the metagabbros orthogneisses and paragneisses of the connemara complex western ireland although now largely disappeared within the 400 ma old galway granite the syntectonic connemara metagabbro gneiss complex which crystallized at 490 ma arenig is the largest intrusion into the dalradian rocks it is part of widespread cambro ordovician volcanism and plutonic injection into continental crust in the appalachian caledonide orogenic belt being synchronous in crystallization with the widely obducted 490 ma ophiolites within the orogeny the peridotites and hornblende gabbros were injected broken up and shouldered aside by quartz diorite granodiorite granite and trondhjemite gneisses and it is shown that these orthogneisses are not the in situ differentiation products of the gabbro magma the hornblende in the metagabbros is mainly igneous but is partly metamorphic and replaces olivine fo 75 92 orthopyroxene en 65 92 clinopyroxene wo 48 5 en 50 39 fs 5 14 and plagioclase typically an 80 92 range an 50 96 an aureole at least 10 km wide in the sillimanite zone was imposed and cordierite garnet sillimanite dalradian hornfelses were partially melted at temperatures up to 1000 o c near to the gabbros at 4 5 1 kbar corresponding to c 18 km depth this suggests that the complex forms part of the root of a now eroded batholith of calc alkaline affinities the gabbros corresponding to the transition zone to a basic bottom which is often supposed to underlie many batholiths within the orthogneisses are sheets of paragneiss formed from dalradian metasediments which have been folded up from the floor and down into sides of the magma chamber which process could be illustrative of the means by which basic magma can intimately interact with crustal material the 18 o 16 o d h nd and sr isotope evidence and the existence of inherited zircons in the gneisses indicate that the gabbro and gneiss magmas were significantly contaminated with crustal possibly dalradian material both before and after intrusion with the lowest initial 87 sr 86 sr at 490 ma being 0 708 even in samples far removed from metasediment the metagabbros are tholeiitic to high alumina basalt in character but the gneisses have distinct calc alkaline geochemistry the chemistry igneous hornblende and highly calcic plagioclase match many arc plutons in the western usa the syntectonic nature and the ubiquitous gneissic fabric in the quartz diorites trondhjemites and granites is a consequence of early movements which were probably in part connected with the separation of the connemara massif and which culminated in slicing off the largely inverted complex and carrying it southwards on the mannin thrust which underlies the whole of connemara the complex is thus a fragment of a now disrupted cambro ordovician continental magmatic arc or continent island arc environment which can be traced along the se edge of the laurentian continent

geological significance of 40ar 39ar mica dates across a mid crustal continental plate margin connemara grampian orogeny irish caledonides and implications for the evolution of lithospheric collisions1 the connemara region is a world class example of a regional scale high temperature metamorphic terrain its rock record documents formation of a bi vergent orogenic wedge and associated calkalkali

new constraints on the timing of early proterozoic tectonism in the black hills south dakota with implications for docking of the wyoming province with laurentia a question regarding the 1900 1600 ma assembly of laurentia is whether the wyoming province west central united states was part of the hearne province west central canada prior to the early proterozoic trans hudson orogeny or a separate entity welded later to a hearne superior continent central canada new 40 ar 39 ar mica dates help to address this question by extending a middle proterozoic geochronologic front long established along the southern wyoming province into the black hills of south dakota this suggests that previously unexplained north directed fold nappes f 1 in the black hills resulted from island arc accretion to the south ca 1780 ma north northwest trending upright f 2 folds which formed during east west collision of the wyoming and superior provinces must therefore be younger new 40 ar 39 ar hornblende dates recently published age data and crustal heat flow considerations further suggest that this collision began at or before ca 1770 ma and culminated with posttectonic magmatism beginning ca 1715 ma the harney peak granite this tectonic magmatic interval is 50 60 m y younger than that reported for the hearne superior collision trans hudson orogeny in canada comparably young metamorphic dates 1810 1710 ma also typify the eastern and northern wyoming province periphery western dakotas and southwestern montana collectively these data suggest that the hearne and wyoming provinces were once separate continents that were ultimately welded to the superior province and to each other during distinct early proterozoic orogenies regional relationships further suggest that final docking of the eastern wyoming province with laurentia began during the ca 1780 1740 ma interval of island arc accretion along the southern margin of the growing craton

controls of tor formation cairngorm mountains scotland tors occur in many granitic landscapes and provide opportunities to better understand differential weathering we assess tor formation in the cairngorm mountains scotland by examining correlation

a novel rockbolt formulation for a gpu accelerated finite discrete element method code and its application to underground excavations abstract rockbolting is widely used in civil and mining engineering to increase the inherent strength of the rock mass and reduce deformations around underground excavations rockbolt design by means of computer aided numerical simulations has been playing an increasingly important role in geotechnical engineering the research work presented herein introduces a novel rockbolt logic for the finite discrete element method fdem a numerical modelling approach capable of explicitly capturing brittle fracturing in complex geological media adoption of a gpu based implementation was required to achieve substantial simulation speed ups compared to conventional cpu computing rockbolts are discretized by 1d structural elements which are coupled to the solid finite element mesh by dedicated spring slider connectors representing the bolt anchoring system the formulation is verified by comparing simulated stress distributions with closed form solutions for the cases of i a pull out test on a fully grouted rockbolt and ii a circular tunnel excavated in a bolted elastic medium the effectiveness of the method for practical design applications is demonstrated by simulating the behavior of a bolted underground excavation in a heavily jointed rock mass the effect of bolt spacing on the fracturing and deformational response of the rock mass is analyzed together with the force distributions in the rockbolts

the geology of sw connemara ireland a fold and thrust dalradian and metagabbroic gneiss complex sillimanite grade dalradian schists composed of pelites impure psammites quartzites and calcite marbles all containing amphibolites were intruded and hornfelsed giving hornfels sillimanite garnet and cordierite by a plutonic basic to acid igneous rock series now metamorphosed and folded important folding denoted d 2 d 3 d 4 and d 5 as been recognized with a major southward facing d 2 anticline the cashel antiform being repeatedly folded by d 3 which was a very strong phase and accompanied and followed by d 3 d 4 major ductile slides and thrusting although the meta igneous suite includes rare peridotites olivine fo 75 87 and anorthosites it is mostly hornblende augite labradorite or bytownite metagabbro and later quartz diorite or trondhjemite gneiss which has injected the earlier more basic rocks variably preserved igneous layering in the basic rocks indicates that the whole intrusive basic sheet is flat lying and inverted lying on the inverted limb of the cashel antiform about 460 ma ago the d 3 d 4 mannin thrust carried the igneous complex including the largely crystallized gneisses and the cover of dalradian metasediment over a now largely mylonitized set of acid volcanic rocks rhyolites or ignimbrites which enclose a separate suite of massive amphibolites intruded or extruded into the acid volcanic rocks before the thrusting the base of the overthrust metagabbro sheet which had cooled to albite epidote amphibolite facies conditions was ground down into a fine grained nnw lineated amphibolite the volcanic rocks the mannin thrust and the overlying basic complex were folded by d 4 and d 5 into a domed structure about 400 ma the aplopegmatitic facies of the inish granite intruded and caused hornfelsing and folding while the galway granite was intruded in the south lamprophyric sills and dykes and porphyry dykes were followed by the final phase of the inish granite the southward facing folding and thrusting of the connemara dalradian block and the gabbro gneiss emplacement are major elements in the caledonide history of the british isles it is postulated that there was a tectonic and genetic connection between the gabbro gneiss intrusion into these dalradian rocks the unusually rapid decrease in metamorphic pressure already documented for connemara and the exceptionally southern position of the connemara block

basic magmatism in connemara ireland evidence for a volcanic arc it is found by the use of pearce cann diagrams that basic magmatism during dalradian sedimentation in connemara was of a fundamentally different type to that which led to later synorogenic basic intrusions the dalradian magmatism is of a transitional within plate to divergent plate margin type whereas the synorogenic intrusions are of volcanic arc type it is suggested that the synorogenic basic intrusions of connemara tyrone and ne scotland represent the roots of a volcanic arc that developed by arenig times over a northerly directed subduction zone

u pb isotopic dating of fluid infiltration and metasomatism during dalradian regional metamorphism in connemara western ireland a metasomatic diopside rock occurs at the top of the dolomitic connemara marble formation of western ireland and contains titanite and k feldspar in addition to around 90 diopside xmg 0 90 0 97 u pb isotopic measurements on this mineral assemblage show that the titanite is both unusually uranium rich and isotopically concordant with the result that a precise u pb age of 478 2 5 ma can be determined the age is identical within error to a less precise rb sr age of diopside k feldspar of 483 6 ma petrological evidence indicates that the assemblage crystallized at c 620 c close to or below the closure temperature of titanite the age thus provides a precise estimate of the time of metamorphism this age is 11 3 ma younger than the 490 ma age for nearby gabbroic plutons which has previously been used to constrain the peak metamorphic age this difference accords well with geological evidence that the gabbros were emplaced prior to the metamorphic peak analysis of minerals with high closure temperature from assemblages whose crystallization is unambiguously associated with a specific episode of fluid infiltration at the peak of metamorphism provides the basis for a new approach to dating metamorphism the success of this approach is demonstrated by the results from connemara

characterizing in situ stress domains at the aecl underground research laboratory the underground research laboratory access shaft was excavated from the surface to about the 185 m depth in jointed pink granite below this depth to the 443 m depth the shaft was excavated in massive grey granite the grey granite is essentially unjointed except for a major low dipping thrust fault and associated minor splays overcoring hydraulic fracturing convergence measurements microseismic monitoring and observations of shaft wall failure and core discing indicate that unusually high in situ stresses can be associated with large volumes of massive unjointed granite at fairly shallow depth the database of in situ stress measurements collected at the underground research laboratory indicates that major geological features such as thrust faults can act as boundaries for in situ stress domains and that both the magnitude and direction of the in situ stress state can change when these geological features are traversed key words in situ stress anisotropy stress domains thrust faults overco

geochronological constraints on the magmatic metamorphic and thermal evolution of the connemara caledonides western ireland the connemara region of the western irish caledonides records the evolution of a short lived mid ordovician c 475 463 ma continental magmatic arc that intruded into dalradian metasedimentary rocks during regional ductile deformation new u pb geochronological data for intermediate intrusive phases and anatexis in southern connemara are consistent with the relative age succession suggested by field relationships calc alkaline plutons quartz diorites were emplaced into the dalradian sequence and into the connemara gabbros at about 467 2 ma coeval with anatexis which was manifested by a 467 2 ma granitic pegmatite and 468 2 ma leucosome formation in a metapelite metasomatic diopside rocks from west central connemara and a calcsilicate rock from southern connemara yield u pb titanite dates of c 462 2 ma and 463 2 ma respectively these dates postdate the metamorphic peak by at least five million years and indicate titanite crystallization at a late stage during the metamorphic history on the basis of u pb and 40 ar 39 ar geochronological data we conclude that the cooling history of southern connemara following anatexis was simple and brief at a minimum rate of 35 c ma 1 between 468 and 460 ma and 14 c ma 1 between 460 and 450 ma

predicting the deformation moduli of rock masses abstract predictive empirical models for the mechanical properties of rock masses have been used in rock engineering because direct measurement of the properties is difficult due to the presence of discontinuities such empirical models are open to improvement because they are based on collected data the purposes of the present study are to assess the existing empirical equations and to develop a new empirical approach for this reason in the first stage of the study the prediction performance of the existing models proposed for predicting the deformation modulus of rock masses were evaluated statistically by using a database including 115 data values obtained from in situ plate loading and dilatometer tests a new empirical approach with higher prediction capacity than the existing empirical models was developed in the subsequent stage of the study the new empirical model considers the modulus ratio of intact rock e i ucs rock quality designation rqd and weathering degree wd although data obtained from very weak and weak rock masses were included in the development of the new empirical equation the type of rocks employed in the study were limited therefore a crosscheck between the new empirical equation and previous empirical approaches should be performed in the design stage

geochemistry of dalradian pelites from connemara ireland new constraints on kyanite genesis and conditions of metamorphism whole rock and mineral analyses of dalradian pelites from w connemara show that kyanite pelites are not unusually mg rich as previously supposed their chemistry is transitional especially in ca content between overlying fe rich staurolite pelites and underlying ca rich rocks the flysch basin in which they were deposited was established relatively early in the west its sediment fill including carbonate rich influxes derived from an adjacent swell to the east which later subsided to form an enlarged basin kyanite has a very restricted spatial distribution because its development was controlled by fe deficiency associated with the carbonate rich influxes which in turn led to relatively high x mg during metamorphism p t estimates for the metamorphic peak are 650 25 c and 8kbar about 50 c and 3kbar greater than for similar rocks in the east the difference can be related to structural level with respect to regional scale folds which may have developed as a huge backfolded complex during the emplacement of the connemara allochthon

modelling of the thermal history of metamorphic zoning in the connemara region western ireland abstract the connemara region of the irish caledonides is a classic example of regional scale metamorphism of low pressure and high temperature this terrane is considered as part of a fold belt comprising metasedimentary and metavolcanic rocks that are correlated with the neoproterozoic lower paleozoic dalradian supergroup of scotland in mid ordovician time the extensive and high temperature metamorphism was superimposed on the dalradian rocks resulting in the connemara zoning the key feature of the zoning is elevated horizontal thermal gradient of ca 14 c km geological data and geochronological evidence point to a causative link between metamorphism and associated magmatic intrusions and a brief period of development for the metamorphic zoning magmatic intrusion into the middle part of continental crust is treated as a most plausible source of heat for metamorphism and other conjectures as to the origin of the zoning flow of hot fluid through the permeable rocks fracture conduit flushed by flowing magma are believed to be improbable to examine in sufficient detail the problem of the nature of heat source a series of appropriate calculations have been performed to reach the best agreement between the observed and simulated spatial distribution of maximum temperatures at different times the mathematical modelling shows that the temperature spatial structure of the connemara zoning is best explained by the model version based on mid crustal heating above the upper contact of magmatic intrusive body gently curved and tilted at an angle between 20 and 40 with an initial temperature of the magma appropriate to a basaltic melt the model estimate of total lifetime of the temperature anomaly in the crust is of the order of 5 6 ma in general this is in rather good agreement with the currently available evidence of geochronological duration of metamorphism and magmatism in connemara

observed and numerically simulated structure of a mature supercell thunderstorm abstract through the interactive use of doppler radar analyses and a three dimensional numerical storm simulation the detailed structure of a supercell tornadic storm is analyzed this storm named the del city storm occurred in central oklahoma on 20 may 1977 the storm exhibits certain important features which are essential to maintaining its longevity and which promote the storm s transition to its tornadic phase these features are strongly influenced by the rotational character of the storm separates the precipitation from the updraft and which orients the resulting downdrafts to which reinforce low level convergence along the gust front and sustain the storm analyses of air parcel and rain trajectories within the storm provide a detailed visualization of this internal structure these trajectories reveal that air parcels rising through the cyclonically rotating updraft actually turn anticyclonically with height owing to the influence of the storm relative environmental wind field downdraft traj

impact of the dual polarization doppler radar data on two convective storms with a warm rain radar forward operator abstractthe dual polarization dual pol doppler radar can transmit receive both horizontally and vertically polarized power returns the dual pol radar measurements have been shown to provide a more accurate precipitation estimate compared to traditional radars in this study the horizontal reflectivity zh differential reflectivity zdr specific differential phase kdp and radial velocity vr collected by the c band advanced radar for meteorological and operational research armor are assimilated for two convective storms a warm rain scheme is constructed to assimilate zh zdr and kdp data using the three dimensional variational data assimilation 3dvar system with the advanced research weather research and forecasting model arw wrf the main goals of this study are first to demonstrate and compare the impact of various dual pol variables in initialization of real case convective storms and second to test how the dual pol fields may be better used with a 3dvar system the results show that the zh

geochemical evolution of arc magmatism during arc continent collision south mayo ireland the lough nafooey arc in the western irish caledonides collided with laurentia during the early ordovician this event is recorded in the stratigraphy of the south mayo trough the preserved forearc basin of this system lavas at the base of the oldest lough nafooey group show intraoceanic arc composition end t decreases and light rare earth elements rees become more enriched upsection in the lough nafooey group ca 495 481 ma reflecting early collision with laurentia the subsequent tourmakeady group ca 481 470 ma is rhyolitic light ree enriched and has strongly negative end t these rocks were erupted during the grampian orogeny the rosroe and mweelrea formations 470 ma show wide scatter of la sm and nb zr values suggesting mixed mantle sources this correlates with rapid exhumation of the adjacent connemara metamorphic terrane the chemical evolution of the arc supports models of collision orogeny and tectonic unroofing within 15 m y and shows that genesis of magmas more enriched than continental crust can occur during arc continent collision clarifying the potential role of arc volcanism in continental crust formation

identifying crack initiation and propagation thresholds in brittle rock recent work at the underground research laboratory of atomic energy of canada limited in pinawa manitoba has shown that high compressive stresses near the tunnel face significantly contribute to

the ordovician evolution of the south mayo trough western ireland the south mayo trough a broad synclinorium containing a 10 km sequence of early ordovician turbidites passing up into shallow water sandstones is interpreted as a forearc basin with an ophiolitic basement that formed a backstop to an accretionary prism on the northern edge of a north facing arc the arc collided with the laurentian margin in early llanvirn times to deform the dalradian supergroup rifted margin clastic sequence prior to the late llandovery sinistral transcurrent faulting transposed the connemara dalradian terrane to its present position on the outboard ocean ward side of the south mayo trough the south mayo trough was fed principally by arc and ophiolite derived elastics during the arenig with an increasing metamorphic component during the llanvirn the late ordovician transpressional docking of connemara provided the southerly source for high grade metamorphic clasts in the deny veeny formation

mechanical analysis and interpretation of excavation damage zone formation around deep tunnels within massive rock masses using hybrid finite discrete element approach case of atomic energy of canada limited aecl underground research laboratory url test tunnel the construction of an underground opening leads to changes in the in situ stress regime surrounding the excavation the opening influences the rock mass owing to the redistribution of the stresses

in situ measurements of rock mass deformability using fiber bragg grating strain gauges abstract in order to examine how the mechanical properties of a rock mass vary from the centimeter to meter scale we performed two field point loading tests 89 kn and 890 kn to determine the in situ modulus of deformation of a rock mass the experimental setup is analogous to plate jacking type tests but instead using a point load the experiments were done in the poorman formation on the 4100 level 1250 m underground of the sanford underground research facility surf at the site of the former homestake gold mine in lead sd for comparison with in situ values we also conducted laboratory mechanical tests and used two geotechnical classification systems to evaluate rock stiffness the in situ modulus of deformation increases with depth into the rock mass this increase in stiffness is a result of the differences in mechanical properties due to the effect of excavation of the underground space near the surface 0 1 2 m depth the rock is softest due to induced fractures and damage from blasting beyond this damaged zone is the stress relief zone 1 2 1 5 m depth where open joint sets affect rock stiffness and beyond that lies the undisturbed zone 1 5 m depth where the rock is the stiffest if done properly in situ measurements of rock stiffness are a valuable tool to fully characterize the gradient in stiffness of a rock mass which laboratory tests or geotechnical classification systems do not fully capture

seventeenth canadian geotechnical colloquium the effect of cohesion loss and stress path on brittle rock strength stress strain curves for brittle rocks show three characteristic stress levels crack initiation long term strength and peak strength damage controlled testing at low confining stresses has shown that the long term and peak strengths are sensitive to the amount of induced damage i e the greater the amount of damage the lower the long term and peak strengths these tests also showed that the brittle failure process is characterized by a loss of cohesion as friction is mobilized excavation of a circular test tunnel in massive brittle rock resulted in failure around the tunnel the back calculated strength for the failed rock around the tunnel is approximately one half of that measured in laboratory tests crack induced damage of lac du bonnet granite both in the laboratory and in situ begins when the load exceeds approximately one third of the unconfined compressive strength however the stress level associated with failure is a function of loading path in the laboratory where the loading path monotonically increases the ultimate strength of an unconfined sample is 225 mpa numerical studies suggest that in situ the loading path around the tunnel is more complex involving stress increase and decrease and stress rotation for this loading path failure initiates at a stress between 100 and 120 mpa conventional frictional failure criteria did not adequately predict the extent of brittle failure measured around the circular tunnel the results from the damage controlled laboratory tests and the microseismic monitoring carried out during tunnel construction indicate a constant deviatoric stress criterion is a reliable indicator for predicting the onset of damage this criterion was also found to give a reasonable prediction for the maximum depth of failure around the test tunnel the fundamental assumption in the constant deviatoric stress criterion is that at low confining stresses such as those which occur around underground openings the brittle failure process is dominated by cohesion loss

the cooling history of connemara western ireland from k ar and rb sr age studies k ar age determinations are reported on 26 hornblendes 17 coexisting muscovites and biotites nine muscovites and nine biotites from the dalradian connemara schists metagabbros and gneisses these are supplemented by 19 rb sr whole rock mica ages and four 40 ar 39 ar incremental heating ages on micas a long at least 75 ma and complex cooling history without a simple pattern of ages has been obtained the ages are not correlated with the grain sizes or the chemical compositions of the analysed minerals or the topographic elevation from which the samples came but there is an irregular increase of hornblende k ar ages to 480 10 ma with increase of metamorphic grade southwards towards the metagabbros and gneiss the preservation of the complex cooling pattern is ascribed to the action of syn and post metamorphic slides or faults which moved slices of the massif upwards by varying amounts closely spaced samples give results which rule out simple tilting of the massif rapid cooling c 30 ma 1 at 480 10 ma arenig llanvirn during the f3 fold phase was followed by slower cooling until 455 10 ma caradoc when renewed rapid uplift occurred possibly correlated with the southward thrusting of connemara and with synchronous renewed uplift in the scottish dalradian rocks widespread biotite k ar and rb sr ages of 440 5 ma end ordovician throughout connemara and the dalradian rocks of scotland are ascribed to the major taconic tectonic event which docked the dalradian rocks against the flanking folded ordovician successions of the midland valley and the south mayo trough biotites giving k ar ages of about 415 ma may have been reset during the late silurian folding of the cover rocks the importance of very close sampling integrated with structural studies is emphasized

impacts of lapse rates on low level rotation in idealized storms abstractadiabatic lapse rates appear to be a common feature in the lower troposphere on tornado days this article reviews physical reasons why lapse rates may influence surface vortex intensification and reports on numerical simulations designed to study the key processes in the idealized numerical model an initial mesocyclone like vortex and nonvarying convection like heat source are used in different environmental stability profiles the scales of interest in these simulations typify those of a parent supercell and the developing circulations constitute direct responses to the imposed heating downward parcel displacements are needed for surface vortex development in environments with no preexisting surface vorticity in the simulations under neutral stratification there is strong heating induced subsidence anchored near the storm edge whereas under stable stratification there are instead gravity waves that propagate away to the far field in addition under weak or neutral low level stratification

the structure and classification of numerically simulated convective storms in directionally varying wind shears abstract using a three dimensional numerical cloud model we investigate the effects of directionally varying wind shear on convective storm structure and evolution over a wide range of shear magnitudes as with a previous series of experiments using unidirectional wind shear profiles weisman and klemp the current results evince a spectrum of storm types ranging from short lived single cells at low shears multicells at intermediate shears to supercells at high shears with a clockwise curved hodograph the supercellular growth is confined to the right flank of the storm system while multicellular growth is favored on the left flank an analysis of the dynamic structure of the various cells reveals that the quasi steady supercell updrafts are strongly enhanced by dynamically induced pressure gradients on the right flank of the storm system we use this feature along with other related storm characteristics such as updraft rotation to propose a dynamically based storm classification scheme following

the influence of helicity on numerically simulated convective storms abstract a three dimensional numerical cloud model is used to investigate the influence of storm relative environmental helicity sreh on convective storm structure and evolution with a particular emphasis on the identification of ambient shear profiles that are conducive to the development of long lived strongly rotating storms eleven numerical simulations are made in which the depth and turning angle of the ambient vertical shear vector are varied systematically while maintaining a constant magnitude of the shear in the shear layer in this manner an attempt is made to isolate the effects of different environmental felicities on storm morphology and show that the sreh and bulk richardson number rather than the mean shear in the low levels determine the rotational characteristics and morphology of deep convection the results demonstrate that storms forming in environments characterized by large sreh are longer lived than those in less helical surroundings further it appears that the storm relat

finestructure of the del city edmond tornadic mesocirculation abstract interrelationships among severe thunderstorm wind flow tornado parent circulation and tornado are examined with dense single and dual doppler radar observations from the del city edmond oklahoma storm of 20 may 1977 beginning with tornadogenesis rising inflow air from right hand quadrants and subsiding air from a developing downdraft on the storm s rear are wrapped in a large spiral pattern about the tornado the updraft appears to drive the tornado while the downdraft appears to form as entrained environmental air concentrated by the intensifying parent circulation is cooled evaporatively

a stable isotope study of retrograde alteration in sw connemara ireland dalradian metamorphic rocks lower ordovician meta igneous rocks mgs and caledonian granites of the connemara complex in sw connemara all show intense retrograde alteration alteration primarily involves sericitization and saussuritization of plagioclase the alteration of biotite and hornblende to chlorite and the formation of secondary epidote the alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs and was the result of a phase of fluid influx into these rocks in hand specimen k feldspar becomes progressively reddened with increasing alteration mineralogical alteration in the mgs and caledonian granites took place at temperatures 275 15 c and in the mgs pfluid is estimated to be 1 5 kbar during alteration the d values of alteration phases are 18 to 29 fluid inclusions 47 to 61 chlorites and 11 to 31 epidotes chlorite 18o values are 0 2 to 4 3 while 18o values for quartz k feldspar pairs show both positively sloped mgs and highly unusual negatively sloped caledonian granites arrays diverging from the normal magmatic field on a plot the stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200 140 c the retrograde fluid had d 20 to 30 in all lithologies but the fluid 18o varied both spatially and temporally within the range 4 to 7 the fo2 of the fluid that deposited the epidotes in the mgs varied with its 18o value with the most 18o depleted fluid being the most oxidizing the d values together with low 0 18o values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin this meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration the variation in retrograde fluid 18o values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid rock interaction infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the galway granite soon after intrusion at 400 ma however convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later

validation and implementation of a new method for monitoring in situ strain and temperature in rock masses using fiber optically instrumented rock strain and temperature strips abstract fiber optically instrumented rock strain and temperature strips frosts are a new method for monitoring in situ strain and temperature in intact rock masses frosts are an alternative to other techniques such as borehole extensometers or instrumented rock bolts for monitoring strain around underground openings frosts have six fiber optic strain and temperature gages installed at 30 cm intervals along specially designed strips of 304 stainless steel and are embedded into the rock mass frosts are modified rock strain strips ross if pretensioned prior to installation the frosts can measure both shortening and elongation two frosts were pretensioned and installed on the 4100 level 1250 m below the surface of the sanford underground research facility surf in lead sd data from the initial monitoring of these frosts record strain in the rock mass due to the closure of microcracks and fractures created during drilling for installation and then stabilization of the frosts sensors the fiber optic temperature sensors on the frosts also record a detailed thermal gradient of increasing temperature with depth into the rock mass laboratory experiments show that the frosts accurately measure strain are more compliant than the rock mass they are embedded into and thoroughly couple to the rock mass to ensure accurate readings frosts provide an accurate and detailed record of in situ strain and temperature in rock masses and are useful for the structural health monitoring of underground spaces

initialization of a modeled convective storm using doppler radar derived fields abstract a method is developed to initialize convective storm simulations with doppler radar derived fields input fields for initialization include velocity rainwater derived from radar reflectivity and pressure and temperature fields obtained through thermodynamic retrieval a procedure has been developed to fill in missing wind data followed by a variational adjustment to the filled wind field to minimize shocks that would otherwise cause the simulated fields to deteriorate rapidly a series of experiments using data from a simulated storm establishes the feasibility of the initialization method multiple doppler radar observations from the 20 may 1977 del city tornadic storm are used for the initialization experiments simulation results are shown and compared to observations taken at a later time the simulated storm shows good agreement with the subsequent observations though the simulated storm appears to be evolving faster than observed possible reasons for the discrepancies are discussed

laurentian crustal recycling in the ordovician grampian orogeny nd isotopic evidence from western ireland because magmatism associated with subduction is thought to be the principal source for continental crust generation assessing the relative contribution of pre existing subducted and assimilated continental material to arc magmatism in accreted arcs is important to understanding the origin of continental crust we present a detailed nd isotopic stratigraphy for volcanic and volcaniclastic formations from the south mayo trough an accreted oceanic arc exposed in the western irish caledonides these units span an arc continent collision event the grampian taconic orogeny in which an intra oceanic island arc was accreted onto the passive continental margin of laurentia starting at 475 ma arenig the stratigraphy corresponding to pre syn and post collisional volcanism reveals a progression of end t from strongly positive values consistent with melt derivation almost exclusively from oceanic mantle beneath the arc to strongly negative values indicating incorporation of continental material into the melt using end t values of meta sediments that represent the laurentian passive margin and accretionary prism we are able to quantify the relative proportions of continent derived melt at various stages of arc formation and accretion mass balance calculations show that mantle derived magmatism contributes substantially to melt production during all stages of arc continent collision never accounting for less than 21 of the total this implies that a significant addition of new rather than recycled continental crust can accompany arc continent collision and continental arc magmatism

ultrasonic tomography and acoustic emission in hydraulically fractured lac du bonnet grey granite ultrasonic tomography and acoustic emission ae data were obtained during laboratory hydraulic fracturing tests on two large unconfined cylinders of lac du bonnet grey granite the cylinders were internally pressurized over four to five cycles prior to final failure compressional velocities were measured before and after each pressurization cycle with an array of 16 evenly spaced transducers around the central cross sectional plane of each sample sixteen channels of whole waveform ae data were recorded during most pressurization cycles and for a period of about 1 hour after final failure in one sample compressional velocities were found to be strongly anisotropic with the in situ vertical direction being the most rapid direction in both samples the velocity anisotropy is related to the rock s preexisting microcrack fabric owing to radial penetration of fluid into the rock compressional velocities rose over the course of the experiment a regression analysis showed that the velocity changes can be explained by variations in crack density inferred from initial velocities and radial distance from the borehole saturation levels consistent with the observed velocity changes were calculated on the basis of the o connell and budiansky theory acoustic emissions reoccurred in a few distinct zones over several pressurization cycles the ae locations allowed two distinct fracture planes to be sharply delineated in one sample the fracture plane orientations were controlled by the preexisting microcrack fabric in both samples ae occurred too rapidly during peak pressure failure to permit us to isolate distinct events source mechanism analysis of the ae which occurred prior to peak pressure failure in both samples and during postfailure monitoring in one sample showed a predominance of double couple sources compressive sources thought to be related to crushing of asperities during crack closure and tensile sources related to mode i crack growth were also recorded as well as more complex sources that could not be modeled by the simple source types listed above

assimilation of doppler radial winds into a 3d var system errors and impact of radial velocities on the variational analysis and model forecasts a pre processing approach to the assimilation of doppler radar radial wind data into a high resolution numerical weather prediction nwp model is described we discuss the types of errors which might occur in radar radial winds the construction of simulated high resolution radar data containing such errors is described examples of these data are presented and compared with actual radar data from the chilbolton s band radar located in central southern england a new approach to specifying the radial velocity observation error is proposed based upon the radial gradient of the velocity along the pulse volume the production of super observations for input to a 3d var assimilation system is discussed impact of the assimilation of doppler velocities on the 3d var analysis and on the model forecasts for two case studies are shown copyright 2008 royal meteorological society

a model for continental crust genesis by arc accretion rare earth element evidence from the irish caledonides abstract the formation of continental crust is a complex problem with a paradox at its center continental material is believed to form by arc magmatism a model that does not reconcile the bulk mafic and light rare earth element lree depleted composition of intra oceanic arcs with the andesitic lree enriched composition of continents we present evidence supporting an arc origin for continental crust by demonstrating significant changes in magmatic chemistry during arc continent collision we use as an example the connemara region of the western irish caledonides where metamorphism and orogenesis of dalradian sedimentary sequences record the collision of the oceanic lough nafooey arc with the passive margin of laurentia at 475 ma arenig this arc was mafic and lree depleted during its oceanic activity during collision rhyolites more lree enriched than the surrounding continental crust were erupted while the mid crust was intruded by similarly lree enriched gabbro and diorite crystal fractionation caused lree enrichment to exceed that expected by assimilation of continental crust alone we propose that subsequent loss of the corresponding lower crustal cumulates into the mantle removed this lree depleted material from the net crust added to the continent the combined processes of crystal fractionation and lower crustal loss during arc continent collision drive the average bulk arc composition toward that of average continental crust

dynamic adjustment in a numerically simulated mesoscale convective system impact of the velocity field abstract an identical twin methodology is applied to a three dimensional cloud model to study the dynamics of adjustment in deep convective storms the principal goal is to diagnose how mass and velocity fields mutually adjust in order to better understand the relative information content value of observations the physical interdependency among variables and to help in the design of dynamically consistent analyses to ensure smooth startup of numerical prediction models using a control simulation truth or nature run of an idealized long lived bow echo convective system a series of adjustment experiments is created by resetting in various combinations the horizontal and vertical velocity components of the control run to their undisturbed base state values during the mature stage of storm system evolution the integrations then are continued for comparison against the control this strategy represents a methodology for studying transient response to an impulsive perturbation in a manner concept

a three dimensional numerical simulation of splitting severe storms on 3 april 1964 abstract a three dimensional numerical storm model is used to investigate the observed splitting of several reflectivity echoes on 3 april 1964 in oklahoma representative soundings from this day exhibit a nearly one directional environmental wind shear vector and the presence of strong low level wind shear in the numerical simulation an initial cloud splits into two long lived rotating storms one that moves to the left of the mean winds and the other to the right the left moving storm develops more slowly than the right moving one due to the deviation of the environmental wind hodograph from a straight line below 1 km further the left mover eventually splits convergence induced by the cold low level storm outflow plays a major role in the development of both the first and second splits however the second split appears to be dynamically different than the first as the left moving updraft remains essentially unchanged while a new updraft forms immediately adjacent to it because of the different p

470 ma granitoid magmatism associated with the grampian orogeny in the slishwood division nw ireland ion microprobe u pb zircon geochronology demonstrates that magmatic rocks that cut the slishwood division are early ordovician in age and relate to the earliest stages of the grampian orogeny these tonalite and granite intrusions yield ages of 474 5 ma 472 6 ma 471 5 ma and 467 6 ma a sm nd mineral isochron of 457 36 ma confirms an ordovician age for one of the tonalite bodies and demonstrates that they were affected by ordovician metamorphism whereas biotite rb sr mineral ages from two of the tonalite bodies show that the slishwood division had cooled below c 350 c at 449 7 ma the early orogenic tonalite and granite intrusions are mylonitized in structures that overthrust the dalradian supergroup onto the slishwood division during major nappe formation and thus date the onset of such deformation at or before 471 5 ma the age of the youngest intrusion where such field relations can be demonstrated

metamorphic conditions in central connemara ireland metamorphic conditions have been estimated for an area in central connemara that includes cashel and lissoughter hill pressures lie in the range 3 0 6 0 kbar temperatures increase from 625 675 c on the n slopes of lissoughter hill to 650 700 c on the s slopes to 700 750 c in the migmatized metasediments n of the cashel ultrabasic intrusion before increasing sharply towards the contact away from the area adjacent to the intrusion a horizontal thermal gradient of between 30 c and 40 c km may be inferred differences in the relative spatial position with increasing temperature of the staurolite out muscovite and quartz out and beginning of partial melting isograds imply that the rocks exposed at the eastern end of the steep belt at maam cross were metamorphosed at a lower pressure than those farther w at recess similarly the stable co existence of muscovite and quartz in the recess area may indicate that the second sillimanite isograd dips towards the s a condition that would be consistent with sub vertical isotherms associated with a thermal anticline centred on the cashel volcanic arc

rock reinforcement systems a terminology for reinforcement practice is proposed based on the idea that a reinforcement device rock mass and reinforced rock mass are all systems of components it follows that the force deformation behaviour of each system is a consequence of the particular physical and mechanical characteristics of the system components and their interactions using this systems approach and the associated terminology a method is proposed for the design of reinforcement for excavations in jointed rock the design method is based on identifying and stabilising the blocks of rock that may form at the excavation boundary it uses the early developments in block theory for identification and stability assessment of the blocks these developments are supplemented with new reinforcement design and stability assessment procedures for the unstable blocks

u pb and rb sr geochronology of magmatism and metamorphism in the dalradian of connemara western ireland new geochronological data which clarify the timing of syn orogenic magmatism and regional metamorphism in the connemara dalradian are presented u pb zircon data on four intermediate to acid foliated magmatic rocks show important inherited components but the most concordant fractions demonstrate that major magmatism continued until 465 ma whereas the earliest basic magmatism has been dated previously at 490 ma a fine grained fabric cutting granite contains discordant zircons which also appear to be 465 ma old arc magmatism in connemara therefore spanned a period of at least 25 ma recent u pb data on titanite from central connemara which gave a peak metamorphic age of 478 ma are supplemented by u pb data on titanite and monazite from metamorphic veins in the east of connemara which indicate that low p high t regional metamorphism continued there to 465 ma i e at least 10 ma later than in the central region dated previously new rb sr data on muscovites from coarse grained segregations in different structural settings range from 475 to 435 ma in part this range probably also reflects differences in age from west to east with three ages close to 455 ma from the eastern area which is also the site of the lowest pressure metamorphism thermal modelling indicates that at any one locality the duration of metamorphism was probably as little as 1 2 ma the new dates emphasize the complexity in the spatial and temporal distribution of high level regional metamorphism caused by magmatic activity the relatively simple overall distribution of mineral appearance isograds revealed by regional mapping masks the complexity of a prolonged but punctuated metamorphic history related to multiple intrusions primarily in the southern part of connemara the later stages of magmatic activity followed progressive uplift and erosion after the onset of magmatism and were localized in the eastern part of the region

a fluid inclusion and stable isotope study of 200 ma of fluid evolution in the galway granite connemara ireland fluid inclusions in granite quartz and three generations of veins indicate that three fluids have affected the caledonian galway granite these fluids were examined by petrography microthermometry chlorite thermometry fluid chemistry and stable isotope studies the earliest fluid was a h2o co2 nacl fluid of moderate salinity 4 10 wt nacl eq that deposited late magmatic molybdenite mineralised quartz veins v1 and formed the earliest secondary inclusions in granite quartz this fluid is more abundant in the west of the batholith corresponding to a decrease in emplacement depth within veins and to the east this fluid was trapped homogeneously but in granite quartz in the west it unmixed at 305 390 c and 0 7 1 8 kbar homogeneous quartz 18o across the batholith 9 5 0 4 n 12 suggests v1 precipitation at high temperatures perhaps 600 c and pressures 1 3 kbar from magmatic fluids microthermometric data for v1 indicate lower temperatures suggesting inclusion volumes re equilibrated during cooling the second fluid was a h2o nacl kcl low moderate salinity 0 10 wt nacl eq moderate temperature 270 340 c high d 18 2 low 18o 0 5 2 0 fluid of meteoric origin this fluid penetrated the batholith via quartz veins v2 which infill faults active during post consolidation uplift of the batholith it forms the most common inclusion type in granite quartz throughout the batholith and is responsible for widespread retrograde alteration involving chloritization of biotite and hornblende sericitization and saussuritization of plagioclase and reddening of k feldspar the salinity was generated by fluid rock interactions within the granite within granite quartz this fluid was trapped at 0 5 2 3 kbar having become overpressured this fluid probably infiltrated the granite in a meteoric convection system during cooling after intrusion but a later age cannot be ruled out the final fluid to enter the granite and its host rocks was a h2o nacl cacl2 kcl fluid with variable salinity 8 28 wt nacl eq temperature 125 205 c d 17 to 45 18o 3 to 1 2 13cco2 19 to 0 and 34ssulphate 13 23 that deposited veins containing quartz fluorite calcite barite galena chalcopyrite sphalerite and pyrite v3 correlations of salinity temperature d and 18o are interpreted as the result of mixing of two fluid end members one a high d 17 to 8 moderate 18o 1 2 2 5 high 13cco2 4 low 34ssulphate 13 high temperature 205 230 c moderate salinity 8 12 wt nacl eq fluid the other a low d 61 to 45 low 18o 5 4 to 3 low 13c 10 high 34ssulphate 20 23 low temperature 80 125 c high salinity 21 28 wt nacl eq fluid geochronological evidence suggests v3 veins are late triassic the high d end member is interpreted as a contemporaneous surface fluid probably mixed meteoric water and evaporated seawater and or dissolved evaporites whereas the low d end member is interpreted as a basinal brine derived from the adjacent carboniferous sequence this study demonstrates that the galway granite was a locus for repeated fluid events for a variety of reasons from expulsion of magmatic fluids during the final stages of crystallisation through a meteoric convection system probably driven by waning magmatic heat to much later mineralisation concentrated in its vicinity due to thermal tectonic and compositional properties of granite batholiths which encourage mineralisation long after magmatic heat has abated

simulation of a midlatitude convective storm initialized with bistatic doppler radar data abstract an analysis is developed to initialize a cloud resolving model from an explicit structure of a precipitating convective system derived from multiple doppler radar observations the different fields of the model prognostic variables that compose the initial state of the simulation are estimated or retrieved using a 4dvar assimilation method in which the model is used as a weak constraint using two time level observations this allows for the retrieval of physical fields consistent with the observations and the equations of the model this method is applied on a midlatitude summer storm sampled by the mcgill bistatic doppler radar network that occurred on 2 august 1997 during the 30 min forward simulation the model succeeds in representing the observed features of the three main cells that compose the storm in terms of precipitation distribution and evolution of the convective activity after this period the model produces less stratiform precipitations comparisons with a lagrangian persistency

late ordovician to early silurian amalgamation of the dalradian and adjacent ordovician rocks in the british isles from detailed radiometric and pressure temperature estimates of the metamorphic history uplift and erosion of the dalradian rocks of the british isles we find that 15 25 km of erosion took place mainly in ordovician time none of this vast volume of material is apparently present in the ordovician sedimentary basins that now flank the dalradian block we conclude that the ordovician basins to the south of the dalradian block are exotic terranes and we document their emplacement into their present position during late ordovician to early silurian time i e taconic by using evidence mainly from western ireland

seismic anisotropy in granite at the underground research laboratory manitoba the shear wave experiment at atomic energy of canada limited s underground research laboratory was probably the first controlled source shear wave survey in a mine environment taking place in conjunction with the excavation of the mine by test tunnel at 420 m depth the shear wave experiment was designed to measure the in situ anisotropy of the rockmass and to use shear waves to observe excavation effects using the greatest variety of raypath directions of any in situ shear wave survey to date inversion of the shear wave polarizations shows that the anisotropy of the in situ rockmass is consistent with hexagonal symmetry with an approximate fabric orientation of strike 023 degree and dip 35 degree the in situ anisotropy is probably due to microcracks with orientations governed by the in situ stress field and to mineral alignment within the weak gneissic layering however there is no unique interpretation as to the cause of the in situ anisotropy as the fabric orientation agrees approximately with both the orientation expected from extensive dilatancy anisotropy and that of the gneissic layering eight raypaths with shear waves propagating wholly or almost wholly through granodiorite rather than granite do not show the expected shear wave splitting and indicate a lower in situ anisotropy which maymore be due to the finer grain size and or the absence of gneissic layering within the granodiorite these results suggest that shear waves may be used to determine crack and mineral orientations and for remote monitoring of a rockmass this has potential applications in mining and waste monitoring less

retrieval of model initial fields from single doppler observations of a supercell thunderstorm part ii thermodynamic retrieval and numerical prediction in this two part study a single doppler parameter retrieval technique is developed and applied to a real data case to provide model initial conditions for a short range prediction of a supercell thunderstorm the technique consists of the sequential application of a single doppler velocity retrieval sdvr followed by a variational velocity adjustment a thermodynamic retrieval and a moisture specification step in part i the sdvr procedure is described and results from its application to a supercell thunderstorm are presented in part ii results from the thermodynamic retrieval and the numerical model prediction for this same case are presented for comparison results from parallel sets of experiments using dual doppler derived winds and winds obtained from the simplified velocity retrieval described in part i are also shown following the sdvr the retrieved wind fields available only within the storm volume are blended with a base state background field obtained from a proximity sounding the blended fields are then variationally adjusted to preserve anelastic mass conservation and the observed radial velocity a gal chen type thermodynamic retrieval procedure is then applied to the adjusted wind fields for all experiments full retrieval simplified retrieval and dual doppler the resultant perturbation pressure and potential temperature fields agree qualitatively with expectations for a deep convective storm an analysis of the magnitude of the various terms in the vertical momentum equation for both the full retrieval and dual doppler experiments indicates a reasonable agreement with predictions from linear theory in addition the perturbation pressure and vorticity fields for both the full retrieval and dual doppler experiments are in reasonable agreement with linear theory predictions for deep convection in sheared flow following a simple moisture specification step short range numerical predictions are initiated for both retrieval experiments and the dual doppler experiment in the full single doppler retrieval and dual doppler cases the general storm evolution and deviant storm motion are reasonably well predicted for a period of about 35 minutes in contrast the storm initialized using the simplified wind retrieval decays too rapidly indicating that the additional information obtained by the full wind retrieval primarily low level polar vorticity is vital to the success of the numerical prediction sensitivity experiments using the initial fields from the full retrieval indicate that the predicted storm evolution is strongly dependent on the initial moisture fields overall the numerical prediction results suggest at least some degree of short term predictability for this storm and provide an impetus for continued development of single doppler retrieval procedures

core disking and its relationship with stress magnitude for lac du bonnet granite abstract core disking is an indicator of elevated stress magnitudes disked cores from boreholes drilled from underground excavations in massive unfractured granite where the stress magnitudes are known with confidence were used to establish a relationship between core disk thickness and the stress magnitude relationships were established for three disk thickness categories 1 thin t d 0 2 2 medium 0 2 t d 0 4 and 3 thick 0 4 t d 2 2 and partial disking the data suggests that core disking initiates when the maximum principal stress normalized to the tensile strength is 6 5

assimilation impact of high temporal resolution volume scans on quantitative precipitation forecasts in a severe storm evidence from nudging data assimilation experiments with a thermodynamic retrieval method

conditions of high grade metamorphism in the dalradian of connemara ireland in e connemara ireland dalradian metasediments were initially metamorphosed to kyanite staurolite grade at pressures above 7kbar the subsequent emplacement of basic to intermediate magmas accompanied by uplift and erosion produce a steepening of the geothermal gradient and led to the formation of migmatitic garnet cordierite sillimanite gneisses in the highest grade regions in the s cation exchange equilibria between coexisting mineral pairs suggest that partial melting took place under high temperatures 750 c and moderate pressures 4 5 6 kbar fluid inclusion studies and andalusite occurrences from migmatite leucosomes suggest that crystallization of the melts occurred at lower pressures

analytical model of fully grouted bolts in pull out tests and in situ rock masses abstract the dynamic evolution characteristic of the bond strength at the interface of a bolt and a rock mass under an axial tensile load and the mechanical behavior of fully grouted bolts in situ were investigated considering the non uniform stress of the surrounding rock along the bolts a new dynamic bond slip model was first proposed to describe the dynamic evolution characteristic of the bond strength at bolt rock interfaces based on the proposed dynamic bond slip model analytical solutions of the shear stress distribution along the bolts load displacement relationship and relative displacement considering the slip of the free end were developed then incorporating the non uniform normal stress of the surrounding rock along the bolts the shear stress distribution and load displacement behavior of the fully grouted bolts were presented moreover analytical approaches were also proposed for determining the stress distribution along the bolt and rock deformation in cases of in situ prestressed and non prestressed bolts the proposed model and analytical solution were validated by published results from laboratory model tests and in situ tests respectively the new analytical solution completes the theoretical framework for addressing the fundamental problem of fully grouted bolts in pull out tests and in situ rock masses and provides a useful theoretical tool that can potentially be applied to bolt design and laboratory and in situ testing

a laboratory acoustic emission experiment under in situ conditions in this paper we revisit acoustic emission ae data from an in situ rock fracture experiment conducted at the underground research laboratory url in manitoba canada the mine by experiment a large scale excavation response test was undertaken at a depth of 420 m and involved the mechanical excavation of a cylindrical tunnel during the experiment a small array of 16 panametrics v103 ae sensors enclosed a 0 7 m 0 7 m 1 1 m rectangular prism of lac du bonnet granite located in the tunnel wall the v103 sensors were later calibrated in the laboratory and a source parameter analysis was undertaken using a spectral fitting method corner frequency and moment magnitude were found to be inside the ranges 250 khz fc 490 khz and 7 5 mw 6 8 respectively static stress drops ranged from 0 3 to 4 mpa which is consistent with large seismicity recorded at the url

rapid tectonic exhumation detachment faulting and orogenic collapse in the caledonides of western ireland collision of the oceanic lough nafooey island arc with the passive margin of laurentia after 480 ma in western ireland resulted in the deformation magmatism and metamorphism of the grampian orogeny analogous to the modern taiwan and miocene new guinea orogens after f470 ma the metamorphosed laurentian margin sediments dalradian supergroup now exposed in connemara and north mayo were cooled rapidly 35 jc m y and exhumed to the surface we propose that this exhumation occurred mainly as a result of an oceanward collapse of the colliding arc southwards probably aided by subduction rollback into the new trench formed after subduction polarity reversal following collision the achill beg fault in particular along the southern edge of the north mayo dalradian terrane separates very low grade sedimentary rocks of the south mayo trough lough nafooey forearc and accreted sedimentary rocks of the clew bay complex from high grade dalradian meta sedimentary rocks suggesting that this was a major detachment structure in northern connemara the unconformity between the dalradian and the silurian cover probably represents an eroded major detachment surface with the renvyle bofin slide as a related but subordinate structure blocks of sheared mafic and ultramafic rocks in the dalradian immediately below this unconformity surface probably represent arc lower crustal and mantle rocks or fragments of a high level ophiolite sheet entrained along the detachment during exhumation orogenic collapse was accompanied in the south mayo trough by coarse clastic sedimentation derived mostly from the exhuming dalradian to the north and to a lesser extent from the lough nafooey arc to the south sediment flow in the south mayo trough was dominantly axial deepening toward the west volcanism associated with orogenic collapse rosroe and

u pb zircon ages of basic rocks and gneisses intruded into the dalradian rocks of cashel connemara western ireland new isotopic ages are presented from the syntectonic cashel lough wheelaun basic intrusion and an associated k feldspar granite gneiss of the connemara gneiss complex from lettershinna hill the linear normally discordant distribution of data points from the cashel lough wheelaun metagabbro indicates that the zircons in this intrusion have no significant inherited radiogenic pb they yield an upper concordia intercept age of 477 25 6 ma and a more precise 207 pb 206 pb age of 490 1 ma in contrast zircons from the k feldspar granite gneiss show distinct reverse discordance the non magnetic fractions show a good linear arrangement yielding a lower intercept age of 454 6 14 ma and a very uncertain upper intercept age of 1807 646 570 ma the lower intercept age is younger than the 477 9 ma k ar age of hornblendes in gneisses from lettershinna hill elias et al 1988 and therefore reflects a pb loss episode younger than igneous crystallization the imprecise proterozoic upper intercept age indicates contamination by older inherited and only partially reset zircons

wind and temperature retrievals in the 17 may 1981 arcadia oklahoma supercell ensemble kalman filter experiments abstract the feasibility of using an ensemble kalman filter enkf to retrieve the wind and temperature fields in an isolated convective storm has been tested by applying the technique to observations of the 17 may 1981 arcadia oklahoma tornadic supercell radial velocity and reflectivity observations from a single radar were assimilated into a nonhydrostatic anelastic numerical model initialized with an idealized horizontally homogeneous base state the assimilation results were compared to observations from another doppler radar the results of dual doppler wind syntheses and in situ measurements from an instrumented tower observation errors make it more difficult to assess enkf performance than in previous storm scale enkf experiments that employed synthetic observations and a perfect model nevertheless the comparisons in this case indicate that the locations of the main updraft and mesocyclone in the arcadia storm were determined rather accurately especially at midlevels the magnitudes of v

the influence of the shear induced pressure gradient on thunderstorm motion abstract in the present investigation we propose a simple theory to explain how a veering environmental wind shear vector can cause an initially symmetric updraft to grow preferentially to the right of the shear vector and acquire cyclonic rotation the explanation offered is based on linear theory which predicts that interaction of the mean shear with the updraft produces favorable vertical pressure gradients along its right flank to asses the validity of linear theory for large amplitude updrafts the three dimensional shallow anelastic equations are numerically integrated using a simple parameterization for latent heating within a cloud and the linear and nonlinear forcing terms are separately analyzed these results suggest that although the nonlinear effects strongly promote splitting of the updraft the linear forcing remains the dominant factor in preferentially enhancing updraft growth on the right flank we believe this differential forcing is a major contributor to the observed predominance o

structural age of the connemara gabbros western ireland a d2 age of intrusion for the connemara gabbros is rejected the gabbros were intruded 490 ma ago probably just prior to the d3 deformation and together with younger members of the metagabbro and gneiss complex were responsible for a widespread sillimanite grade contact metamorphism which overprinted the regional d2 gamet staurolite kyanite metamorphism and the major d3 folds comparison with the ne scotland gabbros is thereby strengthened supporting the idea that they were both part of a coeval magmatic arc developed at the margin of the caledonian fold belt

single doppler velocity retrievals with phoenix ii data clear air and microburst wind retrievals in the planetary boundary layer abstract a new three dimensional single doppler velocity retrieval is introduced and tested with reflectivity and radial velocity data gathered during the phoenix ii field program near boulder colorado this retrieval is based on reflectivity conservation with provision for raindrop fall speed the incompressibility condition and a temporal constraint on the velocity field two temporal constraints are considered velocity stationarity and taylor s frozen turbulence approximation velocity stationarity in a moving reference frame it is demonstrated that either of these temporal constraints can be used to derive a second conserved scalar from the original conserved scalar reflectivity this two scalar system is in general overdetermined but a least squares formulation reduces the problem to a poisson equation for a pseudostreamfunction the requisite boundary conditions arise naturally from the least squares formulation and require only single doppler measurements for their evaluation the new r

the arcadia oklahoma storm of 17 may 1981 analysis of a supercell during tornadogenesis abstract on 17 may 1981 an extensive dataset was collected for a supercell thunderstorm that produced an f2 tornado near arcadia in central oklahoma coordinated dual doppler scans of the storm by 10 cm research radars were collected at approximately 5 min intervals from 30 min before the tornado touched down until 15 min after the tornado had dissipated the arcadia storm was also well sampled by a 444 m tall instrumented tower the low level inflow updraft mesocyclone and rear precipitation core of the supercell all passed across the tower a comparison of the instrumented tower measurements with a dual doppler synthesis reveals that the latter qualitatively resolved the low level flow however the magnitudes of the low level horizontal winds and updraft speed were underestimated in addition the vertical shear of the horizontal wind in the lowest kilometer was unresolved in the doppler winds in the storm environment horizontal vorticity was strong 1 5 10 2 s 1 and approximately streamwise

timing of deformation associated with the syn tectonic dawros currywongaun doughruagh complex nw connemara western ireland new data are presented that demonstrate the syn tectonic intrusion of a suite of mafic and ultramafic magmas into the connemara dalradian magma was intruded during the local d2 episode but immediately prior to the onset of d3 both deformation episodes affect the gabbros forming two distinct groups of fabrics formed at different stages during the history of the intrusion applying thermal considerations to this history suggest that any gap in time between the formation of these fabrics was

a pre d2 age for the 590 ma ben vuirich granite in the dalradian of scotland regional mapping demonstrates that s2 is the main fabric in the central highland dalradian and that it is this fabric not s3 as previously thought which overprints the 590 ma ben vuirich granite the granite appears to have been emplaced following a tectonic event d1 in the dalradian rocks for a finely spaced penetrative fabric seen in newly discovered hornfelses from the granite aureole is overgrown by contact metamorphic cordierite and andalusite porphyroblasts now both altered which predate the d2 metamorphism the ben vuirich granite cuts the neoproterozoic dalradian sequence of the central highlands of scotland fig 1 inset and was first recognized as an older foliated granite by barrow et al 1905 later workers bradbury et al 1976 bradbury 1978 concluded that the granite was intruded between d2 and d3 in the dalradian rocks harris et al 1976 and for many years an u pb zircon age of 514 7 ma from the intrusion pankhurst pidgeon 1976 provided a valuable datum point in the evolution of the scottish caledonides however dalradian chronology has recently undergone a radical revision following the determination of a precise u pb age of 590 2 ma for the emplacement of the ben vuirich granite rogers et al 1989 in accepting the interpretation of bradbury et al 1976 that the regional penetrative fabric which affects the country rocks and is continuous with that in the granite is of d3 age rogers et al were also guided by the conclusions of harte et al 1984 and dempster harte

characterizing rock mass deformation mechanisms during plate load tests at the bakhtiary dam project abstract the results of 26 plate load tests carried out at the bakhtiary dam site were analyzed to define and characterise the mechanisms governing the rock mass deformation during the tests tests were categorized into groups based on the relative direction of loading to the orientation of major discontinuity sets running through the rock mass five mechanisms were distinguished as the main modes controlling deformations of the rock mass during the tests these mechanisms were based on analysis of the shape of stress deformation curves total and plastic deformation anisotropy and deformation hysteresis this study shows that part of the scatter commonly observed in the moduli calculated from plate load tests can be attributed to the different deformation mechanisms that are mobilized during the tests incompatibility of the theoretical assumptions made for the interpretation of the test results with actual deformation mechanisms is shown to be another factor causing scatter in the calculated moduli

major southward thrusting of the dalradian rocks of connemara western ireland the connemara schists are of dalradian late precambrian cambrian age and since the work of kilburn et al 1 it has been apparentthat they occupy an anomalous geographical position south southeast of the strike continuation of the dalradian rocks of scotland and ireland and south of the inferred position of the highland boundary fault fig 1 also the connemara schists are unusual in having reached a higher metamorphic grade and having had a different metamorphic history from most other parts of the dalradian the model which we propose here for the connemara dalradian that of an allochthonous thrust sheet offers an explanation for these anomalies and highlights hitherto unsuspected similarities between the tectonic histories of the south east margins of the metamorphic caledonides in the british isles and scandinavia

evidence for a regional scale fluid loss event during mid crustal metamorphism how fluid is released from the deep crust during metamorphism remains controversial whereas some authors advocate large scale fluid fluxes due to convective circulation of metamorphic fluid1 others consider that only one way flow is possible2 3 furthermore some flow models imply that fluid moves across and largely independently of sedimentary layering1 2 whereas many fluid based studies find evidence for focusing of flow by particular lithologies2 4 7 here we report a study of metamorphic fluid flow on a regional rather than an outcrop scale using a combination of field geology petrology and theoretical and isotope geochemistry we identify metasomatic lithologies at the top of a dolomitic marble unit which must have drawn in water over a kilometre scale from adjacent pelitic formations we suggest that this flow was part of a single major fluid loss event near the metamorphic peak fluid followed the metasomatic layers to structural highs where it broke out into adjacent schists to form skarns this fluid loss may have changed the rheology of the rock involved and terminated regional folding

fluid disturbed hornblende k ar ages from the dalradian rocks of connemara western ireland the results of k ar age determinations and hydrogen and oxygen stable isotope measurements on hornblendes from the poly metamorphic dalradian schists of connemara western ireland indicate that the hornblende k ar systems have been significantly disturbed by low temperature fluid reaction correlations between k ar ages d values structural water contents and the occupancy of the hornblende structural a sites suggest that excess water as h 3 o occupies vacant a site positions during stable isotope exchange and displaces ar causing lowering of the k ar ages this process occurs below the normally accepted closure temperature for ar in hornblende and is not detectable by optical or x ray investigation of the mineral this process may not be unique to connemara hornblendes and so is of potential importance to geochronology in other metamorphic terranes

alpine metamorphism in the south east tauern window austria 2 rates of heating cooling and uplift existing geochronological data are reviewed and new rb sr k ar and 39ar 40ar ages are presented including a suite of 33 mica ages from a 20 km north south tunnel section these data are discussed in relation to the thermal history from the overthrusting of the autroalpine nappes c 65 myr ago to the present the earliest phase of metamorphism involving lawsonite crystallization is associated with emplacement of these nappes subsequently temperatures in the rocks beneath rose at a mean rate of 3 6 c myr until the climax of metamorphism at high structural levels published data indicate an age 35 myr for the metamorphic climax in contrast a new 39ar 40ar step heating age of 23 8 0 8 myr on amphibole from near the base of peripheral schieferhulle closely approximates the age of metamorphism and provides the first clear indication that the climax of metamorphism occurred later at deeper structure levels following the climax near isothermal uplift and erosion reduced pressure to c 1 kbar before white mica closure at 19 myr this implies uplift at 3 mm yr along the tunnel section white mica k ar ages vary systematically from 24 myr to 16 5 myr with position relative to a late 4 km amplitude dome whereas biotite rb sr ages are uniform at 16 5 myr across the whole profile doming is thus dated at 16 5 myr with transient uplift rates 5 mm yr at other times uplift rates were 1 mm yr

estimation of in situ stress along deep tunnels buried in complex geological conditions abstract the headrace tunnels of the jinping ii hydropower station are 16 7 km in length and have a maximum depth of 2525 m many difficulties have been encountered in estimation of virgin rock stresses along the tunnels one method was presented including the macroscopic analysis of the region geological structures and topography and the integrated analysis of in situ stresses based on the multi source information in local tunnel sections the characteristics of geological structures and tectonic movement were studied to determine the orientations of the tectonic stresses within the jinping ii tunnel project region the influences of the topography on the distribution of in situ stress were analyzed using numerical methods the virgin stress regimes were preliminarily estimated based on the geological and topographical analysis and the world stress map under the guidance of these results multi source information was collected regarding rock brittle failures edzs core disking and large scale deformation of soft rock several techniques were adopted including multivariate regression numerical simulation and stereographic projection an iterative method for the orientations and magnitudes of in situ stresses is presented the in situ stress regimes orientations and magnitudes in tunnel sections of different depths were obtained and verified they can provide the basic conditions for analysis of the stability of surrounding rock mass during excavation

the origin and significance of the delaney dome formation connemara ireland dalradian meta sediments of the laurentian margin and mafic intrusions thereof in sw connemara ireland tectonically overlie meta rhyolites of the delaney dome formation the two units are separated by the mannin thrust a new u pb age of 474 6 5 5 ma shows that the delaney dome formation is a temporal equivalent of arc volcanic rocks preserved in the adjacent south mayo trough the tourmakeady volcanic group erupted during the collision of an oceanic island arc with the laurentian margin in the grampian orogeny new rare earth and high field strength element data show that the delaney dome formation and tourmakeady volcanic group are chemically similar and arc like in character this suggests that the delaney dome formation is an along strike equivalent of the tourmakeady group strike slip faulted south of the south mayo trough during or after the grampian orogeny further correlation of these units with northern appalachian rhyolites is also possible the delaney dome formation is an extrusive temporal equivalent of intrusions that penetrate the connemara dalradian thus movement along the mannin thrust brought mid crustal plutons and dalradian country rocks tectonically above the extrusive volcanic sequence the mannin thrust is identified as a major imbricating structure within a continental arc but not a terrane boundary

assessment of rock mass strength for underground excavations abstract when the stability of underground openings is assessed one must concern with local and global failure modes local failures may take place as long as rock blocks are kinematically movable into openings while global failure modes are associated with the stress state and the strength of rock mass surrounding openings this fact is always confused in underground rock engineering first the authors briefly describe several approaches how to assess the strength of rock masses together with some new proposals for underground excavations then the estimations by these methods are compared with each other as well as with experimental data finally the validity of these methods are discussed and some recommendations are made for practical applications

a comparison of predicted and actual tunnel behaviour in the istanbul metro turkey abstract the empirical method proposed by hoek and brown is combined with rock mass classifications to predict the deformation behaviour of istanbul metro the rock mass was assessed using both bieniawski s rmr 89 and its strength was estimated from the formula of hoek and brown for the rmr 89 system the applicability and validity of the proposed procedure has been checked by comparing the predictions with actual observations it is found that the predictions agree well with observations in the intact rock although there are some differences between predictions and observations in the faulted rock these probably reflect the inevitable inaccuracies in empirical approaches and differences in behaviour of the actual support system that is assumed in modelling in addition anisotropy features like faults which are not accounted properly in the hoek et al equation that assumes isotropic behaviour

age and geologic setting of quartz vein hosted gold mineralization at curraghinalt northern ireland implications for genesis and classification acknowledgments we are grateful to dalradian gold ltd for providing the sections for petrographic analysis geochemical data and general support we would also like to thank the following john still alison sandison and jenny johnston of the school of geosciences university of aberdeen for assistance with the sem studies js and with preparing figures as and jj nerc for ongoing funding of the argon isotope facility at suerc jim imlach and ross dymock at suerc for technical assistance and martin lee at the school of geographical and earth sciences at the university of glasgow for use of the sem cl equipment the paper has benefitted significantly from comments by the official reviewers and unofficial reviews by garth earls jamie wilkinson mark cooper and adrian boyce and detailed conversations with ian alsop structural geology of the sperrins and nyree hill and gawen jenkin gold mineralization in the caledonides the authors are entirely responsible for the conclusions expressed

characterizing block geometry in jointed rockmasses the intersection of discontinuities in a jointed rockmass creates in situ blocks of variable three dimensional 3d geometry the size and shape of rock blocks in a rockmass assembly have a dominant influence on the engineering properties of a rockmass and control for example the failure geometry of a rock face and the optimum associated support and surface restraint strategy the distribution of block volumes within a rockmass can be effectively analyzed and communicated using a cumulative volume distribution curve integrated with this analysis a methodology has been developed to characterize the shape and volumetric shape distribution of rock blocks in 3d models of jointed rockmasses the proposed block shape characterization method takes into account two factors the first describes the shortening of the minor principal axis of the block while describes the elongation of the major axis when merged with the block volume distribution the block shape characterization method can effectively describe and classify both the size and shape distributions of any jointed rockmass and is not limited to orthogonal blocks or hexahedra this methodology can classify any polyhedra and has been developed and calibrated based on synthetic joint data and simulated block assemblies a demonstration is given of its effectiveness in characterizing block geometries in the field using mapped fracture data

empirical estimation of rock mass modulus the deformation modulus of a rock mass is an important input parameter in any analysis of rock mass behaviour that includes deformations field tests to determine this parameter directly are time consuming expensive and the reliability of the results of these tests is sometimes questionable consequently several authors have proposed empirical relationships for estimating the value of rock mass deformation modulus on the basis of classification schemes these relationships are reviewed and their limitations are discussed based on data from a large number of in situ measurements from china and taiwan a new relationship based upon a sigmoid function is proposed the properties of the intact rock as well as the effects of disturbance due to blast damage and or stress relaxation are also included in this new relationship