the exposed base of a collapsing wedge the nestos shear zone rhodope metamorphic province greece 1 the nestos shear zone nsz in the rhodope metamorphic province is a major high strain zone between two metamorphic terranes microdiamond bearing ultrahigh pressure uhp rocks occur in the nsz which was therefore interpreted as a suture zone where subduction and exhumation of these rocks and terrain accretion occurred during the mesozoic our petrological study of samples from the lower part of the nsz together with monazite dating of a microdiamond bearing garnet schist structural observations already published results from the upper part and other published timing constraints results in a fundamentally different picture the nsz is the base of an eocene age southwestward thrust wedge which included not only the structurally higher parts of the rhodope metamorphic province but also the entire internal hellenides the uhp rocks for the peak pressure of which we derive an age of 200 ma by monazite dating are unrelated to the tectonic processes in the nsz and probably represent slivers of a higher tectonic unit captured by thrusting along the nsz pressure decrease in the footwall and regional extension and basin formation in the hanging wall during the activity of the nsz show that the overlying thrust wedge was collapsing in late eocene times we hypothesize that the transition from subduction to continental collision may start with a pronounced accretion event when the first detachment horizon forms in the middle crust of the downgoing plate such an event could trigger slab retreat an extensional collapse of the internal wedge and subsequent magmatism

petrological geochemical and statistical analysis of eocene oligocene sandstones of the western thrace basin greece and bulgaria abstract the rhodopian orogen developed since the late cretaceous early eocene during accretionary processes following the closure of the vardar ocean basin a branch of neotethys through a multidisciplinary approach including sandstone petrology and geochemistry of the clastic and volcanoclastic sediments we reconstruct the unroofing history of the rhodopian orogen and characterize the formation and the evolution of the western portions of the thrace basin in greece and bulgaria between the late eocene and oligocene detrital modes of 127 sandstone samples provide evidence of three distinctive petrofacies quartzolithic quartzofeldspathic and volcanoclastic the petrographic composition gives evidence of contributions from three key source areas corresponding to the three main tectonic units the circum rhodope belt the variegated complex ultramafic complex and the gneiss migmatite complex the three petrofacies reflect multiple provenance from different tectonic settings as they evolve from quartzolithic to quartzofeldspathic to volcanoclastic corresponding to collisional orogen crustal block uplift and volcanic arc settings respectively geochemical data on major elements and trace elements are used to discuss the efficacy of tectonic setting discrimination diagrams and compare them to the dickinson model as well as to distinguish and characterize i petrographically homogeneous gneiss supplied subbasins and ii volcanic contributions to sandstone composition multivariate statistical techniques are used to unravel the complex web of factors controlling sediment composition biplot analysis highlights the influence of two independent processes 1 mixing between carbonate and silicate phases and 2 evolution from mafic to felsic source rocks the latter indicates progressively increasing supply rates from deeper crustal levels the compositional evolution of the sandstone suites of thrace basin in ne greece and se bulgaria is strictly related to various geodynamic stages of the rhodope region provenance analysis of thrace sandstones provide an example of the changing nature of orogenic belt sand associate basins through time and may contribute to the general understanding of similar geodynamic settings

late cenozoic extension in sw bulgaria a synthesis abstract southwest bulgaria forms the northern margin of the aegean extensional province since the early pliocene c 4 ma this region has accommodated southward or sse extension at several millimetres per year superimposed on c 400 m of post early pliocene regional uplift this sense of deformation superseded earlier extension oriented ene wsw which is estimated to have begun in the early late miocene c 10 9 ma and lasted until c 4 ma the regional topography is dominated by nnw sse striking grabens and normal fault escarpments relics from this time normal faults that are now active cut across these older structures although in some localities normal faults that were oriented obliquely to the earlier extension have remained active also oblique to the modern extension sense it is suggested that this present phase of extension relates to the modern sense of deformation throughout the aegean region and to the modern geometry of the north anatolian fault zone nafz which is independently inferred to have existed since c 4 ma the earlier ene wsw extension is inferred to have involved two phases the first predating the nafz and the second synkinematic with its initial phase of slip during c 7 4 ma when its geometry and the overall sense of deformation in the aegean region were different from at present some previous studies have inferred that sw bulgaria experienced large scale extension on low angle normal faults in the mid miocene or earlier however the limited evidence in support of this view is open to other interpretations and after due consideration can be discounted

the thrace basin in the rhodope province of ne greece a tertiary supradetachment basin and its geodynamic implications abstract detailed tectonic analysis and geological mapping on the tertiary molassic and volcanosedimentary rocks of the thrace basin in northeastern greece allowed us to reconstruct the structural evolution of the basin and its geotectonic setting as well as the orientation of the regional paleostress field sedimentation was linked with a calc alkaline and locally shoshonitic magmatism associated with the tertiary syn to late orogenic extension in the rhodope province we interpret the molassic tertiary greek part of the thrace basin as a supradetachment basin associated with sedimentary and volcanic infilling five 5 deformational events t1 to t5 have been distinguished during basin evolution from eocene to quaternary time t1 is related to a low angle normal detachment fault zone with a top to the sw to ssw sense of movement and initial basin subsidence during middle late eocene to oligocene time simultaneously with uplift and exhumation of the footwall rhodope metamorphic rocks stacking and crustal thickening in the more external parts of the hellenic orogenic belt have taken place during the same time t2 evolved during oligocene miocene time it was characterized by transpressional tectonics and formation of large strike slip faults and extensional fractures as well as conjugate thrust faults and folds with n nw or s se sense of movement during miocene pliocene time the third t3 event took place it was responsible for the high angle normal faults dismembering the eocene oligocene molassic basin into neogene grabens the t4 event affected the neogene sediments of the basin with minor reverse strike slip faults as well as normal faults the following t5 event is related to large normal active faults they coincided with the active tectonics of the study area defined by the earthquake focal mechanisms

the real southern basin and range mid to late cenozoic extension in mexico much of northern and central mexico underwent east northeast extension in the mid to late cenozoic this area constitutes a major but little recognized part of the basin and range province the extended region is bounded on the east by the laramide thrust front of the sierra madre oriental on the west the relatively unfaulted sierra madre occidental separates the extended area in central mexico from that around the gulf of california extension occurred as far south as what is now the trans mexican volcanic belt and in oaxaca south of the belt the basin and range province in mexico constitutes approximately half of the 19 x 10 5 km 2 of western north america that underwent mid to late cenozoic extension north northwest orientations of numerous epithermal vein systems indicate that east northeast extension began as early as 30 ma in areas north of the volcanic belt major episodes of faulting began at about 23 to 24 ma and 12 to 13 ma both in mexico and in the southwestern united states faulting was commonly accompanied by eruption of alkali basalts typical of intraplate rifting widespread quaternary fault scarps and alkali basalts indicate that extension continues to the present in the region north of the trans mexican volcanic belt in contrast the tectonics in and south of the belt are now probably related to subduction of the rivera plate contemporaneity of the 12 ma episode with early extension around the gulf of california attributed to pacific north american plate boundary reorganization suggests that extension is related predominantly to plate boundary effects the beginning of extension at 30 ma may be related to initial encroachment of the east pacific rise upon the trench that lay off western north america

tectonics and volcanism in central mexico a landsat thematic mapper perspective abstract digitally enhanced landsat thematic mapper tm images were used to map neotectonic deformation in central mexico this region has been studied for decades using a variety of geological and geophysical techniques but synoptic mapping of neotectonic activity and major fault zones there and an evaluation of their regional relationship to the character and location of volcanism were not previously possible until the application of synoptic high resolution satellite imagery interpretation of the tm images shows that the tectonic deformation is closely linked in time and space to the dominantly calc alkaline volcanics of the mexican volcanic belt mvb the eruptive style and distribution of the volcanics is clearly related to the deformation resulting from relative motions of three large crustal blocks south of the mvb therefore zones of weakness within the crust of the central mexico which may be inherited from earlier episodes of deformation are a principal factor controlling the oblique orientation of the mvb relative to the acapulco trench

late cenozoic extension in northeastern greece strymon valley detachment system and rhodope metamorphic core complex the strymon valley detachment system accommodated at least 25 km of extension at the northern margin of the aegean extensional province from middle miocene through early pliocene time the primary detachment surface is exposed as a gently southwest dipping low angle normal fault similar to those widely known in core complex settings of the u s basin and range province for more than 150 km along strike from the aegean sea coast in northeastern greece northward into the struma valley of southern bulgaria hanging wall rocks in the strymon valley detachment system moved in a s53 w direction relative to the footwall resulting ultimately in the tectonic unroofing of the rhodope metamorphic core complex several segments of the strymon valley detachment have previously been interpreted as thrust faults formed during a miocene compressional event our results negate the principal evidence for this event and imply instead that extensional deformation has characterized the northern aegean region since at least middle miocene time displacement ceased on the strymon valley detachment with the late pliocene development of the strymon and drama basins we propose that those basins together with the other principal basins of the northern aegean region are subsiding above an active northeast dipping extensional detachment zone that forms a unified kinematic system with the western offshore continuation of the dextral north anatolian strike slip fault the north aegean trough if this hypothesis is correct then the north aegean trough the western strands of the north anatolian fault and the principal modern depocenters of the northern aegean region may all have originated no earlier than late pliocene time

cenozoic landforms and post orogenic landscape evolution of the balkanide orogen evidence for alternatives to the tectonic denudation narrative in southern bulgaria continental denudation is the mass transfer of rock fromsource areas to sedimentary depocentres and is typically the result of earth surface processes however a process known as tectonic denudation is also understood to expose deep seated rocks in short periods of geological timeby displacing largemasses of continental crust along shallow angle faults and without requiring major contributions from surface erosion some parts of the world such as the basin and range in theusa or the aegean province in europe have been showcased for their cenozoic tectonic denudation features commonly described as metamorphic core complexes or as supradetachment faults based on 22 new apatite fission track aft and 21 helium ahe cooling ages among rock samples collectedwidely from plateau summits and their adjacent valley floors and elaborating on inconsistencies between the regional stratigraphic topographic and denudational records this study frames a revised perspective on the prevailing tectonic denudation narrative for southern bulgaria we conclude that conspicuous landforms in this region such as erosion surfaces on basement cored mountain ranges are not primarily the result of paleogene to neogene core complex formation they result instead from ordinary erosion driven subaerial denudation rock cooling each time suggesting at least 2 km of crustal denudation has exposed shallow paleogene granitic plutons and documents a 3 stage wave of erosional denudation which progressed from north to south during themiddle eocene oligocene early tomiddlemiocene and late miocene denudation initially prevailed during the paleogene under a syn orogenic compressional regime involving piggyback extensional basins phase 1 but subsequently migrated southward in response to post orogenic upper plate extension driven by trench rollback of the hellenic subduction slab phase 2 rare insight given by the denudation pattern indicates that trench rollback progressed at amean velocity of 3 to 4 km ma the neogene horst and grabenmosaic that defines the modern landscape phase 3 has completely overprinted the earlier fabrics of phases 1 and 2 and has been the prime focus of tectonic geomorphologists working in the region the new narrative proposed here for linking the geodynamic evolution of se europe with surface landform assemblages raises issues in favour of better documenting the regional sedimentary record of existing paleogene basins which constitute a poorly documented missing link to the thermochronological evidence presented here

neotectonics in central mexico regional neotectonic activity in central mexico was mapped through analysis of eleven landsat thematic mapper images the study area stretches from mexico city on the east to the gulf of california on the west between 17 and 21 n latitude fault scarps of plio quaternary age define several large scale tectonic features within the mexican volcanic belt dominated by rifting transtension and shear with probable sinistral components three large crustal blocks south of the mexican volcanic belt are separated from the north american plate and from each other by zones of neotectonic activity that express the relative motions between the adjacent blocks a simple vector diagram for plates and crustal blocks in central mexico has been constructed using information from the literature combined with the orientations of fault zones as mapped in this study the relative motion between the blocks varies from about 2 5 to 8 mm year 1 which is comparable to motions of crustal blocks in areas of active rifting in other parts of the world in the mexican volcanic belt there is a clear relationship between volcanism and neotectonic activity fault zones that traverse nearly the entire region have the same location and orientation as the volcanic belt this may indicate that deformation within the crust of the overriding slab plays a significant role in determining the unusual orientation of the mexican volcanic belt relative to the trench the ultimate factor controlling the location of plio quaternary volcanism and tectonism in central mexico may be large zones of crustal weakness formed during major mesozoic and cenozoic tectonic events

dike emplacement near paricutin volcano mexico in 2006 a major seismic swarm occurred near paricutin volcano between the end of may and early july 2006 more than 700 earthquakes with magnitude ml exceeding 2 4 were located paricutin located in the michoacan guanajuato volcanic field in western mexico is well known as the site of the 1943 eruption in which a new 400 m cinder cone was constructed in what had been farmland the 2006 swarm exhibits all of the characteristics typically associated with swarms of volcanic origins the earthquake rate showed the typical ramp up and ramp down over the course of several days magnitudes were evenly distributed in time with a notably high b value of 2 45 the earthquake locations cluster around a northeast striking trend extending approximately 6 km over the first two weeks hypocenters migrated steadily a few hundred meters per day rising from 9 to 5 km depth and moving northeast about 5 km on approximately june 7 the ascent of hypocenters stalled for the next three weeks hypocenters held their depth while migrating laterally back to the southwest focal mechanisms during the first part of the swarm reflected the increased stress caused by dike inflation following june 7 the stress orientation changed and became more consistent with the inflation of horizontal sill like structures though only limited information is available from the seismic swarm preceding the 1943 eruption several features including the swarm duration and magnitude relationships were comparable to those of the 2006 episode the strong indicators of a magmatic origin to the 2006 swarm suggest that at this location there are few if any traditional seismic discriminants that could be used to distinguish which seismic swarms and dike emplacement events might culminate in eruption

magma intrusion near volcan tancitaro evidence from seismic analysis abstract between may and june 2006 an earthquake swarm occurred near volcan tancitaro in mexico which was recorded by a temporary seismic deployment known as the mars network we located 1000 events from this seismic swarm previous earthquake swarms in the area were reported in the years 1997 1999 and 2000 we relocate and analyze the evolution and properties of the 2006 earthquake swarm employing a waveform cross correlation based phase repicking technique hypocenters from 911 events were located and divided into eighteen families having a correlation coefficient at or above 0 75 90 of the earthquakes provide at least sixteen phase picks we used the single event location code hypo71 and the p wave velocity model used by the jalisco seismic and accelerometer network to improve hypocenters based on the correlation adjusted phase arrival times we relocated 121 earthquakes which show clearly two clusters between 9 10 km and 3 4 km depth respectively the average location error estimates are

earthquake swarms and dike intrusions off the east coast of izu peninsula central japan abstract relationships between earthquake swarms and dike intrusions are investigated in the monogenetic volcano region off the east coast of the izu peninsula central japan hypocentral distribution of an earthquake swarm associated with the 1989 ito oki submarine eruption and those of eight major earthquake swarms for 7 years before the eruption in the same region are precisely relocated comparison of the hypocentral distribution with a dike model obtained from crustal movement measurements by okada and yamamoto 1991 ensures that hypocentral areas of the earthquake swarms can be used as reliable indicators of intruded dikes the epicentral area of each earthquake swarm shows an elliptic shape with a 3 5 km long axis and a 2 4 km short axis the long axis trending from a nw se to wnw ese direction the total hypocentral distribution of the nine swarms forms a seismic zone of about 20 km long and about 5 km wide with each of the swarm areas overlapping focal migrations from deep 10 km to shallow 3 km depths are found in the two largest events in 1988 and 1989 indicating that dikes propagated from deep to shallow areas in the upper crust these features of the hypocentral distributions suggest that the seismic swarms were induced by dike intrusions which ascended from a deep seated magma reservoir with dike like geometry located beneath the seismic zone solidification time of a dike with thickness comparable to that of the dike model of okada and yamamoto 1 45 m at the bottom of the dike is several days indicating that the dikes inducing the earthquake swarms solidified almost during the swarm period the physical mechanisms of the dike induced earthquake swarms are investigated for the izu region the focal depth migration and fault type of the earthquake swarm suggest that stress change in the region surrounding the dike due to dike emplacement is the most important factor for the cause of the earthquakes

late cenozoic development of the strouma and mesta fluviolacustrine systems sw bulgaria and northern greece abstract the strouma and mesta are two of the largest rivers that drain across sw bulgaria and northern greece into the northern aegean sea their modern valleys flanked by quaternary river terraces are incised into a diverse landscape which records the region s complex tectonic history a network of lacustrine basins existed in the region in the late oligocene to earliest miocene but was disrupted by thrusting and folding related to early miocene transpression this deformation was followed by a period of erosion covering most of the early and middle miocene which probably marked the initiation of the strouma and mesta fluviolacustrine system with geometries unrelated to the older systems the first clear evidence of these river systems dates from the middle miocene late badenian to sarmatian the systems evolved in the late miocene maeotian to early pontian when lakes existed characterized by diatomaceous algae and by occasional burial of abundant plant fragments and coal formation areas in the south south of the kerkini fault were intermittently submerged beneath the aegean sea at this time intense localized uplift of horst blocks in late pontian and pliocene associated with crustal extension resulted in deposition of thick alluvial fans with tilting of sedimentary successions in adjacent grabens evident by the end of the pliocene the highest horsts osogovo rila pirin and belasitsa experienced additional uplift in the pleistocene in part as a result of regional uplift and in part through continued normal faulting pleistocene climate change also resulted in influxes of glacial and fluvioglacial systems the present form of the strouma and mesta fluviolacustrine systems is thus the result of interplay between crustal extension regional uplift and global climate change

the oligocene xanthi pluton northern greece a granodiorite emplaced during regional extension the xanthi pluton is one of a series of oligocene subduction related granodiorites in northern greece its emplacement was controlled by major faults it is located on the ene trending kavala komotini fault zone which probably originated as a strike slip fault geophysical data show that the pluton is laccolith shaped extending many kilometres south of the fault andesitic dykes several million years older than the pluton indicate a ne sw directed extensional stress field mineral lineations plunging to the sw reflect continued extension during cooling of the pluton subsequent jointing and dykes of aplite and lamprophyre reflect continued extension although this could result from extensional pull apart at a bend during dextral strike slip motion on the kavala komotini fault there is no evidence for subsequent strike slip deformation furthermore two similar laccolithic plutons are unrelated to the kavala komotini fault and the regional extent of thick oligocene sediments suggests an extensional environment during the extension that created a ramp space along the listric fault bounding the xanthi basin into which the granite was intruded the kavala komotini fault acted as a transfer fault reactivation of early joints occurred during late oligocene early miocene compression faults within the pluton parallel to the kavala komotini fault accompanied extension during neogene basin formation emplacement of subduction related magma into ramp space developed along listric faults to produce laccolith like plutons may be a common feature of back arc extension

seismic structure beneath the rivera subduction zone from finite frequency seismic tomography 1 the subduction zone of western mexico is a unique region on earth where microplate capture and overriding plate disruption are occurring today the young small rivera plate and the adjacent cocos plate are subducting beneath the jalisco block of mexico here we present a p wave tomographic model of the upper mantle to 400 km depth beneath the jalisco block and surrounding regions using teleseismic p waves recorded by the mapping the rivera subduction zone mars and colima volcano deep seismic experiment codex seismic arrays the inversion used 12 188 p wave residuals and finite frequency theory to backproject the 3 d traveltime sensitivity kernels through the model below a depth of 150 km the tomography model shows a clear gap between the rivera and cocos slabs that increases in size with depth the gap between the plates lies beneath the northern part of the colima graben and may be responsible for the location of colima volcano the images indicate that the deep rivera plate is subducting more steeply than does the adjacent cocos plate and also has a more northerly trajection at a depth of about 100 km both the rivera and cocos slabs have increased dips such that the slabs are deeper than 200 km beneath the trans mexican volcanic belt tmvb it is also found that the rivera plate is at roughly 140 km depth beneath the young central jalisco volcanic lineament our images suggest that the rivera plate and westernmost cocos plate have recently rolled back toward the trench this scenario may explain the unusual magmatic activity seen in the tmvb

characteristics of the october 2005 microearthquake swarm and reactivation of similar event seismic swarms over decadal time periods near socorro new mexico seismicity in the rio grande rift in central new mexico southwestern united states has been dominated by microearthquakes occurring above the midcrustal socorro magma body smb for at least the past century the smb is a sill like feature 3400 km2 in area with a top surface at 19 km depth and centered below the inner rift half graben system a recent swarm of microearthquakes above the magma body began on 20 october 2005 the activity intensified toward 30 october 2005 with the largest event being a shallow felt local magnitude m l 2 4 earthquake at 02 57 35 utc seismicity increased in the region following this event with over 1600 earthquakes detectable at a minimum of one local seismic station during the subsequent month seismic waveforms for the earthquakes in this sequence are remarkably similar implying consistently similar location and faulting geometry the time space distribution of earthquakes indicates that this sequence is highly swarmlike in contrast to tectonic mainshock aftershock sequences given the local tectonic setting and shallow 8 km depth of individual events above the smb a likely explanation for the socorro earthquake sequence is fluid flow or pressure induced triggering associated with the evolution of the smb swarms such as the 2005 sequence are not uncommon in this area e g prominent previous sequences occurred in may and july of 1983 here we characterize the 2005 earthquake sequence by presenting composite focal mechanisms magnitude estimates and high precision relative locations based on waveform cross correlation techniques that capitalize on the similar waveforms a new waveform scanning technique identifies over 1600 small similar earthquakes during this period from continuous seismic records waveforms and locations are also observed to be similar between the 2005 and 1983 sequences suggesting consistency in source location geometry and thus mechanism over decadal time scales

separate eocene early oligocene and miocene stages of extension and core complex formation in the western rhodopes mesta basin and pirin mountains bulgaria abstract the rhodope metamorphic province in bulgaria and northern greece has been affected by significant extensional tectonics since the middle to late eocene an important fault system active in the eocene and early oligocene includes the ribnovo fault on the eastern side of the mesta basin in bulgaria and the vertiskos kerdilion fault in greece together with several minor normal fault relicts identified during this study these represent an originally west southwest dipping low angle at least at the end of faulting normal fault with greenschist facies mylonites in the footwall and cataclasites along the fault plane the mesta kerdilion detachment exposed over ca 150 km along strike and about 50 km parallel to the slip direction during the intrusion of several plutons in the pirin mountains at ca 32 ma the footwall of the fault was uplifted to form a large anticline parallel to fault strike and the fault was offset by a system of antithetic northeast dipping normal faults along the northeastern flank of this anticline dobrotino and breznitsa faults the mesta kerdilion detachment was later in the miocene again crosscut and offset by the southwest dipping strimon valley detachment which accommodated important core complex like exhumation to the south strongly diminishing and finally ceasing towards north this rotational activity of the strimon valley detachment represents the onset of the extension that led to opening of the aegean basin the mesta kerdilion detachment can be viewed as a precursor of this but with slightly different kinematics i e not involving significant vertical axis rotation and separated in time from the following events by a phase of relative tectonic quiescence in the late oligocene

active rifting in southwestern mexico manifestations of an incipient eastward spreading ridge jump a major ongoing episode of continental rifting has formed a system of three intersecting grabens in the western mexican volcanic belt these structures may mark the initial stage of an eastward spreading ridge jump beneath continental crust eastward ridge segment jumps have been propagating northward along this part of the east pacific rise for the past 12 m y but this is the first plate boundary reorganization event to involve continental crust since the separation of baja california in the miocene since pliocene time small volumes of unusual alkaline magmas have erupted in the graben areas in close association with the more abundant subduction related calc alkaline magmas erupted from andesitic stratovolcanoes the alkaline magmas are varieties found in zones of active rifting elsewhere in the world

lateral growth of the continental crust through deep level subduction accretion a re evaluation of central greek rhodope abstract the rhodope massif of northern greece and southern bulgaria has been variably interpreted as a fragment of pre alpine possibly hercynian or precambrian age continental crust that was actively involved in european margin convergent tectonics during the mesozoic and tertiary alternatively we propose that for central greek rhodope the lithological associations and tectonothermal history are consistent with progressive south directed mesozoic crustal growth through deep level subduction accretion a process which involved the near continuous transferral of material of oceanic and continental margin affinity from footwall to hanging wall within a north directed palaeotethyan subduction system central greek rhodope comprises a sequence of schists gneisses and migmatites of wide compositional variation that have undergone intense tectonic intermixing extensive occurrences of marble are associated with amphibolites variably retrogressed eclogites meta gabbros and ultramafic rocks quartzo feldspathic gneisses are abundant throughout the area and are associated with psammitic meta greywacke sequences pelites and quartzites the presence of intercalated marble slivers and thin manganiferous and iron rich siliceous bands is significant the various components exposed in the subduction accretion complex were first underthrust northwards to deep crustal levels subjected to high pressure eclogite facies metamorphism and underplated to the base of the overriding eurasian plate this latter accretion event was characterised by intense southwest directed ductile thrusting and pervasive amphibolite facies metamorphic overprinting it was accompanied by migmatisation and intracrustal melt generation and followed by subduction related magmatism deep level subduction accretion leads to southward growth of the continental margin which in turn leads to subduction retreat allowing the encroachment of the magmatic arc from the north subsequent extensional tectonic exhumation brought the complex up to its present position within the southern margin of eurasia this new interpretation may have implications for other high grade terrains within convergent and collisional systems that have been assumed to represent ancient or pre existing continental crust if so then the importance of deep level subduction accretion as a mechanism of continental crustal growth has hitherto been underestimated

northern east pacific rise magnetic anomaly and bathymetric framework the oceanic crust in the eastern pacific between 7on and 30on and east of 127ow contains a fairly complete history of the spreading centers associated with the east pacific rise since 25 m y b p late oligocene in this paper we have summarized the seafloor spreading magnetic anomaly data and the bathymetric data that reflect the record of this tectonic history the well defined magnetic lineations north of the clarion fracture zone in the mouth of the gulf of california and on the east flank of the east pacific rise epr are carefully examined and used to provide a guide for interpreting the spreading pattern between the clarion and clipperton fracture zones southward of the rivera fracture zone over the mathematician ridge and over the entire epr east of the mathematician ridge between the rivera and siqueiros fracture zones the bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas the fracture zone bathymetry and the seafloor spreading magnetic lineations on the epr south of the rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations all these data provide a good record of the plate reorganizations in the middle miocene at magnetic anomaly 5a time 12 5 to 11 m y b p in the late miocene at magnetic anomaly 3 4 time 6 5 m y b p and in the pliocene at magnetic anomaly 2 3 time 3 5 m y b p several abandoned spreading centers including the mathematician ridge were left behind as a result of these reorganizations the mathematician ridge is shown to be a set of ridges and trough whose origin is related to the tectonic activity associated with each of the above mentioned reorganizations since anomaly 5a

structure of the michoacan guanajuato volcanic field mexico abstract the distribution and the alignment of volcanoes and fault scarps provide new insights into the structural framework of the michoacan guanajuato volcanic field a total of 1894 volcanoes occur over an area of 34 500 km 2 contour maps of the density of volcanoes and average volcano height indicate a shift from polygenetic to monogenetic volcanism from north to south in the field volcano edifice height has a bimodal density distribution which can be described by two populations with mean heights of 95 m and 510 m plotting the distribution of these two populations on separate contour maps reveals a n35e trend in monogenetic volcanoes and a n60w trend in polygenetic volcanoes fault scarps cut tertiary volcanic rocks and older quaternary volcanoes but are overprinted by volcanoes and lava flows in the central part of the field fault scarps define two fault zones oriented n60e in the northeastern part of the area and n60w in the northwest part of the area e w trending faults are common and alignments of volcanoes often parallel these faults regional trends in volcano distribution appear to be related to plate convergence the n60w trend of the polygenetic volcanoes is colinear to the western trans mexican volcanic arc parallel to the middle america trench and parallel to a major fault zone and represents an extinct volcanic arc the n35e band of monogenetic volcanoes may reflect the segmentation of the subducted plate

evidence from the mesta half graben sw bulgaria for the late eocene beginning of aegean extension in the central balkan peninsula abstract the ene tilted mesta half graben contains a 3 km thick section of priabonian late eocene to oligocene sedimentary and volcanic rocks that rest unconformably on basement metamorphic rocks along its west side basal strata dip 50 60 e and dip at progressively lower angles upward indicating synrotational deposition the southern part of the half graben contains nested volcanic caldera complexes formed during the deposition of the middle part of the sedimentary sequence which have been rotated by about half the total rotation of the sedimentary succession the half graben is bounded on the east by a fault that steepens from more deeply exposed structural levels in the south 8 18 w to shallower exposed structural levels in the north 70 w and together with the rotation of paleogene strata during deposition indicate the mesta half graben is underlain by a listric detachment fault the mesta detachment subhorizontal middle miocene strata that unconformably overlie tilted paleogene strata yield an upper age limit to the extension west and northwest of the mesta half graben are many other nnw trending ne tilted paleogene half grabens which we suggest are part of an important extended area in sw bulgaria and eastern macedonia that lies above one or more west dipping detachment faults and date the beginning of aegean extension in the southern balkan region as at least as old as priabonian the mesta detachment is oblique to the trend of a contemporaneous paleogene magmatic arc in the southern balkans and the origin of the detachment is probably related to gravitationally induced spreading of thickened hot arc crust and hellenic trench roll back

tectonic interpretation of the trans mexicano volcanic belt abstract although some workers interpret subduction along the middle america trench to be directly associated with volcanism in the trans mexico volcanic belt geographic distribution of intermediate depth earthquakes analysis of sn propagation and a limited number of focal mechanism solutions suggest that the belt is largely independent of subduction these data in conjunction with the position of the volcanic belt with respect to known plate boundaries in the region suggest that the belt represents the incompletely developed northern boundary of a developing micro plate it is a zone of transtension that probably results from slightly different rates of absolute plate velocities in the region

stress field estimations for colima volcano mexico based on seismic data for first time during 1991 seismic activity was recorded during an eruption at colima volcano we analyze these data to obtain a stress pattern using a composite focal mechanism technique from the analysis of regional seismicity the tamazula fault and the armeria river appear as active features and the dip of the slab east of the jalisco block is approximately 12 southwest of colima volcano a vertical alignment of seismic events was observed we estimate five different composite focal mechanism solutions from our data set which indicate a change of the stress field at the volcano after the 1991 eruption these solutions suggest that the stress field in the volcanic edifice was controlled by stresses related to the emplacement of magma superimposed on the regional stress field no evidence of active local faults in the volcanic edifice was found we propose a model for the eruptive process that involves tilting of the volcanic edifice

evolution of the december 14 1989 precursory long period event swarm at redoubt volcano alaska abstract the intermittency pattern and evolution in waveforms of long period lp seismic events during the intense 23 h swarm that preceded the december 14 1989 eruption of redoubt volcano are investigated utilizing cross correlation to exploit the high degree of similarity among waveforms a substantially more complete event catalog is generated than was available from near realtime detection based on short term long term amplitude ratios which was saturated by the high rate of activity the temporal magnitude distribution of the predominant lp events is found to have an unusual banded structure in which the average magnitude of each band slowly increases and then decreases through time a bifurcation that appears in the uppermost band shortly after the peak in magnitudes is characterized by a quasi periodicity in intermittency and magnitude that is reminiscent of one of the classic routes to chaotic behavior in some non linear systems the waveforms of the predominant events evolve slowly but unsteadily through time these gradual changes appear to result from variations in the relative amplitudes of spectral peaks that remain stable in frequency which suggests that they are due to differential excitation of a single resonant source two other previously unrecognized repetitive waveforms are also identified but the signals from these secondary events are not clearly recorded at distances beyond the closest station similarities among the spectra of the predominant and secondary events suggest that the signals from these events also could represent different modes of exciting the same source significant changes in the rates and the sizes of the largest of these secondary events appear to coincide with the peak in the size distribution of the predominant lps at least some of the non repetitive lp waveforms in the swarm appear to be the result of the superposition of signals from the rapid repetition of predominant lp source thus placing a constraint on the repeat time of the triggering mechanism for this source a lone hybrid event which has a waveform character intermediate between the predominant lp events and high frequency volcano tectonic events was also identified in the swarm the occurrence of this event provides important evidence that the low frequency character of the lp events is a source rather than a path or site effect

volcano tectonic earthquakes a new tool for estimating intrusive volumes and forecasting eruptions abstract we present data on 136 high frequency earthquakes and swarms termed volcano tectonic vt seismicity which preceded 111 eruptions at 83 volcanoes plus data on vt swarms that preceded intrusions at 21 other volcanoes we find that vt seismicity is usually the earliest reported seismic precursor for eruptions at volcanoes that have been dormant for decades or more and precedes eruptions of all magma types from basaltic to rhyolitic and all explosivities from vei 0 to ultraplinian vei 6 at such previously long dormant volcanoes because large eruptions occur most commonly during resumption of activity at long dormant volcanoes vt seismicity is an important precursor for the earth s most dangerous eruptions vt seismicity precedes all explosive eruptions of vei 5 and most if not all vei 4 eruptions in our data set surprisingly we find that the vt seismicity originates at distal locations on tectonic fault structures at distances of one or two to tens of kilometers laterally from the site of the eventual eruption and rarely if ever starts beneath the eruption site itself the distal vt swarms generally occur at depths almost equal to the horizontal distance of the swarm from the summit out to about 15 km distance beyond which hypocenter depths level out we summarize several important characteristics of this distal vt seismicity including swarm like nature onset days to years prior to the beginning of magmatic eruptions peaking of activity at the time of the initial eruption whether phreatic or magmatic and large non double couple component to focal mechanisms most importantly we show that the intruded magma volume can be simply estimated from the cumulative seismic moment of the vt seismicity from log10 v 0 77 log moment 5 32 with volume v in cubic meters and seismic moment in newton meters because the cumulative seismic moment can be approximated from the size of just the few largest events and is quite insensitive to precise locations the intruded magma volume can be quickly and easily estimated with few short period seismic stations notable cases in which distal vt events preceded eruptions at long dormant volcanoes include nevado del ruiz 1984 1985 pinatubo 1991 unzen 1989 1995 soufriere hills 1995 shishaldin 1989 1999 tacana 1985 1986 pacaya 1980 1984 rabaul 1994 and cotopaxi 2001 additional cases are recognized at frequently active volcanoes including popocateptl 2001 2003 and mauna loa 1984 we present four case studies pinatubo soufriere hills unzen and tacana in which we demonstrate the above mentioned vt characteristics prior to eruptions using regional data recorded by neic we recognized in near real time that a huge distal vt swarm was occurring deduced that a proportionately huge magmatic intrusion was taking place beneath the long dormant sulu range new britain island papua new guinea that it was likely to lead to eruptive activity and warned rabaul volcano observatory days before a phreatic eruption occurred this confirms the value of this technique for eruption forecasting we also present a counter example where we deduced that a vt swarm at volcan cosiguina nicaragua indicated a small intrusion insufficient to reach the surface and erupt finally we discuss limitations of the method and propose a mechanism by which this distal vt seismicity is triggered by magmatic intrusion

high precision relative locations of earthquakes at mount st helens washington several earthquake sequences have occurred at mount st helens as clusters of shallow events with nearly identical waveforms multiplets we present a technique that allows the relative relocation of events within a multiplet to at least an order of magnitude higher precision than is typically possible with traditional techniques a multiplet is studied in pairs of events called doublets each doublet is made up of a reference event and one other event from the multiplet the cross spectrum of a short window beginning just before the p arrival is used to compute differences in arrival times between seismograms from the same station for each doublet these time differences computed with a precision of 1 2 ms are then used to locate each earthquake relative to the reference event engineering explosions with well known locations are used to test the relocation technique explosions can be relocated with accuracy better than 20 m for events within 250 m of the reference explosion the relocation technique is applied to earthquakes preceding the september 10 1984 and the may june 1985 dome building eruptions of mount st helens forty events that occurred during a 12 hour period in september 1984 are located in a volume approximately 30 m in diameter beneath the lava dome the earthquakes following the extrusion do not occur in multiplets and appear to be distributed over a much larger volume in the may june 1985 eruption we recognize three multiplet sets that took place successively in time the multiplets are interpreted as repeated failure or slip within a relatively small volume due to high strain rates around the magma supply conduit

the effect of early alpine thrusting in late stage extensional tectonics evidence from the kulidzhik nappe and the pelevun extensional allochthon in the rhodope massif bulgaria abstract in the northeastern rhodope massif the kulidzhik nappe exposes a unique juxtaposition of a high grade basement allochthon onto a low grade mesozoic unit and the counterpart pelevun extensional allochthon belonging to the same unit the kulidzhik nappe tectonostratigraphy comprises structurally upward i a lower unit consisting of high grade basement orthogneisses ii a low grade greenschist phyllite unit consisting of jurassic extrusive rocks and metasedimentary rocks iii the nappe allochthon built by the lower high grade basement unit orthogneisses and iv eocene sedimentary rocks and oligocene volcanic cover rocks the pelevun extensional allochthon is heterogeneous and consists of mesozoic low grade unit marbles and greenschists and the upper high grade basement unit we have combined structure and kinematics with lithological information and 40 r 39 r geochronology to constrain the tectonic evolution and regional significance of the kulidzhik nappe and the pelevun extensional allochthon mineral chemistry reveals igneous phases of the granitic protolith of the allochthonous orthogneisses with textures related to ductile deformation and metamorphism higher than 500 c their trace element patterns are indistinguishable from the high grade basement orthogneisses in the eastern rhodope mineral chemistry of the metamorphic assemblage in the underlying greenschists is consistent with medium grade greenschist facies metamorphism at temperatures well below 450 c whose geochemistry defines transitional morb to iat affinities with a strong arc imprint the greenschist s composition is extremely similar to the composition of a supra subduction zone jurassic arc extrusive suite that occurs in the low grade unit of the eastern rhodope the structural elements in all of the tectono metamorphic units and the nappe surface indicate top to the nne tectonic transport deformation evolved from ductile to brittle conditions coevally with a progressive decrease from lower amphibolite to weak greenschist facies metamorphism towards the structural top two klippen gave plateau 40 r 39 r mica ages of 154 23 0 66 ma and 156 70 0 81 ma respectively which reflect cooling following the greenschist facies event below 350 c during shallow crustal level thrust emplacement and exhumation of the kulidzhik allochthon the hanging wall pelevun extensional allochthon preserves an internal nne directed ductile tectonic transport trend but is underlain by a ssw directed ductile brittle extensional detachment and has experienced ne sw brittle extension on high angle normal faults an amphibole 40 r 39 r inverse isochron age of 156 58 0 60 ma constrains a late jurassic upper greenschist facies tectono metamorphic event whereas a white mica plateau age of 39 66 0 47 ma provides evidence for middle eocene cooling and exhumation of the pelevun extensional allochthon in the hanging wall of the detachment we relate the kulidzhik nappe to late jurassic crustal deformation during arc continental margin collision that involved nne directed nappe staking and metamorphism of continental margin basement and island arc units the nappe shares a tectono metamorphic history with the nappes of the adjacent strandzha massif implying a region wide early alpine orogenic system our results reveal a record of early alpine thrust tectonics and show the significance of crustal accretion related assembly for the tectonic evolution of the rhodope massif both the late jurassic thrusting event and the subsequent cretaceous thrusting event thickened the rhodope crust creating crustal instability which influenced tertiary crustal extension

neotectonic development of the struma kraistid lineament southwest bulgaria and northern greece the struma kraistid lineament is a part of a fault belt of regional importance it strikes nnw sse and cuts through different alpine tectonic zones along the whole balkan peninsula normal and strike slip faults occurred in environments of extension and graben formation during collapse after or between collision epochs in the palaeogene and early neogene and in a back arc extensional environment during the neotectonic end of middle miocene quaternary stage the last alpine compression phase occurred in the beginning of the miocene and early middle miocene planation formed the initial peneplain new intense faulting marked the beginning of the neotectonic stage late badenian and the neotectonic development including sedimentation proceeded in four regional macrocycles badenian sarmatian maeotian pontian dacian and eopleistocene pleistocene the neotectonic development was marked by formation of the serbo macedonian swell as well as by rifting the vardar and struma rifts

basement types of the thrace basin and a new approach to the pre eocene tectonic evolution of the northeastern aegean and northwestern anatolia a review of data and concepts in northwestern turkey the pre eocene basement of the thrace basin consists of the strandja rhodope metamorphics in the north northwest the istanbul zonguldak paleozoic sequence in the northeast a tectonic mixture of the fragments from the sakarya continent and pre upper cretaceous ophiolites in the southeast and the uppermost cretaceous paleocene transgressive sediments the ophiolites belong to a dogger early cretaceous oceanic basin the northeastern vardar ocean between the rhodope and sakarya continents the ne trending oceanic branch closed diachronously during the early late malm to the northeast but during latest early cretaceous to late cretaceous time toward the main vardar ocean in the southwest during the final closure the suture zone acted as a strike slip fault zone the latest cretaceous paleocene transpressional to transtensional activities caused the juxtaposition of different basement types and the development of a tectonic mixed zone the biga armutlu ovacik zone between the rhodope and sakarya continents under the regional n s compression on the plate overlying the north northeastward dipping vardar subduction zone the southwestward escape of an area of crust bounding by the wnw trending balkan thrace dextral fault zone to the north and the ne trending biga armutlu ovacik sinistral zone to the southeast caused a triangular shaped and isolated depression area for the deposition of the uppermost cretaceous paleocene transgressive sediments in a transtensional setting the tectonically bounded depression area constitutes also a necessary accommodation space for the deposition of the initial deposits of early eocene age in the thrace basin

the origin of volcano tectonic earthquake swarms volcano tectonic vt seismicity is commonly recorded prior to and during eruptions vt seismicity may reflect stresses induced by dike propagation as indicated by propagating hypocenters and fault plane solutions fps reflecting regional stresses or stresses induced by dike inflation indicated by randomly distributed hypocenters and fps with pressure axes rotated 90 to regional maximum compression although numerical models of dike induced stresses indicate that both regimes should occur during dike emplacement this has not yet been observed according to published seismic data instead 90 rotated fps are observed in some cases while propagating hypocenters mark dike formation in other cases we suggest that differences in the seismic expression of upper crustal magma migration may result from differences in the regional tectonic setting and in the nature of magma wall rock interactions ultimately it may be possible to use information contained in vt seismicity to forecast changes in a volcano s behavior by establishing the characteristic stress field response for a given volcano or through a deeper understanding of the complex relationships between vt seismicity local crustal stresses and the physical mechanisms of magma migration

metal fixation by bacterial cell walls all biomass contains a significant quantity of metallic constituents and mineralization in living and dead biodebris may contribute to element transport from the hydrosphere into sediments the anionic cell walls of bacteria are remarkable in their ability to fix metals and provide sites for nucleation and growth of minerals results presented show the types of cell wall polymers that are responsible for metal binding in walls of gram positive and gram negative bacteria

40ar 39ar age constraints on the timing of tertiary crustal extension and its temporal relation to ore forming and magmatic processes in the eastern rhodope massif bulgaria we quantify the timing of the tertiary crustal extension in the eastern rhodope massif of south bulgaria using 40 r 39 r geochronology to constrain the temporal evolution of exhumation of the metamorphic domes 40 r 39 r analyses of mineral phases with different closure temperatures extracted from metamorphic rocks collected in the footwall and the hanging wall of the extensional system reveal the low temperature cooling history towards shallow crustal levels the results reveal that subsequent to regional amphibolite facies metamorphism i the hanging wall gradually cooled between 500 and 300 c during the paleocene to late eocene 64 34 ma starting at a low rate of 25 c ma and increasing to 50 67 c ma during 38 34 ma ii cooling below 400 300 c of the footwall beneath the extensional detachments occurred in the middle late eocene 39 35 5 ma at an average rate of 35 c ma 40 r 39 r data from the metamorphic basement has been combined with 40 r 39 r data from the volcanic and hydrothermal rocks in the vicinity to the extensional domes to determine the temporal relationships between extensional tectonics ore forming and magmatic processes in the region extension of the high grade basement the ore formation and volcanism overlaps within a 5 ma lasting time interval especially during the cooling and exhumation of the footwall the eastern rhodope massif records an early stage of eocene extension within the aegean extensional province where distinct crustal scale processes occurred simultaneously implying the presence of cause and effect processes and thus represents a key example of coeval continental extension magmatism and hydrothermal activity in the late stage evolution of the orogens

palaeogene alluvial volcaniclastic deposits in the mesta basin sw bulgaria depositional setting and basin evolution the mesta half graben is one in a series of extensional basins in sw bulgaria that record the onset of extension within the rhodope zone in the late eocene tectonic activity on a continuous detachment along the eastern margin was a major control on subsidence accommodation space creation sediment supply and facies distribution in the basin the sedimentary architecture was complicated by synsedimentary rotation the presence of intrabasinal faults and the resulting compartmentalization as well as synsedimentary volcanic activity facies and structural analysis of a key transverse section in the central part of the basin together with supporting observations from other parts of the basin indicate a pulsed tectono sedimentary evolution of the basin with three distinct stages the first stage late eocene is a phase of rapid extension with an initial alluvial setting basin margin fans and an axial fluvial through drainage system were the major depositional systems in this stage the second stage early oligocene marks the onset of volcanic activity within the mesta basin and is characterized by the formation of volcanic centres an intense phase of explosive volcanism and rapid infilling of the previous basin topography with volcanic material deposited from pyroclastic density currents the third stage late oligocene represents waning volcanic activity in a mixed alluvial volcaniclastic environment this stage is characterized by alternating alluvial and volcaniclastic depositional cycles as well as partial reworking of volcanic material

foreshock sequence of the 1992 landers california earthquake and its implications for earthquake nucleation the june 28 1992 landers california earthquake mw 7 3 was preceded for about 7 hours by a foreshock sequence consisting of at least 28 events in this study we examine the geometry and temporal development of the foreshocks using high precision locations based on cross correlation of waveforms recorded at nearby stations by aligning waveforms rather than trying to obtain travel time picks for each event independently we are able to improve the timing accuracy greatly and to make very accurate travel time picks even for emergent arrivals we perform a joint relocation using the improved travel times and reduce the relative location errors to less than 100 m horizontally and less than 200 m vertically with the improved locations the geometry of the foreshock sequence becomes clear the landers foreshocks occurred at a right step of about 500 m in the mainshock fault plane the nucleation zone as defined by the foreshock sequence is southeast trending to the south and nearly north trending to the north of the right step this geometry is confirmed by the focal mechanisms of the foreshock sequence which are right lateral and follow the trend as determined by the foreshock locations on the two straight segments of the fault and are rotated clockwise for foreshocks that occur within the step the extent of the foreshock sequence is approximately 1 km both vertically and horizontally modeling of the coulomb stress changes due to all previous foreshocks indicates that the foreshocks probably did not trigger each other this result is particularly clear for the mw 4 4 immediate foreshock since stress transfer in the sequence appears not to have played a significant role in its development we infer an underlying aseismic nucleation process probably aseismic creep other studies have shown that earthquake nucleation may be controlled by fault zone irregularities this appears to be true in the case of the landers earthquake although the size of the irregularity is so small that it is not detectable by standard location techniques

the relationship between earthquake swarms and magma transport kilauea volcano hawaii a detailed investigation of earthquake locations and focal mechanisms for swarms associated with intrusive events at kilauea volcano hawaii further illuminates the relationships among stress state faulting and magma transport we determine the earthquake locations and mechanisms using a three dimensional crustal model to improve their accuracy and consistency swarms in kilauea s upper east and southwest rift zones from the years 1980 through 1982 provide clear evidence for the propagation and or dilation of dikes focal mechanisms are predominantly strike slip and the faulting and inferred dike orientations can be interpreted quite consistently in terms of the model ofhill 1977 stresses induced by the summit magma reservoir system strongly control faulting and magma transport in the rift zones close to the summit

distribution and speciation of gold in biogenic and abiogenic calcium carbonates implications for the formation of gold anomalous calcrete abstract calcrete pedogenic ca carbonate is an important sampling medium for geochemical gold au exploration in semi arid and arid regions of australia because it is widespread easy to sample and calcium ca shows a strong positive correlation with au but not with base metals in calcrete overlying buried au mineralization in this study we show that the formation of au anomalous calcrete can be biomediated through the activity of resident microorganisms and may not simply be the result of passive nucleation on inactive cells or evapotransporative processes calcified microfossils are highly abundant in calcrete from the barns au prospect in south australia these microfossils are morphological analogues of calcified cells and biofilms formed in laboratory experiments conducted with active bacterial cultures enriched from au anomalous calcareous sand from the barns prospect calcium carbonates precipitated by these cultures consisted mostly of calcite which is the main carbonate mineral in calcrete synchrotron micro x ray fluorescence s xrf mapping was used to assess the distribution of au zn ca and other metals in ca carbonates precipitated by active bacterial cultures on a m scale the distribution of au was heterogeneous in these ca carbonates and differed from base metal distribution thus mimicking the spatial separation of these metals observed in calcrete the speciation of au in ca carbonates precipitated by active bacteria was measured using micro x ray absorption near edge structure spectroscopy xanes and resembled that observed in au anomalous calcrete closely while metallic au was observed in au hotpots ionic au was detected in the halo surrounding the hotspot in contrast the precipitates produced in the presence of dead bacterial cells or by raising solution ph or pco 2 i e hydroxylapatite portlandite and vaterite respectively did not reflect the mineralogy of calcrete gold distribution and speciation in vaterite formed by raising pco 2 were homogenous and did not reproduce the variation observed in calcrete and ca carbonates precipitated by active cells increasing the supersaturation with respect to ca in solution by incremental drying of the medium produced only x ray amorphous precipitates or hydroxylapatite in the presence heat killed cells in conclusion this study shows that active microbial processes that combine biogenic ca carbonatogenesis with au precipitation are likely to drive the formation of au anomalous calcrete

microstructural compositional and petrophysical properties of mylonitic granodiorites from an extensional shear zone rhodope core complex greece at the southern boundary of the rhodope massif ne greece the kavala shear zone ksz represents an example of the eastern mediterranean deep seated extensional tectonic setting during miocene time extensional deformation favoured syntectonic emplacement and subsequent exhumation of plutonic bodies this paper deals with the strain related changes in macroscopic geochemical and microstructural properties of the lithotypes collected along the ksz comprising granitoids from the pluton aplitic dykes and host rock gneisses moreover we investigated the evolution of seismic anisotropy on a suite of granitoid mylonites as a result of progressive strain isotropic compressional and shear wave velocities v p v s and densities calculated from modal proportions and single crystal elastic properties at given pressure temperature p t conditions are compared to respective experimental data including the directional dependence anisotropy of wave velocities compared to the calculated isotropic velocities which are similar for all of the investigated mylonites average values v p 5 87 km s 1 v s 3 4 km s 1 v p v s 1 73 and density 2 65 g cm 3 the seismic measurements give evidence for marked p wave velocity anisotropy up to 6 92 at 400 mpa in the most deformed rock due to marked microstructural changes with progressive strain as highlighted by the alignment of mica chlorite minerals and quartz ribbons the highest p and s wave velocities are parallel to the foliation plane and lowest normal to the foliation plane importantly v p remains constant within the foliation with progressive strain but decreases normal to foliation the potential of the observed seismic anisotropy of the ksz mylonites with respect to detectable seismic reflections is briefly discussed

volcan tancitaro michoacan mexico 40ar 39ar constraints on its history of sector collapse abstract volcan tancitaro is a 97 3 km3 stratovolcano located in the michoacan guanajuato volcanic field mgvf part of the trans mexican volcanic belt prior to this study there was only one k ar date 530 60 ka ban m hasenaka t delgado granados h takaoka n 1992 k ar ages of lavas from shield volcanoes in the michoacan guanajuato volcanic field mexico geofisica internacional 31 4 467 473 and one sector collapse event reported for this volcano in the literature garduno monroy v h corona chavez p israde alcantara i mennella l arreygue e bigioggero b chiesa s 1999 carta geologica de michoacan scale 1 250 000 universidad michoacana de san nicolas de hidalgo capra l macias j l scott k m abrams m garduno monroy v h 2002 debris avalanches and debris flows transformed from collapses in the trans mexican volcanic belt mexico behavior and implications for hazard assessment journal of volcanology and geothermal research 113 81 110 twenty six new 40ar 39ar ages indicate that volcan tancitaro became active 793 22 ka and that the most recent effusive activity occurred at 237 34 ka two catastrophic sector collapse events are identified and dated the first one occurred on the west side between 694 and 571 ka whereas the second one occurred on the east side between 261 and 238 ka the older collapse produced a 2 3 3 4 km3 debris avalanche and laharic deposit spread over 567 km2 whereas the more recent collapse left a 3 km wide horseshoe shaped scar on the eastern flank and produced a 3 6 7 0 km3 debris avalanche and laharic deposit that covers 654 km2 reconstruction of the main edifice of volcan tancitaro using arcgis software and digital elevation models indicates that the volume removed during the eastern sector collapse was 4 7 km3

using automated high precision repicking to improve delineation of microseismic structures at the soultz geothermal reservoir an automatic adaptive correlation based algorithm for adjusting phase picks in large digital seismic data sets provides significant improvement in resolution of microseismic structures using only a small fraction of the time and manpower which would be required to re analyze waveforms manually or semi automatically we apply this technique to induced seismicity at the soultz sous forets geothermal site france the method is first applied to a small previously manually repicked subset of the catalogue so that we may compare our results to those obtained from painstaking visual cross correlation based techniques relative centroid adjusted hypocenters show a decrease in median mislocation from 31 to 7 m for preliminary and automatically adjusted picks respectively compared to the manual results narrow intersecting joint features not observed in the preliminary hypocenter cloud but revealed through manual repicking are also recovered using the automatic method we then address a larger catalogue of 7000 microearthquakes after relocating the events using automatic repicks the percentage of events clustering within 5 m of their nearest neighbor increases form 5 to 26 of the catalogue hypocenter relocations delineate narrow linear features previously obscured within the seismic cloud interpreted as faults or fractures which may correspond to fluid propagation paths or to changes in stress as a result of elevated pore pressures rms travel time residuals for the larger data set are reduced by only 0 2 however phase pick biases in the preliminary catalogue have influenced both the velocity model and station correction calculations which will affect location residuals these pick biases are apparent on the adjusted stacked waveforms and correcting them will be important prior to future velocity model refinements

the immobilization of gold from gold iii chloride by a halophilic sulphate reducing bacterial consortium a consortium containing halophilic dissimilatory sulphate reducing bacteria was enriched from basque lake 1 located near ashcroft british columbia canada to evaluate the role these bacteria have on the immobilization of soluble gold the consortium immobilized increasing amounts of gold from gold iii chloride solutions under saline to hypersaline conditions over time gold iii chloride was reduced to elemental gold in all experimental systems salinity did not affect gold immobilization scanning electron microscopy and transmission electron microscopy demonstrated that reduced gold iii chloride was immobilized as c 3 10 nm gold colloids and c 100 nm colloidal aggregates at the fluid biofilm interface the precipitation of gold at this organic interface protected cells within the biofilm from the toxic effect of ionic gold analysis of these experimental systems using x ray absorption near edge spectroscopy confirmed that elemental gold with varying colloidal sizes formed within minutes the immobilization of gold by halophilic sulphate reducing bacteria highlights a possible role for the biosphere in intercepting mobile gold complexes within natural hydraulic flow paths based on the limited toxicity demonstrated in this experimental model significant concentrations of elemental gold could accumulate over geological time in natural systems where soluble gold concentrations are more dilute and presumably non toxic to the biosphere