structural setting of the bay of naples italy seismic reflection data implications for campanian volcanism abstract this paper focuses on the recent tectonic evolution of the bay of naples with the aim of exploring the connection between local tectonics and volcanism we reprocessed the seismic reflection dataset acquired in the area in the late 1973 the new processing was highly successful in obtaining a decisive strong reduction of random noise removal of coherent noise and reduction of spatial aliasing classical interpretative schemes and complex attributes of seismic traces were used to reconstruct fault kinematics and reflector patterns the results show that the faults affecting the bay of naples exhibit prevailing ne structural strikes with the exception of the pozzuoli caldera where nw patterns are also common many faults are subvertical and show seismic evidence of volcanic activity along them a main alignment of conjugate ne sw faults named here as magnaghi sebeto line intersects several submarine volcanic banks and separates the bay into two sectors characterized by important geological geophysical and petrochemical differences the structural configuration of the bay may reflect the occurrence of either oblique extension or a transfer zone of the nw se fault system along which in the campanian lucanian apennine chain great vertical displacements occur

geometry of the livingstone mountains border fault nyasa malawi rift east africa we use multifold seismic reflection profiles to constrain the geometry and slip sense of a half graben border fault and the extension direction in the adjacent rift basin our data are from the western branch of the east african rift system often cited as an analog of early stage passive continental margin formation in this case study classic tilt block half graben clearly occur along a documented strike slip fault the livingstone mountains border fault bounds the northernmost basin in the nyasa malawi rift and is a series of straight dextral oblique slip fault segments which mimic the characteristics of a parallel underlying prerift ductile shear zone structures adjacent to the border fault show extension slightly oblique to the border fault indicating that the border fault is predominantly a strike slip fault consistent with studies of border fault exposures data indicate overall extension in the adjacent livingstone basin is at a much higher angle to the strike slip border fault consistent with the tilt block half graben architecture this characteristic is similar to basins bounded by weak strike slip faults some aspects of livingstone basin fault geometry resemble pull apart strike slip duplex and extensional imbricate fan fault geometries however the overall inexact match suggests the livingstone basin may be an incipient form of these classic strike slip basin models

the diagenesis of continental karoo tertiary siliciclastics from an east african rift valley rukwa tukuyu area tanzania abstract the diagenetic history of the karoo and jurassic tertiary beds of east african rift valleys is related to the tectonic activity and sedimentary evolution of the rift valley area in the karoo beds early diagenetic calcite and hematite formation are succeeded by mechanical compaction and minor quartz kaolinite and calcite precipitation renewed tectonic activity possible half graben formation and exposure of the karoo beds in jurassic tertiary time resulted in alluvial fan deposition the red sandstone group and associated fresh water flushing caliche formation and hematite precipitation late diagenetic precipitation of potash feldspar and feldspar leaching were the final controls on the porosity and permeability development of the sediments

experiments on simultaneous faulting and folding above a basement wrench fault abstract wrench zones commonly show en echelon patterns of folds in the stratified cover above a basement fault examples are the darien basin in panama and the inglewood fault trend in california folds are often associated with synthetic and antithetic wrench faults but the time relationships between folds and faults may not be obvious we have done experiments where simultaneous faulting and folding occur above a basement fault four experiments were performed using a simple apparatus capable of imposing localised strike slip motions this apparatus consists of two plastic plates one can be moved laterally past the other by a piston thus modelling lateral motion on a single basement fault models were properly scaled to account for gravitational forces brittle behaviour of sandstone and ductile behaviour of clay or shales in the upper crust each model is a vertical succession of silicone layers and sand layers each layer is 2 mm thick except for the basal silicone layer which is 2 4 6 or 8 mm thick in experiments 1 2 3 or 4 respectively all models were deformed at the same slip rate on the basal fault 1 cm h 1 experiments 1 2 and 3 with 8 cm total horizontal sinistral offset were designed to investigate the influence of basal silicone layer thickness on the deformation of a multilayered model experiment 4 with 20 cm of total offset was designed to investigate the influence of an increasing left lateral offset on folding and faulting with a 2 mm thick basal silicone layer experiment 1 synthetic strike slip faults appeared en echelon above the basement fault no folds were visible at the surface of the experiment but the interfaces between sand and silicone layers showed millimetric folds en echelon above the basement fault with a 4 mm thick basal silicone layer experiment 2 en echelon synthetic strike slip faults and folds appeared above the basement fault faults and folds rotated progressively anticlockwise and synclines were activated as dextral antithetic shear zones with a 6 mm thick basal silicone layer experiment 3 synthetic faults and en echelon folds appeared as before but the fold amplitude was larger than in experiment 2 an increasing left lateral offset produced anticlockwise rotation of faults and folds as before and synclines were activated as dextral antithetic shear zones in experiment 4 after 16 cm of left lateral offset the anticlockwise rotation of the folds was such that antithetic dextral shear zones became almost parallel to the basement fault and were then reactivated as synthetic sinistral shear zones

terrestrial heat flow in the malawi rifted zone east africa implications for tectono thermal inheritance in continental rift basins abstract rift basins show the widest range of heat flow values compared to passive continental margins and intracratonic sag basins elevated heat flow is often used to infer asthenospheric upwelling or subsurface magmatic activity for magma assisted rifts despite the lack of surface volcanism for magma poor rifts it is possible that magmatic bodies will be present at lower and mid crustal levels but yet to breach the surface thus necessitating consideration of heat flow from tectono thermal inheritance in addition to more recent magmatism we use aeromagnetic data to investigate the terrestrial heat flow distribution in the malawi rifted zone mrz in east africa defined as the neogene malawi rift and surrounding permo triassic karoo rift basins we use the two dimensional power density spectrum technique to estimate the curie point depth cpd geothermal gradient and heat flow beneath the mrz our results reveal predominance of shallow cpds 18 20 km high geothermal gradients 29 32 c km and elevated heat flow 70 82 mw m 2 within the karoo rift basins along the malawi rift geothermal gradient 25 27 c km and heat flow 60 66 mw m 2 are generally lower except pronounced high heat flow 70 82 mw m 2 at the rungwe volcanic province rvp in the north and at the central rift segment where the rift overprints karoo rift basins the surrounding cratonic blocks show deeper cpds 24 27 km lower geothermal gradients 22 24 c km and lower heat flow 53 63 mw m 2 we interpret that the elevated heat flow in the karoo rift basins are related to residual heat flow from the permo triassic rifting phase replenished by later jurassic cretaceous diking events apart from the thermal anomaly beneath the rvp which is due to neogene magmatism other important targets for geothermal explorations in the mrz are the residual thermal anomalies in the karoo rift basins we infer that in areas of active magma poor rifting pronounced heat flow may not only occur in regions of asthenospheric upwelling but may concentrate in the ancient magmatic rift segments our findings have implications for crustal stretching tectono thermal inheritance and geothermal energy potentials in east africa and other segments of magma poor rifting

signs of potential renewal of eruptive activity at la fossa vulcano aeolian islands since the end of the last magmatic eruption 1890 activity of la fossa southern tyrrhenian sea italy has consisted of fumarolic emissions of fluctuating intensity fluids are discharged principally at two fumarolic fields located in the northern rim of the active crater and at the beach sited at its northern foot increased thermal seismic and geochemical activity has been recorded since 1978 when an earthquake of m 5 5 occurred in the region this paper combines available geophysical and geochemical information in order to develop a tentative interpretation of two episodes of apparent unrest which occurred in 1985 and 1987 1988 enhancing the risk of renewal of the eruptive activity the 1985 unrest consisted essentially of a sharp build up of the internal pressure in the shallow hydrothermal system which was induced by the injection of hot gases of magmatic origin the crater fumaroles displayed significant increases in co2 and other acid species but their outlet temperature did not change conversely the 1987 1988 episode was characterized by appreciable modifications at the crater fumaroles with only secondary effects at the fumarole system of the beach the sliding of part of the eastern flank of the la fossa cone into the sea occurred on 20 april 1988 when the region was affected by crustal dilatation producing a seismic sequence of relatively high intensity both episodes of unrest were accompanied by increases of local microseismic activity which affected the nothern sector of the island in 1985 and the southern one in 1988 finally a phase of appreciable areal contraction was detected in 1990 probably due to the effect of the cooling and crystallization of magma at relatively shallow depths accompanying the increased thermal activity at the crater fumaroles regional tectonic stress seems to play an important role in the transition of the volcanic system from a phase of relative stability to a phase of apparent unrest inducing the heating and the expansion of shallow hydrothermal fluids available information is insufficient to indicate whether or not the volcano is building towards the renewal of a magmatic eruption and there is no evidence to hypothesize episodes of significant magma migration the frequency of measurements of many parameters needs to be increased in order to learn more about the temporal relationships between geochemical and geophysical variations preceding and accompanying periods of increased thermal activity this will probably be a valid tool for recognizing short term precursors of a future eruption reducing the risk of false alarms

the north tanganyika hydrothermal fields east african rift system their tectonic control and relationship to volcanism and rift segmentation the two branches of the east african rift system include numerous hydrothermal fields which are closely related to the present fault motion and to volcanic and seismic activity in this study structural data from pemba and cape banza hydrothermal fields western branch north tanganyika zaire are discussed in terms of neotectonic phenomena different types of records such as fieldwork onshore and underwater and landsat and spot imagery are used to explain structural controls on active and fossil hydrothermal systems and their significance the pemba site is located at the intersection of 000 020 trending normal faults belonging to the uvira border fault system and a 120 130 trending transtensional fault zone and is an area of high seismicity with events of relatively large magnitude ms 6 5 the cape banza site occurs at the northern end of the ubawari peninsula horst it is bounded by two fault systems trending 015 and is characterized seismically by events of small magnitude ms 4 the hydrothermal area itself is tectonically controlled by structures striking 170 180 and 080 the analysis of both hydrothermal areas demonstrates the rejuvenation of older proterozoic structures during recent rift faulting and the location of the hydrothermal activity at the junctions of submeridian and transverse faults the fault motion is compatible with a regional direction of extension of 090 110 the cape banza and pemba hydrothermal fields may testify to magma chambers existing below the junctions of the faults they appear to form at structural nodes and may represent a future volcanic province together with the four surface volcanic provinces existing along the western branch they possibly indicate an incipient rift segmentation related to valley valley or transverse fault valley junctions contrasting with the spacing of the volcanoes measured in the eastern branch these spacings appear to express the different elastic thicknesses between the eastern and western branches of the east african rift system perhaps related to a difference in stage of evolution of the two branches

analogue modelling of orthogonal and oblique rifting abstract the three dimensional progressive development of orthogonal and oblique rift systems has been simulated using scaled analogue sandbox models the orientation of the zone of rifting where angle between the rift axis and the extension direction was varied systematically from 90 orthogonal rifting to 75 60 and 45 oblique rifting completed models were impregnated and sectioned both vertically and horizontally orthogonal rift models are characterized by long straight rift border faults and intra rift faults perpendicular to the extension direction oblique rift models are characterized by shorter segmented rift border faults and intrarift faults in the oblique models the rift border faults formed en echelon arrays parallel to the inderlying zone of basement stretching whereas the intra rift faults formed at a high angle to the extension vector increased extension in the moderately oblique and oblique rift systems 60 and 45 caused the intra rift faults to rotate towards parallelism with the rift border faults no strike slip or oblique slip transfer faults were found in any experiments rift border faults and intra rift faults in the models are segmented along strike with relay ramp structures formed between overlapping fault tips along the strike of the rift variations in half graben polarities and offsets of depocentres are accomplished by accommodation zones formed by interlocking conjugate fault arrays the experimental fault patterns compare well with the fault architectures found in those modern or relatively young rift systems where well defined basement controlled strike slip or oblique slip transfer faults are absent an accommodation zone model consisting of interlocking conjugate extension faults is proposed for the along strike switching of half graben asymmetries and offsetting of depocentres in rift systems the fault geometries in the analogue models can be used as templates for recognition of fault styles in both orthogonal and in oblique rift environments

evidence for high frequency cyclic fault activity from high resolution seismic reflection survey rukwa rift tanzania a high resolution seismic survey of the rukwa rift has imaged the upper 300 m of the pliocene holocene section the sediments are characterized by aggradational deposition in shallow lacustrine conditions that episodically dried out overall the reflection package expands northeastwards towards the lupa fault half graben bounding fault isopach maps for nine intervals 6 m to 65 m thick show four periods of marked expansion of the section towards the lupa fault interpreted to represent times of fault activity or infilling of fault created topography during the early stage of fault quiescence there are three periods of little or much reduced expansion interpreted to represent infilling of the accommodation space between the lake floor and the lake surface during periods of fault inactivity cyclicity of such high frequency has not been widely reported for faults which penetrate the crust the periods of activity show remarkably similar displacement patterns with no lateral migration of the main depocentre implying that seismic and aseismic slip has persistently clustered in the same parts of the fault identification of high frequency fault cyclicity has implications for sequence stratigraphy in tectonically active areas since there is a tendency to assume faults do not have cyclic effects on the scale of tens of thousands of years

crustal structure at a young continental rift a receiver function study from the tanganyika rift the southern tanganyika rift within the western rift africa has earthquakes to depths of 37 km yet few constraints exist on crustal thickness or of early stage rifting processes in apparently amagmatic rift sectors the aim of the tanga14 experiment was to constrain bulk crustal properties to test whether magmatic processes modify the lithosphere in areas of deep seismicity and the degree of lithospheric thinning we use eleven broadband seismometers to implement receiver function analysis using h stacking a method sensitive to crustal thickness and vp vs ratio to determine bulk crustal properties analyses include extensive error analysis through bootstrap variance and phase weighted stacking results show the archean tanzanian craton and bangweulu block are characterized by vp vs ratios of 1 75 1 77 implying a felsic bulk composition crust beneath the fault bounded basins has high vp vs 1 9 anorthosite bodies and surface sediments within the region may contribute to localized high vp vs however elevated vp vs values within fault bounded extensional basins where elevated heat flow hydrothermal vent sites and deep earthquakes are observed suggest that magma may be intruding the lower crust beneath the southern tanganyika rift crustal thicknesses on near the relatively un extended tanzanian craton and bangweulu block are 41 6 42 0 km this contrasts with the tanganyika rift where crustal thicknesses are 31 6 km to 39 km from north to south our results provide evidence for 20 crustal thinning localized to fault bounded basins taken together they suggest a previously unrecognized role of magma intrusion in early stage continental rifting in the western rift africa

sand box modelling of basement controlled transfer zones in extensional domains the interaction modalities of transfer zones connecting rift segments may be influenced by several factors amongst these the location and architecture of transfer zones in narrow rifts has been repeatedly associated with the presence of inherited basement anisotropies sand box models were made to investigate how the orientation geometry and kinematics of transfer zones depend upon pre existing basement anisotropies analogue models reproduced offset rift segments linked by transfer zones bordered by arcuate normal faults strike slip faults are present inside the transfer zone provided that angle between the extension direction and the axis of the transfer zone is less than 50 narrower transfer zones striking oblique to the extension direction occur for angle between the direction perpendicular to the extension direction and the direction of the basement anisotropy less than 90 wider transfer zones subparallel to the extensional direction occur for 90 increasing the overstep induces narrower transfer zones striking subparallel to the extension direction similar geometrical and kinematical patterns have been found at transfer zones in narrow rifts the comparison between experimental and natural data shows how the geometry kinematics and orientation of natural transfer zones depends upon the trend of inherited anisotropies transfer zones along inherited basement structures set at lower angles to the extension direction and display lower aspect ratios than transfer zones where inherited anisotropies are absent

structural evolution of lake malaŵi africa over 2 000 km of seismic reflection profiles have been collected in lake mala i nyasa the southernmost of the east african rift lakes these studies reported here reveal a severely faulted lake floor bounded by rift structures of pliocene or greater age faults that penetrate the uppermost sedimentary units and numerous earthquakes1 attest to continuing activity in the rift inter basinal differences in fault spacing orientation and sedimentary thicknesses have led to a subdivision of lake mala i into four discrete structural provinces these provinces only now are linked by faults attributed to the most recent episodes of extension an evolutionary sequence of 1 initial block faulting and subsidence 2 fragmentation of fault blocks 3 uplift and 4 renewed subsidence and rotation of fault blocks is proposed for the central part of the mala i rift

factors controlling normal fault offset in an ideal brittle layer we study the physical processes controlling the development and evolution of normal faults by analyzing numerical experiments of extension of an ideal two dimensional elastic plastic brittle layer floating on an inviscid fluid the yield stress of the layer is the sum of the layer cohesion and its frictional stress faults are initiated by a small plastic flaw in the layer we get finite fault offset when we make fault cohesion decrease with strain even in this highly idealized system we vary six physical parameters the initial cohesion of the layer the thickness of the layer the rate of cohesion reduction with plastic strain the friction coefficient the flaw size and the fault width we obtain two main types of faulting behavior 1 multiple major faults with small offset and 2 single major fault that can develop very large offset we show that only two parameters control these different types of faulting patterns 1 the brittle layer thickness for a given cohesion and 2 the rate of cohesion reduction with strain for a large brittle layer thickness 22 km with 44 mpa of cohesion extension always leads to multiple faults distributed over the width of the layer for a smaller brittle layer thickness the fault pattern is dependent on the rate of fault weakening a very slow rate of weakening leads to a very large offset fault and a fast rate of weakening leads to an asymmetric graben and eventually to a very large offset fault when the offset is very large the model produces major features of the pattern of topography and faulting seen in some metamorphic core complexes

volcanic steam output directly measured in fumaroles the observed variations at vulcano island italy between 1983 and 1987 the mass of steam emitted by the fumaroles of the crater of vulcano aeolian islands italy was evaluated by using a direct measuring method measurements were effected with this method between 1983 and 1987 in nine field campaigns the results of which are given in this paper the steam flux measurements were performed by an instrument expressly designed for steam condensation the estimates of the thermal energy transported daily by the steam gave values of up to 10e12 j the sharp variations in the total mass outputs recorded in 1984 and 1985 are here interpreted as being a consequence of the probable accumulation of fluid pressure at depth during the evolution of volcanic activity the different results obtained from the various areas of the fumarolic field during the evolutionary phases have led to the hypothesis that different subsystems exist that feed the fumaroles and that their activity is triggered by volcano tectonics this method can be applied in the evaluation of both fumarolic steam and thermal energy outputs and therefore it is particularly useful in geothermal exploration in the evaluation of the environmental impact of volcanic degassing and in the forecasting of volcanic eruptions the evaluation of the steam output is also useful for quantifying the release of other gaseous species and giving univocal interpretations regarding their variations in concentrations furthermore this direct method provides a new way of calibrating the flux estimates effected by other telemetric techniques lidar cospec etc

cosmogenic 36cl and 10be ages of quaternary glacial and fluvial deposits of the wind river range wyoming we measured cosmogenic 36 cl in 56 samples from boulders on moraines and fluvial terraces in the vicinity of the wind river range wyoming we also measured 10 be in 10 of the same samples most of the 10 be ages were in good agreement with the 36 cl ages indicating that rock surface erosion rates were very low the oldest moraine investigated the type sacagewea ridge site yielded only a limiting minimum age of 232 ka the oldest moraines in the type bull lake complex also could be constrained only to 130 ka the main sequence of type bull lake moraines yielded age distributions indicating deposition within the intervals 130 to 100 ka and 120 to 100 ka the best estimates are closer to the upper limits of these ranges and associated uncertainties are in the range of 10 to 15 these uncertainties could permit deposition in either marine isotope stage 6 or stage 5d we found no evidence of glacial deposits dating to marine isotope stage 4 both bull lake age moraines from fremont lake on the opposite side of the wind river range and boulders on a fluvial terrace above the wind river gave age distributions very similar to that of the second oldest bull lake advance ca 130 to 100 ka the distribution of boulder ages for pinedale moraines at bull lake indicated deposition between 23 and 16 ka nearly identical to the distribution of 10 be ages previously reported for the type pinedale moraines at fremont lake

topographic analysis of devana chasma venus implications for rift system segmentation and propagation abstract devana chasma is a rift system on venus formed in association with the beta regio and phoebe regio volcanic highlands which are interpreted as mantle plumes we present a new analysis of a 2500 km long segment of devana based on the rift topography the horizontal extension across the rift boundary faults is 3 9 km this is a lower bound on the total rift extension because the altimetry does not resolve the topographic relief across the numerous faults that are visible in radar images of the rift floor the total extension across devana is approximately 20 km similar in magnitude to continental rift systems on earth rift flank elevations are up to 3 1 km in the regions nearest the mantle plumes and decay strongly with increasing distance from the plumes indicating a strong thermal component to the rift flank topography unlike the situation usually reported for terrestrial rifts as on earth there is also a flexural uplift component to the flank topography rift depths are up to 2 5 km below the surrounding plains with considerable along strike variability there is a 600 km lateral offset along devana chasma near the mid point between the two mantle plumes devana most likely formed as two distinct rifts due to the horizontal stresses created by outflow from the upwelling plumes the offset zone formed as a result of the interaction between the two rift tips which requires that upwelling at the two mantle plumes overlapped in time

origin of the permian triassic iberian basin central eastern spain abstract the iberian basin was an intracratonic rift basin in central eastern spain developed since early permian times the basin boundary faults were normal listric faults controlling an asymmetric extension propagating northeast with time hercynian or older lineaments controlled the orientation of the iberian basin and extension was accommodated basically in the hanging wall block by the formation of secondary grabens and a central high the basin was related with the coeval ebro catalan and cuenca mancha basins and their connections are discussed subsidence curves show that the early permian early jurassic period of extension can be subdivided into three rifting episodes and a flexural one extension factor increases from 1 17 in the northwest to 1 29 near the mediterranean coast the increasing extension rate was accommodated by transfer faults trending nne ssw more important in the levante area the rift evolution is intermittent and seems to reflect distinct stress fields the collapse of the late hercynian orogen and related increased heat flux extension and rifting is the most probable origin of the iberian basin and related basins the origin of the catalan and the valencia prebetic basins is related to the southwards migration of the hesse burgundy rift along the eastern margin of the iberian microplate

short term development of intracontinental rifts with reference to the late quaternary of the rukwa rift east african rift system abstract relatively low resolution seismic data and high contemporaneous rift topography normally limit quantitative analysis of normal faults in rifts the availability of a recently collected high resolution reflection seismic survey in the se part of the presently active rukwa rift east african rift system coupled with high sedimentation rates in the submerged part of the rift makes detailed quantitative analysis possible high resolution down to about 1 m seismic data penetrate ca 300 m representing about 150 000 years of the uppermost sediments and show fine details of normal faulting and related structures displacements on the faults which occur in the hanging wall of the major rift boundary fault range from a few metres up to 100 m they show increasing displacements with depth and characteristic rollover folding of the hanging walls fault propagation occurred upwards through the rapidly accumulating lake sediments and was preceded by flexuring and folding of the sediments the geometry of the seismic sequences with alternating wedge shaped and tabular units reflects pulsed activity on the faults fault displacement rates of up to 1 6 mm yr 1 have been estimated each extensional pulse has a duration of 1000s to 10 000s of years the quiescent stages have a similar duration up to 2 5 extension has occurred during the recent evolution

paleogene initiation of the western branch of the east african rift the uplift history of the rwenzori mountains western uganda abstract the two branches of the east african rift system ears are believed to have initiated diachronously however a growing body of work continues to suggest the onset of rifting in the western branch occurred in the paleogene coeval to the eastern branch due to a lack of pre miocene stratigraphy attempts to resolve the geological history of the western branch must study the uplift and erosional histories of the modern rift topography in this study the rock uplift history of the rwenzori mountains western uganda is resolved to better our understanding of the tectonic history of the western branch of the ear through the application of low temperature thermochronology mapping and the modelling of river profiles we show that rock uplift of the rwenzori dates back to the oligocene with thermal history models suggesting uplift induced exhumation may date back as far as the eocene this provides tangible evidence that extension began in the region in the paleogene coeval with the eastern branch and not the late neogene these results have broad implications for the tectonic evolution of the entire east african rift system and suggest our current understanding of the region s rift history remains incomplete

patterns of displacement along large normal faults implications for basin evolution and fault propagation based on examples from east africa seismic reflection data across six boundary faults from east africa have revealed information about the way boundary faults develop with respect to the synkinematic basin fill previous models of basin fill assume that lateral fault propagation and deposition occur simultaneously which gives rise to along axis onlap of the basin fill onto the prerift basement propagating basin model seismic reflection data from boundary faults in east africa show only rare evidence for along axis broadening of the basins instead the basin margins appear to be fixed from a very early stage in the basin history nonpropagating basin model depocenters shift not by gradual lateral propagation but by abrupt changes in location such observations indicate that boundary fault propagation to near maximum length occurs rapidly during the very early stages of rifting probably by linkage of numerous small faults displacement then builds following the b value earthquake model along the fault during basin development out of phase with the main propagation phase mature fault systems may have experienced several phases of jumps in fault length or the location of fault activity major boundary faults exhibit three basic patterns of evolution these patterns of evolution can have many variants and include 1 simple displacement where maximum displacement is approximately at the center of the fault and decreases gradually toward the fault tips 2 variable along strike displacement that incorporates linkage of in line or en echelon relatively large displacement faults of similar age leaving transverse anticlines and synclines and 3 asymmetric propagation where one tip of a fault remains more or less fixed while the other tip propagates a relatively long distance asymmetric propagation can occur smoothly and gradually or alternatively there can be a jump in the location of the fault and a new fault of different age can form along strike from the older fault eventually the new fault propagates and links with the older fault segment reactivating the older fault to some extent addition ally long lived faults may be composites of fault types 1 3

geology and geophysics of the rukwa rift east africa exploration in the rukwa rift using gravity and seismic reflection surveys fieldwork and drilling has defined the structure and stratigraphy of the basin in greater detail than any other part of the western rift the stratigraphy comprises precambrian basement karroo sandstones shales and coals upper miocene red beds and miocene recent lacustrine and fluvial sediments during miocene recent rifting the greatest sediment input apparently came from axial fluvial systems flowing from the northwest and southeast the southwestern area experienced alternating shallow lacustrine and fluviodeltaic conditions during the miocene recent cenozoic age rift structures have a dominant nw se and a subordinate n s trend the nw se trend tends to follow a precambrian basement and later karroo structural trend ne sw seismic lines indicate up to 10 km extension of the tertiary section in a direction oblique to the probable e w regional extension direction in the southeastern portion of the basin both karroo and tertiary quaternary sediments expand into the lupa fault zone reaching thicknesses of up to 3 and 7 km respectively tertiary quaternary sediment thicknesses decrease northwestward accompanied by a decrease in the amount of extension and a broadening of the basin as extension is transferred to the lake tanganyika rift

east african rift system offset age and tectonic significance of the tanganyika rukwa malawi intracontinental transcurrent fault zone abstract the 1000 200 km tanganyika rukwa malawi fractures area is shown to be a right lateral intracontinental transform zone belonging to the east african rift system using the results carried out from complementary techniques remote sensing field structural analysis and k ar isotopic dating it appears that tectonics in this area have acted at different times the oldest being at 2000 1400 m y the youngest being still active today and are mainly due to the reactivation of nw se structures the area consists mainly of large nw se en echelon dextral transcurrent faults along which the southern tanganyika rukwa and northern malawi troughs are opening ne sw transverse faults showing a curved horizontal shape end these troughs axially eocene to recent volcanic activity is associated with the intersection of the northeastern main nw se transcurrent fracture the livingstone fault

extension in mona passage northeast caribbean this paper is not subject to u s copyright the definitive version was published in tectonophysics 493 2010 74 92 doi 10 1016 j tecto 2010 07 002

deep crustal earthquakes and active faults along the rukwa trough eastern africa summary since june 1992 a seismic network of five digital stations has been operating in southwestern tanzania with the aim of investigating the seismic activity and its partitioning with regard to depth in the area between lake rukwa and lake malawi during the period 1992 june 15 to 1994 december 31 a reliable location was obtained for 199 local earthquakes 13 were recorded by all five seismic stations 71 by four stations and 115 by three seismic stations with both p and s wave arrival time measurements many earthquakes arc located in the south eastern part of the rukwa basin along its eastern border in a 20 km narrow zone centred on the lupa fault but the more active area is the songwe valley characterized by a narrowing of the basin in the proximity of the important uplift of the mbeya range seismic activity is also present inside intrabasinal faulted blocks the earthquake depth distribution presents an upper seismicity cut offal a depth of 10 to 12 km this upper stability zone is followed by the peak of seismic activity in the depth range 12 to 14 km where 20 per cent of the earthquakes occurred at greater depths the level of activity continuously decreases up to a depth of 34 km a crustal thickness of 42 4 5 km is estimated using arrivals identified as the pmp waves reflected at the base of the crust indicating that the deeper earthquakes are really occurring in the lower crust and not in the upper mantle this analysis confirms at a local scale what is suggested by geophysical and geological observations at a global scale in the western branch of the east african rift system border faults penetrate to lower crustal levels in a lithosphere that is cold and mechanically strong

interplay of structural climatic and volcanic controls on late quaternary lacustrine deltaic sedimentation patterns in the western branch of the east african rift system rukwa rift basin tanzania abstract this paper presents the first detailed outcrop based sedimentologic investigation of the pleistocene holocene upper lake beds succession in the rukwa rift basin located in the western branch of the east african rift system southwestern tanzania the goal of this investigation is to examine the sedimentary facies and reconstruct the depositional environments of this important archive of quaternary climate and environmental change eleven diagnostic facies associations comprising 24 facies were identified and provide the basis for recognition of three key deposystems 1 alluvial to fluvial channel system 2 lake delta system and 3 profundal lacustrine system analysis of paleocurrent indicators and sandstone provenance indicate widely dispersed source regions and drainage patterns that were strongly influenced by major border fault systems and episodic volcanism six stratigraphic sequences a f ranging from 2 to 17 m thick were identified based on stratal stacking patterns and the development of sequence bounding unconformities and lacustrine flooding surfaces sedimentation processes facies architecture and stratigraphic packaging record a complex interplay between quaternary climate fluctuations and intense episodic volcanism in the nearby rungwe volcanic province set against large scale tectonic controls associated with synchronous development of the east african rift system sequence stratigraphic analysis reveals that the rukwa rift basin episodically shifted between a balanced fill lake basin and an overfilled lake basin deep water basin wide lake expansion occurred at different times during the late quaternary the final depositional sequence preserved in the basin a fluvial underfilled lake basin initiated 7 9 ka and has persisted to the present day high frequency climate change played the key role in sequence development in the upper lake beds however voluminous rift related volcanism and erosion of abundant labile volcanic materials from the rungwe volcanic province as well as syntectonic evolution of the rift led to high sedimentation rates and transformation of flash floods and debris flows in the hinterlands rift margin to hyperpycnal flows towards the basin depocenter

african stress pattern from formal inversion of focal mechanism data abstract the kinematic models and the associated orientation of extensional stress of the east african rift system have been subjected to much debate since a long time in the past decades the proposed models relied on the interpretation of the overall rift geometry geological fault slip data and the few focal mechanisms available these models generally suffer of a poor time control and an underestimation of the possible changes in the stress field and geodynamic regime with time and space in the recent years there has been a significant increase in the number of focal mechanisms available for the entire rift system and it is now possible to estimate the present day stress field in relative detail based on seismotectonic data alone we compile 347 focal mechanism data from the global harvard cmt catalogue and various other sources and grouped 332 of them in 24 distinct regions boxes on the basis of their geographical proximity kinematic homogeneity and tectonic setting for each box and for the same data set reduced stress tensors have been obtained by formal stress inversion using both the tensor program delvaux sperner 2003 and the slick method michael 1984 1987 both inversion methods show in comparable results in terms of horizontal stress axes orientations and tectonic stress regimes which stem for the robustness of the approach the obtained stress pattern reflects a complex interaction between 1st order effects as different driving forces including plate boundary forces and 2nd and 3rd order effects as gravitational potential of topography intra lithospheric processes and the influence of structural heterogeneities of the rift structures the evidence present in the stress orientations of the 2nd and 3rd order stress pattern as the variations in the horizontal stress axes along the axis of the rift are of particular interest as they were not yet captured or shown in earlier numerical models of the stress field additional sources of tectonic forces in supplement to the gravitational potential energy forces as considered in the earlier models are necessary to explain the observed patterns

mechanisms of inheritance of rift faulting in the western branch of the east african rift tanzania the western branch of the east african rift system is commonly cited as a result of phanerozoic reactivation of the paleoproterozoic ubendian belt in western tanzania geological evidence is provided to show that prominent mechanical anisotropies successively appeared during proterozoic evolution of the precambrian basement and that their different reactivation behavior contributed to the phanerozoic rift pattern the ubende belt 1950 1850 ma is a nw oriented amphibolite facies ductile lateral shear belt in which older 2100 2025 ma and complex granulite facies terranes are included along trend retrograde multiphase sinistral strike slip mylonites developed along the nw oriented ductile shear belt they reflect persistent proterozoic wrench fault reactivation of the latter shallow level sedimentary basins upon and along the ductile shear belt display deformational structures attributable to the proterozoic wrench fault reactivation neoproterozoic sinistral transpression produced the final geometrical pattern of the wrench fault zone which appears as an elongate and nw trending positive flower structure locally enhanced by late proterozoic contraction phanerozoic rifting is demonstrated by others to occur in three distinct episodes during which the complex rift segment formed upon the multiphase proterozoic wrench fault zone the evaluation of the relationship between multiphase rift and multiphase prerift fabrics is reconsidered the proterozoic prerift fabrics correspond with a dextral transpressional and ductile deformational pattern which became selectively reactivated by sinistral transpressional ductile brittle mylonites proterozoic mylonites constitute shallow level mechanical anisotropies and define the general trend of the rift faults according to the position of these mylonites in the center or in the external parts of their nw oriented neoproterozoic transpression they reactivate as complex and multiphase rift faults or as normal and recent faults respectively the paleoproterozoic nw oriented and ductile lateral shear belt constitutes the deep level mechanical anisotropy its reactivation in phanerozoic stress fields is likely dextral oblique transtension considered as a leading mechanism of the pluriphase and nw oriented deep rift basins

structure and stratigraphy of the rukwa rift abstract combining recently acquired multifold seismic data with well and gravity information and field mapping a comprehensive picture of the structure and stratigraphy of the rukwa rift has emerged the rukwa rift lies between the tanganyika and nyasa malawi rifts in the western branch of the east african rift system in southwest tanzania the rukwa rift is a nw trending half graben basin that is 350 km long and 40 km wide unlike the neighboring tanganyika and nyasa rifts there is no evidence of half graben polarity reversals in the rukwa rift the nw trending boundary fault system lies on the northeastern side of the basin and comprises a series of listric faults most internal faults also show listric forms and trend n s oblique to the boundary fault the basal sedimentary section is the permo triassic karroo sequence this is overlain by the red bed sandstone sequence in which both mesozoic and tertiary fauna have been found the cenozoic lake bed sequence is the highest unit and covers nearly all of the present basin sediment thicknesses commonly reach 7 km and attain a maximum of 12 km at the southeastern end of the basin the lake bed sequence is the thickest unit in the main depocentre but the karroo sequence is often the thickest unit on the shoaling side of the half graben the rukwa rift is here interpreted to have evolved as a strike to oblique slip pull apart basin based on numerous indications of nw trending strike slip faulting

new biostratigraphic age dates from the lake rukwa rift basin in western tanzania geologic note 1 the rukwa rift basin in western tanzania is a segment of the western branch of the east african rift system three major stratigraphic units have been recognized in the basin from oldest to youngest karroo supergroup the red sandstone and the lake beds these units have traditionally been assigned the following ages respectively based upon lithologic correlations permian triassic jurassic cretaceous and tertiary recently microfloral assemblages collected from sidewall cores and cuttings from two deep exploration wells drilled in the basin have provided new data on the age of these formations the biostratigraphic data suggest the formations should be assigned the following ages karroo supergroup late permian red sandstone neogene miocene late pliocene and the lake beds late pliocene holocene the new age dates indicate that the post karroo to pre miocene history of the basin is one of relative quiescence and the modern rift is a relatively young feature this interpretation is more consistent with the tectonic histories of the other basins of the western rift

geodynamic significance of the trm segment in the east african rift w tanzania active tectonics and paleostress in the ufipa plateau and rukwa basin abstract the tanganyika rukwa malawi trm rift segment in western tanzania is a key sector for understanding the opening dynamics of the east african rift system ears in an oblique opening model it is considered as a dextral transfer fault zone that accommodates the general opening of the ears in an nw se direction in an orthogonal opening model it accommodates pure dip slip normal faulting with extension orthogonal to the rift segments and a general e w extension for the entire ears the central part of the trm rift segment is well exposed in the ufipa plateau and rukwa basin within the paleoproterozoic ubende belt it is also one of the most seismically active regions of the ears we investigated the active tectonic architecture and paleostress evolution of the ufipa plateau and adjacent rukwa basin and in order to define their geodynamic role in the development of the ears and highlight their pre rift brittle tectonic history the active fault architecture fault kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the trm segment two pre rift brittle events are evidenced an older brittle thrusting is related to the interaction between the bangweulu block and the tanzanian craton during the late pan african early paleozoic it was followed by a transpressional inversion during the early mesozoic this inversion stage is the best expressed in the field and caused dextral strike slip faulting along the fault systems that now control the major rift structures it has been erroneously interpreted as related to the late cenozoic ears which instead is characterized by pure normal faulting our third and last stress stage

the influence of preexisting structure on the evolution of the cenozoic malawi rift east african rift system this paper analyzes the importance of preexisting structure for the evolution of the cenozoic malawi rift which constitutes the southernmost part of the western branch of the east african rift system kinematic analyses demonstrate that the regional extension direction rotated clockwise from ene to se during rifting cenozoic rift faults of dip oblique and strike slip character rejuvenated crustal structures whenever those were properly oriented with respect to the extension directions depending on these boundary conditions the rift attempts to find the easiest pathway in order to develop in a mechanically modest way proterozoic basement structures represent the basic anisotropy which already influenced pre cenozoic rifts and also the cenozoic malawi rift amongst these basement structures pan african retrograde to cataclastic strike slip shear zones have the strongest influence on later rift structures rift related transfer faults appear as differently striking passive structures and their orientation seems to be controlled by a variety of steep basement structures retrograde shear zones foliation planes and fracture arrays

depth extent and kinematics of faulting in the southern tanganyika rift africa unusually deep earthquakes occur beneath rift segments with and without surface expressions of magmatism in the east african rift system ears the tanganyika rift is part of the western rift and has no surface evidence of magmatism the tang14 array was deployed in the southern tanganyika rift where earthquakes of magnitude up to 7 4 have occurred to probe crust and upper mantle structure and evaluate fault kinematics 474 earthquakes detected between june 2014 and september 2015 are located using a new regional velocity model the precise locations magnitudes and source mechanisms of local and teleseismic earthquakes are used to determine seismogenic layer thickness delineate active faults evaluate regional extension direction and evaluate kinematics of border faults the active faults span more than 350 km with deep normal faults transecting the thick bangweulu craton indicating a wide plate boundary zone the seismogenic layer thickness is 42 km spanning the entire crust beneath the rift basins and their uplifted flanks earthquakes in the upper mantle are also detected deep earthquakes with steep nodal planes occur along subsurface projections of tanganyika and rukwa border faults indicating that large offset 5 km faults penetrate to the base of the crust and are the current locus of strain the focal mechanisms continuous depth distribution and correlation with mapped structures indicate that steep deep border faults maintain a half graben morphology over at least 12 my of basin evolution fault scaling based on our results suggests m 7 earthquakes along tanganyika border faults are possible

paleomagnetism of permian sedimentary rocks from tanzania and the permian paleogeography of pangea abstract we report new paleomagnetic results from karoo permian rocks in tanzania k1 and k3 redbeds and k5 siltstones and limestones from the songwe kiwira basin ndeke redbeds from the mikumi basin and group viii redbeds from the nyakatitu basin were sampled and thermally demagnetized palynologic data and lithologic correlations suggest that the k1 redbeds are lower permian and that the k3 ndeke and group viii redbeds as well as the k5 siltstones and limestones are upper permian stable magnetic directions were obtained from the k3 ndeke and group viii redbeds yielding an upper permain pole at 26 n 267 e characteristic remanence directions were also obtained from the k5 siltstones and limestones however because these directions define a pole 66 n 269 e that is very close to the upper cretaceous pole for africa and significantly different from the upper permian redbed poles these rocks may have been remagnetized the k1 redbeds did not yield stable results using our new results together with published permian poles for africa and the other gondwanan continents we revise the mean lower and upper permian poles for africa west gondwana and gondwana and investigate whether or not these revised poles can discriminate between the various pangea reconstructions proposed for the permian with any greater certainty than previous unrevised mean poles when compared to the mean lower and upper permian poles for laurussia we find that our revised west gondwanan and gondwanan poles do not necessarily provide stronger support for any particular pangea reconstruction than the previous poles therefore even though this study improves the paleomagnetic data base for gondwana for the permian it is not clear that the combination of our results with other paleomagnetic data from the gondwanan continents yields significant new insights about the permian configuration of pangea as suggested previously strong non dipole fields during the permian may provide an explanation for why it is not easy to discriminate with certainty between the various permain pangea reconstructions even with new paleomagnetic results

the diagenesis of continental karoo tertiary siliciclastics from an east african rift valley rukwa tukuyu area tanzania discussion

seismic anisotropy of the upper mantle below the western rift east africa although the east african rift system formed in cratonic lithosphere above a large scale mantle upwelling some sectors have voluminous magmatism while others have isolated small volume eruptive centers we conduct teleseismic shear wave splitting analyses on data from 5 lake bottom seismometers and 67 land stations in the tanganyika rukwa malawi rift zone including the rungwe volcanic province rvp and from 5 seismometers in the kivu rift and virunga volcanic province to evaluate rift perpendicular strain rift parallel melt intrusion and regional flow models for seismic anisotropy patterns beneath the largely amagmatic western rift observations from 684 sks and 305 skks phases reveal consistent patterns within the malawi rift south of the rvp fast splitting directions are oriented northeast with average delays of 1 s directions rotate to n s and nnw north of the volcanic province within the reactivated mesozoic rukwa and southern tanganyika rifts delay times are largest 1 25 s within the virunga volcanic province our work combined with earlier studies shows that sks splitting is rift parallel within western rift magmatic provinces with a larger percentage of null measurements than in amagmatic areas the spatial variations in direction and amount of splitting from our results and those of earlier western rift studies suggest that mantle flow is deflected by the deeply rooted cratons the resulting flow complexity and likely stagnation beneath the rungwe province may explain the ca 17 myr of localized magmatism in the weakly stretched rvp and it argues against interpretations of a uniform anisotropic layer caused by large scale asthenospheric flow or passive rifting