the peraluminous aurumina granite suite in central brazil an example of mantle continental crust interaction in a paleoproterozoic cordilleran hinterland setting abstract peraluminous granites and tonalites granodiorites of the aurumina suite crop out in the external zone of the brasilia fold belt on the western margin of the sao francisco craton rocks of this suite intrude retrograde medium grade schists and paragneisses of the ticunzal formation and display a magmatic muscovite biotite garnet assemblage and discrete graphite lamellae the suite is divided into six members au1 through au6 which grade from synkinematic to post kinematic in character with ages spanning from 2 11 to 2 16 ga according to zircon u pb data compositional features of the aurumina suite and associated coeval metaluminous mafic to intermediate plutons suggest an origin by source hybridization processes characterized by reaction between metasedimentary rocks and basaltic melts that would have taken place at shallow depths pressure

regional scale pressure shadow controlled mineralization in the principe orogenic gold deposit central brazil abstract the principe gold deposit situated in the natividade gold district resulted from establishment of the regional transbrasiliano strike slip system during the late neoproterozoic brasiliano event the host rocks however were formed in the paleoproterozoic with sm nd model ages from 2250 to 2500 ma therefore the principe gold deposit is epigenetic the local lithological association is a tonalitic granodioritic suite formed in an island arc environment that later experienced continental collision tectonics leading to the intrusion of the peraluminous principe granite with an age of 2169 42 ma by zircon u pb during the neoproterozoic these units underwent deformational greenschist facies metamorphism and hydrothermal alteration forming metamorphic tectonites inside the principe granite and hydrothermally altered rocks at the northern termination of the granite where the principe gold deposit is located a strong structural control is identified in the deposit with n10 w n20 e trending brittle ductile shear zones that are visible at all scales from thin sections to regional satellite images these shear zones played an important role in the formation of the deposit acting as pathways that promoted a channelized fluid flow to metal precipitation sites hydrothermal alteration processes of different grades occur along these structures mainly characterized by saussuritization biotitization chloritization sericitization carbonatization silicification and sulfidation reactions producing a neoformed mineral assemblage the principe granite acted as a regional scale porphyroclast for migration of the hydrothermal solutions as well as deformation forming two pressure shadows that acted as structural traps for the ore as stress release zones these structures concentrated hydrothermal solutions during seismic fault movement events under a transpressive regime they also changed the physicochemical conditions in the fluid by abruptly reducing the pressure and increasing the fluid rock interaction rate producing a structural framework characterized by a pervasively interconnected system of discontinuous and anastomosed quartz carbonate sulfide gold veins fieldwork petrographic analysis and mineral chemistry characterization suggest that the fluid had an aqueous carbonic nature and low salinity values thermometric studies suggest that gold mineralization occurred between 250 c and 400 c stable isotopes of s c and o indicate a metamorphic source for the fluid whole rock geochemistry and microprobe studies highlight hydrothermal alteration processes involving fe ca mg k na au and ag metasomatism the principe gold deposit belongs to the orogenic class but it is distinguished from other orogenic type occurrences in the natividade gold district and from most orogenic deposits of the world for not being located along a shear zone instead it is situated within a regional scale auriferous pressure shadow that was brought about by a short lived pressure drop during the brasiliano cycle

brazilian structural provinces an introduction abstract the territory of brazil coincides almost entirely with the south american platform the crystalline core of the continent its basement is composed of ancient metamorphic and igneous rocks and it has not suffered any tectonic regeneration since the beginning of the phanerozoic sedimentary rocks with almost horizontal bedding cover this crystalline basement this latter shows ages as old as early precambrian although ages between 500 and 1000 m y are conspicuously frequent the cratonic areas became consolidated more than 1700 m y ago whereas the fold belts formed essentially between 500 and 1700 m y ago the sedimentary cover accumulated from the early silurian in three large intracratonic basins until the platform became completely stabilized a late jurassic to early cretaceous reactivation caused by the break up of the ancient gondwana continent created another basin sequence chiefly along the atlantic continental margin based on the nature of the crystalline basement rocks and the sedimentary cover ten structural provinces can be distinguished 1 rio branco province in the north of the country occupied by the guyana shield and still only poorly known with an important fold belt developed during the so called transamazonian cycle 2000 200m y with high grade metamorphic rocks and only slight influence of later events 2 tapajos province in central brazil corresponding to the amazonas or guaporecraton showing chiefly precambrian crystalline rocks and behaving as an cratonic area during the phanerozoic 3 sa o francisco province located on the atlantic shield with its basement covered by rocks of different ages chiefly affected by the brasiliano cycle between 1000 and 500 m y and constituting another cratonic area 4 tocantins province between the amazonas and sa o francisco cratons with the oldest rocks in its centre ages over 2600 m y and at the eastern and western borders metamorphic sequences of various fold belts and almost no phanerozoic deposits 5 mantiqueira province located along the southern part of the atlantic coast affected chiefly by the brasiliano folding cycle 6 borborema province in the northeast brazilian fold belt affected by the brasiliano cycle in a very complex way and with important faulted zones it was reactivated in phanerozoic times when also sedimentary covers accumulated 7 amazonas province represented by the amazonas sedimentary basin syneclise and subdivided into four parts by three important arcs 8 parnaiba province coinciding with the piauf maranha o syneclise and filled with a rather thick sedimentary sequence 9 paranaprovince the sedimentary basin of southern brazil in which the well known late paleozoic glaciation features are found and which possesses an extensive cover of basaltic rocks of late jurassic to early cretaceous age 10 coastal province and continental margin the youngest structural unit developed during the separation of the continent and represented by rift valleys and coastal basins filled with mesozoic cenozoic deposits of various kinds

age and depth evidence for pre exhumation joints in granite plutons fracturing during the early cooling stage of felsic rock this paper documents the fracture process associated with the early cooling stage of felsic magma characteristics of pre exhumation joints include their spatial distribution in granite bodies their fracture surface morphology and geological and petrological evidence for the depth of fracture initiation these characteristics allow inferences about the depth and the time of joint origin in the south bohemian pluton the intrusion levels of presently exposed granites of the pluton were 7 4 km in the northern part and 14 3 km in the southern part within the northern mrakotin granite borsov early nne joints propagated while the granite was at a temperature near the solidus and in part magma was still being injected post dated by thin granite dykes along nne joints evidence for the pre exhumation initiation of these joints comes from the geochronological dating of this late granite dykes 1 2 cm thick at 324 9 ma in age which were creating their own rupture in the rock the time of the pluton emplacement at 330 to 324 ma and the cooling ages of 328 to 320 ma were given by scharbert 1998 and gerdes et al 1998 from fluid inclusions within the late granite dyke that occupy joint surfaces the trapping depth of the analysed inclusions was calculated to 7 4 km near the solidus h2o separates by crystallization of anhydrous phases the associated increasing h2o pressure can initiate the first cracks and can generate a small portion of new granitic melt which forces the cyclic fracture propagation together with mobile low viscosity residual melt input into the fracture the determination of the level and time of the cooling dykes give evidence for the joint initiation at a depth of 7 4 km which was connected with the level and process of final emplacement and early cooling of the mrakotin granite long before the main exhumation at the earliest the erosion of the upper rock pile of 7 4 km thickness started significantly after generation of the early joint sets the nne trending joints are persistent in orientation throughout the south bohemian pluton but the joint surface morphology is varying in all sub plutons and occupy all sections of the stress intensity versus crack propagation velocity curve wiederhorn bahat curve statement of problems granite bodies can fracture in various characteristic manners relative to the density of fractures the number of joint sets and their distribution and the type of fractographic features on joint surfaces some granite plutons are dominated by only one orthogonal subvertical joint system e g in the hercynian south bohemian pluton czech republic fig 1 a whereas other plutons contain two or more subvertical joint systems of different generation time e g the cadomian lausitz pluton germany d the density of fractures in the earth s crust decreases with depth e g price 1966 ramsay huber 1987 this observation does not exclude fracture initiation within plutons at depths below 7 km we consider two problems 1 age and depth for propagation of pre

tectonic evolution of south america during the late proterozoic abstract this paper discusses the evolution and the late proterozoic assembly of the south american continent i e the west gondwana under the light of global tectonics the northern portion of the continent the amazonian craton is a pre brasiliano domain it may be a fragment derived from laurentia this domain behaved as a large continental plate which was accreted to the central and southeastern portions of the continent brasiliano domain the brasiliano domain had a more complex history and composition during the brasiliano cycle middle proterozoic to early paleozoic in the brasiliano domain several late proterozoic continental plates have been identified sao luiz west africa congo kasai sao francisco rio de la plata arequipa antofalla which acted as forelands to the brasiliano orogenic belts that surround and amalgamate these plates smaller fragments of pre brasiliano continental lithosphere are common in the interior of the brasiliano orogenic belts and played diversified roles microplates microcontinents structural highs some of them have acted as true backlands hinterlands flanked by arc magmatism two principal types of brasiliano orogenic belts are recognized between the continental plates a marginal orogenies to the late proterozoic plates with pelitic carbonatic rocks and discrete volcanism which were thrust by collision onto the margin of the plates and which seem to represent final products of previous passive margin sequences b distal orogenics internal belts within the continental masses sometimes a branching system of orogenics that contain varied clastic and minor carbonate sedimentary rocks accompanied by important bimodal volcanism and calc alkaline plutonism for these orogenies a greater variety of basinal scenarios and tectonic settings may be visualized the amalgamation of the continent during the late proterozoic i e the formation of the brasiliano structures indicates the existence of practically synchronous multilateral stresses within lithospheric plates this can be produced by complementary adjustment of the continental plates as a response to major global events elsewhere analogous to modern continental collisions two large and important tectonic zones may be candidates to such a scenario the hijaz mozambique zone site of connection of east and west gondwana and the transbrasiliano lineament which cuts across south america and extends to north africa following the zone of connection between pre brasiliano and brasiliano domains other small ocean openings and closings inside the various brasiliano areas dom feliciano gariep for instance were minor events and complementary to the other two major tectonic zones mentioned above

preuplift joints in granites evidence for subcritical and postcritical fracture growth this study relates to jointing in granite that took place in the crust before uplift thus offering an insight into paleo fracture processes our investigation reveals a unique set of joints within granite of the south bohemian pluton exposed in the borsov quarry southeast of prague in the czech republic these joints occur in close proximity and exhibit a great variety of fracture surface morphologies the joints in the borsov granite may be divided into four groups based on fractographic features 1 partial mirror planes without fringes 2 mirror planes rimmed by en echelon fringes 3 complex en echelon fringes and 4 hackled fringes on the basis of theoretical experimental and fractographic data obtained in outcrops we have constructed a curve for the change in crack velocity v as a function of the stress intensity factor k i and we have plotted the various joints in the borsov granite on this curve the spread of the joints along the curve indicates that the joints terminated under widely different physical conditions possibly responding to repeated extensional events and different fracture mechanisms hence a new quantitative method of joint classification is introduced such a great variety of fractographic features is unknown from joint sets that occur in a single quarry in sedimentary rock because their formation always relates to a particular fracture mechanism we argue that the joints in the borsov granite formed before uplift in a fluid enriched environment while the granite responded to diverse local effective stress conditions

is there a relationship between magmatic fabrics and brittle fractures in plutons a view based on structural analysis anisotropy of magnetic susceptibility and thermo mechanical modelling of the tanvald pluton bohemian massif abstract the present study focuses on the thermal and mechanical aspects of cooling of plutonic systems with respect to their internal structure analysis of the tanvald pluton and the nearby liberec granite the krkonose jizera plutonic complex bohemian massif using the anisotropy of magnetic susceptibility ams method indicates the decoupled magnetic fabrics formed by different processes in these two plutons two regional sets of vertical fractures cut across the plutons and their host rocks they are interpreted as having been formed as opening mode fractures joints after emplacement and cooling our thermo mechanical finite element modelling indicates that the thermal stresses within the tanvald pluton were compressive and that fracture criteria were not met during pluton cooling these results imply that the emplacement depth and confining pressure significantly affect the state of stress within a pluton during cooling and may play a crucial role in the formation of early fractures in plutons consequently the formation of early fractures during pluton cooling is driven by external conditions overriding the role of internal magmatic fabrics we argue that no genetic geometric or temporal correlation can exist between magmatic fabrics and fractures in granitoid plutons and thus that the original concept of hans cloos based on fabric joints relationships should be reconsidered instead an alternative classification of fractures in plutons should include cooling fractures syntectonic fractures uplift fractures and post uplift fractures

spatial and temporal distribution of the orogenic gold deposits in the late palaeozoic variscides and southern tianshan how orogenic are they abstract a principal uncertainty in models of orogenic ore deposits concerns their ages relative to orogenic processes the yardstick of the relation has resided loosely in the peak of metamorphism age estimates in the variscides and tianshan indicate that most orogenic ore deposits were formed in the course of the late carboniferous to middle triassic with a peak between 305 and 280 ma their locations settings and ages suggest an association with coeval lithosphere scale strike slip deformation which played a role in the destruction of the orogenic system following crustal shortening this destruction tends to invalidate the orogenic association of the orogenic ore deposits observation of a mantle signature in some of these ore deposits and in coeval magmatic rocks suggests that the strike slip belts tapped into sub crustal levels here lithological composition had been modified by subduction during the stage of construction consequently any orogenic element in the ore deposit models is apart from location only an element of inheritance of subduction modified lithosphere features acquired during construction of the orogen these features may however well have been crucial for the formation of the ore deposits in view of the translithospheric extent of the strike slip belts fluids which contributed to the ore deposits may have come from at least the entire in part metasomatized lithosphere column the ore deposits could probably not have been formed without these deep reaching strike slip systems a model is proposed for the geological setting of the orogenic gold deposits in the variscides and the southern tianshan it consists of plutono metamorphic elements in the mantle in the lower and in the middle crust within a transpressional to transtensional tectonic framework of translithospheric faults and associated domes and pull apart basins with shallow marine to terrestrial sediments and interlayered felsic and mafic volcanics the thermal engines of these systems were probably in localized upwellings of the asthenosphere prompted and controlled by the lithosphere scale deformation at the time at an even larger scale oroclinal bending of the old orogenic backbone may have played yet another role in the localization of the ore deposits the thesis of specific localized tectono thermal engines is at odds with the original proposals of a relation between orogenic ore deposits and regional metamorphism it suggests that the late palaeozoic gold antimony mercury ore deposits in the variscides and the southern tianshan are more akin to the intrusion related ore systems

melt inclusions in pegmatite quartz complete miscibility between silicate melts and hydrous fluids at low pressure fluorine boron and phosphorus rich pegmatites of the variscan ehrenfriedersdorf complex crystallized over a temperature range from about 700 to 500 c at a pressure of about 1 kbar pegmatite quartz crystals continuously trapped two different types of melt inclusions during cooling and growth a silicate rich h2o poor melt and a silicate poor h2o rich melt both melts were simultaneously trapped on the solvus boundaries of the silicate fluorine boron phosphorus water system the partially crystallized melt inclusions were rehomogenized at 1 kbar between 500 and 712 c in steps of 50 c by conventional rapid quench hydrothermal experiments glasses of completely rehomogenized inclusions were analyzed for h2o by raman spectroscopy and for major and some trace elements by emp electron microprobe both types of melt inclusions define a solvus boundary in an xh2o t pseudobinary system at 500 c the silicate rich melt contains about 2 5 wt h2o and the conjugate water rich melt about 47 wt h2o the solvus closes rapidly with increasing temperature at 650 c the water contents are about 10 and 32 wt respectively complete miscibility is attained at the critical point 712 c and 21 5 wt h2o many pegmatites show high concentrations of f b and p this is particularly true for those pegmatites associated with highly evolved peraluminous granites the presence of these elements dramatically reduces the critical pressure for fluid melt systems at shallow intrusion levels at t 720 c water is infinitely soluble in a f b and p rich melt simple cooling induces a separation into two coexisting melts accompanied with strong element fractionation on the water rich side of the solvus very volatile rich melts are produced that have vastly different physical properties as compared to normal silicate melts the density viscosity diffusivity and mobility of such hyper aqueous melts under these conditions are more comparable to an aqueous fluid

an improved tilt euler deconvolution and its application on a fe polymetallic deposit abstract the tilt euler deconvolution based on the first derivatives of the tilt angle is advanced from the routine euler deconvolution and it is widely used it estimates both the horizontal location and the depth of magnetic bodies without the known structural index since the derivatives of the tilt angle cannot be calculated when the first horizontal derivatives of the magnetic anomaly are equal to zero there are singularities in the inversion from the tilt euler method we present an improved method for the tilt euler deconvolution which avoids the occurrence of singularities in the calculation and reduces the unstable factors in the inversion since the euler methods should be implemented in a window we apply the standard deviation of the euler solutions as the measure of dispersion to determine the optimal window size both the model test and the field application show that the solutions of the improved tilt euler deconvolution are more concentrated than that of the tilt euler deconvolution and subsequently result in a more robust interpretation in the field application the results of the proposed method imply that the source body is probably a dike with limited extent

magmatic history and geophysical signature of a post collisional intrusive center emplaced near a crustal scale shear zone the plechý granite pluton moldanubian batholith bohemian massif the plech pluton southwestern bohemian massif represents a late variscan complexly zoned intrusive center emplaced near the crustal scale pfahl shear zone the pluton thus provides an opportunity to examine the interplay among successive emplacement of large magma batches magmatic fabric acquisition and the late variscan stress field associated with strike slip shearing the magmatic history of the pluton started with the emplacement of the porphyritic plech and haidmuhler granites based on gravity and structural data we interpret that the plech and haidmuhler granites were emplaced as a deeply rooted ne sw elongated body its gross shape and internal fabric steep ne sw magmatic foliation may have been controlled by the late variscan stress field the steep magmatic foliation changes into flat lying foliation particularly recorded by ams presumably as a result of divergent flow magnetic lineations correspond to a sub horizontal ne sw finite stretch associated with the divergent flow subsequently the t istolicnik granite characterized by steep margin parallel magmatic foliation was emplaced as a crescent shaped body in the central part of the pluton the otherwise inward younging intrusive sequence was completed by the emplacement of the outermost and the most evolved garnet bearing granite the marginal granite along the southeastern margin of the pluton

brittle deformation events at the western border of the bohemian massif germany investigations of brittle deformation structures present within the crystalline rocks of the bavarian oberpfalz reveal a complex late to post variscan crustal evolution upper carboniferous mainly westphalian granites were emplaced into semibrittle to brittle rocks of the zev zone of erbendorf vohenstraus and the egz erbendorf greenschist unit respectively from both the alignment of the granites and the direction of granite related tension gashes a north east south west extension must be assumed for the period of magmatic activities apart from the granite intrusions rapid crustal uplift about 1 5 km my led to an increase in the geothermal gradient from 40 c km late variscan post granitic the increased geothermal gradient persisted during the succeeding reverse faulting which results from late carboniferous probably stephanian east west and northeast south west compression although not evidenced directly in the area considered strike slip faults seem to have played an important part during the late variscan crustal evolution particularly in the early permian the strike slip events indicate further crustal shortening and indentation under north south compression a similar indentation was present in cretaceous time after a weak phase of early cretaceous reverse faulting which results from north south compression strike slip faults formed under north west south east and north south compression all these faults in particular the strike slip faults seem to be related to the cretaceous and lowermost tertiary convergence of the alpine carpathian orogeny a late stage of crustal extension characterized by a radial stress tensor 2 3 is indicated through high angle normal faults which probably formed during the subsidence of the adjacent neogene eger graben

mass dependent and mass independent sulfur isotope fractionation δ34s and δ33s from brazilian archean and proterozoic sulfide deposits by laser ablation multi collector icp ms abstract mass independent sulfur isotope fractionation mif has been observed in rocks of the geological record older than about 2 45 ga a characteristic which is thought to be related to processes in the neoarchean atmosphere samples recording a mif effect therefore have to contain sulfur of the exogenic sulfur cycle while endogenic sulfur should not show this effect the sulfides analysed from six brazilian deposits represent either exogenic or endogenic sulfur sources with supposed ages ranging from about 1 9 to 2 7 ga sulfur isotopes were analysed by in situ laser ablation mc icp ms a range of experiments were conducted using international and in house isotope standards which were run under various conditions and set ups these include the reference materials iaea s1 iaea s3 nbs123 sphalerite nbs127 barite and in house standards bsb py pyrite and bsb cpy chalcopyrite during six days of analysis an internal precision of sulfide analyses of 0 10 0 15 1 s for 34 s and 0 40 0 60 1 s for 33 s and an accuracy of 0 30 for 34 s and 33 s was achieved the standard measurements define a 33 s 34 s relationship of 33 s 0 513 34 s 0 149 with r 0 9997 which is close to the theoretical relationship for mass dependent fractionation the by far best analytical errors were obtained for natural pyrite reaching a within run precision of about 0 05 0 15 for 34 s 1 s and 0 10 0 15 1 s for 33 s determinations including all precision and accuracy data we arrive at the following 1 s error limits to which sulfur isotope analyses for mif studies obtained with this method are reliable 0 32 0 34 and 0 46 for pyrite 34 s 33 s and 33 s determinations respectively 0 34 0 42 and 0 54 for pyrrhotite and 0 34 0 50 and 0 58 for chalcopyrite pyrites and pyrrhotites from 2200 ma old sediments and volcanics associated with the pilar greenstone belt goias have 34 s from 15 0 to 2 0 and 33 s from 8 0 to 1 0 with 33 s being slightly but not significantly positive pyrites from supposed ca 2060 ma old clastic sediments of the aguas claras formation carajas para have 34 s 9 5 12 5 and 33 s 5 0 6 5 with 33 s close to zero chalcopyrites from the salobo and sequerinha sulfide deposits also carajas are genetically related to 2570 ma old a type alkaline granites with endogenic sources they have 34 s 1 6 2 9 and 33 s 1 0 1 5 and 34 s 0 2 0 9 and 33 s 0 65 respectively with 33 s ranging from 0 15 to 0 56 the only 33 s values of this study which clearly suggest sulfur isotope mif come from the mineralized banded iron formations of the quadrilatero ferrifero minas gerais pyrites from the mina de cuiaba deposit 2700 ma have 34 s 3 8 5 1 and 33 s 2 9 4 8 with 33 s 0 9 2 2 while pyrites and chalcopyrites from sao bento 2720 ma have 34 s 1 6 3 2 and 33 s 1 5 2 8 with 33 s 0 2 1 5 the sulfides represent an epigenetic mineralization derived from supracrustal rocks making part of an exogenic sulfur cycle the study shows that in situ laser ablation icp ms is sufficiently sensitive for detecting mif effects in neoarchean rocks whether or not such samples show mif related 33 s values depends on the age and provenance of the sulfur

late collisional granites in the variscan erzgebirge germany the late collisional erzgebirge granites 325 318 ma were introduction emplaced at shallow crustal levels in the variscan metamorphic the erzgebirge is a ne sw trending antiformal structure basement shortly after large scale extension caused by orogenic exposing variscan crystalline basement rocks at the northcollapse these granites comprise mildly peraluminous transitional ern margin of the bohemian massif the region is famous i s types and strongly peraluminous s type rocks which can be among economic geologists for its extensive and highly subdivided into three major groups low f biotite granites low f variable metallic ore deposits which have been mined two mica granites and high f high p2o5 li mica granites the since the middle ages e g stemprok seltmann 1994 highest degree of differentiation is reached in the li mica granites tischendorf forster 1994 and for the classic studies which exhibit strongly elevated concentrations of p f li rb cs in the fields of economic geology mining and metallurgy ta sn w and u but very low ti mg co ni sr ba y zr chemistry and mineralogy e g werner 1791 breithaupt hf th and rare earth elements crystal melt fractionation is the 1849 agricola 1974 dominant process controlling the bulk composition of all groups of as in many of the other variscan provinces in central granites however metasomatic processes involving late stage residual europe granitic rocks make up a large proportion of the melts and high t orthomagmatic fluids became increasingly more exposed rocks in the erzgebirge and a great variety of important in highly evolved units and have modified the abundances compositional and textural types occur fig 1 knowof mobile elements p f li rb cs ba sr in the li mica ledge of the processes involved in the generation and granites particularly isotopic and geochemical characteristics suggest evolution of these silicic magmas is essential for underthat the three granite groups cannot be derived from a common standing heat and mass transport during the variscan precursor magma their discrete compositions are source related orogeny and also for the formation of metallic ore and are attributed to melting of quartzo feldspathic and pelitic deposits several lines of evidence indicate that early crustal lithologies in different proportions granites are common in high temperature sn w deposits are associated with the the central european variscides but the erzgebirge is unusual for emplacement of highly evolved volatile rich granitic the predominance of evolved li mica granites associated with melts tischendorf 1986 forster tischendorf 1992 economically important sn w and u deposits the abundance of stemprok 1993 the role of the granites in formation of li mica granites is attributed to a combination of favourable factors later permian u pb zn and younger ore mineralization 1 low degrees of anatectic melting of crustal protoliths 2 wide f ba is controversial but good evidence exists that the distribution of fertile lithologies rich in large ion lithophile elements vein type u deposits owe their uranium to leaching from and ore elements 3 extended magmatic differentiation by crystal the uraninite rich granites e g tischendorf forster melt fractionation and subsequent autometasomatism 1994

changes of crack velocities at the transition from the parent joint through the en echelon fringe to a secondary mirror plane abstract a trefoil joint in granite of the bohemian massif in the variscan belt of europe displays intriguing surface morphologies it consists of primary and secondary mirrors as well as primary and secondary fringes an arrangement not previously described these fractographic features are seen to record two cycles of increase and decrease in fracture velocities fracture velocities increased along the propagating mirrors in association with the increase of released energy however beyond a certain velocity energy dissipated along the new multi surfaces at the fringes and this involved reduction in fracture velocities

seismic hazard of the enriquillo plantain garden fault in haiti inferred from palaeoseismology the enriquillo plantain garden fault zone is the primary plate bounding fault system in haiti and was initially thought to be responsible for the 2010 earthquake palaeoseismic analyses of the fault system indicate that it ruptured during a large earthquake in either 1750 or 1770 but did not rupture during the 2010 earthquake the enriquillo plantain garden fault zone is recognized as one of the primary plate bounding fault systems in haiti1 2 the strike slip fault runs adjacent to the city of port au prince and was initially thought to be the source of the 12 january 2010 mw 7 0 earthquake haiti experienced significant earthquakes in 1751 and 1770 refs 3 4 5 but the role of the enriquillo plantain garden fault zone in these earthquakes is poorly known we use satellite imagery aerial photography light detection and ranging lidar and field investigations to document quaternary activity on the enriquillo plantain garden fault we report late quaternary left lateral offsets of up to 160 m and a set of small offsets ranging from 1 3 to 3 3 m that we associate with one of the eighteenth century earthquakes the size of the small offsets implies that the historical earthquake was larger than mw 7 0 but probably smaller than mw 7 6 we found no significant surface rupture associated with the 2010 earthquake the lack of surface rupture coupled with other seismologic geologic and geodetic observations6 7 suggests that little if any accumulated strain was released on the enriquillo plantain garden fault in the 2010 earthquake these results confirm that the enriquillo plantain garden fault remains a significant seismic hazard

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

interseismic plate coupling and strain partitioning in the northeastern caribbean summary the northeastern caribbean provides a natural laboratory to investigate strain partitioning its causes and its consequences on the stress regime and tectonic evolution of a subduction plate boundary here we use gps and earthquake slip vector data to produce a present day kinematic model that accounts for secular block rotation and elastic strain accumulation with variable interplate coupling on active faults we confirm that the oblique convergence between caribbean and north america in hispaniola is partitioned between plate boundary parallel motion on the septentrional and enriquillo faults in the overriding plate and plateboundary normal motion at the plate interface on the northern hispaniola fault to the east the caribbean north america plate motion is accommodated by oblique slip on the faults bounding the puerto rico block to the north puerto rico subduction and to the south muertos thrust with no evidence for partitioning the spatial correlation between interplate coupling strain partitioning and the subduction of buoyant oceanic asperities suggests that the latter enhance the transfer of interplate shear stresses to the overriding plate facilitating strike slip faulting in the overriding plate the model slip rate deficit together with the dates of large historical earthquakes indicates the potential for a large m w7 5 or greater earthquake on the septentrional fault in the dominican republic similarly the enriquillo fault in haiti is currently capable of a m w7 2 earthquake if the entire elastic strain accumulated since the last major earthquake was released in a single event today the model results show that the puerto rico lesser antilles subduction thrust is only partially coupled meaning that the plate interface is accumulating elastic strain at rates slower than the total plate motion this does not preclude the existence of isolated locked patches accumulating elastic strain to be released in future earthquakes but whose location and geometry are not resolvable with the present data distribution slip deficit on faults from this study are used in a companion paper to calculate interseismic stress loading and together with stress changes due to historical earthquakes derive the recent stress evolution in the ne caribbean

the tectonics and active faulting of haiti from seismicity and tomography oblique convergence of the caribbean and north american plates has partitioned strain across a major transpressional fault system that bisects the island of hispaniola the devastating mw 7 0 2010 earthquake that struck southern haiti rupturing an unknown fault highlighted our limited understanding of regional fault segmentation and its link to plate boundary deformation here we assess seismic activity and fault structures across haiti using data from 33 broadband seismic stations deployed for 16 months we use travel time tomography to obtain relocated hypocenters and models of vp and vp vs crustal structure earthquake locations reveal two clusters of seismic activity the first corresponds to aftershocks of the 2010 earthquake and delineates faults associated with that rupture the second cluster shows shallow activity north of lake enriquillo dominican republic interpreted to have occurred on a north dipping thrust fault crustal seismic velocities show a narrow low velocity region with an increased vp vs ratio 1 80 1 85 dipping underneath the massif de la selle which coincides with a southward dipping zone of hypocenters to a depth of 20 km beneath southern haiti our observations of seismicity and crustal structure in southern haiti suggests a transition in the enriquillo fault system from a near vertical strike slip fault along the southern peninsula to a southward dipping oblique slip fault along the southern border of the cul de sac enriquillo basin this result consistent with recent geodetic results but at odds with the classical seismotectonic interpretation of the enriquillo fault system is an important constraint in our understanding of regional seismic hazard

formation of gold deposits review and evaluation of the continuum model abstract the continuum model has been one of the more widely advocated genetic models for gold only deposits such as those found in archaean greenstone belts it postulates that hydrothermal gold deposits were formed throughout a 20 25 km vertical crustal profile from temperatures above 700 c to below 180 c and that the deposition occurred synchronous with the peak of metamorphism the continuum model is reviewed at this stage because we believe that it does not successfully account for many aspects of gold deposit formation the most obvious shortcoming is in considering ore deposits found in rocks of uppermost amphibolite and granulite facies domains where temperatures were appropriate for partial melting the main chemical condition that favours melting is access to h2o from either aqueous fluid or the breakdown of hydrous minerals a major gold forming hydrothermal event at the peak of high grade metamorphism as implied by the continuum model is incompatible with partial melting of wallrocks instead of forming a hydrothermal gold deposit an aqueous fluid introduced during partial melting would be consumed to produce further melt five gold deposits are documented from high metamorphic grade domains within four separate archaean cratons one is the type example used in the continuum model the other four have been significant producers partial melting has been recorded in the wallrocks adjacent to gold mineralisation at big bell hemlo challenger and renco gold deposits in the sulphide rich ore itself at challenger and hemlo deposits and as cross cutting dykes and migmatites at griffins find for these five deposits and indeed in general the continuum model does not easily account for aspects of the fluid source fluid composition gold transport and metal deposition the evidence that has been used to support deposit formation at the peak of high grade metamorphism as required by the continuum model is generally compatible with one or more alternative genetic models textural and structural siting of the gold high variance mineral assemblages proportion of various gold host rocks and relative element enrichments at high metamorphic grade can be accounted for by gold formation at greenschist facies conditions followed by progress of the deposit to high metamorphic grade metamorphic model moreover the type examples in the continuum model of deposits in sub greenschist facies domains appear to be incorrectly ascribed and are likely to be in greenschist facies domains the continuum model does not adequately explain archaean gold deposits

fan delta uplift and mountain subsidence during the haiti 2010 earthquake the 2010 haiti earthquake was initially thought to have ruptured the enriquillo plantain garden fault but previously unrecognized faults were later implicated radar imaging of surface deformation caused by the earthquake reveals uplift of alluvial fans and subsidence of mountains consistent with reverse motion on a blind thrust fault

the 2010 haiti earthquake a complex fault pattern constrained by seismologic and tectonic observations after the january 12 2010 haiti earthquake we deployed a mainly offshore temporary network of seismologic stations around the damaged area the distribution of the recorded aftershocks together with morphotectonic observations and mainshock analysis allow us to constrain a complex fault pattern in the area almost all of the aftershocks have a n s compressive mechanism and not the expected left lateral strike slip mechanism a first order slip model of the mainshock shows a n264 e north dipping plane with a major left lateral component and a strong reverse component as the aftershock distribution is sub parallel and close to the enriquillo fault we assume that although the cause of the catastrophe was not a rupture along the enriquillo fault this fault had an important role as a mechanical boundary the azimuth of the focal planes of the aftershocks are parallel to the north dipping faults of the transhaitian belt which suggests a triggering of failure on these discontinuities in the western part the aftershock distribution reflects the triggering of slip on similar faults and or alternatively of the south dipping faults such the trois baies submarine fault these observations are in agreement with a model of an oblique collision of an indenter of the oceanic crust of the southern peninsula and the sedimentary wedge of the transhaitian belt the rupture occurred on a wrench fault at the rheologic boundary on top of the under thrusting rigid oceanic block whereas the aftershocks were the result of the relaxation on the hanging wall along pre existing discontinuities in the frontal part of the transhaitian belt

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

geology and stable isotope o h c s constraints on the genesis of the cachoeira gold deposit gurupi belt northern brazil the cachoeira gold deposit is one of several large n20 tonnes au shear zone hosted hydrothermal gold deposits of the proterozoic gurupi belt in northern brazil o h c and s isotope compositions of carbonate silicate and sulfide minerals and from graphite and inclusion fluids from this deposit have been measured in order to infer the composition of ore forming fluids the data show small variation at the deposit scale irrespective of host rock calculated y 18 o values of h2o in the fluid in equilibrium with quartz hydrous silicates and carbonates are respectively 6 2 to 12 4x 5 0 to 9 0x and 5 9 to 11 0x smow the ydh2o of inclusion fluids is 22x whereas values for chlorite and white mica are 16x and 20 to 28x smow respectively these values are compatible with a metamorphic origin which is in agreement with the postmetamorphic timing of the mineralization the calculated y 13 c value of co2 of the fluid in equilibrium with the carbonates is from 9 5x to 12 7x pdb whereas the graphite bearing host rocks have y 13 c value of graphite carbon of 29 7x the calculated y 34 so f h2s of the fluid varies mainly between 0 7x and 5 5x cdt and is interpreted as reflecting a magmatic or average crustal source for sulfur the restricted isotopic compositions indicate a relatively homogeneous fluid and deposition under restricted temperature conditions nonetheless a relatively wide temperature range of 272 383 8c is estimated for the ore bearing fluid using the quartz dolomite oxygen isotope thermometer collectively the data indicate that gold was transported as a reduced sulfur complex by a metamorphic fluid having a near neutral ph at relatively low co2 furthermore the data suggest that gold was deposited during the structural evolution of the associated shear zone probably as a result of sulfidation and carbonatization reactions with the fe and c rich host rocks which resulted in changes of the ph and in the redox state of the ore fluid d 2005 elsevier b v all rights reserved

granite tectonics revisited insights from comparison of k feldspar shape fabric anisotropy of magnetic susceptibility ams and brittle fractures in the jizera granite bohemian massif in the jizera granite of the krkonose jizera plutonic complex northern bohemian massif contrasting patterns of magmatic k feldspar fabrics and brittle fractures characterize different structural levels of the pluton the uppermost exposed level at 800 1 100 m above sea level is dominated by flat foliation that overprints two steep foliations in contrast k feldspar shape fabric in an underground tunnel 660 m above sea level shows complex variations in orientation and intensity magnetic fabric carried by coaxial contributions of biotite magnetite and maghemite is homogeneous along the examined section of the tunnel and is decoupled from the k feldspar fabric the jizera granite is crosscut by two regional sets of subvertical fractures ne sw and nw se and by near surface exfoliation joints the multiple fabrics are inferred to reflect a complex magmatic strain history at different structural levels of the pluton bearing little or no relationship to the fracture network in contrast to the original concept of hans cloos granite tectonics we conclude that no simple genetic relationship exists between fabrics and fractures in plutons an alternative classification of fractures in plutons thus should avoid relationships to magmatic fabrics and should instead consist of cooling syntectonic uplift and post uplift fractures

magmatic evolution of the penon rosado granite petrogenesis of garnet bearing granitoids garnet is an uncommon accessory mineral in igneous rocks but is petrologically significant the penon rosado granite 469 4ma at cerro asperecito is an s type granite that contains an unusual amount of magmatic garnet combined petrology chemistry mineralogy and whole rock geochemistry indicates that the magma was produced by partial melting of the surrounding metasedimentary rocks and subsequent differentiation by fractional crystallization during emplacement with garnet occurring throughout the crystallization sequence three facies are recognised prg1 sio2 65 70 represents cumulates prg2 sio2 70 88 represents a differentiated melt and prg3 sio2 74 59 a residual melt the fractionation of mn in garnet and the proportion of garnet crystallizing are roughly controlled by the evolving composition of the different granitic facies geothermobaric calculations reveal an initial crystallization temperature of 764 792 cand a pressure of 5 9 6 0 kb indicating that the parental magma was emplaced atmiddle crustal depths 1920 km in moderate low magmatic temperature conditions major cao na2o k2o and trace element rb sr ba contents in the penon rosado granite strongly suggest anatexis was the outcome of h2o fluxed melting of metagreywacke with heat input from a major metaluminous suite our studies reveal that garnet formed by direct crystallization from peraluminous magma in equilibrium with solid phases such as biotite and white mica we confirm previous suggestions that zoning in garnet is strongly temperature dependent thus magmatic garnets in granitic rocks crystallized above 700 c have spessartine inverse bell shaped profile or are unzoned whereas garnet exhibiting spessartine bell shaped profile must be considered of metamorphic origin i e xenocrystic or formed in very felsic magmas sio2 73 76 crystallizing below 700 c 2006 elsevier b v all rights reserved

strong tin enrichment in a pegmatite forming melt to investigate processes of magmatic tin enrichment and cassiterite deposition we studied the abundances of major trace and volatile elements in a large number of rehomogenized silicate melt inclusions in quartz and topaz from a pegmatite body at the ehrenfriedersdorf sn w deposit this deposit is associated with evolved variscan granites of the central erzgebirge southeast germany the melt inclusions are peraluminous the molar aluminum saturation index asi ranges from 1 15 to 2 0 and many inclusions are characterized by a very high content of fluxing components and volatiles some inclusions contain more than 20 wt of h2o f cl and p2o5 plus li as well as very high levels of sn some rare highly evolved fractions of late stage pegmatite forming liquid at ehrenfriedersdorf contained up to 7000 ppm sn the presence of hydrogen and methane in addition to water and carbon dioxide in the vapor phase of the melt inclusions suggests a very low oxygen fugacity for some fractions of magma the extreme levels of tin volatiles and fluxing components in this magma had an important influence on processes of melt movement and cassiterite precipitation melts like these that are high in volatiles and alkalis sum of li2o na2o k2o rb2o and cs2o is 8 wt have low densities 1 8 g cm3 low viscosities 10 pa s at 700 c facilitate relatively rapid diffusion of ions through melts and hence are excellent solvents for extracting and transporting ore forming elements

complex rupture during the 12 january 2010 haiti earthquake initially the devastating mw 7 0 12 january 2010 haiti earthquake seemed to involve straightforward accommodation of oblique relative motion between the caribbean and north american plates along the enriquillo plantain garden fault zone here we combine seismological observations geologic field data and space geodetic measurements to show that instead the rupture process involved slip on multiple faults primary surface deformation was driven by rupture on blind thrust faults with only minor deep lateral slip along or near the main enriquillo plantain garden fault zone thus the event only partially relieved centuries of accumulated left lateral strain on a small part of the plate boundary system together with the predominance of shallow off fault thrusting the lack of surface deformation implies that remaining shallow shear strain will be released in future surface rupturing earthquakes on the enriquillo plantain garden fault zone as occurred in inferred holocene and probable historic events we suggest that the geological signature of this earthquake broad warping and coastal deformation rather than surface rupture along the main fault zone will not be easily recognized by standard palaeoseismic studies we conclude that similarly complex earthquakes in tectonic environments that accommodate both translation and convergence such as the san andreas fault through the transverse ranges of california may be missing from the prehistoric earthquake record

investigating the effect of mechanical discontinuities on joint spacing in rocks without systematic mechanical discontinuities e g granite joint spacing follows an approximately log normal frequency distribution i e the distribution has a kurtosis near zero joint spacing in rocks with systematic mechanical boundaries differs from the spacing in isotropic rocks exhibiting consistently positive values of kurtosis i e the distribution is more clustered around the mode than a perfectly log normal distribution we attribute this difference in joint spacing distribution to mechanical boundaries such as bed partings in sedimentary rocks that constrain joint height and control joint spacing existing systematic joints can also act as mechanical boundaries during the development of later cross joints two parallel mechanical boundaries determine the mechanical layer thickness that influences joint spacing in this paper we investigate the effect of sampling geometry and mechanical discontinuities on joint spacing statistics in many situations neither pavement surfaces nor properly oriented boreholes are available for measuring the spacing of cross joints that develop between existing systematic joints when joint spacing data come from scanlines that are oblique to a systematic joint set e g crossing many systematic joints on a sub vertical outcrop face we consider whether the median spacing of the systematic joint set is statistically equivalent to the mechanical layer thickness thought to control cross joint spacing between individual pairs of systematic joints the basis of our analysis is the fracture spacing index fsi which is the slope of a line fitted to a plot of mechanical layer thicknesses vs median joint spacing we collected joint spacing data along oblique scanlines from a large outcrop of the devonian brallier formation a distal turbidite sequence near huntingdon pa our analysis indicates that the spacing of cross joints correlates better with a mechanical layer thickness defined by the median systematic strike joint spacing r 2 d 0 78 fsid 1 02 than with a mechanical layer thickness defined by the stratigraphic bed thickness r 2 d 0 69 fsid 0 97 this is consistent with the conclusions of previous workers we also note that the spacing data from the cross joints exhibit a higher i e more positive value of kurtosis than the data from the earlier strike joints 1 66 vs 0 98 this is consistent with the idea that mechanical discontinuities alter joint spacing in a systematic manner in this case the cross joints may have been influenced by two sets of mechanical boundaries bedding and existing joints whereas the earlier strike joints were constrained by only one set bedding 1998 elsevier science b v all rights reserved

relative motion between the caribbean and north american plates and related boundary zone deformation from a decade of gps observations global positioning system gps measurements in 1986 1994 and 1995 at sites in dominican republic puerto rico cuba and grand turk define the velocity of the caribbean plate relative to north america the data show eastward motion of the caribbean plate at a rate of 21 1 mm yr 1 standard error in the vicinity of southern dominican republic a factor of 2 higher than the nuvel 1a plate motion model prediction of 11 3 mm yr independent measurements on san andres island and an euler vector derived from these data also suggest a rate that is much higher than the nuvel 1a model available data combined with simple elastic strain models give the following slip rate estimates for major left lateral faults in hispaniola 1 the north hispaniola fault offshore the north coast of hispaniola 4 3 mm yr 2 the septentrional fault in northern dominican republic 8 3 mm yr and 3 the enriquillo fault in southern dominican republic and haiti 8 4 mm yr the relatively high plate motion rate and fault slip rates suggested by our study combined with evidence for strain accumulation and historical seismicity imply that seismic risk in the region may be higher than previous estimates based on low plate rate low fault slip rate models and the relatively low rate of seismicity over the last century

microthermometric study of silicate melt inclusions in variscan granites from se germany volatile contents and entrapment conditions melt inclusions in granitic rocks are generally crystalline and must oberpfalz regions along the northern margin of the be homogenized to glass before analysis we employ a simple kinetic bohemian massif some of these granites particularly in technique with microthermometry to estimate total volatile contents the german erzgebirge are highly evolved geochemically and p t conditions of trapping of the melts from their hoand famous for the tin and uranium mineralization mogenization behaviour this information complements chemical associated with them several publications have condata from microprobe or ion probe analysis and can be obtained centrated on the geology geochemistry and ore from inclusions too small for direct analysis we present here values associations of the granites forster tischendorf 1994 for volatile contents as equivalent wt h2o trapping temperatures seltmann 1994 tischendorf forster 1994 hecht et and trapping pressures derived from studies of melt inclusions in some al 1997 siebel et al 1997 but their magmatic volatile variscan granites of the erzgebirge fichtelgebirge and oberpfalz contents and emplacement level are difficult to determine germany the volatile concentrations range from 3 to 10 equiv wt and have not often been addressed the granites from h2o microprobe analysis shows that the most volatile rich these regions contain abundant melt inclusions and these inclusions contain up to 8 wt f estimates of trapping offer the potential of constraining melt water contents pressures and temperatures suggest that crystallization began at an and conditions of trapping emplacement level of 3 6 5 km near 700 c with normal biotite all three regions contain composite plutons or plutonic and two mica granites and ended with topaz albite granite complexes which range in composition from un 650 c and pegmatitic phases down to 520 c this wide differentiated biotite granites to more highly evolved tworange of trapping temperatures and volatile contents is a general mica granites and finally to extremely evolved granites feature of melt inclusions in granites many of the granites studied containing li micas and topaz in some cases this comare highly evolved geochemically but the extreme volatile enrichment positional range is covered by different units of a single typical for these also occurs locally in the unspecialized granites pluton e g falkenberg granite oberpfalz whereas in other places individual plutons are more restricted in composition the erzgebirge region is particularly rich

transpressional rupture of an unmapped fault during the 2010 haiti earthquake the enriquillo plantain garden strike slip fault accommodates the relative motion between the north american and caribbean plates and was thought to have ruptured during the 2010 haiti earthquake satellite data instead indicate that a blind thrust fault possibly related to the haitian fold thrust belt was responsible and caused some contractional deformation on 12 january 2010 a mw 7 0 earthquake struck the port au prince region of haiti the disaster killed more than 200 000 people and caused an estimated 8 billion in damages about 100 of the country s gross domestic product1 the earthquake was initially thought to have ruptured the enriquillo plantain garden fault of the southern peninsula of haiti which is one of two main strike slip faults inferred to accommodate the 2 cm yr 1 relative motion between the caribbean and north american plates2 3 here we use global positioning system and radar interferometry measurements of ground motion to show that the earthquake involved a combination of horizontal and contractional slip causing transpressional motion this result is consistent with the long term pattern of strain accumulation in hispaniola the unexpected contractional deformation caused by the earthquake and by the pattern of strain accumulation indicates present activity on faults other than the enriquillo plantain garden fault we show that the earthquake instead ruptured an unmapped north dipping fault called the leog ne fault the leog ne fault lies subparallel to but is different from the enriquillo plantain garden fault we suggest that the 2010 earthquake may have activated the southernmost front of the haitian fold and thrust belt4 as it abuts against the enriquillo plantain garden fault as the enriquillo plantain garden fault did not release any significant accumulated elastic strain it remains a significant seismic threat for haiti and for port au prince in particular

crustal scale seismic profiles across the manila subduction zone the transition from intraoceanic subduction to incipient collision 1 we use offshore multichannel seismic mcs reflection and wide angle seismic data sets to model the velocity structure of the incipient arc continent collision along two trench perpendicular transects in the bashi strait between taiwan and luzon this area represents a transition from a tectonic regime dominated by subduction of oceanic crust of the south china sea west of the philippines to one dominated by subduction and eventual collision of rifted chinese continental crust with the luzon volcanic arc culminating in the taiwan orogeny the new seismic velocity models show evidence for extended to hyperextended continental crust 10 15 km thick subducting along the manila trench at 20 5 n along transect t1 as well as evidence indicating that this thinned continental crust is being structurally underplated to the accretionary prism at 21 5 n along transect t2 but not along t1 to the south coincident mcs reflection imaging shows highly stretched and faulted crust west of the trench along both transects and what appears to be a midcrustal detachment along transect t2 a potential zone of weakness that may be exploited by accretionary processes during subduction an additional seismic reflection transect south of t1 shows subduction of normal ocean crust at the manila trench

observations of microseismicity in the southern kuril trench area by arrays of ocean bottom seismometers summary two ocean bottom seismometer obs arrays were deployed to study microearthquake activity in the southernmost kuril trench area at a junction of the kuril and japan trenches the first obs observation was carried out from 1982 june to 1982 july and the second was from 1983 july to 1983 august each array consisted of 10 obss covering adjacent areas with an overlap during the observation periods each obs recorded about 50 earthquakes a day in average a tenth of which were located in and near the arrays a detailed picture of seismic activity associated with subduction and or bending of the pacific plate was obtained at the very point where it started to subduct spatial distribution of microseismicity in the southern kuril trench area is in general similar to that found in the japan trench area off sanriku a prominent microseismicity was found both landward and seaward of the axis of the kuril trench the seaward activity had a sharp seaward boundary along the edge of the seaward trench wall in the pacific basin beyond which no detectable event with magnitude of greater than 2 was observed although seismicity was high beneath a continental slope between the kuril trench and hokkaido there was a seismicity gap beneath the inner trench wall the gap coincided with an area of between 3 and 5 km in sea depth the depth of the events beneath the seaward trench wall ranged from 0 to 30 km and just beneath the trench axis it was slightly deeper 0 50 km a detailed comparison of seismicity between the kuril and japan trenches showed a variation in spatial distribution along the trench axis microseismicity near the trench axis is not uniform the activity beneath the continental slope formed a seismic zone dipping landward with a low dip angle of less than 10 which seemed to be a shallower extension of the lower plane of the double structured seismic zone in the kuril trench area it shows a contrast to the japan trench area where the seismicity corresponds to the upper plane

how transpressive is the northern caribbean plate boundary transpressive deformation at the northern caribbean plate boundary is accommodated mostly by two major strikeslip faults but the amount and location of accommodation of the compressional component of deformation is still debated we collected marine geophysical data including multi beam bathymetry and multichannel seismic reflection profiles along this plate boundary around hispaniola in the jamaica passage and in the gulf of gon ve the data set allows us to image the offshore active strike slip faults as well as the compressional structures we confirm that the enriquillo plantain garden fault zone epgfz in the jamaica passage has a primary strike slip motion as indicated by active left lateral strike sliprelated structures i e restraining bend asymmetrical basin en echelon pressures ridges and horsetail splay based on topographic cross sections across the epgfz we image a very limited compressional component if any for at least the western part of the jamaica passage toward the east of the jamaica passage the fault trace becomes more complex and we identify adjacent compressional structures in the gulf of gon ve distributed folding and thrust faulting of the most recent sediments indicate active pervasive compressional tectonics estimates of shortening in the jamaica passage and in the gulf of gon ve indicate an increase of the compressional component of deformation towards the east which nonetheless remains very small compared to that inferred from block modelling based on gps measurements

magnetotelluric evidence of the tectonic boundary between the rio de la plata craton and the pampean terrane chaco pampean plain argentina the extension of the transbrasiliano lineament abstract the transbrasiliano lineament represents a continental shear belt that transversely intersects the south american platform from nne to ssw much evidence of this lineament exists to the north but it remains uncharacterized in the distal andean foreland to the south where it is associated with the tectonic boundary between the rio de la plata craton and the pampean terrane this tectonic boundary is mostly unexposed in the chaco pampean plain argentina debate continues about the existence of an east or west dipping subduction zone and a later collisional event between the terranes here we report the results of a magnetotelluric survey along a w e profile at 27 s between 63 45 and 60 30 w to characterize the geoelectric structure the magnetotelluric data were processed the dimensionality and distortion of the geoelectrical medium were analyzed and a 2 d inversion model was developed the distribution of the resistivities at the lithospheric scale indicates a highly resistive crust 20 000 m on the east side of the profile that is correlated with the rio de la plata craton on the west side of the profile a less resistive but still highly resistive crust 12 000 m is correlated with the pampean terrane the highly resistive blocks are separated by an east dipping conductive anomaly 150 250 m that is correlated with the transbrasiliano lineament this conductive feature is consistent with the east dipping subduction model and can be explained by the presence of graphite in paleosutures in long stable geological terranes oblique convergence between the terranes may have developed the transpressional shear belt the results provide new geophysical evidence of the tectonic boundary between the rio de la plata craton and the pampean terrane beneath the chaco pampean plain that extends southward into the transbrasiliano lineament the study also improves the knowledge of the amalgamation of western gondwana

a ductile to brittle shear zone hosted cu mineralization geological geochronological geochemical and fluid inclusion studies of the lingyun cu deposit southern tianshan nw china abstract the lingyun cu deposit is located at the northern margin of the south tianshan accretionary complex nw china in the lingyun mine area the rocks are cut by a nw trending yanxingshan ductile to brittle shear zone all orebodies are hosted in crystal tuff the sulfide mineralization in the lingyun cu deposit can be divided into early e and late l paragenetic stages the e stage is characteristic of fault controlled sulfide assemblages chalcopyrite bornite chalcocite quartz veins in the foliation fabric of the crystal tuff with albite sericite epidote biotite assemblages in the l stage the assemblages of ankerite chalcopyrite bornite chalcocite are present in veinlets that cut the e stage assemblages the sulfide assemblages in the lingyun deposit are characterized by striations in the metamorphosed crystal tuff ribbon like silicate minerals in the crystal tuff share common deformation features with the sulfide assemblages the host rock of the lingyun cu deposit yields a concordia age of ca 405 ma indicating that the aerbishibulake formation formed during southward subduction of the south tianshan ocean beneath the tarim block moreover crystal tuff samples show well developed negative sr anomaly and positive rb th u nd and p anomalies which are common in arc related volcanic rocks the ca 297 ma re os isochron age yielded by sulfides is much younger than the host rock which implies that the lingyun cu deposit is a typical epigenetic deposit both similar ree fractionated patterns between sulfide ores and crystal tuff and the high initial 187 os 188 os ratio 18 54 0 67 indicate significant crustal materials input the 40 ar 39 ar plateau age of ca 292 ma from the ribbon like sericite in crystal tuff is coeval with the mineralization occurrence in the lingyun cu deposit by contrast diorite dikes that crosscut the crystal tuff formed at ca 221 ma which is much younger than the sulfide mineralization thus the mineralization in the lingyun deposit is likely to have been generated by shear zone activity rather than the intrusion of diorite dikes three types of fluid inclusions have been identified in the lingyun cu deposit aqueous w type mixed aqueous carbonic m type and pure carbonic c type inclusions these three types of fluid inclusions are all found in the e stage quartz whereas only the w type fluid inclusions have been observed in l stage ankerite fluid inclusions from the e stage commonly contain co 2 and h 2 o locally with n 2 with low salinity which are common in orogenic deposits by contrast l stage fluid inclusions show low co 2 concentrations and salinity indicating a significant inflow of meteoric water given the regional geology ore geology coeval ore forming and deformation and fluid inclusion features the lingyun cu deposit may be associated with the orogenic class of mineral systems

the role of manganese in the paragenesis of magmatic garnet an example from the old woman piute range california a reply strongly peraluminous plutons of the old woman piute range southeastern california display the differentiation sequence muscovite biotite granite rightarrow muscovite garnet biotite granite rightarrow garnet muscovite granite rightarrow garnet muscovite aplite and pegmatite the garnets show no evidence of reaction but biotites in garnet bearing rocks are rimmed by muscovite metamorphic assemblages in the country rocks suggest pressures of emplacement less than 4 5 kb the plutons become relatively enriched in manganese with differentiation whole rock ratios of molar mn fe mg increase from 0 01 in least felsic garnet free rocks to 0 3 in most felsic garnet rich rocks mno concentrations show a corresponding rise in biotites 0 4 to 1 8 wt and less clearly in garnets 9 to 25 the differentiation sequence textural relations and mineral and whole rock compositions suggest that garnet paragenesis was controlled by the reaction biotite mn rich liquid rightarrow garnet

polyphase tectonic history of the southern peninsula haiti from folding and thrusting to transpressive strike slip abstract the southern peninsula of haiti is a seismically active east west trending transpressive mountain range with elevations over 2 km present day deformation is mainly partitioned along the left lateral enriquillo plantain garden fault zone epgfz and associated oblique reverse faults and or folds the configuration of these faults their respective timing and the role of structural heritage on their development is poorly understood to address these questions we present the results of extensive field campaigns combined with satellite imagery interpretation and published data which allows us to constrain the cenozoic evolution of the southern peninsula our results show a polyphase tectonic history consisting of three major tectonic events 1 maastrichtian to early paleocene crustal scale folding that developed coevally with predominantly north to northeast dipping thrusts resulting in uplift and erosion of the cretaceous sedimentary cover in large parts of the southern peninsula 2 early miocene uplift and erosion which was strongest in the southwestern part of the peninsula and decreased eastwards did not affect the massif de la selle uplift is most likely unrelated to strike slip activity but resulted from folding in response to ne sw shortening that possibly reactivated older predominantly n to ne dipping thrusts 3 late miocene to present day deformation and uplift spatially distributed strike slip started during the late miocene and became progressively focused along the epgfz in the latest miocene oblique and thrust faults locally post date strike slip activity from the pliocene onward increase in compressional deformation from west to east is reflected by a change in structural style with predominantly strike slip faults in the west and transpressional faults in the east the latter possibly rooted on the epgfz at depth paleo stresses associated with a strike slip regime are at a significantly high angle to the trace of the epgfz indicating that the epgfz is a mechanically weak fault

mineral deposits of canada a synthesis of major deposit types district metallogeny the evolution of geological provinces and exploration methods wayne d goodfellow editor 1 068 pp geological association of canada mineral deposits division special publication no 5 2007 hardcover isbn 13 978 1 897095 24 9 price members cdn 60 00 non members cdn 80 00 following in the footsteps of other landmark reviews of major ore producing countries such as australia hughes 1990 solomon and groves 1994 and south africa anhaeusser and maske 1986 this substantial 1 000 pages monograph is a great achievement that should be in every geologic research library in the world in many ways it sets a new standard most notably in that all figures and photographs are in color and that the entire volume is available in electronic form both as an included dvd and mostly on the gac website it is common in such compendia to have a spectacular cover photo or frontispiece to catch the reader s attention and this book does not disappoint the frontispiece photo is of a 61 8 kg sample from the dome mine timmins ontario and is stated to contain 20 wt percent gold at today s prices the gold alone would be worth 1 5 million dollars

locating distributed faulting contributions from insar imaging to probabilistic fault displacement hazard analysis pfdha abstract prediction of location and amount of slip for distributed faulting associated to strong earthquakes is a recently explored issue with major implications in terms of hazard assessment currently the best practice involves the applications of probabilistic fault displacement hazard analysis pfdha whose results fit sufficiently well real data in the near range of the primary fault but show considerable inaccuracies in the far range we believe that this inaccuracy descends from the biased earthquake databases used for regression analysis whose data relative to old earthquakes were largely collected only by field surveys focused close to the primary fault i e near range remotely sensed data i e interferometric radar imaging insar offer the opportunity to precisely measure the surface deformation induced by strong earthquakes and thus to explore its possible relation with distributed faulting we analyze the l aquila earthquake case study 29th april 2009 mw 6 3 and explore the correlation between location and slip on distributed faulting and insar derived deformation field we find a significant correlation between occurrence of distributed faulting and profile curvature of the dislocation field in spite of the distance from the primary fault moreover distributed faults tend to occur within the area deformed by the earthquake as imaged by insar data and whose extent is directly proportional to the earthquake magnitude mw according to a dataset of 30 recent earthquakes we then propose that these observations have to be incorporated into the present pfdha practice as limit boundaries to possible scenarios of probabilistic analysis and that an integrated use of field based and remotely data collection have to be implemented following strong earthquakes

oblique collision in the northeastern caribbean from gps measurements and geological observations 1 previous caribbean gps studies have shown that the rigid interior of the caribbean plate is moving east northeastward 070 at a rate of 18 20 3 mm yr relative to north america this direction implies maximum oblique convergence between the island of hispaniola on the caribbean plate and the 22 27 km thick crust of the bahama carbonate platform on the adjacent north america plate we present a tectonic interpretation of a 15 site gps network which spans the hispaniola bahama oblique collision zone and includes stable plate interior sites on both the north america and caribbean plates measurements span the time period of 1994 1999 in a north america reference frame gps velocities in puerto rico st croix and the lesser antilles indicate that these areas move as a single block in an east northeast direction 070 at a rate of 19 20 mm yr consistent with the movement of the rigid interior of the caribbean plate gps velocities at six sites in central and eastern hispaniola dominican republic show drastically different behavior with more eastwardly strikes 080 and much slower rates 4 17 mm yr than areas of the stable caribbean plate the boundary between the relatively slower moving hispaniola collisional zone and the relatively faster moving uncollided puerto rico virgin islands area is the mona passage where late neogene rifting occurs in a broad zone elastic modeling favors strain partitioning with oblique slip on the outer low angle submarine thrust faults north hispaniola muertos and strike slip on the inner subvertical subaerial strike slip faults septentrional enriquillo

offshore sedimentary effects of the 12 january 2010 haiti earthquake although the 12 january 2010 haiti earthquake was one of the deadliest earthquakes in history it left no clear geological evidence of rupture on land as a tectonic event the earthquake was complex even the faults involved remain unclear using geophysical and coring data we document direct evidence of the sedimentation generated by the catastrophic 12 january 2010 earthquake offshore these studies document submarine paleoseismology methods that can be used for assessing seismic risk in this and other tectonic settings such as the california san andreas fault where deeper buried blind thrusts may exist shaking by the 12 january main shock triggered sediment failures and turbidity currents from coastal sources to deep water sinks an 0 05 km 3 turbidite was deposited in the canal du sud basin 1750 m water depth over 50 km 2 almost 2 months after the main shock a 600 m thick sediment plume was still present in the lowermost water column at this location the turbidite was time correlated to the 12 january earthquake by the excess 234 th in the sediments with a half life of 24 days its presence documents an infl ux of terrigenous sediment mixing with marine sources derived from the basin slopes this turbidite and older ones observed beneath it displays complex cross bedded and fi ning upward stratigraphy indicative of long waves and seiche oscillations that are consistent with locally reported tsunamis this 12 january sedimentary record highlights the potential for submarine paleoseismology to unravel the seismic history of continental transform boundaries such as the enriquillo plantain garden fault in the dominican republic haiti and jamaica as well as other tectonic settings where no clear land based evidence for a rupture exists

active tectonics along the cul de sac enriquillo plain and seismic hazard for port au prince haiti abstract the active faults in haiti were not well known and no detailed mapping of active fault traces was available before the 2010 m7 0 earthquake the lack of detailed fault mapping hindered the interpretation of the event and the seismic hazard assessment here using high resolution lidar topography aerial photographs bathymetric charts together with geological data complemented with field observations we carried out a morphotectonic analysis at a variety of scales we analyzed the drainage network at the northern front of the massif de la selle sierra de bahoruco msb by mapping the fans of the main rivers and their associated drainage basins we found that the areas of all the fans were compatible with the sizes of their drainage basins except the paleofan of port au prince we interpret that this paleofan has been offset by 7 9 0 3 km across the main strike slip enriquillo plantain garden fault epgf and we estimate a minimum horizontal slip rate of 3 mm yr over the pleistocene moreover in the cul de sac enriquillo plain within which the capital city of port au prince is located we mapped numerous nw se to wnw ese striking quaternary folds and thrust faults some of the thrust faults are north dipping and located to the southern front of the matheux neiba lower miocene fold other thrusts such as those near ganthier jacquet nan cadastre and port au prince are south dipping and located along the northern front of the msb lower miocene fold previously saint fleur et al 2015 showed that the 2010 haiti earthquake activated both one of the young thrusts lamentin and the epgf consistent with oblique convergence between the caribbean and the north american plates

correlation of plume morphologies on joint surfaces with their fracture mechanic implications the fractography and conditions of propagation of joints that cut devonian siltstones in the appalachian plateau new york and eocene chalks from the beer sheva syncline israel are investigated the joints cutting the siltstones are marked by s type and c type plumes and the joints cutting the lower eocene and middle eocene chalks are marked by coarse and delicate plumes respectively the four plume types propagated under sub critical slow propagation conditions on the semi quantitative fracture velocity v versus the tensile stress intensity ki c urves the sa nd c plume types fall in the ki 0 073 0 79 mpa m 1 2 and v 2 10 4 10 2 m s and ki 0 073 0 79 mpa m 1 2 and v 10 6 10 4 m s ranges respectively the coarse and delicate plumes fall in the ki 0 03 0 17 mpa m 1 2 and v 10 6 4 10 5 m s and ki 0 03 0 17 mpa m 1 2 and v 10 4 5 10 3 m s ranges respectively generally slow plumes are relatively short show periodicity and typically exhibit superposition of arrest marks on the other hand faster plumes are longer and continuous occur particularly in thinner layers and show no superposition of arrest marks there is a clear distinction between two ensegmentation end members in the joint fringe the discontinuous breakdown type and the continuous breakdown type there are also transitional variations between the end members only curved discontinuous breakdown type boundaries of en echelon fringes can be equated with mirror boundaries

analogue modelling of fracturing in cooling plutonic bodies abstract fractures formed when igneous rocks cool below the surface of the earth are of considerable current interest in studies of hydrology mineral systems and radioactive waste disposal however little is known about the geometry and kinematics of such fractures conceptual models suggest that early fractures result from emplacement forces the cloos model while two dimensional numerical modelling suggests that fractures may result from the contraction of cooling bodies we use analogue modelling to investigate the geometry of fractures formed in a cylindrical static contracting body our experiments show that dehydration of buried starch flour is a workable analogue fractures in the analogue material result from drying and contraction of a cylindrical volume which differs from previous experiments in which drying was from a single planar surface and resulted in the formation of columnar joints in buried analogue models two key fracture sets form internally producing sub vertical radial fractures and concentric fractures that curve downwards with depth fracture density decreases towards the centre and bottom of the samples samples that were buried more deeply have fewer and less curved concentric fractures than those with shallow burials radial fractures have similar orientations to those predicted from numerical models and concentric fractures are comparable to marginal fissure orientations of the cloos model the analogue models suggest that both radial and concentric fractures may result from the contraction of plutonic bodies

earthquake source parameters for the 2010 january haiti main shock and aftershock sequence summary previous analyses of geological and geodetic data suggest that the obliquely compressive relative motion across the caribbean north america plate boundary in hispaniola is accommodated through strain partitioning between near vertical transcurrent faults on land and low angle thrust faults offshore in the dominican republic earthquake focal mechanism geometries generally support this interpretation little information has been available about patterns of seismic strain release in haiti however due to the small numbers of moderate to large earthquakes occurring in western hispaniola during the modern instrumental era here we analyse the damaging mw 7 0 earthquake that occurred near port au prince on 2010 january 12 and aftershocks occurring in the four months following this event to obtain centroid moment tensor cmt solutions for 50 earthquakes with magnitudes as small as mw 4 0 while the 2010 january main shock exhibited primarily strike slip motion on a steeply dipping nodal plane strike 250 dip 71 and rake 22 we find that nearly all of the aftershocks show reverse faulting motion typically on high angle 30 45 nodal planes two small aftershocks mw 4 5 and 4 6 located very close to the main shock epicentre show strike slip faulting with geometries similar to the main shock one aftershock located off the south coast of haiti shows low angle thrust faulting we also examine earthquakes occurring in this region from 1977 2009 successful analysis of four such events provides evidence for both strike slip and reverse faulting the pattern of seismic strain release in southern haiti thus indicates that partitioning of plate motion between transcurrent and reverse structures extends far west within hispaniola while we see limited evidence for low angle underthrusting offshore most reverse motion appears to occur on high angle fault structures adjacent to the enriquillo fault our results highlight the need to incorporate seismogenic slip on compressional structures into hazard assessments for southern haiti

joint inversion of insar gps teleseismic and strong motion data for the spatial and temporal distribution of earthquake slip application to the 1999 izmit mainshock the space time distribution of slip of the 17 august 1999 izmit earthquake is investigated by inverting synthetic aperture radar sar interferometry and global positioning system gps data together with teleseismic broadband and near field strong motion records surface offsets are used as an added constraint special emphasis is given to analysis of the resolution of the different data sets we use a four segment finite fault model and a nonlinear inversion scheme allowing slip to vary in amplitude direction and duration as well as variable rupture velocity from the inversion of synthetic data we find that the best spatial resolution can be expected in the upper half of the fault model above 12 km where coverage of the interferometric sar data is good western half of the rupture and near the gps and strong motion stations teleseismic data are found to have a lower resolution that is more evenly distributed over the fault model the joint inversion of all the data sets has an increased resolving power compared with the separate inversions and gives a more robust description of the space and time distribution of slip our study shows the importance of resolution tests in evaluating the reliability of earthquake kinematic models and it confirms that an excellent fit of a single kind of data does not necessarily imply a good retrieval of the kinematic properties of an earthquake the izmit rupture which is almost pure right lateral strike slip faulting is dominated by the bilateral breaking of a central asperity located between 29 7 e about 10 km west of the city of golcuk and 30 4 e eastern margin of sapanka lake with slip reaching 6 8 m in the depth range 6 12 km the western termination of the rupture is found near the city of yalova but large slip ends around 29 7 e about 10 km east of hersek delta a second area of large slip is required by all the data sets further east toward the city of duzce between 30 7 e and 31 1 e karadere and duzce faults this eastern slip zone which is separated from the main central asperity by an area of greatly reduced slip is less well constrained by the data however a strong motion station near the city of duzce helps to locate a high slip patch near 31 1 e in the depth range 6 12 km the total seismic moment resulting from the joint inversion is 2 4 1027 dyne cm most of the energy release occurred in a short time less than 15 sec corresponding to the bilateral breaking of the central asperity rupture propagation is relatively uniform and fast toward the west with a rupture velocity close to 3 5 km sec propagation of large slip toward the east is initially slower but it accelerates during a short time interval about 10 sec after rupture nucleation eastward progression then slows down to less than 2 km sec after 15 sec and rupture almost vanishes in amplitude ca 20 sec after initiation rupture propagation then proceeds on the easternmost karadere and duzce fault segments east of 30 7 e from 22 to ca 50 sec supershear rupture propagation is not required for modeling the waveforms considered in this study the hypocenter of the duzce earthquake which occurred 3 months later 12 november 1999 m w 7 2 is located in the immediate vicinity of the easternmost slip patch of the izmit earthquake manuscript received 28 july 2000

strain partitioning and fault slip rates in the northeastern caribbean from gps measurements 1 gps data collected in the dominican republic from 1994 to 2001 show that oblique convergence between the north american and caribbean plates is partitioned between 5 2 2 mm yr 1 of dip slip reverse motion on the north hispaniola thrust approximately n s and 12 8 2 5 mm yr 1 and 9 0 9 0 mm yr 1 of approximately e w left lateral strike slip motion on the septentrional and enriquillo faults 95 confidence the agreement between gps and paleoseimological slip rates on the septentrional fault together with the 770 960 years since the last major earthquake and the 800 1200 years maximum repeat time of major earthquakes may indicate that the septentrional fault is currently in the late phase of its rupture cycle

lithospheric controls on the formation of provinces hosting giant orogenic gold deposits ages of giant gold systems 500 t gold cluster within well defined periods of lithospheric growth at continental margins and it is the orogen scale processes during these mainly late archaean palaeoproterozoic and phanerozoic times that ultimately determine gold endowment of a province in an orogen a critical factor for giant orogenic gold provinces appears to be thickness of the subcontinental lithospheric mantle sclm beneath a province at the time of gold mineralisation as giant gold deposits are much more likely to develop in orogens with subducted oceanic or thin continental lithosphere a proxy for the latter is a short pre mineralisation crustal history such that thick sclm was not developed before gold deposition in constrast orogens with protracted pre mineralisation crustal histories are more likely to be characterised by a thick sclm that is difficult to delaminate and hence such provinces will normally be poorly endowed the nature of the lithosphere also influences the intrinsic gold concentrations of potential source rocks with back arc basalts transitional basalts and basanites enriched in gold relative to other rock sequences thus segments of orogens with thin lithosphere may enjoy the conjunction of giant scale fluid flux through gold enriched sequences although the nature of the lithosphere plays the crucial role in dictating which orogenic gold provinces will contain one or more giant deposits the precise siting of those giants depends on the critical conjunction of a number of province scale factors such features control plumbing systems traps and seals in tectonically and lithospherically suitable terranes within orogens

mechanisms controlling rupture shape during subcritical growth of joints in layered rocks during joint propagation the orientation of plume lines on joint faces allows for mapping the path taken by the crack tip line during rupture growth rupture shapes in layered clastic sediments of the devonian catskill delta finger lakes district new york indicate joint growth through three stages where velocity of the tip line v tl varies as a function of the crack tip stress intensity k i the initial stage of growth is characterized by a rupture of approximately circular or elliptical shape that expands from an initiation fl aw with a velocity v tl in some cases primary growth involves self correction where an elliptical rupture redistributes the crack tip stress so that the rupture returns to a more stable circular shape the crack tip line eventually propagates to a bedding interface where properties of either a plastic or a noncohesive bedding interface cause v tl 0 along a portion of the tip line the onset of secondary growth occurs when the rupture tip line intersects both bedding interfaces and splits into two discontinuous segments that propagate synchronously as a single coherent rupture nonuniform nonsystematic v tl eventually interferes with the rupture s ability to grow coherently and thus leads to the transition to tertiary growth characterized by the detachment of the coherent rupture into one or more independently propagating noncoherent tip lines throughout all three stages of rupture growth the k i dependent v tl points to subcritical propagation variation from a smooth to rough plume morphology is consistent with propagation through region i of the subcritical regime with a transition at v tl 10 5 m sec rupture velocity may enter region ii of the subcritical regime but such a broad range of k i must be crossed to reach region iii and quasistatic behavior at the critical stress intensity k ic that region ii acts as a barrier through which few joints pass thus greatly limiting the number of postcritical joints in the catskill delta if not in the crust of the earth

neoproterozoic crustal accretion in central brazil recent geochronological studies have demonstrated the existence of several neoproterozoic orthogneiss and metavolcanic are suites ca 900 to 600 ma in the southern part of the tocantins province a major neoproterozoic orogenic area in central brazil exposed between the amazon and sao francisco cratons nd and sr isotopic characteristics of these metamorphic suites are primitive initial 87 sr 87 sr ratios vary from 0 7024 to 0 7042 and initial nd values are positive varying between 0 2 and 6 9 the most primitive initial sr and nd isotopic compositions are very similar to model depleted mantle compositions at the time of formation of the original magmas the mantle like characteristics of these are suites in western goias contradict previous ensialic evolution models for the tocantins province and reveal that crustal accretion processes were important in large areas of central brazil during neoproterozoic time

the tectonic evolution of the transbrasiliano lineament in northern parana basin brazil as inferred from aeromagnetic data data from six airborne magnetic surveys were compiled and analyzed to develop a structural interpretation for the transbrasiliano lineament in northern parana basin brazil magnetic lineaments interpreted to reflect geologic contacts and structures at different depths were illuminated using the matched filter technique applied to aeromagnetic anomalies field based structural measurements generally support our magnetic analysis we estimated three primary magnetic zones i a zone of deep magnetic sources at 20 km depth ii an intermediate basement zone at 6 km depth and iii a shallow zone of near surface geological features at 1 5 km depth the deepest zone exhibits three major ne trending crustal discontinuities related to the transbrasiliano lineament dividing the region into four geotectonic blocks anomalies associated with the intermediate zone indicate directional divergence of subsidiary structures away from the main transbrasiliano fault which strikes n30 e the shallow magnetic zone includes near surface post brasiliano orogenic granites our analysis identified ne trending sigmoidal lineaments around these intrusions indicating intense zones of deformation associated with probable shear structures at the shallow depth zone magnetic anomalies caused by cretaceous alkaline intrusive bodies and basalts of the serra geral formation are enhanced by the matched filter method these igneous bodies are related to extensional nw striking lineaments and seismicity aligned along these lineaments suggests that they currently are reactivated prior to flexural subsidence of the parana basin reactivation processes along transcurrent elements of the transbrasiliano lineament promoted extensional processes and formed initial parana basin depocenters cretaceous and more recent sedimentation also correlate with reactivations of ne striking structures

loading configurations and driving mechanisms for joints based on the griffith energy balance concept abstract using the griffith energy balance concept to model joint propagation in the brittle crust two laboratory loading configurations serve as appropriate analogs for in situ conditions the dead weight load and the fixed grips load the distinction between these loading configurations is based largely on whether or not a loaded boundary moves as a joint grows during displacement of a loaded boundary the energy necessary for joint propagation comes from work by the dead weight i e a remote stress when the loaded boundary remains stationary as if held by rigid grips the energy for joint propagation develops upon release of elastic strain energy within the rock mass these two generic loading configurations serve as models for four common natural loading configurations a joint normal load a thermoelastic load a fluid load and an axial load each loading configuration triggers a different joint driving mechanism each of which is the release of energy through elastic strain and or work the four mechanisms for energy release are joint normal stretching elastic contraction poroelastic contraction under either a constant fluid drive or fluid decompression and axial shortening respectively geological circumstances favoring each of the joint driving mechanisms are as follows the release of work under joint normal stretching occurs whenever layer parallel extension keeps pace with slow or subcritical joint propagation under fixed grips a substantial crack normal tensile stress can accumulate by thermoelastic contraction until joint propagation is driven by the release of elastic strain energy within the earth the rate of joint propagation dictates which of these two driving mechanisms operates with faster propagation driven by release of strain energy like a dead weight load acting to separate the joint walls pore fluid exerts a traction on the interior of some joints joint propagation under fluid loading may be driven by a release of elastic strain energy and or work by the pore fluid during poroelastic contraction again propagation velocity dictates the driving mechanism with critical to supercritical joint propagation accompanying fluid decompression and subcritical crack propagation taking place under a constant fluid drive during axial shortening a jointing process called axial splitting may occur following wing crack growth from an initial crack tilted relative to the maximum compressive stress here the joint driving mechanism may be either the work of a remote stress i e a dead weight or the release of elastic strain energy i e fixed grips

carbon isotope studies of auriferous quartz carbonate veins from two orogenic gold deposits from the neoarchean chitradurga schist belt dharwar craton india evidence for mantle magmatic source of auriferous fluid abstract carbon and oxygen isotopic compositions of carbonates from auriferous quartz carbonate veins qcvs of two orogenic gold deposits ajjanahalli and guddadarangavvana halli g r halli from the neoarchean chitradurga schist belt of the dharwar craton southern india are examined to understand the origin of the mineralizing fluids the average carbonate carbon 13cpdb and oxygen 18osmow isotope compositions of qcvs of ajjanahalli are 5 5 1 3 and 14 1 2 7 respectively the same ratios for the qcvs of g r halli are 6 2 1 9 and 14 1 0 5 the corresponding average fluid 13c and 18o compositions are 5 81 1 14 13 78 5 1 for ajjanahalli and 4 64 0 7 6 50 0 6 for g r halli the 13cpdb of syn sedimentary carbonates of bif of ajjanahalli 1 8 0 1 carbonated metabasalts of ajjanahalli 1 4 and g r halli 1 3 fall in the compositional range of marine carbonates 0 2 as dissolution decarbonation reactions during metamorphism of pre existing carbonate carbonated rocks produce co2 with 13c values similar to or more enriched than parent rock the carbonate or fluid 13c ratios of the qcvs which fall in the compositional range of mantle magmatic derived co2 or carbonates obtained in this work cannot be the result of metamorphism it is proposed that gold mineralizing fluids were derived from juvenile magmatic melts and were channeled through crustal scale shear zones to give rise to the gold deposits

diversity within a unified model for archaean gold mineralization in the yilgarn craton of western australia an overview of the late orogenic structurally controlled gold deposits abstract the archaean yilgarn craton has produced 3000 tonnes of gold mainly from structurally controlled deposits that formed during the latest stages of an orogenic event that affected the entire craton and culminated in the period 2 66 2 63 ga as a group these late orogenic deposits encompass a wide range of host rocks structural settings and structural styles and alteration types however several consistent features justify grouping the deposits into a single class of mineralization these features include timing relative to orogenesis high gold to base metal ratios an association with potassium metasomatism and carbonation of host rocks low sulfide contents and a low salinity h 2 o co 2 ch 4 ore fluid most deposits formed in domains of low mean stress during east west regional compression and preserve evidence in the form of quartz vein arrays and hydraulic breccias for high fluid pressures and rock dilation the range of ore depositional conditions implied by alteration assemblages at various deposits makes the term mesothermal an inappropriate description for this class of mineralization the term late orogenic structurally controlled gold deposits is proposed as one which more completely encompasses the class of mineralization described in this overview late orogenic structurally controlled gold deposits formed in thermal equilibrium with high grade metamorphic rocks at the margins of the greenstone belts but were retrograde with respect to lower grade host rocks in the cores of greenstone belts these relationships probably reflect diachronous metamorphism and a single gold mineralization event which was contemporaneous with the later high grade metamorphism geochronological data indicate gold deposition at ca 2 63 ga in the western part of the yilgarn craton isotopic data suggest similar depositional ages in the eastern part of the craton eastern goldfields superterrane but this timing is difficult to reconcile with field relationships that suggest broad contemporaneity between regional metamorphism and gold mineralization at ca 2 66 ga the main competing genetic models for late orogenic structurally controlled gold mineralization in the yilgarn craton propose an orthomagmatic deeply sourced or metamorphogenic ore fluid none of these models can account satisfactorily for all the features of the late orogenic structurally controlled gold deposits

magnetic fabric and modeled strain distribution in the head of a nested granite diapir the melechov pluton bohemian massif abstract the melechov pluton bohemian massif is interpreted as a mid crustal nested granitic diapir with an apical part exposed at the present day erosion level the diapir head exhibits a concentric structure defined by lithologic zoning and by the anisotropy of magnetic susceptibility ams in concert with theoretical models outward dipping margin parallel magnetic foliations are associated with oblate shapes of the susceptibility ellipsoids and higher degree of anisotropy passing inward into weaker triaxial to prolate fabric by contrast magnetic fabric in an inner granite unit is in places oriented at a high angle to internal contacts and is interpreted as recording an internal diapir circulation we use inverse modeling to calculate strain variations across the diapir from the ams data the magnetic fabric parameters and calculated strains are in agreement with strain distribution in heads of model newtonian diapirs traveling a distance of two body radii and suggest granitic magma ascent as a crystal poor suspension followed by crystallization of fabric markers and their response to strain near the final emplacement level the intrusive fabric thus formed late but though generally weak was still capable of recording incremental strain gradient in the granite diapir

three dimensional fracture distribution in relation to local cooling in a granitic body an example from the toki granitic pluton central japan this paper describes a spatial distribution of fracture frequency fracture number per unit interval in the toki granitic pluton central japan and their evaluation with respect to cooling behavior after solidification of the pluton three dimensional distribution of fracture frequency of all fractures all angle fractures based on borehole television data collected from 19 boreholes shows that 1 the central region of the granite has a high fracture frequency and 2 fracture frequency decreases with decreasing elevation measured from the mean sea level with the exception of the west side of the body the development of sub solidus reaction textures reflects the annealing duration of the pluton after solidification the extent of sub solidus reaction textures was measured at two neighboring positions and the difference was divided by the distance between the two positions the resulting quantity is here defined as a local cooling indicator lci we observed a related pattern between the distribution of fracture frequency and lci the high lci region corresponds to the region with a high frequency of all fractures and vice versa this relation indicates that fracture genesis has been mostly controlled by local cooling after solidification which caused thermal stress thus the three dimensional pattern of lci is a potential diagnostic tool for obtaining the spatial distribution of all fractures

plate boundary readjustment in oblique convergence example of the neogene of hispaniola greater antilles the haitian fold and thrust belt is the major mountain belt of haiti western part of hispaniola greater antilles and resembles a compressive restraining bend between the two major faults which have driven the opening of the cayman basin since the eocene during the rifting stage from the middle to the late eocene this area underwent an extensional evolution with fissural volcanic activity along ne sw tilted blocks the haitian fold and thrust belt was constructed from the early miocene until the present by stacking sedimentary units into a collisional wedge perpendicular to the tilted blocks which was propagating to the southwest during the construction of the wedge piggyback basins were formed and progressively uplifted during the late neogene convergence is localized in the cul de sac enriquillo trough where the active front proceeds southward onto the beata ridge in this area miocene to quaternary wrench structures of the lower plate like the southern peninsula and the enriquillo plantain garden faults are reactivated as normal faults owing to the loading of the fold and thrust belt

fringe cracks key structures for the interpretation of the progressive alleghanian deformation of the appalachian plateau vertical joints in devonian clastic sedimentary rocks of the finger lakes area of new york state are ornamented with arrays of fringe cracks that reveal the complex deformational history of the appalachian plateau detachment sheet during the alleghanian orogeny three types of fringe cracks were mapped gradual twist hackles abrupt twist hackles and kinks gradual twist hackles are curviplanar en echelon fringe cracks that propagate with an overall vertical direction within the bed hosting the parent crack and are found in all clastic lithologies of the detachment sheet abrupt twist hackles propagate as planar features in thick shale beds above or below the siltstone beds hosting parent joints kinks propagate horizontally as planar surfaces from the tips of parent joints in siltstone beds the breakdown of the parent joint into either gradual or abrupt twist hackles depends on the orientation and magnitude of the remote stress field internal fluid pressure and the elastic properties of the bed the twist angle of gradual twist hackles is larger in coarser clastic beds indicating that stress and internal pressure are more important parameters than elastic properties in controlling breakdown assuming that the vertical stress axis s v equals 78 mpa at 3 km burial depth the difference in twist angle between sandstone and shale beds is used to estimate the maximum horizontal stress difference in the shale beds as s h s h 2 5 mpa when s h s h 12 mpa in sandstone beds the twist angle of the fringe cracks and the abutting relationships of parent joints give an indication of the overall change in stress field orientation within the detachment sheet during alleghanian tectonics these parent joints indicate a regional clockwise stress rotation of alleghanian age concordant with the twist angle of fringe cracks throughout the western part of the study area a counterclockwise twist angle in the eastern portion indicates a local stress attributed to drag where no salt was available to detach the eastern edge of the plateau sheet the clockwise change in stress orientation is consistent with the rotation in stress orientation found in the anthracite belt of the pennsylvania valley and ridge but is opposite to the sense of rotation in the southwestern portion of the detachment sheet western pennsylvania and west virginia the two regional rotation domains are separated by the juniata culmination

geodynamic settings of mineral deposit systems mineral deposits represent extraordinary metal concentrations that form by magmatic magmatic hydrothermal or hydrothermal processes in geodynamic environments typified by anomalously high thermal and or mechanical energy near plate boundaries as they require the conjunction of specific environmental conditions to form particular mineral deposit types tend to occupy specific geodynamic niches the temporal distributions of mineral deposit types reflect both formational and preservational processes in the archaean and palaeoproterozoic these were linked because of preservation in continental crust connected to thick buoyant subcontinental lithospheric mantle sclm but were decoupled by the neoproterozoic and phanerozoic as a result of evolution to thinner increasingly dense sclm the transition marks a change from mantle plume influenced plate tectonics to modern style plate tectonics with broadly coincident environmental changes and a major impact on the nature and abundance of preserved mineral deposit types as mineral deposits represent an integral part of tectonic process they are essential indicators of that process and geodynamic settings and should be incorporated into any holistic tectonic terrane analysis their distribution also provides a particularly critical test on ancient continental reconstructions derived from palaeomagnetic data conversely such reconstructions provide a first order targeting tool for the conceptual exploration required to discover new mineral provinces and deposits under cover

the 2005 heidelberg and speyer earthquakes and their relationship to active tectonics in the central upper rhine graben we determine the source parameters of three minor earthquakes in the upper rhine graben urg a cenozoic rift using waveforms from permanent and temporary seismological stations two shallow thrust faulting events m l 2 4 and 1 5 occurred on the rift shoulder just south of heidelberg in march 2005 they indicate a possible movement along the sediment crystalline interface due to tectonic loading from the near by odenwald in february 2005 an earthquake with a normal faulting mechanism occurred north of speyer this event m l 2 8 had an unusual depth of about 22 km and a similar deep normal faulting event occurred there in 1972 m l 3 2 other lower crustal events without fault plane solutions are known from 1981 and 1983 at such a depth inside the lower crust ductile behaviour instead of brittle faulting is commonly assumed and used for geodynamic modelling based on the newly available fault plane solutions we can confirm the brittle extensional regime in the upper and lower crust in the central to northern urg indicated in earlier studies

the iugs systematics of igneous rocks in order to create a sustainable classification of igneous rocks which all geologists might use an international body was set up by the iugs the iugs subcommission on the systematics of igneous rocks in the course of creating the classification the subcommission has established ten principles for its construction and for defining an appropriate nomenclature the principles are 1 use descriptive attributes 2 use actual properties 3 ensure suitability for all geologists 4 use current terminology 5 define boundaries of rock species 6 keep it simple to apply 7 follow natural relations 8 use modal mineralogy 9 if mode not feasible use chemistry 10 follow terminology of other iugs advisory bodies these principles and their rationale have not previously been enunciated the classification separates and individually classifies the pyroclastic carbonatitic melititic lamprophyric and charnockitic rocks before entering the main qapf classification for plutonic and volcanic rocks which is based on the modal mineral proportions of quartz q alkali feldspar a and plagioclase p or of alkali feldspar a plagioclase p and feldspathoids f rocks with mafic content 90 have their own classification if the mineral mode cannot be determined as is often the case for volcanic rocks then a chemical classification of total alkalis versus silica tas is used the nomenclature for these classifications necessitates only 297 rock names out of the c 1500 that exist

granites and the geodynamic history of the neoproterozoic brasilia belt central brazil a review abstract recent field and geochronological studies have demonstrated the importance of granitic magmatism in the evolution of the neoproterozoic brasilia belt in central brazil this is an orogenic belt developed in response to the convergence between the amazon sao francisco congo and parana continental blocks the presence of neoproterozoic juvenile arc rocks and syn collisional peraluminous granites challenged previous intracontinental evolution models for the belt the granitoid intrusions reviewed in this paper record the different stages of evolution of the orogen and their field and isotopic characteristics can be used to reconstruct the tectonic history of the belt the main field and isotopic characteristics of four granite suites associated with the brasilia belt are reviewed i 1 77 1 58 ga old rift related a type granite intrusions ii ca 0 8 0 7 syn collisional granitoids iii arc metatonalites and metagranodiorites ca 0 9 to 0 63 ga and iv bimodal post orogenic suite ranging in age from ca 0 59 to 0 48 ga these rocks suggest that during most of the neoproterozoic the western margin of the sao francisco continent faced a large oceanic basin where subduction and oceanic lithosphere consumption started at ca 0 9 ga roughly coeval with the initial stages of the break up of rodinia final ocean closure happened at ca 0 63 0 60 ga with crustal thickening uplift and erosion post orogenic extension related magmatism took place between ca 0 6 and 0 5 ga and was partially contemporaneous with the deposition of the paraguay and tucavaca sedimentary successions resulting from the rifting event related to the break up of laurentia from southwestern gondwana