data driven modeling of multiple longshore bars and their interactions abstract long term bathymetric surveys at a coastal segment of the southern baltic coast were investigated with empirical orthogonal functions eof to determine the characteristic evolution patterns of multiple longshore bars and with canonical correlation analysis cca to evaluate the importance of interactions among them the investigated beach is located at lubiatowo on the polish coast and is mildly sloping with multiple usually four bars and a median grain size of 0 22 mm being typical for the coast in the southern baltic sea data on bed topography have been collected at lubiatowo since 1987 predominantly twice a year to record changes in the seabed along 27 lines covering a longshore cross shore area of 2600 m 1000 m the eof analysis revealed three persistent long term cross shore patterns accounting for about 2 3 of the overall signal variance and describing key elements of the evolution of multiple bars moreover it detected subsystems of two inner and outer bars the cca study demonstrated that more that 60 of the evolution of inner bars can be explained by the variability of outer bars the two subsystems thus display significant interactions they can be largely attributed to vertical variations of the whole nearshore zone expressed through changes in the equilibrium dean type profiles such changes can only be produced by large scale phenomena e g sequences of extreme events affecting the whole nearshore topography hence part of the variability of inner bars not related to the evolution of outer bars should stem from changes occurring during calm periods when small waves pass over outer bars unaffected the paper demonstrates usefulness of the cca method in coastal engineering and a more general strategy of data driven investigations with more than one method in order to make use of synergy generated with such a complex approach the benefit of such a synergy is that results from both investigations can be critically intercompared so more accurate joint interpretations become feasible

use of numerical models to study land based sedimentation and subsequent nearshore morphological evolution a beach sedimentation problem is presented this problem involves assessing the impact and importance of land based sediment sources erosion from gullies during intense rainfall and directly from cliffs by wave action on morphodynamic changes at a beach the site motivating the study is la barrosa beach spain the location is described and a discussion of possible approaches presented a schematized representation of a gully and beach is used a hybrid approach is adopted in which sediment deposition by run off and to a lesser extent cliff erosion is modelled using wave resolving hydrodynamic models it is found that significant amounts of sediment can be supplied by gully run off during storms for small run offs the swash can be involved in determining the region of deposition within the gully area with longer period motions favouring increased sediment deposition at gully sides simulations also show that swash motions can erode gully sides and the presence of a cross shore jet associated with the swash and gullies can also impact on sediment movement longer term wave averaged morphodynamic modelling without a swash zone indicates that run off deposits subsequently diffuse laterally whether under normal or oblique incidence these simulations also reveal the possibility of underlying crescentic bar shedding dynamics that may pertain during changes of wave conditions

palaeoseismology review of the state of the art abstract historical seismicity provides only a partial indication of the seismotectonic character i e earthquake potential of a given region even in italy where a relatively long historical record exists available catalogues are generally unsatisfactory for this purpose fortunately strong earthquakes often leave geological evidence herein referred to as seismites that are mainly related to surface faulting folding or other deformation and occasionally to secondary ground failures e g landslides liquefaction features etc these features may be preserved and therefore palaeoseismological studies may detect and date them thereby permitting extension of knowledge beyond the local historical threshold up to 2000 years in the most fortunate cases this paper provides a summary of criteria which may aid in the identification of areas suitable for palaeo earthquake investigation historical seismicity and the presence of well developed tectonic geomorphic features are recognized as the most reliable criteria for identifying active faulting however lack of these characteristics cannot be considered conclusive evidence for lack of activity palaeoseismological techniques aim at identifying not only the obvious effects of surface faulting such as offset of young geologic units but also the more subtle tectonic or non tectonic features including liquefaction structures gravity features and coseismic uplift and or subsidence finally we discuss some questions that pertain to palaeoseismicity evaluation techniques among these are the reliability of the quaternary dating techniques the evaluation of the seismic energy released minimum magnitude and principally the unequivocal identification of a seismic origin for the considered geological structures

tectonothermal evolution of the mayuan assemblage in the cathaysia block implications for neoproterozoic collision related assembly of the south china craton the mayuan assemblage in the cathaysia block southeast china consists of felsic paragneiss pelitic schist greenschist amphibolite marble calcsilicate and quartzite that underwent three episodes of deformation d1 d3 and four episodes of metamorphism m1 m4 in the early neoproterozoic the m1 assemblage consists of mineral inclusions defining an early foliation s1 within porphyroblasts represented by chlorite muscovite biotite plagioclase quartz in pelitic schist and actinolite chlorite epidote albite quartz enclosed in amphibolite m2 coincides with the development of the regional schistosity s2 and represents the formation of the porphyroblasts and growth of matrix minerals resulting in development of prograde metamorphic zones chlorite biotite garnet staurolite and kyanite zones m3 is simultaneous with the third phase of deformation d3 and produced sillimanite bearing mineral assemblages in pelitic schist and hornblende bearing assemblages in amphibo lite the last metamorphic episode m4 gave rise to the retrogressive assemblage chlorite muscovite in pelitic rock and actinolite chlorite epidote in amphibolite the sequence of mineral assemblages and history of metamorphic reactions built from the petrogenetic grid of pelites suggest a near isothermal decompression clockwise p t path for the mayuan pelitic schists using the tweequ software program the garnet biotite thermometer and garnet muscovite biotite plagioclase barometer yield p t conditions for m1 of 5 5 to 6 0 kb and 450 to 500 c and conditions for the garnet staurolite and kyanite zones of m2 of 6 0 to 7 0 kb and 550 to 600 c 6 0 to 7 5 kb and 600 c and 11 0 to 11 5 kb and 600 c the p t conditions of m3 were estimated at 570 to 625 c and 4 0 to 4 5 kb using the muscovite biotite thermometer and hornblende plagioclase geothermo barometer the garnet chlorite thermometer yields temperatures of 300 to 400 c for m4 but the pressures of m4 cannot be quantitatively estimated because of the lack of a suitable geobarometer these p t estimates also define an near isothermal decompression clockwise p t path which is involved in initial crustal thickening followed by rapid exhumation and final cooling and is related to amalgamation of the cathaysia and yangtze blocks to form the south china craton

cambrian depositional history of the zanskar valley region of the indian himalaya tectonic implications a well preserved cambrian section in the zanskar valley of northern india has previously been interpreted to record the transition from a passive to an active tectonic margin related to cambrian ordovician orogenesis this interpretation has been used to support the tectonostratigraphic interpretation of other successions across the tethyan himalaya our detailed paleoenvironmental analysis significantly revises the tectonic and depositional history of these cambrian deposits no definitive record of impending cambrian ordovician orogenesis is recorded in these late middle cambrian rocks a critical transition from an 125 m thick stromatolite bearing carbonate deposit the karsha formation into shale and sandstone of the kurgiakh formation was interpreted to represent tectonically induced drowning of a carbonate platform siliciclastic strata of the kurgiakh formation were thought to record deep water flysch deposition in a tectonically active foreland basin next to an arc trench system this interpretation was based on sandstone beds with classic bouma sequences we show that these event beds in the kurgiakh instead contain hummocky cross stratification quasi planar lamination and combined flow ripple stratification all of which reflect deposition in shallow marine storm influenced environments thus although the karsha carbonate platform may have been drowned it did not culminate in deep sea flysch deposition and this in turn eliminates a major line of evidence linking kurgiakh deposition to the onset of cambrian ordovician orogenesis other aspects of cambrian ordovician deposits of northern india also shed doubt on the proposed link between kurgiakh sedimentation and the cambrian ordovician orogenic event first our improved biostratigraphic database suggests that the transition from the karsha carbonate to the kurgiakh formation may have predated the main phase of cambrian ordovician orogenesis as recorded by overlying ordovician molasse by as much as 20 30 my second published data from the ordovician molasse indicate northward paleocurrents which are parallel to those recorded by siliciclastic deposits of the parahio formation below the karsha and thus are at odds with standard models of foreland basin development for the cambrian ordovician event our sedimentological analysis of depositional cycles of the parahio formation indicates that these strata record storm influenced environments from offshore marine to shoreface to fluvial settings this is at odds with previous paleoenvironmental interpretations that ranged from deep sea flysch to intertidal deposits paleocurrent data for marine and fluvial facies of the parahio formation in both zanskar and the spiti valley to the south indicate northeast sediment transport this supports the view that the parahio and overlying carbonate of the karsha formation record the ancient northern passive margin of india during the cambrian and that these strata may be distal equivalents of the younger cambrian deposits of the lesser himalaya

separation of u pb lu and hf from single zircons for combined u pb dating and hf isotope measurements by tims and mc icpms abstract the u pb system has long been used to precisely date zircons because the high u to common pb ratio in zircon produces very radiogenic pb isotope compositions over time in contrast to u pb zircon has very low lu hf and therefore unradiogenic hf making this mineral ideally suited for determining the initial hf composition of its original host rock a new chemical separation technique presented here enables the determination of both u pb age and initial hf isotope composition of individual zircon grains the acquisition of such complementary information for single detrital zircons is especially useful for provenance analyses and crustal growth studies zircons are spiked with mixed 176 lu 180 hf and 233 u 205 pb tracers and then digested in hf hno 3 lead lu u and hf are sequentially separated from the zircon matrix on a single ion exchange column filled with eichrom ln spec resin using only 100 l of resin for the separation keeps pb blanks low 5 pg while achieving better than 90 yields for each of the four elements hafnium isotope compositions and lu concentrations are measured with multiple collector inductively coupled plasma mass spectrometry mc icpms whereas u and pb are analyzed by thermal ionization mass spectrometry tims the minimum grain size that can be processed is dictated by the amounts of pb and hf needed for an analysis the smallest grains we currently analyze as small as 50 m 12pg of pb and 3ng of hf can be analyzed with an external 176 hf 177 hf precision of 100 ppm 2 s d the utility of this method is demonstrated with a population of detrital zircons from a cambrian sediment of the takaka terrane new zealand in addition the technique has been used for 14 analyses of the standard zircon 91500 which yield a mean present day 176 hf 177 hf of 0 282305 12 2 s d i e an external reproducibility of 43 ppm the hf isotopic compositions and u pb ages presented here are in good agreement with those of previous studies e g wiedenbeck m alle p corfu f griffin w l meier m oberli f von quadt a roddick j c spiegel w 1995 three natural zircon standards for u th pb lu hf trace element and ree analyses geostandards newsletter 19 1 23 but our data suggest that the 91500 zircon is heterogeneous with respect to lu and hf contents and lu hf

nourishing the shoreface observations and hindcasting of the egmond case the netherlands abstract although beach nourishment policy in the netherlands is generally successful in maintaining the 1990 shoreline the efficiency of nourishments at several locations along the north sea coast is unacceptably low these locations are identified as erosion hotspots egmond aan zee is such a hotspot the bathymetric longshore irregularities make this coastal stretch highly susceptible to rip currents and horizontal circulations which transport large volumes of nourished sand to the sea in 1999 an alternative nourishment design was implemented this consisted of a shoreface nourishment at the outer bar at 7 5 m depth combined with a nourishment of the beach behind it high resolution bathymetric surveys carried out with the wesp revealed that the shoreface nourishment resulted in a significant shoreward migration of the outer bar during 1999 2001 after 2 years the system started to return to its natural dynamic equilibrium and lost the positive influence of the shoreface nourishment area shoreward movement of bars and increase of bar height which forms the first defense line of the mainland against the sea and positive contribution to the sand budget which increased as a result of the nourishment after 3 years may 1999 to april 2002 the sediment volume still had an increase of 477 500 m3 45 of the applied sand relative to may 1999 the shoreface nourishment area did not have a direct effect on the beach the shoreface nourishment area probably will have to be maintained to retain the sediment on the beach in the long run in egmond the shoreface nourishment started to disappear before the sediment could reach the beach the time scale of sediment feed to the beach zone probably is of the order of 5 10 years the shoreface nourishment seems to function as a reef creating a lee side effect that influences both cross shore and longshore sediment transport resulting in two main hypotheses firstly the longshore effect in which large waves break at the shoreface nourishment cause a calmer wave climate shoreward of the shoreface nourishment area and a reduction of the longshore current the shoreface nourishment partially blocks the wave driven longshore current secondly the cross shore effect in which shoaling waves generate onshore transport these hypotheses are supported by generated model results with both a process based profile model unibest tc and a process based coastal area model delft3d mor the unibest tc model was able to predict the detachment of the outer bar from the shoreface nourishment and to some extent the shoreward bar movements in the lee of the shoreface nourishment area the model found an increase in sediment confirming the shielding effect of the shoreface nourishment area the delft3d model found as a result of the shoreface nourishment area a decrease of the flow velocity and the wave height just shoreward of the shoreface nourishment area the model was able to predict the similar trend in sedimentation erosion pattern although the intensities were smaller in the lee of the shoreface nourishment area a clear sedimentation was found erosion was found south and seaward of the shoreface nourishment area the modeled profiles did not follow the measured profile changes the separation of the shoreface nourishment from the outer bar and the shoreward migration of the bars could not be accurately modeled because the cross shore transport caused by wave asymmetry is not taken into account in the standard version of delft3d these results were in line with the expectations

initiation of crustal scale thrusts triggered by metamorphic reactions at depth insights from a comparison between the himalayas and scandinavian caledonides active eclogitization has recently been inferred at depth beneath the himalaya from geophysical observations and the mechanical consequences of eclogitization can be observed in the field in the eroded and extended nappe stack of the scandinavian caledonides there proterozoic metastable granulites and igneous protoliths underwent partial eclogitization during the collision of baltica with laurentia the reaction began in pseudotachylites and veins and eventually formed a connected network of eclogite facies shear zones that localized deformation and weakened the lower crust of baltica during the collision with laurentia all these features can be compared with the seismic activity of the indian lower crust its strength loss beneath the himalayan ranges and its delayed density increase regarding its penetration in the eclogite facies the caledonian bergen arc eclogites and the himalayan ama drime eclogites are both derived from continental crust in both cases these eclogites were formed contemporaneously with the activation of the main thrusts responsible for the construction of the orogenic wedges the main central thrust in the himalayas and the main thrust below the jotun nappe complex in the caledonides the similarities in these two orogens which compare both in size and structure highlight the importance of eclogitization at depth as a mechanism for weakening of the lower crust and for decoupling of the crust and lithospheric mantle in collision zones

lower crustal granulite xenoliths from the pannonian basin hungary part 2 sr nd pb hf and o isotope evidence for formation of continental lower crust by tectonic emplacement of oceanic crust mafic granulite xenoliths from the lower crust of the pannonian basin are dominated by lree depleted bulk rock compositions many of these have morb like 143nd 144nd but 87sr 86sr is elevated relative to most morbs their 18o values cover a wide range from 3 8 to 9 5 a group of lree enriched mafic granulites have higher 87sr 86sr 0 704 0 708 and lower 143nd 144nd 0 5128 0 5124 with higher 18o values on average 7 8 to 10 6 than the lree depleted granulites the lree enriched granulites are however isotopically similar to newly discovered metasedimentary granulite xenoliths a sublinear correlation in ehf end isotope space has a shallower slope than the crust mantle array with the metasedimentary rocks forming the low ehf end member the radiogenic end is restricted to the lree depleted granulites and these overlap the field of morb pb isotopes for the lree depleted samples are less radiogenic on average than those of the lree enriched and metasedimentary xenoliths and metasedimentary granulites have consistently higher 208pb 204pb the wide range in 18o over a restricted range in nd and sr isotope values in combination with the predominance of lree depleted trace element compositions is consistent with an origin as a package of hydrothermally altered oceanic crust the existence of 18o values lower than average morb and or mantle peridotite requires that at least some of these rocks were hydrothermally altered at high temperature presumably in the oceanic lower crust the low 143nd 144nd of the lree enriched mafic granulites cannot be explained by simple mixing between a lree depleted melt and an enriched component represented by the recovered metasediments instead we interpret these rocks as the metamorphic equivalent of the shallowest levels of the ocean crust where pillow basalts are intimately intercalated with oceanic sediments a possible model is accretion of oceanic crustal slices during subduction and convergence followed by high grade metamorphism during the alpine orogeny

process based modelling of a shoreface nourishment abstract a state of the art process based model is applied to hindcast the morphological development of a shoreface nourishment along the barrier island of terschelling the netherlands the applied morphodynamic model is delft3d for fully three dimensional flow and sediment transport in coastal environments owing to a complex geomorphological setting of the study area the curvi linear model includes adjacent tidal inlets and covers 40 70 km with an increasing grid size resolution towards the nourishment site in the center of the island in 1993 a total of 2 mm3 of sand was supplied to the nearshore bar zone off terschelling filling up the trough between the middle and outer bar by spring 1994 most of the nourished sediment had been redistributed onshore and welded onto the middle bar where it remained in the following years the morphodynamic model is applied to the prediction of this rapid nearshore profile behaviour the calibration of the model against an extensive set of full scale hydrodynamic data at several locations throughout the nearshore bar zone shows a good representation of the measured hydrodynamics morphodynamic results show a dependency on spatial scale on the scale of precise bed level evolution with respect to bar migration and growth model predictions are poor as the nearshore bars are predicted to flatten out resorting to bulk volumes integrated over larger spatial scales the model clearly has skill in predicting the overall effects of the nourishment the lack of phase shift between sediment transport and bathymetry is identified as the key controlling factor for the poor sandbar predictions

medium term 2dh coastal area modelling the state of the art in depth averaged mathematical modelling of 3 d coastal morphology is described for the medium term morphodynamic model type in which constituent models of waves currents and sediment transport based on first physical principles are linked together to describe the time evolution of the bed topography various aspects of the combined system of equations are discussed such as its mathematical character its inherent stability and its equilibrium state the results of an intercomparison of different models are shown for two test cases and the potentials and limitations of the model concept are discussed

geochronology and petrogenesis of pan african syn tectonic s type and post tectonic a type granite namibia products of melting of crustal sources fractional crystallization and wall rock entrainment abstract the oetmoed granite migmatite complex ogmc central damara orogen namibia consists mainly of 526 to 516 ma garnet and cordierite bearing granite and subordinate 488 to 494 ma hornblende and titanite bearing granite in the form of planar sheets and dykes additionally a slightly elongated granite body occurs in the center of the complex the garnet and cordierite bearing granite has major and trace element characteristics of s type granite but the hornblende and titanite bearing granite has higher hfse and ree contents similar to a type granite whereas the garnet and cordierite bearing granite contains numerous restitic xenoliths the hornblende and titanite bearing granite is xenolith free the country rocks are cordierite sillimanite k feldspar garnet bearing metasedimentary rocks and migmatite cordierite and garnet rich xenoliths in the s type granite do not represent primary restite their depleted chemical composition is best explained by varying and large degrees of partial melting of incorporated country rocks most chemical variations among the garnet and cordierite bearing granite can be explained by processes linked with fractional crystallization of plagioclase biotite and accessory phases mostly monazite and zircon major and trace element data and high 18 o values suggest that the least evolved members of the garnet and cordierite bearing granite were derived from metapelitic rocks at ca 800 c as inferred from monazite and apatite dissolution thermometry higher cao and na2o but lower sio2 contents and lower rb sr ratios as well as lower 18 o values of the hornblende and titanite bearing granite suggest that they are more likely generated by partial melting of non pelitic sources metagranitoids at temperatures in excess of 900 c decreasing tio2 na2o feotot mgo cao total ree content but increasing al2o3 and k2o indicate fractionation of mainly hornblende and titanite in the case of the hornblende and titanite bearing granite the differing compositions of the garnet and cordierite bearing granite and the hornblende and titanite bearing granite are attributed to different source rocks metapelite instead of metagranitoid and different temperatures during melting as inferred from accessory phase dissolution thermometry furthermore significant entrainment of country rock in some samples played a major role during petrogenesis of the garnet and cordierite bearing granite but was not important during the evolution of the hornblende and titanite bearing granite intrusion of such hot felsic magmas close to the inferred peak of metamorphism has probably caused in part the high temperature metamorphism and anatexis of the country rocks at relatively low pressures

u pb and 40ar 39ar geochronology of the baiyunshan gneiss central guangdong south china constraints on the timing of early palaeozoic and mesozoic tectonothermal events in the wuyun wuyi yunkai orogen composite sensitive high resolution ion microprobe shrimp u pb zircon and 40 ar 39 ar step heating biotite hornblende ages are used to provide constraints on the timing and origin of the felsic gneissic rocks in the baiyunshan mountains region and to elucidate their tectonothermal history shrimp dating and cl imaging of zircons give magmatic zircon crystallization ages between late ordovician and early silurian c 453 5 ma 446 ma and 439 ma for three representative felsic gneisses suggesting that most of the baiyunshan gneiss cannot represent basement rocks of the cathaysia block as previously thought including the present age information a synthesis of available age data for regional wuyun wuyi yunkai events reflects the emergence of orogen wide magmatism that could be syn orogenic and have occurred mainly between 460 and 420 ma in the south china block inherited zircons are abundant with ages clustering at late mesoproterozoic 1189 1017 ma and middle mesoproterozoic 772 ma which reveals that the baiyunshan orthogneiss samples a crustal basement containing significant igneous or recycled components related to the rodinia amalgamation and break up a shrimp date of 212 12 ma from a white rim of zircon provides evidence for metamorphic overprinting of an indosinian tectonothermal event on the baiyunshan gneiss incremental heating experiments with six biotite samples and one hornblende sample from a variety of metamorphic rocks yielded two distinct 40 ar 39 ar age groups 150 155 and 94 98 ma the older ages are similar to zircon u pb dates for widespread granitic intrusions in central guangdong we attribute them to late jurassic magmatism induced thermal resetting of the biotite k ar system on the other hand the younger age group is interpreted to record either cooling through the biotite closure temperature of 300 350 c or a second resetting of biotite ar isotopes at c 94 98 ma due to contemporaneous magmatic activity our present age data suggest that the maofengshan orthogneiss was exhumed to 8 to 10 km crustal levels at c 150 ma whereas the eastward components of gneissic rock masses appear to have passed upward through the same crustal depth synchronously or later by c 94 ma exhumation of middle crustal level rocks in the study area since c 155 ma is roughly coeval with exhumation of gneissic rocks from elsewhere in the wuyun orogen suggesting a large scale mechanism for the exhumation pulse related to the yanshanian extensional tectonic regime

a hybrid origin for lachlan s type granites the murrumbidgee batholith example the murrumbidgee batholith is typical of other composite s type granite batholiths in the lachlan fold belt lfb of southeastern australia consisting of discrete peraluminous cogenetic granite suites however it contains a unique suite murrumbucka at its southern extremity that has chemical and petrological features transitional with metaluminous i type granites previous detailed structural and metamorphic studies have shown that the batholith is tilted northward exposing subvolcanic plutons in the north and root zones in the south originally located at depths of not vert similar10 km a transition from mafic foliated sheet like granites in the south to felsic generally less foliated homogeneous granites in the north is consistent with magma ascent via subvertical structurally controlled sheets to emplacement in an overlying magma chamber in the inferred root zones the murrumbucka suite hosts migmatitic metasedimentary and gabbroic rocks both of which have transitional contacts and show evidence for mafic felsic interaction with the murrumbucka suite the migmatites extend southward to become part of the high t low p cooma metamorphic complex which contains a core of heterogeneous remobilised diatexitic granite cooma suite lenses of which also occur throughout the southern deeper parts of the murrumbidgee batholith the composition of the most mafic rocks from the batholith lies on a chemical tie line between cooma suite granites and the gabbros for almost all elements this chemical coincidence is interpreted to reflect derivation of parental murrumbidgee s type granite magmas by bulk mixing between a felsic crustal and mafic mantle derived component consistent with sr and nd isotopic results and field observations based on the tie lines and simple numerical modelling the murrumbucka suite is estimated to be a 50 50 mix of mantle and crustal derived magmas whereas the more peraluminous and widespread clear range suite which is very typical of lachlan s type granites is modelled as a 40 60 mix chemical variation trends diverge from the mixing lines and suggest that much of the fractionation process operated after mixing mixing occurred within sheets during the ascent of the magmas whereas fractionation was the dominant process generating chemical diversity during emplacement in the magma chamber generation of the s type granites probably occurred in an extensional tectonic environment

beach face evolution in the swash zone we investigate swash on an erodible beach using the one dimensional shallow water equations fully coupled to a bed evolution exner equation in particular the dam break bore collapse initial condition of shen meyer j fluid mech vol 16 1963 pp 113 125 and peregrine williams j fluid mech vol 440 2001 pp 391 399 is investigated using a numerical model based on the method of characteristics a sediment transport formula cubic in velocity u au 3 is used here this belongs to a family of sediment transport formulae for which pritchard hogg coastal engng vol 52 2005 pp 1 23 showed that net sediment transport under the shen meyer 1963 bore collapse is offshore throughout the swash zone when a non erodible bed is considered it is found that full coupling with the beach although still resulting in the net offshore transport of sediment throughout the swash zone leads to a large reduction in the net offshore transport of sediment from the beach face this is particularly true for the upper third of the swash zone moreover in contradistinction to swash flows over non erodible beds flows over erodible beaches are unique to the bed mobility and porosity under consideration this has very important implications for run up predictions the conclusion is that it is essential to consider full coupling of water and bed motions i e full morphodynamics in order to understand and predict sediment transport in the swash regardless of other physical effects e g turbulence infiltration pre suspended sediment etc

structural development of the lower paleozoic belt of south china genesis of an intracontinental orogen abstract an extensive structural study of wuyishan and surrounding areas south china brings data on the structures formed prior to the devonian unconformity building the lower paleozoic belt an ordovician tectonic event was responsible for i south directed structures in the wuyishan proper and its southern border related to both thin and thick skinned tectonics accompanied by metamorphism and crustal thickening ii north directed structures to the west of ganjiang fault and north of jiangshan shaoxing fault where only thin skinned tectonics is visible the southward deformation accommodating the shortening includes emplacement of thrust sheets involving deep crustal material and some mantle peridotite and likely repetition of continental material both responsible for crustal thickening the orogeny was due to the underthrusting of the southern part of the south china block beneath the northern part of this block closing the pre existing nanhua rift created at around 850 800 ma and involving the rift sedimentary fill in the southward thrusting the syn metamorphic tectonic piling was followed by anatexis and granite emplacement at around 440 390 ma our new u th pb epma monazite dating gives ages of 433 9 ma and 437 5 ma early silurian for the main anatectic event and a younger age of 412 5 ma late silurian early devonian for a late re heating process the lower paleozoic belt is an intracontinental orogen without oceanic suture record it shows some similarities with the cenozoic european pyrenees chain with a strong asymmetry

are strongly peraluminous magmas derived from pelitic sedimentary sources igneous compositions that require the presence of a phase more aluminous than biotite are here designated as strongly peraluminous ps such compositions are common but subordinate in felsic rocks and exceedingly rare in more mafic rocks the term s type has been applied to many igneous rocks based largely or even solely upon their ps compositions neglecting or placing less emphasis on other criteria for sedimentary parentage in chappell and white s i and s type classification system the s type designation was in fact initially restricted to granites which were thought to have been derived from a chemically mature strongly weathered pelitic shaly source application of chappell s and white s criteria together with others based upon isotopic and phase equilibria considerations leads to the following conclusions about ps igneous rocks worldwide 1 very few ps rocks are derived entirely from pelitic sources 2 a majority are derived largely from intermediate to felsic crustal sources including

a mechanism for the generation of wave driven rhythmic patterns in the surf zone the coupling between topographic irregularities and wave driven mean water motion in the surf zone is examined this coupling occurs because the topographic perturbations produce excess gradients in the wave radiation stress that cause a steady circulation this circulation in turn creates a sediment transport pattern that can reinforce the bottom disturbance and may thereby lead to the growth of large scale bed forms to investigate this coupling mechanism the linearized stability problem with an originally plane sloping beach and normal wave incidence is solved in two different cases first the breaking line is considered to be fixed and second the perturbations in water depth that produce a displacement of the breaker line are accounted for the first case shows that the basic topography can be unstable with respect to two different modes a giant cusp pattern with shore attached transverse bars that extend across the whole surf zone and a crescentic pattern with alternate shoals and pools at both sides of the breaking line showing a mirroring effect in the second case the varying breaker line may have a strong influence on the circulation this is clear for the giant cusp topography whose growth is totally inhibited in contrast the morphology and the growth of the crescentic pattern remains almost unchanged

causes and consequences of protracted melting of the mid crust exposed in the north himalayan antiform gneiss domes exposed by the north himalayan antiform in southern tibet provide evidence for protracted melting of the mid crust during convergent tectonics anatexis was initiated during underthrusting and recurred during the southwards extrusion of a low viscosity crustal sheet sr nd isotope systematics establish that the cores of the domes dominated by cambrian gneiss form a window of the high himalayan crystalline series hhcs indian plate combined trace element and isotopic analyses from 4 two mica granites that intrude both core and the metasedimentary mantle of the domes indicate an origin from melting of the high himalayan crystalline series by the incongruent breakdown of muscovite and to a lesser extent biotite at temperatures from 680 to 760 c u pb dating of accessory phases extends the known period of granite magmatism from the late oligocene to mid miocene a ca rich garnet bearing leucogranite of oligocene age 27 5 ma provides a rare insight into the pre miocene history of the underthrust indian plate reflecting prograde melting at greater depths during a period of crustal thickening the origin of the miocene granites 15 10 ma can be modeled from the exhumation of an extruding channel at a rate of ca 1 mm year constrained by ar isotope data melting over a protracted time scale along the leading edge of the indian plate less than 50 km from the suture accelerated horizontal shortening within the collision zone and provided a positive feedback mechanism between magmagenesis and deformation

source regions of granites and their links to tectonic environment examples from the western united states this review in honor of ilmari haapala s retirement reflects on lessons learned from studies of three granitic systems in western north america 1 mesoproterozoic samples from west texas and east new mexico 2 laramide granitic systems associated with porphyry copper deposits in arizona and 3 granites of the colorado mineral belt the studies elucidate relationships amongst tectonic setting source material and magma chemistry mesoproterozoic basement samples are from two different felsic suites with distinct elemental and isotopic compositions the first suite the plutonic province is dominantly magnesian calc alkalic to alkali calcic and metaluminous it has low k2o na2o and rb sr and nd model ages of 1 56 to 1 40 ga the second suite the panhandle igneous complex is magnesian metaluminous alkalic and is part of the mesoproterozoic belt of magmatism that extends from finland to southwestern united states samples from the panhandle igneous complex demonstrate three episodes of magmatism the first pulse was intrusion of quartz monzonite at 1380 to 1370 ma the second was comagmatic epizonal granite and rhyolite at 1360 to 1350 ma both of these rock types are high k to slightly ultra high k the third pulse at 1338 to 1330 ma was intrusion of ultra high k quartz syenite nd model ages 1 94 to 1 52 ga are distinct from those of the plutonic province and systematically older than crystallization ages implying a substantial crustal input to the magmas at the sierrita porphyry copper deposit in the mazatzal province of southeastern arizona trace element sr and nd isotopic compositions were determined for a suite of andesitic and rhyolitic rocks 67 ma intruded by granodiorite and granite isotopic composition and chemical evolution are well correlated throughout the suite andesite has the least negative initial end 4 3 and lowest 87sr 86sri 0 7069 it is also the oldest and chemically most primitive having low concentrations of rb sio2 and high concentrations of transition elements these parameters change through the system to the youngest unit granite which has the most negative end 8 5 the highest 87sr 86sri 0 7092 and is chemically most evolved correlation between chemical and nd isotopic evolution probably resulted from a continuous process of progressive assimilation in which mafic magmas invade and incorporate continental crust deposits in arizona with end values more negative than the 8 5 of sierrita lie in the older yavapai province in the northwestern part of the state the difference in the most negative epsilon nd implies that nd isotopic signature is sensitive to the age of the precambrian domain the granites from the colorado mineral belt were emplaced during the transition from laramide convergence to mid tertiary extension three different groups of granites are recognized the first is laramide and was formed during assimilation fractional crystallization involving lower crustal mafic source materials the second and third groups are mid tertiary and represent intracrustal melting of heterogeneous sources this change in source regions and melt regimes in transition from convergence to extension is fundamental to the mesozoic and cenozoic evolution of western north america

the development of small scale sandy alluvial fans at the base of a modern coastal cliff process observations and implications abstract the development of a series of small scale alluvial fans has been studied at the base of a sandy coastal cliff on the torre del loro beach near huelva southwestern spain these fans are small enough to permit the experimental modification of flow sediment load and morphology elongate sandy debris flow deposits are also present the fans are related to sources with perennial discharges and are fed by solitary shifting distributary channels the fans have radial morphologies and grow by localized lobe building at the intersection point in a mid fan or fan toe position and or by bulk aggradation due to overflow sheet flow sediment dispersal is by channelized or unconfined water flow but also involves slugs of hyperconcentrated flows and occasionally sandy debris flows the radial fans channelized flow dominated have surface slopes of up to 20 their medial segments are often the steepest and sediment at their toes and lateral flanks can be coarser than in the inner zones the elongated sandy debris flow deposits are related to sources with ephemeral discharges and are mass flow dominated these deposits are smaller and are built chiefly by sandflows finger like sandy debris flows their surface slopes are rather uniform but only up to 6 and there is no obvious downfan variation in grain size when regarded as small scale analogues for larger alluvial fans these fans deviate from the textbook models particularly in grain size distribution simultaneity of quiet and energetic processes and longitudinal gradient profile our study indicates that the relationship between fan morphometry and depositional processes still requires a better knowledge

crustal structure and contact relationship revealed from deep seismic sounding data in south china abstract a 400 km long wide angle seismic profile in the south china crosses three tectonic domains southeast continental margin of yangtze block northwest continental margin of cathaysia block and south china suture zone separating these two blocks the crustal velocity model constructed from traveltime fitting shows that the crust thickness thins from the northwest to the southeast along the profile it also reveals the crustal contact relationship between the yangtze and cathaysia blocks where the wuchuan sihui fault is the boundary between them combining this profile with two more profiles in the continental south china and three profiles in the northern margin of south china sea constructs a continent ocean transition section this cross section reveals that the moho depth shallows gradually along the cross section from the yangtze block to the cathaysia block and the northern margin of south china sea but shallows abruptly in the continent ocean transition to the south china sea

morphodynamic modelling of rip channel growth the morphological evolution of a rip channel system due to normally incident waves has been investigated using two different approaches the first approach is a state of the art commercial 2dh coastal area model whereas the second approach is a linear stability analysis the results of the two different approaches have been compared and both models predict rip channel spacings and initial growth rates of similar magnitudes

u pb and hf isotopic study of zircons from migmatised amphibolites in the cathaysia block implications for the early paleozoic peak tectonothermal event in southeastern china abstract amphibolites occur in a number of localities in the cathaysia block some of them have been migmatised and their protoliths represent basaltic magmas erupted in various tectonic settings four migmatised amphibolites were collected from jiangxi and fujian provinces cathodo luminescence images of zircons extracted from the representative amphibolites show unzoned or sector zoned structure la icp ms analysis indicates that most zircons have high th u ratios and yield u pb zircon ages of 446 5 435 2 434 4 and 423 2 ma respectively lu hf isotopic analysis on these zircons gives hf model ages ranging from 900 to 1200 ma based on lithological observations and previously published geochronological data we interpret that these u pb ages record an important tectonothermal event that led to the migmatization this early paleozoic caledonian tectonothermal event in the southeastern china has a great tectonic implication for the evolutionary history of the cathaysia block

self organization mechanisms for the formation of nearshore crescentic and transverse sand bars the formation and development of transverse and crescentic sand bars in the coastal marine environment has been investigated by means of a nonlinear numerical model based on the shallow water equations and on a simplified sediment transport parameterization by assuming normally approaching waves and a saturated surf zone rhythmic patterns develop from a planar slope where random perturbations of small amplitude have been superimposed two types of bedforms appear one is a crescentic bar pattern centred around the breakpoint and the other herein modelled for the first time is a transverse bar pattern the feedback mechanism related to the formation and development of the patterns can be explained by coupling the water and sediment conservation equations basically the waves stir up the sediment and keep it in suspension with a certain cross shore distribution of depth averaged concentration then a current flowing with against the gradient of sediment concentration produces erosion deposition it is shown that inside the surf zone these currents may occur due to the wave refraction and to the redistribution of wave breaking produced by the growing bedforms numerical simulations have been performed in order to understand the sensitivity of the pattern formation to the parameterization and to relate the hydro morphodynamic input conditions to which of the patterns develops it is suggested that crescentic bar growth would be favoured by high energy conditions and fine sediment while transverse bars would grow for milder waves and coarser sediment in intermediate conditions mixed patterns may occur

the effects of accretion erosion and radiogenic heat on the metamorphic evolution of collisional orogens petrological and thermochronological data provide our best record of the thermal structure of deeply eroded orogens and in principle might be used to relate the metamorphic structure of an orogen to its deformational history in this paper we present a two dimensional thermal model of collisional orogens that includes the processes of accretion and erosion to examine the p t evolution of rocks advected through the orogen calculated metamorphic patterns are similar to those observed in the field metamor phic temperatures depths and ages generally increase with distance from the toe of the orogen p t paths are anti clockwise with rocks heating during burial and early stages of unroofing followed by cooling during late stage unroofing the results indicate that peak metamorphic temperatures within the core of a collisional orogen and the distance from the toe of an orogen to the metamorphic core can be related to the relative rates of accretion erosion and plate convergence model orogens displaying high metamorphic temperatures 600 c are associated with low ratios of accretion rate to plate convergence velocity and with high heat flow through the foreland model orogens with metamorphic cores far from the toe of the orogen are associated with high ratios of accretion rate to erosion rate calculated metamor phic gradients mimic steady state geotherms and inverted thermal gradients can be preserved in the metamorphic record suggesting reconsideration of the concept that the metamorphic record does not closely reflect geothermal gradients within an orogen

on beach cusp formation a system of shallow water equations and a bed evolution equation are used to examine the evolution of perturbations on an erodible initially plane beach subject to normal wave incidence both a permeable under darcy s law and an impermeable beach are considered it is found that alongshore periodic morphological features reminiscent of swash beach cusps form after a number of incident wave periods on both beaches on the permeable impermeable beach these patterns are accretional erosional in both cases flow is horn divergent spacings of the cusps are consistent with observations and are close to those provided by a standing synchronous linear edge wave an analysis of the processes leading to bed change is presented two physical mechanisms are identified concentration gradient and flow divergence which are dominant in the lower and upper swash respectively and their difference over a wave cycle leads to erosion or deposition on an impermeable beach infiltration enters this balance in the upper swash a bed wave of elevation is shown to advance up the beach at the tip of the uprush with a smaller wave of depression on the backwash it is found that cusp horns can grow by a positive feedback mechanism stemming from decreased increased backwash on positive negative bed perturbations

an efficient solver for nearshore flows based on the waf method abstract we describe an efficient and robust flow solver for the integration of the classic nonlinear shallow water equations nswe on a beach of arbitrary topography on the basis of the shock capturing weighted average flux waf method a numerical code is implemented which employs a space splitting technique to integrate the nswe over a horizontally two dimensional domain 2dh special care is put in handling the moving shoreline and a new efficient formulation of the shoreline boundary conditions is presented this is based on the hydrodynamic equivalent of the cavitation condition used in gas dynamics model capabilities are illustrated by means of a number of tests both 1dh and 2dh these reveal that though primarily conceived for modelling nearshore hydrodynamics the solver can be successfully adopted even for studying the run up of large tsunami waves

extensional tectonics within a subduction type orogen the case study of the wugongshan dome jiangxi province southeastern china abstract in southeastern china the wugongshan massif consists of metamorphic rocks and granites generally considered as basement rocks formed during an early paleozoic orogeny our structural and radiometric reappraisal of this massif shows that it results from a mesozoic doming in the metamorphic rocks the foliation defines an e w elliptical shape and bears a n s stretching lineation the axial zone of the dome is occupied by oriented plutons the outer part of the dome consists of devonian quartzite carboniferous permian limestone and triassic jurassic sandstone ductile deformation observed in the permian carbonates and older units develops contrasting kinematics the northern and southern flanks present top to the north and top to the south motions respectively the same divergent pattern of motion is recorded from brittle structures up to the jurassic sandstone the late cretaceous red beds are undeformed in the axial zone coaxial flow indicated by symmetric pressure shadows and quartz fabrics predominates along the n and s flanks of the dome post folial recumbent folds are symmetrically overturned to the n and s respectively but at the two extremities of the dome the fold axes are parallel to the stretching lineation 40 ar 39 ar ages of biotite and muscovite from mylonite and granite suggest a late triassic age for the ductile deformation and an early cretaceous age for the final doming the wugongshan dome is similar to a metamorphic core complex formed in an extensional tectonic regime a model which emphasizes plutonism is discussed from permian to early cretaceous southeastern china was a subduction type orogen the crust of which was thickened by accretion of mantle derived magmas the emplacement of a large amount of mesozoic granitoids in southeastern china promoted thermal softening and gravitational instability that allowed the crust to extend the formation of the wugongshan dome and other metamorphic core complexes appears to be a the direct consequence of plutonic activity and crust rheology

partial melting of two amphibolites contrasting experimental results under fluid absent conditions a large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase as a consequence h2o undersaturated or fluid absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events in an attempt to determine the systematics of melting under fluid absent conditions a series of piston cylinder experiments was conducted on two natural amphibolites one a meta alkali basalt aba with a total water content of wt contained in hornblende and the other a meta island arc tholeiite iat which has 1 1 3 wt water contained in hornblende cummingtonite and biotite the experimentally determined melting ranges of the two amphibolites showed that the solidus temperatures and sta temperature interval over which amphibole was stable were controlled by the amphibolites different bulk compositions and their resulting metamorphic assemblages the volume of melt produced by melting of the two amphibolites were compared with estimated amounts based on burnham s 1979 water melt solubility model and the fluid absent melting model presented by clemens and vielzeuf 1987 the observed melt volumes were greater than estimated as the water content of melt largely detemines the volume of melt produced independent measurements of the water content of the glass formed during partial melting in the aba were made by thermogravimetric analyses the water content of the aba glass is 2 wt which is less than the assumed melt water content water content of the melt used in previous modeling of fluidabsent anatexis in mafic lithologies as a consequence more melt can be expected during fluid absent partial melting of mafic lower crust as is observed in the experiments a modification of the clemens and vielzeuf 1987 fluid absent melting model for mafic compositions has been made using the experimental data available on melting in basaltic systems and is presented here for pressures of 5 8 and 10 kbar tectonic scenarios in which the crust is thickened i e by collision then undergoes extension or where a previously thinned crust is later rethickened provide enough heat so that amphibolite melting under fluid absent conditions can become importan and hence responsible for some melts produced during post collisional magmatism the results may also have applications to melting in hydrated oceanic crust in subduction zones and in island arc terains

anatexis and metamorphism in tectonically thickened continental crust exemplified by the sevier hinterland western north america the generation of granitoid magmas by partial melting of crustal rocks during continental thickening events is well documented in many geological provinces throughout the world including the late mesozoic sevier belt of western north america we present a thermal and petrologic model of anatexis and metamorphism in regions of crustal thickening where the only mantle contribution is the normal conductive supply of heat through the base of the lithosphere i e advection of mass and energy are excluded we distinguish between formation of migmatites and generation of mobile granitoid magmas and examine the temporal and spatial relationships between these two distinct anatectic processes between anatexis and regional deformation and between anatexis and metamorphism a fundamental conclusion is that if protoliths rich in hydrous minerals are present regional anatexis is the end product of classical barrovian metamorphism in thickened continental crust even in the absence of a free water rich fluid phase barrovian metamorphic facies series are predicted with thickening ratios maximum crustal thickness attained initial crustal thickness as low as 1 3 but mobile granitoid magmas are not formed if this ratio is less than approximately 1 5 above these lower bounds barrovian metamorphism and anatectic granitoid magmatism occur independently of the magnitude of thickening and of the way in which thickening is accomplished both processes are sensitive to a diminished heat supply lowering either moho heat flow or crustal radioactive heat production results in blueschist eclogite metamorphism and inhibits the formation of mobile granitoid magmas we model anatexis under fluid absent conditions and show that with such a constraint migmatization is always a syn kinematic process relative to the crustal thickening event whereas generation of mobile granitoid magmas is in most cases post kinematic relative to crustal thickening but can be syn kinematic if thickening takes more than approximately 50 myr the typical time intervals for melting are consistent with geological observations mobile granitoid magmas are predicted by most of our models within approximately 10 myr of the end of the crustal thickening event this incubation period results primarily from the temperature increase required for the dehydration melting reactions capable of producing large melt fractions to occur the energetic requirements of anatexis are relatively minor compared to conductive crustal thermal budgets as shown by the fact that once the necessary p t conditions are attained melting reactions are completed within time intervals on the order of 1 myr i e 1 2 orders of magnitude smaller than the characteristic time scales of the tectonic processes involved in crustal thickening

relict proterozoic basement in the nanling mountains se china and its tectonothermal overprinting 1 the basement beneath the caledonian belt in se china has been overprinted by indosinian and yanshanian events and is poorly known in situ u pb and hf isotope analysis of zircons from granites and surrounding rocks in the nanling mountains area of the fold belt reveal that the lanhe felsic gneiss is an outcrop of mesoproterozoic basement probably with a partly late archean protolith this is consistent with nd model ages of granites in this region and exposures of cathaysia basement in the coastal area of se china in the nanling mountains this basement was reactivated to generate granitoid rocks during the caledonian indosinian and yanshanian tectonothermal events the caledonian overprint is documented in extensive exposures of the zhuguang migmatites 425 470 ma and by previous u pb zircon dating of adjacent granites the jiangnan granite may be of similar age but strongly reworked the indosinian overprint resulted in the formation of granites such as the luxi and xiazhuang bodies 233 246 ma in the guidong complex the yanshanian overprint produced the most widely distributed granites circa 160 ma such as the jiufeng and fogang bodies and parts of the guidong complex hf isotope data show that all of the phanerozoic magmatic rocks were derived from the mesoproterozoic basement and minor archean components without obvious contributions from juvenile sources the presence of zircons with archean age 2 5 2 7 ga in both the lanhe gneiss and devonian sediments indicates that the badu and mayuan groups may not be the oldest basement of the cathaysia block some archean basement circa 2 5 2 7 ga may still be exposed but unrecognized in this region and cathaysia may include archean microcontinental fragments

kwangsian crustal anatexis within the eastern south china block geochemical zircon u pb geochronological and hf isotopic fingerprints from the gneissoid granites of wugong and wuyi yunkai domains abstract gneissoid granites were traditionally thought to be the components of the precambrian basement in the eastern south china block but twenty four gneissoid granite samples from the wugong northern wuyi southern wuyi and yunkai domains gave zircon u pb ages of 424 456 ma 410 457 ma 426 438 ma and 415 450 ma respectively the existence of the abundant kwangsian gneissoid granites which have incorrectly been assigned to the precambrian basement indicates that the so called precambrian stratigraphic sequence of the cathaysia block should be termed complex rather than group these gneissoid granites are peraluminous granites with relatively high al 2 o 3 mgo tio 2 feot and cao na 2 o but low cao al 2 o 3 mgo feot and rb sr ratios they exhibit strongly negative ba sr nb p and ti and positive pb anomalies in primitive mantle normalized diagrams and have initial 87 sr 86 sr ratios ranging from 0 70924 to 0 72935 and negative end t values from 6 4 to 11 4 similar to those of paragneissic enclaves and precambrian sedimentary rocks in the eastern south china block the zircons crystallized in the kwangsian gneissoid granites gave ehf t values ranging from 2 4 to 19 4 with the peak at 4 almost all grains clustering at 1 to 12 and hf model ages of 1 1 2 1 ga the synthesis of these geochemical and in situ zircon hf isotopic data indicates that the kwangsian gneissoid granites dominantly originated from proterozoic metapelitic and meta igneous components with insignificant input of juvenile mantle derived magmas a model of two stage crustal anatexis is proposed for the kwangsian granitic magma in the eastern south china block with 1 the formation of 460 430 ma granite through the breakdown of hydrous minerals under the condition of the doubly thickened crust and 2 the generation of the 430 400 ma granite accompanying promoted melting along a path of isothermal decompression due to the increasing thermal weakening for the collapse of the thickened crust the crustal anatexis has probably occurred in an intracontinental tectonic regime that was geodynamically linked to the far field response to the assembly of the australian indian plate with the cathaysia block during middle paleozoic kwangsian time

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

modelling morphological processes in the vicinity of shore parallel breakwaters abstract a coastal area morphological modelling system is used to investigate the planform development tombolo or salient behind a single surface piercing detached breakwater a quasi three dimensional q3d description of the flow and the sediment transport together with a revised bed level update scheme were incorporated recently in the morphological modelling suite applied in the present investigation the q3d sediment transport formulation used allows simulating beach profile evolution and planform development simultaneously several breakwater layouts were investigated in a series of tests in which the incident wave condition was taken as constant in time the investigation was done for surface piercing shore parallel breakwaters in a non tidal environment the morphological simulation results for the planform shape agree qualitatively with field observations and predictions from empirical rules using the simulation results simple design curves for surface piercing breakwaters are derived the importance of properly accounting for the influence of wave diffraction when modelling sediment transport and morphology in the vicinity of shore parallel structures is also investigated the present paper summarises much of the work performed at dhi water environment over the past 10 years within the field of coastal area morphological modelling

investigation of a self organization model for beach cusp formation and development a recent numerical investigation of self organization werner and fink 1993 suggests that the feedback process between currents and sediment response can result in self organized patterns and can be used to predict beach cusp formation and spacing a similar model based on self organization is tested here in order to understand the processes occurring during beach cusp formation and development to evaluate the sensitivity toward the parameters used and to examine how the model might relate to field observations results obtained confirm the validity of the self organization approach and its capacity to predict beach cusp spacing with values in fair agreement with the available field measurements with most of the input parameters primarily affecting the rate of the process rather than the final spacing however changes in the random seed and runs for large numbers of swash cycles reveal a dynamical system with significant unpredictable behavior cusp spacing tends to change with time and cusp regularity shows large long term variations cusps are found to be accretionary in the swash zone and in agreement with most observations mean flows are horn divergent over developed topography simulations over nonplanar slopes characterized by the presence of preexisting nonrhythmic or cuspate features have been performed results indicate that preexisting large amplitude cusps are destroyed if their spacing is substantially different from that expected under self organization and that the final spacing is consistent with that predicted by the model for an equivalent plane beach these findings support the hypothesis that self organization is a robust mechanism for beach cusp formation

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

tectonics of south china key to understanding west pacific geology abstract south china is not a post caledonian platform but a composite of orogenic belts this late proterozoic mesozoic orogen is a collage of three continental fragments the three blocks are yangzi huanan and dongnanya and they are separated by the banxi nanpanjiang formerly xianggangzhe and gunanhai suture zones yangzi was separated from gondwanaland during late precambrian when an open ocean called banxi was present between the two continents tectonic processes at an active margin during sinian and early paleozoic time led to the genesis of an accretionary wedge complex the banxi melange and the huanan flysch nappes on the northern margin of huanan which was then the northern margin of the gondwana continent reorganization of plates during the devonian suspended subduction at the huanan active margin huanan was uplifted and unconformably overlain by transgressive deposits of devonian and or carboniferous age a remnant ocean the nanpanjiang sea still existed between yangzi and huanan and deep water sedimentation continued both at the southern margin of yangzi and at the northwestern margin of huanan the latter again became an active margin during late paleozoic when permian and triassic flysch sediments were deposited in foredeeps ahead of advancing nappes huanan and yangzi collided during the triassic and resulted in the deformation of the passive margin of the latter to form the yangzi deformed belt huanan was separated from a more southerly continent dongnanya in the devonian by seafloor spreading which created a late paleozoic and early mesozoic ocean gunanhai ocean a continuously deposited sequence ranging in age from devonian to triassic was laid down on the southern passive margin of huanan on the other side of the ocean the dongnanya permian strata include glacial marine deposits of gondwanaland affinity dongnanya became separated from gondwanaland during the late permian when it marched northward to be reunited with huanan the huanan passive margin sequence was deformed by folding and overthrusting after the late mesozoic collision of huanan and dongnanya scattered outcrops of the suture melange resulting from this collision occur at a few localities in coastal fujian dongnanya in our model was the mesozoic continent of southeast asia peripheral to mainland asia this may or may not have been the eastern continuation of the microcontinent sibumasu siam thailand burma malaysia sumatra the collision of dongnanya and asia gave rise not only to the gunanhai melange of coastal fujian but also to the ophiolite melanges parts of which are present in taiwan tailuko the philippines and western malaysia

early palaeozoic orogenesis along the indian margin of gondwana tectonic response to gondwana assembly abstract shrimp u pb dating of zircons from a peralkaline s type lesser himalayan granite from the kathmandu region nepal indicate an age of emplacement of 475 ma the granites along with metasedimentary xenoliths show a similar signature of inherited detrital zircon ages ranging from archaean to early palaeozoic with prominent late mesoproterozoic grenvillian and neoproterozoic pan african age peaks and have a maximum age of 500 ma based on the youngest detrital grains deformation structures in xenoliths are truncated by the granite and along with the granites are assigned to a cambro ordovician orogenic event herein termed the bhimphedian orogeny that can be traced across the himalaya from pakistan to the eastern himalaya and possibly extends west into afghanistan we interpret the orogeny as being related to andean type orogenic activity on the northern margin of the indian continent following gondwana assembly the magmatic arc was associated with andesitic and basaltic volcanism and was active from c 530 to 490 ma the arc activity overlaps with and is succeeded by regional deformation crustal melting and s type granite emplacement that extended to 470 ma orogenic activity was driven by coupling across the plate margin either during on going subduction or through accretion of microcontinental ribbons possibly represented by the lhasa and qiangtang blocks it represents the termination of an orogenic cycle termed the north indian orogen that commenced with neoproterozoic rifting and passive margin development and terminated with the bhimphedian orogeny this was succeeded by a return to passive margin setting along the northern indian margin of gondwana which continued until the cenozoic himalayan orogeny

a 2d numerical model of wave run up and overtopping a two dimensional 2d numerical model of wave run up and overtopping is presented the model called ott 2d is based on the 2d nonlinear shallow water nlsw equations on a sloping bed including bed shear stress these equations are solved using an upwind finite volume technique and a hierarchical cartesian adaptive mesh refinement amr algorithm the 2d nature of the model means that it can be used to simulate wave transformation run up overtopping and regeneration by obliquely incident and multi directional waves over alongshore inhomogeneous sea walls and complex submerged or surface piercing features the numerical technique used includes accurate shock modeling and uses no special shoreline tracking algorithm or shoreline coordinate transformation which means that noncontiguous flows and multiple shorelines can easily be simulated the adaptivity of the model ensures that only those parts of the flow that require higher resolution such as the region of the moving shoreline receive it resulting in a model with a high level of efficiency the model is shown to accurately reproduce analytical and benchmark numerical solutions existing wave flume and wave basin datasets are used to test the ability of the model to approximate 1d and 2d wave transformation run up and overtopping finally we study a 2d dataset of overtopping of random waves at off normal incidence to investigate overtopping of a sea wall by long crested waves the data set is interesting as it has not been studied in detail before and suggests that in some instances overtopping at an angle can lead to more flooding than at normal incidence

the origin of himalayan anatexis and inverted metamorphism models and constraints abstract the key to comprehending the tectonic evolution of the himalaya is to understand the relationships between large scale faulting anatexis and inverted metamorphism the great number and variety of mechanisms that have been proposed to explain some or all of these features reflects the fact that fundamental constraints on such models have been slow in coming recent developments most notably in geophysical imaging and geochronology have been key to coalescing the results of varied himalayan investigations into constraints with which to test proposed evolutionary models these models fall into four general types 1 the inverted metamorphic sequences within the footwall of the himalayan thrust and adjacent hanging wall anatexis are spatially and temporally related by thrusting 2 thrusting results from anatexis 3 anatexis results from normal faulting and 4 apparent inverted metamorphism in the footwall of the himalayan thrust is produced by underplating of right way up metamorphic sequences we review a number of models and find that many are inconsistent with available constraints most notably the recognition that the exposed crustal melts and inverted metamorphic sequences not temporally related the generalization that appears to best explain the observed distribution of crustal melts and inverted metamorphic sequences is that due to specific petrological and tectonic controls episodic magmatism and out of sequence thrusting developed during continuous convergence juxtaposing allochthonous igneous and metamorphic rocks this coincidental juxtaposition has proven to be something of a red herring unduly influencing attention toward finding a causal relationship between anatexis and inverted metamorphism

partial melting below the magmatic arc in the central andes deduced from geoelectromagnetic field experiments and laboratory data abstract magnetotelluric and geomagnetic deep soudings in northern chile revealed a pronounced high conductivity zone hcz below the western cordillera which constitutes the present magmatic arc with active volcanism of the south american continental margin conductivities in the range of 1 s m are observed the anomalously high conductivities in a broad depth range from approximately 20 km to at least 60 km are interpreted in terms of partial melting other geophysical observations such as a zone of low seismic velocities lvz at similar depths high heat flow values 100 mw m2 and a pronounced negative anomaly in the residual gravity field are also considered impedance spectroscopic laboratory experiments up to and in the temperature range of partial melting were performed under controlled oxygen fugacities at sub solidus temperatures electrical behavior is described by defect electrons with an activation energy of 1 34 ev and a conductivity of 2 5 ms m at 900 c model calculations using a modified brick layer model mbl were compared with experimental observations a good agreement between calculations and experiments is achieved with an electrical resistivity of the melt phase of 7 s m at 1250 c assuming an activation energy of 1 ev the same mbl model is used to calculate melt proportions beneath the western cordillera between 14 and 27 vol of interconnected melt are necessary to explain the observed hcz the stability of the melt rich crust is explained by a dynamic melting crystallisation behavior during crustal anatexis and by magma filled dikes

the effects of rotation on flow of a single layer over a ridge the effects of the coriolis force on the hydrostatic flow of a single lower layer over a two dimensional ridge are described for short periods the flows resemble those of the non rotating case but after a few hours in the atmospheric context effects of rotation become significant for steady state flow over ridges and plateaux critical conditions near the crest of the obstacle can control the flow in the same manner as for conventional hydraulics however steady disturbances are only manifested a finite distance upstream for initial froude number fo 1 upstream bores where they exist become arrested at a finite distance ahead of the barrier when flow on the lee side is supercritical steady lee side disturbances consist of nonlinear inertial oscillations obstacle shape is important in determining upstream and downstream flow the results are useful for understanding atmospheric flows over mesoscale ridges

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

detrital zircon geochronology of the northeastern tibetan plateau u pb geochronologic analyses have been conducted on 413 detrital zircon grains collected from 16 samples in the altun shan nan shan and qilian shan the samples come primarily from quartz arenites and metaturbidites of middle to late proterozoic age and from feldspathic and volcanic clast rich sandstones of early paleozoic age zircon grains in proterozoic strata resting on tarim basement yielded mainly 2 0 1 9 ga ages whereas proterozoic strata of the qaidam and qilian terranes yielded mainly ca 930 820 ma and ca 1 9 1 1 ga ages the younger grains were apparently shed from local igneous rocks whereas the grains older than 1 1 ga were shed from an undetermined continental source grains in the lower paleozoic strata are mainly ca 500 430 ma and were shed from nearby plutonic and possibly volcanic rocks that formed in a magmatic arc setting our detrital zircon ages are consistent with a model first proposed by e r sobel and n arnaud in which early paleozoic magmatism occurred within a single northeast facing magmatic arc that was constructed across an assemblage of middle to late proterozoic accretionary complexes remnants of magmatic arcs and shallow marine strata this arc system was accreted to the tarim and sino korean cratons during silurian devonian time the resulting suture has been reactivated as tertiary thrust faults that currently define the structural and topographic margin of the tibetan plateau our data also provide two new estimates for the offset along the eastern altyn tagh fault a belt of middle proterozoic shallow marine strata is offset by 400 km whereas a belt of 490 480 ma magmatic arc rocks is offset by 370 km these values are generally similar to the 350 400 km offset reported in most previous studies

numerical simulation of wave overtopping of coastal structures using the non linear shallow water equations a one dimensional high resolution finite volume model capable of simulating storm waves propagating in the coastal surf zone and overtopping a sea wall is presented the model amazon is based on solving the non linear shallow water nlsw equations a modern upwind scheme of the godunov type using an hll approximate riemann solver is described which captures bore waves in both transcritical and supercritical flows by employing a finite volume formulation the method can be implemented on an irregular structured boundary fitted computational mesh the use of the nlsw equations to model wave overtopping is computationally efficient and practically flexible though the detailed structure of wave breaking is of course ignored it is shown that wave overtopping at a vertical wall may also be approximately modelled by representing the wall as a steep bed slope the amazon model solutions have been compared with analytical solutions and laboratory data for wave overtopping at sloping and vertical seawalls and good agreement has been found the model requires more verification tests for irregular waves before its application as a generic design tool

landscapes on the edge examining the role of climatic interactions in shaping coastal watersheds using a coastal terrestrial landscape evolution model incised coastal gullies icgs are dynamic features found at the terrestrial coastal interface their geomorphic evolution is driven by the interactions between processes of fluvial knickpoint migration and coastal cliff erosion under scenarios of future climate change the frequency and magnitude of the climatological drivers of both terrestrial fluvial and hillslope and coastal cliff erosion processes are likely to change with an adjunct impact on these types of coastal features here we explore the response of an incised coastal gully to changes in both terrestrial and coastal climate in order to elucidate the key process interactions which drive icg evolution we modify an extant landscape evolution model child to incorporate processes of soft cliff erosion this modified version termed the coastal terrestrial child ct child model is then employed to explore the interactions between changing terrestrial and coastal driving forces on the future evolution of an icg found on the south west isle of wight uk it was found that the magnitude and frequency of storm events will play a key role in determining the future trajectory of icgs highlighting a need to understand the role of event sequencing in future projections of landscape evolution furthermore synergistic positive and antagonistic negative interactions were identified between coastal and terrestrial parameters such as wave height intensity and precipitation duration which act to modulate the impact of changes in any one parameter of note was the role played by wave height intensity in driving coastal erosion which was found to play a more important role than sea level rise in determining rates of coastal erosion this highlights the need for a greater focus on wave height in studies of soft cliff erosion this article is protected by copyright all rights reserved

softening the lower crust modes of syn transport transposition around and adjacent to a deep crustal granulite nappe parry sound domain grenville province ontario canada 1 the parry sound domain is a granulite nappe stack transported cratonward during reactivation of the ductile lower and middle crust in the late convergence of the mesoproterozoic grenville orogeny field observations suggest the following with respect to the ductile sheath 1 formation of a carapace of transposed amphibolite facies gneiss derived from and enveloping the western extremity of the parry sound domain and separating it from high strain gneiss of adjacent allochthons this ductile sheath formed dynamically around the moving granulite nappe through the development of systems of progressively linked shear zones 2 transposition initiated by hydration amphibolization of granulite facies gneiss by introduction of fluid along cracks accompanying pegmatite emplacement shear zones nucleated along pegmatite margins and subsequently linked and rotated the source of the pegmatites was most likely subjacent migmatitic and pegmatite rich units or units over which parry sound domain was transported comparison of gneisses of the ductile sheath with high strain layered gneiss of adjacent allochthons show the mode of transposition of penetratively layered gneiss depended on whether or not the gneiss protoliths were amphibolite or granulite facies tectonites before initiation of transposition resulting in e g folding before shearing no folding before shearing respectively meter scale truncation along high strain gradients at the margins of both types of transposition related shear zones observed within and marginal to parry sound domain mimic features at kilometer scales implying that apparent truncation by transposition originating in a manner similar to the ductile sheath may be a common feature of deep crustal ductile reworking

late ordovician to earliest silurian graptolite and brachiopod biozonation from the yangtze region south china with a global correlation late ordovician to earliest silurian is an important geological period marked by large geological and biological events however the strata and fossils of this interval are not complete in many parts of the world based on studies of 43 sites in south china in particular the continuous sections on the yangtze platform we recognize a complete succession including seven graptolite zones and two shelly faunas in ascending order the graptolite zones are the dicellograptus complanatus dicellograptus complexus paraorthograptus pacificus including lower subzone tangyagraptus typicus subzone and diceratograptus mirus subzone normalograptus extraordinarius normalograptus ojsuensis normalograptus persculptus akidograptus ascensus and parakidograptus acuminatus zones the shelly faunas are the foliomena nankinolithus and hirnantia faunas which may be correlated with d complanatus zone and n extraordinarius n ojsuensis to part of n persculptus zones respectively the biozonation through this interval from the yangtze region can be correlated with that of other parts of the world such as dob s linn in scotland spain and portugal thuringia saxonia bavaria bohemia poland kazakhstan kolyma malaya peninsula yukon canadian arctic islands nevada argentina niger and victoria australia the hirnantian substage which has been proposed by us recently includes the n extraordinarius n ojsuensis zone hirnantia fauna and n persculptus zone the base of the hirnantian substage is marked by the first appearance data fads of n extraordinarius and n ojsuensis which have been determined to be synchronous on a global scale

neoproterozoic bimodal magmatism in the cathaysia block of south china and its tectonic significance shrimp u pb zircon age geochemical and sm nd isotopic results are reported for the mamianshan volcanic rocks in the cathaysia block of southeastern south china the mamianshan volcanic rocks are bimodal in composition and are dominantly transitional to mildly alkaline basalts and subordinate alkaline rhyolite with an eruption age of 818 9 ma the basaltic samples are characterized by lree enriched and humped trace element patterns similar to many alkali basalts in continental rifts variablend t values between 3 33 and 4 35 indicate that the primary magma of these basalts was derived from an oib like mantle source and underwent fractional crystallization plus crustal contamination the rhyolitic rocks are highly enriched in th ta nb ree zr hf and y and depleted in sr p eu and ti sharing affinity to a 1 type granites combined with their slightly positive nd t values 0 22 to 0 92 the mamianshan felsic rocks were most likely generated by partial melting of the regional paleoproterozoic mayuan amphibolites the mamianshan bimodal volcanic rocks in the cathaysia block are coeval with the widespread intraplate magmatism around the yangtze block our results support the idea that a coherent south china craton was formed during the ca 1 0 ga sibao orogeny and it subsequently underwent extensive continental rifting related to mantle plume or superplume activities beneath rodinia since ca 825 ma 2004 elsevier b v all rights reserved

contrasting geochemical and sm nd isotopic compositions of archean metasediments from the kongling high grade terrain of the yangtze craton evidence for cratonic evolution and redistribution of ree during crustal anatexis abstract twenty three clastic metasediments from the kongling high grade terrain of the yangtze craton south china were analyzed for major trace and rare earth elements and sm nd isotopic ratios associated dioritic tonalitic trondhjemitic dtt and granitic gneisses as well as amphibolites were also analyzed in order to constrain provenance the results show that the clastic metasediments can be classified into 3 distinct groups in terms of mineralogical geochemical and sm nd isotopic compositions group a is characterized by having no to slight negative eu anomalies eu eu 0 82 1 07 being high in cr 191 396 ppm and ni 68 137 ppm and low in th 3 3 7 8 ppm and ree ree 99 156 ppm these characteristics are similar to those of metasediments from archean greenstone belts in addition the group a metasediments have the value of the chemical index of alteration ciw close to felsic gneisses their sm nd isotopic ree and trace element compositions can be interpreted by mixtures of the dtt gneisses and amphibolites dating of detrital zircons from 2 group a samples by shrimp reveals a major concordant age group of 2 87 3 0 ga which is identical to the age of the trondhjemitic gneiss these results strongly suggest that group a was principally the first cycle erosion product of the local kongling dtt gneiss and amphibolite moreover the higher than amphibolite cr content and slight eu depletion exhibited by some samples from this group infer that ultramafic rocks like komatiite and granite of probably 3 0 3 3 ga in age also played a role group b is characterized by the presence of graphite and shows a more evolved composition similar to post archean shales with a prominent negative eu anomaly eu eu 0 48 0 77 and high ciw on paired cr th vs la co and co th plots group b samples conform to a two end member mixing line of the kongling granitic gneiss and amphibolite however data on nd model age and ciw suggest that the granite component should be younger than the sampled granitic gneiss and derived from a distal source both groups a and b exhibit a clear positive correlation between ciw and tdm and a negative one between ciw and eu eu these correlations point to the crustal evolution of the yangtze craton towards coupled increasing ciw and eu depletion with decreasing age this in turn reflects the change of granitoid magmatism from local na rich dioritic tonalitic trondhjemitic rocks to widespread k feldspar granite the change led to the intracrustal differentiation stabilization and growth of the craton group c is restite and contains abundant sillimanite and garnet and unusually high ilmenite 7 11vol which can be seen to be dehydration melting products of biotite under the microscope this group shows extremely varied ree distributions from lree enriched to depleted and from negative to strong positive eu eu 1 63 eu anomalies compared to groups a and b group c is severely depleted in na2o k2o lree rb and ba whereas tio2 co v sc and hree and y are considerably enriched this is accompanied by anomalous high sm nd 0 21 0 28 147sm 144nd 0 1361 0 1738 and 143nd 144nd 0 511589 0 511958 ratios tdm correlates clearly with sm nd ratio and 2 out of 3 samples give significantly older to unrealistic tdm 3 9 4 9 ga the results document redistribution of ree and an open behavior of the sm nd isotope system during the biotite dehydration melting of metasediments

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

mirror image thrusting in the south china orogenic belt tectonic evidence from western fujian southeastern china abstract the mesozoic orogenic belt in south china is readily divided into two fold and thrust belts and a central multiply deformed zone of ductile deformation dominated by folds with steeply dipping axial planes southeast directed thrusting in the eastern belt and northwest directed thrusting in the western belt resulted in a mirror image of one another during the mesozoic the eastern fold and thrust belt can be further divided into three domains that overlap one another and exhibit a southeast verging wedge like geometry and kinematics deviatoric stress has been calculated from quartz dislocation density at 91 5 mpa 74 5 mpa and 73 8 mpa decreasing toward the southeast upper devonian and lower carboniferous sandstones have been used to constrain bed length for cross section balancing to estimate crustal shortening from three typical areas these indicate 45 41 6 and 37 3 shortening and suggest that 110 km of contraction has been achieved as a result of thrusting this orogen correlates with the ogcheon belt in south korea to the northeast to the southwest it appears to correlate with a thrust belt in western guangdong this southeast verging thrusting may be at least partially controlled by cathaysia to the east

thermal control on post orogenic extension in collision belts abstract intracontinental extension develops in two different ways in the rhine graben the baikal or the east african rifts it is localized in a long and narrow zone along a few normal faults which often delineate a single graben in contrast in the basin and range province or the tibetan plateau it is distributed over a much broader area up to more than 1000 km across this difference arises from differences in rheology and applied forces widespread extension probably reflects the thinning of a previously thickened crust geological observations indicate that only wide orogenic belts undergo late or post orogenic thinning a related fact is that anatectic granites seem to be most abundant in wide orogenic belts the general correlation between belt width and occurrence of both extension and anatectic granites suggest that it reflects in part the characteristics of horizontal heat transfer between thickened crust and surroundings in wide orogenic plateaux the large amount of heat produced in the crust by radioactive decay and lack of erosion leads to high temperatures in narrow mountain belts horizontal heat transfer and high erosion rates concur to prevent temperatures from rising to values at which the crust may yield in extension we have tested this hypothesis using transient two dimensional numerical models of orogenic belts focussing on the effects of the shortening rate the final width of the belt and the rate of crustal radiogenic heat production in the range of geological values the shortening rate has little influence on the results crustal temperatures increase as a function of belt width we find that the sensitivity of crustal temperatures to belt width is most pronounced in the 100 300 km width range and for large values of crustal heat generation the pressure temperature paths followed by geological formations depend on the belt width which is consistent with available data the integrated shear strength of the lithosphere decreases with time as the belt is being built and then eroded this evolution is sensitive to belt width if extension occurs when the integrated shear strength drops below a critical value our results yield a framework for comparing different orogenic belts we predict that extension starts late in the history of wide belts and never occurs in narrow belts a final implication of this study is that the average rate of crustal heat production is probably close to 1 1 10 6 w m 3 which is in the upper range of possible values we present a simple and convenient diagram summarizing the thermal characteristics of orogenic belts as a function of width and shortening rate

shrimp u pb zircon geochronology and geochemistry of metavolcanic and metasedimentary rocks in northwestern fujian cathaysia block china tectonic implications and the need to redefine lithostratigraphic units abstract northwestern fujian province is one of the most important pre palaeozoic areas in the cathaysia block of south china metavolcano sedimentary and metasedimentary rocks of different types ages and metamorphic grades granulite to upper greenschist facies are present and previously were divided into several formations and groups tectonic contacts occur between some units whereas deformed unconformities have been reported between others new shrimp u pb zircon ages presented here indicate that the original lithostratigraphy and the old group and formation terminology should be abandoned thus the tianjingping formation was not formed in the archaean or palaeoproterozoic as previously considered but must be younger than its youngest detrital zircons 1790 ma but older than regional metamorphism 460 ma besides magmatic zircon ages of 807 ma obtained from metavolcano sedimentary rocks of the nanshan formation and 751 728 ma for the mamianshan group many inherited and detrital zircons with ages ranging from 1 0 to 0 8 ga were also found in them these ages indicate that the geological evolution of the study area may be related to the assembly and subsequent break up of the rodinia supercontinent the new zircon results poorly constrain the age of the mayuan group as neoproterozoic to early palaeozoic 728 458 ma and not palaeoproterozoic as previously thought many older inherited and detrital zircons with ages of 3 6 2 8 2 7 2 6 2 5 2 0 1 8 and 1 6 ga were found in this study a 3 6 ga detrital grain is the oldest one so far identified in northwestern fujian province as well as throughout the cathaysia block nd isotope tdm values of eight volcano sedimentary and clastic sedimentary rock samples centre on 2 73 1 68 ga being much older than the formation ages of their protoliths and thus showing that the recycling of older crust played an important role in their formation these rocks underwent high grade metamorphism in the early palaeozoic 458 425 ma during an important tectono thermal event in the cathaysia block