flow and fabric development during the diapiric rise of magma scaled isothermal experiments of the internal circulation induced by viscous drag at a diapir country rock interface are compared with published theoretical studies of flow induced finite deformation inside a rising sphere and new numerical results are presented for the incremental strain pattern developed in spherical diapirs the results predict a time dependent deformation history within rising diapirs that produces finite strains characterized by strong oblate flattening strains at the margin and strong vertical prolate strains in the center with an intervening zone of low plane strain finite strains are discussed in terms of the different sub fabrics expected to form in granitoids after considering the history of rheology and temperature distribution in rising magma strong rheological and temperature gradients are predicted for the margins of internally circulating diapirs that can lead to the formation of strong penetrative foliations at the margin and magmatic or even isotropic fabrics in the i

tidal mixing and trapping in mangrove swamps lateral trapping in mangrove swamps is a dominant process controlling longitudinal mixing in mangrove fringed tidal rivers in the dry season the effective value of the longitudinal diffusivity is increased by the trapping effect by typically two orders of magnitude from its value in the absence of swamps in the wet season freshwater is trapped within the swamp and the adjoining boundary in the tidal river for long periods following the passage of a short lived flood this may have important ecological implications a fluid mud layer appears to be created by strong tidal currents over colloidal mangrove mud

finite deformation in and around a fluid sphere moving through a viscous medium implications for diapiric ascent abstract different types of geodynamically active regions like mountain belts hot spots or areas of salt tectonics are characterized by diapirism one key for the reconstruction of the dynamic history of such structures is the progressive strain which can sometimes be determined from field observations successful interpretation of such observations requires a quantitative model of the finite strain in and around a rising diapir a constant viscosity fluid sphere of radius r rising through another isoviscous fluid is assumed to approximate the buoyant motion of a diapir known analytical solutions for the velocity fields are used to numerically evaluate the finite deformation in and around the sphere regions of very high strains are found in a tube with a radius 1 2 r behind the sphere and in a shell of thickness of 0 1r around the sphere the following three dimensional strain regimes can be identified in the half space above the sphere down to its equator finite strains are oblate behind the sphere they progressively change to plane strain in the diapiric source region they are prolate viscous drag at the sphere s surface leads to an internal circulation with one overturn after 10r of rise if the sphere has a relatively low viscosity finite strains within the fluid sphere show a continuous increase with superimposed cyclic straining and unstraining after several body radii of rise the strains become highly inhomogeneous inside the sphere except along the vertical axis and just inside the sphere s surface where strong prolate and oblate strains are observed respectively finite strain determinations in a falling ball experiment cruden 1988 are compared with the theoretical results at horizontal distances of a few body radii from the fall axis the effect of confining container walls is clearly seen in the experimental strain data the results are compared briefly with available strain data from the field which seem to be significantly lower than predicted proposed explanations include a short memory of the rock fabric and a lack of recognition of the strain concentration which would be expected for a temperature dependent rheology it might also be possible that few natural diapirs rise more than a few radii in the solid state

structure of turbulent flow in a shallow tidal estuary a high resolution current profiler hrcp which belongs to a pulse to pulse coherent doppler sonar has been used to measure vertical profiles of turbulence parameters such as the reynolds stresses eddy viscosity production and dissipation rates etc and to test the parametrization of dissipation rate and eddy viscosity the hrcp and automatic ascending descending ctd are deployed during the autumn of 2001 for 24 h in a tidal estuary reliable velocities along the beams with hrcp are collected with 3 s intervals and a vertical resolution as fine as 0 03 m in the range 0 02 0 98 m above the bottom density profiles with the ctd are taken nominally every 30 sec the turbulent velocity variables depend largely on the tidal phase the variables during the ebb deviate from those in neutral equilibrium boundary layer this deviation during the ebb presumably arises from the inactive motion the stability function sm in the mellor yamada m y model is smaller than 0 39 even when the stratification is ne

characteristics of flow fluctuations in a tide dominated estuary application of triple decomposition technique small tide dominated estuaries are affected by both large scale flow structures manifested as oscillatory residual currents and small scale bed generated turbulence the present understanding of the effects and relative contributions of these factors are inadequate due to limited systematic observations a field study was conducted in a small sub tropical estuary in which high frequency 50 hz turbulence data were recorded continuously for about 48 h a triple decomposition technique was introduced to isolate the contributions of tides slow fluctuations and true turbulence in the flow field a striking feature of the data set was the slow fluctuations which exhibited large velocity amplitudes up to 50 of the tidal amplitude under neap tide conditions the skewness of the fast true turbulence were within the range of 4 and 2 the analysis of the fast fluctuations revealed that variation in the turbulence characteristics are linked with the tidal velocity suggesting that the dispersion and mixing are dependent on some large scale flow properties the results also indicated enhanced mixing associated with the slow fluctuation in the flow field the results provided useful sets of information about the properties of slow and fast fluctuating components and their variations through tidal cycles in a micro tidal estuary

ferrimagnetic iron sulfide formation and methane venting across the paleocene eocene thermal maximum in shallow marine sediments ancient west siberian sea

origin of ooidal ironstones in relation to warming events cretaceous eocene bakchar deposit south east western siberia abstract an integrated study involving petrographical mineralogical and geochemical investigations proposes the origin of the bakchar ironstone deposit by upward migration of a mixture of fe rich brine and hydrothermal fluid through marine sediments trace element concentrations of the ironstone deposits rule out continental derivation of fe while high ree concentrations indicate mixed hydrogeneous and hydrothermal source three main types of ironstone within the bakchar deposit are characterized by distinct mineralogical assemblage of authigenic minerals corresponding to oxic methanic and weakly sulfidic dysoxic conditions changing redox conditions of the depositional environment methane seepage in warm seawater and availability of iron influx possibly determined the final mineralogy of three varieties of ironstones the association of siderite with ferrimagnetic sulfides like greigite and pyrrhotite in type 1 ore indicate anaerobic oxidation of methane with limited bacterial sulfate reduction the ironstone deposits of narym kolpashevo and bakchar are contemporaneous with geological events like ocean anoxic event 3 oae 3 cretaceous paleogene k pg boundary and palaeocene eocene thermal maximum petm respectively all corresponding to warm seawater conditions

sub millimeter heterogeneity of yttrium and chromium during growth of semi pelitic garnet x ray maps of yttrium and chromium in two garnets from a semipelitic schist from central nepal reveal parallel spiraling bands of high and low concentration 10 30 m wide this zoning mimics similar concentration bands defined by foliation in the matrix outside the garnets the garnets apparently incorporated the matrix zoning intact during growth at conditions up to lower amphibolite facies these observations and interpretations indicate that yand cr concentrations remained heterogeneous at the scale of tens of micrometers during breakdown of matrix minerals and growth of garnet this conclusion extends results of previous work which showed that y and cr do not homogenize at the centimeter to millimeter scale during metamorphism to amphibolite facies the width of the concentration bands in the garnets places a constraint on the maximum effective intracrystalline diffusion coefficient for both y and cr in garnet of about 10 21 cm 2 s for peak metamorphic conditions of about 9 kbar at 5708c different concentrations of yand cr at different positions around the rim of each garnet indicate disequilibrium for these elements between garnet and matrix phases the presence of an internal foliation defined by the yand cr concentration bands rules out pre kinematic garnet growth most useful in conjunction with other indicators zoning of these elements in garnet is thus a tool for deciphering the relative timing of deformation and garnet growth

early diagenesis of inner shelf phosphorite and iron silicate minerals lower cretaceous of the orpheus graben southeastern canada implications for the origin of chlorite rims wells in the orpheus graben encountered the most proximal part of the deltaic lower cretaceous rocks of the scotian basin more distal sandstones are important gas reservoir rocks with good reservoir quality where fe rich chlorite chamosite rims on framework grains have inhibited quartz cementation cutting samples from the orpheus graben show the presence of fe rich sheet silicates berthierine or chamosite and early diagenetic phosphorite these minerals were analyzed by electron microprobe and their textures were mapped with backscattered electron images studies in the north sea have shown a relationship between high phosphorus and the presence of good chlorite rims in reservoir rocks the mineralization of pore water phosphorus instead of its return to seawater is favored by fe rich sediments and sorption on iron oxides during shallow sea floor diagenesis the fe ti and p contents are uncommonly high in scotian basin shales compared with global average shale compositions the uncommon occurrence of inner shelf phosphorite in this study is interpreted to be a consequence of the same high fe content of the sediment that also favors the formation of fe rich sheet silicates in rapidly deposited deltaic sandstones of the offshore reservoirs the dominance of type 3 kerogen led to sulfate depletion occurring at depths of tens of meters and a corresponding great thickness for overlying eh oxidation potential controlled diagenetic zones the thick fe reduction zone allowed the formation of early diagenetic berthierine which on burial formed the chamosite rims that resulted in the improved reservoir quality in sandstones the distribution of phosphorus minerals may be an indicator of conditions suitable for berthierine formation

local displacement of diapir contacts and its importance to pluton emplacement study abstract the extent to which mid crustal plutons have grown by diapirism cannot be deduced from the horizontal shortening of ductilely deformed host rocks and associated displacement of lateral intrusive contacts by contrast the vertical shortening above plutons and upward displacement of their roof contacts may provide a good measure of the diapiric component of pluton emplacement this is related to the vertical bulk translation of buoyant material in immature diapirs and associated escape flow of overlying rocks the length change of a vertical material line situated above the crest of an immature upright diapir corresponds to the upward displacement of the local contact the length change of horizonal material lines situated at lateral contacts of model diapirs however differs markedly from the contact displacement this is related to the absence of horizontal symmetry planes in the finite strain field about upright diapirs of any shape and the importance of vertical shear at the lateral contacts the host rock strain held of a hypothetical pluton grown in situ by spherical expansion ballooning has an infinite number of symmetry planes the strain held is characterized by large volume losses but the length change of all radial lines corresponds to the local magnitude of contact displacement this precludes the possibility of differentiating in ductile host rocks above plutons between vertical diapirism and spherical expansion unless gauges of volume change are available

oblique diapirism the criffel granodiorite granite zoned pluton southwest scotland abstract strain trajectories strain gradients and quartz c fabrics have been used to propose an emplacement history of the criffel zoned pluton strain has been estimated from the microdioritic xenoliths included in the outer granodiorite textural criteria have been used to complete the pattern of strain variations throughout the pluton strain gradients are found to be related to the granodiorite granite boundary zone with highest strain towards the northeast side of the pluton giving an asymmetric horseshoe pattern quartz c fabrics allow two strain histories to be distinguished within the pluton an early coaxial flattening in the granodiorite followed by a non coaxial deformation in the granite and the adjacent granodiorite these features are interpreted as the result of an oblique diapiric intrusion of the inner granite into the partially emplaced and crystallized granodiorite

measuring suspended sediment concentrations using acoustic backscatter devices abstract in recent years the requirement to develop a technique for measuring suspended sediment concentration profiles with similar temporal and spatial resolution to that of electromagnetic current meter measurements of the flow has led to the development of an acoustic approach acoustic backscatter devices have been constructed and deployed in marine environments and measurements of backscattered signal profiles obtained however the translation from acoustic returns to suspended load has been an empirical procedure resulting in some uncertainty regarding the accuracy and reliability of the conversion process to address this problem a series of laboratory measurements of acoustic backscattering from marine suspensions were conducted using two acoustic backscatter instruments operating at 3 0 and 5 65 mhz a simple semi empirical backscattering theory has been developed to predict the form of the scattered signal and comparisons have been made of the concentrations predicted from the theory against concentration measurements made in laboratory tanks the results show that the main features of the backscattering signal can be explained and accurate concentration estimates can be made from the acoustic returns it is concluded that acoustic backscatter techniques are potentially powerful tools for examining at high resolution the structure of suspended sediment concentration profiles near the seabed

a view from the roof magmatic stoping in the shallow crust chita pluton argentina nearly 2 km of vertical relief and exposure of continuous pluton roof wall corners around the chita pluton northwest argentina provides constraints on the 3 d host rock displacement field attending magma emplacement in the shallow crust the pluton is rectangular in crosssectional view and consists of weakly to non deformed granite to granodiorite structures in surrounding metasedimentary host rocks are truncated at a knife sharp contact and are only weakly deflected from their regional orientations final emplacement occurred by stoping together with minor doming of the earth s surface structural restoration of a cross section indicates that host rocks above the pluton may have been domed upwards during emplacement by as much as a few hundred meters accounting for up to 20 of the exposed pluton volume the remaining 80 of the space for pluton emplacement was made by downward removal of host rock from the present level of exposure although mechanisms such as floor subsidence are permissive late stoping has destroyed evidence for the early emplacement history however geometrical constraints provided by exposure of continuous wall to roof contacts indicate that early emplacement mechanisms at this level in the crust and immediately below were also dominated by the downward displacement of host rocks through a conduit that now is represented by the solidified pluton q 2002 elsevier science ltd all rights reserved

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

turbulent perturbations of velocity in the conwy estuary abstract field measurements of the vertical and horizontal components of fluid velocity 0 43 m above the bed have been made with an electromagnetic flowmeter in a partially mixed reach of the conwy estuary for parts of a flood and an ebb tide the turbulent mean velocity and density fields showed different effects for flood and ebb tides caused by the interaction of shear and the longitudinal density gradient the turbulent velocity parameters were generally dominated by bed generated turbulence effects but significant longer period contributions attributed to the shear density interactions were detected the shear stress measurements made by two independent methods showed good agreement the results generally show good agreement with previous less complete data the use of the richardson number to quantify vertical stability needs further consideration for partially mixed estuarine flows

occurrence and origin of minerals in a chamosite bearing coal of late permian age zhaotong yunnan china the minerals found in the no 5 coal late permian from the zhaotong coalfield yunnan province southwestern china have been examined and found to consist mainly of kaolinite pyrite chamosite quartz and calcite with trace amounts of illite and mixed layer illite smectite the proportion of chamosite in clay minerals ranges from 32 to 56 wt with an average of 46 wt chamosite is distributed not only in collodetrinite but also occurs as cell fillings in fusinite semifusinite and telinite the high content and mode of occurrence of chamosite in this mine indicate its formation by interaction of kaolinite with fe mg rich fluids during early diagenesis except for a minor amount of terrigenous quartz most quartz is of authigenic origin and formed from kaolinite desilication the calcite content of the no 5 coal is 1 4 6 3 with an average of 3 and is distributed in collodetrinite and as cell fillings of coal forming plants calcite originated from seawater invasion during peat accumulation pyrite occurs in several ways as massive framboidal isolated enhedral anhedral and euhedral forms in addition the presence of a large amount of pyritized red algae provides strong evidence of seawater invasion during peat accumulation the red algae may have played an important role in the enrichment of sulfur in the coal the characteristic assemblage of minerals in this mine resulted from a unique basinal environment in which the mineral matter was derived from a basaltic source region volcanic activity and seawater transgression during coal formation

erratum crude quantitative estimates of the original northwest southeast dimension of the sudbury structure south central canadian shield the sudbury structure central ontario is the remnant of a large cryptoexplosion structure whose oval map pattern diameter ratio 2 2 differs markedly from the circular outline of many meteorite impact craters finite element modelling shows that i the original northwest southeast dimension could have been 2 3 times larger than at present and ii the vertical dimension of the sudbury structure was 10 km before tectonic deformation although our structural analyses furnish data that govern the geometric modelling large uncertainties remain where the state of tectonic deformation is poorly constrained a series of two dimensional models was made to cope with kinematic uncertainties and to assess their effect on the estimates of the geometry of the original sudbury structure

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

iron rich carbonate tidal deposits angepena formation south australia a redox stratified cryogenian basin abstract the cryogenian angepena formation ca 650 ma of south australia records deposition in a peritidal environment equivalent to and landward of the balcanoona reef complex and offers valuable insights into shallow marine chemistry during the nonglacial interlude between two global ice ages the sedimentary facies comprise an iron rich marine red bed succession and include red mudcracked dolomitic shales tepee dolostone crossbedded intraclastic ooid grainstone and tepee related sheet cavities with marine cements these facies are interpreted to have been deposited in a cryogenian tidal flat to subtidal setting that is laterally equivalent to the reefal and back reef environments of the balcanoona formation marine cements from this environment are characterized by well preserved non and bright cathodoluminescent zoning and strong negative to slightly positive cerium ce anomalies ce ce we suggest that the angepena formation is indicative of intermittent synsedimentary iron oxide precipitation in an oxidized peritidal environment in an otherwise strongly ferruginous and anoxic oceanic setting large negative ce anomalies develop over a narrower depth range when compared to modern oxic marine settings highlighting the importance of dissolved mn and fe concentrations in controlling the magnitude of the negative ce anomalies overall coupled sedimentological and geochemical evidence suggest a neoproterozoic shallow marine system at the interface of an oxidizing atmosphere and an anoxic ferruginous marine system

mineralogical and compositional characteristics of late permian coals from an area of high lung cancer rate in xuan wei yunnan china occurrence and origin of quartz and chamosite abstract some townships in xuan wei county yunnan province have one of the highest lung cancer mortality rates in china and the epidemic disease in the area has generally been attributed to the polycyclic aromatic hydrocarbons pahs released from domestic coal burning however the cancer causing culprit is not settled as tian tian l 2005 coal combustion emissions and lung cancer in xuan wei china ph d thesis university of california berkeley found nanometer quartz in these coals soot emissions and lung cancer tissues we have conducted mineralogical and geochemical studies of the coals from xuan wei for the purpose of shedding light on the minerals which may be related to the epidemic lung cancer in this paper abundances modes of occurrence and origins of minerals and elements in the coals from two mines in xuan wei have been studied using optical microscope low temperature ashing x ray diffraction analysis scanning electron microscope equipped with energy dispersive x ray spectrometer and inductively coupled plasma mass spectrometry the minerals in the coals are mainly composed of quartz chamosite kaolinite and calcite the particle size of quartz is rather small mostly less than 20 m and it is of authigenic origin chamosite occurs mainly as cell fillings the occurrence of quartz and chamosite indicates that they were derived from the hydrothermal fluids epigenetic calcite is derived from calcic fluids kaolinite is derived mainly from sediment source region of kangdian oldland to the west of coal basin the composition of xuan wei coal is high in sio2 fe2o3 tio2 cao mno v co ni cu and zn the high sio2 content is attributed to quartz and the fe2o3 content to chamosite the high mn and low mg contents in the coal indicate the inputs of hydrothermal fluids cao occurs mainly in epigenetic calcite elements ti co ni cu zn and rare earth elements were derived from the basaltic rocks at sediment source region

sedimentology and oceanography of early ordovician ironstone bell island newfoundland ferruginous seawater and upwelling in the rheic ocean abstract the bell island and wabana groups together comprise a ca 150 m thick succession of interbedded clastic and chemical sedimentary rocks composed of eight distinct lithofacies that accumulated along the northern margin of the rheic ocean lithofacies stacking patterns indicate that deposition occurred during a marine transgression with superimposed small scale sea level fluctuations producing at least six parasequences parasequences containing ironstone are 10 to 20 m thick and composed of hummocky cross stratified sandstone interbedded with organic rich mudstone and phosphatic fe silicate bearing siltstone which is overlain by hematitic granular ironstone capped by an erosive flooding surface this lithofacies association is interpreted to record the deposition of upwelling related ironstone on a storm dominated shelf the close relationship between fe silicates and phosphorite typical of upwelling systems suggests that fe was delivered from deep anoxic nutrient rich seawater that also stimulated high surface productivities the result was the precipitation of authigenic sedimentary apatite in anoxic organic rich sediments that accumulated near the upwelling front the gradual advection of fe rich waters away from the upwelling front initiated precipitation of fe silicate coated grains and cements in suboxic pore waters iron pumped into shallower environments through advection and fe redox cycling is interpreted to have precipitated fe oxyhydr oxide grains in sediment of the oxygenated middle shelf these coated grains were subsequently concentrated by fairweather and storm currents on the shoreface to create granular economic fe deposits we challenge conventional models of paleozoic ironstone deposition that rely on a continental source of fe by proposing a hydrothermal source that supplied fe2 to the shelf through upwelling it also highlights the potential connection between the delivery of anoxic ferruginous seawater to the margins of the rheic ocean and the early ordovician extinctions that punctuated the beginning of the great ordovician biodiversification event

emplacement kinematics of a granite diapir the chindamora batholith zimbabwe the geometric features of a large 50 40 km granitic batholith and its surrounding greenstone belt envelope are described the batholith is made up of several intrusive components and an intrusion sequence based on contact relations and xenoliths has been established the igneous rocks show a local foliation s fabric and preferred orientation of minerals the intensity of this fabric accords with the finite strain determined from xenolith shape analysis when the strain variations are analysed in detail it appears that the batholith was built up by a succession of magmatic pulses each of which led to a stretching of the previously consolidated igneous material so called balloon tectonics evidence is presented that xenolith deformation commences only when the surrounding igneous material has crystallized and a method is suggested whereby the position of the surface separating crystal supported phase plastic behaviour from melt supported phase liquid behaviour at different stages in the plutonic history can be determined ductile shear zones are present and their geometry accords well with the shape changes necessary to allow the outer parts of the pluton to stretch

continuous high frequency turbulence and suspended sediment concentration measurements in an upper estuary the present study details new turbulence field measurements conducted continuously at high frequency for 50 hours in the upper zone of a small subtropical estuary with semi diurnal tides acoustic doppler velocimetry was used and the signal was post processed thoroughly the suspended sediment concentration wad further deduced from the acoustic backscatter intensity the field data set demonstrated some unique flow features of the upstream estuarine zone including some low frequency longitudinal oscillations induced by internal and external resonance a striking feature of the data set is the large fluctuations in all turbulence properties and suspended sediment concentration during the tidal cycle this feature has been rarely documented

structure and emplacement history of a multiple center cone sheet bearing ring complex the zarza intrusive complex baja california mexico the cretaceous zarza intrusive complex located in the peninsular ranges of baja california norte mexico is perhaps the bestpreserved multiple center cone sheet bearing ring complex documented in north america the 7 km 2 elliptical complex hosts three nested non concentric intrusive centers that are successively younger to the south the northern and central centers show the same evolutionary sequence of 1 intrusion of concentric gabbroic cone sheets 2 intrusion of massive core gabbros and 3 development of subvertical ductile ring faults ring fault kinematics indicate that both centers moved down relative to the surrounding country rocks suggesting collapse into an underlying magma chamber the southern center is composed of approximately equal proportions of gabbro and tonalite and lacks cone sheets aluminumin hornblende barometry on the tonalite indicates a maximum emplacement depth of 2 3 0 6 kbar the zarza intrusive complex is surrounded by a ductile deformation aureole and bedding is inward dipping and inward younging around the entire complex excellent preservation of the intrusive history allowed us to evaluate the origin of the aureole and the three most applicable models are 1 collapse of the complex into its underlying magma chamber 2 sinking of the complex and its chamber after solidification and 3 formation of the aureole prior to emplacement of the complex the preserved structural and intrusive relationships provide information on the dynamic evolution of subvolcanic magma chambers and suggest that the complex may have been overlain by a caldera

the structure and dynamics of the thin near bed layer in a complex marine environment a case study in beatrix bay new zealand abstract the 1 3 cm thick near bed layer at the interface between sea water and the sea bed was studied using two acoustic doppler velocimeter adv deployments in beatrix bay new zealand which relate to late autumn and early winter conditions the data strongly support the multi mechanism nature of the near bed layer and show that the turbulent stresses and energy may be non zero even at nearly zero or zero mean velocities the turbulent fluctuations in the near bed layer are highly intermittent and consist of two components 1 low energy background fluctuations and 2 relatively rare high energy events hee the structure dynamics and influence of these components on bed erosion particle aggregation and re suspension are significantly different our results suggest that the revealed high energy events are the main contributors to bed erosion and sediment re suspension the estimates of the local reynolds number and other turbulence parameters show that hee may change the near bed flow regime from viscous or transitional at low energy background conditions to fully turbulent during the high energy events although the physical origin of hee is not yet clear most probably they are generated by intermittent highly energetic internal waves or near bed convective mixing or both these results provide a base for future research in this complex near bed region

the solid body tilt of deformed paleohorizontal planes application to an archean transpression zone southern canadian shield abstract the solid body tilt sbt of deformed paleohorizontal planes is equal to the angle between their unstrained top direction and an upward pointing vertical axis kinematic models of important tectonic processes such as transpression and ductile thrusting have specific sbt requirements these models can be tested in ancient and modern orogens by determining the actual sbt of strata early magmatic sills and late horizontal intrusions with relict primary layering classical transpression models predict that except for sheath structures all folds in bedding be upright and horizontal i e that sbt values be close to zero within the hinge zones moreover all passive folding is accomplished by amplification of asperities and caused by the pure shear component of the transpression tensor nine sbt analyses were made in the archean crust of northwest ontario to test the transpression hypothesis north of the quetico wabigoon boundary western superior province central canada the nine sbt values do not discredit the hypothesis that the quetico fault marks an archean transpression zone which included the wabigoon rocks adjacent to the quetico metasediments

from black and white to colour in the silurian abstract ironstones and iron rich limestones regularly occur as components of time specific intervals of the palaeozoic as well as in younger times brett et al 2012 this issue silurian sediments deposited at high latitudes along the peri gondwana border are characterized by black and white limestone and graptolitic shale sequences those in the carnic alps southern austria additionally contain colourful pink to red limestones and ironstones laminated structures such as the ferruginous coatings around skeletal fragments mostly trilobites and some cephalopods and echinoderms and stromatolitic features along discontinuity surfaces display dark red green white and brownish colours due to the presence of goethite magnetite hematite chamosite calcite and subordinate apatite confocal laser raman microscopy and complementary microscopic analysis of these ferruginous laminated structures document the presence of carbonaceous matter associated with fossilized microbial structures in the form of stromatolites filaments and coccoids suggesting a microbial role in the colouring of the silurian world of the carnic alps iron concentrations up to 30 that of matrix and surrounding non ferruginous rocks suggest blooms of iron microbe activity in response to the time specific occurrence of chemically charged sea water during global biotic events

granite emplacement in orogenic compressional conditions the la alberca bejar granitic area spanish central system variscan iberian belt abstract the la alberca bejar granitic area comprises a set of intrusions of upper carboniferous to lower permian age located in the hinterland of the variscan belt of western spain gravity data anisotropy of magnetic susceptibility and microstructural studies carried out in the granitoid and its country rocks indicate that the granitoids of this region have tabular and inverted drop shapes and show sub horizontal magmatic fabrics and sw ne lineations the granitoid bodies were intruded episodically with single intrusive pulses recorded by deformation in the country rocks all intrusive events took place during d 3 compressive stage in the core of large d 1 anticlines and are not related to structures in the country rock a syn orogenic emplacement model for granite intrusion in such conditions is proposed the proposed model implies the activity of coeval emplacement mechanisms and room generation

turbulence characteristics of a small subtropical estuary during and after some moderate rainfall in natural estuaries scalar diffusion and dispersion are driven by turbulence in the present study detailed turbulence measurements were conducted in a small subtropical estuary with semi diurnal tides under neap tide conditions three acoustic doppler velocimeters were installed mid estuary at fixed locations close together the units were sampled simultaneously and continuously at relatively high frequency for 50 hours the results illustrated the influence of tidal forcing in the small estuary although low frequency longitudinal velocity oscillations were observed and believed to be induced by external resonance the boundary shear stress data implied that the turbulent shear in the lower flow region was one order of magnitude larger than the boundary shear itself the observation differed from turbulence data in a laboratory channel but a key feature of natural estuary flow was the significant three dimensional effects associated with strong secondary currents including transverse shear events the velocity covariances and triple correlations as well as the backscatter intensity and covariances were calculated for the entire field study the covariances of the longitudinal velocity component showed some tidal trend while the covariances of the transverse horizontal velocity component exhibited trends that reflected changes in secondary current patterns between ebb and flood tides the triple correlation data tended to show some differences between ebb and flood tides the acoustic backscatter intensity data were characterised by large fluctuations during the entire study with dimensionless fluctuation intensity ib ib between 0 46 and 0 54 an unusual feature of the field study was some moderate rainfall prior to and during the first part of the sampling period visual observations showed some surface scars and marked channels while some mini transient fronts were observed

genesis of unusual lithologies associated with the late middle devonian taghanic biocrisis in the type taghanic succession of new york state and pennsylvania abstract the middle devonian late middle givetian tully formation in new york state is the type regional expression of the global taghanic biocrisis it is marked by anomalous development of massive to rhythmically bedded micritic limestone deposits within a vastly thicker acadian foreland basin clastic succession lower medial tully carbonates record the incursion of tropical old world realm owr taxa tully fauna and the outage of the long standing higher diversity cooler water endemic eastern americas realm ear biota hamilton fauna succeeding tully strata record a return of the hamilton fauna followed by its demise due both to replacement by the lower diversity cosmopolitan genesee fauna and by the overspread of widespread anoxic bottom conditions coupled with the onset of drastically increased sediment input following tully group deposition massive micritic limestones yielding modest diversity tully fauna assemblages are particularly characteristic of the lower medial tully succession on the western new york tully platform these are coeval with nearly barren ribbon limestone and siltstone deposits in the adjacent new berlin east central new york and central pennsylvania basins these depocenters trapped terrigenous sediment and helped to create sediment starved conditions on the platform anomalous tully carbonate deposition is believed to be coincident with strong super estuarine water mass stratification in offshore tully shelf and basin settings where a warmer denser more saline water mass flowed northward shoreward across the study area beneath a counter flow of oxygenated river influenced surface water dysoxic conditions would have developed below the pycnocline favoring the tully fauna incursion precipitation of carbonate mud and possibly promoting the formation of ooidal chamosite at least five thin 1 30 cm thick mappable beds of black ooidal chamosite are observed in taghanic shelf margin slope and basin deposits these beds are typically intensely bioturbated variably rich in associated siderite contain corroded low diversity fossil assemblages and are regionally associated with condensed lag deposits above unconformities work by others suggests that chamosite formation occurs under minimally reducing post oxic interstitial conditions which are followed in turn by more strongly reducing conditions which allow for variable siderite and pyrite formation terrestrial pedogenic alteration of silicates by evolving land plant communities under warm humid conditions led to an increased supply of kaolinite as well as iron oxides and hydroxides that served as precursors to chamosite formation in the new berlin basin the transgressive top hamilton base taghanic succession is marked by a succession of diastems associated with basin deepening and upward increasing chamosite occurrence in dysoxic facies occurrence of ooidal chamosite in upper medial tully platform deposits smyrna bed may reflect water mass stratification and extreme sediment starvation at the shelf margin eastward spectral transformation of sparsely fossiliferous smyrna ooidal chamosite in the western new berlin basin into richly fossiliferous non chamositic equivalent neritic deposits east of that basin suggests that the counter flow of oxygen and nutrient rich lower salinity water had blocked the denser restricted water layer from advancing over the eastern tully clastic shelf closer to shore

chamosite siderite and the environmental conditions of their formation in chamosite type phanerozoic ooidal ironstones abstract two characteristic ironstone minerals occurring in chamosite type ironstone deposits were investigated these are the minerals of the chlorite and the carbonate series the samples are from 31 localities and 8 countries czech republic france germany united kingdom egypt nigeria and usa these deposits are identical to those presented by mucke and farshad mucke a farshad f in press whole rock and mineralogical composition of phanerozoic ooidal ironstones comparison and differentiation of subtypes ore geology reviews with ordovician to late cretaceous ages electron microprobe analyses of 197 carbonates and 64 chlorites were carried out the analytical points of the carbonates in a magnesite calcite siderite rhodochrosite 100 mol diagram are distributed within a limited area close to the siderite end member the area can be subdivided into two fields 1 the carbonates of the ordovician ironstones of the welsh prague and thuringian basins have high siderite concentrations 87 1 to 90 6 mol magnesite contents from 6 7 to 8 3 mol and calcite concentrations from 1 6 to 2 4 mol in the ordovician ironstone of krusna hora prague basin the siderite concentrations are lower 78 3 mol and those of magnesite 15 6 mol and calcite 5 7 mol are higher 2 the carbonates of the other ironstones jurassic to late cretaceous have lower siderite 72 5 to 79 mol and higher magnesite 12 6 to 15 7 mol and calcite 6 9 to 12 2 mol contents the average values of the rhodochrosite end member lie in the range between 0 13 and 2 31 mol and the siderite rhodochrosite ratio 158 on average the analytical points of the chlorite analyses are presented in the fetot mg alvi 100 atom diagram one field containing exclusively chlorites with green internal reflections can be subdivided into two areas one area contains the chlorites of the ordovician ironstones consisting of 62 8 to 77 7 atom fetot 17 5 to 30 9 atom alvi and 4 1 to 7 4 atom mg and the other those of the jurassic to late cretaceous ironstones consisting of 55 7 to 62 5 atom fetot 26 to 33 8 atom alvi and 9 to 13 atom mg the second field contains altered chlorites of ferruginized ironstones aswan and red mountain formation these chlorites present brown internal reflections and have compositions 34 9 to 46 7 atom fetot 24 8 to 42 2 atom alvi and 16 0 to 28 5 atom mg that do not reflect the original diagenetic environment within the al al fe mg mg mg fe atom diagram the chlorite analyses are concentrated in a limited field which is distinctly separated from chlorites formed in other environments the occurrence of carbonate and chlorite both with slightly varying compositions dominated by their iron end members which occur characteristically in association with framboidal pyrite and organic matter are indications that three prerequisites for the formation of the ironstones are comparable in narrow limits these are 1 the composition of the protoliths 2 the depositional environment of the protoliths and their rates of deposition and 3 the environmental conditions that occurred during the lithification of the protoliths due to submarine diagenesis the protoliths consist of mixtures of kaolinite fe3 oxide hydroxide and organic matter the depositional environments are marine basins in which fully marine conditions occur and thus the availability of mg and ca not contained in the protoliths exists the rates of deposition control the amount of mg in the chloritess and that of mg and ca in the carbonatess and the environmental conditions during submarine diagenesis depend on the availability of organic matter creating reducing conditions due to bacterial oxidation the resulting conditions are reducing and depending on the amount of organic matter pass successively from post oxic formation of chamosite and authigenic rice grain shaped siderite via sulphidic formation of framboidal pyrite into methanic formation of abundant xenomorphic siderite that replaces chamosite

mineralogy and geochemistry of the coals from the karmozd and kiasar coal mines mazandaran province iran abstract the karmozd and kiasar mines are two major coal producing areas in the central alborz coal bearing field northern iran this study focused on the mineralogy and geochemistry with respect to the mode of occurrence of elements in feed coals and element partitioning during coal preparation the low sulfur content in the coal seams indicates a non marine origin i e deposition in lacustrine and swamp environments detrital minerals in the coal seams are quartz feldspar albite and orthoclase mica muscovite and biotite amphibole hornblende and kaolinite authigenic minerals include pyrite calcite and chlorite the contents of most elements are within the general worldwide ranges with the exceptions of mn co and cr in some coal seams correlation coefficients between elements and the ash yield identified four separate groups of elements the sequential extraction results indicate that al na k zn cu and co principally occur in the silicates whereas pb and cr mainly occur in the organic fraction calcium and mg display strong affinities to the carbonate phase while cd mainly occurs in the water soluble and organic fractions the calculated removability index shows that the coal cleaning method in zirab not only removes mineral matter and pyritic sulfur but also reduces the content of most inorganic elements

observations of turbulence in a partially stratified estuary the authors present a field study of estuarine turbulence in which profiles of reynolds stresses were directly measured using an adcp throughout a 25 h tidal day the dataset that is discussed quantifies turbulent mixing for a water column in northern san francisco bay that experiences a sequence of states that includes a weak ebb and flood that are stratified followed by a strong and eventually unstratified ebb and flood these measurements show that energetic turbulence is confined to a bottom mixed layer by the overlying stratification examination of individual reynolds stress profiles along with profiles of richardson number and turbulent froude number shows that the water column can be divided into regions based on the relative importance of buoyancy effects using the measured turbulence production rate p the dissipation rate e is estimated the observed turbulence had values of e nn 2 20 all of the time and e nn 2 200 most of the time suggesting that the observed motions were buoyancy affected turbulence rather than internal waves however at times turbulent froude numbers in much of the upper water column were less than one indicating important stratification effects taken as a whole the data show that stratification affects the turbulent velocity variance q2 most severely that is observed reductions in u9w9 are largely associated with small values of q2 rather than with a dramatic reduction in the efficiency with which turbulent motions produce momentum fluxes finally the dataset is compared to predictions made using the popular mellor yamada level 2 5 closure these comparisons show that the model tends to underestimate the turbulent kinetic energy in regions of strong stratification where the turbulence is strongly inhomogeneous and to overestimate the turbulent kinetic energy in weakly stratified regions the length scale does not appear to compensate for these errors and as a result similar errors are seen in the eddy viscosity predictions it is hypothesized that the underestimation of q2 is due to an inaccurate parameterization of turbulence self transport from the near bed region to the overlying stratification

evaluation of multiple emplacement mechanisms the huichizi granite pluton qinling orogenic belt central china three end member granite emplacement mechanisms host rock ductile shortening hrds host rock rigid displacement hrrd and magmatic absorption ma are identified in this study of the huichizi pluton the internal fabrics are mainly flattening typesona 0 4 0 9u and strain is highoesa 1 0 0 6u near the boundaries and lowoesa 0 7 0 30u toward the central parts of the pluton in the 1 5 km wide contact aureole extension e is measured in syn emplacement deformed veins and the calculated average shortening normal to the sides and tips of the pluton are 1 14 km and 0 74 km respectively from this we conclude that the hrds produced only about 20 space for the present volume of the pluton the regional hrrd derived from the uplift by about 8 km of the qinling group in a flower structure contributed 19 032 space ms including stoping and material transfer processes yielded another 37 space of this stoping contributed a minimum of 1 space estimated from the surface area of 2 8 km 2 covered by xenoliths transfer processes provided about 36 of the needed space deduced from the average 64 36 ratio of hybridization of mantle derived to crustal qinling group derived magma the three mechanisms may act nearly simultaneously as a multiple emplacement mechanism this situation may apply to many other plutons as well 2000 elsevier science ltd all rights reserved

stratification and turbulence in subtidal channels through intertidal mudflats 1 field observations in san francisco bay of subtidal channels that drain through intertidal mudflats indicate that substantial periodic stratification develops in very shallow flows with distinct asymmetries between flood and ebb conditions the greatest variability in salinity and stratification occurs during the wet winter months very strong longitudinal salinity gradients develop across the intertidal zone between salty subtidal water and fresher water draining into the marsh upstream tidal straining of the longitudinal gradient creates the periodic stratification stratifying through ebbs and destratifying through floods the stratification can be very strong in very shallow flows with n2 0 1 s 2 in about 0 5 m water depth analysis of the data with dimensionless numbers shows that at times the stratification is strong enough to suppress turbulence and mixing the asymmetry in stratification between ebbs and floods results in asymmetries in eddy viscosity and eddy diffusivity with lower values during the stratified ebbs because of the intertidal elevation of the system the strong longitudinal salinity gradient is regenerated each time the mudflats and marsh drain the system approaches a tidally periodic steady state where the flow dynamics are dominated by the sharp front of salty water that advects into the intertidal zone on the rising tide and exits the system by each lower low water the field data are supported by a numerical model with simple mudflat channel bathymetry both the field and numerical work indicate that the shallow low energy flows in mudflat channels transition between strongly stratified suppressed turbulence and relatively unstratified active turbulence each tidal cycle

late ordovician ice marginal processes and sea level change from the north gondwana platform evidence from the valongo anticline northern portugal abstract in the valongo anticline northern portugal the upper ordovician age sobrido formation records glacioeustatic sea level changes and glacially influenced depositional environments on the north gondwana platform associated with the hirnantian glaciation new stratigraphic data from the sobrido formation taking into account lateral facies variations not exposed in the type section allow for a better understanding of hirnantian glacial sedimentary processes sea level changes and palaeogeography the lower member of the sobrido formation is composed of quartzites alternating with siltstones and mudstones the transition to the upper member is most commonly an erosional contact marked by a ferruginous horizon the lowermost part of the upper member contains a thinly laminated and rhythmically bedded mudstone that is capped by a thin mm scale shelly bed and overlain by massive diamictites laterally conglomerate beds that have erosion bases are rhythmically interbedded with slates and diamictites that sometimes contain outsized mudstone clasts the uppermost part of the upper member is very variable in thickness laterally and contains massive to laminated diamictite beds intercalated with quartzites conglomerates and slates massive diamictites commonly exhibit thin horizons with fe oxides and occasionally manganese phosphate and oolitic chamosite the lower member of the sobrido formation is interpreted as ice proximal outwash that is transitional laterally to subaqueous ice contact fans formed by debris and mass flows erosion followed by chemical weathering of the lower member and variably within the lowermost part of the upper member is interpreted as a response to sea level fluctuations and development of spatially variable anoxic conditions and groundwater migration within isolated marine basins facies within the upper member of the sobrido formation are interpreted as ice distal laminated diamictites and ice proximal deposits massive diamictites quartzites and conglomerates groove casts and hummocky cross stratification within quartzite beds suggest deposition in a shallow shelf setting the upper ordovician lower silurian transition is locally marked by a ferruginous horizon black basal quartzites are interpreted to record development of an erosional unconformity during silurian sea level rise in other areas a chloritoid layer indicates proximity to dry land these palaeoenvironmental interpretations suggest dynamic changes in sedimentary and geochemical processes in response to sea level and related palaeogeographic changes during the upper ordovician and transitional to the lower silurian on the north gondwana platform

granitoid emplacement and deformation along a major crustal lineament the cordillera blanca peru abstract the cordillera blanca batholith and ignimbrites of the intermountain callejon de huaylas basin represent the last magmatic event in the andean cycle of central northern peru this most spectacular example of an extensional regime is characterised by acid magmatism spanning some 10 ma with both magma emplacement and subsequent deformation being fundamentally controlled by a ca 300 km lineament known as the cordillera blanca fault complex the western margin of the batholith has been strongly deformed by the cordillera blanca fault resulting in a series of ductile to brittle structures that increase with intensity away from the relatively undeformed core towards the margin the late stage brittle fabrics are coeval with extensional structures in the callejon de huaylas basin and relate to uplift and extension along the fault zone the more ductile fabrics as indicated by combined k ar and 40 ar 39 ar mineral dates formed earlier in the intrusion history and are consistent with emplacement into an active dextral strike slip shear zone the rapid uplift and high erosion rates seen from the late miocene onwards and the current state of stress in this region of thickened crust are due to gravitational instability body forces set up at high topographical levels and buoyancy forces resulting from the intrusion of young acid magmas at high crustal levels

re examining pluton emplacement processes discussion in a recent review paterson fowler 1993 showed decreasing away from the pluton as discussed by gughow estimated volumes of displaced wall rock are lielmo 1993b smaller than pluton volumes and how the widths of laboratory experiments indicate that rocks behave as strain aureoles around natural plutons are considerably power law fluids with exponents n between 2 5 and 5 narrower than in models of diapirs where spheres rise hansen carter 1982 kirby 1983 wilks carter through newtonian fluids cruden 1988 schmeling et 1990 the power law exponent n of a viscous fluid is a al 1988 they then argued that mechanisms other than measure of the sensitivity of its viscosity stress or ductile flow of the wall rocks were necessary to account strain role for n 1 newtonian fluid the viscosity is for these observations although i accept that several constant for any strain rate for n 1 the fluid softens mechanisms may act simultaneously and change in imwith increased strain rate the strain rate dependency of portance as plutons are emplaced i argue here that i the viscosity of power law fluids has important effects on the displaced volumes of wall rocks may be underestithe velocity and flow patterns of the ambient fluid mated because of difficulties in assessing the shape and around rising spheres or diapirs and therefore the size of the three dimensional flow cell in the wall rocks width of their strain aureoles crochet et al 1984 caused by pluton emplacement and more importantly kawase moo young 1986 weinberg podladchikov ii the narrow strain aureoles may result from diapiric in press in the following discussion the difficulties in rise of plutons through power law rocks and or result determining the volumes of rock displaced by diapir from the effects of thermal softening of the wall rocks emplacement are first considered the effect which several field studies have measured the width of the power law rocks might have on the width of the strain strain aureole caused by pluton emplacement see gugaureole is then discussed and finally the possible effects lielmo 1993a paterson fowler 1993 and references of thermal softening of the wall rocks by the diapir are therein the measured width depends on three main examined factors i the finite strain of the wall rocks which depends on the velocity field imposed by the diapir this in turn depends on the diapir s mechanism and depth of rock volumes displaced by diapirs emplacement and on the rheology and physical boundaries of its wall rocks the longer a rock volume is paterson fowler 1993 studied horizontal shortensubmitted to a particular strain rate velocity field the ing in strain aureoles around plutons and then integrated larger is its strain the velocity of flow decreases with shortening to three dimensions around plutons of differdistance from the contact of rising spheres so that ent shapes the amount of shortening they obtained for strains have to accumulate a long time to be distinguishseveral natural examples only accounted for about 30 able from any background strain ii late deformation of the volume of the plutons they argued that this will mask the strain aureoles of pre tectonic plutons volume difference implies that other mechanisms such while interference with regional tectonic strains will as doming of the roof stoping assimilation and rigid affect the width of the aureoles of syn tectonic plutons translation of wall rock must have operated at the same guglielmo 1993b iii the measurable width of the time as viscous flow of the wall rock aureole depends on distinguishing the strain due to the however this discrepancy may largely be due to pluton from regional strains of any age paterson difficulties in measuring small pluton related strains fowler 1993 this distinction becomes increasingly beyond the obvious strain aureole and difficulties in more difficult as strains are spread over larger volumes determining the shape of the flow cell around the pluton the width of the strain aureole around a rising sphere depends on the power law exponent n of the country current address research school of earth sciences anu act rocks it is widest in newtonian fluids and narrows as n 6200 canberra australia increases however even in the case of rocks with high n

magma emplacement during arc perpendicular shortening an example from the cascades crystalline core washington it is increasingly inferred by others that active arcs at all crustal levels are undergoing arc perpendicular extension and that magma utilizes this extension or extension along arc parallel strike slip faults during emplacement however a review of stress fields in modern arcs and deformation which occurred during magmatism in ancient arcs and our own emplacement studies of individual plutons indicate that magma emplacement typically occurred during arc perpendicular shortening without the aid of strike slip faulting this conclusion raises the question of how host rock is displaced during magma emplacement in shortening and thickening orogens evaluation of host rock material transfer processes that operated during emplacement of the 93 ma 10 to 14 km deep mount stuart batholith washington provides one example and includes the following 1 ductile downward flow in a narrow 0 2 body radii structural aureole 2 stoping and of lesser importance 3 regional folding thrusting and subhorizontal arc parallel extension we see no evidence that arc perpendicular extension or local extension along strike slip faults made space for this pluton nor for most other plutons in contractional arcs instead we argue that both localized and rapid around plutons and regional and slower downward flow during growth of crustal roots is a common process in such arcs

preliminary estimates of the amount of continuous horizontal shortening across an archean greenstone belt simple two dimensional techniques are used to make an estimate of the total shortening across a narrow greenstone belt in northwestern ontario the techniques are based on the basic principle of restoring the predeformational geometry of a horizontal traverse across the belt depending on the technique used this traverse is a string of line elements or a chain of finite elements the strain ratios available for the restoration are minimal values and need to be increased significantly to obtain realistic results depending on the strain values selected for the restoration amounts of horizontal shortening range from 17 to 49 the actual amount remains unknown but is thought to be 50 in view of the apparent variation in longitudinal strain along the greenstone belt a three dimensional treatment seems to be necessary this would require that strain measurements be taken systematically throughout rather than along a single traverse across a greenstone belt segment

analysis of three dimensional strain modified uniform distributions andalusite fabrics from a granite aureole a method of analysing finite strain from an initial random distribution of lines or planes is presented the shape of the strain ellipsoid is mapped to the eigenvalue ratios of an orientation matrix the method is used to interpret the andalusite fabrics from the aureole of the ardara granite county donegal ireland the high flattening strains determined in the aureole are accompanied by oblate strains in the granite margins and support the concept of deformation produced by expansion of the pluton

paleoenvironmental significance of aluminum phosphate sulfate minerals in the upper cretaceous ooidal ironstones e ne aswan area southern egypt aluminum phosphate sulfate aps minerals are present as small disseminated crystals in the upper cretaceous shallow marine ooidal ironstones e ne aswan area southern egypt their association with the ironstones is considered as a proxy of subaerial weathering and post diagenetic meteoric water alteration the mineralogical composition of the ooidal ironstones was investigated by optical and scanning electron microscopes x ray diffraction fourier transform infrared and raman spectroscopy the ooidal ironstones are composed mainly of ooids and groundmass both of which consist of a mixture of detrital quartz and diagenetic fluorapatite chamosite and pyrite mineral assemblages these mineral assemblages are destabilized under acidic and oxidizing continental conditions these conditions resulted from the oxidation of pyrite and probably organic matter under warm and humid tropical climate followed the santonian sea regression and subaerial exposure these pedogenic conditions promoted corrosion of quartz dissolution of chamosite and apatite and hydrolysis of feldspars of the nearby exposed granitoids the released si al and sr from quartz chamosite and feldspars fe and s from pyrite and p ca and light rare earth elements lree from apatite are reprecipitated as hematite kaolinite apatite and aps minerals from the pore fluids or along fractures the paragenetic sequence and textural relationships of this post diagenetic mineral assemblage indicate that hematite was formed by replacement of chamosite followed by formation of a secondary generation of pore filling chlorapatite and aps minerals and finally the precipitation of kaolinite in the remaining pore spaces the formation of aps minerals and chlorapatite is simultaneous but aps minerals are stable at shallow depths under acidic to neutral ph conditions whereas chlorapatite is stable under alkaline ph conditions alkaline conditions were maintained at greater depths when the infiltrated acidic fluids reacted with chamosite the aps minerals display a homogeneous chemical composition in all ironstone locations in aswan area corresponding to a solid solution between crandallite caal3 po4 2 oh 5 h2o goyazite sral3 po4 2 oh 5 h2o svanbergite sral3 po4 so4 oh 6 and woodhouseite caal3 po4 so4 oh 6 end members the variations in the aps mineral chemistry ab3 xo4 2 oh 6 are essentially due to variable substitutions of sr and lree for ca at the a site and limited s for p at the x site the spatial distribution of aps minerals and their composition in the ooidal ironstones of aswan area permitted to consider them as good tracers of physicochemical and paleoenvironmental changes in particular those associated with subaerial exposure and pedogenesis the post diagenetic phosphatization and kaolinization of the aswan ironstones decrease their economic potentiality thus understanding paragenetic sequence and textural relationships is essential for the iron ore beneficiation

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

provenance and tectonic implications of the 3 28 3 23 ga fig tree group central barberton greenstone belt south africa abstract sedimentary rocks provide a valuable record of non uniformitarian paleoarchean tectonic processes the rocks of the 3 28 3 23 ga mapepe formation mark the initiation of orogenesis in the barberton greenstone belt south africa however reconstruction of the mapepe basin s is challenging because the rocks occur in fault bounded structural belts that are characterized by lateral heterogeneity and whose correlation remains uncertain we have studied the petrography geochemistry and detrital zircon geochronology from outcrop and drill core samples from two adjacent structural belts the manzimnyama syncline and the eastern barite valley area to evaluate the timing of basin formation correlate between these two adjacent areas and provide constraints on the character of tectonic uplift in the eastern barite valley area sedimentation was initiated at about 3260 ma the section includes a lower deep water unit of mainly mudstone overlain by a shoaling upward sequence of fan delta sandstone and conglomerate the sandstone throughout the formation was derived by erosion of local uplifts of the underlying greenstone belt sequence except at the top of the section where sedimentation was dominated by dacitic volcaniclastic sediments dated at 3239 ma in contrast rocks of the mapepe formation in the manzimnyama syncline area 1 2 km south of the eastern barite valley area record the initiation of sedimentation at about 3277 ma with deposition of a rhyolitic tuffaceous unit followed by persistent deep water sedimentation of banded iron formation banded ferruginous chert and turbiditic sandstone siliciclastic sediments are immature and were derived by erosion of older supracrustal greenstone belt rocks no fig tree age volcanism younger than 3260 ma is recorded in this belt overall mapepe sedimentary rocks record the formation of numerous local uplifts of underlying supracrustal rocks with periodic volcanic activity and the dispersal of debris to form mainly small fan deltas flanked by deep water systems the contrasting ages lithologies depositional settings and provenance of the sedimentary rocks in the now adjacent eastern barite valley and manzimnyama syncline belts suggest that they were deposited in either different parts of a large complex fig tree basin or represent separate basins that have been juxtaposed during post fig tree tectonism and shortening

igneous emplacement in a shear zone termination the biotite granite at strontian scotland deformed xenolith strain data together with other structural information indicate that the biotite granite body 90 sq km of the strontian complex scotland was emplaced in the extensional termination of a dextral transcurrent shear zone this shear zone is a splay of the major great glen fault which lies along the southern boundary of the granite siting of the shear zone splay was probably controlled by a a slight releasing bend in the great glen fault in this area and b a large pre existing asymetric synform in proterozoic metasedimentary country rocks which intersects the great glen fault trace at a high angle a model is proposed in which moine thrust caledonian compression at ca 435 ma activated the great glen fault dextrally dextral movements around the releasing bend detached a flat segment from the inside fault wall and the biotite granite was emplaced side ways at depths of about 15 km as a sheet into this extensional listric fault bounded cavity

cannibal creek granite post tectonic ballooning pluton or pre tectonic piercement diapir the cannibal creek granite in northern queensland australia previously has been interpreted to be a post tectonic pluton which underwent solid state deformation during in situ ballooning a reinterpretation of structures in and around the pluton indicates that this pluton is more appropriately viewed as a pierce ment diapir emplaced by magmatic flow significant deformation took place after pluton emplacement in fact the cannibal creek granite has some characteristics similar to pre tectonic granites examined elsewhere therefore it is somewhat misleading to view the granite as a post tectonic pluton

rates of processes in magmatic arcs implications for the timing and nature of pluton emplacement and wall rock deformation abstract the construction of arcs and in many cases the emplacement of plutons occur in tectonically active regions it is critical therefore to evaluate the rates of structural and magmatic processes when trying to understand the evolution of arcs and the associated pluton wall rock systems our best estimates of average rates or durations of processes in shallow to moderate level arc environments are the following 1 crystal growth rates in magma of 10 4 cm year 1 2 growth rates of metamorphic porphyroblasts between 10 5 and 10 2 cm year 1 3 long term magma supply rates of 10 1 km 3 year 1 and short term rates of up to 350 km 3 year 1 4 diapiric ascent rates for mafic plutons of 1 3 m year 1 5 cooling of plutons to ambient wall rock temperatures in 10 5 10 6 years 6 final crystallization of plutons in a small fraction of the time needed for complete cooling 7 fault displacements of 3 cm year 1 8 development of cleavages in fault zones in less than 10 6 years at strain rates of 10 13 s 1 or higher and 9 the development of regional cleavages in 10 6 years at strain rates of 10 14 s 1 these rates indicate that processes operating in magmatic arcs are relatively rapid pluton emplacement cleavage development etc occur over time spans of tens of thousands to no more than a few million years however the rate of ascent and crystallization of plutons at shallow levels is generally shorter than that needed to get large displacements on faults or widespread cleavages developed at deeper levels or in zones undergoing faster strain rates the time spans of the various processes approach one another thus plutons with otherwise similar characteristics emplaced in regions undergoing fast strain rates or at deeper crustal levels may appear quite different structurally from those emplaced at shallow levels or in regions undergoing slower strain rates comparison of these data also suggests that the rate at which wall rock deforms is the limiting factor controlling the rates of other structural processes during emplacement of plutons unless fast strain rates or multiple deformation mechanisms are considered thus emplacement mechanisms that rely on the transport of magma over 10 5 to 10 6 years are favored and need further consideration finally we argue that the structural and other characteristics of pluton wall rock systems will depend on rates of various processes involved and that these rates at the very least influence and sometimes invalidate the timing criteria previously published by us and others

interference between pluton expansion and non coaxial tectonic deformation three dimensional computer model and field implications abstract structures in orogenic belts are greatly controlled by interactions between pluton related and tectonic related strain fields however many aspects of the geometry and evolution of these structures are poorly known for example 1 what is the geometry of these structures if regional deformation is coaxial 2 how does this geometry change with progressive deformation this paper describes a three dimensional simulation of strain shape and magnitude as well as foliation and lineation patterns formed by interactions between pluton expansion and homogeneous coaxial deformation this simulation suggests that interactions between pluton expansion and regional uniaxial shortening generate patterns that are distinct from the patterns produced by regional uniaxial extension or regional non coaxial deformation for example shortening produces doughnut shaped constrictional rings about the pluton whereas extension produces apple shaped flattening regions around the pluton in addition shortening produces one continuous doughnut shaped low strain region around the pluton on the other hand extension creates two separate ellipsoidal low strain regions at the ends of the pluton furthermore shortening forms foliation rings that have triangular two dimensional sections and lineation is concentric around the axis of maximum shortening in contrast extension produces two separate foliation and lineation cones at the ends of the pluton all these structural and strain elements migrate away from the pluton with increasing expansion rates and towards the pluton with increasing tectonic deformation rates although structural studies around plutons should always integrate microstructural radiometric and field measurements simulation generated patterns can be used to evaluate 1 origin geometry and evolution of structures around plutons 2 mechanisms that explain inclusion trails within porphyroblasts 3 contribution of pluton related strains to strains measured in the country rock and 4 type and three dimensional orientation of regional kinematic schemes

emplacement of rapakivi granite and syenite by floor depression and roof uplift in the palaeoproterozoic ketilidian orogen south greenland in the palaeoproterozoic ketilidian orogen of south greenland tabular intrusions of the rapakivi granite suite exposed at graah fjelde lindenow fjord and qernertoq and a mesoproterozoic syenite of the gardar province exposed at paatusoq were emplaced by a combination of roof uplift and floor depression the strain associated with the emplacement of the intrusions mainly involved redistribution of mass vertically within the lithosphere space for the emplacement of the rapakivi plutons was not created during regional extension on low angle ductile shear zones as claimed by some previous workers and there is no evidence that emplacement of the intrusions coincided with extensional collapse of the orogen following crustal thickening the rapakivi granites post date peak metamorphism in the orogen by 35 46 ma and their contacts cross cut and clearly post date intense flat lying d1 d2 fabrics that formed by partitioning of deformation into arc normal and arc parallel components during oblique convergence

controls on emplacement of the caledonian ross of mull granite nw scotland anisotropy of magnetic susceptibility and magmatic and regional structures abstract anisotropy of magnetic susceptibility ams was measured from 139 sites across the exposed portion of the caledonian ross of mull granite argyllshire nw scotland to investigate the internal architecture of the pluton field and petrographic observations support the results of the ams study and a complementary suite of rock magnetic experiments was used to quantify the magnetic mineralogy of the granite ams data reveal a fabric that records a partial tectonic overprint of an emplacement related magma inflow fabric the partially preserved inflow pattern indicates a south to north emplacement of subhorizontal sheets that coalesced to form a tabular pluton the ams data are remarkably consistent across the intrusion with clear north south strikes and trends dominating the magnetic foliation and lineation patterns respectively these ams fabrics are discordant to internal zonation in the granite in the southernmost part of the granite ams data are parallel to bedding cleavage orientations preserved in many large 100 m proterozoic moine blocks the scarcity of moine blocks in the northern part of the intrusion and the prevalence of randomly oriented stoped blocks suggest that this part of the intrusion is nearer to the ceiling of the pluton the partial tectonic overprint consistent with east west compression occurred during the latter stages of emplacement and mainly affected the younger granite facies rm2 while the oldest granite facies rm1 and certain magmatic structures diorite enclaves preserve the original emplacement fabric an alternative explanation interprets the magnetic lineations as an intersection fabric between a shallowly dipping emplacement fabric and a steep tectonic fabric we argue that emplacement was not associated with eastward orogenic collapse of the scandian moine nappes as proposed by previous workers but occurred either before orogenic collapse or during a period of compressional reactivation

dike transport of granitoid magmas thermal and fluid dynamical analyses suggest that for viscosities and density contrasts spanning the range considered typical for many calc alkalic granitoids dike ascent is a viable mechanism for the transport of large volumes of granitoid melt through the continental crust we present calculations showing that a granitoid melt with calculated viscosity of the order of 10 6 pa s and a density contrast between magma and crust of 200 kg m 3 can be transported 30 km through the crust in 1 month corresponding to a mean ascent velocity of 1 cm s using analysis modified from numerical studies of the flow of basaltic magmas in dikes we also present an expression that allows the calculation of the critical minimum dike or fault width required for granitic magma to ascend without freezing for all reasonable estimates of cordilleran granitoid viscosity and density contrast the critical dike width is determined to be between 2 and 7 m calculated peak batholith filling rates are orders of magnitude greater than mean cavity opening rates based on estimated fault slippage which is consistent with chemical evidence for intermittent supply of magma pulses