rainfall intensity and slope gradient effects on sediment losses and splash from a saline sodic soil under coastal reclamation abstract rainfall intensity and slope gradient play important roles in soil erosion processes this study was conducted to investigate the effects of rainfall intensity and slope gradient as well as of their interactions on splash and overland flow transport on saline sodic soil slopes rainfall intensities of 85 95 110 and 125 mm h 1 were applied to slope gradients of 6 11 22 and 35 splash was partitioned into four directional components runoff sediment and splash samples were collected throughout the rainstorms and infiltration was calculated the final infiltrations under the lower rainfall intensities of 85 mm h 1 were the largest for every slope gradient but they decreased by 39 3 as the slope gradient increased from 6 to 35 however the final infiltration rates exhibited an increasing decreasing trend for rainfall intensities higher than 85 mm h 1 as the slope gradient increased the critical slope gradient was about 11 the influence of rainfall intensity on runoff was considerably reduced at the higher slope gradients due to increased infiltration the influence of slope gradient on sediment loss was reduced as rainfall intensity increased while the effect of rainfall intensity on sediment losses was greater on the gentler slopes than on the steeper slopes the upslope splash mean value initially increased from 4 8 to 7 2 g m 1 h 1 before it decreased to 3 g m 1 h 1 as the slope gradient increased the maximum measured value occurred when the slope gradient was 22 total splash increased to maximum levels as the slope gradient increased to 11 but decreased with further increases in gradient these results indicated that the effects of slope gradient and rainfall intensity on sediment losses runoff and splash were interconnected

on the enigma of day to day variability in equatorial spread f 1 we show that large scale wave structure lsws in plasma density in the bottomside f layer is a hitherto unheralded contributor to the long standing enigma of day to day variability in equatorial spread f esf little is known about lsws it seems to appear in altitude near a vertical shear in zonal plasma drift during the post sunset rise of the f layer and its growth via an interchange instability appears to predispose quasi periodically spaced regions to development of plasma bubbles first indications are that lsws development is necessary and sufficient for esf occurrence we suggest that variability in lsws development perhaps together with the shear in zonal drift may contribute to day to day esf variability a need revealed by this study is that a cluster of distributed sensors not isolated ones is necessary to pursue the problem of day to day variability

mineral chemical and isotopic studies of namaqualand granulites south africa a grenville analogue the northwestern part of south africa and southern south west africa namibia is amongst the most extensive granulite terranes in africa this work reports the results of electron microprobe studies of minerals from two pyroxene cordieriteorthopyroxene gedrite sapphirine and garnet and or cordierite parageneses from namaqualand in the n w cape province of south africa determined pt conditions of prograde metamorphism based on thermodynamic calculations are 800 900 c and ca 6 7 kb and it is argued that rocks of unusual composition notably cordierite orthopyroxene rocks are restites after the extraction of granitic liquid from former argillites this interpretation is consistent with previously published data on similar rocks and with mccarthy s 1976 suggestion of extensive partial melting in the quartzofeldspathic rocks in the area

terrestrial heat flow in botswana and namibia we report terrestrial heat flow measurements from 25 new sites in botswana and namibia twelve sites from the archean kaapvaal zimbabwe craton and the limpopo belt have a mean of 47 4 mw m 2 standard error of the mean but show a trend of increasing heat flow from less than 40 mw m 2 within the cratonic nucleus to about 60 mw m 2 at its edge thirteen sites in the proterozoic and pan african mobile belts that surround the craton have a mean of 66 3 mw m 2 increasing from about 60 mw m 2 at the cratonic margin to more than 70 mw m 2 several hundred kilometers away radiogenic heat production in near surface basement rocks was measured for four sites on the craton and seven sites in the mobile belts the limited heat flow heat production data from the craton are insufficient to establish a correlation heat flow and heat production data from the mobile belts when combined with published data from six sites in zambia exhibit a linear trend with an intercept of 50 3 mw m 2 and a slope of 5 5 1 1 km some but not all of the observed difference in surface heat flow between the mobile belts and the cratonic nucleus may be due to differences in crustal heat production that part of the regional variation in surface heat flow which originates at greater depths implies a fundamental difference in thermal structure of the lithosphere between the craton and the mobile belts in southern africa

average equatorial zonal and vertical ion drifts determined from san marco d electric field measurements san marco d electric field measurements have been averaged in terms of their equivalent ion drift to produce an average pattern of equatorial zonal and vertical ion drifts variations with season solar activity kp lunar phase and longitude have been analyzed similarities and some differences from previous jicamarca de 2 and ae e results are seen confirmation is given of the dominance of the f region dynamo in the 1900 2100 local time region the daytime zonal ion drift is larger for high f10 7 values than that for low values there is little variation between high and low values of kp superrotation is evident in this data set and is larger at equinox compared to solstice at the june solstice there are significant differences between the average ion drifts in the longitude sector where the geomagnetic equator is north of the geographic equator indian sector and the sector where the geomagnetic equator is south of the geographic equator peruvian sector the daytime upward velocity is larger in the indian sector than in the peruvian sector and it reverses later in the evening in the indian sector daytime westward zonal velocities are larger and the nighttime eastward velocities are smaller in the indian sector a presunrise enhancement is seen in the downward velocity in the indian sector but not in the peruvian sector significant variations are also seen with the phase of the moon in light of current theory the lunar variations suggest a complex interaction of e and f region dynamo sources with conductivity changing in phase and character with latitude

magnetic mineralogy of the lower continental crust rocks that were once present in the deep continental crust can be found in surface exposure as xenoliths as parts of high grade metamorphic and plutonic terrains and as obducted lower crustal cross sections a review of magnetic and mineralogic studies of samples representing all such occurrences shows that magnetite is the only magnetic phase present in significant amounts in these rocks thermodynamic considerations indicate that tipoor magnetite is the expected magnetic oxide under equilibrium conditions that exist in the lower crust regardless of the primary magmatic composition of the spinel phase furthermore it seems unlikely that serpentinites with metal alloys contribute significantly to the magnetization of the lower crust or mantle thus magnetite in the deep crust is the most likely candidate for the source of the long wavelength magnetic anomalies observed in regional aeromagnetic and satellite magnetometer surveys if so the entire crust should be magnetic in most continental areas including shields in areas of high heat flow the bottom of the magnetic crust may lie considerably above the moho

investigating reservoir sediment and watershed erosion using a geographical information system most economic developments may have been at the expense of soil conservation soil erosion results in impacts on reservoir sediment crop yield and water quality this study introduces the procedure of using a geographical information system for investigating reservoir sediments and soil erosion of the corresponding watershed first the bathymetric surface of a reservoir is surveyed using two real time kinematic global position systems and a sonar based depth gauge using the on board computer receivers and sonar bathymetric readings are recorded three times a second to establish actual coordinates and depth measurements data are then converted using a digital terrain model to obtain the current image bathymetric surface the image of original bathymetric surfaces when constructed can be obtained by digitizing the existing map the subtraction of these two images is used to estimate the amount of sediment deposits next parameters of rainfall runoff erosivity factor soil erodibility factor slope length factor slope steepness factor cover management factor and support practice factor are evaluated for each grid of the corresponding watershed the average annual soil loss from each grid is estimated by the revised universal soil loss equation to obtain the total amount of the soil loss for the watershed using the example of charles mill lake ohio usa the estimated average amount of sediment deposits in the lake was about 2 44 x 10 4 m 3 year 1 on the other hand the estimated soil erosion from the corresponding watershed was about 4 22 x 10 8 kg year 1 or 1 56 x 10 5 m 3 year 1 hence it can be concluded that about 15 6 of the soils eroded from the watershed have been deposited in the lake

cloud components of the intertropical convergence zone 1 this study explores the roles of different synoptic scale cloud systems in the making of the intertropical convergence zone itcz outgoing longwave radiation olr data are used to represent both the mean itcz and cloud systems an olr threshold of 205 w m 2 is used to distinguish daily mean deep convective clouds from nondeep clouds zonally moving synoptic scale cloud systems are identified through a cloud tracking method mean olr of the itcz is decomposed into five components westward and eastward moving synoptic scale deep convective clouds random nonpropagating deep convective clouds nondeep clouds and clear sky backgrounds hypothetical itczs each composed of one of the cloud components and the clear sky background are constructed and compared the largest synoptic scale cloud constituents of the itcz are nondeep clouds and deep clouds with no persistent tendency of zonal propagation each of the two comprises about 40 45 of total cloud signals in the itcz a weak itcz could exist solely because of westward propagating synoptic scale deep convective clouds in reality these westward propagating clouds contribute 25 40 of deep convective clouds and 10 20 of total clouds in the itcz contributions from eastward propagating synoptic scale clouds are much smaller 8 of the deep convective clouds and less than 5 of total clouds in the itcz an itcz without any zonally propagating synoptic scale deep convective clouds would be diffused in latitude the cloud compositions in the itcz and other tropical convective zones are compared their discrepancies indicate fundamental characteristics in large scale environments for the cloud components in different regions

the thermal regime of south african continental margins abstract we present thermal data from 100 oil exploration boreholes on the continental margins of south africa near surface temperature profiles are constrained with temperatures acquired during reservoir tests corrected bottom hole temperatures and seafloor temperatures the thermal conductivity profiles are estimated from geophysical well logs using a neural network method available data allow us to determine 41 new heat flow values computed from depth ranges greater than 1000 m located on the western and southern continental margins of south africa we believe that the variations in surface heat flow are not controlled by the contribution of the sediments or the basement but rather by the mantle heat flow an upper bound of 30 mw m 2 for the mantle heat flow on the interior of the continent can be inferred from the lowest available estimates located near the coastline on the southern continental margin on both continental margins heat flow values reach a maximum of about 60 mw m 2 100 km away from the shore and consistently decrease further away towards values typically encountered in old oceanic domains 50 mw m 2 this indicates that 1 the mantle heat flow increases over a short distance at the edge of the continent which is consistent with studies on the effect of continents on mantle convection and 2 it may increase to a value greater than heat flow on the adjacent ocean as a possible consequence of the effect of the transition between thin oceanic lithosphere and thick and cold continental lithosphere on mantle convection

heat flow anomaly in lesotho implications for the southern boundary of the kaapvaal craton heat flow studies in southern africa reveal a pattern of low heat flow in archean cratons compared with proterozoic mobile belts that provides grounds for modeling in which cratons have lower mantle heat flux and greater lithospheric thickness there is little detailed information regarding thermal transitions across craton boundaries but new data from lesotho provide insights into the nature of the boundary between the kaapvaal craton and the natal belt measurements at nine localities in a 90 km long north south traverse show an increase of heat flow from typically cratonic values of about 45 mw m 2 in the north to about 80 mw m 2 where the craton abuts on the natal belt in the south the change occurs within 30 km suggesting that the anomaly largely reflects an increase in radioactive heat from the upper crust in the orogenic front the change in mantle heat flux across the boundary is probably considerably smaller these and other results suggest that the surficial craton boundary is further north than usually depicted

satellite traces an ionogram signature for large scale wave structure and a precursor for equatorial spread f 1 although the source that controls day to day variability in the occurrence of equatorial plasma structure i e equatorial spread f or esf remains to be identified progress is being made there is evidence that the appearance of large scale wave structure lsws in the bottomside f layer around the time of its post sunset rise pssr is a more direct precursor of esf than the pssr itself the bulk of the evidence however is in the form of satellite f traces in ionograms which may be viewed as less than convincing because these signatures have not been shown to be causally related to lsws in this paper incoherent scatter radar and ionosonde data both collected on 24 july 1979 from the kwajalein atoll marshall islands are used to show that this is indeed the case

variation of radiogenic heat production rate in 2 8 1 8 ga old rocks in the central fennoscandian shield abstract we present results of a geochemical survey based on 1150 outcrop samples for heat production studies in a e w oriented band 120 km 500 km located approximately between 62 and 63 n in finland the central fennoscandian shield the results provide representative averages of heat production rate in the studied tectonic units but also demonstrate the heterogeneity and spatial variation in radiogenic heat production rate of the precambrian lithosphere the study area covers formations from the archaean granite greenstone terrain in the east via a palaeoproterozoic mobile belt to a major granitoid complex surrounded by schist belts in central and western finland in this study we review the heat production rates as calculated from the u th and k total analyses and densities of the samples and the relations of heat production rate values with major tectonic setting lithological types major composition and petrophysical properties of rocks the data is further correlated with heat flow values measured in boreholes and applied in a lithospheric heat production model in the central part of the shield generally heat production rate increases from archaean to proterozoic rocks in e w direction but this trend is relatively weak and often overrun by lithological variations the arithmetic means are 1 1 1 3 w m 3 in the archaean domain 1 3 0 6 w m 3 in the hoytiainen autochthonous proterozoic domain 1 2 0 5 w m 3 in the suvasvesi domain characterized by allochthonous proterozoic cover 1 0 0 6 w m 3 in the proterozoic raahe ladoga mobile belt 1 3 1 1 w m 3 in the proterozoic rantasalmi haukivuori domain 1 6 0 8 w m 3 in the central finland granitoid complex and 1 4 0 8 w m 3 in the bothnian schist belt the standard deviations of the mean values are considerable and reflect the heterogeneity of heat production all distributions overlap heat production rate shows spatial variations which range in scale from kilometres to tens of kilometres well defined systematic variations of heat production rate values with either sio2 content density or p wave velocity could not be found although the correlations are statistically significant at 1 risk level the correlations are weak and scattered and sometimes opposite in sign in the major rock groups plutonic metavolcanic and metasedimentary heat flow density measured in boreholes increases with increasing heat production rate but the present data do not support a strict linear dependence between the variables and the regression line parameters vary depending on the applied heat production values drill core analyses versus hole site averages from the present study this indicates that the heat production rate is spatially heterogeneously distributed in the scale of the boreholes and their formations a lithospheric heat production model was constructed using data from the present study for the upper crust literature data for lower crustal xenoliths in the study area and a xenolith derived heat flow density value for the mantle the total crustal contribution to the surface heat flow density 37 mw m 2 from radiogenic heat sources is calculated as 26 mw m 2 and the contributions from the lower middle and upper crust are 4 11 and 11 mw m 2 respectively

effects of tidal forcing conductivity gradient and active seeding on the climatology of equatorial spread f over kwajalein plasma structure in nighttime equatorial f layer referred to as equatorial spread f esf displays climatology whose seasonal variation depends on longitude at longitudes where esf favors equinoxes times when maxima occur can be predicted in terms of the day of year when e region sunset is simultaneous in conjugate hemispheres i e sunset nodes aside from occurrences around equinoxes there are only three longitudes where esf also occurs during a solstice one is the central pacific region here esf activity is strong during the june solstice when solar activity is high to understand this puzzling behavior esf climatology over the kwajalein atoll was compared with properties of the postsunset rise pssr of the f layer and seeding activity in the troposphere the key findings are as follows 1 maxima in pssr velocity vpssr are better aligned with equinoxes than with sunset nodes hence seasonal pattern of vpssr not only sunset nodes should be included in interpretation of esf climatology 2 the source of vpssr during solstice appears to differ from that during equinoxes 3 equinoctial maxima in vpssr could be related to a semiannual variation in equatorial electrojet strength and its contribution to polarization of the f region dynamo current 4 enhanced vpssr during the june solstice is interpreted in terms of tidal forcing with a wave number of 2 5 displacements of maxima in esf climatology from maxima in vpssr are shown to be consistent with deep convective activity

the distribution of radiogenic heat production as a function of depth in the sierra nevada batholith california geochemical analyses and geobarometric determinations have been combined to create a depth vs radiogenic heat production database for the sierra nevada batholith california this database shows that mean heat production values first increase then decrease with increasing depth heat production is 2 aw m 3 within the 3 km thick volcanic pile at the top of the batholith below which it increases to an average value of 3 5 aw m 3 at 5 5 km depth then decreases to 0 5 1 aw m 3 at 15 km depth and remains at these values through the entire crust below 15 km below the crust from depths of 40 125 km the batholith s root and mantle wedge that coevolved beneath the batholith appears to have an average radiogenic heat production rate of 0 14 aw m 3 this is higher than the rates from most published xenolith studies but reasonable given the presence of crustal components in the arc root assemblages the pattern of radiogenic heat production interpreted from the depth vs heat production database is not consistent with the downward decreasing exponential distribution predicted from modeling of surface heat flow data the interpreted distribution predicts a reasonable range of geothermal gradients and shows that essentially all of the present day surface heat flow from the sierra nevada could be generated within the 35 km thick crust this requires a very low heat flux from the mantle which is consistent with a model of cessation of sierran magmatism during laramide flat slab subduction followed by conductive cooling of the upper mantle for 70 m y the heat production variation with depth is principally due to large variations in uranium and thorium concentration potassium is less variable in concentration within the sierran crust and produces relatively little of the heat in high heat production rocks because silica content is relatively constant through the upper 30 km of the sierran batholith while u th and k concentrations are highly variable radiogenic heat production does not vary directly with silica content d 2005 elsevier b v all rights reserved

morphology and influencing factors of rills in the steep slope in yuanmou dry hot valley sw china abstract it is very important to understand rill morphology in order to understand its dynamics to reveal the morphology and influencing factors of rills in the steep slope rss in the yuanmou dry hot valley the total station photogrammetric technique and microtopographic profiler were used to obtain the parameters of the cross sections and longitudinal profiles of the rss and 12 parameters were used to characterize the rill morphology the results show that the morphology of rills clearly varied between each layer the topography soil properties and ferruginous cemented layer all exerted important influences on the rill morphology the average depth decreased with increasing slope length and the depths dominated by silt and sand were larger than that dominated by clay the average width and average width depth ratio increased with increasing slope length and the width and the width depth ratio that was dominated by clay was larger than that dominated by silt and sand the shape ratio of the rill cross section ranged from 0 50 to 0 58 and the shape of the cross section gradually changed from narrow and deep to wide and shallow with increasing slope length concave convex degree tended to be larger in the segment with ferruginous cement in the longitudinal profile the gradient gradually decreased with decreasing slope gradient and increasing slope length the presence of the ferruginous cemented layer and topsoil crust resulted in abnormal changes in the shape of the rill it is helpful to further understand the mechanisms of rill erosion under different conditions

the application of 137cs to post fire erosion in north west spain abstract wildfires are a frequent occurrence in the cantabrian mountain range in north west spain causing erosion and soil degradation with the aim of measuring this erosion 43 soil cores were taken from four slopes with different degrees of fire frequency and 137 cs concentration the four slopes are located in the same geographical area they have a quartzitic substrate with slopes of between 20 and 30 and share the same type of soil elevation and orientation however vegetation cover is different as a result of the action of fire maps of the area showing the burnt areas over the period 1984 to 2004 remote sensing data confirm the effects that fire has had soil cores were taken from transects on each slope and three reference samples were also taken from a high plateau in order to establish a reference value for 137 cs inventory soil redistribution rates erosion and deposit for the slopes could thus be calculated according to whether 137 cs inventory was higher or lower than the reference value the values obtained show that 137 cs inventory is lower for the slopes with shrubby vegetation than for the reference samples and its distribution indicates higher erosion rates for the upper slope samples mean erosion rates obtained for these slopes were 6 75 t ha 1 year 1 and 6 6 t ha 1 year 1 these data are compared with erosion rates for 137 cs obtained in areas with different climates and patterns of land use 137 cs redistribution was not found on slopes with tree cover suggesting that surface erosion has not occurred or at least not during the time period for which 137 cs can be measured 137 cs distribution was compared with the distribution of other variables and topographical indices distance from the hilltop accumulated flow slope curvature and cti the application of 137 cs in studies of post fire erosion is relatively novelty and it a useful technique in post fire erosion studies over long timescales and for study sites larger than point and plot scales

the heat flow heat generation relationship implications for the nature of continental crust abstract the apparent linear relationship between surface heat flow q and heat generation a is usually interpreted in terms of heat flow provinces i e terrains that have a common tectonothermal history and a uniform mantle component of heat flow the slope d of the linear regression of heat flow on heat generation is an indication of the thickness of the upper heat producing layer for many terrains d is numerically similar to the depth of a major mid crustal transition zone these observations are modelled by a two layer crust consisting of an upper layer approximately 10 15 km thick of variable heat generation underlain by a layer about 20 km thick in which heat generation is lower and more uniform than that in the upper layer the model is well able to simulate q a regression parameters for different sets of real data it is also consistent with other geological and geophysical observations the higher and more variable heat generation of the upper layer is consistent with ideas concerning removal of heat producing elements from the lower layer during amphibolite to granulite metamorphism and their redistribution into the upper crust further redistribution of heat producing elements may occur in zones of hydrothermal circulation whose depth is a function of stress pressure and temperature and which may migrate vertically in response to stress changes during uplift and erosion large scale metamorphism to granulite facies has been postulated as one mechanism for stabilisation of continental crust in the late archaean it is shown however that redistribution of heat producing elements in such a process would have only a small effect on crustal geotherms so that partitioning of heat production was not a major factor in the crustal stabilisation

longitudinal variation of the e region electric fields caused by atmospheric tides 1 polarization electric fields created by the e and f region dynamos cause the uplift of f region plasma the subsequent redistribution of that plasma along the magnetic field lines creates the equatorial ionospheric anomaly eia observations of the post sunset eia made by the image and timed satellites are compared here with champ orsted and sac c observations of the noontime equatorial electrojet eej during magnetically quiet periods around equinox the eia and eej show a remarkably similar four peaked wave like longitudinal variation its structure is consistent with the longitudinal variation in the strength of diurnal tides that drive the e region dynamo this indicates a strong vertical coupling between the ionosphere and troposphere because the four peaked tidal structure is driven by tropospheric weather furthermore the dayside ionospheric conditions are found to perform the global scale longitudinal structure of the post sunset ionosphere at low latitudes

the heat flow from the continents the terrestrial heat flow is defined as the quantity of heat escaping per unit time from the earth s interior across each unit area of the earth s solid surface the quantity varies from place to place over the surface of the earth as well as with time throughout earth history the total heat being lost from the earth at a given time is the integral of the heat flow taken over the entire surface of earth the heat flow from the continents is therefore but a part of the larger picture of global heat loss indeed the lesser part when compared to the heat loss through the floor of the ocean basins pollack 1980 sclater et al 1980 davies 1980 this is so not only because of the lesser continental area but also because of the generally smaller heat flow found on the continents than in the ocean basins thus a full discussion of the thermal regime of the earth and the mechanisms by which it exhausts heat from the interior must center on the heat loss through the oceans a topic which lies beyond the scope of this review nonetheless because of the geological antiquity of at least some of their constituent terranes the continents provide the only direct evidence about the thermal tectonic and petrologic processes of the earth at times before the birth of any of the modem ocean basins some two hundred million years ago because inferences about earlier times are drawn wholly from materials now preserved in continents one must be cautious not to overgeneralize about global tectonothermal processes from observations confined to continents

first observations of large scale wave structure and equatorial spread f using certo radio beacon on the c nofs satellite 1 first observations of large scale wave structure lsws and the subsequent development of equatorial spread f esf using total electron content tec derived from the ground based reception of beacon signals from the certo coherent electromagnetic radio tomography radio beacon on board c nofs communications navigation outage forecasting system satellite are presented selected examples of tec variations using measurements made during january 2009 from bac lieu vietnam 9 2 n 105 6 e geographic 1 7 n magnetic dip latitude are presented to illustrate two key findings 1 lsws appears to play a more important role in the development of esf than the post sunset rise pssr of the f layer and 2 lsws can appear well before e region sunset other findings that lsws does not have significant zonal drift in the initial stages of growth and can have zonal wavelengths of several hundred kilometers corroborate earlier reports

erosional effects on runout of fast landslides debris flows and avalanches a numerical investigation the mechanism of mass changes in debris transportation process is an important topic in the study of fast landslides debris flows and avalanches basal erosion is recognised as a dynamic interaction between the original moving material and the entrained basal topsoil shearing along their non slip contact surface in this paper we propose a new concept of yield rate and establish the erosional relationship to bridge these two systems a pertinent mathematical model and numerical implementation are formulated parametric numerical experiments are conducted to compare the erosional effects the simulated results are consistent with available experimental and field observations the influence of the involvement of the erosive material on runout behaviour and the global mobility of the moving material are elucidated the proposed method is then employed to analyse a recent debris flow event in northern italy the excellent match to the field data gives it a plausible potential application to the analysis of this type of gravity driven flow with significant erosion defined in a dimensionless form the proposed yield rate can be estimated conveniently in general geotechnical practices

is the indian shield hotter than other gondwana shields abstract geothermal data on various precambrian terrains from the african australian indian and south american brazil only gondwana landmasses have been compiled synthesised and statistically analysed the results do not support the prevailing notion that the indian shield is hotter than other shields the study clearly shows that the mean surface heat flow values from the various precambrian cratons and mobile belts of the indian landmass for which the data have become available are either equal to or even lower in some cases than that in similar terrains from other gondwana continents further on the basis of available data it is found that the moho and the reduced heat flow values and moho temperatures in the south indian south african western australian and brazilian shields fall within a narrow range thus indicating within the error limits of the estimation the similarity of these shields in terms of these characteristics in conclusion it is shown that the indian landmass is not hotter than the other gondwana landmasses including even the presently immobile african continent and that the super mobility of the indian landmass does not appear to be associated with its thermal characteristics the cause of the latter lies elsewhere

some characteristics of spread f at the magnetic equatorial station fortaleza spread f in ionograms of both the range and frequency spread types is studied for the magnetic equatorial station fortaleza geographic coordinates 38 w 4 s dip latitude 1 7 for a 1 year period during 1978 1979 satellite traces suggesting ionization structures with scale sizes of 100 200 km are found to be necessary precursors to the formation of the irregularities that give rise to range type spread f whereas frequency type spread f was observed under different circumstances striking differences are noted in the spread f characteristics and related parameters over fortaleza as compared with huancayo geographic coordinates 75 3 w 12 05 s dip latitude 0 6 and jicamarca geographic coordinates 76 8 w 11 95 s dip latitude 0 9 situated within only 38 in longitude west of fortaleza the postsunset maximum in h f in winter is delayed by about 1 hr with respect to other seasons over fortaleza as compared with huancayo where it occurs earlier in winter than in other seasons similar differences also exist in the prereversal peak near sunset in the vertical drift velocity vz between fortaleza and jicamarca the differences are attributed possibly to the large difference in the magnetic field declination and to other factors such as the difference in the magnetic field intensity and the relative separation between geographic and magnetic equators that exist between fortaleza and the other stations

heat flow in the witwatersrand basin and environs and its significance for the south african shield geotherm and lithosphere thickness the late archaean early proterozoic witwatersrand basin is situated in the center of the kaapvaal craton south africa two new heat flow determinations and 71 new heat flow estimates permit excellent definition of the heat flow pattern nonvertical heat conduction explains much of the observed local heat flow variability regionally the heat flow in the basin is uniform and the overall mean 51 6 mw m 2 is higher than the mean heat flow for archaean cratons published data indicate that heat generated in the basin s strata 7 5 mw m 2 is largely responsible for the excess heat flow the subsediment heat flux is 43 5 mw m 2 seven new heat flow and heat production determinations in archaean granite domes northwest of the basin average 33 2 mw m 2 and 2 3 0 8 w m 3 respectively contrasted with the heat flux across the floor of the basin the lower heat flow in the domes probably reflects a smaller radiogenic contribution from the crystalline crust below the domes published heat production data from upturned granitic basement exposed in the vredefort dome in the center of the basin indicate that the radioactive contribution from the crust below the basin is 26 5 m w m 2 subtracting this value and the contribution from the strata 7 5 mw m 2 from the basin s surface heat flow 51 mw m 2 indicates that the heat flux through the moho is approximately 17 mw m 2 calculated lithospheric temperatures agree closely with pressure temperature regimes inferred from studies of mantle inclusions in kimberlites in the kaapvaal craton both data sets indicate that the cratonic lithosphere is considerably cooler and thicker than that below an equilibrium ocean implications of the cold thick cratonic lithosphere for understanding the distribution of southern african diamondiferous kimberlites and the density and buoyancy of the lithosphere are discussed

crustal radiogenic heat production and the selective survival of ancient continental crust if the oldest terrestrial rocks are to be used as a representative sample of the early terrestrial crust it is important to consider the possibility that they may represent a biased sample chemical data indicate that archean crust is on average depleted in potassium uranium and thorium relative to younger crust radiogenic isotopes of these elements produce a significant portion of surface heat flow from continents and low mean heat flow in archean terrains relative to younger terrains also indicates that these elements are relatively depleted in archean crust in stable continental lithosphere the primary variable controlling variations in the geotherm is crustal radiogenic heat production qualitative evidence suggests that terrains with low radiogenic heat production and thus a relatively cool geotherm are less susceptible to magmatic and tectonic reactivation than terrains with higher heat production and a hotter geotherm since crustal radiogenic isotope abundances must have been greater in the past if the isotopes were immobile in stable crust the relative effect of crustal heat production must have been greater and thus the range in geotherms must have been greater for the same mantle heat flow it is suggested that crust with low heat production is less susceptible to orogenic reworking than high heat production crust and thus there may have been selective stabilization of low heat production low potassium uranium and thorium crust early in earth history either archean crustal generation was by a mechanism that perhaps fortuitously produced only low heat production crust or all high heat production crust was reworked by orogenesis during the archean and did not stabilize in significant volumes until the earliest proterozoic perhaps in association with a reduction in mantle temperatures and mean heat flow if selective crustal reworking did operate during the archean surviving archean terrains may represent a biased sample of the early terrestrial continental crust

the chronology and tectonic style of landscape evolution along the elevated atlantic continental margin of south africa resolved by joint apatite fission track and u th sm he thermochronology atlantic type continental margins have long been considered passive tectonic settings throughout the entire postrift phase recent studies question the long term stability of these margins and have shown that postrift uplift and reactivation of preexisting structures may be a common feature of a continental margin s evolution the namaqualand sector of the western continental margin of south africa is characterized by a ubiquitously faulted basement but lacks preservation of younger geological strata to constrain postrift tectonic fault activity here we present the first systematic study using joint apatite fission track and apatite u th sm he thermochronology to achieve a better understanding on the chronology and tectonic style of landscape evolution across this region apatite fission track ages range from 58 3 2 6 to 132 2 3 6ma with mean track lengths between 10 9 0 19 and 14 35 0 22 m and mean u th sm he sample ages range from 55 8 31 3 to 120 6 31 4ma joint inverse modeling of these data reveals two distinct episodes of cooling at approximately 150 130ma and 110 90ma with limited cooling during the cenozoic estimates of denudation based on these thermal histories predict approximately 1 3 km of denudation coinciding with two major tectonic events the first event during the early cretaceous was driven by continental rifting and the development and removal of synrift topography the second event during the late cretaceous includes localized reactivation of basement structures as well as regional mantle driven uplift relative tectonic stability prevailed during the cenozoic and regional denudation over this time is constrained to be less than 1 km

aspects of the dynamic and thermal metamorphic history of the vredefort cryptoexplosion structure implications for its origin abstract the vredefort structure is the oldest and the largest known cryptoexplosion structure on earth an approximately 36 km deep section through the archean sialic crust and the overlying precambrian strata of the kaapvaal craton is exposed in the core of the structure the geology presented in the exposed section includes all the principal metamorphic facies in the crust and records a long and complex thermo tectonic history which dates back to at least 3 5 ga the petrographie and geological observations in the basement rocks indicate that there is a complex interrelationship between the archean geology and the 2 0 ga dynamic and thermal metamorphic overprint some of which are postulated to be indicative of impact processes the dynamic and thermal metamorphic effects do not increase progressively towards the centre of the structure as found at known impact structures in particular dynamic deformation phenomena such as pseudotachylite and planar features in quartz reach maximum intensity in the rocks close to the vredefort discontinuity a brittle ductile shear zone which separates upper crustal amphibolite facies rocks from lower crustal granulites in certain other lithological zones deformation phenomena are noticeably absent or diminished we suggest that changes in the physical and chemical properties of the rocks from margin to centre of the basement may account for the variation in the intensity of the 2 0 ga thermal and dynamic metamorphic effects observed at vredefort in conclusion our overall impression of the vredefort structure is that it is a relic of an ancient meteorite impact crater but that there were thermo tectonic events which occurred both prior to and after the postulated impact event which complicates the interpretation of its origin

equatorial f region vertical plasma drifts seasonal and longitudinal asymmetries in the american sector longitudinal and seasonal asymmetries in the evening ionospheric f region plasma vertical drift v sub z enhancements between two longitudinally separated stations situated along the magnetic equator in the american sector are investigated under solar maximum conditions based on results obtained from the analysis of ionosonde data for these stations the two stations are huancayo peru and fortaleza brazil which have markedly different magnetic declination angles the observed asymmetries are interpreted using a detailed numerical simulation of the e and f region electrodynamic coupling process that takes into account also its asymmetry about the magnetic equator arising from the finite magnetic declination angle the results of the simulation show in agreement with observations that the occurrence time of the evening f region vertical drift prereversal peak and its seasonal variation at a station are controlled by the magnetic declination angle at that station which determines the seasonal variation of the sunset times and hence the integrated pedersen conductivity longitudinal gradient at its magnetic conjugate e layers the amplitude of the prereversal peak on the other hand undergoes the influence of the magnetic declination angle as well as of the thermospheric zonal wind component

a seismic refraction investigation of the namaqualand metamorphic complex south africa the namaqualand metamorphic complex forms part of the precambrian shield of southern africa and hosts several major base metal deposits a long line seismic refraction experiment traversing the complex was conducted in order to complement geological and geophysical studies of the structure and evolution of this region seismograms were obtained at approximately 10 km intervals along the 290 km profile seismic ray tracing techniques were used to model the travel time and amplitude data it was found that the namaqualand lower crust is comprised of a substantial proportion of intermediate velocity 6 2 to 6 9 km s rocks these intermediate velocity rocks approach the surface near the midpoint of the profile moho was found to be at a depth of 42 km no correlation was found between the seismic and electrical resistivity models of the crust when the seismic velocity structure of the middle proterozoic namaqualand metamorphic complex is compared with that of adjacent geological provinces it is found to differ significantly from the archaean kaapvaal province but resemble the late proterozoic damara province these differences might be attributed to variations in the principal mechanisms of crustal growth between archaean and proterozoic times

a comparison of heat flow from the gondwana continents with velocities of gondwana plates geodynamic implications abstract the velocities of the lithospheric plates generally differ from each other and the cause of the super mobility of the indian subcontinent is an unresolved problem as the lithospheric plates and the sub lithospheric mantle form the two key elements of plate tectonic movement the thermal characteristics of the three constituent plates of gondwanaland i e the indian african and australian landmasses have been compared in this study it has been clearly shown that the mean surface heat flow values q s in those gondwana terrains of india which remained unaffected by tectonic and igneous activity during the last 150 m y i e after the break up of gondwanaland are either equal to or mostly lower by 5 22 mw m 2 than those in similar terrains of australia and even the immobile african continent and that q s values for the terrains of these landmasses which were affected by such activity during the last 150 m y are uniformly equal it is inferred that the indian lithosphere is neither hotter nor thinner than that beneath the above mentioned continents and that the sub lithospheric upper mantle beneath the indian peninsula is not hotter or less viscous than that beneath the african and australian shields these results and inferences evidently imply that the thermal regime and the other related parameters of the continental lithosphere do not contribute to the mobility of the plates to which it is attached that the rapid movement of the indian landmass is not coupled with the thermal characteristics of its lithosphere and that the drag force which the present studies have shown to be insignificant would not have been lower on the base of the indian lithosphere than beneath the african and australian landmasses accordingly the earlier reported postulate that the high velocity of the indian landmass is due to its thin and hot continental lithosphere and less viscous upper mantle is not valid the paleo reconstruction indicates the existence of the reunion and kerguelen plumes one on each side of the indian landmass it is likely that these plumes created in the sub lithospheric mantle favourable conditions which worked together with forces that resulted from slab pull and ridge push to give a high velocity to the indian landmass

how long is a hillslope hillslope length is a fundamental attribute of landscapes intrinsically linked to drainage density landslide hazard biogeochemical cycling and hillslope sediment transport existing methods to estimate catchment average hillslope lengths include inversion of drainage density or identification of a break in slope area scaling where the hillslope domain transitions into the fluvial domain here we implement a technique which models flow from point sources on hilltops across pixels in a digital elevation model dem based on flow directions calculated using pixel aspect until reaching the channel network defined using recently developed channel extraction algorithms through comparisons between these measurement techniques we show that estimating hillslope length from plots of topographic slope versus drainage area or by inverting measures of drainage density systematically underestimates hillslope length in addition hillslope lengths estimated by slope area scaling breaks show large variations between catchments of similar morphology and area we then use hillslope length relief structure of landscapes to explore nature of sediment flux operating on a landscape distinct topographic forms are predicted for end member sediment flux laws which constrain sediment transport on hillslopes as being linearly or nonlinearly dependent on hillslope gradient because our method extracts hillslope profiles originating from every ridgetop pixel in a dem we show that the resulting population of hillslope length relief measurements can be used to differentiate between linear and nonlinear sediment transport laws in soil mantled landscapes we find that across a broad range of sites across the continental united states topography is consistent with a sediment flux law in which transport is nonlinearly proportional to topographic gradient

radioelement concentrations in the deep profile through precambrian basement of the vredefort structure the vredefort basement granite in south africa forms the core of an undomed and overturned sequence of precambrian strata slawson 1976 proposed that the granite core has also been overturned exposing to view a thick section through the archean crust incrasing in depth toward the center of the dome profiles across the vredefort basement provide an opportunity for studying the distribution of u th and k with depth in the upper and middle crust detailed radioelement concentration profiles across the granitic basement showed that 1 the central part of the basement core is depleted in th and u relative to the perimeter and the concentration of th and u falls off regularly from the basement margin inward 2 the distribution of the radioelements and the distribution of heat production with depth over the outer 8 km are consistent with an exponential depth function 3 the felsic rocks of the central basement are characterized by high k u and th u ratios and the ratios k u k th and th u increase from the margin inward and 4 mafic granulites which occur in the central regions of the dome have normal k u k th and th u ratios high grade metamorphic environment resulted in the depletion of bothmore u and th relative to k in the greater proportion of the felsic rocks from the central regions of the vredefort basement depletion of u was far greater than that of th the normal th u k u and k th ratios in mafic rocks in close proximity to the felsic rocks suggest that mineral assemblages have a strong control on the behavior of the radioelements during regional metamorphism in the vredefort basement less

soil erosion processes on row sideslopes within contour ridging systems abstract soil erosion from row sideslopes can result in contour failure and reduce the soil conservation capacity of contour ridges understanding soil erosion processes on row sideslopes and their effects will improve our understanding of soil erosion in contour ridge systems this knowledge will provide guidance for improving the use of contour ridges in this study 32 rainfall simulation experiments were conducted in order to analyze the effects of two different microtopography indices row grade and field slope two ridge geometry indices ridge height and ridge width and rainfall intensity on erosion of sandy brown soil with two replications based on the runoff and sediment yield time series which was monitored over 1 min intervals the soil erosion process was classified into periods of interrill or rill erosion the runoff values for the two periods accounted for approximately 44 2 and 55 8 of the entire runoff value respectively sediment was mainly generated from rill erosion 87 2 however interrill erosion occurred most of the time 72 3 during the interrill erosion period the ridge width and rainfall intensity significantly and positively affected the amount of runoff contributions of 33 1 and 28 7 respectively and sediment yield per min 14 8 and 17 0 respectively ridge height significantly and positively affected the runoff per min but not the sediment yield per min in contrast field slope negatively affected runoff per min which indicated that the runoff during the interrill period was mainly affected by the ridge geometry while the sediment yield per min was mainly affected by the microtopography relief during the rill erosion period the ridge height significantly and negatively affected the runoff per min because the increasing ridge height prolonged the duration of this period and enhanced infiltration and the row grade significantly and positively affected the sediment yield per min which resulted from decreasing soil cohesiveness with increasing row grade the entire runoff and sediment yield per min during the experiment were influenced by the same factors that influenced the interrill and rill erosion periods respectively interactions between the different factors especially between ridge height row grade and rainfall intensity play an important role during the erosion process by increasing runoff and sediment yield per min therefore reducing the field slope and using high ridges may reduce contour failure during rainfall events

on equatorial spread f establishing a seeding hypothesis 1 a comprehensive explanation for the complex climatology of the so called equatorial spread f esf has eluded researchers for more than 70 years recently however a seeding hypothesis has been proposed which appears to provide the final major piece of this puzzle the hypothesis is based on the discovery that a direct link exists between regions of deep convective activity in the troposphere where atmospheric gravity waves gws are spawned and the occurrence frequency of esf during solstices the objective here is to answer two questions that may impede the general acceptance of this hypothesis we first show why seed plasma perturbations should develop from gw driven neutral wind perturbations but only when the gw source region is located very close to the magnetic dip equator we then reexamine this relationship using a data set on gw source regions that is better matched in time and longitudinal coverage than that used previously to the data set on esf activity used by tsunoda 2010a we conclude that seeding is indeed playing an important role in the development of esf

the effect of slope length on the amount and size distribution of eroded silt loam soils short slope laboratory experiments on interrill erosion abstract the data of rainfall simulation experiments on a sandy loam and a loamy sand were compared to assess the effect of slope length on the soil loss from short slopes between 0 3 and 0 9 m the total soil loss and the aggregate size distribution in the total soil loss were determined after 90 min of rainfall with rainfall intensities between 22 0 and 78 5 m h 1 the experimental results indicated that the slope length effect is different for the two soils although for both soils the total soil loss increased with increasing slope length the soil loss per unit slope length increased with increasing slope length only for the sandy loam soil 1 and decreased with increasing slope length for the loamy sand soil 2 the difference in slope length effect between the two soils was also reflected in the aggregate size distribution in the soil loss the different aggregate sizes displayed different relationships between soil loss and slope length for the loamy sand the slope length effect was less for the large aggregate sizes which contained more sand than the original soil for both soils the slope length effect was most pronounced for the aggregate sizes smaller than 0 05 mm

relationship of the onset of equatorial f region irregularities with the sunset terminator observed with the equatorial atmosphere radar 1 the relationship between sunset terminators and the onset of radar backscatter plumes associated with equatorial spread f esf observed with the 47 mhz equatorial atmosphere radar from october 2002 to april 2004 is discussed almost all irregularity echoes began to appear at or before sunset time at the altitude of the apex of the geomagnetic field line connected with the observed area and the onset time of more than half of the events corresponded exactly to apex sunset time this tendency should be due to two causes 1 the rapid change of the evening zonal electric field and 2 damping of 3 m scale irregularities by the solar radiation before the apex sunset

a detailed study of the distribution of heat flow and radioactivity in new hampshire u s a abstract we present a set of 39 new determinations of heat flow and radiogenic heat production for several different geological environments in the state of new hampshire u s a with the extensive data set now available for the state the linear relation of heat flow and heat production appears as a very useful generalization for the study of the heat flow field of a geological province our measurements indicate that the vertical distribution of radiogenic heat production is similar in plutonic and metasedimentary rocks our data are compatible with the linear relationship established earlier by f birch and his co workers in 1968 young granites are markedly enriched in radioactive elements and those which do not outcrop are revealed by anomalies in the general relation of heat flow versus radioactivity heat flow is high for plutons by low elsewhere the mean heat flow through metasedimentary formations is 1 15 cal cm2 s 48 mw m2 a value near the mean heat flow for old cratons the lowest heat flow measured is 0 76 cal cm2 s 32 mw m2 for a unit poor in radioactivity the heat flow field grades smoothly into the low heat flow regions of the canadian shield the new hampshire region is in thermal equilibrium its heat flow is in secular equilibrium with the heat generated by crustal sources and that supplied from the mantle in this area the thermal perturbations due to orogenic events decrease below the detection level in less than 200 275 ma the thickness of the layer which is thermally affected during continent continent collision type orogenies cannot be greater than about 190 km

heat flow variations in continental rifts abstract in the terrestrial thermal field continental rifts stand out as rather narrow regional thermal anomalies in which augmented heat flow is unevenly distributed heat flow variations are discussed on the example of the baikal east african cordilleran and rhine lybian rift systems rift related disturbance of the asthenosphere lithosphere system is accompanied by a general increase in the surficial heat flow regional thermal anomalies are mainly caused by conductive heat transfer from the asthenosphere local thermal anomalies are caused by magmatic mass transfer into the crust and by fluid convection along porous fracture systems

geochronology of the deep profile through archean basement at vredefort with implications for early crustal evolution the presence of archean granite forming the core of an updomed and overturned sequence of strata at vredefort south africa has been known for over 70 years recent geophysical geochemical and geological evidence has given rise to the proposal that the basement granite core has also been overturned presenting a section of the earth s granitic crust to view and that radial traverses in the vredefort basement penetrate through a 15 km thick section of the archean crust when moving from the contact of collar strata to the center of the dome the upper levels of the vredefort crust are dominated by a relatively homogeneous outer granite gneiss ogg displaying marked gradients in large ion lithophile elements these rocks grade inward into the deeper levels which occur in granulite facies metamorphism the deeper levels of the vredefort crust exposed in the central parts of the dome consist predominantly of felsic inlandsee leucogranofels ilg which occurs interleaved with inclusions of mafic metavolcanic and metasedimentary rocks termed steynskraal metamorphic zone smz a comprehensive isotopic study using four decay schemes 87rb 232th 238u and 235u on this crustal section is now reported the results permit unique and direct tests on the theories of archean crust forming processes in the upper vredefort crust whole rock isochron ages of 3050 m y are obtained from the four decay schemes and almost all evidence of an extended crustal history prior to 3050 m y has been obliterated establishment of strong vertical gradients in rb sr ratio shortly before setting of rb sr whole rock systems has wide implications for the interpretation of sr initial ratios although the vredefort upper levels of the crust has a low 87sr 86sr initial ratio of 0 7019 0 0002 it probably participated in a crustal prehistory for at least 500 m y in the deeper levels of the vredefort basement the geochronology is much more complex rb sr and th pb isochrons of 3500 m y are recorded in the mafic granulite relicts a companion paper welke and nicolaysen this issue provides evidence for an early crust forming event in this sector 3800 m y ago from 3500 m y onward these deeper crustal levels did not undergo addition of new archean crust forming material on a major scale nevertheless a most important younger archean event affected these levels 2800 m y ago cessation of high grade metamorphism is recorded by setting of the rb sr isotopic system in the felsic rocks and zircon u pb ages an episode of strong uranium depletion affected both the felsic and mafic rocks of this sector 2800 m y ago the inlandsee leucogranofels is evidently a rock unit with a long and complex history beginning with the emplacement as a crustal unit at least 3800 m y ago since then it has been subject to reworking and resetting of isotopic systems which terminated 2800 m y ago in the deeper crust there is scant evidence of a 3050 m y event similarly there is no record of a 2800 m y old imprint in the upper vredefort crust thus the last major events that affected the geochemical constitution of the vredefort upper and deeper crustal sectors differed in time and nature nevertheless they brought about isotopic setting in a downward moving sequence while the overlying crust remained cooler rigid and unaffected these events probably reflect significant discontinuities in the cooling of the archean crust

is there a relationship between seismic velocity and heat production for crustal rocks abstract several investigators proposed an empirical relationship between heat production and seismic velocity for rocks typical of the continental crust these relationships could allow for indirect resolution of the distribution of heat producing elements with depth new heat production data for rock samples from the pikwitonei granulite domain and the sachigo granite greenstone subprovince of the superior province do not follow these relationships indicating that heat production cannot be reliably predicted from seismic velocity these two parameters are not likely to be related as velocity depends upon the major mineral constituents of rocks whereas heat production results from radiogenic components concentrated in both major and trace minerals in rocks

the vredefort structure an introduction and a guide to recent literature abstract the 50 km wide vredefort structure appears to present the eroded roots of an area affected by rapid uplift and violent rock deformation widely regarded as shock deformation on an immense scale the origin of the structure is disputed external impact and internal agencies have been suggested this note introduces the vredefort structure and its geological environment emphasizing information published in the decade prior to the 1987 international workshop on cryptoexplosions and catastrophes in the geological record with a special focus on the vredefort structure this typical cryptoexplosion structure has a central and polygonal basement uplift containing violently deformed and brecciated rocks with the northern half surrounded by steeply dipping and heavily faulted collar strata and then by a rim synclinorium of less deformed strata the gains made in research on all three sectors are noted traverses through the basement from collar to centre effectively penetrate through a 15 km thick section of crust the archaean history of the crustal section has been documented the thermal and fluid inclusion evolution near the time of uplift has been studied and a deep seated co 2 rich gas explosion has been proposed as an alternative to the impact hypothesis for the shock deformation meticulous study of the effects of thermal metamorphism on the shock deformations in the collar strata led to a bold proposal more than one shock event in the evolution of vredefort analysis of the character of the faulting of the collar supports an earlier proposal regarding inward movement of blocks of collar strata renewed research on shatter cone orientations in the collar strata and two detailed studies of the structural history within the rim synclinorium are noted through the intensive mapping geophysical exploration and drilling which have been completed within the witwatersrand and transvaal basins close spatial and temporal connections between vredefort and the bushveld complex have been documented in both cases basin centres were intruded by horizontal mafic eruptives and basin subsidence took place after these eruptives had consolidated and cooled the vredefort structure has long been discussed as a possible deeply eroded remnant of a major cratering event or events the connections of this structure with the bushveld complex carry important implications for such discussion

a detailed study of equatorial electrojet phenomenon using orsted satellite observations 1 detailed analysis of the scalar magnetic field data from orsted satellite for quiet days from april 1999 to march 2000 has been undertaken to study the equatorial electrojet eej phenomenon an objective technique has been adopted for the identification of the eej from the satellite data and estimation of the standard parameters associated with it eej strength computed using the satellite data and simultaneous ground magnetic observatory data for the indian and american sectors correlate very well authenticating the method used estimated zonal variation in the eej parameters such as peak current intensity j0 and total current i are broadly consistent with the earlier observations we however observe that the width of the eej varies considerably with longitude a feature not seen in the pogo data the study shows that the eej axis center of eej closely follows the dip equator at altitude of 106 km but there is a small departure that undergoes diurnal variation with a minimum at noon the globally averaged eej amplitude follows the expected diurnal pattern principal component analysis technique reveals that first four components can explain around two thirds of the electrojet variability the first component which contributes a little over 30 to the observed variance could be identified with the global variation of the eej emanating from the day to day variability of the migrating tides the second and fourth components which account for around 15 and 10 of the variance respectively are driven by forcing that depends on whether the location of the eej in that sector is in the northern or southern hemisphere the third component provides maximum contributions wherever the geomagnetic and dip equators are sufficiently close accounting for 12 5 of the variance the remaining components could be associated with contribution of nonmigratory tides or other unknown mechanisms thus the present study suggests that besides conductivity atmospheric tidal modes play important role in defining the zonal variability of the eej current system

the vredefort structure a perspective with regard to new tectonic data from adjoining terranes abstract the deformational history of the area surrounding the vredefort structure in south africa is long and complex involving several periods of contraction and extension a general chronology of events covering a time span of 1000 ma is established the vredefort deformation is identified as a separate structural event which is distinct from the earlier deformations it is essential therefore that deformational structures related to the pre vredefort event should be identified and subtracted from the total spectrum of tectonism so that only those structures which can be related with certainty to the formation of the vredefort structure are defined this approach could influence interpretations of the origin of the vredefort structure which attribute most structural and geological associations to the deposition of sediments onto a granitoid basement followed by a vredefort deformational event

the time bound character of uranium mineralising processes with special reference to the proterozoic of gondwana abstract it is more useful to consider the time bound character of uranium mineralising processes than the time bound character of uranium deposits this is because present uranium deposits are the result of a series of mineralising steps which occurred over hundreds of millions of years we have identified five periods which are characterised by moderately distinct mineralising processes 1 1 before 2800 ma uranium was fractionated into the upper crust during late archaean early proterozoic cratonisation by magmatic and metamorphic processes the granitic terranes were an important source of uranium for subsequent mineralising events 2 2 2800 2200 ma although the atmosphere was probably not reducing at this time the level of oxygen was sufficiently low for uraninite to be transported and concentrated in sedimentary basins cratonisation was a prerequisite for the formation and preservation of long lived basins rapid burial and reducing conditions during diagenesis were important for preserving the uranitite the uranium was mobilised during diagenesis and metamorphism 3 3 2200 1200 ma after 2000 ma when the oxygen level in the atmosphere increased markedly the movement of uranium in solution as uranyl ions became more important the first marine shelf sequences containing chemical and organic sediments to be deposited on the cratons formed excellent sites for the syn sedimentary diagenetic or metamorphic concentration of uranium in some cases this mineralisation was economic in other cases it may have been just a step in a succession of mineralising events continental clastic sediments which overlie these shelf sediments were excellent hosts for large hydrothermal circulation systems which could remobilise the uranium from either granites or sediments the lack of organic and argillaceous material in these continental sequences resulted in the precipitation of uranium near the basal unconformity where there were reducing sediments 4 4 1200 400 ma with the start of modern plate tectonics there was greater potential for the thermally activated remobilisation of uranium the period 1200 900 ma marked the final mineralisation in some important deposits the pan african and brazilian events 700 400 ma mobilised uranium of uncertain origin and concentrated it in previously deposited marginal marine sediments 5 5 400 0 ma the incorporation of organic material into continental clastic sediments allowed uranyl ions to be precipitated before they reached the sea to form the important sandstone type of deposits any time bound mineralising process may be either the final or an intermediate step in forming an economic uranium deposit which of these it is depends on the subsequent history of the area on whether the uranium is preserved dispersed or reconcentrated that many major uranium deposits occur on late archaean early proterozoic cratons emphasises the importance of the long term preservation of sedimentary sequences even though the uranium may be remobilised several times within the sediments

on the generation and growth of equatorial backscatter plumes 1 wave structure in the bottomside f layer we examine the initial conditions that lead to backscatter plume development in the equatorial f region ionosphere by analyzing altair radar data we obtained the following principal results 1 prior to plume development an altitude modulation of electron density contours exists in the bottomside f layer these quasi periodic variations were mapped spatially over a 1200 km east west distance by using incoherent scatter measurements and found to consist of three cycles with an average spatial wavelength of 400 km 2 the wave structure observed in the bottomside electron density contours grew in amplitude at a rate consistent with that predicted by the generalized gradient drift instability 3 bottomside backscatter developed on the west walls of all three altitude modulated regions followed by plume development from near the crests of these regions

terrestrial heat flow in the sirt basin libya and the pattern of heat flow across northern africa we report 66 new heat flow and 24 new heat production measurements from the sirt basin a late jurassic miocene sedimentary depression in north central libya underlain by late proterozoic basement heat flow determinations were made using bottom hole temperatures from oil wells and thermal conductivity measurements from drill core and cuttings heat production measurements come from core samples of basement rock heat flow is fairly uniform throughout the basin with a mean of 72 9 s d mw m 2 it is not clear if heat flow from the sirt basin is elevated as a consequence of its origin as a late mesozoic rift the difference between the mean basin heat flow and the global mean heat flow from tectonically undisturbed late proterozoic terrains 55 17 mw m 2 is 17 mw m 2 but this difference lies within the uncertainties associated with these mean heat flow estimates if heat flow from the sirt basin is elevated it could be caused by enhanced crustal heat production and need not be attributed to thermal alteration of the lithosphere related to basin formation mean crustal heat production is 3 9 2 1 w m 3 1 2 to 3 times greater than surface heat production in other proterozoic terrains in africa from west to east the pattern of heat flow across northern africa is characterized by high 80 110 mw m 2 heat flow throughout most of northwestern africa normal to perhaps slightly elevated heat flow in the sirt basin low to normal 35 55 mw m 2 heat flow in egypt inboard of the red sea and high heat 75 100 mw m 2 flow along the red sea high heat flow near the red sea and in northwestern africa along the mediterranean coast can be readily attributed to cenozoic tectonic activity but high heat flow in the paleozoic sahara basins of southern algeria is harder to understand within the tectonic framework of northern africa a possible explanation advanced previously is that elevated heat flow in the sahara basins arises from a regional thermal anomaly within the north african lithosphere if that explanation is correct then the heat flow distribution in the sirt basin and in egypt away from the red sea suggests that the postulated lithospheric thermal anomaly does not extend beyond the sahara basins to the east

post break up tectonic inversion across the southwestern cape of south africa new insights from apatite and zircon fission track thermochronometry the south west african margin is regarded as an example of a passive continental margin formed by continental rifting following a phase of lithospheric extension and thinning recent attention focused on this margin has included theoretical modelling studies of rift processes plate kinematic studies of the opening geometry and timing and empirical studies focused on documenting the crustal structure and offshore sedimentary record here we examine the onshore geomorphic and tectonic response to rifting and breakup with a specific focus on the sw cape of south africa we present 75 new apatite and 8 new zircon fission track analyses from outcrop samples and onshore borehole profiles along the western margin of south africa the data are used to derive robust thermal histories that record two discrete phases of accelerated erosional cooling during the early cretaceous 150 130 ma and late cretaceous 100 80 ma respectively both periods of enhanced erosion are regional in extent involved km scale erosion and extend well inland of the current escarpment zone albeit with spatially variable intensity and style the late cretaceous episode is also expressed more locally by tectonic reactivation and inversion of major faults causing km scale differential displacement and erosion the new aft data do not exclude the possibility of modest surface uplift occurring during the cenozoic but they restrict the depth of regional cenozoic erosion on the western margin to less than c 1 km the inferred pattern and chronology of erosion onshore is consistent with the key features and sediment accumulation patterns within the offshore orange and bredasdorp basins it is suggested that the late cretaceous event was triggered by a combination of regional dynamic uplift augmented along the western margin and in the sw cape by local tectonic forces arising from dextral displacement of the falkland plateau along the falkland agulhas fracture zone

characteristics of large scale wave structure observed from african and southeast asian longitudinal sectors the spatial large scale wave structure lsws at the base of f layer is the earliest manifestation of seed perturbation for rayleigh taylor instability hence found to play a deterministic role in the development of equatorial plasma bubbles epbs except for a few case studies a comprehensive investigation has not been conducted on the characteristics of lsws because of the complexity involved in detecting the lsws particularly in spatial domain in this scenario a comprehensive study is carried out for the first time on the spatial and temporal characteristics of lsws observed in spatial domain over african and southeast asian longitudinal sectors during the year 2011 the observations indicate that these wave structures can be detected a few degrees west of e region sunset terminator and found to grow significantly at longitudes past the sunset terminator the phase fronts of these spatial structures are found to align with the geomagnetic field b lines over a latitudinal belt for at least 5 6 500 600 km centered on dip equator the zonal wavelengths of these structures are found to vary from 100 to 700 km which is consistent with the earlier reports and the epbs were consistently observed when the amplitudes of lsws were grown to sufficient strengths these results would provide better insights on the underlying physical processes involved in excitation of lsws in terms of important roles being played by e region electrical loading and polarization electric fields induced via spatially varying dynamo current due to neutral wind perturbations associated with atmospheric gravity waves

the o okiep copper district namaqualand south africa a review of the geology with emphasis on the petrogenesis of the cupriferous koperberg suite the o okiep copper district is the oldest formal mining area in south africa between 1852 and 2002 the 2 500 km2 area yielded two million tons of copper from 32 mines ranging in ore tonnages from 140 000 to 37 million tons this paper summarizes the calendar of events from the formation of the first primitive crust 1 700 2 000 ma ago to early cambrian times 500 ma ago with particular emphasis on the namaquan grenville orogeny notably the o okiepian episode 1 180 1 210 ma ago of alpine type folding regional granite plutonism and granulite facies metamorphism and the klondikean episode 1 020 1 040 ma ago of open and tight folding and the intrusion of the rietberg granite and the koperberg suite almost all of the copper in the o okiep district occurs in the koperberg suite of which there are 1 700 small bodies that constitute 0 7 of the outcrop area the suite comprises jotunite anorthosite biotite diorite and hypersthenic rocks ranging from leuconorite to hypersthenite and it is one of only two world examples of economic copper mineralization in rocks of the anorthosite charnockite kindred the second example is caraiba brazil high isr and low end for a 1 030 ma intrusion age and high 2 of 10 1 for koperberg rock types indicate a crustal progenitor for the suite and the presence of jotunite suggests a subducted crustal source at ca 40 50 km depth the magmatic sulphide paragenesis in the koperberg suite is chalcopyrite pyrrhotite narrap type ore that in a number of ore bodies has been inverted under upper amphibolite facies conditions to bornite ti free magnetite carolusberg type ore meteoric fluids resulted in supergene cu enrichment in koperberg bodies to 500 m below the pre nama peneplane and lower greenschist facies metamorphism 500 570 ma ago is reflected by inter alia hoits type ore bearing second generation bornite chalcopyrite covellite chalcocite

heat flow in southern australia and connections with east antarctica viscosity and melt generation at the base of ice sheets are critically dependent upon heat flow yet subglacial heat flow is poorly constrained due to the logistical challenges of obtaining boreholes that intersect the bedrock beneath thick ice cover currently continental estimates of antarctic heat flow are derived from geophysical methods that provide ambiguous constraints of crustal heat sources despite their demonstrated importance for accurate predictions of future ice sheet behavior this study pursues an alternative approach by using heat flow measurements from rock units in the coompana province of southern australia which represent the geological counterparts of those beneath wilkes land in east antarctica we present nine new surface heat flow estimates from this previously uncharacterized region ranging from 40 to 70 mw m2 with an average of 57 3 mw m2 these values compare favorably to recent geophysically derived estimates of 50 75 mw m2 for the totten glacier catchment of east antarctica and to the single in situ measurement of 75 mw m2 from the law dome deep ice borehole however they are appreciably lower than the range of 56 120 mw m2 83 13 mw m2 average for the abnormally enriched proterozoic terranes of the central australian heat flow province this study provides the first regional heat flow map of geological provinces formerly contiguous with east antarctica through the application of continent scale heat flow data sets tied to a jurassic plate tectonic reconstruction for gondwana our approach reveals several discrepancies with current heat flow models derived from geophysical methods and provides a more robust analysis of subglacial heat flow using this plate tectonic synthesis as a proxy for east antarctica

the characteristics and generation mechanism of small amplitude and large amplitude esf irregularities observed by the c nofs satellite it is well understood that equatorial plasma bubbles are initiated in the bottomside f region and grow into the topside f region producing equatorial spread f esf irregularities in both bottomside and topside f regions however it is not known whether small amplitude and large amplitude irregularities have the same occurrence pattern and how the generation of small amplitude and large amplitude irregularities is related to the postsunset vertical plasma drift and potential seeding processes in this study we use ion density and velocity data measured by the communications navigation outage forecasting system c nofs satellite during may 2008 july 2014 to derive the longitude month distributions of the occurrence probability of esf irregularities at different amplitudes it is found that the occurrence probability of large amplitude irregularities is well correlated with the postsunset vertical plasma drift and that small amplitude irregularities does not show a clear pattern at low solar activity but is anti correlated with that of large amplitude irregularities at moderate solar activity that is the months and longitudes with high occurrence probability of large amplitude irregularities are exactly those with low occurrence probability of small amplitude irregularities and vice versa esf irregularities are mostly limited below 500 km during low solar activity in 2008 2010 but large amplitude irregularities can reach 700 800 km in altitude during moderate solar activity in 2011 2014 the generation of large amplitude esf irregularities is controlled by the postsunset vertical plasma drift at both low and moderate solar activities in contrast small amplitude esf irregularities at moderate solar activity occur more frequently in the areas where the postsunset vertical plasma drift is small

effects of rainfall and slope on runoff soil erosion and rill development an experimental study using two loess soils runoff generation and soil loss from slopes have been studied for decades but the relationships among runoff soil loss and rill development are still not well understood in this paper rainfall simulation experiments were conducted in two neighbouring plots scale 1m by 5m with four varying slopes 17 6 26 8 36 4 and 46 6 and two rainfall intensities 90 and 120mmh 1 using two loess soils data on rill development were extracted from the digital elevation models by means of photogrammetry the effects of rainfall intensity and slope gradient on runoff soil loss and rill development were different for the two soils the runoff and soil loss from the anthrosol surface were generally higher than those from the calcaric cambisol surface higher rainfall intensity produced less runoff and more sediment for almost each treatment with increasing slope gradient the values of cumulative runoff and soil loss peaked except for the treatments with 90mmh 1 rainfall on the slopes with anthrosol with rainfall duration runoff discharge decreased for anthrosol and increased for calcaric cambisol for almost all the treatments for both soils sediment concentration was very high at the onset of rainfall and decreased quickly almost all the sediment concentrations increased on the 17 6 and 26 8 slopes and peaked on the 36 4 and 46 6 slopes sediment concentrations were higher on the anthrosol slopes than on the calcaric cambisol slopes at 90mmh 1 rainfall intensity increasingly denser rills appeared on the anthrosol slope as the slope gradient increased while only steep slopes 36 4 and 46 6 developed rills for the calcaric cambisol soil the contributions of rill erosion ranged from 36 to 62 of the cumulative soil losses for anthrosol while the maximum contribution of rill erosion to the cumulative soil loss was only 37 9 for calcaric cambisol copyright c 2014 john wiley sons ltd

the influence of groundwater on surface flow erosion processes during a rainstorm surface erosion rates on a disturbed natural soil in a 10 m indoor flume increased by an order of magnitude when a water table developed at a 10 cm depth during simulated rainstorms erosion rate increases did not correlate well with surface hydraulic flow conditions and all significant erosion increases began before the full soil depth was saturated before the water table reached the soil surface and before seepage was possible groundwater influenced erosion processes primarily by increasing unsaturated pore water pressures and decreasing soil shear strength in surface rainflow rather than through the direct entrainment of soil particles by seepage flow there was no unique morphologic expression of the influence of groundwater during a rainstorm subsurface processes influencing surface erosion were detected only by appropriate subsurface instrumentation which included micropiezometers tensiometers and time domain reflectometry erosion rate increases occurred all along the slope and were not concentrated at the base of slope due to a seepage zone soil depth was crucial to determining surface erosion increase it is likely that confusing trends in surface flow erosion rates in past studies have occurred due to unrecorded groundwater development or an emphasis on seepage effects groundwater must be monitored along hillslopes under all moisture and soil conditions in order to avoid misleading and inconsistent conclusions derived solely from surface flow or seepage data copyright 2002 john wiley sons ltd

radiogenic heat production in the continental crust abstract the thermal structure and evolution of continents depend strongly on the amount and distribution of radioactive heat sources in the crust determining the contribution of crustal rocks beneath a superficial layer is a major challenge because heat production depends weakly on major element composition and physical properties such as seismic wavespeed and density enriched granitic intrusives that lie at the current erosion level have a large impact on the surface heat flux but little influence on temperatures in the deep crust many lower crustal rocks that are poor in heat producing elements are restites from ancient orogenic events implying that enrichment of the upper crust was achieved at the expense of deeper crustal levels for the same total heat production concentrating heat sources in an upper layer acts to reduce temperatures in the lower crust thereby allowing stabilization of the crust the present day structure of the crust is a consequence of orogeny and should not be adopted for thermal models of the orogenic event itself this review summarizes information extracted from large data sets on heat flow and heat production and provides estimates of crustal stratification and heat production in several geological provinces analysis of global and regional data sets reveals the absence of a positive correlation between surface heat flow and crustal thickness showing that the average crustal heat production is not constant differences of heat flow between geological provinces are due in large part to changes of crustal structure and bulk composition collating values of the bulk crustal heat production in a few age intervals reveals a clear trend of decrease with increasing age this trend can be accounted for by radioactive decay indicating that thermal conditions at the time of crustal stabilization have not changed significantly for the average crustal thickness of 40 km moho temperatures are near solidus values at the time of stabilization suggesting an intrinsic thermal control on crustal thickness and heat production distribution crustal thickening by more than about 10 km above this mean value induces changes of gravitational potential energy that exceed the strength of the lithosphere for several provinces where strong constraints on heat production are available it is shown that prior to intracrustal fractionation only modest amounts of thickening were needed to generate the conditions of ultra high temperature metamorphism the tell tale signature of crustal heat production is anatectic and metamorphic events that lag the cessation of orogenic activity by several tens of million years crustal heat production is decreasing with time because it is due to the radioactive decay of uranium thorium and potassium its rundown is responsible for the secular cooling of lithospheric roots at a typical rate of about 100 k gy 1 implying complex thermal interactions with a convecting mantle that is not cooling at the same rate

heat flow and heat production in the namaqua mobile belt south africa results of heat flow and heat production surveys at 13 localities in the namaqua mobile belt southern africa are presented twelve stations traverse the 1200 1100 m y old gneissic and metamorphic bushmanland and gordonia subprovinces one station is situated in the richtersveld subprovince a 2000 1730 m y old volcano sedimentary domain mildly affected by the 1200 1100 m y old orogeny surface heat flow in the mobile belt ranges from 39 to 81 mw m 2 and averages at 61 11 mw m 2 surface heat production ranges from 0 8 w m 3 in mafic rocks to extreme values of 6 9 12 3 w m 3 in the springbok district western namaqualand high heat production in the springbok district is associated with a thin tabular granitic intrusive and is not representative of the basement the mean heat production of the remaining stations in the mobile belt is 2 3 1 1 w m 3 linear regression analysis of the heat flow heat production data yields a poor fit correlation coefficient 0 62 and imprecise estimates for the intercept 34 6 mw m 2 and slope 11 3 km the eastern margin of the mobile belt has relatively low heat flow and heat production geothermal geological and gravity data suggest a relative depletion of crustal radiogenic heat production in the region however the average namaqua heat flow is higher than worldwide averages for proterozoic terrains there is no geological or geophysical evidence for recent mantle heating below the namaqua mobile belt suggesting that an elevated crustal radioactive component is largely responsible for the elevated heat flow in this respect the mobile belt is similar to several mid late proterozoic heat flow provinces that are characterized by high average surface heat flow and probably have elevated crustal radiogenic heat input these observations and seismic data suggest that the namaqua crust consists of an upper layer that contributes 40 50 on average to the heat flow and a depleted lower layer the inferred heat flow at midcrustal levels is 50 60 of the average surface heat flow the mobile belt s average surface heat flow is 40 85 higher than that from the basement of the adjacent archaean kaapvaal craton and its inferred midcrustal heat flow is similar to the lowest surface values in the craton heat production data from the kaapvaal craton indicate that its upper crust is not depleted of heat sources while enhanced radiogenic heat input from the namaqua upper crust may account for part of the higher than craton heat flow it cannot account for the full excess consequently a larger equilibrium mantle heat flow related to a reduced lithospheric thickness below namaqualand seems to be required by the new data

thermal evolution of the upper yangtze craton secular cooling and short lived thermal perturbations abstract the upper yangtze craton uyc has stayed in a long term stabilization state its thermal history can be portioned into two parts secular evolutionary trend and short lived thermal perturbations the former is simulated by a two dimensional forward transient thermal model and the latter is discussed by reviewing previous studies the numerical modeling indicates the uyc tended to be cooling as it adjusted to the asynchronous rates of change in the internal radiogenic heat production and in the convecting mantle temperature below the cratonic root the average cooling rate of the uyc has been 58 c ga since the end of archean faster than that of the convecting mantle the surface heat flow presents a decreasing trend from 82 mw m2 at 2 5 ga to 53 mw m2 at present day which constructs the long term evolutionary path the thermal perturbations derived from the occasional tectono thermal events such as mantle plume activity and regional lithosphere extension serves as paroxysmal factors the thermal effects of the emeishan mantle plume were very strong yielding to the maximum heat flow anomaly of 100 mw m2 at the late permian in contrast the influences of regional lithosphere extension during both the early paleozoic period and the early permian middle triassic period were rather weak resulting in a surface heat flow increase of

longitudinal variability of annual changes in activity of equatorial spread f and plasma bubbles global distribution maps of equatorial spread f esf activity for various annual periods were derived from the topside soundings by the ionosphere sounding satellite b iss b in 1978 1980 the esf activity during the northern winter period reveals maximum enhancement at the atlantic longitudes of large westward geomagnetic declination and during the northern summer at the pacific longitudes of large eastward declination on several orbits passing over the region of the esf activity enhancement abrupt depletions of the electron density or equatorial plasma bubbles were observed at the satellite altitude of about 1100 km it has also been found that the background electron density distributions tend to be symmetric with respect to the magnetic equator in the region of the enhanced esf activity and asymmetric in the region of the suppressed esf activity these observations are taken account of by the influence of a transequatorial thermospheric wind upon the suppression of the rayleigh taylor type plasma instability

magnetic declination control of the equatorial f region dynamo electric field development and spread f we have carried out a comparative study of the evening prereversal enhancements in the equatorial f region vertical ionization drift velocities vz over fortaleza 4 s 38 w brazil and jicamarca 12 s 77 w peru two magnetic equatorial stations in the american zone the results show profound dissimilarities in the seasonal trends in the times and widths of the vz prereversal peak which reflect in the spread f characteristics as well at the two stations the dissimilarities are shown to be arising mainly from the difference in the magnetic field declination angles that causes differences in the conjugate e region sunset durations and hence in the f region polarization electric field development rates at the two stations

ultramafic rocks in the centre of the vredefort structure south africa geochemical affinity to bushveld rocks abstract the geochemistry and mineral chemistry of ultramafic rocks in the centre of the vredefort structure have been reinterpreted a detailed examination of previously published major element trace and ree analyses as well as mineral analyses strongly suggests a magmatic origin in contrast to previously postulated tectonic emplacement of mantle material a strong geochemical affinity to ultramafic rocks from the bushveld complex is evident the magmatic nature of the ultramafic rocks in the centre of the vredefort structure has implications for the discussion of the metamorphic history of the vredefprt structure which shows evidence of unusually high and as yet not satisfactorily explained geothermal gradients during peak metamorphism

effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread f we use radar observations from the jicamarca observatory from 1968 to 1992 to study the effects of the f region vertical plasma drift velocity on the generation and evolution of equatorial spread f the dependence of these irregularities on season solar cycle and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts in the early night sector the bottomside of the f layer is almost always unstable the evolution of the unstable layer is controlled by the history of the vertical drift velocity when the drift velocities are large enough the necessary seeding mechanisms for the generation of strong spread f always appear to be present the threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux the geomagnetic control on the generation of spread f is season solar cycle and longitude dependent these effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields the occurrence of early night spread f decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset the generation of late night spread f requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour these irregularities occur most often at 0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes the occurrence of late night spread f is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux

heat flow structure and evolution of the lithosphere of mongolia abstract the geothermal characteristics of mongolia are presented based on heat flow measurements taken in boreholes and at the bottom of lake khubsugul and on heat flow values inferred from 3he 4he isotope ratios in spontaneous spring gases three types of regional heat flow distribution are recognized a narrow linear anomaly in the khubsugul segment of the baikal rift zone an area of regularly varying heat flow controlled by the age of the last tectonomagmatic activity in central mongolia and a zone of anomalously low heat flow in the south mongolian hercynian belt the radiogenic contribution to the terrestrial heat flow is determined a contribution which proved to be different in the southern and northern megablocks of mongolia variations in the thermal regime of the northern central and southern megablocks of mongolia are accounted for by their tectonic evolution

on monthly seasonal longitudinal variations of equatorial irregularity occurrences and their relationship with the postsunset vertical drift velocities 1 monthly variation of global equatorial density irregularity distribution has been obtained with the data taken by rocsat 1 at the 600 km topside ionosphere from march 1999 to june 2004 during high to moderate solar activity years this global distribution of monthly irregularity occurrence rate not only provides the best spatial temporal distribution in existence so far but also serves to fill the gap of irregularity distribution missing over some eastern pacific region where no ground observation is available the 5 1 2 year result of the monthly occurrence pattern indicates a smooth variation across the longitudes contrary to some beliefs that a drastic change in irregularity occurrence pattern has occurred across the eastern pacific longitudes excellent agreement is noted for the current results with aarons 1993 conjectured sketch of the global scintillation distribution furthermore the seasonal longitudinal s l variations of quiet time postsunset vertical drift velocities are found to track closely with the s l variations of irregularity occurrences linear regression analysis between the vertical drift velocity and the irregularity occurrence rate indicates that the vertical drift velocities at three different longitude zones of magnetic declination have good correlations with the irregularity occurrences for all seasons this implies that the averaged postsunset vertical drift velocity is a good indicator for the occurrences of equatorial density irregularities in a longitude region of similar magnetic declination the smooth variation of monthly seasonal longitudinal distributions of the vertical drift velocities that results in the smooth variation of topside density irregularity occurrences implies that the global occurrence pattern of either distribution is controlled by the smooth global variation of the postsunset ionospheric condition related to the magnetic declination effect and the seasonal variation of the ionospheric density level at the dip equator located with respect to the geographic equator there seems little need to include the global distribution of instability perturbation seeds from atmospheric disturbances to complete the global distribution of topside irregularity occurrences

longitudinal structure of the equatorial anomaly in the nighttime ionosphere observed by image fuv 1 the far ultraviolet imager fuv on board the image satellite provides an instantaneous global view of the oi 135 6 nm nightglow with 2 min time resolution because the oi 135 6 nm emission from the nighttime ionosphere is determined by the line of sight integrated plasma density the nightglow images are useful for studying the nighttime low latitude ionosphere globally with the image fuv 135 6 nm observations from march to june 2002 we have examined the global characteristics of the nighttime equatorial anomaly ea by constructing a constant local time map lt map in which pixels within an assigned local time range are extracted from the image fuv nightglow images obtained over an observation period of 3 days or more and are put together to compose a global distribution map of emission intensities at that local time these lt maps show that the development of the ea has a significant longitudinal structure in which peaks and dips of the crest emission intensity and the crest latitude have about 90 longitudinal separation in the longitude range from 0 to 250 although there is not enough data over the american sector this result suggests that the ea longitudinal structure has a prominent zonal component of the wave number 4 the observed longitudinal structure of the nighttime ea could not be fully explained by factors such as the empirical electric field and neutral wind models the geomagnetic declination angle or the displacement of the geomagnetic equator from the geographic equator to explain the observed longitudinal structure of the ea in particular the wave number 4 feature we may need to consider other forcing for example nonmigrating tide originated from the lower atmosphere

radar and satellite global equatorial f region vertical drift model we present the first global empirical model for the quiet time f region equatorial vertical drifts based on combined incoherent scatter radar observations at jicamarca and ion drift meter observations on board the atmospheric explorer e satellite this analytical model based on products of cubic b splines and with nearly conservative electric fields describes the diurnal and seasonal variations of the equatorial vertical drifts for a continuous range of all longitudes and solar flux values our results indicate that during solar minimum the evening prereversal velocity enhancement exhibits only small longitudinal variations during equinox with amplitudes of about 15 20 m s is observed only in the american sector during december solstice with amplitudes of about 5 10 m s and is absent at all longitudes during june solstice the solar minimum evening reversal times are fairly independent of longitude except during december solstice during solar maximum the evening upward vertical drifts and reversal times exhibit large longitudinal variations particularly during the solstices in this case for a solar flux index of 180 the june solstice evening peak drifts maximize in the pacific region with drift amplitudes of up to 35 m s whereas the december solstice velocities maximize in the american sector with comparable magnitudes the equinoctial peak velocities vary between about 35 and 45 m s the morning reversal times and the daytime drifts exhibit only small variations with the phase of the solar cycle the daytime drifts have largest amplitudes between about 0900 and 1100 lt with typical values of 25 30 m s we also show that our model results are in good agreement with other equatorial ground based observations over india brazil and kwajalein

redistribution of u and th in shallow plutonic environments radioactive heat production in the idaho batholith and in the alamosa river stock in the san juan mountains correlates with the degree of hydrothermal alteration of plutons by meteoric groundwater fission track mapping shows that as much as half of the u in whole rock samples of the most intensively altered zone of the alamosa river stock is associated with secondary minerals the hydrothermally altered shallow plutons in the idaho batholith contain significant amounts of u in secondary minerals whereas unaltered deeply emplaced plutons contain virtually all of their u in primary accessory minerals the relative distributions of u and th measured by gamma ray spectrometry the associations of u observed by fission track mapping and a depth dependence in thermally induced hydraulic fracturing suggest a depth dependent geochemical process that could produce an upward increase in the abundance of u and th in batholiths the process adds u and th to chemically receptive secondary minerals during alteration of plutons by convecting groundwater

ionogram signatures of large scale wave structure and their relation to equatorial spread f 1 observations of signatures of the large scale wave structure lsws and subsequent development of equatorial spread f esf by using data from a newly installed digital ionosonde at trivandrum 8 5 n 77 e 0 5 n magnetic dip latitude are presented the lsws signatures are observed using the ionograms with echo directions the satellite traces are shown as echoes from oblique directions when an upwelling associated with lsws is not directly over the ionosonde location when an upwelling is centered overhead and the radius of curvature of the isodensity contours matches the height of reflection signals from various directions can add in phase to enhance the ionospheric reflection coefficient and produce another ionogram signature referred to as multireflected echoes mres it is also shown that the generation of esf is related to the presence of lsws the skymaps also show the presence of small scale wave structures in the bottomsidefregion the investigation also indicates that the range spread f rsf occurs because of the reflections from the embedded smaller scale structures within the large scale upwelling

multi reflected echoes another ionogram signature of large scale wave structure 1 one or more steeply sloped traces have been found in evening ionograms taken from the kwajalein atoll 4 3 n dip latitude during july 1979 their resemblance to the normal f trace suggests that they are echoes that have undergone a large number of reflections from the f layer these multi reflected echoes mres are interpreted in terms of focusing produced by curved isodensity contours in the bottomside f layer which appear to be associated with large scale wave structure lsws that develops in the bottomside f layer mres appear to be another signature for lsws together with satellite traces that appear later in time closer to the onset of plasma structure referred to as equatorial spread f mres are interesting because they display for the data set examined a strong preference to occur during the post sunset rise of the f layer which includes e region sunset how this finding affects our understanding of lsws is discussed

heat production and thermal conductivity of rocks from the pikwitonei sachigo continental cross section central manitoba implications for the thermal structure of archean crust the pikwitonei and sachigo subprovinces of central manitoba provide a cross sectional view of the superior province crust in cross section the upper to mid level crust is composed of synformal greenstone belts surrounded by tonalitic gneisses both of which are intruded by granitoid plutons this crustal structure persists downward into the granulite facies where keels of the greenstone belts can be found to constrain thermal models of the crust we measured heat production and thermal conductivity in 60 rocks from this terrain using standard gamma ray spectrometry and divided bar techniques large vertical and lateral heterogeneities in heat production in the upper crust are evident heat production is high in granites and metasedimentary rocks intermediate in tonalite gneisses and low in the portions of greenstone belts dominated by mafic meta igneous rocks in the deeper granulite facies rocks heat production decreases by a factor of two in the tonalitic gneisses and remains low in the high grad

effect of atmospheric tides on the morphology of the quiet time postsunset equatorial ionospheric anomaly longitudinal wave number four pattern in the magnetic latitude and concentration of the f region peak ion density when measured at a fixed local time in a new comparison of two data sets with observations made by the ogo 4 satellite this pattern is seen to be persistent over many days around equinox during magnetically quiet conditions close to solar maximum but can be dominated by other processes such as cross equator winds during other periods it is found that the longitudinal variability is created by a processes occurring in the dayside ionosphere a longitudinal modulation of the dayside equatorial fountainisthemostlikelydrivingmechanism throughcomparisonwithgwsm 02model it isshownthatthepredictedmodulationofthedaysidethermosphericwindsandtemperaturesat e region altitudes created by non migrating diurnal tides can explain the modulation in the dayside equatorial fountain this result highlights the importance of understanding the temporal variability of tropospheric weather systems on our understanding and possible predictability of the development of the f region ionosphere it may also provide a possible further means of testing our understanding of atmospheric tides on a global scale

time evolution and dynamics of equatorial backscatter plumes 1 growth phase much of our understanding of equatorial spread f phenomena has resulted from vhf radar studies of backscatter plumes i e patterns of backscatter that appear to extend from the bottomside into the topside of the f layer by using altair a fully steerable backscatter radar to map selected plumes repeatedly it was found that the dynamic behavior of plumes can be characterized by a growth and a decay phase the growth phase characteristics described in this paper are found to be generally consistent with equatorial irregularity generation as predicted by the rayleigh taylor and gradient drift instabilities in particular 1 plumes are generated primarily in the local time around f layer sunset 2 plumes develop from local perturbations in plasma density in the bottomside of the f layer 3 plumes develop upward with growth velocities ranging from 125 to 350 m s and 4 backscatter strength increases during upward plume development and decreases when upward plume growth slows or ceases however certain characteristics namely an east west asymmetry in backscatter strength found in the bottomside f layer have been found that suggest key roles played by the eastward neutral wind and by altitude modulation of the bottomside f layer in establishing the initial conditions for plume growth

processed and enhanced gravity and magnetic images over the vredefort structure and their interpretation abstract cryptoexplosion structures are polygonal features which have experienced violent disruption during their formation the vredefort structure is one of the largest known cryptoexplosion structures and the geology is well exposed over its northern half the origin of the violent disruption experienced by the vredefort structure is controversial and many aspects of its history are under intensive study since most of the southern half of the vredefort structure is blanketed by a cover of karoo permian strata geophysical data are essential in any attempt to map the pre karoo geology data sets of the regional gravity and magnetic fields over the vredefort structure have been processed and enhanced with the aid of an image processor the results are presented as a series of images each one enhancing particular attributes of the data sets an interpretation of the geophysical images is presented focusing on the regional geometry and setting of the structure striking features of the geophysical images include a simple concentric geometry and polygonal shape which reflect the distribution of dense and magnetic lithologies within and surrounding the structure the kinematics of the development of a polygonal uplift are discussed inward movement of about seven collar sectors separated by radial faults and uplift of the central sections of each of the sectors may account for the gross polygonal shape pull apart voids formed at kinks in the radial faults might account for the positions of several alkali stocks within the stratified collar of the vredefort structure the enhanced image of the gravity field highlights a se trending gravity low which extends beyond the southeastern quadrant of the vredefort structure this feature forms part of a fundamental nw se trending intracratonic lineament the vredefort axis

ultramafic rocks in the centre of the vredefort structure south africa possible exposure of the upper mantle abstract the rocks in the central region of the vredefort structure are interpreted as lower crust that has undergone uplift of 36 km during the vredefort cryptoexplosion event 2 0 ga ago the outcrops in this central region are mainly high grade leucogranulites interbanded with mafic granulites and supracrustals rocks from a borehole located near the centre of the structure indicate that the core region is underlain by ultramafic rocks which probably represent the upper mantle beneath this region of the kaapvaal craton the main lithologies sampled by the borehole are serpentinized hornblende bearing harzburgite with minor bands of pyroxenite and glimmerite the major and trace element chemistry of these ultramafic rocks is similar to that of fertile oceanic lithosphere mineral chemistry and petrographic data suggest that the vredefort ultramafics are metamorphic rocks which have undergone a complex tectonic and metamorphic history sm nd and rb sr isotopic data together with the field relationships provide some evidence that these rocks are archaean but also that they have been chemically and isotopically altered similar hydrated and chemically altered ultramafic rocks occur in the jamestown ophiolite complex in the barberton greenstone belt accordingly we speculate that the crust mantle transition zone in the kaapvaal craton consists of a zone of hydrated archaean oceanic lithosphere

quiet time equatorial f region vertical plasma drift model derived from rocsat 1 observations 1 we have used five years of measurements on board the rocsat 1 satellite to develop a detailed quiet time global empirical model for equatorial f region vertical plasma drifts this model describes the local time seasonal and longitudinal dependence of the vertical drifts for an altitude of 600 km under moderate and high solar flux conditions the model results are in excellent agreement with measurements from the jicamarca radar and also from other ground based and in situ probes we show that the longitudinal dependence of the daytime and nighttime vertical drifts is much stronger than reported earlier especially during december and june solstice the late night downward drift velocities are larger in the eastern than in the western hemisphere at all seasons the morning and afternoon december solstice drifts have significantly different longitudinal dependence and the daytime upward drifts have strong wave number four signatures during equinox and june solstice the largest evening upward drifts occur during equinox and december solstice near the american sector the longitudinal variations of the evening prereversal velocity peaks during december and june solstice are anti correlated which further indicates the importance of conductivity effects on the electrodynamics of the equatorial ionosphere

age dependence of continental heat flow fantasy and facts abstract extensive use of empirical heat flow age relations in the field of thermal studies indicates that the basic concept of a relation between heat flow and age is deeply entrenched the idea of a thermal time constant and thermal thickness for the lithosphere depends on the validity of a heat flow age relation several thermal and thermo mechanical lithospheric models are constrained by a heat flow age relation a corrected heat flow age relation or a reduced heat flow age relation the theory of plate tectonics provides a physical basis for a heat flow age relation for the oceans reliable heat flow measurements from well sedimented areas of the oceans are known to support it on the contrary the theory of plate tectonics does not support an age relation for the continents which is not well realized it is pointed out that according to the theory of plate tectonics a distinct heat flow profile should characterize a cenozoic mesozoic orogenic belt over the continents and a variety of profiles could be expected on account of several possible interactions at convergent plate boundaries a specific characteristic heat flow value corresponding to a particular age loses meaning and therefore a heat flow age relation or curve becomes conceptually invalid presently available continental heat flow data statistically analysed in a proper manner do not as they should not support an age relation attempts at correcting age dependent heat flow means for crustal radiogenic heat to obtain an age relation for mantle heat flow do not yield meaningful results