a geophysically constrained litho structural analysis of the eburnean greenstone belts and associated granitoid domains burkina faso west africa abstract interpretation of airborne geophysical data integrated with field structural and lithological observation was successfully employed in the creation of the litho structural framework in a poorly exposed paleoproterozoic granite greenstone terrain of the west african craton the geophysical data portray with sufficient detail all of the lithological units and structural features present the results suggest that the granitoid domains are formed by numerous small to medium sized plutons the existence of several generations of magmatic episodes has a significant impact on the development of a regional tectonic model the magnetic data provided a better definition of the actual pluton shapes and several highly magnetic late orogenic plutons were reliably identified relic f1 fold hinges were recognized in the hounde and boromo greenstone belts the d1 penetrative structures are generally affected by the d2 transcurrent shear zones which often form as well the granite greenstone belt boundaries previously unreported s2 shear zones including the bossie shear zone transecting the sideradougou granitoid domain and abundant small scale shear zones affecting all of the lithologies represent prospective areas for gold exploration airborne gamma ray spectrometry data aided in the mapping process in areas with less regolith cover including erosional ridges and parts of the banfora greenstone belt the magnetic data revealed at least three generations of doleritic dykes crosscutting the western burkina faso

models for midcontinent tectonism an update during the past decade significant progress has been made in defining the nature of midcontinent tectonism as a result of an improved geophysical geologic data base which permits an integration of seismicity data crustal structures and current stress directions critically placed microseismic networks have shown that many earthquakes with common focal mechanisms occur in specific spatial patterns the direction of the maximum horizontal compressive stress is generally directed east northeast which supports an origin associated with ridge push forces related to movement of the north american plate crustal structures have been mapped locally by seismic studies and regionally by extensive gravity and magnetic anomaly data these data have been used to relate current seismicity and associated tectonism to one of two models increasing evidence from across the midcontinent supports reactivation of preexisting zones of crustal weakness appropriately oriented with respect to the prevailing stress field the zone of weakness model as the dominant control on contemporary tectonism and the local basement inhomogeneity model as a mechanism for minor low energy release earthquake activity

dendrogeomorphic reconstruction of past snow avalanche events in bâlea glacial valley făgăras massif southern carpathians romanian carpathians abstract snow avalanches are a major hazard in the southern carpathians romanian carpathians and cause damage to transportation routes or infrastructure and losses of human lives in these mountains the scientific understanding of avalanches is still poor the main objectives of this study were to reconstruct spatio temporal patterns of avalanche events to complement written records in the b lea glacial valley located in the central part of northern slope of the f g ras massif and to identify the winter weather conditions responsible for avalanche occurrence using a dendrogeomorphologic approach the analysis was based on tree ring series from 293 affected picea abies trees in four avalanche tracks our results from tree ring records yielded 24 and 17 snow avalanches in the 1867 2012 chronology in first and second track 24 and 12 snow avalanches in the 1870 2012 chronology in third and in fourth track the tree ring based analysis of the 586 extracted increment cores allowed the identification of 853 growth disturbances related to past avalanche activity the most frequent response is found as reaction wood 64 1 followed by abrupt growth changes 20 6 traumatic resin ducts 13 and callus tissue 2 3 a total of 77 event years with aai 10 were reconstructed the reconstruction revealed five high magnitude avalanches aai 30 25 medium magnitude avalanches 20 aai 30 and 47 small magnitude avalanches 10 aai 20 the return period values vary between 16 7 and 23 6 years based on the reconstructed chronologies our analyses identified 13 cases of synchronicity of events with aai 10 this synchronicity indicates the decisive role of local weather conditions which are responsible for the occurrence of extreme snow avalanches the weather conditions triggering extreme avalanche correspond with high amounts of snowfall and consequently thick snowpack even if the largest snowfalls are not necessarily associated with extreme avalanches

linking stress field deflection to basement structures in southern ontario results from numerical modelling abstract analysis of stress measurement data from the near surface to crustal depths in southern ontario show a misalignment between the direction of tectonic loading and the orientation of the major horizontal principal stress the compressive stress field instead appears to be oriented sub parallel to the major terrane boundaries such as the grenville front the central metasedimentary belt boundary zone and the elzevir frontenac boundary zone this suggests that the stress field has been modified by these deep crustal scale deformation zones in order to test this hypothesis a geomechanical model was constructed using the three dimensional discontinuum stress analysis code 3dec the model consists of a 45 km thick crust of southern ontario in which the major crustal scale deformation zones are represented as discrete faults lateral velocity boundary conditions were applied to the sides of the model in the direction of tectonic loading in order to generate the horizontal compressive stress field modelling results show that for low strength low friction angle and cohesion fault slip causes the stress field to rotate toward the strike of the faults consistent with the observed direction of misalignment with the tectonic loading direction observed distortions to the regional stress field may be explained by this relatively simple mechanism of slip on deep first order structures in response to the neotectonic driving forces

fluid compartmentalization and dolomitization in the cambrian and ordovician successions of the huron domain michigan basin abstract strata bound dolomite occurs in deep seated ordovician and cambrian sediments within the huron domain of southern ontario canada core samples were analyzed for petrographic stable and sr isotopic composition and fluid inclusion microthermometry to characterize dolomitization and evaluate diagenetic fluid composition the samples represented a range of host rocks from dolomitized limestones dolostones sandy dolostones and sandstones within ordovician black river group and underlying cambrian formation the petrographic and geochemical attributes have provided a basis to gain insight on the source fluids that modified these rocks as well as the possible timing of formation evidence indicates that the formations were subjected to high temperatures average 115 c that cannot be explained by burial history alone this suggests the occurrence and migration of hydrothermal fluids within the low permeability dolomite horizons possibly during paleozoic orogenesis dolomite and calcite fracture infill isotopic and fluid inclusion data point to two possibly individual diagenetic fluid systems i an earlier cambrian system that is characterized by a pronounced negative shifts in oxygen and carbon isotopic composition 18o average 9 0 for dolomite and 13 9 for calcite respectively and 13c 3 06 for dolomite and 4 82 for calcite respectively a more radiogenic sr87 sr86 ratios range from 0 70977 to 0 71100 warm th values range from 84 to 156 c for dolomite average 113 6 c and 87 141 c for calcite average 101 5 c and saline signature salinity range from 23 2 to 27 2 wt nacl eq for dolomite average 24 3 for dolomite and 23 6 wt nacl eq for calcite and ii a later ordovician system that is characterized by less negative shifts in both oxygen and carbon isotopes 18o average 8 7 for dolomite and 7 5 for calcite and 13c average 0 37 for dolomite and 0 36 for calcite respectively hypersaline salinity range from 22 4 to 30 1 wt nacl eq average 27 0 for dolomite and 27 5 to 29 7 for calcite average 29 2 comparable homogenization temperature th ranges from 85 to 132 c for dolomite average 109 6 c and 66 153 c for calcite average 107 2 c and a less radiogenic sr87 sr86 ratios range from 0 70818 to 0 71 000 fluid system the observation of highly discrete strata bound dolomites combined with only trace quantities of saddle dolomite and its associated geochemical signature suggest that diagenesis as a result of hydrothermal fluids was neither pervasive in volume or extent within the north western huron domain

understanding sedimentation in the song hong yinggehai basin south china sea the cenozoic song hong yinggehai basin in the south china sea contains a large volume of sediment that has been used in previous studies together with regional geomorphology to argue for the existence of a large palaeodrainage system that connected eastern tibet with the south china sea to test this and to understand the significance of sediment volumes deposited in the song hong yinggehai basin this study compared erosion histories of source regions with sediment volumes deposited during the two main stages in basin evolution spanning active rifting and subsidence 30 15 5 ma and postrift sedimentation 15 5 ma to present the study of basin provenance by detrital zircon u pb dating revealed hainan was an important and continuous source of sediment and a bedrock thermochronological study quantified its overall contribution to basin sedimentation comparison between the accumulated mass of basin sediment and volumes of eroded bedrock calculated from apatite thermochronometry across the modern red river drainage in northern vietnam as well as hainan island accounted for the bulk of sediment deposited since 30 ma consequently if an expanded paleodrainage ever existed it must have predated the oligocene

linear zones seismicity and the possibility of a major earthquake in the intraplate western lake ontario area of eastern north america seismic hazard assessments conducted in eastern canada rely on seismological data which are essential but alone inadequate that is because the earthquake record is too short to provide a representative picture of where large earthquakes have occurred in the past consequently seismic hazard may be underestimated in areas such as that encompassing western lake ontario that are devoid of documented large earthquakes to attempt to ascertain the likelihood of a major earthquake occurring in that highly populated and industrialized area three regionally extensive geophysically expressed lineaments were investigated and the results were combined with available seismological information the most conspicuous is the niagara pickering linear zone within which there have been at least two if not three periods of brittle faulting including displacements compatible with the current stress field it also appears to represent the same major structure as the akron magnetic boundary in eastern ohio the site of the mb 4 9 leroy earthquake the second is the georgian bay linear zone which extends from georgian bay to new york state it displays evidence of recent outcrop scale faulting an alignment of earthquakes along its southwestern boundary and a possible spatial relationship to other earthquakes including two of m 5 lastly there is the hamilton lake erie lineament which is parallel and proximal to a possible fault and coincides with a linear array of small to moderate earthquakes all three converge on the western lake ontario area which has a higher frequency of seismicity than the adjacent areas thus the western lake ontario area might have a greater potential to experience a major earthquake than heretofore believed resume les evaluations des risques sismiques dans l est du canada sont fondees sur les donnees sismologiques dont

cenozoic paleoaltimetry of the se margin of the tibetan plateau constraints on the tectonic evolution of the region abstract an improved understanding of the elevation history of the tibetan plateau is crucial in discriminating among the various tectonic models for the evolution of the india asia continental collision we reconstruct the paleoelevation history for three cenozoic sedimentary basins from se tibet and yunnan china to provide more constraints on the tectonic processes for raising the se margin of the tibetan plateau the results presented here together with those of previous studies indicate that 1 the plateau margin of nw yunnan was near its elevation 2 6 km by the latest middle eocene 40 ma 2 the plateau margin of se yunnan reached its current elevation 1 6 km by the middle miocene 13 ma interpretations of the tectonic processes responsible for this inferred surface uplift of the region are made in the context of well documented surface geology we conclude that high landscape 2 6 km elevation in nw yunnan may represent the remnants of the eocene tibetan plateau that originally formed in the northeastern qiangtang block by crustal thickening associated with the india asia continental collision the near modern elevation of se yunnan since 13 ma probably reflects the initiation of lower crustal flow in this area by at least that time collectively our paleoaltimetric interpretations disagree with previously proposed models of middle miocene to pliocene crustal flow acting as a sole tectonic process for raising the se margin of the plateau but support a protracted history of surface uplift that most likely involved crustal thickening during the eocene southeastward extrusion of a portion of eocene tibetan plateau during the oligocene to early miocene and lower crustal flow beneath this region since at least the early miocene

provenance and time constraints on the formation of the first bend of the yangtze river 1 the upper yangtze river flows southward on the southeastern tibet characterizing by uniquely low and continuous relief the river makes a sharp turn at shigu heading northeast and forms the first bend of the yangtze river many previous studies assumed southward flow of the ancestral yangtze river from shigu to the south china sea however field evidence of southward flow of the paleo yangtze is lacking in this paper we report our identification based on detrital zircon u pb age distributions of a range of fluvial sands left by the paleo yangtze in tongdian madeng and nanjian basins cosmogenic10be and 26al burial dating provides burial ages for these fluvial sands from 1 7 to over 8 7 ma rerouting of the yangtze river therefore occurred within the last 1 7 ma postdating the major uplift of the central tibet we attribute the rerouting of the yangtze river to response to activation of the dali fault system and in a larger scale initiation of crustal deformation by clockwise rotation around eastern himalayan syntaxis 2 4 ma ago reorganization of the yangtze drainage pattern most likely reflects regional uplift and displacement due to lower crust flowing beneath major faults in the southeastern tibet and yunnan

a thermochronological perspective on the morphotectonic evolution of the southeastern tibetan plateau a large part of the southeastern tibetan plateau tp is characterized by low relief surfaces at high elevations 3 5 km the origin of these landscapes and their geodynamic implications with regard to evolution of the southeastern tp has been the subject of considerable debate focusing on this topic this study utilizes fission track and u th he thermochronology to reconstruct the thermal history of the late triassic daocheng granite on which a low relief high elevation landscape has developed results suggest that the plateau surface experienced widespread late jurassic to early cretaceous cooling at a rate of 1 2 c ma followed by minimal regional cooling 0 3 c ma and early miocene enhanced cooling 2 3 c ma along deep valleys at the southern edge of the landscape given the subdued late jurassic to early cretaceous crustal deformation in the study area we relate the coeval cooling to crustal refrigeration and exhumation triggered by northward subduction of the meso tethys ocean along the bangong suture subsequent late cretaceous to cenozoic minimal cooling supports arguments for the formation of a low elevation landform prior to uplift of the southeastern tp the enhanced cooling commenced at the early miocene 15 22 ma along deep valleys and heralded the onset of river incision and surface uplift of the southeastern tp this finding does not support previous proposals claiming that high elevations of the southeastern tp were formed in late miocene time resulting from lower crustal flow but rather supports a model highlighting continental subduction and extrusion along the large tanggula yushu batang red river fault system

a tale of two sutures cocorp s deep seismic surveys of the grenville province in the eastern u s midcontinent a pair of oppositely dipping crustal scale shear zones imaged within grenville basement beneath the paleozoic cover of ohio can be correlated via geopotential lineaments with similarly oriented geologic and seismically imaged structures hundreds of kilometres to the northeast and southwest suggesting a relatively simple structural framework for the eastern midcontinent region an east dipping zone extending from lake huron through western ohio and possibly farther southwest marks the western edge of the grenville province perhaps of greater consequence to an understanding of grenville tectonics is the discovery of a west dipping zone underlying the appalachian basin from northern alabama to new york within the grenville province correlation of this feature with the seismogenic clarendon linden fault in western new york and a boundary between terranes containing magmatic arc rocks exposed in canada suggests that it could mark the site of an intra grenville province suture zone implications of this interpretation are that the precambrian foundation of the eastern u s midcontinent comprises a relatively simple assemblage of laterally extensive terranes or belts of coeval terranes accreted by familiar plate tectonic processes and that deep seismic profiling is an effective tool for mapping the three dimensional distribution of these terranes

mineral prospectivity analysis for bif iron deposits a case study in the anshan benxi area liaoning province north east china abstract banded iron formation bif deposits are the most important source of iron in china and they are dominantly distributed in the north china craton ncc the anshan benxi area is situated in the northeastern part of the ncc and is considered to be the most fertile and productive iron metallogenic province in china the recent successive discoveries of large bif deposits in this area especially the world class dataigou bif deposit indicates that there is great potential for iron resources in this area the bif deposits are well defined by magnetic and gravity anomalies and thereby extensive petrophysical and geophysical studies are critical for bif prospective mapping a data driven weights of evidence wofe analysis was used for bif prospectivity modeling the results indicated that prospective areas are generally confined to the precambrian greenstone belt basin and high prospectivity zones class a are mainly distributed in the middle and northeastern parts of the study area moderate prospectivity zones class b are mainly distributed in southwestern and northeastern parts of the study area finally we employed selective human intervention to redefine priority targets to be more reliable the results suggest the method is successful as 82 target areas were narrowed to class a 20 and 11 class b targets the total of class a and class b targets was just over one third of the total number of targets offering a much smaller but effective selection of targets for consideration by mineral explorers

constraints on cenozoic regional drainage evolution of sw china from the provenance of the jianchuan basin 1 detrital zircon u pb geochronology was applied to cenozoic fluvial sedimentary rocks from the jianchuan basin yunnan province china to constrain the provenance and the nature of paleo drainage local geology testifies to a large river flowing through the jianchuan basin during the paleogene and this previously has been linked to a paleo drainage system that connected the qiangtang and lhasa blocks to the south china sea the detrital zircon results from this study do not fit with this model and instead show provenance consistent with a river draining a watershed within the songpan garze complex most likely from the northeast from the late oligocene and thereafter zircon provenance records greater contributions from erosion of local sources that surround the basin including the south china block and yidun arc rocks that suggest loss of the northern sources the timing for these changes overlap with regional deformation related to strike slip faulting or displacement by shear strain rather than the later uplift associated with an expanding margin of the tibetan plateau

tectonic history of the illinois basin the illinois basin began as a failed rift that developed during breakup of a supercontinent approximately 550 ma a rift basin in the southernmost part of the present illinois basin subsided rapidly and filled with about 3 000 m of probable early and middle cambrian sediments by the late cambrian the rift bounding faults became inactive and a broad relatively slowly subsiding embayment extending well beyond the rift and open to the iapetus ocean persisted through most of the paleozoic era widespread deformation swept through the proto illinois basin beginning in the latest mississippian continuing to the end of the paleozoic era uplift of basement fault blocks resulted in the formation of many major folds and faults the timing of deformation and location of these structures in the forelands of the ouachita and alleghanian orogenic belts suggest that much of the deformation resulted from continental collision between north america and gondwana the associated compressional stress reactivated the ancient rift bounding faults upthrusting the northern edge of a crustal block approximately 1 000 m within the rift concurrently dikes radiometrically dated as early permian sills and explosion breccias formed in or adjacent to the reactivated rift subsequent extensional stress probably associated with breakup of pangea causedmore the crustal block within the rift to sink back to near its original position high angle northeast to east west trending normal faults with as much as 1 000 m of displacement formed in the southern part of the basin these faults displace some of the northwest trending early permian dikes structural closure of the southern end of the illinois basin was caused by uplift of the pascola arch sometime between the late pennsylvanian and late cretaceous less

proterozoic crustal boundary in the southern part of the illinois basin abstract recently acquired cocorp and proprietary seismic reflection data in the southern part of the illinois basin combined with other geological and geophysical data indicate that a wnw trending proterozoic terrane boundary 40 km wide lies within basement the boundary is characterized by the termination of subhorizontal proterozoic reflectors and associated diffraction patterns along a line coinciding with the major magnetic lineament in this region south central magnetic lineament north of the boundary where reflectors thought to represent a sequence of layered proterozoic rocks in the upper crust are widespread and as much as 11 km thick total magnetic intensity values are relatively high suggesting layers of rock with high magnetic susceptibility to the south the proterozoic rocks are acoustically transparent on seismic reflection sections and total magnetic intensity values are relatively low moreover relatively high bouguer gravity anomaly values to the south may be caused by a dense altered lower crustal layer similar to that interpreted from deep seismic refraction studies to underlie the northern mississippi embayment the boundary lies along the projected trend of the northern margin of the early proterozoic central plains orogen and we suggest that it marks the convergent margin of this orogen reactivation of the boundary and the associated zone of weakness during late paleozoic times apparently resulted in structural deformation in the southern part of the illinois basin including movement along the cottage grove fault system and ste genevieve fault zone and igneous activity at hicks dome in addition to the role played by this crustal boundary in the evolution of the illinois basin its location between the wabash valley seismic zone to the northeast and the new madrid seismic zone to the southwest may be a significant factor in present day seismicity

spatial and temporal analysis of mass movement using dendrochronology tree growth and inclination on sloping land is affected by mass movement suitable analysis of tree growth and tree form can therefore provide considerable information on mass movement activity this paper reports a new automated method for studying the temporal and spatial aspects of mass movement activity ringwidth data from only a few cores per tree are required the method uses filtering techniques and statistical time series analysis preliminary results for two landslides in the barcelonnette area of the french alps show a relative stability of movement activity over the last hundred years no trend and short periodicity six to seven year periods of mass movement activity the advantages of the method over other mostly visual methods are its clearness flexibility repeatability and rapidity however further testing is needed to examine its reliability

thermochronological evidence for the movement of the ailao shan red river shear zone a perspective from vietnam in order to explore the timing of strike slip movement along the ailao shan red river shear zone an 40ar 39ar thermochronological study of the day nui con voi metamorphic massif in northern vietnam was undertaken the massif exposed in the southeastern segment of the ailao shan red river shear zone reveals a rapid cooling in the early miocene 25 21 ma after a very slow cooling ca 34 25 ma the slow cooling period most likely resulted from a geothermal perturbation in the lithosphere owing to the late paleogene 40 30 ma extension in eastern tibet and western yunnan china the rapid cooling consistent with evidence of a wider rapid cooling span from 27 to 17 ma compiled from the entire ailao shan red river shear zone constrains the duration of left lateral shearing which eventually offset indochina from south china by about 600 km the time constraints we have established reinforce the argument that the onset of the ailao shan red river shear zone postdates the opening of the south china sea that began ca 30 ma this result highlights the necessity for reevaluating the cenozoic tectonic models of southeast asia

state of stress and intraplate earthquakes in the united states recently compiled data on the state of stress have been used to define stress provinces in the conterminous united states in which the orientation and relative magnitude of the horizontal principal stresses are fairly uniform the observed pattems of stress constrain mechanisms for generating intraplate lithospheric stresses coupled with new information on geologic structure and tectonism in seismically active areas of the midcontinent and east these data help to define some characteristics common to these areas and to identify key questions regarding why certain faults seem to be seismically active

a first dendrogeomorphologic approach of snow avalanche magnitude frequency in northern iceland abstract the paper examines the potential of dendrogeomorphic analyses to deliver a one year resolution chronology of snow avalanche winters in northern iceland at the scale of a colluvial cone covered with european white birch trees and shrubs betula pubescens ehrh reconstruction of the avalanche history is performed using tree ring analyses determination of the most reliable growth disturbance class 1 of growth eccentricity and applying a tempering index value with threshold 10 of trees responding in the same year and at least two trees affected avalanche activity years are highlighted resulting in 52 avalanche winters amongst those 5 winters have activity index over 40 indicating major years calculation of frequency of similar growth disturbances at each tree provides a return period ranging from 4 2 to 19 years inferred spatial extent of snow avalanche events induces flow like snow avalanches with limited extent around the tree less parts of the cone with a return period under 6 years the cone is totally covered and the distal tree limit over passed with a return period of 15 20 years

tracing the transhimalayan magmatic belt and the lhasa block southward using zircon u pb lu hf isotopic and geochemical data cretaceous cenozoic granitoids in the tengchong block yunnan china abstract a number of cretaceous cenozoic granitoid bodies in the tengchong block were analyzed for their u pb zircon ages lu hf zircon isotopic compositions and whole rock geochemistry zircons from six different granite bodies in the central tengchong block have weighted mean 206 pb 238 u ages ranging from 76 to 65 ma and negative e hf t values ranging from 2 7 to 15 5 with t dm c ranging from 1312 to 1928 ma one dextrally sheared and gneissic granodiorite sample of the nabang shear zone in the western tengchong block yielded a weighted mean 206 pb 238 u age of 19 7 0 4 ma and positive e hf t values ranging from 0 2 to 10 7 with t dm c ranging from 418 to 1092 ma the late cretaceous granites have metaluminous and peraluminous affinities with strong enrichment of u and th and significant negative anomalies of eu ba sr nb p and ti the miocene granodiorite displays strong negative anomalies of nb ta p and ti and a weak negative eu anomaly the data suggest that the late cretaceous granites in the tengchong block were derived from partial melting of ancient most likely proterozoic continental crustal material whereas the miocene gneissic granodiorite was derived from partial melting of juvenile crustal material possibly within a supra subduction setting and intruded synkinematically into the active nabang shear zone lu hf isotopic data of late cretaceous paleocene granites are indistinguishable from those of granites of the central lhasa block thus we tentatively correlate the late cretaceous granites of the tengchong block with those of the central lhasa block the boundary between the south and central lhasa blocks in western tengchong may be exposed in the nne striking dextral nabang shear zone along the chinese myanmar border region which hosts early eocene granitoids with e hf t values 0 the lu hf data of the zircons from the gneissic miocene granodiorite indicate a juvenile crustal substrate in the western tengchong block as well the synkinematic miocene granodiorite provides an important age constraint for dextral shear at mid crustal levels which was active until at least c 19 20 ma in the nabang shear zone this miocene intrusion may be a first indication that active margin tectonics lasted 20 25 ma longer than in the gangdese belt and possibly was associated with deformation partitioning in the hinterland produced by increasing obliquity of subduction during clockwise rotation of sundaland during the india asia collision

geological framework of the laurentian trough aquifer system southern ontario the laurentian trough lt a depression 100 km long 3000 km2 in area and 100 m deep at the base of the niagara escarpment extends from within georgian bay to lake ontario it has a complex er

temporal and spatial patterns of sediment routing across the southeast margin of the tibetan plateau insights from detrital zircon the cenozoic deposits of the tibetan plateau s southeastern margin are often cited as part of a continental scale river system connecting the paleo yangtze river with the paleo red river confirming the purported connection and any subsequent drainage reorganization has garnered significant attention and varied proposed ages for reorganization this study presents detrital zircon u pb ages and paleocurrents in eocene to pleistocene sedimentary basin deposits distributed over a broad area of the southeast tibetan plateau margin within the area of proposed paleoriver connectivity when combined with previously published studies our u pb ages allow examination of the temporal and spatial distributions of provenance throughout the cenozoic we identify six key age components of the detrital u pb age distributions and use these to examine the patterns of sediment provenance for different cenozoic epochs detailed analysis of these components shows that provenance for both onshore and offshore deposits is best described by local bedrock sources and provides little to no evidence of regional changes in provenance this suggests that a stable fluvial system similar to the modern drainage network has existed since the eocene with no evidence for major provenance altering river capture paleoflow measurements taken throughout the se margin further corroborate the results of detrital zircon provenance the combination of u pb age components and paleocurrent directions does not support a cenozoic connection between the paleo yangtze and paleo red rivers

ductile thrusting at mid crustal level southwestern grenville province the northwestern boundary zone of the central metasedimentary belt grenville province in the haliburton area ontario is a stack of alternating tonalitic and syenitic crystalline thrust sheets transported toward the northwest on out of sequence upper amphibolite facies ductile thrust zones during the grenvillian orogeny at 1060 ma approximately 100 ma after the initiation of thrusting in the underlying central gneiss belt kinematics of the deformation are complex predominant northwestward thrusting was at least partly coeval with subordinate northeastward thrusting late synmetamorphic extensional shears cut both thrusts and thrust sheets minor late thrusting on discrete ductile shear zones postdates the extensional structures belts of mechanically weak pelite appear to have localised the thrust sheets highly mobile marble behaved as a relatively low viscosity fluid during transport able to intrude and erode more competent wall rock

magnetostratigraphy of the dali basin in yunnan and implications for late neogene rotation of the southeast margin of the tibetan plateau 1 the rotation pattern and fault activity in the southeast margin of the tibetan plateau semtp provide meaningful constraints on the geodynamic evolution of the plateau however the lack of cenozoic paleomagnetic studies and accurate age constraints on neogene sediments prevents a better understanding of the late cenozoic tectonic activity in this area to clarify the tectonic rotation pattern and deformation history of the semtp we report new magnetostratigraphic data from a late neogene sedimentary sequence in the dali basin northwestern yunnan province china rock magnetic analyses indicate that both magnetite and hematite are the main carriers of the characteristic remanent magnetizations chrms magnetostratigraphic results show that the sedimentary profile spans from chron c4n 1r to chron c2n the age of the sedimentary sequence in the dali basin can thus be paleomagnetically constrained to an interval from late miocene to early pleistocene the basal age of the sediments is 7 6 ma which indicates that the unroofing of diancang shan and activation of the dali fault system were initiated at this time the appearance of conglomerates and syntectonic sediments suggests the reactivation of the dali fault system at 2 5 ma moreover the overall mean chrm direction suggests that the dali basin experienced significant 4 4 2 5 but minor post late miocene rotation this indicates that most of the clockwise rotation demonstrated by previous paleomagnetic studies in the semtp occurred prior to late miocene and may be concentrated between eocene and miocene which is contemporaneous with the sinistral slip of the ailao shan red river fault

petrologic and geochemical attributes of fracture related dolomitization in ordovician carbonates and their spatial distribution in southwestern ontario canada abstract middle ordovician trenton group carbonates are fractured and extensively dolomitized along the axis of the algonquin arch in southwestern ontario hydrocarbon reservoirs formed where these dolomitized fracture zones penetrate otherwise impermeable host limestones three different types of dolomite d1 d2 and d3 are distinguished petrographic characteristics and 18 o values indicate that d1 formed during early diagenesis from middle ordovician seawater and recrystallized during progressive burial whereas fracture related replacive matrix dolomite d2 formed by hydrothermal fluids 68 99 c late stage saddle dolomite d3 and calcite c3 cements occlude fractures based on petrographic fluid inclusion and stable isotope data d3 dolomite and c3 calcite formed from warm 68 144 c saline 22 24 wt nacl cacl 2 hydrothermal fluids the least radiogenic 87 sr 86 sr values 0 70830 0 70842 of d2 are consistent with estimated values of devonian and silurian seawater whereas the slightly enriched 87 sr 86 sr ratios of d2 and d3 0 70902 0 70918 suggest their precipitation from fluids similar in composition to oil field brines rare earth element ree results of d2 d3 and c3 indicate enrichment in rees content of these mineral phases relative to undolomitized host rock the similarity in the average rees pattern of d2 d3 and c3 and the overlying blue mountain shale and basement rocks suggest progressive water rock interaction magnesium required for dolomite precipitation was supplied by mg rich seawater derived silurian and or devonian saline waters from dissolution of silurian evaporites which descended along faults and fractures to reservoir depths at the center of the basin while being heated hot basinal brines migrated laterally through basal sandstones and ascended into the network of faults and fractures and precipitated fracture related dolomite the abundance of fracture related dolomite in the periphery of michigan basin in southwestern ontario suggests that dolomitizing fluids originated from the michigan basin rather than appalachian basin

major circular structure beneath southern lake huron defined from potential field data newly compiled and merged canadian and united states potential field data for the area of southern lake huron reveal a large circular structure that has a diameter that may extend to 100 km the aeromagnetic image shows a circular central high with a diameter of 6 km located at fat 43 14 21 n long 82 19 88 w surrounded by a principal ring with a diameter of 50 km and indications of conformable arcuate structure extending to a diameter of about 100 km the prevailing northeast striking aeromagnetic signature of the grenville front and adjacent grenville front tectonic zone is interrupted and may be overprinted by the circular feature the bouguer gravity field shows a strong positive anomaly that extends southeast from the grenville front and terminates in an arcuate complex of positive anomalies that correlate with the aeromagnetic field the gravity field illustrates the circular structure with an annular low and central high as well as positive extensions that follow the foliate pattern of magnetic anomalies marking the outer area of the feature there is no strong evidence of the feature in the bathymetry data of southern lake huron although the general coastline of the southern end of lake huron closely follows the outline of the main circular feature the interruption of the grenville trends the clear regular circular signature of the feature and the interpreted magnetic source depths at the precambrian surface suggest an event possibly as young as early paleozoic in the absence of basement samples the origin of the feature is unconfirmed however the scale and potential field anomaly pattern of the feature are comparable to several of the larger impact structures exposed on the canadian shield

tectonic evolution of the paranoa basin new evidence from gravimetric and stratigraphic data abstract field gravimetric and stratigraphic surveys were conducted with the aim to constraint the mechanisms responsible for the initiation of the stenian tonian paranoa basin central brazil a subject not yet studied in detail the paranoa group crops out in the external zone of the brasilia belt a neoproterozoic orogen in the western margin of the sao francisco craton detailed geological mapping confirmed the existence of a regional scale fault that controlled sedimentation of the paranoa group during the deposition of its basal formations revealing important details about basin initiation and early evolution gravimetric modeling indicates the existence of paleorift structures beneath the paranoa sequence in the study area results from both stratigraphic and gravimetric surveys show strong evidence of mechanical subsidence by faulting during basin initiation unsorted angular clasts cut by quartz veins and brecciated boulders present in the basal conglomerate support this hypothesis basin initiation faults coincide with deeper paleorift faults and are thus interpreted as reactivations of the older statherian arai rift the reactivations favored an initial regime of mechanical subsidence dominated by the development of epirogenic arches subsiding at different rates apart from faulting activity the post basal sequence presents no evidence of rift environment in the strict sense besides the great lateral continuity and relatively constant thickness of facies indicate that an initial mechanic subsidence rapidly gave way to flexural subsidence during subsequent stages of basin evolution the paranoa group do not present reliable characteristics that would allow its strict classification as a passive margin its main stratigraphic characteristics tectonic location and basement architecture indicate that the paranoa group was deposited in a cratonic margin basin and may have been either connected to a passive margin basin at times of sea level rise or evolved to a passive margin later in time

basement controlled faulting of paleozoic strata in southern ontario canada new evidence from geophysical lineament mapping abstract basement fault reactivation is now recognized as an important control on sedimentation and fault propagation in intracratonic basins in southern ontario the basement consists of complexly structured mid proterozoic ca 1 2 ga crystalline rocks and metasedimentary rocks that are overlain by up to 1500 m of paleozoic sedimentary strata reactivation of basement structures is suspected to control the location of paleozoic fault and fracture systems but evaluation has been hindered by a limited understanding of the regional structural characteristics of the buried basement new aeromagnetic and gravimetric lineament mapping presented in this paper better resolves the location of basement discontinuities and provides further evidence for basement controls on the distribution of paleozoic fault and fracture systems lineament mapping was facilitated by reprocessing and digital image enhancement micro levelling regional residual separation derivative filtering of existing regional gravity and aeromagnetic datasets reprocessed images identify new details of the structural fabric of the basement below southern ontario and delineate several previously unrecognized aeromagnetic and gravity lineaments and linear zones linear zones parallel the projected trends of mid proterozoic terrane boundaries identified by field mapping on the exposed shield to the north of the study area and are interpreted as zones of shearing and basement faulting mapped aeromagnetic and gravity lineaments show similar trends to paleozoic faults and fracture networks and broad zones of seismicity in southern ontario these new data support an inheritance model for paleozoic faulting involving repeated reactivation and upward propagation of basement faults and fractures into overlying cover strata

new tectonic divisions of the grenville province southeast canadian shield on the basis of geological geophysical and geochronological data the grenville province has been divided into three first order longitudinal belts the parautochthonous belt pb allochthonous polycyclic belt apb and allochthonous monocyclic belt amb these are set apart by three first order tectonic boundaries the grenville front gf allochthon boundary thrust abt and monocyclic belt boundary zone mbbz the belts are subdivided into terranes based on internal lithological character the gf separates the archean to proterozoic foreland northwest of the orogen from reworked equivalents to the southeast continuous at the scale of the orogen its main characteristic is that of a crustal scale contraction fault the pb although less clearly identified along the length of the orogen in most places represents upgraded and tectonically reworked rocks of the adjacent foreland the boundary between the pb and the apb to the southeast the abt is most clearly delineated in the eastern half of the province it is the locus of major crustal delamination along which high grade mostly middle proterozoic polycyclic terranes were tectonically transported northwest toward and onto the pb the amb comprises two separate areas underlain by the wakeham supergroup and what is currently known as the grenville supergroup respectively its basal contact the mbbz is a decollement zone of variable kinematic significance between older polycyclic rocks and tectonically overlying monocyclic rocks this first order zonation implies a tectonic polarity to the grenville province superimposed on which are second order features evident from contrasting tectonic styles and radiometric ages these characteristics are consistent with a diachronous or oblique collisional model for the grenville orogen

some seismological and geometric features of intraplate earthquakes to understand the nature and cause of intraplate earthquakes we carried out a systematic search for common features associated with them various geological geophysical and seismic data were analyzed and geometric and seismic parameters were compared for 29 intraplate events m 4 5 occurring worldwide the results suggest that intraplate earthquakes occur by the reactivation of pre existing zones of weakness in a compressional stress regime which is generally oriented parallel to the absolute direction of plate motion two styles of faulting were observed for type a earthquakes observed in the eastern united states eastern china western europe and west africa deformation occurs by strike slip motion on steeply dipping faults type b events are usually associated with thrust or normal faulting and were observed in eastern canada fennoscandia australia and peninsular india focal depths did not explain the differences between type a and type b earthquakes rather the differences are due to the perturbation of a regional stress field by a local stress field the regional stress field for type a events is primarily due to ridge push forces the method of stress perturbation varied from region to region the earthquakes in the type b category were further divided into three subcategories type b1 occurring in eastern canada and fennoscandia type b2 occurring in australia peninsular india and central brazil and type b3 occurring in the gulf coast of the u s the inferred causes of the perturbing stresses are deglaciation intracontinental resistive forces resulting from the collision of plates and the deposition of a large thickness of sediments respectively type a events were found to be associated with intersecting faults and generally supported the intersection model of talwani 1988 and had analogs in plate boundary events

lake sediments as natural seismographs earthquake related deformations seismites in central canadian lakes abstract central canada experiences numerous intraplate earthquakes but their recurrence and source areas remain obscure due to shortness of the instrumental and historic records unconsolidated fine grained sediments in lake basins are natural seismographs with the potential to record ancient earthquakes during the last 10 000 years since the retreat of the laurentide ice sheet many lake basins are cut into bedrock and are structurally controlled by the same precambrian basement structures shear zones terrane boundaries and other lineaments implicated as the source of ongoing mid plate earthquake activity a regional seismic sub bottom profiling of lakes gull muskoka joseph rousseau ontario wanapitei fairbanks vermilion nipissing georgian bay mazinaw simcoe timiskaming kipawa parry sound and lake of bays encompassing a total of more than 2000 kilometres of high resolution track line data supplemented by multibeam and sidescan sonar survey records show a consistent sub bottom stratigraphy of relatively thick lowermost lateglacial facies composed of interbedded semi transparent mass flow facies debrites slumps and rhythmically laminated silty clays mass flows together with cratered kettled lake floors and associated deformations reflect a dynamic ice contact glaciolacustrine environment exceptionally thick mass flow successions in lake timiskaming along the floor of the timiskaming graben within the seismically active western quebec seismic zone wqsz point to a higher frequency of earthquakes and slope failure during deglaciation and rapid glacio isostatic rebound though faulting continues into the postglacial lateglacial faulting diapiric deformation and slumping of coeval lateglacial sediments is observed in parry sound lake muskoka and lake joseph which are all located above prominent precambrian terrane boundaries lateglacial sediments are sharply overlain by relatively thin rhythmically laminated and often semi transparent postglacial silty clay laminations postglacial neotectonic activity is recorded by co seismic water escape structures faults slumps and debris flows in lake simcoe above a terrane boundary and especially within lakes timiskaming and kipawa recording ongoing deformation within the wqsz high resolution seismo stratigraphic data presented here support the model that ongoing mid plate earthquake activity is a consequence of brittle deformation of the upper crust of the north american plate such activity appears to have been greatest during deglaciation but continues today

seismic images of a grenvillian terrane boundary a series of gently dipping reflection zones extending to mid crustal depths is recorded by seismic data from lakes ontario and erie these prominent reflection zones define a broad complex of southeast dipping ductile thrust faults in the interior of the grenville orogen one major reflection zone provides the first image of a proposed grenvillian suture the listric boundary zone between allochthonous terranes of the central gneiss and central metasedimentary belts curvilinear bands of reflections that may represent ramp folds and ramp anticlines that originally formed in a deep crustal scale duplex abut several faults vertical stacking of some curvilinear features suggests coeval or later out of sequence faulting of imbricated and folded thrust sheets grenvillian structure reflections are overlain by a thin wedge shaped package of shallow dipping reflections that probably originates from sediments deposited in a local half graben developed during a period of post grenville extension this is the first seismic evidence for such extension in this region which could have occurred during terminal collapse of the grenville orogen or could have marked the beginning of pre appalachian continental rifting

seismicity of the southern great lakes revised earthquake hypocenters and possible tectonic controls using data from 27 seismograph stations for the period 1990 2001 we have relocated 106 hypocenters of earthquakes with magnitudes from 0 9 to 5 4 in the region of the southern great lakes two complementary methods were used for relocation a conventional least squares approach lienert and havskov 1995 and joint hypocentral determination pujol 2000 these two methods yielded mutually consistent spatial patterns of seismicity with an average difference of 3 7 km in epicentral locations and 1 1 km in focal depths we show that the hypocenter locations are not very sensitive to realistic uncertainties in 1d crustal velocity our sharpened definition of zones of seismicity delineates several clusters beneath lake ontario around niagara falls and near the south shore of lake erie these seismicity zones appear to correlate with areas where the regional magnetic data exhibit prominent short wavelength 5 km linear anomalies the magnetic anomalies are associated with basement structures that formed during the precambrian mesoproterozoic grenville orogen both the seismicity and magnetic anomalies exhibit statistically significant preferred orientations at n40 e n45 e but the correlation of the earthquake clusters with specific aeromagnetic lineaments remains uncertain three preliminary focal mechanisms of earthquakes with magnitudes m n 3 1 to 3 8 show unusual normal faulting with nodal planes in almost the same direction as the magnetic trends n42 e n52 e proximity of the earthquake clusters to large bodies of water coupled with colinearity with magnetic anomaly trends suggests that both surface water and pre existing basement structures may play significant roles in controlling intraplate seismicity in the southern great lakes region manuscript received 3 january 2003

evaluating the evolution of the red river system based on in situ u pb dating and hf isotope analysis of zircons 1 the red river originates from sw china and se tibet and has a total length 1000 km in this study we present new u pb dating and hf isotopic analysis of zircon grains from both modern and paleoriver sands in order to constrain the provenance of the modern river and to decipher drainage evolution through time our data show that the yangtze and songpan garze blocks are the most important sources for sediment although this material is mostly reworked via younger sedimentary rocks in the upper reaches of the red river sands in the da river and to a lesser extent the lo river have zircon ages indicating that they are minor contributors to the net flow consistent with rock uplift which is strongest in the upper reaches of the red river rather than precipitation being the primary control on erosion sediments eroded from the metamorphic rocks along the red river fault zone appear to have made a greater contribution during the miocene zircon ages suggest that the red river flowed north of the day nui con voi in the middle late miocene the red river appears to have had a largely stable provenance since at least the late miocene upper miocene sedimentary rocks ne of the red river indicate the presence of a separate large river in the late miocene hf isotope data indicate that the irrawaddy river was never part of the red river system although we do not exclude the salween mekong and yangtze rivers from having been part of the red river any connection must have been pre middle miocene

nd isotope mapping of the allochthon boundary thrust on the shores of georgian bay ontario significance for grenvillian crustal structure and evolution nearly 50 new nd isotope analyses are presented for the shawanaga region of georgian bay ontario to study crustal evolution in the grenvillian central gneiss belt depleted mantle t dm nd model ages are used to map a major grenvillian tectonic boundary the allochthon boundary thrust abt which in the shawanaga area separates gneisses with t dm ages above and below 1 65 ga this is lower than the 1 8 ga age cut off observed further north and is attributed to a southward increase in mesoproterozoic magmatic reworking of an original palaeoproterozoic continental margin causing a progressive southward decrease in nd model ages between shawanaga island and franklin island nd isotope mapping yields an abt trajectory that closely matches published geological mapping and passes within 100 m of four retrogressed eclogite bodies typically associated with the thrust boundary this validation of the method gives confidence in the mapped trajectory south of snake island where sparse outcrop inhibits lithological mapping the new results suggest that published 1 7 1 9 ga t dm ages in the lower go home domain of the central gneiss belt further south are also indicative of parautochthonous crust hence we propose that the main ramp of the abt is located in the immediate hangingwall of the go home domain much further south than generally recognized this has important implications for the large scale crustal structure of the sw grenville province suggesting that the abt ramp has a similar curved trajectory to the grenville front and the central metasedimentary belt boundary thrust

debris flow activity and snow avalanches in a steep watershed of the valais alps switzerland dendrogeomorphic event reconstruction and identification of triggers debris flows and snow avalanches are common processes in the headwaters of steep watersheds worldwide in forested areas dendrogeomorphic analyses of trees affected by debris flows and snow avalanches have regularly been used to date past events previous studies have however almost never focused on both processes at once as snow avalanche impacts cannot easily be distinguished from debris flow scars in a similar way tree ring studies have often been limited to conifers and sites colonized with broad leaved forests have been widely disregarded we report on a case from the valais alps switzerland where past debris flow and snow avalanche activity was dated with intraseasonal precision using different broad leaved and conifer trees in total the analysis of 171 cores 34 wedges and 11 crosssections from 93 trees allowed identification of 20 debris flow and 3 snow avalanche events between a d 1930 and 2008 results also indicate that some of the events would have been missed without the sampling of broad leaved trees

a study of the microearthquakes of the gobles oil field area of southwestern ontario abstract from july 1980 to august 1984 the university of western ontario operated a small seismic telemetry network over the gobles oil field in southwestern ontario a total of 478 small earth tremors mainly in the 1 to 2 magnitude range were detected by this array there were three events greater than magnitude 3 felt by residents up to 15 km from the oil field approximately 10 events month were recorded on average although the actual number was rather erratic and tended to have a winter maximum event locations did not correlate with the actual positions of the oil and gas wells in the field but rather are confined to two main areas one lying 1 5 km northwest of the town of gobles and the other just south of the town the depths of the well recorded events were found to be near the depth of the producing horizon the observed first motion patterns indicated that at least two active faults almost perpendicular to each other are present in the area the results are consistent with the hypothesis that the events are induced or triggered by fluids which are pumped in and out of wells during secondary recovery activities

the central metasedimentary belt grenville province as a failed back arc rift zone nd isotope evidence abstract nd isotope data are presented for granitoid orthogneisses from the central metasedimentary belt cmb of the grenville province in order to map the extent of juvenile grenvillian age crust within this orogenic belt that is composed mostly of older crustal terranes the data reveal a 150 km wide belt of juvenile crust in ontario but this belt contains a block of pre grenvillian crust containing the elzevir pluton which yields an estimated crustal formation age of 1 5 ga the recognition of an older block within the cmb has profound implications for its structure and tectonic evolution because it implies that juvenile grenvillian crust apparently forming a wide ne sw belt is in fact distributed in two narrower segments with approximately n s strike we suggest that the cmb comprises an en echelon series of ensimatic rift segments created by back arc spreading behind a continental margin arc these rift segments extend southwards in the subsurface into the northeastern unites states the rift segments contain abundant marble outcrops consistent with marine incursion into the rift zone and these deposits also continue northwards into a marble domain of the cmb in quebec however crustal formation ages in the latter domain are largely pre grenvillian implying that the quebec rift segment was ensialic hence we interpret the cmb in ontario and quebec as the northern termination of a failed back arc rift zone

spatio temporal reconstruction of snow avalanche activity using tree rings pierres jean jeanne avalanche talus massif de l oisans france snow avalanches are a major threat in many parts of the alps where they periodically damage infrastructure disrupt transportation corridors or even cause loss of life nonetheless the spatial behavior of past avalanche activity and the analysis of areas affected during particular events remain often imprecise it was therefore the purpose of this study to reconstruct spatio temporal patterns of past avalanche activity on a forested avalanche talus in the french alps pierres jean jeanne talus massif de l oisans france a total of 232 european larches larix decidua mill with clear signs of snow wasting events was analyzed and growth disturbances gd related to avalanche activity was assessed such as tangential rows of traumatic resin ducts the onset of compression wood or abrupt growth suppression and release in total 901 gd were identified in the tree ring samples indicating that 20 high magnitude avalanches occurred between ad 1919 and 1994 the mean return period of snow avalanches was 4 years with a 26 probability that an avalanche occurs in any particular year interpolated maps allowed for explicit spatial estimates of return periods throughout the talus showing a rapid increase of return frequency from 2 5 to 50 years with increasing distance from the talus apex the distribution of avalanche years seems to be quite homogeneous in time with a gap between 1951 and 1959 snowfall from a nearby meteorological station saint christophe en oisans 10 km from the study site indicated that the five most recent high magnitude events on record occurred due to above average snowfall anomalies in december and january associated with abnormally low air temperatures findings suggest that a strong snow metamorphism under high temperature gradients in january could explain the occurrence of high magnitude snow avalanches 2010 elsevier b v all rights reserved

mass movements and tree rings a guide to dendrogeomorphic field sampling and dating abstract trees affected by mass movements record the evidence of geomorphic disturbance in the growth ring series and thereby provide a precise geochronological tool for the reconstruction of past activity of mass movement the identification of past activity of processes was typically based on the presence of growth anomalies in affected trees and focused on the presence of scars tilted or buried trunks as well as on apex decapitation for the analyses and interpretation of disturbances in tree ring records in contrast clear guidelines have not been established with largely differing or no thresholds used to distinguish signal from noise at the same time processes with a large spatial footprint e g snow avalanches landslides or floods will likely leave growth anomalies in a large number of trees whereas a falling rock would only cause scars in one or a few trees along its trajectory based on the above considerations we examine issues relating to the interpretation and dendrogeomorphic dating of mass movements particular attention is drawn to sampling in terms of sample distribution across a study site the actual selection of trees as well as to sample size i e number of trees sampled based on case studies from snow avalanche debris flow and landslide sites we demonstrate that thresholds can indeed improve dating quality and at the same time minimize noise in time series we also conclude that different thresholds need to be used for different processes and different periods of the reconstruction especially for the early stages of the reconstruction when the number of potentially responding trees will be much smaller this paper seeks to set standards for dendrogeomorphic fieldwork analysis and interpretation for different processes of mass movements

seven centuries of avalanche activity at echalp queyras massif southern french alps as inferred from tree rings the purpose of this study was to reconstruct spatiotemporal patterns of avalanche events in a forested avalanche path of the queyras massif echalp avalanche path southeast french alps analysis of past events was based on tree ring series from 163 heavily affected multicentennial larch trees larix decidua mill growing near or next to the avalanche path a total of 514 growth disturbances such as tangential rows of traumatic resin ducts the onset of compression wood as well as abrupt growth suppression or release were identified in the samples indicating 38 destructive snow avalanches between 1338 and 2010 the mean return period of snow avalanches was 22 years with a 4 probability that an avalanche occurs in a particular year on a temporal plan three maxima in snow avalanche frequency were reconstructed at the beginning of the 16th and 19th centuries and around 1850 correlating with below average winter temperatures and glacier advances analysis of the spatial distribution of disturbed trees contributed to the determination of four preferential patterns of avalanche events the comparison of dendrogeomorphic data with historical records demonstrate that at least 18 events six of which were undocumented reached the hamlet of echalp during the last seven centuries but no significant temporal trend was detected concerning the frequency of these extreme events

tectonostratigraphy and base metal mineralization controls aravalli province western india new interpretations from geophysical data analysis analysis and synthesis of multi disciplinary geoscience information from geological literature maps and from digitallyprocessed aeromagnetic and gravity data pertinent to the aravalli province were carried out to address some hitherto unresolved questions about the tectonostratigraphy of this archaean proterozoic metallogenic province based on the magnetic anomalies several tectonic domains were identified these domains bounded by regional scale geophysical lineaments have distinct crustal lithological metamorphic and metallogenic characteristics and correlate broadly with lithostratigraphic belts identified by several earlier workers new interpretations on the tectonostratigraphy and the base metal mineralization controls in the aravalli province are as follows the hindoli sequences in the eastern parts of the province constitute an independent palaeo proterozoic tectonic domain and do not form part of the archaean basement complex the base metal bearing metasedimentary enclaves in the central parts of the province also constitute an independent palaeo proterozoic tectonic domain which is quite distinct from the surrounding basement complex rocks the base metal bearing metavolcano sedimentary sequences in the western parts of the province constitute an independent neo proterozoic tectonic domain the base metal deposits in the province are spatially associated with the regional scale lineaments and with the mafic metavolcanic rocks deduced from the aeromagnetic data the regional scale lineaments which possibly represent proterozoic crustal scale faults are plausible structural controls on the basemetal mineralization in the province the mafic metavolcanic rocks are plausible heat source controls on the sedex and or vmstype base metal mineralizations and are possible metal source controls on the vms type base metal mineralization in the province d 2005 elsevier b v all rights reserved

neotectonic reactivation of shear zones and implications for faulting style and geometry in the continental margin of ne brazil abstract the eastern continental margin of south america comprises a series of rift basins developed during the breakup of pangea in the jurassic cretaceous we integrated high resolution aeromagnetic structural and stratigraphic data in order to evaluate the role of reactivation of ductile neoproterozoic shear zones in the deposition and deformation of post rift sedimentary deposits in one of these basins the paraiba basin in northeastern brazil this basin corresponds to the last part of the south american continent to be separated from africa during the pangea breakup sediment deposition in this basin occurred in the albian maastrichtian eocene miocene and in the late quaternary however our investigation concentrates on the miocene quaternary which we consider the neotectonic period because it encompasses the last stress field this consisted of an e w oriented compression and a n s oriented extension the basement of the basin forms a slightly seaward tilted ramp capped by a late cretaceous to quaternary sedimentary cover 100 400 m thick aeromagnetic lineaments mark the major steeply dipping ductile e w to ne striking shear zones in this basement the ductile shear zones mainly reactivated as strike slip normal and oblique slip faults resulting in a series of miocene quaternary depocenters controlled by ne e w and a few nw striking faults faulting produced subsidence and uplift that are largely responsible for the present day morphology of the valleys and tablelands in this margin we conclude that precambrian shear zone reactivation controlled geometry and orientation as well as deformation of sedimentary deposits until the neogene quaternary

zircon u pb and hf isotope constraints from the ailao shan red river shear zone on the tectonic and crustal evolution of southwestern china abstract the ailao shan red river asrr shear zone one of the most prominent geologic strike slip shear zones in southeast asia consists of high grade metamorphic complexes that provide a rare opportunity to sample the mid crustal rocks along the western margin of the yangtze block of south china here we report combined in situ analyses of zircon u pb and lu hf isotopes of eight gneisses from the diancang shan and ailao shan segments of the asrr shear zone our zircon u pb data indicate that the rocks contain abundant magmatic zircons ranging in age from 1785 to 25 ma with peak ages at ca 770 350 and 240 ma suggesting three major periods of protolith formation the 350 ma zircons observed only in an orthogneiss from the diancang shan show uniform initial hf isotopic ratios marked by high and positive e hf t values from 16 to 10 this is in contrast with the other two zircon populations that are more common occurring in both the diancang shan and ailao shan and overall delineate very heterogeneous hf isotopic compositions with e hf t values ranging from 15 to 16 many zircons reveal distinctive core rim age variations zircon rims formed between ca 34 and 26 ma show significant variations in th u ratios 5 0 01 and e hf t values 14 to 10 that suggest complicated magmatic and metamorphic zircon overgrowth during the oligocene the presence of both metamorphic and magmatic overgrowths on zircons suggests that the metamorphism reached upper amphibolite facies corresponding to mid crustal level p t conditions as also suggested by structural and petrologic data our data furthermore suggest that the asrr gneisses were not produced solely by shear heating during the tertiary strike slip faulting but are uplifted mid crustal basement rocks that formed essentially during two major stages of magmatism represented by the neoproterozoic kangding complex and late permian emeishan large igneous province as a result of the india asia collision these basement rocks underwent regional magmatic and metamorphic overprinting in the oligocene that based on our relevant work searle et al 2010 geosphere 6 1 23 predated the initial left lateral movement along the asrr shear zone the 350 ma protolith which requires a dominant depleted mantle input in the petrogenesis cannot be linked to any major magmatic events in south china but may be interpreted as part of the paleotethys remnants that were later incorporated into the asrr shear zone

fault geometry and earthquakes in continental interiors abstract although large earthquakes in continental interiors are much less frequent than those along plate boundaries they have been responsible for a disproportionate amount of destruction i present a testable model for strain accumulation and seismicity in the upper crust of continental interiors intersecting faults provide a focus for strain build up resulting in local pockets of high strain accumulation rigid plates typically deform at strain rates 10 10 to 10 9 strain yr 1 but at intersecting fault zones strain accumulates at anomalously high rates of 10 8 to 10 7 strain yr 1 i e the strain rates are comparable with those at plate boundaries the resulting large earthquakes are associated with relatively short return times hundreds of years typically one of the intersecting faults appears to split and to offset the other main fault defined as a fault on which the larger offset occurs forming two parallel strands separated by a jog i also observe a rotation of one leg of the main fault with respect to the other the region of intersection is usually associated with intense fracturing increased microseismicity and uplift

buried bedrock valleys and glacial and subglacial meltwater erosion in southern ontario canada morphometric features from a recently compiled bedrock topography map by the ontario geological survey suggest a glacial erosion origin for the buried large bedrock valleys and troughs in southern ontario the bedrock valleys at milverton wingham and mount forest are tunnel valleys resulting from subglacial meltwater erosion beneath the huron ice lobe probably during or shortly after the late wisconsinan glacial maximum diagnostic features for this interpretation include abrupt valley beginning and termination uneven longitudinal valley profiles and up slope gradients the dundas bedrock valley is the western extension of the lake ontario basin no comparable bedrock valleys were found to connect it to the milverton valley for a joint drainage system as previously suggested the laurentian bedrock trough is the southeastward extension of the georgian bay basin both developed along shale bedrock between the precambrian shield highlands and the niagara escarpment resulting from long term mechanical weathering associated with pleistocene glacial erosion this bedrock low has a floor that exceeds 50 km in width and is 26 m and more below the current water level of georgian bay it could drain georgian bay should the drift cover be removed there is no evidence to suggest that a preglacial river channel if it existed is still preserved in the floor of the laurentian trough as previously suggested the framework for an intensely glacially sculpted bedrock surface differs from the previous view for simple modification of a preglacial landscape and is therefore important in regional subsurface geological mapping and groundwater studies

using vegetation to characterize the avalanche of canal del roc roig vall de nuria eastern pyrenees spain avalanche hazard maps of high accuracy are difficult to produce for land use planning and management purposes a good knowledge of extreme run out zones and frequencies of avalanches is required in the present work vegetation recognition especially focused on pinus uncinata trees and dendrochronological techniques are used to characterize avalanches that have occurred in historical times helping to determine both the extent of large or extreme avalanches and their occurrence in time vegetation was studied at the canal del roc roig eastern pyrenees spain avalanche path the avalanches descending this path affect the railway that reaches the vall de nuria resort and the run up to the opposite slope during winter 1996 two important avalanches affect ing this path were well documented these are compared with the results of the vegetation study consisting of an inventory of flora the recording of vegetation damages along eight transverse profiles at different altitudes on the path and a dendrochronological sampling campaign the data obtained contributed to a characterization of the predominant snow accumulation in the starting zone the 1996 avalanches and the range of frequencies of large avalanches also traces of avalanches that increase the path mapped in the avalanche paths map published by the institut cartogra fic de catalunya in 2000 were identified improving the initial existing information

tectonics controls on fluvial landscapes and drainage development in the westernmost part of switzerland insights from dem derived geomorphic indices abstract this work focuses particularly on the geomorphological evidence for the tectonic controls on the development of the present day fluvial landscapes in the westernmost part of switzerland the tectonic deformation was evaluated on the basis of a combined analysis of several classical geomorphic indices hypsometric curves and integrals transverse topographic symmetry index and channel s bottom gradients through high precision dem processing a new optimization strategy was applied for defining geomorphic anomalies related to tectonic activity along the channels of three rivers based on a combined investigation of topographic swath longitudinal profiles geological and geophysical observations the results show that the abnormally high values of hypsometric integral are spatially occurred on the hanging walls of thrust faults while abnormally low ones are spatially observed in the same locations of paleo ice stream pathways observations obtained from transverse topographic symmetry index display asymmetries in the most of the studied drainage basins with a predominant se direction of lateral migration this direction is in agreement with the dominant dip direction of the bedding planes within the study area abnormal changes in the channel s bottom gradients which almost coincide in space with pronounced change in the depth of the subsurface geologic layers and in the geophysical properties are marked by distinct topographic relief in areas where rivers flow above blind and emergent faults our analysis not only confirms that there is a significant tectonic control on the evolution of drainage systems but also revealed a possible evidence for the reactivation of some inherited faults

neotectonic faulting in metropolitan toronto implications for earthquake hazard assessment in the lake ontario region persistent small scale seismicity around the western end of lake ontario together with larger events in eastern north america have focused attention on the seismotectonic and neotectonic conditions of southern ontario and adjacent new york state newly discovered normal faults that offset both bedrock and overlying quaternary sediments by as much as 1 25 m were discovered along the rouge valley in metropolitan toronto this location is within a zone marked by the intersection of three major lineaments and an elevated level of seismicity these faults result from reactivation of east west oriented fractures in ordovician shales structures are exposed in section only and have no surface expression suggesting that others may have gone undetected the origin of the faults is not yet well established although they may represent the effects of uplift consequent upon isostatic rebound aided by high horizontal compressive stress nevertheless their development in the recent geologic past has important implications for regional seismic hazard assessment because they occur within 7 km of the pickering nuclear power plant

dendrochronological study of the canal del roc roig avalanche path first results of the aludex project in the pyrenees historical data about ancient avalanches are scarce in the pyrenees dendrochronology can provide new data about past avalanches and their return period but up to now little research has been carried out with this purpose the aludex project aims to obtain information about the frequency and extent of extreme avalanches using a dendrochronological and a nivo meteorological approach in this paper we present the results of a dendrochronological study of the canal del roc roig avalanche path which was affected by two extreme avalanches in february 1996 this first dendrochronological study has permitted us to assess the tree ring signals due to avalanche events in 53 out of 132 dated trees the trees presented a variety of responses to the 1996 avalanche events it is shown that the type of tree ring signal depends on tree age the methodology has proved successful in detecting the 1996 and 1972 documented avalanche events and pro vided outstanding evidence of undocumented past events such as one in 1930

deep structure beneath lake ontario crustal scale grenville subdivisions lake ontario marine seismic data reveal major grenville crustal subdivisions beneath central and southern lake ontario separated by interpreted shear zones that extend to the lower crust a shear zone bounded transition between the elzevir and frontenac terranes exposed north of lake ontario is linked to a seismically defined shear zone beneath central lake ontario by prominent aeromagnetic and gravity anomalies easterly dipping wide angle reflections and fractures in paleozoic strata we suggest the central lake ontario zone represents crustal scale deformation along an elzevir frontenac boundary zone that extends from outcrop to the south shore of lake ontario seismic images from lake ontario and the exposed western central metasedimentary belt are dominated by crustal scale shear zones and reflection geometries featuring arcuate reflections truncated at their bases by apparent east dipping linear reflections the images show that zones analogous to the interpreted grenville front tectonic zone are al

seismites within ordovician silurian carbonates and clastics of southern ontario canada and implications for intraplate seismicity abstract a regional survey of lower paleozoic sedimentary strata ordovician silurian exposed across some 7000 km2 of southern ontario canada has identified the sedimentary record of paleo seismicity at a time of known faulting and rapid subsidence of appalachian foreland basins shallow marine shoreface sandstones and shales of the lower silurian thorold formation show laterally extensive beds of large

neotectonic movement earthquakes and stress state in the eastern united states abstract a regional pattern of crustal movement across the eastern united states is suggested by relations found by investigations into the cause of earthquakes the pattern consists of zones of fractures and vertical movement most of the seismic source areas appear to be related to northwest trending fracture zones that commonly have apparent righ lateral strike slip offset where they cross broad northeast trending belts of vertical movement the fracture zones also appear to control the positions of local northwest trending basins embayments on the atlantic and gulf coastal plains these embayments seem to be relatively subsiding at present and have earthquakes associated with them intervening arches have very few earthquakes some earthquakes are also spatially related to north trending extensional fault zones that commonly lie north of northwest trending fracture zones a slight northward tilt of the entire region and possible lingering effects of glacial rebound in the northeast show no relation with seismicity both the broad belts of vertical movement and embayments are apparently those initiated by the late cretaceous as the north atlantic basin widened and the northwest trending fracture zones can be directly or indirectly related to the offshore transform fracture zones the interplate movements in the eastern united states are thus directly related to those in the north atlantic basin the fracture pattern is also similar to that of the western united states but the movements less these tectonic movements in the eastern united states can be accounted for by a maximum horizontal compressive stress oriented approximately north northwest south southeast to north south and an extension oriented approximately east west