magnetic anisotropy of the trenton limestone revisited previous studies have shown clear differences between the anisotropies of low field magnetic susceptibility lfs and of anhysteretic remanent magnetization arm in samples of the ordovician trenton limestone from trenton falls ny arm was found to be significantly more anisotropic than lfs and to exhibit a well defined east northeasterly lineation which was not apparent in anisotropy of magnetic susceptibility ams because of significant local variation in mean lfs by approximately a factor of two at this locality it has been possible to reanalyze the ams of these samples by the method of henry 1983 which in some cases allows mathematical differentiation of the ferromagnetic and paramagnetic susceptibility tensors the ferromagnetic susceptibility tensor obtained in this way shows the same tectonic shortening apparent in the arm anisotropy but surprisingly it shows no evidence of horizontal foliation the paramagnetic tensor is horizontally foliated with no lineation the difference between the ferromagnetic susceptibility and arm tensors suggests different ferrromagnetic sources of arm and lfs

enhanced velocity tomography practical method of combining velocity and attenuation parameters acoustic ultrasonic tomography is now a well acepted method for investigating the internal structure of rock samples and rock masses in this article we describe a new parameter to be imaged which combines the robustness of velocity tomography and the sensitivity of attenuation tomography resulting in enhanced velocity tomography the theoretical considerations are illustrated by a computer simulation and then by application to data from a granite sample subjected to induced damage by heating in both cases the enhanced velocity tomography is found to be more sensitive to the internal rock structure than classical velocity tomography and overcomes instability problems characteristic of attenuation tomography

evidence for syntectonic intrusion of plutons in the bear mountains fault zone california in the foothills terrane western metamorphic belt california the bear mountains fault zone bmfz a zone of complex multiple deformation has deformed composite maficfelsic granitoids of the guadalupe igneous complex gic and the hornitos pluton at magmatic to upper amphibolite facies temperatures evidence for high temperature deformation includes the occurrence of orthopyroxene clinopyroxene and brown hornblende in syndeformationally recrystallized aggregates in deformed rocks of the gic and the occurrence of melt leucosomes in the axial surfaces of folds in cordierite k feldspar migmatites in contact metamorphic country rocks in the bmfz away from the bmfz composite granitoids of the gic show no evidence of magmatic flow so that deformation of the gic granitoids in the bmfz was entirely by solid state flow this suggests that the gic was intruded before this mylonitic deformation in the bmfz however other evidence suggests some deformation in the bmfz before intrusion of the pluton in the hornitos pluton components of composite granitoids showing relatively weak solid state deformation are strongly elongate suggesting a component of magmatic flow although later subsolidus deformation also occurred in most places supporting evidence of magmatic flow in the hornitos pluton also includes dimensional alignment of plagioclase laths and prismatic hornblende grains as well as preferred orientation of twins in recrystallized aggregates of elongate grains of plagioclase away from the bmfz the regional metamorphic grade is low suggesting that heat for the high temperature deformation and metamorphism was supplied by the intrusions u pb zircon ages are consistent with emplacement of the gic and the hornitos pluton as well as their deformation in the bmfz around 150 ma 40 ar 39 ar ages of hornblende in foliations in the deformed granitoids and of biotite in foliations in the contact aureole rocks suggest that the plutons and the country rocks in the bmfz remained hot enough for amphibolite to upper greenschist facies conditions to persist for 5 to 15 ma after emplacement of the plutons

seismic attenuation spectra in rock mass characterization a case study in open pit mining the application of engineering geophysics to the characterization of rock masses is exemplified through a case study of three phases of a research project into the design of efficient blasting systems in open pit mining seismic experiments are used before and after mine blasting to monitor the efficiency of explosions in terms of rock fragmentation spectral analysis of seismic signals after they have been used to interrogate rock masses is used to compute preblast and postblast attenuation and velocity parameters the results show that fragmentation efficiency of a mine blast and fracture anisotropy of a rock mass can be quantified in terms of three dimensional 3 d attenuation spectra and polar anisotropy diagrams these seismic data are correlated with the blast design and the energy used by the excavating dragline machine to dig to rock mass an overview of the seismic attenuation technique and instrumentation used in the project phases i and ii is given a case study from phase iii highlights the scope and interpretation of the relationship between excavation parameters and seismically characterized blasting efficiency

tomographic imaging of thermally induced fractures in granite using bayesian inversion the internal structure of rock samples studied in laboratory experiments can be described by a variety of physical parameters some of them like the velocity of acoustic waves enhanced velocity or quality factor can be reconstructed by means of ultrasonic tomography this article presents the results of classical velocity tomography imaging accompanied by the results of attenuation tomography and recently introduced enhanced velocity tomography obtained for a lac du bonnet granite sample subjected to thermal stresses to invert acoustic data recorded during six heating cycles a bayesian inversion scheme accompanied by a genetic algorithm optimization approach and the robust cauchy norm have been used to obtain the highest possible spatial resolution of images the inversion was performed in two steps in the first step a crude parameterization of the sample was used the result of this stage was next taken as an a priori model for a final inversion with refined parameterization the choice of parameterization cell sizes and damping parameters at both stages was based on an analysis of the resolution operator both velocity and enhanced velocity tomography accurately imaged changes in the rock microstructure caused by thermal stresses however enhanced velocity tomography gave a much better spatial resolution than velocity tomography on the other hand attenuation tomography based on inversion of pulse rise times was able to image only a rough structure of the sample and it has difficulty with reasonable imaging of the crack formed in the sixth heating cycle

magnetic fabric determined from arm and irm anisotropies in paleozoic carbonates southern appalachian basin we have undertaken a comparative study of arm and irm anisotropies in paleozoic carbonate rocks from the nashville and jessamine domes in the southern appalachian basin the arma ellipsoids differ markedly from the irma ellipsoids arma appears to reflect a pre deformation magnetic fabric due to deposition and or compaction with minimum axes near vertical and a weak lineation conversely irma has minimum axes near horizontal and oriented ne sw which is compatible with a tectonic fabric due to alleghanian deformation percent arma is consistently greater than irma arm was imparted at low alternating fields 30 mt and thus arma may reflect the fabric residing in low and intermediate coercivity coarse grained magnetite however the irm was imparted in saturating fields 300 mt and appears to be dominated by the single domain fraction which is believed to carry the observed kiaman superchron remagnetization

late shortening and extensional structures and veins in the western margin of the taconic orogen new york to vermont abstract along the western margin of the taconic orogen in new york and vermont undeformed quartz calcite veins commonly occur in the belt of melange that formed beneath the westward advancing taconic allochthon during the middle late ordovician taconic orogeny the veins have mineral slickenfibers recording either reverse or normal slip in new york the reverse motion veins recording the latest phase of shortening are crosscut by the normal motion veins and faults the shortening indicated by the reverse motion veins is correlated with the convergence along the champlain thrust in vermont which is also crosscut by a significant strike parallel normal fault fluid inclusion data from the veins complemented by stable isotope data lead to a reconstruction of the sequence of events in the context of a cooling of the fluids which is consistent with crosscutting relationships among the veins following cessation of the convergence there was regional extension of the western margin of the taconic orogen

the eastern ghats mobile belt india a collage of juxtaposed terranes abstract examination of landsat tm images reconnaissance field traverses and the published geological maps from the eastern ghats mobile belt egmb india reveal a network of major ductile shear zones both within and at the margins these shear zones are characterized by mylonitic foliation grain size reduction metamorphic retrogression stretching lineations and distinct signatures of alkaline anorthositic and granitic magmatism these shear zones divide the egmb into distinct terranes which are heterogeneously deformed with extensive tracts of foliated mylonitic gneisses and ultramylonites the main gneissic foliation in all the terranes is refolded in near non coaxial manner generally about the axis subparallel to the elongation of the terrane structural history in each terrane is distinct in the orientation of stretching lineations attitude of gneissosity and early fold axial planes lithological assemblages and available geochronological data it is possible to recognise nine large terranes within the egmb and the characteristics of each terrane have been described the terrane distribution in the egmb could well fit a thrust tectonic allochthonous model of amalgamation and accretion different terranes could be different thrust nappes or allochthonous tectonic sheets representing tectono stratigraphic terranes

deformation and magnetization of the hudson valley eastern new york results of a study of calcite twinning and anisotropy of magnetic remanence in the onondaga limestone abstract results of a study of calcite twin analysis and anisotropy of anhysteretic remanent magnetization aarm for the onondaga limestone in the hudson valley fold and thrust belt hvb raise questions about the deformation history of this area and the nature of aarm two bedding parallel shortening directions are inferred from calcite twinning one normal to hvb fold axes nw se to ene wsw and the other at high angles to this direction nne ssw to n s two hypotheses are put forward to explain the inconsistent shortening direction 1 even during the initial stages of folding and thrusting in the hvb deformation was three dimensional in character 2 the hvb developed synchronous with main phase alleghanian deformation aarm results are consistent with the magnetic anisotropy being in part caused by the deformation associated with folding and thrusting this is a surprising result because the magnetization is presumably of diagenetic origin and it was acquired after folding

deformation history of the kunavaram complex eastern ghats belt india implications for alkaline magmatism along the indo antarctica suture abstract the kunavaram alkaline complex is a ne sw trending elongate body located along a major lineament the sileru shear zone ssz that is regarded as a proterozoic suture related to indo antarctica collision the complex is hosted within migmatitic quartzofeldspathic gneisses mafic granulites retrogressed to amphibolites and quartzites the structural evolution of the country rocks and the alkaline complex are similar the first phase of deformation d1 produces a pervasive segregation banding s1 in all rock units within and outside the complex a second deformation phase d2 isoclinally folded s1 along subvertical axial planes with shallow plunging axes f2 isoclinal folds are ubiquitous in the country rocks and the eastern extremity of the complex in the interior of the alkaline body d2 strain decreases and s1 is commonly subhorizontal while amphibolite to granulite facies conditions prevailed during deformation post d2 annealing textures testify to persisting high grade conditions in the west a nne ssw trending dextral shear zone with strike slip sense d3 truncates the complex within this shear zone quartzofeldspathic country rocks are plastically deformed while hornblende k feldspar assemblages of the complex are retrogressed to biotite and plagioclase warping related to d3 shears also resulted in fold interference patterns on the subhorizontal s1 foliation in low d2 strain domains based on its steep dip north easterly trend and non coaxial nature with dextral strike slip sense the d3 shear zone can be correlated with the ssz since this shear zone i e the ssz is not associated with primary igneous fabrics and resulted in solid state deformation of the complex it cannot be considered as a conduit for alkaline magmatism but is probably responsible for the post tectonic disposition of the pluton

structure and tectonics of the hudson valley fold thrust belt eastern new york state analysis of structural features displayed in silurian and devonian strata of the hudson valley region indicate that these rocks form the western edge of a now largely eroded west verging fold thrust belt the hudson valley fold thrust belt or hvb west of the hudson river remnants of this fold thrust belt define a miniature valley and ridge province faults of the hvb die out to the west as blind thrusts in the basal units of the catskill clastic wedge structural geometries displayed in the hvb vary rapidly along strike and are locally complicated by internal deformation of thrust sheets and by movement on out of the syncline faults it is proposed that exposed faults of the hvb west of the river arise from a basal detachment here called the rondout detachment that lies above the taconic unconformity the rondout detachment and the overlying thrust system have been bent into large amplitude folds ordovician units beneath the rondout detachment must have shortened during development of these folds area balancing of cross sectional models suggests that the shortening affecting ordovician units could be restricted to rock above a lower blind detachment the austin glen detachment positioned within ordovician strata at a depth of 400 m below ground surface the age of deformation and the tectonic setting of the hvb is enigmatic its spatial relation to the catskill clastic wedge and to acadian metamorphic terranes suggests that the belt represents foreland shortening developed during the acadian orogeny

alkaline magmatism versus collision tectonics in the eastern ghats belt india constraints from structural studies in the koraput complex abstract linear domains of deformed alkaline rocks and carbonatites have recently been identified as representing sites of ancient suture zones in peninsular india the western margin of the proterozoic eastern ghats belt egb is characterized by a series of alkaline plutons that are aligned close to the contact with the archaean craton most of the complexes were deformed and metamorphosed during a subsequent orogenic event unlike other plutons in the belt the alkaline complex at koraput reportedly escaped deformation and granulite facies metamorphism forming an anomalous entity within the zone multiply deformed country rocks hosting this complex underwent syn d1cr granulite facies metamorphism followed by d2cr thrusting with pervasive shearing along a ne sw trending foliation a second granulite facies event followed localized d3cr shearing within the koraput complex strain partitioning was responsible for preserving igneous textures in the gabbroic core but aligned magmatic amphibole needles and plagioclase laths occasionally define a s1ac fabric along the margins s1ac is rotated parallel to a ne trending east dipping s2ac fabric in the gabbro fringing syenodiorite and nepheline syenite bands locally d3ac shearing follows d2ac deformation s2ac and s3ac parallel s2cr and s3cr in the country rocks high grade metamorphism represented by recrystallization of amphibole and plagioclase and breakdown of amphibole and biotite to garnet pyroxene and k feldspar in the complex follows d3ac unlike earlier reports therefore the koraput body is also deformed and metamorphosed the aligned alkaline complexes in the egb probably represent deformed alkaline rocks and carbonatites formed by rifting related to an earlier episode of continental break up that were deformed during subsequent juxtaposition of the egb with the archaean craton this supports the contention that the western margin of the egb and its contact with the archaean craton is a suture zone related to the indo antarctica collision event

natural deformation and recrystallization of some intermediate plagioclase feldspars abstract intermediate an25 an48 plagioclase feldspars from the nordre stromfjord shear zone central west greenland have undergone extensive ductile deformation by intracrystalline slip and by twinning the plagioclases were deformed under low granulite facies conditions optical substructures include undulatory extinction deformation bands subgrains and deformational twins mainly on the albite law dynamic recrystallization occurred primarily by subgrain rotation with bulge nucleation migration of a high angle boundary as a secondary mechanism in some cases recrystallization is accompanied by a small decrease in the an content which is thought to indicate prograde metamorphic conditions the plagioclases exhibit a good crystallographic preferred orientation which is compatible with 010 001 being the principal slip system quartz has in the same rocks undergone more plastic deformation and more extensive recovery than plagioclase this is at least in part due to the fact that most dislocations in plagioclase are dissociated

ultrasonic imaging and acoustic emission monitoring of thermally induced microcracks in lac du bonnet granite concurrent ultrasonic tomography and acoustic emission monitoring were employed to study thermally induced microfracturing in an unconfined 15 cm cube of lac du bonnet granite from atomic energy of canada limited s underground research laboratory an electrical resistance cartridge heater placed in a central vertical borehole was used to cycle the sample to progressively higher peak temperatures between 75 c and 175 c tomography data were collected at room temperature before and after each thermal cycle acoustic emission monitoring proceeded during both heating and cooling phases of each thermal cycle microfractures opened above 80 c and eventually coalesced into a macroscopic fracture plane the macroscopic fracture originated at the outer edges of the sample and then extended inward parallel to the fast velocity direction and eventually intersected the borehole both acoustic emission locations and slowness difference tomography clearly delineated the fracture plane we attribute the development of the macroscopic fracture to a thermal gradient cracking mechanism acting upon a brittle anisotropic medium

the observations of faulting in westerly granite under triaxial compression by x ray ct scan abstract observations of the spatial development of cracks in granite undergoing triaxial compression provide new insights into the proces of fault formation dry intact westerly granite samples were loaded under confining pressure of 100 mpa and the progress of fault formation was controlled by maintaining the increment of circumferential displacement at a constant rate the samples were unloaded when they experienced stress drops and were successfully recovered without severe crushing a stereo microscope was used to observe the spatial pattern of cracks on the sample surfaces and an x ray ct scanning system was used to non destructively image the sample interiors microscope observations show that several fault like linear cracks developed on the surfaces of all the samples and have an angle of about 30 degrees to the maximum compression axis this suggests that fault nucleation began just after peak stress the x ray ct images show that a fault like linear crack grew inward toward the sample interior as axial stress decreased it is concluded that the fault nucleated locally on the sample surface just after peak stress and developed into an apparent fault by the plateau stage of the complete stress strain relationship

the transition from magmatic to high temperature solid state deformation implications from the mount stuart batholith washington criteria for syntectonic emplacement of plutons are commonly ambiguous the strongest single criterion is probably the preservation of a continuous transition from submagmatic to high temperature solidstate deformation this transition is not commonly documented an exception is the mount stuart batholith which displays a variety of syntectonic structures within its sheared northeastern margin including the following 1 s c fabrics that range from submagmatic to high temperature solid state 2 solid state foliation and lineation defined by amphibolite facies assemblages that overprint and are parallel to magmatic foliation and lineation 3 folds of magmatic and solid state foliation that have hinge lines parallel to magmatic and solid state lineation and to equivalent structures in wall rocks 4 dikes that were folded and boudinaged over a wide range of rheological states with boudin necks locally filled by tonalite 5 pegmatite dikes and mineralized joints that are sub perpendicular to magmatic and solid state lineation and 6 submagmatic and high temperature solidstate ductile shear zones we suggest that many plutons emplaced during regional deformation do not preserve evidence for syntectonic deformation because of the transitory nature of the submagmatic state and the obscuring effects of postemplacement deformation syntectonic features are most likely preserved in plutons cooled at slow to moderate rates or in plutons deformed at high strain rates during emplacement the optimum conditions for preservation may occur in plutons emplaced along fault zones in the mid crust such as the mount stuart batholith and in intrusions at deeper levels that were rapidly exhumed and or intruded during the waning stages of regional deformation

metamorphism of the koraput alkaline complex eastern ghats province india evidence for reworking of a granulite terrane abstract an assemblage of predominantly metasedimentary rocks in the eastern ghats province india underwent granulite facies metamorphism and deformation in early neoproterozoic times and was subsequently intruded by the koraput alkaline complex the intrusion was earlier believed to be syn to late tectonic the gabbroic core of the complex hosts nepheline bearing syenitic dykes and veins following emplacement magmatic amphibole within the syenites and early orthopyroxene in feldspathic gneisses within the country rocks were retrogressed to biotite during pervasive solid state deformation subsequent prograde metamorphism resulted in the formation of anhydrous assemblages at the expense of relict magmatic amphibole within the syenites and metamorphic biotite in both the complex and the country rocks reactions reconstructed from textural observations indicate breakdown of biotite and amphibole to garnet clinopyroxene orthopyroxene bearing assemblages schreinemakers analysis on the relevant mineral associations suggests that heating was followed by loading of the region this indicates thermal rejuvenation of the complex and the host granulites during an intracrustal orogeny that post dates emplacement and cooling of the pluton available ages suggest that this event occurred in the mid neoproterozoic and is probably unrelated to the amalgamation of the granulite belt with the archaean bastar dharwar craton

a direct comparison between vibrational resonance and pulse transmission data for assessment of seismic attenuation in rock for the same volume of rock i compare the attenuation obtained by seismic pulse transmission over the frequency range 1 150 khz with that obtained by vibrational resonance techniques over the frequency range 1 50 khz the initial studies were performed on a rectangular block of medium grained granite which was large enough to permit the installation of a seismic pulse transmission array over a 1 8 m path length yet small enough to permit whole body resonance a q of 82 for the p wave was derived from the vibrational resonance results whereas a q of 15 was derived from the pulse transmission results in light of models proposed for the viscoelastic geometric and elastic scattering attenuation mechanisms the experimental results suggest that this large discrepancy in q values is due to elastic scattering by grain clusters rather than individual grains within the granite scattering is significant in the high frequency pulse transmission tests but is considered insignificant in the lower frequency

structural evolution across the eastern ghats mobile belt bastar craton boundary india hot over cold thrusting in an ancient collision zone along the western margin of the eastern ghats mobile belt egmb ultrahigh temperature granulites are thrust westward over hornblende granites and sedimentary rocks of the bastar craton multiply deformed migmatitic gneisses and porphyritic charnockite of the egmb unit preserve thrust related shear fabrics s3m in the cratonic foreland undeformed granites show a progressive decrease in grain size and increase in penetrative foliation to the east evolving into orthogneiss near the mylonitized contact zone with charnockite foreland fabrics with a consistent top to the west shear sense are conformable with s3m in charnockite and correlate with s3b in polydeformed orthogneisses of cratonic windows s3b in the windows parallels s3m in overlying egmb migmatitic gneisses while s3m accompanied granulite metamorphism in the egmb s3b temperature estimates vary from t 700 c in the windows to t 550 c in the west decreasing temperature and later fabric formation in the west are explained by an evolving thermal profile in the cold craton which is caused by thrusting against hot lower crustal egmb rocks based on lithologic structural and metamorphic variations across the contact and resemblances between the egmb and rayner complex the craton mobile belt boundary is considered a result of indo antarctic collision leading to the formation of an ancient supercontinent

coupled deformation and metamorphism in the roof of a tabular midcrustal igneous complex the 370 377 ma mooselookmeguntic igneous complex was emplaced at 14 km depth into steeply dipping metaturbidites that were folded and metamorphosed ca 400 405 ma during the acadian orog eny gravity and drill hole data isograd geometry thermal modeling and struc tural measurements all indicate that the eastern aureole of the complex represents an areally extensive roof above the gently east dipping tabular shaped intrusion this roof preserves a classic example of low pressure high temperature metamorphism caused by the underlying intrusion ther mal modeling indicates that the roof is no more than 1000 m thick over an area exceed ing 100 km2 unlike other roofs described in the literature the mooselookmeguntic igneous complex roof preserves a thick 600 m emplacement related strain gradi ent with a deformational fabric that evolved through all stages of crenulation cleavage to become an intense nondifferentiated folia tion approximately parallel to the intrusive contact and perpendicular to the steeply dip ping regional acadian age foliation fabric evolution through all stages of crenulation cleavage requires the vertical growth of the tabular intrusion to have been largely accommodated by dissolution precipitation creep which is a linear viscous deformation mechanism that can occur at lower differ ential stress than for example dislocation creep as the crenulation cleavage evolves a stage is reached where further deformation requires a change in deformation mecha nism which may lead to hardening of the rock development of crenulation cleavage requires a mica rich foliation at an initially high angle to the emplacement related fl at tening plane and this confi guration may be the primary reason why the strain aureole in the mooselookmeguntic igneous complex roof is so well developed compared to other published examples of midcrustal roofs

contrasting pressure temperature deformation history across a vestigial craton mobile belt boundary the western margin of the eastern ghats belt at deobhog india at deobhog migmatitic gneisses and granulites of the eastern ghats belt are juxtaposed against a cratonic ensemble of banded augen gneiss amphibolite and calcsilicate gneiss intruded by late hornblende granite and dolerite in the migmatitic gneiss unit early isoclinal folds syn d1m and d2m are reoriented along n s trending and e dipping shear planes s3m with s1m s3m intersection lineations having steep to moderate plunges the near peak p t condition was syn d3m 900 c 9 5 kbar as inferred from syn d3m grt opx bearing leucosomes in mafic granulites and from thermobarometry on grt corona opx cpx pl qtz assemblages the p t values are consistent with the occurrence of opx spr crd assemblages in spatially associated high mg al pelites a subsequent period of cooling followed by isothermal decompression 800 850 c c 7 kbar is documented by the formation of coronal garnet and its decomposition to opx pl symplectites in mafic granulites hydrous fluid infiltration accompanying the retrograde changes is manifested in biotite replacing opx in some lithologies the cratonic banded gneiss granite unit also documents two phases of isoclinal folding d1b d2b with the l2b lineation girdle different from the lineation spread in the migmatitic gneiss unit calcsilicate gneiss hbl pl cpx scap cal and amphibolite hbl pl grt cpx within banded gneisses record syn d2b peak metamorphic conditions c 700 c 6 5 kbar followed by cooling to c 500 c manifested in the stabilization of coronal clinozoisite epidote the d3b shear deformation post dates granite and dolerite intrusions and is characterized by top to the west movement along n s trending e dipping shear planes deformation mechanisms of quartz and feldspar in granites and banded gneisses and amphibole plagioclase thermometry within shear bands in dolerites document an inverted syn d3b thermal gradient with temperature increasing from 350 to 550 c in the west to 700 c near the contact with the migmatitic gneiss unit the thermal gradient is reflected in the stabilization of chlorite after hornblende in s3b shears to the west and post d2b neosome segregation along d3b folds and shears to the east the contrasting lithologies early structures and peak metamorphic conditions in the two units indicate unconnected pre d3p t deformation histories the shared d3 deformation in the two units the syn d3 inverted thermal gradient preserved in the footwall cratonic rocks and the complementary cooling and hydration of the hanging wall granulites across the contact are attributed to westward thrusting of hot eastern ghats granulites on cool cratonic crust it is suggested that the eastern ghats migmatitic gneiss unit is not a reworked part of the craton but a para autochthonous allochthonous unit emplaced on and amalgamated to the craton

archaean cambrian crustal development of east antarctica metamorphic characteristics and tectonic implications abstract the east antarctic shield consists of a variety of archaean and proterozoic cambrian high grade terranes that have distinct crustal histories and were amalgamated at various times in the precambrian cambrian high grade pan african tectonism at 600 500ma is recognized from four distinct belts the dronning maud land lutzow holm bay prydz bay and denman glacier belts these high grade belts juxtapose distinct mesoproterozoic and neoproterozoic crustal provinces maud rayner and wilkes the rauer terrane and have also marginally affected archaean cratonic remnants in the napier complex and southern prince charles mountains the wilkes province experienced its principal tectonothermal events prior to 1130ma and was not affected by the younger events that characterize the maud province 1150 and 1030 990ma the rayner province 990 920ma and the rauer terrane 1030 990ma these differences between the isotopic event records of the basement provinces now separated by the pan african belts require that the older provinces were not formerly parts of a continuous grenville belt as proposed in the sw us east antartic model east antarctica was not a single unified crustal block within either east gondwana or rodinia until the cambrian which is now demonstrated to be the key phase of high grade and ultrahigh temperature uht metamorphism associated with supercontinent assembly the high grade pan african tectonism is characterized by extensive infracrustal melting clock wise p t paths rapid post peak exhumation along isothermal decompression paths to shallow or mid crustal levels by 500 ma and the generation at least locally of uht conditions a significant flux of heat from the mantle into the deep and initially overthickened crust is required to produce these observed metamorphic effects whilst the thermal evolution can be explained by models that invoke the removal of most of the lithospheric mantle following crustal thickening and prior to rapid extension of the remaining crust these one dimensional models are inconsistent with present crustal thicknesses of 25 35km in the pan african domains of the east antarctic shield

timelapse ultrasonic tomography for measuring damage localization in geomechanics laboratory tests variation of mechanical properties in materials can be detected non destructively using ultrasonic measurements in particular changes in elastic wave velocity can occur due to damage i e micro cracking and particles debonding here the challenge of characterizing damage in geomaterials i e rocks and soils is addressed geomaterials are naturally heterogeneous media in which the deformation can localize so that few measurements of acoustic velocity across the sample are not sufficient to capture the heterogeneities therefore an ultrasonic tomography procedure has been implemented to map the spatial and temporal variations in propagation velocity which provides information on the damage process moreover double beamforming has been successfully applied to identify and isolate multiple arrivals that are caused by strong heterogeneities natural or induced by the deformation process the applicability of the developed experimental technique to laboratory geomechanics testing is illustrated using data acquired on a sample of natural rock before and after being deformed under triaxial compression the approach is then validated and extended to time lapse monitoring using data acquired during plane strain compression of a sample including a well defined layer with different mechanical properties than the matrix

fluid inclusion studies on the koraput alkaline complex eastern ghats province india implications for mid neoproterozoic granulite facies metamorphism and exhumation abstract following ultrahigh temperature granulite metamorphism at 1 ga the eastern ghats province of india was intruded by the koraput alkaline complex and was subsequently re metamorphosed in the granulite facies in the mid neoproterozoic time fluid inclusion studies were conducted on silica undersaturated alkali gabbro and syenites in the complex and a pre metamorphic pegmatitic granite dyke that intrudes it high density 1 02 1 05 g cc pseudo secondary pure co2 inclusions are restricted to metamorphic garnets within the gabbro and quartz within the granite whereas moderate 0 92 0 95 g cc and low density 0 75 g cc secondary inclusions occur in garnet magmatic clinopyroxene plagioclase hornblende and quartz the isochores calculated for high density pseudo secondary inclusions pass very close to the peak metamorphic window 8 kbar 750 c and are interpreted to represent the fluid present during peak metamorphism that was entrapped by the growing garnet microscopic round inclusions of undigested relict calcite in garnet suggest that the co2 present during metamorphism of the complex was internally derived through carbonate breakdown pure to low salinity 0 00 10 1 wt nacl equivalent aqueous intra intergranular inclusions showing unimodal normal distribution of final ice melting temperature tm and temperature of homogenization th are present only in quartz within the granite these represent re equilibrated inclusions within the quartz host that were entrapped at the metamorphic peak rare chemically precipitated graphite along the walls of carbonic inclusions is interpreted as a post entrapment reaction product formed during decompression the fluid inclusion evidence is consistent with rapid exhumation of a thickened lower crust following the mid neoproterozoic granulite facies metamorphic event the study suggests that mantle co2 transported by alkaline magma into the crust was locked up within carbonates and released during granulite metamorphism

p t x relationships deduced from corona textures in sapphirine spinel quartz assemblages from paderu southern india the sapphirine sa spinel sp quartz qz bearing rocks from paderu occur as lenticular enclaves within the precambrian khondalitecharnockite terrane of southern india in addition these rocks contain orthopyroxene opx sillimanite sill garnet gt cordierite cd biotite potash feldspar kf plagioclase and symplectites of cd kf qz opx the symplectites may have formed from the breakdown of osumilite grain contacts of sapphirine and spinel with quartz are rarely observed and the incompatibility with quartz during later stages is displayed by the development of several types of polymineralic reaction coronas the coronas in the different rock types a b etc are minerals listed from core to rim of corona a 1 sapphirine bearing rock type without spinel sa sill opx sa sill cd sa cd opx a 2 sapphirine and spinel bearing sp sa sill opx qz sp sa sill sp sa opx sp sill opx sp sa sill gt qz sa sill opx sp sa sill opx sa sill opx gt sp sa opx gt sp sa sill gt and b spinel bearing but sapphirine free sp sill opx sp sill gt sp cd commonly the coronas in the rock type a 2 and b also contain ilmeno hematite corundum in the core in association with spinel these rock types also provide textural evidence for later crystallization of cd cd sa and gt qz from opx sill qz and gt sill qz sapphirine is aluminous near 7 mg fe 2 o 9 al fe 3 2 o 3 3sio 2 and contains up to 12 2 wt per cent iron as feo orthopyroxene is also aluminous containing up to 10 4 wt per cent al 2 o 3 sapphirine and spinel have relatively high contents of fe 2 o 3 x mg in the fe mg minerals increases from rock type b to a2 to a1 a sequence of reactions has been deduced from coronas and other reaction textures and from the phase compatibility relations in the feo mgo al 2 o 3 sio 2 h 2 o system the p t x relationships from geothermobarometry and petrogenetic grids viz fe 2 o 3 vs feo and h 2 o vs fe 2 o 3 suggest 1 a retrograde mildly decompressive trajectory from 900 60 c 65 0 7 kb core to 760 50 c 5 0 6 kb rim and 2 the observed mineralogy of the coronas and reactions deduced from them are dependent on the relative feo fe 2 o 3 and h 2 o contents of the rocks feo 3 fe 2 o 3 and h 2 o

petro tectonic imprints in the sapphirine granulites from anantagiri eastern ghats mobile belt india sapphirine granulite occurring as lenses in charnockite at anantagiri eastern ghat india displays an array of minerals which developed under different p t x conditions reaction textures in conjunction with mineral chemical data attest to several fe mg continuous reactions such as spinel rutile quartz mgfe 1 sapphirine ilmenite cordierite sapphirine quartz mgfe 1 sapphirine quartz orthopyroxene sillimanite mgfe 1 orthopyroxene sapphirine quartz garnet mgfe 1 orthopyroxene sillimanite garnet quartz mgfe 1 orthopyroxene sillimanite quartz mgfe 1 cordierite calculated positions of the reaction curves in p t space together with discrete p t points obtained through geothermobarometry in sapphirine granulite and the closely associated charnockite and mafic granulite define an anticlockwise p t trajectory this comprises a high t p prograde metamorphic path which culminated in a pressure regime of 8 3 kb above 950 c a nearly isobaric cooling ibc path from 950 c 8 3 kb to 675 c 7 5kb and a terminal decompressive path from 7 5 to 4 5 kb spinel quartz high mg cordierite and sapphirine were stabilized during the prograde high t p metamorphism followed by the development of orthopyroxene sillimanite and garnet during the ibc retrograde low mg cordierite appeared as a consequence of decompression in the sapphirine granulite deformational structures reported from the eastern ghat granulites and the available geochronological data indicate that prograde metamorphism could have occurred at 3000 100 and 2500 100 ma during a compressive orogeny that was associated with high heat influx through mafic magmatism ibc ensued from p max and was thus a direct consequence of prograde metamorphism however in the absence of sufficient study on the spatial variation in p t paths and the strain histories in relation to time the linkage between ibc and isothermal decompression itd has remained obscure a prolonged ibc followed by itd could be the consequence of one extensional mechanism which had an insufficient acceleration at the early stage or itd separately could be caused by an unrelated extensional tectonism the complex cooled nearly isobarically from 2500 ma it suffered rapid decompression accompanied by anorthosite and alkaline magmatism at 1400 1000 ma

significance of a hiatus in down temperature fabric development within syn tectonic quartz diorite complexes channel islands uk detailed fabric development histories have been deduced for neoproterozoic foliated quartz diorite complexes of the channel islands uk the plutons were emplaced during regional d2 deformation magmatic fabrics formed at low crystal contents pre rheologically critical melt percent are only locally preserved due to overprinting by solid state deformation which occurred at moderate temperatures 400 550 c this is demonstrated by brittle microcracking of plagioclase and amphibole with only local ductile bending and dynamic recrystallization marginal recrystallization and myrmekite development on alkali feldspar ductile deformation of quartz to form types 2 3 ribbons quartz recrystallization by sub grain rotation associated with a slip but not c slip biotite recrystallization within micro shears and variable amphibole recrystallization the deformation histories display a distinct division between magmatic state and moderate temperature solid state deformation features with little evidence for intervening high temperature solid state fabrics this contrasts with criteria widely considered diagnostic of syn tectonic plutons which envisage development of a continuum of magmatic through high temperature solid state deformation fabrics however we consider the plutons syn tectonic and attribute the hiatus to contrasting strain and pluton cooling rates length and nature of deformation events and host rock ambient temperatures intermediate magmas emplaced at moderate to shallow levels in the crust may be more prone to develop such apparently punctuated deformation histories than sio 2 richer granitoids

using pluton ages to date regional deformations problems with commonly used criteria studies of pretectonic plutons in the foothills terrane central sierra nevada california along with a review of studies on syntectonic and post tectonic plutons indicate that no single criterion can establish the relative timing of pluton emplacement and regional deformation criteria most often used are whether a pluton is deformed cuts regional structures or is associated with porphyroblasts that postdate regional structures however all three types of plutons may 1 appear deformed or nondeformed 2 have contacts that appear to cut structures in the wall rocks and 3 have porphyroblasts in their aureoles that display varied timing relations the ambiguity of these criteria emphasize the need for careful studies of the structures present throughout the pluton and surrounding wall rock with particular attention paid to regions where the pluton contact is at high angles to regional structures porphyroblast cleavage relations are an important tool in this regard but also must be used with caution

role of melt during deformation in the deep crust deformation in the deep crust is strongly influenced by the presence of melt injected melt or magma weakens the crust because strain will tend to localize where melt is present the amount of strain a pluton may accommodate is dependent on the length of time it takes for a pluton to crystallize and the strain rate for plutons that intrude into rocks which are near the solidus temperature of the melt crystallization times can be quite long 1myr partial melting of deep crustal rocks can lead to melt enhanced embrittlement this occurs because the volume change for most melting reactions is positive therefore when the rate of melt production outpaces the rate at which melt can leave the system the melt pressure increases eventually the melt pressure may become sufficiently high that the melting rocks behave in a brittle fashion and fracture conjugate sets of dilatant shear fractures filled with melt occur in migmatite from the central gneiss belt canada this suggests that melt enhanced embrittlement occurred in these rocks an expression which relates the magnitude of differential stress to the angle between conjugate dilatant shear fractures is derived assuming that migmatite has a small tensile strength differential stresses are 20 mpa in migmatitic rocks at the time melt enhanced embrittlement occurs the occurrence of melt enhanced embrittlement shows that a switch in deformation mechanism from plastic flow to cataclasis is possible in the deep crust during melting furthermore repeated episodes of melt enhanced embrittlement in migmatitic rocks may be an efficient mechanism for extracting melt from partially melted terrains

microlithon alteration associated with development of solution cleavage in argillaceous limestone textural trace elemental and stable isotopic observations abstract comparison of microlithons the rock between adjacent cleavage domains in strongly cleaved argillaceous limestone with samples of uncleaved limestone from the same stratigraphic horizon lower devonian kalkberg formation hudson valley of eastern new york indicates that the process of cleavage formation results in significant changes in microlithon fabric and in the chemistry of microlithon calcite petrographic observation indicates that at least 50 of the calcite in microlithons is recrystallized as calcite fibers whose long axes are subparallel to cleavage domains the fibrous calcite occurs as overgrowths on larger grains in thin bed parallel veins and in diffuse extension zones areas of the microlithons in which inequant crystals of microcrystalline calcite are aligned parallel to cleavage domains chemical analyses show that calcite in microlithons of strongly cleaved limestone is enriched in mn and sr relative to calcite in uncleaved limestone 18 o and possibly 13 c values for calcite in strongly cleaved rock are significantly smaller than values for calcite in uncleaved rock these results indicate that microlithon calcite is completely recrystallized i e much more calcite is recrystallized than is visible in thin section and that it underwent exchange with a fluid external to the local rock system calculation of the water rock ratio suggests that 0 1 2 6 volumes of water may have exchanged with the calcite during cleavage formation comparison of the minimum integrated and the inferred instantaneous water rock ratios suggests that bulk fluid flow occurred during microlithon recrystallization comparison of the amount of shortening across cleavage domains with the amount of extension in microlithons and of the volume of calcite dissolved in domains with the amount of fibrous presumably added calcite in microlithons suggests that microlithons are a major sink for the calcite dissolved in domains during cleavage formation and that at this locality development of disjunctive solution cleavage in the kalkberg formation resulted in volume constant plane strain

bulge migration and pinnacle reef development devonian appalachian foreland basin abstract detailed stratigraphic analyses of late emsian and early eifelian lower to middle devonian carbonate dominated strata in the northern appalachian basin indicate anomalous locally varying relative sea level changes and inversions of topography the distribution of a major basal bounding unconformity basinal pinnacle reefs local absence of parasequences and eastward migration of shallow marine carbonate lithofacies and related biofacies in the onondaga limestone and underlying strata mark the retrograde migration of an elongate northeast southwest trending area of positive relief bordered on its cratonward side by a similarly migrating basin of intermediate depth these features are thought to represent the forebulge and back bulge basin of the appalachian foreland basin system as it developed during a time of relative quiescence within the acadian orogeny however the relatively small size of the bulgelike feature ca 80 100 km wide 20 50 m positive relief its great distance from the

spider texture and amphibole preferred orientations abstract foliation in blueschist facies chert from california is defined by layers of oriented alkali amphibole which consistently curve towards and converge on pyrite and possibly pyrrhotite crystals these foliation nodes not previously described are called here spider texture the texture is interpreted in terms of perturbations of the stress field in a matrix undergoing strain about rigid pyrite or pyrrhotite crystals and it has important implications for understanding the mechanisms of amphibole preferred orientation development geometrical relationships between spider texture pressure shadows and quartz preferred orientations suggest that amphiboles grew with a strong preferred orientation along planes of maximum shearing stress the mechanism of foliation and preferred orientation development probably involved competitive anisotropic growth of amphibole prisms within the small gaps that open at steps on shear planes followed by additional micro porphyroblastic growth the first stage of the mechanism is similar to slickenfibre development

zircon geochronology of the koraput alkaline complex insights from combined geochemical and u pb hf isotope analyses and implications for the timing of alkaline magmatism in the eastern ghats belt india zircon formation and modification during magmatic crystallization and high grade metamorphism are explored using tims and la icp ms u pb geochronology lu hf isotope chemistry trace element analysis and textural clues on zircons from the koraput alkaline intrusion eastern ghats belt egb india the zircon host rock is a granulite facies nepheline syenite gneiss with an exceptionally low zr concentration prohibiting early magmatic zr saturation with zircon formation occurring at a late stage of advanced magmatic cooling significant amounts of zr were incorporated into biotite nearly the only other zr bearing phase in the nepheline syenite gneisses investigated zircons experienced a multi stage history of magmatic and metamorphic zircon growth with repeated solid state recrystallization and partial dissolution precipitation these processes are recorded by complex patterns of internal zircon structures and a wide range of apparently concordant u pb ages between 869 7 ma and 690 1 ma the oldest ages are interpreted to represent the timing of the emplacement of the koraput alkaline complex which significantly postdates the intrusion ages of most of the alkaline intrusion in the western egb however hf model ages of tdm 1 5 to 1 0 ga suggest an earlier separation of the nepheline syenite magma from its depleted mantle source overlapping with the widespread mesoproterozoic rift related alkaline magmatism in the egb zircons yielding ages younger than 860 ma have most probably experienced partial resetting of their u pb ages during repeated and variable recrystallization events consistent youngest la icp ms and ca tims u pb ages of 700 690 ma reflect a final pulse of high grade metamorphism in the koraput area and underline the recurrence of considerable orogenic activity in the western egb during the neoproterozoic within the nepheline syenite gneisses this final high grade metamorphic event caused biotite breakdown releasing sufficient zr for local saturation and new subsolidus zircon growth along the biotite grain boundaries

application of cross hole radar tomograph in karst area electromagnetic wave ct containing velocity ct and attenuation ct is one of the effective geophysical prospecting methods to detect underground caves the accuracy is low when applying the velocity ct and the attenuation ct separately into investigation in a karst area this paper briefs the basic theory of electromagnetic wave ct imaging and then mainly introduces the basic theory and applying methodology of cross hole radar tomography for exploration in a karst area through numerical value simulation and practice verification the advantage and disadvantage of the velocity ct and the attenuation ct of electromagnetic wave based on very high frequency have been studied respectively it has been found that the attenuation ct does better in confirming the location of karst caves and the velocity ct is better in determining the shape of the karst caves although the whole distribution regular of the velocity ct is almost consistent with the attenuation ct

sm nd and rb sr dating of amphibolite from the nellore khammam schist belt se india constraints on the collision of the eastern ghats terrane and dharwar bastar craton the nellore khammam schist belt se india is sandwiched in between the proterozoic eastern ghats terrane and the archaean dharwar bastar craton we report sm nd and rb sr mineral isochron ages of amphibolite from the schist belt the sm nd and rb sr ages are 824 43 ma and 481 16 ma respectively the sm nd age indicates the timing of peak metamorphism whereas the rb sr age indicates the pan african thermal overprint the peak metamorphism was related to collision of the eastern ghats terrane with the dharwar bastar craton which occurred during early neoproterozoic time

high temperature dehydration melting and decompressive p t path in a granulite complex from the eastern ghats india the granulite complex of paderu in the south central sector of the eastern ghats belt india consists of closely related pelitic granulites and peraluminous granitoids which could be linked via dehydration melting in pelitic and greywacke like precursors the pelitic granulites including high mg al sapphirine granulites with early deformation microstructures also record a high temperature decompression from 10 to 8 kbar at 1 000 c preceding isobaric cooling from above 900 to 600 c at 8 kbar highly magnesian biotite in the pelitic granulites the presence of spinel in some of the granitoids and granitoids of two distinct compositions namely granite and quartz monzonite all suggest dehydration melting in highly magnesian pelitic and greywacke like precursors moreover high temperature melting in highly magnesian pelitic precursors is indicated by the migmatitic spinel bearing layers which besides having significant abundance of quartz and feldspar also contain aluminous orthopyroxene and cordierite these melting reactions occurring above 9 kbar may constrain the prograde arm of the p t trajectory this and the high temperature decompression constitute a clockwise p t path this clockwise p t path is consistent with the tectonic model in which crustal thickening and granulite metamorphism in the eastern ghats belt is interpreted as the result of homogeneous shortening in a compressional setting

mafic granulites from the eastern ghats india further evidence for extremely high temperature crustal metamorphism mafic granulites occurring as conformable lenses within khondalite leptynite and calc silicate rocks from the anantagiri araku areas of the eastern ghats belt contain orthopyroxene clinopyroxene garnet quartz ilmenite and plagioclase as major constituents orthopyroxene contains 100 lamellae of clinopyroxene and clinopyroxene contains 100 orthopyroxene lamellae and 001 spindles of pigeonite reaction textures indicate formation of garnet through coupling of two reactions viz orthopyroxene anorthite garnet clinopyroxene quartz and anorthite ilmenite hematite ss quartz garnet ilmenite o 2 thermobarometry indicates exsolution of pigeonite at 950 c of 100 clinopyroxene in orthopyroxene and vice versa at 750 820 c and formation of garnet at around 700 725 c 7 kb all in response to cooling of the rock this shows a nearly isobaric cooling path subsequent to peak metamorphic conditions subsequently the rock suffered nearly isothermal decompression to 5 kb

numerical modeling of crenulation cleavage development a polymineralic approach abstract the finite element method was used to investigate how the elastic interactions of quartz and muscovite minerals affect grain scale stress and strain distributions at different stages of crenulation cleavage development the polymineralic structure comprises individual grains that were each assigned their own 3d stiffness tensor and orientation gradients in mean stress and volumetric strain within quartz grains develop between the limbs and hinges of microfolds at the earliest stages of crenulation development with higher values in the microfold limbs these gradients decrease with development of the crenulation cleavage as the microfold limbs become phyllosilicate rich p domains and the hinges become quartz and feldspar rich qf domains crystallographic orientations of the quartz grains have a relatively minor effect on the mean stress and volumetric strain distributions our findings are broadly consistent with both pressure solution and strain driven dissolution models for crenulation cleavage development however because crenulation cleavage development typically involves metamorphic reactions we favor a model in which dissolution is driven by those reactions and mass transfer leading to development of the mineralogically segregated fabric is driven by pore fluid pressure gradients that follow gradients in volumetric strain local concentrations of stress and strain across mineral interfaces may identify sites of enhanced reaction

evolution of the continental crust in the proterozoic eastern ghats belt india and new constraints for rodinia reconstruction implications from sm nd rb sr and pb pb isotopes abstract for this study nd sr and pb isotope compositions were analyzed for ortho and paragneisses from the eastern ghats belt of india in order to determine its crust formation and crustal evolution this belt represents a proterozoic orogen that extends along the east coast of peninsular india and forms part of the mobile belts in east gondwana and rodinia the eastern ghats belt was affected by mesoproterozoic granulite facies metamorphism in the western segment western charnockite zone and a grenvillian regional scale high grade event in the central and eastern segments western khondalite zone charnockite migmatite zone and eastern khondalite zone as well as a local pan african overprint the results of the isotope studies are used for the large scale reconstruction of the indo antarctic part of the rodinia supercontinent based on nd model ages and pb isotope ratios from leached feldspars four crustal domains can be distinguished in the eastern ghats belt these domains can in part be correlated with the lithological division of the belt 1 the western charnockite zone south of the godavari graben is characterized by nd model ages between 2 3 and 2 5 ga for orthogneisses and 2 6 and 2 8 ga for metasediments domain 1 the pb isotopes are primitive indicating reworking of dominantly archean and mixing with minor proterozoic material 2 north of godavari graben nd model ages for orthogneisses are significantly higher with values ranging from 3 2 to 3 9 ga the pb isotopes are strongly retarded 3 the north eastern parts of the charnockite migmatite zone and western khondalite zone form a distinct and almost homogeneous crustal domain domain 3 with nd model ages between 1 8 and 2 2 ga 4 between the isotopically homogeneous terranes stretches a broad transition zone domain 2 enclosing parts of the western khondalite zone charnockite migmatite zone and eastern khondalite zone the nd model ages for metasediments 2 1 2 5 ga are younger than paragneiss ages of the adjoining western charnockite zone the nd model ages for orthogneisses 1 8 3 2 ga display a large spread which is consistent with the pb isotope signatures that indicate mixing of archean with proterozoic material the border zone between domain 3 and the archean eastern indian craton forms a second transition zone domain 4 characterized by metasediments with nd model ages between 2 2 and 2 8 ga and orthogneisses with model ages around 3 2 ga reworking of archean crustal material is most intense along the border zones of the belt and juvenile material is more dominant away from the orogenic front this scenario is indicative of an active continental margin setting for the two proterozoic episodes of orogenesis in the eastern ghats belt a correlation of domain 3 with the rayner complex and the prydz bay region antarctica for the early crustal evolution is supported by the similarity of the isotope signatures the napier complex is very different to the eastern ghats belt and an early joint evolution of these terranes is ruled out on the basis of the pb pb and sm nd systematics

dynamic recrystallization of feldspar a mechanism for ductile shear zone formation feldspar aggregates experimentally deformed in the dislocation creep regime undergo dynamic recrystallization because recovery is difficult due to the limited climb of dislocations recrystallizing aggregates have a lower strength because of the cyclic production of small strain free grains and they develop a strong preferred orientation consistent with that observed in mylonites thus recrystallization accommodated dislocation creep may be responsible for the grain size reduction and strain softening that lead to the formation of many mylonites and ductile shear zones

possible mesozoic age of ellenville zn pb cu ag deposit shawangunk mountains new york ore textures epithermal open space filling of permian structures of the alleghanian orogeny and largely postorogenic mineralization of the ellenville new york composite zn pb cu ag vein system provide permissive evidence for post permian mineralization isochron ages determined by 40ar 39ar laser fusion techniques for k bearing liquid inclusions in main stage quartz from the ellenville deposit additionally suggest a mesozoic time of mineralization associated with extensional formation of the newark basin the best 40ar 39ar total fusion age range is 165 30 to 193 35 ma the mesozoic 40ar 39ar age agrees with that of many other dated northern appalachian zn pb cu ag deposits with near matching lead isotope ratios and adds new evidence of jurassic tectonism and mineralization as an overprint to late paleozoic tectonism at least as far north as ellenville lat 41 43 n

comparison of fry strain ellipse and ams ellipsoid trends to tectonic fabric trends in very low strain sandstone of the appalachian fold thrust belt abstract in moderately to highly strained sandstones both the long axis of the bedding parallel finite strain ellipse as calculated by the normalized fry method and the projection of the long axis of the ams ellipsoid on the plane of bedding align well with local structural grain trends of cleavage folds and faults this relationship implies that results of both 2d fry and ams analyses represent the local layer parallel tectonic strain component do both methods provide comparable results for very low strain sandstone e g

anisotropy of magnetic susceptibility sedimentological igneous and structural tectonic applications as was noted by graham 1954 anisotropy of magnetic susceptibility ams data has many applications to the study of geological processes this type of anisotropy expresses directional variation in the magnetization induced in a rock most notably in its iron oxides and especially in its magnetite and hematite the ams is commonly expressed by an ellipsoid of which the principal axes are k1 k2 and k3 from greatest to least this ellipsoid is generally interpreted in terms of the distribution and shape of grains of magnetic minerals in a rock although the ellipsoid determined depends also on magnetocrystalline anisotropy and on factors of instrumental technique ellwood et al in press 1987 the challenge for the geoscientist in analyzing ams data is first to identify the origin of the ams geometry then second to relate that geometry to the natural processes which produced the inferred or measured distribution of magnetic materials

collision tectonics in the late precambrian eastern ghats mobile belt mesoscopic to satellite scale structural observations regional mapping of a section across the eastern ghats mobile belt egmb north of the godavari graben in eastern peninsular india by using landsat thematic mapper data enables recognition of a number of shear zones lineaments and structural domes and basins a conspicuous megashear occurs at the western boundary of the granulite facies rocks of the egmb adjacent to the archean granite greenstone craton the confinement of a suite of alkaline igneous rocks to this shear zone is a notable feature the strike extensions of this shear belt extend through to the elchuru alkaline complex prakasam district andhra pradesh and the syenite plutons of koraput district orissa the contrasting lithologies metamorphism and structural history on either side of the shear zone suggests that it might be a precambrian suture zone the mesoscopic structural features in the egmb include prominent foliation with moderate to steep dips folds faults shears s c fabrics pinch and swell structures and other linear fabric elements these observations favour the consideration of drastic crustal shortening and thickening and a complex deformational sequence the major rock units in this part of egmb comprise garnetiferous sillimanite gneisses quartzites and calc granulites forming the khondalitic suite of rocks and a wide variety of charnockitic rocks the contact of the two rock units is generally sheared and often migmatised the structural fabric suggests two major tectonic events an essentially horizontal tectonic regime resulting in thrust systems and associated structures subsequently followed by strike slip tectonics characterized by high shear strains features such as westward verging thrusts large scale recumbent folds major shear zones structural domes and basins indications of tectonic crustal shortening extensive calc alkali magmatism and widespread migmatization in the region are attributed to collisional processes during proterozoic times the spatial disposition of the egmb and its linkage with the distribution of similar rock units during the late precambrian time in a global tectonic scenario are discussed

a review of criteria for the identification of magmatic and tectonic foliations in granitoids abstract foliations in granitoids can form by magmatic flow submagmatic flow high temperature solid state deformation and moderate to low temperature solid state deformation a review of previous work suggests that no single criterion can consistently distinguish foliations in granitoids formed by flow during ascent diapiric emplacement and expansion emplacement during regional deformation or regional deformation post dating emplacement however a magmatic origin is favoured for foliations defined by the alignment of igneous commonly euhedral minerals particularly where the foliation is parallel to internal or external pluton contacts foliations formed during expansion or ballooning of diapirs may be strictly magmatic in origin although some studies suggest that solid state deformation also may occur if so we would hope to find evidence of deformation of crystal melt systems and that the solid state deformation occurred at high temperatures the inference of syntectonic foliations is most convincing where magmatic and high temperature solid state foliations are subparallel these foliations are continuous with regionally developed foliations in the wall rocks synkinematic porphyroblasts are present in the wallrocks and igneous minerals have the same age as metamorphic minerals associated with the regional cleavage a strictly tectonic origin for foliations in granitoids is favoured when the foliation is defined by metamorphic minerals no alignment of igneous minerals occurs the foliation is locally at high angles to pluton wallrock contacts and the foliation is continuous with a regionally developed cleavage

alkaline magmatism along the southeastern margin of the indian shield implications for regional geodynamics and constraints on craton eastern ghats belt suturing abstract deformed alkaline complexes at the contact between the eastern ghats belt egb and the archaean cratons in southeastern india mark the location of a collisional suture superimposing an earlier mesoproterozoic 1 5 1 3 ga rift this article offers a plausible geodynamic model explaining the alkaline magmatism and its relationship to regional crustal evolution the mesoproterozoic rift can be correlated to the breakup of the supercontinent columbia and may have opened an ocean between eastern india and east antarctica where the sedimentary sequences of the eastern ghats province egp were deposited between 1 4 and 1 2 ga inversion of the rift basin during the late mesoproterozoic 1 0 ga led to the collision of eastern india with east antarctica during rodinia assembly the collision formed the grenvillian egp rayner complex orogen where the egp sediments and the rocks of the rayner complex were deformed metamorphosed and migmatized at granulite facies condition the mesoproterozoic rifting and grenvillian basin closure may thus represent a wilson cycle related to the breakup of columbia and the assembly of rodinia the craton egb suture was subsequently modified significantly during pan african tectonism 0 5 0 6 ga when the egb granulites were thrust westward over the cratonic foreland along a number of amphibolite facies shear zones at the contact the shearing deformed and metamorphosed the cratonic margin and the alkaline complexes it hosts the thrust stacking in many places has the craton boundary and the alkaline rocks in the footwall and the egb granulites in the hanging wall the continuity of the pan african shear fabric across the craton granulite contact and the lack of grenvillian ages from the alkaline and other craton margin rocks in such regions give the apparent impression that the two crustal segments amalgamated during pan african tectonism and not during the earlier grenvillian collision geodynamic constraints however indicate that this was unlikely and the inconsistency arises because the present crustal geometry exposes only the eroded pan african thrust contact between the craton and the egb and not the original grenvillian suture which may be lying unexposed under the granulite thrust sheets

criteria for distinguishing primary evaporite features from deformation features in sulfate evaporites abstract in many tectonized regions evaporites which served as decollement zones are brought to the surface where they are studied as part of the normal sedimentary succession and their internal structures are commonly treated as the primary products of deposition and synsedimentary deformation evaporites however respond to tectonism in a manner that is vastly different from other rocks in the succession associated limestone dolostone and siliciclastic beds may remain virtually unaffected by the same degree of deformation that significantly alters evaporites even modest differential stresses with geologically reasonable strain rates applied at low temperatures 20 200 c result in significant recrystallization foliation and flow in evaporites whereas other rocks non evaporites in the same succession may show little apparent change the large differences in physical properties between evaporites and both carbonate and siliciclastic lithologies in such tectonized sections result in evaporites that no longer reflect their original sedimentary environment because of recrystallization and plastic deformation yet because their structures and fabrics may not be recognized as secondary they can be misinterpreted as original features indicative of primary depositional environments

unraveling sedimentary provenance and tectonothermal history of high temperature metapelites using zircon and monazite chemistry a case study from the eastern ghats belt india abstract the geochemical behavior of detrital zircon and monazite during granulite facies anatexis in metapelites from the eastern ghats belt egb india is explored using u pb geochronology hf isotopes and trace elements in a metapelite from the ongole domain detrital zircon reequilibrated by coupled dissolution reprecipitation and diffusion reaction during ultrahigh temperature metamorphism at 1 63 ga the event completely reset the u pb systems but hf isotopes and trace elements were only partially reequilibrated overgrowths on the altered cores date migmatization at 1 61 ga monazite yields metamorphic ages similar to those of zircon in metapelites from the eastern ghats province egp detrital zircon grains give 2 44 1 40 ga ages and metamorphic ones 1 2 0 5 ga ages metamorphic components include detrital grains reequilibrated by coupled dissolution reprecipitation in the presence of anatectic melt and newly crystallized overgrowths and grains in reequilibrated domains the u pb system wa

high resolution cat imaging of fractures in consolidated materials abstract high resolution measurements of fracture aperture of granite and sandstone rocks were performed using cat scanner the aperture distribution was statistically characterized for future experimental and numerical studies on single and multiphase flow and transport the fracture aperture can be measured in situ and non destructively with cat scanning the minimum pixel size is 0 27 0 27 mm but fractures as small as 35 m can be accurately measured using a calibration standard for the variation in ct number due to the missing rock mass in a given pixel a calibration standard for each rock type yields distinctly different calibration slopes about 17 greater for granite compared to sandstone indicating that each rock type should be analyzed against its own calibration standard the aperture distribution is rather heterogeneous and is best described by a lognormal function corroborated by comparing the theoretical to actual ratio of hydraulic to mechanical apertures mechanical roughness of the fractures ranged from 0 17 to 1 5 the variability in fracture aperture displayed only short range structure with correlation lengths of 0 8 mm to 7 mm which is at most one tenth of the minimum dimension width of the fracture plane potential flow channels can be deduced from the fracture aperture distribution

seismic characterization of a highly stressed rock mass using tomographic imaging and induced seismicity a seismic tomography study was carried out at falconbridge s lockerby mine sudbury canada in april 1989 the objective was to determine the integrity of a rock mass at 1 km depth and to investigate the correlation between induced seismicity and p wave velocity structure the tomographic image showed two distinct and significant p wave velocity anomalies a low velocity zone at the source region of a mn 2 3 mining induced tremor recorded in 1985 and a high velocity zone at the source region of a mn 2 6 mining induced tremor recorded in 1988 analysis of mining induced microseismicity showed that the high velocity zone was the focus for seismic activity prior to and after the 1988 tremor in contrast to the low velocity zone which remained aseismic for the same period the seismic anomalies were diamond drilled following the tomographic imaging to verify the physical characteristics of the zones the seismically active high velocity zone showed severe core disking indicative of a highly stressed strong rock while the low velocity zone was characterized by extensive fracturing and failed rock the results showed that the 1985 tremor and rock burst sequence resulted in a major failure of the rock mass in the source region of the event and stress was redistributed and concentrated in the source region of the 1988 tremor the 1988 event and rock burst sequence did not result in failure of the source region which therefore remains a seismically active high velocity zone with a potential for significant seismic energy release and further rock bursting the study has highlighted a correlation between p wave velocity structure and induced seismicity which can be used to characterize highly stressed rock masses in underground mines

mechanisms of thrust propagation some examples and implications for the analysis of overthrust terranes abstract evidence is presented for the existence of three fundamental mechanisms by which thrust sheets move the mechanisms are 1 failure of a stiff layer to form ramp flat geometry imbricated thrust sheets 2 detachment of a layer by folding decollement thrust sheets 3 differential layer parallel shortening lps thrust sheets the mechanisms are independent but may operate interactively to form families of hybrid thrust sheets since lps thrust sheets have not been previously described or documented data from the new york plateau deformed almost exclusively by differential lps is presented to demonstrate the physical characteristics of this thrust mechanism information from the plateau indicates that finite strain behavior closely reflects the geometric boundary conditions and is independent of temperature and depth of burial finite strain data are used to construct a set of iso strain maps in both the deformed and undeformed states the iso strain maps are in turn used to determine the displacement field for the thrust sheet the displacement field allows visualization of the effects of both lagrangian and eulerian transformations on an initially orthogonal grid utilizing sections from a number of overthrust belts it is shown that the three mechanisms occur universally although in various proportions lps is regionally developed throughout the central and northern appalachians the presence of the lps thrust sheets probably accounts for the failure of structural cross sections to bed length balance in these blind thrust terranes finally a series of examples drawn from the field as well as the literature are used to illustrate both the characteristics of hybrid thrust sheet families as well as to indicate how knowledge of their behavior can be utilized in developing strategies for the construction and balancing of structural cross sections

deformation related recrystallization processes abstract recrystallization is a common microstructural transformation that occurs during deformation metamorphism and diagenesis of rocks studies on minerals and rock analogues have demonstrated that a wide range of recrystallization mechanisms can occur the range of mechanisms is related to the various ways in which two basic processes grain boundary migration and new grain boundary formation combine to transform the microstructure two recent papers drury et al 1985 urai et al 1986 have proposed different schemes for the description of recrystallization mechanisms the purpose of this paper is to provide a unified framework for the description of mechanisms recrystallization mechanisms are divided into three main types rotation mechanisms which principally involve the formation of new grain boundaries migration mechanisms which principally involve grain boundary migration and general mechanisms which involve both basic processes a further distinction is made on the basis of the continuity of the microstructural transformation with respect to time each of the three main types of mechanism can be divided into a number of sub types depending on whether the processes of grain boundary migration new grain boundary formation and new grain formation occur in a discontinuous or continuous manner with respect to time as the terms continuous and discontinuous have been used in the metallurgical literature to signify the spatial continuity of the microstructural transformation the terms discontinuai and continual are used to refer to the temporal continuity of the transformation it is recommended that the following aspects should be specified if possible in a general description of recrystallization mechanisms 1 1 how do the basic processes combine to transform the microstructure 2 2 if new grain development occurs what is the development mechanism and does new grain formation occur in a continual or discontinuai manner 3 3 if grain boundary migration is involved in the transformation what is the migration mechanism i e fast solute escape migration slow solute loaded migration fluid assisted migration etc and is migration a continual or discontinuai process the application of the unified scheme is illustrated by reviewing studies that have provided detailed information on the recrystallization mechanisms involved the complicating effects of solid solution impurities dispersed second phase particles and grain boundary fluid films are also considered and it is demonstrated that variations in content of these types of impurity can significantly effect the types of recrystallization that occur in a given material

a new correlation of sapphirine granulites in the indo antarctic metamorphic terrain late proterozoic dates from the eastern ghats province of india abstract uranium lead and thorium lead ages were obtained from perrierite and zircons in two samples from the eastern ghats province of south india a sapphirine bearing granulite from anakapalle and a charnockite from visakhapatnam the isotopic data are concordant or close to concordant at 1 ga which is interpreted to be the age of granulite facies metamorphism and charnockite plutonism in the vicinity of anakapalle and visakhapatnam and provides the first report of a late proterozoic granulite facies event in the eastern ghats province in reassemblies of gondwanaland based on dutoit s original proposal the eastern ghats province is juxtaposed against a high grade terrain in east antarctica affected by a granulite facies event and charnockitic plutonic activity 800 1100 ma ago the ages reported here suggest that a portion of the eastern ghats province represents an extension of the late proterozoic terrain from antarctica into india the radiometric results on the anakapalle rocks are the first evidence in south india for sapphirine formation during the late proterozoic other south indian sapphirine localities appear to be archaean in age a review of sapphirine localities in the indo antarctic metamorphic terrain indicates that sapphirine developed under a range of pressure temperature conditions during the archaean and proterozoic evidence for a systematic change in peak metamorphic conditions with time is obscured by these regional variations characterization of the entire pressure temperature path in addition to estimates for the peak conditions is needed to distinguish the archaean and proterozoic metamorphic regimes