a major late devonian early carboniferous hercynian thermotectonic event at the nw margin of the arabian nubian shield evidence from zircon fission track dating zircon fission track zft ages of 17 precambrian samples from deep boreholes and outcrops in southern israel and sinai fall within the range 328 373 ma late devonian early carboniferous single zircon grain age distributions are unimodal with a high chi square probability the age data indicate total resetting of the zft clocks but only partial resetting of coexisting sphenes constraining the temperatures attained to about 225 50 c followed by relatively rapid regional cooling at the times indicated in the study area the lower paleozoic section presently overlying precambrian rocks is limited to cambrian strata up to 300 m thick further stratigraphic evidence for sub carboniferous erosion is preserved only in sw sinai to the east in southern jordan a 2 2 5 km thick lower paleozoic succession is reported despite the lack of stratigraphic evidence in the study area the zft data 1 strongly suggest that an equivalent or thicker section also existed 2 constrain the timing of the erosion to late devonian early carboniferous hercynian and 3 indicate that thermal gradients may have reached 50 c km prior to the uplift erosion event regional stratigraphic evidence indicates that the late devonian early carboniferous event was confined to a relatively narrow belt extending from the gulf of suez area to the vicinity of ne syria and se turkey

magmatic history of red sea rifting perspective from the central saudi arabian coastal plain a newly recognized tertiary dike complex and comagmatic volcanic rocks exposed on the central saudi arabian coastal plain record early stages of magmatism related to red sea rifting intrusive and stratigraphic relationships and new potassium argon dating indicate episodic magmatism from about 30 ma to the present additional stratigraphic and radiometric evidence suggests that limited rift related magmatism began as early as about 50 ma an early phase of crustal extension in the region was accompanied by faulting and graben formation and by dike swarm intrusion the style of extension and intrusion changed at 20 ma localized volcanism and sheeted dike injection ceased and were replaced by the intrusion of thick gabbro dikes this change may mark the onset of sea floor spreading in the central red sea the dikes and volcanic rocks consist of a bimodal mafic felsic suite with transitional subalkaline to alkaline chemistry although no unique petrogenetic model can be developed for the suite the following observations and conclusions have been drawn from the available reconnaissance geochemistry 1 strontium isotopic initial ratios overlap in the range 0 7031 to 0 7047 and are not clearly related to alkalinity or silica content the bimodality and alkalinity of the suite are therefore not products of contamination by the radiogenic precambrian upper crustal granitic rocks exposed in the region 2 several of the evolved rocks rhyolites and comendite show large to extreme negative europium anomalies and heavy rare earth element hree enrichment features that cannot be explained by low pressure crystal fractionation of potential parent magmas an intriguing possibility is that hree enrichments and large negative eu anomalies of some peraluminous rhyolites and granites may result from the complete melting of garnet from middle or lower crustal rocks 3 most of the basalts are light rare earth element lree enriched consistent with derivation from fertile mantle in a continental rift setting however interaction of the mafic melts with lower continental crust cannot be ruled out a model of poly baric mantle melt derivation producing several alkaline subalkaline cycles best explains magmatism in the red sea region differences in the depths and dynamics of mantle melt extraction and transport brought about through changes in crust and mantle structure as the rift and paar developed may account for the transition from mixed alkaline subalkaline bimodal magmatism of the pre 20 ma rift basin to exclusively subalkaline tholeiitic magmatism at the red sea spreading axis and to predominantly alkali basalt volcanism inland within the arabian shield

upwelling asthenosphere beneath western arabia and its regional implications two distinct phases of continental magmatism are evident in western arabia the first from about 30 to 20 ma produced tholeiitic to transitional lavas emplaced along nw trends the second from about 12 ma to recent produced transitional to strongly alkalic lavas emplaced along n s trends the older phase is attributed to passive mantle upwelling during extension of the red sea basin whereas the younger phase is attributed to active mantle upwelling but was facilitated by minor continental extension perpendicular to plate collision the younger magmatic phase is largely contemporaneous with a major period of crustal uplift to produce the west arabian swell after about 14 ma a variety of evidence suggests that the west arabian swell is thermally supported by hot upwelling asthenosphere in contrast to the distinct asymmetry of uplift and magmatism on opposing sides of the red sea basin these processes were symmetric across a n s line marking the central axis of the west arabian swell this axis coincides with two fundamental features the ha il rutbah arch in the north and the makkah madinah nafud mmn volcanic line in the south the symmetry of magmatism is demonstrated by petrochemical evidence that the mmn harrats were derived by greater degrees of partial melting at shallower depths than those harrats lying to the west and east of the mmn line the potential temperature of the asthenosphere is estimated to be about 1436 c beneath the mmn line and about 1354 c beneath the flanking more undersaturated harrats the source of upwelling is either a mantle plume centrally located beneath the west arabian swell or an elongated and extended lobe of hot asthenosphere emanating from the ethiopian mantle plume convective flow may have been channelled along a preexisting regional flexure in the continental lithosphere which concentrated hot asthenosphere beneath the central axis of the afroarabian dome this crest of mantle upwelling underlies the mmn line in the north and the danakil depression and ethiopian rift system in the south it also passes through the red sea basin at the midpoint of an unusual doubly propagating rift system where axial seafloor spreading began 4 5 m y ago the nw trend of the red sea basin was well established by crustal attenuation during the older magmatic phase the pliocene invasion of this basin by a n s zone of mantle upwelling has resulted in seafloor spreading parallel to the preexisting structure along a rift system that has continued to propagate away from its eccentric mantle source in two opposing directions

controls on erosional retreat of the uplifted rift flanks at the gulf of suez and northern red sea the gulf of suez and red sea rifts are currently bordered by large asymmetric uplifts that are undergoing erosion we find that the amount and timing of erosion vary systematically along the strike of the margin and have been controlled by variations in the prerift stratigraphy the prerift strata are composed of cliff forming eocene cretaceous carbonates overlying the easily eroded cretacous cambrian nubian sandstone this lithologic succession promotes scarp retreat of the sedimentary section followed by dissection of the underlying basement the prerift section thins from over 2000 rn at the northern end of the rift to less than 400 rn at its junction with the red sea thus at the northern part of the gulf of suez the nubian sandstone is minimallyexposed and the carbonates form a scarp at the rift border fault farther south undercutting of the carbonates by erosion of the sandstone has resulted in scarp retreat the escarpment cuts diagonally away from the border fault and is over 100 km inland from the border fault at the southernmost gulf of suez the amount of retreat varies inversely with the sediment thickness exposure and erosion of basement are initiated by the retreat of the escarp ment and the depth of erosion as indicated by fission track ages increases with distance from the escarpment these observations are explained by a model in which erosion along the gulf of suez is initiated as rift flank uplift becomes sufficiently large to expose the friable sandstones undercutting of the escarpment and exhumation of basement has been propagating northward and westward for at least 20 m y the average rate of scarp retreat has been 6 km m y and the along strike propagation of the erosion has been 12 km m y the diachronous erosion of the the rift flanks at the gulf of suez highlights the importance of distinguishing between the timing of uplift and of erosion both thermochronometric and stratigraphic data primarily indicate the timing of erosion which may differ significantly from the timing of the uplift that initiates it they must be interpreted carefully to avoid erroneous conclusions about rift tectonics

reply to comment on timing of mantle upwelling evidence for a passive origin for the red sea rift by a v mcguire and r g bohannon

geochemistry and volcanic features of harrat el fahda a young volcanic field in northwest arabia jordan abstract the wadi fill basalt of harrat el fahda was derived from the youngest volcanic activity in northeast jordan and forms one of the most recent harrats of the arabia plate it is characterized by the presence of abundant well preserved pressure ridges and pahoehoe lava structures it was developed due to intermittent eruption from an isolated volcanic center in a form of 3 5 successive basaltic pahoehoe flows the associated pressure ridges are elliptical in shape up to 50 m high and 200 m long the orientation with regard to flow direction is sub parallel along the margins and perpendicular along the center of the flow these ridges were formed by inflation and heaving pressure from below petrographical data show that the basalt is hollocrystalline fine grained and golmeroporphyritic modally three petro types are recognized olivine plagioclase basalt 20 olivine pyroxene basalt 25 and olivine basalt 55 geochemically the three petro types can be classified as alkaline to sub alkaline and termed as alkali olivine basalt they have similar compositional ranges of major and trace elements the magmas may have been derived from low degrees i e 5 9 of partial melting of an enriched garnet peridotite mantle source with limited fractionation and crustal contamination

late cenozoic tectonics and volcanism in the northwestern corner of the arabian plate a consequence of the strike slip dead sea fault zone and the lateral escape of anatolia abstract the study area is the northwestern corner of the arabian plate near the triple junction of anatolian arabia and africa late cenozoic tectonics and volcanism have developed essentially east of the dead sea fault zone dsfz the strike slip boundary of the arabian and african plates including vents situated in front of the bitlis collisional belt isotopic and rare elements data indicate deep mantle sources for volcanism our mapping based on radar imagery and digital elevation models suggests that elongate volcanoes volcanic ridges and linear clusters of adjacent volcanic vents are rooted on tension fractures which are a kilometer or several kilometers in length and infers similar development in depth we have also observed non volcanic tension fractures we have been able to map the northern segment of the dsfz as a continuous but broken fault line the ghab pull apart basin connects with appended faults including the choukhour fault that ends northward in a tail crack feature and the aafrine fault that ends in a tail thrust the amik pull apart basin is bounded in the west by a small but distinct scarp shown by radar imagery our image analysis and field data suggest that the left lateral amanos fault has a reverse throw component in consequence the amanos range has to be regarded as an anticline and the karasu valley as a syncline in the southern part of the study area the regional stress field is mainly strike slip with n020 striking tension fractures east of the amanos fault it becomes transpressive with n120 to n140 striking tension fractures in the north near the triple junction albeit compressional faults and belt environment predominate it is influenced by e w lowering horizontal stress component triggered by the lateral escape of anatolia and remains of the strike slip type associated with n020 striking tension fractures more east of the dsfz in front of the bitlis belt isolated volcanoes e g karacadag elongated n160 show in the rigid arabian crust local weak lines that can be influenced at a distance by the lowering horizontal stress component

lithospheric extension and the opening of the red sea sediment basalt relationships in yemen this paper analyses new field and radiometric age data on the timing of extension sedimentation and magmatism related to the opening of the red sea the first evidence of widespread extension is found in synsedimentary fissures in the fluviatile to shallow marine tawilah formation of cretaceous to early tertiary age the first indication of magmatism is the eruption of alkaline basalts 43 5 21 2 ma on to marine and non marine sandstones of lower to middle tertiary age the lack of an angular unconformity at the sediment basalt contact over a period of 25 myr corroborates a diachronous relationship between the tawilah sandstones and the yemen volcanics these data also indicate that the onset of volcanism in yemen was in the eocene as is the case in ethiopia and saudi arabia a passive rifting model is supported by early extension and sedimentation followed by syn and post tectonic magmatism

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

timing and composition of continental volcanism at harrat hutaymah western saudi arabia abstract harrat hutaymah is an alkali basalt volcanic field in north central saudi arabia at the eastern margin of a large neogene continental intraplate magmatic province lava flow tephra and spatter cone compositions in the field include alkali olivine basalts and basanites these compositions contrast with the predominantly tholeiitic fissure fed basalts found along the eastern margin of the red sea the hutaymah lava flows were erupted through proterozoic arc associated plutonic and meta sedimentary rocks of the arabian shield and commonly contain a range of sub continental lithospheric xenoliths although the lavas themselves show little indication of crustal contamination previous radiometric dating of this volcanic field a single published k ar age 1 8 ma is suspiciously old given the field measurement of normal magnetic polarity only i e brunhes interval 780 ka we report new age determinations on 14 lava flows by the 40ar 39ar laser step heating method all younger than 850 ka to better constrain the time frame of volcanism and major trace and rare earth element compositions to describe the chemical variation of volcanic activity at harrat hutaymah crystal fractionation was dominated by olivine clinopyroxene at a range of upper mantle and crustal pressures rapid ascent and eruption of magma is indicated by the array of lower crustal and lithospheric xenoliths observed in lava flows and tephra modeling suggests 1 7 melting of an enriched asthenospheric mantle source occurred beneath harrat hutaymah under a relatively thick lithospheric cap 60 80 km

fission track lengths in the apatite annealing zone and the interpretation of mixed ages abstract measurements of confined fission tracks in apatites from deep boreholes show that their mean length is reduced and the length distribution becomes progressively broader through the fission track annealing zone at subsurface temperatures of around 100 c and above the length distribution characteristically becomes very broad without a pronounced peak the lengths of the longest tracks remain essentially constant at all stages of natural annealing observed in the boreholes this pattern is similar to that found in laboratory annealing of spontaneous fission tracks in apatite from an outcrop sample of the same formation these observations show that confined track lengths can be used as important indicators of the type of thermal history that a sample has experienced in the temperature zone of increasing track stability the length distributions reported here provide a basis for interpretation of fission track ages that might otherwise be ambiguous an apatite age which results from a uniform slow cooling history will have a broad negatively skewed length distribution while a bimodal distribution provides clear evidence of a two stage history involving partial annealing by a discrete thermal event the apparent fission track age associated with a bimodal length distribution will be a mixed age intermediate between the original age and that of the later event

hopane sterane and n alkane distributions in shallow sediments hosting high arsenic groundwaters in cambodia the presence of elevated as in ground waters exploited for drinking water and irrigation in south east asia is causing serious impacts on human health a key mechanism that causes the mobilization of as in these waters is microbially mediated reductive transformation of as bearing fe iii hydrated oxides and the role of degradable organic matter om in this process is widely recognized a number of different types of om that drive as release in these aquifers have been suggested including petroleum derived hydrocarbons naturally seeping into shallow sediments from deeper thermally mature source rocks however the amount of information on the characteristics of the om in south east asian aquifers is limited here the organic geochemical analyses of the saturated hydrocarbon fractions and radiocarbon analysis of two additional sites in se asia are reported the results show that the om in a given sedimentary horizon likely derives from multiple sources including naturally occurring petroleum the importance of naturally occurring petroleum as one of the sources was clearly indicated by the n alkane cpi of approximately 1 the presence of an unresolved complex mixture and hopane dominated by 17 h 21 h hopanes and sterane distribution patterns the results also indicate that the om in these aquifers varies tremendously in content character and potential bioavailability furthermore the presence of petroleum derived om in sediments at both sites doubles the number of locations where their presence has been observed in association with as rich shallow aquifers suggesting that the role of petroleum derived om in microbially mediated as release might occur over a wider range of geographical locations than previously thought

the timing of uplift volcanism and rifting peripheral to the red sea a case for passive rifting prior to the formation of the red sea the northeastern afro arabian continent had low relief and was largely below sea level from the late cretaceous to the early oligocene the events leading to the formation of the red sea followed the sequence 1 alkaline volcanism and rifting beginning about 30 32 ma affecting a narrow linear zone in the continent 2 rotational block faulting and detachment faulting well underway by 25 ma 3 gabbro and diorite magmatism andesite to rhyolite volcanism and fine grained nonmarine sedimentation in the rift between 20 and 25 ma 4 fine grained marine sedimentation in the rift as the early shelves started to subside in the middle miocene and 5 uplift of the adjacent continents about 3 km and subsidence of the shelves about 4 km between 13 8 and 5 ma the youth of the uplift is suggested by 44 fission track dates on apatites from rocks of the proterozoic arabian shield that range in age from 13 8 to 568 ma the youngest of these ages coupled with the present high relief along the arabian escarpment and published heat flow measurements indicate that 2 5 4 km uplift has occurred in the last 13 8 m y the sequence volcanism rifting followed by uplift leads to our adoption of a passive mantle model for rift origin models that require uplift to create the rift are rejected because of the late uplift we advocate a model of lithospheric extension caused by two dimensional plate stress over those requiring tractional drag at the base of the lithosphere caused by vigorous flow in the asthenosphere it is acknowledged that traction models could explain the observed data but they imply a rigid static lithosphere and seem to require a link between the direction of flow in the asthenosphere and plate motions neither requirement is necessary in the extension model the rift starts with mechanical extension in a narrow zone of lithosphere between 25 32 ma in our model the thinned lithosphere is replaced by upwelling asthenosphere and by rocks from the adjacent deep continental lithosphere which flow into the rift ductile flow of the deep continental lithosphere is accelerated by partial melting as rocks flow upward toward the rift axis once partially melted rocks formerly part of the continental lithosphere join the upwelling asthenosphere resulting in a rapid erosion of the lithospheric mantle beneath the continent near the rift edge the resulting density decrease explains the uplift we think that the red sea began as a consequence of changing plate geometries resulting from the collision of india and eurasia after the collision the segment of the owens fracture zone north of the carlsberg ridge became locked forcing the northeast corner of afro arabia to rotate with the indian plate away from the rest of africa

new k ar ages of basalts from the harrat ash shaam volcanic field in jordan implications for the span and duration of the upper mantle upwelling beneath the western arabian plate the volcanism in the western arabian plate extends from the red sea through the harrat ash shaam system to western syria as far north as the bitlis suture in the taurides the harrat ash shaam volcanic system in jordan consists of northwest trending dikes and a volcanic field that together encompass a width of 220 km in terms of width direction and age of the main volcanic phases the system is similar to the red sea dike belt about 130 new k ar age determinations show that the ages of the harrat ash shaam system dikes and flows range from oligocene to quaternary however there is a distinct gap in the ages between 22 and 13 ma this gap coincides with an apparent decrease in volcanism in the red sea region from around 20 to 12 ma we interpret this 9 m y gap as a quiescent period interrupting the volcanic activity in the region and suggest that from 22 to 13 ma tectonic activity in the arabian plate was mainly restricted to the red sea region a renewal of volcanism along the western margins of the arabian plate at 13 ma was very likely associated with the sinistral movement along the north trending dead sea transform this renewal of volcanism and tectonic activity may reflect the emergence of upper mantle upwelling beneath the western arabian plate at that time

the strontium and oxygen isotopic record of hydrothermal alteration of syenites from the abu khruq complex egypt hydrothermal convection initiated by emplacement of the gabbro syenite complex of abu khruq into the egyptian basement 89 ma ago systematically altered the trace element and isotopic compositions of the syenites the scale of sr transport in migrating solutions was far larger than the scale of sr isotopic equilibration within rocks as a result sr exchange was heterogeneous in the syenites an effect which can be observed on three different scales within grains of a single mineral species heterogeneities are related to grain boundaries and microfractures through which fluids migrated among minerals within rock samples heterogeneities are related to differences in susceptibility to sr alteration among samples within a single unit heterogeneous alteration is apparently related to differences in permeability close to fracture zones during the early stages of alteration radiogenic sr derived from the country rocks was added to the syenites causing small net changes in concentration 5 ppm ave some rb sr mineral isochrons from single rock samples yield the emplacement age because isotopic equilibration of this added sr sometimes occurred within rock specimens however regressions of the whole rock rb sr data yield apparent ages that are about 10 ma too old later stage alteration involved larger changes in whole rock sr concentration 45 ppm ave but had little further effect on the isotopic relationships because the sr was derived from cogenetic gabbros rather than the country rocks alterations of rb sr and sr isotopic compositions are not well correlated with changes in 18o 16o ratio because mineralogy played an important role in decoupling trace element and oxygen isotopic alteration in general the absence of such correlations for whole rock data is not diagnostic of rocks with unaltered trace element and isotopic compositions mineral scale sr isotopic heterogeneities associated with grain boundaries and microfractures may be the most unambiguous evidence of trace element mobility

fission track analysis of basement apatites at the western margin of the gulf of suez rift egypt evidence for synchroneity of uplift and subsidence fifty six apatite fission track ages and 52 horizontal confined track length measurements are reported from precambrian crystalline rocks along the western margin of the gulf of suez egypt ages fall in the range of ca 11 385 m y and older ages often occur within very close geographic proximity to younger ones indicating non uniform uplift the wide range in ages is accompanied by a systematic variation in the distribution of horizontal confined fission track lengths on the basis of apatite fission track ages and their length distributions data fall into three distinct groups group i ages ranging from 43 to 385 m y length distributions are all positively skewed and with decreasing age become progressively broader with shorter mean track length group ii ages ranging from 23 to 31 m y length distributions are negatively skewed with either a distinct tail or a small peak of short tracks group iii ages ranging from 11 to 20 5 m y length distributions are al unimodal narrow negatively skewed and have the longest mean lengths among samples studied apatite ages from groups i and ii are interpreted as mixed ages as a result of cooling during uplift from different levels within the apatite partial track annealing zone ages from group iii are interpreted as cooling ages due to uplift from the apatite total track annealing zone with minor partial annealing correcting the ages of the two oldest samples in this group for track length reduction yields ages of21 2 2and23 1 5m y it is proposed that the onset of rift flank uplift in the gulf of suez northern red sea area occurred between 21 and 23 m y ago fission track analysis in combination with subsidence data from the gulf of suez basin indicate that commencement of basement uplift postdate the start of rifting and is interpreted as evidence for passive rifting at the gulf of suez furthermore this uplift is contemporaneous with and is directly related to the process of extension and subsidence at the gulf of suez

comment on structural control of young basaltic fissure eruptions in the plateau basalt area of the arabian plate northeast jordan by guba and mustafa 1988

propagation of gravity waves and spread f in the low latitude ionosphere over tucuman argentina by continuous doppler sounding first results results of systematic analysis of propagation directions and horizontal velocities of gravity waves gws and spread f structures in low latitude ionosphere magnetic inclination 27 in tucuman region argentina are presented measurements were carried out by multipoint continuous doppler system during 1 year from december 2012 to november 2013 it was found that meridian propagation of gws dominated and that southward propagation prevailed in the local summer oblique spread structures observed in doppler shift spectrograms and associated with spread f propagated roughly eastward at velocities from 70 to 180 m s and were observed at night from september to march the velocities were computed for 182 events and the azimuths for 64 events continuous doppler sounding makes it possible to analyze more events compared to optical observations often used for propagation studies since the measurements do not depend on weather

a climatology of f region gravity wave propagation over the middle and upper atmosphere radar by observing the ionospheric f region simultaneously in multiple beams with the middle and upper atmosphere radar we have been able to track the passage of gravity waves and measure their propagation characteristics here we develop a climatology of wave propagation based on the observation of 58 daytime experiments conducted during 1986 1994 the thermosphere seems to be continuously swept by waves detectable by an incoherent scatter radar these waves generally come for hours on end from a consistent or slowly varying direction which can be any direction on a given day statistically the waves show a moderate preference for southward travel with this preference being reduced or shifted to southeastward travel during disturbed times on average the horizontal phase trace speed remains near 240 m s for all periods inspected 40 130 min this speed matches the behavior expected for lossless waves with 150 200 km vertical wavelength we find small variability in this relation for different times of day seasons solar and magnetic conditions and directions of wave travel though waves on disturbed days seem to travel moderately faster on solar minimum mornings

accelerated transformation of organic matter below the silica transition zone in immature sediments from the japan sea abstract notable compositional changes of organic matter are observed below the silica transition zone in thermally immature sediments the increase of bitumen ratio and hopane and sterane isomerization parameters indicate an acceleration of the kinetics of the chemical reactions which transform the organic matter this phenomenon is probably due to the numerous mineral and textural changes induced by the transformation of amorphous biogenic silica into crystalline authigenic silica

uplift and extension at the gulf of suez indications of induced mantle convection reconstruction of tectonic movements since the initiation of the gulf of suez rift indicates that there has been 25 27 km of extension the uplift bordering rift indicates that lithosphere heating greatly exceeds that producible by uniform lithosphere extension i propose that small scale convection induced by the rifting augments the heating introduced by extensional rifting and produces the broad uplifts flanking the rift

new data on the late cenozoic basaltic volcanism in syria applied to its origin abstract new data on geology and 21 k ar dates of the late oligocene quaternary basalts in syria combined with analysis of the new and previous data are used to reconstruct the volcanic history and relations between it and tectonic events volcanism began at the end of oligocene 26 24 ma and was concentrated in the late oligocene early miocene along a n trending band which stretches from the jebel arab harrat ash shaam up to kurd dagh and southern turkey activity waned in the middle miocene 17 12 ma but was resumed in the same band in the tortonian and increased in the messinian and early pliocene 6 3 4 ma when volcanism spread to the shin plateau and its coastal extension after a brief hiatus 4 3 5 ma volcanism became still more intensive and spread from the n trending band to the east into the northern margin of the mesopotamian foredeep and to the west into the dead sea transform zone additional eruptions continued into the holocene volcanism lasted 25 million years in the jebel arab highland and 15 million years in the aleppo plateau the long duration of volcanism in the same parts of the moving arabian plate and absence of records of one way migration of the activity mean that the magmatic sources moved together with the plate i e they were situated within the lithosphere mantle coincidence of the tectonic and volcanic stages of the arabian plate development proves that volcanic activity depended on the geodynamic situation caused by the plate motion situated within the lithosphere magmatic sources within this transverse band were possibly caused by thermal and deforming influences of the asthenospheric lateral flow moved laterally from the ethiopia afar deep superplume

temporal and spatial relations between large scale fault systems evidence from the sinai negev shear zone and the dead sea fault abstract in the major zones of crustal deformation within the arabia sinai nubia plates the interactions between the sinai negev shear zone snsz and the dead sea fault system dsf shed light on the interplay between neighboring large scale fault systems the snsz is composed of several e w to ene wsw trending mainly normal and dextral strike slip faults that are tens to hundreds of kilometers long these faults form a 120 km wide shear zone in the sinai sub plate on reaching the plate bounding dead sea fault system dsf individual lineaments of the snsz are observed in the arabian plate offset left laterally by 105 km which is the total estimated offset of the dsf in this contribution we review the geologic setting of the snsz and its complex relations with the dsf in light of newly obtained age strain analyses for this we use in situ u pb geochronology in conjunction with twin analysis of syn faulting calcite from both systems the results indicate that the deformation along the snsz initiated in the campanian maastrichtian or earlier as the oldest dates are 73 71 ma the main phase of fault activity began in the late oligocene early miocene 27 22 ma as documented by numerous dates that were obtained along several lineaments of the snsz the activity continued until 10 ma after which no direct ages have been obtained the dominant phase of activity along the snsz at 27 22 ma preceded the timing of initiation of lateral faulting along the dsf at 20 18 ma by a few myr for the overlapping period of activity between 20 and 10 ma episodes of fault activity along the snsz followed by episodes of fault activity along the dsf moreover dominant episodes of activity along one fault system were associated with a decrease in activity along the other system the temporal relations between the snsz and dsf highlight the possibility that these fault systems are mechanically interrelated but the exact mechanism for this fault interaction needs further study we consider the paleo strain or paleo stress that control the evolution and style of the snsz and assess them at the central sinai negev region during the cenozoic we show that the formation of new plate boundaries at the region i e the red sea suez rift and the dsf affected the strain field within the snsz the proximity of the two systems indicates that the dsf related stress originated within the snsz and possibly caused structural and style changes in the latter system syn faulting calcite twins analyses within the snsz show pronounced spatial and temporal variations of the principal strain directions between and along individual faults this observation demonstrates that the imposed stress within the central sinai negev were not uniform over time the high angle 70o between the traces of the snsz and the direction of the dsf related maximum shortening likely suppressed the dextral motion along the snsz post 20 ma field evidence u pb dates and recent seismicity shows that the current snsz is a long lived structure that has been active during the miocene alongside the dominantly dsf and may still be sporadically active today

timing of mantle upwelling evidence for a passive origin for the red sea rift mantle xenoliths from western saudi arabia some 220 km east of the red sea margin indicate temperatures as high as 900 c in the mantle at about 40 km depth beneath an area of the arabian shield where surface heat flow is lower than the world average this suggests that there has been a large increase in the mantle temperature that has not had time to equilibrate at the surface the amount of uplift and the difference between the observed xenolith temperature and that obtained by projecting the surface heat flow to depth suggests that the lithosphere has been thinned by 30 to 100 km to its present calculated thickness of about 80 km calculations of the time necessary for thermal reequilibration indicate that the lithospheric thinning probably occurred less than 20 m y ago so it postdates rifting which started about 30 ma if there was a prolonged upwelling of deep mantle material resulting in a thinner lithosphere prior to rifting there should have been enough time for some reequilibration at the surface and the observed heat flow should be higher over the broad area of uplift adjacent to the red sea our calculations are consistent with a postrift age of uplift adjacent to the red sea as determined from regional geologic evidence and fission track ages on apatites from shield rocks the red sea appears to have begun with alkaline volcanism on the arabian shield followed by rifting uplift and lithospheric thinning adjacent to the red sea rift began 5 10 m y after rifting this suggests that the red sea is a passive rift that formed because of two dimensional plate motions rather than as a consequence of mantle upwelling a possible cause for the stress in the plates might have been the change of plate motions in the indian ocean that resulted from the collision of india with eurasia

uplift and cooling pathways derived from fission track analysis and mica dating a review definition of time and temperature pathways for episodes of lithospheric movement provides not simply a chronological framework for crustal dynamism but also permits estimation of rates of crustal cooling and uplift important aspects of such pathways are the constraints provided for timing of both plate collision and lithospheric extension classically rb sr and k ar mica ages have been used to delineate rates of cooling and exhumation in the central alps by comparison of the measured ages with estimates of temperatures for the retention of daughter isotopes similar use of fission track apatite and zircon ages has provided data for lower temperature intervals 100 and 200 c respectively recent detailed studies of the annealing kinetics of fission tracks in apatite yield more precise estimates of cooling rate and permit predictive modelling of age and length parameters for given t t pathways in continental collision zones fast episodic uplift in the western alps can be contrasted with contemporaneous monotonic uplift in the central alps additional examples may be seen in the tibet himalayan orogenic belt in the southern alps of new zealand and in the bolivian andes in divergent teceonic regimes the record of uplift associated with rifting has been recorded by fission track ages in the southeastern australian margin and around the red sea in an intra plate tectonic setting our current fission track reconnaissance study in the british isles is revealing a hitherto unrecognised thermal history for crystalline and sediment alike

silica diagenesis i solubility controls abstract the diagenetic sequence of silica is examined in terms of several thermodynamic and kinetic concepts the relationship between solubility and surface area or particle size is sufficient to explain simple opal a opal ct quartz transformations suggesting that the role of temperature and other physical parameters may not be as critical as previously thought complexation and adsorption in an impure system when added to the model allow for possibilities of opal a transformation directly to quartz of clay and zeolite formation from an opaline silica source and of variations in silica transformation rates due to presence of impurities in the system

fission track evidence on the initial rifting of the red sea two pulses no propagation fission track analyses indicate that the red sea initially opened simultaneously along its entire length two distinct pulses of uplift and erosion characterized the early stages of rifting in the red sea throughout egypt and in southwestern saudi arabia the first pulse began at 34 million years ago ma the second pulse began in the early miocene 21 to 25 ma and marked the start of the main phase of extension these data support a rigid plate model for continental extension these results also indicate that the initiation of rift flank uplift and therefore rifting and volcanism occurred nearly simultaneously this conflicts with classical models of active and passive extension that predict sequential development of these features

growth destruction and facies architecture of effusive and explosive volcanics in the miocene shama basin southwest of saudi arabia subaqueous subaerial volcanism in a lacustrine setting abstract this paper presents for the first time detailed stratigraphical and petrographical analyses of the harrat shama volcanic basin hsvb of miocene age in sw saudi arabia this basin is filled by abundant volcanics intercalated with fluvio lacustrine sedimentary successions these successions are characterized by a syneruptive intereruptive cycle which results from the intercalation periods of volcanics and volcaniclastic sedimentation along with periods of fluvial incision two depositional sequences showing an overall fining upward trend are preserved within the hsvb the first comprises hyaloclastites zeolite bearing bedded tuffs and bedded accretionary lapilli tuffs interpreted as deep lake whereas the second is made up of extensive pumiceous pyroclastic flows peperitic breccias and basaltic lava flows which are in turn capped by siliciclastic deposits of lacustrine deposits the passage between two sequences is defined by lateral variations of the lithofacies and textural features reflecting a change in paleogeography the fining upward volcaniclastic deposits of the hsvb sequence are interpreted to represent the sedimentation pattern induced by tectonic subsidence with the influence of volcaniclastic sediment input indicating well established proximal distal relationship hsvb was evolved through three stages including pre syn and post caldera stages the first two stages correspond to proximal aggradational syn eruptive event whereas the latter stage refers to distal degradational inter eruptive event these stages overlap in time as shown by the alternation of explosive effusive and their resedimented deposits reflecting diverse eruptive sequences formed by different fragmentation processes the difference in the latter coupled with the variability in the magma water interaction and the nature of substrate are responsible for such diversity resulting in progressive environmental changes from subaqueous to subaerial regime from bottom to top the development of such contrast in the depositional sequences reflects variation in the sediment flux and subsidence rate during the evolution of the hsvb

the afro arabian rift system an overview abstract the afro arabian rift system is reviewed beginning with the dead sea transform and gulf of suez in the north followed by the gulf of aden and red sea and ending with a brief mention of rifting through eastern and southern africa a consistent interpretation is obtained for geophysical data from the gulf of aden and red sea and geological data for the dead sea transform suez graben and red sea and gulf of aden margins geophysical data are used to estimate the locations of the ocean continent boundaries in the northern red sea these are found to coincide when the total 107 km shear along the dead sea is restored the red sea is therefore reconstructed in stages beginning with the 45 km post miocene shear and 62 km early miocene shear along the dead sea transform followed by estimates for extension in the early red sea suez graben when this is done there is a remarkable alignment of various features revealed on landsat tm imagery for both sides of the northern red sea north south differences in the red sea and west east differences hi the gulf of aden are discussed and found to be best explained by a propagating rift model

investigating the p wave velocity structure beneath harrat lunayyir northwestern saudi arabia using double difference tomography and earthquakes from the 2009 seismic swarm 1 in 2009 a swarm of more than 30 000 earthquakes occurred beneath the harrat lunayyir lava field in northwest saudi arabia this event was just one of several seismic swarms to occur in this region over the past decade surface deformation associated with the seismicity modeled in previous studies using interferometric synthetic aperture radar insar data is best attributed to the intrusion of a 10 km long dyke however little is known about the velocity structure beneath harrat lunayyir making assessment of future seismic and volcanic hazards difficult in this study we use local double difference tomography to generate a p wave velocity model beneath harrat lunayyir and to more precisely locate earthquakes from the 2009 seismic swarm a pronounced fast velocity anomaly centered at 15 km depth with a shallower extension to the n nw is interpreted as an area of repeated magmatic intrusion the crust surrounding the fast intrusion is slower than that suggested by broader scale models for the arabian shield the largest magnitude events occurred early in the swarm concentrated at shallow depths 2 8 km beneath northern harrat lunayyir and these events are associated with the dyke intrusion later deep earthquakes 15 km beneath the southern end of the study region as well as a group of intermediate depth events connecting the shallow and deep regions of seismicity occurred these later events likely represent responses to the local stress conditions following the intrusion our results are unique since harrat magma systems are rarely imaged and our observations coupled with the seismic history in this region suggest that future volcanic intrusions beneath harrat lunayyir are likely

an empirical model of the earth s horizontal wind fields hwm07 1 the new horizontal wind model hwm07 provides a statistical representation of the horizontal wind fields of the earth s atmosphere from the ground to the exosphere 0 500 km it represents over 50 years of satellite rocket and ground based wind measurements via a compact fortran 90 subroutine the computer model is a function of geographic location altitude day of the year solar local time and geomagnetic activity it includes representations of the zonal mean circulation stationary planetary waves migrating tides and the seasonal modulation thereof hwm07 is composed of two components a quiet time component for the background state described in this paper and a geomagnetic storm time component dwm07 described in a companion paper

comment on topographic and volcanic asymmetry around the red sea constraints on rift models by t h dixon e r ivins and j f brenda

structure of yemeni miocene dike swarms and emplacement of coeval granite plutons abstract dike swarms in the yemeni sector of the eastern margin of the red sea basin have been mapped and sampled the greatest concentration of mafic dikes occurs along the tihama coastal escarpment zone less profuse swarms lace the plateau interior the escarpment zone also hosts microgranitic dike swarms related to a chain of closely spaced miocene granite plutons dolerite irruption overlapped in time and space with this plutonism southern red sea basin evolution commenced with flood basalt eruptions upon the late proterozoic arabian craton subsequent continental rifting and crustal fissuring focussed dike swarms along a zone of coeval anatectic granites that largely blocked further flood basalt eruption immediately following this crustal fissuring diking episode severe crustal stretching and thinning led to block faulting and tilting eventually rupture near the rift axis initiated sea floor spreading the resulting crust beneath the outer parts of the red sea basin is new igneous material that has generated two layer neo continental crust

the influence of the sabatayn evaporites on the hydrocarbon prospectivity of the eastern shabwa basin onshore yemen the shabwa basin is the northeastern extension of the marib al jawf shabwa system of mesozoic grabens located onshore in the republic of yemen an evaporitic sequence with an estimated maximum depositional thickness of 300 metres was deposited during the tithonian it is designated the sabatayn formation and exerts significant control on most of the play elements in the principal hydrocarbon play systems anticipated in the northeastern part of the basin migration of hydrocarbons from pre salt source rocks into intra and post salt reservoirs is restricted by the evaporites localised heat flow perturbations introduced by the salt increase the maturity of post salt source rocks post and intra salt reservoirs are structured by listric faulting on a salt detachment salt pillowing due to post depositional loading by local salt dissolution and by late folding due to gravity sliding of the post salt section on a salt detachment early dissolution and reprecipitation of salt is responsible for occlusion of porosity in intra salt clastic reservoirs

possible evidence of gravity wave coupling into the mid latitude f region ionosphere during the seek campaign on five of eight observation nights during the 1996 seek sporadic e experiment over kyushu campaign japan unusual wave like structures were imaged in the 630 nm thermospheric nightglow emis sion four of these events were observed to travel to wards the southwest providing new evidence in support of recent theories describing the coupling of medium scale gravity waves into the mid latitude f region iono sphere available ionosonde data and the visual charac teristics of the wave structures indicate no association

tectonic development of passive continental margins of the southern and central red sea with a comparison to wilkes land antarctica abstract the continental margins of the southern and central red sea and most of wilkes land antarctica have bulk crustal configurations and detailed structures that are best explained by a prolonged history of magmatic expansion that followed a brief but intense period of mechanical extension extension on the red sea margins was spatially confined to a rift that was 20 30 km in width the rifting phase along the arabian margin of the central and southern red sea occurred 25 32 ma ago primarily by detachment faulting at upper crustal levels and ductile uniform stretching at depth rifting was followed by an early magmatic phase during which the margin was invaded by dikes and plutons primarily of gabbro and diorite at 20 24 ma after the crust was mechanically thinned from 40 km to 20 km we infer continued spreading after that in which broad shelves were formed by a process of magmatic expansion because the offshore crust is only 8 15 km thick including sediment and seismic reflection data do not depict horst and graben or half graben structures from which mechanical extension might be inferred the wilkes land margin is similar to the arabian example the margin is about 150 km in width the amount of upper crustal extension is too low to explain the change in sub sediment crustal thickness from 35 km on the mainland to

comment on timing of mantle upwelling evidence for a passive origin for the red sea rift by a v mcguire and r g bohannon

high ti continental tholeiites from the aznam trough northwestern saudi arabia evidence of abortive rifting in the embryonic stage of red sea opening abstract the aznam trough is a nw trending asymmetric graben on the northern saudi arabian coast of the red sea miocene or younger high ti tholeiitic basalts are exposed in the northern part of the trough these aznam basalts contain microphenocrysts of altered olivine calcic plagioclase and clinopyroxene with subordinate amounts of ilmenite and orthopyroxene in a cryptocrystalline groundmass a minor xenocryst xenolith assemblage consists of quartz sieve textured plagioclase and a variety of crustal rock fragments the aznam basalts have tio2 contents 3 0 elevated 87sr 86sr ratios 0 70486 0 70546 feo mgo ratios 2 0 and mg numbers between 47 and 50 they are compositionally and isotopically more evolved than tholeiites morb from the red sea trough minor crustal contamination of the initial basaltic magmas is shown by the elevated sr isotopic composition and enrichment in some lil components major element modeling indicates that the aznam basalts can be generated by fractionation of the major phenocryst phases out of typical red sea morb trace element distributions are mostly consistent with this conclusion with the exception of minor crustal contamination at aznam the aznam basalts are compositionally almost identical with high ti basalts formed in abortive volcanically dormant rifts in iceland apparently the same process of magmatism and rift jumping that occurred in iceland also occurred and may still be occurring in the northern red sea region as a short lived embryonic rifting that is a precursor to sea floor spreading in the red sea trough

magmatism of the eastern red sea margin in the northern part of yemen from oligocene to present the northern part of yemen during the last 30 ma has been the site of an intense magmatic activity which can be divided into three main episodes the first episode lasted from 30 to 18 ma and was characterized by two climaxes huge flood basalt eruptions between 30 to 26 ma were succeeded by massive ignimbrite sheet deposits and intrusion of silicic subvolcanic masses 22 to 20 ma ago contemporaneously along the present day western margin of the yemen plateau a basaltic dike swarm was emplaced additionally alkaline and peralkaline granites were intruded at the end of the first climax and throughout the second after a long quiescence magmatic activity occurred again in late miocene time about 10 ma with extrusion of lava flows in scattered areas e g al harf wadi as sirr maswar al hada jabal an nar the third magmatic episode has been concentrated in three well defined areas it began about 6 5 ma ago in the dhamar rada area and later in the san a amram and sirwah marib areas new chemical and isotopic data on the magmatic products of north yemen indicate that extensive crustal contamination together with simple crystal fractionation processes have been operating during the magmatic evolution the most primitive products of each of the three episodes share isotopic and petrological features suggesting a similar mantle source isotope geochemistry indicates an important asthenospheric component in the mantle source for the magmas of all three episodes finally a comparison between the coeval igneous rocks of the yemen and ethiopia plateaus is attempted

tectonic configuration of the western arabian continental margin southern red sea the young continental margin of the western arabian peninsula is uplifted 3 5 to 4 km and is well exposed rift related extensional deformation is confined to a zone 150 km wide inland of the present coastline at 17 to 18 n and its intensity increases gradually from east to west extension is negligible near the crest of the arabian escarpment but it reaches a value of 8 to 10 in the western asir a highly dissected mountainous region west of the escarpment there is an abrupt increase in extensional deformation in the foothills and pediment west of the asir about 40 km inland of the shoreline where rocks in the upper plate of a system of low angle normal faults with west dips are extended by 60 to 110 the faults were active 23 to 29 ma ago and the uplift occurred after 25 ma ago tertiary mafic dike swarms and plutons of gabbro and granophyre 20 to 23 ma old are concentrated in the foothills and pediment as well the chemistry of the dikes suggests 1 fractionation at 10 to 20 kbar 2 a rapid rise through the upper mantle and lower crust and 3 differentiation and cooling at 1 atm to 5 kbar structural relations between dikes faults and dipping beds indicate that the mechanical extension and intrusional expansion were partly coeval but that most of the extension preceded the expansion a tectonic reconstruction of pre red sea afro arabia suggests that the early rift was narrow with intense extension confined to an axial belt 20 to 40 km wide steep moho slopes probably developed during rift formation as indicated by published gravity data two published seismic interpretations and the surface geology

propagation directions of gravity wave patterns observed in oh ccd images during the seek campaign oh airglow about 87 km altitude was observed with a ccd imager at shigaraki 34 9 n 136 1 e in august 1996 during the seek campaign period from nine night observations the characteristics of the gravity wave modulation of the oh airglow layer were extracted and analyzed the distributions of the horizontal wavelength observed wave period and horizontal phase speed were 10 30 km 5 30 min and 20 60 m s respectively the horizontal propagation direction was mainly north eastward this preferential direction is similar to previous mu radar observations of mesospheric gravity waves 68 80km in summer months but different from the propagation direction of gravity waves expected from fai theories and observations in the e region

two phases of cretaceous tertiary magmatism in the eastern desert of egypt paleomagnetic chemical and k ar evidence abstract paleomagnetic and radiometric data confirm the existence of two phases of igneous activity in the late mesozoic and cenozoic history of eastern egypt in the mid to late cretaceous the earlier and more extensive episode produced the wadi natash alkaline basalts and numerous small trachytic intrusions the ring complexes of abu khrug and gebel el kahfa were also emplaced at this time the mean paleopole position for the intrusive rocks is at 65 3 n 111 2 w a 95 11 4 31 sites chemical analyses of the trachytes show that they are enriched in nb zr and y and depleted in sr ba cr and ni suggesting either prolonged fractionation or limited partial fusion the second phase of activity during oligo miocene time is represented by small tholeiitic basalt flows on the red sea coast and along the nile valley the mean paleopole position for the flows is at 68 2 n 101 5 e a 95 27 8 3 sites the wide scatter is interpreted as reflecting secular variation the chronological and chemical data are used with studies of sedimentary formations coeval with the igneous rocks to apply a general model of continental rifting to the northern red sea the earlier alkaline phase of igneous activity is related to regional uplift while the second tholeiitic phase is associated with widening of the rift valley

evolution and mineralization of the arabian nubian shield edited by s a tahoun pergamon press 1979 1980 vol 1 186pp s30 vol 2 205 pp 30 vol 3 164 pp 30 vol 4 168 pp 34

nighttime medium scale traveling ionospheric disturbances detected by network gps receivers in taiwan 1 the nighttime medium scale traveling ionospheric disturbances mstids are detected by the network gps receivers in taiwan for the first time the two dimensional mapping technique a spatial resolution of 0 05 0 05 in latitude and longitude with 5 5 pixels smoothing is applied on the data of tec perturbations tecp and gps phase fluctuations tec min the results show that the mstids move southwestward to latitude of 20 5 n with a horizontal velocity between 100 and 160 m s and a wavelength of about 500 km the wavefronts of the mstids are aligned along the northwest southeast direction furthermore the greater tec min values are corresponding to the wave peak and trough of tecp this coincidence indicates that the mstids play an important role for the generation of f region irregularities in the low latitude ionosphere

miocene magmatism of sinai related to the opening of the red sea extension associated with the initial early miocene stages of opening of the red sea resulted in intrusion of a widespread system of dikes and smaller bodies primarily along the northeastern margin of the red sea gulf of suez axis dikes some up to more than 800 km in length were emplaced dominantly parallel to the red sea gulf of suez from the sinai peninsula to yemen intrusive rocks are mainly basaltic in composition but minor granophyres are also present in the sinai this magmatic event is about 20 m y old dikes of the southern and southeastern sinai crop out in precambrian terrane in the central and northern sinai they occur in phanerozoic terrane where they may be associated with linear grabens and cryptovolcanic features basaltic dikes of the sinai underwent variable degrees of alteration alteration phases include seriate quartz smectite chlorite and serpentine x ray diffraction and petrographic analysis indicate that in spite of extensive alteration primary minerals still control the major element compositions of the rocks basalts are tholeiitic in composition with sio2 48 5 to 50 and na2o k2o 3 to 3 5 rb and sr concentrations are probably dominated by alteration and by introduction of secondary material primarily carbonate zr tio2 which is relatively unchanged during alteration substantiates that the basaltic rocks are subalkaline initial 87sr 86sr determined after leaching of samples is approximately 0 7043 0 7063 much higher than red sea axial trough basalts 0 703 we infer that these sinai basalts equilibrated at depths of 35 50 km possibly within an enriched mantle whether the main trough of the red sea is underlain by extended and modified continental crust or by oceanic crust is controversial since miocene dikes were intruded along both coasts but primarily the saudi arabian coast of the red sea gulf of suez axis in a zone up to 150 km wide they may also underlie the main trough of the red sea and result at least partially in the discontinuous magnetic and gravity anomalies observed there possibly the abundance of dikes beneath the main trough is much greater than adjacent to the red sea giving rise to properties intermediate between those of continental and oceanic crust downwarping and widespread intrusion of dikes along the red sea 18 26 m y ago probably signified crustal dilation and the initiation of a continental rift because tholeiitic basalts of the sinai are higher in 87sr 86sr than red sea axial trough basalts we infer that the conditions of their origin must also be very different we suggest that the sinai basalts may have been generated within but near the base of subcrustal continental lithosphere perhaps indicating thermal thinning of lithospheric mantle above upwelled asthenosphere associated with continental rifting this inference if correct would indicate that the lithosphere was at least 35 50 km thick during the early miocene phase of rifting but possibly not much thicker since dikes farthest from the red sea are apparently identical in composition to those closest asthenospheric upwarping must have been broad enough that all magmas were derived from approximately the same depth in the yemen ethiopia areas volcanism began earlier about 30 m y ago and was much more voluminous than elsewhere along the red sea gulf of suez axis suggesting the presence of underlying mantle upwelling accompanying rifting of the red sea in spite of differences in age and volume the presence of large volumes of tholeiites among the miocene basalts of the yemen ethiopia areas suggests that the lithosphere was similarly thinned along the entire length of the red sea

40ar 39ar age and duration of tholeiitic magmatism related to the early opening of the red sea rift the early opening of the red sea rift is accompanied by tholeiitic magmatism stretching at least 1700 km along the western coast of saudi arabia and consisting of thick gabbroic dykes dense dyke swarms plutons and discrete lava flows whereas the conventional k ar measurements have furnished a wide variety of ages the 40ar 39ar analyses presented here giving 17 plateau ages display a pronounced cluster of ages from 24 to 21 ma such a short lived magmatic event has been suggested for other continental rifts

have wet and dry precambrian crust largely governed cenozoic intraplate magmatism from arabia to east africa to explain cenozoic continental volcanism between arabia and east africa the existing model infers that a plume impinged beneath ethiopia between 30 ma and 20 ma and volcanism extruded within a 1000 km radius because relative motion of the afro arabian plate was about northeast in the last 120 ma we infer that at 84 ma a plume originated from the core mantle boundary impinged beneath nubia arabia and is now under the tanzania craton this plume caused uplift afro arabian swell and magma under plating after fyfe s idea 1992 the conceptual model proposed herein suggests that following plume impact there was in nubia arabia only intrusion of mafic dykes because the crust was largely unprocessed wet at about 50 ma the plume was under ethiopia and coeval volcanism extruded because the crust was highly recycled dry in zaire burundi and tanzania volcanism is explained to be coeval with the arrival of the plume because there also the crust is recycled in arabia and yemen ethiopia continental flood basalts younger than 30 ma formed because lithospheric extension along the red sea gulf of aden was the cause of or the result of plume s probably originated from the upper mantle

a type granite and the red sea opening abstract miocene oligocene a type granite intrudes the eastern side of the red sea margin within the zone of extension from jiddah saudi arabia south to yemen the intrusions developed in the early stages of continental extension as arabia began to move slowly away from africa around 30 20 ma within the narrow zone of extension silicic magmas formed dikes sills small plutons and extrusive equivalents in the jabal tirf area of saudi arabia these rocks occur in an elongate zone consisting of late precambrian basement to the east which is gradually invaded by mafic dikes the number of dikes increases westward until an igneous complex is produced parallel to the present red sea axis the jabal tirf igneous complex consists of diabase and rhyolite granophyre sills 20 24 ma although these are intrusine intrusive rocks their textures indicate shallow depths of intrusion the alkali granites of yemen consist primarily of perthitic feldspar and quartz with some minor alkali amphiboles and acmite these granites represent water poor hypersolvus magmas generated from parent alkali basalt magmas the granophyric two feldspar granites associated with the mafic dike swarms and layered gabbros formed by fractional crystallization from tholeiitic basalt parent developed in the early stages of extension initial 87sr 86sr ratios of these rocks and their bulk chemistry indicate that production of peralkaline and metaluminous granitic magmas involved both fractionation and partial melting as they ascended through the late precambrian crust of the arabian plate

cenozoic epeirogeny of the arabian peninsula from drainage modeling it is generally accepted that the arabian peninsula has been uplifted by subcrustal processes positive residual depth anomalies from oceanic crust in the red sea and in the gulf of aden suggest that a region surrounding this peninsula is dynamically supported admittance calculations surface wave tomography studies and receiver function analyses all imply that regional topography is generated and maintained by some combination of mantle convective circulation and lithospheric thickness changes despite these significant advances the spatial and temporal uplift rate history of the arabian peninsula is not well known here we show that a regional uplift rate history can be obtained by jointly inverting 225 longitudinal river profiles that drain this peninsula our strategy assumes that shapes of individual river profiles are controlled by uplift rate history and moderated by erosional processes we used local measurements of incision rate to calibrate the relevant erosional parameters in our inverse algorithm uplift rate is permitted to vary smoothly as a function of space and time but upstream drainage area remains invariant we also assume that knickzone migration is not lithologically controlled implications of these important assumptions have been investigated our results suggest that the arabian peninsula underwent two phases of asymmetric uplift during the last 20 30 ma at rates of 0 05 0 1 mm a 1 the southwestern flank of the peninsula has been uplifted by 1 5 2 5 km regional stratigraphic constraints the age and composition of volcanism paleosol formation incised peneplains emergent marine terraces and thermochronometric measurements corroborate our calculated patterns of uplift progressive development of three domal swells along the western margin of the peninsula is consistent with localized upwelling of hot asthenospheric mantle

the cooling history of silurian to cretaceous alkaline ring complexes south eastern desert egypt as revealed by fission track analysis abstract forty fission track ages of apatite zircon and sphene and nine horizontal confined track length distribution patterns in apatite have been used to establish the cooling history of nine silurian to late cretaceous alkaline ring complexes which intrude precambrian basement in the southern eastern desert of egypt zircon or sphene fission track ages were determined from three complexes for whichk ar andrb sr ages on the same samples were also available these ages are concordant and are interpreted as emplacement ages resulting from rapid cooling following high level crustal intrusion into relatively thick volcanic piles average apatite ages for each of the eight ring complexes range from 33 to 167 m y track length distribution patterns for apatites taken together with their ages invite subdivision into two groupings those complexes yielding early oligocene apparent apatite ages suggest cooling from the total track annealing zone followed by a relatively lengthy residence near the base of the partial annealing zone whereas those with late cretaceous ages indicate cooling from a shallower level in the partial annealing zone variations in cooling history resulted from differential uplift between fault bound blocks one block that containing the late cretaceous abu khruq complex was relatively stable and the different degrees of partial resetting recorded in apatites of this complex are attributed to the thermal effect of localised tertiary dyke intrusion fission track analysis in combination with geologic data indicates that in the south eastern desert of egypt a phase of uplift commenced in late oligocene time and was accompanied by paleogeothermal gradients of ca 40 50 c km uplift was more pronounced at least 2 2 5 km in areas within about 100 km from the present red sea coast this uplift which is viewed as part of a broader regional tectonism related to the opening of the red sea occurred along a northwest fracture pattern and was controlled by pre existing lines of weakness in the basement complex

thermochronological data from sudan in the frame of the denudational history of the nubian red sea margin low temperature thermochronology provides information on the timing of rifting and denudation of passive margins and the red sea with its well exposed young rift margins is a suitable setting for its application here we present new apatite fission track aft data from sudan northern hinterland and red sea coastal areas from the former region we obtained ages between 270 2 ma ad 253 53 ma and from the coastal belt between 83 8 ma and 39 7 ma these data prompted a review and comparison with low temperature thermochronological data from the whole nubian red sea margin and a discussion on their implication in assessing the margin evolutionary style aft data are available for egypt and eritrea as well as apatite u th he ahe ages for two transects transversal to the margin in eritrea both in egypt and eritrea aft data record a cooling event at about 20 25 ma early miocene and an earlier more local cooling event in egypt at about 34 ma early oligocene the thermal modeling of the sudan samples provides an indication of a rapid cooling in miocene times but does not support nor rules out an early oligocene cooling phase the re assessment of new and existing thermochronological data within the known geological framework of the nubian and conjugate arabian margins favours the hypothesis that early rifting stages were affecting the whole gulf of suez red sea gulf of aden system since the oligocene these precocious more attenuated phases were followed by major extension in miocene times as to the mode of margin evolution aft age patterns both in egypt and eritrea are incompatible with a downwarp model the distribution of ahe ages across the eritrean coastal plain suggests that there the escarpment was evolving predominantly by plateau degradation copyright 2009 john wiley sons ltd

rifts and swells geophysical constraints on causality abstract analyses are developed to examine whether rifting can generate broad topographic swells and whether swells formed by lithospheric thinning can generate rifts although swells can be supported by deep lithospheric cracks filled with low density intrusions observed topography and gravity constrain how this might occur single deep dikes apparently cannot explain the width of swells the low gravity gradients on swell flanks or the lack of a large negative free air anomaly over swell crests if swells are supported by deep cracks there must be numerous narrow dikes distributed over the full breadth of each swell comparing the hydrostatic pressure of various columns of lithosphere to that of an ocean ridge crest suggests the conditions under which a swell might spread apart oceanic basins are under deviatoric horizontal compression due to ridge push the uplift caused by lithospheric thinning will reduce this compression but because swells never rise higher than ridge crests oceanic swells should not develop deviatoric tensile stresses continental platforms are under less compression so formation of a continental swell can generate significant rifting forces

age and petrology of the tertiary as sarat volcanic field southwestern saudi arabia abstract harrat as sarat forms the second smallest and southernmost of the basalt fields of western saudi arabia and is part of a voluminous red sea rift related continental alkali basalt province the rocks of the as sarat were emplaced during the first stage of red sea rifting and represent the northernmost extension of the tertiary trap series volcanics that occur mainly in the yemen arab republic and ethiopia the field consists of up to 580 m of basalt flows that are intruded by basaltic plugs necks minor dikes and highly evolved peralkaline trachyte intrusions k ar ages indicate that the as sarat field formed between 31 and 22 ma and contains an eruption hiatus of one million years that began about 25 ma ago pre hiatus flows are primarily hypersthene normative intersertal subalkaline basalt whereas the majority of post hiatus flows are nepheline normative alkali basalt and hawaiite with trachytic textures normative compositions of the basalts are consistent with their genesis by partial melting at varying depths trace element abundances in the basalt indicate that varying degrees of partial melting and fractional crystallization or crystal accumulation had major and minor roles respectively in development of compositional variation in these rocks modeling indicates that the pre hiatus subalkaline basalts represent 8 10 percent mantle melting at depths of about 70 km and the post hiatus alkali basalts represent 4 9 percent mantle melting at depths greater than 70 km

structural architecture and tectonic evolution of the maghara inverted basin northern sinai egypt abstract large ne sw oriented asymmetric inversion anticlines bounded on their southeastern sides by reverse faults affect the exposed mesozoic and cenozoic sedimentary rocks of the maghara area northern sinai seismic data indicate an earlier jurassic rifting phase and surface structures indicate late cretaceous early tertiary inversion phase the geometry of the early extensional fault system clearly affected the sense of slip of the inverted faults and the geometry of the inversion anticlines rift parallel fault segments were reactivated by reverse slip whereas rift oblique fault segments were reactivated as oblique slip faults or lateral oblique ramps new syn inversion faults include two short conjugate strike slip sets dissecting the forelimbs of inversion anticlines and the inverted faults as well as a set of transverse normal faults dissecting the backlimbs small anticline syncline fold pairs ornamenting the steep flanks of the inversion anticlines are located at the transfer zones between en echelon segments of the inverted faults

thermal evolution of rifted continental margins new evidence from fission tracks in basement apatites from southeastern australia the palaeozoic granitic basement of southeastern australia shows a regular pattern of apatite fission track ages which is dominated by a rapid decrease in apparent age towards the rifted continental margin apparent ages away from the margin vary between about 230 and 360 myr but drop sharply to minimum values of around 80 myr near the coast just south of the sydney basin and 150 175 myr elsewhere along the coast fission track length information allows the age pattern to be interpreted as the result of partial to complete resetting of the older ages by a widespread thermal event at about 80 100 myr this event accompanied the rift phase of passive margin development and peaked just before the onset of sea floor spreading in the adjacent tasman sea the zone of reduced apatite ages is deeply embayed around the gippsland basin supporting the suggestion that it originated as a cretaceous failed arm of the tasman rift system the thermal event has affected apatites up to about 130 km from the margin and has produced a characteristic set of bimodal track length distributions in apatites with partially reset ages the bimodality gradually disappears towards the oldest apatite ages which have negatively skewed unimodal distributions the youngest apatites also tend towards unimodal length distributions indicating that thermal annealing of pre existing tracks in these samples went almost to completion maximum temperatures reached in samples presently exposed in the coastal area were thus probably about 110 120 c thermal activity was accompanied by considerable uplift across the region followed by gradual erosion to expose the present land surface post breakup erosion was generally greater towards the new coastline with near coastal samples being previously buried a probable 1 5 2 5 km

crustal structure of the northern harrat rahat volcanic field saudi arabia from gravity and aeromagnetic data abstract new gravity data reveal a prominent negative anomaly along the main vent axis of the northern harrat rahat volcanic field in saudi arabia the low continues north of the volcanic field onto exposures of proterozoic rocks indicating that the low is caused not only by the volcanic field and possibly also underlying cenozoic sediments but also the underlying proterozoic basement an inversion of the gravity field guided by analysis of aeromagnetic data indicates 1 a broad depression of the basement surface that is deeper along the main vent axis in the eastern part of the harrat and in the southwest part of the volcanic field and 2 less dense basement beneath the vent axis low densities within the basement most likely arise from lithologic variations in the basement predating cenozoic volcanism although our analysis does not rule out small volumes of partial melt and higher temperatures or extensive fracturing at depth

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

monogenetic volcanism personal views and discussion monogenetic volcanism produces small volume volcanoes with a wide range of eruptive styles lithological features and geomorphic architectures they are classified as spatter cones scoria or cinder cones tuff rings maars maar diatremes and tuff cones based on the magma water ratio dominant eruption styles and their typical surface morphotypes the common interplay between internal such as the physical chemical characteristics of magma and external parameters such as groundwater flow substrate characteristics or topography plays an important role in creating small volume volcanoes with diverse architectures which can give the impression of complexity and of similarities to large volume polygenetic volcanoes in spite of this volcanic facies complexity we defend the term monogenetic volcano and highlight the term s value especially to express volcano morphotypes this study defines a monogenetic volcano a volcanic edifice with a small cumulative volume typically 1 km3 that has been built up by one continuous or many discontinuous small eruptions fed from one or multiple magma batches this definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism

horizontal velocities and propagation directions of gravity waves in the ionosphere over the czech republic 1 using a five point continuous doppler sounding system operating at 3 59 mhz developed at the institute of atmospheric physics as cr iap we investigate propagation directions and velocities of gravity waves gws at altitudes from 150 to 250 km over the western part of the czech republic the velocities and directions are computed from the time delays between the observations of corresponding gws at different reflection points that correspond to various sounding paths we focused on the gws that produce an s shaped trace in doppler shift spectrograms and are observed close to sunrise and sunset we have selected about 100 of such events our results show that the analyzed gws propagate with typical horizontal velocities from 100 to 200 m s the north south component of gw velocities depends on the season it is directed northward in the summer and southward in the winter at the same time the north south component of the neutral winds calculated by the horizontal wind model hwm07 has the opposite sign typical observed periods of the analyzed waves range from 10 to 30 min

recent kinematics of the tectonic plates surrounding the red sea and gulf of aden this work was funded by the miur prin prot 20125jkany the geodas ship track data used in this study can be found at ngdc http www ngdc noaa gov mgg geodas trackline html

the zagros core deformation of the continental lithospheric mantle 1 the zagros of iran form one of the youngest collisional orogenic belts on earth at shallow depths shortening across the zagros is accommodated by folding in the sediments high angle thrust faulting in the basement and thickening of the lower crust but how shortening is accommodated by the lithospheric mantle has been uncertain largely because the upper mantle seismic structure has been poorly known we map the lateral variations in upper mantle shear wave speed beneath this region using a large multimode surface wave data set the upper mantle is slow for most of the middle east but a high shear wave speed lid extending to 225 km depth exists beneath the zagros we use at vs z relation to convert the shear wave speed profiles to temperature profiles and fit these with geotherms to identify the base of the lithosphere the upper mantle temperatures from the seismic model are consistent with temperatures derived from geochemical modeling the lithosphere is less than 120 km thick over the region except for a thick lithospheric root beneath the zagros implying that shortening in the mantle is accommodated by lithospheric thickening the composition of the volcanic rocks from above the area of the thickened lithosphere has depleted magma source regions with densities 60 kg m 3 less than the morb source elsewhere in the middle east the volcanic source regions have compositions and densities similar to that of morb the shortening across the zagros is accommodated by lithospheric thickening but the cool thickened lithosphere has been stabilized from delamination by depletion

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

dwm07 global empirical model of upper thermospheric storm induced disturbance winds 1 we present a global empirical disturbance wind model dwm07 that represents average geospace storm induced perturbations of upper thermospheric 200 600 km altitude neutral winds dwm07 depends on the following three parameters magnetic latitude magnetic local time and the 3 h kp geomagnetic activity index the latitude and local time dependences are represented by vector spherical harmonic functions up to degree 10 in latitude and order 3 in local time and the kp dependence is represented by quadratic b splines dwm07 is the storm time thermospheric component of the new horizontal wind model hwm07 which is described in a companion paper dwm07 is based on data from the wind imaging interferometer on board the upper atmosphere research satellite the wind and temperature spectrometer on board dynamics explorer 2 and seven ground based fabry perot interferometers the perturbation winds derived from the three data sets are in good mutual agreement under most conditions and the model captures most of the climatological variations evident in the data

the arabian continental alkali basalt province part i evolution of harrat rahat kingdom of saudi arabia the harrat rahat lava field forms a major component of an extensive but poorly known continental alkali basalt province extending from yemen in the south through saudi arabia and jordan to syria in the north the continental intraplate volcanism which produced the arabian lava fields harrats was contemporaneous with opening of the red sea collision of the arabian and eurasian plates and uplift of the afro arabian dome harrat rabat has evolved over the past 10 m y it contains two prominent lateritic disconformities which separate three stratigraphic units the shawahit 10 2 5 ma hammah 2 5 1 7 ma and madinah 1 7 recent basalts comprising 68 19 and 13 of the total harrat volume respectively the shawahit basalt is composed of coarse grained dictytaxitic olivine transitional basalt otb and minor 10 alkali olivine basalt aob which erupted through scoria cones and shield volcanoes in contrast the hammah basalt is dominated by equal volumes of fine grained intergranular to intersertal aob and hawaiite which erupted mainly through scoria cones and relatively few shield volcanoes sparse domes and flows of mugearite and benmoreite first appear in the hammah basalt the madinah basalt spans the full compositional range of harrat rahat 103 analyzed samples comprise otb 8 aob 47 hawaiite 32 mugearite 4 benmoreite 8 and trachyte 2 here scoria cones dominate whereas shield volcanoes are sparse and occur only in the lower madinah basalt domes and associated pyroclastic deposits are common the final events of harrat volcanism include 11 post neolithic eruptions 4 500 yr old and two historical eruptions in 641 and 1256 a d arabian harrat magmatism may have been initiated by partial melting of garnet perido tite in the asthenosphere at a depth 100 km accumulation of this partial melt at the crust mantle boundary 37 44 km may have resulted in miocene uplift of the afro arabian dome harrat rahat volcanism began shortly after significant initial uplift with the voluminous extrusion of shawahit otb lava chemical and petrographic data suggest that these otb magmas ascended rapidly with little crustal residence time the data support a model of open system fractionation for aob and hawaiite lavas of the younger hammah and madinah basalts in this model some of the potential shawahit otb was trapped in crustal chambers during magma ascent crystal fractionation in these chambers was accompanied by their periodic replenishment by rising otb magma this resulted in the mixing of magma types and the development of aob and hawaiite magmas which are anomalously enriched in highly incompatible elements the mugearite benmoreite and trachyte lavas are the products of advanced fractionation in these crustal chambers with little or no magma replenishment

characterisation of organic matter and microbial communities in contrasting arsenic rich holocene and arsenic poor pleistocene aquifers red river delta vietnam abstract high concentrations of geogenic as in the groundwaters of south and se asia which are used as drinking waters are causing severe health impacts to the exposed human populations it is widely accepted that as mobilisation from sediments into these shallow reducing groundwaters requires active metal reducing microbes and electron donors such as organic matter om although om in such holocene aquifers has been characterised there is a dearth of data on pleistocene aquifers from the same areas reported here are preliminary studies of om and microbial communities present in two aquifers one of pleistocene and one of holocene age with contrasting concentrations of as viz pleistocene low as

statistical investigation of horizontal propagation of gravity waves in the ionosphere over europe and south africa 1 a statistical investigation into the horizontal propagation of 8 30 min gravity waves gws in the ionosphere over a 1 year period from june 2010 to may 2011 is presented the gws were observed by multipoint continuous doppler sounding systems installed in the czech republic and in the western cape south africa measurements of gw propagation in the ionosphere over south africa have never been presented before simultaneous measurements from nearby ionosondes made it possible to estimate the height of the gw observations and show that the analyzed gws propagated at altitudes from 150 to 250 km the analyzed waves were mainly observed after sunrise and around sunset our statistical study shows that the analyzed gws propagated with horizontal velocities from 70 to 250 m s the average observed horizontal velocities were 100 m s in the local summer and 125 150 m s in the local winter the waves propagated approximately poleward in the local summer whereas roughly equatorward propagation was observed in the local winter westward propagation was rarely observed in the czech republic and eastward southeast propagation was seldom observed in south africa a comparison with neutral wind velocities shows that the analyzed gws propagated approximately against the neutral winds calculated by the hwm07 model the estimated horizontal wavelengths of the analyzed waves were 100 300 km

the seek sporadic e experiment over kyushu campaign the seek sporadic e experiment over kyushu campaign was conducted in late august 1996 from the southern region of kyushu japan to investigate the mechanism for the generation of quasi periodic qp radar backscatter from field aligned irregularities imbedded in nighttime sporadic e es layers seek was designed to determine in situ small scale electrodynamical properties using two sounding rockets and large scale dynamics and electrodynamics using ground based sensors which included a transportable radar and other radio and optical instruments deployed in the vicinity of the rocket range it was observed by this campaign that es layers existed in a convergent wind shear region where large electric fields were induced and when active atmospheric gravity waves existed in the mesosphere however there was little evidence which positively supported the hypothesis that es layers were deeply modulated in altitude

ionospheric disturbances infrasound waves over the czech republic excited by the 2011 tohoku earthquake 1 a train of large amplitude infrasound wave packets was observed by multipoint continuous doppler sounding system in the ionosphere over the czech republic on 11 march 2011 it is shown that these infrasound wave packets originated from vertical motion of the ground surface that was caused by arrival of seismic waves generated by the strong tohoku earthquake the infrasound wave packets were observed in the ionosphere at heights of 210 220 km about 9 min after the detection of corresponding wave packets on the ground which is consistent with the calculated time for vertically propagating infrasound waves absolute values of cross correlation coefficients between ionospheric and ground measurements are typically higher than 0 9 for two wave packets 0 98 the individual wave packets recorded on the ground have different observed horizontal velocities and correspond to different types of seismic waves a comparison of vertical velocities of ground motion with oscillation velocities of air particles in the ionosphere indicates that almost 1 10 of the infrasound energy flux excited at the ground reached the altitudes of 210 220 km for wave periods longer than 30 s estimates of sound attenuation are performed it is also shown that it is necessary to consider the value of electron density gradient at the reflection height of the sounding radio wave and air plasma compression owing to the infrasound wave to get reasonable estimates of oscillation velocities of air particles from doppler shift frequencies

seismicity and tectonics of the red sea and western arabia summary search in a number of seismological sources revealed that in the period 1913 86 some 135 earthquakes 3 m s 6 9 occurred in the red sea and western arabia between latitudes 14 and 27 2 n in the same period 49 earthquakes m s 6 9 and 247 earthquakes m c 4 9 are reported to have occurred in the gulfs of suez and aqaba respectively twenty three historical earthquakes are reported to have been felt in the region with intensities iv ix and a few more with unassigned intensities during the period ad 627 1884 the epicentral distribution of both instrumental and historical data and their characteristics show a general correlation with the regional geology and tectonics sixty per cent of the total energy released from all instrumental earthquakes is released from earthquakes epicentred within the spreading zone concentrations of activity are seen where the spreading zone is intersected by the ne transform faults and where this zone shifts in direction much of the seismicity of this region is of the swarm type and volcanic related both instrumental and historical data show an apparent lower seismicity in the northern red sea region between latitudes 22 and 27 2 n but the whole region is of a noticeable seismic risk that is mostly associated with regional land faults some of which are continuations of the red sea transform faults the instrumental seismicity of the whole region conforms with the relation log n 4 23 0 53m when historical data are considered both datasets conform with the relation log n 4 1 0 47m the b constant correlates with the shield type of environment and seems to increase gradually northwards to attain a value of 0 71 in the gulfs region this may be caused by either heterogeneity in the lithosphere or most probably asymmetry of the regional stress field in the vicinity of latitude 27 5 n or both causes

geochemistry of bimodal amphibolitic felsic gneiss complexes from eastern massif central france high grade basic and acidic meta igneous rocks are widespread in the bimodal amphibolitic felsic gneiss complexes which are characteristic formations of the middle allochthonous unit from eastern and southern french massif central the metabasites from the lyonnais and doux complexes are chemically diverse and range from n morb type tholeiitic to transitional types the two populations are not related by fractional crystallization or crustal contamination processes and their chemical characteristics reflect differences in their mantle sources an ensialic setting is supported by the crustally derived character of some of the associated felsic rocks but the presence of n morb type metabasites argues for an extensional environment this bimodal association compares well with the magmatism of rifted continental margins and may reflect a transitional stage between continental rifting and oceanic crust formation during the cambro ordovician spreading event

broad accommodation of rift related extension recorded by dyke intrusion in saudi arabia volcanic fields at the eastern margin of the red sea rift were regarded as seismically quiet until a swarm of 30 000 earthquakes struck in 2009 geological analyses reveal the intrusion of a volcanic dyke and indicate that rift related extension is spread over a broad region far from the rift axis