levee morphology and sedimentology along the lower tuross river south eastern australia levees on the lower tuross river in south eastern australia reflect a complex interplay between depositional and erosional processes stream power conditioned primarily by valley width is the key determinant of levee morphology and sedimentology in this confined valley setting three styles of levee are described the rewlee levee is functionally linked to a flood channel in narrow valley settings 250 m these levees contain a diverse facies assemblage characterized by various scales of erosion surfaces vertical accretion on levees has produced conditions under which stream power values exceed the threshold for catastrophic floodplain stripping the levee at the mortfield site is associated with less confined settings valley width 500 600 m which present lower flood stage and stream power conditions this levee hosts a wide range of facies but erosion surfaces are seldom observed in the more open valley setting at the central site valley width 700 1000 m levees comprise uniform fine grained deposits which grade to pronounced distal floodplains with backswamps as levees reflect a combination of within channel and overbank processes both depositional and erosional these geomorphic features influence the character and sedimentology of adjacent landforms and the associated alluvial architecture of the basin

australasian evidence for mid holocene climate change implies precessional control of walker circulation in the pacific abstract at its simplest the pacific cell of the walker circulation may be regarded as a thermal circulation driven by the temperature contrast between the west and east pacific evidence from australasia is summarized indicating that this circulation was greatly weakened in the early holocene but was enhanced at about 5000 bp the initial effect of this enhancement was the intensification of the northern australian monsoon within the australian tropics but this was reversed abruptly after 3700 bp the enhancement is attributed to an increased polar equator pressure gradient after 5000 bp with consequent intensification of the overall circulation pattern in the southern hemisphere including the mid latitude westerlies and the trade winds this in turn appears to be a result of increased southern hemisphere seasonality driven by the precessional cycle it is proposed that increased wind speeds off south america after 5000 bp in both mid and low latitudes enhanced upwelling and reduced sea surface temperatures ssts this created a greater east west surface temperature contrast across the pacific compounding a pre existing trend towards enhanced circulation and flipping climates in the southern hemisphere pacific basin from an early holocene mode to a late holocene mode under reduced circulation conditions early holocene climates at low latitudes in the southern hemisphere may have been dominated by monsoonal heat transfers

fluid infiltration through metachert layers at the contact aureole of the bufa del diente intrusion northeast mexico implications for wollastonite formation and fluid immiscibility

mire development and environmental change barrington tops new south wales australia abstract sediments began accumulating in nine mires on barrington tops on the northern tablelands of new south wales before 11 000 yr b p and peat became common in the region by 8600 yr b p sedimentation rates were low but increased markedly about 3000 yr b p and again around 500 yr b p as a result of regional climatic change a comparison of the results with other environmental data from the region suggests that conditions in the early holocene were warmer and moister than at present but that cooler and drier environments developed about 3000 yr b p in the last 500 yr a slight warming and either increased precipitation or cloudiness has become evident

transport of stable isotopes kinetics dispersive advection and the isotopic fronts of baumgartner and rumble 1988 baumgartner and rumble 1988 apply a kinetic continuum theory for stable isotope transport to unidimensional infiltration of fluid into rock their numerical applications are restricted to the simplified case of rapid isotope exchange between phases where the sharp isotope fronts of pure advection are distended by dispersive mechanisms only however kinetic limitations of isotope exchange are potentially an equally important distending mechanism and it will only rarely be possible to ascribe front gradients to diffusion dispersion alone abrupt isotopic changes at vein boundaries are more often a secondary signal of lithologic change than the expression of a retarded advective front at such boundaries diffusion and dispersion play a role that is comparable to or greater than that of advection so that the detailed shapes of isotope fronts depend upon boundary conditions for the infiltration process zerodimensional box models have legitimate if limited uses in the modelling of fluid rock interaction and are reexamined

river terrace systems in north west europe an archive of environmental change uplift and early human occupation abstract staircases of large scale aggradational river terraces are a notable feature of many valleys in the temperate lattitudes particularly in areas beyond the reach of the erosive activities of pleistocene ice sheets it is now recognized that the cyclic fluctuations of climate during the quaternary have driven the generation of terraces through the direct and indirect influence of both temperature and precipitation on fluviatile activity where fossiliferous deposits are preserved within terrace sequences it is often possible to date these and to correlate them with the oceanic record thus providing an important framework for the evidence of environmental change on land middle and late pleistocene terraces in different areas can commonly be seen to have formed in synchrony with glacial interglacial cycles or with longer periodicity megacycles climatic forcing alone is insufficient to cause terraces to form however uplift is also necessary so that terrace sequences can provide a useful record of crustal movement in northwest europe where some of the best known studies of river terrace sequences have been carried out the fluviatile deposits are also an important repository for palaeolithic artefacts from which a record of early human occupation can be reconstructed

contrasting fluid flow patterns at the bufa del diente contact metamorphic aureole north east mexico evidence from stable isotopes impure limestones with interstratified metachert layers were contact metamorphosed and metasomatized by the bufa del diente alkali syenite massive marbles exhibit mineralogical and stable isotope evidence for limited fluid infiltration confined to a 17 m wide zone at the contact influx of magmatic brines along most metacherts produced up to 4 cm thick wollastonite rims according to calcite cc quartz qz wollastonite wo co2 and were observed at distances of up to 400 m from the contact the produced co2 exsolved as an immiscible low density co2 rich fluid chert protolith isotope compositions were 18o qz 27 30 and 18o cc 24 27 many wollastonites in infiltrated metacherts have low 18o ranging from 11 17 and confirm that decarbonation occurred in presence of a magmatic signatured fluid large gradients in 18o wo across the rims may reach 6 the 18o of remaining quartz is often lowered to 15 20 whereas caleites largely retained their original compositions the isotopic reversals of up to 10 between quartz and calcite along with reaction textures demonstrate non equilibrium between infiltrating fluid in the aquifer and the assemblage calcite quartz wollastonite this is compatible with the assumption of a down temperature flow of magmatic fluids that occurred exclusively in the remaining quarzite layer the 13c cc and 18o cc of marble calcites measured perpendicular to two metachert bands reveal significant isotopic alterations along distances of 4 5 cm and 7 5 cm from the wollastonite marble boundary only into the hanging wall marble suggesting an advection process caused by a fluid phase which movel upwards covariation trends of 13c cc and 18o cc across the alteration front indicate that this fluid was co2 rich mass balance calculations show that all co2 rich fluid produced by the decarbonation reaction was lost into overlying marble the metachert aquifers did not leak with respect to water rich fluids

late quaternary floodplain reworking and the preservation of alluvial sedimentary archives in unconfined and confined river valleys in the eastern interior of south africa abstract in this study geomorphological sedimentological and geochronological work was conducted on unconfined and confined reaches of three rivers in the eastern interior of south africa in order to quantify the relative rates of floodplain reworking and alluvial preservation along river courses with variable valley confinement and lithology using optically stimulated luminescence osl dating techniques new chronologies for the schoonspruit and mooi river were created and the existing klip river chronology was expanded the results suggest that floodplains in both unconfined and confined reaches preserve complex spatial and temporal patterns of alluviation although differences in boundary conditions lead to variation in the processes and rates of floodplain construction and reworking on the klip and mooi rivers where local base levels are stable channels in unconfined reaches rework floodplain sediments through slow lateral migration punctuated by local erosion during avulsion events on the schoonspruit where base level has lowered the channel in the unconfined reach is incised the floodplain is abandoned and a large gully has formed in the confined reaches of all three rivers the narrow floodplains are reworked by scour and fill activity and limited lateral migration the osl results suggest that unconfined reaches preserve relatively continuous alluvial records that extend into the pleistocene while the floodplains in the confined reaches preserve relatively discontinuous alluvial records biased toward the late holocene the alluvial geochronologic records in these systems preserve signals of changes in local base level controlled by variation in lithology and incision rather than climate change by defining the processes rates and patterns of floodplain reworking in reaches with different degrees of valley confinement and channel incision the findings contribute to understanding how rivers build modify and preserve alluvial sedimentary archives

nonsynchronous episodic incision evidence of threshold exceedance and complex response as controls of terrace formation terrace sequences can represent regional or continental scale factors such as climatic fluctuations neotectonic activity and base level change however they can also reflect random incision events brought about by local scale geomorphic threshold exceedance and subsequent complex response this study explores the formative processes of three discontinuous but adjacent late pleistocene to late holocene step terrace sequences in southeastern australia correlation of river terrace fills was undertaken by comparing terrace remnants based on topography morphology sedimentology stratigraphy and chronology a geomorphic model of floodplain abandonment and terrace formation for this valley setting is presented most of southeastern australia has shown no evidence of tectonic uplift during the late quaternary bedrock bars on the hunter river isolate the study reach from downstream base level changes the nonsynchronous episodic behavior of incision events in this catchment strongly indicates that climate is not a dominant control on terrace formation with the exclusion of climatic fluctuations tectonic uplift and base level change as causes of incision catastrophic floods and the exceedance of geomorphic thresholds emerge as the dominant controls of terrace formation

vapour loss boiling as a mechanism for fluid evolution in metamorphic rocks the calculation of fluid evolution paths during reaction progress is considered for multicomponent systems and the results applied to the ternary system co2 h2o nacl fluid evolution paths are considered for systems in which a co2 rich phase of lesser density vapour is preferentially removed from the system leaving behind a saline aqueous phase liquid such boiling leads to enrichment of the residual aqueous phase in dissolved components and for certain reaction stoichiometries to eventual saturation of the fluids in salt components distinctive textures particularly radiating growths of prismatic minerals such as tremolite or diopside are associated with saline fluid inclusions and solid syngenetic salt inclusions at a number of field localities the most thoroughly studied of these localities is campolungo switzerland where metasomatic rocks have developed in association with fractures and veins at 500 c and 2 000 bars of pressure the petrography of these rocks suggests that fluid phase separation into liquid and vapour has been an important process during metasomatism fracture systems with fluids at pressure less than lithostatic may facilitate the loss of the less dense vapour phase to conditions of the amphibolite facies

fluid flow mineral reactions and metasomatism a general model that relates fluid flow along a temperature gradient to chemical reaction in rocks can be used to quantitatively interpret petrologic and geochemical data on metasomatism from ancient flow systems in terms of flow direction and time integrated fluid flux the model is applied to regional metamorphism quartz veins and a metasomatized ductile fault zone

the role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism carbon and oxygen isotopic profiles around a low pressure metasomatic wollastonite reaction front in a marble of the hida metamorphic terrain central japan display typical metamorphic fluid enhanced isotopic zonations isotopic profiles obtained from detailed microscale analyses perpendicular to the chemical reaction front in calcite marble show that diffusion enhanced isotopic exchange may control these profiles carbon and oxygen isotopic behaviour in grain boundaries is remarkably different oxygen isotopic troughs 18o depleted rims around the calcite grain boundaries are widely observed in this contact aureole demonstrating that diffusion of oxygen in calcite grain boundary dominates over lattice diffusion in calcite in contrast no difference is observed in carbon isotopic profiles obtained from grain cores and rims there is thus no specific role of the grain boundary for diffusion of carbonic species in the metamorphic fluid during transportation carbon chemical species such as co2 and co3 ions in metamorphic fluid migrate mainly through lattice diffusion the carbon and oxygen isotope profiles may be modelled by diffusion into a semi infinite medium empirically lattice diffusion of oxygen isotopes is almost six times faster than that of carbon isotopes and oxygen grain boundary diffusion is ten times faster than oxygen lattice diffusion oxygen isotopic results around the wollastonite vein indicate that migration of the metamorphic fluid into calcite marble was small and was parallel to the aquifer from the stability of wollastonite and the attainment of oxygen isotopic equilibrium we suggest that diffusion of oxygen occurred through an aqueous fluid phase the timescale of formation of the oxygen isotopic profile around the wollastonite vein is calculated to be about 0 76 106 years using the experimentally determined diffusion constant

resolving the holocene alluvial record in southeastern australia using luminescence and radiocarbon techniques a previous assessment of radiocarbon 14 c dates from alluvial units in southeastern australia revealed a gap in the geochronological record that coincides with the holocene climatic optimum thisgapin the alluvial recordcanbe further refined usingoptically stimulatedluminescence osl the chronology of holocene river terraces on widden brook a sandy alluvial stream in southeastern australia was established using 14 c and osl techniques combined use of these independent techniques allows for a more rigorous assessment of the alluvial record the robust chronology consisting of 38 14 c and 11 osl samples permitted identification of significant deposi tionalvariationwithin thecatchment resulting fromlocalisedgeomorphicprocesses thethree terrace sequences identified yielded distinct chronologies suggesting alluvial deposition at different times the sequences exhibited a continuous chronology which indicated continuous deposition throughout the holocene the chronology of terrace sequences within this catchment suggests that terrace formation can be attributed to localised geomorphic processes rather than climatic forcing copyright 2010 john wiley sons ltd supporting information can be found in the online version of this article

stream response to quaternary climate change evidence from the shoalhaven river catchment southeastern highlands temperate australia abstract luminescence ages from a flight of four paired alluvial terraces in the upper catchment of the shoalhaven river southeast highlands australia provide a record of stream behaviour throughout the late quaternary ages ranging from 7 ka in the modern floodplain to nearly 500 ka for the uppermost dated terrace allow comparisons to be made of the response of streams throughout southeastern australian to late quaternary climatic perturbations the alluvial record of the shoalhaven river highlights the broad regional synchronicity of episodes of heightened fluvial activity during oxygen isotope stage ois 5 terminating 75 ka 60 40 30 25 and 20 15 ka the shoalhaven record also shows an absence of fluvial activity during the last glacial maximum suggesting that southeastern australia was most likely dry at this time as compared to northern australia which was probably wet fluvial activity while still significant decreased substantially after approximately 60 ka suggesting a general drying of climate towards the present

assessment of downstream trends in channel gradient total and specific stream power a gis approach geographic information systems gis analyses of digital elevation models dems coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient total stream power and in riverscapes conducive to regime analysis also specific stream power for a small high relief coastal catchment in se australia good agreement was obtained between channel gradients derived from a 25 m cell size dem and field survey equivalents over distances of several kilometres indicating that channel gradients derived from dems can have a reasonable degree of absolute as well as relative accuracy over multi kilometre reach scales assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream modelling of downstream trends in channel gradient total and specific stream power from catchment wide dems has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient stream power and the form and dynamics of river systems

a mid to late holocene history of floodplain and terrace reworking along the middle delaware river valley usa abstract this study tests and refines the traditional floodplain development model for the partly confined middle delaware river valley which has shown that the main channel was relatively stable and flanked by a 6000 8000 year old vertically accreting alluvial terrace the holocene alluvial processes and history presented here in 6 fluvial phases were reconstructed using morphostratigraphy 36 profile descriptions 332 grain size analyses and 82 14 c ages from soil trenches auger borings and archaeological excavations fluvial phases i iii largely validate previous reconstructions showing a late pleistocene i 10 7 ka braided stream transition into an early holocene wandering stream with prolonged floodplain stability ii 10 7 8 ka followed by early middle holocene erosion and then deposition iii 8 5 ka the early and middle holocene changes in alluvial stratigraphy and sedimentology broadly correlate with climatically derived holocene subdivisions suggesting climate change partly controls alluvial response along the middle delaware river valley this study documents for the first time a middle holocene episode of channel incision occurring sometime between 6 0 and 5 0 ka although the results reconfirm that the majority of alluvial landforms are composed of vertical accretion deposits we present here new evidence of oblique abandoned channel and lateral accretion deposits inset to similar landforms with different formation histories i e polycyclic terrace development depicting a river valley that has experienced floodplain and terrace reworking the majority of floodplain and terrace reworking occurs during the late middle and late holocene phases iv vi 5 5 0 ka following the middle holocene incision event these phases demonstrate floodplain reworking processes in the form of channel abandonment stripping flood channeling and convex bank erosion the subsequent space filled rapidly with evidence of multistory soil formation and eventually resulted in alluvial fill terraces with heights comparable to older surfaces the most recent fluvial phase vi 1 0 0 ka shows markedly faster sedimentation rates and coarser flood deposits associated with peak prehistoric population and the onset of euroamerican settlement the results presented here contribute newly documented evidence of erosion and depict a river valley that has undergone middle holocene incision and floodplain and terrace reworking since the late middle holocene stream modelers fluvial geomorphologists and geoarchaeologists working in the ne usa should consider floodplain reworking processes when examining alluvial history and predicting changes in stream dynamics

antecedent controls on river character and behaviour in partly confined valley settings upper hunter catchment nsw australia abstract a partly confined river is one along which the contemporary channel abuts the valley margin along 10 90 of its length they occur along sections of longitudinal profiles that are transitional from fully bedrock confined to fully alluvial rivers at this position in the landscape there is sufficient accommodation space for discontinuous floodplain pockets to form segregation of the river s load and dissipation of flow energy result in sediments being stored outside the channel bedrock and planform controlled variants of these rivers and associated floodplains are differentiated terraces fans and piedmont zones act as secondary confining features on channel planform and floodplain formation in these valleys the influence of these antecedent features on contemporary river character and behaviour in partly confined valleys of the upper hunter catchment new south wales australia is appraised the balance of formative and reworking processes and associated capacity for geomorphic adjustment is influenced by the site specific configuration of antecedent controls at any floodplain pocket downstream patterns of these river types are analysed along all major tributaries of the upper hunter catchment to highlight the extent of antecedent control on contemporary river forms and processes in this landscape setting

holocene river dynamics in northland new zealand the influence of valley floor confinement on floodplain development abstract valley floor mapping sedimentology and 14c dating have been used to reconstruct the fluvial history at eight floodplain sites spread throughout northland a region removed from the main areas of tectonic and volcanic activity in new zealand we present a probability based record of holocene river behaviour for northland using 14c dated holocene fluvial deposits and compare this with independent palaeoclimate proxy records from the north island holocene floodplain evolution and fluvial behaviour have been conditioned by the degree of valley floor confinement in the most and least confined valley settings holocene floodplain evolution has involved the development of a single floodplain surface at partly confined sites the river terrace and floodplain geomorphology are more complex region wide progressive floodplain alluviation through the mid to late holocene and a period of increased river activity between 3500 and 2800 cal ybp in response to climatically driven increases in sediment supply was followed by a period of valley floor incision and terrace formation beginning after 1900 cal ybp in partly confined valley settings this was followed by the aggradation of a lower holocene floodplain surface with rapid rates of vertical accretion in response to post settlement catchment disturbance the results of this study indicate that valley floor confinement has played a major role in controlling northland holocene river floodplain development producing a continuum of floodplain and river terrace landforms in response to climatically and anthropogenically driven variations in sediment flux

holocene palaeoecology and formation of the shoalhaven river deltaic estuarine plains southeast australia the shoalhaven river is one of the largest rivers on the south coast of new south wales and the deltaic estuarine plains associated with its mouth represent a mature stage of infill of a barrier estuary the stratigraphy of sediments from more than 60 drillholes from the plains indicates that the area has infilled during the mid holocene as a result of input of marine sands associated with a sand barrier on the high energy coast and fluvial mud and sands from the shoalhaven river molluscan assemblages indicate that marine influence was initially widespread throughout the eastern and southern parts of the embayment and that most of the plains infilled under estuarine conditions prominent levees across the plains surface are interpreted to be part of a birdsfoot delta distributary complex and individual floodbasins accreted progressively as they were encapsulated by distributary extension these former tidal environments mean that there are extensive potential acid sulphate soil conditions beneath the

topographically associated but chronologically disjunct late quaternary floodplains and terraces in a partly confined valley south eastern australia the bellinger river catchment in the new england fold belt on the mid north coast of new south wales is characterized by an assemblage of stepped late quaternary alluvial units late pleistocene terraces were formed by large more competent rivers that eroded almost entire valley floors however a decline in discharge prior to the holocene has resulted in the abandonment of these deposits as elevated terraces or residual alluvium onlapped by contemporary floodplains intrinsic controls on floodplain formation appear to be superimposed over an early mid holocene climatic signature a fluvially active period known as the nambucca phase from 10 to 4 5 ka eroded late pleistocene terraces two floodplain surfaces one higher than the other both started to accrete vertically from 4 ka but with some valley locations remaining vulnerable to episodes of erosion resulting in substantial units of even younger basal alluvium the high floodplain is dominated by horizontally laminated vertically accreted sequences while the low floodplain which overlaps in age is characterized by pronounced cut and fill stratigraphy terraces and floodplains in partly confined settings can have similar elevations but be polycyclic with very different basal ages in such landscapes the classical assumption that individual terrace or floodplain profiles along a valley represent periods of coeval formation is shown to be frequently invalid copyright 2007 john wiley sons ltd

episodes of vertical accretion and catastrophic stripping a model of disequilibrium flood plain development this paper describes flood plains formed episodically by vertical accretion along high energy laterally stable channels in southeastern australia overbank deposition gradually builds a flood plain of fine textured alluvium over a period of hundreds or thousands of years following which catastrophic erosion by a single large flood or a series of more moderate floods strips the flood plain to a basal lag deposit from which it slowly reforms this periodic destruction appears due to the progressive development of large levee banks and flood plain surfaces of highly variable relief as the levees and flood plain grow overbank flow is gradually displaced from the broad flood plain into the main channel and flood plain backchannels with a resulting concentration of erosional energy eventually high flows greatly exceed erosional thresholds and wholesale scour of the channel boundary and flood plain occurs vertical accretion flood plains at different stages of development result in a wide range of bankfull recurrence intervals even along the same river some of these flood plains are so infrequently flooded that they can be mistaken for terraces formed under a prior flow regime the almost random but catastrophic nature of this flood plain erosion means that sediment supply and transport are highly variable and probably impossible to predict this model of flood plain formation is seen as only part of a continuum of alluvial environments ranging from vestigial coarsegrained traction load flood plains along high energy rivers in narrow gorges to extensive low gradient flood plains in which alluvial stratigraphy is dominated by fine grained overbank deposition

the effect of fluid salinity on infiltration driven contact metamorphism of carbonate rocks calculated phase equilibria involving minerals and h2o co2 nacl fluid lead to predictions of how infiltration of rock by h2o nacl fluids with xnacl in the range 0 0 3 0 58 wt nacl drives the reactions calcite quartz wollastonite co2 and dolomite periclase calcite co2 calculations focus on metamorphism in four aureoles that together are representative of the normal p t conditions and processes of infiltration driven contact metamorphic reactions the effect of salinity on the spatial extent of oxygen isotope alteration was also computed the time integrated input fluid flux q that displaces the mineral reaction front an increment of distance along the flow path always increases with increasing xnacl for input fluids with salinity up to approximately five times that of seawater xnacl 0 05 values of q required to explain the spatial extent of decarbonation reaction are no more than 1 1 1 5 times that computed assuming the input fluid was pure h2o for more saline fluids values of q may be up to 1 4 7 9 times that for pure h2o except for reaction in the presence of halite and vapor v infiltration of h2o nacl fluids expands the region of oxygen isotope alteration relative to the size of the region of mineral reaction the expansion is significant only for saline fluids with xnacl 0 1 immiscible fluid phase separation and differential loss of the liquid l or v phase from the mineral reaction site increases the amount of reactive fluid required to advance the mineral reaction front compared to conditions under which equilibration of minerals and fluid is attained with no loss of l or v decarbonation reactions driven by infiltration of fluids with even modest seawater like salinity can explain the occurrence of salt saturated fluid and solid halide inclusions in contact metamorphosed carbonate rocks

steep oxygen isotope gradients at marble metagranite contacts in the northwest adirondack mountains new york usa products of fluid hosted diffusion steep gradients in oxygen isotope ratios are recorded from two contacts between grenville marbles calcite 18o 21 24 and metamorphosed granitic intrusives whole rock 18o 11 12 in the northwest adirondacks oxygen and carbon isotope fractionations between coexisting minerals in the marbles and the metagranites are consistent with isotopic equilibration at peak metamorphic temperatures the 18o profiles are sigmoidal with inflection points at the contacts and are developed over 5 6 m quantitative fluid infiltration diffusion modeling suggests that the isotopic gradients are best explained as the result of fluid hosted diffusion for porosities of 10 3 to 10 6 the profiles could have formed in 103 107 years via an interconnected grain boundary fluid the granites were probably emplaced at shallow crustal levels prior to the regional grenville metamorphism and isotopic exchange is most likely to have occurred at that time contact metamorphism at these localities involved devolatilisation of the marbles and the time estimates may reflect the periods over which fluid producing reactions took place and an enhanced porosity was maintained in the marbles there is a progressive increase in the percentage of diopside and k feldspar at the expense of phlogopite and tremolite towards the metagranites these mineralogical changes probably occurred due to the temperature increase associated with granite intrusion and diffusion of h2o from the granite the two localities lie on either side of the regional metamorphic amphibolite to granulite facies transition the preservation of isotopic profiles formed during contact metamorphism suggests that there was little pervasive fluid flow at this crustal level during the regional metamorphism or at any time thereafter steep isotopic gradients are present at orthogneiss marble contacts elsewhere in the adirondacks suggesting that this conclusion may be generally applicable to this terrain

limited fluid rock interaction at marble gneiss contacts during cretaceous granulite facies metamorphism seward peninsula alaska stable isotope profiles show that flat lying marble units acted as impermeable barriers to upward fluid flow in transitional amphibolite granulite grade rocks of the kigluaik mountains seward peninsula alaska the degree of permeability is related to the composition of the marble the margin of a thick pure dolomite marble chemically reacted with underlying metasyenite ah2o 0 2 to form a 2 cm boundary layer of calcite forsterite by introduction of sio2 no fluid penetrated past this reaction front although the high temperature of metamorphism 800 c allowed transport of carbon and oxygen isotopes for an additional 2 cm by diffusion through the solid dolomite a second marble with a higher silica content underwent more decarbonation which enhanced porosity and lead to a greater extent of isotope transport 2 3 m in contact with quartzo feld spathic gneiss below an estimate of total fluid flux across the bottom of this marble layer based on the shape of the isotope profile is 1 cm3 cm2 directed down out of the marble at two other marble gneiss contacts steep isotopic gradients coincide with lithologic contacts indicating very little cross lithology fluid flow the extent of diffusional transport of isotopes in the marbles is limited and interpreted as indicating the transient presence of a pore fluid generated by thermally driven devolatilization reactions no wholesale pervasive advection of c o h fluid occurred across the thick continuous marble units near the exposed base of the kigluaik group section during the entire regional metamorphic cycle activities of pore fluid species were controlled by internal processes movement of volatiles and stable isotopes between contrasting rock types was dominantly diffusive channelized fluid pathways through the marble units developed during uplift and cooling but were not present during peak metamorphism heating of the section occurred by conduction probably from an underlying magma source and not by advection of a c o h fluid

elemental dispersion and stable isotope fractionation during reactive fluid flow and fluid immiscibility in the bufa del diente aureole ne mexico evidence from radiographies and li b sr nd and pb isotope systematics the 31 6 0 3 ma old bufa del diente alkali syenite ne mexico intruded a sequence of cretaceous limestones with intercalated sub horizontal chert layers the cherts acted as aquifers that facilitated transport of brines and pegmatitic melts within the shallow level 1 kbar contact metamorphic aureole fluid driven reactions between chert and marble wallrock and the influx of late melts and various fluids gave rise to distinct chemical and isotopic signatures within the aquifer and across the zones of infiltration and fluid driven reaction aqueous brines of magmatic origin produced thick wollastonite mantles around the chert layers wollastonite formation occurred at the expense of limestone and chert and generated co2 this co2 induced fluid unmixing into an aqueous brine and a low density co2 rich fluid which was lost to the overlying marble where it oxidized organic matter and caused 13c and 18o shifts in a zone some 5 10 cm wide after wollastonite formation the chert aquifers were locally intruded by pegmatite veins carrying alkali feldspar quartz aegirine augite eudialyte zircon and apatite aqueous fluids that exsolved during crystallization of the pegmatite veins escaped along late cross fractures and migrated along the inner and outer borders of the wollastonite margins chemical dispersion patterns of u al na k p s fe and ree across the chert to marble boundary and its metasomatic rims are shown by autoradiography and neutron induced radiography scavenging of cations at mineralogical contacts and cation transport into the marbles occurred only on the mm to cm scale isotopic data for pb and sr across a simple metachert marble boundary and for pb sr nd b and li across a metachert pegmatite marble sequence demonstrate the following 1 the pb and sr isotopic signature of early fluids was buffered by the carbonate wallrock only late fluids shielded from wallrock interaction by a wollastonite mantle variably preserved a memory of their initial magmatic signature 2 since the nd isotope signature of marble and chert is bound to calcite and clay minerals systematic shifts to unradiogenic nd in marble reflect loss of carbonate bound nd as the wollastonite margin is approached nd in the wollastonite margin is dominated by nd originally bound to clay minerals the later emplacement of the pegmatite which carried the nd isotope signature of its alkali syenite source had little effect on the nd isotopic composition of the wollastonite rim 3 although the li and b isotopic compositions reflect the alkali syenite source they are also affected by isotopic fractionation and partitioning between melt fluid and solids

late quaternary channel and floodplain formation in a partly confined subtropical river eastern australia along the eastern margin of australia hydrological variability reaches a peak in the subtropics of south east queensland and many rivers have entrenched characteristics to address the nature of entrenchment and the relationship with adjacent alluvium this paper presents the results of detailed chrono stratigraphic analysis of alluvial units in the partly confined mid reaches of lockyer creek australia four sites were investigated using topographic sedimentological and chronological data radiocarbon and single grain optically stimulated luminescence dating indicate a large proportion of the valley fill reflects a major phase of aggradation of fine grained alluvium from ca 35 ka throughout the last glacial cold period synchronous incision of pleistocene alluvial fills between 11 5 and 9 3 ka suggests the current entrenched lockyer creek formed in response to changes in late quaternary climate holocene floodplains set within the entrenched pleistocene valley floor have basal ages of ca 7 5 ka but whose proximal margins are still actively accreting this holocene fill has accreted over the mid to late holocene but overlaps with the contemporary hydrological regime the sedimentary nature of the holocene fill appears to be related to persistent antecedent controls in the form of bedrock and terrace constriction

garnet composition as a petrogenetic indicator an example from a marble calc silicate granulite interface at kondapalle eastern ghats belt india thep t fluid histories of aluminous garnet clinopyroxene bearing calc silicate granulites are commonly constrained through interpretation of sequential reaction textures based on activity corrected petrogenetic grids for model systems for example the widely used cas co2 h2o topologies application of these topologies to calc silicates of diverse bulk composition is limited by the fact that the role of clinopyroxene and hence of garnet composition in the garnet forming reactions is ignored or not adequately considered in this contribution the complexities that arise from the involvement of clinopyroxene in the garnet forming reactions are critically evaluated as an example the paragenetic relations and compositional features of clinopyroxene and coronitic garnet across paired scapolite and wollastonite dominated reaction zones scp cpx qtz cal qtz wo cal cpx scp developed between marble layers cal cpx wo scp and their host calc silicate granulite cpx pl qtz scp at an exposure in the high grade eastern ghats belt india are examined the microtextural features and systematic changes of modal and phase compositions across the profile indicate that clinopyroxene scapolite plagioclase quartz and calcite as well as wollastonite participated in the garnet forming reactions using the sub assemblage qtz cal cpx scp grt v in the system cao feo al2o3 sio2 co2 it is demonstrated that at the ambient p t xfluid conditions the reaction coefficients of the participating phases are uniquely defined by the garnet composition as a result the p t slope of a garnet forming reaction changes with the garnet composition with sharp changes at singular points across which one or more phases change their sides with respect to garnet in a given reaction to consider the consequences of these complexities on the reaction topology of calc silicate granulites a new petrogenetic grid for the system cao feo al2o3 sio2 co2 involving clinopyroxene has been constructed the effects of fluid composition co2 h2o o2 fluid pressure pfluid

floodplain evolution in a new south wales coastal valley australia spatial process variations abstract floodplain types and their evolution are dependent on the valley floor trough the site of the alluvial store the trough may be entirely fluvial in origin or it may have been cut under some different antecedent condition or morphogenetic system or even produced by tectonic activity in the bellinger valley the trough is fluvial in origin but spatially variable along the profile in the upper valley it is very narrow and recently incised in lower central parts it is wider and older with inset pleistocene terraces lag gravels and floodplains the lowest parts or backwater reaches have a trough which was drowned by the post pleistocene transgression there floodplains are lower much wider and overly estuarine and deltaic deposits these three type sites produce different floodplains which have two dominant levels the upper has holocene roots but it is inundated often enough in flood dominated regimes to be capped by contemporary sediments the lower floodplain is much narrower and often more sandy making it prone to erosion in the present post 1949 wet regime it seems likely that much of the material at this level was deposited in the last drought dominated regime 1900 1949 although these floodplain types can be spatially differentiated along the profile the dateable evidence presented seems to confirm that most parts are recent or post 5000 yr bp with the older parts of the high floodplain dating from 3000 5000 years

late quaternary changes in flow regime on the gwydir distributive fluvial system southeastern australia abstract ages for large palaeochannels of the gwydir distributive fluvial system dfs in northern new south wales australia have been determined using single grain optically stimulated luminescence two palaeochannel systems have been found to dominate the here named coocalla 43 34 ka and kamilaroi 19 16 ka which have inferred palaeodischarges 25 100 times the bankfull discharges of nearby channels of the contemporary gwydir system which appears to have been established during the mid holocene this scale differential is very much larger than that reported for other catchments in southeastern australia and reflects both a decline in catchment runoff through the last glacial cycle and the adoption of a distributary pattern sometime after 16 ka actual decline in catchment runoff determined by comparing estimated palaeodischarge with contemporary flows upstream of the dfs where flow is confined to a single channel indicate contemporary discharge to be 0 1 times and 0 25 times that of the coocalla and kamilaroi respectively the chronology presented here shows periods of increased discharge in the gwydir to be more or less coincident with those observed elsewhere in the murray darling basin although no evidence of a gum creek fluvial phase from 35 to 25 ka was found the coocalla and kamilaroi palaeochannel systems broadly conform in age to kerarbury and yanco fluvial phases on the murrumbidgee and murray systems this synchronicity with more southern catchments supports the hypothesis that la nina like conditions were semi permanent for much of the last glacial cycle with moisture derived largely from the western pacific ocean

late quaternary river evolution of floodplain pockets along mulloon creek new south wales australia valley confinement along upper middle reaches of mulloon creek in the upper shoalhaven catchment of southern new south wales australia restricts floodplain development to a series of distinct pockets these pockets comprise a downstream thinning wedge of vertically accreted fine grained deposits atop basal gravels some time before 12500 years ago a bedload dominated river was transformed into a suspended load system in the mid late holocene swamps developed in the middle lower part of each floodplain pocket within a few decades of european settlement of this region circa ad 1820 discontinuous watercourses in some floodplain pockets had incised to form a low sinuosity gravel bed channel wedge shaped units of post incisional alluvium that thicken downstream overlie the swamp and floodplain deposits in the downstream part of these pockets in the downstream most pocket incision commenced prior to colonization while upstream swamps retain a continuous swamp across the valley floor the late quaternary evolution of this variant of discontinuous watercourse is summarized in a schematic model

comparison of thermoluminescence and radiocarbon age determinations from late pleistocene alluvial deposits near sydney australia abstract radiocarbon and thermoluminescence tl age determinations have been obtained for a large pleistocene alluvial terrace on the nepean river near sydney new south wales australia the deposit was laid down by a braided river system prior to the last glacial maximum six thoroughly pretreated samples of charcoal and degraded wood buried within gravels at the base of the terrace yielded apparent 14 c ages of 37 000 42 000 yr b p these compare favorably with four tl determinations that gave apparent ages of 41 000 47 000 yr b p for the same deposit adjustment of the 14 c ages to take geomagnetic effects into account further improves the correlation between these two independent dating techniques in addition 14 c and tl correctly identified a reworked portion of the fine grained alluvial overburden as being substantially younger than the main body of the terrace these results augur well for the usefulness of tl age determinations of certain alluvial deposits

holocene valley aggradation driven by river mouth progradation examples from australia since the end of the post glacial sea level rise 6800 years ago progradation of river mouths into estuaries has been a global phenomenon the responses of upstream alluvial river reaches to this progradation have received little attention here the links between river mouth progradation and holocene valley aggradation are examined for the macdonald and tuross rivers in south eastern australia optical and radiocarbon dating of floodplain sediments indicates that since the mid holocene sea level highstand 6800 years ago vertical floodplain aggradation along the two valleys has generally been consistent with the rate at which each river prograded into its estuary this link between river mouth progradation and alluvial aggradation drove floodplain aggradation for many tens of kilometres upstream of the estuarine limits both rivers have abandoned their main holocene floodplains over the last 2000 years and their channels have contracted a regional shift to smaller floods is inferred to be responsible for this change though a greater relative sea level fall experienced by the macdonald river since the mid holocene sea level highstand appears to have been an additional influence upon floodplain evolution in this valley copyright 2006 john wiley sons ltd

floodplain persistence and dynamic equilibrium conditions in a canyon environment abstract canyon river systems are laterally constrained by steep walls strath terraces and bedrock intrusions however semialluvial reaches are nested within these environments as discontinuous floodplains along the river margins these semialluvial floodplains provide an example of dynamic equilibrium set within high energy fluvial systems marking areas where the river is free to alter its boundary conditions most research has focused on hydraulic conditions necessary for floodplain formation and persistence in unconfined systems whereas little is known about canyon streams this paper focuses on 1 characterizing dynamic equilibrium 2 describing the controls on floodplain formation and distribution and 3 evaluating the performance of extremal hypotheses to identify dynamic equilibrium and floodplain persistence in high energy semiconfined canyon environments these objectives were addressed with field and numerical data derived from a one dimensional hydraulic model for bankfull and 100 year return interval flood events supported by closely spaced cross sections for the lower 38 km canyon reach of the deadwood river idaho under bankfull conditions critical energy thresholds for equilibrium floodplain persistence at this study site present the upper limits of slope 0 018 shear stress 175 n m 2 and specific stream power 400 w m 2 channel and floodplains near equilibrium quantified with a near zero sediment transport divergence exner equation were successfully identified by the minimum unit stream power extremal hypothesis and to a lesser degree by the other extremal hypotheses that minimize energy expenditure minimum specific stream power minimum total stream power and minimum froude number provided backwater environments and major tributaries could be identified extremal results were compared to hydraulic geometry relations to evaluate how closely equilibrium floodplains approached values for unconfined alluvial river systems

relations among net transfer reaction progress 18 o 13 c depletion and fluid infiltration in a clinohumite bearing marble a siliceous dolomitic marble xenolith within a mid crustal jurassic diorite exhibits mineralogical and stable isotopic evidence for infiltration of water rich fluid adjacent to endoskarn which bounds the xenolith forsterite has been replaced by clinohumite as a result of a devolatilization reaction driven by addition of aqueous fluid and extraction of heat isotopic compositions of calcite also record infiltration of aqueous fluid concentrated near contacts with endoskarn marble calcite 18osmow values range from 19 5 at the center of the xenolith to 12 6 adjacent to endoskarn calcite 13cpdb decreases sympathetically from 3 0 to 1 4 the calculated equilibrium composition of coexisting c o h f fluid and a quantitative characterization of the whole rock reaction which produced clinohumite and consumed graphite are used to place inequality contraints on the composition of the infiltrated fluid continnum mechanical transport models based on the resulting fluid compositions suggest that a small time integrated darey flux of 44 cm3 cm2 coupled with diffusive transport in the fluid was sufficient to produce both the isotopic shifts and the net transfer reactions evidenced in the xenolith the calculations demonstrate the importance of graphite as an indicator of time integrated flux the maximum possible ch4 content of the infiltrated fluid is sufficiently high to impart a 2 0 uncertainty in the 13c of the fluid the isotopic composition of the fluid is consistent with a magmatic origin when this uncertainty is taken into account

unravelling the conundrum of river response to rising sea level from laboratory to field part ii the fly strickland river system papua new guinea the most recent deglaciation resulted in a global sea level rise of some 120 m over ca 12 000 years a moving boundary numerical model is developed to predict the response of rivers to this rise the model was motivated by experiments at small scale which have identified two modes describing the transgression of a river mouth i autoretreat without abandonment of the river delta no sediment starvation at the topset foreset break and ii sediment starved autoretreat with abandonment of the delta in the latter case transgression is far more rapid and its effects are felt much further upstream of the river mouth a moving boundary numerical model that captures these features in experimental deltas is adapted to describe the response of the fly strickland river system papua new guinea in the absence of better information the model is applied to the case of sea level rise without local climate change in new guinea the model suggests that i sea level rise has forced the river mouth to transgress over 700 km since the last glacial maximum ii sediment starved autoretreat has forced enough bed aggradation to block a tributary with a low sediment load and create the present day lake murray iii the resulting aggradation was sufficient to move the gravel sand transition on the strickland river upstream iv the present day fly estuary may be in part a relict river valley drowned by sea level rise and partially filled by tidal effects and v the fly river is presently reforming its bankfull geometry and prograding into the fly estuary a parametric study with the model indicates that sediment concentration during floods plays a key role in determining whether or not and to what extent transgression is expressed in terms of sediment starved autoretreat a sufficiently high sediment concentration can prevent sediment starved autoretreat during the entire sea level cycle this observation may explain why some present day river mouths are expressed in terms of deltas protruding into the sea and others are wholly contained within embayments or estuaries in which water has invaded landward

contact metamorphism of layered carbonate shale sequences in the oslo rift ii migration of isotopic and reaction fronts around cooling plutons abstract intrusion of felsic plutons of permian age into lower paleozoic shale carbonate sequences caused extensive contact metamorphism in the oslo rift oxygen and carbon isotope data from both carbonates and shales are presented to demonstrate that the progress of metamorphic reactions in the contact aureole around the drammen granite was to a large extent controlled by the infiltration of water rich fluids of a magmatic oxygen and with a carbon isotope signature highly integrated fluid fluxes were confined to shale rich lithologies massive limestones were relatively impermeable to fluid flow the spatial distribution of isotopic and reaction fronts in the aureole and coupled 18 o 13 c isotope variations of carbonates from interlayered shale carbonate units fits well to a 1 d transport model with fluid flow away from the intrusive contact whereas the same isotope variations in limestones containing thin shale intercalations do not the high fluid fluxes estimated from 1 d models 2000 m 3 m 2 require either focused flow of magmatic fluids in the study area or large scale convective flow possibly involving fluids of meteoric origin limited kinetic broadening of the oxygen isotopic front indicates fluid fluxes of 8 m s fluid flow must have persisted for 10 4 yr to have moved the oxygen front 1000 m from the intrusive contact simple 2 d transport models involving dominant fluid flow along aquifers or fractures and involving diffusion as well as advection explain most of the coupled 18 o 13 c trends reported for carbonates from contact aureoles

migration of reaction and isotopic fronts in infiltration zones assessments of fluid flux in metamorphic terrains abstract criteria are presented for recognising fluid infiltration driven reactions in metamorphic rocks and quantifying the associated fractionations of oxygen and carbon isotopic compositions in medium or high grade metamorphic rocks with local equilibrium between fluid and solid phases reactions or isotopic changes driven by infiltrating fluid are expected to migrate as relatively sharp fronts with limited diffusive broadening fluid leaving such reaction fronts is compositionally buffered by the reacting phases in suitably reactive rocks a series of reaction fronts will develop each driven by infiltration of fluid buffered by the upstream reaction knowledge of the spatial arrangement of such fronts allows calculation of the time integrated fluid fluxes total fluid volume per unit area distinctive stable isotope fractionations are predicted adjacent to infiltration driven reactions with the distribution and magnitude of the fractionation effects dependent upon the relative velocities of the reaction and isotopic fronts the various possibilities are illustrated by reference to a hypothetical infiltration driven decarbonation reaction the calculated isotopic fractionations do not in general resemble those predicted by the open or closed system water rock ratio calculations

oxygen isotope thermometry based on a refined increment method and its application to granulite grade rocks from sri lanka abstract in this paper we first present a revision of the increment method a semi empirical technique which allows the calculation of o isotope fractionation factors between all silicates provided their structure and chemical composition is known for the temperature dependency the experimentally calibrated high pressure mineral calcite fractionation factors of chiba et al 1989 are taken as a basis then this method is applied to granulite facies parageneses from sri lanka including quartz k feldspar sillimanite garnet pyroxenes amphiboles cordierite magnetite and ilmenite it can be shown that o isotope equilibration occurred at granulite facies conditions at about 830 c due to static recrystallization locally retrograde re equilibration occurred also at much lower temperatures due to late d4 in most cases however o isotope disequilibria resulted from retrograde oxygen intracrystalline diffusion it can be proved by model calculations that the o diffusion data for water saturated systems reported in the literature are too high by two orders of magnitude to explain the measured isotopic compositions the fractionation patterns allow the discrimination between open and closed system behaviour the regional distribution of open and closed system patterns corresponds to the frequency of occurrence of late stage migmatization western part and to differences in amount and composition of fluid inclusions

implications of geochemical fronts in the notch peak contact metamorphic aureole utah usa abstract the geochemistry of the notch peak contact metamorphic aureole was examined to determine the dominant source of fluid attendant on metamorphism and to estimate fluid fluxes progressive metamorphism of calc silicate rocks is defined by phlogopite diopside and wollastonite isograds mineral assemblages at wollastonite and diopside grades indicate water rich conditions during decarbonation reactions near the intrusion the rocks are highly fractured in both the horizontal and the vertical direction the 18o values of most unmetamorphosed through diopside grade rocks range from 16 3 to 20 2 whereas in the wollastonite zone and near a pre intrusion fault the values approach the 9 5 value of the granitic stock coincident with the zone of18o depletion are zones of ba and zn enrichment consideration of solubilities of these elements in magmatic fluids and of published mineral water distribution coefficients indicates that these elements were advected from the magma model 18o profiles for up temperature flow of formation water assuming variable damko hler numbers and both static and variable thermal gradients fit poorly most data and do not reproduce the broadened front in the observed profile in contrast model profiles for radial one dimensional flow of magmatic water with variable damko hler number under static or variable thermal gradients fit the data well although the model isotopic front remains less distended that the one observed the integrated radial flux of magmatic water indicated by the position of the isotopic front is 1 8 107 mol m 2 additional broadening of the observed front and the scatter of the data suggest diffusion or hydrodynamic dispersion of oxygen regression of the data indicates an effective porosity of 12 in the inner aureole during fluid flow the porosity was largely fracture controlled and resulted from decarbonation sustained exsolution of water from the magma and up to 30 reaction produced volume loss in the high grade rocks the coincidence of the ba zn and 18o fronts suggests that bulk of the magmatic water flow was confined to the wollastontie zone the exception is the proximity of the fault where fluids emanating from an underlying part of the intrusion may also have flowed upward through lower grade rocks

metasomatism and graphite formation at a lithological interface in malaspina alpine corsica france multiple pieces of geologic evidence suggest that interfaces between contrasted lithologies exert a strong control on the fate of volatiles in subduction zones here we present results from a contact between serpentinites and sediments located in corsica and metamorphosed in the blueschist facies during the alpine orogeny it was shown previously that carbonates in the sediments have been reduced to graphitic carbonaceous material within a 5 10 cm thick reaction zone at the contact with serpentinites in an effort to investigate the mechanisms governing this unusual process bulk rock geochemical analyses incorporating a statistical analysis of compositional data are presented observations show that the fate of c was decoupled from that of other elements such as o h and large ion lithophile elements e g k sr ba as that were extensively leached from the reaction zone notably na is strongly enriched in the reaction zone and structurally linked to pectolite reducing conditions manifested by the depletion of o in the reaction zone compared to the bulk metasediment were likely maintained by the presence of fe ii in the serpentinite moreover thermodynamic calculations show that the low solubility of carbon in coh fluids at high pressure and low temperature conditions was the main driver for graphite precipitation synchronously with carbonate destabilization this may have been kinetically favored by the presence of already existing graphitized carbonaceous material and phengite in the metasediment limited lateral flow might have contributed as well to the geochemical and petrological patterns observed in these rocks

alluvium of antiquity polycyclic terraces in a confined bedrock valley confined river valleys are not the localities where long term preservation of alluvium would be expected the 25 km long low gradient 0 0014 m m 1 confined valley setting of the shoalhaven river has archived alluvium of middle pleistocene age to maintain a relatively uniform channel as an efficient conduit for a wide range of flows in a confined bedrock valley of variable morphology single grain optically stimulated luminescence osl dating has identified polycyclic terraces up to 193 ka in age marine isotope stage mis 7 with lower terrace remnants dating from 173 140 ka mis 6 and 106 ka mis 5 holocene alluvium 2 3 5 ka in age caps these old pleistocene units and a well constrained combination of one dimensional and two dimensional hydraulic modelling demonstrates that these polycyclic terraces are clearly within reach of the modern hydrological regime the 106 ka terrace at 17 m above low flow is inundated by floods recurring on average every 20 years and the 140 193 ka terraces at 20 22 m are overtopped every 50 100 years these ancient diachronous landforms exhibit complex depositional histories and are on lapped by longitudinal benches of modern sand and gravel their polycyclic nature appears to be a response to flow reduction using alluvium to adjust the boundary of the otherwise inflexible morphology of a bedrock gorge

fluid flow patterns and infiltration isograds in melilite marbles from the bufa del diente contact metamorphic aureole north east mexico in the inner aureole of the bufa del diente alkali syenite north east mexico thin calcareous argillite bands horizontally embedded in impure marbles acted as contact metamorphic aquifers for hypersaline brines of magmatic origin thick bedded marbles were largely impervious from 180 m up to the intrusion contact argillites were completely decarbonated resulting in melilite wollastonite phlogopite perovskite bearing parageneses in marbles this assemblage is confined to a narrow 7 12 m wide infiltration zone adjacent to the contact up to this distance calcite wollastonite diopside alkali feldspar titanite was stable indicating that the fluid evolution in these marbles was internally buffered brine infiltration from the metaargillite aquifer into the marbles occurred perpendicular to the marble metaargillite boundaries and was confined to a zone 4 6 cm wide above the boundaries this is documented by the three reactions cc di mel co2 1 cc kfs di h2o phl wo co2 2 cc ttn prv wo co2 3 melilites ak32 45gh13 32sm32 40 to ak52 72gh0 1sm28 48 occur as rims around diopsides and become continuously thicker towards the metaargillite beds fluid inclusion observations suggest that the infiltrating brine was hypersaline nacl kclcq 65 wt and that the reactions took place at the water rich side of the h2o co2 salts immiscibility field at about 600d c 2 3 and 660 to 680d c 1 at p 1200 bar and xco2 0 02 mass balance calculations show that the amount of brine infiltrated from the aquifer into the marble was very low and decreased continuously with increasing distance from the boundary the maximum width of brine infiltration was about 6 cm this confirms that brine flow was largely parallel to the aquifer not perpendicular to it the co2 produced by the decarbonation reactions probably escaped as an immiscible low density h2o co2 fluid of xco2 0 5 into overlying marble via grain edge flow the metaargillite marble boundary acted as a semipermeable membrane 6 cm in thickness keeping back the brine in the aquifer and losing the in situ produced low density co2 rich fluid

thermodynamics and lattice vibrations of minerals 5 applications to phase equilibria isotopic fractionation and high pressure thermodynamic properties in previous papers in this series a model that uses available elastic structural and spectroscopic data on minerals has been used to predict the thermodynamic functions cv heat capacity s entropy e internal energy and f helmholtz free energy in this paper four applications to problems of current geochemical and geophysical interest are presented 1 interpretation of complex trends of calorimetric data 2 calculation of phase equilibria 3 calculation of oxygen isotopic fractionation factors and 4 estimation of the effect of pressure on thermodynamic functions the model demonstrates that trends in high temperature thermodynamic properties of silicates are determined by the position and relative numbers of high frequency modes generally antisymmetric si al o stretching modes the position of these modes varies systematically with degree of polymerization of tetrahedra and therefore high temperature calorimetric behavior is relatively systematic as a function of crystal structure and mineral composition trends at low frequency are much more complex because the low frequency optic modes that most strongly influence the low temperature thermodynamic functions depend in a complex way on the size coordination and mass of cations and various polyhedra in the minerals the heat capacity curves of kyanite andalusite and sillimanite and of quartz coesite and stishovite show crossovers that cannot be explained by debye theory which accounts only for acoustic mode behavior but can be explained by the model spectra proposed because proper account is taken of the changing low and high frequency optic modes upon polymorphic transformations the proposed model is sufficiently accurate that phase equilibrium problems can be addressed the quartz coesite stishovite equilibrium curves the kyanite andalusite sillimanite triple point and the breakdown of albite to jadeite plus quartz are cited as specific examples for each example predicted slopes of equilibrium curves agree moderately well to excellently with slopes determined experimentally the calculated slopes are sensitive to spectroscopic parameters particularly to the distribution of optic modes in the far infrared this sensitivity is discussed in detail for the albite breakdown reaction the model can be used for prediction of isotopic fractionation factors if spectra of the isotopic forms of the mineral are known or postulated a simple set of rules for generating hypothetical spectra of 18o minerals from measured spectra of the 16o forms is given reduced partition functions are calculated for 13 minerals at 298 k the model values of reduced partition function 1000 ln of these minerals decrease in the order quartz calcite albite muscovite clinoenstatite anorthite diopside pyrope grossular zircon forsterite andradite rutile in good agreement with experimental data at 1000 k the first six minerals show small crossovers so that the order becomes calcite muscovite albite quartz anorthite and clinoenstatite the differences in 1000 ln at high temperature for these minerals are so small that the model probably cannot address the deviations from experimental trends the model clearly defines the region in which the fractionation factors do not follow a 1 t trend and should be useful for extrapolation of experimental data to low temperatures finally a modified gruneisen parameter model is proposed for shift of the lattice vibrational frequencies under compression and thermodynamic properties to 1000 kbar 1000 k are given for nine minerals at 1 mbar the predicted decrease in entropy at 298 k ranges from 54 of the 1 bar value for periclase to 25 for stishovite

alluvial terrace preservation in the wet tropics northeast queensland australia alluvial terraces provide a record of aggradation and incision and are studied to understand river response to changes in climate tectonic activity sea level and factors internal to the river system terraces form in all climatic regions and in a range of geomorphic settings however relatively few studies have been undertaken in tectonically stable settings in the tropics the preservation of alluvial terraces in a valley is driven by lateral channel adjustments vertical incision aggradation and channel stability processes that can be further understood through examining catchment force resistance frameworks this study maps and classifies terraces using soil type surface elevation sedimentology and optically stimulated luminescence dating across five tropical catchments in northeast queensland australia this allowed for the identification of two terraces across the study catchments t1 t2 the t1 terrace was abandoned 13 9 ka with its subsequent removal occurring until 7 4 ka abandonment of the t2 terrace occurred 4 9 ka with removal occurring until 1 2 ka differences in the spatial preservation of these terraces were described using an index of terrace preservation tpi assessments of terrace remnant configuration highlighted three main types of terraces paired unpaired and disconnected indicating the importance of different processes driving preservation regional scale variability in tpi was not strongly correlated with catchment scale surrogate variables for drivers of terrace erosion and resistance however catchment specific relationships between tpi and erosion resistance variables were evident and are used here to explain the dominant processes driving preservation in these tropical settings this study provides an important insight into terrace preservation in the tectonically stable humid tropics and provides a framework for future research linking the timing of fluvial response to palaeoclimate change

mind the gap an absence of valley fill deposits identifying the holocene hypsithermal period of enhanced flow regime in southeastern australia the holocene sedimentary record in southeastern australia is present in a range of landscape settings such as upland swamps dells internally drained lake basins alluvial fans and mid catchmen

uplift driven valley incision and river terrace formation in southern england outside the limits of middle pleistocene glaciation the river basins of southern england contain long cenozoic terrestrial sedimentary records of greatest importance are the river terrace sequences which contain biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary however trends in valley development cannot easily be accommodated within the framework of quaternary climatic change it is argued in this paper that episodic incision and terrace development result from uplift a consequence of the interplay between continuing alpine orogenic movements and erosion driven isostasy using a simple linear model height age an uplift rate of ca 7 cm ka 1 is estimated for the terrace sequence in the upper thames valley this preliminary model is evaluated using the records of adjacent basins 1997 john wiley sons ltd

fluviatile evidence for a period of late quaternary pluvial climate in coastal southeastern australia abstract the cranebrook terrace near sydney new south wales yields sound evidence of a period of exceptional fluvial activity in lowland basins of southeastern coastal australia well prior to the last glacial maximum this episode titled here the cranebrook pluvial is dated from radiocarbon and thermoluminescence age determinations as ending about 40 000 45 000 yr b p it was characterised along the lower nepean river by abundant gravel transported over a braid plain proximal to confining sandstone gorges thick basal gravels were deposited almost contemporaneously with a sandy clay overburden until this time when the river quite quickly became confined to two laterally stable channels additional overbank deposition probably accompanied this stable phase the easternmost channel was abandoned about 34 000 37 000 yr b p and the nepean river appears to have occupied only the western channel since then isolated from eustatic changes occurring downstream the nepean river has left no significant alluvial deposits from the last glacial maximum or from the holocene periods of time which in this fluvial environment appear quiescent by comparison with preglacial pluvial however stripping and replacement of the fine overburden appears to have occurred over the western part of the terrace about 14 000 yr b p or somewhat younger from 14 c determinations these conclusions are at odds with the proposal that the main period of alluvial deposition in coastal valleys of southeastern australia was triggered by widespread slope instability during the last glacial maximum alluvial and pollen data suggest the glacial was a cool dry period of relatively little fluvial activity in basins not affected by glaciation the cranebrook pluvial was probably the most important erosional depositional episode in the non glacially effected areas of southeastern australia in the last 50 000 years

immiscible fluids in metamorphism implications of two phase flow for reaction history fluid immiscibility between a co 2 rich fluid and brine has been described from several medium to high grade marbles and calcsilicates here we also report evidence for ch 4 h 2 o immiscibility in low grade metamorphic rocks from wales and suggest that the flow of such immiscible fluids may be comparable to that of water oil or water gas mixtures in petroleum reservoirs this analogy implies that where one fluid is being produced by reaction it will flow out of the rock while the other remains immobile except insofar as it is soluble in the more abundant fluid phase hence extensive reaction may take place in the presence of coexisting immiscible fluids each having high activities it is proposed that this type of flow behavior not only accounts for the development of salt saturated fluids in marbles but also may be responsible for the elimination of carbonate and extensive loss of graphite from pelites in the lower part of the greenschist facies

experimental kinetic study of the reaction calcite quartz wollastonite carbon dioxide from 1 to 3 kilobars and 500 degrees to 850 degrees c

stratigraphic architecture resulting from late quaternary evolution of the riverine plain south eastern australia the riverine plain of south eastern australia is the result of prolonged cenozoic fluvial activity single thread anabranching and distributary channels and floodplains and associated aeolian dunes characterize the uppermost sequences based on detailed interpretations of late quaternary fluvial sedimentation and surficial stratigraphy for this 77 000 km2 basin earlier prior stream and ancestral stream models of fluvial deposition deduced from limited stratigraphic and chronological evidence are replaced with aggradational palaeochannel and migrational palaeochannel models thermoluminescence dating reveals four distinct phases of palaeochannel activity between 105 and 12 ka the first coleambally phase late in oxygen isotope stage 5 the second kerarbury phase in stage 3 the third gum creek phase before and the fourth yanco phase after the last glacial maximum lgm in stage 2 the first three of these phases were characterized by mixed load laterally migrating sinuous palaeochannels with occasional transitions to a straighter bedload dominated mode and vice versa the first two phases concluded with a bedload dominated episode resulting in aggradational palaeochannels on the surface of the plain and the third phase prior to the lgm did also in its downstream reaches the phase following the lgm was characterized entirely by large mixed load sinuous migrational palaeochannels these exhibited no terminating bedload episode because the onset of holocene climates reduced the size of the flood peaks greatly diminished the supply of bedload from the upper catchments and resulted in streams evolving to their present highly sinuous suspended load form the result is a complex stratigraphic architecture consisting of vertically and laterally accreted units extending over hundreds of kilometres in the form of channel sand stringers sand sheets and derivative aeolian dunes partially or wholly encased in overbank fines

late cretaceous tectonic framework of the tibetan plateau abstract new research coupled with previous data reveals the late cretaceous paleo geography and related paleo tectonic movement of the tibetan plateau a vast ocean the neo tethys ocean perhaps as wide as 7000 km existed between the indian and eurasian continental plates in the early late cretaceous in addition a himalaya marginal sea lay along the border of the indian plate and other marginal seas were present to the north in both the southern lhasa and southwestern tarim blocks northward subduction of the neo tethys oceanic plate along the yalung zangbu suture closed most of the ocean and led to intensive thrusting tight folding magmatic plutonism and volcanic eruptions in the central plateau to the north a magmatic arc up to 500 km wide formed across the southern margin of the continental plate in central tibet and its varying granitic composition appears to reflect the depth to the subducted plate and define its geometry a series of large chiefly north dipping thrust systems also developed across central tibet these include thrusts along the yalung zangbu and bangong nujiang sutures the north gangdese and north lhasa thrusts in the lhasa block the qiangtang and north tangula thrusts in the qiangtang block the hoh xil and bayan har thrusts in the hoh xil block as well as the sinistral slip south kunlun and altyn tagh faults in northern tibet uplifts formed above the hanging walls of the major thrusts and their eroded debris formed thick red beds in basins below them the central tibetan plateau maintained a low elevation and coastal vegetation was dominant during the late cretaceous

tourmaline bearing rocks in the singhbhum shear zone eastern india evidence of boron infiltration during regional metamorphism frozen in reaction textures combined with mineral chemistry of tourmaline bearing metamorphic assemblages provide valuable information about fluid rock interaction during orogenesis tourmaline occurs in four distinct mineralogical associations in the singhbhum shear zone ssz of the precambrian east indian craton the tourmaline bearing rocks are associated intimately with pelitic to psammopelitic and quartzofeldspasthic rocks including meta granite the rocks were affected by two sets of folding f1 and f2 and ductile shearing associated with f1 during ca 1 6 1 8 ga tectonic activity in this belt quantitative geothermobarometry and the stability relations of the metamorphic assemblages developed in the pelitic rocks establish the presence of two episodes of metamorphism a prograde m1 event that culminated at 480 40 c 6 4 0 4 kbar and an m2 event that caused retrogression of the m1 assemblages field and petrographic observations in combination with data on chemical composition of tourmaline indicate three stages of tourmaline growth the earliest stage is represented by pretectonic pre metamorphic greenish yellow tourmaline cores in the tourmalinite from the surda area association a the textural relations demonstrate that in the second stage greenish yellow cores of oscillatory zoned tourmaline in the metagranite albite quartz biotite chlorite muscovite apatite magnetite association c very fine tourmaline grains in muscovite schist muscovite quartz association b and greenish yellow cores of tourmaline in biotite muscovite schist biotite muscovite magnetite chlorite apatite quartz association d crystallized during the f1 m1 events post tectonic greenish blue tourmaline belonging to the third stage replaces the earlier tourmaline grains along their margins and cracks compositionally tourmalines of all four associations fall in the alkali group most of the data fall in the dravite field with a few analyses straddling the boundary between schorl and dravite an abrupt compositional change was noted across the different color zones in the tourmaline grains this change is explained by one or more of the coupled substitutions al nar 1 car naal 1 and mg fe 1 where r mg fe2 mn integrating the field petrographic and phase compositional data it has been demonstrated that tourmaline growth in the second and third stages was induced by infiltration driven b metasomatism during prograde metamorphism of the rocks deep seated magma was the source of the b bearing hydrothermal fluid

reaction induced fluid flow in synthetic quartz bearing marbles the reaction kinetics and fluid expulsion during the decarbonation reaction of calcite quartz wollastonite co2 in water absent conditions were experimentally investigated using a paterson type gas apparatus starting materials consisted of synthetic calcite quartz rock powders with variable fractions of quartz 10 20 and 30 wt and grain sizes of 10 m calcite and 10 and 30 m quartz prior to reaction samples were hiped at 700 c and 300 mpa confining pressure and varying pore pressures initial porosity was low at 2 7 6 3 depending on pore pressure during hip and the amount and grain size of quartz particles samples were annealed at reaction temperatures of 900 and 950 c at 150 and 300 mpa confining pressures well within the wollastonite stability field run durations were between 10 min and 20 h sem micrographs of quenched samples show growth of wollastonite rims on quartz grains and co2 filled pores between rims and calcite grains and along calcite grain boundaries measured widths of wollastonite rims vs time indicate a parabolic growth law the reaction is diffusion controlled and reaction progress and co2 production are continuous porosity increases rapidly at initial stages of the reaction and attains about 10 12 after a few hours permeability at high reaction temperatures is below the detection limit of 10 21 m2 and not affected by increased porosity this makes persistent pore connectivity improbable in agreement with observed fluid inclusion trails in form of unconnected pores in sem micrographs release of co2 from the sample was measured in a downstream reservoir the most striking observation is that fluid release is not continuous but occurs episodic and in pulses ongoing continuous reaction produces increase in pore pressure which is once having attained a critical value pcrit spontaneously released connectivity of the pore space is short lived and transient the resulting cycle includes pore pressure build up formation of a local crack network pore pressure release and crack closure using existing models for plastic stretching and decrepitation of pores along with critical stress intensity factors for the calcite matrix and measured pore widths it results that pcrit is about 20 mpa patterns of fluid flow based on mineralogical and stable isotope evidence are commonly predicted using the simplifying assumption of a continuous and constant porosity and permeability during decarbonation of the rock however simple flow models which assume constant pore pressure constant fluid filled porosity and constant permeability may not commonly apply properties are often transient and it is most likely that fluid flow in a specific reacting rock volume is a short lived episodic process

late quaternary floodplain sedimentation along the pomme de terre river southern missouri abstract new cross sections and dates from along the pomme de terre river clarify the complex local history of valley development and floodplain sedimentation the observed history begins with a series of ancient bedrock strath terraces that record past bedrock valley positions at 15 5 to more than 58 m above the modern bedrock floor each strath is capped by 1 2 m of channel gravel and sand permeated by red clay sometime previous to ca 140 000 yr b p a much lower bedrock valley only about 5 6 m above the modern level was excavated by 140 000 yr b p accumulation of red and gray mottled silty clay had commenced and had reached to 8 5 m above the modern floodplain before 48 900 900 14 c yr b p sometime between ca 49 000 and 45 000 14 c yr b p erosion caused abandonment of an oxbow meander and lowered the bedrock valley to about its present depth younger yellowish red and gray mottled silty clay alluvium then began accumulating this mid wisconsinan fill reached to 2 5 m above the modern floodplain sometime before 31 800 1340 14 c yr b p at which time another erosional phase was in progress a late wisconsinan olive clay accumulated between 27 480 1950 and ca 23 000 14 c yr b p followed by approximate stability until 13 550 400 14 c yr b p after stability an erosional episode began but by 10 200 330 14 c yr b p deposition of a distinctive brown clayey silt was underway this early holocene fill reached to about the same level as the mid wisconsinan fill by 8100 140 14 c yr b p erosion occurred between this date and 7490 170 14 c yr b p but the former floodplain level was rapidly reattained and was apparently stable until ca 5000 14 c yr b p finally erosional unconformities and 17 dates from the brown clayey silt and from younger grayish brown silty sand underlying the modern floodplain record subsequent episodes of floodplain erosion at ca 5000 2900 1500 and 350 14 c yr b p the timing of pomme de terre floodplain sedimentary regimes characterized by net aggradation erosion or stability may have been controlled by climate in particular both periods of stability appear to have been coeval to times of strongly zonal upper atmospheric circulation intensified zonal circulation would have resulted in less frequent large floods and an increased dominance by floods of small to moderate size in contrast there are no obvious parallels to be drawn between this local alluvial history and sea level or glacial outwash induced baselevel changes

chronology of murrumbidgee river palaeochannels on the riverine plain southeastern australia four major periods of palaeochannel activity have been identified on the murrumbidgee sector of the riverine plain of southeastern australia on the basis of stratigraphic information the channels reveal a picture of changing flow conditions during the last full glacial cycle the ages of the periods were determined from nearly 40 thermoluminescence dates on surficial fluvial and aeolian sediments these are named the coleambally phase which occurred from 105 to 80 ka the mid to latter part of oxygen isotope stage 5 the kerarbury phase from 55 to 35 ka stage 3 the gum creek phase from 35 to 25 ka late stage 3 to early stage 2 and the yanco phase from 20 to 13 ka late stage 2 the present flow regime was established by about 12 ka stage 1 the first two phases correlate with episodes of enhanced fluvial activity in northern and central australia and with reduced dust activity globally the phases in stage 2 appear to be associated with seasonal snow melt and increased peak flows in periods flanking the last glacial maximum source bordering aeolian dunes associated with the coleambally kerarbury and yanco phases were found however the tl dates show that some have undergone aeolian reworking thermoluminescence dating and fluvial stratigraphy have revealed a detailed picture of late quaternary climate and flow regime changes that has the potential to extend to identified deposits stratigraphically older than those described here

a 40 000 year vegetation history and climatic interpretations of burraga swamp barrington tops new south wales abstract burraga swamp a small basin surrounded by cool temperate rainforest at 985 m in the central new south wales highlands has provided a record of 40 000 years from 40 000 30 000 years bp the site was a lake with a very slow rate of deposition of fine grained sediments and flourishing aquatic swamp vegetation the dryland vegetation was an open or sparsely treed grassland herbfield from 30 000 21 000 years bp the dryland vegetation remained much the same but the aquatic vegetation disappeared from 21 000 17 500 years bp sandy sediments were deposited at an accelerated rate culminating in a layer of gravelly sand possibly the result of periglacial activity only one band of clay in this section contained sufficient pollen to study indicating treeless vegetation after 17 000 years bp the rate of sediment accumulation slowed or ceased and after 15 000 years some mesic elements started to return at 6500 years bp peat started forming and cool temperate rainforest was fully developed remaining on the site to the present this site extends the record of treeless condition at the last glacial maximum to more northerly localities than previously known