landslide generated tsunamis at reunion island 1 landslides that occur on oceanic volcanoes can reach the sea and trigger catastrophic tsunamis reunion island has been the location of numerous huge landslides involving tens to hundreds of cubic kilometers of material we use a new two fluid seawater and landslide numerical model to estimate the wave amplitudes and the propagation of tsunamis associated with landslide events on reunion island a 10 km3 landslide from the eastern flank of piton de la fournaise volcano would lift the water surface by about 150 m where it entered the sea the wave thus generated would reach saint denis the capital of reunion island population of about 150 000 people in only 12 min with an amplitude of more than 10 m and would reach mauritius island in 18 min although mauritius is located about 175 km from the impact waves reaching its coast would be greater than those for reunion island this is due to the initial shape of the wave and its propagation normal to the coast at mauritius but generally coast parallel at reunion island a submarine landslide of the coastal shelf of 2 km3 would trigger a 40 m high wave that would severely affect the proximal coast in the western part of reunion island for a landslide of the shelf of only 0 5 km3 waves of about 2 m in amplitude would affect the proximal coast

first early permian paleomagnetic pole for the yili block and its implications for late paleozoic postorogenic kinematic evolution of the sw central asian orogenic belt we conducted a paleomagnetic study on the early permian volcanic and sedimentary rocks and the neoproterozoic mafic dikes in the yili block nw china magnetite and hematite were proven to be the principal magnetic remanence carriers demagnetizations revealed stable characteristic remanence magnetizations with a sole reversed magnetic polarity the magnetic remanence of only the early permian strata turned out to be primary based on positive fold tests meanwhile the magnetic remanence age of the mafic dikes is ambiguous accordingly the first early permian paleomagnetic pole for the yili block is calculated at 81 5 n 256 5 e n 11 and a95 10 9 comparisons of this new pole with published ones from the yili tarim and south junggar blocks provide new quantitative constraints on late paleozoic kinematic evolution of the sw central asian orogenic belt 1 between the yili and tarim blocks significant relative movement took place along major strike slip faults during the late carboniferous to early permian 580 290 km and the early to late permian 585 340 km and the displacement rate increased from the late carboniferous to early permian 19 3 9 7 mm yr to the early to late permian 29 3 17 0 mm yr 2 a significant relative rotation of 28 3 18 3 in the late permian and a lateral displacement of 630 295 km after the late permian occurred between the yili and south junggar blocks the significant strike slip movements played an important role in the formation of the central asian orogenic belt and should be considered with great attention in tectonic and paleogeographic reconstructions

fluidized breccias a record of brittle transitions during ductile deformation abstract unusual breccias of caledonian age are described in relation to the tectonic and metamorphic history of their greywacke sandstone and siltstone parent rocks the variety of field and textural relationships displayed by the breccias indicate a combination of dilational and non dilational components in a fluidized system of breccia development the velocity of the escaping fluid phase and the viscosity of the fluidized suspension are strongly influenced by competency controls due to their finer grained nature the pelite based breccias allow a greater mobility of the fluid phase and locally record a turbulent expanded bed stage of the fluidized system however the sandstone based breccias lacking the intricate flow patterns retain a replacive non dilational fracture network the breccias occur in a zone of intense d2 deformation the age relationships of the breccias indicate a repeated pattern of brecciation with syntectonic temporal and partly genetic affinities to the s 2 cleavage development the syntectonic dilational elements involving boudinage and hydraulic fracture are coupled with intense pressure solution and conjugate cleavage development metamorphism to lower greenschist facies is synchronous with deformation and brecciation a focussing of the metamorphic fluid phase within the breccia zones is indicated contributing the non dilational components of the brecciation process a simple shear model of the d2 deformation within this zone is proposed the orientation of the breccia zones suggests that their localization is determined by tensional components within the overall d2 stress field the cyclical pattern of the brecciation during the d2 deformation is considered to represent rapid brittle transitions during the ductile deformation stratigraphie controls on the generation of the increased fluid pressures are identified the presence of an impermeable barrier facilitating the necessary conditions for the excess fluid pressures to accumulate is indicated it is suggested that the brecciation process is fundamentally controlled by a seismic pumping phenomenon following periodic shear failure on a major basement fault at depth

chemical remagnetizations in the illizi basin saharan craton algeria and their acquisition process summary during remagnetization chemical changes limited to moderate grain growth from pre existing single domain sd grains do not modify the palaeomagnetic direction carried by these grains palaeomagnetic direction from new sd grains on the contrary is that of the magnetic field during remagnetization the resulting direction becomes intermediate between the directions carried by previous and new sd grains as it appears often in case of a partial magnetic overprint if the growth of pre existing grains is more important these grains become large multidomain md and loose the primary magnetization stable magnetization is then only related to the new sd grains which carry the total remagnetization in the illizi basin saharan platform these different cases of partial or total magnetic overprint have been observed resulting from palaeomagnetic studies of different palaeozoic and mesozoic formations

sector collapse at kick em jenny submarine volcano lesser antilles numerical simulation and landslide behaviour kick em jenny volcano is the only known active submarine volcano in the lesser antilles it lies within a horseshoe shaped structure open to the west northwest toward the deep grenada basin a detailed bathymetric survey of the basin slope at kick em jenny and resulting high resolution digital elevation model allowed the identification of a major submarine landslide deposit this deposit is thought to result from a single sector collapse event at kick em jenny and to be linked to the formation of the horseshoe shaped structure we estimated the volume and the leading edge runout of the landslide to be ca 4 4 km3 and 14 km respectively we modelled a sector collapse event of a proto kick em jenny volcano using volcflow a finite difference code based on depth integrated mass and momentum equations our models show that the landslide can be simulated by either a coulomb type rheology with low basal friction angles 5 5 6 5 and a significant internal friction angle above 17 5 or with better results by a bingham rheology with low bingham kinematic viscosity 0 b 30 m2 s and high shear strength 130 180 m2 s2 the models and the short runout distance suggest that the landslide travelled as a stiff cohesive flow affected by minimal granular disaggregation and slumping on a non lubricated surface the main submarine landslide deposit can therefore be considered as a submarine mass slide deposit that behaved like a slump

mapping and characterization from aeromagnetic data of the foum zguid dolerite dyke anti atlas morocco a member of the central atlantic magmatic province camp abstract a high resolution aeromagnetic survey was carried out in the anti atlas morocco covering the main areas traversed by the great camp foum zguid dyke fzd this doleritic dyke belongs to the central atlantic magmatic province camp a large igneous province which is associated with the fragmentation of the supercontinent pangaea and the initial stages of rifting of the central atlantic ocean it also coincides in time with the mass extinction of the triassic jurassic boundary based on the study of geological maps and google earth satellite images it appears that the fzd is poorly exposed and often covered by quaternary deposits this work proposes aeromagnetic modelling and interpretation of the fzd in order to better constrain its structural extent the data have allowed i mapping of the dyke over great distances under the quaternary deposits and through areas where it was poorly characterized on the geological map ii identifying major tectonic lineaments interpreted as faults iii recognizing magnetic anomalies related to mafic intrusive bodies and iv informing about regional structural context

dynamic development of fault rocks in a crustal scale detachment an example from western norway 1 the nordfjord sogn detachment nsd zone of western norway juxtaposes eclogites and gneisses of lower crustal affinity with sedimentary deposits suggesting that the zone experienced substantial displacement during devonian extensional denudation of the caledonides renewed activation occurred in permian and jurassic cretaceous times the detachment zone consists of a succession of fault related rocks reflecting various crustal positions and deformation mechanisms during activation and unroofing in more detail the lower 1 2 km thick section of the nsd zone consists of mylonites with various protoliths showing a general upward decrease in metamorphic grade the mylonitic section is truncated by the nsd fault defining the boundary toward hanging wall nappe rocks that are topped by sedimentary basins in an attempt to provide precise descriptions of the observed fault rocks we classify these rocks into 1 noncohesive breccias 2 cemented and indurated breccias of secondary cohesion and 3 cataclasites phyllonites and mylonites formed with primary cohesion along and across strike sections of the fault reveal the spatial and temporal relationships of the nsd fault the fault zone consists of a lower section of phyllonites and cataclasites reaching a total thickness of 50 70 m significant volumes of pseudotachylyte were injected into these fault rocks and were later reworked reactivation of the fault is suggested by overprinting carbonate cemented breccias that are cut by a discrete fault itself associated with breccias and gouge by comparing the various fault rocks and their formation mechanisms some constraints can be applied to the unroofing history the nsd fault developed in the ductile brittle transition zone of the crust where it experienced an initial shift from mainly frictional to plastic flow caused by reaction softening before hardening caused a return to frictional flow at the same time repeated pulses of pseudotachylyte were generated possibly lubricating the fault zone and contributing to strain localization these pseudotachylyte pulses also show that the fault was affected by seismic slip events before returning to a creep regime within a wider section than that ruptured by earthquakes younger cemented breccias and noncohesive breccias and gouge reflect earthquake rupturing and frictional flow within the seismogenic crust

migration of orogenic fluids through the siluro devonian helderberg group during late paleozoic deformation constraints on fluid sources and implications for thermal histories of sedimentary basins abstract fluid inclusion data and fracture filling cement fabrics in deformed but non overthrusted carbonate and siliciclastic rocks of the siluro devonian helderberg group central appalachians indicate post cementation late paleozoic migration of high pressure high temperature fluids void filling quartz and calcite cements contain secondary two phase fluid inclusions liquid vapor which occur in annealed microfractures most melting temperatures last occurrence of ice are 20 to 25 c which correspond to salinities of greater than 22 equivalent wt nacl pressure corrected liquid vapor homogenization temperatures are 200 to 300 c and greatly exceed maximum paleotemperatures 150 c given by conodont cai values vitrinite reflectance illite crystallinity or temperatures calculated from known sedimentary overburden completely cemented sandstone and limestone also have multiple crosscutting trains of secondary hydrocarbon inclusions hydrocarbon inclusions occur along deformation microstructures in cements some hydrocarbon inclusion trains crosscut cement filled fractures the nature of occurrence of the secondary inclusions suggests that fluids moved along intracrystalline deformation microstructures either during or after late paleozoic deformation rare fractures contain transported skeletal grains exotic clasts lithologies different from wall rock recemented clasts of fracture filling cement and mud cement clasts contain solid inclusions of mud and skeletal fragments and indicate several episodes of particle transport cementation and refracturing prior to final fracture filling and cementation these fracture fills locally crosscut stylolites coarse grained poorly sorted clastic fracture fills suggest migration of rapidly moving fluids which were capable of transporting clasts through fracture conduits under deep burial conditions conduction calculations place upper limits on size and duration of thermal anomalies which were caused by extrabasinal fluids these calculations indicate that hot fluid migration events most likely were short lived heat transfer by extraformational fluids moving along faults and fractures may have been the mechanism by which thermal anomalies developed in the helderberg group stratigraphic constraints suggest that likely sources for the hot brines are overthrusted terranes to the east of the study area possible stratigraphic horizons which were sources for the overpressured hot fluids may have been thick cambrian shales which are important detachment horizons for major late paleozoic thrust sheets in the eastern valley and ridge province east of the study area fluids may have migrated during thrusting along thrust faults which ramp upwards from east to west into stratigraphically higher units thrust faults ultimately die out in devonian units some of the dissolved ions in the secondary two phase inclusions may have been incorporated when shale derived fluids moved through silurian evaporites or cambro ordovician carbonates which contain evidence of cryptic evaporites potential source rocks for secondary hydrocarbon inclusions may have been lower silurian through lower devonian strata based on lopatin modeling and assuming that migration occurred during late paleozoic deformation this study may help to explain many apparently anomalous geologic phenomena in deformed foreland basin sediments it also has implications for tracking migration pathways for fluids which facilitate regional scale deformation in fold and thrust belts and how tectonic fluids may affect the rocks through which they move

large scale flank collapse events during the activity of montagne pelee martinique lesser antilles 1 a horseshoe shaped structure already identified on the southwestern flank of montagne pelee martinique lesser antilles arc was previously interpreted as resulting of a flank collapse event but no debris avalanche deposits were observed at the time new offshore high resolution bathymetry and geophysical data aguadomar cruise december 1998 to january 1999 r v l atalante lead us to identify three debris avalanche deposits on the submarine western flank of montagne pelee extending down to the grenada basin they display morphological fronts and hummocky morphology on bathymetric data speckled pattern on backscatter data and hyperbolic facies on 3 5 khz and seismic profiles new on land geological studies lead us to identify two other horseshoe shaped structures on the same flank of the volcano the three submarine deposits have been traced back to the structures identified on land which confirms the occurrence of repeated flank collapse events during the evolution of montagne pelee the ages of the last two events are estimated at 9 ka and 25 ka on the basis of 14c and 238u 230th dates every flank collapse produced debris avalanches which flowed down to the caribbean sea we propose that the repeated instabilities are due to the large asymmetry of the island with western aerial and submarine slopes steeper than the eastern slopes the asymmetry results from progressive loading by accumulation of volcanic products on the western slopes of the volcano and development of long term gravitational instabilities meteoric and hydrothermal fluid circulation on the floor of the second flank collapse structure also creates a weakened hydrothermalized area which favors the recurrence of flank collapses

variation of magnetic properties in sedimentary rocks hosting the foum zguid dyke southern morocco combined effects of re crystallization and fe metasomatism the effects of dyke intrusion on the magnetic properties of host sedimentary rocks are still poorly understood therefore we have evaluated bulk magnetic parameters of standard palaeomagnetic samples collected along several sections across the sediments hosting the foum zguid dyke in southern morocco the study has been completed with the evaluation of the magnetic fabric after laboratory application of sequential heating experiments the present study shows that 1 close to foum zguid dykes the variations of the bulk magnetic parameters and of the magnetic fabric is strongly related with re crystallization and fe metasomatism intensity 2 the thermal experiments on ams of samples collected farther from the dyke and thus less affected by heating during dyke emplacement indicate that 300 400 c is the minimum experimental temperature necessary to trigger appreciable transformations of the pre existing magnetic fabrics for temperatures higher than ca 580 c the magnetic fabric transformations are fully realized with complete transposition of the initial fabric to a fabric similar to that of samples collected close to the dyke therefore measured variations of the magnetic fabric can be used to evaluate re crystallization temperatures experienced by the host sedimentary rock during dyke emplacement the distinct magnetic behaviour observed along the cross sections strongly suggests that samples collected farther from the dyke margins did not experience thermal episodes with temperatures higher than 300 c after dyke emplacement 3 ams data shows a gradual variation of the magnetic fabric with distance from the dyke margin from sub horizontal k3 away from the dyke to vertical k3 close to the dyke experimental heating shows that heat alone can be responsible for this strong variation therefore such orientation changes should not be unequivocally interpreted as the result of a stress field resulting from the emplacement of the dyke for instance 4 magnetic studies prove to be a very sensitive tool to assess rock magnetic transformations thermally and chemically induced by dyke intrusion in hosting sediments

remagnetization 1100ma of voosges lake tuff 1542ma and other mid proterozoic rocks nipigon graben northern ontario abstract recently discovered horizons of non deformed felsic welded crystal tuff in the proterozoic rift system of northern ontario yield a geologically stable paleomagnetic vector using alternating field af thermal td and low temperature demagnetization ltd techniques a single stable characteristic remanence chrm vector is found in all specimens declination inclination 115 73 5 95 2 1 n 58 it is overprinted by a bruhnes epoch vrm the tuffs paleopole position coincides with that of ubiquitous sub horizontal diabase sheets which intruded at 1110 ma during late proterozoic keewanawan volcanism the latter produced numerous volcanic and intrusive rocks along the margins of the lake superior paleo rift system during the interval 1087 1120 ma but the sills are most extensive although the voosges lake tuff shares the same paleopole location as the diabase sheets 1109 ma the nearby seagull pluton 1112 ma and the keweenawan volcanic rocks its primary zircons yielded a mesoproterozoic crystallization age of 1542 3 ma this is similar to the nearby english bay felsic intrusions dated at 1537 2 10 ma davis d w sutcliffe r h 1985 u pb ages from the nipigon plate sic and northern lake superior geol soc am bull 96 1572 1579 whereas the paleomagnetic magnetic signal appears primary in the 1542 ma voosges tuff it was completely reset by the late proterozoic keewanawan paleofield 1100 ma the tuff units are separated from the diabase sills by stratigraphic thicknesses of 50 m and show no traditional petrographic evidence of annealing or thermal metamorphism since it is improbable that the 1542 ma tuff returned to the same paleolatitude at 1109 ma we postulate that metasomatic processes caused a 1109 ma remagnetization a similar event could explain unusual chrms reported for certain other pre keweenawan proterozoic sites with adjacent keewanawan diabase sheets for example some paleopoles reported for the gunflint formation 1878 ma and sibley formation 1339 ma perhaps 1537 ma by association with the english bay intrusions might have been acquired due to secondary remagnetization

palaeomagnetism in the sines massif sw iberia revisited evidences for late cretaceous hydrothermal alteration and associated partial remagnetization summary this study revisits the palaeomagnetism of the sines massif 76 ma in the southwestern iberian margin portugal the palaeomagnetic analysis was complemented by a comprehensive study of the magnetic mineralogy by means of rock magnetic measurements and petrographicobservations theoveralldispersionofpalaeomagneticdirections declinationranging between n0 and n50 and their migration observed during stepwise demagnetizations have revealed the superposition of remanence components we interpret this complex palaeomagnetic behaviour as related to the regional hydrothermalism associated with the last stages of late cretaceous magmatic activity this environment favoured mineralogical alteration and a partial chemical remagnetization giving in most samples a composite magnetization which has been erroneously interpreted as the primary one in a previous study then leading to a questionable model for cretaceous iberia rotation nonetheless for some samples a single component has been isolated interesting rock magnetic properties and microscopic observations point to a well preserved magnetic mineralogy for these samples with magnetite clearly of primary origin the associated chrm mean direction d i 3 9 46 5 95 1 7 n 31 samples then represents the true primary magnetization of the sines massif this new palaeomagnetic direction and the corresponding palaeomagnetic pole long 332 0 l at 79 5 a95 1 7 agrees with those from the other palaeomagnetic works for the same period and region e g the sintra and monchique massifs yielding a lack of significant rotation of iberia relative to stable europe since the uppermost late cretaceous campanian maastrichtian

40ar 39ar dating and geochemistry of tholeiitic magmatism related to the early opening of the central atlantic rift tholeiitic effusive and intrusive magmatism from iberia morocco algeria and mali related to the early opening of the central atlantic rift was dated by the 40ar 39ar step heating method four plateau ages ranging from 203 7 2 7 to 197 1 1 8 ma were obtained on plagioclase from dykes from the taoudenni area mali and two lava flows from morocco the messejana dyke iberia which previously yielded discrepant conventional kar dates did not furnish any 40ar 39ar plateau dates however there is a clear inverse relationship between apparent age and k ca ratio for gas fractions from a plagioclase separate proportional to the alteration degree which combined with dates obtained on amphibole biotite and pyroxene allows us to determine an age of around 200 ma for this body these data and those obtained on the foum zguid morocco and the ksi ksou algeria dykes give evidence of a brief magmatic event between 206 and 195 ma ago which affected a large area ca 2500 km long trace element modelling shows that most of these formations originated from a homogeneous enriched source material such a brief magmatic episode related to the opening of a continental rift is in agreement with findings in other magmatic provinces e g the deccan traps and the red sea rift precisely dated by the 40ar 39ar method as well

laminated veins and hydrothermal breccia as markers of low angle faulting rhenish massif germany abstract the emplacement of bedding veins and vein breccia in a fold and thrust belt setting is discussed we relate vein types to thrusting regimes using the rhenish massif in germany as case example the rhenish massif is a slate belt in a hercynian fold and thrust system the slate belt cleavage generally dips to the southeast and locally has been rotated into low angle shear zones parts of these are parallel to bedding and marked by quartz carbonate veins both shear veins and extensional veins are distinguished on the basis of fibrous crack seal microstructures most shear veins grew by incremental pull apart between en echelon slip surfaces s0 the overlap of which produced a vein stack the stacks have a lineation l0 resulting from a combination of slip fibre growth and dissolution pressure solution slip the attitude of l0 relative to fold axes and the asymmetry of vein microstructures are consistent with vein emplacement during the hercynian thrusting early shear zone veins were thrusted mylonitized and finally boudinaged or folded depending on their setting the shear veins include coeval sheets of vein hosted breccia the breccia contains angular fragments of mylonitized veins and slate the orientation of s0 and s1 in the breccia varies randomly per fragment indicating random fragment rotation unencumbered spin of country rock debris implies rock expansion possibly by rapid pull apart events during the thrusting

palaeomagnetic study of a subaerial volcanic ridge sao jorge island azores for the past 1 3 myr evidence for the cobb mountain subchron volcano flank instability and tectonomagmatic implications we present a palaeomagnetic study on 38 lava flows and 20 dykes encompassing the past 1 3 myr on s jorge island azores archipelagonorth atlantic ocean the sections sampled in the southeastern and central western parts of the island record reversed and normal polarities respectively they indicate a mean palaeomagnetic pole 81 3 degrees n 160 7 degrees e k 33 and a95 3 4 degrees with a latitude shallower than that expected from geocentric axial dipole assumption suggesting an effect of non dipolar components of the earth magnetic field virtual geomagnetic poles of eight flows and two dykes closely follow the contemporaneous records of the cobb mountain subchron odp dsdp programs and constrain the age transition from reversed to normal polarity at ca 1 207 0 017 ma volcano flank instabilities probably related to dyke emplacement along an nnwsse direction led to southwestward tilting of the lava pile towards the sea two spatially and temporally distinct dyke systems have been recognized on the island the eastern is dominated by nnwsse trending dykes emplaced before the end of the matuyama chron whereas in the central western parts the eruptive fissures oriented wnwese controlled the westward growth of the s jorge island during the brunhes chron both directions are consistent with the present day regional stress conditions deduced from plate kinematics and tectonomorphology and suggest the emplacement of dykes along pre existing fractures the distinct timing and location of each dyke system likely results from a slight shift of the magmatic source

a new 200 ma paleomagnetic pole for africa and paleo secular variation scatter from central atlantic magmatic province camp intrusives in morocco ighrem and foum zguid dykes available apparent polar wander apw paths for the 200 ma configuration of pangea just prior to the opening of the central atlantic ocean differ as much as 10o in arc length here we add new data from northwest africa for this time obtained from the northeasttrending foum zguid and ighrem dykes ca 200 ma these dykes form part of the northern domain of the central atlantic magmatic province camp and crosscut the anti atlas ranges in morocco and compositionally correspond to quartz normative tholeiites intruded in continental lithosphere shortly before the opening of the central atlantic ocean the foum zguid dyke has been intensively studied whereas the ighrem dyke has received less scientific focus we sampled both dykes for paleomagnetic investigation along 100 km of each dyke 12 sites for foum zguid and 11 for ighrem 188 samples included in the final analyses rock magnetic experiments indicate a mixture of multidomain and single domain magnetite and or low ti titanomagnetite particles as the principal remanence carriers in both dykes the primary nature of the characteristic remanent magnetization is supported by positive contact tests related to fe metasomatism or baked overprints of the corresponding sedimentary country rocks the directions of the characteristic magnetization exhibit exclusively normal polarity site mean virtual geomagnetic poles are differently grouped in each dyke suggesting distinct geomagnetic secular variation records the foum zguid paleomagnetic pole n 12 plat 67 9 n plon 247 9 e 125 a95 3 9 plots close to that of ighrem n 11 plat 78 4 n plon 238 2 e 47 a95 6 7 confirming those mineralogical and geochemical evidences supporting that they represent dissimilar magmatic stages virtual geomagnetic poles dispersion from both dykes s 10 5 13 0 8 1 is in line with those obtained from recent studies of a camp related dyke in iberia and results from camp lavas in the argana basin these three new estimates of paleosecular variation at low latitudes around the triassic jurassic boundary are concordant with a recently proposed dispersion curve for the jurassic but suggest a slightly lower geomagnetic scatter than considered so far after combining results from both dykes the resulting paleomagnetic pole plat 73 0 n plon 244 7 e n 23 55 a95 4 1 is statistically compared with existing and coeval african paleopoles and with global synthetic 200 ma running mean poles in northwest africa coordinates

syntectonic vein development in a thrust sheet from the external french alps abstract the geometry and age relations of syntectonic veins within calcareous rocks of one imbricate sheet within a thrust belt in the external french alps are described the earliest veins developed during the main ductile deformation by cleavage parallel extension the majority of the syntectonic veins developed towards the end of the deformation and after the formation of second folds they include a conjugate set of normal shears an abundant set of upright extension veins and en echelon sets the dominantly simple shear strain making up the main ductile phase of deformation occurred by a mechanism of grain to grain pressure solution the stretching lineation records the overall direction of thrust sheet movement a change in the microchemical mechanism of pressure solution is thought to have caused the change from first to second phase deformation as recorded by slaty cleavage and crenulation folds in the field from the shear and vein geometries directions of principal stress have been inferred the directions rotated throughout the deformation the maximum principal stress being inclined to bedding during simple shear strain becoming normal to bedding during the phase of abundant vein growth and becoming vertical at the very end of the deformation

calderas or gravity slide structures in the lesser antilles island arc abstract large arcuate depressions up to about 10 km in diameter on the back arc side of st lucia dominica and st vincent in the lesser antilles arc are discussed the qualibou depression on st lucia has been previously described as a caldera partly because it was believed to be the source of ignimbrites on the island remapping and stratigraphic studies of these ignimbrites show they were not erupted from the depression but from central vents in the highland rainforests and are much younger dominica is geologically similar and has two scarped depressions at the southern end of the island soufriere volcano st vincent has a prominent arcuate scarp opening to the west the southern half of which has been buried under the youngest volcanic products of the volcano we interpret these structures as the root zones of gravity slides perhaps eruption related and triggered by magmatic inflation post slide activity lava domes and fumaroles has occurred within them due to reduction in lithostatic load and pressure release on the flanks of these island volcanic complexes the presence of these structures only on the western coasts is correlated with the steeper 9 slopes into the grenada basin in contrast to the 1 submarine slopes of the atlantic side

evidence for non coaxiality of ferrimagnetic and paramagnetic fabrics developed during magma flow and cooling in a thick mafic dyke abstract a detailed analysis of fabrics of the chilled margin of a thick dolerite dyke foum zguid dyke southern morocco was performed in order to better understand the development of sub fabrics during dyke emplacement and cooling ams data were complemented with measurements of paramagnetic and ferrimagnetic fabrics measured with high field torque magnetometer neutron texture and microstructural analyses the ferrimagnetic and ams fabrics are similar indicating that the ferrimagnetic minerals dominate the ams signal the paramagnetic fabric is different from the previous ones based on the crystallization timing of the different mineralogical phases the paramagnetic fabric appears related to the upward flow while the ferrimagnetic fabric rather reflects the late stage of dyke emplacement and cooling stresses

paleomagnetic study of the great foum zguid dyke southern morocco a positive contact test related to metasomatic processes 1 when a paleomagnetic pole is sought for in an igneous body the host rocks should be subjected to a contact test to assure that the determined paleopole has the age of the intrusion if the contact test is positive it precludes the possibility that the measured magnetization is a later effect therefore we investigated the variations of the remanent magnetization along cross sections of rocks hosting the foum zguid dyke southern morocco and the dyke itself a positive contact test was obtained but it is mainly related with chemical crystalline remanent magnetization due to metasomatic processes in the host rocks during magma intrusion and cooling and not only with thermo remanent magnetization as ordinarily assumed in standard studies paleomagnetic data obtained within the dyke then reflect the earth magnetic field during emplacement of this well dated 196 9 1 8 ma intrusion

thick dyke emplacement and internal flow a structural and magnetic fabric study of the deep seated dolerite dyke of foum zguid southern morocco 1 knowledge on forced magma injection and magma flow in dykes is crucial for the understanding of how magmas migrate through the crust to the earth s surface because many questions still persist we used the long thick and deep seated foum zguid dyke morocco to investigate dyke emplacement and internal flow by means of magnetic methods structural analysis petrography and scanning electron microscopy we also investigated how the host rocks accommodated the intrusion regarding internal flow 1 important variations of the rock magnetic properties and magnetic fabric occur with distance from dyke wall 2 anisotropy of anhysteretic remanent magnetization reveals that anisotropy of magnetic susceptibility ams results mainly from the superposition of subfabrics with distinct coercivities and that the imbrication between magnetic foliation and dyke plane is more reliable to deduce flow than the orientation of the ams maximum principal axis and 3 a dominant upward flow near the margins can be inferred the magnetic fabric closest to the dyke wall likely records magma flow best due to fast cooling whereas in the core the magnetic properties have been affected by high temperature exsolution and metasomatic effects due to slow cooling regarding dyke emplacement this study shows that the thick forceful intrusion induced deformation by homogeneous flattening and or folding of the host sedimentary strata dewatering related to heat as recorded by thick quartz veins bordering the dyke in some localities may have also helped accommodating dyke intrusion the spatial arrangement of quartz veins and their geometrical relationship with the dyke indicate a preintrusive to synintrusive sinistral component of strike slip

mapping the volcanic hazards from soufriere hills volcano montserrat west indies using an image processor we have used a digital model of the topography of montserrat a simple mathematical model of gravitational flow and some assumptions of the way in which the next eruption will develop to create a map of the volcanic hazards from soufriere hills volcano this has been done using an image processing computer to simulate the deposits produced by pyroclastic flows this technique has the advantages over more traditional cartographic methods of spatial precision rapid computation of multiple eruption models and the explicit nature of the physical model used soufriere hills volcano is a small andesitic volcano characterized by a cluster of summit domes and an apron of pyroclastic flow deposits and mudflows upon which several thousand people now live most of the flanks were covered by deposits from a series of eruptions from 24000 to 16000 a bp though there is some evidence that dome growth and small pyroclastic flows have occurred since the modelling is constrained by field evidence from the deposits of previous eruptions although the evidence is not good enough to model individual flow units the cumulative deposits can be used from the eruption deposit models we have created a new type of map specifically for emergency planning this sequential hazard zone map attempts to portray the regions that would be at hazard from pyroclastic flows during successive stages from the start of an eruption whose energy release was increasing with time

late structural control of mesothermal vein hosted gold deposits in central victoria australia mineralization mechanisms and exploration potential abstract comparison of the structural relationships between five gold deposits in ordovician rocks of the central victorian slate belt reveals a similar history and structural control of gold mineralization large quartz veins spatially associated with gold mineralization such as the famous saddle reefs of bendigo formed during the second deformation earlier than the gold mineralization itself where they were overprinted by the effects of the fourth deformation they provided structural sites for gold deposition on their boundaries with country rock where brecciation jostling and fracture were favoured access of fluids resulting from metamorphism and deformation to the brecciated fractured and jostled blocks of country rock created conditions suitable for the precipitation of gold through a sequence of alteration replacement and infill the dominant structural relationships that resulted in the generation of these sites were a the high angle of the axial plane of the fourth deformation to earlier structures and b the presence during mineralization of large pre existing quartz veins that acted as structural discontinuities on which brecciation could occur these factors allow a predictive capacity for exploration in the region

vein geometry in the hilton area mount isa queensland implications for fluid behaviour during deformation abstract folding and shear zone movement occurred synchronously in rocks of the mid proterozoic mount isa group in the hilton area northwest queensland syndeformational veins developed in shear zones and in sets spatially associated with shear zone intersections veins can be divided into the following two types 1 1 fibrous and non fibrous quartz dolomite veins which formed in orientations consistent with the regional e w subhorizontal shortening direction 2 2 fibrous and non fibrous quartz dolomite veins which formed parallel to shear planes s 3 cleavage and bedding indicating local syndeformational extension parallel to the regional shortening direction the complex geometry of the shear zones suggests that shear parallel veins formed as a result of movement over asperities during shear zone movement s 2 parallel veins on the other hand appear to have formed during restricted episodes of fluid overpressuring during post failure stress drops shear zones are divisible into highly graphitic and weakly graphitic end member types highly graphitic shear zones show abundant dissolution and little veining while weakly graphitic shear zones show abundant veining and little dissolution this indicates that highly graphitic shear zones were syndeformational fluid pathways while weakly graphitic shear zones were syndeformational fluid sinks