fractal structure of spatial distribution of microfracturing in rock summary a constant stress fracture experiment of oshima granite was carried out at the confining pressure of 40mpa hypocentres of 2064 acoustic emissions were located during the experiment using the correlation integral we found that the spatial distribution of hypocentres of acoustic emission is a fractal and that the fractal dimension decreases with the evolution of rock fracturing the spatial distribution of earthquake s hypocentres reveals fractals ranging from regional to worldwide distribution if we extrapolate from laboratory measurements it is possible to predict the occurrence of large earthquakes by the decrease in the fractal dimension

on the space time pattern formation of the earthquake strain field abstract the dynamical strain field of a lithospheric plate is described by a simple mathematical model of two factors which denote the visco elasticity and plasticity of the media this model consists of two cooperative equations of diffusion and advection type which denote the dislocation flow along the fault and the visco elastic behaviour of the plate respectively this is a generalization of the models previously proposed for describing the stress and strain field of the plate model study shows that the local concentration of the elastic strain in certain regions is caused as a result of diffusive instability and that space and time patterns of the strain field are created by cooperative interactions of these two effects numerical simulations also show that creep motions or crustal movements can be accompanied with concentration of the elastic strain which is consistent with the field observation the predicted pattern of the strain field is compared with the actual seismicity prior to large earthquakes and the generation of the seismically quiet and active zones and the occurrence of foreshocks are explained

identifying space time clustering properties of the 1983 1997 irpinia basilicata southern italy seismicity abstract the fractality of the earthquake sequence 1983 1997 of irpinia basilicata southern italy one of the most seismically active regions of the mediterranean area has been analysed by temporal and spatial fractal tools the fractal exponent estimated by the allan factor method characterises the time clustering behaviour of the set of earthquakes while the correlation dimension d c calculated by means of the correlation integral method gives information on the space clustering behaviour of the sequence of seismic events analysing the variations of both the parameters we recognised the presence of a strong space time clusterisation associated with the major events that occurred in the investigated area

1 fβ fluctuations and self similarity in earthquake dynamics observational evidences in southern italy abstract recently it has been determined that many statistical features of earthquakes are scale invariant with universal values for exponents the analysis of scaling laws has led to the development of a wide variety of physical models of seismogenesis involving nonlinear dynamics and it can be used to better characterize the seismicity pattern in this work the presence of scale invariance properties in the seismicity of a selected area of the southern appennine chain is revealed 1 f fluctuations are detected from the analysis of earthquake sequences using the counting statistics and at the spatial scale a self similar structure in the epicentre aggregate is determined by the estimation of its fractal dimension finally correlations between temporal exponent fractal dimension and b value variations are described

spatial distribution of earthquakes in aftershock zones of the garm region soviet central asia summary we examined the spatial distribution of earthquakes in aftershock zones of eight m4 5 to m6 3 earthquakes that occurred during the period january 1969 february 1987 in the garm region of soviet central asia this seismically active region is a part of the collisional plate boundary between the indian and eurasian plates spatial patterns in earthquake distribution were studied using the technique of pair analysis which is based on a quantitative comparison between observed and randomly simulated distributions of interevent distances similar to our previous findings from other seismically active areas of various scales and tectonic settings we show that the spatial distribution of earthquakes in all of the aftershock zones studied is characterized by significant non random features most prominent of the spatial patterns observed is spatial clustering at short interevent distances the degree of non randomness is usually higher for the aftershocks than for the background seismicity i e the remainder of the catalogue after space time clusters have been removed in some of the study areas the spatial distribution of aftershocks appears to be self similar in magnitude but in most cases is not self similar with respect to the size of the study areas more specifically the seismic activity in the smallest subareas of only few kilometres in size exhibits a higher degree of spatial clustering than the activity in larger subareas furthermore some of the spatial patterns observed change systematically in time one such change is the gradual increase of the degree of pre shock clustering as the main event approaches other temporal features are observed during the aftershock sequences themselves when the degree of spatial non randomness often increases to a peak value and then gradually decreases reaching a reduced background level at some time after the sequences are over some of the temporal changes observed are similar to patterns previously identified in central california aftershock areas

the reduction of aliasing in gravity anomalies and geoid heights using digital terrain data summary observations of gravity can be aliased by virtue of the logistics involved in collecting these data in the field for instance gravity measurements are often made in more accessible lowland areas where there are roads and tracks thus omitting areas of higher relief in between the gravimetric determination of the geoid requires mean terraincorrected free air anomalies however anomalies based only on the observations in lowland regions are not necessarily representative of the true mean value over the topography a five stage approach is taken that uses a digital elevation model which provides a more accurate representation of the topography than the gravity observation elevations to reduce the unrepresentative sampling in the gravity observations when using this approach with the australian digital elevation model the terrain corrected free air anomalies generated from the australian gravity data base change by between 77 075 and 84 335 mgal 0 193 mgal mean and 2 687 mgal standard deviation subsequent gravimetric geoid computations are used to illustrate the evect of aliasing in the australian gravity data upon the geoid the diverence between aliased and non aliased gravimetric geoid solutions varies by between 0 732 and 1 816 m 0 058 m mean and 0 122 m standard deviation based on these conceptual arguments and numerical results it is recommended that supplementary digital elevation information be included during the estimation of mean gravity anomalies prior to the computation of a gravimetric geoid model

optimal design of a gravity survey network and its application to delineate the jabera damoh structure in the vindhyan basin central india fractal dimension analysis was carried out for optimal designing of 2 d gravity survey network and to determine an optimum range of gridding interval to generate least aliased bouguer anomaly maps as a test case this method has been successfully applied to the jabera damoh region of the vindhyan basin which is considered as a potential hydrocarbon bearing area in particular we aim to delineate accurately the lateral extent of a possible hydrocarbon bearing structure to achieve this aim fractal dimension of survey network was computed using 2 d distributions of observation points in the planning phase of the survey so that the optimum station spacing for gravity survey can be obtained a range of optimum gridding interval for the gravity data set was suggested using the box counting method of fractal dimension determination bouguer anomaly maps of the region are prepared utilizing the optimum gridding interval for the first time these anomaly maps clearly outline the gravity evidence of an anomalous rifted structure which is bounded by parallel faults on either side this structure is interpreted as a favorable basin for the occurrence of hydrocarbons another finding of this study has been the delineation of an apparently small ridge like structure running east west dividing this basin in two parts a subsurface geological model along a profile across the jabera structure has also been presented

tectonic implications and seismicity triggering during the 2008 baluchistan pakistan earthquake sequence abstract a damaging and widely felt moderate earthquake mw 6 4 hit the rural mountainous region of southwestern pakistan on october 28 2008 the main shock was followed by another earthquake of identical magnitude mw 6 4 on the next day the spatial distribution of aftershocks and focal mechanism revealed a nw se striking rupture with right lateral strike slip motion which is sympathetic to the nnw sse striking active mapped urghargai fault the occurrence of strike slip earthquakes suggests that along with the thrust faults strike slip faults too are present beneath the fold and thrust belt of sulaiman kirthar ranges and accommodates some of the relative motion of the indian and eurasian plates to assess the characteristics of this sequence the statistical parameters like aftershocks temporal decay b value of g r relationship partitioning of radiated seismic energy due to aftershocks and spatial fractal dimension d value have been examined the b value is estimated as 1 03 0 42 and suggests the tectonic genesis of the sequence and crustal heterogeneity within rock mass the low p value of 0 89 0 07 implies slow decay of aftershocks activity which is probably an evidence for low surface heat flow a value of spatial fractal dimension of 2 08 0 02 indicates random spatial distribution and that the source is a two dimensional plane filled up by fractures the static coseismic coulomb stress changes due to the foreshock mw 5 3 were found to increase stress by more than 0 04 bars at the hypocenter of the main shock thus promoting the failure the cumulative coseismic coulomb stress changes due to the foreshock and mainshocks suggest that most of the aftershocks occurred in the region of increased coulomb stress and to the se to the mainshock rupture

extreme element mobility during transformation of neoarchean ca 2 7ga pillow basalts to a paleoproterozoic ca 1 9ga paleosol schreiber beach ontario canada abstract this study reports petrographic major and trace element and oxygen isotopic data for a subaerial weathering profile at schreiber beach ontario canada the weathering profile developed on neoarchean ca 2 7 ga pillow basalts and is unconformably overlain by the paleoproterozoic ca 1 88 ga gunflint chert and basal conglomerates this stratigraphy suggests that the basalts were uplifted and subaerially weathered prior to deposition of the gunflint formation rocks at schreiber beach have been classified as pillow cores pillow rims hyaloclastites weathered red basalts and weathered brown to green basalts there are gradual textural mineralogical and geochemical transitions from unweathered basalts to intensely weathered hematite bearing basalts with stratigraphic height rocks at schreiber beach underwent seafloor hydrothermal alteration and greenschist facies regional metamorphism in the neoarchean following the subaerial weathering they were buried and re metamorphosed to greenschist facies in the paleoproterozoic given the preservation of primary igneous textures and trace element patterns in pillow cores they are used as a protolith to estimate element mobility during seafloor alteration metamorphism and subaerial weathering chloritized pillow rims and hyaloclastites are characterized by moderate losses or gains of major si ca na fe ti k and trace lile ree hfse and transition metals elements during neoarchean seafloor alteration alteration of these rocks at relatively low temperatures is indicated by enrichment in 18 o 18 o 10 4 to 12 7 relative to fresh basalt 5 5 subaerial weathering resulted in significant textural mineralogical e g hematite precipitation and geochemical variations in metamorphosed basalts causing additional redistribution of most major and trace elements and further enrichment in 18 o the highest 18 o values 16 1 to 17 1 occur at the silica rich base of the weathering profile many elements including lile ree and hfse are strongly enriched 100 or depleted up to 96 relative to their original abundances alkaline metasomatism which is a characteristic of precambrian paleosols is also evident at schreiber beach where extreme enrichment in k 280 to 1000 rb 390 to 660 and cs 1160 to 2560 occurs in the weathering profile

u pb ages and tectonic significance of late archean alkalic magmatism and nonmarine sedimentation timiskaming group southern abitibi belt ontario the paper presents u pb ages for zircons of the calc alkalic to alkalic igneous suite and associated alluvial fluvial sedimentary rocks of the timiskaming group in the late archean abitibi greensto

anomalous crustal and lithospheric mantle structure of southern part of the vindhyan basin and its geodynamic implications abstract tectonically active vindhyan intracratonic basin situated in central india forms one of the largest proterozoic sedimentary basins of the world possibility of hydrocarbon occurrences in thick sediments of the southern part of this basin has led to surge in geological and geophysical investigations by various agencies an attempt to synthesize such multiparametric data in an integrated manner has provided a new understanding to the prevailing crustal configuration thermal regime and nature of its geodynamic evolution apparently this region has been subjected to sustained uplift erosion and magmatism followed by crustal extension rifting and subsidence due to episodic thermal interaction of the crust with the hot underlying mantle almost 5 6 km thick sedimentation took place in the deep faulted jabera basin either directly over the bijawar mahakoshal group of mafic rocks or high velocity high density exhumed middle part of the crust detailed gravity observations indicate further extension of the basin probably beyond nsl rift in the south a high heat flow of about 78 mw m2 has also been estimated for this basin which is characterized by extremely high moho temperatures exceeding 1000 c and mantle heat flow 56 mw m2 besides a very thin lithospheric lid of only about 50 km many areas of this terrain are thickly underplated by infused magmas and from some segments granitic gneissic upper crust has either been completely eroded or now only a thin veneer of such rocks exists due to sustained exhumation of deep seated rocks a 5 8 km thick retrogressed metasomatized zone with significantly reduced velocities has also been identified around mid to lower crustal transition

sedimentary and structural evidence for 2 7 ga continental arc oceanic arc collision in the savant sturgeon greenstone belt western superior province canada the western superior province sustained rapid crustal growth in the interval 2 72 2 68 ga through amalgamation of microcontinental crustal blocks and juvenile oceanic terranes recent field isotopic and geophysical surveys provide insight on the nature timing and scale of this accretionary growth however few places offer the rich tectono stratigraphic and structural detail with which to establish accretion of oceanic and continental blocks as does the savant sturgeon area here 3 4 2 8 ga continental crust of the winnipeg river terrane is juxtaposed with 2 775 2 718 ga juvenile oceanic rocks of the western wabigoon terrane across a 2 85 2 75 ga southwest facing continental margin sequence the continental margin was reactivated at 2 715 ga with the establishment of an arc recorded by 2 715 2 70 ga tonalite and associated intermediate volcanic rocks this magmatic activity is interpreted to reflect north and east dipping subduction that led to consumption of a small tract of oceanic crust betwe

comment on archean hydrothermal zircon in the abitibi greenstone belt constraints on the timing of gold mineralization by j c claoue long r w king and r kerrich

faulting style controls for the space time aftershock patterns abstract to understand the complexity and thus to predict earthquake occurrence in size time and space seismicity patterns are characterized by two robust empirical laws the exponential distribution of magnitude and the power law decrease of aftershock rate over time these laws are known as the gutenberg richter law and the omori law respectively using global earthquake catalogs we resolve that on average the k aftershock productivity and the p value exponent of the power law decrease of aftershock rate over time are dependent on the mainshock faulting style strike slip events have a lower aftershock rate n and k values and a larger p value than thrust and normal events respectively within the epidemic type aftershock sequence model strong k n values are driven by a high branching ratio value n within the same framework a relatively higher n value for the thrust events also predicts the lower p value we observe for thrust events as compared to strike slip and normal faulting events respectively furthermore we observed that earthquake interactions through time and space are a function of the faulting style when measured by t the exponent of the power law decrease of earthquake density over space the t values of thrust events for different time windows always remain smaller than those of the strike slip events when changes in faulting styles are driven by stress pattern the anderson faulting theory predicts thrust faulting that requires somewhat larger stresses in absolute magnitude than do normal and strike slip faulting within the framework of rate and state friction law changes in the stress heterogeneity patterns reproduce the p value changes we observe our results suggest that only stress perturbations associated with mainshock rupture affect the productivity and decay rate over time of aftershocks

an appraisal of the 2001 bhuj earthquake mw 7 7 india source zone fractal dimension and b value mapping of the aftershock sequence we examined seismic characteristics b value and fractal dimension of the aftershock sequence of the january 26 2001 bhuj earthquake mw 7 7 that occurred in the kutch failed rift basin western margin of the stable continental region scr of india a total of about 2 000 events m 2 0 were recorded within two and a half months immediately after the main shock some 795 events were precisely relocated by simultaneous inversion these relocated events are used for mapping the frequency magnitude relation b value and fractal correlation dimension dc to understand the seismic characteristics of the aftershocks and the source zone of the main shock the surface maps of the b value and dc reveal two distinct tectonic arms or zones of the v shaped aftershock area western zone and eastern zone the b value is relatively higher 1 6 in the western zone compared to a lower value 1 4 in the eastern zone the dc map also shows a higher value 1 2 1 35 in the western zone compared to a lower dc 0 80 1 15 in the eastern zone this implies a positive correlation between dc and b value two cross sections e w and n s are examined the e w sections show similar characteristics higher b value and higher dc in the western zone and lower in the eastern zone with depth the n s sections across the fault zones however show unique features it imaged both the b and dc characteristics convincingly to identify two known faults the kutch mainland fault and the south wagad fault swf one stepping over the other with a seismogenic source zone at depth 20 35 km the source zone at depth is imaged with a relatively lower b and higher dc at the fault end of the swf showing a negative correlation these observations corroborated with the seismic tomography as well as with the proposed geological tectonic model shed a new light to our understanding on seismogenesis of the largest scr earthquake in india in the recent years

application of pattern recognition techniques to earthquake catalogs generated by model of segmented fault systems in three dimensional elastic solids techniques and seismicity parameters described by eneva and ben zion 1997 are used to examine synthetic earthquake catalogs generated by ben zion 1996 for precursory patterns of large model events different model realizations represent various levels of fault zone disorder these include models with uniform properties u a parkfield type asperity a fractal brittle properties f and multi size scale heterogeneities m the seismicity parameters used are based on information contained in typical earthquake catalogs reflecting earthquake distribution in space time and size the analysis highlights the complexity of the information content of the synthetic earthquake catalogs simple repetitive precursory signals have not been found however local extrema in the examined parameters are found to have significant association in time with large events thus our techniques and parameters may be useful for intermediate term earthquake prediction especially when parameters are used in combinations some analysis results are the same for all model realizations and some depend on the model features characterizing all catalogs are as follows 1 large model events are statistically predictable on the basis of patterns in the distribution of smaller events 2 for a given parameter the type of precursory extrema maxima or minima is the same for all models 3 the interparameter correlation for any parameter pair has the same sign positive or negative in all models 4 the large events are neither slip nor time predictable based on previous large events results that differ from model to model include the following 1 the degree of predictability of large events correlates with the degree of regularity in the assumed fault properties following the order u f a and m 2 there is no one to one correlation between type of precursory extrema maxima or minima and type of precursory trends increase or decrease this produces great variations in observable trends for any given parameter both from model to model and for different events in the same model 3 the interparameter correlations vary among models with the highest correlations in model f most discussed patterns are in agreement with observations from seismically active zones laboratory models and mining induced seismicity

seismic characteristics and seismic hazard assessment source region of the 2015 nepal earthquake mw 7 8 in central himalaya seismicity and seismic characteristics like b value fractal dimension energy release and recurrence period are assessed for the region 80 e 89 e and 26 n 31 n which includes the 2015 large nepal earthquake mw 7 8 in central himalaya the international seismological centre isc catalogue of earthquakes with mb 3 8 for the period august 1964 january 2013 are used the b values are estimated using the maximum likelihood and least square methods the fractal dimension is estimated using the correlation integral method the events are also used for estimating radiated energy in the region the probability of occurrence of moderate earthquakes mb 5 0 using isc data and mw 6 0 using usgs data for the period 1964 2015 during a specified interval of time is estimated on the basis of three probabilistic models namely weibull gamma and lognormal the model parameters are estimated by the maximum likelihood estimates it is found that there is a 99 probability for occurrence of at least one earthquake mb 5 0 in this region in a time window of 2 3 years from the year 2013 and in 20 30 years for an earthquake mw 6 0 from the year 2015 the b value maps identified variable stressed zones and the fractal dimension maps fractal characteristics of the active fault zones the energy release map identified the zones of higher and lower energy release the percent probability maps prepared using the poisson distribution identify the zones of higher and lower probability earthquakes and thus indicate the areas of future probable earthquakes

geology alteration and origin of archean au ag cu mineralization associated with the synvolcanic chibougamau pluton the brosman prospect abitibi greenstone belt canada the au ag cu brosman prospect is located in the line lake area on the northern limb of the chibougamau anticline in the northeast part of the archean abitibi greenstone belt this prospect comprises a broad n s subvertical mineralized envelope formed in a synvolcanic fault related environment this envelope is at least 300 m long up to 30 m wide and is known to a depth of 950 m where it remains open it exhibits two contrasting mineralized zones that are representative of the varying styles of mineralization in the area the auriferous zone consists of both ubiquitous pyrite disseminations and au bearing silicate sulfide veins in strongly fractured intrusive effusive and volcaniclastic rocks showing propylitic and chloritic alteration assemblages the polymetallic zone on the other hand is characterized by discrete cu ag au rich magnetite sulfide veins and lesser pyrite disseminations within distal propylitic and proximal potassic to sodic alteration zones the polymetallic zone is hosted by a chaotic assemblage of gabbro and tuff bodies interpreted as a talus megabreccia several lines of evidence including the spatial distribution pattern and nature of the alteration and mineralization assemblages metal associations mass balance calculations pyrite composition and crosscutting relationships are indicative of a preregional deformation synvolcanic origin for the hydrothermal activity crosscutting relationships alteration characteristics as well as whole rock and la icp ms pyrite analyses reveal two stages of hydrothermal alteration and mineralization stage i consists of both ubiquitous disseminated pyrite found in the polymetallic and auriferous zones and contemporaneous magnetite sulfide veins restricted to the polymetallic zone stage ii is restricted to the auriferous zone and corresponds to au bearing silicate sulfide veins with characteristic vein halo chloritic alteration overprinting stage i alteration and mineralization this hydrothermal activity is interpreted to have occurred concurrently with the development of the fertile deeper magmatic hydrothermal system related to the chibougamau pluton stage i hydrothermal activity related to the early build up of the volcanic sequence formed a continuum of mineralization from discrete massive magnetite sulfide veins to ubiquitous pyrite disseminations in a submarine talus megabreccia generated along synvolcanic faults afterward a late au rich contribution to the hydrothermal fluids possibly related to intermediate to felsic magmatism the 2707 6 1 4 ma line lake stock produced stage ii silicate sulfide veins overprinting mineralization and alteration in favorably oriented and sustainably permeable fracture zones of the auriferous zone overall this study suggests that the brosman prospect is a rare example of archean polymetallic mineralization produced by a shallow subaqueous epithermal style subsystem developed in a broader fertile magmatic hydrothermal arc setting

metallogeny of the marco zone corvet est disseminated gold deposit james bay quebec canada the corvet est gold deposit is hosted by archean rocks of the superior province in the james bay region northern quebec canada the marco zone is hosted by amphibolite grade strongly foliated volcanic rocks and consists of disseminated gold with an apparent thickness ranging from 1 8 to 39 5 m and gold grades up to 23 g t 1 over 1 m that is continuous along strike for 1 3 km the lithotectonic sequence comprises footwall basaltic andesite amphibolite overlain by a lenticular unit of metadacite and then by hanging wall basaltic andesite amphibolite all intruded by quartz feldspar porphyry dikes dacite basaltic andesite amphibolite and quartz feldspar porphyry show a calc alkaline to transitional affinity and plot in the plate margin arc basalt field with typical volcanic arc trace element patterns mineralization consists of pyrite arsenopyrite pyrrhotite chalcopyrite and gold disseminated in deformed dacite in andesite amphibolite and in quartz feldspar porphyry dikes dacite and andesite display weak alteration characterized by silicification native gold forms inclusions in metamorphic quartz garnet feldspar arsenopyrite and pyrite or free grains interstitial to quartz feldspar pyrite chalcopyrite and arsenopyrite free gold in late quartz veins cut the serici tized metamorphic fabric inclusion and interstitial native gold within minerals annealed during metamorphism shows that gold mineralization is pre to syn metamorphic with some gold remobilized in later veins rhenium osmium dating of arsenopyrite yields an isochron age of 2663 13 ma for mineralization and a weighted average model age of 2632 7 ma for arsenopyrite formed during peak metamorphism the 2663 ma arsenopyrite has a low initial 187 os 188 os of 0 19 0 10 suggesting a juvenile crust or a mantle os source the sulfur isotope composition of marco zone pyrite and arsenopyrite shows that sulfur could have been leached from its volcanic host rocks or from reduction of archean seawater the corvet est deposit is interpreted to be an oro genic gold deposit 2663 ma deformed and recrystallized during amphibolite grade metamorphism 2632 ma

development of sedimentary basins in the archean abitibi belt canada an overview sedimentation in the archean abitibi greenstone belt occurred during four depositional episodes i sedimentary cycle 1 2730 2720 ma ii sedimentary cycle 2 2715 2705 ma iii sedimentary cycle 3 2700 2687 ma and iv sedimentary cycle 4 2685 2675 ma records of the first two sedimentary cycles are preserved in basins within the northern volcanic zone whereas basins formed during the latter two sedimentary cycles are located within the southern volcanic zone of the abitibi belt sedimentary cycles 1 and 3 represent deep water facies as indicated by turbidites resedimented conglomerates pelagic sediments and ubiquitous iron formations subaerial deposits have not been identified in contrast sedimentary cycles 2 and 4 show a prevalence of fluvial to shallow water marine and or lacustrine deposits tectono magmatic influence on sedimentation during cycles 2 and 4 is documented by i the presence of numerous unconformities underlain by plutonic and volcanic rocks ii locally voluminous sh

statistical analysis of the spatial distribution of earthquakes variation of the spatial distribution of earthquakes before and after large earthquakes abstract we have investigated the spatial distribution of earthquakes using the polya eggenberger model and the morishita index which is used for the analysis of the spatial dispersion of bio species first we found that the spatial distribution of earthquakes is characterised by clustering when we divide the certain area into equal area meshes the frequency distribution of meshes with same number of events fits well to the polya eggenberger model on the basis of this result we examined the degree of spatial clustering of earthquakes by using the morishita index defined by i q i 1 q n i n i 1 n n 1 where q n and ni are the numbers of meshes total events and events of the i th mesh respectively the index i corresponds to the contagious coefficient plus 1 in the polya eggenberger statistics the dependence of i on the mesh size provides information about clustering we analysed the actual distribution patterns of earthquakes before and after the miyagi oki 1978 m 7 4 the tokachi oki 1968 m 7 9 and the nihonkai chubu 1983 m 7 7 earthquakes large scale clusters of about 50 100 km are dominant in the aftershock sequences after the aftershock activity earthquakes tend to distribute randomly prior to large earthquakes small patches of 10 20 km are created this statistical feature of the earthquake distribution seems to be related to the phenomena of the precursory clusterings of earthquakes doughnut patterns preseismic quiescence and foreshocks prior to large earthquakes

the fractal dimension of gravity data sets and its implication for gridding gravity survey station locations are in general inhomogeneously distributed this inevitably results in interpolation errors in the computation of a regular grid from the gravity data the fractal dimension of the station distribution can be used to determine if an interpolated map is aliased at a specific wave length and moreover it is often possible to determine an optimum gridding interval synthetic distributions of gravity station locations have been used for theoretical studies and it is found that for randomly distributed data there is a range of sizes for which the spatial data distribution has a fractal dimension of 2 that is euclidean the minimum length scale at which the distribution ceases to be euclidean is the optimum interpolation interval obeying shannon s sampling theorem for dimensions less than 2 the optimum interpolation interval is the shortest length at which the scaling regime is constant in this case the gravity field cannot be interpolated without introducing some aliasing as the fractal dimension characterizes the data distribution globally over the whole study area the actual gridding interval in some cases will be smaller in order to represent short wavelength features properly in the more densely sampled sub areas but this may generate spurious anomalies elsewhere the proposed technique is applied to the station distribution of the canadian national gravity data base and a series of sub areas a fractal dimension of 1 87 is maintained over a range of sizes from 15 km to over 1600 km although aliasing occurs since the gravity field certainly contains much shorter wavelength anomalies aliasing errors may be minimized by selecting the proper interpolation interval from the fractal analysis

stratigraphic and structural setting of the hemlo gold deposit ontario canada results of detailed surface and underground mapping and a compilation of data from the three gold mines in the hemlo area ontario are presented in particular the lithostratigraphy of the area is established the nature of the lithologic units spatially closely associated with the ore and the protolith of the ore are determined and the deformation history and the three dimensional geometry of the area are elucidated the genesis of the gold deposit is discussed in context of these results four generations g 1 to g 4 of ductile structures as well as brittle faulting are recognized g 2 deformation is the strongest and the geometry of the hemlo camp is dominated by macroscopic camp scale s shaped f 2 folds the two ore zones at hemlo the main and lower ore zones are spatially associated with the two limbs of a newly recognized camp scale f 2 fold the moose lake fold and the orebody is folded by f 2 at outcrop scale mine scale and possibly camp scale g 2 deformation is most intense in the hemlo shear zone interpreted to be a sinistral transpressional zone the hemlo gold deposit is hosted in the shear zone mainly in the segment that trends east southeasterly where deformation is stronger the main gold mineralization at hemlo occurred before g 2 or early during g 2 deformation and before peak metamorphism the latter took place during late g 2 to after g 2 deformation the ore and alteration zones are dominantly but not exclusively spatially associated with the stratigraphically lower contact of a volcanic quartz feldspar porphyry the moose lake porphyry a mafic fragmental unit altered felsic fragmental rock and a barite horizon are spatially closely associated with the ore zones the protolith of the ore is mainly the fragmental rock and the barite the stratigraphically lower contact of the moose lake porphyry and the fragmental rock at the contact probably served as mechanical traps and the barite horizon as a chemical trap

shallow crustal configuration of the narmada son lineament transition zone near the sahdol katni area of central india using simultaneous gravity and magnetic observations gravity and magnetic studies have been carried out to map the different depth formations of alluvium gondwana vindhyan mahakoshal and the crystalline basement in the narmada son lineament nsl near the sahdol katni area india higher elevations in the northern part of the study area have lower gravity the southern part of the study area however is moderately elevated and also has a higher gravity anomaly which justifies the isostatic adjustment this indicates the presence of high density material for example mahakoshal rocks in the upper crust which causes the higher anomaly value the mahakoshal rocks are widely exposed at mau chanaura nadawar khamaria umria and near the tala barhi area and also extend from sidhi to agoni village further east of the area the mahakoshal rocks are thinner between the river son and tikwa village which causes a different gravity anomaly pattern changing from the nne ssw direction to the n s direction however the trend of magnetic anomaly follows the same pattern toward the nne ssw direction mainly because of the effect of the crystalline basement two magnetic highs are prominent in the tikwa and amarpur regions 800 and 400 ntesla respectively because of the presence of the crystalline basement the depth of the crystalline basement obtained by 2 d gravity magnetic modelling varies from 2 7 to 2 9 km from spectral analysis the average depth of the crystalline basement varies from 2 83 to 3 05 km the different crustal depth sections obtained by 2 d simultaneous gravity magnetic modelling correlate well with other constrained data

archean terrane docking upper crust collision tectonics abitibi greenstone belt quebec canada abstract the northern nvz and southern volcanic zones svz of the abitibi greenstone belt are separated by the major e trending destor porcupine manneville fault zone dpmfz the dpmfz is interpreted to be the locus of archean terrane docking between the older diffuse volcanic arc of the nvz 2730 2710 ma and the younger arc segments of the svz 2705 2698 ma two distinct evolutionary phases can be documented along the dpmfz of the abitibi greenstone belt and include 1 arc arc collision occurring between 2697 and 2690 ma and 2 arc fragmentation between 2689 and 2680 ma identification of these two events along the dpmfz is based on detailed structural studies sedimentary basin analysis and precise u pb age determinations the thrusting event representative of the arc arc collision phase is characterized by shallow north dipping foliations 20 40 and dip parallel stretching lineations in the eastern manneville segment of the dpmfz local overturned mafic pillowed units suggest recumbent folding late strike slip or transcurrent movement displayed in the late orogenic sedimentary duparquet basin records the arc fragmentation phase basin geometry e trending en echelon folds shallow e plunging stretching lineations and a late ne striking cleavage cross cutting the folds support a dextral shear sense along the western destor porcupine segment of the dpmfz the sedimentary facies observed in the basin are consistent with those of modern strike slip basins located along the east anatolian fault turkey hazar lake and the hope fault new zealand hanmer basin precise u pb zircon age determinations from porphyry stocks located at the northern and southern limits of the duparquet basin yielded 2681 1 ma and 2689 3 2 2 9 ma respectively these ages constrain the rapid change from thrusting to transcurrent movement it is apparent that once thrusting ceased the response to oblique subduction continued in the form of strike slip displacement modern fold and thrust belts commonly show this evolution the deformation pattern is the result of oblique convergence the abitibi greenstone belt is considered to be an archean analogue of modern subducting oceanic plates such as those found in the western pacific

some premonitory phenomena of the 1995 hyogo ken nanbu kobe earthquake seismicity b value and fractal dimension abstract this paper presents a detailed and complex analyses of the spatio temporal evolution of seismic activity between 1976 and 1998 in a broad area surrounding the epicentre of the 1995 hyogo ken nanbu kobe earthquake as well as in the source area various precursory changes in seismicity such as quiescence followed by increased seismic activity b value and fractal dimension correlation dimension d2 anomalies appear approximately two years before the occurrence of the major event an increased level of background seismicity is clearly observed after the occurrence of the kobe earthquake particularly in the northeast extension of the source area all these anomalous changes in seismic activity before and after the occurrence of the 1995 hyogo ken nanbu earthquake appear in a relatively large region surrounding the epicentre of the main shock as well as in the source area

unraveling the geologic history of the hemlo archean gold deposit superior province canada a u pb geochronological study the hemlo deposit is one of canada s largest gold camps gold is both structurally and lithologically controlled but shows unusual relationships relative to many other archean lode deposits field evidence suggests that gold was emplaced within mechanical and chemical traps along a jog in a major sinistral shear zone most likely during early formation of second generation g2 structures which represent the most intense phase of regional deformation mineralization was followed by amphibolite facies regional metamorphism u pb geochronology has been carried out on zircons from rocks associated with the deposit in order to determine the precise chronology of geologic events and their relationship to mineralization zircon populations are commonly affected by both inheritance and hydrothermal metamorphic crystal growth meaningful and precise age information can only be determined by precise single zircon dating on rocks from a well constrained structural and stratigraphic context gold is mostly found near the deformed contact between the moose lake quartz porphyry volcanic complex and stratigraphically underlying metasedimentary rocks these rocks have been folded by a camp scale noncylindrical f2 fold zircon from the moose lake quartz porphyry is dominated by inheritance and gives ages that extend from 2800 to 2690 ma metasedimentary rocks that underlie and overlie the moose lake porphyry show a much narrower range of provenance ages and are dominated by 2 690 to 2 693 million year old zircon two detrital zircons from a metasedimentary rock directly beneath the porphyry define an age of 2685 4 ma this should be an older age limit on volcanism deformation and gold mineralization the four youngest near concordant zircons from the cedar lake pluton define a magmatic age of 2680 1 ma this pluton was emplaced prior to or early during g2 deformation while emplacement of gold was most likely controlled by g2 structures therefore 2680 1 ma probably also represents an older age limit on gold mineralization a feldspar porphyry dike that cuts gold ore gives a younger age bracket of 2677 1 ma the results of zircon dating suggest that a volcanosedimentary complex was constructed in the area over the period of 2693 to 2685 ma this developed on earlier crust ca 2720 ma in age but there is evidence from detritus and xenocrysts for older rocks dating back to over 2800 ma deposition of supracrustal rocks was followed by granodiorite plutonism at 2680 1 ma then major deformation g2 and gold mineralization overprinted by amphibolite facies metamorphism previously dated at 2676 ma from titanite ages late tectonic sanukitoid suite plutons were emplaced at 2677 1 ma thus the primary gold forming event occurred near the beginning of a period of plutonism and crustal reworking that lasted at most a few million years this time association supports the view that granitoid magmas were the source of auriferous fluids plutons intruded into an actively deforming crust and were probably also the heat source for regional metamorphism the most likely environment was a tectonically active timiskaming type sedimentary basin similarly aged basins are found in the timmins area to the east and the shebandowan greenstone belt to the west

magmatic and tectonic emplacement of the pukaskwa batholith superior province ontario canadathis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh the neoarchean pukaskwa batholith consists of pre syn and post tectonic phases emplaced over an interval of 50 million years pre tectonic phases are broadly synvolcanic and have a high al tonalite trondhjemite granodiorite ttg affinity interpreted to reflect derivation by partial melting of basaltic crust at lower crustal or upper mantle depths minor syn tectonic phases slightly post date volcanism and have geochemical characteristics suggesting some involvement or interaction with an ultramafic mantle source component magmatic emplacement of pre and syn tectonic phases occurred in the midcrust at paleopressures of 550 600 mpa and these components of the batholith are thought to be representative of the midcrust underlying greenstone belts during their development subsequent to emplacement of the syntectonic phases and likely at approximately 2680 ma the pukaskwa batholith was uplifted as a structural dome relative to flanking greenstone belts synchronously with ongoing regional sinistral t

neoarchean trans subprovince sediment transport in southwestern superior province sedimentological geochemical and geochronological evidence at 2700 ma volcanism spawned by northward directed subduction under wabigoon subprovince canadian shield fed sediment into an adjacent fore arc basin trench system volcanically active island arcs to the south wawa subprovince were transported northward during this interval and at 2690 ma collided with the accretionary complex quetico subprovince metamorphosed sedimentary units intercalated with the ocean floor and island arc volcanic rocks of northern wawa subprovince provided the opportunity to amass data useful in extending the paleogeographic interpretation of the area this study examines the mckellar harbour formation a several kilometre thick assemblage of graded metasandstone beds outcropping to the north of lake superior its sedimentology geochemistry and detrital u pb zircon geochronology were investigated in conjunction with the same attributes of possible correlative units in the region similarities between the mckellar harbour formation and sedimentary rocks composing the fore

crustal scale auriferous shear zones in the central superior province canada a proposed correlation of major archean shear zones across different metamorphic terranes of the central superior province implies that the same shear zones are exposed at greenschist to granulite facies coalignment of the shear zones is recognized after systematic removal of regional proterozoic dextral transcurrent and shortening deformation associated with the intracratonic kapuskasing uplift subvertical in the upper crust the structures become shallowly north dipping at deeper levels the connection of these archean shear zones provides limits on any sinistral transcurrent component associated with the tectonic evolution of the kapuskasing uplift

waveform analysis of two preshock main shock aftershock sequences in utah we use waveform cross correlation to study clustering of small earthquakes that occurred from 1981 to 1983 within 20 km of 1 an ml 4 3 main shock near salt lake city utah on 8 october 1983 and 2 an ml 4 0 main shock near richfield utah on 24 may 1982 no clusters of earthquakes were observed prior to the salt lake city event during the time period studied however a cluster of four nearly identical preshocks within 80 m of each other possibly representing the failure of a critical asperity occurred 5 km northwest of the richfield event during a 4 hour period 10 months before the main shock we found no similar clusters among the other preshocks within the richfield study area all of which were located more than 10 km from the main shock the aftershocks in both study regions during the first 17 days after the respective main shocks occupied areas smaller than the rupture areas estimated for the main shocks from initial pulse width measurements both aftershock sequences showed a spatial migration of the initial events that could only be discerned from the waveform data one possible explanation for this migration could be propagating stress changes caused by the occurrence of the aftershocks themselves or by postseismic creep

long term seismicity behavior of the zagros region in iran to achieve a comprehensive attitude about seismicity it is necessary to consider spatial and magnitude distributions of earthquakes earthquake distributions in space and magnitude can be quantified by means of spatial fractal dimension d s and gutenberg richter b value in this paper b value and d s are used to evaluate seismicity of the zagros zone iran in time interval 1964 to 2012 seismic catalog of the zagros zone is extracted from unified seismic catalog of the iranian plateau the b value and d s are estimated using frequency magnitude distribution kijko sellevoll bull seism soc am 79 3 645 654 1989 and correlation integral methods correlations between spatial variations in b value and d s along individual profiles across the north zagros and the central zagros indicate different stress release regimes for north and central parts of the zagros zone evaluation of b value with respect to depth along the profiles indicates larger b values at shallower depths temporal variations in b value and d s are also obtained from background seismicity to evaluate seismicity behavior of the zagros zone our results indicate high b values and moderate d s for seismicity of the north zagros while seismicity of the central zagros has low b values and high d s during time interval 1964 2012 asperities of the main zagros thrust are also located by investigating ratio d s b along the main zagros thrust

loading rate impact on fracturing pattern lessons from hydrocarbon recovery lacq gas field france using scaling parameters of induced seismicity in size and space domains seismic b value and spatial correlation dimension d respectively we analyze the fracturing pattern of the gas reservoir of lacq in correlation with the production rate on the basis of previous observations and a previous model segall et al 1994 we assume that the cause of induced seismicity is a poroelastic stressing such that the production rate can be viewed as a stress rate for the rocks adjacent to the reservoir during the 20 year study period the production rate has decreased dramatically leading to a change of poroelastic stress rate from 4 5 10 3 to 1 5 10 3 mpa yr accordingly we observe a significant decrease in the size of activated fractures and a reduction of the spatial clustering of fracturing both arguing for a stress rate impact on the fracturing pattern in the gas field we interpret these changes in terms of a change in the deformation mode of stressed rocks from a more brittle to a more ductile behavior as the stress rate was decreased this hypothesis is supported by independent evidence from a number of experimental numerical and field studies the loading rate thus appears as a possible candidate to drive changes of b and d in time and space the apparent sensitivity of the earth s crust fracturing pattern to loading rate variations of much lower frequency than the tidal variations suggests that the earth s crust deformation mode itself be frequency dependent also our observations may have strong implications in contexts where the loading rate is induced by human intervention e g hydrocarbon recovery mines suggesting the possibility of adjusting the loading rate so as to shape the fracturing pattern locally according to human needs

techniques and parameters to analyze seismicity patterns associated with large earthquakes a pattern recognition algorithm is developed to provide potential improvements over existing earthquake prediction practices the parameters employed in the analysis include degree of spatial nonrandomness in two distance ranges spatial correlation dimension spatial repetitiveness of earthquakes with a similar size average depth of events time interval for the occurrence of a constant number of events and ratio of the numbers of events in two magnitude intervals the parameter temporal variations are compared quantitatively with the time series of large events using a technique of association in time the significance of the association frequencies is evaluated by comparison with chance associations estimated from corresponding simulated random time series the developed techniques differ from existing approaches in the following aspects the parameters here emphasize the spatial distribution of earthquakes possible correlations among the parameters are evaluated to determine the final set of parameters to be monitored threshold values for the assumed anomalies are chosen with consideration of properties of the available earthquake catalogs such as the number of large events to be retrospectively predicted equal weight is given to both locally high and locally low parameter values care is taken to distinguish between anomalies preceding large events and those following previous events it is shown that the relationship between precursory local extrema and precursory trends is nonunique with precursory local extrema of the same type frequently associated with opposite observable precursory trends the application of the seismicity parameters and pattern recognition techniques is demonstrated using synthetic earthquake catalogs generated by models of segmented fault systems in a three dimensional elastic solid ben zion 1996

magmatism metamorphism and deformation at hemlo ontario and the timing of au mo mineralization in the golden giant mine the golden giant mine is developed in the archean hemlo gold molybdenum deposit hosted within the hemlo heron bay greenstone belt in northwestern ontario canada the ore occurs in steeply dipping tabular zones within metasedimentary rocks and within quartz eye muscovite schists in association with microcline mica pyrite alteration and a variety of other minerals the hemlo area has been intruded by quartz feldspar porphyries the golden giant porphyry and sceptre porphyry these porphyries are altered mineralized and highly deformed the calc alkalic granodioritic cedar creek stock and cedar lake pluton occur near the deposit feldspar porphyry sills and dikes generated from the stock and pluton cut the earlier porphyries mineralized rocks and many of the fabric elements the golden giant rocks have been regionally metamorphosed to amphibolite grades this early m 1 metamorphisin t 500 degrees 600 degrees c p 5 6 kbars probably accompanied the intrusion of the cedar lake pluton and produced mineral assemblages in metasedimentary rocks containing hornblende kyanite staurolite garnet and micas a second m 2 metamorphic event t 300 degrees 400 degrees c p 1 3 kbars produced mineral assemblages containing actinolite fibrolite andalusite calcite garnet epidote chlorite and muscovite the golden giant mine rocks are strongly foliated and commonly exhibit mylonitic and transposed fabrics isoclinal folds and boudinage in both mineralized and nonmineralized rocks it is proposed that the primary au mo mineralization occurred before the m 1 metamorphic event possibly related to emplacement of the golden giant quartz porphyry in a premineralization structural zone the mineralization was modified by the m 1 event and severely deformed during mylonitization dikes from the cedar creek stock intruded the deposit sequence and overprinted the m 1 event with an m 2 metamorphism

potential field power spectrum inversion for scaling geology we propose a method for inverting the power spectrum of gravity and magnetic data the method is demonstrated on aeromagnetic and bore well data from the german continental deep drilling project ktb density and susceptibility distributions in the earth s crust exhibit scaling behavior with power spectra proportional to f where f is the wavenumber and is the scaling exponent of the source distribution we model the sources of the potential field by a random function with scaling properties defined on a half space with its top at a specified depth beneath the observation plane comparing the theoretical power spectrum for this model with the power spectrum of the measured data we obtain the best values for the depth to source and the scaling exponent as a global minimum of the misfit function despite the simplicity of the model it offers a new understanding of the factors influencing the shape of the potential field power spectrum in particular the low wavenumber part of the power spectrum can be dominated by the scaling properties of the source distribution and not by the depth to some kind of basement the scaling exponent of the field varies with the type of surface geology the question of whether the scaling exponent can actually be used to identify different types of geology gives an interesting new aspect to power spectrum inversion

aftershock patterns of ms 7 earthquakes in the india asia collision belt anomalous results from the muzaffarabad earthquake sequence kashmir 2005 the seismicity rate triggered by the muzaffarabad kashmir 2005 m w 7 6 m s 7 7 earthquake is above the average when analyzing the aftershock rate of the 18 m s 7 0 events in the india asia collision belt between 1973 and 2008 all 17 m s 7 0 events occurred within 10 latitude and 20 longitude distance from the 2005 muzaffarabad earthquake epicenter we determined the huge aftershock productivity for this earthquake is not driven by a specific omori law parameter this anomaly in aftershock rate value corresponds to a relatively higher rate decay as measured by the p value and a larger density value in a higher background seismicity rate setting prestress conditions than the other 17 sequences respectively after normalizing by the mainshock size and by the magnitude range of observation we resolved the anomalies with a 95 confidence level for five aftershock sequences for either the duration the productivity the density or the background seismicity rate when we did not include the local processes that drive these specific anomalies two other global results emerged for the averaged data from the 18 m s 7 0 aftershock sequences first for all sequences background seismicity and duration are anticorrelated graphic 1 within the framework of rate and state friction law this result supports the assertion that the observed background seismicity rate can be used as a proxy for the stressing rate dieterich 1994 second we robustly resolve the dependence of aftershock productivity on the mainshock faulting styles for example the aftershock productivity for strike slip mainshocks is on average four times smaller than the productivity of thrust faulting mainshocks 1 embed inline graphic 1 gif

magnetic data interpretation for the source edge locations in parts of the tectonically active transition zone of the narmada son lineament in central india the study has been carried out in the transition zone of the narmada son lineament nsl which is seismically active with various geological complexities upwarp movement of the mantle material into the crust through fault fractures lamination and upwelling nsl is one of the most prominent lineaments in central india after the himalaya in the indian geology the area of investigation extends from longitude 80 25 e to 81 50 e and latitude 23 50 n to 24 37 n in the central part of the indian continent different types of subsurface geological formations viz alluvial gondwana deccan traps vindhyan mahakoshal granite and gneisses groups exist in this area with varying geological ages in this study area tectonic movement and crustal variation have been taken place during the past time and which might be reason for the variation of magnetic field magnetic anomaly suggests that the area has been highly disturbed which causes the narmada son lineament trending in the ene wsw direction magnetic anomaly variation has been taken place due to the lithological variations subject to the changes in the geological contacts like thrusts and faults in this area shallow and deeper sources have been distinguished using frequency domain analysis by applying different filters to enhance the magnetic data various types of derivatives to identify the source edge locations of the causative source bodies the present study carried out the interpretation using total horizontal derivative tilt angle derivative horizontal tilt angle derivative and cos derivative map to get source edge locations the results derived from various derivatives of magnetic data have been compared with the basement depth solutions calculated from 3d euler deconvolution it is suggested that total horizontal derivative tilt angle derivative and cos derivative are the most useful tools for identifying the multiple source edge locations of the causative bodies in this tectonically active and transition zone area as this area is highly prone to hydrocarbon bearing zone hence the integrated interpretation could reliably image various thrusts and faults boundaries and the source edge locations with dip and strike orientation along with the basement lineation in encouraging exploration for better understanding of the geo scientific data

are aftershocks of large californian earthquakes diffusing we analyze 21 aftershock sequences of california to test for evidence of space time diffusion aftershock diffusion may result from stress diffusion and is also predicted by any mechanism of stress weakening here we test an alternative mechanism to explain aftershock diffusion based on multiple cascades of triggering in order to characterize aftershock diffusion we develop two methods one based on a suitable time and space windowing the other using a wavelet transform adapted to the removal of background seismicity both methods confirm that diffusion of seismic activity is very weak much weaker than reported in previous studies a possible mechanism explaining the weakness of observed diffusion is the effect of geometry including the localization of aftershocks on a fractal fault network and the impact of extended rupture lengths which control the typical distances of interaction between earthquakes

geological evolution of the manitouwadge greenstone belt and wawa quetico subprovince boundary superior province ontario constrained by u pb zircon dates of supracrustal and plutonic rocks fifty million years of archean evolution is recorded in the manitouwadge greenstone belt and the wawa quetico boundary region from ca 2720 ma volcanism and subvolcanic plutonism associated with m

multifractal analysis of the spatial distribution of earthquakes in southern italy summary we evaluate the complete spectrum of the generalized fractal dimension of the spatial pattern of microearthquakes in southern italy revealing a multifractal distribution structure our analysis is focused on the dependence of the multifractal distribution on the size of the selected area and the kind of seismicity in the area as the size of the window varies we observe that the capacity information and correlation dimensions vary significantly while both d and d remain unchanged within their errors limits we interpret this result in terms of the observation that our data are mainly clustered around a linear fault the sisifo fault when we restrict the selected windows around the fault clustering around a line the fault is highlighted the capacity dimension changes from about 1 8 to about 1 4 and the correlation dimension decreases because we observe in detail the clustering of the seismicity along the fault which approximates the maximum intense clustering of the whole data set although our results are strongly influenced by the fact that the data are dominated by the epicentres located on the fault we can conclude that multifractal analysis can be a very useful tool to discriminate the seismicity linked to a particular fault in a given area

metamorphic history of the hemlo gold deposit from al2sio5 mineral assemblages with implications for the timing of mineralization textural relations between al2sio5 phases and deformation fabrics provide constraints on the metamorphic history of the hemlo gold deposit kyanite in the deposit is most common within and on the margins of boudinaged quartz realgar veins and less commonly as rotated porphyroblasts within the matrix of schistose rocks kyanite predates the main d2 schistosity sillimanite postdates kyanite occurring irregularly as discrete knots and foliae that run parallel to but sometimes cut across the principal d2 foliation indicating that sillimanite postdates the d2 foliation we regard kyanite to be part of the peak metamorphic assemblage with sillimanite representing a partial later overprint most likely related to fluid infiltration rare andalusite occurs in two associations as late stage clean idioblastic crystals and as large fractured grains locally overprinted by sillimanite in boudinaged quartz realgar veins we suggest two possible origins for this second form of andalusite one involving generally late growth the second involving early growth prior to the development of peak metamorphic kyanite although not unambiguous we prefer the second scenario p t conditions from petrogenetic grid constraints and new geothermobarometric estimates indicate 6 7 gpa 600 650 c for the peak kyanite grade metamorphism ca 2677 ma and 4 5 gpa 600 c for the later sillimanite overprint ca 2672 ma we see these two events as part of an evolving p t path in a single metamorphic event in our early andalusite scenario the andalusite may have formed from pyrophyllite breakdown at 2 4 gpa 450 c possibly associated with emplacement of the regional suite of granodiorite plutons ca 2686 ma late andalusite formed sporadically on the retrograde path the occurrence of deformed andalusite and aligned kyanite in and on the margins of boudinaged auriferous realgar stibnite quartz veins provides evidence in support of a premetamorphic mineralization event

chromium isotope fractionation during oxidative weathering implications from the study of a paleoproterozoic ca 1 9ga paleosol schreiber beach ontario canada abstract this study reports detailed stable cr sm nd and rb sr isotope data for a ca 1 9 ga old subaerial weathering profile at schreiber beach ontario canada from which detailed major and trace element signatures and 18 o values were previously reported the weathering profile developed on neoarchean 2 7 ga pillow basalts and is unconformably overlain by the paleoproterozoic 1 88 ga gunflint chert and basal conglomerates this stratigraphy suggests that the basalts were uplifted and subaerially weathered prior to deposition of the gunflint formation the aim was to investigate the behaviour of chromium during ancient weathering processes and to contribute to the question whether or not stable isotope fractionation accompanied the release of chromium from the weathering rocks at times when atmospheric oxygen was supposedly high enough in a period following the great oxygenation event goe 2 45 ga ago and prior to the deposition of the gunflint cherts at 1 82 ga these iron rich cherts belong to one of the last regionally extensive banded iron formations bifs deposited before the 1 billion year long mesoproterozoic period during which a drastic change in ocean chemistry prevented deposition of bifs the gradual textural mineralogical and geochemical changes from unweathered basalts to strongly weathered hematite bearing basalts with increasing stratigraphic height are associated with shifts in the chromium isotope compositions the 53 cr value of unweathered pillow basalt cores 0 19 0 02 2 is within the range of mantle inventory values whereas weathered brown to green basalts soils exhibiting up to 30 lower cr concentrations compared to unweathered pillow cores are isotopically lighter 53 cr 0 35 0 11 in contrast red hematite rich basalts and hyaloclastites underlying the brown to green basaltic soils with the highest 18 o enrichment in the profile are isotopically heavier 53 cr 0 05 0 15 rb sr isotope data of weathered basalts define a correlation line with a slope corresponding to an age of 1574 24 ma mswd 13 which we interpret to reflect a diagenetic event accompanied by alkaline metasomatism during subsidence burial of the gunflint basin the non correlation of k enrichment factors with 53 cr 18 o and other major and trace elements in the weathered rocks indicates that alkaline metasomatism did not affect the geochemical signatures produced during in situ subaerial weathering instead correlations between 53 cr and 18 o and between 53 cr ce ce u and v indicate coupled mobilization of the redox sensitive elements during oxidative processes and their partial re deposition at depth from high 18 o freshwaters partial re precipitation of heavy cr at depth can be explained on the basis of the weak positive correlation between 53 cr and fe enrichment factors it is seen as a consequence of the reduction of mobile cr vi and co precipitation as mixed fe iii cr iii oxhydroxides during contemporaneous oxidation of the fe 2 bearing groundwaters at depth a process similar to the one governing the deposition of most precambrian bifs redistribution of certain elements during the weathering process in this case rees is furthermore indicated by a correlation line in a sm nd isochron diagram defined by the schreiber beach data with a slope corresponding to an age of 1 93 0 19 ga mswd 26 an age which is compatible with the direct geological constraints for the timing of the paleosol formation at this locality an oxidative atmosphere at 1 9 ga as implied by the results from the schreiber profile is furthermore supported by positively fractioned cr isotopes 53 cr from 0 06 to 0 39 recorded in the iron rich gunflint cherts directly above the palaeo weathered horizons at schreiber beach these values are interpreted to stem from a positively fractionated shallow seawater chromium composition at 1 88 ga potentially reflecting a continental run off characterized by positive 53 cr and are in accordance with cr isotope signatures in worldwide bifs including the gunflint iron formation our results show the potential of cr isotope studies on ancient paleosols to untangle the presence of oxidative weathering processes making this isotope system a viable and important tracer for the reconstruction of surface oxygenation in earth s history

shebandowan greenstone belt western superior province u pb ages tectonic implications and correlations the shebandowan greenstone belt of the western wawa subprovince consists of successions of volcanic and sedimentary rocks impinging onto the metasedimentary quetico subprovince to the north and cored by a batholithic complex to the south u pb geochronology using mainly zircon and titanite demonstrates a relatively rapid accretion of the greenstone belt in the late archean the oldest ages were obtained for 2750 ma tonalitic gneiss and sporadic 2830 2750 ma detrital or xenocrystic zircons a major phase of greenstone belt construction at 2720 ma formed ultramafic to felsic volcanic rocks and peridotitic gabbroic and anorthositic bodies probably in an extensional arc backarc setting these units are laterally correlative with volcanogenic massive sulfide bearing assemblages in the central wawa subprovince and probably with similar successions in northern minnesota the second major stage of felsic volcanism and plutonism at about 2695 ma was associated with d 1 compression causing thrusting imbrication and sedimentation this was succeeded by the deposition of an unconformable sequence of calc alkalic to alkalic volcanic and sedimentary rocks and emplacement of tonalitic to syenitic plutons at about 2690 ma transpressive deformation d 2 constrained between 2685 and 2680 ma caused the development of locally penetrative structures and deposition of clastic sedimentary packages the emplacement of plutons at 2683 2680 ma concluded the evolution of the greenstone belt titanite and rutile yield ages in the same range as zircon showing that the greenstone belt was situated at high crustal levels by 2680 ma and escaped the younger and intense deformational metamorphic events recorded in greenstone belts farther east in the central wawa subprovince as well as in the immediately adjacent migmatitic quetico subprovince to the north

long term earthquake clustering summary we analyse statistically the long term properties of several instrumental earthquake catalogues complete catalogues exhibit both short and long term clustering for earthquakes of all depth ranges after accounting for the effect of short term clustering we find that in residual declustered catalogues long term clustering not periodicity characterizes the occurrence of all earthquakes shallow intermediate and deep the degree of clustering in residual catalogues is the same for earthquakes in different depth ranges circumstantial evidence indicates that the long term v ariation of seismicity is governed by a power law temporal distribution as in short term clustering it is scale invariant the fractal dimension of an earthquake set on the time axis is of the order of 0 8 0 9 therefore mainshock occurrence is closer to a stationary poisson process than standard aftershock sequences of shallow earthquakes

recurrent patterns in the spatial behaviour of italian seismicity revealed by the fractal approach three are the essential parameters needed to describe seismicity the b value of the gutenberg richter relation and the spatial and temporal fractal dimensions ds and dt several cases have been reported when a significant decrease in the b value or in the spatial fractal dimension preceded major earthquake sequences or aftershocks here we use the fractal method based on the correlation integral to study the temporal changes in the spatial 2 d distribution of earthquakes in three important seismic zones of italy in all three zones ds shows significant variability which correlates well with the major events and clearly marks the beginning and the end of an earthquake cycle finally the nucleation of most major events is associated with a fractal dimension value which corresponds to the topological dimension of a plane

magnitude of completeness b value and spatial correlation dimension of earthquakes in the south baikal basin baikal rift system abstract magnitude of completeness b value and correlation dimension of spatial epicenter distribution were estimated for the south baikal basin using earthquake catalogue for the period of digital observations all estimated parameters were mapped with a one for all approach that allowed revealing their spatial variability the value of the completeness magnitude which was evaluated on the frequency magnitude distribution was found to range from mc 1 0 to 1 6 over the basin depending on network configuration change with the average value of 1 1 0 1 then b value in the gutenberg richter relation was estimated by maximum likelihood method based on the catalogue with m 1 1 earthquakes the lower b value 0 81 0 03 was revealed for the southern part of the basin which is under transtension stress regime in contrast to pure extension characteristic for the rest of the territory the higher b value 1 01 0 01 was obtained for the area to the north east of the selenga delta where two of the largest baikal earthquakes occurred in the last 150 years and which is characterized by more heterogeneous crust structure correlation dimension in the southern part of the basin was found to be closed to 1 that is interpreted as a tendency of epicenters to be distributed along a line whereas the central part is characterized by a higher value that corresponds to a tendency of epicenters to be distributed over a plane rather than along lineaments a comparison of the southern and central basins which make up the tectonically single south baikal basin shows that seismicity of the central basin is characterized by higher b values and correlation dimension that may imply different stress level and or faulting type

spatio temporal analysis of stress diffusion in a mining induced seismicity system the spatio temporal correlation of micro earthquakes occuring in a mining induced seismic system creighton mine ontario canada is investigated it is shown that when considering only the after events correlated to a main event i e not accounting for the uncorrelated regime of background activity the spatial distribution of these after events occuring at t after the main event change with t this change takes the form of an expanding pattern characterized by a typical scale l c t varying as l c t similar to t h h being estimated to 0 18 this diffusion exponent is found to increase when considering only a subset of the most energetic events as mainshocks we interpret this result as the indication of a stress sub diffusion mechanism involving propagation on the heterogeneous fractal fault network

observation of diffusion processes in earthquake populations and implications for the predictability of seismicity systems scale invariance either in space or in time has been shown in many papers to characterize earthquake distributions unfortunately little work has been dedicated to looking at the general space time scaling invariance of seismicity systems even though a better understanding of how the two domains spatial and temporal link together could help the development of the stochastic dynamical modeling of earthquake populations in this paper we report the observation of diffusion processes of temporally correlated seismic activity for three different data sets a mine creighton mine canada the long valley caldera in eastern california and a 7 year period of recorded seismic activity in southern california the observed subdiffusion processes are indicative of the general space time scaling of the system taking the form of a slow power law growth r t similar to t h of the mean distance r t between the main event arid the temporally correlated afterevents occuring after a delay t h is found on average to be small 0 1 for creighton mine 0 22 for the long valley caldera and 0 22 for the southern california main events with magnitude greater than or equal to 1 5 but fluctuates significantly from one main event to the other the diffusion is found to be intermittent non gaussian and multiscaling and except for the long valley caldera a systematic correlation between the sizes of the main event and subsequent afterevents and the growth exponent h is observed while classical viscous relaxation models e g elastic listhosphere plastic asthenosphere coupling or fluid flow triggered by sudden changes in pore pressure have been proposed to characterize this relaxation by homogeneous i e nonintermittent normal h 0 5 diffusion processes the direct implication of the reported results is that seismicity systems at spatial scales from meters to hundreds of kilometers and small microearthquakes in a mine to intermediate magnitudes relax spatiotemporally in a nonelastic way revealing the stochastic space time scale invariant nature of such systems since these diffusion processes correspond to a loss of information with time on the location of the main event they can be used to investigate the limits of predictability at all spatial scales of seismicity systems in terms of the spatiotemporal clustering of temporally correlated earthquakes

archaean crustal growth processes in southern west greenland and the southern superior province geodynamic and magmatic constraints abstract eo to mesoarchaean greenstone belts e g 3800 3700 ma isua c 3075 ma ivisaartoq 3071 ma qussuk occur within orthogneisses of the southern west greenland craton greenstone belts are composed mainly of metavolcanic rocks with minor ultramafic and sedimentary schists compositionally volcanic rocks are dominantly tholeiitic basalts boninites and picrites with minor intermediate to felsic volcanic rocks these greenstone belts appear to have formed in convergent margin geodynamic settings detailed field observations contrasting ages and metamorphic and structural histories suggest that this craton was assembled in several accretionary tectonothermal events involving accretion of arcs back arcs forearcs and continental fragments by horizontal tectonics the superior province of canada was also built by the amalgamation of oceanic and continental fragments ranging in age from 3700 to 2650 ma during five discrete tectonothermal events over 40 ma between 2720 and 2680 ma the neoarchaean 2750 2670 ma wawa greenstone belts are composed of tectonically juxtaposed fragments of oceanic plateaux oceanic island arcs back arcs and siliciclastic trench turbidites following juxtaposition these diverse lithologies were collectively intruded by syn to post kinematic granitoids with subduction zone geochemical signatures oceanic island arc lavas are easily distinguished from oceanic plateau counterparts because they possess positively fractionated rare earth element la sm cn 1 and gd yb cn 1 and high field strength element depleted nb th pm pm c 1000 km scale subduction accretion complex that formed along an intra oceanic convergent plate margin during trenchward migration of the magmatic arc axis several first order geological observations on archaean greenstone belts of sw greenland and the superior province suggest that phanerozoic style plate tectonic models can provide an elegant explanation for their structural lithological metamorphic and geochemical characteristics

possible effects of erosional changes of the topographic relief on pore pressures at depth formation fluid pressures are said to be anomalous or abnormal if they differ from hydrostatic for the depth considered explanations of the origin and maintenance of anomalies seldom include the possibility of delayed adjustment of subsurface pore pressures to erosional modifications of the topographic relief yet the present paper shows that it is entirely possible for subaerial erosion to generate pore pressure changes at great depths by cross formational energy transfer in realistic field conditions conversely pressures may survive changes in the topography and be in a transient state for hundreds to millions of years thus appearing anomalous at the time of observation according to calculations for the red earth region in alberta canada present pore pressures in the devonian immediately above the precambrian basement at a depth of approximately 1400 meters may have been induced originally by erosionally shaped topography during pliocene times 12 to 1 m y b p but be adjusting now to new boundary conditions created by the erosional exposure of the sub cretaceous unconformity a 12 adjustment may already have taken place during the last 300 thousand years leaving nearly 90 of pliocene age pressures to survive to date as slowly decaying transient pressure relicts of the geologic past in view of the possible erosional effects on pore pressures demonstrated in this paper the question of anachronous formation pressures may deserve consideration in problems related to deep basin hydrology including regional groundwater resource development migration and accumulation of hydrocarbons radioactive waste isolation dating of various geologic events and so on

the late archean hemlo gold deposit ontario canada a review and synthesis abstract the hemlo gold deposit northwestern ontario canada is situated within the late archean hemlo heron bay greenstone belt of the wawa subprovince of the superior province the greenstone belt represents an ancient volcanic island arc and has subsequently been subjected to a complex history of evolution including two episodes of regional metamorphism three main pulses of granitoid plutonism and four generations of structures related to two major deformational events the main second regional metamorphism was a low p t event and generally belonged to greenschist amphibolite transition facies but climaxed at middle amphibolite facies along both margins and the central axis of the greenstone belt the hemlo gold deposit is located within the central metamorphic zone of middle amphibolite facies the main orebody contains approximately 80 mt of ore averaging 7 7 g t au and is 2900 m along strike 1300 m down dip and 3 to 45 m thick additional gold mineralization extends sporadically and discontinuously westward and includes the c zone of the williams mine and the north south and highway zones of the golden sceptre resources limited property the main orebody and north zone are contained within a major shear zone proximal to a lithological contact between structurally underlying felsic rocks and overlying metasedimentary rocks the c and south zones are entirely within the felsic rocks and commonly are present as intensively sheared and altered lenses the hemlo deposit is enriched in as ba hg mo s sb te tl and v its economic gold concentrations correlate with the isotopic compositions of sulphide minerals but not their total abundances the hemlo gold deposit is characterized by intensive and extensive hydrothermal alteration including potassic alteration calc silicate alteration sulphidation and less significant silicification tourmalinization and carbonatization field occurrence textural relationships quantitative p t x t data from mineral equilibria oxygen isotope geothermometry fluid inclusion microthermometry and u pb and 40 ar 39 ar geochronology suggest a protracted history of hydrothermal activity which commenced with an earlier calc silicate alteration 550 c and 3 4 kbar 2678 2676 ma immediately after the peak of the second regional metamorphism followed by pervasive potassic alteration mica schists and microcline rich rocks 450 500 c 2672 2670 ma and terminated with a later low to very low grade calc silicate alteration 200 400 c 1 2 kbar and 2643 2632 ma there remains uncertainty among investigators regarding the timing and style of gold mineralization of the hemlo deposit consequently many ore forming processes have been proposed for its origin including syngenetic metamorphic replacement and porphyry models suggesting gold mineralization either pre dating or during the second regional metamorphism and also structural and hot spring epithermal models indicating mineralization post dating the second regional metamorphism we suggest that the deposition of metals and sulphides in the hemlo deposit is most consistent with a multistage late replacement model the hemlo shear zone was activated as a regional planar structure during the second regional metamorphism and became a conduit for regional fluids during periods of dilatancy orogenic activity was protracted and fluids focused along the conduit could have been variously of metamorphic and magmatic origin at different stages in the development of the hemlo deposit gold mineralization most likely occurred during the late calc silicate alteration event about 40 ma after the second regional metamorphism

multifractal patterns of seismicity spatial distribution of earthquake epicentres is investigated using a multifractal approach involving a whole spectrum of non integer dimensions of the set under consideration the multifractal approach allows to analyze not only geometrical characteristics of the spatial distribution but also intensities of seismicity at particular sites or probabilities of visiting particular sites by seismic events multifractal characteristics spectra of dimensions f and d q are calculated for three seismic regions pamir caucasus and california the functions f and d q contain information about concentration clustering properties and intermittency of spatial earthquake distribution

spatial distribution of aftershocks and background seismicity in central california we examine the spatial distribution of earthquake hypocenters in four central california areas the aftershock zones of the 1 1984 morgan hill 2 1979 coyote lake and 3 1983 coalinga earthquakes as well as 4 the aseismically creeping area around hollister the basic tool we use to analyze these data are frequency distributions of interevent distances between earthquakes these distributions are evaluated on the basis of their deviation from what would be expected if earthquakes occurred randomly in the study areas we find that both background seismic activity and aftershocks in the study areas exhibit nonrandom spatial distribution two major spatial patterns clustering at small distances and anomalies at larger distances are observed depending on tectonic setting while both patterns are seen in the strike slip environments along the calaveras fault morgan hill coyote lake and hollister aftershocks of the coalinga event a thrust earthquake seem to be characterized by clustering only the spatial distribution of earthquakes in areas gradually decreasing in size does not seem to support the hypothesis of a self similar distribution over the range of scales studied here regardless of tectonic setting spatial distributions are independent of magnitude for the coalinga aftershocks but events in strike slip environments show increasing clustering with increasing magnitude finally earthquake spatial distributions vary in time showing different patterns before during and following the end of aftershock sequences

temporal variation of multifractal properties of seismicity in the region affected by the mainshock of the october 6 2000 western tottori prefecture japan earthquake m 7 3 1 the temporal variation of multifractal properties in spatial distribution of seismicity in the region affected by the main shock of the western tottori prefecture japan earthquake of october 6 2000 m 7 3 and its aftershock sequence are investigated we use earthquake catalog data from 1985 to 2001 in order to understand the process and mechanism preceding a large shallow earthquake a monotonous decrease of multifractal dimension dq with a wide range of q appeared clearly for about two years prior to this large shallow earthquake dq then increased to a maximum at the time of the main shock during the aftershock sequence dq oscillated between 2 0 and 0 7 the decrease and then increase of dq with respect to the spatial distribution of seismic events indicate clustering and declustering in multifractal structure respectively the temporal variation of dq reflects the accumulation and release of strain energy within the tectonic stress field

fractal characterization of the south australian gravity station network summary the spatial distribution of the south australian gravity station network over 65 000 stations can be approximated by a fractal point set of correlation dimension dc 1 4 the fractality is established over more than 2 decades of distance the fractal nature of the grid is possibly due to the multistage decisions involved in establishing a network in each step previously unexplored areas are dissected by geophysical traverses as in the classical fractal fragmentation process it is shown that we cannot observe the short wavelength components of the gravity field if the dimension of the network is less than two and any attempt to interpolate onto a regular grid could lead to spurious anomalies due to aliasing

synchronous vertical and horizontal tectonism at late stages of archean cratonization and genesis of hemlo gold deposit superior craton ontario canada the hemlo gold deposit 700 t au northwestern ontario canada is hosted in a shear zone in the hemlo greenstone belt which is a synclinal keel between two granitoid domes the dome and keel structure formed by diapirism and sagduction vertical tectonism that was synchronous with regional horizontal shearing horizontal tectonism mineralization occurred during shearing and mineralizing fluids probably had a magmatic source that is interpreted to be related to syntectonic mantle derived granodiorite sanukitoid intrusions the gold deposit the intrusions and the hosting shear zone all developed within a regime characterized by synchronous vertical and horizontal tectonism they were all possibly linked to a range of processes associated with the accretionary growth and stabilization of the craton in particular slab breakoff and the associated extensional orogenic collapse following terrane accretion

fractal properties of seismicity in regions affected by large shallow earthquakes in western japan implications for fault formation processes based on a binary fractal fracture network model 1 the temporal variation in the b value which is defined as the slope of the gutenberg richter frequency n magnitude m relationship log n a bm and the multifractal dimension of the spatial distribution dq of seismic activity are analyzed using earthquake catalog data for regions affected by two recent large earthquakes in japan an anomalous decrease in dq and an increase in b value appear as a common seismic rupture response during the period of decreasing seismic energy release in the lead up to these large shallow earthquakes the change in fractal dimensions of faults inferred from sequential seismic events reflects the transition of fracture from a dispersive rupture process to an anomalous rupture process and shows that the growth of the fault network through fault linkage is abruptly restrained in the fault formation process leading up to the main shock the anomalies in the fractal and multifractal dimensions prior to large earthquakes indicate that the anomalous activation and clustering of smaller earthquakes represents criticality of the state around asperities along a fault

mantle derived archaean monozodiorites and trachyandesites the 2 680 2 750 myr old1 5 intrusive granite greenstone terranes6 8 in the rainy lake region ontario and in and adjacent to the vermilion district minnesota of the superior province in north america include a wide variety of volcanic and intrusive rocks with initial pb sr and nd isotope ratios close to those for the mantle4 5 9 12 the isotopic constraints require the production of large volumes of silica oversaturated magmas from silica undersaturated mantle within 100 200 myr we present here geochemical data on monzodiorites and trachyandesites from the rainy lake area which are strongly enriched in large ion lithophile elements lile we conclude that they are derived by direct melting of the mantle at depths of 50km in either anhydrous or hydrous conditions their rare earth element ree abundances and initial 143nd 144nd ratios suggest that their mantle sources were enriched in lile shortly before melting the monzodiorites trachyandesites and their granodioritic derivatives may comprise up to 20 of the exposed igneous rocks in the rainy lake region and vermilion district if these rocks are as abundant in other archaean terranes a significant part of the early continental crust could have formed by direct melting of lile enriched mantle

evolution and tectonic significance of intermediate to felsic plutonism associated with the hemlo greenstone belt superior province canada abstract plutonic rocks from the hemlo area in the southern superior province span a period from ca 2720 to 2677 ma early ttg plutons intruded into lower basaltic volcanic sequences and were probably derived from melting of basaltic crust at upper mantle depths they predate major regional deformation and span ages from 2719 to 2697 ma felsic to intermediate volcanism 2697 2688 ma partially overlaps ttg plutonism but is mostly slightly younger and lacking plutonic equivalents regional deformation and metamorphism of the greenstone belt and ttg plutons progressed rapidly following deposition of the youngest supracrustal rocks syn to late tectonic plutons emplaced between 2684 and 2677 ma have a distinctive dual primitive evolved character that is interpreted to reflect their derivation by direct melting of long term depleted mantle that was metasomatically enriched in a wide range of lile and hfse this secular evolutionary change in the nature of intermediate to felsic plutonism at hemlo and its relationship to regional deformation and metamorphism parallels that occurring more regionally within the superior province and is interpreted to be the consequence of a transition in the nature of large scale tectonic processes intermediate to felsic magmatism within a protracted period of volcanism and ttg plutonism originated primarily by melting of subducted basaltic crust probably in an oceanic arc related environment the termination of this style of magmatic activity and initiation of regional deformation and metamorphism at ca 2688 ma is interpreted to be a consequence of collisional orogeny the petrogenetic characteristics of the latest period of magmatism at 2684 2677 ma requires that the melting regime migrate into sub arc lithospheric mantle that was metasomatized during the earlier magmatic stage slab breakoff following terrane accretion is suggested as one possible mechanism for the abrupt termination of ttg magmatism and ensuing rapid and progressive introduction of large amounts of heat into sub arc mantle and basal portions of the crust this pattern of development is seen in many superior province greenstone belts but is older in the north therefore it is probably an inevitable consequence of the tectonic processes that led to accretion of the superior province

multifractal analysis of earthquakes multifractal properties of the epicenter and hypocenter distribution and also of the energy distribution of earthquakes are studied for california japan and greece the calculateddq q curves the generalized dimension indicate that the earthquake process is multifractal or heterogeneous in the fractal dimension japanese earthquakes are the most heterogeneous and californian earthquakes are the least since the earthquake process is multifractal a single value of the so called fractal dimension is not sufficient to characterize the earthquake process studies of multifractal models of earthquakes are recommended temporal changes of thedq q curve are also obtained for californian and japanese earthquakes thedq q curve shows two distinctly different types in each region the gentle type and the steep type the steeptype corresponds to a strongly heterogeneous multifractal which appears during seismically active periods when large earthquakes occur dq for smallq or negativeq is considerably more sensitive to the change in fractal structure of earthquakes thandq forq 2 we recommend use ofdq at smallq to detect the seismicity change in a local area

scale invariance properties in seismicity of southern apennine chain italy advanced statistical methodologies have been applied to detect temporal and spatial scaling invariance laws in seismicity observed in a seismogenetic area of the southern apennine chain which in past and recent years was devastated by destructive events a deeper analysis of the seismicity observed in this area during the period 1983 1995 is presented a counting statistical procedure has been applied to highlight scaling laws in the time domain and a fractal approach has been carried out to reveal spatial self similarity the main features of the dynamic system under study have been depicted using the key parameters of the more recurrent scaling laws observed in the spatial and temporal domains and we point out that the seismotectonic environment of the southern apennine chain can be considered as an extended dissipative system the comparative analysis of different dynamical parameters of earthquake sequences provides a more comprehensive evaluation of seismotectonic processes in the investigated area

the hemlo gold deposit ontario an example of melting and mobilization of a precious metal sulfosalt assemblage during amphibolite facies metamorphism and deformation the timing of mineralization at the hemlo gold deposit has long been a controversial issue we present arguments that use partial melting of the ore assemblage to explain the mechanism of ore mobilization and resolve problems with the model of premetamorphic mineralization the results have implications for mine exploitation and exploration strategies we show that the ore mineral assemblage underwent partial melting during middle amphibolite facies metamorphism 600 650 c 6 7 kbars primarily through breakdown of stibnite and arsenopyrite in a high s2 environment concurrent deformation led to segregation of the resulting sb and as rich sulfosalt melt interaction between this melt and a range of unmelted sulfides led to further melting and incorporation of other elements into the melt the gold bearing melt was mobilized from compressional high strain sites into dilational domains such as boudin necks and extensional fractures developed in competent lithologies ore minerals that did not melt significantly pyrite molybdenite pyrrhotite and sphalerite were not extensively mobilized and largely remained within high strain compressional domains this segregation of melt from residue thus resulted in the observed heterogeneous distribution of ore minerals within the deposit crystallization of the sulfosalt melt produced a diverse suite of ore minerals dominated by stibnite and realgar and containing an array of rare sulfosalts native elements intermetallic compounds and tellurides some sulfosalt melt persisted to low temperature 300 c allowing continued small scale localized mobilization during late deformation although gold occurs at moderate concentrations within the compressional high strain domains it is particularly concentrated in the dilational domains a consequence of its mobilization within a sulfosalt melt our model of partial melting of the ore mineral assemblage with consequent mobilization explains how ore minerals that are unstable even at greenschist facies conditions came to be hosted in structures that formed at or near the peak of amphibolite facies metamorphism

petrogenesis and geodynamic setting of the neoarchaean haines gabbroic complex and shebandowan greenstone belt southwestern superior province ontario canada abstract the 2722 2 ma archaean megacrystic anorthosite bearing haines gabbroic complex in the wawa subprovince of the western superior province formed contemporaneously with the spatially associated greenwater assemblage of the shebandowan greenstone belt ontario canada both field and petrographic observations indicate that the haines gabbroic complex and the spatially and temporally associated ultramafic to intermediate volcanic and intrusive rocks of the greenwater and burchell assemblages experienced extensive metamorphic recrystallization and alteration as a consequence of greenschist facies metamorphism these metamorphic processes resulted in pervasive replacement of igneous minerals by metamorphic counterparts metamorphic alteration also mobilised lile and transition metals and slightly reset the u th pb and sm nd isotope systems consequently the haines gabbroic complex and greenwater assemblage have respective sm nd errorchron ages of 2765 110 280 ma and 3108 120 380 ma major and trace element compositions suggest that the least altered anorthosites leucogabbros and gabbros of the haines gabbroic complex are not cogenetic with the greenwater and burchell assemblages and have distinct parental magmas and depleted mantle sources the calc alkaline andesites of the burchell assemblage the tholeiitic basalts and gabbros of the greenwater and burchell assemblages the transitional gabbros of the greenwater and burchell assemblages and the picrites serpentinites and peridotites of the greenwater assemblage are all petrogenetically distinct and have different parental magmas and depleted mantle sources the pyroxenites are genetically distinct from the other greenwater assemblage lithologies the burchell assemblage and the haines gabbroic complex the haines gabbroic complex crystallised from hydrous ca and al rich tholeiitic parental magmas that fractionated from more primitive hydrous boninitic parental magmas the initial end values of the haines gabbroic complex end 3 0 to 4 1 and the greenwater end 1 8 to 4 1 and burchell end 2 0 to 3 7 assemblages are indicative of variably depleted mantle sources the major and trace element characteristics of the haines gabbroic complex and the greenwater and burchell assemblages and geological relationships indicate that they formed in a japan style mature intra oceanic continental arc with a large volume of ttgs intra oceanic arc rifting was most likely triggered by slab rollback followed by mantle plume emplacement on the basis of rock association and geochemical data we suggest that the haines gabbroic complex and the greenwater and burchell assemblages represent a dismembered subduction related archaean ophiolite that marks a neoarchaean suture zone between the wawa and wabigoon subprovinces

age and tectonic setting of the jingangku besshi type volcanogenic massive sulfide deposit from the northern shanxi north china craton abstract the jingangku volcanogenic massive sulfide deposit is one of the largest archean deposits in china it is located in the wutai greenstone belt in the northern part of the central orogenic belt in the north china craton the deformed deposit is hosted in a suite of neoarchean metamorphosed volcano sedimentary rocks mica quartz schist plagioamphibolite plagioclase schist and bif the orebodies are characterized by massive pyrite and contain varied amounts of chalcopyrite pyrrhotite and sphalerite the country rock of the jingangku vms ores shows intense chloritization silicification sericitization and carbonation the vms hosted pyrite and copper deposit is represented by the jingangku deposit that yielded a la icp ms zircon age of 2500 15 ma mswd 0 87 the other two vms hosted pyrite and copper deposits are represented by the houping and haoditang deposits that formed between 2494 ma and 2507 ma the late neoarchean vms deposits can be interpreted to have formed in a forearc setting and subsequently tectonically transported in melange belts during continental collision quite similar to the younger besshi type deposits in japan analyses of fluid inclusions from ore bearing magnetite quartzite showed the composition of metamorphic fluid to be h2o nacl co2 ch4 n2 h2 the analysis also showed that during the peak of metamorphism the fluid was characterized by medium high temperature 322 473 and low salinity 2 2 6 74 sulfide orebodies are closely associated with the magnetite quartzite and therefore it is proposed that both the sulfide and magnetite quartzite were derived from the same material source and have the same formation age and underwent the same history of deformation and metamorphism consequently the jingangku deposit most likely formed from submarine exhalative sedimentation and later superimposed and transformed by metamorphic fluid

u pb zircon geochronology in the southwestern abitibi greenstone belt superior province the abitibi belt is the largest continuous greenstone belt in the superior province of the canadian shield it comprises several composite komatiitic tholeiitic calc alkalic and sedimentary sequences that are folded transected by major faults and intruded by various generations of plutonic rocks precise u pb geochronology has been carried out in the belt for the past decade to solve chronostratigraphic and metallogenetic problems this paper presents new zircon ages and reassesses previously published ones now refined by the addition of abraded and concordant zircon analyses volcanic and subvolcanic units of the timmins area yield the following ages 2727 1 5 ma for a tuff of the upper deloro formation 2703 1 5 ma for a tuff of the upper tisdale formation and 2698 4 ma for the krist fragmental assigned to the top of the tisdale formation the age of a dunite intrusive into the upper deloro formation is revised at 2707 3 ma whereas the aquarius diorite east of timmins yields a poorly define

mineral equilibria and zircon garnet and titanite u pb ages constraining the ptt path of granite related hydrothermal systems at the big bell gold deposit western australia the big bell deposit 75 t gold is located in a narrow spur of the meekatharra greenstone belt yilgarn craton western australia two ore bodies are located in a calcic potassic contact alteration zone overprinting lineated granodiorite dykes and amphibolite almandine cummingtonite hornblende skarn 1 3 g t au 1700 g t as 330 g t w and the muscovite microcline gneiss 3 5 g t au 580 g t sb 620 g t w of the main lode genetic models vary from pre to post metamorphic replacement hornblende plagioclase pairs in amphibolite constrain peak metamorphic temperature to 670 50 c in contrast garnet biotite thermometry provides estimates of 578 50 and 608 50 c for garnet cordierite biotite schist bordering the skarn and enveloping the main lode garnet cordierite and garnet hornblende pairs extend the range of fluid temperature to 540 65 c well below peak metamorphic temperature at 540 600 c the alteration assemblage andalusite sillimanite constrains pressure to 300 400 mpa corresponding to 11 14 km crustal depth published u pb ages indicate that metamorphism took place in the aureole of the southeast granodiorite tonalite batholith 2740 2700 ma followed by gold mineralization at 2662 5 ma and by the emplacement of biotite granite and sn ta nb granite pegmatite dykes at 2625 2610 ma amphibolite xenoliths in granite northwest of the deposit record the lowest temperature 628 50 c suggesting it lacks a metamorphic aureole the rare metal dykes are spatially associated with epidote albite and andradite diopside skarns 1 5 g t au mined where enriched in the weathered zone we analysed hydrothermal zircon intergrown with andradite concordant u pb ages of 2612 7 and 2609 10 ma confirm the presence of a second granite related system the zircons display oscillatory zoning and have low th u ratios 0 05 0 08 low th titanite from an albite granite dyke has a concordant but reset u pb age of 2577 7 ma

structural analysis of hypocentral distribution of an earthquake sequence using anisotropic wavelets method and application 1 spatial organization of earthquake sequences is investigated to localize active rupture planes and to reconstruct the geometry of the inferred rupture zone we have developed a new approach the normalized optimized anisotropic wavelet coefficient noawc method to extract from a set of hypocenters the active ruptures planes our approach permits the detection of organized structures within a plane regardless of its size location shape anisotropy and orientation it includes the determination of a system of three perpendicular sections minimizing the effects of projections of the hypocenters and intrinsically accounts for uncertainty in the location of the seismic events the accuracy and the effectiveness of the noawc procedure are illustrated on both synthetic and real data an application to the m 5 1 arudy french pyrenees aftershock sequence shows how a combination of the possible mathematically reconstructed geometries can be combined with the available fault plane solutions and geomorphological markers to determine the active rupture planes and to propose and validate a local tectonic model this new multitool approach lends itself to quantitative and computer assisted analyses of large data sets