cold water coral habitats of rockall and porcupine bank ne atlantic ocean sedimentary facies and benthic foraminiferal assemblages the extent of the cold water coral mounds in the modern ocean basins has been recently revealed by new state of the art equipment however not much is known about their geological extent or development through time in the facies model presented here seven different types of seabed substrate are distinguished which may be used for reconstruction of fossil coral habitats the studied substrates include off mound settings foram sands hardgrounds dead coral debris and substrates characterized by a variable density of living coral framework whereas sediment characteristics only provide a basis for distinguishing on and off mound habitats and the loci of most prolific coral growth benthic foraminiferal assemblages are the key to identifying different mound substrates in more detail specific foraminiferal assemblages are distinguished that are characteristic of these specific environments assemblages from off mound settings are dominated by attached epifaunal species such as cibicides refulgens and cibicides variabilis the attached epibenthic species discanomalina coronata is also common in off mound sediments but it is most abundant where hardgrounds have formed in contrast the settings with coral debris or living corals attract shallow infaunal species that are associated with more fine grained soft sediments the typical living coral assemblage is composed of cassidulina obtusa bulimina marginata and cassidulina laevigata the abundance of these species shows an almost linear increase with the density of the living coral cover the benthic foraminifera encountered from off mound to top mound settings appear to represent a gradient of decreasing current intensity and availability of suspended food particles and increasing availability of organic matter associated with fine grained sediment trapped in between coral framework

lithoherms on the florida hatteras slope sections of the florida hatteras slope were investigated during dives of the johnson sea link i submersible and us navy s submarine nr 1 numerous calcareous coral capped lithoherms often exceeding 40 m in elevation were encountered in the subphotic depths below 440 m one huge lithoherm complex was explored that forms a long slope parallel ridge perched on the seaward edge of mid slope terrace this lithoherm belt is 400 m wide more than 4 4 km long and 150 m high on its down slope flank direct observations and side scan imaging indicate that the long axes of individual ridge crest mounds trend perpendicular to the regional current flow away from the ridge individual lithoherms trend more parallel with regional current flow and occur without obvious bedrock control all of these structures have very steeply sloping flanks frequently 30 60 where cemented crusts are exposed by erosion thickets of living ahermatypic coral coat the crest and up stream flanks of these topographic features living deep water coral have modern 14c ages 700 80 year bp and trap older 3250 100 year bp sediment rich in fine grained aragonite elsewhere older deep water coral rubble 20 230 230 year bp traps younger sediment 13 760 140 year bp the trapped sediments contain 50 aragonite fines 62 5 m the friable crusts exposed on these flanks are generally similar in composition to the sediments that accumulate on the crests of these structures they are older 14c ages of 17 770 330 and 32 710 570 year bp and contain less aragonite 20 and more high magnesium calcite apparently lithoherms grow upwards by trapping fine sediments within ahermatypic coral thickets on their crests and upstream flanks cemented crusts may be a consequence of earlier paleoceanographic conditions or a result of gradual and ongoing cementation and diagenesis the large size platform edge position and linear trend of this deep water lithoherm complex are strikingly similar to a shallow marginal reef system

short paper the age and origin of boulders in the highland border complex constraints on terrane movements mid proterozoic rb sr muscovite ages on metasedimentary boulders within the highland border complex together with archean t dm ages on the same clasts provide constraints on terrane movements in the scottish caledonides an origin for these clasts from cratonic north america is ruled out combined radiometric age t dm and fauna1 province studies on basement materials provide a potentially productive method of determining the provenance of terranes

giant carbonate mud mounds in the southern rockall trough seismic profiles sidescan sonar data bottom photography and sampling proved for the first time that there are giant carbonate mounds bioherms in the rockall trough the pelagia mounds on the northern porcupine bank are relatively isolated whereas most of the logachev mounds on the southeast rockall bank form a field of closely spaced contiguous mounds they are all found on the upper slope at depths between about 500 and 1200 m and as a result of this study about 500 have been mapped they have a variety of shapes and the larger ones are very steep sided up to 350 m high and 2 km wide at the base sediment samples show that the mounds consist of pale coloured muds mainly aragonite usually with live and or dead cold water corals at the seafloor and with buried dead corals coral thickets appear to be detected as a brush like signature on high resolution profiles and as a speckled pattern on high resolution sidescan sonar records shelly sands are found on the seabed between the mounds currents in the mound areas are strong enough to transport sands along slope as medium sized sand waves and to prevent pelagic deposition thus providing surfaces for initial coral settlement by the winnowing of fines to leave glacial dropstones and exposed rocks these observations show that the poleward directed upper slope current of the eastern north atlantic extends further south than hitherto known and that there is a southwesterly directed current on rockall bank there are waves on the logachev mounds with a wavelength of about 20 30 m that are thought to be moulded in carbonate muds by across slope directed internal tidal currents and or cascading currents mounds develop above erosional surfaces seen on seismic data the huge amount of carbonate mud seems to be produced by the rapid growth and breakdown of cold water corals living in a very favourable environment intermediate nepheloid layers formed upstream by the strong currents may provide the food source for the deep water suspension feeders conditions for giant mound growth require an ideal balance between current speed and sedimentation rate among other factors no evidence for the suggested link to methane seepage has been found so far

garnet provenance studies juxtaposition of laurentian marginal terranes and timing of the grampian orogeny in scotland a study of the composition and zoning patterns of detrital garnets from ordovician greywackes from the northern belt of the southern uplands terrane of scotland reveals characteristics of the metamorphic sources very similar to the dalradian supergroup of the scottish grampian terrane the radiometric cooling and uplift ages of the dalradian metamorphic zones and the depositional ages of the southern uplands greywackes support the hypothesis for local provenance detrital metamorphic garnet identical to dalradian garnet has also been identified in the upper ordovican sandstones of the highland border complex these observations do not support proposals that the grampian midland valley and southern uplands terranes were exotic to each other in the late ordovician time these new results together with a review of published age dates clarify the late ordovician palaeogeography for this part of the laurentian margin the distances between the grampian midland valley and southern uplands terranes may have been similar to the present day it is concluded that large rivers flowed out of the uplifting mountainous grampian terrane and across the midland valley into a southern uplands trench during the late ordovician time the main orogeny i e mountain building in the grampian terrane was therefore post cambrian producing the first high mountains and resultant flysch in the caradoc

testing for the presence of a terrane boundary within neoproterozoic dalradian to cambrian siliceous turbidites at callander perthshire scotland the southern highland group dalradian and keltie water grit formation which includes the lower cambrian leny limestone form an inverted 1 4 km thick largely arenaceous sequence at callander the grits have the same detrital mineralogy throughout mainly quartz plagioclase an 1 3 muscovite and biotite chlorite formed from detrital biotite during low grade regional metamorphism t 40 ar 39 ar laser fusion dating of detrital muscovites yields an age spectrum with a peak at 1600 1800 ma in the dalradian rocks similar old ages occur in the keltie water grits but are diluted by ages of 507 886 ma we interpret these new data as showing that the rocks were most likely deposited as a single sequence possibly with a disconformity in neoproterozoic to early cambrian times before the onset of grampian orogenesis in the early palaeozoic no major structural or stratigraphical breaks have been identified and there is no direct evidence for the presence of two separate terranes

a cryptic caledonian flysch terrane in scotland a substantial part of the lower old red sandstone crawton group in the north east midland valley of scotland has a first cycle provenance from the south and east i e from a source block within the midland valley from the clast assemblages in proximal conglomerates it is clear that this provenance comprised a flysch terrane cut by granodioritic and tonalitic plutons angular clasts of lithic arenite and metagreywacke derived from this cryptic flysch sequence show it to be distinct from a metasedimentary sequence which flanked the lower old red sandstone basin to the north and north east the basin must overlie or lie adjacent to a boundary between two quite different sedimentary assemblages petrographic examination and chemical analysis of the clasts show that the southerly cryptic succession includes an important mafic ultramanc provenance implying that ophiolitic source rocks may have originally contributed to it sr and nd isotopic compositions for the clasts establish that the midland valley flysch is isotopically unrelated to either southern uplands shales and greywackes or dalradian metasedimentary rocks the clasts have lower sr contents than either suite and sr isotopic compositions 87 sr 86 sr in the range 0 7099 0 7176 at 450 ma which are more radiogenic than the southern uplands but less radiogenic than the dalradian crustal residence ages t dm have a narrow range of 1 76 1 94 ga the mean of 1 87 0 06 ga compares with a mean residence age of 1 49 0 21 ga for southern uplands greywackes and shales mixing calculations demonstrate that the incorporation of young ophiolite derived basaltic detritus into the caledonian sedimentary mass can explain properties of the nd data previously attributed to a bimodal proterozoic provenance the distinct compositions of the southern uplands and midland valley flysch sediments suggest they originally tapped different parts of the laurentian margin and have subsequently been brought together structurally as displaced fore arc slivers the diverse isotopic compositions of outboard flysch terranes has implications for the nature of the sedimentary component incorporated in inboard magma suites

colonsay and islay a suspect terrane within the scottish caledonides colonsay and the western part of islay southern hebridean islands of scotland consist of unfossiliferous deformed low grade metasedimentary rocks which rest with sheared unconformity upon gneissic basement the area has a long history of investigation but its stratigraphic affinities have been a persistent problem the speculative assignment of the basement rocks to the lewisian has never been substantiated the age of the cover sequence remains unclear its deformation differs from that of nearby caledonian successions small igneous bodies have yielded a tentative intrusion age of ca 600 ma which is abnormal for the region because the area is bounded by major strike slip faults it is suggested that the colonsay western islay terrane is allochthonous probably emplaced between 620 and ca 540 ma the terrane concept explains the long standing difficulties of correlation recognition of suspect terranes even of this small size within orogens such as the orthotectonic caledonides can help resolve some long standing problems

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

gas hydrate crystals may help build reefs during a recent cruise in the porcupine basin off southwest ireland we discovered two extensive and hitherto largely unsuspected deep water reef provinces including a giant cluster of hundreds of buried mounds the ring shapes of many reefs suggest that they are caused by an axial fluid expulsion at the sea bed a transient flow well confined in space and time we are exploring various hypotheses but a stimulating avenue for research is opened by a glacially controlled growth pulse and subsequent decay of a shallow layer of gas hydrates as a methane buffer and probably indirectly as a ground for overlying biological communities

the isotopic and chemical evolution of mount st helens isotopic and major and trace element analysis of nine samples of eruptive products spanning the history of the mt st helens volcano suggest three different episodes 1 40 000 2500 years ago eruptions of dacite with end 5 esr 10 variable 18o 206pb 204pb 18 76 ca sr 60 rb ba 0 1 la yb 18 2 2500 1000 years ago eruptions of basalt andesite and dacite with end 4 to 8 esr 7 to 22 variable 18o thought to represent melting of differing mantle crust reservoirs 206pb 204pb 18 81 18 87 variable ca sr rb ba la yb and high zr 3 1000 years ago to present day eruptions of andesite and dacite with end 6 esr 13 18o 6 variable206pb 204pb ca sr 77 rb ba 0 1 la yb 11 none of the products exhibit eu anomalies and all are lree enriched there is a strong correlation between87sr 86sr and differentiation indices these data are interpreted in terms of a mantle heat source melting young crust bearing zircon and garnet but not feldspar followed by intrusion of this crustal reservoir by mantle derived magma which caused further crustal melting and contaminated the crustal magma system with mafic components since 1000 years ago all the eruptions have been from the same reservoir which has displayed a much more gradual re equilibration of pb isotopic compositions than other components suggesting that pb is being transported via a fluid phase the nd and sr isotopic compositions lie along the mantle array and suggest that the mantle underneath mt st helens is not as depleted as morb sources there is no indication of seawater involvement in the source region

corals on seamount peaks provide evidence of current acceleration over deep sea topography geological and physical studies of seamounts have suggested the existence of distinct deep sea habitats characterized by exposed rocky bottom and a unique current regime1 9 however few biological data have been collected for deep seamounts10 12 here we present some of the first quantitative observations of hard bottom non hydrothermal fauna in the deep sea these observations show that black corals antipatharians and horny corals gorgonians present on the slopes of a multi peaked seamount are more abundant near peaks compared with mid slope sites at corresponding depths on narrow peaks corals are most abundant on the crest whereas on wide peaks coral densities are highest at the edge of the crest the abundance of corals also increases on knobs and pinnacles physical models and observations2 4 9 13 15 together with our direct measurements suggest that the seamount topography affects the local current regime corals appear to benefit from flow acceleration and some of their patterns of distribution can be explained by current conditions these results suggest that suspension feeders have some potential as indicators of prevailing currents at deep hard bottom sites

fault associated seabed mounds carbonate knolls off western ireland and north west australia abstract groups of seabed mounds suspected to be modern carbonate knolls or bioherms have been located on reflection seismic data in the porcupine basin off western ireland and in the vulcan sub basin off north west australia the size of these mounds is impressive often being over 1 km across and over 100 m high in the porcupine basin they occur in water depths of 650 1000 m whereas in the vulcan sub basin they occur in water depths of 200 350 m shallow seabed coring in the porcupine basin has provided data on the age lithological composition and hydrocarbon concentrations in the upper 3 m layer of sediment both on and off the mounds in both basins the mounds occur close to faults which may provide conduits for upward migrating hydrocarbons the seepage of hydrocarbons is suspected to have caused local eutrophication or fertilization by providing nutrients to bacteria which in turn are part of the food chain for higher organisms the dominant organism in the porcupine basin examples appears to be the deep water coral lophelia sp whereas in the vulcan sub basin the mounds appear to be halimeda dominated

isotopic dating in metamorphic belts isotopic dating in metamorphic rocks is concerned with the timing of processes whose operation is controlled by continually changing physical conditions of these temperature has a pervasive influence and the use of physical models to elucidate the ways in which temperature is likely to vary is briefly reviewed the central concept of closure temperature is critically discussed and quantitative estimates for biotite and hornblende are evaluated in order to illustrate the factors which control closure temperatures and limit their application in practice the possibility of dating crystallization using minerals which crystallize below their respective closure temperatures is examined taking examples involving k ar rb sr sm nd and u pb analyses the indirect dating of metamorphism via structurally dated plutons is briefly considered and the problems of interpreting both discordant u pb zircon ages and rb sr whole rock isochrons in metamorphosed granites are discussed the value of near concordant zircon ages is emphasized the extent of isotopic equilibration during metamorphism specifically of sr isotopes in metasediments is shown not to be a simple function of metamorphic grade the flow of fluids produced by metamorphic reactions appears to be crucial and there is a potential for dating metamorphism using whole rock samples where such flow can he demonstrated independently the concluding discussion briefly examines existing data for the dalradian and indicates the potential for further progress using both well established and novel approaches

the highland border complex scotland a paradox resolved a previously inexplicable difference between the highland border complex scotland and its correlative in ireland the clew bay complex is that rocks of caradoc ashgill age occur only in the former we reject evidence from supposed chitinozoa for this dichotomy no sedimentary rocks of proven age younger than arenig occur in the highland border complex consequentially the stratigraphy must be totally recast and the exotic terrane model replaced by one in which a largely autochthonous highland border complex in stratigraphical continuity with the dalradian grampian terrane was overridden by the highland border ophiolite midland valley terrane tectonic models for se laurentia are thereby considerably simplified

modern deep water coral mounds north of little bahama bank criteria for recognition of deep water coral bioherms in the rock record abstract deep water ahermatypic coral mounds are present at water depths of 1 000 1 300 m on the lower slope north of little bahama bank the mounds are patchily distributed over a minimum area of 2 500 km2 and typically display 5 40 m of relief above the surrounding sea bottom a diverse benthic community exists on these apparently unlithified mounds including l 1 genera and 16 species of ahermatypic coral bathypsammia caryophyllia deltocyathus desmophyllum enallopsammia javania madrepora polymyces solenosmilia stephanocyathus and a previously undescribed genus alcyonaceans gorgonians antipatharians hydroids ophiuroids crinoids barnacles galatheid crabs polychaetes gastropods bivalves and sponges conspicuously absent from the coral fauna are lop elia and dendrophyllia common deep water corals in other parts of the atlantic radiocarbon dates on fresh coral and gorgonian fragments of 940 40 and 860 50 years indicate the mounds are at least in part recent and are probably actively forming today bored and stained corals date at around 22 10314c years b p which establishes a minimum age for these mounds we speculate that the mounds develop on sea floor perturbations in areas where strong bottom currents provide needed oxygen and nutrients to the fauna the mounds may have undergone multi stage evolution from colony to thicket to coppice to bank this evolution may be accomplished through the in situ contribution of skeletal material along with the baffling and trapping of fine grained carbonate sediment winnowed from adjacent areas by bottom currents if found in the rock record the coral mounds north of little bahama bank would probably be considered bioherms geologists should thus be aware that scleractinian bioherms are not uniquely shallow water in origin the distinction between ancient deep and shallow water coral buildups involves using multiple recognition criteria including 1 presence or absence of algae 2 diversity of corals 3 coral morphology and microstructure 4 abundance of planktonic benthonic components 5 microborings 6 surrounding litho and biofacies 7 stable isotopes of carbon and oxygen and 8 trace element geochemistry particularly sr and u concentrations the distinction between deep and shallow water bioherms is crucial to regional paleoenvironmental and stratigraphic interpretations

influence of benthic sediment transport on cold water coral bank morphology and growth the example of the darwin mounds north east atlantic the darwin mounds are small up to 70 m in diameter discrete cold water coral banks found at c 950 m water depth in the northern rockall trough north east atlantic formerly described in terms of their genesis the darwin mounds are re evaluated here in terms of mound growth processes based on 100 and 410 khz side scan sonar data the side scan sonar coverage is divided into a series of acoustic facies representing increasing current speed and sediment transport erosion from south to north pockmark facies mounds within depressions facies darwin mound facies stippled seabed facies and sand wave facies mound morphometric changes are quantified and show a south to north divergence from an inherited morphology reflecting the outline of coral colonized fluid escape structures to developed downstream elongated elevated mound forms it is postulated that increasing current speeds and bedload sand transport favour mound growth and development by a process of enhanced sand sedimentation within mounds due to current deceleration by frictional drag around coral colonies comparisons are made with similar growth processes attributed to comparably sized cold water coral mounds in the porcupine seabight offshore ireland

the moira mounds small cold water coral banks in the porcupine seabight ne atlantic part a an early stage growth phase for future coral carbonate mounds this paper presents a comprehensive overview of the moira mounds in the porcupine seabight combining a review of currently published material with new data and interpretations the moira mounds are circular to ovoid shaped individual or clustered coral banks referred to as scleractinian spaced cluster macroreefs located in the belgica carbonate mound province porcupine seabight west of ireland they are up to 10 m high and 20 to 35 m in diameter for the first time a map showing the complete extent and location of the moira mounds is published revealing 256 examples grouped into four areas mainly between 800 and 1100 m water depth rov groundtruthing revealed the importance of bedload sand transport in moira mound formation and development processes through sediment entrapment by coral frameworks lophelia pertusa and madrepora oculata new estimated growth rates for the moira mounds are comparable to those measured for much larger irish coral carbonate mounds but an order of magnitude lower than rates from comparably sized reefs offshore norway as well as the framework corals 26 macrobenthic invertebrate species were identified from a single box core that were similar to those communities found in adjacent off mound habitats it is proposed that the moira mounds are an example of the early stage growth phase of nearby giant coral carbonate mounds and represent a westward extension of the zone of active cold water coral mound growth and therefore a deepening of the zone of cold water coral growth over recent climate cycles

recirculating components to the deep boundary current of the northern north atlantic abstract the meridional overturning system of the north atlantic is conventionally thought of as transporting warm water 4 c to high latitudes and covd water to low latitudes the northern cold water sources for this system are dense overflow from the nordic seas and less dense water from the labrador sea lsw the overflow components are carried westward by a deep northern boundary current dnbc that is shown here actually to begin southeast of the overflow regions the dnbc lies along the southern side of a system of islands and submarine ridges that divides the nordic seas from the subpolar basins the overflows act to increase the transport of the dnbc and this transport is further increased through the entrainment of warm waters once inside the labrador sea the dnbc is joined by lsw before continuing south to low latitudes as a cold deep western boundary current dwbc however published transport estimates are larger than can be explained by warm water entrainment alone thus indicating entrainment also of recirculating cold components the subject of this paper their sources are shown to be the lsw and cold abyssal waters originating from the southern hemisphere the lsw is entrained downward into the denser part of the dnbc and laterally into the upper part of the dwbc whereas the cold abyssal waters are supplied by an eastern intensified northward flow in the eastern atlantic that serves as the initial source of the dnbc and by a similar northward flow in the western atlantic the meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system the cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin but their influence in the northwestern atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the newfoundland and labrador basins this influence is detected by a deep silicate maximum extending poleward from the mid latitude western atlantic through the two gyres with eastern concentration and recirculating back diluted toward the south in the dwbc within the respective basins such a maximum also extends northward through the irminger basin into the dnbc but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin or if it comes from the mid latitude eastern basin by way of westward flow through the charlie gibbs fracture zone it is perhaps consequence of both estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north

sediment magnetic signature of climate in modern loessic soils from the great plains our magnetic analysis of 40 modern loessic soil profiles from the midwestern united states shows that the upper soil horizons of all sites are characterized by an increase in the concentration of fine grained do0 1mm ferrimagnetic minerals magnetite and or maghemite our sites were selected from stable upland positions along a precipitation gradient extending from sw nebraska mean ann precip o500 mm yr to central missouri mean ann precip 41000 mm yr changes in magnetic remanence parameters irm arm and magnetic susceptibility w between soil and parent material vary systematically along the transect and are likely to reflect changes in source area and transport distance magnetic enhancement is calculated for several magnetic parameters by taking the ratio menhanced mparent material where m stands for either arm irm or w our analyses show that magnetic enhancement of modern soils based on irm and w correlates with changes in mean annual precipitation the best correlation however is observed when arm is used as a proxy of magnetic enhancement which might reflect the bias of arm towards small single domain grains of likely pedogenic origin our study shows that magnetic soil properties in combination with non magnetic proxies such as solum depth b horizon color depth to carbonates or other weathering indices have the potential to yield reliable reconstructions of paleoclimate in parts of the great plains where well preserved loessic paleosols exist

uplift patterns and orogenic evolution in the scottish dalradian rb sr and k ar mineral ages from the dalradian rocks of angus and perthshire indicate considerable diachronism of cooling following the caledonian regional metamorphism the oldest mineral ages 515 ma are similar to the independent estimates of peak metamorphic age and hence indicate very rapid cooling they occur in the highest grade samples of the angus region and are associated with localized uplift regional rapid uplift events at 460 440 ma and 410 390 ma may also be recognized and correlated with structural and igneous activity and metamorphic age dates within the scottish highlands thermal models show the importance of localized and discontinuous uplift in determining both the timing of metamorphism and the shape of the p t paths they suggest that the major diachronous metamorphism and granite production in the scottish highlands is depth controlled rather than representing major lateral diachronism of thickening or heat sources localized uplift may exercise considerable control on mineral facies variation within orogenic belts the local uplift in angus introduces hot high pressure tarfside nappe rocks into higher level tay nappe rocks thus the uniform block uplift models frequently used in the interpretation of metamorphic and structural phenomena in orogenic belts are an oversimplification of the real events