from partial to full strain partitioning along the indo burmese hyper oblique subduction abstract the andaman nicobar trench and its onshore prolongation the indo burmese wedge is the least studied segment of the india australia subduction new offshore geological and geophysical data have recently been collected along the burma scarp during a marine survey conducted with the r v marion dufresne andaman cruise swath bathymetric mapping combined with shallow and deep seismic show that the dominant active tectonics is dextral strike slip faulting accompanied by various amounts of shortening the southern portion of the burma scarp is transpressive north andaman islands the central portion is pure strike slip on nne oriented segments southern myanmar the northern portion shows sedimentary wedge growth along nw segments both onshore and offshore arakan yoma prism further north the wedge bends to the west while dextral shear faults more or less parallel to the sagaing fault develop within the internal part of the wedge and elongated ns folds form in its external part abutting onto the shillong plateau we propose a simple kinematic model involving evolution from partial to full partitioning from south to north along the west burma scarp wbs and we test it quantitatively using the most recent geodetic results in the south half of the 3 5 cm year of india motion is taken at the trench itself the other half being accommodated onto a single shear fault the sagaing fault in myanmar in the north where the bangladesh fold system developed dextral strike slip faults are activated within the arakan yoma belt and at the accretionary prism backstop contact resulting in full partitioning there faults accommodating the oblique component of motion of india are progressively migrating in space from far field faults andaman sagaing to near trench faults arakan yoma belt and trench itself the burma sliver being buttressed by the eastern himalayas this kinematic extends back to 4 ma which is the time of initiation of the last pulse of oceanic accretion in the andaman basin

evidences for cessation of indian plate subduction in the burmese arc region the issue of whether subduction is still active in the india burma plate boundary zone has been rather controversial while the presence of an eastward dipping indian lithospheric slab is undisputed different opinions have been voiced regarding the continuance of subduction at present analysis of the harvard cmt data in comparison with major subduction zones of the world demonstrates that the burmese arc is a unique region where there is a subducted slab but the direction of plate motion is nearly perpendicular to the down dip direction we propose a major right lateral shearing of the indian plate along with its subducted slab past the burmese plate in the nne direction

new insights into the tectonic evolution of the andaman basin northeast indian ocean multibeam swath bathymetry data acquired over an area of about 30 000 km2 together with magnetic and single channel seismic data have been analyzed to understand the tectonic evolution of the andaman basin northeast indian ocean swath bathymetry data revealed several morphotectonic features that divide the basin into a complex western part comprising arc parallel seamount chains and n s trending fault systems and a relatively smooth eastern part a sw ne trending spreading ridge bisects the basin an offset of about 11 8 km at 94 21 e longitude divides the spreading ridge into sw and ne segments high resolution bathymetry and magnetic data enabled us to identify two finer scale segments over the sw part of the ridge that display distinct topographic fabric compared to the ne segment thin sediment cover and presence of axial seamounts characterize sw segments of the ridge whereas the ne segment has thick sediment cover and well maintained rift valley kinematics of basin evolution derived from the identification of the seafloor spreading magnetic anomalies suggest very slow initial opening rates of about 1 6 cm yr and an increase in the spreading rate to about 3 8 cm yr from anomaly 2 to present although this interpretation relies only on magnetic anomalies in the two westernmost segments it is suggested that the true seafloor spreading started about 4 ma in the andaman backarc basin rather than the 11 ma postulated previously we infer based on the integrated analysis of swath bathymetry magnetic and seismological data that the basin has evolved as a consequence of extrusive tectonics that prompted extension and rifting along the plane joining the sagaing and semengko fault systems extension by seafloor spreading during the past 4 myr resulted in the formation of the deep andaman backarc basin this phase has also experienced westward propagation of the spreading center

the lappajarvi meteorite crater finland petrography rb sr major and trace element geochemistry of the impact melt and basement rocks abstract impact melt lithologies of the 77 m y old finnish meteorite crater lappajarvi as well as the precambrian target rocks have been studied in detail to identify and characterize different impact melt types clast poor clast rich suevitic melt and to study their chemical major and trace elements and isotopic rb sr compositions in comparison to the composition of the target rocks the rb sr system of the whole melt body including the suevitic melt is shown to have been reequilibrated by the impact by extensive turbulent mixing of the various melted or vaporized target rocks chemical interactions exchange of alkali elements 87sr redistribution between feldspar clasts and impact melt surrounding them are the result of thermal metamorphism following the incorporation of target rock fragments of various degrees of shock metamorphism into the superheated melt exchange reactions between clasts and melt are determined by thermal activation but the degree of shock metamorphism in the clasts plays an important role too major and trace element distributions in impact melt and basement rocks indicate that the lappajarvi melt body chemically is extremely homogeneous even volatile elements such as zn and cu were not strongly fractionated comparison of the abundances of siderophile elements in the impact melt e g 118 177 ppm cr 195 340 ppm ni 6 12 ppb ir and calculated target rock mixture 79 mica schist 11 granite pegmatite 10 amphibolite e g 85 6 ppm cr 54 8 ppm ni 0 5 ppb ir revealed the chondritic nature c or h chondritic of the meteoritic projectile less than 2 of the meteorite can be detected in the coherent melt whereas the suevitic melt is uncontaminated by the projectile

mentawai fault zone off sumatra a new key to the geodynamics of western indonesia the geodynamic evolution of the western part of the sunda arc is controlled by the change from frontal subduction of the indo australian plate along java to oblique subduction along sumatra this obliquity gives rise to the sumatra fault zone that links the accretionary zone of the andaman sea to the sunda strait previous studies have shown a decrease of displacement rate of the movement along the fault zone from north to south consequently it has been proposed that the area between the subduction zone and the fault zone i e the sumatra sliver platelet was deformed an oceanographic cruise on the indonesian ship r v baruna jaya iii was designed to study this area seismic reflection data reveal the existence of a major strike slip fault parallel to the sumatra fault zone that we called the mentawai fault zone located in the fore arc area just east of the mentawai islands it is at least 600 km long thus the sumatra sliver plate appears to be composed of several strips that move toward the northwest to accommodate the oblique subduction

crustal structure of the central sunda margin at the onset of oblique subduction summary the convergent margin of the central sunda arc in indonesia was the target of a reflection and refraction seismic survey conducted in 1998 and 1999 along two seismic lines across the subduction complex off southern sumatra and off sunda strait coincident multichannel and wide angle data were collected complemented by two refraction strike lines in the forearc basin off sumatra the combined analysis of the acquired data allows us to present a detailed model of the subduction zone where initiation of strain partitioning occurs due to the onset of oblique subduction the dip of the subducted plate is well defined along both dip lines and a lateral increase from 5 to 7 from beneath the outer high off sumatra to sunda strait is supported by complementary gravity modelling the downgoing slab is traced to a depth of more than 30 km on both reflection dip lines a clearly developed backstop structure underlying a trench slope break defines the landward termination of the active accretionary prism and separates it from the outer high active subduction accretion is supported by laterally increasing velocities between the deformation front and the active backstop structure seismic velocities of the outer high are moderate along both lines 5 8 km s 1 at 20 km depth suggesting a sedimentary composition reduced reflectivity beneath a rugged top basement traced along the outer high of both dip lines supports a high degree of deformation and material compaction several kilometres of sediment has accumulated in the forearc domain although a distinct morphological basin is only recognized off southern sumatra and is not developed off sunda strait the bathymetric elevation of the java shelf that is encountered in the southern sunda strait corresponds to increased velocities of a basement high there and is connected to extensional structures of the sunda strait transtensional basin differences observed in the morphology of the forearc domain are also reflected in the lower crustal structure off southern sumatra the velocity depth model clearly indicates a continental type crust underlying the forearc basin whereas lower velocities are found beneath the sunda strait forearc domain off sumatra some 3 d constraint on the upper plate structure is gained from the refraction strike lines which in addition is supported by synthetic data modelling

microirghizites recovered from a sediment sample from the zhamanshin impact structure microscopic glass spherules called microirghizites have been recovered from a stream deposit in the zhamanshin crater the microirghizites partly overlap the irghizites tektites and sio2 rich zhamanshinites impactites in composition but exhibit greater variations in composition and have lower average sio2 contents a similar relationship has been observed between microtektites and tektites in the australasian ivory coast and north american strewn fields the compositions and oxide trends observed for the microirghizites sio2 rich zhamanshinites and irghizites are rather similar to those observed for the australasian microtektites and tektites the major differences are the al2o3 and feo versus sio2 trends which could be explained by differences in amount of meteoritic contamination the irghizites and microirghizites contain higher nickel contents up to 0 41 than the sio2 rich zhamanshinites and australasian tektites and microtektites the major oxides versus silica trends for the microirghizites support a previous conclusion that the impacting body was a chondrite meteorite and the bulk parent material was terrestrial although the irghizites may have been more contaminated by the impacting body than were the sio2 rich zhamanshinites we find that the major differences in composition between the irghizites and sio2 rich zhamanshinites may be due to different parent materials rather than meteoritic contamination

geochemistry and neodymium strontium isotope signature of tektite like objects from siberia urengoites south ural glass we report sr nd isotope parameters rare earth element ree and major element data for isolated findings of tektite like objects from western siberia urengoites south ural glass as well as for two indochinites the latter were recovered in vietnam and their overall geochemical characteristics equal those of other tektites from the indochinite subgroup of the australasian strewn field the three urengoites 24 ma are extremely silica rich 89 to 96 wt sic2 and their ree abundances vary between 45 and 76 ppm with lan ybn ranging from 7 6 to 10 4 and eun eu between 0 69 and 0 75 their ree distribution patterns match that of average upper crust the urengoites have present day sr of 155 to 174 and nd ranging from 18 to 23 their model ages in million years are tsrur 1200 up to 4060 and tndchur 1570 up to 2070 data points for the urengoites plot colinearly in the rb sr evolution diagram the age corresponding to the slope is 183 30 ma 2s which is indistinguishable from the intercept age of 211 ma in the tsrurvs l frb diagram rubidium strontium and sm nd systematics of the urengoites indicate a heterogeneous precursor material derived from paleoproterozoic continental crust which underwent rb sr fractionation and partial sr isotope homogenization in jurassic times any relation between the urengoites and the haughton impact crater having within 2s errors an identical age can be excluded on the basis of isotope relationships and geochemical data the only known south ural glass 6 2 ma is characterized by intermediate sio2 65 wt high al2o3 14 wt and cao 12 wt and low feotot 0 4 wt contents this unique tektite like object contains 110 ppm ree displaying a steeply negative c1 normalized distribution with lan ybn of 17 and eun eu1 of 0 71 the rb abundance 10 ppm and rb sr ratio are low and combined with a crustal 87sr 86sr ratio of 0 722 yielding an unrealistic tsrur age of 2 5 ga the rb sr systematics imply a rather recent parent daughter element decoupling the tndchur age of the south ural glass is 1690 ma geochemical data suggest that urengoites and the south ural glass belong to two discrete groups of tektites whose source craters remain to be discovered

geochemistry of muong nong type tektites iv selected trace element correlations muong nong type tektites are distinct from other tektites in their shape size petrographical characteristics and chemistry volatile elements are enriched but other trace elements do not show large differences when compared to normal splash form tektites an analysis is made of nineteen muong nong type tektites for 40 50 elements fifteen nonvolatile elements are discussed in this paper it is shown that the muong nong type tektites are very restricted in chemical composition and are almost indistinguishable from the australasian tektites elemental ratios calculated from the data reported here show the same genetic connection all elementary abundances and ratios are fully consistent with terrestrial sediments the nonvolatile elements may record more about the conditions of the origin

cometary impacts into ocean their recognition and the threshold constraint for biological extinctions the montagnais impact crater is presently the only site in the ocean where the effect of a meteorite fall on marine organisms has been studied the impact crater is 45 km in diameter and was formed at 50 8 ma by a fall of probably an old cometary nucleus 3 4 km in diameter into shallow 600 m ocean comparison of the impact structure and related deposits with those on land shows several major differences of which the most significant is the absence of an elevated crater rim instead the crater perimeter is bevelled and eroded as a consequence of impact induced bottom currents and turbulent return water flow into the excavating cavity by this process most of the fall out breccia is reworked back into the crater cavity where it accumulates in much larger thickness than in impact craters on land at a microscopic scale the shock metamorphism features are about the same as those for land impacts geochemically impacts of comet nucleii may not leave a recognizable signature at the impact horizon except for a minor increase in iridium thus stratigraphic horizons associated with extinctions and or major changes in biota have to be closely examined for other impact indicators like the presence of tectites glass spherules and quartz grains with shock features occurrence of megatsunami wave deposits extensive erosion on continental margins margin failures and faunal mixing above erosional unconformities are other potential impact indicators there is no single indicator that can provide sufficient proof of an impact event such interpretations have to be based on multiparameter studies of global extent since many of the impact indicators are only of regional extent the lack of extinction of any marine plankton genera or of bottom dwellers at the montagnais impact site allows us to place a lower limit for biological extinctions caused by cometary impacts on those with nucleus 4 km in diameter the calculated frequency for a cometary impact which could result in a 10 extinction of marine genera is about 6 10 7 yr 1 and for the k t boundary type of extinctions about 2 10 8 yr 1 even allowing for a large degree of uncertainty in these estimates it is unlikely that the biological extinction events for the last 250 ma identified by sepkoski 1990 could have been all caused by meteorite impacts

nd and sr isotopic compositions of tektite material from barbados and their relationship to north american tektites isotopic analyses of nd and sr on individual microtektites and a bulk microtektite sample from barbados show them to have a very well defined isotopic composition these data plot on an e sr e nd diagram precisely within the narrow field determined by north american tektites e sr 111 e nd 6 2 they yield an nd model age of 0 6 ae these results show that the microtektites from the oceanic beds of late eocene age are derived from the same target as the north american tektites and should be associated with the same event samples of the deep sea sediments in which the barbados microtektites occur are found to have isotopic signatures which appear to reflect ambient sea water and detrital sediments they cannot be the source of sr or nd in the tektites following the arguments of shaw and wasserburg 1982 we conclude that the target area which produced the north american tektite field was composed of sediments eocambrian or younger derived from very late precambrian crust glass beads from lake wanapitei crater are isotopically different from all other tektites e sr 960 e nd 31 4 and cannot be related to the north american tektites

the west andaman fault and its influence on the aftershock pattern of the recent megathrust earthquakes in the andaman sumatra region 1 distinctly different rupture patterns of december 2004 and march 2005 megathrust earthquakes occurred in the andaman sumatra region suggest strong influence of tectonic and structural elements we have analysed the shipboard gravity bathymetry and seismic data across the west andaman fault waf a major tectonic feature in the andaman sea to infer the crustal structure and to examine its influence in controlling the aftershock pattern our results support the idea of singh et al 2005 that waf forms a lithospheric scale boundary and together with other tectonic elements modulate the occurrence of large earthquakes and their rupture pattern the active strike slip motion along the waf presence of backarc spreading coupled with increased obliquity of subduction in the andaman sector reduce the probability of occurrence of major or great earthquakes north of 10 n

soil moisture fluctuations recorded in saharan dust deposits on lanzarote canary islands over the last 180 ka abstract aeolian sediments trapped in volcanically dammed valleys on lanzarote canary islands were investigated in order to reveal environmental changes over the last 180 ka clay content and frequency dependent magnetic susceptibility were used as proxies for pedogenesis and palaeo soil moisture during the last 180 ka these proxies showed a general pattern of enhanced soil moisture during glacials and stadials and more arid conditions during interglacials and interstadials comparisons of these results with proxies from regional palaeoclimate studies identified a positive correlation with proxies of trade wind strength off northwest africa and inverse correlations with both sea surface temperatures in the northeast atlantic and the extent of mediterranean vegetation possible causes for the observed pattern include a glacial enhancement of precipitation from westerly cyclones a change in relative humidity due to fluctuating air temperatures and an occasional influence of the african summer monsoon although it is not yet possible to clearly differentiate among these factors it is clear that the first two factors must have been primarily dominant these results represent the first quasi continuous terrestrial data testifying to environmental changes in the northwest african coastal area for the last 180 ka and complement the abundant data derived from marine cores of the region high latitude dynamics had a major influence in this area and were intermediated by north atlantic sea surface temperatures a possible negative correlation can also be observed with the orbital obliquity cycle with a 10 ka time lag which is similar to the lag recorded from north atlantic sea surface temperatures

magnetic properties of tektites and other related impact glasses we present a comprehensive overview of the magnetic properties of the four known tektite fields and related fully melted impact glasses aouelloul belize darwin libyan desert and wabar glasses irghizites and atacamaites namely magnetic susceptibility and hysteresis properties as well as properties dependent on magnetic grain size tektites appear to be characterized by pure fe2 paramagnetism with ferromagnetic traces below 1 ppm the different tektite fields yield mostly non overlapping narrow susceptibility ranges belize and darwin glasses share similar characteristics on the other hand the other studied glasses have wider susceptibility ranges with median close to paramagnetism fe2 and fe3 but with a high susceptibility population bearing variable amounts of magnetite this signs a fundamental difference between tektites plus belize and darwin glasses and other studied glasses in terms of oxygen fugacity and heterogeneity during formation thus bringing new light to the formation processes of these materials it also appears that selecting the most magnetic glass samples allows to find impactor rich material opening new perspectives to identify the type of impactor responsible for the glass generation

comment on the great sumatra andaman earthquake of 26 december 2004 lay et al research articles 20 may 2005 p 1127 estimated a 600 km length for the tsunami source region adding tide gauge data from paradip the northernmost of the indian east coast stations and therefore the most critical constraint on the northern extent of the source we estimate that its length was greater by 30

identification of the projectile at the brent crater and further considerations of projectile types at terrestrial craters abstract impact melt samples from drill hole b1 59 at the 3 8 km diameter brent crater ontario have been analysed for siderophile trace elements indicative of meteoritic contamination samples from the basal melt zone at 823 857 m depth are enriched in ir os pd ni co cr and se over basement with the abundance pattern suggesting a chondritic projectile for brent from a ni cr correlation of 10 melt samples an l or ll chondrite is inferred the contribution of an ultramafic country rock alnoite in the melt is too small to significantly influence its ni cr ratio glass rich breccias from the allochthonous breccias filling the crater also contain a meteoritic component interelement ratios e g ni cr are however fractionated relative to the melt zone samples this as well as the low au content of all brent samples is probably a product of alteration additional data on impact melts from the 65 km diameter crater manicouagan still did not reveal a meteoritic component as also for the mistastin crater 28 km diameter where cr analyses set an upper limit of 1 of an achondritic projectile component in the melt irghizites tektite like glasses from the zhamanshin impact structure have been found to contain high ni and co concentrations and our data show that ir is also enriched it is however not possible to define the projectile type enrichment of an ivory coast tektite in ir is confirmed there are large differences in siderophile element concentrations among tektites with otherwise similar chemical composition there are now four known craters formed by chondrites clearwater east lapparjarvi wanapitei and brent with brent being the smallest of these for smaller craters the projectiles appear to be limited to iron or stony iron meteorites because of atmospheric destruction of relatively small stony meteorites it appears however that all major classes of meteorites are represented among the projectiles at terrestrial impact craters

structural geology and the seismotectonics of the 2004 great sumatran earthquake y the authors acknowledge funding support from the australian research council discovery project dp120103554 a unified model for the closure dynamics of ancient tethys constrained by geodesy structural geology argon geochronology and tectonic reconstruction and linkage project lp130100134 where to find giant porphyry and epithermal gold and copper deposits the research was also supported by the satellites seismometers and mass spectrometers initiative within the research school of earth sciences at anu bob engdahl is thanked for his support during earlier versions and for providing data

distribution of chlorite and kaolinite in eastern atlantic sediments off north africa chlorite in the atlantic sediments is predominantly derived from the atlas mountains kaolinite originates in the southern sahara and sahel zone these minerals may be used to reconstruct the tracks of two superimposed wind systems trade winds and harmattan wind a modified method for determining relative abundances of chlorite and kaolinite is presented

late pleistocene holocene environmental conditions in lanzarote canary islands inferred from calcitic and aragonitic land snail shells and bird bones aragonitic and calcitic land snails from carbonate rich paleosols in northwestern lanzarote canary islands were analyzed for 13c 12c and 18o 16o ratios to deduce the pleistocene holocene transition in the westernmost sahara zone modern mid late holocene 2 1 5 5 cal ka bp and late pleistocene 23 3 24 0 cal ka bp aragonitic shells exhibited respective values of 9 5 1 6 7 7 1 5 and 2 3 2 8 for 13c and 0 3 0 3 0 1 0 7 and 2 5 0 4 for 18o holocene and pleistocene calcitic shells of the endemic slug cryptella canariensis showed respective values of 0 7 2 6 and 8 5 2 5 for 13c and 0 8 1 5 and 3 6 0 4 for 18o both aragonitic and calcitic shells showed equivalent temporal isotopic trends higher 13c values during 23 3 24 0 cal ka bp suggest higher abundance of c4 and or cam plants likely associated with drier conditions and or lower atmospheric co2 concentration maximum shell 18o values during 23 3 24 0 cal ka bp opposes minimal values of greenland ice cores and probably reflect the combined effects of 1 higher rain 18o values linked to higher glacial seawater 18o values and or larger snail activity during summer seasons 2 relative humidity values similar or slightly lower than at present 3 higher evaporation rates and 4 cooler temperatures bone remains of the extinct dune shearwater puffinus holeae were only recovered from the holocene bed collagen 13c and 15n values 13 5 0 2 pdb and 13 7 1 0 air respectively match with the signature of a low trophic level macaronesian seabird that fed upon local fish bone carbonate 13c 7 4 1 0 pdb and phosphate 18o 18 2 0 4 smow values exhibited pristine signals denoting their potential value in future paleoenvironmental studies in the region the age of p holeae 2 1 2 7 cal ka bp supports that the aboriginal population possibly caused its extinction in contrast the extinction of the endemic helicid theba sp 23 3 24 0 cal ka bp was likely caused by environmental change

palaeoclimatic considerations of talus flatirons and aeolian deposits in northern fuerteventura volcanic island canary islands spain abstract fuerteventura volcanic island has been subject to considerable aeolian activity since the late pleistocene the aeolian record includes inactive aeolian deposits with interbedded entisols whose age by osl dating ranges between 46 and 26 ky bp the corralejo active dune field where sand sheets nebkhas coppice dunes blowouts barchans and transverse dunes have been described constitutes a more recent aeolian deposit here the age is about 14 ky bp on fuerteventura island aeolian dust has been deposited on valleys and slopes this last type of accumulation has been affected by gully incision producing talus flatirons samples taken on the apex of these palaeo slopes indicate an osl age of 30 and 50 ky bp a palaeoclimatic succession has been interpreted during which a prevailing arid period took place in ois 4 with the accumulation of aeolian dust a humid period occurred in ois 2 during which slopes were dissected and formed talus flatirons an arid period about 14 ky bp gave rise to the corralejo dune field which has continued until present with slight climatic oscillations

geophysical characteristics of the ninetyeast ridge andaman island arc trench convergent zone abstract the convergence tectonics of the ninetyeast ridge ner upon the andaman island arc trench system is examined through an analysis of etopo2 bathymetry satellite derived free air gravity and seismic data oblique subduction and the buoyancy forces arising from subduction of the ner render the subduction processes near the andaman arc highly complex the bathymetric expression of the ner is visible up to lat 10 n but seismic reflection data indicate that it extends up to about lat 17 n the gravity anomalies are strongly positive over the exposed segment of the ridge but are subdued over the buried portion there is a prominent break in the continuity of the trench gravity low where the ner seems to impinge upon the island arc further a strong curvilinear belt of negative anomalies just behind and running parallel to the island arc associated with the forearc basin is a dominant feature of the gravity map an offset in the continuity of this strong negative anomaly occurs at about the same latitude where the ner seems to be converging upon the island arc seismic reflection data indicate that the ner is very close to the trench flexural modeling of the gravity anomalies for the subducting indian ocean lithosphere loaded by sediments and the ner indicates that the ner is at the starting phase of its collision with the island arc and may not have started affecting the subduction process itself we infer that the en echelon block structure of the ner in the proximity of the convergent zone is a consequence of complex strike slip and subduction related tectonic forces

seismicity gravity anomalies and lithospheric structure of the andaman arc ne indian ocean abstract the andaman arc in the northeastern indian ocean defines nearly 1100 km long active plate margin between the india and burma plates where an oblique benioff zone develops down to 200 km depth several east trending seismologic sections taken across the andaman benioff zone abz are presented here to detail the subduction zone geometry in a 3 d perspective the slab gravity anomaly computed from the 3 d abz configuration is a smooth long wavelength and symmetric gravity high of 85 mgal amplitude centering to the immediate east of the nicobar island where a prominent gravity high follows the nicobar deep the slab residual gravity anomaly srga and mantle bouguer anomaly mba maps prepared for the andaman plate margin bring out a double peaked srga low in the range of 150 to 240 mgal and a wider cum larger mba low having the amplitude of 280 to 315 mgal demarcating the andaman arc trench system the gravity models provide evidences for structural control in propagating the rupture within the lithosphere the plate margin configuration below the andaman arc is sliced by the west andaman fault waf as well as by a set of sympathetic faults of various proportions often cutting across the fore arc sediment package some of these fore arc thrust faults clearly give rise to considerably high post seismic activity but the seismic incidence along the waf further east is comparatively much less particularly in the north although the lack of depth resolution for many of the events prohibits tracing the downward continuity of these faults tectonic correlation of the gravity derived models presented here tends to favour the presence of oceanic crust below the andaman nicobar outer arc ridge

quaternary palaeoclimates in the eastern canary islands abstract in the eastern canary islands aeolian formations interbedded with palaeosols have been studies the sequences cover the last 40 ka as evidenced by one 14 c accelerator analysis and several classical radiocarbon dates as in the sahara at least two wet episodes characterize isotopic stage 3 a short pedogenesis corresponds to the first deglaciation step at 15 ka after a new aeolian episode the holocene wet phase begins at around 10 ka the aeolian sedimentation is of saharian dust in particular during the stage 3 dry episode s u th and osl dating are current

nickel iron spherules in tektites non meteoritic in origin abstract the concentrations of several diagnostic trace elements were determined in two comparatively large nife spherules extracted from tektites the purpose of the study was to obtain some clues about the chemistry of the projectile that is presumed responsible for the formation of these tektites however the trace element pattern is distinctly terrestrial implying that the spherules are the result of in situ reduction of the host rock and are not meteoritic in origin

seismology speed and size of the sumatra earthquake we now have a clearer picture of the seismic features of last year s gigantic event our seismological results reveal that indonesia s devastating sumatra andaman earthquake on 26 december 2004 was 2 5 times larger than initial reports suggested second only to the 1960 chilean earthquake in recorded magnitude they indicate that it slowly released its energy by slip along a 1 200 km fault generating a long rupture that contributed to the subsequent tsunami now that the entire rupture zone has slipped the strain accumulated from the subduction of the indian plate beneath the burma microplate has been released and there is no immediate danger of a similar tsunami being generated on this part of the plate boundary although large earthquakes on segments to the south still present a threat

the magnetism of a glacial aeolianite sequence from lanzarote canary islands coupling between luvic calcisol formation and saharan dust trapping processes during wet deposition events off northwestern sahara summary in order to better document the climatic origin of pedogenized loess deposits west of sahara rock magnetic measurements were performed on a last glacial coastal sand sequence from la mala lm quarry lanzarote canary islands containing six interbedded loess palaeosol units hysteresis and susceptibility data point to a coarse grained magnetic enhancement in the coastal sand which contrasts with the superparamagnetic sp to pseudo single domain psd behaviour of the saharan loess and palaeosol high and low temperature experiments show that oxidized titanomagnetite contributions dominate in the sand while fine grained sp to psd iron oxidation products such as maghemite and goethite are evidenced in the saharan loess palaeosol units at room temperature the detrital psd multidomain titanomagnetite contribution of local origin is tentatively estimated from the ac field dependence of magnetic susceptibility surface oxidation of detrital spinel grains and authigenesis of fine grained iron oxides including sp goethite are proposed to explain the magnetic properties of the primarily fine saharan dust bearing material the dry local climate of the present day and late holocene means that loess deposits are not preserved the six pedogenized loess units however point to dust trapping under semi arid wetter conditions probably illustrating periods of reduced latitudinal temperature gradients and climate variability of the north atlantic climate respectively these findings suggest that both the canary palaeosol and its content of ultra fine iron oxide might be constrained by wet deposition and trapping of fine saharan dust

complexity of quaternary aeolian dynamics canary islands abstract carbonate aeolianites are important quaternary archives at the point of intersection between marine and terrestrial systems since they are composed of alternating aeolian sediments and several paleosol units these sequences are highly suitable to reconstruct palaeoenvironmental conditions in northern fuerteventura at least five different areas are characterised by successions of different dune generations and paleosols few studies have addressed the stratigraphic order of individual dune areas therefore a comprehensive consideration spanning several dune fields is needed here we aim to present a detailed stratigraphy of two different dune areas and to identify the contribution of different materials shelf origin dust origin volcanic origin along with processes accumulation soil formation erosion preservation that build up these archives four key sections were selected and sampled for laboratory analyses texture elemental composition caco3 content palaeoenvironmental magnetics luminescence dating and gastropod assemblages based on main stratigraphic features five major sedimentary sequences were identified indicating differences in prevailing sediment supply humidity and volcanic activity first luminescence dating irsl of the sequences revealed sedimentation ages between 360 ka and 15 ka finally we are able to demonstrate that different dune areas show comparable stratigraphic patterns but each studied site is defined by certain characteristics depending on the respective features of the closer surrounding the knowledge of these peculiarities and the underlying background is essential in order to correlate different sites and to attempt an appropriate environmental interpretation of the sedimentary sequences

age and provenance of the target materials for tektites and possible impactites as inferred from sm nd and rb sr systematics sm nd and rb sr analyses of tektites and other impactites can be used to place constraints on the age and provenance of target materials which were impact melted to form these objects tektites have large negative e nd 0 values and are uniform within each tektite group while the e sr 0 are large positive values and show considerable variation within each group chemical trace element and isotopic compositions of tektites are consistent with production by melting of sediments derived from old terrestrial continental crust each tektite group is characterized by a uniform nd model age t chur nd interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites 1 1 15 ae for australasian tektites 2 1 91 ae for ivory coast tektites 3 0 9 ae for moldavites 4 0 65 ae for north american tektites and 5 0 9 ae for high si irghizites sr model ages t ur sr are variable within each group reflecting rb sr fractionation and in the favorable limit of very high rb sr ratios approach the time of sedimentation of the parent material which melted to form the tektites australasian tektites are derived from 0 25 ae sediments moldavites from 0 0 ae sediments ivory coast tektites from 0 95 ae sediments possible parent sediments of other tektite groups have poorly constrained ages our data on moldavites and ivory coast tektites are consistent with derivation from the ries and bosumtwi craters respectively irghizites are isotopically distinct from australasian tektites and are probably not related sanidine spherules from a cretaceous tertiary boundary clay have initial e nd 2 e sr 5 and are not derived from old continental crust or meteoritic feldspar they may represent a mixture of basaltic oceanic crust and sediments implying an oceanic impact these isotopic results are also consistent with a volcanic origin for the spherules

rupture process of the 2004 sumatra andaman earthquake the 26 december 2004 sumatra andaman earthquake initiated slowly with small slip and a slow rupture speed for the first 40 to 60 seconds then the rupture expanded at a speed of about 2 5 kilometers per second toward the north northwest extending 1200 to 1300 kilometers along the andaman trough peak displacements reached 15 meters along a 600 kilometer segment of the plate boundary offshore of northwestern sumatra and the southern nicobar islands slip was less in the northern 400 to 500 kilometers of the aftershock zone and at least some slip in that region may have occurred on a time scale beyond the seismic band

tectonic and volcanic implications of a cratered seamount off nicobar island andaman sea the region of the nicobar earthquake swarm of january 2005 has been explored during a recent cruise using multibeam swath bathymetry seafloor imaging and tv guided sampling to decipher the seafloor morphology nature and tectonic frame work a seamount with well developed crater at the summit was discovered near to the center of the nicobar swarm rock samples collected by tv guided grab from the seamount crater are dacite rhyolite and andesite type with a veneer of ferromanganese oxide coating the aggregates recovered from the slope consisted of manganese globules the geochemistry of the globules suggests 66 97 mn oxide indicative of hydrothermal origin the morphology of the seamount seafloor video footage and geochemistry of the seabed samples suggest that the cratered seamount has erupted in the recent geological past and is dormant at present this is the first documented report of submarine arc volcanism in the andaman sea this finding substantiates the prediction of a submarine volcano east of nicobar island study of the seismicity and the stress pattern in the region suggest that the earthquake swarm in the region occurred due to 2004 sumatra andaman megathrust earthquake the derived stress pattern suggests that the 2004 earthquake greatly reduced the normal stress in the region of west andaman fault from the planes or unclamped them thus unclamping of the region by the 2004 sumatra andaman earthquake led to the initiation of the swarm through predominantly strike slip faulting the newly discovered dormant submarine volcano indicates the volcanic nature of the region we suggest that this submarine volcano is a link between sub aerial volcanoes of barren narcondam islands of the andaman sea and the volcanoes of sumatra

influence of total organic carbon deposition on the inventory of gas hydrate in the indian continental margins abstract total organic carbon toc content of marine sediments represents residual carbon originally derived from terrestrial and marine sources which has survived seafloor and shallow subseafloor diagenesis ultimately its preservation below the sulfate reduction zone in marine sediments drives methanogenesis within the gas hydrate stability zone ghsz methane production along continental margins can supersaturate pore fluids and lead to the formation of gas hydrate in this paper we examine the inventory and sources of toc in sediments collected from four regions within the ghsz along the indian continental margins the recovered sediments vary in age from oligocene to recent mean toc abundance is greatest in the krishna godavari k g basin and decreases progressively to the mahanadi basin andaman wedge and kerala konkan k k basin this decrease in toc is matched by a progressive increase in biogenic caco3 and increasing distance from terrestrial sources of organic matter and lithogenic materials organic carbon sources inferred from c n and 13ctoc range from terrestrial k g basin to mixed marine and terrestrial mahanadi basin to marine dominant andaman wedge and k k basin in the k g basin variation in the bulk 13ctoc is consistent with changes in c3 and c4 vegetation driven by monsoon variability on glacial interglacial timescales whereas in the mahanadi basin a shift in the 13ctoc likely reflects the onset of c4 plant deposition in the late miocene a large shift the 13ctoc in the k k basin is consistent with a change from c3 to c4 dominated plants during the middle miocene we observe a close relationship between toc content and gas hydrate saturation but consider the role of sedimentation rates on the preservation of toc in the zone of methanogenesis and advective flow of methane from depth although toc contents are sufficient for in situ methanogenesis at all the sites where gas hydrates were observed or inferred from proxy data seismic borehole log pressure core and gas composition data coupled with relatively high observed gas hydrate saturations suggest that advective gas transport may also play a role in the saturation of methane and the formation of gas hydrates in these regions although toc content may be a first order indicator for gas hydrate potential the structural and stratigraphic geologic environment along a margin will most likely dictate where the greatest gas hydrate saturations will occur

the great sumatra andaman earthquake of 26 december 2004 the two largest earthquakes of the past 40 years ruptured a 1600 kilometer long portion of the fault boundary between the indo australian and southeastern eurasian plates on 26 december 2004 seismic moment magnitude mw 9 1 to 9 3 and 28 march 2005 mw 8 6 the first event generated a tsunami that caused more than 283 000 deaths fault slip of up to 15 meters occurred near banda aceh sumatra but to the north along the nicobar and andaman islands rapid slip was much smaller tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer

gps measurements of postseismic deformation in the andaman nicobar region following the giant 2004 sumatra andaman earthquake 1 we report gps measurements of postseismic deformation from 22 campaign mode and one continuous gps sites in the andaman nicobar region following the great sumatra andaman earthquake of 26 december 2004 large horizontal displacements toward west to southwest varying in magnitude from 10 to 40 cm and with uplift reaching 16 cm occurred in the region in the first year after the earthquake the observed motion decreased logarithmically in the subsequent year we suggest that in the andaman region frictional afterslip occurred farther downdip of the coseismic rupture while in the little andaman and nicobar regions the coseismic rupture and afterslip patch partly overlapped the afterslip was mostly aseismic and did not contribute to the aftershocks the aftershocks and postseismic displacements appear to follow a similar relationship although with different decay times the temporal dependence of the two differs only by a term linear in time thus the temporal evolution of the afterslip seems to be consistent with a mechanism governed by frictional afterslip available rates of interseismic and postseismic deformation and coseismic static offsets allow us to approximately estimate a return period of about 400 years for great earthquakes in the andaman region

on the nature of the ni rich component in splash form australasian tektites abstract the australasian tektite strewn field is exceptional not only as the largest and most recent but also as the only strewn field without an identified source impact crater therefore scenarios without the formation of an impact crater such as a low altitude cometary airburst have proven hard to discard here new geochemical evidence is presented for mixing of projectile and target material which implies the formation of an australasian tektite related impact crater first ninety two australasian tektites were grouped according to their cr co and ni concentrations based on this data australasian tektites with the highest ni contents 200 g g occur more than 1500 km south southeast sse of the northern indochina region with the highest concentration of ni rich tektites in south vietnam the islands of borneo belitung and java and reports in literature for ni rich tektites in central australia the tektites with the highest cr and ni abundances often also show highly siderophile element hse enrichments of up to 4 ng g ir the most ni rich samples exhibit broadly chondrite relative hse proportions however a chondritic impactor contribution appears to be inconsistent with the observed ni cr ni co and cr co ratios a previously suggested significant terrestrial mantle contribution can also not explain the siderophile element enrichments in combination with relatively low feo tot

elastic thickness structure of the andaman subduction zone implications for convergence of the ninetyeast ridge abstract we use the bouguer coherence morlet isostatic response function technique to compute the spatial variation of effective elastic thickness te of the andaman subduction zone the recovered te map resolves regional scale features that correlate well with known surface structures of the subducting indian plate and the overriding burma plate the major structure on the india plate the ninetyeast ridge ner exhibits a weak mechanical strength which is consistent with the expected signature of an oceanic ridge of hotspot origin however a markedly low strength 0

a late miocene early pliocene biogenic silica crash in the andaman sea and bay of bengal abstract variations in the mass accumulation rate of biogenic silica bsi in continental margin sediments can be used to reconstruct relative changes in productivity through time in these settings in the northern bay of bengal a lack of long sedimentary records has historically precluded this type of reconstruction the acquisition of 21 new long sedimentary records during the 2006 indian national gas hydrate program nghp expedition 01 has made it possible for the first time to reconstruct paleoproductivity in this important region of the world that is dominated by intense changes in the geological and biological fluxes largely driven by tectonic and climate related mechanisms in the research presented here fluctuations in the mass accumulation rate of biogenic opal during the past 9 4 myrs are reconstructed using continental margin sediment cores from the andaman sea site nghp 01 17a and the northern bay of bengal site nghp 01 19 within these records a biogenic silica crash is recorded at 6 ma and is consistent with previous geotectonic geochemical and paleontological studies of the southern indian ocean and pacific ocean that suggest connectivity and thus exchange of nutrient rich water masses between the eastern tropical indian ocean and western tropical pacific ocean was diminished as a result of the tectonic restriction of the northerly sector of the indonesian throughflow itf the biogenic silica crash at sites 17 and 19 is consistent with a decrease in surface water productivity that may have been driven by the reduction of nutrient rich pacific waters delivered to the andaman sea and bay of bengal via the northerly route of the itf following the bsi crash at 6 ma subsequent recovery of the bsi mass accumulation rates at sites 17 and 19 occurred and was perhaps renewed by an enhanced supply of nutrient rich freshwater from the nearby irrawaddy and mahanadi rivers which could have occurred during a documented increase in the intensity of the indian monsoon at 5 ma although recovery is noted at both core locations biogenic silica mass accumulation rates did not fully recover in the andaman sea this could be explained by the restricted nature of the andaman basin and its more distal location from a major source of nutrient rich freshwater

40ar 39ar laser probe dating of the central european tektite producing impact event a new 40ar 39ar data set is presented for tektites from the central european strewn field moldavites this is the only strewn field that is entirely situated in a continental environment and still characterized by scattered ages 14 15 3 myr the main objectives of the study were to define more precisely the moldavite formation age and provide a good calibration for a glass standard proposed for fission track dating the laser total fusion ages obtained on chips from 7 individual specimens from the southern bohemian and moravian subfields are restricted to a narrow interval of time with an average of 14 34 0 08 myr relative to the 27 95 0 09 myr of the fish canyon tuff biotite this result gives a more precise age not only for the tektite field but also for its producing impact if the genetic link between the moldavites and the nordlinger ries impact crater is maintained then this new age has to be considered a reliable estimate for the ries crater also this new value places the formation of central european tektites within the lower serravallian period in the latest geologic timescales evidence of their impact products such as glass spherules or shocked minerals can therefore be sought in sedimentary marine formations in a more precisely defined age interval

distribution of rees and yttrium among major geochemical phases of marine fe mn oxides comparative study between hydrogenous and hydrothermal deposits abstract mineralogy and geochemistry of the ferromanganese oxides collected from two seamounts in the andaman sea have been investigated with special reference to the solid phase partitioning behavior of rare earth elements rees bulk elemental compositions indicate that the oxides from a volcanic cratered seamount csm are hydrothermal while those from another seamount sm2 are hydrogenous in origin the distributions of rees and yttrium in four geochemical phases viz easily exchangeable mn oxide fe oxyhydroxide and residual of csm oxides were distinctly different from that of sm2 oxides in csm oxides the rees and yttrium are mainly associated with fe oxyhydroxide phase while in sm2 oxides both mn oxide and fe oxyhydroxide phases contain the major fraction of these elements the exchangeable and residual phases of both hydrothermal and hydrogenous oxides have extremely low ree content the shale normalized negative ce anomalies and relative enrichment of heavy ree characteristic of hydrothermal oxides are retained in fe oxyhydroxide phase in hydrogenous oxides the positive ce anomalies occurred in both fe and mn oxide phases while negative y anomalies were found only in fe oxyhydroxide phase the phase distribution of rees and yttrium in hydrothermal oxides is described in terms of co precipitation and adsorption of their halide complexes and available free ions in hydrothermal solutions instead adsorption of major carbonate species from seawater primarily regulates the partitioning of rees among the co existing phases of hydrogenous oxides

neotectonics of the sumatran fault indonesia the 1900 km long trench parallel sumatran fault accommodates a significant amount of the right lateral component of oblique convergence between the eurasian and indian australian plates from 10 n to 7 s our detailed map of the fault compiled from topographic maps and stereographic aerial photographs shows that unlike many other great strike slip faults the sumatran fault is highly segmented cross strike width of step overs between the 19 major subaerial segments is commonly many kilometers the influence of these step overs on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry geomorphic offsets along the fault range as high as 20 km and may represent the total offset across the fault if this is so other structures must have accommodated much of the dextral component of oblique convergence during the past few million years our analysis of stretching of the forearc region near the southern tip of sumatra constrains the combined dextral slip on the sumatran and mentawai faults to be no more than 100 km in the past few million years the shape and location of the sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere nonetheless active volcanic centers of the sumatran volcanic arc have not influenced noticeably the geometry of the active sumatran fault on the basis of its geologic history and pattern of deformation we divide the sumatran plate margin into northern central and southern domains we support previous proposals that the geometry and character of the subducting investigator fracture zone are affecting the shape and evolution of the sumatran fault system within the central domain the southern domain is the most regular the sumatran fault there comprises six right stepping segments this pattern indicates that the overall trend of the fault deviates 4 clockwise from the slip vector between the two blocks it separates the regularity of this section and its association with the portion of the subduction zone that generated the giant m w 9 earthquake of 1833 suggest that a geometrically simple subducting slab results in both simple strike slip faulting and unusually large subduction earthquakes

dust deposits on la graciosa island canary islands spain texture mineralogy and a case study of recent dust plume transport abstract la graciosa volcanic island evolved in the late pleistocene holocene it is situated along the northeast of the canarian archipelago with a subaerial surface of 27 km2 this island is located close to the western sahara being 80 km from the north western african continental shelf and 145 km from the coast the island supports a very small permanent population the climate is coastal arid 116 mm precipitation per annum regular occurrences of saharan dust plumes about 30 of the year with a dust accumulation rate of 20 g 2 year 1 produce sedimentation of dust on the island of ca 540 t year 1 wind blown sediments cover a large area more than 52 of the otherwise volcanic island forming sandy beaches sand sheets nebkhas and other aeolian deposits re distributed dust deposits often occur on the leeward sides of inter volcano areas inter dune areas and in endorheic sediment traps many of these deposits are edaphized and carbonatized textural analysis of the dust deposit samples shows a variable proportion of silt 80 20 clay 19 9 and fine to very fine sand 71 4 the general mineralogical composition of these sediments as measured by xrd and sem eds is calcite 26 illite 26 quartz 11 augite 10 aragonite 6 anorthite 8 kaolinite 5 and montmorillonite 3 the mineralogy in different size fractions is very consistent for example quartz content decreases from 15 in the coarse silt fraction to 5 in the fine sand a mineral and grain size comparison with airborne dust collected on gran canaria island was undertaken close similarities were found in the two sample sets such closely matched characteristics point to a similar origin for both airborne dust and dust deposits in line with the saharan plume dust that regularly traverses this archipelago it is unusual to find so much quartz in the fine sand fraction of these aeolian dust deposits individual quartz grains with an intermediate axial length of 160 m were identified by sem eds previous investigators have found similar giant particles in long range transported aeolian dust middleton et al 2001 in contrast to the classic model for gravity settling of airborne dust particles the debate on this subject remains open for discussion we present evidence of long range wind transported large mineral particles and a 2004 case study of uplift wind velocity vs plume dust generation as well as a transport efficiency model that can explain the existence of fine sand in the dust deposits on la graciosa island and in the airborne samplers on gran canaria island recent saharan dust shows that about 10 of similar coarse grained particulate matter is also present

a contribution to the understanding of late pleistocene dune sand paleosol sequences in fuerteventura canary islands abstract this paper describes dune sand paleosol sequences of four pits in northern fuerteventura canary islands the elaborated stratigraphy is reinforced with luminescence dating to provide a first chronological estimation apart from a holocene colluvial layer the sequence spans the period from ca 50 ka to ca 280 ka paleosols were formed during glacial times and point to a standstill in sand supply the isotopic composition of terrestrial gastropod shells retrieved from soil horizons reflects fluctuations in humidity conditions during different edaphic phases because eolian sands were deposited during glacial times as well it is inferred that soil development was simply caused by a decrease in sand supply independent of climate change our geomorphic geochronological and isotopic results are discussed considering different perspectives of dune sand paleosol intercalation and more broadly soil forming conditions in general

sedimentation rates from calcareous nannofossil and planktonic foraminifera biostratigraphy in the andaman sea northern bay of bengal and eastern arabian sea abstract in this study we determined calcareous nannofossil and planktonic foraminifera events in sediments recovered during the 2006 indian national gas hydrate program nghp expedition 01 selected bioevents permitted the assignment of orbitally calibrated ages derivative sedimentation rate estimates and identification of sedimentary discontinuities in the andaman sea at hole nghp 01 17a a late miocene to recent record was recovered but with a significant hiatus during the latest miocene and pliocene sedimentation rates here vary from 50 m myr during the pleistocene to 130 m myr for the late miocene in the northern bay of bengal at hole nghp 01 19a the base of the cored record also reaches the late miocene and extends to recent but the same hiatus missing the pliocene is present at this hole a the early pleistocene at hole nghp 1 19a shows sensible variation in sedimentation rates ranging between 130 m myr and 10 m myr during the last 0 5 ma for the late miocene the sedimentation rate was ca 50 m myr in the western bay of bengal at hole nghp 01 10b d calcareous nannofossils were sparse and only foraminifera datums are available the base of the section is latest early pliocene to late pliocene and the majority of the record is considered younger than late pliocene due to the scarcity of calcareous nannofossils and the few foraminifera datums sedimentation rates were not determined here however hole nghp 01 16a in the same region recorded the highest occurrence of pseudoemiliania lacunosa an event that confirms a pleistocene age allowing us to estimate a sedimentation rate between 110 m myr and 450 m myr along the western peninsular indian margin at hole nghp 01 01a a continuous record from the holocene to the early oligocene indicates sedimentation rates of ca 25 m myr until the middle miocene and a sensible reduction downward reaching 4 m myr in the early miocene to the early oligocene no hiatuses were observed the large changes in sedimentation rates observed in these cores reflect long timescale changes in the environment likely induced by changes in the strength of the indian monsoon system

the great sumatra andaman earthquakes imaging the boundary between the ruptures of the great 2004 and 2005 earthquakes segmentation along convergent margins controls earthquake magnitude and location but the physical causes of segment boundaries and their impact on earthquake rupture dynamics are still poorly understood one aspect of the 2004 and 2005 great sumatra andaman earthquakes is their abrupt termination along a common boundary this has led to speculation on the nature of the boundary its origin and why it was not breached for the first time the boundary has been imaged and with newly acquired marine geophysical data we demonstrate that a ridge on the subducting indo australian oceanic crust may exert a control on margin segmentation this suggests a lower plate influence on margin structure particularly its segmentation the ridge is masked by the sedimentary cover in the trench its most likely trend is nne ssw it is interpreted as a fracture zone on the subducting oceanic plate a ramp or tear along the eastern flank of the subducting fracture zone beneath simeulue island may be considered as an intensification factor in terms of rupture propagation barrier

the lake bosumtwi impact crater ghana the 1 m y old bosumtwi crater ghana has a nearly circular shape with a rim diameter of 11 km north south and 10 km east west it is surrounded by a circular depression and an outer ridge of diameter 20 km polymict breccias averaging at least 20 m thick with clasts as much as 5 m long occur on the outer ridge and the crater rim shows in situ shattered rock patches of suevite have been found in the circular depression north and south of the crater analogy with better known craters suggests that bosumtwi has a central uplift rising to 200 m beneath the lake floor an aeromagnetic anomaly of amplitude 50 nanotesla nt over the northern half of the lake is interpreted as due to a layer of magnetized fallback breccia beneath the lake sediments the normal polarity of the breccia shows that the crater was formed during the normal jaramillo event of 0 97 to 0 85 m y ago which agrees with the magnetic stratigraphy of the related ivory coast microtektites a regional gravity survey indicates a negative bouguer anomaly over the crater there is some geochemical evidence that the meteorite was an iron and its mass and energy are suggested as about 108 tons and 3 1019 joules or 7 3 103 megatons

muong nong type tektites from the moldavite and north american strewn fields muong nong type tektites are a very important group of tektites because they differ from splash form tektites in several important characteristics e g volatile element enrichment major and minor element inhomogeneities bubbles inclusions layered and sometimes brecciated structure they seem to have experienced a lower peak temperature and pressure thus preserving the precursor material much better than the splash forms do they lead to important conclusions about the impact process especially regarding the behaviour of the trace elements during impact melting to date they have been found only within the australasian strewn field finding such tektites within other strewn fields would be very important in proving a genetic relationship between them and splash form tektites two samples one bediasite from the north american strewn field and one moldavite from the czechoslovakian strewn field that show some muong nong features layered structure have been analyzed for major and minor as well as trace elements to test for the presence of chemical muong nong signatures although these three samples show a somewhat larger internal variation of major elements than normal splash form tektites this variation is not as large as that of typical muong nong tektites likewise there is no enrichment in volatiles at least no significant one which is one of the most obvious characteristics of muong nong type thus these samples deviate to some extent from splash forms but do not constitute real muong nong tektites so no genetic relationship between muong nong tektites and normal splash forms has yet been established beyond doubt

climatic cycles inferred from the aminostratigraphy and aminochronology of quaternary dunes and palaeosols from the eastern islands of the canary archipelago aminochronological and aminostratigraphical methods have been used to study the quaternary a e o l i a n deposits f r om the islands located east of the canary archipelago fuerteventura and lanzarote islands and la graciosa montana clara and alegranza islets t h e extent of racemisation epimerisation of four amino acids isoleucine aspartic acid phenylalanine and glutamic acid was measured in land snail shells of the genus theba the age calculation algorithms of these amino acids h a v e b e e n determined to permit t he numerical dating of these deposits eight a m i n o z o n e s e a ch defining dune palaeosol formation episodes have been distinguished and dated at 4 8 6 6 4 42 5 6 0 37 8 4 6 29 4 4 8 22 4 4 5 14 9 3 6 11 0 4 0 and 5 4 1 1 ka b p t h e first f i ve of t h em defining c y c l e s of 5 7 ka the alternation of palaeosols and a e o l i a n deposits w h i c h are related to abrupt transitions from humid to arid conditions are t he reflection of globally induced changes in north africa palaeoenvironmental conditions linked to the effect of african palaeomonsoons on the trade w i n d s and the saharan air layer probably these a eolian cycles with a recurrence neriod of 5 7 ka are t he expression of multiples of the 2 4 ka solar cycle

astronomical forcing of northwest african climate and glacial history during the late messinian 6 5 5 5 ma abstract high resolution physical chemical and biological based climate proxies from the ain el beida aeb section in atlantic morocco reveal the imprint of the three main orbital parameters precession 19 23 kyr obliquity 41 kyr and eccentricity 95 125 and 400 kyr between 6 5 and 5 5 million years before present ma the precession related variations are most prominently reflected in the color reflectance and chemical composition of the sediment showing that precession minimum configurations lead to more humid climate conditions in northwest africa probably related to the atlantic system while more arid climate conditions prevailed during precession maxima in addition precession bound changes in planktonic foraminifera and calcareous nannofossil assemblages indicate that sea surface temperature sst increased during the humid phases while productivity conditions increased during the dry periods the clear imprint of the short and long term eccentricity cycles is explained by a non linear climatic response to the precession forcing with overall more humid climate conditions during eccentricity maxima the obliquity controlled variations in sst and aridity conditions concur with glacial interglacial variability that is conspicuously recorded in both planktonic and benthic 18 o records of aeb the observed warm and wet climates during interglacial periods most likely reflect the direct ice driven thermal response to the reduced ice sheets and more active atlantic depressions similar as during the pliocene and pleistocene obliquity controlled variations in the planktonic and benthic carbon isotope 13 c records of aeb are inversely related to the oxygen isotope records with more depleted values during glacial stages although with a small lag the close correspondence between the 13 c records of aeb and other open ocean sites i e sites 982 and 926 may therefore point to large scale glacial controlled variations in the deep sea carbon reservoir superimposed on the orbital variations the imprint of the onset of the messinian salinity crisis can be traced by a marked 1 0 negative excursion in planktonic 13 c at 6 0 ma followed by a prominent peak in ti al at 5 97 ma

tectonics and history of the andaman sea region abstract the andaman sea is an active backarc basin lying above and behind the sunda subduction zone where convergence between the overriding southeast asian plate and the subducting australian plate is highly oblique the effect of the oblique convergence has been formation of a sliver plate between the subduction zone and a complex right lateral fault system the late paleocene collision of greater india and asia with approximately normal convergence started clockwise rotation and bending of the northern and western sunda arc the initial sliver fault which probably started in the eocene extended through the outer arc ridge offshore from sumatra through the present region of the andaman sea into the sagaing fault with more oblique convergence due to the rotation the rate of strike slip motion increased and a series of extensional basins opened obliquely by the combination of backarc extension and the strike slip motion these basins in sequence are the mergui basin starting at 32 ma the conjoined alcock and sewell rises starting at 23 ma east basin separating the rises from the foot of the continental slope starting at 15 ma and finally at 4 ma the present plate edge was formed alcock and sewell rises were separated by formation of the central andaman basin and the faulting moved onshore from the mentawai fault to the sumatra fault system bisecting sumatra

fossil bee cells from the canary islands ichnotaxonomy palaeobiology and palaeoenvironments of palmiraichnus castellanosi fossil bee cells attributable to the ichnospecies palmiraichnus castellanosi are recorded from the pleistocene and holocene of the easternmost canary islands cells bear a chamber with internal smooth lining spiral closure and an antechamber they have a discrete wall that surrounds both the chamber and antechamber the antechamber shows an internal smooth surface and a structureless filling of palaeosol material these features enable this material to be assigned to the ichnospecies p castellanosi originally described from the palaeogene of uruguay this record constitutes the first documented evidence for bees and hymenoptera in the quaternary of the canaries and the first for this ichnospecies from africa by comparison with extant cells the potential constructors are bees of the genus andrena andrenidae palaeoecological and statistical data suggest that five species may have produced p castellanosi in the canary islands one on lanzarote in the holocene another in south fuerteventura in the upper pleistocene two on gran canaria and another on montana clara islet during the middle pleistocene a high level of breeding success was probably favoured by the lack of predators or parasites and optimal environmental conditions at least in the pleistocene during the pleistocene the abundance of p castellanosi in the lowlands suggests a rich endemic shrubby flora and palaeoclimatic conditions similar to the present but probably with a higher humidity the land snail assemblage associated with low densities of p castellanosi in the holocene mid altitude belt suggests a cool moist palaeoenvironment less favourable for p castellanosi producers

pleistocene holocene environmental change in the canary archipelago as inferred from the stable isotope composition of land snail shells abstract the isotopic composition of land snail shells was analyzed to investigate environmental changes in the eastern canary islands 28 29 n over the last 50 ka shell 13c values range from 8 9 to 3 8 at various times during the glacial interval 15 to 50 ka moving average shell 13c values were 3 higher than today suggesting a larger proportion of c4 plants at those periods shell 18o values range from 1 9 to 4 5 with moving average 18o values exhibiting a noisy but long term increase from 0 1 at 50 ka to 1 6 1 8 during the lgm 15 22 ka subsequently the moving average 18o values range from 0 0 at 12 ka to 0 9 at present calculations using a published snail flux balance model for 18o constrained by regional temperatures and ocean 18o values suggest that relative humidity at the times of snail activity fluctuated but exhibited a long term decline over the last 50 ka eventually resulting in the current semiarid conditions of the eastern canary islands consistent with the aridification process in the nearby sahara thus low latitude oceanic island land snail shells may be isotopic archives of glacial to interglacial and tropical subtropical environmental change

on the mechanism of seismic decoupling and back arc spreading at subduction zones to address the problem of the great variability of the mechanical state of subduction zones we investigate the mechanics of back arc spreading and seismic decoupling back arc spreading is assumed to be due to rifting of the upper plate and hence occurs when trench normal tension reaches a critical value seismic decoupling is assumed to occur when the normal stress at the frictional interface is decreased by an amount sufficient to cross the friction stability transition two forces are important in this problem the first is a small component of the slab pull force which remains unbalanced by the subduction resistance and exerts a vertical suction force at the trench the second is a sea anchor force exerted on the slab that resists its lateral motion assumed to occur at the upper plate velocity both forces contribute to the coupling problem only the sea anchor force is responsible for back arc spreading the unbalanced slab pull force is determined from a force balance for subduction the sea anchor force is computed as the hydrodynamic resistance to the facewise translation of an elliptical disc through a viscous fluid the model predicts three regimes seismically coupled compressional arcs with advancing upper plates seismically decoupled extensional arcs with retreating upper plates and strongly extensional arcs which also have back arc spreading this model is applied in detail to the izu bonin marianas system it shows that back arc spreading occurs when the integrated tension in the upper plate exceeds a value of about 1 1013 n m 1 and requires a residual tension of about a third that to drive the back arc spreading once rifting is completed it shows why the plate interface near guam is seismically coupled while the plate boundary everywhere farther north is decoupled when applied globally it successfully predicts the state of seismic coupling and back arc spreading in more than 80 of the world s subduction zones of the remaining half can be seen to contain additional complications not included in the model about 10 of cases remain unexplained but some of these may have incorrectly determined seismic coupling coefficients

constraints on 2004 sumatra andaman earthquake rupture from gps measurements in andaman nicobar islands the 26 december 2004 sumatra andaman earthquake mw 9 0 9 3 is the greatest earthquake of the modern seismological era the rupture characteristics of the earthquake particularly in the andaman nicobar region are not well resolved from seismological or far field geodetic data here in this article we present campaign mode global positioning system gps measurements of coseismic displacements at 13 sites in the andaman nicobar islands before and after the 2004 sumatra andaman earthquake these measurements provide improved estimates of rupture characteristics in the region coseismic horizontal ground displacement of 1 5 6 5 m towards the southwest and coseismic vertical displacement mostly subsidence of 0 5 2 8 m occurred along the andaman nicobar islands with maximum displacements in the nicobar islands we estimate coseismic slip under the andaman and nicobar islands as 3 8 7 9 m and 11 15 m respectively the length of the rupture is estimated to be about 1500 km with a width varying from 120 km under middle andaman island to 160 km under great nicobar island gps measurements during january 11 22 2005 from port blair suggest rapid afterslip in the postseismic period limited gps data available from 1995 measurements at two sites in andaman provide evidence of strain accumulation that varied significantly in the 10 yr preceding the earthquake d 2005 elsevier b v all rights reserved

structural evolution and strike slip tectonics off north western sumatra abstract based on new multi channel seismic data swath bathymetry and sediment echosounder data we present a model for the interaction between strike slip faulting and forearc basin evolution off north western sumatra between 2 n and 7 n we examined seismic sequences and sea floor morphology of the simeulue and aceh forearc basins and the adjacent outer arc high we found that strike slip faulting has controlled the forearc basin evolution since the late miocene the mentawai fault zone extends up to the north of simeulue island and was most probably connected farther northwards to the sumatran fault zone until the end of the miocene since then this northern branch jumped westwards initiating the west andaman fault in the aceh area the connection to the mentawai fault zone is a left hand step over in this transpressional setting the tuba ridge developed we found a right lateral strike slip fault running from the conjunction of the west andaman fault and the tuba ridge in ssw direction crossing the outer arc high as a result extrusion formed a marginal basin north of simeulue island which is tilted eastwards by uplift along a thrust fault in the west the shift of strike slip movement in the aceh segment is accompanied by a relocation of the depocenter of the aceh basin to the northwest forming one major neogene unconformity the simeulue basin bears two major neogene unconformities documenting that differences in subsidence evolution along the northern sumatran margin are linked to both forearc evolution related to subduction processes and to deformation along major strike slip faults

morphology and tectonics of the andaman forearc northeastern indian ocean summary the andaman sea has developed as the result of highly oblique subduction at the western sunda trench leading to partitioning of convergence into trench perpendicular and trench parallel components and the formation of a northward moving sliver plate to accommodate the trench parallel motion the andaman forearc contains structures resulting from both components of motion the main elements of the forearc are the accretionary prism and outerarc ridge a series of forearc basins and major n s faults the accretionary prism is an imbricate stack of fault slices and folds consisting of ophiolites and sediments scrapped off the subducting indian plate the western outer slope of the accretionary prism is very steep rising to depths of 1500 2000 m within a distance of 30 km there is a difference in the short wavelength morphology between the western and eastern portions of the accretionary prism the outer portion consists of a series of faulted anticlines and synclines with amplitudes of a few 100 to 1000 m and widths of 5 15 km resulting from ongoing deformation of the sediments the inner portion is smoother with lower slopes and forms a strong backstop the width of the deforming portion of the accretionary prism narrows from 80 to 100 km in the south to about 40 km between 10 n and 11 30 n it remains at about 40 km to 14 40 n north of there the inner trench wall becomes a single steep slope up to the myanmar shelf the eastern edge of the outerarc ridge is fault bounded and north of the nicobar islands a forearc basin is located immediately to the east a deep gravity low with very steep gradients lies directly over the forearc basin the west andaman fault waf and or the seulimeum strand of the sumatra fault system form the boundary between the burma and sunda plates south of the andaman spreading centre the waf is the most prominent morphologic feature of the andaman sea and divides the sea into a shallow forearc and a deeper backarc region the diligent fault runs through the forearc basin east of little andaman island although it has the general appearance of a normal fault multichannel seismic data show that it is a compressional feature that probably resulted from deformation of the hanging wall of the eastern margin fault this could occur if the forearc basins were formed by subduction erosion of the underlying crust rather than by east west extension

stress change and effective friction coefficient along the sumatra andaman sagaing fault system after the 26 december 2004 m w 9 2 and the 28 march 2005 m w 8 7 earthquakes the 2004 aceh and 2005 nias events are the two greatest earthquakes of the past 40 years with a total rupture of 1700 km long and a coseismic slip reaching up to 25 m these two earthquakes have caused large stress perturbations which significantly altered seismic activity in the sumatra andaman region using both detailed mapping of failure planes and various slip distributions we calculate this stress change along the sumatra andaman sagaing fault system from central sumatra to southern myanmar the static coulomb stress change delta cff and the observed seismic activity are in very good agreement with a coulomb index similar to 20 greater than the one obtained for random events compared to previous studies this high coulomb index confirms two important issues on the use of static stress change criterion unsuited to study near field aftershocks and only relevant for aftershocks analysis on large and mature faults at a time scale of several months the calculated delta cff distribution suggests that the 2004 and 2005 earthquakes inhibit failure on the north andaman rift and on the sagaing fault while failure is encouraged along the transform andaman zone the central andaman rift the west andaman fault the sumatra fault system and the offshore thrust faults west of sumatra island the maximum value of similar to 15 20 bar 1 5 2 mpa for delta cff is reached in the northern part of the sumatra fault system this high value together with the lack of major earthquake in the last 170 years result in a high seismic hazard for this region our results are also consistent with temporal evolution of both earthquakes location and focal mechanism prior to and after the events in particular we explain the occurrence and the mechanism of seismic swarms observed in the central andaman rift and along the west andaman fault finally our calculations reveal that the seismicity in the andaman rift zone can only be explained if mu 0 5 this result leads to two end member models one with a constant and high fault friction and one with spatial variations for which friction may depend on either the nature of the lithosphere oceanic versus continental or the fault type

changes in pleistocene gastropod faunas on fuerteventura canary islands and implications on shifting palaeoenvironmental conditions abstract malacological studies on middle to late pleistocene aeolianite palaeosurface sequences have been approached in order to detect environmental changes and system shifts on the eastern canary islands our results reveal that over the last approximately 360 ka gastropod associations changed fundamentally allowing the derivation of eight different biozones the majority of these malacozones and particular species were limited to specific stratigraphic positions and periods we therefore assume that quaternary gastropods on fuerteventura may offer the opportunity to correlate lithostratigraphic units on the basis of key species furthermore environmental conditions could be derived from these associations pointing to colder semi arid conditions related to the obelus zone around 360 to 340 30 ka a subsequent temperature rise around 340 30 ka leading to moderate and dryer conditions for the cochlicella zone a strong environmental change around 300 30 ka with frequent ephemeral rainfalls for the pomatias zone and an increase in temperature and aridity for late pleistocene deposits linked to the rumina zone we assume that shifts in malacozonation were triggered by changing climate conditions furthermore the alternation between sand layers and palaeosurfaces is not continuously in conformity with malacozonation we therefore assume these stratigraphic changes to be not primarily related to climatic forcing but instead biased by an overlap of multiple factors as palaeosurfaces indicate favourable conditions increased gastropod biodiversities and distinct shrub vegetation we assume that these were caused by increased edaphic moisture due to a better water holding capacity in silty palaeosurfaces rather than by more humid climate conditions

seismic coupling and uncoupling at subduction zones seismic coupling has been used as a qualitative measure of the interaction between the two plates at subduction zones kanamori 1971 introduced seismic coupling after noting that the characteristic size of earthquakes varies systematically for the northern pacific subduction zones a quantitative global comparison of many subduction zones reveals a strong correlation of earthquake size with two other variables age of the subducting lithosphere and convergence rate the largest earthquakes occur in zones with young lithosphere and fast convergence rates while zones with old lithosphere and slow rates are relatively aseismic for large earthquakes results from a study of the rupture process of three great earthquakes indicate that maximum earthquake size is directly related to the asperity distribution on the fault plane asperities are strong regions that resist the motion between the two plates the zones with the largest earthquakes have very large asperities while the zones with smaller earthquakes have small scattered asperities this observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between the two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface while the variation in asperity size is used to establish a connection between earthquake size and tectonic stress it also implies that plate age and rate affect the asperity distribution plate age and rate can control asperity distribution directly by use of the horizontal compressive stress associated with the preferred trajectory i e the vertical and horizontal velocities of subducting slabs are determined by the plate age and convergence velocity indirect influences are many including oceanic plate topography and the amount of subducted sediments all subduction zones are apparently uncoupled below a depth of about 40 km and we propose that the basalt to eclogite phase change in the down going oceanic crust may be largely responsible this phase change should start at a depth of 30 35 km and could at least partially uncouple the plates by superplastic deformation throughout the oceanic crust during the phase change

implication of welded breccia in muong nong type tektites tektites are considered to have originated 1 as ejecta from terrestrial cometary impacts1 2 or from terrestrial meteorite or asteroid impacts3 4 2 in cometary impacts in which splash form tektites were ejected and muong nong type tektites were produced in their place5 6 or 3 as volcanic ejecta from the moon7 welded breccias fig 1 have recently been reported in several muong nong type tektites from thailand8 two additional welded breccia structures of a more complex nature are described here which show evidence of having experienced two distinct periods of high temperatures during their formation separated by a minimum of several minutes of cooling through the annealing range this implies a prolonged multi stage formation process entirely at the site of origin in contrast theories of ejection of tektite glass from terrestrial meteorite impact craters or cometary collision events imply instant formation

characteristics nature and formation of palaeosurfaces within dunes on fuerteventura the appearances of palaeosurfaces intercalated into palaeo dune fields on fuerteventura are multifaceted although reddened layers in these dune sediments might suggest that strong soil formation processes have taken place the combination of aridity and parent material namely biogenic carbonate sand of shelf origin reveals that strong soil formation seems unlikely these sediments rather represent de and recalcification processes only solely in the case of admixed material of volcanic origin and dust deposits further soil forming processes seem to be possible hematite rich saharan dust contributes to reddish colouration of the palaeosurfaces in addition caco3 coated iron particles appear to be ingredients of dust being leached after deposition and transformed to hematite overall we propose much weaker soil forming processes during the pleistocene than previously postulated our findings support the relevance of local environments carbonate sands of shelf origin hinder strong soil formation and the reddish layers separating dune generations are palaeosurfaces which mainly consist of saharan dust after deposition of allochthonous material these layers are overprinted by weak soil forming processes the formation of palaeosurfaces primarily depends on morphodynamically stable periods during limited sand supply our data suggest a cyclicity of processes in the following order 1 sand accumulation 2 dust accumulation and weak soil formation and 3 water induced erosion for the canary islands we support the assumption of glacial maxima being periods of increased levels of moisture in combination with rising sea level we propose that favorable conditions of surface stability occur immediately after glacial maxima during periods of starting transgression whereas regression periods immediately after sea level high stands seem to yield the highest sand supply for the study area

multiple microtektite horizons in upper eocene marine sediments no evidence for mass extinctions microtektites have been recovered from three horizons in eight middle eocene to middle oligocene marine sediment sequences five of these occurrences are coeval and of latest eocene age 37 5 to 38 0 million years ago three are coeval and of early late eocene age 38 5 to 39 5 million years ago and three are of middle oligocene age 31 to 32 million years ago in addition rare probable microtektites have been found in sediments with ages of about 36 0 to 36 5 million years the microtektite horizon at 37 5 to 38 0 million years can be correlated with the north american tektite strewn field which has a fission track age minimum of 34 to 35 million years and a paleomagnetic age of 37 5 to 38 0 million years there is no evidence for mass faunal extinctions at any of the microtektite horizons many of the distinct faunal changes that occurred in the middle eocene to middle oligocene can be related to the formation of the antarctic ice sheet and the associated cooling phenomena and intensification of bottom currents that led to large scale dissolution of calcium carbonate and erosion which created areally extensive hiatuses in the deep sea sediment records the occurrence of microtektite horizons of several ages and the lack of evidence for faunal extinctions suggest that the effects of extraterrestrial bolide impacts may be unimportant in the biologic realm during middle eocene to middle oligocene time

geochemistry of tektites and impact glasses glass produced by melting during impact events is called impact glass or impactite although impact crate ring produces a great variety of shock metamorphosed rocks all of which are called impactites by various authors to a differing extent we restrict the use of this term here to material completely converted into glass the degree of metamorphism seen in different classes of impact materials starting with those showing simple shock effects shock lithification shatter cones diaplectic glasses coesite stishovite lechatelierite impact breccias glass depends on the peak pressure and temperature the rock has experienced as a result of mixing brecciation and similar processes impact glasses also tend to include fragments of less shocked or less homogeneous metamorphosed rocks we limit our discussion here however to the more homogeneous members of the terrestrial impactite family a discussion of lunar impact glasses was given by delano et al 1981 another group of natural glasses are tektites which at first glance are similar to obsidian most tektites are very homogeneous often aerodynam ically shaped spherically symmetric objects that are several centimeters in size and are found in various areas referred to as tektite strewn fields in reflected light they are usually black but in transmitted light they show variations of grey brown and green the surface features gouges furrows grooves pits striations clearly distinguish them from terrestrial volcanic glasses and have probably originated from solution etching and weathering effects on earth baker 1963 lamarche et a1 1984 and from surface stresses occurring during their cooling tektites found in geographically adjacent

regional conductance map of andaman and nicobar region abstract to image the electrical conductivity distribution fluxgate magnetometers are operated at five sites in andaman and nicobar region transfer functions are estimated for the period range 8 128 min from nighttime transient geomagnetic variations using robust regression analysis the observed induction arrows in andaman islands are found to point towards east despite deep sea located towards its west this indicates that fore arc basin andaman nicobar deep is more conducting than the region of outer non volcanic island arc thin sheet model requires the conductance of 10 000 35 000 s with increase conductivity towards the south for explaining the observed induction pattern the observed induction pattern at andaman nicobar stations can be explained in terms of high conducting cretaceous tertiary sediments filling the andaman nicobar deep high conductivity over invisible bank has been attributed to the partial melts volatile fluids derived from the subducting indian plate that are intruding into the eastern margin of fore arc basin through the west andaman fault waf the induction pattern at great nicobar station campbell bay may be related to the highly conducting sediments filling the mergui basin along with mafic intrusions also crustal transition occurs below the mergui terrace at the malayan coast contributing to the enhanced conductivity anomaly

the potential for giant tsunamigenic earthquakes in the northern bay of bengal the sumatra andaman earthquake and indian ocean tsunami of 2004 came as a surprise to most of the earth science community while it is now widely recognized that the risk of another giant earthquake is high off central sumatra just east of the 2004 earthquake there seems to be relatively little concern about the subduction zone to the north in the northern bay of bengal along the coast of myanmar formerly burma phil cummins suggests however that giant earthquake activity is possible in this region and that a large and vulnerable population may be facing a significant earthquake and tsunami hazard there is a high potential for giant earthquake activity along the coast of myanmar indications that this may be the case include the tectonic environment historical earthquake activity and stress and crustal strain observations these findings suggest that giant earthquakes do occur off the coast of myanmar and that a very large and vulnerable population is thereby exposed to a significant earthquake and tsunami hazard the great sumatra andaman earthquake and indian ocean tsunami of 2004 came as a surprise to most of the earth science community although it is now widely recognized that the risk of another giant earthquake is high off central sumatra1 just east of the 2004 earthquake there seems to be relatively little concern about the subduction zone to the north in the northern bay of bengal along the coast of myanmar here i show that similar indicators suggest a high potential for giant earthquakes along the coast of myanmar these indicators include the tectonic environment which is similar to other subduction zones that experience giant megathrust earthquakes stress and crustal strain observations which indicate that the seismogenic zone is locked and historical earthquake activity which indicates that giant tsunamigenic earthquakes have occurred there in the past these are all consistent with active subduction in the myanmar subduction zone and i suggest that the seismogenic zone extends beneath the bengal fan i conclude therefore that giant earthquakes probably occur off the coast of myanmar and that a large and vulnerable population is thereby exposed to a significant earthquake and tsunami hazard

chemical systematics among the moldavite tektites the compositional variations that occur among the moldavite tektites are caused principally by incomplete mixing of two components during fusion with the possible exception of silica there is no evidence for significant losses of volatile species by fractional vaporization chemical constraints have been calculated for the two source materials that contributed to the moldavites if these tektites were formed by impact fusion as is commonly believed then the compositional systematics preserved within the moldavites suggest that hypersonic flow and ejection of impact melts are orderly processes insights gained from the study of tektites should prove useful in interpreting the chemistries of impact glasses from other bodies in the solar system

geoarchaeological and chronometrical evidence of early human occupation on lanzarote canary islands abstract two desert loess paleosol sequences in sediment traps were investigated using pedo stratigraphy sedimentology soil mineralogy and irsl dating so far we cannot recognise significant irsl age underestimates from the polymineral fine grain fraction of our samples we establish a first palaeoclimatic sequence spanning the past ca 200 ka which can be compared to data from other canary islands and surrounding areas including terrestrial and deep sea records more humid phases on lanzarote are apparently triggered by milankovich forcing but the climate remained semi arid to arid all over the past 200 ka the onset of human occupation of the island during a slightly moister period is bracketed between 5 and 10 ka based on the occurrence of archaeosediments containing bones of ovicaprid this is the first proof of much earlier occupation than witnessed so far from archaeological records the early subsidiary economy had a strong impact on soil stability and landscape shaping of the island

back arc extension in the andaman sea tectonic and magmatic processes imaged by high precision teleseismic double difference earthquake relocation 1 the geometry kinematics and mode of back arc extension along the andaman sea plate boundary are refined using a new set of significantly improved hypocenters global centroid moment tensor cmt solutions and high resolution bathymetry by applying cross correlation and double difference dd algorithms to regional and teleseismic waveforms and arrival times from international seismological centre and national earthquake information center bulletins 1964 2009 we resolve the fine scale structure and spatiotemporal behavior of active faults in the andaman sea the new data reveal that back arc extension is primarily accommodated at the andaman back arc spreading center absc at 10 which hosted three major earthquake swarms in 1984 2006 and 2009 short term spreading rates estimated from extensional moment tensors account for less than 10 of the long term 3 0 3 8 cm yr spreading rate indicating that spreading by intrusion and the formation of new crust make up for the difference a spatiotemporal analysis of the swarms and coulomb stress modeling show that dike intrusions are the primary driver for brittle failure in the absc while spreading direction is close to ridge normal it is oblique to the adjacent transforms the resulting component of e w extension across the transforms is expressed by deep basins on either side of the rift and a change to extensional faulting along the west andaman fault system after the mw 9 2 sumatra andaman earthquake of 2004 a possible skew in slip vectors of earthquakes in the eastern part of the absc indicates an en echelon arrangement of extensional structures suggesting that the present segment geometry is not in equilibrium with current plate motion demands and thus the ridge experiences ongoing re adjustment

burma plate motion 1 plate motion in the indo burmese arc andaman sumatra region of burma plate is poorly resolved this is mainly due to lack of relevant data and complex tectonics of the region we analyze 1 azimuths of coseismic displacements due to the 2004 sumatra andaman and 2005 nias earthquakes 2 estimates of interseismic deformation in the indo burmese arc andaman sumatra and sagaing fault regions all based on gps measurements 3 long term plate motion rates across sumatra fault system sagaing fault and andaman sea from geomorphological and other geophysical studies and 4 the earthquake focal mechanisms in the region we suggest that the ssw motion of sunda plate with respect to indian plate may be partitioned into the dextral strike slip motion across the sagaing fault in the north and sumatra fault system in south in the back arc region and the arc normal motion across the sumatra subduction zone which becomes oblique in andaman and southern indo burmese arc region and dextral in the northern indo burmese arc region of the fore arc under the rigid plate approximation we estimate a pole for india burma plate pair at 27 1 n 82 1 1 e with an angular velocity of 0 845 0 12 ma and for burma sunda at 22 3 1 1 n 109 3 2 5 e with an angular velocity of 0 67 0 12 ma thus the plate motion in the northern and southern regions of burma plate namely the indo burmese arc and andaman sumatra arc may be explained by a single pole and does not require a boundary between the two

homogeneous impact melts produced by a heterogeneous target sr nd isotopic evidence from the popigai crater russia the 35 7 0 2 ma old popigai crater siberia with a diameter of about 100 km is one of the best preserved large terrestrial impact structures the heterogeneous target at the impact site consists of archean to lower proterozoic metamorphic rocks of the crystalline basement upper proterozoic quartzites and other clastic deposits as well as cambrian to cretaceous clastic sediments and sedimentary rocks including carbonate rocks moreover proterozoic and permo triassic dolerite dykes are found in the target area we report major element sr and nd isotope data for 13 of these target rocks and for various types of impactites the 15 analysed impactite samples include tagamites impact melt rocks suevites and impact glass from small veins furthermore two impact breccias and two impact glass coated gneiss bombs were analysed we discuss the relation of these impactites to the target lithologies and evaluate on the basis of literature data the relation of microkrystites and associated microtektites in upper eocene sediments to the popigai event the impactites have sio2 abundances ranging from 59 to 66 wt and show significant variations in the content of fe ca and ti they have present day 87sr 86sr ratios between 0 7191 and 0 7369 their sr model ages tsrur range from 1 9 to 2 3 ga the 143nd 144nd ratios for the impactite samples cluster between 0 5113 and 0 5115 the nd model ages tndchur range from 1 9 to 2 1 ga in an echur nd eur sr diagram the impactites and upper eocene microkrystites and associated microtektites plot in a field delimited by popigai target lithologies the impactites are restricted to the field of crystalline basement rocks and upper proterozoic quartzites but they show different isotopic signatures in different crater sectors impactites and upper eocene microkrystites plot in different only partly overlapping clusters the leucocratic microkrystites and microtektites have a higher affinity to the post proterozoic rocks in the target area than the impactites seemingly the melanocratic microkrystites originated mostly from crystalline basement this data alignment supports the assumption that popigai is the source crater for all three types of ejecta for the first time clear relations are established of the geochemically variable upper eocene microkrystites and associated microtektites to specific target lithologies at popigai crater finally the observed range in sr and nd isotope parameters determined for impact melt lithologies that originated during the popigai event show a much higher variability than known from other craters this result indicates that mixing of impact melt which later formed tagamite sheets and glass particles in different impact breccias was incomplete at the time of ejecta dispersal