications Warehouse

    Ratajeski, K.; Sisson, T.W.; Glazner, A.F.

    2005-01-01

    Partial melting of mafic intrusions recently emplaced into the lower crust can produce voluminous silicic magmas with isotopic ratios similar to their mafic sources. Low-temperature (825 and 850??C) partial melts synthesized at 700 MPa in biotite-hornblende gabbros from the central Sierra Nevada batholith (Sisson et al. in Contrib Mineral Petrol 148:635-661, 2005) have major-element and modeled trace-element (REE, Rb, Ba, Sr, Th, U) compositions matching those of the Cretaceous El Capitan Granite, a prominent granite and silicic granodiorite pluton in the central part of the Sierra Nevada batholith (Yosemite, CA, USA) locally mingled with coeval, isotopically similar quartz diorite through gabbro intrusions (Ratajeski et al. in Geol Soc Am Bull 113:1486-1502, 2001). These results are evidence that the El Capitan Granite, and perhaps similar intrusions in the Sierra Nevada batholith with lithospheric-mantle-like isotopic values, were extracted from LILE-enriched, hydrous (hornblende-bearing) gabbroic rocks in the Sierran lower crust. Granitic partial melts derived by this process may also be silicic end members for mixing events leading to large-volume intermediate composition Sierran plutons such as the Cretaceous Lamarck Granodiorite. Voluminous gabbroic residues of partial melting may be lost to the mantle by their conversion to garnet-pyroxene assemblages during batholithic magmatic crustal thickening. ?? Springer-Verlag 2005.

  1. Mineralogical Evidence for the Bulk Transformation of Continental Crust to Ultrahigh-Pressure Conditions in Subduction Zones

    NASA Astrophysics Data System (ADS)

    Peterman, E. M.; Hacker, B. R.; Kylander-Clark, A. R.

    2005-12-01

    Evidence for (ultra)high-pressure --(U)HP-- metamorphism in modern orogenic belts and the preservation of exhumed (U)HP terranes around the world suggest that subduction and exhumation of continental crust plays an important role in Phanerozoic plate tectonics. The Western Gneiss region (WGR) of Norway, a major (U)HP province extending over 60,000 km2, provides an excellent opportunity to study how subduction to depths >100 km affects continental crust. By studying a ~60 km wide transect bounded to the north by Vartdalsfjorden and Rovdefjorden and the south by the Möre og Romsdal county boundary, we are able to examine mineralogical changes that occurred during subduction and exhumation within a rock composed predominantly of orthogneiss and variably transformed mafic bodies, which indicate the depths to which these rocks were subducted. Previous studies (e.g. Hacker et al., 2005) have suggested that Caledonian deformation in WGR host gneisses is primarily limited to brittle-ductile fabrics characterized by greenschist to lower-amphibolite facies metamorphism; the majority of the deformation in the rocks, including the pervasive foliation and foliation-parallel isoclinal folds, occurred between 1200 and 900 Ma. On the northern half of our study area, however, locally occurring neoblastic garnet crosscuts the foliation in the gneiss. The boundary of this garnet zone coincides with the local HP-UHP boundary, as determined by the presence of coesite in eclogite. Because garnet can retain information about changes in pressure and temperature, as well as the availability of water within the crust to catalyze chemical reactions, our findings suggest that 1) portions of the orthogneiss did transform at high pressures, 2) the presence of garnet within the orthogneiss may indicate conditions that approximate UHP and can therefore be useful in defining the boundaries between UHP and HP conditions, and 3) the growth of garnet during (U)HP metamorphism may be controlled by

  2. Featureless spectra on the Moon as evidence of residual lunar primordial crust

    NASA Astrophysics Data System (ADS)

    Yamamoto, S.; Nakamura, R.; Matsunaga, T.; Ogawa, Y.; Ishihara, Y.; Morota, T.; Hirata, N.; Ohtake, M.; Hiroi, T.; Yokota, Y.; Haruyama, J.

    2015-12-01

    We report the global distribution of areas exhibiting no absorption features (featureless or FL) on the lunar surface, based on the reflectance spectral data set obtained by the Spectral Profiler onboard Kaguya/SELENE. We found that FL sites are located in impact basins and large impact craters in the Feldspathic Highlands Terrane, while there are no FL sites in the Procellarum regions nor the South Pole-Aitken basin. FL sites in each impact basin/crater are mainly found at the peak rings or rims, where the purest anorthosite (PAN) sites are also found. At the local scale, most of the FL and PAN points are associated with impact craters and peaks. Most of the FL spectra show a steeper (redder) continuum than the PAN spectra, suggesting the occurrence of space weathering effects. We propose that most of the material exhibiting a FL spectrum originate from space weathered PAN. Taking into account all the occurrence trends of FL sites on the Moon, we propose that both the FL and PAN materials were excavated from the primordial lunar crust during ancient basin formations below the megaregolith in the highlands. Since the FL and PAN sites are widely distributed over the lunar surface, our new data may support the existence of a massive PAN layer below the lunar surface.

  3. East African cheetahs: evidence for two population bottlenecks?

    PubMed Central

    O'Brien, S J; Wildt, D E; Bush, M; Caro, T M; FitzGibbon, C; Aggundey, I; Leakey, R E

    1987-01-01

    A combined population genetic and reproductive analysis was undertaken to compare free-ranging cheetahs from east Africa (Acinonyx jubatus raineyi) with the genetically impoverished and reproductively impaired south African subspecies (Acinonyx jubatus jubatus). Like that of their south African counterparts, the quality of semen specimens from east African cheetahs was poor, with a low concentration of spermatozoa (25.3 X 10(6) per ejaculate) and a high incidence of morphological abnormalities (79%). From an electrophoretic survey of the products of 49 genetic loci in A. jubatus raineyi, two allozyme polymorphisms were detected; one of these, for a nonspecific esterase, shows an allele that is rare (less than 1% incidence) in south African specimens. Estimates of polymorphism (2-4%) and average heterozygosity (0.0004-0.014) affirm the cheetah as the least genetically variable felid species. The genetic distance between south and east African cheetahs was low (0.004), suggesting that the development of genetic uniformity preceded the recent geographic isolation of the subspecies. We propose that at least two population bottlenecks followed by inbreeding produced the modern cheetah species. The first and most extreme was ancient, possibly late Pleistocene (circa 10,000 years ago); the second was more recent (within the last century) and led to the south African populations. PMID:3467370

  4. Continental growth through time by underplating of subducted oceanic crust: Evidence from kimberlites in South Africa and SW Pacific

    NASA Technical Reports Server (NTRS)

    Taylor, Lawrence A.; Neal, Clive R.

    1988-01-01

    In the dynamic model of plate tectonics, it is evident that crustal components are returned to the mantle by subduction. Chemical signatures of these subducted components were identified in ocean island volcanics and in island arc volcanics. Indeed, an origin involving a subducted protolith was postulated for certain types of xenoliths in kimberlite, including diamonds. Recent studies of eclogite xenoliths in kimberlite from southern Africa and megacrysts form the Malaitan alnoite, Solomon islands, indicate that lithospheric underplating by subducted oceanic crust has occurred in these two contrasting areas. The results of new eclogite studies from the Bellsbank kimberlite, South Africa, and isotopic data from the Malaitan alnoite megacryst suite. This forms the basis for discerning the role of lithospheric underplating in the growth of cratons and in the evolution of mantle-derived magma.

  5. Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust

    NASA Astrophysics Data System (ADS)

    Guitreau, Martin; Blichert-Toft, Janne; Martin, Hervé; Mojzsis, Stephen J.; Albarède, Francis

    2012-07-01

    Combined whole-rock and zircon MC-ICP-MS Lu-Hf isotope data are reported for a large collection of Archean granitoids belonging to typical tonalite-trondhjemite-granodiorite (TTG) suites. Our data demonstrate that the time-integrated Lu/Hf of the mantle source of TTGs has not significantly changed over the last 4 Gy. Continents therefore most likely grew from nearly primordial unfractionated material extracted from the deep mantle via rising plumes that left a depleted melt residue in the upper mantle. The deep mantle could retain its primitive relative element abundances over time because sinking plates are largely stripped barren of their oceanic and continental crust components at subduction zones; this process results in only small proportions (<15-25%) of present-day continental mass getting recycled to great depths. Zircon populations extracted from the analyzed TTGs have Hf isotopic compositions broadly consistent with those of their host whole-rocks, whereas the U-Pb system in the same grains is often disturbed, causing a discrepancy that creates spurious initial ɛHf values. This problem is endemic to the Archean detrital zircon record and consistent with experimental results bearing on the relative retentivity of Hf vs. U and Pb in zircon. We argue that this behavior biases the Archean zircon record toward negative ɛHf values, which are at odds with the present TTG data set. If Hadean Jack Hills zircons are considered in light of these results, the mantle source of continents has remained unchanged for the last 4.3 Gy.

  6. Living in biological soil crust communities of African deserts-Physiological traits of green algal Klebsormidium species (Streptophyta) to cope with desiccation, light and temperature gradients.

    PubMed

    Karsten, Ulf; Herburger, Klaus; Holzinger, Andreas

    2016-05-01

    Green algae of the genus Klebsormidium (Klebsormidiales, Streptophyta) are typical members of biological soil crusts (BSCs) worldwide. The phylogeny and ecophysiology of Klebsormidium has been intensively studied in recent years, and a new lineage called superclade G, which was isolated from BSCs in arid southern Africa and comprising undescribed species, was reported. Three different African strains, that have previously been isolated from hot-desert BSCs and molecular-taxonomically characterized, were comparatively investigated. In addition, Klebsormidium subtilissimum from a cold-desert habitat (Alaska, USA, superclade E) was included in the study as well. Photosynthetic performance was measured under different controlled abiotic conditions, including dehydration and rehydration, as well as under a light and temperature gradient. All Klebsormidium strains exhibited optimum photosynthetic oxygen production at low photon fluence rates, but with no indication of photoinhibition under high light conditions pointing to flexible acclimation mechanisms of the photosynthetic apparatus. Respiration under lower temperatures was generally much less effective than photosynthesis, while the opposite was true for higher temperatures. The Klebsormidium strains tested showed a decrease and inhibition of the effective quantum yield during desiccation, however with different kinetics. While the single celled and small filamentous strains exhibited relatively fast inhibition, the uniserate filament forming isolates desiccated slower. Except one, all other strains fully recovered effective quantum yield after rehydration. The presented data provide an explanation for the regular occurrence of Klebsormidium strains or species in hot and cold deserts, which are characterized by low water availability and other stressful conditions. PMID:26422081

  7. Living in biological soil crust communities of African deserts—Physiological traits of green algal Klebsormidium species (Streptophyta) to cope with desiccation, light and temperature gradients

    PubMed Central

    Karsten, Ulf; Herburger, Klaus; Holzinger, Andreas

    2015-01-01

    Green algae of the genus Klebsormidium (Klebsormidiales, Streptophyta) are typical members of biological soil crusts (BSCs) worldwide. The phylogeny and ecophysiology of Klebsormidium has been intensively studied in recent years, and a new lineage called superclade G, which was isolated from BSCs in arid southern Africa and comprising undescribed species, was reported. Three different African strains, that have previously been isolated from hot-desert BSCs and molecular-taxonomically characterized, were comparatively investigated. In addition, Klebsormidium subtilissimum from a cold-desert habitat (Alaska, USA, superclade E) was included in the study as well. Photosynthetic performance was measured under different controlled abiotic conditions, including dehydration and rehydration, as well as under a light and temperature gradient. All Klebsormidium strains exhibited optimum photosynthetic oxygen production at low photon fluence rates, but with no indication of photoinhibition under high light conditions pointing to flexible acclimation mechanisms of the photosynthetic apparatus. Respiration under lower temperatures was generally much less effective than photosynthesis, while the opposite was true for higher temperatures. The Klebsormidium strains tested showed a decrease and inhibition of the effective quantum yield during desiccation, however with different kinetics. While the single celled and small filamentous strains exhibited relatively fast inhibition, the uniserate filament forming isolates desiccated slower. Except one, all other strains fully recovered effective quantum yield after rehydration. The presented data provide an explanation for the regular occurrence of Klebsormidium strains or species in hot and cold deserts, which are characterized by low water availability and other stressful conditions. PMID:26422081

  8. Geochronological and isotopic evidence for early Proterozoic crust in the eastern Arabian Shield.

    USGS Publications Warehouse

    Stacey, J.S.; Hedge, C.E.

    1984-01-01

    Zircon U/Pb, feldspar common Pb, whole-rock Sm/Nd, and Rb/Sr data indicate that the fine-grained granodiorite (Z103) has yielded conclusive evidence for rocks of early Proterozoic age in the eastern Arabian Shield (21o19' N, 44o50' W). Z103 may have been emplaced approx 1630 m.y. ago and subsequently was severely deformed or perhaps even remobilized at approx 660 m.y. Furthermore, lead isotope data, along with other evidence, show that the 1630 m.y. crustal rocks inherited material from an older, probably Archaean, source at the time of their formation. At that time addition of mantle material considerably modified the Rb-Sr and Sm-Nd systems so that they now yield similar, or only slightly older apparent ages (1600-1800 m.y.).-L.diH.

  9. Xenoliths in ultrapotassic volcanic rocks in the Lhasa block: direct evidence for crust-mantle mixing and metamorphism in the deep crust

    NASA Astrophysics Data System (ADS)

    Wang, Rui; Collins, William J.; Weinberg, Roberto F.; Li, Jin-xiang; Li, Qiu-yun; He, Wen-yan; Richards, Jeremy P.; Hou, Zengqian; Zhou, Li-min; Stern, Richard A.

    2016-07-01

    δ18O (+6 to 7.5 ‰), intermediate (δ18O +8.5 to 9.0 ‰), and high δ18O (+11.0 to 12.0 ‰). The fourth is almost pure andradite with δ18O 10-12 ‰. Both the low and intermediate δ18O groups show significant variation in Fe content, whereas the two high δ18O groups are compositionally homogeneous. We interpret these features to indicate that the low and intermediate δ18O group garnets grew in separate fractionating magmas that were brought together through magma mixing, whereas the high δ18O groups formed under high-grade metamorphic conditions accompanied by metasomatic exchange. The garnets record complex, open-system magmatic and metamorphic processes in a single rock. Based on these features, we consider that ultrapotassic magmas interacted with juvenile 35-20 Ma crust after they intruded in the deep crust (>50 km) at ~13 Ma to form hybridized Miocene granitoid magmas, leaving a refractory residue. The ~13 Ma zircons retain the original, evolved isotopic character of the ultrapotassic magmas, and the garnets record successive stages of the melting and mixing process, along with subsequent high-grade metamorphism followed by low-temperature alteration and brecciation during entrainment and ascent in a late UPV dyke. This is an excellent example of in situ crust-mantle hybridization in the deep Tibetan crust.

  10. Giant seismites and megablock uplift in the East African Rift: Evidence for large magnitude Late Pleistocene earthquakes

    NASA Astrophysics Data System (ADS)

    Hilbert-Wolf, Hannah; Roberts, Eric

    2015-04-01

    -dkm-scale clastic injection dykes. Our documentation provides evidence for M 6-7.5+ Late Pleistocene earthquakes, similar to the M7.4 earthquake at the same location in 1910, extending the record of large-magnitude earthquakes beyond the last century. Our study not only expands the database of seismogenic sedimentary structures, but also attests to repeated, large-magnitude, Late Pleistocene-Recent earthquakes along the Western Branch of the East African Rift System. Understanding how seismicity deforms the crust is critical for predicting and preparing for modern seismic hazards, especially along the East African Rift System and other tectonically active, developing regions.

  11. A comparative Rb-Sr, Sm-Nd, and K-Ar study of shocked norite 78236 - Evidence of slow cooling in the lunar crust

    NASA Technical Reports Server (NTRS)

    Nyquist, L. E.; Bogard, D. D.; Wooden, J. L.; Bansal, B. M.; Wiesmann, H.; Shih, C.-Y.; Reimold, W. U.

    1982-01-01

    The sample 78236 was chipped from the top of a norite boulder at Station 8 by the Apollo 17 landing team. Jackson et al. (1975) concluded that this rock formed at a depth of 8-30 km in the lunar crust and suggested that it was excavated by a large basin-forming impact event. A petrographic description of the boulder is provided, and isotopic analyses are discussed. Attention is given to a chronology for 78236 which seems to be most consistent with radiometric and other evidence. It is proposed that cumulate norite 78236 formed deep in the lunar crust approximately 4.4 AE ago. The rock cooled slowly in the crust until it was excavated by a major basin-forming event. Excavation may have occurred about 4.2 AE ago, but the time of this event is not well constrained.

  12. The Cool Early Earth: Oxygen Isotope Evidence for Continental Crust and Oceans on Earth at 4.4 Ga

    NASA Astrophysics Data System (ADS)

    Valley, J. W.; King, E. M.; Peck, W. H.; Graham, C. M.; Wilde, S. A.

    2001-05-01

    oceans at that time. The evidence for liquid water and possibly oceans at 4.4 Ga suggests a Cool Early Earth. This contrasts with the Hot Early Earth and global magma oceans envisioned at 4.5-4.3 Ga based on: an impact origin of the Moon (4.45-4.50 Ga), core formation, higher Hadean radioactive heat production, and intense early meteorite bombardment. Magma on the surface of the Earth cools quickly by radiation to form a crust, but a magma ocean caused by these processes might persist beneath the initially thin crust for up to 400 m.y. and might erupt as massive flood basalts in response to major meteorite impacts, boiling surface waters. The thermal contrasts presented by these lines of evidence are minimized if the Moon and core formed earlier (\\sim4.5 Ga), if the Moon formed by a process not involving a Mars-size impactor, or if the early meteorite bombardment was less intense or irregular in timing. It is possible that periods of Cool vs. Hot Early Earth alternated, with boiling of early oceans after major impact events followed by periods of cooler surface conditions. If life evolved in these seas, multiple extinctions before 3.9 Ga are suggested.

  13. Implementation of Evidence-Based HIV Interventions for Young Adult African American Women in Church Settings

    PubMed Central

    Stewart, Jennifer M.

    2015-01-01

    Objective To assess the barriers and facilitators to using African American churches as sites for implementation of evidence-based HIV interventions among young African American women. Design Mixed methods cross-sectional design. Setting African American churches in Philadelphia, PA. Participants 142 African American pastors, church leaders, and young adult women ages 18 to 25. Methods Mixed methods convergent parallel design. Results The majority of young adult women reported engaging in high-risk HIV-related behaviors. Although church leaders reported willingness to implement HIV risk-reduction interventions, they were unsure of how to initiate this process. Key facilitators to the implementation of evidence-based interventions included the perception of the leadership and church members that HIV interventions were needed and that the church was a promising venue for them. A primary barrier to implementation in this setting is the perception that discussions of sexuality should be private. Conclusion Implementation of evidence-based HIV interventions for young adult African American women in church settings is feasible and needed. Building a level of comfort in discussing matters of sexuality and adapting existing evidence-based interventions to meet the needs of young women in church settings is a viable approach for successful implementation. PMID:25139612

  14. Anisotropic low-velocity lower crust beneath the northeastern margin of Tibetan Plateau: Evidence for crustal channel flow

    NASA Astrophysics Data System (ADS)

    Shen, Xuzhang; Yuan, Xiaohui; Ren, Junsheng

    2015-12-01

    Detailed seismic structure in the crust beneath the northeastern margin of Tibetan Plateau was revealed by receiver functions of a regional permanent seismic network. At most stations, negative P-to-S converted phases can be detected in the radial receiver functions, prior to the Moho phases, indicating low velocities in the midlower crust. Prominent azimuthal variations in the transverse receiver functions with polarity reversal suggest azimuthal anisotropy in the crust. We used time variations of the P-to-S converted phases at the Moho in the radial receiver functions and the azimuth-weighted stacking of transverse receiver functions to determine the fast direction and magnitude of anisotropy. The low-velocity midlower crust with the coherent azimuthal anisotropy in the northeastern margin of Tibetan Plateau is consistent with the lower crustal channel flow model.

  15. African American Preschoolers' Emotion Explanations Can Provide Evidence of Their Pragmatic Skills

    ERIC Educational Resources Information Center

    Curenton, Stephanie M.

    2015-01-01

    This study provides qualitative and quantitative evidence of how an emotion explanation task can reflect African American preschoolers' pragmatic skills. We used an emotion explanation task to assess pragmatic skills among 19 children (aged 3-5 years) related to (1) engaging in conversational turn-taking, (2) answering "Wh-" questions,…

  16. Ancient recycled crust beneath the Ontong Java Plateau: Isotopic evidence from the garnet clinopyroxenite xenoliths, Malaita, Solomon Islands

    NASA Astrophysics Data System (ADS)

    Ishikawa, Akira; Kuritani, Takeshi; Makishima, Akio; Nakamura, Eizo

    2007-07-01

    We present a Sr, Nd, Hf and Pb isotope investigation of a set of garnet clinopyroxenite xenoliths from Malaita, Solomon Islands in order to constrain crustal recycling in the Pacific mantle. Geological, thermobarometric and petrochemical evidence from previous studies strongly support an origin as a series of high-pressure (> 3 GPa) melting residues of basaltic material incorporated in peridotite, which was derived from Pacific convective mantle related to the Ontong Java Plateau magmatism. The present study reveals isotopic variations in the pyroxenites that are best explained by different extents of chemical reaction with ambient peridotite in the context of a melting of composite source mantle. Isotopic compositions of bimineralic garnet clinopyroxenites affected by ambient peridotite fall within the oceanic basalt array, similar to those of Ontong Java Plateau lavas. In contrast, a quartz-garnet clinopyroxenite, whose major element compositions remain intact, has lower 206Pb/ 204Pb- 143Nd/ 144Nd and higher 87Sr/ 86Sr- 207Pb/ 204Pb ratios than most oceanic basalts. These isotopic signatures show some affinity with proposed recycled sources such as the so-called EM-1 or DUPAL types. Constraints from major and trace element characteristics of the quartz-garnet clinopyroxenite, the large extent of Hf-Nd isotopic decoupling and the good coincidence of Pb isotopes to the Stacey-Kramers curve, all indicate that pollution of southern Pacific mantle occurred by the subduction or delamination of Neoproterozoic granulitic lower crust (0.5-1 Ga). This crustal recycling could have taken place around the suture of Rodinia supercontinent, a part of which resurfaced during mantle upwelling responsible for creating the Cretaceous Ontong Java Plateau.

  17. Evidence for Archean inheritance in the pre-Panafrican crust of Central Cameroon: Insight from zircon internal structure and LA-MC-ICP-MS Usbnd Pb ages

    NASA Astrophysics Data System (ADS)

    Ganwa, Alembert Alexandre; Klötzli, Urs Stephan; Hauzenberger, Christoph

    2016-08-01

    The main geological feature of Central Cameroon is the wide spread occurrence of granitoids emplaced in close association with transcurrent regional shear zones. The basement of this vast domain is a Paleoproterozoic ortho-and para-derivative formation, which has been intensely reworked, together with subsequent intrusions and sediments, during the Panafrican orogenesis in the Neoproterozoic. As consequence, the area underwent pervasive metamorphism and intense deformation. This makes it difficult to distinguish between Panafrican metasediments or syntectonic plutonites and their respective basement. Our study presents zircon features (CL-BSE-SE) and in-situ U-Th-Pb LA-MC-ICP-MS geochronology of a meta-sedimentary pyroxene-amphibole-bearing gneiss of the Méiganga area in Central Cameroon. Based on the Internal structures of the zircon four characteristic zonation patterns can be deciphered: 1) cores with magmatic oscillatory zonation 2) zircons with oscillatory or sector zonation, 3) zircons with sector zoning or blurred zoning, and 4) narrow bright un-zoned rims. These groups suggest that the rock experienced a number of geological events. Considering this zircon characteristic, the U-Th-Pb data allow to distinguish four ages: 2116 ± 57 Ma, consistent with ages from the Paleoproterozoic West Central African Belt; 2551 ± 33 Ma which marks a late Neoarchean magmatic event; 2721 ± 27 Ma related to a Neoarchean magmatic even in Central Cameroon, similar to one found in the Congo Craton. A zircon core gives ages around 2925 Ma which provides some evidence of the presence of the Mesoarchean basement prior to the Neoarchean magmatism. A weighted average of lower intercepts ages gives a value of 821 ± 50 Ma, representing the age of later metamorphism event. The various characteristic group and related ages reflect not only the complexity of the history of the pyroxene amphibole gneiss, but also show that the meta-sediment has at least three zircon

  18. Evidence for the Snowball Earth hypothesis in the Arabian-Nubian Shield and the East African Orogen

    NASA Astrophysics Data System (ADS)

    Stern, R. J.; Avigad, D.; Miller, N. R.; Beyth, M.

    2006-01-01

    Formation of the Arabian-Nubian Shield (ANS) and the East African Orogen (EAO) occurred between 870 Ma and the end of the Precambrian (˜542 Ma). ANS crustal growth encompassed a time of dramatic climatic change, articulated as the Snowball Earth hypothesis (SEH). SEH identifies tremendous paleoclimatic oscillations during Neoproterozoic time. Earth’s climate shifted wildly, from times when much of our planet’s surface was frozen to unusually warm episodes and back again. There is evidence for four principal icehouse episodes: ˜585 582 Ma (Gaskiers), ˜660 635 Ma (Marinoan), ˜680 715 Ma (Sturtian), and ˜735 770 Ma (Kaigas). Evidence consistent with the SEH has been found at many locations around the globe but is rarely reported from the ANS, in spite of the fact that this may be the largest tract of Neoproterozoic juvenile crust on the planet, and in spite of the fact that Huqf Group sediments in Oman, flanking the ANS, record evidence for Sturtian and Marinoan low-latitude glaciations. This review identifies the most important evidence preserved in sedimentary rocks elsewhere for SEH: diamictites, dropstones, cap carbonates, and banded iron formation (BIF). Expected manifestations of SEH are integrated into our understanding of ANS and EAO tectonic evolution. If Kaigas and Sturtian events were global, sedimentary evidence should be preserved in ANS sequences, because these occurred during an embryonic stage of ANS evolution, when crustal components (island arcs, back-arc basins, and sedimentary basins) were mostly below sea level. Previous SEH investigations have been largely reconnaissance in scope, but potentially diagnostic sedimentary units such as diamictites, marine carbonates with δ13C excursions and banded iron formations are reported from the ANS and are worthy of further investigation. Collision and uplift to form the EAO destroyed most marine sedimentary basins about 630 Ma ago, so evidence of Marinoan and Gaskiers glaciations will be more

  19. No evidence that selection has been less effective at removing deleterious mutations in Europeans than in Africans.

    PubMed

    Do, Ron; Balick, Daniel; Li, Heng; Adzhubei, Ivan; Sunyaev, Shamil; Reich, David

    2015-02-01

    Non-African populations have experienced size reductions in the time since their split from West Africans, leading to the hypothesis that natural selection to remove weakly deleterious mutations has been less effective in the history of non-Africans. To test this hypothesis, we measured the per-genome accumulation of nonsynonymous substitutions across diverse pairs of populations. We find no evidence for a higher load of deleterious mutations in non-Africans. However, we detect significant differences among more divergent populations, as archaic Denisovans have accumulated nonsynonymous mutations faster than either modern humans or Neanderthals. To reconcile these findings with patterns that have been interpreted as evidence of the less effective removal of deleterious mutations in non-Africans than in West Africans, we use simulations to show that the observed patterns are not likely to reflect changes in the effectiveness of selection after the populations split but are instead likely to be driven by other population genetic factors. PMID:25581429

  20. Infusing Culture into Practice: Developing and Implementing Evidence-Based Mental Health Services for African American Foster Youth

    ERIC Educational Resources Information Center

    Briggs, Harold Eugene; McBeath, Bowen

    2010-01-01

    The lack of culturally appropriate health and mental health care has contributed to the large number of African American youth and families involved in the child welfare system. This article reviews the consequences of the insufficient access to culturally sensitive, evidence-supported interventions for African American foster youth. The authors…

  1. Genome-wide Evidence Reveals that African and Eurasian Golden Jackals Are Distinct Species.

    PubMed

    Koepfli, Klaus-Peter; Pollinger, John; Godinho, Raquel; Robinson, Jacqueline; Lea, Amanda; Hendricks, Sarah; Schweizer, Rena M; Thalmann, Olaf; Silva, Pedro; Fan, Zhenxin; Yurchenko, Andrey A; Dobrynin, Pavel; Makunin, Alexey; Cahill, James A; Shapiro, Beth; Álvares, Francisco; Brito, José C; Geffen, Eli; Leonard, Jennifer A; Helgen, Kristofer M; Johnson, Warren E; O'Brien, Stephen J; Van Valkenburgh, Blaire; Wayne, Robert K

    2015-08-17

    The golden jackal of Africa (Canis aureus) has long been considered a conspecific of jackals distributed throughout Eurasia, with the nearest source populations in the Middle East. However, two recent reports found that mitochondrial haplotypes of some African golden jackals aligned more closely to gray wolves (Canis lupus), which is surprising given the absence of gray wolves in Africa and the phenotypic divergence between the two species. Moreover, these results imply the existence of a previously unrecognized phylogenetically distinct species despite a long history of taxonomic work on African canids. To test the distinct-species hypothesis and understand the evolutionary history that would account for this puzzling result, we analyzed extensive genomic data including mitochondrial genome sequences, sequences from 20 autosomal loci (17 introns and 3 exon segments), microsatellite loci, X- and Y-linked zinc-finger protein gene (ZFX and ZFY) sequences, and whole-genome nuclear sequences in African and Eurasian golden jackals and gray wolves. Our results provide consistent and robust evidence that populations of golden jackals from Africa and Eurasia represent distinct monophyletic lineages separated for more than one million years, sufficient to merit formal recognition as different species: C. anthus (African golden wolf) and C. aureus (Eurasian golden jackal). Using morphologic data, we demonstrate a striking morphologic similarity between East African and Eurasian golden jackals, suggesting parallelism, which may have misled taxonomists and likely reflects uniquely intense interspecific competition in the East African carnivore guild. Our study shows how ecology can confound taxonomy if interspecific competition constrains size diversification. PMID:26234211

  2. Geochemical and Sr-Nd-Pb isotopic evidence for ancient lower continental crust beneath the Xi Ujimqin area of NE China

    NASA Astrophysics Data System (ADS)

    Gao, Xiaofeng; Guo, Feng; Xiao, Peixi; Kang, Lei; Xi, Rengang

    2016-05-01

    The Central Asian Orogenic Belt (CAOB) is the largest Phanerozoic accretionary orogen on Earth. The role that Precambrian continental microblocks played in its formation, however, remains a highly controversial topic. New zircon U-Pb age data and whole-rock geochemical and Sr-Nd-Pb isotopic studies on Permian (253-251 Ma) andesites from the Xi Ujimqin area provide the first evidence for the existence of a continental lower mafic crust in the eastern segment of the CAOB. These Permian lavas generally have chemical compositions similar to experimental melts of garnet pyroxenites. Based on Sr-Nd-Pb isotopic compositional differences, they can be further subdivided into two groups. Group 1 has moderately radiogenic Sr (87Sr/86Sr(i) = 0.7060-0.7062) and nonradiogenic Nd (εNd(t) = - 9.0-8.3) and Pb (e.g., 206Pb/204Pb = 17.18-17.23) isotopic compositions similar to the ancient lower mafic crust beneath the North China Craton (NCC). Compared with Group 1, Group 2 has less radiogenic Sr (87Sr/86Sr(i) = 0.7051-0.7055), and more radiogenic Nd (εNd(t) = - 0.2-+1.4) and Pb (e.g., 206Pb/204Pb = 18.04-18.20) isotopic compositions as observed in the Phanerozoic granitoids and felsic lavas of the CAOB. The combined geochemical and isotopic data indicate that Group 1 was derived from ancient lower mafic crust of the NCC affinity, with a residual assemblage of pyroxene + plagioclase + amphibole. The source for Group 2 was a mixture of ancient lower mafic crust and a juvenile crustal component, and melting left a residue of orthopyroxene + clinopyroxene + plagioclase + garnet + amphibole. Generation of these two types of late Permian andesites favors a model whereby breakoff of a subducted slab and subsequent lithospheric extension triggered extensive asthenospheric upwelling and melting of the continental mafic lower crust of the eastern CAOB. The discovery of ancient lower continental crust of the NCC affinity in the CAOB implies that the NCC experienced continental breakup during

  3. Faulting and hydration of the upper crust of the SW Okinawa Trough during continental rifting: Evidence from seafloor compliance inversion

    NASA Astrophysics Data System (ADS)

    Kuo, Ban-Yuan; Crawford, Wayne C.; Webb, Spahr C.; Lin, Ching-Ren; Yu, Tai-Chieh; Chen, Liwen

    2015-06-01

    The elastic response of seafloor to ocean gravity wave loading, or seafloor compliance, provides a constraint on the elastic properties of the crust. We measured seafloor compliance at three ocean bottom seismometer (OBS) sites around Taiwan—two in the southwestern (SW) Okinawa Trough and one on the Ryukyu arc—and performed inversion for crustal structures beneath them. Models best fitting the data demonstrate a decrease in upper crustal shear velocity and an increase in the compressional/shear velocity ratio from the arc site to the trough sites with increasing amount of back-arc extension. This variation suggests that the upper continental crust is highly faulted and hydrated during rifting of the Eurasian lithosphere.

  4. The crust-mantle interaction in continental subduction channels: Zircon evidence from orogenic peridotite in the Sulu orogen

    NASA Astrophysics Data System (ADS)

    Li, Hai-Yong; Chen, Ren-Xu; Zheng, Yong-Fei; Hu, Zhaochu

    2016-02-01

    A combined secondary ion mass spectrometer and laser ablation-(multicollector)-inductively coupled plasma mass spectrometer study of zircon U-Pb ages, trace elements, and O and Hf isotopes was carried out for orogenic peridotite and its host gneiss in the Sulu orogen. Newly grown zircon domains exhibit weak zoning or no zoning, relatively low Th/U ratios (<0.1), low heavy rare earth element (HREE) contents, steep middle rare earth element-HREE patterns, negative Eu anomalies, and negative to low δ18O values of -11.3 to 0.9‰ and U-Pb ages of 220 ± 2 to 231 ± 4 Ma. Thus, these zircons would have grown from metasomatic fluids during the early exhumation of deeply subducted continental crust. The infiltration of metasomatic fluids into the peridotite is also indicated by the occurrence of hydrous minerals such as amphibole, serpentine, and chlorite. In contrast, relict zircon domains exhibit magmatic zircon characteristics. Their U-Pb ages and trace element and Hf-O isotope compositions are similar to those for protolith zircons from ultrahigh-pressure metamorphic rocks in the Dabie-Sulu orogenic belt. Thus, these relict magmatic zircons would be physically transported into the peridotite by metasomatic fluids originated from the deeply subducted continental crust. Therefore, the peridotite underwent metasomatism by aqueous solutions derived from dehydration of the deeply subducted continental crust during the early exhumation. It is these crustally derived fluids that would have brought not only such chemical components as Zr and Si but also tiny zircon grains from the deeply subducted crustal rocks into the peridotite at the slab-mantle interface in continental subduction channels. As such, the orogenic peridotite records the crust-mantle interaction at the deep continental subduction zone.

  5. Evidence for partial melt in the crust beneath Mt. Paektu (Changbaishan), Democratic People’s Republic of Korea and China

    PubMed Central

    Kyong-Song, Ri; Hammond, James O. S.; Chol-Nam, Ko; Hyok, Kim; Yong-Gun, Yun; Gil-Jong, Pak; Chong-Song, Ri; Oppenheimer, Clive; Liu, Kosima W.; Iacovino, Kayla; Kum-Ran, Ryu

    2016-01-01

    Mt. Paektu (also known as Changbaishan) is an enigmatic volcano on the border between the Democratic People’s Republic of Korea (DPRK) and China. Despite being responsible for one of the largest eruptions in history, comparatively little is known about its magmatic evolution, geochronology, or underlying structure. We present receiver function results from an unprecedented seismic deployment in the DPRK. These are the first estimates of the crustal structure on the DPRK side of the volcano and, indeed, for anywhere beneath the DPRK. The crust 60 km from the volcano has a thickness of 35 km and a bulk VP/VS of 1.76, similar to that of the Sino-Korean craton. The VP/VS ratio increases ~20 km from the volcano, rising to >1.87 directly beneath the volcano. This shows that a large region of the crust has been modified by magmatism associated with the volcanism. Such high values of VP/VS suggest that partial melt is present in the crust beneath Mt. Paektu. This region of melt represents a potential source for magmas erupted in the last few thousand years and may be associated with an episode of volcanic unrest observed between 2002 and 2005. PMID:27152343

  6. Evidence for partial melt in the crust beneath Mt. Paektu (Changbaishan), Democratic People's Republic of Korea and China.

    PubMed

    Kyong-Song, Ri; Hammond, James O S; Chol-Nam, Ko; Hyok, Kim; Yong-Gun, Yun; Gil-Jong, Pak; Chong-Song, Ri; Oppenheimer, Clive; Liu, Kosima W; Iacovino, Kayla; Kum-Ran, Ryu

    2016-04-01

    Mt. Paektu (also known as Changbaishan) is an enigmatic volcano on the border between the Democratic People's Republic of Korea (DPRK) and China. Despite being responsible for one of the largest eruptions in history, comparatively little is known about its magmatic evolution, geochronology, or underlying structure. We present receiver function results from an unprecedented seismic deployment in the DPRK. These are the first estimates of the crustal structure on the DPRK side of the volcano and, indeed, for anywhere beneath the DPRK. The crust 60 km from the volcano has a thickness of 35 km and a bulk V P/V S of 1.76, similar to that of the Sino-Korean craton. The V P/V S ratio increases ~20 km from the volcano, rising to >1.87 directly beneath the volcano. This shows that a large region of the crust has been modified by magmatism associated with the volcanism. Such high values of V P/V S suggest that partial melt is present in the crust beneath Mt. Paektu. This region of melt represents a potential source for magmas erupted in the last few thousand years and may be associated with an episode of volcanic unrest observed between 2002 and 2005. PMID:27152343

  7. Seismic evidence for the presence of Jurassic oceanic crust in the central Gulf of Cadiz (SW Iberian margin)

    NASA Astrophysics Data System (ADS)

    Sallarès, Valentí; Gailler, Audrey; Gutscher, Marc-André; Graindorge, David; Bartolomé, Rafael; Gràcia, Eulàlia; Díaz, Jordi; Dañobeitia, Juan José; Zitellini, Nevio

    2011-11-01

    We investigate the crustal structure of the SW Iberian margin along a 340 km-long refraction and wide-angle reflection seismic profile crossing from the central Gulf of Cadiz to the Variscan continental margin in the Algarve, Southern Portugal. The seismic velocity and crustal geometry model obtained by joint refraction and reflection travel-time inversion reveal three distinct crustal domains: the 28-30 km-thick Variscan crust in the north, a 60 km-wide transition zone offshore, where the crust abruptly thins ~ 20 km, and finally a ~ 7 km-thick and ~ 150 km-wide crustal section that appears to be oceanic in nature. The oceanic crust is overlain by a 1-3 km-thick section of Mesozoic to Eocene sediments, with an additional 3-4 km of low-velocity, unconsolidated sediments on top belonging to the Miocene age, Gulf of Cadiz imbricated wedge. The sharp transition between continental and oceanic crust is best explained by an initial rifting setting as a transform margin during the Early Jurassic that followed the continental break-up in the Central Atlantic. The narrow oceanic basin would have formed during an oblique rifting and seafloor spreading episode between Iberia and Africa that started shortly thereafter (Bajocian) and lasted up to the initiation of oceanic spreading in the North Atlantic at the Tithonian (late Jurassic-earliest Cretaceous). The velocity model displays four wide, prominent, south-dipping low-velocity anomalies, which seem to be related with the presence of crustal-scale faults previously identified in the area, some of which could well be extensional faults generated during this rifting episode. We propose that this oceanic plate segment is the last remnant of an oceanic corridor that once connected the Alpine-Tethys with the Atlantic ocean, so it is, in turn, one of the oldest oceanic crustal fragments currently preserved on Earth. The presence of oceanic crust in the central Gulf of Cadiz is consistent with geodynamic models suggesting the

  8. Granitic rocks and metasediments in Archean crust, Rainy Lake area, Ontario: ND isotope evidence for mantle-like SM/ND sources

    NASA Technical Reports Server (NTRS)

    Shirey, S. B.; Hanson, G. N.

    1983-01-01

    Granitoids, felsic volcanic rocks and clastic metasediments are typical rocks in Archean granite-greenstone belts that could have formed from preexisting continentasl crust. The petrogenesis of such rocks is assessed to determine the relative roles of new crust formation or old crust formation or old crust recycling in the formation of granite-greenstone belts.

  9. Pinch and swell structures: evidence for strain localisation by brittle-viscous behaviour in the middle crust

    NASA Astrophysics Data System (ADS)

    Gardner, R. L.; Piazolo, S.; Daczko, N. R.

    2015-09-01

    The flow properties of middle crustal rocks are commonly represented by viscous flow. Examples of pinch and swell structures found in a high strain zone at St. Anne Point (Fiordland, New Zealand) and Wongwibinda (N.S.W., Australia) suggest pinch and swell structures may be initiated by brittle failure of the more competent layer in conjunction with subsequent material softening. On this basis we develop a numerical model where Mohr-Coulomb constitutive strain localising behaviour is utilised to initiate pinch and swell structure development. Results show that pinch and swell structures develop in a competent layer in both Newtonian and non-Newtonian flow, provided the competent layer has sufficient viscosity contrast and can localise strain to form shear bands. The flow regime and strain localising characteristics of the surrounding country rock appear not to impact pinch and swell structure formation. The degree of material softening after the initial strain localising behaviour is shown to impact pinch and swell characteristics, while extensive material softening causes the formation of thick necks between swells by limiting the focused localisation of strain into shear bands. To aid analysis of the structures and help derive the flow properties of rocks in the field, we define three stages of pinch and swell development and offer suggestions for measurements to be made in the field. Our study suggests that Mohr-Coulomb strain localising behaviour combined with viscous flow is a viable alternative representation of the heterogeneous rheological behaviour of rocks seen in the middle crust. This type of mid-crustal rheological behaviour can have significant influence on the localisation of strain at all scales. For example, inclusion of Mohr-Coulomb strain localising behaviour with viscous flow in just some mid-crustal layers within a crustal-scale model can result in significant strain localisation, extending from the upper crust into the middle crust. This

  10. Seismic velocity structure at Deep Sea Drilling Project site 504B, Panama Basin: Evidence for thin oceanic crust

    NASA Astrophysics Data System (ADS)

    Collins, John A.; Purdy, Michael G.; Brocher, Thomas M.

    1989-07-01

    We present an analysis of wide-angle reflection/refraction data collected in the immediate vicinity of Deep Sea Drilling Project hole 504B in the Panama Basin, currently the deepest drill hole (1.288 km) into oceanic crust. The data were acquired with a 1785 inch3 air gun array and fixed-gain sonobuoy receivers and consist of four intersecting profiles shot along three different azimuths. Near-normal-incidence, multichannel seismic (MCS) reflection data were acquired simultaneously. Observed P and S wave arrivals out to maximum ranges of 30 km provide constraints on the velocity structure of the middle and lower crust and on total crustal thickness. Comparison of the travel times and amplitudes of the P and S wave arrivals on all four profiles revealed important similarities which were modeled using the reflectivity synthetic seismogram method. Forward modeling shows that in contrast to standard oceanic velocity models, a velocity-depth profile that better explains the observed data is characterized by high-velocity gradients (up to 0.6 km/s/km) in the middle crust, a 1.8-km-thick low-velocity zone (Vp = 7.1-6.7 km/s) immediately above Moho, and a total crustal thickness of only 5 km. Interpretation of the high-velocity gradients in the middle crust is constrained by the observation of P wave amplitude focusing at ranges of 16-19 km. Although not as well developed in comparison to the P wave arrivals, S wave arrivals show similar focusing. Total crustal thickness is constrained by the combined interpretation of a P wave, wide-angle reflection event observed at a range of 16-28 km and an MCS reflection event with a crustal travel time of 1.4-1.5 s. Although these events cannot be directly correlated, their travel times are consistent with the assumption that both have a common origin. Amplitude modeling of the wide-angle event demonstrates that these events are generated at the Moho.

  11. Genome-wide scan of 29,141 African Americans finds no evidence of directional selection since admixture.

    PubMed

    Bhatia, Gaurav; Tandon, Arti; Patterson, Nick; Aldrich, Melinda C; Ambrosone, Christine B; Amos, Christopher; Bandera, Elisa V; Berndt, Sonja I; Bernstein, Leslie; Blot, William J; Bock, Cathryn H; Caporaso, Neil; Casey, Graham; Deming, Sandra L; Diver, W Ryan; Gapstur, Susan M; Gillanders, Elizabeth M; Harris, Curtis C; Henderson, Brian E; Ingles, Sue A; Isaacs, William; De Jager, Phillip L; John, Esther M; Kittles, Rick A; Larkin, Emma; McNeill, Lorna H; Millikan, Robert C; Murphy, Adam; Neslund-Dudas, Christine; Nyante, Sarah; Press, Michael F; Rodriguez-Gil, Jorge L; Rybicki, Benjamin A; Schwartz, Ann G; Signorello, Lisa B; Spitz, Margaret; Strom, Sara S; Tucker, Margaret A; Wiencke, John K; Witte, John S; Wu, Xifeng; Yamamura, Yuko; Zanetti, Krista A; Zheng, Wei; Ziegler, Regina G; Chanock, Stephen J; Haiman, Christopher A; Reich, David; Price, Alkes L

    2014-10-01

    The extent of recent selection in admixed populations is currently an unresolved question. We scanned the genomes of 29,141 African Americans and failed to find any genome-wide-significant deviations in local ancestry, indicating no evidence of selection influencing ancestry after admixture. A recent analysis of data from 1,890 African Americans reported that there was evidence of selection in African Americans after their ancestors left Africa, both before and after admixture. Selection after admixture was reported on the basis of deviations in local ancestry, and selection before admixture was reported on the basis of allele-frequency differences between African Americans and African populations. The local-ancestry deviations reported by the previous study did not replicate in our very large sample, and we show that such deviations were expected purely by chance, given the number of hypotheses tested. We further show that the previous study's conclusion of selection in African Americans before admixture is also subject to doubt. This is because the FST statistics they used were inflated and because true signals of unusual allele-frequency differences between African Americans and African populations would be best explained by selection that occurred in Africa prior to migration to the Americas. PMID:25242497

  12. The slavery hypothesis for hypertension among African Americans: the historical evidence.

    PubMed

    Curtin, P D

    1992-12-01

    The slavery hypothesis for hypertension has stated that the high blood pressures sometimes measured in African Americans are caused by one or more of these conditions: first, salt deficiency in the parts of Africa that supplied slaves for the Americas; second, the trauma of the slave trade itself; third, conditions of slavery in the United States. A review of the historical evidence shows that there was no salt deficiency in those parts of Africa, nor do present-day West Africans have a high incidence of hypertension. Historical evidence does not support the hypothesis that deaths aboard slave ships were caused mainly by conditions that might be conductive to hypertension, such as salt-depleting diseases. Finally, the hypothesis has depended heavily on evidence from the West Indies, which is not relevant for the United States. There is no evidence that diet or the resulting patterns of disease and demography among slaves in the American South were significantly different from those of other poor southerners. PMID:1456349

  13. African, southern Indian and South American cratons were not part of the Rodinia supercontinent: evidence from field relationships and geochronology

    NASA Astrophysics Data System (ADS)

    Kröner, Alfred; Cordani, Umberto

    2003-11-01

    We discuss the question whether the late Mesoproterozoic and early Neoproterozoic rocks of eastern, central and southern Africa, Madagascar, southern India, Sri Lanka and South America have played any role in the formation and dispersal of the supercontinent Rodinia, believed to have existed between about 1000 and 750 Ma ago. First, there is little evidence for the production of significant volumes of ~1.4-1.0 Ga (Kibaran or Grenvillian age) continental crust in the Mozambique belt (MB) of East Africa, except, perhaps, in parts of northern Mozambique. This is also valid for most terranes related to West Gondwana, which are made up of basement rocks older than Mesoproterozoic, reworked in the Brasiliano/Pan-African orogenic cycle. This crust cannot be conclusively related to either magmatic accretion processes on the active margin of Rodinia or continental collision leading to amalgamation of the supercontinent. So far, no 1.4-1.0 Ga rocks have been identified in Madagascar. Secondly, there is no conclusive evidence for a ~1.0 Ga high-grade metamorphic event in the MB, although such metamorphism has been recorded in the presumed continuation of the MB in East Antarctica. In South America, even the Sunsas mobile belt, which is correlated with the Grenville belt of North America, does not include high-grade metamorphic rocks. All terranes with Mesoproterozoic ages seem to have evolved within extensional, aulacogen-type structures, and their compressional deformation, where observed, is normally much younger and is related to amalgamation of Gondwana. This is also valid for the Trans-Saharan and West Congo belts of West Africa. Third, there is also no evidence for post-1000 Ma sedimentary sequences that were deposited on the passive margin(s) of Rodinia. In contrast, the MB of East Africa and Madagascar is characterized by extensive structural reworking and metamorphic overprinting of Archaean rocks, particularly in Tanzania and Madagascar, and these rocks either

  14. Chemical and isotopic composition of the lower crust beneath the Meguma Lithotectonic Zone, Nova Scotia: evidence from granulite facies xenoliths

    NASA Astrophysics Data System (ADS)

    Eberz, G. W.; Clarke, D. B.; Chatterjee, A. K.; Giles, P. S.

    1991-03-01

    Granulite-facies xenoliths from an Upper Devonian lamprophyre dyke near Tangier, Nova Scotia, provide new information about the lower crust in the Meguma Zone. Two mineralogically and chemically distinet groups of xenoliths occur. Both groups contain quartz+feldspar+biotite+Fe-Ti oxides+sulfides. In addition, group A contains garnet+graphite±[aluminosilicates+spinel±sapphirine (hight Al2O3 subgroups A1 and A2)] or [clinopyroxene+sphene+apatite (high CaO sub-group A3)]. Group B has highly variable proportions of orthopyroxene (B1), clinopyroxene (B2), and amphibole (B3). Trace-element contents of the highly aluminous xenoliths compare closely with average to upper crustal model compositions and are similar in many aspects to other “undepleted” granulite-facies rocks. Low P-T sedimentary assemblages of quartz-chlorite-clay minerals-calcite-albite or paragonite can account for the compositions of group A xenoliths. Within group B, a high-MgO (MgO>13 wt%) subgroup with high transition-metal contents, and low-MgO (MgO<9 wt%) sub-groups with higher LIL (large-ion-lithophile) element contents exist. Although the rare-earth and high-field-strength elements indicate a tholeiitic or low-K calc-alkaline chemistry, the LIL elements are as high as those from high-K calc-alkaline volcanic are rocks. Isotopically, group A ranges from ɛNdt=-2.56 to-0.80 and87Sr/86Sr t =0.7046 to 0.7182 for t=370 Ma. For group B these values are +1.45 to +5.33 and 0.7028 to 0.7048, respectively. Model ages (TCHUR) are correspondingly low and are tightly constrained (544±52 Ma). These “young” ages contrast with the middle Proterozoic Nd model ages of the overlying Meguma Zone low-grade flysch. This time-inverted stratigraphy appears to be the product of a tectonic break between a younger autochthonous Tangier lower crust (≡Avalon), and an older allochthonous Meguma Group upper crust.

  15. Within-plate magmatism under condition of abnormally thick sialic crust: Evidence for Proterozoic anorthosite-rapakivi granite complexes of the East-European Craton

    NASA Astrophysics Data System (ADS)

    Sharkov, Evgenii

    2010-05-01

    Mid-Proterozoic (1.8-1.5 Ga) large bimodal multistage anorthosite-rapakivi granite complexes (ARGCs) are distinct magmatic assemblages in central part of the East European Craton. ARGCs formation commenced after stabilization of the Svecofennian orogen and relics of its abnormally thick (up to 50-60 km now) crust survived here in many places. Such massifs are practically absent at the eastern part of the craton (Kola-Karelian, Volga-Urals, etc. domains) with normal thickness (~40 km) of the crust. The ARGCs formation was accompanied by emplacement of diabase, quartz porphyry and complex dike swarms. Intra-plutonic diabase dikes (Fe-Ti basalts plume-related type), intruding the rapakivi granites, are often crossed in turn by later portions of granites; injections of basaltic melt into granitic magma chambers resulted in magma mingling. It indicates that melted out occurred simultaneously in mantle and crust during ARGC formation. Geochemical peculiarities of the ARGC rocks are enrichment in alkali (especially in K), Ti, Zn, Pb, and Zr, relatively high concentrations of Be, Sn, In, Y, Nb, Rb, F, Cu, W and Mo, and sometimes - Li and U. ɛNd value, ranges from -1.2 to +1.6, and relative high Th and Zn contents, most frequently observable in anorthosites, imply that the mafic magmas were considerably contaminated by crustal components. According to geophysical data, ARGCs represent upper parts of large transcrustal systems, composed by alternation of basic and silicic rocks, which located above rises of the mantle up to 10-20 km high. Such localization of ARGCs, probably evidence that such protuberances were mantle plume heads in time, where melting of their material occurred due to adiabatic decompression. Newly-formed basaltic melts (apparently Fe-Ti basalts, similar in composition to intra-plutonic dike rocks) intruded at different depths into abnormally thick sialic crust of stabilized by then Svecofennian orogen in form of large sills and caused melting of crustal

  16. The Andesites of the Tancítaro Volcanic Field, Michoacán Mexico: Evidence for their Formation in the Lower Crust.

    NASA Astrophysics Data System (ADS)

    Ownby, S. E.; Lange, R. A.

    2006-12-01

    that the andesites of the Tancítaro volcanic field are generated in the lower crust and are emplaced into the upper crust as hydrous, crystal-poor liquids. There is no evidence to support their origin through magma mixing of basalt and rhyolite. Degassing appears to be the primary drive for crystallization, and there is no evidence of any differentiation of these andesites toward dacite and/or rhyolite in an upper crustal chamber. Nor do the andesites appear to be directly related to one another by crystal fractionation processes in the upper crust, as there is no correlation between their silica content and 40Ar/39Ar eruption age (from numerous scattered and isolated vents peripheral to Volcán Tancítaro). Therefore, the primary staging area for the compositional diversity among the andesites in the Tancítaro volcanic field is within the lower crust and is not a result of magmatic processes in the upper crust. The variation in their phenocryst assemblages reflects different initial water concentrations and ascent rates toward the surface.

  17. Early Archean crust in the northern Wyoming province Evidence from U-Pb ages of detrital zircons

    USGS Publications Warehouse

    Mueller, P.A.; Wooden, J.L.; Nutman, A.P.; Mogk, D.W.

    1998-01-01

    U-Pb ages of individual detrital and metamorphic zircons from 12 Archean metasedimentary rocks, including quartzites, from the Beartooth, Ruby, and Tobacco Root uplifts of the northern Wyoming province indicate that they were deposited between 2.7 and 3.2 Ga. Younger, metamorphic zircons are found as overgrowths and new grains in some samples, and yield ages between 2.7 and 1.9 Ga. They are, however, much less abundant than detrital grains, which constitute >75% of the 355 grains analyzed. The majority of the detrital grains have ages between 3.2 and 3.4 Ga; none are younger than 2.9 Ga. Grains with 207Pb/206Pb ages between 3.4 and 4.0 Ga constituted approximately 15% of all grains with analyses within 10% of concordia, but are concentrated in samples from the eastern Beartooth Mountains. Comparison of the average of the Pb-Pb ages of individual zircons within 10% of concordia with previously published Lu-Hf chondritic model ages for some individual samples suggests that the age distribution recorded by the U-Pb system in these zircons has not been significantly disturbed by pre- or post-depositional Pb-loss. Collectively, these data suggest that the individual metasedimentary rocks did not completely share a common provenance and that a major crust-forming cycle occurred 3.2 to 3.4 Ga. In conjunction with previously published U-Th-Pb whole-rock data, these results suggest that rocks with a relatively high proportion of > 3.4 Ga grains may have had crust of comparable age in their provenance. ?? 1998 Elsevier Science B.V.

  18. Models and realities in modern human origins: the African fossil evidence.

    PubMed

    Smith, F H

    1992-08-29

    The recent application of such chronometric techniques as electron spin resonance (ESR), thermoluminescence (TL), and uranium series dating has had a significant impact on perceptions of modern human origins. Claims for the presence of anatomically modern humans in Africa prior to 100 ka and for the transition leading to modern Africans at an even earlier date have been made, partly based on results of these techniques. However, a careful examination of the pertinent record shows that these claims are not unequivocally supported by the available fossil and chronological evidence. PMID:1357699

  19. Palaeoproterozoic high-pressure granulite overprint of the Archaean continental crust: evidence for homogeneous crustal thickening (Man Rise, Ivory Coast)

    NASA Astrophysics Data System (ADS)

    Pitra, Pavel; Kouamelan, Alain N.; Ballèvre, Michel; Peucat, Jean-Jacques

    2010-05-01

    The character of mountain building processes in the Palaeoproterozoic times is subject to much debate. The local observation of Barrovian-type assemblages and high-pressure granulite relics in the Man Rise (Côte d'Ivoire), led some authors to argue that Eburnean (Palaeoproterozoic) reworking of the Archaean basement was achieved by modern-style thrust-dominated tectonics (e.g., Feybesse & Milési, 1994). However, it has been suggested that crustal thickening and subsequent exhumation of high-pressure crustal rocks can be achieved by virtue of homogeneous, fold-dominated deformation of hot crustal domains even in Phanerozoic orogenic belts (e.g., Schulmann et al., 2002; 2008). We describe a mafic granulite of the Kouibli area (Archaean part of the Man Rise, western Ivory Coast) that displays a primary assemblage (M1) containing garnet, diopsidic clinopyroxene, red-brown pargasitic amphibole, plagioclase (andesine), rutile, ilmenite and quartz. This assemblage is associated with a subvertical regional foliation. Symplectites that develop at the expense of the M1 assemblage contain orthopyroxene, clinopyroxene, plagioclase (bytownite), green pargasitic amphibole, ilmenite and magnetite (M2). Multiequilibrium thermobarometric calculations and P-T pseudosections calculated with THERMOCALC suggest granulite-facies conditions of ca. 13 kbar, 850°C and <7 kbar, 700-800°C for M1 and M2, respectively. In agreement with the qualitative information obtained from reaction textures and chemical zoning of minerals, this suggests an evolution dominated by decompression accompanied by moderate cooling. A Sm-Nd garnet - whole-rock age of 2.03 Ga determined on this sample indicates that this evolution occurred during the Palaeoproterozoic. We argue that from the geodynamic point of view the observed features are best explained by homogeneous thickening of the margin of the Archaean craton, re-heated and softened due to the accretion of hot, juvenile Palaeoproterozoic crust, as

  20. Pyroxenite and granulite xenoliths from beneath the Scottish Northern Highlands Terrane: evidence for lower-crust/upper-mantle relationships

    NASA Astrophysics Data System (ADS)

    Upton, B. G. J.; Aspen, P.; Hinton, R. W.

    2001-08-01

    Xenolith suites from Permian host rocks in Orkney and the extreme NE of the Scottish mainland (Duncansby Ness) are described and compared to those from elsewhere in the Northern Highlands Terrane. Those from the Tingwall dyke, Orkney, comprise roughly equal proportions of ultramafic rocks (wehrlites, clinopyroxenites, websterites, hornblendites) and mafic to felsic rocks (gabbroic, noritic and dioritic granulites, with subordinate tonalites and trondhjemites). Those from Duncansby (45 km to the south) are dominantly olivine-poor ultramafic rocks (clinopyroxenites, pargasite pyroxenites, biotite-pyroxenites), together with granulites grading from gabbroic through to tonalites and trondhjemites. Most of the granulites are meta-igneous, comprising plagioclase and one- or two-pyroxene species with equilibration temperatures of 810-710 °C, and are regarded as samples of the lower crust. Absence of garnet and olivine, together with the association of relatively sodic plagioclase and aluminous pyroxenes, is consistent with derivation from depths corresponding to 5-10 kbar. Positive Eu anomalies in the granulites imply that most originated as plagioclase-rich cumulates from basaltic magmas. Scarce peraluminous quartzo-feldspathic xenoliths, such as a garnet-sillimanite-bearing sample from Duncansby, are regarded as metasedimentary in origin. Pyroxenes (and biotites) in the ultramafic xenoliths tend to have higher mg numbers than those of the granulites, reflecting higher temperatures of formation. Whereas the pyroxene-rich ultramafic rocks may be partly interleaved with the granulites in the lower crust, it is concluded that they also constitute a zone of substantial thickness at or around Moho level, separating the granulites from underlying peridotites, and that they originated as cumulates cognate to the granulites. They have, however, been variably metasomatised with formation of amphibole. This zone may constitute a density trap at which melt fractions, rich in K, Fe

  1. Three-dimensional electrical structure of the crust and upper mantle in Ordos Block and adjacent area: Evidence of regional lithospheric modification

    NASA Astrophysics Data System (ADS)

    Dong, Hao; Wei, Wenbo; Ye, Gaofeng; Jin, Sheng; Jones, Alan G.; Jing, Jianen; Zhang, Letian; Xie, Chengliang; Zhang, Fan; Wang, Hui

    2014-06-01

    magnetotelluric (MT) data from project SINOPROBE were acquired and modeled, using three-dimensional (3D) MT inversion, to study the electrical structure of Ordos Block, a component of the North China Craton. For the first time, a high-resolution 3D resistivity model of the lithosphere is defined for the region. Contrary to what would be expected for a stable cratonic block, a prominent lithospheric conductive complex is revealed extending from the upper mantle to the mid-to-lower crust beneath the northern part of Ordos. Correlating well with results of seismic studies, the evidence from our independent magnetotelluric data supports regional modification of the lithosphere under the north Ordos and lithosphere thinning beneath Hetao Graben. The abnormally conductive structure may result from upwelling of mantle material in mid-to-late Mesozoic beneath the northern margin of the Ordos block.

  2. 207Pb-206Pb zircon ages of eastern and western Dharwar craton, southern India : Evidence for contemporaneous Archaean crust

    NASA Astrophysics Data System (ADS)

    Maibam, B.; Goswami, J. N.; Srinivasan, R.

    2009-04-01

    Dharwar craton is one of the major Archaean crustal blocks in the Indian subcontinent. The craton is comprised of two blocks, western and eastern. The western domain is underlain by orthogneisses and granodiorites (ca. 2.9-3.3 Ga) collectively termed as Peninsular Gneiss [e.g., 1] interspersed with older tracts of metasedimentary and metamorphosed igneous suites (Sargur Group and Dharwar Group; [2]). The eastern part of the craton is dominated by Late Archaean (2.50-2.75 Ga) granitoids and their gneissic equivalents. They are interspersed with schist belts (also of Sargur Group and Dharwar Group), which are lithologically similar to the Dharwar Supergroup in the western block, but are in different metamorphic dress. Here we report 207Pb-206Pb age of zircons separated from the metasedimentary and gneissic samples from the two blocks to constrain the evolution of the Dharwar craton during the early Archaean. Detrital zircons of the metasedimentary rocks from both the blocks show a wide range of overlapping ages between ~2.9 to >3.5 Ga. Zircon ages of the orthogneisses from the two blocks showed that most of the analysed grains of the eastern Dharwar block are found to be of the age as old as the western Dharwar gneisses. Imprints of younger events could be discerned from the presence of overgrowths in zircons from the studied samples throughout the craton. Our data suggest that crust forming cycles in the two blocks of the Dharwar craton occurred contemporaneously during the Archaean. References [1] Beckinsale, R.D., Drury, S.A., Holt, R.W. (1980) Nature 283, 469-470. [2] Swami Nath J., Ramakrishnan M., Viswanatha M.N. (1976) Rec. Geol. Surv. Ind., 107, 149-175.

  3. No evidence that selection has been less effective at removing deleterious mutations in Europeans than in Africans

    PubMed Central

    Do, Ron; Balick, Daniel; Li, Heng; Adzhubei, Ivan; Sunyaev, Shamil; Reich, David

    2014-01-01

    Non-African populations have experienced size reductions in the time since their split from West Africans, leading to the hypothesis that natural selection to remove weakly deleterious mutations has been less effective in the history of non-Africans. To test this hypothesis, we measured the per-genome accumulation of non-synonymous substitutions across diverse pairs of populations. We find no evidence for a higher load of deleterious mutations in non-Africans. However, we detect significant differences among more divergent populations, as archaic Denisovans have accumulated non-synonymous mutations faster than either modern humans or Neanderthals. To reconcile these findings with patterns that have been interpreted as evidence of less effective removal of deleterious mutations in non-Africans than in West Africans, we use simulations to show that the observed patterns are not likely to reflect changes in the effectiveness of selection after the populations split, and instead are likely to be driven by other population genetic factors. PMID:25581429

  4. Silicon Isotope Geochemistry of Ocean Island Basalts: Search for Deep Mantle Heterogeneities and Evidence for Recycled Altered Oceanic Crust

    NASA Astrophysics Data System (ADS)

    Pringle, E. A.; Savage, P. S.; Jackson, M. G.; Moreira, M. A.; Day, J. M.; Moynier, F.

    2014-12-01

    recycled altered oceanic crust in the plume source. However, the sampling of a primitive reservoir enriched in the light isotopes of Si, as suggested by [4], cannot be ruled out as a potential source of Si isotope variations in OIBs. References: [1] Ziegler et al., GCA 2005 [2] Savage et al., GCA 2011 [3] Savage et al., EPSL 2010 [4] Huang et al., GCA 2014

  5. Formation of iddingsite veins in the martian crust by centripetal replacement of olivine: Evidence from the nakhlite meteorite Lafayette

    NASA Astrophysics Data System (ADS)

    Lee, M. R.; Tomkinson, T.; Hallis, L. J.; Mark, D. F.

    2015-04-01

    common microstructural control on water-mineral interaction between Mars and Earth, and indicates that prior shock deformation was not a prerequisite for aqueous alteration of the martian crust.

  6. Instrumental evidence of an unusually strong West African Monsoon in the 19th century

    NASA Astrophysics Data System (ADS)

    Gallego, David; Ordoñez, Paulina; Ribera, Pedro; Peña-Ortiz, Cristina; Garcia-Herrera, Ricardo; Vega, Inmaculada; Gomez, Francisco de Paula

    2016-04-01

    The precipitation in the Sahel -which is mainly controlled by the dynamics of the West African Monsoon-, has been in the spot of the climate community for the last three decades due to the persistence of the drought period that started in the 1970s. Unfortunately, reliable meteorological series in this area are only available since the beginning of the 20th Century, thus limiting our understanding of the significance of this period from a long term perspective. Currently, our knowledge of what happened in times previous to the 20th Century essentially relies in documentary or proxy sources. In this work, we present the first instrumental evidence of a 50 year-long period characterised by an unusually strong West African monsoon in the19th Century. Following the recent advances in the generation of climatic indices based on data from ship's logbooks, we used historical wind observations to compute a new index (the so-called ASWI) for characterising the strength of the West African Monsoon. The ASWI is based in the persistence of the southwesterly winds in the [29°W-17°W;7°N-13°N] area and it has been possible to compute it since 1790 for July and since 1839 for August and September. We show that the ASWI is a reliable measure of the monsoon's strength and the Sahelian rainfall. Our new series clearly shows the well-known drought period starting in the 1970s. During this dry period, the West African Monsoon was particularly weak and interestingly, we found that since then, the correlations with different climatic patterns such as the Pacific and Atlantic "El Niño" changed significantly in relation to those of the previous century. Remarkably, our results also show that the period 1839-1890 was characterised by an unusually strong and persistent monsoon. Notwithstanding, two of the few dry years within this period were concurrent with large volcanic eruptions in the Northern Hemisphere. This latter result supports the recently suggested relationship between major

  7. The genome sequence of African rice (Oryza glaberrima) and evidence for independent domestication.

    PubMed

    Wang, Muhua; Yu, Yeisoo; Haberer, Georg; Marri, Pradeep Reddy; Fan, Chuanzhu; Goicoechea, Jose Luis; Zuccolo, Andrea; Song, Xiang; Kudrna, Dave; Ammiraju, Jetty S S; Cossu, Rosa Maria; Maldonado, Carlos; Chen, Jinfeng; Lee, Seunghee; Sisneros, Nick; de Baynast, Kristi; Golser, Wolfgang; Wissotski, Marina; Kim, Woojin; Sanchez, Paul; Ndjiondjop, Marie-Noelle; Sanni, Kayode; Long, Manyuan; Carney, Judith; Panaud, Olivier; Wicker, Thomas; Machado, Carlos A; Chen, Mingsheng; Mayer, Klaus F X; Rounsley, Steve; Wing, Rod A

    2014-09-01

    The cultivation of rice in Africa dates back more than 3,000 years. Interestingly, African rice is not of the same origin as Asian rice (Oryza sativa L.) but rather is an entirely different species (i.e., Oryza glaberrima Steud.). Here we present a high-quality assembly and annotation of the O. glaberrima genome and detailed analyses of its evolutionary history of domestication and selection. Population genomics analyses of 20 O. glaberrima and 94 Oryza barthii accessions support the hypothesis that O. glaberrima was domesticated in a single region along the Niger river as opposed to noncentric domestication events across Africa. We detected evidence for artificial selection at a genome-wide scale, as well as with a set of O. glaberrima genes orthologous to O. sativa genes that are known to be associated with domestication, thus indicating convergent yet independent selection of a common set of genes during two geographically and culturally distinct domestication processes. PMID:25064006

  8. Evidence of Positive Selection in Mitochondrial Complexes I and V of the African Elephant

    PubMed Central

    Finch, Tabitha M.; Zhao, Nan; Korkin, Dmitry; Frederick, Katy H.; Eggert, Lori S.

    2014-01-01

    As species evolve, they become adapted to their local environments. Detecting the genetic signature of selection and connecting that to the phenotype of the organism, however, is challenging. Here we report using an integrative approach that combines DNA sequencing with structural biology analyses to assess the effect of selection on residues in the mitochondrial DNA of the two species of African elephants. We detected evidence of positive selection acting on residues in complexes I and V, and we used homology protein structure modeling to assess the effect of the biochemical properties of the selected residues on the enzyme structure. Given the role these enzymes play in oxidative phosphorylation, we propose that the selected residues may contribute to the metabolic adaptation of forest and savanna elephants to their unique habitats. PMID:24695069

  9. The categorization of African descent populations in Europe and the USA: should lexicons of recommended terminology be evidence-based?

    PubMed

    Aspinall, P J

    2008-01-01

    This review attempts to evaluate a proposed lexicon for African-descent populations from the viewpoint of saliency amongst those described and wider official and scientific usage, focusing on Britain and the USA. It is argued that it is unsatisfactory to privilege the term 'African American' over 'Black' for African-descent populations in the USA as the evidence base shows that both labels compete as self-designations on co-equal terms, while 'Black' is the prevalent term in scientific writing. Moreover, 'African American' is not an inclusive term for the African-descent population and it is not known how prevalent and enduring the term will prove to be. With respect to Britain, the census terms of 'Black African' and 'Black Caribbean' are well established, the increasing popularity of 'Black British' also being recognized in census labels. Given the increasing interest in the relationship between ethnic identity and health, there are arguments for documenting the diversity of terminology amongst different user constituencies in country-specific settings. The approach of synthetic glossaries of consensual terms may, through the need for economy and parsimony in the use of terminology, contribute to an unsatisfactory paring of that diversity. PMID:17645900

  10. Evidence of common signatures of selection in the genomes of West African cattle and the Yoruba human population

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In 1954, Allison found that the sickle-cell anemia mutation in the beta hemoglobin gene was highly prevalent in West African people because it is protective against malaria, so carriers would thrive and leave offspring in spite of the genetic disease. This is one of the earliest evidences of an envi...

  11. Recycled oceanic crust in the source of 90-40 Ma basalts in North and Northeast China: Evidence, provenance and significance

    NASA Astrophysics Data System (ADS)

    Xu, Yi-Gang

    2014-10-01

    Major, trace element and Sr-Nd-Pb isotopic data of basalts emplaced during 90-40 Ma in the North and Northeast China are compiled in this review, with aims of constraining their petrogenesis, and by inference the evolution of the North China Craton during the late Cretaceous and early Cenozoic. Three major components are identified in magma source, including depleted component I and II, and an enriched component. The depleted component I, which is characterized by relatively low 87Sr/86Sr (<0.7030), moderate 206Pb/204Pb (18.2), moderately high εNd (∼4), high Eu/Eu∗ (>1.1) and HIMU-like trace element characteristics, is most likely derived from gabbroic cumulate of the oceanic crust. The depleted component II, which distinguishes itself by its high εNd (∼8) and moderate 87Sr/86Sr (∼0.7038), is probably derived from a sub-lithospheric ambient mantle. The enriched component has low εNd (2-3), high 87Sr/86Sr (>0.7065), low 206Pb/204Pb (17), excess Sr, Rb, Ba and a deficiency of Zr and Hf relative to the REE. This component is likely from the basaltic portion of the oceanic crust, which is variably altered by seawater and contains minor sediments. Comparison with experimental melts and trace element modeling suggest that these recycled oceanic components may be in form of garnet pyroxenite/eclogite. These components are young (<0.5 Ga) and show an Indian-MORB isotopic character. Given the share of this isotopic affinity by the extinct Izanaghi-Pacific plate, currently stagnated within the mantle transition zone, we propose that it ultimately comes from the subducted Pacific slab. Eu/Eu∗ and 87Sr/86Sr of the 90-40 Ma magmas increases and decreases, respectively, with decreasing emplacement age, mirroring a change in magma source from upper to lower parts of subducted oceanic crust. Such secular trends are created by dynamic melting of a heterogeneous mantle containing recycled oceanic crust. Due to different melting temperature of the upper and lower ocean

  12. Evidence from facial morphology for similarity of Asian and African representatives of Homo erectus.

    PubMed

    Rightmire, G P

    1998-05-01

    with some flexion of the malar pillar, and a posterior position for the incisive canal are present in all groups. These characters seem to be plesiomorphic, in comparison to the derived states evolved in later humans. Much or all of the variation in facial form can be attributed to sex dimorphism and/or local differentiation of populations within the Asian and African geographic regions. Metric differences among the fossils are comparable to those documented in a subset of recent H. sapiens, and there is no evidence that the Pleistocene specimens show greater dispersion than expected within a single species. This finding is generally in keeping with observations made on other parts of the cranium, lower jaw, and teeth. All of the hominids can be placed in H. erectus. Although its phylogenetic origins remain obscure, this lineage must be rooted in Africa. The species flourished for a long time. At several sites in China, H. erectus is known from deposits of the later Middle Pleistocene, while at Ngandong in Indonesia, archaic people may have survived even into the Late Pleistocene (Swisher et al. [1996] Science 274:1870-1874). The Ngandong fossils may record the last appearance of the lineage. PMID:9590525

  13. The Continental Crust.

    ERIC Educational Resources Information Center

    Burchfiel, B. Clark

    1983-01-01

    Continental crust underlies the continents, their margins, and also small shallow regions in oceans. The nature of the crust (much older than oceanic crust) and its dynamics are discussed. Research related to and effects of tectonics, volcanism, erosion, and sedimentation on the crust are considered. (JN)

  14. This Too Shall Pass: Evidence of Coping and Fading Emotion in African Americans' Memories of Violent and Nonviolent Death.

    PubMed

    Henderson, Dawn X; Bond, Gary D; Alderson, Courtney J; Walker, W Richard

    2015-01-01

    Two studies examined African Americans essays on coping with violent and nonviolent death and fading affect bias. Essays from 101 African Americans were coded for psychological resolution (resolved or unresolved) and for type of death (violent or nonviolent). Linguistic analyses were used to examine the experience of loss and coping methods. Religious coping was important for nonviolent death events while social support and emotion (e.g., crying) were themes that emerged for violent death events. For unresolved violent death events, dissociation was a common theme. The perceived change in the emotional intensity of the events was examined and revealed that the negative emotion showed evidence of substantial fading. Overall, these results suggest religious coping, social support and sharing enhance coping among African American participants. These processes can help negative affect associated with death events fade, allowing for psychological resolution, healing, and resilience. PMID:26665961

  15. North Atlantic Deep Water export to the Southern Ocean over the past 14 Myr: Evidence from Nd and Pb isotopes in ferromanganese crusts

    USGS Publications Warehouse

    Frank, M.; Whiteley, N.; Kasten, S.; Hein, J.R.; O'Nions, K.

    2002-01-01

    The intensity of North Atlantic Deep Water (NADW) production has been one of the most important parameters controlling the global thermohaline ocean circulation system and climate. Here we present a new approach to reconstruct the overall strength of NADW export from the North Atlantic to the Southern Ocean over the past 14 Myr applying the deep water Nd and Pb isotope composition as recorded by ferromanganese crusts and nodules. We present the first long-term Nd and Pb isotope time series for deep Southern Ocean water masses, which are compared with previously published time series for NADW from the NW Atlantic Ocean. These data suggest a continuous and strong export of NADW, or a precursor of it, into the Southern Ocean between 14 and 3 Ma. An increasing difference in Nd and Pb isotope compositions between the NW Atlantic and the Southern Ocean over the past 3 Myr gives evidence for a progressive overall reduction of NADW export since the onset of Northern Hemisphere glaciation (NHG). The Nd isotope data allow us to assess at least semiquantitatively that the amount of this reduction has been in the range between 14 and 37% depending on location.

  16. Evidence from Olivine-Hosted Melt Inclusions that the Martian Mantle has a Chondritic D/H Ratio and that Some Young Basalts have Assimilated Old Crust

    NASA Technical Reports Server (NTRS)

    Usui, Tomohiro; Alexander, O'D.; Wang, J.; Simon, J. I.; Jones, J. H.

    2012-01-01

    Magmatic degassing of volatile elements affects the climate and near-surface environment of Mars. Telescopic and meteorite studies have revealed that the Martian atmosphere and near-surface materials have D/H ratios 5-6 times terrestrial values [e.g., 1, 2]. Such high D/H ratios are interpreted to result from the preferential loss of H relative to heavier D from the Martian atmosphere, assuming that the original Martian water inventory had a D/H ratio similar to terrestrial values and to H in primitive meteorites [e.g., 1, 3]. However, the primordial Martian D/H ratio has, until now, not been well constrained. The uncertainty over the Martian primordial D/H ratio has arisen both from the scarcity of primitive Martian meteorites and as a result of contamination by terrestrial and, perhaps, Martian surface waters that obscure the signature of the Martian mantle. This study reports a comprehensive dataset of magmatic volatiles and D/H ratios in Martian primary magmas based on low-contamination, in situ ion microprobe analyses of olivine-hosted melt inclusions from both depleted [Yamato 980459 (Y98)] and enriched [Larkman Nunatak 06319 (LAR06)] Martian basaltic meteorites. Analyses of these primitive melts provide definitive evidence that the Martian mantle has retained a primordial D/H ratio and that young Martian basalts have assimilated old Martian crust.

  17. Two stage melt-rock interaction in the lower oceanic crust of the Parece Vela basin (Philippine sea), evidence from the primitive troctolites from the Godzilla Megamullion

    NASA Astrophysics Data System (ADS)

    Sanfilippo, A.; Dick, H. J.; Ohara, Y.

    2011-12-01

    Godzilla Megamullion is a giant oceanic core complex exposed in an extinct slow- to intermediate-spreading segment of the Parece Vela Basin (Philippine sea) [1; 2]. It exposes lower crust and mantle rocks on the sea-floor, offering a unique opportunity to unravel the architecture and the composition of the lower oceanic lithosphere of an extinct back arc basin. Here we present data on primitive troctolites and associated olivine-gabbros from the breakaway area of the Godzilla Megamullion. On the basis of the olivine/plagioclase volume ratio, the troctolites are subdivided into Ol-troctolites (Ol/Pl >1) and Pl-troctolites (Ol/Pl<1), which show evident textural differences. Ol-troctolites have rounded to polygonal olivine, subhedral plagioclase, and poikilitic clinopyroxene. This texture suggests chemical disequilibrium between the olivine and a melt crystallizing plagioclase and clinopyroxene. We interpret these rocks as reaction products of a dunite matrix with transient basaltic melts [e.g. 3; 4]. Pl-troctolites have euhedral plagioclase and poikilitic olivine and clinopyroxene. Irregular shapes and inverse zoning of the plagioclase chadacrysts within the olivine indicate disequilibrium between existing plagioclase and an olivine-clinopyroxene saturated melt. The occurrence of plagioclase chadacrysts within clinopyroxene ranging from irregular to euhedral in shape suggests crystallization of new lower-Na plagioclase with the clinopyroxene. Olivine oikocrysts in the Pl-troctolites have low-NiO olivine in equilibrium with a high-MgO melt. The Pl-troctolites, then, may be the product of reaction between a plagioclase cumulate and a basaltic melt produced by mixing the high-MgO melt residual to the formation of the Ol-troctolites with new magma. The effect of melt-rock reaction in the Pl- and Ol- troctolites explains the sharp decrease in plagioclase An with respect to Mg# in clinopyroxene and olivine. Furthermore, the melt is shifted towards lower Na, which is

  18. Double-layer structure of the crust beneath the Zhongdian arc, SW China: U-Pb geochronology and Hf isotope evidence

    NASA Astrophysics Data System (ADS)

    Cao, Kang; Xu, Ji-Feng; Chen, Jian-Lin; Huang, Xiao-Xiao; Ren, Jiang-Bo; Zhao, Xiang-Dong; Liu, Zhen-Xing

    2016-01-01

    U-Pb ages and Hf isotopes of zircons in Late Triassic and Cretaceous intrusive rocks from the Zhongdian arc, SW China, are used to decipher the tectonic, magmatic, and metallogenic processes that occurred during this period. New U-Pb dating of zircons from Late Triassic porphyries yielded ages of ca. 216 Ma and εHf(t) values of -2.1 to +6.1. Combined with previous results, the data indicate that these Late Triassic rocks were most likely derived from a juvenile mafic lower-crust with minor old crust material. However, the Cretaceous granites (∼80 Ma) have lower εHf(t) values (-7.6 to -2.4) than the Late Triassic rocks, indicating that the former originated from old crust. Based on the new data and previous studies of Mesozoic magmatic activity, a plausible model for the tectono-magmatism and metallogenesis of the Zhongdian arc is proposed. The westwards subduction of the Ganzi-Litang oceanic crust began before ∼230 Ma, resulting in the formation of a juvenile lower crust beneath the Zhongdian arc due to the underplating of mafic arc magmas during ca. 230-216 Ma. At ca. 216 Ma, break-off or slab-tearing of the west-dipping Ganzi-Litang oceanic slab led to partial melting of the juvenile lower crust, which gave rise to Cu-bearing porphyries. In the Late Cretaceous, the Zhongdian arc probably underwent post-collision extension, triggering the partial melting of the old middle-upper crustal materials and producing various granites and related Mo-Cu deposits. According to this model, the crust beneath the Zhongdian arc probably has a double-layer structure, with older crust at shallow levels and juvenile crust at deeper levels.

  19. Reexaming the Development of African American English: Evidence from Isolated Communities.

    ERIC Educational Resources Information Center

    Wolfram, Walt

    2003-01-01

    Examines several longstanding, isolated biracial sociolinguistic situations in the coastal and Appalachian regions of North Carolina: a core community of African Americans and two case studies of isolated speakers. Compares diagnostic phonological and morphosyntactic variables for speakers representing different generations of African American and…

  20. Thermomagmatic evolution of Mesoproterozoic crust in the Blue Ridge of SW Virginia and NW North Carolina: Evidence from U-Pb geochronology and zircon geothermometry

    USGS Publications Warehouse

    Tollo, Richard P.; Aleinikoff, John N.; Wooden, Joseph L.; Mazdab, Frank K.; Southworth, Scott; Fanning, Mark C.

    2010-01-01

    New geologic mapping, petrology, and U-Pb geochronology indicate that Mesoproterozoic crust near Mount Rogers consists of felsic to mafic meta-igneous rocks emplaced over 260 m.y. The oldest rocks are compositionally diverse and migmatitic, whereas younger granitoids are porphyritic to porphyroclastic. Cathodoluminescence imaging indicates that zircon from four representative units preserves textural evidence of multiple episodes of growth, including domains of igneous, metamorphic, and inherited origin. Sensitive high-resolution ion microprobe (SHRIMP) trace-element analyses indicate that metamorphic zircon is characterized by lower Th/U, higher Yb/Gd, and lower overall rare earth element (REE) concentrations than igneous zircon. SHRIMP U-Pb isotopic analyses of zircon define three episodes of magmatism: 1327 ± 7 Ma, 1180–1155 Ma, and 1061 ± 5 Ma. Crustal recycling is recorded by inherited igneous cores of 1.33–1.29 Ga age in 1161 ± 7 Ma meta-monzogranite. Overlapping ages of igneous and metamorphic crystallization indicate that plutons of ca. 1170 and 1060 Ma age were emplaced during episodes of regional heating. Local development of hornblende + plagioclase + quartz ± clinopyroxene indicates that prograde metamorphism at 1170–1145 Ma and 1060–1020 Ma reached upper-amphibolite-facies conditions, with temperatures estimated using Ti-in-zircon geothermometry at ~740 ± 40 °C during both episodes. The chemical composition of 1327 ± 7 Ma orthogranofels from migmatite preserves the first evidence of arc-generated rocks in the Blue Ridge, indicating a subduction-related environment that may have been comparable to similar-age systems in inliers of the Northern Appalachians and the Composite Arc belt of Canada. Granitic magmatism at 1180–1155 Ma and ca. 1060 Ma near Mount Rogers was contemporaneous with anorthosite-mangerite-charnockite-granite (AMCG) plutonism in the Northern Appalachian inliers and Canadian Grenville Province. Metamorphism at ca. 1160

  1. Socioeconomic Differences in Dietary Patterns in an East African Country: Evidence from the Republic of Seychelles

    PubMed Central

    Mayén, Ana-Lucia; Bovet, Pascal; Marti-Soler, Helena; Viswanathan, Bharathi; Gedeon, Jude; Paccaud, Fred; Marques-Vidal, Pedro; Stringhini, Silvia

    2016-01-01

    Background In high income countries, low socioeconomic status (SES) is related to unhealthier dietary patterns, while evidence on the social patterning of diet in low and middle income countries is scarce. Objective In this study, we assess dietary patterns in the general population of a middle income country in the African region, the Republic of Seychelles, and examine their distribution according to educational level and income. Methods Data was drawn from two independent national surveys conducted in the Seychelles among adults aged 25–64 years in 2004 (n = 1236) and 2013 (n = 1240). Dietary patterns were assessed by principal component analysis (PCA). Educational level and income were used as SES indicators. Data from both surveys were combined as no interaction was found between SES and year. Results Three dietary patterns were identified: “snacks and drinks”, “fruit and vegetables” and “fish and rice”. No significant associations were found between SES and the “snacks and drinks” pattern. Low vs. high SES individuals had lower adherence to the “fruit and vegetables” pattern [prevalence ratio (95% CI) 0.71 (0.60–0.83)] but a higher adherence to the traditional “fish and rice” pattern [1.58 (1.32–1.88)]. Income modified the association between education and the “fish and rice” pattern (p = 0.02), whereby low income individuals had a higher adherence to this pattern in both educational groups. Conclusion Low SES individuals have a lower consumption of fruit and vegetables, but a higher consumption of traditional foods like fish and rice. The Seychelles may be at a degenerative diseases stage of the nutrition transition. PMID:27214139

  2. Palaeohydrology of the Fazzan Basin, Libyan Sahara: Evidence for multiple phases of North African humidity.

    NASA Astrophysics Data System (ADS)

    Armitage, S. J.; White, K.; Drake, N.

    2008-12-01

    The Fazzan is a large closed basin with an area of 450,000 km2, located in south-western Libya. The present-day climate is hyper-arid. Modern human occupation is restricted to oases, notably at the foot of the Messak Sattafat, a Nubian Sandstone escarpment which divides the Fazzan into two sub-basins. However widespread lithic scatters with varying inferred ages, and numerous Holocene hearth fields, indicate that the Fazzan has a long history of human occupation. In addition, regionally extensive lake deposits attest to the presence of a large palaeolake, here termed Lake Mega-Fazzan, at various periods in the past. Although the Sahara contains evidence for several other large palaeolakes, Lake Mega-Fazzan is the only one fed exclusively by rivers draining the Sahara proper. Thus, the Lake Mega-Fazzan sediments and archaeological remains provide an important resource for advancing our understanding of climate change in this part of the Sahara. Optically stimulated luminescence (OSL) dating techniques have been applied to a range of lacustrine deposits, and more experimentally to the Holocene hearth fields, to provide an internally consistent chronology for the Fazzan record. Results indicate that sediments within the Fazzan Basin record a very long history of palaeohydrological change. The oldest lacustrine sediments are beyond the range of conventional OSL dating techniques, but younger humid periods during oxygen isotope stages 11, 5 and 1 are recognised. Initial results from one hearth field also indicate that OSL has the potential to reveal human responses to changes in hydrology during the Holocene. These results, when compared with similar studies of adjacent closed basins, indicate that the Sahara may not always have provided as formidable a barrier to faunal migration as it does at present. The implications of this finding for our understanding of North African palaeoclimate and biogeography will be discussed.

  3. The Impact of the Great Migration on Mortality of African Americans: Evidence from the Deep South

    PubMed Central

    Black, Dan A.; Sanders, Seth G.; Taylor, Evan J.

    2015-01-01

    The Great Migration—the massive migration of African Americans out of the rural South to largely urban locations in the North, Midwest, and West—was a landmark event in U.S. history. Our paper shows that this migration increased mortality of African Americans born in the early twentieth century South. This inference comes from an analysis that uses proximity of birthplace to railroad lines as an instrument for migration. PMID:26345146

  4. African herbal medicines in the treatment of HIV: Hypoxis and Sutherlandia. An overview of evidence and pharmacology

    PubMed Central

    Mills, Edward; Cooper, Curtis; Seely, Dugald; Kanfer, Izzy

    2005-01-01

    In Africa, herbal medicines are often used as primary treatment for HIV/AIDS and for HIV-related problems. In general, traditional medicines are not well researched, and are poorly regulated. We review the evidence and safety concerns related to the use of two specific African herbals, which are currently recommended by the Ministry of Health in South Africa and member states for use in HIV: African Potato and Sutherlandia. We review the pharmacology, toxicology and pharmacokinetics of these herbal medicines. Despite the popularity of their use and the support of Ministries of Health and NGOs in some African countries, no clinical trials of efficacy exist, and low-level evidence of harm identifies the potential for drug interactions with antiretroviral drugs. Efforts should be made by mainstream health professionals to provide validated information to traditional healers and patients on the judicious use of herbal remedies. This may reduce harm through failed expectations, pharmacologic adverse events including possible drug/herb interactions and unnecessary added therapeutic costs. Efforts should also be directed at evaluating the possible benefits of natural products in HIV/AIDS treatment. PMID:15927053

  5. Freshly brewed continental crust

    NASA Astrophysics Data System (ADS)

    Gazel, E.; Hayes, J. L.; Caddick, M. J.; Madrigal, P.

    2015-12-01

    Earth's crust is the life-sustaining interface between our planet's deep interior and surface. Basaltic crusts similar to Earth's oceanic crust characterize terrestrial planets in the solar system while the continental masses, areas of buoyant, thick silicic crust, are a unique characteristic of Earth. Therefore, understanding the processes responsible for the formation of continents is fundamental to reconstructing the evolution of our planet. We use geochemical and geophysical data to reconstruct the evolution of the Central American Land Bridge (Costa Rica and Panama) over the last 70 Ma. We also include new preliminary data from a key turning point (~12-6 Ma) from the evolution from an oceanic arc depleted in incompatible elements to a juvenile continental mass in order to evaluate current models of continental crust formation. We also discovered that seismic P-waves (body waves) travel through the crust at velocities closer to the ones observed in continental crust worldwide. Based on global statistical analyses of all magmas produced today in oceanic arcs compared to the global average composition of continental crust we developed a continental index. Our goal was to quantitatively correlate geochemical composition with the average P-wave velocity of arc crust. We suggest that although the formation and evolution of continents may involve many processes, melting enriched oceanic crust within a subduction zone, a process probably more common in the Achaean where most continental landmasses formed, can produce the starting material necessary for juvenile continental crust formation.

  6. Additional evidence for bone technology in the southern African Middle Stone Age.

    PubMed

    d'Errico, Francesco; Henshilwood, Christopher S

    2007-02-01

    Few Middle Stone Age sites have yielded convincing evidence for a complex bone technology, a behavior often associated with the emergence of modern cultures. Here, we review the published evidence for Middle Stone Age bone tools from southern Africa, analyze an additional nine bone artifacts recently recovered from Middle Stone Age levels at Blombos Cave, describe an unpublished bone tool from probable Middle Stone Age levels at Peers Cave, examine a single bone awl found at Blombosch Sands (an open site near Blombos Cave), and reappraise marked bone artifacts and a bone point recovered from Klasies River. To determine the chronological and cultural attribution of these artifacts, document bone-manufacturing techniques associated with the southern African MSA, and discuss the symbolic significance of the markings present on some of these objects we use (1) available contextual information; (2) morphometric comparison of Later Stone Age, Modern San, and purported Middle Stone Age projectile points; (3) analysis of the carbon/nitrogen content of bone tools and faunal remains from Peers and Blombos caves; and (4) microscopic analysis of traces of manufacture and use. Previously undescribed bone artifacts from Blombos Cave include a massive point manufactured on weathered bone, two complete awls and two awl tips manufactured on small-sized mammal and bird bone, a probable projectile point with a tang manufactured by knapping and scraping, a shaft fragment modified by percussion, used as retoucher and bearing a set of incised lines on the middle of the periosteal surface, and two fragments with possible engravings. The point from Peers Cave can be assigned to the Middle Stone Age and bears tiny markings reminiscent of those recorded on projectile points from Blombos and used as marks of ownership on San arrow points. The awl from Blombosch Sands and the bone point from Klasies River can be attributed to the Later Stone Age. Two notched objects from Klasies are

  7. Recycling of oceanic crust from a stagnant slab in the mantle transition zone: Evidence from Cenozoic continental basalts in Zhejiang Province, SE China

    NASA Astrophysics Data System (ADS)

    Li, Yan-Qing; Ma, Chang-Qian; Robinson, Paul T.; Zhou, Qin; Liu, Ming-Liang

    2015-08-01

    Cenozoic continental basalts from Zhejiang Province, southeast China are tholeiitic to weakly alkalic in composition, with moderate MgO contents (6-11 wt.%) and an average Mg# of 62. They display typical OIB-like trace element features, including enrichment in most incompatible elements, both LILE and LREE, and negative K, Pb, Zr, Hf anomalies. In particular, they are characterized by high Fe/Mn (73 ± 5), La/Yb (19 ± 6) and Nb/Ta (18.8 ± 0.4) ratios, which can be attributed to the presence of residual clinopyroxene, garnet and rutile in the mantle source. Based on these minerals, the following hybrid source rocks are hypothesized: garnet pyroxenite/eclogite and peridotite. Clinopyroxene-liquid thermobarometry indicates clinopyroxene crystallization temperatures of > 1257 °C. This is higher than the assumed temperature at the base of the sub-continental lithospheric mantle (SCLM) (~ 1220 °C) beneath Zhejiang, thus the magmas were presumably derived from the asthenosphere. Some typical geochemical features such as negative K, Pb anomalies, positive Ba, Sr, Nb, Ta anomalies and the extremely high Os isotopic signatures, suggest participation of EM-like mantle sources, indicative of ancient subducted oceanic crust. (87Sr/86Sr)i (0.7037-0.7046) and 143Nd/144Nd (0.512832-0.512990) isotope ratios point to the presence of mixed components in the source region, i.e., DMM, EM1 and EM2. Recent seismic tomographic images of the mantle beneath Zhejiang suggest the presence of a subducted slab of oceanic lithosphere in the transition zone. Based on the combined geophysical and geochemical evidence, we propose that the major source of the Zhejiang basaltic magmas was the ancient subducted oceanic slab in the transition zone with an EM-like signature. The other magma sources include depleted asthenospheric peridotite possessing a DMM-like signature. The dynamics of this upwelling hybrid magma was apparently related to westward subduction of the Pacific plate underneath the

  8. Seismic evidence of bending and unbending of subducting oceanic crust and the presence of mantle megathrust in the 2004 Great Sumatra earthquake rupture zone

    NASA Astrophysics Data System (ADS)

    Singh, Satish C.; Chauhan, Ajay P. S.; Calvert, Andrew J.; Hananto, Nugroho D.; Ghosal, Dibakar; Rai, Abhishek; Carton, Helene

    2012-03-01

    In subduction zones the plate interface (megathrust) is typically poorly imaged at depths > 12 km, however its precise geometry and nature as well as the positions of updip and downdip limits of the seismogenic zone are important elements to understand the generation of megathrust earthquakes. Using deep marine seismic reflection and refraction data, we observed discontinuous reflections off the top of the subducting oceanic crust down to 60 km depth in the 2004 great Sumatra-Andaman earthquake rupture zone. We find that the top of the downgoing plate does not dip gently into the subduction zone but instead displays a staircase geometry with three successive, 5-15 km vertical steps, spaced ~ 50 km apart. Micro-earthquake data indicate that most of the seismicity lies below this interface, suggesting that the oceanic plate is deforming actively. Along part of the profile, we also image a second reflector located 8-10 km below the top of the oceanic crust. The forward modelling of the gravity data along the profile supports the presence of a high-density material above this reflector. The presence of a staircase shape for the top of the oceanic crust, together with constraints from gravity data and earthquake data, require that the megathrust goes through this second reflector. This leads us to conclude that the megathrust is at least partly located in the oceanic mantle and that underplating of oceanic crust beneath the wedge and underplating of upper mantle beneath the forearc basin are taking place in this region.

  9. Genetic Evidence of African Slavery at the Beginning of the Trans-Atlantic Slave Trade

    PubMed Central

    Martiniano, Rui; Coelho, Catarina; Ferreira, Maria Teresa; Neves, Maria João; Pinhasi, Ron; Bradley, Daniel G.

    2014-01-01

    An archaeological excavation in Valle da Gafaria (Lagos, Portugal), revealed two contiguous burial places outside the medieval city walls, dating from the 15th–17th centuries AD: one was interpreted as a Leprosarium cemetery and the second as an urban discard deposit, where signs of violent, unceremonious burials suggested that these remains may belong to slaves captured in Africa by the Portuguese. We obtained random short autosomal sequence reads from seven individuals: two from the latter site and five from the Leprosarium and used these to call SNP identities and estimate ancestral affinities with modern reference data. The Leprosarium site samples were less preserved but gave some probability of both African and European ancestry. The two discard deposit burials each gave African affinity signals, which were further refined toward modern West African or Bantu genotyped samples. These data from distressed burials illustrate an African contribution to a low status stratum of Lagos society at a time when this port became a hub of the European trade in African slaves which formed a precursor to the transatlantic transfer of millions. PMID:25104065

  10. Genetic evidence of African slavery at the beginning of the trans-Atlantic slave trade.

    PubMed

    Martiniano, Rui; Coelho, Catarina; Ferreira, Maria Teresa; Neves, Maria João; Pinhasi, Ron; Bradley, Daniel G

    2014-01-01

    An archaeological excavation in Valle da Gafaria (Lagos, Portugal), revealed two contiguous burial places outside the medieval city walls, dating from the 15(th)-17(th) centuries AD: one was interpreted as a Leprosarium cemetery and the second as an urban discard deposit, where signs of violent, unceremonious burials suggested that these remains may belong to slaves captured in Africa by the Portuguese. We obtained random short autosomal sequence reads from seven individuals: two from the latter site and five from the Leprosarium and used these to call SNP identities and estimate ancestral affinities with modern reference data. The Leprosarium site samples were less preserved but gave some probability of both African and European ancestry. The two discard deposit burials each gave African affinity signals, which were further refined toward modern West African or Bantu genotyped samples. These data from distressed burials illustrate an African contribution to a low status stratum of Lagos society at a time when this port became a hub of the European trade in African slaves which formed a precursor to the transatlantic transfer of millions. PMID:25104065

  11. Continued Evidence for Input of Chlorine into the Martian Crust from Degassing of Chlorine-Rich Martian Magmas with Implications for Potential Habitability

    NASA Astrophysics Data System (ADS)

    Filiberto, J.; Gross, J.

    2014-12-01

    The chlorine-concentration (or salinity) of a fluid affects the potential for that fluid to be a habitable environment, with most known terrestrial organisms preferring low salinity fluids [1, 2]. The Martian crust (as analyzed by the Gamma Ray Spectrometer) is chlorine-rich with up to 0.8 wt% Cl; while the MER rovers Spirit and Opportunity as well as MSL Curiosity have analyzed rocks with even higher chlorine concentrations [e.g., 3]. This suggests that any potential fluid flowing through the crust would have high chlorine concentrations and therefore high salinity. Here we investigate the bulk and mineral chemistry of the SNC meteorites to constrain the pre-eruptive chlorine concentrations of Martian magmas as the potential source of chlorine in the Martian crust. Bulk SNC meteorites have Cl concentrations similar to terrestrial Mid Ocean Ridge Basalts which would suggest a Cl content of the Martian interior similar to that of the Earth [4]. However, based on Cl/La ratios, the Martian interior actually has 2-3 times more Cl than the Earth [5]. This is also reflected in the composition of Cl-rich minerals within the SNC meteorites [5, 6] and suggests that the pre-eruptive parental magmas to the SNC meteorites were Cl-rich. Eruption and degassing of such Cl-rich magmas would have delivered Cl to the Martian crust, thereby increasing the salinity of any fluids within the crust. [1] Rothschild L.J. and R.L. Mancinelli (2001) Nature. 409: 1092-1101. [2] Sharp Z.D. and D.S. Draper (2013) EPSL. 369-370: 71-77. [3] Taylor G.J. et al. (2010) GRL. 37: L12204. [4]. Burgess R. et al (2013) GCA 77: 793. [5] Filiberto J. and A.H. Treiman (2009) Geology. 37: 1087-1090. [6] McCubbin F.M. et al. (2013) MaPS. 48: 819-853.

  12. Partial melting of thickened continental crust in central Tibet: Evidence from geochemistry and geochronology of Eocene adakitic rhyolites in the northern Qiangtang Terrane

    NASA Astrophysics Data System (ADS)

    Long, Xiaoping; Wilde, Simon A.; Wang, Qiang; Yuan, Chao; Wang, Xuan-Ce; Li, Jie; Jiang, Ziqi; Dan, Wei

    2015-03-01

    The composition of the deep crust is a key to understanding the formation of the low-velocity zone in the middle to lower crust of the Tibetan Plateau. The Suyingdi rhyolites exposed in the northern Qiangtang Terrane have high Sr (296-384 ppm) and low Y (5.81-7.93 ppm), with therefore high Sr/Y ratios (42-56), showing geochemical features of adakitic rocks. Zircon U-Pb dating yields an eruption age of 38.2 ± 0.8 Ma (MSWD = 0.78). These adakitic rhyolites are high-K calc-alkaline in composition, displaying a weakly peraluminous character. They have low MgO content (0.20-0.70 wt.%) and Mg# values (24-39), as well as low Sc (2.25-2.76 ppm), Cr (8-14 ppm), Co (1.6-3.5 ppm) and Ni (2-3 ppm) concentrations. The rocks are LREE-enriched ((La/Yb)N = 50-62) and display weakly negative Eu anomalies (Eu/Eu* = 0.82-0.95) and pronounced negative Nb and Ta anomalies. They have low initial (87Sr/86Sr)i ratios (0.707860 to 0.708342) and enriched Nd isotopic compositions with εNd (t) values ranging from -8.4 to -5.0, which are indistinguishable from those of Cenozoic potassic and ultra-potassic lavas exposed in northern Tibet. Their much higher SiO2 and lower Fe2O3 contents, yet similar MgO, Cr, Co, Ni, and Mg# values to the potassic and ultra-potassic lavas, however, indicate that the rhyolites are unlikely to have formed by fractional crystallization of these lavas. Because of their low Nb/Ta ratios and similar Sr-Nd isotopic compositions to granulite xenoliths within the Cenozoic potassic rocks, we infer that the Suyingdi adakitic rhyolites were most likely produced by partial melting of a thickened lower crust in the garnet stability field. The magma source is most likely dominated by granulite facies metabasalts and clay-poor metamorphosed sedimentary rocks which indicate that the lower crust of northern Tibet is heterogeneous. In combination with data from previously-reported peraluminous and metaluminous adakitic rocks in the same region, the age and petrogenesis of the

  13. Using Collaborative Learning Exercises to Transfer Pervasive Skills: Some South African Evidence

    ERIC Educational Resources Information Center

    Strauss-Keevy, Monique

    2015-01-01

    The Competency Framework, introduced by the South African Institute of Chartered Accountants (SAICA) details technical competencies, but also places emphasis on the pervasive skills that need to be attained by candidates for them to qualify as chartered accountants (CAs). Thus, an additional onus has been placed on academics to ensure that they…

  14. Variations in the Pb isotope composition in polyformational magmatic rocks of the Ketkap-Yuna igneous province of the Aldan Shield: Evidence for mantle-crust interaction

    NASA Astrophysics Data System (ADS)

    Polin, V. F.; Dril, S. I.; Khanchuk, A. I.; Velivetskaya, T. A.; Vladimirova, T. A.; Il'ina, N. N.

    2016-06-01

    The Pb isotope composition of polyformational Mesozoic igneous rocks of the Ketkap-Yuna igneous province (KYIP) and lower crustal metamorphic rocks of the Batomga granite-greenstone area (the complex of the KYIP basement) of the Aldan Shield was studied for the first time. Based on the data obtained, several types of material sources participating in petrogenetic processes were distinguished. The mantle source identified as PREMA is registered in most of the igneous formations and predominates in mafic alkaline rocks. According to the isotope characteristics, the upper crustal source corresponds to a source of the "Orogen" type by the model of "plumbotectonics" or to the average composition of the continental crust by the Stacey-Kramers model. The lower crust is the third material source; however, the type of lower crustal protolith involved in the igneous process is still not defined, which makes difficult to estimate its role in the petrogenetic processes.

  15. Growth of continental crust and its episodic reworking over >800 Ma: evidence from Hf-Nd isotope data on the Pietersburg block (South Africa)

    NASA Astrophysics Data System (ADS)

    Laurent, Oscar; Zeh, Armin; Moyen, Jean-François; Doucelance, Régis; Martin, Hervé

    2014-05-01

    The formation and evolution of the continental crust during the Precambrian, and in particular during the Archaean eon (4.0-2.5 Ga), is still a matter of debate. In particular, it is not yet clear in which tectonic environment the genesis of crust took place and how the large volume of granitoid rocks that form ~70% of the Archaean crust were extracted from the mantle. Many studies highlighted that radiogenic isotope systems, especially Lu-Hf and Sm-Nd, are powerful tools to unravel the respective extent of crustal growth and recycling in Archaean terranes. This work presents coupled Hf and Nd isotope data (analyzed both in situ in accessory minerals and in whole rock samples) of Meso- to Neoarchaean granitoids, applied to unravel the processes of crust formation and evolution of the Pietersburg crustal block in South Africa. This crustal segment, the northermost one of the Archaean Kaapvaal Craton, is separated from older crust (3.65-3.10 Ga) by a large-scale suture zone, and the processes related to amalgamation of both blocks and their subsequent evolution are still unclear. The Pietersburg block is made up of a wide range of Archaean granitoid rocks, including tonalite-trondhjemite-granodiorite (TTG) series, high-K monzogranites as well as (grano)diorites belonging to the so-called "sanukitoid" group [1], all intruded by late Paleoproterozoic alkaline complexes. Age determinations highlighted two stages of granitoid formation: (1) TTG magmatism took place episodically over >400 Ma between 3.34 and 2.89 Ga, with a major pulse at 2.97-2.90 Ga; while (2) all the other (high-K) granitoid types emplaced subsequently between 2.84 and 2.69 Ga before a long magmatic shutdown until the intrusion of alkaline complexes at ~2.00 Ga [2-3]. Isotope systematics reveal that these two stages are related to juvenile crust formation and crust reworking, respectively. Indeed, all Hf-Nd isotope data from TTG gneisses are suprachondritic, pointing to a juvenile origin and precluding

  16. Receiver function probing of the crust and the upper mantle underneath north German basin, Scandinavia and the Baltic shield: evidence of ancient collision zones

    NASA Astrophysics Data System (ADS)

    Alinaghi, A.; Kind, R.; Bock, G.

    2002-05-01

    Teleseismic earthquakes (distance: 30-90 degrees)recorded by TOR (passive-source seismic experiment, north Germany and Scandinavia, 1996-1997), GRSN (German Regional Seismic Network, 1992-1999), and SVEKALAPKO (seismic experiment, Finland, 1998-1999) have been used for calculating receiver functions. Source and epicentral distance equalized receiver functions were utilized to probe into the crust and upper mantle beneath the recording stations. Detailed images of the crust-mantle boundary across the studied regions show a pronounced increase of the crustal thickness at the junction between northern Europe Paleozoic and Precambrian provinces known as TESZ( TransEuropean Suture Zone). This is accompanied by some north dipping intracrustal structures which run deep into the lower crust and are believed to be remnants of an ancient subduction zone. Another significance of the TESZ is its effect on the two major upper mantle discontinuities and thereby on the upper mantle transition zone. The deepening of the moho is associated with early arrival of 410 km discontinuity compared to predicted time by IASP91 velocity model, while the 660 km discontinuity has been affected to a lesser degree. The crust, underneath the Baltic shield, is thicker (on average 45-50 km) than beneath the north German Basin( 30-35 km on average ), and the moho shows a complex topography in sharp contrast to rather flat surface topography. Beneath SVEKALAPKO, both in stacked time domain and migrated receiver function sections the 410 km and 660 km upper mantle discontinuities arrive earlier than predicted by IASP91 velocity model. This is an indication of higher shear velocity of upper mantle in the Baltic shield compared to that of the Paleozoic northern Europe. We found no sign of the lithosphere-asthenosphere in our study which might be explained by the masking effect of the moho multiples and/or lack of strong Ps conversions due to gradual lithosphere-asthenosphere boundary

  17. Southward shift of the Intertropical Convergence Zone in the western Pacific during the late Tertiary: Evidence from ferromanganese crusts on seamounts west of the Marshall Islands

    NASA Astrophysics Data System (ADS)

    Kim, Jonguk; Hyeong, Kiseong; Jung, Hoi-Soo; Moon, Jai-Woon; Kim, Ki-Hyune; Lee, Insung

    2006-12-01

    Hydrogenetic ferromanganese crusts were dredged from four seamounts in the western Pacific, OSM7, OSM2, Lomilik, and Lemkein, aligned in a NW-SE direction parallel to Pacific Plate movement. The crusts consist of four well-defined layers with distinct textural and geochemical properties. The topmost layer 1 is relatively enriched in Mn, Co, Ni, and Mo compared to the underlying layer 2, which is relatively enriched in Al, Ti, K, and Rb and Cu, Zn, and excess Ba. Textural and geochemical properties of layer 2 suggest growth conditions under high biogenic and detrital flux. Such conditions are met in the equatorial Pacific (i.e., between the Intertropical Convergence Zone (ITCZ) and equatorial high-productivity zone). Layer 2 likely formed when each seamount was beneath the equatorial Pacific along its back track path. On the other hand, layer 1 probably started to grow after seamounts moved northwest from the ITCZ. This interpretation is consistent with the thickness of layer 1 across the four crusts, which increases to the northwest. Ages of the layer 1-layer 2 boundary in each crust, a potential proxy for northern margin of the ITCZ, also increase to the northwest at 17, 11, 8, and 5 Ma for OSM7, OSM2, Lomilik, and Lemkein, respectively. Assuming Pacific Plate motion of 0.3°/Myr, the seamounts were located at 12°N, 11°N, 9°N, and 8°N at the time of boundary formation. This result suggests that the north edge of the ITCZ has shifted south since the middle Miocene in the western Pacific, which agrees with information from the eastern Pacific.

  18. First findings of Paleo- and Mesoarchean zircons in the rocks from the Central Arctic province of oceanic rises as an evidence of the ancient continental crust

    NASA Astrophysics Data System (ADS)

    Sergeev, S. A.; Presnyakov, S. L.; Antonov, A. V.; Belyatsky, B. V.; Rodionov, N. V.; Shevchenko, S. S.

    2015-07-01

    This report presents the results of local U-Pb zircon dating (SIMS SHRIMP II) for a sample of migmatite gneiss dredged on the western slope of Alpha Ridge in the Arctic Ocean in the course of the "Arktika-2012" Russian polar expedition. The distribution of U-Pb ages of the examined zircon points to the Early Precambrian origin of this gneiss, for the bulk of the zircon was crystallized at least 3450 Ma ago from a magmatic melt under acidic volcanism at the primary crust formation. Zircon of the second generation was crystallized 3300 Ma ago under the remelting of acid volcanics and appearance of migmatite gneisses under the amphibolite facies of metamorphism. Most likely, a partial recrystallization of zircon and formation of microfolded structures and foliation took place 3000 Ma ago at the stage of rocks deformation. The latest zircon was formed 1900 Ma ago from the crust fluid or melt under the low-gradient metamorphism. In view of the possibility of the appearance of the treated clastogenic gneiss fragment under current oceanic erosion, the obtained results allow one to affirm that the occurrence of a fragment of the most ancient sialic continental crust formed at least 3450 Ma ago is possible at the submarine rises of the Arctic Ocean (Alpha Ridge and the Mendeleev Rise).

  19. Orbital forcing and the spread of C4 grasses in the late Neogene: stable isotope evidence from South African speleothems.

    PubMed

    Hopley, Philip J; Marshall, Jim D; Weedon, Graham P; Latham, Alf G; Herries, Andy I R; Kuykendall, Kevin L

    2007-11-01

    Reconstructing Plio-Pleistocene African paleoenvironments is important for models of early hominin evolution, but is often hampered by low-resolution or discontinuous climatic data. Here, we present high-resolution stable oxygen and carbon isotope time series data from two flowstones (secondary cave deposits) from the South African hominin-bearing Makapansgat Valley. The age of the older of the two flowstones (Collapsed Cone) is constrained by magnetostratigraphy to approximately 4-5 Ma; the younger flowstone (Buffalo Cave) grew between 2.0-1.5 Ma, as determined by magnetostratigraphy and orbital tuning of the isotopic data. The carbon isotope data is used as a proxy for the proportion of C(4) grasses in the local environment and the oxygen isotope data reflects monsoon rainfall intensity. The carbon isotope evidence indicates that in the late Miocene/early Pliocene, the local environment was dominated by C(3) vegetation, whereas, in the Plio-Pleistocene, it was composed of a mixture of C(3) and C(4) vegetation. This suggests that C(4) grasses became a significant part of the Makapansgat Valley ecosystem at approximately 4-5 Ma, towards the end of the late Neogene global expansion of C(4) grasses. After this initial expansion, South Africa experienced further fluctuations in the proportion of C(3) and C(4) vegetation during the Plio-Pleistocene, in response to regional and global climatic changes. Most notably, the Buffalo Cave flowstone provides evidence for C(4) grass expansion at ca. 1.7 Ma that we suggest was a response to African aridity caused by the onset of the Walker Circulation in the Pacific Ocean at this time. PMID:17942141

  20. The Crusts of Mars and Earth

    NASA Astrophysics Data System (ADS)

    McLennan, S. M.; Taylor, S. R.; Hahn, B. C.

    2007-05-01

    The differentiation of terrestrial planets and large moons results in crusts with compositions differing greatly from primitive mantles. Typically, large fractions of incompatible elements, including heat-producing elements, are transferred into the crust. Mechanisms and timing of this process differ greatly from planet to planet. Accordingly, in order to understand planetary evolution, it is necessary to understand the composition and evolution of planetary crusts. Crustal evolution on Earth is perhaps the least representative of the terrestrial planets and large moons of the solar system. Although Earth substantially melted after the giant impact that resulted in the Moon, there is little evidence for the existence of a primary crust suggesting that such crust was recycled and mixed into the mantle during the Hadean. Instead, Earth has a very young, continually recycled basaltic secondary (oceanic) crust and an andesitic tertiary (continental) crust, unique in the solar system, that grew episodically over 4 Gyr, but with an average age of about 2 Gyr. The continental - oceanic crust dichotomy, temporal changes in continental crust composition, role of plume volcanism and continental growth are largely consequences of evolving plate- tectonic processes. Mars provides a valuable comparison to Earth because it is a planet that is, in many ways, intermediate between Earth and planetary bodies, such as the Moon and Mercury, that completed crustal development by about 3 Gyr and have been dormant since. Martian crust is mostly ancient (>3.5 Gyr) but volcanism has persisted, possibly episodically, to 200 Myr or younger. Proposals of early plate tectonics persist, but the weight of evidence suggests Mars is a one-plate planet. The 50 km thick crust constitutes 3.2% of the mass of the planet and, even with modest levels of LILE enrichment (K=0.33%), has had well in excess of 50% of incompatible elements removed from the mantle during early differentiation that likely

  1. The Oceanic Crust.

    ERIC Educational Resources Information Center

    Francheteau, Jean

    1983-01-01

    The earth's oceanic crust is created and destroyed in a flow outward from midocean ridges to subduction zones, where it plunges back into the mantle. The nature and dynamics of the crust, instrumentation used in investigations of this earth feature, and research efforts/findings are discussed. (JN)

  2. Lower-crustal xenoliths from Jurassic kimberlite diatremes, upper Michigan (USA): Evidence for Proterozoic orogenesis and plume magmatism in the lower crust of the southern Superior Province

    USGS Publications Warehouse

    Zartman, Robert E.; Kempton, Pamela D.; Paces, James B.; Downes, Hilary; Williams, Ian S.; Dobosi, Gábor; Futa, Kiyoto

    2013-01-01

    Jurassic kimberlites in the southern Superior Province in northern Michigan contain a variety of possible lower-crustal xenoliths, including mafic garnet granulites, rare garnet-free granulites, amphibolites and eclogites. Whole-rock major-element data for the granulites suggest affinities with tholeiitic basalts. P–T estimates for granulites indicate peak temperatures of 690–730°C and pressures of 9–12 kbar, consistent with seismic estimates of crustal thickness in the region. The granulites can be divided into two groups based on trace-element characteristics. Group 1 granulites have trace-element signatures similar to average Archean lower crust; they are light rare earth element (LREE)-enriched, with high La/Nb ratios and positive Pb anomalies. Most plot to the left of the geochron on a 206Pb/€204Pb vs 207Pb/€204Pb diagram, and there was probably widespread incorporation of Proterozoic to Archean components into the magmatic protoliths of these rocks. Although the age of the Group 1 granulites is not well constrained, their protoliths appear to be have been emplaced during the Mesoproterozoic and to be older than those for Group 2 granulites. Group 2 granulites are also LREE-enriched, but have strong positive Nb and Ta anomalies and low La/Nb ratios, suggesting intraplate magmatic affinities. They have trace-element characteristics similar to those of some Mid-Continent Rift (Keweenawan) basalts. They yield a Sm–Nd whole-rock errorchron age of 1046 ± 140 Ma, similar to that of Mid-Continent Rift plume magmatism. These granulites have unusually radiogenic Pb isotope compositions that plot above the 207Pb/€204Pb vs 206Pb/€204Pb growth curve and to the right of the 4·55 Ga geochron, and closely resemble the Pb isotope array defined by Mid-Continent Rift basalts. These Pb isotope data indicate that ancient continental lower crust is not uniformly depleted in U (and Th) relative to Pb. One granulite xenolith, S69-5, contains quartz, and has a

  3. Evidence for Thin Oceanic Crust on the Extinct Aegir Ridge, Norwegian Basin, N.E. Atlantic Derived from Satellite Gravity Inversion

    NASA Astrophysics Data System (ADS)

    Greenhalgh, E. E.; Kusznir, N. J.

    2006-12-01

    Satellite gravity inversion incorporating a lithosphere thermal gravity correction has been used to map crustal thickness and lithosphere thinning factor for the N.E. Atlantic. The inversion of gravity data to determine crustal thickness incorporates a lithosphere thermal gravity anomaly correction for both oceanic and continental margin lithosphere. Predicted crustal thicknesses in the Norwegian Basin are between 7 and 4 km on the extinct Aegir oceanic ridge which ceased sea-floor spreading in the Oligocene. Crustal thickness estimates do not include a correction for sediment thickness and are upper bounds. Crustal thicknesses determined by gravity inversion for the Aegir Ridge are consistent with recent estimates derived using refraction seismology by Breivik et al. (2006). Failure to incorporate a lithosphere thermal gravity anomaly correction produces an over-estimate of crustal thickness. Oceanic crustal thicknesses within the Norwegian Basin are predicted by the gravity inversion to increase to 9-10 km eastwards towards the Norwegian (Moere) and westwards towards the Jan Mayen micro-continent, consistent with volcanic margin continental breakup at the end of the Palaeocene. The observation (from gravity inversion and seismic refraction studies) of thin oceanic crust produced by the Aegir ocean ridge in the Oligocene has implications for the temporal evolution of asthenosphere temperature under the N.E. Atlantic during the Tertiary. Thin Oligocene oceanic crust may imply cool (normal) asthenosphere temperatures during the Oligocene in contrast to elevated asthenosphere temperatures in the Palaeocene and Miocene-Recent as indicated by volcanic margin formation and the formation of Iceland respectively. Gravity inversion also predicts a region of thin oceanic crust to the west of the northern part of the Jan Mayen micro-continent and to the east of the thicker oceanic crust currently being formed at the Kolbeinsey Ridge. Thicker crust (c.f. ocean basins) is

  4. Mafic granulite xenoliths in the Chilka Lake suite, Eastern Ghats Belt, India: evidence of deep-subduction of residual oceanic crust

    NASA Astrophysics Data System (ADS)

    Bhattacharya, S.; Chaudhary, A. K.; Saw, A. K.; Das, P.; Chatterjee, D.

    2012-11-01

    Granulite xenoliths preserve key geochemical and isotopic signatures of their mantle source regions. Mafic granulite and pyroxinite xenoliths within massif-type charnockitic rocks from the Eastern Ghats Belt have recently been reported by us. The mafic granulite xenoliths from the Chilka Lake granulite suite with abundant prograde biotite are geochemically akin to Oceanic Island Basalt (OIB). They can be distinguished from the hornblende-mafic granulite xenoliths with signatures of Arc-derived basalt occurring in the other suites of the Eastern Ghats Belt. These two groups of xenoliths in the Paleoproterozoic Eastern Ghats Province have quite distinct Nd-model ages- 1.9 Ga and 2.5 Ga respectively, which may be interpreted as their crustal residence ages. Strong positive Nb anomalies, indicating subducted oceanic crust in the source, LREE enrichment and strongly fractionated REE pattern are key geochemical signatures attesting to their origin as OIB-type magma. Also low Yb and Sc contents and high (La / Yb)N ratios can be attributed to melting in the presence of residual garnet and hence at great depths (> 80 km). The variable enrichment in radiogenic 87Sr, between 0.70052 and 0.71092 at 1.9 Ga and less radiogenic 143Nd between ɛ-1.54 and 7.46 are similar to those of the OIBs compared to MORBs. As OIBs commonly contain some recycled oceanic crust in their sources, we suggest that the residue of the oceanic crust from a previous melting event (~ 2.5 Ga) that produced the Arc-derived basalts (protoliths of hornblende-mafic granulite xenoliths) could have subducted to great depths and mechanically mixed with the mantle peridotite. A subsequent re-melting event of this mixed source might have occurred at ca. 1.9 Ga as testified by the crustal residence ages of the biotite-mafic granulite xenoliths of the Chilka Lake granulite suite.

  5. Diapirs and cantaloupes: Layering and overturn of Triton's crust

    NASA Technical Reports Server (NTRS)

    Schenk, P.; Jackson, M. P. A.

    1993-01-01

    It has recently been proposed that cantaloupe terrain formed as a result of instability and overturn (i.e., diapirism) of Triton's crust. Morphologic evidence implicates compositional layering within Triton's crust as the driving mechanism for the overturn. Here, we review the morphologic evidence for this origin and evaluate some of the implications.

  6. Neodymium isotopic evidence for decreasing crustal contributions to cenozoic ignimbrites of the western United States. Implications for the thermal evolution of the Cordilleran crust

    SciTech Connect

    Perry, F.V. ); DePaolo, D.J. ); Baldridge, W.S. )

    1993-07-01

    We have estimated the crustal contributions to 12 early Oligocene to Pleistocene rhyolite systems located throughout the Cordillera. We have determined that (1) crustal contributions to large-volume rhyolite systems decrease from the Oligocene to the Miocene, and (2) rhyolite systems younger than 20 Ma are dominated by mantle components. The crustal contributions to rhyolite systems may be controlled by system size and duration, crustal thickness, tectonic setting, crustal composition, crustal density, and crustal temperature. We conclude that regional cooling of the lower crust, which progressively limited the amount of crustal wallrock assimilated by rhyolite systems, is the only parameter that is consistent with geologic and geochemical data for rhyolite systems and the geologic evolution of the Cordillera. A quantitative model that relates the amount of crustal contribution to assimilation/recharge rates and the temperature of the crust indicates that lower-crustal temperatures would have to decrease about 300[degrees]C between early Oligocene and early Miocene time to account for the decrease in crustal contributions. 57 refs., 7 figs., 1 tab.

  7. Oceanic crust in the mid-mantle beneath Central-West Pacific subduction zones: Evidence from S-to-P converted waveforms

    NASA Astrophysics Data System (ADS)

    He, X.

    2015-12-01

    The fate of subducted slabs is enigmatic, yet intriguing. We analyze seismic arrivals at ~20-50 s after the direct P wave in an array in northeast China (NECESSArray) recordings of four deep earthquakes occurring beneath the west-central Pacific subduction zones (from the eastern Indonesia to Tonga region). We employ the array analyzing techniques of 4th root vespagram and beam-form analysis to constrain the slowness and back azimuth of later arrivals. Our analyses reveal that these arrivals have a slightly lower slowness value than the direct P wave and the back azimuth deviates slightly from the great-circle direction. Along with calculation of one-dimensional synthetic seismograms, we conclude that the later arrival is corresponding to an energy of S-to-P converted at a scatterer below the sources. Total five scatterers are detected at depths varying from ~700 to 1110 km in the study region. The past subducted oceanic crust most likely accounts for the seismic scatterers trapped in the mid-mantle beneath the west-central subduction zones. Our observation in turn reflects that oceanic crust at least partly separated from subducted oceanic lithosphere and may be trapped substantially in the mid-mantle surrounding subduction zones, in particular in the western Pacific subduction zones.

  8. Oceanic crust in the mid-mantle beneath west-central Pacific subduction zones: evidence from S to P converted waveforms

    NASA Astrophysics Data System (ADS)

    Yang, Zhongtao; He, Xiaobo

    2015-10-01

    The fate of subducted slabs is enigmatic, yet intriguing. We analyse seismic arrivals at ˜20-50 s after the direct P wave in an array in northeast China (NECESSArray) recordings of four deep earthquakes occurring beneath the west-central Pacific subduction zones (from the eastern Indonesia to Tonga region). We employ the array analysing techniques of fourth root vespagram and beam-forming analysis to constrain the slowness and backazimuth of later arrivals. Our analyses reveal that these arrivals have a slightly lower slowness value than the direct P wave and the backazimuth deviates slightly from the great circle direction. Along with calculation of 1-D synthetic seismograms, we conclude that the later arrival is corresponding to an energy of S-to-P converted at a scatterer below the sources. Total five scatterers are detected at depths varying from ˜700 to 1110 km in the study region. The past subducted oceanic crust most likely accounts for the seismic scatterers trapped in the mid-mantle beneath the west-central subduction zones. Our observation in turn reflects that oceanic crust at least partly separated from subducted oceanic lithosphere and may be trapped substantially in the mid-mantle surrounding subduction zones, in particular in the western Pacific subduction zones.

  9. Evidence from meimechites and other low-degree mantle melts for redox controls on mantle-crust fractionation of platinum-group elements

    PubMed Central

    Mungall, James E.; Hanley, Jacob J.; Arndt, Nicholas T.; Debecdelievre, Anne

    2006-01-01

    Understanding of the geochemistry of the chalcophile elements [i.e., Os, Ir, Ru, Pt, Pd (platinum-group elements), and Au, Cu, Ni] has been informed for at least 20 years by the common assumption that when crust-forming partial melts are extracted from the upper mantle, sulfide liquid in the restite sequesters chalcophile elements until the extent of partial melting exceeds ≈25% and all of the sulfide has been dissolved in silicate melt [Hamlyn, P. R. & Keays, R. R. (1985) Geochim. Cosmochim. Acta 49, 1797–1811]. Here we document very high, unfractionated, chalcophile element concentrations in small-degree partial melts from the mantle that cannot be reconciled with the canonical residual sulfide assumption. We show that the observed high, unfractionated platinum-group element concentrations in small-degree partial melts can be attained if the melting takes place at moderately high oxygen fugacity, which will reduce the amount of sulfide due to the formation of sulfate and will also destabilize residual monosulfide solid solution by driving sulfide melts into the spinel-liquid divariant field. Magmas formed at high oxygen fugacity by small degrees of mantle melting can be important agents for the transfer of chalcophile elements from the upper mantle to the crust and may be progenitors of significant ore deposits of Pt, Pd, and Au. PMID:16908861

  10. Geochemical Evidence from the Kohistan Complex for Differentiation of Garnet Granulitic lower Crust in Island Arcs by Dehydration Melting of Amphibole-bearing Plutonics: Implications for the Andesite Model of Continental Crustal Growth

    NASA Astrophysics Data System (ADS)

    Garrido, C. J.; Bodinier, J.; Burg, J.; Zeilinger, G.; Hussain, S. S.; Dawood, H.; Gervilla, F.

    2005-12-01

    We report a geochemical study of the Jijal and Sarangar complexes constituting the lower crust of the Mesozoic Kohistan paleo-island arc (N. Pakistan). The Jijal complex is composed of basal peridotites topped by a gabbroic section made up of mafic garnet granulite-with minor lenses of garnet hornblendite and granite-grading up section to hornblende gabbronorite. The Sarangar complex is constituted by metagabbro. Sarangar gabbro and Jijal hornblende gabbronorite have melt-like, LREE-enriched REE patterns similar to those of island arc basalts. These rocks and Jijal garnet granulite define altogether negative covariations of LaN, YbN and (La/Sm)N with Eu* (=2xEuN/SmN+GdN; N= chondrite normalized), and positive covariations of (Yb/Gd)N with Eu*. REE modeling indicates that these covariations cannot be accounted for by high-pressure crystal fractionation of hydrous primitive or derivative andesites. They are consistent with formation of garnet granulites as plagioclase-garnet assemblages with variable trapped melt fractions via either high-pressure crystallization of primitive island arc basalts or dehydration melting of hornblende gabbronorite, providing that the amount of segregated or restitic garnet was low (< 5 wt.%). Field, petrographic, geochemical and experimental evidence is more consistent with formation of Jijal garnet granulite by dehydration melting of Jijal hornblende gabbronorite. Similarly, Jijal garnet-bearing hornblendite lenses were most likely generated by coeval dehydration melting of hornblendites. Furthermore, melting models and geochronological data point to intrusive leucogranites in the overlying Metaplutonic complex as the melts generated by dehydration melting of the plutonic protoliths of Jijal garnet-bearing restites. Consistently with the metamorphic evolution of the Kohistan lower arc crust, dehydration melting occurred at the mature stage of this island arc when shallower hornblende-bearing plutonics were buried to depth exceeding 25

  11. Recycled oceanic crust in the source of 90-40 Ma basalts in North and Northeast China: Evidence, provenance and significance

    NASA Astrophysics Data System (ADS)

    Xu, Yi-Gang

    2014-10-01

    Major, trace element and Sr-Nd-Pb isotopic data of basalts emplaced during 90-40 Ma in the North and Northeast China are compiled in this review, with aims of constraining their petrogenesis, and by inference the evolution of the North China Craton during the late Cretaceous and early Cenozoic. Three major components are identified in magma source, including depleted component I and II, and an enriched component. The depleted component I, which is characterized by relatively low 87Sr/86Sr (<0.7030), moderate 206Pb/204Pb (18.2), moderately high εNd (∼4), high Eu/Eu∗ (>1.1) and HIMU-like trace element characteristics, is most likely derived from gabbroic cumulate of the oceanic crust. The depleted component II, which distinguishes itself by its high εNd (∼8) and moderate 87Sr/86Sr (∼0.7038), is probably derived from a sub-lithospheric ambient mantle. The enriched component has low εNd (2-3), high 87Sr/86Sr (>0.7065), low 206Pb/204Pb (17), excess Sr, Rb, Ba and a deficiency of Zr and Hf relative to the REE. This component is likely from the basaltic portion of the oceanic crust, which is variably altered by seawater and contains minor sediments. Comparison with experimental melts and trace element modeling suggest that these recycled oceanic components may be in form of garnet pyroxenite/eclogite. These components are young (<0.5 Ga) and show an Indian-MORB isotopic character. Given the share of this isotopic affinity by the extinct Izanaghi-Pacific plate, currently stagnated within the mantle transition zone, we propose that it ultimately comes from the subducted Pacific slab. Eu/Eu∗ and 87Sr/86Sr of the 90-40 Ma magmas increases and decreases, respectively, with decreasing emplacement age, mirroring a change in magma source from upper to lower parts of subducted oceanic crust. Such secular trends are created by dynamic melting of a heterogeneous mantle containing recycled oceanic crust. Due to different melting temperature of the upper and lower ocean

  12. The syncollisional granitoid magmatism and continental crust growth in the West Kunlun Orogen, China - Evidence from geochronology and geochemistry of the Arkarz pluton

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Niu, Yaoling; Hu, Yan; Liu, Jinju; Ye, Lei; Kong, Juanjuan; Duan, Meng

    2016-02-01

    The West Kunlun orogenic belt (WKOB) at the northwest margin of the Greater Tibetan Plateau records seafloor subduction, ocean basin closing and continental collision with abundant syncollisional granitoids in response to the evolution of the Proto- and Paleo-Tethys Oceans from the early-Paleozoic to the Triassic. Here we present a combined study of detailed zircon U-Pb geochronology, whole-rock major and trace elements and Sr-Nd-Hf isotopic geochemistry on the syncollisional Arkarz (AKAZ) pluton with mafic magmatic enclaves (MMEs) exposed north of the Mazha-Kangxiwa suture (MKS) zone. The granitoid host rocks and MMEs of the AKAZ pluton give the same late Triassic age of ~ 225 Ma. The granitoid host rocks are metaluminous granodiorite and monzogranite. They have initial 87Sr/86Sr of 0.70818 to 0.70930, εNd(225 Ma) = - 4.61 to - 3.91 and εHf(225 Ma) = - 3.01 to 0.74. The MMEs are more mafic than the host with varying SiO2 (51.00-63.24 wt.%) and relatively low K2O (1.24-3.02 wt.%), but have similar Sr-Nd-Hf isotope compositions to the host ((87Sr/86Sr)i = 0.70830-0.70955, εNd(225 Ma) = - 4.88 to - 4.29, εHf(225 Ma) = - 2.57 to 0.25). Both the host and MMEs have rare earth element (REE) and trace element patterns resembling those of bulk continental crust (BCC). The MMEs most likely represent cumulate formed from common magmas parental to the granitoid host. The granitoid magmatism is best explained as resulting from melting of amphibolite of MORB protolith during continental collision, which produces andesitic melts with a remarkable compositional similarity to the BCC and the inherited mantle-like isotopic compositions. Simple isotopic mixing calculations suggest that ~ 80% ocean crust and ~ 20% continental materials contribute to the source of the AKAZ pluton. Thus, the hypothesis "continental collision zones as primary sites for net continental crust growth" is applicable in the WKOB as shown by studies in southern Tibet, East Kunlun and Qilian orogens. In

  13. Isotopically-diverse rhyolites coeval with the Columbia River Basalts Large Igneous Province: evidence for widespread mantle-plume driven hydrothermal alteration and remelting of the crust

    NASA Astrophysics Data System (ADS)

    Colon, D.; Bindeman, I. N.; Stern, R. A.; Fisher, C. M.

    2014-12-01

    The formation of the most recent flood basalt province on Earth, the Columbia River Flood Basalts (CRBs) of the northwestern USA, was accompanied by eruptions of several thousand km3 of rhyolite in a short time window from 16.7 to 15 Ma. These rhyolites span from low (+1‰) to high (+11‰) in δ18O values as recorded by major phenocrysts, and alteration-resistant zircons within each rhyolite commonly display diversity of up to 6‰ δ18O, indicative of batch assembly prior to eruption. Significant variation in ɛHf also exists in zircons, ranging from -39 to 0 in rhyolites erupted through the North American cratonic crust, and from -1 to +9 in rhyolites erupted through accreted oceanic terranes to the east of the Sr87/86Sr = 0.706 line. This isotopic diversity cannot be accounted for by fractionation of a CRB-like parent magma, demonstrating that the syn-CRB rhyolites must have been derived from melting of the crust. Abundant low-δ18Omelt values among syn-CRB rhyolites further constrains this crustal melting to shallow depths of 5-10 km, due to the shallow depths of the necessary hydrothermal alteration of the protolith. By contrast, high-δ18O rhyolites must have been formed by remelting of sedimentary or metasedimentary rocks. Low-δ18O rhyolites are also most common in the vicinity of the crustal suture between the thick lithosphere of the Archean craton and the thin lithosphere of the accreted terranes. Thermomechanical modeling suggests that this contrast concentrates crustal heating and deformation, creating pathways for meteoric water to penetrate the crust and cause extensive hydrothermal alteration less than 1 Ma before those same rocks remelt to form low-δ18O rhyolites. Finally, we suggest that this extensive crustal hydrothermal alteration and melting may be typical of continental flood basalt provinces world wide, and particularly when there is syn-volcanic extension.

  14. Late Triassic melting of a thickened crust in southeastern China: Evidence for flat-slab subduction of the Paleo-Pacific plate

    NASA Astrophysics Data System (ADS)

    Zhu, Kong-Yang; Li, Zheng-Xiang; Xu, Xi-Sheng; Wilde, Simon A.

    2013-09-01

    The Dashuang complex in Zhejiang Province of southeast China is composed of two distinct lithologies: syenite in the west and quartz monzonite in the east. They record similar zircon U-Pb ages of 224 ± 3 Ma (syenite), and 226 ± 2 Ma and 227 ± 1 Ma (quartz monzonite), respectively, but are notably different in petrography, magnetic susceptibility, whole-rock chemistry, zircon Hf isotope and zircon trace element characteristics. The west Dashuang syenitic pluton (the west body) has high modal alkali feldspar, high zircon saturation temperatures, high whole-rock and zircon MREE/HREE ratios, low Fe-Mg-Ti contents, and is depleted in Ba, Sr and Eu. It also has low magnetic susceptibilities, belongs to the ilmenite-series, and is a peraluminous and ferroan granitoid. The east Dashuang quartz monzonitic pluton (the east body) has abundant K-feldspar megacrysts, with hornblende, titanite and biotite being the major ferromagnesian minerals. In contrast to the west body, the east body has lower zircon saturation temperatures, lower whole-rock and zircon MREE/HREE ratios, higher Fe-Mg-Ti contents, and shows no depletion in Ba, Sr or Eu. The east body has higher magnetite contents, high magnetic susceptibilities and belongs to the magnetite-series. It is a metaluminous and magnesian granitoid of arc-affinity. Zircon Hf isotopic data reveal that both bodies were derived from partial melting of Paleoproterozoic igneous protoliths in the lower crust, but the east body possibly incorporated subducted terrigenous sediments. Both bodies have higher melting temperatures and pressures than adjacent Cretaceous granitoids, reflecting their origin in a thickened, hotter lower crust. The most feasible model to explain their differences is variations in water content during crustal melting, resulting in different melting and crystallization behaviors. Such melting in a Triassic thickened crust with variable water involvement, followed by Cretaceous magmatism in an extensional setting

  15. Molecular evidence for an African origin of the Hawaiian endemic Hesperomannia (Asteraceae)

    PubMed Central

    Kim, Hyi-Gyung; Keeley, Sterling C.; Vroom, Peter S.; Jansen, Robert K.

    1998-01-01

    Identification of the progenitors of plants endemic to oceanic islands often is complicated by extreme morphological divergence between island and continental taxa. This is especially true for the Hawaiian Islands, which are 3,900 km from any continental source. We examine the origin of Hesperomannia, a genus of three species endemic to Hawaii that always have been placed in the tribe Mutisieae of the sunflower family. Phylogenetic analyses of representatives from all tribes in this family using the chloroplast gene ndhF (where ndhF is the ND5 protein of chloroplast NADH dehydrogenase) indicate that Hesperomannia belongs to the tribe Vernonieae. Phylogenetic comparisons within the Vernonieae using sequences of both ndhF and the internal transcribed spacer regions of nuclear ribosomal DNA reveal that Hesperomannia is sister to African species of Vernonia. Long-distance dispersal northeastward from Africa to southeast Asia and across the many Pacific Ocean island chains is the most likely explanation for this unusual biogeographic connection. The 17- to 26-million-year divergence time between African Vernonia and Hesperomannia estimated by the DNA sequences predates the age of the eight existing Hawaiian Islands. These estimates are consistent with an hypothesis that the progenitor of Hesperomannia arrived at one of the low islands of the Hawaiian-Emperor chain between the late Oligocene and mid-Miocene when these islands were above sea level. Subsequent to its arrival the southeast Pacific island chains served as steppingstones for dispersal to the existing Hawaiian Islands. PMID:9860987

  16. Evidence for silicic crust formation in an incipient stage of intra-oceanic subduction zone: discovery of deep crustal sections in Izu-Bonin forearc

    NASA Astrophysics Data System (ADS)

    Tani, K.; Shukuno, H.; Hirahara, Y.; Chang, Q.; Kimura, J.; Nichols, A. R.; Ishii, T.; Tatsumi, Y.; Dunkley, D. J.

    2009-12-01

    Recent research cruises surveying forearc slopes of Izu-Bonin-Mariana (IBM) arc have discovered outcrops representing the deep crustal section of the early IBM arc. Ongoing geochemcial, petrological, and geochronological studies of recovered rocks are providing new insights into the magmatism and development of arc crust during the inception of an intra-oceanic subduction system. ROV traverses, conducted at the northern Izu-Bonin forearc, discovered peridotite exposures from deep (~7000 mbsl) sections, and observed a drastic shift in lithofacies towards the upper sections (~5000 mbsl), from gabbro, through dolerite, porphyrite, tonalite, and finally volcanic breccia and sedimentary rocks. This indicates that the traverses covered a full arc crust section from uppermost mantle to upper crust. The gabbroic and doleritic rocks show geochemical signatures (e.g. LREE-depletion and low-Ba/La) similar to those of N-MORB, with minimum arc signatures (e.g. Nb-depletion and LILE-enrichment). The results from zircon and titanite U-Pb geochronology show that this MORB-like basaltic magmatism was episodically active ~52 Ma, predating the boninitic magmatism broadly exposed in the uppermost section of forearc slope, which began ~49 Ma (Ishizuka et al., 2006) and previously considered to be the first magmatism in IBM arc. The collected peridotite samples were mostly dunite and harzburgite, and show variable degrees of serpentinization. Compositions of Cr-spinel and olivine, and the calculated oxygen fugacity indicate that these peridotite samples probably coexisted with MORB-type magma rather than the boninitic or island-arc basaltic magmas. Massive outcrops of tonalitic rocks and associated dacitic-rhyolitic prophyrites were discovered in one of the surveyed area, underlain by gabbro and dolerite with MORB-like geochemical signatures. Tonalitic rocks, weakly-foliated hornblende tonalites, are continuously exposed in a ~300 m-high wall in the middle section of the forearc slope

  17. Opening of the Gulf of Mexico and the Nature of the Crust in the Deep Gulf: New Evidence from Seafloor Spreading Magnetic Anomalies

    NASA Astrophysics Data System (ADS)

    Harry, D. L.; Eskamani, P. K.

    2013-12-01

    The seafloor spreading history in the Gulf of Mexico is poorly constrained due to a lack of recognized seafloor spreading magnetic anomalies, a paucity of deep penetrating seismic data, and absence of drilling to constrain crystalline ocean floor composition and ages. We have identified lineated magnetic anomalies in the eastern Gulf on profiles collected during the Woods Hole R/V Farnella FRNL85-2 cruise that correlate with magnetic chrons M21R to M10. Forward modeling shows that these anomalies formed during creation of weakly magnetized new seafloor in the eastern Gulf between 149-134 Ma at an average half-spreading rate of 3.2 cm/yr. The oldest anomalies are located against stretched continental crust beneath the western Florida shelf on the east and the Yucatan shelf on the west. The youngest anomalies form a juxtaposed conjugate pair that mark the location of an extinct spreading ridge between Yucatan and Florida. Seismic velocities of the crust in the eastern Gulf and the amplitude of the magnetic anomalies are similar to the Iberian and Newfoundland rifted margins, where the early stages of continental breakup were accommodated by exhumation of subcontinental lithosphere rather than creation of new basaltic oceanic crust. We infer that the eastern Gulf of Mexico is underlain by exhumed sub-continental peridotitic mantle intruded by lesser volumes of basaltic igneous rocks generated by decompression melting of the asthenosphere during the late stages of opening of the Gulf. The long wavelength characteristics of the magnetic and gravity fields in the eastern Gulf, as well as the seismic velocity structure of the crust, differ from those in the central and western Gulf, which are more similar to typical magmatic rifted margins. This suggests that the character of the Gulf changes along strike, from a magmatic western portion to an amagmatic eastern portion. Paleogeographic restoration of the lineated magnetic anomaly pattern suggests a 4-phase model for

  18. Receiver Function Images of Crust and Upper Mantle: Evidence For Depp-seated Differences Between Precambrian and Paleozoic Provinces In Northern Europe

    NASA Astrophysics Data System (ADS)

    Alinaghi, A.; Bock, G.; Kind, R.; Tor Working Group; Svekalapko Working Group

    The crust-mantle boundary and upper mantle discontinuities underneath the North German Basin, the Tornquist Zone and the Baltic Shield have been detected and inves- tigated by receiver functions. Teleseismic earthquakes recorded by the TOR seismic profile and the SVEKALAPKO seismic network have been used to calculate distance and source equalized receiver functions. To enhance converted P-to-S amplitudes and to enable a consistent mapping of discontinuities, receiver functions were stacked and the arrival times of Ps were measured and plotted over the study area. The resulting delay time map of Moho is accompanied by crustal thickness measurement made us- ing Zhu &Kanamori Method so that both maps show considerable thickening of crust across the TESZ from 30 km in the German Basin to over 50 km in the Scandinavian Shield. In the Blatic Shield across SVEKALAPKO seismic network Moho takes on a complex shape in sharp contrast to the flat surface topography. Moho depths ranging from 40 to 60 km are observed under the SVEKALAPKO stations . The two major 410 km and 660 km upper mantle discontinuities are clearly observed both under the TOR profile and underneath the SVEKALAPKO network. Maps depicting the arrival times of Ps phases stemming from each of those discontinuities are presented along with a Map of the time difference between the arrival times of the aforementioned phases. While the arrival times of Ps from 410 km and 660 km discontinuities un- dergo changes across the TESZ, the difference between the arrival times of P410s and P660s phases, being a measure of the thickness of the transition zone, grows larger . This is an indication of cooler upper mantle underneath the Baltic Shield( Precam- brian) than that of the North German Basin(Paleozoic). Across the SVEKALAPKO profile the thickness of the transition zone shows signs of increase in the eastern part while traces of some local anomalies can be found in the central parts.

  19. The satellite magnetic anomaly of Ahaggar - Evidence for African Plate motion

    NASA Technical Reports Server (NTRS)

    Phillips, R. J.; Brown, C. R.

    1985-01-01

    The Ahaggar volcanic province of North Central Africa is considered a region of excess heat flow (hot spot) and hence elevated Curie isotherm. Using a modified version of the Parker FFT potential field representation, magnetic signals were calculated at Magsat altitudes for models in which the African Plate is both fixed and moving. The moving-plate model extends the Curie isotherm anomaly in the direction of plate motion and provides a satisfactory match to vertical component anomaly data when the magnitude of plate velocity is 0.75 cm/yr. Although the signal levels are marginal for the scalar component anomalies of this region, the same model provides an adequate match to this data set and is clearly preferable to a fixed-plate model.

  20. Anomalous deep earthquakes beneath the East African Rift: evidence for rift induced delamination of the lithosphere?

    NASA Astrophysics Data System (ADS)

    Lindenfeld, Michael; Rümpker, Georg; Schmeling, Harro; Wallner, Herbert

    2010-05-01

    The over 5000 m high Rwenzori Mountains are situated within the western branch of the East African Rift System, at the border between Uganda and the Democratic Republic of Congo. They represent a basement block within the rift valley whose origin and relation to the evolution of the EARS are highly puzzling. During 2006/2007 a network of 27 seismological stations was operated in this area to investigate crustal and upper mantle structure in conjunction with local seismicity. The data analysis revealed unexpectedly high microseismic activity. On average more than 800 events per month could be located with magnitudes ranging from 0.5 to 5.1. Hypocentral depths go as deep as 30 km with a pronounced concentration of activity at a depth of about 15 km. This presentation focuses on a cluster of seven earthquakes that were located at anomalous depths between 53 and 60 km. According to our present knowledge these are the deepest events so far observed within the EARS and the African Plate. Their origin might be connected to magmatic intrusions. However, the existence of earthquakes at this depth is enigmatic, especially within a rifting regime were one expects hot and weak material close to the surface, which is not capable of seismogenic deformation. We think that these events are closely related to the evolution of the Rwenzoris. A recent hypothesis to explain the extreme uplift of the Rwenzori Mountains is rift induced delamination (RID) of mantle lithosphere that is captured between two approaching rift segments. By numerical modelling we show that the RID-process is also able to bring material that is cold and brittle enough to release seismic energy into greater depth. Therefore the RID-mechanism gives a consistent explanation for the detected deep events as well as for the uplift of a mountain block in a rift setting.

  1. The Process of Adaptation of a Community-Level, Evidence-Based Intervention for HIV-Positive African American Men Who Have Sex with Men in Two Cities

    ERIC Educational Resources Information Center

    Robinson, Beatrice E.; Galbraith, Jennifer S.; Lund, Sharon M.; Hamilton, Autumn R.; Shankle, Michael D.

    2012-01-01

    We describe the process of adapting a community-level, evidence-based behavioral intervention (EBI), Community PROMISE, for HIV-positive African American men who have sex with men (AAMSM). The Centers for Disease Control and Prevention (CDC) Map of the Adaptation Process (MAP) guided the adaptation process for this new target population by two…

  2. Corium crust strength measurements.

    SciTech Connect

    Lomperski, S.; Nuclear Engineering Division

    2009-11-01

    Corium strength is of interest in the context of a severe reactor accident in which molten core material melts through the reactor vessel and collects on the containment basemat. Some accident management strategies involve pouring water over the melt to solidify it and halt corium/concrete interactions. The effectiveness of this method could be influenced by the strength of the corium crust at the interface between the melt and coolant. A strong, coherent crust anchored to the containment walls could allow the yet-molten corium to fall away from the crust as it erodes the basemat, thereby thermally decoupling the melt from the coolant and sharply reducing the cooling rate. This paper presents a diverse collection of measurements of the mechanical strength of corium. The data is based on load tests of corium samples in three different contexts: (1) small blocks cut from the debris of the large-scale MACE experiments, (2) 30 cm-diameter, 75 kg ingots produced by SSWICS quench tests, and (3) high temperature crusts loaded during large-scale corium/concrete interaction (CCI) tests. In every case the corium consisted of varying proportions of UO{sub 2}, ZrO{sub 2}, and the constituents of concrete to represent a LWR melt at different stages of a molten core/concrete interaction. The collection of data was used to assess the strength and stability of an anchored, plant-scale crust. The results indicate that such a crust is likely to be too weak to support itself above the melt. It is therefore improbable that an anchored crust configuration could persist and the melt become thermally decoupled from the water layer to restrict cooling and prolong an attack of the reactor cavity concrete.

  3. Channelling of hydrothermal fluids during the accretion and evolution of the upper oceanic crust: Sr isotope evidence from ODP Hole 1256D

    NASA Astrophysics Data System (ADS)

    Harris, Michelle; Coggon, Rosalind M.; Smith-Duque, Christopher E.; Cooper, Matthew J.; Milton, James A.; Teagle, Damon A. H.

    2015-04-01

    ODP Hole 1256D in the eastern equatorial Pacific is the first penetration of a complete section of fast spread ocean crust down to the dike-gabbro transition, and only the second borehole to sample in situ sheeted dikes after DSDP Hole 504B. Here a high spatial resolution record of whole rock and mineral strontium isotopic compositions from Site 1256 is combined with core observations and downhole wireline geophysical measurements to determine the extent of basalt-hydrothermal fluid reaction and to identify fluid pathways at different levels in the upper ocean crust. The volcanic sequence at Site 1256 is dominated by sheet and massive lava flows but the Sr isotope profile shows only limited exchange with seawater. However, the upper margins of two anomalously thick (>25 m) massive flow sequences are strongly hydrothermally altered with elevated Sr isotope ratios and appear to be conduits of lateral low-temperature off-axis fluid flow. Elsewhere in the lavas, high 87Sr/86Sr are restricted to breccia horizons. Mineralised hyaloclastic breccias in the Lava-Dike Transition are strongly altered to Mg-saponite, silica and pyrite, indicating alteration by mixed seawater and cooled hydrothermal fluids. In the Sheeted Dike Complex 87Sr/86Sr ratios are pervasively shifted towards hydrothermal fluid values (∼0.705). Dike chilled margins display secondary mineral assemblages formed during both axial recharge and discharge and have higher 87Sr/86Sr than dike cores, indicating preferential fluid flow along dike margins. Localised increases in 87Sr/86Sr in the Dike-Gabbro Transition indicates the channelling of fluids along the sub-horizontal intrusive boundaries of the 25 to 50 m-thick gabbroic intrusions, with only minor increases in 87Sr/86Sr within the cores of the gabbro bodies. When compared to the pillow lava-dominated section from Hole 504B, the Sr isotope measurements from Site 1256 suggest that the extent of hydrothermal circulation in the upper ocean crust may be

  4. Frozen magma lenses below the oceanic crust.

    PubMed

    Nedimović, Mladen R; Carbotte, Suzanne M; Harding, Alistair J; Detrick, Robert S; Canales, J Pablo; Diebold, John B; Kent, Graham M; Tischer, Michael; Babcock, Jeffrey M

    2005-08-25

    The Earth's oceanic crust crystallizes from magmatic systems generated at mid-ocean ridges. Whereas a single magma body residing within the mid-crust is thought to be responsible for the generation of the upper oceanic crust, it remains unclear if the lower crust is formed from the same magma body, or if it mainly crystallizes from magma lenses located at the base of the crust. Thermal modelling, tomography, compliance and wide-angle seismic studies, supported by geological evidence, suggest the presence of gabbroic-melt accumulations within the Moho transition zone in the vicinity of fast- to intermediate-spreading centres. Until now, however, no reflection images have been obtained of such a structure within the Moho transition zone. Here we show images of groups of Moho transition zone reflection events that resulted from the analysis of approximately 1,500 km of multichannel seismic data collected across the intermediate-spreading-rate Juan de Fuca ridge. From our observations we suggest that gabbro lenses and melt accumulations embedded within dunite or residual mantle peridotite are the most probable cause for the observed reflectivity, thus providing support for the hypothesis that the crust is generated from multiple magma bodies. PMID:16121179

  5. Oxygen consumption in subseafloor basaltic crust

    NASA Astrophysics Data System (ADS)

    Orcutt, B. N.; Wheat, C. G.; Hulme, S.; Edwards, K. J.; Bach, W.

    2012-12-01

    Oceanic crust is the largest potential habitat for life on Earth and may contain a significant fraction of Earth's total microbial biomass, yet little is known about the form and function of life in this vast subseafloor realm that covers nearly two-thirds of the Earth's surface. A deep biosphere hosted in subseafloor basalts has been suggested from several lines of evidence; yet, empirical analysis of metabolic reaction rates in basaltic crust is lacking. Here we report the first measure of oxygen consumption in young (~ 8 Ma) and cool (<25 degrees C) basaltic crust, calculated from modeling oxygen and strontium profiles in basal sediments collected during Integrated Ocean Drilling Program (IODP) Expedition 336 to 'North Pond', a sediment 'pond' on the western flank of the Mid-Atlantic Ridge (MAR), where vigorous fluid circulation within basaltic crust occurs. Dissolved oxygen concentrations increased towards the sediment-basement interface, indicating an upward diffusional supply from oxic fluids circulating within the crust. A parametric reaction-transport model suggests oxygen consumption rates on the order of 0.5-500 nmol per cubic centimeter fluid per day in young and cool basaltic crust, providing sufficient energy to support a subsurface crustal biosphere.

  6. Early formation of evolved asteroidal crust.

    PubMed

    Day, James M D; Ash, Richard D; Liu, Yang; Bellucci, Jeremy J; Rumble, Douglas; McDonough, William F; Walker, Richard J; Taylor, Lawrence A

    2009-01-01

    Mechanisms for the formation of crust on planetary bodies remain poorly understood. It is generally accepted that Earth's andesitic continental crust is the product of plate tectonics, whereas the Moon acquired its feldspar-rich crust by way of plagioclase flotation in a magma ocean. Basaltic meteorites provide evidence that, like the terrestrial planets, some asteroids generated crust and underwent large-scale differentiation processes. Until now, however, no evolved felsic asteroidal crust has been sampled or observed. Here we report age and compositional data for the newly discovered, paired and differentiated meteorites Graves Nunatak (GRA) 06128 and GRA 06129. These meteorites are feldspar-rich, with andesite bulk compositions. Their age of 4.52 +/- 0.06 Gyr demonstrates formation early in Solar System history. The isotopic and elemental compositions, degree of metamorphic re-equilibration and sulphide-rich nature of the meteorites are most consistent with an origin as partial melts from a volatile-rich, oxidized asteroid. GRA 06128 and 06129 are the result of a newly recognized style of evolved crust formation, bearing witness to incomplete differentiation of their parent asteroid and to previously unrecognized diversity of early-formed materials in the Solar System. PMID:19129845

  7. Magma mixing and crust-mantle interaction in Southeast China during the Early Cretaceous: Evidence from the Furongshan granite porphyry and mafic microgranular enclaves

    NASA Astrophysics Data System (ADS)

    Wang, Hong-Zuo; Chen, Pei-Rong; Sun, Li-Qiang; Ling, Hong-Fei; Zhao, You-Dong; Lan, Hong-Feng

    2015-11-01

    The petrogenesis and tectonic setting of Early Cretaceous granitoids and their enclaves emplaced in the Gan-Hang Tectonic Belt are still controversial. Here, we investigate mafic microgranular enclaves (MMEs) and their host granite porphyry from the Furongshan caldera to elucidate magma mixing and crust-mantle interaction in the Gan-Hang Tectonic Belt. The Furongshan granite porphyry is characterized by enrichments of alkalis, REE, Zr + Nb + Ce + Y contents (averaging 377 ppm), and high zircon saturation temperatures (793-843 °C), suggesting A-type granitic affinities. The granite porphyry can be further classified as an A2 subtype granite based on high Y/Nb ratios (averaging 1.37). Zircon cores from the Furongshan MMEs exhibit the same εHf(t) values (-10.0 to -3.0) and U-Pb ages (127-129 Ma) as zircons form the granite porphyry, implying that they were captured from the felsic magma as xenocrysts. Petrological and mineralogical characteristics (such as needle-like apatite and disequilibrium feldspar xenocryst) suggest that the Furongshan MMEs and host granite porphyry were formed by magma mixing rather than restite, xenolith or fractional crystallization of mafic magma. The Furongshan granite porphyry samples have initial 87Sr/86Sr ratios of 0.7073-0.7099 and εNd(t) values of -3.7 to -3.3, which are similar to those of the MMEs (0.7068-0.7077 and -3.2 to -2.9, respectively). Similar trace element and Sr-Nd isotopic compositions imply a high degree of geochemical equilibration between the granite porphyry and its MMEs, and hence intense magma mixing, although some element contents and zircons εHf(t) values differ due to high zircon closure temperature and rapid cooling of commingled magmas. A binary mixing model based on Sr-Nd isotopes indicates a contribution of ∼50% basaltic melt to the hybrid magma of the Furongshan granite porphyry. A compilation of Sr-Nd-Hf isotopic data of the granitoids and MMEs from the Xiangshan, Furongshan and Muchen areas suggest

  8. Osmium isotope evidence for Early to Middle Proterozoic mantle lithosphere stabilization and concomitant production of juvenile crust in Dish Hill, CA peridotite xenoliths

    NASA Astrophysics Data System (ADS)

    Armytage, Rosalind M. G.; Brandon, Alan D.; Peslier, Anne H.; Lapen, Thomas J.

    2014-07-01

    The 187Os/188Os compositions in peridotite samples from the sub-continental lithospheric mantle (SCLM) can be used to constrain the timing of melt extraction and potentially test the link between large-scale mantle melting and juvenile crust production. The SCLM has often experienced a complex history such that some lithophile elements such as REEs (rare earth elements) in these rocks typically record overprinting during metasomatism. New 187Os/188Os, major and trace element compositional data were obtained on sixteen Dish Hill peridotite xenoliths (California, USA) and are used to examine these issues. The samples show strong correlations between 187Os/188Os and indicators of melt depletion such as Lu abundance in clinopyroxene, modal abundance of clinopyroxene, bulk rock Al2O3 and the Cr# (Cr/(Cr + Al) in spinel. These relationships indicate that metasomatism did not compromise the 187Os/188Os systematics. The data appear to form two melt depletion trends consistent with Re depletion model ages (TRD) obtained from the two Al2O3 versus 187Os/188Os trends are 2.1 ± 0.5 Ga and 1.3 ± 0.3 Ga (±95% conf.). It has been suggested that the SCLM under Dish Hill may be fragments of oceanic lithosphere emplaced as the result of Farallon plate subduction during the Late Cretaceous (Luffi et al., 2009). However, the strong melt depletion trends, major element compositions and Re-depletion ages are not consistent with the interpretation of this suite of xenoliths having an oceanic lithospheric origin. Rather, the 2.1 Ga age coincides with Nd model ages of 2-2.3 Ga (Bennett and DePaolo, 1987; Rämö and Calzia, 1998) for the overlying Mojavia crustal province. The 1.3 Ga age is consistent with large-scale A-type magmatism in the nearby region at this time that is purported to be the result of mantle plume melting processes. Therefore, data from this study point to the SCLM under Dish Hill being formed by two ancient mantle-melting events, which could be the result of

  9. Raindrop induced crust formation

    NASA Astrophysics Data System (ADS)

    Szabó, Judit Alexandra; Jakab, Gergely; Józsa, Sándor; Németh, Tibor; Kovács, Ivett; Szalai, Zoltán

    2016-04-01

    Rainfall simulators are wildly used to study soil erosion because all parts of the erosion process can be simulated with them. Small-scale laboratory rainfall simulator was used to examine the detachment phase of the erosion and study the redistribution trend of the organic and mineral components of the soil. Splash erosion often creates crust on the soil surface that decreases porosity and infiltration. Crusts have crucial role in physical soil degradation processes, erosion and crop production fall. Intensive rainfall on a recently tilled Regosol and a Cambisol plots detached the aggregates and the occurred runoff scattered the individual particles on the surface. Oriented thin sections from the various morphological types of surface crusts were made similar as a thin section from any rock but during the preparation the samples were saturated often with dilute two-component adhesive to solidify the soil to preserve the crust. Raman spectroscopy and XRD analysis measurements are in progress in order to identify spatial changes in organic matter and mineralogical composition among the crust layers. Preliminary results suggest the separation of the mineral and organic soil components. The lighter organic matter seems to be enriched in the soil loss while the heavier minerals are deposited and stratified in the deeper micromorphological positions of the surface. The understanding of this selectivity is necessary in soil loss estimation.

  10. Grenville age of basement rocks in Cape May NJ well: New evidence for Laurentian crust in U.S. Atlantic Coastal Plain basement Chesapeake terrane

    USGS Publications Warehouse

    Sheridan, R.E.; Maguire, T.J.; Feigenson, M.D.; Patino, L.C.; Volkert, R.A.

    1999-01-01

    The Chesapeake terrane of the U.S. mid-Atlantic Coastal Plain basement is bounded on the northwest by the Salisbury positive gravity and magnetic anomaly and extends to the southeast as far as the Atlantic coast. It underlies the Coastal Plain of Virginia, Maryland, Delaware and southern New Jersey. Rubidium/Strontium dating of the Chesapeake terrane basement yields an age of 1.025 ?? 0.036 Ga. This age is typical of Grenville province rocks of the Middle to Late Proterozoic Laurentian continent. The basement lithologies are similar to some exposed Grenville-age rocks of the Appalachians. The TiO2 and Zr/P2O5 composition of the metagabbro from the Chesapeake terrane basement is overlapped by those of the Proterozoic mafic dikes in the New Jersey Highlands. These new findings support the interpretation that Laurentian basement extends southeast as far as the continental shelf in the U.S. mid-Atlantic region. The subcrop of Laurentian crust under the mid-Atlantic Coastal Plain implies unroofing by erosion of the younger Carolina (Avalon) supracrustal terrane. Dextral-transpression fault duplexes may have caused excessive uplift in the Salisbury Embayment area during the Alleghanian orogeny. This extra uplift in the Salisbury area may have caused the subsequent greater subsidence of the Coastal Plain basement in the embayment.

  11. Ferromanganese crusts as indicators for paleoceanographic events in the NE Atlantic

    USGS Publications Warehouse

    Koschinsky, A.; Halbach, P.; Hein, J.R.; Mangini, A.

    1996-01-01

    Hydrogenetic ferromanganese crusts reflect the chemical conditions of the seawater from which they formed. Fine-scale geochemical analysis of crust layers in combination with age determinations can therefore be used to investigate paleoceanographic changes which are recorded in geochemical gradients in the crusts. At Tropic seamount (off northwest Africa), uniform crust growth influenced by terrigenous input from the African continent occurred during approximately the past 12 Ma. Phosphatization of these crusts is minor. In contrast, crusts from Lion seamount, located between Madeira and the Portuguese coast, display a much more variable growth history. A pronounced increase in Ni, Cu, and Zn is observed in some intervals of the crusts, which probably reflects increased surface productivity. A thick older phosphatized generation occurs in many samples. Hydrographic profiles indicate that Mediterranean outflow water (MOW) may play an important role in the composition of these crusts. 10Be dating of one sample confirms that the interruption of the MOW during the Messinian salinity crisis (6.2-5 Ma ago) resulted in changes in element composition. Sr-isotope dating of the apatite phase of the old crust generation has been carried out to obtain a minimum age for the older generation of Atlantic crusts and to determine whether crust phosphatization in the Atlantic can be related to phosphatization episodes recorded in Pacific crusts. The preliminary data show that the old phosphatized crust generation might be as old as approximately 30-40 Ma.

  12. Evidence for widespread infection of African bats with Crimean-Congo hemorrhagic fever-like viruses

    PubMed Central

    Müller, Marcel A.; Devignot, Stéphanie; Lattwein, Erik; Corman, Victor Max; Maganga, Gaël D.; Gloza-Rausch, Florian; Binger, Tabea; Vallo, Peter; Emmerich, Petra; Cottontail, Veronika M.; Tschapka, Marco; Oppong, Samuel; Drexler, Jan Felix; Weber, Friedemann; Leroy, Eric M.; Drosten, Christian

    2016-01-01

    Crimean Congo hemorrhagic fever virus (CCHFV) is a highly virulent tick-borne pathogen that causes hemorrhagic fever in humans. The geographic range of human CCHF cases largely reflects the presence of ticks. However, highly similar CCHFV lineages occur in geographically distant regions. Tick-infested migratory birds have been suggested, but not confirmed, to contribute to the dispersal. Bats have recently been shown to carry nairoviruses distinct from CCHFV. In order to assess the presence of CCHFV in a wide range of bat species over a wide geographic range, we analyzed 1,135 sera from 16 different bat species collected in Congo, Gabon, Ghana, Germany, and Panama. Using a CCHFV glycoprotein-based indirect immunofluorescence test (IIFT), we identified reactive antibodies in 10.0% (114/1,135) of tested bats, pertaining to 12/16 tested species. Depending on the species, 3.6%–42.9% of cave-dwelling bats and 0.6%–7.1% of foliage-living bats were seropositive (two-tailed t-test, p = 0.0447 cave versus foliage). 11/30 IIFT-reactive sera from 10 different African bat species had neutralizing activity in a virus-like particle assay. Neutralization of full CCHFV was confirmed in 5 of 7 sera. Widespread infection of cave-dwelling bats may indicate a role for bats in the life cycle and geographic dispersal of CCHFV. PMID:27217069

  13. Evidence for dietary change but not landscape use in South African early hominins.

    PubMed

    Balter, Vincent; Braga, José; Télouk, Philippe; Thackeray, J Francis

    2012-09-27

    The dichotomy between early Homo and Paranthropus is justified partly on morphology. In terms of diet, it has been suggested that early Homo was a generalist but that Paranthropus was a specialist. However, this model is challenged and the issue of the resources used by Australopithecus, the presumed common ancestor, is still unclear. Laser ablation profiles of strontium/calcium, barium/calcium and strontium isotope ratios in tooth enamel are a means to decipher intra-individual diet and habitat changes. Here we show that the home range area was of similar size for species of the three hominin genera but that the dietary breadth was much higher in Australopithecus africanus than in Paranthropus robustus and early Homo. We also confirm that P. robustus relied more on plant-based foodstuffs than early Homo. A South African scenario is emerging in which the broad ecological niche of Australopithecus became split, and was then occupied by Paranthropus and early Homo, both consuming a lower diversity of foods than Australopithecus. PMID:22878716

  14. Food as an instrument of war in contemporary african famines: a review of the evidence.

    PubMed

    Macrae, J; Zwi, A B

    1992-12-01

    Famine is conventionally portrayed as a natural disaster expressed in terms of food scarcity and culminating in starvation. This view has attracted criticism in recent years as the political, legal and social dimensions of famine have become more clearly understood. This paper draws upon these criticisms to understand the particular conditions of famine creation in conflict situations. Following an examination of six contemporary African famines, it is suggested that the use of food as a weapon of war by omission, commission and provision has contributed to the creation of famine in recent decades. Despite the optimism for peace engendered by the demise of the Cold War, the momentum for conflict would seem to be sustained by internal factors, including economic and environmental decline, political instability and ethnic rivalry. Within these conflicts, the strategic importance of food is likely to remain central. This study highlights the need to link concerns with food security and public health to those of development, human rights and international relations. PMID:20958750

  15. Evidence of cretaceous to recent West African intertropical vegetation from continental sediment spore-pollen analysis

    NASA Astrophysics Data System (ADS)

    Salard-Cheboldaeff, M.; Dejax, J.

    The succession of spore-pollen assemblages during the Cretaceous and Tertiary, as defined in each of the basin from Senegal to Angola, gives the possibility to consider the intertropical African flora evolution for the past 120 M.a. During the Early Cretaceous, xeric-adapted gymnosperms and various ferns were predominant the flora which nevertheless comprises previously unknown early angiosperm pollen. During the Middle Cretaceous, gymnospers were gradually replaced by angiosperms; these became more and more abundant, along with the diversification of new genera and species. During the Paleocene, the radiation of the monocotyledons (mainly that of the palm-trees) as well as a greater diversification among the dicotyledons and ferms are noteworthy. Since gymnosperms had almost disappeared by the Eocene, the diversification of the dicotyledons went on until the neogene, when all extinct pollen types are already present. These important modifications of the vegetation reflect evolutionary trends as well as climatic changes during the Cretaceous: the climate, firstly hot, dry and perhaps arid, did probably induced salt deposition, and later became gradually more humid under oceanic influences which arose in connection with the Gondwana break-up.

  16. A systematic review of physical activity interventions among African American adults: evidence from 2009 to 2013.

    PubMed

    Whitt-Glover, M C; Keith, N R; Ceaser, T G; Virgil, K; Ledford, L; Hasson, R E

    2014-10-01

    This review extends findings from four previous reviews of physical activity (PA) interventions among African Americans (AA) and includes papers published between January 2009 and August 2013. Eligible papers were retrieved using strategies employed in previous reviews. Overall, 16 relevant papers were identified, including four pilot studies and 12 full trials. Interventions were based on a variety of behavioural sciences theories. The most common setting for interventions was churches. Most interventions lasted >6 months; few interventions included >6 months of post-intervention follow-up. Overall, studies identified within-group differences showing positive improvements in PA, and most studies showed statistically significant between-group differences in at least one measure of PA. A quality score was used to rate various elements of the studies and provide a numerical assessment of each paper; scores ranged from 3 to 10 out of 13 possible points. The current review indicates a continued need for studies that use objective PA measures, assess long-term intervention impact, provide specific PA goals for interventions, include more attention to strategies that can increase retention and adherence among AA study participants, include AA men and determine the independent and synergistic effects of individual and environmental (socio-cultural and built) change strategies. PMID:25196410

  17. Evidence for widespread infection of African bats with Crimean-Congo hemorrhagic fever-like viruses.

    PubMed

    Müller, Marcel A; Devignot, Stéphanie; Lattwein, Erik; Corman, Victor Max; Maganga, Gaël D; Gloza-Rausch, Florian; Binger, Tabea; Vallo, Peter; Emmerich, Petra; Cottontail, Veronika M; Tschapka, Marco; Oppong, Samuel; Drexler, Jan Felix; Weber, Friedemann; Leroy, Eric M; Drosten, Christian

    2016-01-01

    Crimean Congo hemorrhagic fever virus (CCHFV) is a highly virulent tick-borne pathogen that causes hemorrhagic fever in humans. The geographic range of human CCHF cases largely reflects the presence of ticks. However, highly similar CCHFV lineages occur in geographically distant regions. Tick-infested migratory birds have been suggested, but not confirmed, to contribute to the dispersal. Bats have recently been shown to carry nairoviruses distinct from CCHFV. In order to assess the presence of CCHFV in a wide range of bat species over a wide geographic range, we analyzed 1,135 sera from 16 different bat species collected in Congo, Gabon, Ghana, Germany, and Panama. Using a CCHFV glycoprotein-based indirect immunofluorescence test (IIFT), we identified reactive antibodies in 10.0% (114/1,135) of tested bats, pertaining to 12/16 tested species. Depending on the species, 3.6%-42.9% of cave-dwelling bats and 0.6%-7.1% of foliage-living bats were seropositive (two-tailed t-test, p = 0.0447 cave versus foliage). 11/30 IIFT-reactive sera from 10 different African bat species had neutralizing activity in a virus-like particle assay. Neutralization of full CCHFV was confirmed in 5 of 7 sera. Widespread infection of cave-dwelling bats may indicate a role for bats in the life cycle and geographic dispersal of CCHFV. PMID:27217069

  18. Multiproxy Evidence for a Positive Hydrological Budget during the Little Ice Age in the East African Rift, Kenya

    NASA Astrophysics Data System (ADS)

    Goman, M.; Ashley, G. M.; Hover, V. C.; Owen, R.

    2011-12-01

    Hominin evolution took place in Africa during the Plio-Pleistocene and climate change is thought to be a factor, with Africa experiencing a general cooling and increasing aridification over the last several million years. Today, the climate of the East African Rift Valley of Kenya is characterized as semi-arid with evapotranspiration four times precipitation. Water resources are a valuable commodity for the many millions of inhabitants of the Valley. The short instrumental record shows precipitation fluctuates at sub-decadal timeframes as a result of the ENSO cycle; while during prehistory variations in monsoonal precipitation occurred on Milankovitch timescales (i.e. African Humid Period). Both timescales exhibit significant impacts on the distribution of surface water. However, little is known regarding precipitation variability over sub-millennial timescales. Emerging paleoclimate data indicates that the near surface presence of water has also varied over century length timescales. We present paleoclimate data from multiple sites along a north-south 600 km transect of the Gregory Rift Valley (Kenya) that indicate the region experienced wetter conditions during the Little Ice Age (A.D. 1400-1850). Our reconstructions of landscape and climate during this time frame rely upon a multiproxy and interdisciplinary approach. We discuss data from a variety of environmental settings (e.g. lakes, wetlands, and springs) that indicate an overall increase in hydrologic balance. Evidence is derived from biologic microfossils such as pollen, diatom and testate amoebae assemblages as well as inorganic components of the sedimentary record and geomorphic changes. The data differs significantly from studies undertaken to the west in Uganda and the Congo, where negative hydrologic balances occurred during the Little Ice Age. While the atmospheric dynamics causing this disparity are not yet recognized, interactions between the Intertropical Convergence Zone and the Congo Air Boundary

  19. Strange Quark Star Crusts

    SciTech Connect

    Steiner, Andrew W.

    2007-02-27

    If strange quark matter is absolutely stable, some neutron stars may be strange quark stars. Strange quark stars are usually assumed to have a simple liquid surface. We show that if the surface tension of droplets of quark matter in the vacuum is sufficiently small, droplets of quark matter on the surface of a strange quark star may form a solid crust on top of the strange quark star. This solid crust can significantly modify the predictions for the photon emission for the surface in an observable way.

  20. Magmatic intrusions in the lunar crust

    NASA Astrophysics Data System (ADS)

    Michaut, C.; Thorey, C.

    2015-10-01

    The lunar highlands are very old, with ages covering a timespan between 4.5 to 4.2 Gyr, and probably formed by flotation of light plagioclase minerals on top of the lunar magma ocean. The lunar crust provides thus an invaluable evidence of the geological and magmatic processes occurring in the first times of the terrestrial planets history. According to the last estimates from the GRAIL mission, the lunar primary crust is particularly light and relatively thick [1] This low-density crust acted as a barrier for the dense primary mantle melts. This is particularly evident in the fact that subsequent mare basalts erupted primarily within large impact basin: at least part of the crust must have been removed for the magma to reach the surface. However, the trajectory of the magma from the mantle to the surface is unknown. Using a model of magma emplacement below an elastic overlying layer with a flexural wavelength Λ, we characterize the surface deformations induced by the presence of shallow magmatic intrusions. We demonstrate that, depending on its size, the intrusion can show two different shapes: a bell shape when its radius is smaller than 4 times Λ or a flat top with small bended edges if its radius is larger than 4 times Λ[2]. These characteristic shapes for the intrusion result in characteristic deformations at the surface that also depend on the topography of the layer overlying the intrusion [3].Using this model we provide evidence of the presence of intrusions within the crust of the Moon as surface deformations in the form of low-slope lunar domes and floor-fractured craters. All these geological features have morphologies consistent with models of magma spreading at depth and deforming an overlying elastic layer. Further more,at floor-fractured craters, the deformation is contained within the crater interior, suggesting that the overpressure at the origin of magma ascent and intrusion was less than the pressure due to the weight of the crust removed by

  1. Recycled oceanic crust and marine sediment in the source of alkali basalts in Shandong, eastern China: Evidence from magma water content and oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Liu, Jia; Xia, Qun-Ke; Deloule, Etienne; Chen, Huan; Feng, Min

    2015-12-01

    The magma water contents and cpx δ18O values in alkali basalts from the Fuyanyshan (FYS) volcano in Shandong, eastern China, were investigated by an inverse calculation based on the water content of clinopyroxene (cpx) phenocrysts, the ivAlcpx-dependent water partitioning coefficient Dwatercpx>/melt, and secondary ion mass spectrometer, respectively. The calculated water content (H2O wt.) of magma ranges from 0.58% to 3.89%. It positively correlates with heavy rare earth element concentrations and bulk rock 87Sr/86Sr ratios, and it negatively correlates with Nb/U ratios. However, it is not correlated with bulk Mg# (Mg# = 100 × Mg / (Mg + Fe)) and (La/Yb)n (n represents primitive mantle normalization). Combined with the rather homogenous distribution of water content within cpx grains, these correlations indicate that the water variations among different samples represent the original magma signature, rather than results of a shallow process, such as degassing and diffusion. The δ18O of cpx phenocrysts varies from 3.6‰ to 6.3‰ (±0.5‰, 2SD), which may be best explained by the involvement of components from the lower and upper oceanic crust with marine sediments within the mantle source. The H2O/Ce ratios of the calculated melts range from 113 to 696 and form a positive trend with bulk rock 87Sr/86Sr, which cannot be explained by the recycled Sulu eclogite or by the metasomatized lithospheric mantle. Our modeling calculation shows that the decoupling of ɛHf and ɛNd could be caused by the involvement of marine sediments. Combing the high Ba/Th ratios, positive Sr spikes, and low Ce/Pb ratios for the Fuyanshan basalts, we suggest that the hydrous nature of the FYS basalts was derived from the hydrous mantle transition zone with ancient sediments.

  2. Direct dating of paleomagnetic results from Precambrian sediments in the Amazon craton: Evidence for Grenvillian emplacement of exotic crust in SE Appalachians of North America

    NASA Astrophysics Data System (ADS)

    D'Agrella-Filho, Manoel S.; Tohver, Eric; Santos, João O. S.; Elming, Sten-Åke; Trindade, Ricardo I. F.; Pacca, Igor I. G.; Geraldes, Mauro C.

    2008-03-01

    We apply a new diagenetic dating technique to determine the age of magnetization for Precambrian sedimentary rocks in the SW Amazon craton. Two new paleomagnetic poles are reported from the rocks of the Aguapeí Gp.: red beds of the Fortuna Fm. (Plat = 59.8°N, Plon = 155.9°E, A95 = 9.5, K = 14, 18 sites, N/n 128/115, Q = 5) and the reverse-polarity mudstones of the overlying Vale da Promissão Formation (Plat = 49.5°N, Plon = 89.3°E, A95 = 12.5, K = 30, 6 sites, N/n = 94/80, Q = 4). The Fortuna Fm. magnetization is hosted by massive, interstitial hematite cement and constitutes a post-depositional remanence. The age of diagenesis of the red beds is well-constrained by the 1149 ± 7 Ma U-Pb age of authigenic xenotime rims on detrital zircons determined by SHRIMP analysis. The magnetite-hosted remanence of the Vale da Promissão Fm. may be detrital in origin, but the age of deposition is poorly constrained. The reliable and precisely-dated Fortuna Fm. paleomagnetic pole fixes the paleogeographic position of the Amazon craton near the SE Appalachians portion of North America at 1.15 Ga. These data demonstrate a mobile Grenvillian link between these two cratons, and support the recent identification of Amazon crust in the Blue Ridge province region of North America.

  3. Association Between Adolescent Drinking and Adult Violence: Evidence From a Longitudinal Study of Urban African Americans*

    PubMed Central

    Green, Kerry M.; Doherty, Elaine E.; Zebrak, Katarzyna A.; Ensminger, Margaret E.

    2011-01-01

    Objective: This study examined the relationship between adolescent alcohol use and adult violence from a developmental perspective, specifically whether frequent adolescent drinking predicts adult violence once shared risk factors are taken into account through propensity score matching. The research considered multiple types of violence, including assault, robbery, and suicidal behavior, as well as other types of offending. It tested whether educational attainment and adult alcohol use and problems contribute to the adolescent drinking–adult violence relationship. Method: Data came from a longitudinal epidemiological study of a community cohort of urban African Americans followed from age 6 to 42 (N = 702; 51% female). Frequent adolescent drinking was operationalized as 20 times or more by age 16. Data on violent arrests and offenses were collected throughout adulthood from self-reports and official criminal records. Matching variables came from childhood and adolescence and included such shared risk factors as childhood externalizing behaviors, school achievement, and family functioning. Results: Adjusted logistic regression analyses on the sample matched on childhood and adolescent risk factors showed that frequent adolescent drinking was associated with an increased risk of violence in young adulthood (in particular assault) but not with other types of crime, self-directed violence, or violence in midlife. Findings varied by gender. Heavy episodic drinking in adulthood seemed to account for some of the association between frequent adolescent drinking and adult assault. Conclusions: The results of this study suggest that preventing frequent adolescent drinking could potentially decrease adult assault. This study adds to the growing body of literature suggesting long-term negative consequences of adolescent alcohol use. PMID:21906497

  4. Does subduction zone magmatism produce average continental crust

    NASA Technical Reports Server (NTRS)

    Ellam, R. M.; Hawkesworth, C. J.

    1988-01-01

    The question of whether present day subduction zone magmatism produces material of average continental crust composition, which perhaps most would agree is andesitic, is addressed. It was argued that modern andesitic to dacitic rocks in Andean-type settings are produced by plagioclase fractionation of mantle derived basalts, leaving a complementary residue with low Rb/Sr and a positive Eu anomaly. This residue must be removed, for example by delamination, if the average crust produced in these settings is andesitic. The author argued against this, pointing out the absence of evidence for such a signature in the mantle. Either the average crust is not andesitic, a conclusion the author was not entirely comfortable with, or other crust forming processes must be sought. One possibility is that during the Archean, direct slab melting of basaltic or eclogitic oceanic crust produced felsic melts, which together with about 65 percent mafic material, yielded an average crust of andesitic composition.

  5. Lu-Hf systematics of the ultra-high temperature Napier Complex, East Antarctica: evidence for the early Archean formation of continental crust

    NASA Astrophysics Data System (ADS)

    Choi, S.; Mukasa, S. B.; Andronikov, A. V.; Osanai, Y.; Harley, S. L.; Kelly, N. M.

    2009-12-01

    The Napier Complex in East Antarctica comprises some of the oldest rocks on earth (~3.8 billion years old), overprinted by an ultra-high temperature (UHT) metamorphic event near the Archean-Proterozoic boundary. Garnet, orthopyroxene, sapphirine, osumilite, rutile and a whole rock representing an equilibrated assemblage from this belt yield a Lu-Hf isochron age of 2,403 ± 43 Ma. Preservation of the UHT mineral assemblage in the rock analyzed suggests rapid cooling with closure likely to have occurred for the Lu-Hf system at post-peak UHT conditions near a temperature of ~800C. Individual zircon grains from Gage Ridge within the Napier Complex yielded a remarkably uniform range of 176Hf/177Hf values between 0.280433 ± 7 and 0.280505 ± 10, corresponding to ɛHf > +5.6 at 3.85 Ga relative to the chondritic uniform reservoir (CHUR). Because of their exceedingly low Lu/Hf values (<0.001), the grains are effectively recording the initial Hf isotope composition of the magmatic systems from which the gneiss protoliths crystallized. These results indicate that (1) the source of the crustal materials that formed the Napier Complex at 3.85 Ga were depleted relative to the CHUR. The extent of depletion involved is higher than has been predicted by extrapolation from the Lu-Hf isotopic evolution inferred for the source of Proterozoic and Phanerozoic basalts, judging from an fLu/Hf value of 0.51, (2) the depleted mantle reservoir has been in existence since very early in Earth’s history, in agreement with the early differentiation of the Earth that the latest core formation models require, and (3) an extremely depleted source also mean that the bulk of continental crust was extracted from the mantle by ~3.8 Ga. Moreover, the results demonstrate that even the oldest silicic rocks in the complex are not likely to have formed from remobilized older crustal materials, but were instead juvenile products of mantle melting. In addition, zircons with metamorphic rims have a similar

  6. Evidence of constant diversification punctuated by a mass extinction in the African cycads

    PubMed Central

    Yessoufou, Kowiyou; Bamigboye, Samuel O; Daru, Barnabas H; van der Bank, Michelle

    2014-01-01

    The recent evidence that extant cycads are not living fossils triggered a renewed search for a better understanding of their evolutionary history. In this study, we investigated the evolutionary diversification history of the genus Encephalartos, a monophyletic cycad endemic to Africa. We found an antisigmoidal pattern with a plateau and punctual explosive radiation. This pattern is typical of a constant radiation with mass extinction. The rate shift that we found may therefore be a result of a rapid recolonization of niches that have been emptied owing to mass extinction. Because the explosive radiation occurred during the transition Pliocene–Pleistocene, we argued that the processes might have been climatically mediated. PMID:24455160

  7. Earthquakes in Stable Continental Crust.

    ERIC Educational Resources Information Center

    Johnston, Arch C.; Kanter, Lisa R.

    1990-01-01

    Discussed are some of the reasons for earthquakes which occur in stable crust away from familiar zones at the ends of tectonic plates. Crust stability and the reactivation of old faults are described using examples from India and Australia. (CW)

  8. Intervention Mapping to Adapt Evidence-Based Interventions for Use in Practice: Increasing Mammography among African American Women

    PubMed Central

    Highfield, Linda; Hartman, Marieke A.; Mullen, Patricia Dolan; Rodriguez, Serena A.; Fernandez, Maria E.; Bartholomew, L. Kay

    2015-01-01

    This paper describes and demonstrates the use of the systematic planning process, Intervention Mapping, to adapt an evidence-based public health intervention (EBI). We used a simplified version of Intervention Mapping (IM Adapt) to increase an intervention's fit with a new setting and population. IM Adapt guides researchers and practitioners in selecting an EBI, making decisions about whether and what to adapt, and executing the adaptation while guarding the EBI's essential elements (those responsible for effectiveness). We present a case study of a project in which we used IM Adapt to find, adapt, implement, and evaluate an EBI to improve mammography adherence for African American women in a new practice setting in Houston, Texas. IM Adapt includes the following (1) assess needs and organizational capacity; (2) find EBIs; (3) plan adaptations based on fit assessments; (4) make adaptations; (5) plan for implementation; and (6) plan for evaluation of the adapted EBI. The case study shows an example of how public health researchers and practitioners can use the tool to make it easier to find and use EBIs, thus encouraging greater uptake. IM Adapt adds to existing dissemination and adaptation models by providing detailed guidance on how to decide on effective adaptation, while maintaining the essential elements of the EBI. PMID:26587531

  9. Evaluation of the Effectiveness and Implementation of an Adapted Evidence-Based Mammography Intervention for African American Women

    PubMed Central

    Highfield, Linda; Hartman, Marieke A.; Bartholomew, L. Kay; Balihe, Philomene; Ausborn, Valerie A.

    2015-01-01

    Breast cancer mortality disparities continue, particularly for uninsured and minority women. A number of effective evidence-based interventions (EBIs) exist for addressing barriers to mammography screening; however, their uptake and use in community has been limited. Few cancer-specific studies have evaluated adapted EBIs in new contexts, and fewer still have considered implementation. This study sought to (1) evaluate the effectiveness of an adapted mammography EBI in improving appointment keeping in African American women and (2) describe processes of implementation in a new practice setting. We used the type 1 hybrid design to test effectiveness and implementation using a quasi-experimental design. Logistic regression and intent-to-treat analysis were used to evaluate mammography appointment attendance. The no-show rate was 44% (comparison) versus 19% (intervention). The adjusted odds of a woman in the intervention group attending her appointment were 3.88 (p < 0.001). The adjusted odds of a woman attending her appointment in the intent-to-treat analysis were 2.31 (p < 0.05). Adapted EBI effectiveness was 3.88 (adjusted OR) versus 2.10 (OR) for the original program, indicating enhanced program effect. A number of implementation barriers and facilitators were identified. Our findings support previous studies noting that sequentially measuring EBI efficacy and effectiveness, followed by implementation, may be missing important contextual information. PMID:26504790

  10. Evidence for the emergence of new rice types of interspecific hybrid origin in West African farmers' fields.

    PubMed

    Nuijten, Edwin; van Treuren, Robbert; Struik, Paul C; Mokuwa, Alfred; Okry, Florent; Teeken, Béla; Richards, Paul

    2009-01-01

    In West Africa two rice species (Oryza glaberrima Steud. and Oryza sativa L.) co-exist. Although originally it was thought that interspecific hybridization is impossible without biotechnological methods, progenies of hybridization appear to occur in farmer fields. AFLP analysis was used to assess genetic diversity in West Africa (including the countries The Gambia, Senegal, Guinea Bissau, Guinea Conakry, Sierra Leone, Ghana and Togo) using 315 rice samples morphologically classified prior to analysis. We show evidence for farmer interspecific hybrids of African and Asian rice, resulting in a group of novel genotypes, and identify possible mechanisms for in-field hybridization. Spontaneous back-crossing events play a crucial role, resulting in different groups of genetic diversity in different regions developed by natural and cultural selection, often under adverse conditions. These new groups of genotypes may have potential relevance for exploitation by plant breeders. Future advances in crop development could be achieved through co-operation between scientists and marginalized farmer groups in order to address challenges of rapid adaptation in a world of increasing socio-political and climatic uncertainty. PMID:19806197

  11. Evolution of the pygmy phenotype: evidence of positive selection fro genome-wide scans in African, Asian, and Melanesian pygmies.

    PubMed

    Migliano, Andrea Bamberg; Romero, Irene Gallego; Metspalu, Mait; Leavesley, Matthew; Pagani, Luca; Antao, Tiago; Huang, Da-Wei; Sherman, Brad T; Siddle, Katharine; Scholes, Clarissa; Hudjashov, Georgi; Kaitokai, Elton; Babalu, Avis; Belatti, Maggie; Cagan, Alex; Hopkinshaw, Byrony; Shaw, Colin; Nelis, Mari; Metspalu, Ene; Mägi, Reedik; Lempicki, Richard A; Villems, Richard; Lahr, Marta Mirazon; Kivisild, Toomas

    2013-01-01

    Human pygmy populations inhabit different regions of the world, from Africa to Melanesia. In Asia, short-statured populations are often referred to as "negritos." Their short stature has been interpreted as a consequence of thermoregulatory, nutritional, and/or locomotory adaptations to life in tropical forests. A more recent hypothesis proposes that their stature is the outcome of a life history trade-off in high-mortality environments, where early reproduction is favored and, consequently, early sexual maturation and early growth cessation have coevolved. Some serological evidence of deficiencies in the growth hormone/insulin-like growth factor axis have been previously associated with pygmies' short stature. Using genome-wide single-nucleotide polymorphism genotype data, we first tested whether different negrito groups living in the Philippines and Papua New Guinea are closely related and then investigated genomic signals of recent positive selection in African, Asian, and Papuan pygmy populations. We found that negritos in the Philippines and Papua New Guinea are genetically more similar to their nonpygmy neighbors than to one another and have experienced positive selection at different genes. These results indicate that geographically distant pygmy groups are likely to have evolved their short stature independently. We also found that selection on common height variants is unlikely to explain their short stature and that different genes associated with growth, thyroid function, and sexual development are under selection in different pygmy groups. PMID:24297229

  12. Long Tree-Ring Chronologies Provide Evidence of Recent Tree Growth Decrease in a Central African Tropical Forest

    PubMed Central

    Battipaglia, Giovanna; Zalloni, Enrica; Castaldi, Simona; Marzaioli, Fabio; Cazzolla- Gatti, Roberto; Lasserre, Bruno; Tognetti, Roberto; Marchetti, Marco; Valentini, Riccardo

    2015-01-01

    It is still unclear whether the exponential rise of atmospheric CO2 concentration has produced a fertilization effect on tropical forests, thus incrementing their growth rate, in the last two centuries. As many factors affect tree growth patterns, short -term studies might be influenced by the confounding effect of several interacting environmental variables on plant growth. Long-term analyses of tree growth can elucidate long-term trends of plant growth response to dominant drivers. The study of annual rings, applied to long tree-ring chronologies in tropical forest trees enables such analysis. Long-term tree-ring chronologies of three widespread African species were measured in Central Africa to analyze the growth of trees over the last two centuries. Growth trends were correlated to changes in global atmospheric CO2 concentration and local variations in the main climatic drivers, temperature and rainfall. Our results provided no evidence for a fertilization effect of CO2 on tree growth. On the contrary, an overall growth decline was observed for all three species in the last century, which appears to be significantly correlated to the increase in local temperature. These findings provide additional support to the global observations of a slowing down of C sequestration in the trunks of forest trees in recent decades. Data indicate that the CO2 increase alone has not been sufficient to obtain a tree growth increase in tropical trees. The effect of other changing environmental factors, like temperature, may have overridden the fertilization effect of CO2. PMID:25806946

  13. Argon, oxygen, and boron isotopic evidence documenting 40ArE accumulation in phengite during water-rich high-pressure subduction metasomatism of continental crust

    NASA Astrophysics Data System (ADS)

    Menold, Carrie A.; Grove, Marty; Sievers, Natalie E.; Manning, Craig E.; Yin, An; Young, Edward D.; Ziegler, Karen

    2016-07-01

    were even older, exceeding the time of eclogite formation by a factor of 1.7. In contrast, lower pressure retrograde muscovite present within the host gneiss and in discrete shear zones cutting the selvage yield 40Ar/39Ar ages that were younger than the time of HP metamorphism and consistent with regional cooling age patterns. Our observation of high 40ArE concentrations in phengite from schistose rocks infiltrated by regionally extensive fluids at HP conditions runs contrary to widely held expectations. Conventional wisdom dictates that low phengite/fluid partition coefficients for argon (Dphg/fluid Ar =10-3to10-5) coupled with the dry, closed systems conditions that are widely reported to characterize HP metamorphism of continental crust explains why high concentrations of 40ArE partitions are able to accumulate within phengite. We alternatively propose that phengite/fluid partition coefficients for argon increase linearly with pressure to values as high as 10-2 to allow phengites to accumulate large amounts of 40ArE from aqueous fluids under HP to UHP conditions.

  14. Low Birth Weight and Cognitive Outcomes: Evidence for a Gradient Relationship in an Urban, Poor, African American Birth Cohort

    ERIC Educational Resources Information Center

    Dombrowski, Stefan C.; Noonan, Kelly; Martin, Roy P.

    2007-01-01

    This study is one of the first to investigate the relationship between low birth weight and cognitive outcomes in an urban, poor, prospectively designed African-American birth cohort. Multivariate analyses of the Pathways to Adulthood study, a subset of the Johns Hopkins Collaborative Perinatal study, compared low birth weight African-American…

  15. Geodynamic evolution of a Pan-African granitoid of extended Dizo Valley in Karbi Hills, NE India: Evidence from Geochemistry and Isotope Geology

    NASA Astrophysics Data System (ADS)

    Majumdar, Dilip; Dutta, Pankhi

    2016-03-01

    enrichment of Ba for the studied granitoids and a gradual depletion of Rb, Sr and Eu values. The Lu-Hf profile produced an initial 176Hf/177Hf (i) ratio of all zircons from 0.2819-0.2821 and have ɛHf(t) values -12.20 to -18.90; suggesting melting of 2.25-2.67 Ga old metasomatized crust (TDM2) of magmatic origin which has been predicted to produce KG granitoids that had gained enrichment in LILE during earlier subduction events. The zircons bear evidence of oscillatory zoning visible in Cathodo Luminescence (CL) images which clearly attributes toward a magmatic origin of KG granitoids.

  16. HIV prevention for South African youth: which interventions work? A systematic review of current evidence

    PubMed Central

    2010-01-01

    Background In South Africa, HIV prevalence among youth aged 15-24 is among the world's highest. Given the urgent need to identify effective HIV prevention approaches, this review assesses the evidence base for youth HIV prevention in South Africa. Methods Systematic, analytical review of HIV prevention interventions targeting youth in South Africa since 2000. Critical assessment of interventions in 4 domains: 1) study design and outcomes, 2) intervention design (content, curriculum, theory, adaptation process), 3) thematic focus and HIV causal pathways, 4) intervention delivery (duration, intensity, who, how, where). Results Eight youth HIV prevention interventions were included; all were similar in HIV prevention content and objectives, but varied in thematic focus, hypothesised causal pathways, theoretical basis, delivery method, intensity and duration. Interventions were school- (5) or group-based (3), involving in- and out-of-school youth. Primary outcomes included HIV incidence (2), reported sexual risk behavior alone (4), or with alcohol use (2). Interventions led to reductions in STI incidence (1), and reported sexual or alcohol risk behaviours (5), although effect size varied. All but one targeted at least one structural factor associated with HIV infection: gender and sexual coercion (3), alcohol/substance use (2), or economic factors (2). Delivery methods and formats varied, and included teachers (5), peer educators (5), and older mentors (1). School-based interventions experienced frequent implementation challenges. Conclusions Key recommendations include: address HIV social risk factors, such as gender, poverty and alcohol; target the structural and institutional context; work to change social norms; and engage schools in new ways, including participatory learning. PMID:20187957

  17. Evidence for Non-neutral Evolution in a Sodium Channel Gene in African Weakly Electric Fish (Campylomormyrus, Mormyridae).

    PubMed

    Paul, Christiane; Kirschbaum, Frank; Mamonekene, Victor; Tiedemann, Ralph

    2016-08-01

    Voltage-gated sodium channels, Nav1, play a crucial role in the generation and propagation of action potentials and substantially contribute to the shape of their rising phase. The electric organ discharge (EOD) of African weakly electric fish (Mormyroidea) is the sum of action potentials fired from all electrocytes of the electric organ at the same time and hence voltage-gated sodium channels are one factor-together with the electrocyte's morphology and innervation pattern-that determines the properties of these EODs. Due to the fish-specific genome duplication, teleost fish possess eight copies of sodium channel genes (SCN), which encode for Nav1 channels. In mormyroids, SCN4aa is solely expressed in the electrocytes of the adult electric organ. In this study, we compared entire SCN4aa sequences of six species of the genus Campylomormyrus and identified nonsynonymous substitutions among them. SCN4aa in Campylomormyrus exhibits a much higher evolutionary rate compared to its paralog SCN4ab, whose expression is not restricted to the electric organ. We also found evidence for strong positive selection on the SCN4aa gene within Mormyridae and along the lineage ancestral to the Mormyridae. We have identified sites at which all nonelectric teleosts are monomorphic in their amino acid, but mormyrids have different amino acids. Our findings confirm the crucial role of SCN4aa in EOD evolution among mormyrid weakly electric fish. The inferred positive selection within Mormyridae makes this gene a prime candidate for further investigation of the divergent evolution of pulse-type EODs among closely related species. PMID:27481396

  18. Aleutian basin oceanic crust

    USGS Publications Warehouse

    Christeson, Gail L.; Barth, Ginger A.

    2015-01-01

    We present two-dimensional P-wave velocity structure along two wide-angle ocean bottom seismometer profiles from the Aleutian basin in the Bering Sea. The basement here is commonly considered to be trapped oceanic crust, yet there is a change in orientation of magnetic lineations and gravity features within the basin that might reflect later processes. Line 1 extends ∼225 km from southwest to northeast, while Line 2 extends ∼225 km from northwest to southeast and crosses the observed change in magnetic lineation orientation. Velocities of the sediment layer increase from 2.0 km/s at the seafloor to 3.0–3.4 km/s just above basement, crustal velocities increase from 5.1–5.6 km/s at the top of basement to 7.0–7.1 km/s at the base of the crust, and upper mantle velocities are 8.1–8.2 km/s. Average sediment thickness is 3.8–3.9 km for both profiles. Crustal thickness varies from 6.2 to 9.6 km, with average thickness of 7.2 km on Line 1 and 8.8 km on Line 2. There is no clear change in crustal structure associated with a change in orientation of magnetic lineations and gravity features. The velocity structure is consistent with that of normal or thickened oceanic crust. The observed increase in crustal thickness from west to east is interpreted as reflecting an increase in melt supply during crustal formation.

  19. Stable isotope and Ar/Ar evidence of prolonged multiscale fluid flow during exhumation of orogenic crust: Example from the Mont Blanc and Aar Massifs (NW Alps)

    NASA Astrophysics Data System (ADS)

    Rossi, M.; Rolland, Y.

    2014-09-01

    The spatial and temporal scales and the geometry of fluid pathways in a collisional orogen are investigated using stable isotope analysis (O, C, and H) and 40Ar/39Ar dating of vein minerals formed at circa 11-16 Ma in the Mont Blanc and the Aar External Crystalline Massifs. In both massifs 40Ar/39Ar dating of veins adularia provides evidence for progressive crystallization from 16 to 9 Ma, and mainly at 11-12 Ma following veins opening during shear zone activity. The fluid flow duration thus ranges from 4 to 5 Ma in the two massifs. The δ18O values of vein quartz and calcite are similar to those of undeformed crystalline and sedimentary host rocks, suggesting rock buffering, while carbon isotope ratios of vein calcites fall into three compositional groups. A-type veins have δ13C values that are buffered by the Helvetic metasediments, which suggests that these veins formed in a closed system from a locally derived CO2-rich fluid. The fluid in equilibrium with C-type veins has depleted δ13C values similar to mantle-CO2, while the intermediate δ13C values of B-type veins suggest mixing between the A-type and C-type fluids. These results are in agreement with crustal- to lithosphere-scale upward vertical fluid flow along vertical shear zones related to the strike-slip system bounding the Adriatic block since 16-20 Ma, connecting a deep-seated fluid to some downward flow in the sedimentary cover of External Crystalline Massifs.

  20. Evidence to support church-based health promotion programmes for African Canadians at risk for cardiovascular disease.

    PubMed

    Tomlinson, Sherldine

    2011-12-01

    High quality management of cardiovascular disease is a critical health issue for people of African descent as this group is more likely than the general population to have greater coexisting cardiovascular comorbidities. The higher than average rates of cardiovascular conditions among Black populations are a cause for concern. In an effort to combat the disproportionate number of African Americans experiencing cardiovascular conditions a significant number of churches within the African American community have initiated health promotion programmes and/or services. Health organisations and agencies in the United States are keen to support and encourage these programmes for cardiovascular disease risk populations (i.e. African Americans and other minority groups, such as the Hispanic community). Indeed these health organisations and agencies recognise the need to promote healthier habits among African Americans and other minority groups as statistics continue to show health disparities among these populations within the US health care system. This paper attempts to encourage Canadian health agencies, organizations and practitioners to support similar CBHPPs initiatives for the African Canadian population. The historical significance of the church in Black Canadian communities is also examined. PMID:21773881

  1. [Crusted scabies: A review].

    PubMed

    Jouret, G; Bounemeur, R; Presle, A; Takin, R

    2016-04-01

    Crusted scabies is a rare and severe form of infestation by Sarcoptes scabies var. hominis. It is characterized by profuse hyperkeratosis containing over 4000 mites per gram of skin, with treatment being long and difficult. The condition is both direct and indirectly contagious. It has a central role in epidemic cycles of scabies, the incidence of which is on the rise in economically stable countries. Recent discoveries concerning the biology of mites, the pathophysiology of hyperkeratosis and the key role of IL-17 in this severe form open up new therapeutic perspectives. PMID:26948093

  2. SiHLEWeb.com: Development and Usability Testing of an Evidence-Based HIV/STI Prevention Website for Female African-American Adolescents

    PubMed Central

    Danielson, Carla Kmett; McCauley, Jenna L.; Gros, Kirstin Stauffacher; Jones, Andrea M.; Barr, Simone C.; Borkman, April L.; Bryant, Brittany G.; Ruggiero, Kenneth J.

    2014-01-01

    African-American adolescent girls are at disproportionate risk for HIV infection. Although numerous evidence-based risk-reduction interventions exist, dissemination and implementation resources remain limited, and prevention services remain notably inaccessible to the very populations at highest risk for HIV infection. Internet delivery of HIV risk-reduction programming has promise as a mechanism for extending the reach of existing prevention efforts and overcoming barriers associated with traditional service delivery. This article: (1) details the development process for the creation of SiHLEWeb, a web-adapted version of an evidence-based, culturally-informed HIV prevention program traditionally delivered to female African-American adolescents via an in-person group format; and (2) presents findings from quantitative and qualitative usability testing conducted among 18 African-American girls (13–18). Results suggest that users found the website improved knowledge and learning, was helpful, efficient to use, and generally attractive. Users reported some concerns about website navigation. Implications for internet delivery of health prevention programming are discussed. PMID:25167865

  3. SiHLEWeb.com: Development and usability testing of an evidence-based HIV prevention website for female African-American adolescents.

    PubMed

    Danielson, Carla Kmett; McCauley, Jenna L; Gros, Kirstin Stauffacher; Jones, Andrea M; Barr, Simone C; Borkman, April L; Bryant, Brittany G; Ruggiero, Kenneth J

    2016-06-01

    African-American adolescent girls are at disproportionate risk for HIV infection. Although numerous evidence-based risk-reduction interventions exist, dissemination and implementation resources remain limited, and prevention services remain notably inaccessible to the very populations at highest risk for HIV infection. Internet delivery of HIV risk-reduction programming has promise as a mechanism for extending the reach of existing prevention efforts and overcoming barriers associated with traditional service delivery. This article (1) details the development process for the creation of SiHLEWeb, a web-adapted version of an evidence-based, culturally informed HIV prevention program traditionally delivered to female African-American adolescents via an in-person group format, and (2) presents findings from quantitative and qualitative usability testing conducted among 18 African-American girls (13-18 years). Results suggest that users found the website improved knowledge and learning, was helpful, efficient to use, and generally attractive. Users reported some concerns about website navigation. Implications for Internet delivery of health prevention programming are discussed. PMID:25167865

  4. Intermittency and lifetime of the 625 Hz quasi-periodic oscillation in the 2004 hyperflare from the magnetar SGR 1806-20 as evidence for magnetic coupling between the crust and the core

    SciTech Connect

    Huppenkothen, Daniela; Watts, Anna L.; Levin, Yuri

    2014-10-01

    Quasi-periodic oscillations (QPOs) detected in the 2004 giant flare from SGR 1806-20 are often interpreted as global magneto-elastic oscillations of the neutron star. There is, however, a large discrepancy between theoretical models, which predict that the highest frequency oscillations should die out rapidly, and the observations, which suggested that the highest-frequency signals persisted for ∼100 s in X-ray data from two different spacecraft. This discrepancy is particularly important for the high-frequency QPO at ∼625 Hz. However, previous analyses did not systematically test whether the signal could also be present in much shorter data segments, more consistent with the theoretical predictions. Here, we test for the presence of the high-frequency QPO at 625 Hz in data from both the Rossi X-ray Timing Explorer (RXTE) and the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) systematically both in individual rotational cycles of the neutron star, as well as averaged over multiple successive rotational cycles at the same phase. We find that the QPO in the RXTE data is consistent with being only present in a single cycle, for a short duration of ∼0.5 s, whereas the RHESSI data are as consistent with a short-lived signal that appears and disappears as with a long-lived QPO. Taken together, this data provides evidence for strong magnetic interaction between the crust and the core.

  5. Intermittency and Lifetime of the 625 Hz Quasi-periodic Oscillation in the 2004 Hyperflare from the Magnetar SGR 1806-20 as Evidence for Magnetic Coupling between the Crust and the Core

    NASA Astrophysics Data System (ADS)

    Huppenkothen, Daniela; Watts, Anna L.; Levin, Yuri

    2014-10-01

    Quasi-periodic oscillations (QPOs) detected in the 2004 giant flare from SGR 1806-20 are often interpreted as global magneto-elastic oscillations of the neutron star. There is, however, a large discrepancy between theoretical models, which predict that the highest frequency oscillations should die out rapidly, and the observations, which suggested that the highest-frequency signals persisted for ~100 s in X-ray data from two different spacecraft. This discrepancy is particularly important for the high-frequency QPO at ~625 Hz. However, previous analyses did not systematically test whether the signal could also be present in much shorter data segments, more consistent with the theoretical predictions. Here, we test for the presence of the high-frequency QPO at 625 Hz in data from both the Rossi X-ray Timing Explorer (RXTE) and the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) systematically both in individual rotational cycles of the neutron star, as well as averaged over multiple successive rotational cycles at the same phase. We find that the QPO in the RXTE data is consistent with being only present in a single cycle, for a short duration of ~0.5 s, whereas the RHESSI data are as consistent with a short-lived signal that appears and disappears as with a long-lived QPO. Taken together, this data provides evidence for strong magnetic interaction between the crust and the core.

  6. Early Formation of Terrestrial Crust

    NASA Astrophysics Data System (ADS)

    Harrison, T. M.; Schmitt, A. K.; McCulloch, M. T.; Lovera, O. M.

    2007-12-01

    indicate essentially continuous derivation of crust from the mantle from 4.5 to 4.2 Ga, concurrent with recycling into the mantle and internal crustal re-working. These results represent further evidence that by 4.35 Ga, portions of the crust had taken on continental characteristics.

  7. Electrical signature of modern and ancient tectonic processes in the crust of the Atlas mountains of Morocco

    NASA Astrophysics Data System (ADS)

    Ledo, Juanjo; Jones, Alan G.; Siniscalchi, Agata; Campanyà, Joan; Kiyan, Duygu; Romano, Gerardo; Rouai, Mohamed; TopoMed MT Team

    2011-04-01

    The Atlas Mountains in Morocco are considered as type examples of intracontinental mountain chains, with high topography that contrasts with moderate crustal shortening and thickening. Whereas recent geological studies and geodynamic modelling suggest the existence of dynamic topography to explain this apparent contradiction, there is a lack of modern geophysical data at the crustal scale to corroborate this hypothesis. To address this deficiency, magnetotelluric data were recently acquired that image the electrical resistivity distribution of the crust from the Middle Atlas to the Anti-Atlas, crossing the tabular Moulouya plain and the High Atlas. All tectonic units show different, distinct and unique electrical signatures throughout the crust reflecting the tectonic history of development of each one. In the upper crust, electrical resistivity values and geometries can be associated to sediment sequences in the Moulouya and Anti-Atlas and to crustal scale fault systems in the High Atlas developed likely during Cenozoic times. In the lower crust, the low resistivity anomaly found below the Moulouya plain, together with other geophysical (low velocity anomaly, lack of earthquakes and minimum Bouguer anomaly) and geochemical (Neogene-Quaternary intraplate alkaline volcanic fields) evidences, infer the existence of a small degree of partial melt at the base of the crust. Resistivity values suggest a partial melt fraction of the order of 2-8%. The low resistivity anomaly found below the Anti-Atlas may be associated with a relict subduction of Precambrian oceanic sediments, or to precipitated minerals during the release of fluids from the mantle during the accretion of the Anti-Atlas to the West African Supercontinent during the Panafrican orogeny (ca. 685 Ma).

  8. Physical constraints on dolomite crust formation, Ambergris Cay Belize

    SciTech Connect

    Birdwell, B.A.; Bischoff, W.D.; Mazzullo, S.J. )

    1990-05-01

    Dolomitic crusts forming on a peritidal flat on Ambergris Cay, Belize, occur beneath surface sediment adjacent to, but not within, small saline (60-90 ppt) ponds. Upper crusts, 2-12 cm thick forming at or slightly below the water table (approximately equivalent to lagoon water level) are areally restricted by (1) ponds where sediment lies below 20-50 cm of water, (2) high and relatively dry areas where sediment accumulation of more than 15 cm above water level supports diverse vegetation, and (3) low areas affected by mangrove encroachment where preexisting crusts are perforated by roots and displaced. The lower crusts occur immediately above the Pleistocene in lows beneath the Holocene sediment and on exposed Pleistocene surfaces. Estimates from x-ray diffraction analysis indicate 80-100% dolomite content within the upper crusts and 50-60% dolomite content in the lower crusts. Unlithified sediment above and below the upper crust contain up to 80% dolomite. Compositions range from Ca{sub 56}, Mg{sub 44} in the upper crusts to Ca{sub 60} Mg{sub 40} in the lower crusts. There is no correlation between stoichiometry and ordering in the dolomites; all are poorly ordered as indicated by very weak (015) and (021) superstructure peaks. Where crusts are not 100% dolomite, the dolomite is evident as euhedral cements within pores, especially within foraminiferal tests, and as micrite along algal laminations and walls of burrows. However, preliminary examinations with scanning electron microscopy and energy dispersive x-ray mapping show that magnesium enrichment is pervasive within these crusts and may represent Mg-enrichment of calcite as an intermediate stage in dolomite formation.

  9. Zircon Lu-Hf isotopes and granite geochemistry of the Murchison Domain of the Yilgarn Craton: Evidence for reworking of Eoarchean crust during Meso-Neoarchean plume-driven magmatism

    NASA Astrophysics Data System (ADS)

    Ivanic, Timothy J.; Van Kranendonk, Martin J.; Kirkland, Christopher L.; Wyche, Stephen; Wingate, Michael T. D.; Belousova, Elena A.

    2012-09-01

    New in situ Lu-Hf data on zircons from GSWA geochronology samples has provided a unique isotopic dataset with a high temporal resolution for the Murchison Domain of the Yilgarn Craton in Western Australia. These data identify extended periods of juvenile mantle input (positive ɛHf values) into the crust firstly at c. 2980 Ma and then from c. 2820 Ma to c. 2640 Ma with significant pulses of crustal recycling at c. 2750 Ma and c. 2620 Ma (highly negative ɛHf values). Geochemical data from well-characterised granitic suites of the Murchison Domain provide additional constraints on the crustal evolution of the area and indicate a prolonged period of crustal melting and remelting at progressively shallower depths from c. 2750 to c. 2600 Ma. At c. 2760-2753 Ma, widespread calc-alkaline, intermediate to silicic volcanic rocks of the Polelle Group were erupted, accompanied by intrusion of felsic to intermediate melts derived from a variety of crustal sources that likely formed by partial mixing with basaltic melts. The intrusive rocks include a wide geochemical array of rocks in the Cullculli and Eelya suites that were sourced over a wide range of crustal depths. At this time a major departure to negative ɛHf values (<-5) occurred, indicating sampling of c. 3.80 Ga model aged source rocks as well as continued juvenile input. Post-volcanic granitic rocks emplaced between c. 2710 and c. 2600 Ma show geochemical evidence for progressive fractionation through time and derivation from an evolving crustal source. We interpret the driving force for this protracted history of mantle and crustal melting to be two mantle plumes at 2.81 and 2.72 Ga. These data document the process of cratonization through progressive melt depletion of the lower crust, progressively fractionating and shallower melts, culminating with a final phase of crustal recycling (ɛHf < - 5) and the cessation of juvenile input at c. 2630-2600 Ma during intrusion of the Bald Rock Supersuite, resulting in

  10. Isobaric heating and cooling path of the lower crust of a Variscan exotic unit: evidences from P -T estimates in NW Iberian metapelitic granulites

    NASA Astrophysics Data System (ADS)

    Alampi, A.; Gomez Barreiro, J.; Alvarez Valero, A.; Castiñeiras, P.

    2012-12-01

    Allochthonous complexes (AC) in NW Iberia consist of a pile of exotic units characterized by distinct tectonothermal evolution and lithological association, and separated from each other by tectonic contacts, either thrust or extensional detachments. In the Órdenes AC, three groups of units are recognized from bottom to top in the pile: Basal, Ophiolitic and Upper units. Upper units comprise an ensemble of arc-related rocks with a lower section that underwent a high-P and high-T (HP-HT) evolution, and an upper section with an intermediate - pressure (IP) evolution. Extensional detachments have been commonly identifying at the boundary between HP-HT and IP Upper units, like the Fornás and Corredoiras detachments. Pelitic granulites from one IP upper unit, the O Pino unit, have been investigated. Petrologic studies reveal an isobaric tectono-metamorphic crustal evolution throughout a multidisciplinary integration of: (i) detailed microstructural analysis; (ii) EMP mineral chemistry; (iii) mass-balance of the key and representative chemical reactions observed in the microstructures and subsequent interpretation of the reaction sequence; (iv) P-T estimates and paths from phase diagram modeling. Results in the NCKFMASHT system describe an isobaric (c. 7 kbar) continuous heating (and later cooling) evolution ranging from c. 620 to 680 C crossing into the melt-bearing stability fields. These achieved anatectic conditions are evidenced by the presence of both leucosomes (quartz, plagioclase and muscovite) and glass inclusions, mainly in local garnet cores through the dehydration/melting reactions of muscovite first and biotite later. Chemically distinct generations of garnet and plagioclase are evident and stoichiometrically balance each other in continuous reactions. They are consistent with the observations of both a garnet overgrowth and large patches of plagioclase which host euhedral, smaller garnets. In the cooling episode, the newly-grown garnet reacted with melt

  11. Steady State Growth of Continental Crust?

    NASA Astrophysics Data System (ADS)

    Bowring, S. A.; Bauer, A.; Dudas, F. O.; Schoene, B.; McLean, N. M.

    2012-12-01

    any age. If one accepts that the probability of preserving old crust decreases with increasing age, the few exposures of rocks older than 3.5 Ga should not be surprising. The thickness and compositional differences between Archean and younger lithospheric mantle are not fully understood nor is the role of thicker buoyant mantle in preserving continental crust; these lead to the question of whether the preserved rock record is representative of what formed. It is notable that the oldest known rocks, the ca. 4.0 Ga Acasta Gneisses, are tonalities-granodiorites-granites with evidence for the involvement of even older crust and that the oldest detrital zircons from Australia (ca. 4.0-4.4 Ga) are thought to have been derived from granitoid sources. The global Hf and Nd isotope databases are compatible with both depleted and enriched sources being present from at least 4.0 Ga to the present and that the lack of evolution of the MORB source or depleted mantle is due to recycling of continental crust throughout earth history. Using examples from the Slave Province and southern Africa, we argue that Armstrong's concept of steady state crustal growth and recycling via plate tectonics still best explains the modern geological and geochemical data.

  12. Neodymium-142 evidence for Hadean mafic crust.

    PubMed

    O'Neil, Jonathan; Carlson, Richard W; Francis, Don; Stevenson, Ross K

    2008-09-26

    Neodymium-142 data for rocks from the Nuvvuagittuq greenstone belt in northern Quebec, Canada, show that some rock types have lower 142Nd/144Nd ratios than the terrestrial standard (epsilon142Nd = -0.07 to -0.15). Within a mafic amphibolite unit, 142Nd/144Nd ratios correlate positively with Sm/Nd ratios and produce a 146Sm-142Nd isochron with an age of 4280(-81)(+53) million years. These rocks thus sample incompatible-element-enriched material formed shortly after Earth formation and may represent the oldest preserved crustal section on Earth. PMID:18818357

  13. Feasibility of Delivering Evidence-Based HIV/STI Prevention Programming to A Community Sample of African-American Teen Girls via the Internet

    PubMed Central

    Danielson, Carla Kmett; McCauley, Jenna L.; Jones, Andrea; Borkman, April O.; Miller, Stephanie; Ruggiero, Kenneth J.

    2014-01-01

    The current study examined the feasibility of an HIV/STI prevention intervention for African American female adolescents. The intervention, SiHLEWeb, is a web-based adaptation of the evidence-based intervention, Sistas, Informing, Healing, Living, and Empowering (SiHLE). Participants were 41 African-American girls aged 13 to 18 years, recruited in collaboration with community partners (local high schools, Department of Juvenile Justice, child advocacy center, medical university). Results support the feasibility of recruitment, screening, and follow-up retention methods. The majority (63.4%) of recruited participants completed the intervention, taking an average of 4.5 site visits. Completers of SiHLEWeb demonstrated increases in knowledge regarding HIV/STI risks and risk reduction behavior, as well as significant increases in condom use self-efficacy. Findings provide preliminary support for the large-scale, randomized-controlled trial of the efficacy of SiHLEWeb to reduce high-risk sexual behavior among female African-American adolescents. PMID:24059877

  14. The geodynamic province of transitional crust adjacent to magma-poor continental margins

    NASA Astrophysics Data System (ADS)

    Sibuet, J.; Tucholke, B. E.

    2011-12-01

    Two types of 'transitional crust' have been documented along magma-poor rifted margins. One consists of apparently sub-continental mantle that has been exhumed and serpentinized in a regime of brittle deformation during late stages of rifting. A second is highly thinned continental crust, which in some cases is known to have been supported near sea level until very late in the rift history and thus is interpreted to reflect depth-dependent extension. In both cases it is typically assumed that formation of oceanic crust occurs shortly after the breakup of brittle continental crust and thus that the transitional crust has relatively limited width. We here examine two representative cases of transitional crust, one in the Newfoundland-Iberia rift (exhumed mantle) and one off the Angola-Gabon margin (highly thinned continental crust). Considering the geological and geophysical evidence, we propose that depth-dependent extension (riftward flow of weak lower/middle continental crust and/or upper mantle) may be a common phenomenon on magma-poor margins and that this can result in a much broader zone of transitional crust than has hitherto been assumed. Transitional crust in this extended zone may consist of sub-continental mantle, lower to middle continental crust, or some combination thereof, depending on the strength profile of the pre-rift continental lithosphere. Transitional crust ceases to be emplaced (i.e., final 'breakup' occurs) only when emplacement of heat and melt from the rising asthenosphere becomes dominant over lateral flow of the weak lower lithosphere. This model implies a two-stage breakup: first the rupture of the brittle upper crust and second, the eventual emplacement of oceanic crust. Well-defined magnetic anomalies can form in transitional crust consisting of highly serpentinized, exhumed mantle, and they therefore are not diagnostic of oceanic crust. Where present in transitional crust, these anomalies can be helpful in interpreting the rifting

  15. Reflections on Creemers' Comprehensive Model of Educational Effectiveness for Reading Literacy: South African Evidence from PIRLS 2006

    ERIC Educational Resources Information Center

    van Staden, Surette; Howie, Sarah

    2014-01-01

    This study reports on a doctoral investigation (Van Staden, 2010) to identify and explain relationships between some major learner- and school-level factors associated with successful reading in Grade 5. South African classrooms are characterised by large variation, with linguistically and socio-economically heterogeneous groups of learners.…

  16. Advancing the Africentric Paradigm Shift Discourse: Building toward Evidence-Based Africentric Interventions in Social Work Practice with African Americans

    ERIC Educational Resources Information Center

    Gilbert, Dorie J.; Harvey, Aminifu R.; Belgrave, Faye Z.

    2009-01-01

    For over a decade, a number of social work scholars have advocated for an Africentric paradigm shift in social work practice with African Americans; yet the paradigm shift has been slow in coming with respect to infusing Africentric theory and interventions into social work practice, education, and research. Interventions that infuse Africentric…

  17. Marriage and Health in the Transition to Adulthood: Evidence for African Americans in the Add Health Study

    ERIC Educational Resources Information Center

    Harris, Kathleen Mullan; Lee, Hedwig; DeLeone, Felicia Yang

    2010-01-01

    This article explores the relationships among early marriage (before age 26 years), cohabitation, and health for African Americans and Whites during the transition to adulthood using the National Longitudinal Study of Adolescent Health (Add Health). The study examines three categories of health outcomes relevant to young adulthood: physical…

  18. College Athletic Reputation and College Choice among African American High School Seniors: Evidence from the Educational Longitudinal Study

    ERIC Educational Resources Information Center

    Braddock, Jomills Henry, II; Lv, Hua; Dawkins, Marvin P.

    2008-01-01

    This study extends research on college choice, with recent national survey data, by examining what African American students say about the importance of college athletic reputation in choosing which school to attend. We use the Educational Longitudinal Survey to examine the overall distribution of self-reported factors that shape college choices…

  19. Continental crust: a geophysical approach

    SciTech Connect

    Meissner, R.

    1986-01-01

    This book develops an integrated and balanced picture of present knowledge of the continental crust. Crust and lithosphere are first defined, and the formation of crusts as a general planetary phenomenon is described. The background and methods of geophysical studies of the earth's crust and the collection of related geophysical parameters are examined. Creep and friction experiments and the various methods of radiometric age dating are addressed, and geophysical and geological investigations of the crustal structure in various age provinces of the continents are studied. Specific tectonic structures such as rifts, continental margins, and geothermal areas are discussed. Finally, an attempt is made to give a comprehensive view of the evolution of the continental crust and to collect and develop arguments for crustal accretion and recycling. 647 references.

  20. Dynamics of the Precambrian Continental Crust

    NASA Astrophysics Data System (ADS)

    Perchuk, L. L.; Gerya, T. V.; van Reenen, D. D.; Smit, C. A.

    2003-04-01

    The Precambrian continental crust is mainly composed of (1) granite greenstone belts (GGB) and (2) granulite facies complexes (GFC). The GFC are often separated from GGB by inward dipping crustal scale shear zones with characteristic sense of movements reflecting thrusting of GFC onto cratonic rocks. The isotope age of the shear zones is identical to GFC, while the latter are always younger than the granite greenstone belts. The dynamics relationships between these two geological units strongly determine tectonic evolution of the Precambrian continental crust. Numerous thermobarometric studies of magmatic and metamorphic rocks show that the Archaean to Early Protorozoic crust as well as the Mantle were hot and therefore relatively soft. Such geothermal regimes may limit separation and movement of micro continents, limiting collisional mechanisms in evolution of the Precambrian crust. The goal of this paper is to show evidence for an alterative model that is based on the mechanism of gravitational redistribution of rocks within the Precambrian continental crust, which might be initiated by a fluid/heat flow related to mantle plumes. The model is tested on the basis of geological, geochemical, geophysical and petrologic data for many paired GFT GGB complexes around the word. Studied granulite complexes are located in between Archaean GGB from which they are separated by inward dipping crustal scale shear zones with reverse sense of movements. The most important evidence for this mechanism is: (i) the near isobaric cooling (IC) and (ii) decompression cooling (DC) shapes of the retrograde P T paths recorded in GFC, while rocks from the juxtaposed GGB in footwalls of the bounding shear zones record P T loops. The Pmax of the loops corresponds to the Pmin, recorded in GFC. Thus the GGB P T loop reflects the burial and ascending of the juxtaposed GGB while the GFC P T path records the exhumation only. The identical isotopic age of GFC and contacting rocks from the shear

  1. Habitability Of Europa's Crust

    NASA Astrophysics Data System (ADS)

    Greenberg, R.; Tufts, B. R.; Geissler, P.; Hoppa, G.

    Physical characterization of Europa's crust shows it to be rich in potentially habitable niches, with several timescales for change that would allow stability for organisms to prosper and still require and drive evolution and adaptation. Studies of tectonics on Europa indicate that tidal stress causes much of the surface cracking, that cracks pen- etrate through to liquid water (so the ice must be thin), and that cracks continue to be worked by tidal stress. Thus a global ocean is (or was until recently) well linked to the surface. Daily tidal flow (period~days) transports substances up and down through the active cracks, mixing surface oxidants and fuels (cometary material) with the oceanic reservoir of endogenic and exogenic substances. Organisms moving with the flow or anchored to the walls could exploit the disequilibrium chemistry, and those within a few meters of the surface could photosynthesize. Cracks remain active for at least ~10,000 yr, but deactivate as nonsynchronous rotation moves them to different stress regimes in less than a million yr. Thus, to survive, organisms squeezed into the ocean must migrate to new cracks, and those frozen in place must hibernate. Most sites remelt and would release captive organisms within about a million yr based on the prevalence of chaotic terrain, which covers nearly half of Europa. Linkage of the ocean to the surface also could help sustain life in the ocean by delivering oxidants and fuels. Suboceanic volcanism (if any) could provide additional sites and support for life, but is not necessary. Recent results support this model. We further constrain the non-synchronous rotation rate, demonstrate the plausibility of episodic melt-through, show that characteristics of pits and uplift features do not imply thick ice, and demonstrate polar wander, i.e. that the ice crust is detached from the solid interior and has slipped as a unit relative to the spin axis. Thus Europa's biosphere (habitable if not inhabited) likely

  2. Composition and origin of ferromanganese crusts from equatorial western Pacific seamounts

    NASA Astrophysics Data System (ADS)

    Wang, Guozhi; Jansa, Luba; Chu, Fengyou; Zou, Can; Sun, Guosheng

    2015-04-01

    In the equatorial western Pacific, iron-manganese oxyhydroxide crusts (Fe-Mn crusts) and nodules form on basaltic seamounts and on the top of drowned carbonate platform guyots that have been swept free of pelagic sediments. To date, the Fe-Mn crusts have been considered to be almost exclusively of abiotic origin. However, it has recently been suggested that these crusts may be a result of biomineralization. Although the Fe-Mn crust textures in the equatorial western Pacific are similar to those constructed by bacteria and algae, and biomarkers also document the existence of bacteria and algae dispersed within the Fe-Mn crusts, the precipitation, accumulation and distribution of elements, such as Fe, Mn, Ni and Co in Fe-Mn crusts are not controlled by microbial activity. Bacteria and algae are only physically incorporated into the crusts when dead plankton settle on the ocean floor and are trapped on the crust surface. Geochemical evidence suggests a hydrogenous origin of Fe-Mn crusts in the equatorial western Pacific, thus verifying a process for Fe-Mn crusts that involves the precipitation of colloidal phases from seawater followed by extensive scavenging of dissolved trace metals into the mineral phase during crust formation.

  3. Where is the faith? Using a CBPR approach to propose adaptations to an evidence-based HIV prevention intervention for adolescents in African American faith settings.

    PubMed

    Lightfoot, Alexandra F; Taggart, Tamara; Woods-Jaeger, Briana A; Riggins, Linda; Jackson, Melvin R; Eng, Eugenia

    2014-08-01

    African American adolescents are at increased risk for HIV/AIDS. Using a community-based participatory research approach, we engaged three black churches in adapting an evidence-based HIV prevention intervention, Focus on Youth (FOY)+ImPACT, for faith settings. To identify potential adaptations to increase FOY's relevance, utility, and efficacy for faith settings, we conducted eight focus groups pre- and post-intervention. Recommendations for maintaining FOY's core elements and enhancing its cultural authenticity include the following: incorporating faith tools, building pastor capacity, strengthening parent-child communication skills, and expanding social support for parents and youth. Engaging faith communities in adapting and implementing evidence-based HIV prevention programs could reduce HIV/AIDS disparities. PMID:24639068

  4. Mean reversion in the current account of forty-eight african countries: Evidence from the Panel SURADF test

    NASA Astrophysics Data System (ADS)

    Chu, Hsiao-Ping; Chang, Tsangyao; Chang, Hsu-Ling; Su, Chi-Wei; Yuan, Young

    2007-10-01

    Here, the Panel seemingly unrelated regressions augmented Dickey-Fuller test (SURADF) test, first introduced and advanced by Breuer et al. [Misleading inferences from panel unit-root tests with an illustration from purchasing power parity, Rev. Int. Econ. 9(3) (2001) 482-493], is used to investigate the mean-reverting behavior of the current account of 48 African countries during the 1980-2004 periods. The empirical results from numerous panel-based unit root tests, conducted earlier, indicated that the current account of each of these countries is stationary; however, when Breuer et al.'s (2001) Panel SURADF test is conducted, it is found that a unit root exists in the current account of 11 of the countries studied. These results have one extremely important policy implication for the 48 African countries studied: the current account deficit of most is sustainable, and thus signifying that those nations should have no incentive to default on their international debt.

  5. Geochemical evidence for African dust inputs to soils of western Atlantic islands: Barbados, the Bahamas, and Florida

    USGS Publications Warehouse

    Muhs, D.R.; Budahn, J.R.; Prospero, J.M.; Carey, S.N.

    2007-01-01

    We studied soils on high-purity limestones of Quaternary age on the western Atlantic Ocean islands of Barbados, the Florida Keys, and the Bahamas. Potential soil parent materials in this region, external to the carbonate substrate, include volcanic ash from the island of St. Vincent (near Barbados), volcanic ash from the islands of Dominica and St. Lucia (somewhat farther from Barbados), the fine-grained component of distal loess from the lower Mississippi River Valley, and wind-transported dust from Africa. These four parent materials can be differentiated using trace elements (Sc, Cr, Th, and Zr) and rare earth elements that have minimal mobility in the soil-forming environment. Barbados soils have compositions that indicate a complex derivation. Volcanic ash from the island of St. Vincent appears to have been the most important influence, but African dust is a significant contributor, and even Mississippi River valley loess may be a very minor contributor to Barbados soils. Soils on the Florida Keys and islands in the Bahamas appear to have developed mostly from African dust, but Mississippi River valley loess may be a significant contributor. Our results indicate that inputs of African dust are more important to the genesis of soils on islands in the western Atlantic Ocean than previously supposed. We hypothesize that African dust may also be a major contributor to soils on other islands of the Caribbean and to soils in northern South America, central America, Mexico, and the southeastern United States. Dust inputs to subtropical and tropical soils in this region increase both nutrient-holding capacity and nutrient status and thus may be critical in sustaining vegetation. Copyright 2007 by the American Geophysical Union.

  6. First U-Pb detrital zircon ages from Numidian sandstones in Southern Apennines (Italy): Evidences of African provenance

    NASA Astrophysics Data System (ADS)

    Fornelli, Annamaria; Micheletti, Francesca; Langone, Antonio; Perrone, Vincenzo

    2015-05-01

    Two samples of quartz-rich sandstones collected in the Numidian Flysch of Southern Apennines (Italy) have been studied to highlight the provenance of detritus using radiometric dating by LA-ICP-MS of detrital zircons and to compare the obtained ages with those of the Betic and Maghrebian Chains. The provenance of quartzose detritus from European or African Plates is still debated in these Chains, accordingly the ages of the detrital zircons can contribute significantly to discriminate the origin of the quartzose supply. The U-Pb zircon ages (n = 47) vary from 3047 ± 13 Ma (Mesoarchean) to 516 ± 19 Ma (Cambrian). The predominance of Paleo-Proteozoic ages (2500-1600 Ma) and the lack of Hercynian and Alpine ones suggest a provenance of the Numidian supply from North-African cratonic areas during the early-middle Langhian, when the Numidian successions of Southern Apennines were deposited. In addition, a cluster of ages at 773 ± 24 Ma and 668 ± 12 Ma in one sample and at 664 ± 17 Ma in the other sample, calculated on zircon domains with magmatic zoning, testify to an important contribution from Neo-proterozoic "granitic" rocks widely outcropping in the North-African Craton. The age data on detrital zircons from Numidian sandstones in Southern Apennines overlap those found in the Numidian sandstones widespread in the Betic Cordillera and in the Maghrebian Chain from south Spain to Sicily. This suggests that the entire depositional zone in which Numidian Flysch deposited, was fed from a southerly source represented by the African Craton where Archean, Proterozoic and Cambrian rocks widely crop out from the Atlantic coast to the Hoggar and Tibesti Massifs. Finally, it must be outlined that a Meso-Archean zircon age (3047 Ma) has been found in the Numidian Flysch of the Southern Apennines whereas in the Numidian Flysch of the Maghrebian Chain, zircons older than Paleo-proterozoic (1840 Ma) have not yet been found.

  7. Further morphological evidence on South African earliest Homo lower postcanine dentition: Enamel thickness and enamel dentine junction.

    PubMed

    Pan, Lei; Dumoncel, Jean; de Beer, Frikkie; Hoffman, Jakobus; Thackeray, John Francis; Duployer, Benjamin; Tenailleau, Christophe; Braga, José

    2016-07-01

    The appearance of the earliest members of the genus Homo in South Africa represents a key event in human evolution. Although enamel thickness and enamel dentine junction (EDJ) morphology preserve important information about hominin systematics and dietary adaptation, these features have not been sufficiently studied with regard to early Homo. We used micro-CT to compare enamel thickness and EDJ morphology among the mandibular postcanine dentitions of South African early hominins (N = 30) and extant Homo sapiens (N = 26), with special reference to early members of the genus Homo. We found that South African early Homo shows a similar enamel thickness distribution pattern to modern humans, although three-dimensional average and relative enamel thicknesses do not distinguish australopiths, early Homo, and modern humans particularly well. Based on enamel thickness distributions, our study suggests that a dietary shift occurred between australopiths and the origin of the Homo lineage. We also observed that South African early Homo postcanine EDJ combined primitive traits seen in australopith molars with derived features observed in modern human premolars. Our results confirm that some dental morphological patterns in later Homo actually occurred early in the Homo lineage, and highlight the taxonomic value of premolar EDJ morphology in hominin species. PMID:27343773

  8. Giant seismites and megablock uplift in the East African Rift: evidence for Late Pleistocene large magnitude earthquakes.

    PubMed

    Hilbert-Wolf, Hannah Louise; Roberts, Eric M

    2015-01-01

    In lieu of comprehensive instrumental seismic monitoring, short historical records, and limited fault trench investigations for many seismically active areas, the sedimentary record provides important archives of seismicity in the form of preserved horizons of soft-sediment deformation features, termed seismites. Here we report on extensive seismites in the Late Quaternary-Recent (≤ ~ 28,000 years BP) alluvial and lacustrine strata of the Rukwa Rift Basin, a segment of the Western Branch of the East African Rift System. We document examples of the most highly deformed sediments in shallow, subsurface strata close to the regional capital of Mbeya, Tanzania. This includes a remarkable, clastic 'megablock complex' that preserves remobilized sediment below vertically displaced blocks of intact strata (megablocks), some in excess of 20 m-wide. Documentation of these seismites expands the database of seismogenic sedimentary structures, and attests to large magnitude, Late Pleistocene-Recent earthquakes along the Western Branch of the East African Rift System. Understanding how seismicity deforms near-surface sediments is critical for predicting and preparing for modern seismic hazards, especially along the East African Rift and other tectonically active, developing regions. PMID:26042601

  9. Giant Seismites and Megablock Uplift in the East African Rift: Evidence for Late Pleistocene Large Magnitude Earthquakes

    PubMed Central

    Hilbert-Wolf, Hannah Louise; Roberts, Eric M.

    2015-01-01

    In lieu of comprehensive instrumental seismic monitoring, short historical records, and limited fault trench investigations for many seismically active areas, the sedimentary record provides important archives of seismicity in the form of preserved horizons of soft-sediment deformation features, termed seismites. Here we report on extensive seismites in the Late Quaternary-Recent (≤ ~ 28,000 years BP) alluvial and lacustrine strata of the Rukwa Rift Basin, a segment of the Western Branch of the East African Rift System. We document examples of the most highly deformed sediments in shallow, subsurface strata close to the regional capital of Mbeya, Tanzania. This includes a remarkable, clastic ‘megablock complex’ that preserves remobilized sediment below vertically displaced blocks of intact strata (megablocks), some in excess of 20 m-wide. Documentation of these seismites expands the database of seismogenic sedimentary structures, and attests to large magnitude, Late Pleistocene-Recent earthquakes along the Western Branch of the East African Rift System. Understanding how seismicity deforms near-surface sediments is critical for predicting and preparing for modern seismic hazards, especially along the East African Rift and other tectonically active, developing regions. PMID:26042601

  10. The evolution of Mercury's crust: a global perspective from MESSENGER.

    PubMed

    Denevi, Brett W; Robinson, Mark S; Solomon, Sean C; Murchie, Scott L; Blewett, David T; Domingue, Deborah L; McCoy, Timothy J; Ernst, Carolyn M; Head, James W; Watters, Thomas R; Chabot, Nancy L

    2009-05-01

    Mapping the distribution and extent of major terrain types on a planet's surface helps to constrain the origin and evolution of its crust. Together, MESSENGER and Mariner 10 observations of Mercury now provide a near-global look at the planet, revealing lateral and vertical heterogeneities in the color and thus composition of Mercury's crust. Smooth plains cover approximately 40% of the surface, and evidence for the volcanic origin of large expanses of plains suggests that a substantial portion of the crust originated volcanically. A low-reflectance, relatively blue component affects at least 15% of the surface and is concentrated in crater and basin ejecta. Its spectral characteristics and likely origin at depth are consistent with its apparent excavation from a lower crust or upper mantle enriched in iron- and titanium-bearing oxides. PMID:19407196

  11. Employing a teen advisory board to adapt an evidence-based HIV/STD intervention for incarcerated African-American adolescent women.

    PubMed

    Latham, Teaniese P; Sales, Jessica M; Renfro, Tiffaney L; Boyce, Lorin S; Rose, Eve; Murray, Colleen C; Wingood, Gina M; DiClemente, Ralph J

    2012-10-01

    This manuscript assesses priorities and challenges of adolescent females by conducting a meeting with teen advisory board (TAB) members to collect information regarding their lives and experiences pre-, during and post-incarceration in a juvenile detention facility. Multiple themes emerged regarding the impact of incarceration on young African-American females, including experiencing a loss of personal liberties, the importance of making money upon release, unfaithfulness by partners on the 'outside', substance use and lack of control over their environment upon release, including parents, peers and male sexual partners. Based on feedback from TAB members, unique barriers and challenges were identified that suggested areas where adaptations to an evidenced-based HIV/sexually transmitted disease (STD) intervention would be justified to more adequately meet the needs of this particular subgroup of young African-American women. Adaptations to the evidence-based interventions included enhancing activities related to goal setting, emotion regulation skills, decision-making, recognizing and utilizing support networks and addressing the relationship between substance use and risky sexual behavior. Future health education efforts focusing on either the creation of new HIV/STD interventions or adaptations to existing interventions should consider utilizing advisory boards with members of the priority population at the earliest stages of intervention planning. PMID:21368023

  12. Estimation of lower crust magnetization form satellite derived anomaly field

    NASA Technical Reports Server (NTRS)

    Schnetzler, C. C.; Allenby, R. J.

    1983-01-01

    Various lines of evidence point to the lower crust as the source of the long-wavelength magnetic anomaly field measured by the POGO and Magsat satellites. Using seismically determined lower crust thicknesses and equivalent source inversion of the satellite anomaly data, magnetization for the lower crust for much of the United States has been calculated. The average magnetization for two hundred sixty-six 150 x 150 km areas is 3.5 A/m with a standard deviation of 1.1 A/m. These values are consistent with laboratory measurements of mafic-ultramafic rocks expected in the lower crust, and in agreement with previous estimates of lower crust magnetization based on long-wavelength aeromagnetic data. Average lower crust thickness for the same areas is 18.2 km (sigma = 6.4). Thus, over large regions, it appears that variation in magnetization and variation in magnetic layer thickness contribute almost equally in causing the anomaly field variation at satellite altitude.

  13. Financial Decision-making Abilities and Financial Exploitation in Older African Americans: Preliminary Validity Evidence for the Lichtenberg Financial Decision Rating Scale (LFDRS)

    PubMed Central

    Ficker, Lisa J.; Rahman-Filipiak, Annalise

    2015-01-01

    This study examines preliminary evidence for the Lichtenberg Financial Decision Rating Scale (LFDRS), a new person-centered approach to assessing capacity to make financial decisions, and its relationship to self-reported cases of financial exploitation in 69 older African Americans. More than one third of individuals reporting financial exploitation also had questionable decisional abilities. Overall, decisional ability score and current decision total were significantly associated with cognitive screening test and financial ability scores, demonstrating good criterion validity. Financially exploited individuals, and non-exploited individuals, showed mean group differences on the Mini Mental State Exam, Financial Situational Awareness, Psychological Vulnerability, Current Decisional Ability, and Susceptibility to undue influence subscales, and Total Lichtenberg Financial Decision Rating Scale Score. Study findings suggest that impaired decisional abilities may render older adults more vulnerable to financial exploitation, and that the LFDRS is a valid tool for measuring both decisional abilities and financial exploitation. PMID:26285038

  14. The Genetic Structure and History of Africans and African Americans

    PubMed Central

    Tishkoff, Sarah A.; Reed, Floyd A.; Friedlaender, Françoise R.; Ehret, Christopher; Ranciaro, Alessia; Froment, Alain; Hirbo, Jibril B.; Awomoyi, Agnes A.; Bodo, Jean-Marie; Doumbo, Ogobara; Ibrahim, Muntaser; Juma, Abdalla T.; Kotze, Maritha J.; Lema, Godfrey; Moore, Jason H.; Mortensen, Holly; Nyambo, Thomas B.; Omar, Sabah A.; Powell, Kweli; Pretorius, Gideon S.; Smith, Michael W.; Thera, Mahamadou A.; Wambebe, Charles; Weber, James L.; Williams, Scott M.

    2010-01-01

    Africa is the source of all modern humans, but characterization of genetic variation and of relationships among populations across the continent has been enigmatic. We studied 121 African populations, four African American populations, and 60 non-African populations for patterns of variation at 1327 nuclear microsatellite and insertion/deletion markers. We identified 14 ancestral population clusters in Africa that correlate with self-described ethnicity and shared cultural and/or linguistic properties. We observed high levels of mixed ancestry in most populations, reflecting historical migration events across the continent. Our data also provide evidence for shared ancestry among geographically diverse hunter-gatherer populations (Khoesan speakers and Pygmies). The ancestry of African Americans is predominantly from Niger-Kordofanian (~71%), European (~13%), and other African (~8%) populations, although admixture levels varied considerably among individuals. This study helps tease apart the complex evolutionary history of Africans and African Americans, aiding both anthropological and genetic epidemiologic studies. PMID:19407144

  15. Rift Valley fever virus infection in African Buffalo (Syncerus caffer) herds in rural South Africa: Evidence of interepidemic transmission

    USGS Publications Warehouse

    LaBeaud, A.D.; Cross, P.C.; Getz, W.M.; Glinka, A.; King, C.H.

    2011-01-01

    Rift Valley fever virus (RVFV) is an emerging biodefense pathogen that poses significant threats to human and livestock health. To date, the interepidemic reservoirs of RVFV are not well defined. In a longitudinal survey of infectious diseases among African buffalo during 2000-2006, 550 buffalo were tested for antibodies against RVFV in 820 capture events in 302 georeferenced locations in Kruger National Park, South Africa. Overall, 115 buffalo (21%) were seropositive. Seroprevalence of RVFV was highest (32%) in the first study year, and decreased progressively in subsequent years, but had no detectable impact on survival. Nine (7%) of 126 resampled, initially seronegative animals seroconverted during periods outside any reported regional RVFV outbreaks. Seroconversions for RVFV were detected in significant temporal clusters during 2001-2003 and in 2004. These findings highlight the potential importance of wildlife as reservoirs for RVFV and interepidemic RVFV transmission in perpetuating regional RVFV transmission risk. Copyright ?? 2011 by The American Society of Tropical Medicine and Hygiene.

  16. Evidence of novel plant-species specific ammonia oxidizing bacterial clades in acidic South African fynbos soils.

    PubMed

    Ramond, Jean-Baptiste; Lako, Joseph D W; Stafford, William H L; Tuffin, Marla I; Cowan, Don A

    2015-08-01

    Ammonia-oxidizing bacteria (AOB) are essential in the biogeochemical cycling of nitrogen as they catalyze the rate-limiting oxidation of ammonia into nitrite. Since their first isolation in the late 19th century, chemolithoautotrophic AOBs have been identified in a wide range of natural (e.g., soils, sediments, estuarine, and freshwaters) and man created or impacted habitats (e.g., wastewater treatment plants and agricultural soils). However, little is known on the plant-species association of AOBs, particularly in the nutrient-starved fynbos terrestrial biome. In this study, we evaluated the diversity of AOBs in the plant canopy of three South African fynbos-specific plant species, namely Leucadendron xanthoconus, Leucospermum truncatulum and Leucadendron microcephalum, through the construction of amoA-gene clone libraries. Our results clearly demonstrate that plant-species specific and monophyletic AOB clades are present in fynbos canopy soils. PMID:25721729

  17. Fine-Scale Genetic Structure and Cryptic Associations Reveal Evidence of Kin-Based Sociality in the African Forest Elephant

    PubMed Central

    Schuttler, Stephanie G.; Philbrick, Jessica A.; Jeffery, Kathryn J.; Eggert, Lori S.

    2014-01-01

    Spatial patterns of relatedness within animal populations are important in the evolution of mating and social systems, and have the potential to reveal information on species that are difficult to observe in the wild. This study examines the fine-scale genetic structure and connectivity of groups within African forest elephants, Loxodonta cyclotis, which are often difficult to observe due to forest habitat. We tested the hypothesis that genetic similarity will decline with increasing geographic distance, as we expect kin to be in closer proximity, using spatial autocorrelation analyses and Tau Kr tests. Associations between individuals were investigated through a non-invasive genetic capture-recapture approach using network models, and were predicted to be more extensive than the small groups found in observational studies, similar to fission-fusion sociality found in African savanna (Loxodonta africana) and Asian (Elephas maximus) species. Dung samples were collected in Lopé National Park, Gabon in 2008 and 2010 and genotyped at 10 microsatellite loci, genetically sexed, and sequenced at the mitochondrial DNA control region. We conducted analyses on samples collected at three different temporal scales: a day, within six-day sampling sessions, and within each year. Spatial autocorrelation and Tau Kr tests revealed genetic structure, but results were weak and inconsistent between sampling sessions. Positive spatial autocorrelation was found in distance classes of 0–5 km, and was strongest for the single day session. Despite weak genetic structure, individuals within groups were significantly more related to each other than to individuals between groups. Social networks revealed some components to have large, extensive groups of up to 22 individuals, and most groups were composed of individuals of the same matriline. Although fine-scale population genetic structure was weak, forest elephants are typically found in groups consisting of kin and based on matrilines

  18. Sustainability of Intervention Effects of an Evidence-based HIV Prevention Intervention for African American Women who Smoke Crack Cocaine*

    PubMed Central

    Wechsberg, Wendee M.; Novak, Scott P.; Zule, William A.; Browne, Felicia A.; Kral, Alex H.; Ellerson, Rachel Middlesteadt; Kline, Tracy

    2010-01-01

    Background HIV prevention intervention efficacy is often assessed in the short term. Thus, we conducted a long-term (mean 4.4 years) follow-up of a Woman-Focused HIV intervention for African American crack smokers, for which we had previously observed beneficial short-term gains. Methods 455 out-of-treatment African American women in central North Carolina participated in a randomized field experiment and were followed up to determine sustainability of intervention effects across three conditions: the Woman-Focused intervention, a modified NIDA intervention, and a delayed treatment control condition. We compared these groups in terms of HIV risk behavior at short-term follow-up (STFU; 3–6 months) and long-term follow-up (LTFU; average 4 years). Results The analyses revealed two distinct groups at STFU: women who either eliminated or greatly reduced their risk behaviors (low-risk class) and women who retained high levels of risk across multiple risk domains (high-risk class). At STFU, women in the Woman-Focused intervention were more likely to be in the low HIV-risk group than the women in control conditions, but this effect was not statistically significant at LTFU. However, low-risk participants at STFU were less likely to be retained at LTFU, and this retention rate was lowest among women in the Woman-Focused intervention. Conclusions Short-term intervention effects were not observed over four years later, possibly due to differential retention across conditions. The retention of the highest risk women presents an opportunity for extending intervention effects through the booster sessions for those who need it the most. PMID:20219294

  19. Oceanic crust deep seismic survey

    NASA Astrophysics Data System (ADS)

    McBride, J. H.; White, R. S.

    In September 1991, the British Institutions Reflection Profiling Syndicate (BIRPS) collected 578 km of deep seismic reflection profiles over the oceanic crust beneath the Cape Verde abssyal plain in approximately 4900 m of water (Fig. 1). The survey, under the direction of J. H. McBride, was undertaken in response to a proposal made by R. S. White at the 1990 BIRPS open syndicate meeting in Birmingham, England, and was acquired using GECO-PRAKLA'S M/V Bin Hai 511. The survey consisted of two strike lines parallel to magnetic sea-floor lineations and nine orthogonal crossing lines oriented parallel to the spreading direction (Fig. 2). Adjacent lines are spaced at 4 km. For the first time, this provides the ability to map oceanic crust in “3D,” since the line spacing is less than or equal to the Fresnel-zone diameter for the lower crust.

  20. Profiling planktonic foraminiferal crust formation

    NASA Astrophysics Data System (ADS)

    Steinhardt, Juliane; de Nooijer, Lennart L. J.; Brummer, Geert-Jan; Reichart, Gert-Jan

    2015-07-01

    Planktonic foraminifera migrate vertically through the water column during their life, thereby growing and calcifying over a range of depth-associated conditions. Some species form a calcite veneer, crust, or cortex at the end of their lifecycle. This additional calcite layer may vary in structure, composition, and thickness, potentially accounting for most of their total shell mass and thereby dominating the element and isotope signature of the whole shell. Here we apply laser ablation ICP-MS depth profiling to assess variability in thickness and Mg/Ca composition of shell walls of three encrusting species derived from sediment traps. Compositionally, Mg/Ca is significantly lower in the crusts of Neogloboquadrina dutertrei and Globorotalia scitula, as well as in the cortex of Pulleniatina obliquiloculata, independent of the species-specific Mg/Ca of their lamellar calcite shell. Wall thickness accounts for nearly half of the total thickness in both crustal species and nearly a third in cortical P. obliquiloculata, regardless of their initial shell wall thickness. Crust thickness and crustal Mg/Ca decreases toward the younger chambers in N. dutertrei and to a lesser extent, also in G. scitula. In contrast, the cortex of P. obliquiloculata shows a nearly constant thickness and uniform Mg/Ca through the complete chamber wall. Patterns in thickness and Mg/Ca of the crust indicate that temperature is not the dominant factor controlling crust formation. Instead, we present a depth-resolved model explaining compositional differences within individuals and between successive chambers as well as compositional heterogeneity of the crust and lamellar calcite in all three species studied here.

  1. Petrological, geochemical and isotopic investigations on a carbonate-dyke and enclosed pyroxenite xenoliths from Val Mastallone (Ivrea-Verbano Zone): evidence of a cumulate carbonatite in the lower crust?

    NASA Astrophysics Data System (ADS)

    Galli, Andrea; Grassi, Daniele; Burg, Jean-Pierre; Schwab, Leo; Rickli, Jörg; Gianola, Omar

    2016-04-01

    The Ivrea-Verbano Zone (Italy/Switzerland) represents one of the best exposed mantle-crust sections worldwide. Its geological evolution has been governed by the Permian underplating of mantle-derived basic magmas („Mafic Complex") into the high-grade basement of the Southern Alps. In the Ivrea-Verbano Zone, marbles occur as concordant bodies or partly discordant carbonate-dykes. Generally, these dykes are constituted of calcite, diopside, scapolite, contain enclave of the host rocks and display sharp contacts to the host lithologies without evidences of alteration zones. In Val Mastallone, an up to 40 m thick carbonate-dyke with different characteristics occurs within mafic granulites. This dyke is composed of calcite, clinopyroxene and subordinate allanite and zircon. No scapolite is observed. The contacts to the host granulites are characterized by alteration zones composed of actinolite, chlorite, clinozoisite, plagioclase and calcite. The carbonate-dyke bears enclave of phlogopite-amphibole-apatite-rutile-ilmenite ± garnet or spinel clinopyroxenites. These rock type is not outcropping elsewhere in the proximity of the dyke, suggesting a significant transport. Host mafic granulite enclave are found exclusively at the margin of the dyke. Calcite dykelets rich in zircon, baddeleyite and other Ba, U, Th, REE-rich phases cut across the enclave. The carbonate-dyke shows an enrichment of LREE over HREE ((La/Yb)N = 14), with a Σ REE = 338 and Y/Ho = 27. On the chondrite-normalized REE abundances diagram, no Eu anomaly is observed. Mantle-normalized pattern shows strong negative anomalies at Cs, Rb, K, Pb, P, Zr, Hf, Ti and positive Ba, Th, Sr, Nd anomalies, similarly to the "world average carbonatites". Measured absolute trace element concentrations are lower than average carbonatites but significantly higher than typical limestones and similar to cumulate carbonatites found elsewhere in the world (e.g. India, China, Brazil). Grt-bearing clinopyroxenite enclave

  2. Early Pan-African evolution of the basement around Elat, Israel, and the Sinai Peninsula revealed by single-zircon evaporation dating, and implications for crustal accretion rates

    SciTech Connect

    Kroener, A. ); Eyal, M.; Eyal, Y. )

    1990-06-01

    The authors report {sup 207}Pb/{sup 206}Pb single-zircon evaporation ages for early Pan-African rocks from southern Israel and the northeastern Sinai Peninsula, the northernmost extension of the Arabian-Nubian shield. The oldest rocks are metamorphic schists of presumed island-arc derivation; detrital zircons date the source terrain at ca. 800-820 Ma. A major phase of tonalite-trondhjemite plutonism occurred at ca. 760-780 Ma; more evolved granitic rocks were emplaced at about 745 Ma. A metagabbro-metadiorite complex reflects the youngest igneous phase at ca. 640 Ma. We find no evidence for pre-Pan-African crust, and our data document important crust-forming events that correlate with similar episodes elsewhere in the shield. The widespread presence of early Pan-African juvenile rocks (i.e., ca. 760-850 Ma) in many parts of the Arabian-Nubian shield makes this period the most important in the magmatic history of the shield and supports earlier suggestions for unusually high crust-production rates.

  3. Statistics of Magnetar Crusts Magnetoemission

    NASA Astrophysics Data System (ADS)

    Kondratyev, V. N.; Korovina, Yu. V.

    2016-05-01

    Soft repeating gamma-ray (SGR) bursts are considered as magnetoemission of crusts of magnetars (ultranamagnetized neutron stars). It is shown that all the SGR burst observations can be described and systematized within randomly jumping interacting moments model including quantum fluctuations and internuclear magnetic interaction in an inhomogeneous crusty nuclear matter.

  4. The relationship between immigration and depression in South Africa: evidence from the first South African National Income Dynamics Study.

    PubMed

    Tomita, Andrew; Labys, Charlotte A; Burns, Jonathan K

    2014-12-01

    Few studies have examined depression among immigrants in post-apartheid South Africa, and factors that strengthen the relationship between immigration and depression. The first wave of the National Income Dynamics Study was used to investigate links between immigration and depression (n = 15,205). Depression symptoms were assessed using a 10-item version of the Center for Epidemiologic Studies Depression (CES-D) Scale. Immigrants in South Africa had fewer depressive symptoms (CES-D ≥ 10) than locally-born participants (17.1 vs. 32.4%, F = 13.5, p < 0.01). Multilevel mixed-effects logistic regression analyses found that among immigrant populations, younger age (adjusted OR 1.03, 95% CI 1.01-1.05) and black African ethnicity (adjusted OR 3.72, 95% CI 1.29-10.7) were associated with higher depression. Younger age was associated with lower depression among locally-born study participants (adjusted OR 0.98, 95% CI 0.97-0.98). The varying relationship between certain demographic factors, depression and the different mental health challenges among these groups requires closer attention. PMID:24526432

  5. The relationship between immigration and depression in South Africa: Evidence from the first South African National Income Dynamics Study

    PubMed Central

    Tomita, Andrew; Labys, Charlotte A.; Burns, Jonathan K.

    2014-01-01

    Few studies have examined depression among immigrants in post-apartheid South Africa, and factors that strengthen the relationship between immigration and depression. The first wave of the National Income Dynamics Study was used to investigate links between immigration and depression (n=15,205). Depression symptoms were assessed using a 10-item version of the Center for Epidemiologic Studies Depression (CES-D) Scale. Immigrants in South Africa had fewer depressive symptoms (CES-D ≥ 10) than locally-born participants (17.1% vs. 32.4%, F = 13.5, p<0.01). Multilevel mixed-effects logistic regression analyses found that among immigrant populations, younger age (adjusted OR=1.03, 95% CI = 1.01-1.05) and black African ethnicity (adjusted OR=3.72, 95% CI = 1.29-10.7) were associated with higher depression. Younger age was associated with lower depression among locally-born study participants (adjusted OR=0.98, 95% CI = 0.97-0.98). The varying relationship between certain demographic factors, depression and the different mental health challenges among these groups requires closer attention. PMID:24526432

  6. Does Heavy Adolescent Marijuana Lead to Criminal Involvement in Adulthood? Evidence from a Multiwave Longitudinal Study of Urban African Americans

    PubMed Central

    Green, Kerry M.; Doherty, Elaine E.; Stuart, Elizabeth A.; Ensminger, Margaret E.

    2010-01-01

    While marijuana use is common during adolescence, it can have adverse long-term consequences, with serious criminal involvement being one of them. In this study, we utilize longitudinal data from the Woodlawn Study of a community cohort of urban African Americans (N=702) to examine the effects of heavy adolescent marijuana use (20 or more times) on adult criminal involvement, including perpetration of drug, property and violent crime, as well as being arrested and incarcerated. Utilizing propensity score matching to take into account the shared risk factors between drug use and crime, regression analyses on the matched samples show that heavy adolescent marijuana use may lead to drug and property crime and criminal justice system interactions, but not violent crime. The significant associations of early heavy marijuana use with school drop-out and the progression to cocaine and/or heroin use only partially account for these findings. Results suggest that the prevention of heavy marijuana use among adolescents could potentially reduce the perpetration of drug and property crime in adulthood, as well as the burden on the criminal justice system, but would have little effect on violent crime. PMID:20598815

  7. Permeability within basaltic oceanic crust

    NASA Astrophysics Data System (ADS)

    Fisher, Andrew T.

    1998-05-01

    Water-rock interactions within the seafloor are responsible for significant energy and solute fluxes between basaltic oceanic crust and the overlying ocean. Permeability is the primary hydrologic property controlling the form, intensity, and duration of seafloor fluid circulation, but after several decades of characterizing shallow oceanic basement, we are still learning how permeability is created and distributed and how it changes as the crust ages. Core-scale measurements of basaltic oceanic crust yield permeabilities that are quite low (generally 10-22 to 10-17 m²), while in situ measurements in boreholes suggest an overlapping range of values extending several orders of magnitude higher (10-18 to 10-13 m²). Additional indirect estimates include calculations made from borehole temperature and flow meter logs (10-16 to 10-11 m²), numerical models of coupled heat and fluid flow at the ridge crest and within ridge flanks (10-16 to 10-9 m²), and several other methods. Qualitative indications of permeability within the basaltic oceanic crust come from an improved understanding of crustal stratigraphy and patterns of alteration and tectonic modification seen in ophiolites, seafloor samples and boreholes. Difficulties in reconciling the wide range of estimated permeabilities arise from differences in experimental scale and critical assumptions regarding the nature and distribution of fluid flow. Many observations and experimental and modeling results are consistent with permeability varying with depth into basement and with primary basement lithology. Permeability also seems to be highly heterogeneous and anisotropic throughout much of the basaltic crust, as within crystalline rocks in general. A series of focused experiments is required to resolve permeability in shallow oceanic basement and to directly couple upper crustal hydrogeology to magmatic, tectonic, and geochemical crustal evolution.

  8. Bioalteration of basaltic glass in the oceanic crust

    NASA Astrophysics Data System (ADS)

    Furnes, Harald; Staudigel, Hubert; Thorseth, Ingunn H.; Torsvik, Terje; Muehlenbachs, Karlis; Tumyr, Ole

    2001-08-01

    Bioalteration of Quaternary to Early Cretaceous basaltic glass from pillow lavas of the upper oceanic crust can be documented in Deep Sea Drilling Project/Ocean Drilling Program (DSDP/ODP) samples from shallow to deep drill holes from the north to central Atlantic Ocean, Lau Basin, and Costa Rica Rift, a wide range of marine settings. Biogenerated textures are rooted in fractures and occur as two main types, a granular type and a tubular type. The granular type, common at all depths within the volcanic pile, appears as solid bands, semicircles or irregular patches of individual and/or coalesced spherical bodies, mostly 0.2-0.6 μm in diameter, with irregular protrusions into the fresh glass. The tubular type is more common at deeper levels in the crust and consists of thin tubes, sometime branching bodies, mostly 20-30 μm long and are more common at deeper levels. The upper crust displays a large variability in the relative importance of biotic to abiotic alteration, and the degree of bioalteration appears to decrease with depth. Thus the fraction of bioalteration of the total alteration of the glass ranges from 20-90% in the upper 300 m down to a maximum of 10% at about 500 m depth. This might be due to a natural variability in the abundance of bioaltered glass or to biased sampling from low drilling recovery of relatively young crust. The proportion of bioaltered to abiotically altered glass does not show any systematic variations with age of the crust. Thus bioalteration lasts as long as abiotic alteration, i.e., for as long as water is available to the hydration of the oceanic crust. Evidence from heat flow measurements suggests that hydrothermal circulation lasts until at least ˜70 Ma, and thus the deep biosphere is likely to expand at least into crust of this age.

  9. Investigating population differentiation in a major African agricultural pest: evidence from geometric morphometrics and connectivity suggests high invasion potential.

    PubMed

    Karsten, M; Addison, P; Jansen van Vuuren, B; Terblanche, J S

    2016-07-01

    The distribution, spatial pattern and population dynamics of a species can be influenced by differences in the environment across its range. Spatial variation in climatic conditions can cause local populations to undergo disruptive selection and ultimately result in local adaptation. However, local adaptation can be constrained by gene flow and may favour resident individuals over migrants-both are factors critical to the assessment of invasion potential. The Natal fruit fly (Ceratitis rosa) is a major agricultural pest in Africa with a history of island invasions, although its range is largely restricted to south east Africa. Across Africa, C. rosa is genetically structured into two clusters (R1 and R2), with these clusters occurring sympatrically in the north of South Africa. The spatial distribution of these genotypic clusters remains unexamined despite their importance for understanding the pest's invasion potential. Here, C. rosa, sampled from 22 South African locations, were genotyped at 11 polymorphic microsatellite loci and assessed morphologically using geometric morphometric wing shape analyses to investigate patterns of population structure and determine connectedness of pest-occupied sites. Our results show little to no intraspecific (population) differentiation, high population connectivity, high effective population sizes and only one morphological type (R2) within South Africa. The absence of the R1 morphotype at sites where it was previously found may be a consequence of differences in thermal niches of the two morphotypes. Overall, our results suggest high invasion potential of this species, that area-wide pest management should be undertaken on a country-wide scale, and that border control is critical to preventing further invasions. PMID:27085997

  10. Biogeography and molar morphology of Pleistocene African elephants: new evidence from Elandsfontein, Western Cape Province, South Africa

    NASA Astrophysics Data System (ADS)

    Smith, Kathlyn M.; Stynder, Deano D.

    2015-05-01

    Elandsfontein (EFT) is a Middle Pleistocene archaeological/paleontological site located in the Western Cape Province of South Africa. The largest herbivore in the assemblage is Loxodonta atlantica zulu, an extinct member of the genus that includes modern African elephants. No Elephas recki specimens were recovered at EFT, despite their common occurrence in other regions of Africa at the same time. Because E. recki and L. atlantica molars are similar in appearance, but the two species are traditionally viewed as dominating different regions of Africa during the Pleistocene, isolated molars may on occasions have been assessed to species level on the basis of geography rather than morphology. The last morphologic evaluation of EFT elephants was conducted in the 1970s, and revisiting this issue with new specimens provides added insight into the evolution of elephants in Africa. Reevaluating morphological characteristics of EFT elephant molars, through qualitative and quantitative description and comparison with Middle Pleistocene E. recki recki, L. atlantica atlantica, and L. atlantica zulu molar morphology, corroborates assessment of EFT elephants as L. a. zulu. Two recently discovered, previously undescribed molars from EFT show that molars of L. a. zulu exhibit greater variation in enamel thickness, lamellar frequency, and occlusal surface morphology than previously reported. An update of the Pleistocene biogeography of Loxodonta and Elephas indicates that fossil remains of both are often found at the same localities in eastern Africa. Their rare co-occurrences in the north and south, however, suggest geographic separation of the two genera in at least some regions of Africa, which may have been based on habitat preference.

  11. Collescipoli - An unusual fusion crust glass. [chondrite

    NASA Technical Reports Server (NTRS)

    Nozette, S.

    1979-01-01

    An electron microprobe study was conducted on glass fragments taken from the fusion crust and an internal glass-lined vein in the H-5 chondrite Collescipoli. Microprobe analyses of the glasses revealed an unusual fusion crust composition, and analyses of glass from inside the meteorite showed compositions expected for a melt of an H-group chondrite. Studies of fusion crusts by previous workers, e.g., Krinov and Ramdohr, showed that fusion crusts contain large amounts of magnetite and other oxidized minerals. The Collescipoli fusion crusts do contain these minerals, but they also contain relatively large amounts of reduced metal, sulphide, and a sodium-rich glass. This study seems to indicate that Collescipoli preserved an early type of fusion crust. Oxidation was incomplete in the fusion crust melt that drained into a crack. From this study it is concluded that fusion crust formation does not invariably result in complete oxidation of metal and sulphide phases.

  12. Devonian Nb-enriched basalts and andesites of north-central Tibet: Evidence for the early subduction of the Paleo-Tethyan oceanic crust beneath the North Qiangtang Block

    NASA Astrophysics Data System (ADS)

    Zhang, Hongrui; Yang, Tiannan; Hou, Zengqian; Bian, Yeke

    2016-07-01

    The early evolution of the Tethyan Ocean in north-central Tibet is currently poorly constrained. A sequence of volcanic rocks ranging from basic to intermediate in composition has been identified in the Zaduo area of the North Qiangtang Block. SHRIMP U-Pb dating of zircons from a sample of Zaduo andesite suggests an eruption age of Late Devonian (~ 380 Ma). The Zaduo volcanic rocks exhibit geochemical characteristics similar to those of typical Nb-enriched basalts, with relatively high Nb, Ta, and Zr contents, resulting in high Nb/La ratios (0.70-1.08) and Nb/U ratios (10.57-34.37). The relative enrichment in high field strength elements, together with positive εNd(t) values of + 4.6 to + 5.8 and low (87Sr/86Sr)i ratios of 0.70367-0.70532, indicates the Zaduo volcanic rocks were derived from a depleted mantle source metasomatized by silicate melts of a subducted oceanic slab. The occurrence of Nb-enriched volcanic rocks in the North Qiangtang Block suggests that the subduction of Paleo-Tethyan oceanic crust was initiated in the Late Devonian. Available geochronological data from ophiolites surrounding the North Qiangtang Block suggest that the subducted slab is most likely the Longmucuo-Shuanghu Paleo-Tethyan oceanic crust.

  13. A Scale To Assess African American Acculturation.

    ERIC Educational Resources Information Center

    Snowden, Lonnie R.; Hines, Alice M.

    1999-01-01

    Investigated an acculturation scale designed for use in the African-American population. Responses from more than 900 African Americans generally indicate an African-American orientation within the sample, although there are notable variations on all 10 scale items. Discusses evidence for scale reliability and validity. (SLD)

  14. The tyrosinase-positive oculocutaneous albinism gene shows locus homogeneity on chromosome 15q11-q13 and evidence of multiple mutations in southern African negroids

    SciTech Connect

    Kedda, M.A.; Stevens, G.; Manga, P.; Viljoen, C.; Jenkins, T.; Ramsay, M. Univ. of Witwatersrand, Johannesburg )

    1994-06-01

    Tyrosinase-positive oculocutaneous albinism (ty-pos OCA) is an autosomal recessive disorder of the melanin pigmentary system. South African ty-pos OCA individuals occur with two distinct phenotypes, with or without darkly pigmented patches (ephelides, or dendritic freckles) on exposed areas of the skin. These phenotypes are concordant within families, suggesting that there may be more than one mutation at the ty-pos OCA locus. Linkage studies carried out in 41 families have shown linkage between markers in the Prader-Willi/Angelman syndrome (PWS/AS) region on chromosome 15q11-q13 and ty-pos OCA. Analysis showed no obligatory crossovers between the alleles at the D15S12 locus and ty-pos OCA, suggesting that the D15S12 locus is very close to or part of the disease locus, which is postulated to be the human homologue, P, of the mouse pink-eyed dilution gene, p. Unlike caucasoid [open quotes]ty-pos OCA[close quotes] individuals, negroid ty-pos OCA individuals do not show any evidence of locus heterogeneity. Studies of allelic association between the polymorphic alleles detected at the D15S12 locus and ephelus status suggest that there was a single major mutation giving rise to ty-pos OCA without ephelides. There may, however, be two major mutations causing ty-pos OCA with ephelides, one associated with D15S12 allele 1 and the other associated with D15S12 allele 2. The two loci, GABRA5 and D15S24, flanking D15S12, are both hypervariable, and many different haplotypes were observed with the alleles at the three loci on both ty-pos OCA-associated chromosomes and [open quotes]normal[close quotes] chromosomes. No haplotype showed statistically significant association with ty-pos OCA, and thus none could be used to predict the origins of the ty-pos OCA mutations. On the basis of the D15S12 results, there is evidence for multiple ty-pos OCA mutations in southern African negroids. 31 refs., 1 fig., 3 tabs.

  15. Is poverty a driver for risky sexual behaviour? Evidence from national surveys of adolescents in four African countries.

    PubMed

    Madise, Nyovani; Zulu, Eliya; Ciera, James

    2007-12-01

    This paper contributes to conflicting evidence on the link between poverty and risky sexual behaviour by examining the effect of wealth status on age at first sex, condom use, and multiple partners using nationally representative adolescents' data from Burkina Faso, Ghana, Malawi, and Uganda. The results show that the wealthiest girls in Burkina Faso, Ghana, and Malawi had later sexual debut compared with their poorer counterparts but this association was not significant for Uganda. Wealth status was weaker among males and significant only in Malawi, where those in the middle quintile had earlier sexual debut. Wealthier adolescents were most likely to use condoms at the last sexual act, but wealth status was not associated with number of sexual partners. Although the link between wealth status and sexual behaviour is not consistent, there is evidence that poor females are vulnerable to infection because of earlier sexual debut and non-use of condoms. PMID:20698061

  16. Relamination and the Differentiation of Continental Crust

    NASA Astrophysics Data System (ADS)

    Hacker, B. R.; Kelemen, P. B.; Behn, M. D.

    2014-12-01

    Most immature crust must be refined to attain the composition of mature continental crust. This refining may take the form of weathering, delamination, or relamination. Although delamination and relamination both call upon gravity-driven separation of felsic rock into the crust and mafic rock into the mantle, delamination involves foundering of rock from the base of active magmatic arcs, whereas relamination involves the underplating/diapirism of subducted sediment, arc crust, and continent crust to the base of the crust in any convergence zone. Relamination may be more efficient than lower crustal foundering at generating large volumes of material with the major- and trace-element composition of continental crust, and may have operated rapidly enough to have refined the composition of the entire continental crust over the lifetime of Earth. If so, felsic rocks could form much of the lower crust, and the bulk continental crust may be more silica rich than generally considered. Seismic wavespeeds require that only ~10-20% of the lowermost 5-15 km of continental crust must be mafic; combined heat-flow and wavespeed constraints permit continental lower crust to have 50 to 65 wt% SiO2.

  17. Socioeconomic inequalities in HIV/AIDS prevalence in sub-Saharan African countries: evidence from the Demographic Health Surveys

    PubMed Central

    2014-01-01

    Introduction Extant studies universally document a positive gradient between socioeconomic status (SES) and health. A notable exception is the apparent concentration of HIV/AIDS among wealthier individuals. This paper uses data from the Demographic Health Surveys and AIDS Indicator Surveys to examine socioeconomic inequalities in HIV/AIDS prevalence in 24 sub-Saharan African (SSA) countries, the region that accounts for two-thirds of the global HIV/AIDS burden. Methods The relative and generalized concentration indices (RC and GC) were used to quantify wealth-based socioeconomic inequalities in HIV/AIDS prevalence for the total adult population (aged 15-49), for men and women, and in urban and rural areas in each country. Further, we decomposed the RC and GC indices to identify the determinants of socioeconomic inequalities in HIV/AIDS prevalence in each country. Results Our findings demonstrated that HIV/AIDS was concentrated among higher SES individuals in the majority of SSA countries. Swaziland and Senegal were the only countries in the region where HIV/AIDS was concentrated among individuals living in poorer households. Stratified analyses by gender showed HIV/AIDS was generally concentrated among wealthier men and women. In some countries, including Kenya, Lesotho Uganda, and Zambia, HIV/AIDS was concentrated among the poor in urban areas but among wealthier adults in rural areas. Decomposition analyses indicated that, besides wealth itself (median = 49%, interquartile range [IQR] = 90%), urban residence (median = 54%, IQR = 81%) was the most important factor contributing to the concentration of HIV/AIDS among wealthier participants in SSA countries. Conclusions Further work is needed to understand the mechanisms explaining the concentration of HIV/AIDS among wealthier individuals and urban residents in SSA. Higher prevalence of HIV/AIDS could be indicative of better care and survival among wealthier individuals and urban adults, or reflect

  18. Deep fracture fluids isolated in the crust since the Precambrian era.

    PubMed

    Holland, G; Lollar, B Sherwood; Li, L; Lacrampe-Couloume, G; Slater, G F; Ballentine, C J

    2013-05-16

    Fluids trapped as inclusions within minerals can be billions of years old and preserve a record of the fluid chemistry and environment at the time of mineralization. Aqueous fluids that have had a similar residence time at mineral interfaces and in fractures (fracture fluids) have not been previously identified. Expulsion of fracture fluids from basement systems with low connectivity occurs through deformation and fracturing of the brittle crust. The fractal nature of this process must, at some scale, preserve pockets of interconnected fluid from the earliest crustal history. In one such system, 2.8 kilometres below the surface in a South African gold mine, extant chemoautotrophic microbes have been identified in fluids isolated from the photosphere on timescales of tens of millions of years. Deep fracture fluids with similar chemistry have been found in a mine in the Timmins, Ontario, area of the Canadian Precambrian Shield. Here we show that excesses of (124)Xe, (126)Xe and (128)Xe in the Timmins mine fluids can be linked to xenon isotope changes in the ancient atmosphere and used to calculate a minimum mean residence time for this fluid of about 1.5 billion years. Further evidence of an ancient fluid system is found in (129)Xe excesses that, owing to the absence of any identifiable mantle input, are probably sourced in sediments and extracted by fluid migration processes operating during or shortly after mineralization at around 2.64 billion years ago. We also provide closed-system radiogenic noble-gas ((4)He, (21)Ne, (40)Ar, (136)Xe) residence times. Together, the different noble gases show that ancient pockets of water can survive the crustal fracturing process and remain in the crust for billions of years. PMID:23676753

  19. Magnetic structure of the crust

    NASA Technical Reports Server (NTRS)

    Wasilewski, P.

    1985-01-01

    The bibuniqueness aspect of geophysical interpretation must be constrained by geological insight to limit the range of theoretically possible models. An additional step in depth understanding of the relationship between rock magnetization and geological circumstances on a grand scale is required. Views about crustal structure and the distribution of lithologies suggests a complex situation with lateral and vertical variability at all levels in the crust. Volcanic, plutonic, and metamorphic processes together with each of the observed anomalies. Important questions are addressed: (1) the location of the magnetic bottom; (2) whether the source is a discrete one or are certain parts of the crust cumulatively contributing to the overall magnetization; (3) if the anomaly to some recognizable surface expression is localized, how to arrive at a geologically realistic model incorporating magnetization contrasts which are realistic; (3) in the way the primary mineralogies are altered by metamorphism and the resulting magnetic contracts; (4) the effects of temperature and pressure on magnetization.

  20. Chronology of early lunar crust

    NASA Technical Reports Server (NTRS)

    Dasch, E. J.; Nyquist, L. E.; Ryder, G.

    1988-01-01

    The chronology of lunar rocks is summarized. The oldest pristine (i.e., lacking meteoritic contamination of admixed components) lunar rock, recently dated with Sm-Nd by Lugmair, is a ferroan anorthosite, with an age of 4.44 + 0.02 Ga. Ages of Mg-suite rocks (4.1 to 4.5 Ga) have large uncertainties, so that age differences between lunar plutonic rock suites cannot yet be resolved. Most mare basalts crystallized between 3.1 and 3.9 Ga. The vast bulk of the lunar crust, therefore, formed before the oldest preserved terrestrial rocks. If the Moon accreted at 4.56 Ga, then 120 Ma may have elapsed before lunar crust was formed.

  1. Continental crust beneath southeast Iceland.

    PubMed

    Torsvik, Trond H; Amundsen, Hans E F; Trønnes, Reidar G; Doubrovine, Pavel V; Gaina, Carmen; Kusznir, Nick J; Steinberger, Bernhard; Corfu, Fernando; Ashwal, Lewis D; Griffin, William L; Werner, Stephanie C; Jamtveit, Bjørn

    2015-04-14

    The magmatic activity (0-16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland--and especially the Öræfajökull volcano--is characterized by a unique enriched-mantle component (EM2-like) with elevated (87)Sr/(86)Sr and (207)Pb/(204)Pb. Here, we demonstrate through modeling of Sr-Nd-Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2-6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ∼350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume. PMID:25825769

  2. Magnetization of the Lunar Crust

    NASA Technical Reports Server (NTRS)

    Carley, R. A.; Whaler, K. A.; Purucker, M. E.; Halekas, J. S.

    2012-01-01

    Magnetic fields measured by the satellite Lunar Prospector show large scale features resulting from remanently magnetized crust. Vector data synthesized at satellite altitude from a spherical harmonic model of the lunar crustal field, and the radial component of the magnetometer data, have been used to produce spatially continuous global magnetization models for the lunar crust. The magnetization is expressed in terms of localized basis functions, with a magnetization solution selected having the smallest root-mean square magnetization for a given fit to the data, controlled by a damping parameter. Suites of magnetization models for layers with thicknesses between 10 and 50 km are able to reproduce much of the input data, with global misfits of less than 0.5 nT (within the uncertainties of the data), and some surface field estimates. The magnetization distributions show robust magnitudes for a range of model thicknesses and damping parameters, however the magnetization direction is unconstrained. These global models suggest that magnetized sources of the lunar crust can be represented by a 30 km thick magnetized layer. Average magnetization values in magnetized regions are 30-40 mA/m, similar to the measured magnetizations of the Apollo samples and significantly weaker than crustal magnetizations for Mars and the Earth. These are the first global magnetization models for the Moon, providing lower bounds on the magnitude of lunar crustal magnetization in the absence of multiple sample returns, and can be used to predict the crustal contribution to the lunar magnetic field at a particular location.

  3. Continental crust beneath southeast Iceland

    PubMed Central

    Torsvik, Trond H.; Amundsen, Hans E. F.; Trønnes, Reidar G.; Doubrovine, Pavel V.; Gaina, Carmen; Kusznir, Nick J.; Steinberger, Bernhard; Corfu, Fernando; Ashwal, Lewis D.; Griffin, William L.; Werner, Stephanie C.; Jamtveit, Bjørn

    2015-01-01

    The magmatic activity (0–16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland—and especially the Öræfajökull volcano—is characterized by a unique enriched-mantle component (EM2-like) with elevated 87Sr/86Sr and 207Pb/204Pb. Here, we demonstrate through modeling of Sr–Nd–Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2–6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ∼350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume. PMID:25825769

  4. Enriched asthenosphere melting beneath the nascent North African margin: trace element and Nd isotope evidence in middle-late Triassic alkali basalts from central Sicily (Italy)

    NASA Astrophysics Data System (ADS)

    Cirrincione, Rosolino; Fiannacca, Patrizia; Lustrino, Michele; Romano, Vanessa; Tranchina, Annunziata; Villa, Igor M.

    2016-03-01

    During the dismembering of the Pangea supercontinent, middle-late Triassic sub-volcanic alkaline rocks were emplaced in central Sicily. These rocks have an alkali basaltic composition and show OIB-like incompatible element patterns in primitive mantle-normalized diagrams (e.g., enrichments in HFSE and LREE coupled with high HFSE/LILE ratios), as well as slightly positive \\varepsilon_{Nd} values. Only subtle effects of crustal contamination at shallow depths emerge from geochemical data. These characteristics are very different compared with the Permian calcalkaline magmas from elsewhere in SW Europe still carrying the geochemical signature of modifications related to the Variscan orogeny. The mineralogical, geochemical and isotopic compositions of the investigated samples from central Sicily are also different from the coeval shoshonitic volcano-plutonic formations of Southern Alps (Dolomites). The incompatible element composition and Nd isotopic ratios are consistent with low-degree partial melting of a moderately depleted asthenospheric mantle source, with a negligible involvement of the thinned continental crust. The studied alkaline basalts represent the only known evidence of a segment of the Triassic rift system associated with early Pangea breakup in central Sicily. The close similarity of the central Sicily Triassic alkali basalts with coeval basalts emplaced along former orogenic sutures across the peri-Mediterranean area suggests a common origin related, at least partly, to asthenospheric passive upwelling following the tectonic collapse of the Variscan Belt. These rocks provide new constraints on the spatial-temporal distribution, magma source evolution and geodynamic meaning of the widespread Permo-Triassic basic magmatism developed after the end of the Variscan Orogeny in southwestern Europe.

  5. Overlapping Sr-Nd-Hf-O isotopic compositions in Permian mafic enclaves and host granitoids in Alxa Block, NW China: Evidence for crust-mantle interaction and implications for the generation of silicic igneous provinces

    NASA Astrophysics Data System (ADS)

    Dan, Wei; Wang, Qiang; Wang, Xuan-Ce; Liu, Yu; Wyman, Derek A.; Liu, Yong-Sheng

    2015-08-01

    In general, the mantle provides heat and/or material for the generation of the silicic igneous provinces (SIPs). The rarity of mafic microgranular enclaves (MMEs), however, hampers understanding of the mantle's role in generating SIPs and the process of crust-mantle interaction. The widespread distributed MMEs in the newly reported Alxa SIP provide an opportunity to study these processes. This study integrates in situ zircon U-Pb age and Hf-O isotope analyses, whole-rock geochemistry and Sr-Nd isotope results for the MMEs and host granitoids in the Alxa Block. SIMS zircon U-Pb dating reveals that there are two generations of MMEs and host granitoids. The MMEs in the Bayannuoergong batholith were formed at ca. 278 Ma, similar to the age (280 Ma) of host granitoids, and the MMEs and host granitoids in the Yamaitu pluton were formed at ca. 272-270 Ma. All MMEs have relatively low SiO2 (50.7-61.4 wt.%) and Th (0.8-2.8 ppm), but relatively high MgO (2.6-4.9 wt.%), Cr (23-146 ppm) and Ni (6-38 ppm) contents compared to the host granitoids, with SiO2 (63.6-77.5 wt.%), Th (5.2-41 ppm), MgO (0.23-2.1 wt.%), Cr (10-38 ppm) and Ni (5-14 ppm). All MMEs have whole rock Sr-Nd and zircon Hf-O isotope compositions similar to their corresponding host granitoids. The 280 Ma MMEs have lower whole rock εNd(t) (- 13.5) and higher initial 87Sr/86Sr values (0.7095) and zircon δ18O values (6.3‰) compared to the εNd(t) (- 11.5), initial 87Sr/86Sr values (0.7070) and zircon δ18O values (5.6‰) of the 270 Ma MMEs. The occurrences of quartz xenocrysts, K-feldspar megacrysts, corroded feldspars and acicular apatites indicate that the MMEs are the products of the mixing between mantle- and crust-derived magmas. The striking similarities in the zircon Hf-O isotopic compositions in both MME-host granitoid pairs indicate that the granitoids and MMEs have similar sources. The granitoids are proposed to be mainly sourced from magmas generated by remelting of newly formed mafic rocks, which

  6. 13C/Palynological evidence of differential residence times of organic carbon prior to its sedimentation in East African Rift Lakes and peat bogs

    NASA Astrophysics Data System (ADS)

    Hillaire-Marcel, Claude; Aucour, Anne-Marie; Bonnefille, Raymonde; Riollet, Guy; Vincens, Annie; Williamson, David

    Most terrestrial plants producing large amounts of organic matter in the East African Rift follow the Calvin (C3) photosynthetic pathway. Their end products have δ13C values of ca. -27 ± 2‰ (vs. PDB). On the contrary, most Cyperaceae (notably Cyperus papyrus and C. latifolius) are characterized by higher 13C contents ° 13C = -10.5 ± 1‰ ) in relation to their Hatch and Slack (C4) photosynthetic cycle. In consequence, δ13C values in total organic matter (TOM) from peat bog or lake cores essentially responded to the proportion of detritus from C4-Cyperaceae. Immediate evidence of the development or disappearance of Cyperaceae around lake margins or in peat bogs can be found in pollen assemblages. Lag times between pollen signals and correlative ° 13C shifts in TOM from cores are therefore indicative of the residence time of organic matter prior to its sedimentation. Delayed sedimentation of TOM will result in 14C anomalies which depend on several parameters, most of them being site specific as shown by examples from a peat bog in Burundi and from southern Lake Tanganyika. An independent assessment of the chronology by high resolution paleomagnetic correlations indicates a ca. 1.5 ka apparent 14C age of TOM in Lake Tanganyika at the Pleistocene-Holocene transition.

  7. The process of adaptation of a community-level, evidence-based intervention for HIV-positive African American men who have sex with men in two cities.

    PubMed

    Robinson, Beatrice E; Galbraith, Jennifer S; Lund, Sharon M; Hamilton, Autumn R; Shankle, Michael D

    2012-06-01

    We describe the process of adapting a community-level, evidence-based behavioral intervention (EBI), Community PROMISE, for HIV-positive African American men who have sex with men (AAMSM). The Centers for Disease Control and Prevention (CDC) Map of the Adaptation Process (MAP) guided the adaptation process for this new target population by two community-based organizations (CBOs) working in partnership with two research organizations. We describe five steps of the MAP, assessment, selection, preparation, pilot, and implementation, and the use of qualitative interviews, field observations, and a cross-sectional survey. We recommend: (1) development of a centralized interactive website, listserv, or other resources where agencies adapting EBIs can share tools, materials, experiences, lessons learned, and best practices; (2) strengthening Funding Opportunity Announcements by funding incrementally in phases linked to the MAP; and (3) research should examine (a) whether EBIs adapted by CBOs remain efficacious and (b) the best "fit" between the cultural and climate characteristics of effective collaborations between community- and research-based organizations. PMID:22676461

  8. Nature of crust in the central Red Sea

    NASA Astrophysics Data System (ADS)

    Mitchell, Neil C.; Park, Yongcheol

    2014-07-01

    A transition between continental crust in the northern Red Sea and oceanic crust in the southern Red Sea coincides broadly with a southward increase in plate tectonic separation rate and with a decrease in upper mantle seismic velocity. We re-evaluate here the nature of crust in the intervening central Red Sea with the results of legacy seismic refraction experiments and recently released marine gravity anomalies derived from satellite altimeter measurements. In the refraction data, collected east of Thetis Deep, velocities of 6.6-6.9 km s- 1 of a deep refracting layer, which are similar to measured velocities of unaltered gabbro samples, extend outside the deep to 65 km from the axis. The new version of the marine gravity field reveals trends crossing the central Red Sea. Whereas some of them connect with major lineaments in the surrounding African-Arabian shield, those around Thetis Deep die out towards the coastlines. They can be paired across the ridge and lie slightly oblique to plate motions, as is typical of oceanic fracture zones or non-transform discontinuities migrating away from hotspots. Taken together these observations support the view that an oceanic rather than extended continental crust underlies this part of the central Red Sea. The crestal mountains around the median valleys of slow-spreading ridges are typically 500-1000 m lower at spreading discontinuities. Around Thetis Deep, the similar pattern in the gravity field to those of slow-spreading ridges suggests that the crestal mountains may variably block or impede flowage of evaporites towards the spreading centre, whereas the discontinuities may mark areas where flowage is unobstructed. Limited multibeam data collected in transits outside Thetis Deep show oblique fabrics as expected from these predicted movements.

  9. Crust Formation and Stabilization of the Western Archean Kaapvaal Craton: Evidence from U-Pb Geochronology of Basement Blocks and Deep Crustal Xenoliths from the Kimberley Region, South Africa

    NASA Astrophysics Data System (ADS)

    Schmitz, M. D.; Bowring, S. A.

    2001-05-01

    The kimberlites of the Kimberley region of South Africa have yielded one of the most abundantly sampled and studied suites of lithospheric mantle xenoliths in the world, providing a detailed picture of the composition and thermal evolution of the continental mantle beneath the western Kaapvaal craton. Surprisingly however, little published data exist regarding the nature of the basement and deeper crustal rocks in the western craton, with which to contrast the evolution of the crustal and mantle portions of this Archean cratonic region. Crustal xenoliths collected in the various mine dumps around Kimberley are predominantly large blocks of near-surface basement lithologies, including deformed granitic to tonalitic gneisses and amphibolites, weakly deformed pegmatoids, and non-deformed biotite granite. U-Pb zircon geochronological data for a number of xenoliths have been used to develop a preliminary framework for the age and evolution of the Archean crust of the Kimberley region. The youngest component of the Kimberley basement is a non-deformed sample of biotite granite with an age of 2724+/-2 Ma. A major episode of metamorphism and crustal anatexis is recorded by 2928+/-2 Ga metamorphic zircon growth in amphibolitic and tonalitic components of banded gneisses, and igneous zircons of identical age in weakly deformed cross-cutting pegmatoids. Zircons from these same pegmatoids also have inherited cores which yield 207Pb/206Pb dates as old as 3265 Ma. These inherited zircons, as well as cores of zircons from a foliated granodioritic xenolith with 207Pb/206Pb dates as old as 3184 Ma, indicate the antiquity of the oldest crustal components of the Kimberley basement. These data are consistent with cursory SHRIMP U-Pb zircon geochronological information reported for lithologies collected in situ in the diamond mine walls of Kimberley. Two important implications of this data are considered: first, we interpret the major metamorphism and crustal anatexis at 2.93 Ga as

  10. Crust-mantle interaction in the central North China Craton during the Mesozoic: Evidence from zircon U-Pb chronology, Hf isotope and geochemistry of syenitic-monzonitic intrusions from Shanxi province

    NASA Astrophysics Data System (ADS)

    Ying, Ji-Feng; Zhang, Hong-Fu; Tang, Yan-Jie

    2011-07-01

    In-situ zircon U-Pb ages, Hf isotopic compositions and whole rock geochemical and Sr-Nd isotopic compositions are presented for three Mesozoic syenitic-monzonitic intrusions from Shanxi province, central North China Craton. Zircons from these intrusions all show core-rim structures in that the oscillatory rims recorded their intrusive ages, whereas the cores are interpreted as xenocrysts. The U-Pb age data reveal that the northernmost Dishuiyan monzonite was emplaced at 241 Ma, while the Huyanshan and Erfengshan syenitic-monzonitic complexes were emplaced at 130 Ma and 128-134 Ma, respectively. The Dishuiyan monzonite is petrologically and geochemically uniform, it shows LREE enrichment and HFSE depletion and exhibits enriched Sr and Nd isotopic compositions with (87Sr/86Sr)i = 0.7065 and εNd(t) = - 8.3--7.9. The zircon rims in the Dishuiyan monzonite show highly varied Hf isotopic compositions with εHf(t) = - 27.8--6.4. The varied Hf isotopic compositions and enriched Sr-Nd isotopic compositions, together with the ubiquitous xenocrystic zircon cores, suggest the Dishuiyan monzonite was produced by the mixing of melts from enriched lithospheric mantle and lower crust. The monzonite and syenite from the Huyanshan complexes exhibit different geochemical features. The εNd(t) values of syenite, which are higher than those of monzonite resemble the enriched lithospheric mantle, and together with the absence of zircon in the syenite, we propose that it was originated by partial melting of enriched lithospheric mantle. Monzonites from Huyanshan and Erfengshan share similar petrological and geochemical characteristics, being enriched in LREE and depleted in HFSE, and they show low εNd(t) values between - 18.2 and - 13.9. Similar to zircon rims in the Dishuiyan monzonite, those in the Huyanshan and Erfengshan monzonites also exhibit highly varied Hf isotopic compositions. The consistent ages between the xenocrystic zircons in monzonites and the lower crustal basement

  11. History of the earth's crust

    SciTech Connect

    Eicher, D.L.; Mcalester, A.L.; Rottman, M.L.

    1984-01-01

    The history of the earth's crust since its formation 4.6 Gyr ago is traced in an introductory textbook, with consideration of the global climate and the general outline of biological evolution. The methodology of paleogeology is introduced, and the origin of the solar system, the accumulation and differentiation of the earth, the beginnings of life, and the history of the moon are examined. Separate chapters are then devoted to the Precambrian, Paleozoic, Mesozoic, and Cenozoic earth. Photographs, maps, diagrams, and drawings are provided. 49 references.

  12. Serological Evidence of Rift Valley Fever Virus Circulation in Domestic Cattle and African Buffalo in Northern Botswana (2010-2011).

    PubMed

    Jori, Ferran; Alexander, Kathleen A; Mokopasetso, Mokganedi; Munstermann, Suzanne; Moagabo, Keabetswe; Paweska, Janusz T

    2015-01-01

    Rift Valley fever (RVF) is endemic in many countries in Sub-Saharan Africa and is responsible for severe outbreaks in livestock characterized by a sudden onset of abortions and high neonatal mortality. During the last decade, several outbreaks have occurred in Southern Africa, with a very limited number of cases reported in Botswana. To date, published information on the occurrence of RVF in wild and domestic animals from Botswana is very scarce and outdated, despite being critical to national and regional disease control. To address this gap, 863 cattle and 150 buffalo sampled at the interface between livestock areas and the Chobe National Park (CNP) and the Okavango Delta (OD) were screened for the presence of RVF virus (RVFV) neutralizing antibodies. Antibodies were detected in 5.7% (n = 863), 95% confidence intervals (CI) (4.3-7.5%) of cattle and 12.7% (n = 150), 95% CI (7.8-19.5%) of buffalo samples. The overall prevalence was significantly higher (p = 0.0016) for buffalo [12.7%] than for cattle [5.7%]. Equally, when comparing RVF seroprevalence in both wildlife areas for all pooled bovid species, it was significantly higher in CNP than in OD (9.5 vs. 4%, respectively; p = 0.0004). Our data provide the first evidence of wide circulation of RVFV in both buffalo and cattle populations in Northern Botswana and highlight the need for further epidemiological and ecological investigations on RVF at the wildlife-livestock-human interface in this region. PMID:26664990

  13. Serological Evidence of Rift Valley Fever Virus Circulation in Domestic Cattle and African Buffalo in Northern Botswana (2010–2011)

    PubMed Central

    Jori, Ferran; Alexander, Kathleen A.; Mokopasetso, Mokganedi; Munstermann, Suzanne; Moagabo, Keabetswe; Paweska, Janusz T.

    2015-01-01

    Rift Valley fever (RVF) is endemic in many countries in Sub-Saharan Africa and is responsible for severe outbreaks in livestock characterized by a sudden onset of abortions and high neonatal mortality. During the last decade, several outbreaks have occurred in Southern Africa, with a very limited number of cases reported in Botswana. To date, published information on the occurrence of RVF in wild and domestic animals from Botswana is very scarce and outdated, despite being critical to national and regional disease control. To address this gap, 863 cattle and 150 buffalo sampled at the interface between livestock areas and the Chobe National Park (CNP) and the Okavango Delta (OD) were screened for the presence of RVF virus (RVFV) neutralizing antibodies. Antibodies were detected in 5.7% (n = 863), 95% confidence intervals (CI) (4.3–7.5%) of cattle and 12.7% (n = 150), 95% CI (7.8–19.5%) of buffalo samples. The overall prevalence was significantly higher (p = 0.0016) for buffalo [12.7%] than for cattle [5.7%]. Equally, when comparing RVF seroprevalence in both wildlife areas for all pooled bovid species, it was significantly higher in CNP than in OD (9.5 vs. 4%, respectively; p = 0.0004). Our data provide the first evidence of wide circulation of RVFV in both buffalo and cattle populations in Northern Botswana and highlight the need for further epidemiological and ecological investigations on RVF at the wildlife–livestock–human interface in this region. PMID:26664990

  14. Implications for the evolution of continental crust from Hf isotope systematics of Archean detrital zircons

    NASA Technical Reports Server (NTRS)

    Stevenson, Ross K.; Patchett, P. Jonathan

    1990-01-01

    Results from the fractionation of zircon by sedimentary processes into continental margin sandstone yield information on the preservation of preexisting continental crust in the form of zircon, making it possible to distinguish between the contrasting theories of gradual growth versus constant volume of continental crust over geologic time. In this work, Hf-176/Hf-177 ratios were determined for detrital zircon fractions from 2.0-2.5, 2.6-3.0, and pre-3.0 Gyr old sandstones from the Canadian-Shield, the North-Atlantic, the Wyoming, and the Kaapvaal Cratons. Results pointed to small amounts of continental crust prior to 3.0 Gyr ago and a rapid addition of continental crust between 2.5 and 3.0 Gyr ago, consistent with the gradual growth of continental crust, and giving evidence against no-growth histories.

  15. Geochemical characteristics and metal element enrichment in crusts from seamounts of the Western Pacific

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoyu; Zhu, Kechao; Du, Yong; Zhang, Fuyuan; Zhang, Weiyan; Ren, Xiangwen; Jiang, Binbin; Huang, Dasong

    2016-03-01

    Elemental geochemistry is an essential part of understanding mineralization mechanisms. In this paper, a data set of 544 cobalt crust samples from seamounts of the Western Pacific are used to study the enrichment characteristics of metal elements. REE normalization is utilized to reveal the origin of the crusts; effects of water depth on Co enrichment and impacts of phosphatization on mineral quality are discussed to obtain the evolution of these marine mineral deposits, which gives support to further resource assessment. Conclusions are reached as follows: 1) Elemental abundances, inter-element relationships, and shale-normalized REE patterns for phosphate-poor crusts from different locations reflect hydrogenetic origin of the crusts. EFs (enrichment coefficients) of REE exhibit exponential increase from surface sediments to phosphorite to polymetallic nodules to crusts, suggesting that the improved degree of hydrogeneous origin induces the enrichment of REE. 2) The crusts in the Western Pacific, formed through hotspot produced guyots trails, have relatively lower REE than those in the Mid-Pacific. The latter could be attributed to the peculiar submarine topography of seamounts formed by intraplate volcanism. 3) The non-phosphatized younger crust layers have 40% higher Co than the phosphatized older layers. This indicates the modification of the elemental composition in these crusts by phosphatization. A general depletion of hydroxide-dominated elements such as Co, Ni, and Mn and enrichment of P, Ca, Ba, and Sr is evident in phosphatized crusts, whereas non-phosphatized younger generation crusts are rich in terrigenous aluminosilicate detrital matter. 4) Co increases above the carbonate compensation depth (CCD) from less than 0.53% to over 0.65% in seamount regions with water depth of less than 2,500 m, suggesting the significance of the dissolution of carbonate in the sea water column to the growth and composition of crusts.

  16. Mars Crust: Made of Basalt

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2009-05-01

    By combining data from several sources, Harry Y. (Hap) McSween (University of Tennessee), G. Jeffrey Taylor (University of Hawaii) and Michael B. Wyatt (Brown University) show that the surface of Mars is composed mostly of basalt not unlike those that make up the Earth's oceanic crust. McSween and his colleagues used data from Martian meteorites, analyses of soils and rocks at robotic landing sites, and chemical and mineralogical information from orbiting spacecraft. The data show that Mars is composed mostly of rocks similar to terrestrial basalts called tholeiites, which make up most oceanic islands, mid-ocean ridges, and the seafloor beneath sediments. The Martian samples differ in some respects that reflect differences in the compositions of the Martian and terrestrial interiors, but in general are a lot like Earth basalts. Cosmochemistst have used the compositions of Martian meteorites to discriminate bulk properties of Mars and Earth, but McSween and coworkers' synthesis shows that the meteorites differ from most of the Martian crust (the meteorites have lower aluminum, for example), calling into question how diagnostic the meteorites are for understanding the Martian interior.

  17. Composition and origin of Archean lower crust, Northern Tanzania

    NASA Astrophysics Data System (ADS)

    Mansur, A. T.; Manya, S.; Rudnick, R.

    2008-12-01

    Granulite-facies xenoliths from tuff cones erupted on the margin of the Tanzanian craton and within the adjacent Mozambique belt in northern Tanzania offer an opportunity to assess the role of lower crustal processes in the tectonic evolution of these two terranes. Both terranes are Archean, but record very different histories, starting in the Proterozoic and continuing today. Whereas the craton experienced little metamorphism or igneous activity following its stabilization around 2.8 Ga, Archean rocks of the Mozambique belt in the study area experienced at least one episode of high-grade metamorphism during the East African orogeny (ca. 640 Ma). Today, the East African rift exists at the contact between the Mozambique belt and the craton, implying a fundamental lithospheric weakness at this boundary. Granulite xenoliths come from Labait, on the craton margin, and Lashaine and Naibor Soito in the metamorphic belt. Most xenoliths are mafic and all are igneous in origin. Cratonic xenoliths (pl- opx±cpx±gt±hbl) are primarily anhydrous two-pyroxene granulites that likely originated as crystallized high-Ni, Archean basaltic melts. Xenoliths from the Mozambique belt are dominated by mafic granulites (pl-cpx-gt±opx) at Lashaine and banded, mafic to intermediate granulites at Naibor Soito. Positive Sr and Eu anomalies imply that the Lashaine granulites originated as plagioclase cumulates. The wide range in SiO2 (47-65 wt%) and correlation of Ni-MgO in the Naibor Soito xenoliths suggests they may have originated as igneous rocks that subsequently underwent partial melting to form the mafic (pl- opx±cpx±gt±hbl±bt) and felsic bands (pl-qtz-opx±kfs). U-Pb zircon ages for xenoliths from both terranes are Archean, as are most TDM ages, though younger TDM ages are seen in some Lashaine samples that were contaminated by rift magma. High pressures (up to 2.7GPa) are recorded by the Mozambique belt xenoliths, suggesting equilibration in thickened crust during the East

  18. Recycling lower continental crust in the North China craton.

    PubMed

    Gao, Shan; Rudnick, Roberta L; Yuan, Hong-Ling; Liu, Xiao-Ming; Liu, Yong-Sheng; Xu, Wen-Liang; Ling, Wen-Li; Ayers, John; Wang, Xuan-Che; Wang, Qing-Hai

    2004-12-16

    Foundering of mafic lower continental crust into underlying convecting mantle has been proposed as one means to explain the unusually evolved chemical composition of Earth's continental crust, yet direct evidence of this process has been scarce. Here we report that Late Jurassic high-magnesium andesites, dacites and adakites (siliceous lavas with high strontium and low heavy-rare-earth element and yttrium contents) from the North China craton have chemical and petrographic features consistent with their origin as partial melts of eclogite that subsequently interacted with mantle peridotite. Similar features observed in adakites and some Archaean sodium-rich granitoids of the tonalite-trondhjemite-granodiorite series have been interpreted to result from interaction of slab melts with the mantle wedge. Unlike their arc-related counterparts, however, the Chinese magmas carry inherited Archaean zircons and have neodymium and strontium isotopic compositions overlapping those of eclogite xenoliths derived from the lower crust of the North China craton. Such features cannot be produced by crustal assimilation of slab melts, given the high Mg#, nickel and chromium contents of the lavas. We infer that the Chinese lavas derive from ancient mafic lower crust that foundered into the convecting mantle and subsequently melted and interacted with peridotite. We suggest that lower crustal foundering occurred within the North China craton during the Late Jurassic, and thus provides constraints on the timing of lithosphere removal beneath the North China craton. PMID:15602559

  19. Earth’s earliest evolved crust generated in an Iceland-like setting

    NASA Astrophysics Data System (ADS)

    Reimink, Jesse R.; Chacko, Thomas; Stern, Richard A.; Heaman, Larry M.

    2014-07-01

    It is unclear how the earliest continental crust formed on an Earth that was probably originally surfaced with oceanic crust. Continental crust may have first formed in an ocean island-like setting, where upwelling mantle generates magmas that crystallize to form new crust. Of the oceanic plateaux, Iceland is closest in character to continental crust, because its crust is anomalously thick and contains a relatively high proportion of silica-rich (sialic) rocks. Iceland has therefore been considered a suitable analogue for the generation of Earth’s earliest continental crust. However, the geochemical signature of sialic rocks from Iceland is distinct from the typical 3.9- to 2.5-billion-year-old Archaean rocks discovered so far. Here we report the discovery of an exceptionally well-preserved, 4.02-billion-year-old tonalitic gneiss rock unit within the Acasta Gneiss Complex in Canada. We use geochemical analyses to show that this rock unit is characterized by iron enrichment, negative Europium anomalies, unfractionated rare-earth-element patterns, and magmatic zircons with low oxygen isotope ratios. These geochemical characteristics are unlike typical Archaean igneous rocks, but are strikingly similar to those of the sialic rocks from Iceland and imply that this ancient rock unit was formed by shallow-level magmatic processes that include assimilation of rocks previously altered by surface waters. Our data provide direct evidence that Earth’s earliest continental crust formed in a tectonic setting comparable to modern Iceland.

  20. Pacific ferromanganese crust geology and geochemistry

    SciTech Connect

    Andreev, S.I.; Vanstein, B.G.; Anikeeva, L.I. )

    1990-06-01

    Cobaltiferous ferromanganese crusts form part of a large series of oceanic ferromanganese oxide deposits. The crusts show high cobalt (commonly over 0.4%), low nickel and copper sum (0.4-0.8%), considerably high manganese (18-20%), and iron (14-18%). Less abundant elements in crusts are represented by molybdenum and vanadium; the rare-earth elements cerium, lanthenum, and yttrium; and the noble metals platinum and rhodium. Co-rich crusts form at water depths of 600 to 2,500 m. Crust thicknesses range from millimeters to 15-17 cm, averaging 2-6 cm. The most favorable conditions for 4-10 cm thick crusts to occur is at water depths of 1,200-2,200 m. The crusts formed on basaltic, calcareous, siliceous, and breccia bedrock surfaces provided there were conditions preventing bottom sedimentation at them. If the sedimentation takes place, it may be accompanied by nodules similar in composition to the crusts. The most favorable topography for extensive crust formation is considered to be subdued (up to 20{degree}) slopes and summit platforms of conical seamounts, frequently near faults and their intersection zones. Subhorizontal guyot summits do not usually favor crust growth. Crust geochemistry is primarily defined by mineralogy and manganese hydroxides (vernadite)/iron ratio. The first associated group of compounds includes cobalt, nickel, molybdenum, vanadium, cerium, and titanium; the other is strontium, yttrium, cerium, and cadmium. The aluminosilicate phase is associated with titanium, iron, chromium, and vanadium; phosphate biogenic phase includes copper, nickel, zinc, lead, and barium. The crucial point in cobaltiferous crust formation is their growth rate on which is dependent the degree of ferromanganese matrix sorption saturation with cobalt. The optimum for cobalt-rich ferromanganese ores is the conditions facilitating long-term and continuous hydrogenic processes.

  1. Pulsar glitches: the crust is not enough.

    PubMed

    Andersson, N; Glampedakis, K; Ho, W C G; Espinoza, C M

    2012-12-14

    Pulsar glitches are traditionally viewed as a manifestation of vortex dynamics associated with a neutron superfluid reservoir confined to the inner crust of the star. In this Letter we show that the nondissipative entrainment coupling between the neutron superfluid and the nuclear lattice leads to a less mobile crust superfluid, effectively reducing the moment of inertia associated with the angular momentum reservoir. Combining the latest observational data for prolific glitching pulsars with theoretical results for the crust entrainment, we find that the required superfluid reservoir exceeds that available in the crust. This challenges our understanding of the glitch phenomenon, and we discuss possible resolutions to the problem. PMID:23368300

  2. A mantle- and a lower crust-derived bimodal suite in the Yusufeli (Artvin) area, NE Turkey: trace element and REE evidence for subduction-related rift origin of Early Jurassic Demirkent intrusive complex

    NASA Astrophysics Data System (ADS)

    Dokuz, Abdurrahman; Tanyolu, Erkan; Genç, Salim

    2006-06-01

    , unfractionated HREE patterns and evolution towards the higher Y concentrations and lower Sr/Y ratios within the body. All these features are obtained in experimentally produced melts from mafic rocks at low pressures (≤5 kbar) and also widespread in the rocks of arc where old (Upper Cretaceous or older) oceanic crust is being subducted. Major and REE modelling supports formation of the quartz dioritic parent to the felsic intrusive rocks by 70% partial melting of a primitive gabbroic sample (G694). Therefore, once taking into account the extensional conditions prevailing in the Pontian arc crust in Early Jurassic time, former basic products (gabbros) seem to be the most appropriate source for the tonalite-trondhjemite body. Magmatic emplacement of stratigraphically similar lithologies in the Pulur Massif, just southwest of the Yusufeli, was dated to be 184 Ma by the 40Ar/39Ar method on amphibole, and is compatible with the initiation of Early Jurassic rifting in the region.

  3. Apulian crust: Top to bottom

    NASA Astrophysics Data System (ADS)

    Amato, Alessandro; Bianchi, Irene; Agostinetti, Nicola Piana

    2014-12-01

    We investigate the crustal seismic structure of the Adria plate using teleseismic receiver functions (RF) recorded at 12 broadband seismic stations in the Apulia region. Detailed models of the Apulian crust, e.g. the structure of the Apulian Multi-layer Platform (AMP), are crucial for assessing the presence of potential décollements at different depth levels that may play a role in the evolution of the Apenninic orogen. We reconstruct S-wave velocity profiles applying a trans-dimensional Monte Carlo method for the inversion of RF data. Using this method, the resolution at the different depth level is completely dictated by the data and we avoid introducing artifacts in the crustal structure. We focus our study on three different key-elements: the Moho depth, the lower crust S-velocity, and the fine-structure of the AMP. We find a well defined and relatively flat Moho discontinuity below the region at 28-32 km depth, possibly indicating that the original Moho is still preserved in the area. The lower crust appears as a generally low velocity layer (average Vs = 3.7 km/s in the 15-26 km depth interval), likely suggestive of a felsic composition, with no significant velocity discontinuities except for its upper and lower boundaries where we find layering. Finally, for the shallow structure, the comparison of RF results with deep well stratigraphic and sonic log data allowed us to constrain the structure of the AMP and the presence of underlying Permo-Triassic (P-T) sediments. We find that the AMP structure displays small-scale heterogeneities in the region, with a thickness of the carbonates layers varying between 4 and 12 km, and is underlain by a thin, discontinuous layer of P-T terrigenous sediments, that are lacking in some areas. This fact may be due to the roughness in the original topography of the continental margins or to heterogeneities in its shallow structure due to the rifting process.

  4. The youngest generation GOCE products in unraveling the mysteries of the crust of North-Central Africa

    NASA Astrophysics Data System (ADS)

    Braitenberg, C.; Pivetta, T.; Li, Y.

    2012-04-01

    The newest GOCE observations produce reliable gravity data in remote areas with a resolution that is sufficient to distinguish tectonic lineaments. We use the data to formulate a model of the crust in Central-North Africa, in an area influenced by the presence of two great cratons with deep lithospheric keels, the West-African craton and the Congo craton. In the study area the crust is affected by rifting and magmatism (Benue trough and Cameroon) by basin fill (Chad basin) and by an unknown process that has produced a 1200km long line of increased density, the Chad-line (Braitenberg et al., 2011). The presence of increased localized density for the latter is demonstrated by the gravity signal it produces and which is recovered by GOCE. We integrate seismological investigations, the lithospheric flexure model, and a sediment thickness model to formulate a starting density model, for which we calculate the gravity field. This field reproduces the GOCE-observations to first order, but presents some significant residuals which we use to invert for the masses missing in our starting model. The inversion is accomplished combining spectral inversion methods with an algorithm that minimizes the constrained nonlinear multivariate potential field function iteratively. The spectral approach includes depth estimates with the continuous wavelet transform (Li et al., 2011) which we use as starting solutions of the inversion. Main results are the evidence of dense magmatic products trapped at the base of the crust beneath the Benue trough, implying that the volcanic deposits that reached the surface are only a portion of the entire melting process, as another portion is residing at lower crustal levels, at the mantle-crust transition. Another result concerns a model for the arched linear positive gravity anomaly situated on the Saharan Metacraton: our present model locates the body at upper crustal depths. The knowledge of the depth and nature of this intracrustal body is

  5. Crustal radiogenic heat production and the selective survival of ancient continental crust

    NASA Technical Reports Server (NTRS)

    Morgan, P.

    1985-01-01

    It is pointed out that the oldest terrestrial rocks have so far revealed no evidence of the impact phase of Earth evolution. This observation suggests that processes other than impact were dominant at the time of stabilization of these units. However, a use of the oldest terrestrial rocks as a sample of the early terrestrial crust makes it necessary to consider the possibility that these rocks may represent a biased sample. In the present study, the global continental heat flow data set is used to provide further evidence that potassium, uranium, and thorium abundances are, on the average, low in surviving Archean crust relative to younger continental crust. An investigation is conducted of the implications of relatively low crustal radiogenic heat production to the stabilization of early continental crust, and possible Archean crustal stabilization models are discussed.

  6. Crustal radiogenic heat production and the selective survival of ancient continental crust

    NASA Technical Reports Server (NTRS)

    Morgan, P.

    1985-01-01

    It is pointed out that the oldest terrestrial rocks have so far revealed no evidence of the impact phase of earth evolution. This observation suggests that processes other than impact were dominant at the time of stabilization of these units. However, a use of the oldest terrestrial rocks as a sample of the early terrestrial crust makes it necessary to consider the possibility that these rocks may represent a biased sample. In the present study, the global continental heat flow data set is used to provide further evidence that potassium, uranium, and thorium abundances are, on the average, low in surviving Archean crust relative to younger continental crust. An investigation is conducted of the implications of relatively low crustal radiogenic heat production to the stabilization of early continental crust, and possible Archean crustal stabilization models are discussed.

  7. Armorican provenance for the mélange deposits below the Lizard ophiolite (Cornwall, UK): evidence for Devonian obduction of Cadomian and Lower Palaeozoic crust onto the southern margin of Avalonia

    NASA Astrophysics Data System (ADS)

    Strachan, Rob A.; Linnemann, Ulf; Jeffries, Teresa; Drost, Kerstin; Ulrich, Jens

    2014-07-01

    Devonian sedimentary rocks of the Meneage Formation within the footwall of the Lizard ophiolite complex in SW England are thought to have been derived from erosion of the over-riding Armorican microplate during collision with Avalonia and the closure of the Rheic Ocean. We further test this hypothesis by comparison of their detrital zircon suites with those of autochthonous Armorican strata. Five samples analysed from SW England (Avalonia) and NW France (Armorica) have a bimodal U-Pb zircon age distribution dominated by late Neoproterozoic to middle Cambrian (c. 710-518 Ma) and Palaeoproterozoic (c. 1,800-2,200 Ma) groupings. Both can be linked with lithologies exposed within the Cadomian belt as well as the West African craton, which is characterized by major tectonothermal events at 2.0-2.4 Ga. The detrital zircon signature of Avalonia is distinct from that of Armorica in that there is a much larger proportion of Mesoproterozoic detritus. The common provenance of the samples is therefore consistent with: (a) derivation of the Meneage Formation mélange deposits from the Armorican plate during Rheic Ocean closure and obduction of the Lizard Complex and (b) previous correlation of quartzite blocks within the Meneage Formation with the Ordovician Grès Armoricain Formation of NW France.

  8. The Search for Water in the Lunar Crust

    NASA Astrophysics Data System (ADS)

    Smith, D. E.; Zuber, M. T.

    2015-10-01

    There is evidence from several sources that water ice is present at a number of locations on the surface at the lunar poles. But there seems little agreement on the source of the ice with most suggestions being of external nature, such as impacts by ice-rich comets. Here we discuss the lunar crust as a possible source of the water ice and investigate whether there is any evidence from the recent GRAIL [1,2] and Lunar Reconnaissance Orbiter (LRO) [3] missions to support this possibility.

  9. Plagioclase flotation and lunar crust formation

    NASA Technical Reports Server (NTRS)

    Walker, D.; Hays, J. F.

    1977-01-01

    Anorthitic plagioclase floats in liquids parental to the lunar highlands crust. The plagioclase enrichment that is characteristic of lunar highlands rocks can be the result of plagioclase flotation. Such rocks would form a gravitationally stable upper crust on their parental magma.

  10. Molecular evidence supports an african affinity of the neotropical freshwater gastropod, Biomphalaria glabrata, say 1818, an intermediate host for Schistosoma mansoni.

    PubMed

    Campbell, G; Jones, C S; Lockyer, A E; Hughes, S; Brown, D; Noble, L R; Rollinson, D

    2000-12-01

    Freshwater snails of the genus Biomphalaria, Preston 1910, are the most important and widely distributed intermediate hosts of Schistosoma mansoni, the blood fluke responsible for human intestinal schistosomiasis, in Africa and the Neotropics. S. mansoni is thought to have been imported repeatedly into the Americas during the last 500 years with the African slave trade. Surprisingly considering that the New and Old World separated 95-106 million years (Myr) ago, the disease rapidly became established due to the presence of endemic susceptible hosts. Reconstructing the phylogenetic relationships within Biomphalaria may provide insights into the successful intercontinental spread of S. mansoni. Parsimony and distance analyses of mitochondrial and nuclear sequences show African taxa to be monophyletic and Neotropical species paraphyletic, with Biomphalaria glabrata forming a separate clade from other Neotropical Biomphalaria, and ancestral to the African taxa. A west to east trans-Atlantic dispersal of a B. glabrata-like taxon, possibly as recently as the Plio-Pleistocene (1.8-3.6 Myr ago) according to a general mitochondrial clock, would fit these observations. Vicariance or an African origin for B. glabrata followed by multiple introductions to South America over the past 500 years with the African slave trade seem unlikely explanations. Knowledge of the phylogenetic relationships among important intermediate host species may prove useful in furthering control measures which exploit genetic differences in susceptibility to parasites, and in elucidating the evolution of schistosome resistance. PMID:11133023

  11. Europium mass balance in polymict samples and implications for plutonic rocks of the lunar crust

    SciTech Connect

    Korotev, R.L.; Haskin, L.A. )

    1988-07-01

    From correlations of SM concentration and Sm/Eu ratio with Th concentration for a large number of polymict samples from various locations in the lunar highlands and the value of 0.91 {mu}g/g for the mean Th concentration of the highlands surface crust obtained by the orbiting gamma-ray experiments. The authors estimate the mean concentrations of Sm and Eu in the lunar surface crust to be between 2 and 3 {mu}g/g Sm and 0.7 and 1.2 {mu}g/g Eu. The compositional trends indicate that there is no significant enrichment or depletion of Eu, on the average, compared to Sm relative to chondritic abundances, i.e., there is no significant Eu anomaly in average upper crust. Although rich in plagioclase ({approximately}70%), the upper crust does not offer evidence for a gross vertical separation of plagioclase from the final liquid from which it crystallized. This and the chondritic ratio of Eu/Al in average highlands material imply that the net effect of the processes that led to formation of the lunar crust was to put most of the Al and incompatible elements in the crust. Among plutonic rocks, only plagioclase in rocks from the magnesian suite can supply the excess Eu in the polymict rocks. Owing to the intermediate value of the mean Mg/Fe ratio of the crust, a significant fraction of the mafic rocks of the lunar highlands must have lower Mg/Fe ratios than the norites and troctolites of the magnesian-suite of plutonic rocks. A large fraction of the plagioclase in the lunar crust is associated not with ferroan anorthosite, but with more mafic rocks. There is little evidence in the Eu data that the lunar crust ever consisted of a thick shell of nearly pure plagioclase, as envisioned in some formulations of the magma ocean model of its formation.

  12. Evolution of the continental crust as recorded in accessory minerals

    NASA Astrophysics Data System (ADS)

    Iizuka, Tsuyoshi

    2013-04-01

    Recent developments in precise in situ isotopic analysis by LA-ICPMS and SIMS allow correlating multiple isotopic systems within single grains of accessory minerals such as zircon and monazite. The combined isotope systematics have provided valuable insights into the evolution of the continental crust. Zircon, a common accessory phase in granitoids, can be precisely dated by the U-Pb system. Zircon Lu-Hf isotopic composition is a function of crustal residence time of the magmatic protolith, whereas the O isotopic composition is a sensitive record of reworking of mature sediments such as pelite. An integration of U-Pb, Lu-Hf and O isotopic data for detrital zircons from modern large rivers indicates that: (1) the preserved continental crust dominantly formed between 3.6 and 1.0 Ga, (2) the major mode of crustal development would change during the supercontinent cycle, i.e., the generation of juvenile crust during supercontinent fragmentation versus the stabilization of the generated crust via crustal remelting during supercontinent fragmentation, and (3) reworking of mature sediments increased abruptly at ca. 2.1 Ga. No granitoids are known to have survived since 4.03 Ga. Yet evidence of an even older evolved crust is provided by detrital zircons with ages up to 4.4 Ga from Mt. Narryer and Jack Hills metasedimentary rocks in the Yilgarn Craton, Western Australia. Recently, such Hadean zircons have been found from outside the Yilgarn Craton, indicating that the young Earth had widespread granitoid crust. In addition, another accessory phase, monazite, in the Mt. Narryer and Jack Hills metasedimentary rocks offers an unique opportunity to advance our knowledge of early crustal evolution. Monazite, a light rare earth element phosphate mineral, occurs as an igneous accessory phase particularly in low-Ca granitoids, in contrast to the occurrence of igneous zircon in a wide range of granitoids. U-Pb and Sm-Nd isotope systematic of monazite are analogous to U-Pb and Lu

  13. Forearc oceanic crust in the Izu-Bonin arc - new insights from active-source seismic survey -

    NASA Astrophysics Data System (ADS)

    Kodaira, S.; Noguchi, N.; Takahashi, N.; Ishizuka, O.; Kaneda, Y.

    2009-12-01

    Petrological studies have suggested that oceanic crust is formed in forearc areas during the initial stage of subduction. However, there is little geophysical evidence for the formation of oceanic crust in those regions. In order to examine crustal formation process associated with a subduction initiation process, we conducted an active-source seismic survey at a forearc region in the Izu-Bonin intra-oceanic arc. The resultant seismic image shows a remarkably thin crust (less than 10 km) at the northern half of the Bonin ridge (at the north of the Chichi-jima) and abrupt thickening the crust (~ 20 km thick) toward the south (at the Haha-jima). Comparison of velocity-depth profiles of the thin forearc crust of the Bonin ridge with those of typical oceanic crusts showed them to be seismologically identical. The observed structural variation also well corresponds to magmatic activities along the forearc. Boninitic magmatism is evident in the area of thin crust and tholeiitic-calcalkaline andesitic volcanism in the area of thick crust. Based on high precision dating studies of those volcanic rocks, we interpreted that the oceanic-type thin crust associated with boninitic volcanism has been created soon after the initiation of subduction (45-48 Ma) and and that the nonoceanic thick crust was created by tholeiitic-calcalkaline andesitic magmatism after the boninitic magmatism was ceased. The above seismological evidences strongly support the idea of forearc oceanic crust (or phiolite) created by forearc spreading in the initial stage of subduction along the intra-oceanic arc.

  14. Millennial-scale ocean acidification and late Quaternary decline of cryptic bacterial crusts in tropical reefs.

    PubMed

    Riding, R; Liang, L; Braga, J C

    2014-09-01

    Ocean acidification by atmospheric carbon dioxide has increased almost continuously since the last glacial maximum (LGM), 21,000 years ago. It is expected to impair tropical reef development, but effects on reefs at the present day and in the recent past have proved difficult to evaluate. We present evidence that acidification has already significantly reduced the formation of calcified bacterial crusts in tropical reefs. Unlike major reef builders such as coralline algae and corals that more closely control their calcification, bacterial calcification is very sensitive to ambient changes in carbonate chemistry. Bacterial crusts in reef cavities have declined in thickness over the past 14,000 years with largest reduction occurring 12,000-10,000 years ago. We interpret this as an early effect of deglacial ocean acidification on reef calcification and infer that similar crusts were likely to have been thicker when seawater carbonate saturation was increased during earlier glacial intervals, and thinner during interglacials. These changes in crust thickness could have substantially affected reef development over glacial cycles, as rigid crusts significantly strengthen framework and their reduction would have increased the susceptibility of reefs to biological and physical erosion. Bacterial crust decline reveals previously unrecognized millennial-scale acidification effects on tropical reefs. This directs attention to the role of crusts in reef formation and the ability of bioinduced calcification to reflect changes in seawater chemistry. It also provides a long-term context for assessing anticipated anthropogenic effects. PMID:25040070

  15. Excavation and melting of the Hadean continental crust by Late Heavy Bombardment

    NASA Astrophysics Data System (ADS)

    Shibaike, Yuhito; Sasaki, Takanori; Ida, Shigeru

    2016-03-01

    No Hadean rocks have ever been found on Earth's surface except for zircons-evidence of continental crust, suggesting that Hadean continental crust existed but later disappeared. One hypothesis for the disappearance of the continental crust is excavation/melting by the Late Heavy Bombardment (LHB), a concentration of impacts in the last phase of the Hadean eon. In this paper, we calculate the effects of LHB on Hadean continental crust in order to investigate this hypothesis. Approximating the size-frequency distribution of the impacts by a power-law scaling with an exponent α as a parameter, we have derived semi-analytical expressions for the effects of LHB impacts. We calculated the total excavation/melting volume and area affected by the LHB from two constraints of LHB on the Moon, the size of the largest basin during LHB, and the density of craters larger than 20 km. We also investigated the effects of the value of α. Our results show that LHB does not excavate/melt all of Hadean continental crust directly, but over 70% of the Earth's surface area can be covered by subsequent melts in a broad range of α. If there have been no overturns of the continental crust until today, LHB could be responsible for the absence of Hadean rocks because most of Hadean continental crust is not be exposed on the Earth's surface in this case.

  16. Empowering Head Start African American and Latino Families: Promoting Strengths-Based Parenting Characteristics through Child Parent Relationship Training--An Evidence-Based Group Parenting Program

    ERIC Educational Resources Information Center

    Sheely-Moore, Angela I.; Ceballos, Peggy L.

    2011-01-01

    With the tendency of low-income African American and Latino children identified at-risk for school readiness and school success compared to their early-childhood counterparts, Head Start personnel are challenged to examine the role of family strengths in the promotion of academic success for these populations. This article provides a rationale for…

  17. Human Capital Development (HCD) through Open, Distance and E-Learning: Evidence from Corporate Annual Reports (CARs) of Top South African Listed Companies

    ERIC Educational Resources Information Center

    Adelowotan, Mo

    2014-01-01

    This paper discusses the role of open, distance and e-learning in the development of human resources by examining human capital development related disclosures in the corporate annual reports (CARs) of top South African listed companies. The study employed content analysis method to analyse the CARs of these companies with the aid of qualitative…

  18. Preliminary Evidence of a Relationship between the Use of Online Learning and Academic Performance in a South African First-Year University Accounting Course

    ERIC Educational Resources Information Center

    Halabi, Abdel K.; Essop, Ahmed; Carmichael, Teresa; Steyn, Blanche

    2014-01-01

    This paper examines the relationship between the use of online learning resources and academic performance in an Accounting 1 course conducted at a South African Higher Education Institution. The study employed a quantitative analysis over three academic years comparing the collection of end of year marks and the time spent online. The results…

  19. Continental Lower Crust: Wavespeeds, Composition, and Relamination

    NASA Astrophysics Data System (ADS)

    Hacker, B. R.; Kelemen, P. B.; Behn, M. D.

    2015-12-01

    The composition of much of Earth's lower continental crust is enigmatic. The available heat-flow and wavespeed constraints can be satisfied if lower continental crust elsewhere contains anywhere from 49 to 62 wt% SiO2 (similar to andesite and dacite), with high to moderate concentrations of K, Th and U. Beneath shields and platforms, Vp suggests that 20-30% of lower crust is mafic. A large fraction of this material could be denser than peridotite. In these settings the underlying upper mantle is too cold to permit development of a convective instability. High Vp lithologies in these settings may be the result of mafic underplating, or slow metamorphic growth of large proportions of garnet. Vp from lower crust of Paleozoic-Mesozoic orogens indicates a smaller amount of mafic rock and little or no material that is denser than peridotite. Beneath rifts, arcs, and volcanic plateaux and beneath continent-collision zones, ~10-20% of lower crust is mafic, and about half that is denser than peridotite. The inferred gravitational instability and high Moho temperatures suggest that the mafic lower crust in these regions may be temporary. During sediment subduction, subduction erosion, arc subduction, and continent subduction, mafic rocks become eclogite and may continue to descend into the mantle, whereas more silica-rich rocks are transformed into felsic gneisses that are less dense than peridotite but more dense than continental upper crust. These more-felsic rocks may rise buoyantly, undergo decompression melting and melt extraction, and may be relaminated to the base of the crust. As a result of this refining/differentiation process, such relatively felsic rocks could form much of lower crust.

  20. Microphytic crusts: 'topsoil' of the desert

    USGS Publications Warehouse

    Belnap, Jayne

    1990-01-01

    Deserts throughout the world are the home of microphytic, or cryptogamic, crusts. These crusts are dominated by cyanobacteria, previously called blue-green algae, and also include lichens, mosses, green algae, microfungi and bacteria. They are critical components of desert ecosystems, significantly modifying the surfaces on which they occur. In the cold deserts of the Colorado Plateau (including parts of Utah, Arizona, Colorado, and New Mexico), these crusts are extraordinarily well-developed, and may represent 70-80% of the living ground cover.

  1. Localization of the gene causing keratolytic winter erythema to chromosome 8p22-p23, and evidence for a founder effect in South African Afrikaans-speakers.

    PubMed Central

    Starfield, M; Hennies, H C; Jung, M; Jenkins, T; Wienker, T; Hull, P; Spurdle, A; Küster, W; Ramsay, M; Reis, A

    1997-01-01

    Keratolytic winter erythema (KWE), also known as "Oudtshoorn skin disease," or "erythrokeratolysis hiemalis," is an autosomal dominant skin disorder of unknown etiology characterized by a cyclical erythema, hyperkeratosis, and recurrent and intermittent peeling of the palms and soles, particularly during winter. Initially KWE was believed to be unique to South Africa, but recently a large pedigree of German origin has been identified. The disorder occurs with a prevalence of 1/7,000 in the South African Afrikaans-speaking Caucasoid population, and this high frequency has been attributed to founder effect. After a number of candidate regions were excluded from linkage to KWE in both the German family and several South African families, a genomewide analysis was embarked on. Linkage to the microsatellite marker D8S550 on chromosome 8p22-p23 was initially observed, with a maximum LOD score (Z(max)) of 9.2 at a maximum recombination fraction (theta(max)) of .0 in the German family. Linkage was also demonstrated in five of the larger South African families, with Z(max) = 7.4 at theta(max) = .02. When haplotypes were constructed, 11 of 14 South African KWE families had the complete "ancestral" haplotype, and 3 demonstrated conservation of parts of this haplotype, supporting the hypothesis of founder effect. The chromosome segregating with the disease in the German family demonstrated a different haplotype, suggesting that these chromosomes do not have a common origin. Recombination events place the KWE gene in a 6-cM interval between D8S550 and D8S552. If it is assumed that there was a single South African founder, a proposed ancestral recombinant suggests that the gene is most likely in a 1-cM interval between D8S550 and D8S265. PMID:9311742

  2. Primary carbonatite melt from deeply subducted oceanic crust

    SciTech Connect

    Walter, M.J.; Bulanova, G.P.; Armstrong, L.S.; Keshav, S.; Blundy, J.D.; Gudfinnesson, G.; Lord, O.T.; Lennie, A.R.; Clark, S.M.; Smith, C.B.; Gobbo, L.

    2008-07-01

    Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here they provide exper8imental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years.

  3. Crust formation and plate motion in the early archean.

    PubMed

    Kröner, A; Layer, P W

    1992-06-01

    Mounting evidence for voluminous continental crust formation in the early Archean involving intracrustal melting and selective preservation of granitoid rocks suggests that initial crust formation crust formation and growth were predominantly by magmatic underplating in plumegenerated Iceland-type settings. Collision of these early islands to give rise to larger blocks is suggested by extensive horizontal shortening in both supracrustal and granitoid assemblages. Preservation of early Archean high-grade gneisses that were once at depths of 20 to 30 kilometers implies that these blocks developed thick, subcrustal roots despite high mantle heat flow. Rigid continental plates must have existed since at least 3.5 billion years ago, and greenstone belts (composed of mixed metavolcanic and metasedimentary sequences intruded by granitoid plutons) probably developed on or near these microcontinents. Paleomagnetic data with good age control from at least one ancient craton suggest that plate motion was at normal minimum average velocities of about 17 millimeters per year with respect to the poles during the period 3.5 billion to 2.4 billion years ago. If this is true on a global scale, Archean plate motion was not faster than in later geologic times. PMID:17791608

  4. Primary carbonatite melt from deeply subducted oceanic crust.

    PubMed

    Walter, M J; Bulanova, G P; Armstrong, L S; Keshav, S; Blundy, J D; Gudfinnsson, G; Lord, O T; Lennie, A R; Clark, S M; Smith, C B; Gobbo, L

    2008-07-31

    Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here we provide experimental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years. PMID:18668105

  5. Granulites: Melts and fluids in the deep crust

    NASA Technical Reports Server (NTRS)

    Valley, John W.

    1988-01-01

    Known examples of granulite facies metamorphism span at least 3.5 by. of Earth history. Mineralogic geobarometry indicates that such metamorphism has occurred in the deep crust, typically at 20 to 30 km (6 to 9 kbar). Geothermometry indicates that peak T = 700 to 900 C and therefore that T was elevated by at least 200 C over an anorgenic geotherm of 15 to 20 C/km. Commonly invoked sources of heat include rising magmas, radioactive decay insulated by continent/continent collision, mantle volatiles, or crustal thinning. Present day crustal thicknesses are normal beneath exposed granulite terranes and the common absence of evidence for post-metamorphic underplating suggests synmetamorphic thicknesses of 60 to 80 km. Thus granulites form in tectonically active regions of thickened crust and elevated geotherm. Xenolith suites suggest that granulite facies mineralogy persists in the deepest crust after tectonism in spite of declining temperature to greenschist/amphibolite facies conditions. The relative proportions of granulite terranes that are formed by Adirondack-type metamorphism dominantly magmatic/fluid-absent), India-type metamorphism (CO2 saturated), or some combination of 1 and 2 remains an important tectonic question.

  6. The breaking strain of neutron star crust

    SciTech Connect

    Kadau, Kai; Horowitz, C J

    2009-01-01

    Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of neutron star crust. With multimillion ion molecular dynamics simulations of Coulomb solids representing the crust, we show that the breaking strain of pure single crystals is very large and that impurities, defects, and grain boundaries only modestly reduce the breaking strain to around 0.1. Due to the collective behavior of the ions during failure found in our simulations, the neutron star crust is likely very strong and can support mountains large enough so that their gTavitational wave radiation could limit the spin periods of some stars and might be detectable in large scale interferometers. Furthermore, our microscopic modeling of neutron star crust material can help analyze mechanisms relevant in Magnetar Giant and Micro Flares.

  7. Drilling to gabbro in intact ocean crust.

    PubMed

    Wilson, Douglas S; Teagle, Damon A H; Alt, Jeffrey C; Banerjee, Neil R; Umino, Susumu; Miyashita, Sumio; Acton, Gary D; Anma, Ryo; Barr, Samantha R; Belghoul, Akram; Carlut, Julie; Christie, David M; Coggon, Rosalind M; Cooper, Kari M; Cordier, Carole; Crispini, Laura; Durand, Sedelia Rodriguez; Einaudi, Florence; Galli, Laura; Gao, Yongjun; Geldmacher, Jörg; Gilbert, Lisa A; Hayman, Nicholas W; Herrero-Bervera, Emilio; Hirano, Nobuo; Holter, Sara; Ingle, Stephanie; Jiang, Shijun; Kalberkamp, Ulrich; Kerneklian, Marcie; Koepke, Jürgen; Laverne, Christine; Vasquez, Haroldo L Lledo; Maclennan, John; Morgan, Sally; Neo, Natsuki; Nichols, Holly J; Park, Sung-Hyun; Reichow, Marc K; Sakuyama, Tetsuya; Sano, Takashi; Sandwell, Rachel; Scheibner, Birgit; Smith-Duque, Chris E; Swift, Stephen A; Tartarotti, Paola; Tikku, Anahita A; Tominaga, Masako; Veloso, Eugenio A; Yamasaki, Toru; Yamazaki, Shusaku; Ziegler, Christa

    2006-05-19

    Sampling an intact sequence of oceanic crust through lavas, dikes, and gabbros is necessary to advance the understanding of the formation and evolution of crust formed at mid-ocean ridges, but it has been an elusive goal of scientific ocean drilling for decades. Recent drilling in the eastern Pacific Ocean in Hole 1256D reached gabbro within seismic layer 2, 1157 meters into crust formed at a superfast spreading rate. The gabbros are the crystallized melt lenses that formed beneath a mid-ocean ridge. The depth at which gabbro was reached confirms predictions extrapolated from seismic experiments at modern mid-ocean ridges: Melt lenses occur at shallower depths at faster spreading rates. The gabbros intrude metamorphosed sheeted dikes and have compositions similar to the overlying lavas, precluding formation of the cumulate lower oceanic crust from melt lenses so far penetrated by Hole 1256D. PMID:16627698

  8. Crustal structure of Precambrian terranes in the southern African subcontinent with implications for secular variation in crustal genesis

    NASA Astrophysics Data System (ADS)

    Kachingwe, Marsella; Nyblade, Andrew; Julià, Jordi

    2015-07-01

    New estimates of crustal thickness, Poisson's ratio and crustal shear wave velocity have been obtained for 39 stations in Angola, Botswana, the Democratic Republic of Congo, Malawi, Mozambique, Namibia, Rwanda, Tanzania and Zambia by modelling P-wave receiver functions using the H-κ stacking method and jointly inverting the receiver functions with Rayleigh-wave phase and group velocities. These estimates, combined with similar results from previous studies, have been examined for secular trends in Precambrian crustal structure within the southern African subcontinent. In both Archean and Proterozoic terranes we find similar Moho depths [38-39 ± 3 km SD (standard deviation)], crustal Poisson's ratio (0.26 ± 0.01 SD), mean crustal shear wave velocity (3.7 ± 0.1 km s-1 SD), and amounts of heterogeneity in the thickness of the mafic lower crust, as defined by shear wave velocities ≥4.0 km s-1. In addition, the amount of variability in these crustal parameters is similar within each individual age grouping as between age groupings. Thus, the results provide little evidence for secular variation in Precambrian crustal structure, including between Meso- and Neoarchean crust. This finding suggests that (1) continental crustal has been generated by similar processes since the Mesoarchean or (2) plate tectonic processes have reworked and modified the crust through time, erasing variations in structure resulting from crustal genesis.

  9. Workshop on the Growth of Continental Crust

    NASA Technical Reports Server (NTRS)

    Ashwal, Lewis D. (Editor)

    1988-01-01

    Constraints and observations were discussed on a fundamental unsolved problem of global scale relating to the growth of planetary crusts. All of the terrestrial planets were considered, but emphasis was placed on the Earth's continental crust. The title of each session is: (1) Extraterrestrial crustal growth and destruction; (2) Constraints for observations and measurements of terrestrial rocks; (3) Models of crustal growth and destruction; and (4) Process of crustal growth and destruction.

  10. Rapid Ascent of Aphyric Mantle Melts through the Overriding Crust in Subduction Zones: Evidence from Variable Uranium-Series Disequilibria, Amorphous Hydrous Alteration Microtextures in Crystal Rims, and Two-Pyroxene Pseudo-Decompression Paths

    NASA Astrophysics Data System (ADS)

    Zellmer, G. F.; Freymuth, H.; Hsieh, H. H.; Hwang, S. L.; Iizuka, Y.; Miller, C. A.; Rubin, K. H.; Sakamoto, N.; Yurimoto, H.

    2014-12-01

    Volcanic hazard mitigation at subduction zones critically depends on knowledge of magma generation and ascent processes and timescales. Two diametrically opposite scenarios are presently debated: One paradigm is the generation of low-silica (basaltic) melts in the mantle wedge, followed by protracted sub-liquidus magma ascent and evolution through crystal growth and fractionation in crustal reservoirs, which are tapped during volcanic eruptions. In contrast, a diametrically opposite model favours the generation of higher silica melts in the mantle or in a lower crustal hot zone, followed by rapid decompression to the surface under super-liquidus conditions. In the latter case, crystals are picked up during magma ascent, and are in the process of dissolving. We present multiple lines of evidence that point to crystal uptake as the principal processes by which arc melts acquire their crystal cargo: (i) variable 234U-238U disequilibria in mineral separates; (ii) hydrous mineral rims with amorphous alteration textures; and (iii) two-pyroxene pseudo-decompression paths; cf. Zellmer et al. (2014a,b,c), doi: 10.1144/SP385.3 and 10.1144/SP385.9 and 10.1144/SP410.1. These observations point to a scarcity of true phenocrysts in many arc magmas, and thus to decompression of aphyric melts that take up their crystal cargo during ascent. The data imply that many hydrous wedge melts are more silica-rich than basalts and achieve super-liquidus conditions during rapid ascent from great depth.

  11. Mafic granulite rheology: Implications for a weak continental lower crust

    NASA Astrophysics Data System (ADS)

    Wang, Y. F.; Zhang, J. F.; Jin, Z. M.; Green, H. W.

    2012-11-01

    The “jelly sandwich” model of continental rheology, long the consensus model, has recently been challenged. The controversy is based on the rheology of mafic granulite that is thought to make up most of the lower continental crust. However, because of technical issues in experimental rock deformation, there are very few data on this problem. Here we report the rheology and fabrics of a reconstituted, fine-grained nominally dry (i.e., no hydrous mineral) mafic granulite (57% plagioclase+24% clinopyroxene+14% orthopyroxene+5% opaque minerals, 0.16-0.28 wt% H2O) deformed at 1.1-1.2 GPa pressure in a modified Griggs-type deformation apparatus. The rheology of this mafic granulite can be described by the constitutive equation of ε˙=Aσexp(-(244±35 kJ/mol)/RT) where ε˙ is in s-1, σ in MPa, T in Kelvin and A=10-2.0±1.6 MPa-3.2 s-1. Our results provide new experimental evidence in support of the “jelly sandwich” lithosphere strength model and imply that mafic granulite with a moderate amount of water (>0.05-0.08 wt% H2O) is likely to be a weak layer in the lithosphere. Both pyroxenes and plagioclase develop pronounced fabrics in responding to axial deformation. The deformation mechanism is dislocation creep with (100)[001], and (001)[100]/(010)[100] being the dominant slip systems for pyroxenes and plagioclase, respectively. The low strength of mafic granulite is ascribed largely to the significant weakening effect of dissolved water in pyroxenes and plagioclase. A weak continental lower crust has many important implications for geodynamics of crust-mantle interactions, such as lower crust channel flow and delamination.

  12. Synthetic petroleum stability under thermobaric conditions of the Earth crust

    NASA Astrophysics Data System (ADS)

    Serovaiskii, Aleksandr; Kolesnikov, Anton; Kutcherov, Vladimir

    2016-04-01

    Nowadays there are several dozens of large crude oil deposits at the depth more than 10 km (Kutcherov and Krayushkin, 2010). The existence of such deep oil fields at the depth exceeding conventional "oil window" could be explained by the migration of the deep fluid from the asthenosphere. This fluid migrates up to the surface and forms oil and gas deposits in different kind of rocks in the on various depths of the Earth's crust. Crude oil consists of a great numbers of different hydrocarbons. Its precise molecular composition is impossible to investigate nowadays. Instead of the natural hydrocarbons mixture synthetic petroleum with simpler composition was used in the experiments. The synthetic petroleum stability was investigated at the Earth crust thermobaric conditions corresponding to the depth down to 50 km. The experiments were carried out in Diamond Anvil Cells (DAC) with the internal resistive heating. Raman spectroscopy was used to analyse the petroleum composition. The analysis of the sample was made in situ during the experiment. Ruby and Sm:YAG Raman shifts were the controllers of the temperature and pressure inside the sample (Trots et al., 2012; Mao et al., 1986). Three series of the experiments were carried out at 320°C and 0.7GPa, 420°C and 1.2GPa, 450°C and 1.4GPa. After the experiment the Raman spectra of the sample was compared to the reference spectra of the petroleum before the experiment. The comparison showed no changes in the sample's composition after the experiment. Obtained data may explain the existence of deep oil fields located deeper than the "oil window". It can broaden the knowledge about the existing range of depths for the crude oil and natural gas deposits in the Earth crust. The evidence of the petroleum existence in the Earth low crust may support the existence of unconventional, deep abyssal hydrocarbons source.

  13. Archaean Crustal Growth, Proterozoic Terrane Amalgamation and the Pan-African Orogeny, as Recorded in the NE African Sedimentary Record.

    NASA Astrophysics Data System (ADS)

    Najman, Y.; Fielding, L.; Millar, I.; Butterworth, P.; Andò, S.; Padoan, M.; Barfod, D. N.; Kneller, B. C.

    2015-12-01

    The cratons of Central Africa are formed of various blocks of Archaean and Palaeoproterozoic crust, flanked or truncated by Palaeoproterozoic to Mesoproterozoic orogenic belts. The geology of east Africa has largely been shaped by the events of the Pan-African Orogeny when east and west Gondwana collided to form 'Greater Gondwana' at the end of the Neoproterozoic. The Pan-African orogeny in NE Africa involved the collision of Archaean cratons and the Saharan Metacraton with the Arabian Nubian Shield, a terrane comprising Neoproterozoic juvenile oceanic island arcs. Phanerozoic cover sedimentary rocks, eroded from the Pan-African orogenies, blanket much of NE Africa. Detrital data from these Phanerozoic cover sedimentary rocks, and modern rivers draining both the cover the basement, provide a wealth of information on basement evolution, of particular relevance for regions where the basement itself is poorly exposed due to ancient or modern sedimentary cover. From samples collected in Uganda, Ethiopia, Sudan and Egypt, we provide combined U-Pb and Hf-isotope zircon, U-Pb rutile and Ar-Ar mica datasets, heavy mineral analyses, and bulk trace element data, from Archaean basement, Phanerozoic cover and modern river sediment from the Nile and its tributaries to document the evolution of the North African crust. The data document early crust-forming events in the Congo Craton and Sahara Metacraton, phased development of the Arabian Nubian Shield culminating in the Neoproterozoic assembly of Gondwana during the Pan African Orogeny, and the orogen's subsequent erosion, with deposition of voluminous Phanerozoic cover.

  14. Barriers to Hospice Use among African Americans: A Systematic Review

    ERIC Educational Resources Information Center

    Washington, Karla T.; Bickel-Swenson, Denise; Stephens, Nathan

    2008-01-01

    The present review was undertaken to explore recent evidence in the professional literature pertaining to use of hospice services by African Americans. The article addresses the research methods that have been used to study African American hospice use, obstacles to African American participation in hospice that have been identified, and…

  15. Some Growth Points in African Child Development Research

    ERIC Educational Resources Information Center

    Serpell, Robert; Marfo, Kofi

    2014-01-01

    We reflect on ways in which research presented in earlier chapters responds to challenges of generating an African child development field and identify additional issues calling for the field's attention. The chapters collectively display a variety of African contexts and reflexive evidence of the authors' African cultural roots.…

  16. Project Among African-Americans to Explore Risks for Schizophrenia (PAARTNERS): Evidence for Impairment and Heritability of Neurocognitive Functioning in Families of Schizophrenia Patients

    PubMed Central

    Calkins, Monica E.; Tepper, Ping; Gur, Ruben C.; Ragland, J. Daniel; Klei, Lambertus; Wiener, Howard W.; Richard, Jan; Savage, Robert M.; Allen, Trina B.; O'Jile, Judith; Devlin, Bernie; Kwentus, Joseph; Aliyu, Muktar H.; Bradford, L. DiAnne; Edwards, Neil; Lyons, Paul D.; Nimgaonkar, Vishwajit L.; Santos, Alberto B.; Go, Rodney C.P.; Gur, Raquel E.

    2015-01-01

    Objective Neurocognitive impairments in schizophrenia are well replicated and widely regarded as candidate endophenotypes that may facilitate understanding of schizophrenia genetics and pathophysiology. The Project Among African-Americans to Explore Risks for Schizophrenia (PAARTNERS) aims to identify genes underlying liability to schizophrenia. The unprecedented size of its study group (N=1,872), made possible through use of a computerized neurocognitive battery, can help further investigation of the genetics of neurocognition. The current analysis evaluated two characteristics not fully addressed in prior research: 1) heritability of neurocognition in African American families and 2) relationship between neurocognition and psychopathology in families of African American probands with schizophrenia or schizoaffective disorder. Method Across eight data collection sites, patients with schizophrenia or schizoaffective disorder (N=610), their biological relatives (N=928), and community comparison subjects (N=334) completed a standardized diagnostic evaluation and the computerized neurocognitive battery. Performance accuracy and response time (speed) were measured separately for 10 neurocognitive domains. Results The patients with schizophrenia or schizoaffective disorder exhibited less accuracy and speed in most neurocognitive domains than their relatives both with and without other psychiatric disorders, who in turn were more impaired than comparison subjects in most domains. Estimated trait heritability after inclusion of the mean effect of diagnostic status, age, and sex revealed significant heritabilities for most neurocognitive domains, with the highest for accuracy of abstraction/ flexibility, verbal memory, face memory, spatial processing, and emotion processing and for speed of attention. Conclusions Neurocognitive functions in African American families are heritable and associated with schizophrenia. They show potential for gene-mapping studies. PMID:20194479

  17. African Aesthetics

    ERIC Educational Resources Information Center

    Abiodun, Rowland

    2001-01-01

    No single traditional discipline can adequately supply answers to the many unresolved questions in African art history. Because of the aesthetic, cultural, historical, and, not infrequently, political biases, already built into the conception and development of Western art history, the discipline of art history as defined and practiced in the West…

  18. Stable isotope and Ar/Ar evidence of prolonged multi-scale fluid flow during exhumation of orogenic crust: example from the Mont Blanc and Aar massifs (NW Alps)

    NASA Astrophysics Data System (ADS)

    Rolland, Yann; Rossi, Magali

    2015-04-01

    The spatial and temporal scales and the geometry of fluid pathways in a collisional orogen are investigated using stable isotope analysis (O, C, H) and 40Ar/39Ar dating of vein minerals formed at c. 11-16 Ma in the Mont Blanc and the Aar External Crystalline Massifs. In both massifs 40Ar/39Ar dating of veins adularia provides evidence for progressive crystallization from 16 to 9 Ma, and mainly at 11-12 Ma following veins opening during shear zone activity. The fluid flow duration thus ranges from 4 to 5 Ma in the two massifs. The δ18O values of vein quartz and calcite are similar to those of undeformed crystalline and sedimentary host-rocks, suggesting rock buffering, while carbon isotope ratios of vein calcites fall into three compositional groups. A-type veins have δ13C values that are buffered by the Helvetic metasediments, which suggests that these veins formed in a closed-system from a locally-derived CO2-rich fluid. The fluid in equilibrium with C-type veins has depleted δ13C values similar to mantle-CO2, while the intermediate δ13C values of B-type veins suggest mixing between the A-type and C-type fluids. These results are in agreement with crustal- to lithosphere-scale upward vertical fluid flow along vertical shear zones related to the strike-slip system bounding the Adriatic block since 16-20 Ma, connecting a deep-seated fluid to some downward flow in the sedimentary cover of External Crystalline Massifs.

  19. Mesozoic invasion of crust by MORB-source asthenospheric magmas, U.S. Cordilleran interior

    NASA Astrophysics Data System (ADS)

    Leventhal, Janet A.; Reid, Mary R.; Montana, Art; Holden, Peter

    1995-05-01

    Mafic and ultramafic xenoliths entrained in lavas of the Cima volcanic field have Nd and Sr isotopic ratios indicative of a source similar to that of mid-ocean ridge basalt (MORB). Nd and Sr internal isochrons demonstrate a Late Cretaceous intrusion age. These results, combined with evidence for emplacement in the lower crust and upper mantle, indicate invasion of the lower crust by asthenospheric magmas in the Late Cretaceous. Constituting the first prima facie evidence for depleted-mantle magmatism in the Basin and Range province prior to late Cenozoic volcanism, these results lend key support to models suggesting crustal heating by ascent of asthenosphere in the Mesozoic Cordilleran interior.

  20. Granitic Perspectives on the Generation and Secular Evolution of the Continental Crust

    NASA Astrophysics Data System (ADS)

    Kemp, A. I. S.; Hawkesworth, C. J.

    2003-12-01

    Every geologist is acquainted with the principle of "uniformitarianism," which holds that present-day processes are the key to those that operated in the past. But the extent this applies to the processes driving the growth and differentiation of the Earth's continental crust remains a matter of debate. Unlike its dense oceanic counterpart, which is recycled back into the mantle by subduction within 200 Ma (see Chapter 3.13), the continental crust comprises buoyant quartzofeldspathic materials and is difficult to destroy by subduction. The continental crust is, therefore, the principal record of how conditions on the Earth have changed, and how processes of crust generation have evolved through geological time. It preserves evidence of secular variation in crustal compositions, and thus the way in which the crust has formed throughout Earth's history. Exploring the nature and origin of these variations is the focus of this chapter.Continental rocks are highly differentiated, and so the crust is enriched in incompatible components compared to the primeval chondritic composition (see Chapter 3.01). Of these, water is perhaps the most relevant, both for the origin and evolution of life, and also for many models of crust generation and differentiation. Similarly, the mass of continental crust is just 0.57% of the silicate Earth, and yet it contains ˜35% of the potassium (using the crustal composition estimates in Table 1). Continental rocks comprise the buoyant shell that was once thought to float on a basaltic substratum, inferred from the wide distribution of chemically similar continental flood basalts (von Cotta, 1858). The links with the adjacent oceans were perhaps unclear, "the greatest mountains confront the widest oceans" ( Dana, 1873). Yet, it has long been argued that the rock that has the most similar composition to the average continental crust, andesite, may be generated by fractional crystallization of basalt ( Daly (1914) and Bowen (1928); but see the

  1. Transdomes sampling of lower and middle crust

    NASA Astrophysics Data System (ADS)

    Teyssier, C. P.; Whitney, D. L.; Roger, F.; Rey, P. F.

    2015-12-01

    Migmatite transdomes are formed by lateral and upward flow of partially molten crust in transtension zones (pull-apart structures). In order to understand the flow leading to this type of domes, 3D numerical models were set-up to simulate the general case of an extensional domain located between two strike-slip faults (pull-apart or dilational bridge). Results show that upper crust extension induces flow of the deep, low-viscosity crust, with rapid upward movement of transdome material when extension becomes localized. At this point a rolling hinge detachment allows rapid removal of upper crust. The internal structure of transdomes includes a subvertical high strain zone located beneath the zone of localized upper crust extension; this shear zone separates two elongate subdomes of foliation that show refolded/sheath folds. Lineation tends to be oriented dominantly subhorizontal when the amount of strike-slip motion is greater than the amount of upward flow of dome rocks. Models also predict nearly isothermal decompression of transdome material and rapid transfer of ~50 km deep rocks to the near surface. These model results are compared to the structural and metamorphic history of several transdomes, and in particular the Variscan Montagne Noire dome (French Massif Central) that consists of two domes separated by a complex high strain zone. The Montagne Noire dome contains ~315 Ma eclogite bodies (U-Pb zircon age) that record 1.4 GPa peak pressure. The eclogite bodies are wrapped in highly sheared migmatite that yield 314-310 Ma monazite ages interpreted as the metamorphism and deformation age. Based on these relations we conclude that the Montagne Noire transdome developed a channel of partially molten crust that likely entrained eclogite bodies from the deep crust (~50 km) before ascending to the near-surface. One implication of this work is that the flowing crust was deeply seated in the orogen although it remained a poor recorder of peak pressure of metamorphism

  2. The content of African diets is adequate to achieve optimal efficacy with fixed-dose artemether-lumefantrine: a review of the evidence

    PubMed Central

    Premji, Zulfiqarali G; Abdulla, Salim; Ogutu, Bernhards; Ndong, Alice; Falade, Catherine O; Sagara, Issaka; Mulure, Nathan; Nwaiwu, Obiyo; Kokwaro, Gilbert

    2008-01-01

    A fixed-dose combination of artemether-lumefantrine (AL, Coartem®) has shown high efficacy, good tolerability and cost-effectiveness in adults and children with uncomplicated malaria caused by Plasmodium falciparum. Lumefantrine bioavailability is enhanced by food, particularly fat. As the fat content of sub-Saharan African meals is approximately a third that of Western countries, it raises the question of whether fat consumption by African patients is sufficient for good efficacy. Data from healthy volunteers have indicated that drinking 36 mL soya milk (containing only 1.2 g of fat) results in 90% of the lumefantrine absorption obtained with 500 mL milk (16 g fat). African diets are typically based on a carbohydrate staple (starchy root vegetables, fruit [plantain] or cereals) supplemented by soups, relishes and sauces derived from vegetables, pulses, nuts or fish. The most important sources of dietary fat in African countries are oil crops (e.g. peanuts, soya beans) and cooking oils as red palm, peanut, coconut and sesame oils. Total fat intake in the majority of subSaharan countries is estimated to be in the range 30–60 g/person/day across the whole population (average 43 g/person/day). Breast-feeding of infants up to two years of age is standard, with one study estimating a fat intake of 15–30 g fat/day from breast milk up to the age of 18 months. Weaning foods typically contain low levels of fat, and the transition from breast milk to complete weaning is associated with a marked reduction in dietary fat. Nevertheless, fat intake >10 g/day has been reported in young children post-weaning. A randomized trial in Uganda reported no difference in the efficacy of AL between patients receiving supervised meals with a fixed fat content (~23 g fat) or taking AL unsupervised, suggesting that fat intake at home was sufficient for optimal efficacy. Moreover, randomized trials in African children aged 5–59 months have shown similar high cure rates to those observed

  3. The content of African diets is adequate to achieve optimal efficacy with fixed-dose artemether-lumefantrine: a review of the evidence.

    PubMed

    Premji, Zulfiqarali G; Abdulla, Salim; Ogutu, Bernhards; Ndong, Alice; Falade, Catherine O; Sagara, Issaka; Mulure, Nathan; Nwaiwu, Obiyo; Kokwaro, Gilbert

    2008-01-01

    A fixed-dose combination of artemether-lumefantrine (AL, Coartem(R)) has shown high efficacy, good tolerability and cost-effectiveness in adults and children with uncomplicated malaria caused by Plasmodium falciparum. Lumefantrine bioavailability is enhanced by food, particularly fat.As the fat content of sub-Saharan African meals is approximately a third that of Western countries, it raises the question of whether fat consumption by African patients is sufficient for good efficacy. Data from healthy volunteers have indicated that drinking 36 mL soya milk (containing only 1.2 g of fat) results in 90% of the lumefantrine absorption obtained with 500 mL milk (16 g fat). African diets are typically based on a carbohydrate staple (starchy root vegetables, fruit [plantain] or cereals) supplemented by soups, relishes and sauces derived from vegetables, pulses, nuts or fish. The most important sources of dietary fat in African countries are oil crops (e.g. peanuts, soya beans) and cooking oils as red palm, peanut, coconut and sesame oils. Total fat intake in the majority of subSaharan countries is estimated to be in the range 30-60 g/person/day across the whole population (average 43 g/person/day). Breast-feeding of infants up to two years of age is standard, with one study estimating a fat intake of 15-30 g fat/day from breast milk up to the age of 18 months. Weaning foods typically contain low levels of fat, and the transition from breast milk to complete weaning is associated with a marked reduction in dietary fat. Nevertheless, fat intake >10 g/day has been reported in young children post-weaning. A randomized trial in Uganda reported no difference in the efficacy of AL between patients receiving supervised meals with a fixed fat content (~23 g fat) or taking AL unsupervised, suggesting that fat intake at home was sufficient for optimal efficacy. Moreover, randomized trials in African children aged 5-59 months have shown similar high cure rates to those observed in

  4. Iron Isotopic Fractionation in Early Planetary Crusts

    NASA Astrophysics Data System (ADS)

    Wang, K.; Moynier, F.; Dauphas, N.; Barrat, J.; Day, J. M.; Sio, C.; Korotev, R. L.; Zeigler, R. A.

    2012-12-01

    Differentiated meteorites (achondrites) derive from planetary bodies that experienced variable degrees of melting and silicate-metal segregation. The oldest achondrites, such as eucrites, angrites, brachinites and the oligoclase-rich meteorites Graves Nunataks 06128/06129 (GRA 06128/9), were formed ~2-5 Ma after the first Solar System solids. They represent the oldest differentiated silicate samples known in the Solar System and the study of these samples provides insight on the origins and conditions of formation of the first planetary crusts. Here, we present new high-precision data for the Fe isotopic compositions of eucrites, angrites, brachinites and GRA 06128/9 and interpret these results in terms of magmatism during formation of these samples. We find that most eucrites and brachinites are not fractionated compared to undifferentiated chondritic meteorites (δ56Fe = 0.00±0.01, 2se), while the rare Stannern-trend eucrites are slightly enriched in the heavier isotopes of Fe. Angrites are also enriched in the heavier isotopes (δ56Fe = 0.12±0.01, 2se), similar to what is observed for terrestrial basalts, reflecting the relatively high oxidation states of the angrite parent body(ies). Contrastingly to the 'basaltic' achondrites, GRA 06128/9 are enriched in light isotopes of Fe (δ56Fe = -0.08±0.02, 2se). Evidence for light Fe isotope enrichments may be the consequence of the segregation of magma rich in sulphide (usually enriched in light isotopes of Fe compared to silicate and metal in undifferentiated meteorites). If correct, this result not only confirms that GRA 06128/9 represent products from <30% partial melting of an asteroidal body, prior to core formation, but also indicates complementary Fe isotope systematics between GRA 06128/9 and brachinites.

  5. Osmium Isotope Straigraphy of Ferromanganese Crusts

    NASA Astrophysics Data System (ADS)

    Bolz, V.; Levasseur, S.; Frank, M.; Hein, J.; Halliday, A.

    2004-12-01

    To interpret the changes in isotopic compositions recorded in hydrogenetic ferromanganese (Fe-Mn) crusts over time it is essential to calibrate them in terms of time. The 10Be method is only reliable for the first 10 Myr. For older parts of the crusts the Co-constant flux method is used. Both approaches however, will fail to account for any growth hiatus or erosion in the sections older than 10 Ma. Attempts at using Sr isotope stratigraphy failed because of post-depositional exchange. For osmium (Os) isotopes on the other hand, calculations of the rate of post-depositional exchange suggest that long-term records in Fe-Mn crusts are reliable. This would allow the 187Os/188Os profile of any hydrogeneous Fe-Mn crust to be fitted against the 187Os/188Os seawater record established for the last 80 Myr. This stratigraphic method would determine the age of crusts at any depth and identify changes in growth rate, cessation of growth and/or intervals of crust erosion. We tested this hypothesis on the hydrogeneous crust CD29-2 from the Central Pacific Ocean which had been subject to many previous radiogenic isotope studies. CD29-2 is a 105mm thick crust with a growth rate of 2.1mm/Myr, as determined from 10Be/9Be ratios and the Co-constant flux method. This gives a minimum age of 50 Ma for the lowermost portions of the crust. Samples were taken every 2mm through the crust which results in a time-spacing of 1Myr assuming a constant growth. For each sample the 187Os/188Os ratio and the 187Os concentration ([187Os]) were determined by ID-NTIMS. The [187Re] was measured by MC-ICPMS, allowing correction for 187 Re-decay. The corrected 187Os/188Os ratios were compared to the seawater record. Using the Be and Co time scales, the 187Os/188Os curve obtained from the crust shows a distorted version of the established seawater record. A good match is found if three hiatuses are allowed. The first hiatus of 15 Myr is assigned to the period between 13 and 28 Ma, a second one of 3 Myr to

  6. Partial melting of subducting oceanic crust

    NASA Astrophysics Data System (ADS)

    Peacock, Simon M.; Rushmer, Tracy; Thompson, Alan Bruce

    1994-01-01

    The conditions under which partial melting of subducting oceanic crust occurs can be determined by combining a partial melting model for basaltic compositions with two-dimensional thermal models of subduction zones. For porosities of approximately 1% containing H2O the amount of partial melt generated at the wet basaltic solidus is limited to less than 5 vol%. At higher temperatures (approximately 1000 C at 1.5 GPa) large amounts of partial melt, up to 50 vol%, form by the breakdown of amphibole and the release of structurally bound H2O. In most subduction zones, substantial partial melting of subducting oceanic crust will only occur if high shear stresses (greater than approximately 100 MPa) can be maintained by rocks close to, or above, their melting temperatures. In the absence of high shear stresses, substantial melting of the oceanic crust will only occur during subduction of very young (less than 5 Ma) oceanic lithosphere. Partial melting of hydrated basalt (amphibolites) derived from the mid-ocean ridge has been proposed as being responsible for the generation of certain recent high-Al andesitic to dacitic volcanic rocks (adakites). Three of these volcanic suites (Mount St. Helens, southern Chile, and Panama) occur in volcanic arcs where oceanic crust less than 25 Ma is being subducted at rates of 1 - 3 cm/yr and the calculated thermal regime is several hundreds of degrees hotter than more typical subduction zone environments. However, oceanic lithosphere is not currently being subducted beneath Baja and New Guinea, where recent adakites are also present, suggesting that some adakite magmas may form by water-undersaturated partial melting of underplated mafic lower crust or previously subducted oceanic crust. Further experimental work on compositions representative of oceanic crust is required to define the depth of possible adakite source regions more accurately.

  7. Crust and Upper Mantle of North Africa Using Libyan Seismic Data

    NASA Astrophysics Data System (ADS)

    Pasyanos, M. E.; Eshwehdi, A.

    2005-12-01

    We investigate the crust and upper mantle structure of North Africa using Libyan seismic data. Libya sits at the transition between the relatively aseismic continental crust of the African plate and the seismically active oceanic crust under the Mediterranean Sea which is subducting under the Eurasian Plate along the Calabrian, Hellenic, and Cyprean Arcs. The country also encompasses the Sirte Basin to the north and the smaller Murzuk and Kufra basins in the south. Broadband data from several seismic stations in Libya provide an opportunity for studying the velocity structure of the region. We have made some preliminary dispersion measurements from these stations and have found notable improvements in the group velocity tomography model by incorporating the additional measurements. We will be adding to this analysis by making dispersion measurements from regional events and receiver functions for teleseismic events. Recently, we have been employing methods to jointly invert both surface wave dispersion data and teleseismic receiver functions. The technique holds great promise in accurately estimating seismic structure, including important tectonic parameters such as basin thickness, crustal thickness, upper mantle velocity, as well as more detail about the upper mantle (lithospheric thickness and presence of anisotropy). We propose to apply this method to data from several Libyan stations where we can and, in the absence of receiver functions, invert the dispersion data only. The technique holds the promise of improving our understanding of the crust and upper mantle in Libya and how it fits into the larger tectonic picture of North Africa.

  8. East African Rift

    NASA Technical Reports Server (NTRS)

    2008-01-01

    Places where the earth's crust has formed deep fissures and the plates have begun to move apart develop rift structures in which elongate blocks have subsided relative to the blocks on either side. The East African Rift is a world-famous example of such rifting. It is characterized by 1) topographic deep valleys in the rift zone, 2) sheer escarpments along the faulted walls of the rift zone, 3) a chain of lakes within the rift, most of the lakes highly saline due to evaporation in the hot temperatures characteristic of climates near the equator, 4) voluminous amounts of volcanic rocks that have flowed from faults along the sides of the rift, and 5) volcanic cones where magma flow was most intense. This example in Kenya displays most of these features near Lake Begoria.

    The image was acquired December 18, 2002, covers an area of 40.5 x 32 km, and is located at 0.1 degrees north latitude, 36.1 degrees east longitude.

    The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

  9. Basin Excavation, Lower Crust, Composition, and Bulk Moon Mass balance in Light of a Thin Crust

    NASA Technical Reports Server (NTRS)

    Jolliff, B. L.; Korotev, R. L.; Ziegler, R. A.

    2013-01-01

    New lunar gravity results from GRAIL have been interpreted to reflect an overall thin and low-density lunar crust. Accordingly, crustal thickness has been modeled as ranging from 0 to 60 km, with thinnest crust at the locations of Crisium and Moscoviense basins and thickest crust in the central farside highlands. The thin crust has cosmochemical significance, namely in terms of implications for the Moon s bulk composition, especially refractory lithophile elements that are strongly concentrated in the crust. Wieczorek et al. concluded that the bulk Moon need not be enriched compared to Earth in refractory lithophile elements such as Al. Less Al in the crust means less Al has been extracted from the mantle, permitting relatively low bulk lunar mantle Al contents and low pre- and post-crust-extraction values for the mantle (or the upper mantle if only the upper mantle underwent LMO melting). Simple mass-balance calculations using the method of [4] suggests that the same conclusion might hold for Th and the entire suite of refractory lithophile elements that are incompatible in olivine and pyroxene, including the KREEP elements, that are likewise concentrated in the crust.

  10. Earthquake Rupturing in Fluid-Overpressured Crust: How Common?

    NASA Astrophysics Data System (ADS)

    Sibson, Richard H.

    2014-11-01

    Whether or not ruptures nucleate in fluid-overpressured crust ( λ v = P f/ σ v > 0.4) is important because pore-fluids overpressured above hydrostatic lower fault frictional strength and may also vary through the earthquake cycle, acting as an independent variable affecting fault failure. Containment of fluid overpressure is precarious because pressure-dependent activation of faults and fractures allows drainage from overpressured portions of the crust. Discharge of fluids through activated fault-fracture permeability (fault-valve action) decreases overpressure so that subsequent failure depends on the cycling of both overpressure and frictional strength as well as tectonic stress. Geometric and mechanical considerations suggest that fluid overpressures are more likely to develop and be sustained in compressional/transpressional regimes as opposed to extensional/transtensional tectonic settings. On the basis of geophysical observations and force-balance analyses, subduction interface shear zones appear to be strongly but variably overpressured to near-lithostatic levels ( λ v > 0.9) over the full depth range of seismogenic megathrusts. Strong overpressuring at seismogenic depths is also documented in active fold-thrust belts and in areas of ongoing compressional inversion (e.g., northern Honshu) where inherited normal faults are reactivated as steep reverse faults, requiring near-lithostatic overpressures ( λ v → 1.0) at depths of rupture initiation. Evidence for overpressuring around strike-slip faults is less clear but tends to be strongest in areas of transpression. In areas of extensional tectonics coincident with particularly high fluid discharge, there is some evidence of overpressuring concentrated towards the base of the seismogenic zone. In general, because of the limited resolution of geophysical techniques, it is easier to make the case for rupture propagation through overpressured crust than to make a definitive case for the direct involvement of

  11. Active Dehydration, Delamination and Deformation of Transitional Continental Crust in an Arc-Continent Collision, Taiwan

    NASA Astrophysics Data System (ADS)

    Byrne, T. B.; Rau, R. J.; Chen, K. H.; Huang, H. H.; Wang, Y. J.; Ouimet, W. B.

    2014-12-01

    A new study of the 3-D velocity structure of Taiwan, using a new tomographic model (Vp and Vs; Huang et al., 2014), suggests that subducted continental crust is delaminated from the subducting mantle of the Eurasia plate and progressively deformed by the subducting Philippine Sea plate. In southern Taiwan, vertical sections show an east-dipping, asymmetric lobe of low velocity that projects down dip to a band of seismicity interpreted as the Wadati-Benioff zone of the subducting Eurasian plate. Seismic tremors in the mid-crust also suggest dehydration (Chuang et al., 2014), consistent with prograde metamorphism of crustal materials. In central Taiwan, however, the seismicity of the W-B zone progressively disappears and the low velocity lobe shallows and broadens. The velocity structure of the lower and middle crust (represented by the 7.5 and 6.5 km/sec isovelocity surfaces, respectively) also appear distinctly out-of-phase, with the lower crust forming a broad, smooth synformal structure that contrasts with the higher amplitude undulations of the middle crust. These mid-crust structures appear as smaller irregular lobes separated by patches of higher velocity. In northern Taiwan, the velocity structure of the lower and middle crust again appear "in phase" and form a symmetrical crustal root centered beneath the Central Range. Seismicity patterns and 3-D analysis of the velocity structure also show the western edge of the PSP subducting beneath the eastern Central Range. We interpret these south-to-north changes to reflect the partial subduction (southern Taiwan), delamination (central Taiwan) and deformation (northern Taiwan) of continental-like crust. Support for these interpretation comes from: 1) unusually high rates of surface uplift (up to 15 mm/yr; Ching et al., 2011); 2) Vp and Vs attenuation studies that suggest anomalously high temperatures; 3) evidence for NE-SW extension; and 4) anomalous areas of low topographic relief.

  12. Genetic Evidence for Rift Valley Fever Outbreaks in Madagascar Resulting from Virus Introductions from the East African Mainland rather than Enzootic Maintenance▿†‡

    PubMed Central

    Carroll, Serena A.; Reynes, Jean-Marc; Khristova, Marina L.; Andriamandimby, Soa Fy; Rollin, Pierre E.; Nichol, Stuart T.

    2011-01-01

    Rift Valley fever virus (RVFV), a mosquito-borne phlebovirus, has been detected in Madagascar since 1979, with occasional outbreaks. In 2008 to 2009, a large RVFV outbreak was detected in Malagasy livestock and humans during two successive rainy seasons. To determine whether cases were due to enzootic maintenance of the virus within Madagascar or to importation from the East African mainland, nine RVFV whole genomic sequences were generated for viruses from the 1991 and 2008 Malagasy outbreaks. Bayesian coalescent analyses of available whole S, M, and L segment sequences were used to estimate the time to the most recent common ancestor for the RVFVs. The 1979 Madagascar isolate shared a common ancestor with strains on the mainland around 1972. The 1991 Madagascar isolates were in a clade distinct from that of the 1979 isolate and shared a common ancestor around 1987. Finally, the 2008 Madagascar viruses were embedded within a large clade of RVFVs from the 2006–2007 outbreak in East Africa and shared a common ancestor around 2003 to 2004. These results suggest that the most recent Madagascar outbreak was caused by a virus likely arriving in the country some time between 2003 and 2008 and that this outbreak may be an extension of the 2006–2007 East African outbreak. Clustering of the Malagasy sequences into subclades indicates that the viruses have continued to evolve during their short-term circulation within the country. These data are consistent with the notion that RVFV outbreaks in Madagascar result not from emergence from enzootic cycles within the country but from recurrent virus introductions from the East African mainland. PMID:21507967

  13. The Continental Crust: A Geophysical Approach

    NASA Astrophysics Data System (ADS)

    Christensen, Nikolas I.

    Nearly 80 years ago, Yugoslavian seismologist Andrija Mohorovicic recognized, while studying a Balkan earthquake, that velocities of seismic waves increase abruptly at a few tens of kilometers depth , giving rise to the seismological definition of the crust. Since that discovery, many studies concerned with the nature of both the continental and oceanic crusts have appeared in the geophysical literature.Recently, interest in the continental crust has cascaded. This is largely because of an infusion of new data obtained from major reflection programs such as the Consortium for Continental Reflection Profiling (COCORP) and British Institutions Reflection Profiling Syndicate (BIRPS) and increased resolution of refraction studies. In addition, deep continental drilling programs are n ow in fashion. The Continental Crust: A Geophysical Approach is a summary of present knowledge of the continental crust. Meissner has succeeded in writing a book suited to many different readers, from the interested undergraduate to the professional. The book is well documented , with pertinent figures and a complete and up-to-date reference list.

  14. Growth of the lower continental crust

    NASA Technical Reports Server (NTRS)

    Rudnick, Roberta L.

    1988-01-01

    One of the largest uncertainties in crustal composition and growth models is the nature of the lower continental crust. Specifically, by what processes is it formed and modified, and when is it formed, particularly in reference to the upper crust? The main reason for this lack of information is the scarcity of lower crustal rock samples. These are restricted to two types: rocks which outcrop in granulite facies terrains and granulite facies xenoliths which are transported to the earth's surface by young volcanics. The important conclusions arising from the xenolith studies are: the majority of mafic lower crustal xenoliths formed through cumulate process, resitic xenoliths are rare; and formation and metamorphism of the deep crust is intimately linked to igneous activity and/or orogeny which are manifest in one form or another at the earth's surface. Therefore, estimates of crustal growth based on surface exposures is representative, although the proportion of remobilized pre-existing crust may be significantly greater at the surface than in the deep crust.

  15. Generation of felsic crust in the Archean: a geodynamic modeling perspective

    NASA Astrophysics Data System (ADS)

    Sizova, Elena; Gerya, Taras; Stüwe, Kurt; Brown, Michael

    2015-04-01

    The relevance of contemporary tectonics to the formation of the Archean terrains is a matter of vigorous debate. Higher mantle temperatures and higher radiogenic heat production in the past would have impacted on the thickness and composition of the oceanic and continental crust. As a consequence of secular cooling, there is generally no modern analog to assist in understanding the tectonic style that may have operated in the Archean. For this reason, well-constrained numerical modeling, based on the fragmentary evidence preserved in the geological record, is the most appropriate tool to evaluate hypotheses of Archean crust formation. The main lithology of Archean terrains is the sodic tonalite-trondhjemite-granodiorite (TTG) suite. Melting of hydrated basalt at garnet-amphibolite to eclogite facies conditions is considered to be the dominant process for the generation of the Archean TTG crust. Taking into account geochemical signatures of possible mantle contributions to some TTGs, models proposed for the formation of Archean crust include subduction, melting at the bottom of thickened continental crust and fractional crystallization of mantle-derived melts under water-saturated conditions. We evaluated these hypotheses using a 2D coupled petrological-thermomechanical numerical model with initial conditions appropriate to the Eoarchean-Mesoarchean. As a result, we identified three tectonic settings in which intermediate to felsic melts are generated by melting of hydrated primitive basaltic crust: 1) delamination and dripping of the lower primitive basaltic crust into the mantle; 2) local thickening of the primitive basaltic crust; and, 3) small-scale crustal overturns. In addition, we consider remelting of the fractionated products derived from underplated dry basalts as an alternative mechanism for the formation of some Archean granitoids. In the context of a stagnant lid tectonic regime which is intermittently terminated by short-lived subduction, we identified

  16. Deep-ocean ferromanganese crusts and nodules

    USGS Publications Warehouse

    Hein, James R.; Koschinsky, Andrea

    2013-01-01

    Ferromanganese crusts and nodules may provide a future resource for a large variety of metals, including many that are essential for emerging high- and green-technology applications. A brief review of nodules and crusts provides a setting for a discussion on the latest (past 10 years) research related to the geochemistry of sequestration of metals from seawater. Special attention is given to cobalt, nickel, titanium, rare earth elements and yttrium, bismuth, platinum, tungsten, tantalum, hafnium, tellurium, molybdenum, niobium, zirconium, and lithium. Sequestration from seawater by sorption, surface oxidation, substitution, and precipitation of discrete phases is discussed. Mechanisms of metal enrichment reflect modes of formation of the crusts and nodules, such as hydrogenetic (from seawater), diagenetic (from porewaters), and mixed diagenetic–hydrogenetic processes.

  17. Elemental composition of the Martian crust.

    PubMed

    McSween, Harry Y; Taylor, G Jeffrey; Wyatt, Michael B

    2009-05-01

    The composition of Mars' crust records the planet's integrated geologic history and provides clues to its differentiation. Spacecraft and meteorite data now provide a global view of the chemistry of the igneous crust that can be used to assess this history. Surface rocks on Mars are dominantly tholeiitic basalts formed by extensive partial melting and are not highly weathered. Siliceous or calc-alkaline rocks produced by melting and/or fractional crystallization of hydrated, recycled mantle sources, and silica-poor rocks produced by limited melting of alkali-rich mantle sources, are uncommon or absent. Spacecraft data suggest that martian meteorites are not representative of older, more voluminous crust and prompt questions about their use in defining diagnostic geochemical characteristics and in constraining mantle compositional models for Mars. PMID:19423810

  18. Rocks of the early lunar crust

    NASA Technical Reports Server (NTRS)

    James, O. B.

    1980-01-01

    Data are summarized which suggest a model for the early evolution of the lunar crust. According to the model, during the final stages of accretion, the outer part of the moon melted to form a magma ocean approximately 300 km deep. This ocean fractionated to form mafic and ultramafic cumulates at depth and an overlying anorthositic crust made up of ferroan anorthosites. Subsequent partial melting in the primitive mantle underlying the crystallized magma ocean produced melts which segregated, moved upward, intruded the primordial crust, and crystallized to form layered plutons consisting of Mg-rich plutonic rocks. Intense impact bombardment at the lunar surface mixed and melted the rocks of the two suites to form a thick layer of granulated debris, granulitic breccias, and impact-melt rocks.

  19. The crust of Iceland- a reassessment

    NASA Astrophysics Data System (ADS)

    Longhinos, Biju

    2014-05-01

    The evolving knowledge is at variance with the expectations build upon the idea of an island in making, around Iceland. Shallow thick crusted Shetland-Greenland ridge, extensive distribution of old and continental rocks along Mid Atlantic Ridge, granitic and dolomitic xenoliths in Quaternary Icelandic lava, rhyolitic to dacitic central volcanoes, voluminous pumice drifted onto eastern shores of Atlantic are a few among the valid reasons to consider that the Iceland bears a hidden continental crust. In present study, gravity, seismic and magnetic data over Iceland were scrutinized to pick up continental characteristics. To test the hypothesis here, Iceland is considered as remnant continent, which failed to be eaten up by mantle during Cenozoic basification. It denies any chance for lithospheric spreading centered to Iceland and looks at crustal- mantle hybridization processes resulting in basalt and its derivatives ( crustal basification) as alternative explanation to the exotic ( in terms of plate tectonics) geological and geophysical behaviour of Icelandic crust.

  20. Translating an Evidence-Based Diabetes Education Approach Into Rural African-American Communities: The “Wisdom, Power, Control” Program

    PubMed Central

    Jiang, Luohua; Ory, Marcia G.; Hollingsworth, Ryan

    2015-01-01

    Purpose. The aim of this exploratory study was to assess the efficacy of the “Wisdom, Power, Control” diabetes self-management education (DSME) program with regard to diabetes knowledge, self-efficacy, self-care, distress level, and A1C in an African-American population. Methods. A prospective, quasi-experimental, repeated-measure design was employed to measure these outcomes. Study participants were assessed at baseline, 6 weeks post-intervention, and at a 3-month A1C follow-up. Results. A total of 103 participants were recruited from the intervention counties, and 14 were identified from the control counties. At the post-test, participants in the intervention group reported a significantly higher level of diabetes knowledge (Δ = 9.2%, P <0.0001), higher self-efficacy (Δ = 0.60, P <0.0001), more self-care behaviors (Δ = 0.48, P <0.0001), lower distress level (Δ = –0.15, P = 0.05), and higher health status (Δ = 0.49, P = <0.0001). About 56% of the intervention group completed all six classes, and 25% attended five classes. Conclusions. Findings from this study demonstrate the initial success of translating a culturally adapted DSME program into rural African-American communities. The study highlights important lessons learned in the process of implementing this type of program in a real-world setting with a minority population. PMID:25987809

  1. Obesity and African Americans

    MedlinePlus

    ... Data > Minority Population Profiles > Black/African American > Obesity Obesity and African Americans African American women have the ... ss6304.pdf [PDF | 3.38MB] HEALTH IMPACT OF OBESITY More than 80 percent of people with type ...

  2. The Early Evolution of Mars' Crust

    NASA Astrophysics Data System (ADS)

    Samuel, H.; Baratoux, D.; Kurita, K.

    2014-12-01

    The Mars crustal density and thickness have been recently re-evaluated using petrological constraints from remote sensing, in-situ data, and SNC meteorites. This work indicates that the present-day Martian crust is denser and thicker than previously proposed if essentially basaltic in composition. As a consequence, the average crustal thickness would be commensurable with the depth of the basalt/eclogite transition, re-opening the question of crustal recycling on Early Mars and more generally throughout all its history. We have therefore investigated the conditions under which a thick ancient crust with an eclogitic root could survive through the history of Mars using numerical modelling. Delamination may occur if the combination of poorly constrained physical parameters induces the presence of gravitationally unstable layers and favors a rheological decoupling. To study the conditions and the time scales for the occurrence of crustal delamination on Mars, we investigated the influence of critical parameters for a plausible range of values corresponding to the Martian mantle. For each case we follow the dynamic evolution over geological times of a three-layer system (i.e., crust-mantle with a distinction between low pressure, buoyant basaltic crust and higher pressure, denser eclogitic material). We systematically varied four governing parameters within plausible ranges: (1) the basalt-eclogite transition depth, (2) the density difference between the mantle and the basaltic crust, (3) the density difference between the eclogitic crust and the lithosphere & mantle, (4) the viscous rheology. These experiments allow determining the average Martian crustal thickness at early and late evolutionary stages.

  3. Burden of Diabetes and First Evidence for the Utility of HbA1c for Diagnosis and Detection of Diabetes in Urban Black South Africans: The Durban Diabetes Study

    PubMed Central

    Hird, Thomas R.; Pirie, Fraser J.; Esterhuizen, Tonya M.; O’Leary, Brian; McCarthy, Mark I.; Young, Elizabeth H.; Sandhu, Manjinder S.; Motala, Ayesha A.

    2016-01-01

    Objective Glycated haemoglobin (HbA1c) is recommended as an additional tool to glucose-based measures (fasting plasma glucose [FPG] and 2-hour plasma glucose [2PG] during oral glucose tolerance test [OGTT]) for the diagnosis of diabetes; however, its use in sub-Saharan African populations is not established. We assessed prevalence estimates and the diagnosis and detection of diabetes based on OGTT, FPG, and HbA1c in an urban black South African population. Research Design and Methods We conducted a population-based cross-sectional survey using multistage cluster sampling of adults aged ≥18 years in Durban (eThekwini municipality), KwaZulu-Natal. All participants had a 75-g OGTT and HbA1c measurements. Receiver operating characteristic (ROC) analysis was used to assess the overall diagnostic accuracy of HbA1c, using OGTT as the reference, and to determine optimal HbA1c cut-offs. Results Among 1190 participants (851 women, 92.6% response rate), the age-standardised prevalence of diabetes was 12.9% based on OGTT, 11.9% based on FPG, and 13.1% based on HbA1c. In participants without a previous history of diabetes (n = 1077), using OGTT as the reference, an HbA1c ≥48 mmol/mol (6.5%) detected diabetes with 70.3% sensitivity (95%CI 52.7–87.8) and 98.7% specificity (95%CI 97.9–99.4) (AUC 0.94 [95%CI 0.89–1.00]). Additional analyses suggested the optimal HbA1c cut-off for detection of diabetes in this population was 42 mmol/mol (6.0%) (sensitivity 89.2% [95%CI 78.6–99.8], specificity 92.0% [95%CI: 90.3–93.7]). Conclusions In an urban black South African population, we found a high prevalence of diabetes and provide the first evidence for the utility of HbA1c for the diagnosis and detection of diabetes in black Africans in sub-Saharan Africa. PMID:27560687

  4. Structure of the crust beneath Cameroon, West Africa, from the joint inversion of Rayleigh wave group velocities and receiver functions

    NASA Astrophysics Data System (ADS)

    Tokam, Alain-Pierre K.; Tabod, Charles T.; Nyblade, Andrew A.; Julià, Jordi; Wiens, Douglas A.; Pasyanos, Michael E.

    2010-11-01

    The Cameroon Volcanic Line (CVL) consists of a linear chain of Tertiary to Recent, generally alkaline, volcanoes that do not exhibit an age progression. Here we study crustal structure beneath the CVL and adjacent regions in Cameroon using 1-D shear wave velocity models obtained from the joint inversion of Rayleigh wave group velocities and P-receiver functions for 32 broad-band seismic stations deployed between 2005 January and 2007 February. We find that (1) crustal thickness (35-39km) and velocity structure is similar beneath the CVL and the Pan African Oubanguides Belt to the south of the CVL, (2) crust is thicker (43-48km) under the northern margin of the Congo Craton and is characterized by shear wave velocities >=4.0kms-1 in its lower part and (3) crust is thinner (26-31km) under the Garoua rift and the coastal plain. In addition, a fast velocity layer (Vs of 3.6-3.8kms-1) in the upper crust is found beneath many of the seismic stations. Crustal structure beneath the CVL and the Oubanguides Belt is very similar to Pan African crustal structure in the Mozambique Belt, and therefore it appears not to have been modified significantly by the magmatic activity associated with the CVL. The crust beneath the coastal plain was probably thinned during the opening of the southern Atlantic Ocean, while the crust beneath the Garoua rift was likely thinned during the formation of the Benue Trough in the early Cretaceous. We suggest that the thickened crust and the thick mafic lower crustal layer beneath the northern margin of the Congo Craton may be relict features from a continent-continent collision along this margin during the formation of Gondwana.

  5. Crusted scabies and multiple dosages of ivermectin.

    PubMed

    Ortega-Loayza, Alex G; McCall, Calvin O; Nunley, Julia R

    2013-05-01

    We present the case of a bone marrow transplant patient who was diagnosed with crusted scabies but did not respond to the usual approach with topical permethrin and ivermectin. The Centers for Disease Control and Prevention were contacted and suggested a 7-dose regimen of ivermectin. The patient started to improve remarkably after the third dose, and the skin eruption was resolved after 7 doses. This case supports the use of a more prolonged course of oral ivermectin for crusted scabies in those who fail the conventional approach. PMID:23652958

  6. Tungsten Stable Isotope Compositions of Ferromanganese Crusts

    NASA Astrophysics Data System (ADS)

    Abraham, K.; Barling, J.; Hein, J. R.; Schauble, E. A.; Halliday, A. N.

    2014-12-01

    We report the first accurate and precise data for mass-dependent fractionation of tungsten (W) stable isotopes, using a double spike technique and MC-ICPMS. Results are expressed relative to the NIST 3136 W isotope standard as per mil deviations in 186W/184W (δ186W). Although heavy element mass-dependent fractionations are expected to be small, Tl and U both display significant low temperature isotopic fractionations. Theoretical calculations indicate that W nuclear volume isotopic effects should be smaller than mass-dependent fractionations at low temperatures. Hydrogenetic ferromanganese (Fe-Mn) crusts precipitate directly from seawater and have been used as paleoceanographic recorders of temporal changes in seawater chemistry. Crusts are strongly enriched in W and other metals, and are a promising medium for exploring W isotopic variability. Tungsten has a relatively long residence time in seawater of ~61,000 years, mainly as the tungstate ion (WO42-). Water depth profiles show conservative behaviour. During adsorption on Fe-Mn crusts, W species form inner-sphere complexes in the hexavalent (W6+) state. The major host phase is thought to be Mn oxides and the lighter W isotope is expected to be absorbed preferentially. Surface scrapings of 13 globally distributed hydrogenetic Fe-Mn crusts display δ186W from -0.08 to -0.22‰ (±0.03‰, 2sd). A trend toward lighter W isotope composition exists with increasing water depth (~1500 to ~5200m) and W concentration. One hydrothermal Mn-oxide sample is anomalously light and Mn nodules are both heavy and light relative to Fe-Mn crusts. Tungsten speciation depends on concentration, pH, and time in solution and is not well understood because of the extremely slow kinetics of the reactions. In addition, speciation of aqueous and/or adsorbed species might be sensitive to pressure, showing similar thermodynamic stability but different effective volumes. Thus, W stable isotopes might be used as a water-depth barometer in

  7. Evolution of the lunar highland crust

    NASA Technical Reports Server (NTRS)

    Taylor, S. R.; Bence, A. E.

    1975-01-01

    The evolution of three distinct element associations in the lunar highland crust is discussed in terms of the Taylor-Jakes model which involves melting of most of the moon during accretion. Sources for (1) high Ca, Al, Sr, Eu, (2) high Mg and Cr, and (3) high K, REE, Zr, Hf, Nb are suggested. Bombardment by large projectiles during the differentiation process causes melting and mixing, which produces a wide range of compositions in the crust. The formation of dunite, troctolite, high-, medium-, and low-K Fra Mauro basalts, and rocks close to the olivine-spinel-plagioclase peritectic point is considered.

  8. Geochemistry of Archean Mafic Amphibolites from the Amsaga Area, West African Craton, Mauritania: What Is the Message?

    NASA Astrophysics Data System (ADS)

    El Atrassi, F.; Debaille, V.; Mattielli, N. D. C.; Berger, J.

    2014-12-01

    While Archean terrains are mainly composed of a TTG (Tonalite-trondhjemite-granodiorite) suite, more mafic lithologies such as amphibolites are also a typical component of those ancient terrains. Although mafic rocks represent only ~10% of the Archean cratons, they may provide key evidence of the role and nature of basaltic magmatism in the formation of the Archean crust as well as the evolution of the Archean mantle. This study focuses on the Archean crust from the West African Craton in Mauritania (Amsaga area). The Amsaga Archean Crust mainly consists of TTG and thrust-imbricated slices of mafic volcanic rocks, which have been affected by polymetamorphic events from the amphibolite to granulite facies. Our main objectives aim to the identification of the mafic lithology origin and a better understanding of their role in the continental crust emplacement. Our petrological observations show that these amphibolites have fine to medium granoblastic and nematoblastic textures. The amphibolites are dominated by amphibolite-facies mineral assemblages (mainly amphibole and plagioclase), but garnet and clinopyroxene occur in a few samples. Two groups are distinct in their geochemical characteristics (major and trace elements), although both have tholeiitic basalt composition. The first group show LREE-enriched patterns and negative Nb-Ta anomalies. The second group is characterized by near-flat LREE patterns and flat HREE patterns. This second group clearly shows no Nb-Ta anomalies. The first group could be related to arc-like basalts, as it is many similarities with some Archean amphibolites probably formed in a supra-subduction zone, for instance the volcanic rocks from the southern edge of the Isua Supracrustal Belt. On the contrary, the second group has a MORB-like signature which is more unusual during the Archean. Different scenarios will be discussed regards to the Archean geodynamics.

  9. Mass and Composition of the Continental Crust Estimated Using the CRUST2.0 Model

    NASA Astrophysics Data System (ADS)

    Peterson, B. T.; Depaolo, D. J.

    2007-12-01

    The mass, age, and chemical composition of the continental crust are fundamental data for understanding Earth differentiation. The inaccessibility of most of the volume of the crust requires that inferences be made about geochemistry using seismic and heat flow data, with additional constraints provided by scarce lower crustal samples (Rudnick and Fountain, Rev. Geophys., 1995; Rudnick and Gao, Treatise on Geochem., 2003). The global crustal seismic database CRUST2.0 (Bassin, et al., EOS, 2000; Mooney, et al., JGR, 1998; hereafter C2) provides a useful template with which the size and composition of the continents can be assessed, and may be a useful vehicle to organize and analyze diverse geochemical data. We have used C2 to evaluate the modern mass and composition of the continental crust and their uncertainties, and explored our results in the context of global mass balances, such as continents versus depleted mantle. The major source of uncertainty comes from the definition of "continent." The ultimate constraint is the total mass of Earth's crust (oceanic + continental), which, from C2, is 2.77 (in units of 1022 kg). Using crustal thickness as a definition of continent, the mass of continental crust (CC) is 2.195 if the minimum thickness is 12-18km, 2.085 for 22.5km, 2.002 for 25km, and 1.860 for 30km. These numbers include all sediment as continental crust. Using C2 definitions to distinguish oceanic and continental crust (and including oceanic plateaus which contain some continental crust), we calculate the CC mass as 2.171. To estimate chemical composition, we use the C2 reservoir masses. For minimum thickness of 22.5km, C2 yields the proportions 0.016 oceanic sediment, 0.038 continental sediment, 0.321 upper crust, 0.326 middle crust, 0.299 lower crust. Upper, middle, and lower crust are assigned compositions from Rudnick and Gao (2003), continental sediments are assigned upper crust composition, and oceanic sediments are assigned GLOSS composition (Plank

  10. Late Pan-African granite emplacement during regional deformation, evidence from magnetic fabric and structural studies in the Hammamat-Atalla area, Central Eastern Desert of Egypt

    NASA Astrophysics Data System (ADS)

    Greiling, R. O.; de Wall, H.; Sadek, M. F.; Dietl, C.

    2014-11-01

    Field investigations, microstructural observations, and magnetic fabric analyses revealed a polyphase, late Pan-African deformational evolution in the Um Sheqila-Um Had (595 Ma) composite pluton and in the Hammamat and Atalla areas of the Central Eastern Desert of Egypt in Ediacaran times. Major stages are early shortening (NNW-SSE), subsequent strike-slip (NW-SE shear zones), and late shortening (NW-SE). Strain studies on pebbles and xenoliths together with AMS data show a predominance of shallow, NW-SE trending X axes or magnetic lineations, associated with steep, NW-SE striking magnetic foliations. Magnetic fabrics and microstructures indicate a tectonic fabric in the Um Sheqila-Um Had granitoid plutons, which is dominated by steep NW-SE striking foliations and shallow NW-SE trending lineations, similar to those in the high-angle Atalla Shear Zone. There is a change of lineation directions from ESE-WNW at Um Sheqila (oldest) to NW-SE to Um Had II (youngest). This pattern may indicate an influence of strike-slip and is also consistent with NE-SW compression. This holds also true for the asymmetry of the contact aureole, which is extended towards NW, parallel with the trend of the magnetic lineation. The character and orientation of the deformation pattern in the Um Sheqila-Um Had plutons and the Atalla Shear Zone is thus similar to the pattern of the late shortening phase. The intrusion of the Um Sheqila-Um Had granitoid rocks, therefore, took place before the late shortening stage, but postdates early deformation, which, according to published data, was associated with lithospheric thinning in the Central Eastern Desert. Therefore, these Pan-African plutons do not represent the earliest post-deformational intrusions but a late stage of syn-deformational magmatic activity. At a regional scale, this deformation with steep foliations and shallow lineations may also be related with lateral escape tectonics. The pluton emplacement, the importance of transcurrent

  11. Microbial Life of North Pacific Oceanic Crust

    NASA Astrophysics Data System (ADS)

    Schumann, G.; Koos, R.; Manz, W.; Reitner, J.

    2003-12-01

    Information on the microbiology of the deep subsurface is necessary in order to understand the factors controlling the rate and extent of the microbially catalyzed reactions that influence the geophysical properties of these environments. Drilling into 45-Ma oceanic basaltic crust in a deepwater environment during ODP Leg 200 provided a promising opportunity to explore the abundance, diversity and activity of micro-organisms. The combined use of culture-independent molecular phylogenetic analyses and enrichment culture techniques is an advantageous approach in investigating subsurface microbial ecosystems. Enrichment culture methods allow the evaluation of potential activities and functions. Microbiological investigations revealed few aerobic cultivable, in part hitherto unknown, micro-organisms in deep submarine sediments and basaltic lava flows. 16S rDNA sequencing of isolates from sediment revealed the next relatives to be members of the genera Halomonas, Pseudomonas, and Lactobacillus. Within the Pseudomonadaceae the closest relative is Acinetobacter sp., which was isolated from a deep subsurface environment. The next phylogenetical relatives within the Halomonadaceae are bacteria typically isolated from Soda lakes, which are considered as model of early life conditions. Interestingly, not only sediment bacteria could be obtained in pure culture. Aerobic strains could also be successfully isolated from the massive tholeiitic basalt layer at a depth of 76.16 mbsf (46 m below the sediment/basement contact). These particular isolates are gram-positive with low G+C content of DNA, phylogenetically affiliated to the phylum Firmicutes. The closest neighbors are e.g. a marine Bacillus isolated from the Gulf of Mexico and a low G+C gram-positive bacterium, which belongs to the microbial flora in the deepest sea mud of the Mariana Trench, isolated from a depth of 10,897 m. Based on the similarity values, the isolates represent hitherto undescribed species of the deep

  12. Perceptual and acoustic evidence for species-level differences in meow vocalizations by domestic cats (Felis catus) and African wild cats (Felis silvestris lybica).

    PubMed

    Nicastro, Nicholas

    2004-09-01

    To test for possible anthropogenic selection effects on meows in domestic felids, vocalizations by domestic cats (Felis catus) were compared with cries by their closest wild relative, the African wild cat (Felis silvestris lybica). Comparisons included analysis of acoustic characteristics and perceptual studies with human (Homo sapiens) listeners. The perceptual studies obtained human listener ratings of call pleasantness. Both the acoustic and perceptual comparisons revealed clear species-level differences: The domestic cat meows were significantly shorter in mean duration than the wild cat meows, showed higher mean formant frequencies, and exhibited higher mean fundamental frequencies. Human listeners at all levels of experience and affinity for cats rated domestic cat meows as far more pleasant sounding than wild cat vocalizations. These results are consistent with a model of cat domestication that posits selective pressure on meows based on human perceptual biases. PMID:15482056

  13. Genetic diversity of simian immunodeficiency viruses from West African green monkeys: evidence of multiple genotypes within populations from the same geographical locale.

    PubMed Central

    Bibollet-Ruche, F; Brengues, C; Galat-Luong, A; Galat, G; Pourrut, X; Vidal, N; Veas, F; Durand, J P; Cuny, G

    1997-01-01

    High simian immunodeficiency virus (SIV) seroprevalence rates have been reported in the different African green monkey (AGM) subspecies. Genetic diversity of these viruses far exceeds the diversity observed in the other lentivirus-infected human and nonhuman primates and is thought to reflect ancient introduction of SIV in the AGM population. We investigate here genetic diversity of SIVagm in wild-living AGM populations from the same geographical locale (i.e., sympatric population) in Senegal. For 11 new strains, we PCR amplified and sequenced two regions of the genome spanning the first tat exon and part of the transmembrane glycoprotein. Phylogenetic analysis of these sequences shows that viruses found in sympatric populations cluster into distinct lineages, with at least two distinct genotypes in each troop. These data strongly suggest an ancient introduction of these divergent viruses in the AGM population. PMID:8985351

  14. Ultrahigh-pressure metamorphism: tracing continental crust into the mantle

    NASA Astrophysics Data System (ADS)

    Chopin, Christian

    2003-07-01

    More and more evidence is being discovered in Phanerozoic collision belts of the burial of crustal rocks to previously unsuspected (and ever increasing) depths, presently on the order of 150-200 km, and of exhumation from such depths. This extends by almost one order of magnitude the depth classically ascribed to the metamorphic cycling of continental crust, and demonstrates its possible subduction. The pieces of evidence for this new, ultrahigh-pressure (UHP) metamorphism exclusively occur in the form of relics of high-pressure minerals that escaped back-transformation during decompression. The main UHP mineral indicators are the high-pressure polymorphs of silica and carbon, coesite and microdiamond, respectively; the latter often demonstrably precipitated from a metamorphic fluid and is completely unrelated to kimberlitic diamond or any shock event. Recent discoveries of pyroxene exsolutions in garnet and of coesite exsolutions in titanite suggest a precursor garnet or titanite containing six-fold coordinated silicon, therefore still higher pressures than implied by diamond stability, on the order of 6 GPa. The UHP rocks raise a formidable geological problem: that of the mechanisms responsible for their burial and, more pressingly, for their exhumation from the relevant depths. The petrological record indicates that large tracts of UHP rocks were buried to conditions of low T/ P ratio, consistent with a subduction-zone context. Decompression occurred in most instances under continuous cooling, implying continuous heat loss to the footwall and hangingwall of the rising body. This rise along the subduction channel - an obvious mechanical discontinuity and weak zone - may be driven by buoyancy up to mid-crustal levels as a result of the lesser density of the acidic crustal rocks (even if completely re-equilibrated at depth) after delamination from the lower crust, in a convergent setting. Chronological studies suggest that the rates involved are typical plate

  15. Collective excitations in neutron-star crusts

    NASA Astrophysics Data System (ADS)

    Chamel, N.; Page, D.; Reddy, S.

    2016-01-01

    We explore the spectrum of low-energy collective excitations in the crust of a neutron star, especially in the inner region where neutron-proton clusters are immersed in a sea of superfluid neutrons. The speeds of the different modes are calculated systematically from the nuclear energy density functional theory using a Skyrme functional fitted to essentially all experimental atomic mass data.

  16. Norwegian crusted scabies: an unusual case presentation.

    PubMed

    Maghrabi, Michael M; Lum, Shireen; Joba, Ameha T; Meier, Molly J; Holmbeck, Ryan J; Kennedy, Kate

    2014-01-01

    Scabies is a contagious condition that is transmitted through direct contact with an infected person and has been frequently associated with institutional and healthcare-facility outbreaks. The subtype Norwegian crusted scabies can masquerade as other dermatologic diseases owing to the heavy plaque formation. Successful treatment has been documented in published reports, including oral ivermectin and topical permethrin. Few case studies documenting the treatment of Norwegian crusted scabies have reported the use of surgical debridement as an aid to topical and/or oral treatment when severe plaque formation has been noted. A nursing home patient was admitted to the hospital for severe plaque formation of both feet. A superficial biopsy was negative for both fungus and scabies because of the severity of the plaque formation on both feet. The patient underwent a surgical, diagnostic biopsy of both feet, leading to the diagnosis of Norwegian crusted scabies. A second surgical debridement was then performed to remove the extensive plaque formation and aid the oral ivermectin and topical permethrin treatment. The patient subsequently made a full recovery and was discharged back to the nursing home. At 2 and 6 months after treatment, the patient remained free of scabies infestation, and the surgical wound had healed uneventfully. The present case presentation has demonstrated that surgical debridement can be complementary to the standard topical and oral medications in the treatment of those with Norwegian crusted scabies infestation. PMID:24370484

  17. Resonant shattering of neutron star crusts.

    PubMed

    Tsang, David; Read, Jocelyn S; Hinderer, Tanja; Piro, Anthony L; Bondarescu, Ruxandra

    2012-01-01

    The resonant excitation of neutron star (NS) modes by tides is investigated as a source of short gamma-ray burst (SGRB) precursors. We find that the driving of a crust-core interface mode can lead to shattering of the NS crust, liberating ∼10{46}-10{47}  erg of energy seconds before the merger of a NS-NS or NS-black-hole binary. Such properties are consistent with Swift/BAT detections of SGRB precursors, and we use the timing of the observed precursors to place weak constraints on the crust equation of state. We describe how a larger sample of precursor detections could be used alongside coincident gravitational wave detections of the inspiral by Advanced LIGO class detectors to probe the NS structure. These two types of observations nicely complement one another, since the former constrains the equation of state and structure near the crust-core boundary, while the latter is more sensitive to the core equation of state. PMID:22304251

  18. Biogeochemical signals from deep microbial life in terrestrial crust.

    PubMed

    Suzuki, Yohey; Konno, Uta; Fukuda, Akari; Komatsu, Daisuke D; Hirota, Akinari; Watanabe, Katsuaki; Togo, Yoko; Morikawa, Noritoshi; Hagiwara, Hiroki; Aosai, Daisuke; Iwatsuki, Teruki; Tsunogai, Urumu; Nagao, Seiya; Ito, Kazumasa; Mizuno, Takashi

    2014-01-01

    In contrast to the deep subseafloor biosphere, a volumetrically vast and stable habitat for microbial life in the terrestrial crust remains poorly explored. For the long-term sustainability of a crustal biome, high-energy fluxes derived from hydrothermal circulation and water radiolysis in uranium-enriched rocks are seemingly essential. However, the crustal habitability depending on a low supply of energy is unknown. We present multi-isotopic evidence of microbially mediated sulfate reduction in a granitic aquifer, a representative of the terrestrial crust habitat. Deep meteoric groundwater was collected from underground boreholes drilled into Cretaceous Toki granite (central Japan). A large sulfur isotopic fractionation of 20-60‰ diagnostic to microbial sulfate reduction is associated with the investigated groundwater containing sulfate below 0.2 mM. In contrast, a small carbon isotopic fractionation (<30‰) is not indicative of methanogenesis. Except for 2011, the concentrations of H2 ranged mostly from 1 to 5 nM, which is also consistent with an aquifer where a terminal electron accepting process is dominantly controlled by ongoing sulfate reduction. High isotopic ratios of mantle-derived 3He relative to radiogenic 4He in groundwater and the flux of H2 along adjacent faults suggest that, in addition to low concentrations of organic matter (<70 µM), H2 from deeper sources might partly fuel metabolic activities. Our results demonstrate that the deep biosphere in the terrestrial crust is metabolically active and playing a crucial role in the formation of reducing groundwater even under low-energy fluxes. PMID:25517230

  19. Biogeochemical Signals from Deep Microbial Life in Terrestrial Crust

    PubMed Central

    Fukuda, Akari; Komatsu, Daisuke D.; Hirota, Akinari; Watanabe, Katsuaki; Togo, Yoko; Morikawa, Noritoshi; Hagiwara, Hiroki; Aosai, Daisuke; Iwatsuki, Teruki; Tsunogai, Urumu; Nagao, Seiya; Ito, Kazumasa; Mizuno, Takashi

    2014-01-01

    In contrast to the deep subseafloor biosphere, a volumetrically vast and stable habitat for microbial life in the terrestrial crust remains poorly explored. For the long-term sustainability of a crustal biome, high-energy fluxes derived from hydrothermal circulation and water radiolysis in uranium-enriched rocks are seemingly essential. However, the crustal habitability depending on a low supply of energy is unknown. We present multi-isotopic evidence of microbially mediated sulfate reduction in a granitic aquifer, a representative of the terrestrial crust habitat. Deep meteoric groundwater was collected from underground boreholes drilled into Cretaceous Toki granite (central Japan). A large sulfur isotopic fractionation of 20–60‰ diagnostic to microbial sulfate reduction is associated with the investigated groundwater containing sulfate below 0.2 mM. In contrast, a small carbon isotopic fractionation (<30‰) is not indicative of methanogenesis. Except for 2011, the concentrations of H2 ranged mostly from 1 to 5 nM, which is also consistent with an aquifer where a terminal electron accepting process is dominantly controlled by ongoing sulfate reduction. High isotopic ratios of mantle-derived 3He relative to radiogenic 4He in groundwater and the flux of H2 along adjacent faults suggest that, in addition to low concentrations of organic matter (<70 µM), H2 from deeper sources might partly fuel metabolic activities. Our results demonstrate that the deep biosphere in the terrestrial crust is metabolically active and playing a crucial role in the formation of reducing groundwater even under low-energy fluxes. PMID:25517230

  20. The African Pediatric Fellowship Program: Training in Africa for Africans.

    PubMed

    Wilmshurst, Jo M; Morrow, Brenda; du Preez, Avril; Githanga, David; Kennedy, Neil; Zar, Heather J

    2016-01-01

    Africa has a significant burden of childhood disease, with relatively few skilled health care professionals. The African Paediatric Fellowship Programme was developed by the Department of Pediatrics and Child Health at the University of Cape Town to provide relevant training for African child health professionals, by Africans, within Africa. Trainees identified by partner academic institutions spend 6 months to 2 years training in the Department of Pediatrics and allied disciplines. They then return to their home institution to build practice, training, research, and advocacy. From 2008 to 2015, 73 physicians have completed or are completing training in general pediatrics or a pediatric subspecialty. At 1 year posttraining, 98% to 100% are practicing back in their home institution. The impact of the returning fellows is evident from their practice interventions, research collaborations, and positions as stakeholders who can change health care policies. Thirty-three centers in 13 African countries are partners with the program, and the program template is now followed by other partner sites in Africa. Increasing and retaining the skills pool of African child health specialists is building a network of motivated, highly skilled clinicians who are equipped to advance child health in Africa. PMID:26659458

  1. A wide-angle seismic survey of the Hecataeus Ridge, south of Cyprus: a microcontinental block from the African plate docked in a subduction zone?

    NASA Astrophysics Data System (ADS)

    Rahimi, Ayda; Welford, Kim; Hall, Jeremy; Hübscher, Christian; Louden, Keith; Ehrhardt, Axel

    2013-04-01

    Cyprus lies at the southern edge of the Aegean-Anatolian microplate, caught in the convergence of Africa and Eurasia. Subduction of the African plate below Cyprus has probably ceased and this has been attributed to the docking in the subduction zone of the Eratosthenes Seamount microcontinental fragment on the northern edge of the African plate. In early 2010, on R.V. Maria S. Merian, we conducted a wide-angle seismic survey to test the hypothesis that the Hecataeus Ridge, another possible microcontinental block lying immediately offshore SE Cyprus, might be related to an earlier docking event. The upper crust of southern Cyprus is dominated by ophiolites, with seismic velocities of up to 7 km s-1. A wide angle seismic profile along Hecataeus Ridge was populated with 15 Canadian and German ocean-bottom seismographs at 5 km intervals and these recorded shots from a 6000 cu. in. air gun array, fired approximately every 100 m. Rough topography of the seabed has made picking of phases and their modelling a demanding task. Bandpass and coherency filtering have enabled us to pick phases out to around 80 km. Tomographic inversion of short-range first arrivals provided an initial model of the shallow sub-seabed structure. Forward modelling by ray-tracing, using the code of Zelt and Smith, was then used to model crustal structure down to depths of around 20 km, with occasional evidence of reflections from deeper boundaries (Moho?). Modelling results provide good control on P-wave velocities in the top 20 km and some indications of deeper events. There is no evidence of true velocities approaching 7 km/s in the top 20 km below the Ridge that might indicate the presence of ophiolitic rocks. Regional gravity and magnetic field data tend to support this proposition. We thus conclude that Hecataeus Ridge is not composed of characteristically ophiolitic, Cyprus (upper plate) crust, and it might well be derived from the African (lower) plate.

  2. Plio-pleistocene African climate

    SciTech Connect

    deMenocal, P.B.

    1995-10-06

    Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps in the evolution of African hominids and other vertebrates are coincident with shifts to more arid, open conditions near 2.8 Ma, 1.7 Ma, and 1.0 Ma, suggesting that some Pliocene (Plio)-Pleistocene speciation events may have been climatically mediated. 65 refs., 6 figs.

  3. Plio-Pleistocene African Climate

    NASA Astrophysics Data System (ADS)

    Demenocal, Peter B.

    1995-10-01

    Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps in the evolution of African hominids and other vertebrates are coincident with shifts to more arid, open conditions near 2.8 Ma, 1.7 Ma, and 1.0 Ma, suggesting that some Pliocene (Plio)-Pleistocene speciation events may have been climatically mediated.

  4. Bioenergy and African transformation.

    PubMed

    Lynd, Lee R; Sow, Mariam; Chimphango, Annie Fa; Cortez, Luis Ab; Brito Cruz, Carlos H; Elmissiry, Mosad; Laser, Mark; Mayaki, Ibrahim A; Moraes, Marcia Afd; Nogueira, Luiz Ah; Wolfaardt, Gideon M; Woods, Jeremy; van Zyl, Willem H

    2015-01-01

    Among the world's continents, Africa has the highest incidence of food insecurity and poverty and the highest rates of population growth. Yet Africa also has the most arable land, the lowest crop yields, and by far the most plentiful land resources relative to energy demand. It is thus of interest to examine the potential of expanded modern bioenergy production in Africa. Here we consider bioenergy as an enabler for development, and provide an overview of modern bioenergy technologies with a comment on application in an Africa context. Experience with bioenergy in Africa offers evidence of social benefits and also some important lessons. In Brazil, social development, agricultural development and food security, and bioenergy development have been synergistic rather than antagonistic. Realizing similar success in African countries will require clear vision, good governance, and adaptation of technologies, knowledge, and business models to myriad local circumstances. Strategies for integrated production of food crops, livestock, and bioenergy are potentially attractive and offer an alternative to an agricultural model featuring specialized land use. If done thoughtfully, there is considerable evidence that food security and economic development in Africa can be addressed more effectively with modern bioenergy than without it. Modern bioenergy can be an agent of African transformation, with potential social benefits accruing to multiple sectors and extending well beyond energy supply per se. Potential negative impacts also cut across sectors. Thus, institutionally inclusive multi-sector legislative structures will be more effective at maximizing the social benefits of bioenergy compared to institutionally exclusive, single-sector structures. PMID:25709714

  5. Southern African continental margin: Dynamic processes of a transform margin

    NASA Astrophysics Data System (ADS)

    Parsiegla, N.; Stankiewicz, J.; Gohl, K.; Ryberg, T.; Uenzelmann-Neben, G.

    2009-03-01

    Dynamic processes at sheared margins associated with the formation of sedimentary basins and marginal ridges are poorly understood. The southern African margin provides an excellent opportunity to investigate the deep crustal structure of a transform margin and to characterize processes acting at these margins by studying the Agulhas-Falkland Fracture Zone, the Outeniqua Basin, and the Diaz Marginal Ridge. To do this, we present the results of the combined seismic land-sea experiments of the Agulhas-Karoo Geoscience Transect. Detailed velocity-depth models show crustal thicknesses varying from ˜42 km beneath the Cape Fold Belt to ˜28 km beneath the shelf. The Agulhas-Falkland Fracture Zone is embedded in a 50 km wide transitional zone between continental and oceanic crust. The oceanic crust farther south exhibits relatively low average crustal velocities (˜6.0 km/s), which can possibly be attributed to transform-ridge intersection processes and the thermal effects of the adjacent continental crust during its formation. Crustal stretching factors derived from the velocity-depth models imply that extension in the Outeniqua Basin acted on regional as well as more local scales. We highlight evidence for two episodes of crustal stretching. The first, with a stretching factor β of 1.6, is interpreted to have influenced the entire Outeniqua Basin. The stresses possibly originated from the beginning breakup between Africa and Antarctica (˜169-155 Ma). The second episode can be associated with a transtensional component of the shear motion along the Agulhas-Falkland Transform from ˜136 Ma. This episode caused additional crustal stretching with β = 1.3 and is established to only have affected the southern parts of the basin. Crustal velocities directly beneath the Outeniqua Basin are consistent with the interpretation of Cape Supergroup rocks underlying most parts of the basin and the Diaz Marginal Ridge. We propose that the formation of this ridge can be either

  6. Oxidation of 13C-labeled methane in surface crusts of pig- and cattle slurry.

    PubMed

    Ambus, Per; Petersen, Søren O

    2005-06-01

    Storage tanks for slurry from animal production constitute important point sources for emission of CH4 into the atmosphere. Recent investigations have demonstrated that surface crust formed on top of animal slurry provides a habitat for CH4 oxidation activity, a finding which may open for new opportunities to reduce greenhouse gas emissions during storage of animal wastes. In this work, 13C-labeled CH4 was used as a tracer to examine the absolute rates of CH4 oxidation and production in intact crust materials, collected from six different pig- and cattle slurry tanks in late autumn. Methane concentrations were generally reduced in the presence of surface crust samples, with the exception of a LECA-based (light expanded clay aggregates) crust from a pig slurry tank. In four samples, CH4 consumption was induced following a 2-4 days lag phase, whereas one cattle slurry crust consumed CH4 immediately and showed a 92% decline in CH4 concentration within the first week. Consumption of 13C-labeled CH4 was paralleled by the production of 13C-labeled CO2, thus providing direct evidence that microbial oxidation of CH4 to CO2 was taking place. Between 23% and 36% of the CH4-13C consumed in the active samples was accounted for in the gas phase CO2 indicating incomplete conversion of CH4 to CO2; however, comparable amounts of 13C was immobilized in the crust samples. Overall, the results showed that significant CH4 oxidation to CO2 in slurry crust samples occurs immediately or is inducible upon exposure to CH4. PMID:16191764

  7. CRUST1.0: An Updated Global Model of Earth's Crust

    NASA Astrophysics Data System (ADS)

    Laske, G.; Masters, G.; Ma, Z.; Pasyanos, M. E.

    2012-04-01

    We present an updated global model of Earth's crustal structure. The new model, CRUST1.0, serves as starting model in a more comprehensive effort to compile a global model of Earth's crust and lithosphere, LITHO1.0. CRUST1.0 is defined on a 1-degree grid and is based on a new database of crustal thickness data from active source seismic studies as well as from receiver function studies. In areas where such constraints are still missing, for example in Antarctica, crustal thicknesses are estimated using gravity constraints. The compilation of the new crustal model initially follows the philosophy of the widely used crustal model CRUST2.0 (Bassin et al., 2000; http://igppweb.ucsd.edu/~gabi/crust2.html). Crustal types representing properties in the crystalline crust are assigned according to basement age or tectonic setting. The classification of the latter loosely follows that of an updated map by Artemieva and Mooney (2001) (http://www.lithosphere.info). Statistical averages of crustal properties in each of these crustal types are extrapolated to areas with no local seismic or gravity constraint. In each 1-degree cell, boundary depth, compressional and shear velocity as well as density is given for 8 layers: water, ice, 3-layer sediment cover and upper, middle and lower crystalline crust. Topography, bathymetry and ice cover are taken from ETOPO1. The sediment cover is essentially that of our sediment model (Laske and Masters, 1997; http://igppweb.ucsd.edu/~sediment.html), with several near-coastal updates. In the sediment cover and the crystalline crust, updated scaling relationships are used to assign compressional and shear velocity as well as density. In an initial step toward LITHO1.0, the model is then validated against our new global group velocity maps for Rayleigh and Love waves, particularly at frequencies between 30 and 40 mHz. CRUST1.0 is then adjusted in areas of extreme misfit where we suspect deficiencies in the crustal model. These currently include

  8. Africans in America.

    ERIC Educational Resources Information Center

    Hart, Ayanna; Spangler, Earl

    This book introduces African-American history and culture to children. The first Africans in America came from many different regions and cultures, but became united in this country by being black, African, and slaves. Once in America, Africans began a long struggle for freedom which still continues. Slavery, the Civil War, emancipation, and the…

  9. African Outreach Workshop 1974.

    ERIC Educational Resources Information Center

    Schmidt, Nancy J.

    This report discusses the 1974 African Outreach Workshop planned and coordinated by the African Studies Program at the University of Illinois at Urbana-Champaign. Its major aim was to assist teachers in developing curriculum units on African using materials available in their local community. A second aim was for the African Studies Program to…

  10. Probing the Lunar Polar Crust with GRAIL Gravity

    NASA Astrophysics Data System (ADS)

    Smith, D. E.; Zuber, M. T.; Goossens, S. J.; Rowlands, D. D.; Neumann, G. A.; Mazarico, E.; Genova, A.; Lemoine, F. G.

    2015-12-01

    The lunar polar crust, from latitude ±80° to the pole, exhibits Bouguer gravity anomalies that result from crustal density variations of order ±45 mGal in the south and ±25 mGal in the north, bandpass filtered to wavelengths representing the top 50 km. Evident in the Bouguer gravity at both poles are the signatures of a few large craters and basins. But at both poles, the Bouguer map also displays a large number of small, rather sinuous features, some outlining crater rims and some structures on crater floors, that are distributed more or less uniformly across the region. The root mean square (rms) variation over the 10° radius cap is less than 11 mGals at the south pole and less than 7 mGals in the north. This difference reflects the greater crustal complexity in the south compared to the north, but these magnitudes are approximately 10% of the total field in the polar regions, indicating that substantial density anomalies exist below 50 km depth. Modeling the crustal anomalies in the top 50 km by density contrasts at various depths suggest the rms magnitudes can be explained by small local variations in porosity, or possibly the presence of H2O at concentrations of a few percent. The required concentration increases with depth for a given volume but the possibility that the source of the polar anomalies includes small concentrations of H2O in the crust, however, cannot be ruled out.

  11. Growth of early continental crust by partial melting of eclogite.

    PubMed

    Rapp, Robert P; Shimizu, Nobumichi; Norman, Marc D

    2003-10-01

    The tectonic setting in which the first continental crust formed, and the extent to which modern processes of arc magmatism at convergent plate margins were operative on the early Earth, are matters of debate. Geochemical studies have shown that felsic rocks in both Archaean high-grade metamorphic ('grey gneiss') and low-grade granite-greenstone terranes are comprised dominantly of sodium-rich granitoids of the tonalite-trondhjemite-granodiorite (TTG) suite of rocks. Here we present direct experimental evidence showing that partial melting of hydrous basalt in the eclogite facies produces granitoid liquids with major- and trace-element compositions equivalent to Archaean TTG, including the low Nb/Ta and high Zr/Sm ratios of 'average' Archaean TTG, but from a source with initially subchondritic Nb/Ta. In modern environments, basalts with low Nb/Ta form by partial melting of subduction-modified depleted mantle, notably in intraoceanic arc settings in the forearc and back-arc regimes. These observations suggest that TTG magmatism may have taken place beneath granite-greenstone complexes developing along Archaean intraoceanic island arcs by imbricate thrust-stacking and tectonic accretion of a diversity of subduction-related terranes. Partial melting accompanying dehydration of these generally basaltic source materials at the base of thickened, 'arc-like' crust would produce compositionally appropriate TTG granitoids in equilibrium with eclogite residues. PMID:14534583

  12. Crusted scabies is associated with increased IL-17 secretion by skin T cells.

    PubMed

    Liu, X; Walton, S F; Murray, H C; King, M; Kelly, A; Holt, D C; Currie, B J; McCarthy, J S; Mounsey, K E

    2014-11-01

    Scabies is an ectoparasitic infestation by the mite Sarcoptes scabiei. Although commonly self-limiting, a fraction of patients develop severely debilitating crusted scabies. The immune mechanisms underlying the development of crusted scabies are unclear, and undertaking longitudinal infection studies in humans is difficult. We utilized a porcine model to compare cellular immune responses in peripheral blood and skin of pigs with different clinical manifestations of scabies (n = 12), and in uninfected controls (n = 6). Although clinical symptoms were not evident until at least 4 weeks post-infestation, the numbers of peripheral IFNγ-secreting CD4(+) T cells and γδ T cells increased in infected pigs from week 1 post-infestation. γδ T cells remained increased in the blood at week 15 post-infestation. At week 15, skin cell infiltrates from pigs with crusted scabies had significantly higher CD8(+) T cell, γδ T cell and IL-17(+) cell numbers than those with ordinary scabies. Peripheral IL-17 levels were not increased, suggesting that localized skin IL-17-secreting T cells may play a critical role in the pathogenesis of crusted scabies development. Given the potential of anti-IL-17 immunotherapy demonstrated for other inflammatory skin diseases, this study may provide a novel therapeutic avenue for patients with recurrent crusted scabies. PMID:25040151

  13. Growth of early continental crust controlled by melting of amphibolite in subduction zones.

    PubMed

    Foley, Stephen; Tiepolo, Massimo; Vannucci, Riccardo

    2002-06-20

    It is thought that the first continental crust formed by melting of either eclogite or amphibolite, either at subduction zones or on the underside of thick oceanic crust. However, the observed compositions of early crustal rocks and experimental studies have been unable to distinguish between these possibilities. Here we show a clear contrast in trace-element ratios of melts derived from amphibolites and those from eclogites. Partial melting of low-magnesium amphibolite can explain the low niobium/tantalum and high zirconium/samarium ratios in melts, as required for the early continental crust, whereas the melting of eclogite cannot. This indicates that the earliest continental crust formed by melting of amphibolites in subduction-zone environments and not by the melting of eclogite or magnesium-rich amphibolites in the lower part of thick oceanic crust. Moreover, the low niobium/tantalum ratio seen in subduction-zone igneous rocks of all ages is evidence that the melting of rutile-eclogite has never been a volumetrically important process. PMID:12075348

  14. The fate of Ceres' original crust

    NASA Astrophysics Data System (ADS)

    Roberts, James H.; Rivkin, Andrew S.

    2015-11-01

    The bulk density of Ceres implies that water ice comprises a substantial fraction of Ceres’ interior. However, water ice is not stable at Ceres orbital distance and if exposed would have a loss rate of 1 km Myr-1 or more. The near-hydrostatic shape of Ceres, and relatively low melting point of ice suggests that the interior is at least partly differentiated. Because Ceres’ surface remains exposed to space, it radiates very effectively, and models predicting differentiation retain an undifferentiated crust. This would be denser than the ice shell beneath it resulting in an unstable stratification. This has led to expectations that the crust would founder and the surface of Ceres might be very smooth and relaxed. But could the crust have remained to the present day?Here, we model global-scale overturn on Ceres using both analytical two-layer linear stability analyses, and numerical models to predict the most unstable wavelength, and growth timescales for Rayleigh-Taylor instabilities. We find that for a 10 km-thick crust above a 75 km-thick ice layer, instabilities grow fastest at spherical harmonic degree l=4. The growth timescale is a function of the viscosity of the upper layer. This timescale is less than the age of the solar system unless the effective viscosity of the crust is > 1024 Pa s. We conclude that the crust of Ceres could remain at the surface if it either has some finite elastic strength over a ~800 km length scale, or is an unconsolidated regolith with a large, (> 50%) macro-porosity, such that the regolith is buoyant relative to water ice.Neither end-member for the crustal strength precludes convective activity in the underlying ice layer. However we note that a thick, porous regolith is a fantastic insulator and may promote heating of the interior and potential foundering of the regolith if the top of the ice becomes too warm. This possibility can be evaluated by models of thermal evolution (e.g., Castillo-Rogez et al., 2010). An episode of

  15. Diffuse degassing through magmatic arc crust (Invited)

    NASA Astrophysics Data System (ADS)

    Manning, C. E.; Ingebritsen, S.

    2013-12-01

    The crust of magmatic arcs plays an important role in the volatile cycle at convergent margins. The fluxes of subduction- and arc-related volatiles such as H2O, C, Cl, S are poorly known. It is commonly believed that gases emitted from volcanoes account nearly quantitatively for the volatiles that cross the Moho beneath the volcanic front. This volcanic degassing may occur during eruption, emission from summit fumaroles and hot springs, or more 'diffuse' delivery to volcano flanks. However, several observations suggest that volatiles also transit arc crust by even more diffuse pathways, which could account for significant volatile loss on long time and length scales. Active metamorphism of arc crust produces crustal-scale permeability that is sufficient to transport a large volume of subducted volatiles (Ingebritsen and Manning, 2002, PNAS, 99, 9113). Arc magmas may reach volatile saturation deeper than the maximum depths recorded by melt inclusions (e.g., Blundy et al., 2010, EPSL, 290, 289), and exhumed sections of magmatic arc crust typically record voluminous plutons reflecting magma crystallization and volatile loss at depths well below the volcanic edifice. At shallower depths, topographically driven meteoric groundwater systems can absorb magmatic volatiles and transport them laterally by tens of km (e.g., James et al., 1999, Geology, 27, 823; Evans et al., 2002, JVGR, 114, 291). Hydrothermal ore deposits formed at subvolcanic depths sequester vast amounts of volatiles, especially sulfur, that are only returned to the surface on the time scale of exhumation and/or erosion. Water-rich metamorphic fluids throughout the crust can readily carry exsolved volcanic gases because the solubilities of volatile bearing minerals such as calcite, anhydrite, and fluorite are quite high at elevated pressure and temperature (e.g., Newton and Manning, 2002, Am Min, 87, 1401; 2005, J Pet, 46, 701; Tropper and Manning, 2007, Chem Geol, 242, 299). Taken together, these

  16. Eoarchean crustal evolution of the Jack Hills zircon source and loss of Hadean crust

    NASA Astrophysics Data System (ADS)

    Bell, Elizabeth A.; Harrison, T. Mark; Kohl, Issaku E.; Young, Edward D.

    2014-12-01

    Given the global dearth of Hadean (>4 Ga) rocks, 4.4-4.0 Ga detrital zircons from Jack Hills, Narryer Gneiss Complex (Yilgarn Craton, Western Australia) constitute our best archive of early terrestrial materials. Previous Lu-Hf investigations of these zircons suggested that felsic (low Lu/Hf) crust formation began by ∼4.4 to 4.5 Ga and continued for several hundred million years with evidence of the least radiogenic Hf component persisting until at least ∼4 Ga. However, evidence for the involvement of Hadean materials in later crustal evolution is sparse, and even in the detrital Jack Hills zircon population, the most unradiogenic, ancient isotopic signals have not been definitively identified in the younger (<3.9 Ga) rock and zircon record. Here we show Lu-Hf data from <4 Ga Jack Hills detrital zircons that document a significant and previously unknown transition in Yilgarn Craton crustal evolution between 3.9 and 3.7 Ga. The zircon source region evolved largely by internal reworking through the period 4.0-3.8 Ga, and the most ancient and unradiogenic components of the crust are mostly missing from the record after ∼4 Ga. New juvenile additions to the crust at ca. 3.9-3.8 Ga are accompanied by the disappearance of unradiogenic crust ca. 3.9-3.7 Ga. Additionally, this period is also characterized by a restricted range of δ18O after 3.8 Ga and a shift in several zircon trace element characteristics ca. 3.9-3.6 Ga. The simultaneous loss of ancient crust accompanied by juvenile crust addition can be explained by a mechanism similar to subduction, which effects both processes on modern Earth. The oxygen isotope and trace element information, although less sensitive to tectonic setting, also supports a transition in zircon formation environment in this period.

  17. A multilevel analysis of the relationship between neighborhood social disorder and depressive symptoms: Evidence from the South African National Income Dynamics Study

    PubMed Central

    Tomita, Andrew; Labys, Charlotte A.; Burns, Jonathan K

    2015-01-01

    The apartheid regime that governed South Africa from 1948 – 1994 established spatial segregation that is understood to have contributed to the magnitude of neighborhood social disorder in the post-apartheid era. Although a number of neighborhood social disorder characteristics, such as perceived violence and crime in the community, are prominent issues in South Africa, the extent to which these perceived spatial attributes are linked to depression is unknown at the population-level. Multilevel modeling of data from the second wave of the South African National Income Dynamics Study (SA-NIDS) was utilized to examine the relationship between depressive symptomatology and neighborhood social disorder as indicated by the perceived frequency of violent, criminal and illicit activities in the community. Depressive symptomatology was assessed using the 10-item version of the Center for Epidemiologic Studies Depression Scale. A cut off score of ten or higher was used to indicate the presence of significant depressive symptomatology. Results showed that perception of neighborhood social disorder was independently associated with significant levels of depressive symptomatology. Gender, race/ethnicity, perceived health status, and education were significant for individual-level covariates of depression. Community intervention strategies that reduce the risk of neighborhood disorganization and emphasize positive social norms in the neighborhood are warranted. Taking into account the residential de-racialization of a country transitioning from apartheid to non-racial democracy, a longitudinal spatial study design assessing the dynamics between depression and the aforementioned perceptions of neighborhood attributes may also be warranted. PMID:25642654

  18. Population genetic structure of the African elephant in Uganda based on variation at mitochondrial and nuclear loci: evidence for male-biased gene flow.

    PubMed

    Nyakaana, S; Arctander, P

    1999-07-01

    A drastic decline has occurred in the size of the Uganda elephant population in the last 40 years, exacerbated by two main factors; an increase in the size of the human population and poaching for ivory. One of the attendant consequences of such a decline is a reduction in the amount of genetic diversity in the surviving populations due to increased effects of random genetic drift. Information about the amount of genetic variation within and between the remaining populations is vital for their future conservation and management. The genetic structure of the African elephant in Uganda was examined using nucleotide variation of mitochondrial control region sequences and four nuclear microsatellite loci in 72 individuals from three localities. Eleven mitochondrial DNA (mtDNA) haplotypes were observed, nine of which were geographically localized. We found significant genetic differentiation between the three populations at the mitochondrial locus while three out of the four microsatellite loci differentiated KV and QE, one locus differentiated KV and MF and no loci differentiated MF and QE. Expected heterozygosity at the four loci varied between 0.51 and 0.84 while nucleotide diversity at the mitochondrial locus was 1.4%. Incongruent patterns of genetic variation within and between populations were revealed by the two genetic systems, and we have explained these in terms of the differences in the effective population sizes of the two genomes and male-biased gene flow between populations. PMID:10447852

  19. Depression, disability and functional status among community dwelling older adults in South Africa: Evidence from the first South African National Income Dynamics Study

    PubMed Central

    Tomita, Andrew; Burns, Jonathan K

    2013-01-01

    Objectives This study examined the relationship between depression and functional status among a community-dwelling elderly population of 65 years and older in South Africa. Method Data from the first wave of the South African National Income Dynamics Study (SA-NIDS) was used, this being the first longitudinal panel survey of a nationally representative sample of households. The study focused on the data for resident adults 65 years and older (n=1,429). Depression was assessed using the 10-item version of the Center for Epidemiologic Studies Depression Scale (CES-D). Functional status, pertaining to both difficulty and dependency in activities of daily living (ADL), instrumental activities of daily living (IADL), and physical functioning and mobility (PFM), were assessed using 11 items. Results Functional challenges were generally higher in the older age group. There was a significant association between depression and functional dependency in ADL (adjusted OR=2.57 [CI: 1.03-6.41]), IADL (adjusted OR=2.76 [CI: 1.89-4.04]) and PFM (adjusted OR=1.66 [CI: 1.18-2.33]) but the relationship between depression and functional status, particularly PFM, appeared weaker in older age. Conclusion The relationship between depression symptoms and function is complex. Functional characteristics between older and younger older populations are diverse, and caution is indicated against overgeneralizing the challenges related to depression and function among this target population. PMID:23512338

  20. Geochemistry and isotopic evolution of the central African Domes, Bangweulu and Irumide regions: Evidence for cryptic Archean sources and a Paleoproterozoic continental arc

    NASA Astrophysics Data System (ADS)

    Debruyne, David; Van Wilderode, Jorik; Balcaen, Lieve; Vanhaecke, Frank; Muchez, Philippe

    2014-12-01

    The interregional cratonic relations between the Paleo- and Mesoproterozoic basement units surrounding the Neoproterozoic Central African Copperbelt are still largely unresolved, although they are regarded as major potential metal sources. This study focuses on the Domes region basement at depth below the Copperbelt and its relationship to the neighboring Bangweulu Block and its destabilized margin, the Irumide Belt. We applied an integrated whole rock petrochemical and Sm-Nd isotopic approach to major lithological units to assess the proposed mid-Proterozoic arc setting for the Domes basement inliers along with their relationship to the neighboring areas. The available petrochemical and isotopic data for the Paleoproterozoic eastern Domes granitoids and magmatic units in the SW Bangweulu Block is consistent with a continental arc setting. Moreover, the mid-Paleoproterozoic Nd isotope ratios preclude an island arc because they are significantly less radiogenic than the depleted mantle. Predominantly Archean and Early Paleoproterozoic depleted mantle model ages in all terranes indicate limited juvenile input during Paleo- and Mesoproterozoic magmatic phases. Finally, broadly similar model ages in the Domes inliers and the Bangweulu-Irumide region suggest a relationship between these terranes.

  1. A multilevel analysis of the relationship between neighborhood social disorder and depressive symptoms: evidence from the South African National Income Dynamics Study.

    PubMed

    Tomita, Andrew; Labys, Charlotte A; Burns, Jonathan K

    2015-01-01

    The apartheid regime that governed South Africa from 1948-1994 established spatial segregation that is understood to have contributed to the magnitude of neighborhood social disorder in the postapartheid era. Although a number of neighborhood social disorder characteristics, such as perceived violence and crime in the community, are prominent issues in South Africa, the extent to which these perceived spatial attributes are linked to depression is unknown at the population level. Multilevel modeling of data from the second wave of the South African National Income Dynamics Study (SA-NIDS) was utilized to examine the relationship between depressive symptomatology and neighborhood social disorder as indicated by the perceived frequency of violent, criminal and illicit activities in the community. Depressive symptomatology was assessed using the 10-item version of the Center for Epidemiologic Studies Depression Scale. A cut-off score of 10 or higher was used to indicate the presence of significant depressive symptomatology. Results showed that perception of neighborhood social disorder was independently associated with significant levels of depressive symptomatology. Gender, race or ethnicity, perceived health status, and education were significant for individual-level covariates of depression. Community intervention strategies that reduce the risk of neighborhood disorganization and emphasize positive social norms in the neighborhood are warranted. Taking into account the residential deracialization of a country transitioning from apartheid to nonracial democracy, a longitudinal spatial study design assessing the dynamics between depression and the aforementioned perceptions of neighborhood attributes may also be warranted. PMID:25642654

  2. Melt evolution and residence in extending crust: Thermal modeling of the crust and crustal magmas

    NASA Astrophysics Data System (ADS)

    Karakas, Ozge; Dufek, Josef

    2015-09-01

    Tectonic extension and magmatism often act in concert to modify the thermal, mechanical, and chemical structure of the crust. Quantifying the effects of extension and magma flux on melting relationships in the crust is fundamental to determining the rate of crustal melting versus fractionation, magma residence time, and the growth of continental crust in rift environments. In order to understand the coupled control of tectonic extension and magma emplacement on crustal thermal evolution, we develop a numerical model that accounts for extension and thermal-petrographic processes in diverse extensional settings. We show that magma flux exerts the primary control on melt generation and tectonic extension amplifies the volume of melt residing in the crustal column. Diking into an extending crust produces hybrid magmas composed of 1) residual melt remaining after partial crystallization of basalt (mantle-derived melt) and 2) melt from partial melting of the crust (crustal melt). In an extending crust, mantle-derived melts are more prevalent than crustal melts across a range of magma fluxes, tectonic extension rates, and magmatic water contents. In most of the conditions, crustal temperatures do not reach their solidus temperatures to initiate partial melting of these igneous lithologies. Energy balance calculations show that the total enthalpy transported by dikes is primarily used for increasing the sensible heat of the cold surrounding crust with little energy contributing to latent heat of melting the crust (maximum crustal melting efficiency is 6%). In the lower crust, an extensive mush region develops for most of the conditions. Upper crustal crystalline mush is produced by continuous emplacement of magma with geologically reasonable flux and extension rates on timescales of 106 yr. Addition of tectonic effects and non-linear melt fraction relationships demonstrates that the magma flux required to sustain partially molten regions in the upper crust is within the

  3. Eu Anomalies Constrain Recycling of Lower Continental Crust

    NASA Astrophysics Data System (ADS)

    Tang, M.; Rudnick, R. L.; McDonough, W. F.; Gaschnig, R. M.; Huang, Y.

    2014-12-01

    Europium is fractionated from Sm and Gd during intra-crustal differentiation since Eu (II) strongly partitions into feldspar. Statistical analysis of Sm-Eu-Gd concentrations in over 2000 samples from the continental crust reveal that the bulk continental crust has a negative Eu anomaly. Samples include (1) shales, loess, and tillites which represent upper continental crust (n = 415); (2) amphibolite facies rocks, which represent the middle continental crust (n = 1325) and (3) granulite facies rocks (n = 845), which represent the lower continental crust. The upper and middle continental crust have a significant negative Eu anomaly, while the lower continental crust has a significant positive Eu anomaly. The Eu deficit in the upper and middle continental crust, however, cannot be compensated by the Eu excess in the lower continental crust, leaving the bulk continental crust with a negative Eu anomaly (Eu/Eu* = 0.81 ± 0.04, 95% conf.). Since the building blocks of the continental crust (mantle-derived basalts or tonalitic slab melts) do not possess a negative Eu anomaly, removal of lower continental crust, which is the only crustal reservoir enriched in Eu, is required during crustal evolution. A mass balance model of the continents, based on Sm-Eu-Gd systematics, indicates that at least 2.2-3.0 crustal masses may have been added back to the mantle over Earth history via lower crustal recycling.

  4. Influence of substrate rocks on Fe-Mn crust composition

    USGS Publications Warehouse

    Hein, J.R.; Morgan, C.L.

    1999-01-01

    Principal Component and other statistical analyses of chemical and mineralogical data of Fe-Mn oxyhydroxide crusts and their underlying rock substrates in the central Pacific indicate that substrate rocks do not influence crust composition. Two ridges near Johnston Atoll were dredged repetitively and up to seven substrate rock types were recovered from small areas of similar water depths. Crusts were analyzed mineralogically and chemically for 24 elements, and substrates were analyzed mineralogically and chemically for the 10 major oxides. Compositions of crusts on phosphatized substrates are distinctly different from crusts on substrates containing no phosphorite. However, that relationship only indicates that the episodes of phosphatization that mineralized the substrate rocks also mineralized the crusts that grew on them. A two-fold increase in copper contents in crusts that grew on phosphatized clastic substrate rocks, relative to crusts on other substrate rock types, is also associated with phosphatization and must have resulted from chemical reorganization during diagenesis. Phosphatized crusts show increases in Sr, Zn, Ca, Ba, Cu, Ce, V, and Mo contents and decreases in Fe, Si, and As contents relative to non-phosphatized crusts. Our statistical results support previous studies which show that crust compositions reflect predominantly direct precipitation from seawater (hydrogenetic), and to lesser extents reflect detrital input and diagenetic replacement of parts of the older crust generation by carbonate fluorapatite.

  5. Eleven years of itching: a case report of crusted scabies.

    PubMed

    Kutlu, Nurdan S; Turan, Enver; Erdemir, Asli; Gürel, Mehmet S; Bozkurt, Erol

    2014-08-01

    Crusted scabies is a rare and highly contagious form of scabies that is characterized by uncontrolled proliferation of mites in the skin, extensive hyperkeratotic scaling, crusted lesions, and variable pruritus. We report the case of a 48-year-old man with an 11-year history of pruritic, hyperkeratotic, psoriasiform plaques and widespread erythematous papules that was diagnosed as crusted scabies. PMID:25184648

  6. Density Sorting During the Evolution of Continental Crust

    NASA Astrophysics Data System (ADS)

    Kelemen, P. B.; Behn, M. D.; Hacker, B. R.

    2015-12-01

    We consider two settings - in addition to "delamination" of arc lower crust - in which dense, mafic eclogites founder into the convecting mantle while buoyant, felsic lithologies accumulate at the base of evolving continental crust. Arc processes play a central role in generating continental crust, but it remains uncertain how basaltic arc crust is transformed to andesitic continental crust. Dense, SiO2-poor products of fractionation may founder from the base of arc crust by "delamination", but lower arc crust after delamination has significantly different trace elements compared to lower continental crust (LCC). In an alternative model, buoyant magmatic rocks generated at arcs are first subducted, mainly via subduction erosion. Upon heating, these buoyant lithologies ascend through the mantle wedge or along a subduction channel, and are "relaminated" at
the base of overlying crust (e.g., Hacker et al EPSL 11, AREPS 15). Average buoyant lavas and plutons
for the Aleutians, Izu-Bonin-Marianas, Kohistan and Talkeetna arcs fall within the range of estimated LCC major and trace elements. Relamination is more efficient in generating continental crust than delamination. Himalayan cross-sections show Indian crust thrust beneath Tibetan crust, with no intervening mantle. There is a horizontal Moho at ca 80 km depth, extending from thickened Indian crust, across the region where Tibetan crust overlies Indian crust, into thickened Tibetan crust. About half the subducted Indian crust is present, whereas the other half is missing. Data (Vp/Vs; Miocene lavas formed by interaction of continental crust with mantle; xenolith thermometry) indicate 1000°C or more from ca 50 km depth to the Moho since the Miocene. We build on earlier studies (LePichon et al Tectonics 92, T'phys 97; Schulte-Pelkum et al Nature 05; Monsalve et al JGR 08) to advance the hypothesis that rapid growth of garnet occurs at 70-80 km and 1000°C within subducting Indian crust. Dense eclogites founder

  7. Outer crust of nonaccreting cold neutron stars

    NASA Astrophysics Data System (ADS)

    Rüster, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Jürgen

    2006-03-01

    The properties of the outer crust of nonaccreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables, updating in particular the classic work of Baym, Pethick, and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 are used and a thorough comparison of many modern theoretical nuclear models, both relativistic and nonrelativistic, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared to check their differences concerning the neutron drip line, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the drip line in the outer crust of nonaccreting cold neutron stars.

  8. Outer crust of nonaccreting cold neutron stars

    SciTech Connect

    Ruester, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Juergen

    2006-03-15

    The properties of the outer crust of nonaccreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables, updating in particular the classic work of Baym, Pethick, and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 are used and a thorough comparison of many modern theoretical nuclear models, both relativistic and nonrelativistic, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared to check their differences concerning the neutron drip line, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the drip line in the outer crust of nonaccreting cold neutron stars.

  9. Towards a metallurgy of neutron star crusts.

    PubMed

    Kobyakov, D; Pethick, C J

    2014-03-21

    In the standard picture of the crust of a neutron star, matter there is simple: a body-centered-cubic lattice of nuclei immersed in an essentially uniform electron gas. We show that, at densities above that for neutron drip (∼ 4 × 1 0(11)  g cm(-3) or roughly one-thousandth of nuclear matter density), the interstitial neutrons give rise to an attractive interaction between nuclei that renders the lattice unstable. We argue that the likely equilibrium structure is similar to that in displacive ferroelectric materials such as BaTiO3. As a consequence, the properties of matter in the inner crust are expected to be much richer than previously appreciated, and we mention possible consequences for observable neutron star properties. PMID:24702357

  10. The ancient lunar crust, Apollo 17 region

    NASA Technical Reports Server (NTRS)

    James, O. B.

    1992-01-01

    The Apollo 17 highland collection is dominated by fragment-laden melt rocks, generally thought to represent impact melt from the Serenitatis basin-forming impact. Fortunately for our understanding of the lunar crust, the melt rocks contain unmelted clasts of preexisting rocks. Similar ancient rocks are also found in the regolith; most are probably clasts eroded out of melt rocks. The ancient rocks can be divided into groups by age, composition, and history. Oldest are plutonic igneous rocks, representing the magmatic components of the ancient crust. The younger are granulitic breccias, which are thoroughly recrystallized rocks of diverse parentages. The youngest are KREEPy basalts and felsites, products of relatively evolved magmas. Some characteristics of each group are given.

  11. Composition of weakly altered Martian crust

    NASA Technical Reports Server (NTRS)

    Mustard, J. F.; Murchie, S. L.; Erard, S.

    1993-01-01

    The mineralogic and chemical composition of weakly altered crust remains an unresolved question for Mars. Dark regions hold clues to the composition since they are thought to comprise surface exposures of weakly altered crustal materials. Understanding the in situ composition of relatively pristine crustal rocks in greater detail is important for investigating basic volcanic processes. Also, this will provide additional constraints on the chemical pathways by which pristine rocks are altered to produce the observed ferric iron-bearing assemblages and inferred clay silicate, sulphate, and magnetic oxide phases. Reflectance spectra of dark regions obtained with the ISM instrument are being used to determine the basic mineralogy of weakly altered crust for a variety of regions on Mars.

  12. Temperature distribution in the crust and mantle

    NASA Technical Reports Server (NTRS)

    Jeanloz, R.; Morris, S.

    1986-01-01

    In an attempt to understand the temperature distribution in the earth, experimental constraints on the geotherm in the crust and mantle are considered. The basic form of the geotherm is interpreted on the basis of two dominant mechanisms by which heat is transported in the earth: (1) conduction through the rock, and (2) advection by thermal flow. Data reveal that: (1) the temperature distributions through continental lithosphere and through oceanic lithosphere more than 60 million years old are practically indistinguishable, (2) crustal uplift is instrumental in modifying continental geotherms, and (3) the average temperature through the Archean crust and mantle was similar to that at present. It is noted that current limitations in understanding the constitution of the lower mantle can lead to significant uncertainties in the thermal response time of the planetary interior.

  13. 40Ar/ 39Ar-ages of phlogopite in mantle xenoliths from South African kimberlites: Evidence for metasomatic mantle impregnation during the Kibaran orogenic cycle

    NASA Astrophysics Data System (ADS)

    Hopp, Jens; Trieloff, M.; Brey, G. P.; Woodland, A. B.; Simon, N. S. C.; Wijbrans, J. R.; Siebel, W.; Reitter, E.

    2008-12-01

    mantle below southern Africa may have been frequently influenced by different episodes of fluid or melt migration during subduction of oceanic crust at active continental margins.

  14. Cyclic growth in Atlantic region continental crust

    NASA Technical Reports Server (NTRS)

    Goodwin, A. M.

    1986-01-01

    Atlantic region continental crust evolved in successive stages under the influence of regular, approximately 400 Ma-long tectonic cycles. Data point to a variety of operative tectonic processes ranging from widespread ocean floor consumption (Wilson cycle) to entirely ensialic (Ampferer-style subduction or simple crustal attenuation-compression). Different processes may have operated concurrently in some or different belts. Resolving this remains the major challenge.

  15. Mesoscopic pinning forces in neutron star crusts

    NASA Astrophysics Data System (ADS)

    Seveso, S.; Pizzochero, P. M.; Grill, F.; Haskell, B.

    2016-02-01

    The crust of a neutron star is thought to be comprised of a lattice of nuclei immersed in a sea of free electrons and neutrons. As the neutrons are superfluid, their angular momentum is carried by an array of quantized vortices. These vortices can pin to the nuclear lattice and prevent the neutron superfluid from spinning down, allowing it to store angular momentum which can then be released catastrophically, giving rise to a pulsar glitch. A crucial ingredient for this model is the maximum pinning force that the lattice can exert on the vortices, as this allows us to estimate the angular momentum that can be exchanged during a glitch. In this paper, we perform, for the first time, a detailed and quantitative calculation of the pinning force per unit length acting on a vortex immersed in the crust and resulting from the mesoscopic vortex-lattice interaction. We consider realistic vortex tensions, allow for displacement of the nuclei and average over all possible orientations of the crystal with respect to the vortex. We find that, as expected, the mesoscopic pinning force becomes weaker for longer vortices and is generally much smaller than previous estimates, based on vortices aligned with the crystal. Nevertheless, the forces we obtain still have maximum values of the order of fpin ≈ 1015 dyn cm-1, which would still allow for enough angular momentum to be stored in the crust to explain large Vela glitches, if part of the star is decoupled during the event.

  16. Thickness of the magnetic crust of Mars

    NASA Astrophysics Data System (ADS)

    Voorhies, Coerte V.

    2008-04-01

    To estimate the thickness of the magnetic crust of Mars, six observational magnetic spectra are fitted with the theoretical spectrum expected from a novel, bimodal distribution of magnetic sources. Observational spectra differ, for each comes from a different map or model of variously selected and analyzed Mars Global Surveyor Magnetometer/Electron Reflectometer measurements of the vector magnetic field around Mars. The new theoretical spectrum represents fields from both compact sources and extended, laterally correlated sources on a spherical shell, so the estimated shell depth can now be doubled to obtain layer thickness. This typical magnetic crustal thickness is put at 47.8 +/- 8.4 km. The extensive sources are enormous, typically 650 km across, and account for over half the magnetic energy at low degrees. There is some indication that these sources are relatively shallow, but the typical area remains about 330,000 km2. Granted such extended sources represent magnetization of Mars' ancient crust in a core source field dominated by a reversing, areocentric paleodipole, each one arguably formed during a single polarity chron. How did such vast regions of magnetic crust form? A survey of many eligible mechanisms suggests magnetization of cooling igneous rock at minimal rates of about 1 to 0.1 km3/a during superchrons of order 15 to 150 Ma long.

  17. Magnetic Sources in the Crust of Mars

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This is a simple schematic representation of localized magnetic sources in the crust of Mars, buried beneath the surface, and revealed by observation of the magnetic field (blue) extending up to satellite altitude (about 120 kilometers). Most of our close passes to date - for which we have data - reveal the presence of one or more magnetic anomalies close to the path of the spacecraft. Since the sources must be close to the path of the satellite, we can only infer that the crust of Mars is strewn with similar magnetic anomalies, awaiting discovery. Where we can obtain enough data - that is to say, spaced more or less evenly in longitude with a spacing comparable to our periapsis altitude - we can construct a detailed image of the magnetic state of the Martian crust. We can then perhaps learn about the history of the now-extinct early Mars dynamo and the evolution of the surface of Mars.

    The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO. JPL is an operating division of California Institute of Technology (Caltech).

  18. Chronology and complexity of early lunar crust

    NASA Technical Reports Server (NTRS)

    Dasch, E. J.; Ryder, G.; Nyquist, L. E.

    1989-01-01

    The petrology and chronology of early lunar crust is examined using the least equivocal of the available petrographic and age data on lunar rock samples, and the possible processes which produced the lunar crust are discussed. The results suggest that the lunar anorthositic crust was formed by about 120 Ma after the primary accretion of the moon at 4.56 Ga. At least some members of the diverse Mg-suites of rocks, such as norites, troctolites, and dunites, crystallized within a very few 100s of Ma after 4.56 Ga. A trace-element-rich material (KREEP) was formed by about 4.3 Ga ago, and this residue was subsequently reworked in melting and impact processes such that most samples which contain it have ages around 3.9-4.0 Ga. The findings also suggest that the onset of ferrous mare basalt volcanism began about 4.33 Ga, much earlier than was once assumed, and was still in process before the end of the most intense period of bombardment (3.9-4.0 Ga ago).

  19. Pyrolysis of waste plastic crusts of televisions.

    PubMed

    Liu, Xinmin; Wang, Zhen; Xu, Dongyan; Guo, Qingjie

    2012-09-01

    The disposal of waste plastic crusts of televisions is an issue that is gaining increasing interest around the world. In this investigation, the pyrolysis and catalytic cracking of the waste television crusts mainly composed of acrylonitrile--butadiene-styrene copolymer was studied. Thermogravimetric analysis was used for initial characterization of the pyrolysis of the waste plastic, but most of the investigations were carried out using a 600 mL tubing reactor. Effects of temperature, reaction time and catalyst on the pyrolysis of the waste television crusts were investigated. The results showed that the oil yield increased with increasing temperature or with prolongation of reaction time. With increasing temperature, the generating percentage of gasoline and diesel oil increased, but the heavy oil yield decreased. Zinc oxide, iron oxide and fluid catalytic cracking catalyst (FCC catalyst) were employed to perform a series of experiments. It was demonstrated that the liquid product was markedly improved and the reaction temperature decreased 100 degrees C when FCC was used. The composition ofpyrolysis oils was analysed using gas chromatography-mass spectrometry, and they contained 36.49% styrene, 19.72% benzenebutanenitrile, 12.1% alpha-methylstyrene and 9.69% dimethylbenzene. PMID:23240191

  20. Palynological evidence for gradual vegetation and climate changes during the "African Humid Period" termination at 13° N from a Mega-Lake Chad sedimentary sequence

    NASA Astrophysics Data System (ADS)

    Amaral, P. G. C.; Vincens, A.; Guiot, J.; Buchet, G.; Deschamps, P.; Doumnang, J.-C.; Sylvestre, F.

    2012-06-01

    Located at the transition between the Saharian and Sahelian zones, at the center of one of the largest endoreic basins, the Lake Chad is ideally located to record regional environmental changes that occurred in the past. However, until now, no continuous archive from Lake Chad covering the Holocene has been studied. In this paper, we present pollen data from the first Holocene sedimentary sequence collected in Lake Chad (13° N; 14° E; Sahel region). Dated between ca. 6700 and ca. 5000 cal yr BP, this record encompasses the termination of the African Humid Period (AHP). Vegetational reconstructions are based on standard analyses of the pollen diagrams and are strengthened by quantitative approaches. Potential biomes that occurred at that time around Mega-Lake Chad are reconstructed using the biomization method and mean annual precipitation is estimated using the modern analogues technique. Results show that between ca. 6700 and ca. 6050 cal yr BP, a vegetation close to humid woodland or humid savanna, including elements currently found much further southward, thrived in the vicinity and/or the extra-local environment of the Mega-Lake Chad in place of the modern steppe, dry woodland and desert vegetation observed today. At the same time, montane forest populations extended further southward on the Adamawa plateau. This vegetation distribution is supported by biome reconstructions as well as by mean annual precipitation estimates of ca. 800 (-400/+700) mm for the period. The high abundance of lowland humid pollen taxa is interpreted as the result of a northward migration of the corresponding plants during the AHP driven by more favorable climatic conditions. Our interpretation in favor of a regional vegetation response to climatic changes is supported by other pollen data from several Northwestern African records. However, we cannot rule out that an increase of Chari-Logone inputs into the Mega-Lake Chad due to variations in hydrological regime might have

  1. Self-rated health and associated factors among older South Africans: evidence from the study on global ageing and adult health

    PubMed Central

    Phaswana-Mafuya, Nancy; Peltzer, Karl; Chirinda, Witness; Kose, Zamakayise; Hoosain, Ebrahim; Ramlagan, Shandir; Tabane, Cily; Davids, Adlai

    2013-01-01

    Background Population ageing has become significant in South African society, increasing the need to improve understandings of health and well-being among the aged. Objective To describe the self-reported ratings of overall health and functioning, and to identify factors associated with self-rated health among older South Africans. Design A national population-based cross-sectional survey, with a sample of 3,840 individuals aged 50 years and older, was completed in South Africa in 2008. Self-reported ratings of overall health and functioning were measured using a single self-reported health state covering nine health domains (used to generate the Study on Global Ageing and Adult Health (SAGE) composite health state score). Disability was measured using the World Health Organization Disability Assessment Schedule II (WHODAS-II) activities of daily living (ADLs), instrumental activities of daily living (IADLs), perceptions of well-being, and the World Health Organization Quality of Life index/metric (WHOQoL). Results Overall, more than three quarters (76.8%) of adults rated their health as moderate or good. On balance, men reported very good or good health more often than women (p<0.001). Older people (aged 70 years and above) reported significantly poorer health status than those aged 50–59 (adjusted odds ratio (AOR) 1.52; 95% confidence interval (CI) 1.00–2.30). Indians and Blacks were significantly more likely to report poorer health status at (AOR=4.01; 95% CI 1.27–12.70) and (AOR=0.42; 95% CI 0.18–0.98; 30 p <0.045), respectively, compared to Whites. Respondents with primary education (AOR=1.83; 95% CI 1.19–2.80) and less than primary education (AOR=1.94; 95% CI 1.37–2.76) were more likely to report poorer health compared to those with secondary education. In terms of wealth status, those in low wealth quintile (AOR=2.02; 95% CI 1.14–3.57) and medium wealth quintile (AOR=1.47; 95% CI 1.01–2.13) were more likely to report poorer health status than

  2. Knowledge and behavior in an animal disease outbreak - Evidence from the item count technique in a case of African swine fever in Madagascar.

    PubMed

    Randrianantoandro, Tiana N; Kono, Hiroichi; Kubota, Satoko

    2015-03-01

    Pig production in Madagascar is not sufficient for domestic consumption. Unfortunately, African swine fever (ASF), which is a severe disease, is endemic in Madagascar and constitutes a constant threat for farmers. Therefore, ASF must be eradicated in order to guarantee the development of pig production. One of the main strategies in controlling ASF is stamping out which requires the farmers' collaboration in reporting cases or suspected cases. The objective of this study was to estimate the proportion of farmers who knowingly sell ASF-infected meat without reporting. Since selling ASF-infected meat is prohibited by the government, we used the item count technique (ICT), an indirect questioning technique appropriate for measuring the proportion of people engaged in sensitive behavior, for one subsample, while another subsample was asked directly whether they sell ASF-infected meat. Based on the ICT, approximately 73.2% of farmers who have experienced ASF sell the ASF-infected meat. This estimate was not statistically different from that obtained by direct questioning. In the 28% of interviewed farmers who believe ASF can affect humans, the ICT yielded a higher estimate than did direct questioning, indicating that pig farmers who sell ASF-infected meat hide that fact because of their belief that infected meat might harm human consumers, not because of the law. The ICT was thus a suitable technique to address the problem of sensitive behavior. In the case of ASF outbreaks, the Malagasy government should enforce the law more strictly and provide compensation as incentive for reporting cases. PMID:25591977

  3. Cytokine response during non-cerebral and cerebral malaria: evidence of a failure to control inflammation as a cause of death in African adults

    PubMed Central

    Mbengue, Babacar; Dagamajalu, Shobha; Fall, Mouhamadou Mansour; Loke, Mun Fai; Nguer, Cheikh Momar; Thiam, Alassane; Vadivelu, Jamuna; Dieye, Alioune

    2016-01-01

    Background. With 214 million cases and 438,000 deaths in 2015, malaria remains one of the deadliest infectious diseases in tropical countries. Several species of the protozoan Plasmodium cause malaria. However, almost all the fatalities are due to Plasmodium falciparum, a species responsible for the severest cases including cerebral malaria. Immune response to Plasmodium falciparum infection is mediated by the production of pro-inflammatory cytokines, chemokines and growth factors whose actions are crucial for the control of the parasites. Following this response, the induction of anti-inflammatory immune mediators downregulates the inflammation thus preventing its adverse effects such as damages to various organs and death. Methods. We performed a retrospective, nonprobability sampling study using clinical data and sera samples from patients, mainly adults, suffering of non-cerebral or cerebral malaria in Dakar, Sénégal. Healthy individuals residing in the same area were included as controls. We measured the serum levels of 29 biomarkers including growth factors, chemokines, inflammatory and anti-inflammatory cytokines. Results. We found an induction of both pro- and anti-inflammatory immune mediators during malaria. The levels of pro-inflammatory biomarkers were higher in the cerebral malaria than in the non-cerebral malaria patients. In contrast, the concentrations of anti-inflammatory cytokines were comparable in these two groups or lower in CM patients. Additionally, four pro-inflammatory biomarkers were significantly increased in the deceased of cerebral malaria compared to the survivors. Regarding organ damage, kidney failure was significantly associated with death in adults suffering of cerebral malaria. Conclusions. Our results suggest that a poorly controlled inflammatory response determines a bad outcome in African adults suffering of cerebral malaria. PMID:27168977

  4. Strontium and neodymium isotopic study of Libyan Desert Glass: Inherited Pan-African age signatures and new evidence for target material

    NASA Astrophysics Data System (ADS)

    Schaaf, P.; Müller-Sohnius, D. M.

    2002-04-01

    Libyan Desert Glass (LDG) is an impact-related, natural glass of still unknown target material. We have determined Rb-Sr and Sm-Nd isotopic ratios from seven LDG samples and five associated sandstones from the LDG strewn field in the Great Sand Sea, western Egypt. Planar deformation features were recently detected in quartz from these sandstones. 87Sr/86Sr ratios and e-Nd values for LDG range between 0.71219 and 0.71344, and between -16.6 and -17.8, respectively, and hence are distinct from the less radiogenic 87Sr/86Sr ratios of 0.70910-0.71053 and e-Nd values from -6.9 to -9.6 for the local sandstones from the LDG strewn field. Previously published isotopic ratios from the Libyan BP and Oasis crater sandstones are generally incompatible with our LDG values. LDG formation undoubtedly occurred at 29 Ma, but neither the Rb-Sr nor the Sm-Nd isotopic system were rehomogenised during the impact event, as we can deduce from Pan-African ages of ~540 Ma determined from the regression lines from a total of 14 LDG samples from this work and the literature. Together with similar Sr and Nd isotopic values for LDG and granitoid rocks from northeast Africa west of the Nile, these findings point to a sandy matrix target material for the LDG derived from a Precambrian crystalline basement, ruling out the Cretaceous sandstones of the former "Nubian Group" as possible precursors for LDG.

  5. Structural analysis of the Itapucumí Group in the Vallemí region, northern Paraguay: Evidence of a new Brasiliano/Pan-African mobile belt

    NASA Astrophysics Data System (ADS)

    Campanha, Ginaldo Ademar da Cruz; Warren, Lucas; Boggiani, Paulo César; Grohmann, Carlos Henrique; Cáceres, Alberto Arias

    The Neoproterozoic (Ediacaran) Itapucumí Group in northern Paraguay is composed of carbonate and siliciclastic rocks, including ooid grainstones, marls, shales and sandstones, containing Cloudina fossils in the eastern region. It is almost undeformed over the Rio Apa Cratonic Block but shows a strong deformational pattern at its western edge. A detailed structural analysis of the Itapucumí Group was conducted in the Vallemí Mine, along with a regional survey in other outcrops downstream in the Paraguay River and in the San Alfredo, Cerro Paiva and Sargento José E. López regions. In the main Vallemí quarry, the structural style is characterized by an axial-plane slaty cleavage in open to isoclinal folds, sometimes overturned, associated with N-S trending thrust faults and shear zones of E-vergence and with a low-grade chlorite zone metamorphism. The structural data presented here are compatible with the hypothesis of a newly recognized mobile belt on the western side of the Rio Apa Cratonic Block, with opposite vergence to that of the Paraguay Mobile Belt in Brazil. Both belts are related to the Late Brasiliano/Pan-African tectonic cycle with a Lower Cambrian deformation and metamorphism age. The deformation could be due to the late collision of the Amazonian Craton with the remainder of Western Gondwana or to the western active plate boundary related to the Pampean Belt. The structural and lithologic differences between the western Itapucumí Group in the Vallemí and Paraguay River region and the eastern region, near San Alfredo and Cerro Paiva, suggest that this group could be divided into two lithostratigraphic units, but more stratigraphic and geochronological analyses are required to confirm this possibility.

  6. Crust-derived potassic fluid in metamorphic microdiamond

    NASA Astrophysics Data System (ADS)

    Hwang, Shyh-Lung; Shen, Pouyan; Chu, Hao-Tsu; Yui, Tzen-Fu; Liou, Juhn G.; Sobolev, Nikolay V.; Shatsky, Vladislav S.

    2005-03-01

    A highly potassic COH fluid, with dissolved phosphate, chloride and sulfate/sulfide, was identified as nanometer-size inclusions in metamorphic microdiamonds of Kokchetav dolomite marble and garnet-quartz-pyroxene rock using an analytical electron microscope (AEM) coupled with an energy-dispersive X-ray (EDX) spectrometer. This provides a direct piece of evidence for the formation of metamorphic microdiamonds from such a fluid. Although this crust-derived potassic fluid and the associated solid precipitates are in some respects similar to the fluid inclusions in fibrous/cloudy mantle diamonds, distinct chemical differences exist. This potassic COH fluid, in addition, has the potential to trigger high to ultrahigh-K magmatic and K metasomatic processes in mantle.

  7. Clinopyroxene precursors to amphibole sponge in arc crust.

    PubMed

    Smith, Daniel J

    2014-01-01

    The formation of amphibole cumulates beneath arc volcanoes is a key control on magma geochemistry, and generates a hydrous lower crust. Despite being widely inferred from trace element geochemistry as a major lower crustal phase, amphibole is neither abundant nor common as a phenocryst phase in arc lavas and erupted pyroclasts, prompting some authors to refer to it as a 'cryptic' fractionating phase. This study provides evidence that amphibole develops by evolved melts overprinting earlier clinopyroxene--a near-ubiquitous mineral in arc magmas. Reaction-replacement of clinopyroxene ultimately forms granoblastic amphibole lithologies. Reaction-replacement amphiboles have more primitive trace element chemistry (for example, lower concentrations of incompatible Pb) than amphibole phenocrysts, but still have chemistries suitable for producing La/Yb and Dy/Yb 'amphibole sponge' signatures. Amphibole can fractionate cryptically as reactions between melt and mush in lower crustal 'hot zones' produce amphibole-rich assemblages, without significant nucleation and growth of amphibole phenocrysts. PMID:25002269

  8. Seismic reflection images of a near-axis melt sill within the lower crust at the Juan de Fuca ridge.

    PubMed

    Canales, J Pablo; Nedimović, Mladen R; Kent, Graham M; Carbotte, Suzanne M; Detrick, Robert S

    2009-07-01

    The oceanic crust extends over two-thirds of the Earth's solid surface, and is generated along mid-ocean ridges from melts derived from the upwelling mantle. The upper and middle crust are constructed by dyking and sea-floor eruptions originating from magma accumulated in mid-crustal lenses at the spreading axis, but the style of accretion of the lower oceanic crust is actively debated. Models based on geological and petrological data from ophiolites propose that the lower oceanic crust is accreted from melt sills intruded at multiple levels between the Moho transition zone (MTZ) and the mid-crustal lens, consistent with geophysical studies that suggest the presence of melt within the lower crust. However, seismic images of molten sills within the lower crust have been elusive. Until now, only seismic reflections from mid-crustal melt lenses and sills within the MTZ have been described, suggesting that melt is efficiently transported through the lower crust. Here we report deep crustal seismic reflections off the southern Juan de Fuca ridge that we interpret as originating from a molten sill at present accreting the lower oceanic crust. The sill sits 5-6 km beneath the sea floor and 850-900 m above the MTZ, and is located 1.4-3.2 km off the spreading axis. Our results provide evidence for the existence of low-permeability barriers to melt migration within the lower section of modern oceanic crust forming at intermediate-to-fast spreading rates, as inferred from ophiolite studies. PMID:19571883

  9. A Pan African age for the HP-HT granulite gneisses of Zabargad island: implications for the early stages of the Red Sea rifting

    NASA Astrophysics Data System (ADS)

    Lancelot, Joël R.; Bosch, Delphine

    1991-12-01

    Up to now the age of granulite gneisses intruded by the Zabargad mantle diapir has been an unsolved problem. These gneisses may represent either a part of the adjacent continental crust primarily differentiated during the Pan African orogeny, or new crust composed of Miocene clastic sediments deposited in a developing rift, crosscut by a diabase dike swarm and gabbroic intrusions, and finally metamorphosed and deformed by the mantle diapir. Previous geochronological results obtained on Zabargad island and Al Lith and Tihama-Asir complexes (Saudi Arabia) suggest an Early Miocene age of emplacement for the Zabargad mantle diapir during the early opening of the Red Sea rift. In contrast, Sm sbnd Nd and Rb sbnd Sr internal isochrons yield Pan African dates for felsic and basic granulites collected 500-600 m from the contact zone with the peridotites. Devoid of evidence for retrograde metamorphic, minerals from a felsic granulite provide well-defined Rb sbnd Sr and Sm sbnd Nd dates of 655 ± 8 and 699 ± 34 Ma for the HP-HT metamorphic event (10 kbar, 850°C). The thermal event related to the diapir emplacement is not recorded in the Sm sbnd Nd and Rb sbnd Sr systems of the studied gneisses; in contrast, the development of a retrograde amphibolite metamorphic paragenesis strongly disturbed the Rb sbnd Sr isotopic system of the mafic granulite. The initial 143Nd/ 144Nd ratio of the felsic granulite is higher than the contemporaneous value for CHUR and is in agreement with other Nd isotopic data for samples of upper crust from the Arabian shield. This result suggests that source rocks of the felsic granulite were derived at 1.0 to 1.2 Ga from either an average MORB-type mantle or a local 2.2 Ga LREE-depleted mantle. Zabargad gneisses represent a part of the disrupted lower continental crust of the Pan African Afro-Arabian shield. During early stages of the Red Sea rifting in the Miocene, these Precambrian granulites were intruded and dragged upwards by a rising peridotite

  10. Melt inclusion evidence for CO2-rich melts beneath the western branch of the East African Rift: implications for long-term storage of volatiles in the deep lithospheric mantle

    NASA Astrophysics Data System (ADS)

    Hudgins, T. R.; Mukasa, S. B.; Simon, A. C.; Moore, G.; Barifaijo, E.

    2015-05-01

    We present new major element, trace element, and volatile (H2O, CO2, S, F, and Cl) concentrations of olivine-hosted melt inclusions from five high-K, low-silica basanites from the western branch of the East African Rift System and use these data to investigate the generation of H2O- and CO2-rich melts at up to ~150 km depth. Measured H2O and CO2 concentrations reach ~2.5 and ~1 wt%, respectively, representing some of the highest CO2 concentrations measured in a melt inclusion to date. These measurements represent direct evidence of the high CO2 and H2O concentrations required to generate high-K alkaline lavas, and the CO2 that has been previously inferred to be necessary for the low mantle potential temperatures in the area. Ratios of CO2/Nb, CO2/Ba, and CO2/Cl are used to estimate an initial melt CO2 concentration of 5-12 wt%. The measured CO2 concentrations are consistent with CO2 solubilities determined by molecular dynamics calculations and high-pressure experiments for melt generation at 3-6 GPa; the depth of melting suggested by previous studies in the area. These melt inclusions measurements represent direct evidence for the presence of H2O- and CO2-rich melts in the deep upper mantle that have been proposed based on experimental and seismic evidence. Primitive-mantle normalized trace element patterns more closely resemble those found in subduction settings rather than ocean island basalt, and ratios of slab fluid tracers such as Li/Dy and B/Be indicate that the measured volatile abundances may be related to Neoproterozoic subduction during the assembly of Gondwana, implying the storage of volatiles in the mantle by subduction-related metasomatism.

  11. Palynological evidence for gradual vegetation and climate changes during the African Humid Period termination at 13°N from a Mega-Lake Chad sedimentary sequence

    NASA Astrophysics Data System (ADS)

    Amaral, P. G. C.; Vincens, A.; Guiot, J.; Buchet, G.; Deschamps, P.; Doumnang, J.-C.; Sylvestre, F.

    2013-01-01

    Located at the transition between the Saharan and Sahelian zones, at the center of one of the largest endorheic basins, Lake Chad is ideally located to record regional environmental changes that occurred in the past. However, until now, no Holocene archive was directly cored in this lake. In this paper, we present pollen data from the first sedimentary sequence collected in Lake Chad (13° N; 14° E; Sahel region). Dated between ca. 6700 and ca. 5000 cal yr BP, this record is continuous and encompasses part of the termination of the African Humid Period (AHP). Vegetation reconstructions are based on standard analyses of pollen diagrams and are strengthened by quantitative approaches. Potential biomes are reconstructed using the biomization method and mean annual precipitation (Pann) is estimated using the modern analogues technique. Results show that, between ca. 6700 and ca. 6050 cal yr BP, a vegetation close to humid woodland or humid savanna, including elements currently found further southward, thrived in the vicinity of the Mega-Lake Chad in place of the modern dry woodland, steppe and desert vegetation. At the same time, montane forest populations extended further southward on the Adamawa Plateau. The high abundance of lowland humid pollen taxa, particularly of Uapaca, is interpreted as the result of a northward migration of the corresponding plants during the AHP. This preferential zonal occurrence of these taxa in Lake Chad Basin (LCB) (rather than extrazonal) is driven by more humid local and regional climate conditions at this latitude, as shown by mean Pann estimated values of ca. 800 (-400/+700) mm during this period. However, we cannot rule out that an increase of the Chari-Logone inputs into the Mega-Lake Chad might have also contributed to control the abundance of these taxa. Changes in the structure and floristic composition of the vegetation towards more open and drier formations occurred after ca. 6050 cal yr BP, following a decrease in mean Pann

  12. Geochemical and isotopic composition of Pan-African metabasalts from southwestern Gondwana: Evidence of Cretaceous South Atlantic opening along a Neoproterozoic back-arc

    NASA Astrophysics Data System (ADS)

    Will, Thomas M.; Frimmel, Hartwig E.; Gaucher, Claudio; Bossi, Jorge

    2014-08-01

    A lithogeochemical and Sr-Nd-Pb isotope study of former oceanic crustal rocks from the Cuchilla Dionisio Terrane in the southern Dom Feliciano Belt, Uruguay (La Tuna amphibolites) and metabasites in the Chameis Subterrane of the Marmora Terrane in the Gariep Belt, Namibia/South Africa shows that these rocks are compositionally very similar and probably represent the same unit on opposite sides of the modern South Atlantic. The mafic rocks from both terranes are tholeiitic metabasalts and -andesites and have depleted rare earth element patterns, generally low TiO2 (< 1.5 wt.%), very low Th/Nb ratios and lack negative Nb-Ta anomalies, all features that are typical of ‘normal' mid-ocean ridge basalts (N-MORB) and/or back-arc basin basalts (BABB). In addition, both rock suites have extremely depleted Nd isotope compositions (εNd630 Ma = 6.7-9.4), superchondritic 147Sm/144Nd ratios, and low 206Pb/204Pb and 207Pb/204Pb initial ratios. The 87Sr/86Sr initial ratios of the La Tuna mafic rocks are low, whereas the Chameis metagabbro samples have higher, possibly alteration-related ratios. The geochemical and isotopic signatures are consistent with the formation of both rock suites in the same mature Neoproterozoic back-arc basin (Marmora Basin), supporting conclusions drawn from earlier provenance studies of metasedimentary units from these terranes. Other mafic rocks from the Marmora Terrane are interpreted as ocean island basalts that formed in a within-plate setting. A corollary of the conclusion that the mafic rocks in the Cuchilla Dionisio and Marmora Terranes formed in the same back-arc basin is (1) that the main Pan-African suture between the Río de la Plata Craton and the Kalahari Craton lies to the west of the Dom Feliciano Belt in South America, and (2) that the opening of the modern South Atlantic did not occur along that suture but along the axis of the Neoproterozoic Marmora back-arc basin.

  13. Biodiversity of Klebsormidium (streptophyta) from alpine biological soil crusts (alps, tyrol, Austria, and Italy).

    PubMed

    Mikhailyuk, Tatiana; Glaser, Karin; Holzinger, Andreas; Karsten, Ulf

    2015-08-01

    Forty Klebsormidium strains isolated from soil crusts of mountain regions (Alps, 600–3,000 m elevation) were analyzed. The molecular phylogeny (internal transcribed spacer rDNA sequences) showed that these strains belong to clades B/C, D, E, and F. Seven main (K. flaccidum, K. elegans, K. crenulatum, K. dissectum, K. nitens, K. subtile, and K. fluitans) and four transitional morphotypes (K. cf. flaccidum, K. cf. nitens, K. cf. subtile, and K. cf. fluitans) were identified. Most strains belong to clade E, which includes isolates that prefer humid conditions. One representative of the xerophytic lineage (clade F) as well as few isolates characteristic of temperate conditions (clades B/C, D) were found. Most strains of clade E were isolated from low/middle elevations (<1,800 m above sea level; a.s.l.) in the pine-forest zone. Strains of clades B/C, D, and F occurred sporadically at higher elevations (1,548–2,843 m a.s.l.), mostly under xerophytic conditions of alpine meadows. Comparison of the alpine Klebsormidium assemblage with data from other biogeographic regions indicated similarity with soil crusts/biofilms from terrestrial habitats in mixed forest in Western Europe, North America, and Asia, as well as walls of buildings in Western European cities. The alpine assemblage differed substantially from crusts from granite outcrops and sand dunes in Eastern Europe (Ukraine), and fundamentally from soil crusts in South African drylands. Epitypification of the known species K. flaccidum, K. crenulatum, K. subtile, K. nitens, K. dissectum, K. fluitans, K. mucosum, and K. elegans is proposed to establish taxonomic names and type material as an aid for practical studies on these algae, as well as for unambiguous identification of alpine strains. New combination Klebsormidium subtile (Kützing) Mikhailyuk, Glaser, Holzinger et Karsten comb. nov. is made. PMID:26504252

  14. A plea to better feed African soils

    NASA Astrophysics Data System (ADS)

    Stroosnijder, Leo

    2014-05-01

    Most African cropping system are rainfed. Rain is distributed at the soil surface over infiltration and runoff. The infiltrated water is stored in the rootable soil layer and the excess drains below that layer into the groundwater. The stored water is partly lost as evaporation to the atmosphere and partly used as transpiration for plant growth. In African cropping system the green water use efficiency (GWUE: fraction transpiration over rainfall) is as low as 15%. This low value is due to the often poor soil quality (physical, chemical and biological) of African soils. The poor physical state causes a weak soil structure resulting in crust formation with low infiltration and high runoff as consequences. The water holding capacity of the rootable soil layer is also poor, causing quite some water lost into deeper layers. African soils are poor due to long time soil mining. Soil life depends on soil organic matter (SOM) which is decreasing everywhere at an average rate of 2% per year. It is common sense that an improved soil quality is essential for improved food security. The key that triggers a sustainable improvement in soil quality is a system's approach that focus on the management of organic resources. Soil is a living organism, and it feeds on SOM. This feed is continuously consumed but a living soil makes new SOM out of fresh organic matter. In order to keep our soils alive we need cropping systems that feed our soils with fresh organic matter in the form of crop residues in the right mix of quality and quantity. The tendency to breed crops with a high harvest index (hence low straw) and the many other uses of crop residues (competing claims) with it recent use for bio-ethanol fabrication is disastrous for our living soils. If we continue to allow SOM to decrease, soil crusting and hard setting will increase with less end less water available for the production of green biomass. Lower available water will trigger a negative spiral with lower food security and

  15. The effect of thicker oceanic crust in the Archaean on the growth of continental crust through time

    NASA Technical Reports Server (NTRS)

    Wilks, M. E.

    1988-01-01

    Present crustal evolution models fail to account for the generation of the large volume of continental crust in the required time intervals. All Archaean plate tectonic models, whether invoking faster spreading rates, similar to today's spreading rates, or longer ridge lengths, essentially propose that continental crust has grown by island arc accretion due to the subduction of oceanic crust. The petrological differences that characterize the Archaean from later terrains result from the subduction of hotter oceanic crust into a hotter mantle. If the oceanic crust was appreciably thicker in the Archaean, as geothermal models would indicate, this thicker crust is surely going to have an effect on tectonic processes. A more valid approach is to compare the possible styles of convergence of thick oceanic crust with modern convergence zones. The best modern analog occurs where thick continental crust is colliding with thick continental crust. Oceanic crustal collision on the scale of the present-day Himalayan continental collision zone may have been a frequent occurrence in the Archaean, resulting in extensive partial melting of the hydrous underthrust oceanic crust to produce voluminous tonalite melts, leaving a depleted stabilized basic residuum. Present-day island arc accretion may not have been the dominant mechanism for the growth of the early Archaean crust.

  16. Black African Traditional Mathematics

    ERIC Educational Resources Information Center

    Zaslavsky, Claudia

    1970-01-01

    Discusses the traditional number systems and the origin of the number names used by several African peoples living south of the Sahara. Also included are limitations in African mathematical development, and possible topics for research. (RP)

  17. Update on CRUST1.0 - A 1-degree Global Model of Earth's Crust

    NASA Astrophysics Data System (ADS)

    Laske, Gabi; Masters, Guy; Ma, Zhitu; Pasyanos, Mike

    2013-04-01

    Our new 1-by-1 degree global crustal model, CRUST1.0, was introduced last year and serves as starting model in a comprehensive effort to compile a global model of Earth's crust and lithosphere, LITHO1.0 (Pasyanos et al., 2012). The Moho depth in CRUST1.0 is based on 1-degree averages of a recently updated database of crustal thickness data from active source seismic studies as well as from receiver function studies. In areas where such constraints are still missing, for example in Antarctica, crustal thicknesses are estimated using gravity constraints. The compilation of the new crustal model initially followed the philosophy of the widely used crustal model CRUST2.0 (Bassin et al., 2000; http://igppweb.ucsd.edu/~gabi/crust2.html) to assign elastic properties in the crystalline crust according to basement age or tectonic setting (loosely following an updated map by Artemieva and Mooney (2001; http://www.lithosphere.info). For cells with no local seismic or gravity constraints, statistical averages of crustal properties, including crustal thickness, were extrapolated. However, in places with constraints the depth to basement and mantle are given explicitly and no longer assigned by crustal type. This allows for much smaller errors in both. In each 1-degree cell, boundary depth, compressional and shear velocity as well as density is given for 8 layers: water, ice, 3 sediment layers and upper, middle and lower crystalline crust. Topography, bathymetry and ice cover are taken from ETOPO1. The sediment cover is based on our sediment model (Laske and Masters, 1997; http://igppweb.ucsd.edu/~sediment.html), with some near-coastal updates. In an initial step toward LITHO1.0, the model is then validated against new global surface wave disperison maps and adjusted in areas of extreme misfit. This poster presents the next validation step: compare the new Moho depths with in-situ active source and receiver function results. We also present comparisons with CRUST2.0. CRUST1.0 is

  18. Basaltic Volcanism and Ancient Planetary Crusts

    NASA Technical Reports Server (NTRS)

    Shervais, John W.

    1993-01-01

    The purpose of this project is to decipher the origin of rocks which form the ancient lunar crust. Our goal is to better understand how the moon evolved chemically and, more generally, the processes involved in the chemical fractionation of terrestrial planetoids. This research has implications for other planetary bodies besides the Moon, especially smaller planetoids which evolved early in the history of the solar system and are now thermally stable. The three main areas focused on in our work (lunar mare basalts, KREEP basalts, and plutonic rocks of the lunar highlands) provide complementary information on the lunar interior and the processes that formed it.

  19. Strange Star Surface: A Crust with Nuggets

    SciTech Connect

    Jaikumar, Prashanth; Reddy, Sanjay; Steiner, Andrew W.

    2006-02-03

    We reexamine the surface composition of strange stars. Strange quark stars are hypothetical compact stars which could exist if strange quark matter was absolutely stable. It is widely accepted that they are characterized by an enormous density gradient (10{sup 26} g/cm{sup 4}) and large electric fields at the surface. By investigating the possibility of realizing a heterogeneous crust, comprised of nuggets of strange quark matter embedded in an uniform electron background, we find that the strange star surface has a much reduced density gradient and negligible electric field. We comment on how our findings will impact various proposed observable signatures for strange stars.

  20. Anatexis, hybridization and the modification of ancient crust: Mesozoic plutonism in the Old Woman Mountains area, California

    USGS Publications Warehouse

    Miller, C.F.; Wooden, J.L.

    1994-01-01

    A compositionally expanded array of granitic (s.l.) magmas intruded the > 2 Ga crust of the Old Woman Mountains area between 160 and 70 Ma. These magmas were emplaced near the eastern (inland) edge of the Jurassic/Cretaceous arcs of western North America, in an area where magma flux, especially during the Jurassic, was considerably lower than to the west. The Jurassic intrusives and over half of the Cretaceous intrusives are predominantly metaluminous and variable in composition; a major Cretaceous suite comprises only peraluminous monzogranite. Only the Jurassic intrusions show clear evidence for the presence of mafic liquids. All units, including the most mafic rocks, reveal isotopic evidence for a significant crustal component. However, none of the Mesozoic intrusives matches in isotopic composition either average pre-intrusion crust or any major unit of the exposed crust. Elemental inconsistencies also preclude closed system derivation from exposed crust. Emplacement of these magmas, which doubled the volume of the mid- to upper crust, did not dramatically change its elemental composition. It did, however, affect its Nd and especially Sr isotopic composition and modify some of the distinctive aspects of the elemental chemistry. We propose that Jurassic magmatism was open-system, with a major influx of mantle-derived mafic magma interacting strongly with the ancient crust. Mesozoic crustal thickening may have led to closed-system crustal melting by the Late Cretaceous, but the deep crust had been profoundly modified by earlier Mesozoic hybridization so that crustal melts did not simply reflect the original crustal composition. The clear evidence for a crustal component in magmas of the Old Woman Mountains area may not indicate any fundamental differences from the processes at work elsewhere in this or other magmatic arcs where the role of pre-existing crust is less certain. Rather, a compositionally distinctive, very old crust may simply have yielded a more

  1. AfricaArray seismological studies of the structure and evolution of the African continent

    NASA Astrophysics Data System (ADS)

    Durrheim, Raymond; Nyblade, Andrew; Brandt, Martin; Tugume, Fred; Mulibo, Gabriel; Kgaswane, Eldridge; Mangongolo, Azangi; Manzi, Musa; El Tahir, Nada; Loots, Letticia

    2014-05-01

    The AfricaArray programme was launched in 2005 to conduct research that promotes development in Africa by building human and infrastructural capacity in support of the mineral exploration, mining, geohazard and environmental sectors. The AfricaArray "backbone" network now consists of 51 geophysical observatories in 20 sub-Saharan countries. Most stations are equipped with broadband seismometers, while 25 stations have continuous GPS sensors and 22 stations have meteorological packs. In addition, several temporary seismic arrays have been deployed to investigate the seismotectonics of the East African Rift System, the extent of the Congo craton, and the rifting of Mozambique and Madagascar. In this paper we will present results pertinent to large-scale crustal and mantle geodynamic processes that have been obtained by AfricaArray researchers. Brandt and Mulibo elucidated the relationship between the African Superplume, Superswell and the East African Rift System by studying the seismic velocity structure of the mantle. Kgaswane jointly inverted P-wave receiver functions (PRFs) and surface waves, and found that the Kalahari Craton lower crust is largely mafic, except for a few terrains such as the Kimberley. Kgaswane also produced evidence that supports a link between the eastern and western lobes of the Bushveld Complex. Mangongolo used surface wave tomography to define the south-western boundary of the Congo Craton. El Tahir used PRFs to investigate the crustal structure of the Khartoum Basin, while Tugume determined the Moho depths and Poisson's ratios of the Precambrian crust in East Africa. Manzi reprocessed 3D reflection seismic data covering part of the Witwatersrand goldfields using seismic attribute analysis methods, and has provided new constraints on the evolution of the Basin during the Neoarchean. Loots interpreted a 105 km 2D seismic reflection profile immediately to the north of the Cape Fold Belt, imaging the Karoo and Cape Supergroup rocks and the

  2. Hydromechanical Modeling of Fluid Flow in the Lower Crust

    NASA Astrophysics Data System (ADS)

    Connolly, J.

    2011-12-01

    The lower crust lies within an ambiguous rheological regime between the brittle upper crust and ductile sub-lithospheric mantle. This ambiguity has allowed two schools of thought to develop concerning the nature of fluid flow in the lower crust. The classical school holds that lower crustal rocks are inviscid and that any fluid generated by metamorphic devolatilization is squeezed out of rocks as rapidly as it is produced. According to this school, permeability is a dynamic property and fluid flow is upward. In contrast, the modern school uses concepts from upper crustal hydrology that presume implicitly, if not explicitly, that rocks are rigid or, at most, brittle. For the modern school, the details of crustal permeability determine fluid flow and as these details are poorly known almost anything is possible. Reality, to the extent that it is reflected by inference from field studies, offers some support to both schools. In particular, evidence of significant lateral and channelized fluid flow are consistent with flow in rigid media, while evidence for short (104 - 105 y) grain-scale fluid-rock interaction during much longer metamorphic events, suggests that reaction-generated grain-scale permeability is sealed rapidly by compaction; a phenomenon that is also essential to prevent extensive retrograde metamorphism. These observations provide a compelling argument for recognizing in conceptual models of lower crustal fluid flow that rocks are neither inviscid nor rigid, but compact by viscous mechanisms on a finite time-scale. This presentation will review the principle consequences of, and obstacles to, incorporating compaction in such models. The role of viscous compaction in the lower crust is extraordinarily uncertain, but ignoring this uncertainty in models of lower crustal fluid flow does not make the models any more certain. Models inevitably invoke an initial steady state hydraulic regime. This initial steady state is critical to model outcomes because it

  3. The African Connection

    ERIC Educational Resources Information Center

    Oguntoyinbo, Lekan

    2012-01-01

    From student and faculty exchanges to joint research projects, U.S. universities maintain a broad spectrum of collaborative relationships with African universities. It's unclear how many U.S. colleges and universities have partnerships with African universities. The African Studies Association, an organization of scholars, doesn't keep that kind…

  4. Possible use of the Passive Remote Sensing for the Study of a two Layered Crust on the Europa Satellite

    NASA Astrophysics Data System (ADS)

    Velasco, V. M.; Cordero, M. G.; Mendoza, B.

    2003-12-01

    On December 7th 1995, the Galileo mission began the study the jovian system. Among the results that his mission has obtained, it is the evidence of the existence of a liquid water ocean beneath the icy crust of Europa. Liquid water is one of the main factors that make life possible, so then life might exist in Europa. Some of the scenes that have been settled out to explain how living organisms could be present in such an extreme environment involve suppositions about the width of the icy crust. The explanation of other geological structures on the satellite also implies an estimation of the crust's width, that is why a good estimation about this parameter is very important in the geological study of this satellite. In this work, we analyze one electrodynamic model of the crust considering a two layered crust. The purpose is to obtain the optimal electrophysical parameters of measurement that permit us to estimate the crust's width. These parameters are calculated from the inverse elements of the Fisher matrix. The results obtained from this work can be used to plan future space missions to jovian satellites (in particular it could be useful for JIMO mission). The optimal algorithms for these measurements can be modified to be used in active systems of remote sensing.

  5. Using of the Passive Remote Sensing for the Study of a two Layered Crust on the Europa Satellite

    NASA Astrophysics Data System (ADS)

    Velasco Herrera, Victor Manuel; Cordero, Guadalupe; Velasco Herrera, Graciela

    On December 7th 1995, the Galileo mission began the study the jovian system. Among the results that his mission has obtained, it is the evidence of the existence of a liquid water ocean beneath the icy crust of Europa. Liquid water is one of the main factors that make life possible, so then life might exist in Europa. Some of the scenes that have been settled out to explain how living organisms could be present in such an extreme environment involve suppositions about the width of the icy crust. The explanation of other geological structures on the satellite also implies an estimation of the crust's width, that is why a good estimation about this parameter is very important in the geological study of this satellite. In this work, we analyze one electrodynamic model of the crust considering a two layered crust. The purpose is to obtain the optimal electrophysical parameters of measurement that permit us to estimate the crust's width. These parameters are calculated from the inverse elements of the Fisher matrix. The results obtained from this work can be used to plan future space missions to jovian satellites (in particular it could be useful for JIMO mission). The optimal algorithms for these measurements can be modified to be used in active systems of remote sensing.

  6. Osmium isotope and highly siderophile element systematics of the lunar crust

    USGS Publications Warehouse

    Day, J.M.D.; Walker, R.J.; James, O.B.; Puchtel, I.S.

    2010-01-01

    Coupled 187Os/188Os and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance data are reported for pristine lunar crustal rocks 60025, 62255, 65315 (ferroan anorthosites, FAN) and 76535, 78235, 77215 and a norite clast in 15455 (magnesian-suite rocks, MGS). Osmium isotopes permit more refined discrimination than previously possible of samples that have been contaminated by meteoritic additions and the new results show that some rocks, previously identified as pristine, contain meteorite-derived HSE. Low HSE abundances in FAN and MGS rocks are consistent with derivation from a strongly HSE-depleted lunar mantle. At the time of formation, the lunar floatation crust, represented by FAN, had 1.4 ?? 0.3 pg g- 1 Os, 1.5 ?? 0.6 pg g- 1 Ir, 6.8 ?? 2.7 pg g- 1 Ru, 16 ?? 15 pg g- 1 Pt, 33 ?? 30 pg g- 1 Pd and 0.29 ?? 0.10 pg g- 1 Re (??? 0.00002 ?? CI) and Re/Os ratios that were modestly elevated (187Re/188Os = 0.6 to 1.7) relative to CI chondrites. MGS samples are, on average, characterised by more elevated HSE abundances (??? 0.00007 ?? CI) compared with FAN. This either reflects contrasting mantle-source HSE characteristics of FAN and MGS rocks, or different mantle-crust HSE fractionation behaviour during production of these lithologies. Previous studies of lunar impact-melt rocks have identified possible elevated Ru and Pd in lunar crustal target rocks. The new results provide no supporting evidence for such enrichments. If maximum estimates for HSE in the lunar mantle are compared with FAN and MGS averages, crust-mantle concentration ratios (D-values) must be ??? 0.3. Such D-values are broadly similar to those estimated for partitioning between the terrestrial crust and upper mantle, with the notable exception of Re. Given the presumably completely different mode of origin for the primary lunar floatation crust and tertiary terrestrial continental crust, the potential similarities in crust-mantle HSE partitioning for the Earth and Moon are somewhat

  7. The giant Pan-African Hook Batholith, Central Zambia: A-type magmatism in a syn-collisional setting

    NASA Astrophysics Data System (ADS)

    Milani, Lorenzo; Lehmann, Jérémie; Naydenov, Kalin V.; Saalmann, Kerstin; Kinnaird, Judith A.; Daly, J. Stephen; Frei, Dirk; Lobo-Guerrero Sanz, Alberto

    2015-04-01

    The Pan-African Hook Batholith formed during the assembly of the Gondwana supercontinent between 570 and 520 Ma (U-Pb on zircon) as a result of syn-collisional stage interaction between the Congo and Kalahari Cratons1. The extension of the batholith, exposed and undercover, is estimated to be between 25,000 and 30,000 km2. The bimodal magmatism (mafic to predominantly felsic) is characterized by both an alkali-calcic and an alkalic suite, with the felsic rocks featuring a typical A-type, metaluminous, high Fe/Mg and K/Na geochemical signature. The scattered outcrops of gabbroic rocks, both tholeiitic and alkaline, suggest periodic input of mantle material, which, in some cases, interacted with metasomatizing fluids. Fractional crystallization is invoked for the most differentiated products, while Sr-Nd isotopes rule out any significant contribution from crustal assimilation. Exceptionally highly radiogenic Pb isotopes have been measured on both unaltered and hydrothermally altered rocks, and attest to the radiogenic character of the batholith. The Pb isotopes indicate that the anomalous signature was acquired during, or soon after, magma emplacement, and was likely enhanced by metasomatizing fluids. An enrichment in Th and U, affecting large portions of the crust along the southern margin of the Congo Craton, is suggested by comparable anomalous Pb isotopes measured in basement gneisses in the Domes Region, Zambian Copperbelt. Geochemical and isotopic evidence support interaction between mantle components and portions of the deep crust at pressures of < 10 kbar, while decompression melting of rising asthenospheric mantle ponding at the base of the crust heated, and ultimately melted, crustal material. Low-pressure mineral phases in metasedimentary wall rocks along the eastern margin of the pluton indicate that the magma was subsequently emplaced at shallow crustal depths. A crucial contribution to the crustal melting was likely provided by internal radiogenic heat

  8. Longitudinal photosynthetic gradient in crust lichens' thalli.

    PubMed

    Wu, Li; Zhang, Gaoke; Lan, Shubin; Zhang, Delu; Hu, Chunxiang

    2014-05-01

    In order to evaluate the self-shading protection for inner photobionts, the photosynthetic activities of three crust lichens were detected using Microscope-Imaging-PAM. The false color images showed that longitudinal photosynthetic gradient was found in both the green algal lichen Placidium sp. and the cyanolichen Peltula sp. In longitudinal direction, all the four chlorophyll fluorescence parameters Fv/Fm, Yield, qP, and rETR gradually decreased with depth in the thalli of both of these two lichens. In Placidium sp., qN values decreased with depth, whereas an opposite trend was found in Peltula sp. However, no such photosynthetic heterogeneity was found in the thalli of Collema sp. in longitudinal direction. Microscope observation showed that photobiont cells are compactly arranged in Placidium sp. and Peltula sp. while loosely distributed in Collema sp. It was considered that the longitudinal photosynthetic heterogeneity was ascribed to the result of gradual decrease of incidence caused by the compact arrangement of photobiont cells in the thalli. The results indicate a good protection from the self-shading for the inner photobionts against high radiation in crust lichens. PMID:24477924

  9. Crusted scabies in the burned patient.

    PubMed

    Berg, Jais Oliver; Alsbjørn, Bjarne

    2011-01-01

    The objectives of this study were 1) to describe a case of crusted scabies (CS) in a burned patient, which was primarily undiagnosed and led to a nosocomial outbreak in the burn unit; 2) to analyze and discuss the difficulties in diagnosing and treating this subset of patients with burn injury; and 3) to design a treatment strategy for future patients. Case analysis and literature review were performed. The index patient had undiagnosed crusted scabies (sive Scabies norvegica) with the ensuing mite hyperinfestation when admitted to the department with minor acute dermal burns. Conservative healing and autograft healing were impaired because of the condition. Successful treatment of the burns was only accomplished secondarily to scabicide treatment. An outbreak of scabies among staff members indirectly led to diagnosis. CS is ubiquitous, and diagnosis may be difficult. This is the first report of a burned patient with CS in the English language literature. CS is also highly contagious and may lead to a nosocomial outbreak. Furthermore, CS seems to have a detrimental impact on the burned patient's course of treatment. A scabicide treatment is necessary to guarantee successful treatment of the burns. PMID:21427595

  10. Surface coating for prevention of crust formation

    DOEpatents

    Kronberg, James W.

    1994-01-01

    A flexible surface coating which promotes the removal of deposits as they reach the surface by preventing adhesion and crust formation. Flexible layers are attached to each side of a flexible mesh substrate comprising of a plurality of zones composed of one or more neighboring cells, each zone having a different compressibility than its adjacent zones. The substrate is composed of a mesh made of strands and open cells. The cells may be filled with foam. Studs or bearings may also be positioned in the cells to increase the variation in compressibility and thus the degree of flexing of the coating. Surface loading produces varying amounts of compression from point to point causing the coating to flex as deposits reach it, breaking up any hardening deposits before a continuous crust forms. Preferably one or more additional layers are also used, such as an outer layer of a non-stick material such as TEFLON, which may be pigmented, and an inner, adhesive layer to facilitate applying the coating to a surface.

  11. CHAMP Magnetic Anomalies of the Antarctic Crust

    NASA Technical Reports Server (NTRS)

    Kim, Hyung Rae; Gaya-Pique, Luis R.; vonFrese, Ralph R. B.; Taylor, Patrick T.; Kim, Jeong Woo

    2003-01-01

    Regional magnetic signals of the crust are strongly masked by the core field and its secular variations components and hence difficult to isolate in the satellite measurements. In particular, the un-modeled effects of the strong auroral external fields and the complicated- behavior of the core field near the geomagnetic poles conspire to greatly reduce the crustal magnetic signal-to-noise ratio in the polar regions relative to the rest of the Earth. We can, however, use spectral correlation theory to filter the static lithospheric and core field components from the dynamic external field effects. To help isolate regional lithospheric from core field components, the correlations between CHAMP magnetic anomalies and the pseudo magnetic effects inferred from gravity-derived crustal thickness variations can also be exploited.. Employing these procedures, we processed the CHAMP magnetic observations for an improved magnetic anomaly map of the Antarctic crust. Relative to the much higher altitude Orsted and noisier Magsat observations, the CHAMP magnetic anomalies at 400 km altitude reveal new details on the effects of intracrustal magnetic features and crustal thickness variations of the Antarctic.

  12. Is Ishtar Terra a thickened basaltic crust?

    NASA Technical Reports Server (NTRS)

    Arkani-Hamed, Jafar

    1992-01-01

    The mountain belts of Ishtar Terra and the surrounding tesserae are interpreted as compressional regions. The gravity and surface topography of western Ishtar Terra suggest a thick crust of 60-110 km that results from crustal thickening through tectonic processes. Underthrusting was proposed for the regions along Danu Montes and Itzpapalotl Tessera. Crustal thickening was suggested for the entire Ishtar Terra. In this study, three lithospheric models with total thicknesses of 40.75 and 120 km and initial crustal thicknesses of 3.9 and 18 km are examined. These models could be produced by partial melting and chemical differentiation in the upper mantle of a colder, an Earth-like, and a hotter Venus having temperatures of respectively 1300 C, 1400 C, and 1500 C at the base of their thermal boundary layers associated with mantle convection. The effects of basalt-granulite-eclogite transformation (BGET) on the surface topography of a thickening basaltic crust is investigated adopting the experimental phase diagram and density variations through the phase transformation.

  13. Color characterization of Arctic Biological Soil Crusts

    NASA Astrophysics Data System (ADS)

    Mele, Giacono; Gargiulo, Laura; Ventura, Stefano

    2015-04-01

    Global climate change makes large areas lacking the vegetation coverage continuously available to primary colonization by biological soil crusts (BSCs). This happens in many different environments, included high mountains and Polar Regions where new areas can become available due to glaciers retreat. Presence of BSCs leads to the stabilization of the substrate and to a possible development of protosoil, with an increase of fertility and resilience against erosion. Polar BSCs can exhibit many different proportions of cyanobacteria, algae, microfungi, lichens, and bryophytes which induce a large variability of the crust morphology and specific ecosystem functions. An effective and easy way for identifying the BSCs in the field would be very useful to rapidly recognize their development stage and help in understanding the overall impact of climate change in the delicate polar environments. Color analysis has long been applied as an easily measurable physical attribute of soil closely correlated with pedogenic processes and some soil functions. In this preliminary work we used RGB and CIE-L*a*b* color models in order to physically characterize fourteen different BSCs identified in Spitsbergen island of Svalbard archipelago in Arctic Ocean at 79° north latitude. We found that the "redness parameter "a*" of CIE-L*a*b* model was well correlated to the succession process of some BSCs at given geomorphology condition. Most of color parameters showed, moreover, a great potential to be correlated to photosynthetic activity and other ecosystem functions of BSCs.

  14. Crusted Demodicosis in an Immunocompetent Pediatric Patient

    PubMed Central

    Gómez-Flores, Minerva; Ocampo-Candiani, Jorge

    2014-01-01

    Demodicosis refers to the infestation by Demodex spp., a saprophytic mite of the pilosebaceous unit. Demodex proliferation can result in a number of cutaneous disorders including pustular folliculitis, pityriasis folliculorum, papulopustular, and granulomatous rosacea, among others. We report the case of a 7-year-old female presenting with pruritic grayish crusted lesions over her nose and cheeks, along with facial erythema, papules, and pustules. The father referred chronic use of topical steroids. A potassium hydroxide mount of a pustule scraping revealed several D. folliculorum mites. Oral ivermectin (200 μg/kg, single dose) plus topical permethrin 5% lotion applied for 3 consecutive nights were administered. Oral ivermectin was repeated every week and oral erythromycin plus topical metronidazole cream was added. The facial lesions greatly improved within the following 3 months. While infestation of the pilosebaceous unit by Demodex folliculorum mites is common, only few individuals present symptoms. Demodicosis can present as pruritic papules, pustules, plaques, and granulomatous facial lesions. To our knowledge, this is the first reported case of facial crusted demodicosis in an immunocompetent child. The development of symptoms in this patient could be secondary to local immunosuppression caused by the chronic use of topical steroids. PMID:25371830

  15. Crusted demodicosis in an immunocompetent pediatric patient.

    PubMed

    Guerrero-González, Guillermo Antonio; Herz-Ruelas, Maira Elizabeth; Gómez-Flores, Minerva; Ocampo-Candiani, Jorge

    2014-01-01

    Demodicosis refers to the infestation by Demodex spp., a saprophytic mite of the pilosebaceous unit. Demodex proliferation can result in a number of cutaneous disorders including pustular folliculitis, pityriasis folliculorum, papulopustular, and granulomatous rosacea, among others. We report the case of a 7-year-old female presenting with pruritic grayish crusted lesions over her nose and cheeks, along with facial erythema, papules, and pustules. The father referred chronic use of topical steroids. A potassium hydroxide mount of a pustule scraping revealed several D. folliculorum mites. Oral ivermectin (200 μg/kg, single dose) plus topical permethrin 5% lotion applied for 3 consecutive nights were administered. Oral ivermectin was repeated every week and oral erythromycin plus topical metronidazole cream was added. The facial lesions greatly improved within the following 3 months. While infestation of the pilosebaceous unit by Demodex folliculorum mites is common, only few individuals present symptoms. Demodicosis can present as pruritic papules, pustules, plaques, and granulomatous facial lesions. To our knowledge, this is the first reported case of facial crusted demodicosis in an immunocompetent child. The development of symptoms in this patient could be secondary to local immunosuppression caused by the chronic use of topical steroids. PMID:25371830

  16. The WORD (Wholeness, Oneness, Righteousness, Deliverance): Design of a randomized controlled trial testing the effectiveness of an evidence-based weight loss and maintenance intervention translated for a faith-based, rural, African American population using a community-based participatory approach

    PubMed Central

    Yeary, Karen Hye-cheon Kim; Cornell, Carol E.; Prewitt, Elaine; Bursac, Zoran; Tilford, J. Mick; Turner, Jerome; Eddings, Kenya; Love, ShaRhonda; Whittington, Emily; Harris, Kimberly

    2014-01-01

    Background The positive effects of weight loss on obesity-related risk factors diminish unless weight loss is maintained. Yet little work has focused on the translation of evidence-based weight loss interventions with the aim of sustaining weight loss in underserved populations. Using a community-based participatory approach (CBPR) that engages the strong faith-based social infrastructure characteristic of rural African American communities is a promising way to sustain weight loss in African Americans, who bear a disproportionate burden of the obesity epidemic. Objectives Led by a collaborative community-academic partnership, The WORD aims to change dietary and physical activity behaviors to produce and maintain weight loss in rural, African American adults of faith. Design The WORD is a randomized controlled trial with 450 participants nested within 30 churches. All churches will receive a 16-session core weight loss intervention. Half of the churches will be randomized to receive an additional 12-session maintenance component. Methods The WORD is a cultural adaptation of the Diabetes Prevention Program, whereby small groups will be led by trained church members. Participants will be assessed at baseline, 6, 12, and 18 months. A detailed cost-effectiveness and process evaluation will be included. Summary The WORD aims to sustain weight loss in rural African Americans. The utilization of a CBPR approach and the engagement of the faith-based social infrastructure of African American communities will maximize the intervention's sustainability. Unique aspects of this trial include the focus on weight loss maintenance and the use of a faith-based CBPR approach in translating evidence-based obesity interventions. PMID:25461496

  17. Phylogenetic Diversity of Young Ocean Crust at the East Pacific Rise 9° N

    NASA Astrophysics Data System (ADS)

    Santelli, C. M.; Bach, W.; Rogers, D. R.; Edwards, K. J.

    2004-12-01

    Numerous studies show increasing evidence for a significant biosphere in oceanic lithosphere. Geochemical modeling suggests that most biological activity at or below the seafloor occurs in young crust (<10 Ma) on mid-ocean ridge flanks where low-temperature fluid circulation is substantial. In this environment, oxygenated seawater reacts with basalt and releases chemical energy that could support the growth of microorganisms. Fluid fluxes rapidly decrease further off-axis in older, more altered crust likely leading to a sharp decline in biological activity. To date, most evidence in support of a deep biosphere relies on anomalous textural features and geochemical signatures in aged basalt glass. In order to unambiguously attribute these alteration features to microbial activity, molecular microbiological data is required to corroborate these morphological and chemical observations. The application of molecular techniques to old ocean crust, however, can be difficult because of issues such as low cell density, contamination, and sluggish activity. Hence, studies on young ocean crust may provide insight and constraints on processes that could also apply to older crust. In this study, we have investigated the initial colonization of very young mid-ocean ridge basalt by endolithic microorganisms, and the changes in microbial diversity as a result of increasing rock alteration. Seafloor basalt samples were collected during RV Atlantis cruise AT11-7 in February 2004, from the East Pacific Rise (EPR) between 9° 28'N and 9° 50'N. Samples representing various flow morphologies, glass contents, and ages (up to ˜20 kyrs) were collected by DSV Alvin and brought to the surface in bioboxes. All basalts contain glass that ranges from very fresh to slightly altered with Fe-oxidation rims and/or Mn-oxide crusts. Total community DNA was successfully extracted from glass samples representative of a variety of alteration states. Clone libraries were constructed from PCR products of

  18. Crust-core coupling in rotating neutron stars

    SciTech Connect

    Glampedakis, Kostas; Andersson, Nils

    2006-08-15

    Motivated by their gravitational wave driven instability, we investigate the influence of the crust on r-mode oscillations in a neutron star. Using a simplistic model of an elastic neutron star crust with constant shear modulus, we carry out an analytic calculation with the main objective of deriving an expression for the slippage between the core and the crust. Our analytic estimates support previous numerical results and provide useful insights into the details of the problem.

  19. Constraining the Conditions Required for the Delamination of Subducting Crust

    NASA Astrophysics Data System (ADS)

    Maunder, B. L.; Van Hunen, J.; Magni, V.; Bouilhol, P.

    2014-12-01

    It is commonly accepted that the building of the continental crust is linked to subduction zone processes, but the refining mechanism isolating the felsic product from its basaltic counterpart, leading to a stratified crust, remains poorly understood. Delamination of subducting material and its subsequent melting and segregation, with the felsic part being underplated and added to the crust from below has been suggested to be a viable scenario.In this study we use thermo-mechanical numerical models of subduction to explore the possibility of delamination of the igneous slab crust and determine the conditions that are required by varying key parameters, such as subduction speed and angle, slab age, crustal thickness and density, overriding plate thickness, mantle temperature, depth of eclogitisation and the rheological properties for crustal and mantle material. We also quantify the extent of the resultant crustal melting, and its composition.Our preliminary models demonstrate that for present day mantle potential temperatures and average slab crustal thickness, the slab crust may only delaminate for extreme rheologies (i.e very weak crust), making slab mafic crust delamination unlikely. Contrastingly, in an early earth setting (High mantle temperature potential and thicker mafic slab crust) we find that the whole crustal scale delamination of the subducting mafic crust is a dynamically viable mechanism for a reasonable rheology when slabs are younger than ~20Ma. The resulting delamination leads to buoyant upwelling and ponding of mafic crustal material beneath the overriding lithosphere. After only ~5 Myrs from the onset of delamination, delaminated mafic crust would sit in the hot mantle wedge, where it would likely cross its solidus. These melts would be readily segregated from the migmatitic mafic source and contribute to the formation of felsic crust with little interaction with the mantle wedge, explaining part of the spectrum of TTG forming the earliest

  20. Phase separation in the crust of accreting neutron stars.

    PubMed

    Horowitz, C J; Berry, D K; Brown, E F

    2007-06-01

    Nucleosynthesis, on the surface of accreting neutron stars, produces a range of chemical elements. We perform molecular dynamics simulations of crystallization to see how this complex composition forms new neutron star crust. We find chemical separation, with the liquid ocean phase greatly enriched in low atomic number elements compared to the solid crust. This phase separation should change many crust properties such as the thermal conductivity and shear modulus. PMID:17677319

  1. Crustal thinning between the Ethiopian and East African Plateaus from modeling Rayleigh wave dispersion

    SciTech Connect

    Benoit, M H; Nyblade, A A; Pasyanos, M E

    2006-01-17

    The East African and Ethiopian Plateaus have long been recognized to be part of a much larger topographic anomaly on the African Plate called the African Superswell. One of the few places within the African Superswell that exhibit elevations of less than 1 km is southeastern Sudan and northern Kenya, an area containing both Mesozoic and Cenozoic rift basins. Crustal structure and uppermost mantle velocities are investigated in this area by modeling Rayleigh wave dispersion. Modeling results indicate an average crustal thickness of 25 {+-} 5 km, some 10-15 km thinner than the crust beneath the adjacent East African and Ethiopian Plateaus. The low elevations can therefore be readily attributed to an isostatic response from crustal thinning. Low Sn velocities of 4.1-4.3 km/s also characterize this region.

  2. The Meaning of KMT (Ancient Egyptian) History for Contemporary African American Experience.

    ERIC Educational Resources Information Center

    Hilliard, Asa G., III

    1992-01-01

    Explores the history of KMT (ancient Egypt) and its importance for contemporary African-American experience. Reviews evidence that ancient Egypt was a black African population bound by history and culture to the rest of Africa. The rescue of Kemetic history can restore a sense of heritage to African Americans. (SLD)

  3. Nickel isotopic compositions of ferromanganese crusts and the constancy of deep ocean inputs and continental weathering effects over the Cenozoic

    NASA Astrophysics Data System (ADS)

    Gall, L.; Williams, H. M.; Siebert, C.; Halliday, A. N.; Herrington, R. J.; Hein, J. R.

    2013-08-01

    The global variability in nickel (Ni) isotope compositions in ferromanganese crusts is investigated by analysing surface samples of 24 crusts from various ocean basins by MC-ICPMS, using a double-spike for mass bias correction. Ferromanganese crusts have δ60Ni isotopic compositions that are significantly heavier than any other samples thus far reported (-0.1‰ to 0.3 ‰), with surface scrapings ranging between 0.9 ‰ and 2.5 ‰ (relative to NIST SRM986). There is no well resolved difference between ocean basins, although the data indicate somewhat lighter values in the Atlantic than in the Pacific, nor is there any evidence that the variations are related to biological fractionation, presence of different water masses, or bottom water redox conditions. Preliminary data for laterite samples demonstrate that weathering is accompanied by isotopic fractionation of Ni, which should lead to rivers and seawater being isotopically heavy. This is consistent with the slightly heavier than average isotopic compositions recorded in crusts that are sampled close to continental regions. Furthermore, the isotopic compositions of crusts growing close to a hydrothermal source are clustered around ∼ 1.5 ‰, suggesting that hydrothermal fluids entering the ocean may have a Ni isotopic composition similar to this value. Based on these data, the heavy Ni isotopic compositions of ferromanganese crusts are likely due to input of isotopically heavy Ni to the ocean from continental weathering and possibly also from hydrothermal fluids. A depth profile through one crust, CD29-2, from the north central Pacific Ocean displays large variations in Ni isotope composition (1.1 - 2.3 ‰) through the last 76 Myr. Although there may have been some redistribution of Ni associated with phosphatisation, there is no systematic difference in Ni isotopic composition between deeper, older parts and shallower, younger parts of the crust, which may suggest that oceanic sources and sinks of Ni have

  4. Crust formation and its effect on the molten pool coolability

    SciTech Connect

    Park, R.J.; Lee, S.J.; Sim, S.K.

    1995-09-01

    Experimental and analytical studies of the crust formation and its effect on the molten pool coolability have been performed to examine the crust formation process as a function of boundary temperatures as well as to investigate heat transfer characteristics between molten pool and overlying water in order to evaluate coolability of the molten pool. The experimental test results have shown that the surface temperature of the bottom plate is a dominant parameter in the crust formation process of the molten pool. It is also found that the crust thickness of the case with direct coolant injection into the molten pool is greater than that of the case with a heat exchanger. Increasing mass flow rate of direct coolant injection to the molten pool does not affect the temperature of molten pool after the crust has been formed in the molten pool because the crust behaves as a thermal barrier. The Nusselt number between the molten pool and the coolant of the case with no crust formation is greater than that of the case with crust formation. The results of FLOW-3D analyses have shown that the temperature distribution contributes to the crust formation process due to Rayleigh-Benard natural convection flow.

  5. Biological Soil Crusts: Webs of Life in the Desert

    USGS Publications Warehouse

    Belnap, Jayne

    2001-01-01

    Although the soil surface may look like dirt to you, it is full of living organisms that are a vital part of desert ecosystems. This veneer of life is called a biological soil crust. These crusts are found throughout the world, from hot deserts to polar regions. Crusts generally cover all soil spaces not occupied by green plants. In many areas, they comprise over 70% of the living ground cover and are key in reducing erosion, increasing water retention, and increasing soil fertility. In most dry regions, these crusts are dominated by cyanobacteria (previously called blue-green algae), which are one of the oldest known life forms. Communities of soil crusts also include lichens, mosses, microfungi, bacteria, and green algae. These living organisms and their by-products create a continuous crust on the soil surface. The general color, surface appearance, and amount of coverage of these crusts vary depending on climate and disturbance patterns. Immature crusts are generally flat and the color of the soil, which makes them difficult to distinguish from bare ground. Mature crusts, in contrast, are usually bumpy and dark-colored due to the presence of lichens, mosses, and high densities of cyanobacteria and other organisms.

  6. Thinning and flow of Tibetan crust constrained by seismic anisotropy.

    PubMed

    Shapiro, Nikolai M; Ritzwoller, Michael H; Molnar, Peter; Levin, Vadim

    2004-07-01

    Intermediate-period Rayleigh and Love waves propagating across Tibet indicate marked radial anisotropy within the middle-to-lower crust, consistent with a thinning of the middle crust by about 30%. The anisotropy is largest in the western part of the plateau, where moment tensors of earthquakes indicate active crustal thinning. The preferred orientation of mica crystals resulting from the crustal thinning can account for the observed anisotropy. The middle-to-lower crust of Tibet appears to have thinned more than the upper crust, consistent with deformation of a mechanically weak layer that flows as if confined to a channel. PMID:15247475

  7. Quantifying glassy and crystalline basalt partitioning in the oceanic crust

    NASA Astrophysics Data System (ADS)

    Moore, Rachael; Ménez, Bénédicte

    2016-04-01

    The upper layers of the oceanic crust are predominately basaltic rock, some of which hosts microbial life. Current studies of microbial life within the ocean crust mainly focus on the sedimentary rock fraction, or those organisms found within glassy basalts while the potential habitability of crystalline basalts are poorly explored. Recently, there has been recognition that microbial life develops within fractures and grain boundaries of crystalline basalts, therefore estimations of total biomass within the oceanic crust may be largely under evaluated. A deeper understanding of the bulk composition and fractionation of rocks within the oceanic crust is required before more accurate estimations of biomass can be made. To augment our understanding of glassy and crystalline basalts within the oceanic crust we created two end-member models describing basalt fractionation: a pillow basalt with massive, or sheet, flows crust and a pillow basalt with sheeted dike crust. Using known measurements of massive flow thickness, dike thickness, chilled margin thickness, pillow lava size, and pillow lava glass thickness, we have calculated the percentage of glassy versus crystalline basalts within the oceanic crust for each model. These models aid our understanding of textural fractionation within the oceanic crust, and can be applied with bioenergetics models to better constrain deep biomass estimates.

  8. Geochemical evidence for African dust and volcanic ash inputs to terra rossa soils on carbonate reef terraces, northern Jamaica, West Indies

    USGS Publications Warehouse

    Muhs, D.R.; Budahn, J.R.

    2009-01-01

    The origin of red or reddish-brown, clay-rich, "terra rossa" soils on limestone has been debated for decades. A traditional qualitative explanation for their formation has been the accumulation of insoluble residues as the limestone is progressively dissolved over time. However, this mode of formation often requires unrealistic or impossible amounts of carbonate dissolution. Therefore, where this mechanism is not viable and where local fluvial or colluvial inputs can be ruled out, an external source or sources must be involved in soil formation. On the north coast of the Caribbean island of Jamaica, we studied a sequence of terra rossa soils developed on emergent limestones thought to be of Quaternary age. The soils become progressively thicker, redder, more Fe- and Al-rich and Si-poor with elevation. Furthermore, although kaolinite is found in all the soils, the highest and oldest soils also contain boehmite. Major and trace element geochemistry shows that the host limestones and local igneous rocks are not likely source materials for the soils. Other trace elements, including the rare earth elements (REE), show that tephra from Central American volcanoes is not a likely source either. However, trace element geochemistry shows that airborne dust from Africa plus tephra from the Lesser Antilles island arc are possible source materials for the clay-rich soils. A third, as yet unidentified, source may also contribute to the soils. We hypothesize that older, more chemically mature Jamaican bauxites may have had a similar origin. The results add to the growing body of evidence of the importance of multiple parent materials, including far-traveled dust, to soil genesis.

  9. Complete genome analyses of the first porcine rotavirus group H identified from a South African pig does not provide evidence for recent interspecies transmission events.

    PubMed

    Nyaga, Martin M; Peenze, Ina; Potgieter, Christiaan A; Seheri, L Mapaseka; Page, Nicola A; Yinda, Claude K; Steele, A Duncan; Matthijnssens, Jelle; Mphahlele, M Jeffrey

    2016-03-01

    Rotaviruses (RVs) are classified into eight species/groups (RVA-RVH) according to the migration patterns of their 11 genome segments, as well as by serological and molecular properties of Viral Protein 6 (VP6). In 1997 a new unclassified RV was reported infecting adults in Bangladesh and China. This virus was initially named novel adult diarrhoea rotavirus (ADRV-N), but later renamed as RVH. Since then, RVH has been detected in humans only very sporadically. However, RVH is increasingly being detected in pig populations in the USA, Brazil and Japan, but not yet in Africa. Unfortunately, whole genome sequence data of porcine RVH strains in GenBank is currently restricted to a single strain (SKA-1) from Japan. Porcine diarrhoeic samples were collected in South Africa and analysed for rotavirus using an RVA ELISA and electropherotyping by PAGE. One sample displayed a 4:2:1:1:1:1:1 migration pattern, typical for RVH. In order to further investigate this strain, sequence-independent amplification followed by random sequencing using the 454/Roche GS FLX Sequencer was performed, resulting in the second complete porcine RVH strain (MRC-DPRU1575) available in databases. Phylogenetically, all segments of MRC-DPRU1575 clustered closely with the SKA-1 strain and in some segments with known porcine RVH strains from Brazil and the USA. In contrast, the porcine RVH strains were only distantly related to human RVH strains from Asia and a partial RVH-like strain recently detected in bats from Cameroon. Overall, strain MRC-DPRU1575 is the first complete genome of a porcine RVH from Africa and allows for the development of improved RVH screening methods. Our analyses indicate that RVH strains cluster according to their host species, not suggesting any evidence of recent interspecies transmission events. However, more RVH genomes from a wider host range are needed to better understand their evolutionary pathways and zoonotic potential. PMID:26658066

  10. Vulnerability of desert biological soil crusts to wind erosion: The influences of crust development, soil texture, and disturbance

    USGS Publications Warehouse

    Belnap, J.; Gillette, Dale A.

    1998-01-01

    Biological soil crusts, consisting of cyanobacteria, green algae, lichens, and mosses, are important in stabilizing soils in semi-arid and arid lands. Integrity of these crusts is compromised by compressional disturbances such as foot, vehicle, or livestock traffic. Using a portable wind tunnel, we found threshold friction velocities (TFVs) of undisturbed crusts well above wind forces experienced at these sites; consequently, these soils are not vulnerable to wind erosion. However, recently disturbed soils or soils with less well-developed crusts frequently experience wind speeds that exceed the stability thresholds of the crusts. Crustal biomass is concentrated in the top 3 mm of soils. Sandblasting by wind can quickly remove this material, thereby reducing N and C inputs from these organisms. This loss can result in reduced site productivity, as well as exposure of unprotected subsurface sediments to wind and water erosion. Actions to reduce impacts to these crusts can include adjustments in type, intensity, and timing of use.

  11. Crust-ocean interactions during midocean ridge eruptions

    NASA Astrophysics Data System (ADS)

    Baker, E. T.

    2011-12-01

    Eruptions are the "quantum event" of crustal accretion, occurring daily to monthly (depending on spreading rate) along the global midocean ridge system. The number of eruptions detected and responded to remain very few, however, so our knowledge of the magnitude and rate of crust-ocean interaction at the instant of an eruption is almost entirely circumstantial. The discovery of uniquely different plumes over a 2008 eruption on the NE Lau spreading center greatly broadened the known range of eruption-initiated transfer of heat, chemicals, and perhaps biota from the crust to the ocean. Serendipitous observations and rapid response cruises have now documented that the "event (mega-) plumes" accompanying eruptions range over a factor of 100 in volume (1-150 km3), yet maintain a distinctive and consistent chemical signature (much lower 3He/heat and Mn/heat and higher H2/heat than typical black smokers). Confirmed event plumes have formed at spreading rates from 55-~90 mm/yr, with some incompletely sampled but "event-like" plumes observed at even slower rates (11-30 mm/yr; Gakkel and Carlsberg Ridges). Presently, only four event plumes can be associated with specific eruptions. Large event plumes in the NE Pacific were found over thick (up to ~75 m), voluminous, and slowly extruded pillow mounds. The 2008 eruption on the fast-spreading NE Lau spreading center demonstrated that thin (a few meters), small, and rapidly emplaced sheet flows can generate smaller event plumes. Available evidence suggests that massive fluid discharge occurs virtually simultaneously with an eruption. At Gorda Ridge in 1996, eruption-indicative seismicity began on the same day and location an event plume was found. At Axial Volcano in 1998, moorings 2 km apart both recorded the appearance of a >100-m-thick plume within minutes of the start of a 72-min-long sheet flow eruption. These observations support inferences from plume modeling and chemistry that event plume generation time is hours, not

  12. Chemical Evolution of the Oceanic Crust on 103 - 108 Year Timescales

    NASA Astrophysics Data System (ADS)

    Brandl, P. A.; Regelous, M.; Beier, C.; Haase, K. M.

    2011-12-01

    compromised by alteration and accumulation of phenocrysts, in which case they do not represent melt compositions. For comparison we have compiled a dataset of zero-age MORB glasses from ridges far from hotspots using the PetDB database. After correction for crystal fractionation to either MgO = 8.0 wt. % or Mg# = 72, we find no statistically significant difference between the average major element composition (e.g. Na and Fe) of MORB older than 80 Ma, and young MORB from active spreading centres. Unlike previous studies therefore, we find no evidence for significantly hotter upper mantle beneath spreading centres during the Cretaceous. Work is in progress to compare lavas from ancient Atlantic and Pacific ocean crust in order to see whether differences between slow-spreading and fast-spreading ridges (more MgO-rich more variable for the latter) also existed in the past. Nine of the sites we sampled penetrated more than 100 m into the oceanic crust and we are examining the chemical stratigraphy of individual boreholes in order to test models for crustal accretion (e.g. Hardarson and Fitton, 1997, etc.). Hardarson, B.S., and Fitton, J.G., 1997, Geology, v. 25, no. 11, p. 1043-1046. Humler, E., Langmuir, C.H., and Daux, V., 1999, Earth and Planetary Science Letters, v. 173, no. 1-2, p. 7-23.

  13. Some growth points in African child development research.

    PubMed

    Serpell, Robert; Marfo, Kofi

    2014-01-01

    We reflect on ways in which research presented in earlier chapters responds to challenges of generating an African child development field and identify additional issues calling for the field's attention. The chapters collectively display a variety of African contexts and reflexive evidence of the authors' African cultural roots. Connecting research with African audiences demands cooperative communication between educational practitioners and parents with low literacy, and cross-sector communication among professionals. Intracultural exploration of factors influencing the pattern of human development has begun to document the potential of indigenous African cultures as a fund of resources for enhancing child development. Priority topics for future African developmental research include multilingualism, musical performance, socially distributed caregiving, and the relation between adolescence and economic activity. Integration of multiple disciplines in the application of research-based principles to service delivery in the fields of community-based (re)habilitation and early childhood care and education calls for researcher collaboration with practitioners. PMID:25512048

  14. Adjoint tomography of the southern California crust.

    PubMed

    Tape, Carl; Liu, Qinya; Maggi, Alessia; Tromp, Jeroen

    2009-08-21

    Using an inversion strategy based on adjoint methods, we developed a three-dimensional seismological model of the southern California crust. The resulting model involved 16 tomographic iterations, which required 6800 wavefield simulations and a total of 0.8 million central processing unit hours. The new crustal model reveals strong heterogeneity, including local changes of +/-30% with respect to the initial three-dimensional model provided by the Southern California Earthquake Center. The model illuminates shallow features such as sedimentary basins and compositional contrasts across faults. It also reveals crustal features at depth that aid in the tectonic reconstruction of southern California, such as subduction-captured oceanic crustal fragments. The new model enables more realistic and accurate assessments of seismic hazard. PMID:19696349

  15. Shear viscosity in magnetized neutron star crust

    NASA Astrophysics Data System (ADS)

    Ofengeim, D. D.; Yakovlev, D. G.

    2015-12-01

    The electron shear viscosity due to Coulomb scattering of degenerate electrons by atomic nuclei throughout a magnetized neutron star crust is calculated. The theory is based on the shear viscosity coefficient calculated neglecting magnetic fields but taking into account gaseous, liquid and solid states of atomic nuclei, multiphonon scattering processes, and finite sizes of the nuclei albeit neglecting the effects of electron band structure. The effects of strong magnetic fields are included in the relaxation time approximation with the effective electron relaxation time taken from the field-free theory. The viscosity in a magnetized matter is described by five shear viscosity coefficients. They are calculated and their dependence on the magnetic field and other parameters of dense matter is analyzed. Possible applications and open problems are outlined.

  16. The velocity structure of the lunar crust.

    NASA Technical Reports Server (NTRS)

    Kovach, R. L.; Watkins, J. S.

    1973-01-01

    Seismic refraction data, obtained at the Apollo 14 and 16 sites, when combined with other lunar seismic data, allow a compressional wave velocity profile of the lunar near-surface and crust to be derived. The regolith, although variable in thickness over the lunar surface, possesses surprisingly similar seismic properties. Underlying the regolith at both the Apollo 14 Fra Mauro site and the Apollo 16 Descartes site is low-velocity brecciated material or impact derived debris. Key features of the lunar seismic velocity profile are: (1) velocity increases from 100 to 300 m/sec in the upper 100 m to about 4 km/sec at 5 km depth, (2) a more gradual increase from about 4 km/sec to about 6 km/sec at 25 km depth,(3) a discontinuity at a depth of 25 km, and (4) a constant value of about 7 km/sec at depths from 25 km to about 60 km.

  17. Core and early crust formation on Mars

    NASA Astrophysics Data System (ADS)

    Golabek, G. J.; Keller, T.; Gerya, T.; Tackley, P. J.; Connolly, J.; Zhu, G.

    2010-12-01

    One of the most striking surface features on Mars is the crustal dichotomy. It is the oldest geological feature on Mars and was formed more than 4.1 Ga ago by either exogenic or endogenic processes [1,2]. In order to find an internal origin of the crustal dichotomy, located within a maximum of 400 Ma of planetary differentiation, the thermal state of the planet resulting from core formation needs to be considered. Additionally, it was suggested that a primordial crust with up to 45 km thickness can be formed already during the Martian core formation [3]. We suggest that the sinking of iron diapirs delivered by predifferentiated impactors induced impact- and shear heating-related temperature anomalies in the mantle that fostered the formation of early Martian crust. Thus, the crustal thickness distribution would largely be a result of planetary core formation, late impact history and the onset of mantle convection. To test this hypothesis we use numerical models to simulate the formation of the Martian iron core and the resulting mantle convection pattern, while peridotite melting is enabled to track melting caused by shear and radioactive heating. We perform 2D simulations using the spherical-Cartesian code I2ELVIS for planetary accretion and the spherical code STAGYY for the consequent onset of mantle convection. We apply a temperature-, stress- and melt-fraction dependent viscoplastic rheology. Radioactive and shear heating as well as consumption of latent heat by silicate melting are taken into account. The depth of neutral buoyancy of silicate melt with respect to solid silicates is determined by the difference in compressibility of the liquid and solid phase. To self-consistently simulate the silicate phase changes expected inside a Mars-sized body, we use the thermodynamical database Perple_X. As initial condition for core formation, we apply randomly distributed iron diapirs with 75 km radius inside the planet, representing the cores of stochastically

  18. Petrology and Wavespeeds in Central Tibet Indicate a Partially Melted Mica-Bearing Crust

    NASA Astrophysics Data System (ADS)

    Hacker, B. R.; Ritzwoller, M. H.; Xie, J.

    2013-12-01

    S-wave speeds and Vp/Vs ratios in the middle to deep crust of Tibet are best explained by a partially melted, mica-bearing middle to lower crust with a subhorizontal to gently dipping foliation. Surface-wave tomography [e.g., Yang et al., 2012; Xie et al., 2013] shows that the central Tibetan Plateau (the Qiangtang block) is characterized by i) slow S-wave speeds of 3.3-3.5 km/s at depths from 20-25 km to 45-50 km, ii) S-wave radial anisotropy of at least 4% (Vsh > Vsv) with stronger anisotropy in the west than the east [Duret et al., 2010], and iii) whole-crust Vp/Vs ratios in the range of 1.73-1.78 [Xu et al., 2013]. The depth of the Curie temperature for magnetite inferred from satellite magnetic measurements [Alsdorf and Nelson, 1999], the depth of the α-β quartz transition inferred from Vp/Vs ratios [Mechie et al., 2004], and the equilibration pressures and temperatures of xenoliths erupted from the mid-deep crust [Hacker et al., 2000] indicate that the thermal gradient in Qiangtang is steep, reaching 1000°C at 30-40 km depth. This thermal gradient crosses the dehydration-melting solidi for crustal rocks at 20-30 km depth, implying the presence or former presence of melt in the mid-deep crust. These temperatures do not require the wholesale breakdown of mica at these depths, because F and Ti can stabilize mica to at least 1300°C [Dooley and Patino Douce, 1996]. Petrology suggests, then, that the Qiangtang middle to deep crust consists of a mica-bearing residue from which melt has been extracted or is being extracted. Wavespeeds calculated for mica-bearing rocks with a subhorizontal to gently dipping foliation and minor silicate melt are the best match to the wavespeeds and anisotropy observed by seismology. Alsdorf, D., and D. Nelson, The Tibetan satellite magnetic low: Evidence for widespread melt in the Tibetan crust?, Geology, 27, 943-946, 1999. Dooley, D.F., and A.F. Patino Douce, Fluid-absent melting of F-rich phlogopite + rutile +quartz, American

  19. Are high p-wave velocity sediments on thin Tethyan crust, deep-water carbonates?

    NASA Astrophysics Data System (ADS)

    Gutscher, Marc-Andre; Graindorge, David; Klingelhoefer, Frauke; Dellong, David; Kopp, Heidrun; Sallares, Valenti; Bartolome, Rafael; Gallais, Flora

    2016-04-01

    Seismic reflection profiles from the Central Mediterranean and Gulf of Cadiz regions indicate the widespread presence of a seismic unit, marked by strong continuous reflectors, directly overlying the basement. Seismic velocity analysis from seismic reflection and refraction studies indicate high p-wave velocities of 3.5 - 4.5 km/s in this layer. These same seismic studies image a thin crust, typically 6-9 km thick, in most cases thought to be oceanic in nature and related to the Tethys oceanic domain separating Africa (Gondwana) from Laurussia. We interpret this 2-3 km thick reflective layer to be carbonates, deposited in the late Triassic, Jurassic and early Cretaceous in the Tethys Ocean, in deep marine basins. Few drilling studies have penetrated into this layer. In one case (DSDP site 135, drilled at 4152 m water depth on Coral Patch Ridge in the western Gulf of Cadiz), Aptian (early Cretaceous) marls and limestone were drilled (560-689 m sub-seafloor depth). The Calcite compensation depth during the Jurassic to Early Cretaceous was about 4000 m to 3500 m according to compilations from the Atlantic and Indian Oceans and is consistent with deposition of deep-water carbonates. For the NW Moroccan margin (Mazagan transect near El Jadida) there is a 2 km thick sedimentary layer with p-wave velocities of 4.0 - 4.5 km/s at the base of a 4 - 6 km thick sedimentary section. This layer extends from seafloor thought to be oceanic crust (west of the West African Coast magnetic anomaly) across a domain of thin/transitional crust with abundant Triassic salt diapirs to the foot of the margin. This reflective basal layer is also observed in reflection and refraction profiles from the Seine abyssal plain, below the toe of the Cadiz accretionary wedge (S. Algarve margin), in the Ionian abyssal plain and below the toe of the Calabrian accretionary wedge, all regions floored by this thin Tethyan crust. Work is in progress to determine the exact nature of this crust.

  20. Moho vs crust-mantle boundary: Evolution of an idea

    NASA Astrophysics Data System (ADS)

    O'Reilly, Suzanne Y.; Griffin, W. L.

    2013-12-01

    The concept that the Mohorovicic Discontinuity (Moho) does not necessarily coincide with the base of the continental crust as defined by rock-type compositions was introduced in the early 1980s. This had an important impact on understanding the nature of the crust-mantle boundary using information from seismology and from deep-seated samples brought to the surface as xenoliths in magmas, or as tectonic terranes. The use of empirically-constrained P-T estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment. The xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere, and revealed that the crust-mantle boundary in off-craton regions commonly is transitional over a depth range of about 5-20 km. Early seismic-reflection data showed common layering near the Moho, correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust-mantle boundary. Developments in seismology, petrophysics and experimental petrology have refined interpretation of lithospheric domains. The expansion of in situ geochronology (especially zircon U-Pb ages and Hf-isotopes; Os isotopes of mantle sulfides) has defined tectonic events that affected whole crust-mantle sections, and revealed that the crust-mantle boundary can change in depth through time. However, the nature of the crust-mantle boundary in cratonic regions remains enigmatic, mainly due to lack of key xenoliths or exposed sections. The observation that the Moho may lie significantly deeper than the crust-mantle boundary has important implications for modeling the volume of the crust. Mapping the crust using seismic techniques alone, without consideration of the petrological problems, may lead to an overestimation of crustal thickness by 15-30%. This will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust-formation processes

  1. Compositional variations of the lunar crust: Results from radiative transfer modeling of central peak spectra

    NASA Astrophysics Data System (ADS)

    Cahill, J. T. S.; Lucey, P. G.; Wieczorek, M. A.

    2009-09-01

    We present model mineralogy of impact crater central peaks combined with crustal thickness and crater central peak depth of origin models to report multiple perspectives of lunar crustal composition with depth. Here we report the analyses of 55 impact crater central peaks and how their compositions directly relate to the lunar highlands sample suite. A radiative transfer model is used to analyze Clementine visible plus near-infrared spectra to place compositional constraints on these central peak materials. Central peaks analyzed are dominantly magnesian- and plagioclase-poor; strong compositional similarities to lunar Mg-suite materials are evident. Relative to crustal thickness estimates, central peak mineralogy becomes more plagioclase-rich as the crust thickens. Relative to the crust-mantle boundary, the origin of peaks with dominantly mafic mineralogy are confined to the lower crust and primarily within the South-Pole Aitken and Procellarum KREEP Terranes (PKT); additionally, central peaks with anorthositic mineralogy (>60 vol % plagioclase) are transported to the surface from all depths in the crustal column and confined to the Feldspathic Highlands Terrane (FHT). The discovery of mafic and magnesian materials, consistent with Mg-suite rocks of the sample collection, in all lunar terranes suggests that the process and sources that give rise to these types of rocks is not unique to the PKT and not necessarily dependent on incompatible elements for formation. The identification of ferroan and magnesian anorthositic material near the crust-mantle boundary of the FHT is also inconsistent with an increasing mafic/feldspar ratio and Mg' with depth in the crust.

  2. Isotopic Composition of Organic and Inorganic Carbon in Desert Biological Soil Crust Systems

    NASA Astrophysics Data System (ADS)

    Alexander, K.; Hartnett, H.; Anbar, A.; Beraldi, H.; Garcia-Pichel, F.

    2006-12-01

    Biological soil crusts (BSCs) are microbial communities that colonize soil surfaces in many arid regions. BSCs are important sources for fixed carbon and nitrogen in these ecosystems, and they greatly influence the structure, function, and appearance of desert soils. Biological activity of BSCs occurs during pulses of hydration requiring desert crusts to tolerate extremes in UV radiation, temperature, and desiccation. These characteristics make desert crusts unique systems that have received little consideration in the study of biogeochemical processes in extreme environments. This project investigates the impact of BSCs on carbon dynamics within desert soils. Soil cores ranging in depth from 8 to 12 cm were taken in March, 2006 from deserts near Moab, Utah. Two major BSC classes were identified: lichen-dominated (dark and pinnacled) soil crusts and cyanobacteria-dominated (light and flat) soil crusts. These two surface morphologies are related to the different biological communities. Carbon content and stable carbon isotopic composition were determined for the bulk carbon pool, as well as for the organic and inorganic carbon fractions of the soils. Expectedly, there was a net decrease in organic carbon content with depth (0.39-0.27 percent). Stable carbon isotope values for the organic fraction ranged from -5.8 per mil to -24.0 per mil (Avg: -14.4 per mil, S.D: 6.42 per mil). Stable carbon isotope values for the inorganic fraction ranged from 0.3 per mil to -3.6 per mil (Avg: -2.4 per mil, S.D.: 1.05 per mil). The variation in the isotopic composition of the organic carbon was due to a strong depletion below the surface soil value occurring between 3 and 5 cm depth, with an enrichment above the original surface value at depths below 6 to 10 cm. These data suggest that within desert soil crust systems the carbon isotopic signal is complex with both a clear biological imprint (lighter organic carbon) as well as evidence for some mechanism that results in

  3. Estimating susceptibility and magnetization within the Earth's continental crust: Petrophysical and Satellite approaches

    NASA Astrophysics Data System (ADS)

    Purucker, M. E.; McEnroe, S. A.

    2014-12-01

    Magnetic models (Xchaos) made from Champ and Orsted data are used to place constraints on the average magnetic susceptibility and its variability in the continental crust. Estimates of magnetic crustal thickness are made in a two-step process. The first step uses a recent seismic model (Crust1.0) to estimate the thickness of crystalline crust above the Moho, modified in the Andes and the Himalayas to account for the non-magnetic lower crust there. The second step calculates the magnetic field expected from such a layer of crystalline rock assuming the magnetization is solely induced in the earth's main field by rock of constant magnetic susceptibility, and modifies the starting crustal thickness to bring it into agreement with the Xchaos model. This global model removes spherical harmonic degrees less than 15 to account for the core field mask. We restrict our attention to the continental crust, in particular to Australia, western North America, and Scandinavia. Petrophysical and petrological data from Scandinavian rocks that have been deep in the crust help place limits on susceptibility values. Our simulations use two susceptibilities, 0.02 and 0.04 SI. The mean crystalline crustal thickness from the seismic model is 42 and 37 km in western North America and Australia, respectively, and the modification with the magnetic data makes little change to the mean crustal thickness, irrespective of whether the susceptibility is 0.02 or 0.04 SI. However, the modification with the magnetic data does make a significant difference to the standard deviation of the crustal thickness, increasing it by a factor of two in the case of a susceptibility of 0.04, and by a factor of four in the case of a susceptibility of 0.02. The changes to the standard deviation of the crustal thickness are also evident in the Scandinavian data, but the mean crystalline crustal thickness of 45 km is significantly larger than that found from either magnetic model (33 and 30 km). The differences

  4. Measurement of palladium crust thickness on catalyst by EPMA

    NASA Astrophysics Data System (ADS)

    Sorbier, L.; Gay, A.-S.; Fécant, A.; Moreaud, M.; Brodusch, N.

    2012-03-01

    Selective hydrogenation is a key process in petrochemistry to obtain good feedstock for polymers synthesis. Common catalysts for this process consist in metallic palladium deposited with an eggshell distribution on porous alumina. For this system, the catalytic activity is known to be in strong relation with the thickness of the palladium crust. Typical catalyst consists of 2 - 4 mm diameter spherical beads having a 200 - 400 μm thick palladium crust and a total palladium amount of about 0.3 to 0.5 wt%. The palladium distribution in the catalyst bead can be easily characterized by electron probe microanalysis (EPMA) using polished cross-sections of the beads trough their diameter. By measuring the local concentration of palladium on several points along the bead diameter we obtain the distribution profile of palladium in the bead. Two strategies are proposed to measure this palladium crust thickness by EPMA. First the crust thickness is defined by the distance to the catalyst bead surface containing a fixed amount of total palladium (for example 95 % or 98 %). Second, the palladium profile is modelled by a parameterized analytical function from which a crust thickness can be extracted. Catalytic tests on four samples having different palladium crust thicknesses confirm the strong relation between activity and crust thickness. However the crust thickness containing 98 % of the palladium content shows the best correlation with activity.

  5. Continental crust composition constrained by measurements of crustal Poisson's ratio

    NASA Astrophysics Data System (ADS)

    Zandt, George; Ammon, Charles J.

    1995-03-01

    DECIPHERING the geological evolution of the Earth's continental crust requires knowledge of its bulk composition and global variability. The main uncertainties are associated with the composition of the lower crust. Seismic measurements probe the elastic properties of the crust at depth, from which composition can be inferred. Of particular note is Poisson's ratio,Σ ; this elastic parameter can be determined uniquely from the ratio of P- to S-wave seismic velocity, and provides a better diagnostic of crustal composition than either P- or S-wave velocity alone1. Previous attempts to measure Σ have been limited by difficulties in obtaining coincident P- and S-wave data sampling the entire crust2. Here we report 76 new estimates of crustal Σ spanning all of the continents except Antarctica. We find that, on average, Σ increases with the age of the crust. Our results strongly support the presence of a mafic lower crust beneath cratons, and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions, followed by magmatic underplating, or a model in which crust formation processes have changed since the Precambrian era.

  6. Composition of the crust beneath the Kenya rift

    USGS Publications Warehouse

    Mooney, W.D.; Christensen, N.I.

    1994-01-01

    We infer the composition of the crust beneath and on the flanks of the Kenya rift based on a comparison of the KRISP-90 crustal velocity structure with laboratory measurements of compressional-wave velocities of rock samples from Kenya. The rock samples studied, which are representative of the major lithologies exposed in Kenya, include volcanic tuffs and flows (primarily basalts and phonolites), and felsic to intermediate composition gneisses. This comparison indicates that the upper crust (5-12 km depth) consists primarily of quartzo-feldspathic gneisses and schists similar to rocks exposed on the flanks of the rift, whereas the middle crust (12-22 km depth) consists of more mafic, hornblende-rich metamorphic rocks, probably intruded by mafic rocks beneath the rift axis. The lower crust on the flanks of the rift may consist of mafic granulite facies rocks. Along the rift axis, the lower crust varies in thickness from 9 km in the southern rift to only 2-3 km in the north, and has a seismic velocity substantially higher than the samples investigated in this study. The lower crust of the rift probably consists of a crust/mantle mix of high-grade metamorphic rocks, mafic intrusives, and an igneous mafic residuum accreted to the base of the crust during differentiation of a melt derived from the upper mantle. ?? 1994.

  7. Precipitation pulse size effects on Sonoran Desert soil microbial crusts.

    PubMed

    Cable, Jessica M; Huxman, Travis E

    2004-10-01

    Deserts are characterized by low productivity and substantial unvegetated space, which is often covered by soil microbial crust communities. Microbial crusts are important for nitrogen fixation, soil stabilization and water infiltration, but their role in ecosystem production is not well understood. This study addresses the following questions: what are the CO2 exchange responses of crusts to pulses of water, does the contribution of crusts to ecosystem flux differ from the soil respiratory flux, and is this contribution pulse size dependent? Following water application to crusts and soils, CO2 exchange was measured and respiration was partitioned through mixing model analysis of Keeling plots across treatments. Following small precipitation pulse sizes, crusts contributed 80% of soil-level CO2 fluxes to the atmosphere. However, following a large pulse event, roots and soil microbes contributed nearly 100% of the soil-level flux. Rainfall events in southern Arizona are dominated by small pulse sizes, suggesting that crusts may frequently contribute to ecosystem production. Carbon cycle studies of arid land systems should consider crusts as important contributors because of their dynamic responses to different pulse sizes as compared to the remaining ecosystem components. PMID:14669007

  8. African and non-African admixture components in African Americans and an African Caribbean population.

    PubMed

    Murray, Tanda; Beaty, Terri H; Mathias, Rasika A; Rafaels, Nicholas; Grant, Audrey Virginia; Faruque, Mezbah U; Watson, Harold R; Ruczinski, Ingo; Dunston, Georgia M; Barnes, Kathleen C

    2010-09-01

    Admixture is a potential source of confounding in genetic association studies, so it becomes important to detect and estimate admixture in a sample of unrelated individuals. Populations of African descent in the US and the Caribbean share similar historical backgrounds but the distributions of African admixture may differ. We selected 416 ancestry informative markers (AIMs) to estimate and compare admixture proportions using STRUCTURE in 906 unrelated African Americans (AAs) and 294 Barbadians (ACs) from a study of asthma. This analysis showed AAs on average were 72.5% African, 19.6% European and 8% Asian, while ACs were 77.4% African, 15.9% European, and 6.7% Asian which were significantly different. A principal components analysis based on these AIMs yielded one primary eigenvector that explained 54.04% of the variation and captured a gradient from West African to European admixture. This principal component was highly correlated with African vs. European ancestry as estimated by STRUCTURE (r(2)=0.992, r(2)=0.912, respectively). To investigate other African contributions to African American and Barbadian admixture, we performed PCA on approximately 14,000 (14k) genome-wide SNPs in AAs, ACs, Yorubans, Luhya and Maasai African</