geophysical techniques for evaluating the internal structure of cheniers southwestern louisiana abstract historically louisiana chenier plain studies have consisted of surficial mapping sediment analyses cores and direct observation of limited exposures from borrow pits ground penetrating radar gpr a shallow geophysical technique provides high resolution profiles of contrasts in electrical permittivity that can be correlated with sedimentary layers in sand and gravel depositional environments not effected by salt water reconnaissance vertical electrical soundings ves were performed at several sites to determine the applicability of gpr on the chenier plain based on resistivity data three field sites were targeted for gpr profiling gpr profiles were collected using a geophysical survey systems inc subsurface interface radar 10a unit with a 500mhz antenna on a grid designed to assess three dimensional variability in subsurface characteristics of each chenier topographic corrections were applied for each processed profile to adjust for surface elevation differences that effect reflection orientation at selected chenier locations subsurface reflections reveal a complex internal structure within these clastic deposits however at the interface with adjacent or subsurface fine grained deposits clay and or conductive pore water limit penetration electrical resistivity proved to be a valuable reconnaissance tool for determining applicability of gpr and ves models correlated directly with vibracore data preliminary interpretations of radar profiles suggest cheniers evolve through multiple processes in different environments radar facies observed in dip oriented profiles at two sites are described as landward stepping foresets and may be interpreted as transgressive washover deposits bedset orientation of strike oriented profiles indicates a westward component of migration at a third site landward and seaward dipping reflections interpreted as upper shoreface and washover deposits indicate shifting shoreline position related to transgression and regression associated with variations in sediment supply

responses of stable bay margin and barrier island systems to holocene sea level highstands western gulf of mexico abstract the microtidal wave dominated coast of the western gulf of mexico displays a variety of holocene geomorphic features indicating higher than present water levels that were previously attributed to storm processes while geoidal sea level was at its present position field and aerial photograph examinations of bay margins barrier islands and beach ridge plains following major hurricanes show that the elevated features are inundated periodically by high storm surge despite their inundation these highstand features are not modified by modern storm processes instead storm related erosion and deposition are always seaward of and lower than the highstand features and are always limited to the extant shorezone where elevations typically are less than 1 5 m above present sea level bay margin and lagoonal highstand indicators include raised marshes and subtidal flats wave cut benches abandoned wave cut scarps with fringing marshes and or beach ridges and accretionary islands and recurved spits other emergent marine features include abandoned compound flood tidal delta and washover fan complexes attached to barrier islands and anomalously high beach ridges within both the barrier island complexes and beach ridge plains the highest beach ridges raised marshes and flats and erosional scarps and benches are manifestations of one or more rising phases and highstands in sea level whereas the lower marshes and accretionary topography are mainly products of the falling phases and shoreface adjustment to present sea level different elevations of beach ridge sets discordant truncation of beach ridges and elevated marine and brackish water faunal assemblages preserved in beach ridges raised marshes and flats and natural levees are compelling evidence of sea level fluctuations of 1 to 1 5 m from about 5500 to 1200 cal yr bp independent evidence from studies of geodynamic climatic and glacio eustatic processes can explain the mid holocene highstands and late holocene lowering of sea level that is observed in tectonically stable coastal regions far from former centers of glaciation

suspended matter and fluid mud off alleppey southwest coast of india abstract time series measurements on suspended particulate matter spm were made at one non mud bank m1 and two mud bank stations m2 and m3 off alleppey south west coast of india the mean spm was low in surface 6 2 mg l and mid depth 3 7 mg l waters and higher in bottom depth waters 24 6 mg l of these stations during both pre monsoon and monsoon seasons near bed suspended sediment results indicated low spm during july 0 042 g l and september 0 018 g l at m1 but very high spm at m2 9 2 g l and m3 6 2 g l during july that decreased m2 0 033 g l m3 0 1 g l again in september observations based on lisst 25x indicated that optical transmission ot was high 80 100 in surface and mid depth waters but decreased with increasing depth near bed waters at m2 and m3 stations showed 1 m thick fluid layer with 0 ot and with high particle volume concentrations 150 200 l l during monsoon bottom sediments were clayey silts sediments of

adakites from continental collision zones melting of thickened lower crust beneath southern tibet adakites are geochemically distinct intermediate to felsic lavas found exclusively in subduction zones here we report the first example of such magmas from southern tibet in an active continental collision environment the tibetan adakites were emplaced from ca 26 to 10 ma and their overall geochemical characteristics suggest an origin by melting of eclogites and or garnet amphibolites in the lower part 50 km of thickened tibetan crust this lower crustal melting required a significantly elevated geotherm which we attribute to removal of the tectonically thickened lithospheric mantle in late oligocene time the identification of collision type adakites from southern tibet lends new constraints to not only the himalayan tibetan orogenesis how and when the indian lithosphere started underthrusting asia can be depicted but also the growth of the early continental crust on earth that consists dominantly of the tonalite trondhjemite granodiorite suites marked by adakitic geochemical affinities

holocene coastal environments and processes in subantarctic temperate cold tierra del fuego argentina chile fil bujalesky gustavo gabriel consejo nacional de investigaciones cientificas y tecnicas centro austral de investigaciones cientificas argentina

quantifying holocene lithospheric subsidence rates underneath the mississippi delta abstract the pattern of holocene relative sea level rsl change on the us gulf coast has been a long standing subject of debate featuring opposing scenarios of continuous submergence versus one or more holocene rsl highstands the significance of this debate is that the relative role of eustasy glacial isostatic adjustment gia and lithospheric flexural subsidence associated with mississippi delta sediment loading remains unresolved here we present a new rsl record from the louisiana chenier plain 100 km west of the mississippi delta margin based on ams 14 c dated marsh basal peat this enables us to provide for the first time constraints on holocene lithospheric subsidence rates underneath one of the world s major deltas our new record conclusively shows that no middle holocene rsl highstands occurred on the central us gulf coast rather it exhibits a pattern of progressive rsl rise comparable to that from the mississippi delta suggesting that long wavelength gia is a dominant deformational process driving lithospheric subsidence in the entire region by means of forebulge collapse nevertheless a 0 15 0 07 mm yr differential rate of subsidence between the chenier plain and key portions of the mississippi delta including the new orleans metropolitan area exists this shows that while the sediment loading effect is real it is about an order of magnitude smaller than recent studies have postulated

deciphering holocene sea level history on the u s gulf coast a high resolution record from the mississippi delta published holocene relative sea level rsl curves for the u s gulf coast are in mutual conflict with some characterized by a smooth rsl rise akin to widely accepted eustatic sea level curves versus others including several recent ones that are characterized by a conspicuous stair step pattern with prolonged millennium scale rsl stillstands alternating with rapid meter scale rises in addition recent work in texas and alabama has revitalized the notion of a middle holocene rsl highstand estimated at 2 m above present mean sea level an extensive sampling program in the mississippi delta louisiana focused on the collection of basal peats that accumulated during the initial transgression of the pre existing consolidated pleistocene basement we used stable carbon isotope ratios to demonstrate that many of these samples accumulated in environments affected by frequent saltwater intrusion in the 30 cm zone between mean spring high water and mean sea level and we selected plant macrofossils that were subjected to ams 14c dating nearly 30 sea level index points from a 20 km2 study area on the eastern margin of the delta suggest that rsl rise followed a relatively smooth trend for the time interval 8000 3000 cal yr b p thus questioning the occurrence of major rsl stillstands alternating with abrupt rises given the narrow error envelope defined by our data set any sea level fluctuations if present would have amplitudes of 1 m although a true middle holocene highstand never occurred in the mississippi delta the high level of detail of our time series enables a rigorous test of this hypothesis correction of our data set for a hypothetical tectonic subsidence rate of 1 1 mm yr 1 assuming a constant subsidence rate compared to the tectonically relatively stable adjacent coast of texas leads to sea levels near 2 m above present during the time interval 6000 4000 cal yr b p however this model also implies a rsl position near 2 m around 8000 cal yr b p which is inconsistent both with data of this age from texas as well as with widely accepted sea level data from elsewhere we therefore conclude that a middle holocene highstand for the u s gulf coast is highly unlikely and that the entire area is still responding glacio isostatically by means of forebulge collapse to the melting of the laurentide ice sheet

mafic magmatic enclaves and mafic rocks associated with some granitoids of the central sierra nevada batholith california nature origin and relations with the hosts abstract the calc alkaline granitoids of the central sierra nevada batholith are associated with abundant mafic rocks these include both country rock xenoliths and mafic magmatic enclaves mme that commonly have fine grained and less commonly cumulate textures scarce composite enclaves consist of either xenoliths enclosed in mme or of mme enclosed in other mme with different grain size and texture enclaves are often enclosed in mafic aggregates and form meter size polygenic swarms mostly in the margins of normally zoned plutons enclaves may locally divert schlieren layering mafic dikes which also occur in swarms are undisturbed composite or largely hybridized in central sierra nevada with the exception of xenoliths that completely differ from the other rocks host granitoids mafic aggregates mme and some composite dikes exhibit a bulk compositional diversity and at the same time important mineralogical and geochemical including isotopic similarities mme and host granitoids display distinct major and trace element compositions however strong correlations between mme host granitoid pairs indicate interactions and parallel evolution of mme and enclosing granitoid in each pluton identical mafic mineral compositions and isotopic features are the result of these interactions and parallel evolution mafic dikes have broadly the same major and trace element compositions as the mme although variations are large between the different dikes that are at distinctly different stages of hybridization and digestion by the host granitoids the composition of the granitoids and various mafic rocks reflects three distinct stages of hybridization that occurred respectively at depth during ascent and emplacement and after emplacement the occurrence and succession of hybridization processes were tightly controlled by the physical properties of the magmas the sequential thorough or partial mixing and mingling were commonly followed by differentiation and segregation processes unusual mme that contain abundant large crystals of hornblende resulted from disruption of early cumulates at depth whereas those richer in large crystals of biotite were formed by disruption of late mafic aggregates or schlieren layerings at the level of emplacement mme and host granitoids are considered cogenetic because both are hybrid rocks that were produced by the mixing of the same two components in different proportions the felsic component was produced by partial melting of preexisting crustal materials whereas the dominant mafic component was probably derived from the upper mantle however in the lack of a clear mantle signature the origin of the mafic component remains questionable

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

a 5200 year paleoecological and geochemical record of coastal environmental changes and shoreline fluctuations in southwestern louisiana implications for coastal sustainability abstract this study presents a 5200 year history of coastal environmental changes and shoreline fluctuations based on a multi proxy sedimentary record developed from the eastern end of louisiana s chenier plain palynological loss on ignition grain size and x ray fluorescence data for a 525 cm sedimentary core indicate five stages of ecosystem development in the rockefeller wildlife refuge since the mid holocene between 5190 and 4240 cal yr bp the relative sea level was much lower than the present level and our study area was occupied by a baldcypress swamp when the sale cypremont subdelta complex formed at a western position approximately 4600 years ago our study area was transformed to a maritime forest about 4240 3440 cal yr bp suggesting shoreline progradation when the mississippi river delta lobe switched to more easterly positions during the teche st bernard lafourche and plaquemine balize complexes our study site was transformed back to a freshwater swamp between 3440 and 1520 cal yr bp and then to a coastal marsh between 1520 and 300 cal yr bp after the atchafalaya wax lake subdelta complex formed at a more westerly position again the modern day beach form at 300 cal yr bp these coastal ecosystem developments suggest that shoreline retreat started at 3440 cal yr bp and persisted to the present day in addition evidence of at least four possible paleohurricane events was found during the late holocene our multi proxy record demonstrates that shoreline fluctuation in southwestern louisiana was tied to the mississippi river delta switch since the mid holocene shoreline progradation occurred during the sale cypremont subdelta phase 5200 3500 years ago when the sediment supply was high retrogradation occurred after 3500 cal yr bp when the mississippi river subdelta complexes occupied more easterly position resulting in diminished sediment supply a significant increase in the delivery of water and total suspended sediment load from the atchafalaya river to the gulf of mexico is needed in order to sustain the southwestern louisiana coastal wetlands

assumed holocene highstands gulf of mexico basic issues of sedimentary and landform criteria discussion record high mid and late holocene relative sea levels significantly above the current sea level have been widely documented in certain areas of the australo pacific region brazil lessa et al 2000 and parts of africa and india that were not characterized by tectonic uplift and or glacio isostatic rebound such elevated sea levels are yet to be reliably identified on our gulf and atlantic shores radically departing from traditional gulf of mexico sea level curves morton et al 2000 now suggest recurring highstands throughout the entire second half of the holocene epoch their findings echo earlier ideas in the same vein see otvos 1995 1997 1999 however a detailed analysis of several lines of evidence presented by morton et al raises serious doubts about these conclusions morton et al accept the position of beach ridge summits as indicative of higher than present elevations thus seaward declining beach ridge summits on bolivar peninsula galveston island and other coastal areas of texas in their view reflect late holocene sea levels that fell from their highest elevations although beach ridges are of wave constructed berm ridge foredune or composite origins otvos 2000 morton et al fail to distinguish adequately among these categories by sediment and landform analysis the problem is that under favorable circumstances wave built berm ridges may be accurate markers of ancient sea levels or lake levels foredunes on the other hand aggrade to varying supratidal elevations rising several meters above the associated high tide level for this reason summit elevations of relict foredunes can not provide precise data on corresponding sea level otvos 1995 foredune ridges foredune ridges often overlie mask and bury wave built berm ridges beal and shepard 1956 because sand is usually readily available for wind transport on most gulf shores the upper interval in most beach ridges tends to be of eolian origin except when wave built

internal architecture and evolution of bioclastic beach ridges in a megatidal chenier plain field data and wave flume experiment beach ridges in macrotidal environments experience strong multi annual to multi decennial fluctuations of tidal inundation the duration of tide flooding directly controls the duration of sediment reworking by waves and thus the ridge dynamics flume modelling was used to investigate the impact of low frequency tidal cycles on beach ridge evolution and internal architecture the experiment was performed using natural bioclastic sediment constant wave parameters and low frequency variations of the mean water level the morphological response of the beach ridge to water level fluctuations and the preservation of sedimentary structures were monitored by using side view and plan view photographs results were compared with the internal architecture of modern bioclastic beach ridges in a macrotidal chenier plain mont st michel bay france surveyed with ground penetrating radar the experimentally obtained morphologies and internal structures matched those observed in the field and the three ridge development stages identified in ground penetrating radar profiles early transgressive late transgressive and progradational were modelled successfully flume experiments indicate that flat bioclastic shapes play a key role in sediment sorting in the breaker zone and in sediment layering in the beach and washover fans water level controls washover geometry beach ridge evolution and internal structure low water levels allow beach ridge stabilization and sediment accumulation lower on tidal flats during subsequent water level rise accumulated sediment becomes available for deposition of new washover units and for bayward extension of the beach ridges in the field low frequency water level fluctuations are related to the 4 4 year and 18 6 year tidal cycles experimental results suggest that these cycles may represent the underlying factor in the evolution of the macrotidal chenier coast at the multi decadal to centennial time scale

petrogenesis of the late yanshanian mantle derived intrusions in southeastern china response to the geodynamics of paleo pacific plate subduction abstract several late yanshanian syenitic and gabbroic rocks from the coastal area of southeastern se china have been studied to determine zircon u pb ages and hf isotopic compositions as well as whole rock elemental and sr nd isotopic compositions to constrain their sources and tectonic settings the systematic la icp ms zircon u pb dating results indicate that they can be divided into two main stages the early stage 141 118 ma and the late stage 98 86 ma which temporally correspond to the regional lower and upper volcanic series respectively the early stage syenitic and gabbroic rocks are accompanied by vast rhyolitic and dacitic volcanic rocks with minor granites their parental magma was derived from an enriched mantle metasomatized by subducted sedimentary materials the late stage syenitic rocks mainly occur as the central intrusion of the caldera with ages close to the accompanied volcanics forming a caldera related volcanic intrusive ring complex they were produced by magma mixing between depleted asthenosphere melts and subduction related enriched mantle melts it is suggested that the late yanshanian tectonic settings of se china transformed from a compressional environment to an extensional environment corresponding to the transformation from forward to rollback subduction of the paleo pacific plate at approximately 110 ma

riverine sediment inflow to louisiana chenier plain in the northern gulf of mexico abstract the louisiana chenier plain is a geomorphologic extension of the mississippi deltaic plain highly influenced by sediments originating from the mississippi river with the mississippi river unable to avulse closer to the plain local riverine sediment resources are integral to maintaining the physical and ecological integrity of the estuaries and marshlands to gain insight into the sediment resources this study assessed two decades 1990 2009 of discharge and total suspended solids tss of four rivers sabine river calcasieu river mermentau river and vermilion river that flow into the chenier plain the study quantified long term sediment delivery analyzed seasonal and inter annual trends of sediment transport and investigated the effect of hydrometeorological conditions on sediment yields total sediment delivery from the rivers over the 20 year period was 6 86 10 6 tonnes with the sabine river contributing 62 of the sediment load the sabine river also showed a significant decreasing trend p 0 03 in annual sediment yield long term trends of sediment loads in all the rivers were influenced by their discharge not their tss concentrations annual mean sediment load was 342 950 tonnes with higher sediment loading during the winter and spring months and lower during the summer and fall months annual sediment inflow has the capacity to create 2 3 10 7 m 2 of land to the depth of 1 cm but most of this sediment is unable to reach the coastline the greatest asset that these rivers provide for the chenier plain is sediment and freshwater for restoration of marsh lost to salinization or inundation

cenozoic k rich adakitic volcanic rocks in the hohxil area northern tibet lower crustal melting in an intracontinental setting it is generally accepted that the cenozoic potassic volcanic rocks of northern tibet were derived from a lithospheric mantle source here we report new chronological geochemical and isotopic data for the miocene ca 18 15 ma k rich adakitic volcanic rocks from the hohxil area of the songpan ganzi block in northern tibet we contend that these rocks were generated by partial melting of the mafic lower crust in an intracontinental setting unrelated to subduction of oceanic crust the hohxil rocks exhibit high sr y and la yb ratios high sr and la contents but low yb and y concentrations similar to adakites formed by slab melting associated with subduction however their relatively low e n d values 2 09 to 4 58 high 8 7 sr 8 6 sr 0 7072 0 7075 th u th ba and rb ba ratios and distinctive potassium enrichments k 2 o na 2 o are very different from the composition of typical adakites in addition those k rich adakitic rocks with the highest sio 2 contents 61 wt exhibit the lowest 8 7 sr 8 6 sr ratios and highest e n d values and are the oldest cenozoic volcanic rocks exposed in the songpan ganzi block suggesting that they were derived neither directly from a mantle source nor by differentiation of a shoshonitic magma taking into account the composition of lower crustal mafic xenoliths in tibet as well as the tectonic and geophysical evidence we conclude that the hohxil adakitic magmas were produced by partial melting of amphibole bearing eclogites with a k rich mafic bulk composition in the lower part 55 km of the thickened northern tibetan crust partial melting of the lower crust may have been triggered by dehydration release of fluids from sedimentary materials in the southward subducted continental lithosphere

evidence and dynamics for the change of strike slip direction of the changle nanao ductile shear zone southeastern china abstract the changle nanao ductile shear zone was developed from a suture zone the evidence from the ductile fabrics and mylonitic microstructures indicates that the strike slip was sinistral during pre collision it became dominantly dextral in the syn collision stage in late early cretaceous the dextral strike slip movement continued in the post collision stage with extension as the dominant process the strike slip movement of the zone was strictly controlled by dynamics of collision between the fujian min taiwan tai microcontinent and the fujian min zhejiang zhe mesozoic volcanic arc during the time interval of 100 120 ma the min tai microcontinent in which the ductile shear zone developed might have been located originally to the south of its present position the northward migration of the microcontinent had contributed to a few hundred kilometers of drift rather than a shear displacement the real shear displacement is small due to the change of strike slip direction from sinistral to dextral

the geomorphology of the mississippi river chenier plain abstract the chenier plain of the mississippi river is a shore parallel zone of alternating transgressive clastic ridges separated by progradational mudflats the term chenier is derived from the cajun term chene for oak the tree species that colonizes the crests of the higher ridges the mississippi river chenier plain stretches 200 km from sabine pass texas to southwest point louisiana and ranges between 20 and 30 km wide with elevations of 2 6 m the timing and the process of formation could be re evaluated in the light of new chronostratigraphic findings in the mississippi river delta plain the stratigraphic relationship between the teche and lafourche delta complexes and ship shoal offshore indicates that these delta complexes belong to different delta plains that developed at different sealevels it appears that the teche delta complex is associated with the late holocene delta plain which developed 7000 to 3000 yrs b p when sealevel stood 5 6 m lower than present a regional transgression occurred between approximately 3000 bp and 2500 yrs b p leading to the transgressive submergence of the late holocene delta plain producing the regional teche shoreline the timing of this transgression conforms to the age of the most landward ridge in the chenier plain the little chenier little pecan island trend which dates at about 2500 yrs b p this ridge trend was originally interpreted as representing the teche delta complex switching event with the landward holocene pleistocene contact representing the high stand shoreline the implication of this new interpretation is that the little chenier little pecan island trend represents the high stand shoreline a continuation of the teche shoreline separating the late holocene and recent delta plains and that the holocene pleistocene contact represents the leading edge of the marshes transgressing onto the prairie terrace significant mudflat progradation seems to require a westerly position of the mississippi river but the numerous different forms and ages of cheniers do not correspond well to the timing of major delta complex switching progradation of the chenier plain appears to be associated with building of the recent delta plain and not the teche complex of the late holocene delta plain the occurrence of individual ridges appears to be primarily tied to delta lobe switching within the lafourche complex and variations in sediment supply from local rivers the recent development of the atchafalaya delta complex to the west is the closest position of an active distributary to the chenier plain since sealevel stabilization a new episode of rapid mudflat progradation is thus taking place

shelly cheniers on a modern macrotidal flat mont saint michel bay france internal architecture revealed by ground penetrating radar abstract the relationship between short term morphodynamics and internal structure of shelly chenier ridges is investigated using ground penetrating radar and core x ray analysis complemented with a comparison of aerial photographs these cheniers are located on the uppermost part of a macrotidal flat in mont saint michel bay north western france they actively migrate landward over the salt marshes by washover processes when they are submerged during the coincidence of spring tides and enhanced wave activity the architecture of the cheniers is imaged using high frequency radar antennas 400 mhz to 2 6 ghz three types of cheniers are recognized featuring differences in morphology and internal structure the altitude of the banks on the tidal flat relative to the level of tidal flooding as well as local sediment supply seem to be important forcing parameters in chenier development and stages of evolution on a multi annual time scale evolution of this chenier system is influenced by a combination of the 18 year and the 4 year tidal cycles superimposed on wave activity during minima of the 18 year cycle spring tide level is globally lower on the tidal flat allowing salt marsh progradation and chenier ridge development during peak periods of the tidal cycle former barriers are reworked by wave action and experience onshore migration associated with salt marsh erosion the 4 year tidal cycle coupled with enhanced wave activity is probably responsible for the deposition of large washover units observed in gpr reflection profiles

geochemical transition shown by cretaceous granitoids in southeastern china implications for continental crustal reworking and growth abstract zircon u pb ages and in situ trace elements and hf o isotope compositions together with whole rock geochemical and sr nd hf isotopic data are presented for cretaceous granitoids in southeastern se china in order to establish their origin and the evolution of the underlying lithosphere during the late mesozoic two stages of cretaceous magmatism with contrasting geochemical features have been identified an earlier adakite like biotite granite as represented by the shangying pluton and a later enclave bearing monzogranite as represented by the zaoshan pluton the shangying biotite granites have a zircon u pb age of 99 1 ma they have relatively low y and yb contents with high la yb and sr y ratios showing geochemical features of adakite their sr nd hf isotope compositions are similar to those of early cretaceous mafic rocks in the same area indicating that they were generated by partial melting of juvenile granulitic crust at a depth of about 40 km the source was formed by underplating of enriched lithosphere mantle derived magmas in contrast the zaoshan calc alkaline monzogranites their enclaves and associated dolerite dykes from the zaoshan pluton have an emplacement age of 88 1 ma the dolerites have high mgo contents relatively low sio 2 concentrations and low la yb ratios and depleted hf isotope compositions all these geochemical features suggest that they were derived from a depleted spinel iherzolite mantle source the enclaves have high sio 2 contents indicating that they were derived from a crustal source they have variable zircon hf and o isotope compositions suggesting that two components i e a high e hf t and a low 18 o component and a low e hf t and high 18 o component were involved in their origin the high zircon e hf t values and low 18 o values are similar to those of the dolerites indicating a common source thus we suggest that the enclaves were generated by partial melting of newly underplated depleted mantle derived materials the monzogranites have distinctly different zircon hf and o isotope compositions from the enclaves indicating that the parental magmas were mainly derived from ancient crust that interacted with underplated depleted mantle derived magmas the monzogranites have relatively high hree contents suggesting a garnet free source

high and low k granites and adakites at a palaeoproterozoic plate boundary in northwestern australia the lamboo complex is one of several palaeoproterozoic terrains in northern australia that is intruded by high k i type granites the oldest granites in the complex consist of the high k 1865 1850 ma paperbark supersuite with initial e nd values between 2 7 and 4 0 tonalite sheets of the c 1850 ma dougalls suite have high al 2 o 3 na 2 o sr sr y and la yb and low y and hree and initial e nd values between 1 4 and 0 7 the rocks have compositions similar to adakites that form by melting of mafic rocks in the deep crust with garnet in the residue granites of the 1835 1805 ma sally downs supersuite range from high k types through to crustally derived adakites all with initial e nd values between 0 1 and 1 2 the two supersuites and the dougalls suite were intruded into different tectonic settings previously all of the granites in the lamboo complex were interpreted as partial melts of a chemically and isotopically uniform underplate beneath a rifted archaean craton however their spatial and temporal distribution and their varied compositions are best explained by large scale horizontal plate motions and subduction of oceanic crust

magnetic tracing of sediment dynamics of mudbanks off southwest coast of india in this study we utilized environmental magnetic in combination with sedimentological and hydrodynamic data to investigate the formative processes of mudbanks along southwest coast of india we document the linkages between enrichment of silt sized magnetic particles and formation processes of mudbanks along alappuzha coast a trend of increasing magnetite concentration and coarsening in magnetic grain size is observed at mudbank stations m2 and m3 while the mud deficient station m1 showed an opposite trend a strong relationship between magnetic and physical grain size for all samples implies that the magnetic particle size and clastic grain size are largely adjunct analysis of rock magnetic and grain size data of surficial and suspended sediments from non mudbank m1 and two mudbank stations m2 m3 reflect the differential sediment partitioning and transport regimes which controlled the formation of mudbanks along alappuzha coast two plausible mechanisms responsible for the formation of mudbanks are identified grain size selective entrainment is the dominant process during pre monsoon weaker hydrodynamics waves and bottom currents favors accumulation of silt sized fine and coarse magnetic and non magnetic fractions resulting in the formation of magnetically low enriched sediment bed of mixed grain sizes at the onset of monsoon wave induced energetic bottom currents enhance the suspension of entire sediment bedload at stations m2 m3 to form fluid mud concurrently mineral density based selective fractionation allows the settling of coarse silt sized magnetic particles while the fine magnetic silt size particles accumulate forming thick fluid mud as a suspension load resulting in the formation of mudbanks an observed increase in magnetic susceptibility and coarsening in magnetic grain size of surficial sediments at mudbank stations m2 m3 during monsoon period supports the interpretation our findings are summarized in a conceptual model which can be very well applied to investigate sediment dynamics associated with mudbank formation in coastal and shelf sedimentary systems

middle holocene sea level rise and highstand at 2 m central texas coast new data suggest a revised picture of middle holocene sea level change for the texas gulf of mexico coast and suggest reevaluation of coastal evolution first brackish marsh facies with calibrated radiocarbon ages of 7 7 to 7 8 ka have been recovered from depths of 8 5 to 9 m in a core from the ancestral colorado river delta and are interpreted to represent a sea level pinning point second a series of ridges along the copano bay margin farther south consist of shelly mud and fine sand with subtidal foram assemblages occur at elevations of 1 95 m above the modern intertidal zone and have produced calibrated radiocarbon ages on foram tests of ca 6 8 to 4 8 ka these ridges are interpreted to represent relict shallow subtidal to intertidal spits that provide minimum sea level positions for the middle holocene and are now emergent because of later sea level fall in aggregate these data show rates of sea level rise during this time period that are very comparable to or even lower than published eustatic rates and suggest a middle holocene sea level highstand for this non uplifting non rebounding and very slowly subsiding part of the north american coastline

high sr y and la yb ratios the meaning of the adakitic signature abstract the name of adakite is used to describe a far too large group of rocks whose sole common feature is high sr y and la yb ratios however such a signature can be achieved via different processes melting of a high sr y and la yb source deep melting with abundant residual garnet fractional crystallization or afc or interactions of felsic melts with the mantle causing selective enrichment in lree and sr over hree a database of the compositions of adakitic rocks including high silica and low silica adakites martin h smithies r h rapp r p moyen j f champion d c 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 2 1 24 continental adakites and archaean adakites was assembled geochemical modeling of the potential processes is used to interpret it and reveals that 1 the classical model of slab melting provides the best explanation for the genesis of high silica adakites 2 low silica adakites are explained by garnet present melting of an adakite metasomatized mantle i e at depths greater than 2 5 gpa 3 continental adakites is a term encompassing a huge range of rocks with a corresponding diversity of petrogenetic processes and most of them are different from both low and high silica adakites 4 archaean adakites show a bimodal composition range with some very high sr y examples similar to part of the ttg suite reflecting deep melting 2 0 gpa of a basaltic source with a relatively high sr y while lower sr y rocks formed by shallower 1 0 gpa melting of similar sources comparison with the archaean ttg suite highlights the heterogeneity of the ttgs whose composition spreads the whole combined range of hsa and archaean adakites pointing to a diversity of sources and processes contributing to the ttg suite

holocene sea level change and coastal landscape evolution in the southern gulf of carpentaria australia a revised holocene sea level history for the southern gulf of carpentaria is presented based on new data from the south wellesley archipelago and age recalibration of previous research results confirm that rising sea levels during the most recent post glacial marine transgression breached the arafura sill ca 11 700 cal yr bp sea levels continued to rise to ca 30 m by 10 000 cal yr bp leading to full marine conditions by 7700 cal yr bp sea level reached present mean sea level pmsl and continued to rise to an elevation of between 1 5 m and 2 m above pmsl sea level remained ca 1 5 between 7000 and 4000 cal yr bp followed by rapid regression to within 0 5 m of pmsl by ca 3500 cal yr bp when placed into a wider regional context results from this study show that coastal landscape evolution in the tropical north of australia was not only dependent on sea level change but also show a direct correlation with holocene climate variability specifically the formation and preservation of beach rock deposits intertidal successions beach and chenier ridge systems hold valuable sea level and holocene climate proxies that can contribute to the growing research into lower latitude holocene sea level and climate histories

ductile deformation and 40ar 39ar dating of the changle nanao ductile shear zone southeastern china abstract an investigation of ductile deformation mylonitization and 40ar 39ar geochronology in the changle nanao ductile shear zone southeastern china is reported in this paper at least two phases of ductile deformation occurred in the shear zone in the mesozoic the first is a ne trending foliation widely developed in metasedimentary rocks and orthogneisses and is associated with metamorphism of amphibolite facies at 165 178 ma the second is a strike slip related ductile deformation developed both in the metamorphic rocks and the mesozoic volcanics and includes folds shear foliation or cleavage s c fabrics ne striking stretching lineation and mylonitic microstructures the ductile deformation and dislocation microstructures of quartz and the brittle deformation microstructures of plagioclase in the mylonites from the shear zone indicate that the second phase of ductile deformation and mylonitization occurred under greenschist facies conditions at temperatures of 300 350 c 40ar 39ar plateau ages of five minerals from deformed and mylonitized rocks in the shear zone are in the range of 118 107 ma the plateau ages record the time of ductile deformation and mylonitization associated with strike slip movement along the changle nanao ductile shear zone

generation of sodium rich magmas from newly underplated basaltic crust sodium rich rocks of trondhjemite tonalite dacite ttd or granodiorite ttg suites form much of precambrian continental crust1 they are thought to have formed by partial melting of subducted oceanic crust2 3 a process that would have been much more widespread early in earth history than at present owing to the higher thermal gradients prevailing at that time4 phanerozoic ttd suites do exist however and seem also to relate to subduction zones5 defant and drummond6 proposed that these suites form where young 25 myr hot oceanic lithosphere is subducted and melts thus locally simulating the conditions that led to widespread crustal growth in the archaean here we describe plutonic and volcanic rocks from the cordillera blanca complex in peru which have characteristics of the high al ttd suite but which were produced above a subduction zone containing a 60 myr old slab we present evidence that the complex formed by partial melting of newly underplated basaltic crust and argue that this mechanism should be considered more generally as an additional way of generating sodium rich arc magmas

coastal morphodynamics and chenier plain evolution in southwestern louisiana usa a geomorphic model abstract using 28 topographic profiles air photo interpretation and historical shoreline change data coastal processes were evaluated along the chenier plain to explain the occurrence distribution and geomorphic hierarchy of primary landforms and existing hypotheses regarding chenier plain evolution were reconsidered the chenier plain of sw louisiana classified as a low profile microtidal storm dominated coast is located west and downdrift of the mississippi river deltaic plain this late holocene marginal deltaic environment is 200 km long and up to 30 km wide and is composed primarily of mud deposits capped by marsh interspersed with thin sand and shell rich ridges cheniers that have elevations of up to 4 m in this study the term ridge is used as a morphologic term for a narrow linear or curvilinear topographic high that consists of sand and shelly material accumulated by waves and other physical coastal processes thus most ridges in the chenier plain represent relict open gulf shorelines on the basis of past movement trends of individual shorelines ridges may be further classified as transgressive regressive or laterally accreted geomorphic zones that contain two or more regressive transgressive or laterally accreted ridges are termed complexes consequently we further refine the chenier plain definition by otvos and price otvos e g and price w a 1979 problems of chenier genesis and terminology an overview marine geology 31 251 263 and define chenier plain as containing at least two or more chenier complexes based on these definitions a geomorphic hierarchy of landforms was refined relative to dominant process for the louisiana chenier plain the chenier plain is defined as a first order feature 5000 km2 composed of three second order features 30 to 300 km2 chenier complex beach ridge complex and spit complex individual ridges of each complex type were further separated into third order features chenier beach ridge and spit to understand the long term evolution of a coastal depositional system primary process response mechanisms and patterns found along the modern chenier plain coast were first identified especially tidal inlet processes associated with the sabine calcasieu and mermentau rivers tidal prism and quantity of littoral transport mtotal are the most important factors controlling inlet stability greater discharge and or tidal prism increase the ability of river and estuarine systems to interrupt longshore sediment transport maintain and naturally stabilize tidal entrances and promote updrift deposition thus prior to human modification and stabilization efforts the mermentau river entrance would be classified as wave dominated sabine pass as tide dominated and calcasieu pass as tide dominated to occasionally mixed hoyt hoyt j h 1969 chenier versus barrier genetic and stratigraphic distinction am assoc petrol geol bull 53 299 306 presented the first detailed depositional model for chenier genesis and mudflat progradation which he attributed to changes in mississippi river flow direction i e delta switching caused by upstream channel avulsion however hoyt s model oversimplifies chenier plain evolution because it omits ridges created by other means thus the geologic evolution of the chenier plain is more complicated than channel avulsions of the mississippi river and it involved not only chenier ridges i e transgressive but also ridges that are genetically tied to regression beach ridges and lateral accretion recurved spits a six stage geomorphic process response model was developed to describe chenier plain evolution primarily as a function of i the balance between sediment supply and energy dissipation associated with mississippi river channel avulsions ii local sediment reworking and lateral transport iii tidal entrance dynamics and iv possibly higher than present stands of holocene sea level consequently the geneses of three different ridge types transgressive regressive and laterally accreted typically occur contemporaneously along the same shoreline at different locations

shoreline changes and morphology of spits along southern karnataka west coast of india a remote sensing and statistics based approach abstract the changes in shoreline positions and morphology of spits along the karnataka coast western india are investigated for the period from 1910 to 2005 using multi dated satellite images and topomaps the study area has been divided into four littoral cells and each cell into a number of transects at uniform intervals the rate of change in shoreline position has been estimated using the statistical linear regression method and cross validated with regression coefficient r 2 and root mean square error rmse methods past and future shoreline positions have been demarcated and future positions of shoreline are estimated for time periods of 10 and 24 years the study reveals that i about 57 of transects exhibit 10 m rmse values indicating better agreement between the estimated and satellite based shoreline positions and ii transects closer to the cell boundaries exhibit about 50 uncertainties in shoreline change rate estimations based on rmse values the influence of natural processes and anthropogenic factors on shoreline changes has been evaluated the cells transects dominated by natural processes reveal low rmse values whereas the cells transects influenced by anthropogenic activities such as sand mining construction of coastal structures exhibit higher rmse values however the variation in rmse values is not significant if the total number of transects is considered significant changes in morphology of spits have been recorded spits demonstrate variations in areal extent i e length and area if 1910 and 1967 are considered separately as base years the present study demonstrates that combined use of satellite imagery and statistical techniques such as linear regression and rmses can be very useful in quantifying shoreline changes and spit morphology

lake sediment record of late holocene hurricane activities from coastal alabama coastal lake sediments contain a stratigraphically and chronologically distinct record of major hurricane strikes during late holocene time frederic a category 3 hurricane that struck the alabama coast on the gulf of mexico in 1979 left a distinct sand layer in the nearshore sediments of lake shelby as a result of storm tide overwash of beaches and dunes sediment cores taken from the center of lake shelby contain multiple sand layers suggesting that major hurricanes of category 4 or 5 intensity directly struck the alabama coast at ca 3 2 3 0 2 6 2 2 1 4 and 0 8 ka 14 c yr with an average recurrence interval of 600 yr the alabama coast is likely to be struck by a category 4 or 5 hurricane within the next century

generation of metaluminous a type granites by low pressure melting of calc alkaline granitoids melting experiments on two calc alkaline rocks a tonalite and a granodiorite demonstrate that shallow dehydration melting of hornblende and biotite bearing granitoids generates metaluminous a type granitic melts profuse crystallization of calcic plagioclase orthopyroxene during low pressure p 4 kbar incongruent melting explains all of the major and trace element characteristics of a type granites e g their low al ca mg sr and eu contents and high ga al and k na ratios as well as their common association with anorthositic and mangeritic rocks the residual assemblage produced during melting of the same rocks in the deep crust p 8 kbar is dominated by clinopyroxene and as a consequence most of the chemical features diagnostic of a type granites are lost the high temperatures 900 c and low h 2 o contents 4 wt that are characteristic of a type magmas are adequately explained by the h 2 o poor nature of the granitoid source materials and require neither a granulitic nor a f rich source previous attempts to explain the origin of a type granites have focused on the nature of the source material these experiments show that pressure of melting is at least as important as source composition in engendering a type melts

new evidence on the spatial temporal distribution of superlobes in the yellow river delta complex abstract unraveling the spatial temporal distribution of delta superlobes precisely is particularly important and challenging in the yellow river delta complex yrdc previous research on this issue can be dated back to the early 1990s when the paleoenvironmental reconstructions mainly hinged on the historical documents and geomorphologic analysis of well developed cheniers from the west coast of bohai bay and only few drilled cores with scant radiocarbon dates were available to build a refined model of the holocene stratigraphic architecture and reconstruct the sedimentary evolution of the yrdc detailed sedimentological investigation of 12 boreholes including 59 new ams 14c radiocarbon dates was combined with other published 25 cores and 174 ams 14c dates therein age depth curves were grouped by stratigraphic positions and facies characteristics of these 233 radiocarbon dated samples across different sectors of the yrdc exhibiting consistent patterns that can be used to identify distinct phases of delta superlobe activities eight new superlobes with relatively accurate dating spans were therefore proposed in the yrdc our results demonstrate that very high aggradation rates almost invariably correlate with the onset of deltaic deposition age depth patterns thus may be very useful to elucidate the complex sedimentary evolution of delta systems with multiple lobes

variable response of coastal environments of the northwestern gulf of mexico to sea level rise and climate change implications for future change the results from nearly three decades of marine geological research in the northwestern gulf of mexico are compiled in an effort to understand those factors e g sea level rise sediment supply subsidence antecedent topography that influenced coastal evolution during the last eustatic cycle 120 ka to present armed with this information we evaluate coastal response to variable sea level rise of the holocene and accelerated rise during historical time to gain a better understanding of how the coast is likely to respond to future changes the early holocene evolution of northwestern gulf of mexico bays was punctuated by rapid and possibly synchronous flooding events that are interpreted as resulting from episodes of rapid sea level rise two of these events one between 8 4 and 8 0 ka and the other between 7 4 and 6 8 ka were associated with known episodes of ice sheet retreat in north america and antarctica respectively during the middle and late holocene the east texas and western louisiana coasts experienced episodes of stability and growth followed by rapid shoreline retreat while the central texas coast remained relatively stable this variability in coastal response to sea level rise resulted mainly from differences in sediment supply and the highly irregular antecedent topography on which coastal environments formed sand that nourished the evolving east and south texas as well as westernmost louisiana coasts was derived mainly from transgressive ravinement of deltas that were formed during the falling stage of sea level mis5e mis2 the loci of these deltas controlled the spatial variability of this offshore sand supply sand supply to the central texas coast has been dominated by converging longshore currents and throughout the middle to late holocene was large enough to keep pace with sea level rise moreover sand supply from rivers has varied considerably in response to climate change during the early holocene when the average rate of linear sea level rise was 4 2 mm yr the brazos colorado and rio grande rivers all formed deltas on the inner continental shelf today only the brazos contributes enough sediment to the gulf of mexico to form a delta but its sand delivery is minimal a reversal from late holocene growth of western louisiana east texas and south texas barrier islands and peninsulas to erosion occurred during the last 2 0 ka after the rate of sea level rise began to decelerate the actual timing of this reversal was diachronous across the coast and was caused by a decrease in sediment supply once offshore sand sources were bypassed by the landward advancing shoreface transgressive ravinement differences in the exact timing and rate of retreat also reflect variability in the offshore profiles of these barriers and their thickness which results from the underlying relief on the pleistocene surface the late holocene was also the time of chenier plain development in western louisiana and east texas that was marked by localized differences in growth and retreat the current rate of eustatic sea level rise in the northern gulf of mexico is in the range of 2 0 and 3 0 mm yr and is approaching rates of the early holocene this is on average about five times the long term rate of the past 4 0 ka this larger rate is associated with an increase in coastal erosion in historical time relative to long term rates current rates of gulf shoreline erosion are approaching rates of the early to mid holocene and the rate of retreat of some barriers is not sustainable core transects off central texas reflect a late holocene history of shoreface progradation but the modern shoreline is currently eroding albeit at slower rates than elsewhere along the coast overall the sand supply needed to sustain the gulf shoreline is lacking likewise baylines are experiencing erosion rates that are faster than the late holocene average and bayhead deltas are at the tipping point of catastrophic retreat spatial variability in erosion rates highlights the importance of factors such as sediment supply subsidence and anthropogenic influences on coastal evolution tropical storms and hurricanes while exerting the most noticeable coastal change merely exacerbate overall shoreline retreat and migration along the entire northwestern gulf coast the impact of human intervention to natural processes is particularly evident primarily due to alterations in river discharge and sediment supply to the coast interruptions in along shore and cross shore sand transport and increases in rates of subsidence through fluid withdrawal compared to natural changes that took place during the holocene the impacts of human activity have been virtually instantaneous the geological record indicates that the ongoing increase in the rate of sea level rise coupled with diminished sediment supply and human intervention will continue to severely impact the low gradient coastal environments of the northwestern gulf of mexico

coastal barriers northern gulf last eustatic cycle genetic categories and development contrasts a review abstract a large body of chronologically well constrained and detailed quaternary data accumulated in the last decades from the coastal shelf region of the northern gulf of mexico consequently a preliminary synthesis of major aspects of the late quaternary barrier and mainland coastal development on the northern gulf of mexico is timely several major factors account for the striking differences between barrier size and development styles in the three northern gulf coast regions barriers are nearly continuous in the nw where they dominate by the greatest dimensions and continuity sand supply from shelf and mainland sources continued at variable rates throughout six stages of the last eustatic cycle lec differences in antecedent topography in fluvial runoff volumes and relative sea level rise including rapid overstepping flooding events were critical in the regional distinctions leaving fewer and smaller relict fluvial delta behind drowned shore and nearshore landforms on the shelf only two large fluvial systems impacted the ne the nw shelf and nearshore received abundant sediment supply from the mississippi and lesser streams indirectly by ravinement erosion of relict landforms and landward directed cross shelf sediment transfer sands originated mainly in relict deltas fluvial tidal channel and inlet fill as well as from submerged shore ridge remnants on the continental shelf shelf margin deltas represented major secondary sources barrier formation categories and their respective importance in specific areas represent critical aspects of coastal development the authorship of various formation concepts e g penck gilbert mcgee haage ganong and keilhack often is still miscredited or remains unrecognized in the literature recognition of the stratigraphic and sedimentological diagnostic characteristics of the basic genetic barrier categories plays a key role in testing the validity of barrier evolution models closely knit process form relationships prevail between hydrodynamic sea level change storm tidal current overwash sedimentary shoal and island aggradation rollover and eolian accumulation processes and the resulting landform morphology the most detailed accounts that deal with the development of the alabama louisiana and apalachicola barrier chains are particularly instructive almost all modern gulf barriers with identifiable genetic background formed by shoal aggradation between 5 5 and 2 0 ka during a marked deceleration in sea level rise concurrently a sizable mainland strand plain complex extended the ne coastal plain tide and storm driven sediment transport to the large mobile bay ebb delta the focal role of composite east dauphin island in establishing the ms la island chain and the island blocking role of mississippi delta advance were prime factors in a complex barrier history migration paradoxically may also occur by transgressive rollover concurrently with regressive landward progradation of island strand plains stream discharge and sand reworked from relict lithosomes on the shelf were insufficient in compensating for wave and tide related sediment loss gulf levels stayed below the present throughout the mid and late holocene

magnitude of hurricane ike storm surge sedimentation implications for coastal marsh aggradation there is a paucity of information on the regional distribution and magnitude of hurricane storm surge sedimentation this study assesses the spatial extent and magnitude of hurricane ike s 2008 storm surge sedimentation and discusses implications for the role of hurricanes in marsh aggradation the characteristics of the storm surge deposit including thickness inland penetration volume and mass were determined for 15 transects across marshes bordering the gulf of mexico in south eastern texas and south western louisiana the deposit is up to 0 85 m thick extends up to 3 6 km inland and has an estimated volume of about 13 7 million m3 and an estimated mass of about 16 2 million metric tons this level of sedimentation is one to two orders of magnitude larger than other potential sources of marsh sedimentation including annual riverine inputs and inputs from alongshore sediment transport the study findings add support to a growing body of evidence that hurricanes may be the predominant sediment source for long term aggradation of many coastal marshes bordering the gulf of mexico copyright 2012 john wiley sons ltd

sea level variation during the holocene deduced from the morphologic and stratigraphic evolution of morgan peninsula alabama u s a abstract recent gulf of mexico shoreline studies interpret middle to late holocene sea level as falling from a level above present elevation or stable at present elevation however the architecture of morgan peninsula alabama does not support this morgan peninsula is a beach ridge strandplain composed of two obliquely aligned holocene beach ridge sets ground penetrating radar profiles discriminate between parallel even to wavy reflectors of the eolian dune environment and the underlying seaward dipping complex sigmoidal oblique reflectors of the foreshore and upper shoreface environment the contact between foreshore and eolian facies in beach ridges can be used as a sea level indicator the average elevation of this contact in morgan peninsula rises throughout shoreline accretion which occurred throughout the last 5 4 ka suggesting that there was continual sea level rise during this time morgan peninsula is a useful modern analog to ancient shoreface shelf parasequences and demonstrates the significant internal complexities that can exist in these deposits erosional discontinuities imaged in the holocene foreshore upper shoreface environment are laterally continuous extend to elevations above mean sea level and correlate to beach ridges and the transition between beach ridge sets an increase in the wave regime or fluctuations in sediment supply appear to be likely mechanisms for forming erosional discontinuities below beach ridges the erosional surface separating beach ridge sets may have formed by increased storm activity and associated barrier breaching or a reconfiguration of the mobile bay tidal delta complex superimposed on a gradual rate of sea level rise this boundary is recognized by a change in beach ridge orientation at the surface and an increase in the aggradational component of shoreline accretion

speculations on the mesozoic plate tectonic evolution of eastern china several orogenic belts transecting eastern china are the sites of former convergent plate margins although there have been varying views on the collisional framework of individual continental blocks styles of convergence at these zones and the timing of respective collisions a tectonic study of eastern china mongolia and the southern soviet far east indicates the collision of the south china block with a combined north china northeast china fold zone block in the late triassic early jurassic their collective suturing to eurasia in the late jurassic early cretaceous followed by the sikhote alin japan block in the mid to late cretaceous the evidence is as follows 1 a linear belt of late triassic early cretaceous granites and granodiorites trends east from the qinlingshan through the dabieshan to the huaiyang massif ophiolites flysch subduction zone melange a paired metamorphic belt indicating north dipping subduction and marine strata of carboniferous to late triassic age from the qinlingshan define the suture between the north and south china blocks 2 a sinuous belt of ultramafics blueschists silicic to intermediate magmatism and west and north vergent folds and thrusts trend from the west margin of the ordos basin through central inner mongolia and along the east great khingan range to the amur river coupled with a mid jurassic early creataceous unconformity a suturing of eastern chinese blocks to eurasia along this zone is suggested 3 a fold and thrust belt with ultramafics flysch blueschists and subduction zone melange along the ussuri river in northeast china indicates the suturing of the sikhote alin japan block to eurasia along a west dipping subduction zone in the mid to late cretaceous similarly a tectonic study of southern china and southeast asia has revealed a complex regional mosaic of suture bounded terrains which nucleated about the eastern western and southern margins of the yangtze craton during the late triassic and early jurassic the evidence is as follows 4 a north south trending belt of ophiolites blueschists calc alkaline volcanics and subduction zone melange including granites granodiorites and strongly deformed marine strata all of late triassic age exposed in the longmenshan of sichuan merge with the kekexilishan ophiolite zone into the ailaoshan tengtiaohe ophiolite and blueschist belt in central yunnan along which the songban ganzi complex and the shan thai malaya block join the craton and 5 a southeastern prolongation of the ailaoshan tengtiaohe belt bifurcates into the southeast trending konvoi zone of northern vietnam and the north south trending pak lay luang prabang zone of laos and eastern thailand zones of ophiolite calc alkaline volcanics and strong late triassic deformation they separate the indosinia and shan thai malaya blocks from the craton respectively these findings differ significantly from previous interpretations of a late paleozoic consolidation of south eastern asia as well as disputing the existence of a true pangea

reduced seasonality of holocene climate and pervasive mixing of holocene marine section northeastern gulf of mexico shelf the large porcelaneous foraminifers cyclorbiculina compressa parasorites orbitolitoides and peneroplis proteus are conspicuous in death assemblages from holocene marine sediments of the alabama and florida panhandle shelf the species inhabited the northeastern gulf of mexico in the holocene ca 6 4 1 9 ka but do not live in the region today these foraminifers require warm clear waters and thus are important paleoclimatic and paleoenvironmental indicators they apparently were derived from sublittoral seagrass habitats and indicate reduced seasonality in the region during the middle to late holocene in addition a mixed foraminiferal fauna a hydrodynamically reworked macrofaunal assemblage and stratigraphic disorder in foraminiferal 14 c dates indicate extensive reworking of the entire holocene marine transgressive package evidence that mollusks are indigenous but large foraminifers are transported supports the generalization that out of habitat transport of macrofauna is negligible in most marine settings

insights on a proposed mid holocene highstand along the northwestern gulf of mexico from the evolution of small coastal ponds abstract small lakes and ponds along the margins of estuaries and lagoons contain valuable records of paleo sea level past storm frequencies and climatic change critical to their use in such studies is an understanding of their evolution using aerial photos surveyed elevation profiles and vibracores we describe the geomorphic and stratigraphic evolution of ponds whose sedimentary floors range in elevation from 0 8 to 0 8 m above sea level on the margins of baffin bay in semiarid south texas these ponds are in various stages of evolution providing an excellent opportunity to study their formation we see a three stage evolution of 1 eolian deflation and creation of pond 2 creation of a pathway to the open bay via headward eroding gullies and 3 open communication with the bay via a small tidal inlet each of these stages of evolution has a unique sedimentary facies associated with it combined with elevation and age control the sedimentary facies from these ponds and two other cores from adjacent baffin bay are used to evaluate a proposed mid holocene sea level highstand within the gulf of mexico deposits from these cores suggest that holocene sea level in the gulf of mexico did not reach above 0 4 m and did not reach above 1 2 m until sometime after 5 6 ka algal mats from cores in baffin bay suggest sea level was 7 6 1 1 m 5 6 ka the sea level constraints suggested by these ponds are in agreement with more traditional reconstructions of sea level since the mid holocene within the gulf of mexico in addition to testing a higher than present mid holocene highstand within the northwestern gulf of mexico we also provide an evolutionary model for the development of these ponds illustrating the important interaction between eolian and estuarine processes

sequence stratigraphy of a coastal plain incised valley estuary lake calcasieu louisiana abstract the stratigraphic profile along a 100 km section of the lake calcasieu incised valley fill was reconstructed from 87 bridge borehole records at four sites along the tidal reaches of the calcasieu river an additional 18 boreholes aligned along the chenier plain near the estuary mouth and shallow seismic data collected along 160 km of track line within the lake calcasieu central basin valley incision occurred during the d18o stage 2 sea level lowstand when the paleo calcasieu river flowed across the inner continental shelf and incised into older fluvial terraces of the prairie formation the valley floor is 57 m deep beneath the modern chenier plain and rises to 30 m along the upper reaches of the modern estuary sea level rise commenced about 20 ka and has continued episodically throughout the holocene shoreline transgression has proceeded at varying rates in response to sea level rise and the incised valley is now occupied by a wave dominated estuary fringed by the chenier plain of western louisiana lowstand deposits are poorly preserved within the calcasieu incised valley deposits constituting the transgressive systems tract tst lie directly above the lower sequence boundary at the top of the prairie formation the tst shows greatest facies diversity and clearest separation of bounding surfaces toward the present seaward end of lake calcasieu here the tst comprises three parasequences that include fluvial bayhead delta and central basin estuarine deposits multiple flooding surfaces within the tst relate to the episodic style of sea level rise highstand infilling of the valley has been characterized by nearshore marine deposition and chenier plain progradation along the lower reaches of the modern calcasieu river the valley fill comprises transgressive central basin nd landward stepping bayhead delta facies overlain by the highstand bayhead delta complex this study documents the most recent phase of deposition within the compound fill of a coastal plain incised valley and demonstrates the potential importance of fluvial controls on facies within incised valley systems

the development of the princess charlotte bay chenier plain new results and insights abstract chenier plains record changes in the mode of coastal progradation between periods of mudflat accumulation and coarse sediment deposition the geomorphic development of the princess charlotte bay chenier plain was last considered in the 1980s and the conclusions have contributed to knowledge of muddy coastal morphodynamics obtaining new data through the use of luminescence dating techniques provided an opportunity to reassess previous findings data were obtained from the south western portion of the bay where the chenier ridges were most distinct whereas previous research had been concentrated on the far eastern periphery of the plain optically stimulated luminescence age estimates and radiocarbon ages from eight of the 11 most seaward chenier ridges yielded a new depositional chronology the recent chenier sequence in this area began forming with the establishment of the most landward chenier ridge ridge 1 no more than 4000 yr bp in the 1500 years following this two more chenier ridges were built ridges 2 and 3 which were not sampled ridge 4 was being built at around 2400 yr bp ridges 5 and 6 at around 2100 yr bp ridge 7 at around 1900 yr bp ridges 8 and 9 at around 1300 yr bp ridge 10 which was not dated between 1300 and 820 yr bp and ridge 11 at around 820 cal yr bp comparing the new data to previous data and conclusions yielded new insights into the holocene development of the chenier plain these new insights may provide a means for australian chenier plains to inform contemporary coastal morphodynamics more broadly

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

formation and tectonic evolution of southeastern china and taiwan isotopic and geochemical constraints abstract the southern part of china consists of the proterozoic yangtze craton and the phanerozoic south china foldbelts including the himalayan foldbelt of taiwan models for continental growth have been many and controversial isotopic and geochemical data from mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of southeastern china and to evaluate whether the young phanerozoic foldbelts are representative of old rejuvenated landmass whether they characterize crustal accretion through successive subduction processes hence suggesting a net growth of continental mass or whether they represent some intermediate situation available sm nd isotopic data for phanerozoic granitoids and metasediments from the south china foldbelts and taiwan invariably show proterozoic model ages t dm ranging from 1 to 2 5 ga with a mean of 1 54 0 30 1 ga all rocks have negative nd t values 2 to 15 suggesting variable but important contributions of old continental materials to the sources of the phanerozoic rocks obviously they do not represent wholesale growth of continental mass the granitoids of the south china foldbelts have multiple origins as viewed from their chemical and isotopic characteristics secular geochemical variation has been established for inland granitoids of proterozoic to mesozoic age their high i sr values 0 710 0 737 suggest that most granitoids are essentially anatectic products of ancient continental crust this is compatible with remelting via microcontinental collision or terrane accretion repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization mesozoic granitoids excluding a type alkaline granites in the coastal region and taiwan show relatively low i sr 0 705 0 710 and high nd values implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks this means that mesozoic magmatism in the coastal region resulted from subduction of a paleo pacific plate kula beneath the asian continent the overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the south china foldbelts the latest arc continent collision began about 4 ma ago in eastern taiwan

temperature and air pollution affected tree ring δ13c and water use efficiency of pine and oak trees under rising co2 in a humid temperate forest abstract to better predict forest productivity under rising atmospheric co 2 concentration co 2 it is critical to understand how intrinsic water use efficiency wue i and its relationship with tree growth are affected by the concomitant changes in environmental conditions such as precipitation temperature and air pollution that either enhance or undermine any potential co 2 fertilization effect we investigated changes in 13 c and wue i in annual rings and basal area increment bai of pinus densiflora from 1968 to 2007 and quercus variabilis from 1970 to 2007 trees in relation to precipitation temperature and air pollution in a humid temperate forest the wue i of p densiflora increased by 39 9 whereas that of q variabilis did not change over time in the study period the wue i was not affected by precipitation for both species but increased p p densiflora and with so 2 emissions for both species multiple regression models suggested that the effect of co 2 on tree growth was much higher than temperature however for the period 1998 to 2007 when so 2 emissions data were available so 2 emission was the driver of changes in bai and wue i and temperature effects became stronger than co 2 overall bai and wue i were positively p p densiflora but not for q variabilis we conclude that temperature and air pollution rather than precipitation were key determinants of wue i at the study site and that the two species had contrasting responses to environmental changes

600 year sedimentary archive of hurricane strikes in a prograding beach ridge plain southwestern louisiana abstract this study tests a novel approach to paleotempestology substituting the lateral time depth of a prograding beach ridge plain for the vertical time depth of an aggrading coastal lake pond lagoon swamp or marsh trenching and coring of a beach ridge plain in southwestern louisiana revealed six sand beds and one shell bed interpreted as hurricane washover deposits the sand beds are readily distinguished from enclosing marsh sediments by their higher sand content lower organic content and contrasting microfossil assemblages based on the modern analogs of hurricanes audrey 1957 rita 2005 and ike 2008 and consideration of nearby landfalling hurricanes in the historical record it was determined that the storm intensity threshold of the study site is equivalent to a category 3 hurricane there is a wide variation in hurricane strike frequency between this site and other sites bordering the gulf of mexico this variation results from differences in site sensitivity and the nature of geologic or geochemical proxies used to derive hurricane strike records the approach demonstrated by this study could have applicability at other sites around the world where beach ridge plains are subject to tropical cyclone strikes

causes of river avulsion insights from the late holocene avulsion history of the mississippi river u s a abstract the emphasis on gradient advantages in studies of avulsion is misleading while gradient advantages are necessary for an avulsion to occur the late holocene avulsion history of the mississippi river in louisiana suggests that factors such as substrate composition and floodplain channel distributions are more important cross valley to down valley slope ratios of the modern floodplain range from 16 to 110 and are typically 30 the slope ratio is 35 at the location of the mississippi atchafalaya diversion old river yet slope ratios are 83 to 110 immediately upvalley of old river all values of mississippi river floodplain slope ratios are significantly larger than values of avulsion threshold calculated by numerical models shallow floodplain cores 14c dating of organic remains and geologic mapping show that the mississippi river has avulsed only four times over the past 5 ky in the southern lower mississippi valley lmv gradient advantages are widespread yet avulsions are rare these observations indicate that factors other than gradient advantage control mississippi river avulsion several examples of mississippi and red river avulsion by channel reoccupation support the idea that channel distributions and substrate compositions are primary influences on avulsion incipient mississippi river avulsion and development of the atchafalaya river involved reoccupation of abandoned mississippi river channels and a red river crevasse splay complex the modern atchafalaya river also incises buried mississippi river channel belt sands abandoned channel belts and crevasse splay complexes consist of sandy substrates that facilitate scour and the development of channels capable of capturing the mississippi river abandoned channels provide ready made conduits for mississippi river flow that can efficiently develop into avulsive channels multi storied sheet sandstones in ancient fluvial deposits may provide additional support for the idea that erodible substrates and floodplain channel distributions are critical influences on avulsion these features record episodic reoccupation of channel belts which at least in some cases may simply reflect successive avulsions rather than major changes in aggradation rate or extrabasinal factors such as climate

apatite dissolution into peraluminous haplogranitic melts an experimental study of solubilities and mechanisms apatite ap dissolution and solubility in the peraluminous haplogranite system were investigated in three sets of experiments at 750 c and 200 mpa ph2o as functions of ap grain size abundance melt ap ratio and melt asi alumina saturation index mol al2o3 na2o k2o cao between an asi of 1 1 1 metaluminous to mildly peraluminous the solubility of ap as measured by p2o5 in the melt is low 0 1 wt p2o5 which agrees with previous work in equilibrium runs with more strongly peraluminous compositions however ap solubility increases linearly with asi to p2o5 0 63 wt in melt at asi 1 3 and can be denned by a simple equation p2o5 3 4 3 1 asi r 0 833 which agrees within error with previous calculations reported in the literature in experiments where ap grains are sparce and widely separated i e simulating ap distribution in an ap bearing peraluminous protolith undergoing anatexis the dissolution of ap involves transient disequilibrium that promotes higher solubility of p2o5 up to nearly six times the equilibrium values adjacent to ap at a given bulk asi of melt and this increases the al si of melt in the ap dissolution aureole the approach to equilibrium between ap and melt is hastened by increasing the ap melt ratio within the local melt pool e g the capsule or by decreasing ap grain size for a similar melt ap ratio diffusivity calculations using inverse error function methods for the normal diffusion of p and ca yield dp 10 11 cm2 s and dca 10 10 cm2 s confirming prior results that diffusion of p away from ap surfaces is the rate limiting factor in ap dissolution these results combined with previous work at higher temperatures but on similar hydrous melts yield an activation energy e for p diffusion of 16 5 kcal mol and a frequency factor d0 of 1 4 10 3 cm2 s phosphorus diffusion through the melt is accompanied by uphill diffusion of al resulting in an increase of up to 2 wt al2o3 in melt near the ap within the ap dissolution aureole melt contains one additional al cation for every p cation i e al p 1 1 which is suggestive of an associated alpo4 complex the exchange reaction in melt is represented by alpsi 1 in which 2 to4 clusters are created in the place of 1 this exchange should be accompanied by discernable changes in melt properties e g density molar volume viscosity the results have applications to equilibrium and local disequilibrium effects during anatexis of apbearing metapelites and to the saturation limits of ap during crystallization of peraluminous magmas the dissolution of flux bearing minerals such as ap e g those containing p b or f may influence the stability and solubility of other trace element bearing minerals during anatexis of metapelites texture e g grain size and distribution and spacial relationship to other minerals plays an important role in reaction kinetics and at least temporarily in mineral solubilities the disequilibrium behavior of accessory minerals has critical consequences for ree modelling of granites

late holocene morphodynamics in the littoral zone of the iwik peninsula area banc d arguin mauritania abstract in the littoral zone of the banc d arguin both littoral sedimentary units and man made deposits shell middens abound they were formed during the late holocene after the final onset of the post glacial transgression here a geo archaeological approach is used to study them the geomorphological and sedimentological characteristics of the coastal features define two distinct coastal sedimentary units in the iwik aouatil zone between an ancient shoreline which formed on the tafaritian substratum ca 6 7 5 7 cal ka bp and the present one i very extensive sand flats and ii linear relief features both covered by a thin veneer of anthropogenic anadara senilis shell middens they developed under a stable sea level regime the sand flats expanded at variable rates throughout the period the linear relief features represent beach barriers and coastal dunes which can be dated archaeologically thanks to the superimposed shell middens supplemented by 14 c dating two series of linear sedimentary units are identified first a complex north south system of dunes and hook ended sand barriers developed from 4 8 to 4 1 cal ka bp and secondly two regular and linear beach barriers developed between 3 7 and 3 3 cal ka bp their morphological characteristics suggest that they were generated through littoral drift processes directional changes observed between the first and the second groups demonstrate that the wave refraction pattern was dramatically modified after the closure of the strait between the former iwik island and the land a comparison with the nearby jerf el oustani coastal area in the late holocene shows that both sites shared similarities in depositional patterns but also differences in the chronology of the sedimentary units processes involved in the development of the linear units are indicative of the enhancement of both sand influx and longshore drift due to climatic change

petrogenesis of cretaceous 133 84 ma intermediate dykes and host granites in southeastern china implications for lithospheric extension continental crustal growth and geodynamics of palaeo pacific subduction abstract this paper presents u pb zircon geochronology petrology and major and trace element sr nd and zircon hf isotopic geochemistry of cretaceous granites and intermediate dykes in the quanzhou and xiamen regions of southeastern china these data are used to investigate igneous petrogenesis and cretaceous tectonic evolution and interpret the geodynamics of palaeo pacific slab subduction granites in quanzhou and xiamen range in age from 133 ma to 87 ma have high sio2 and k2o contents low abundances in p2o5 and an a cnk index that ranges from 0 97 to 1 09 indicating that they are high k calc alkaline metaluminous i type rocks slightly negative nd t values 1 2 to 4 4 young nd model ages 0 87 ga to 1 20 ga and positive hf t values 0 5 to 9 9 of zircon grains indicate that the granites were derived from magmas that melted amphibolite in the middle lower crust and which may have assimilated country rocks during emplacement in shallow chambers the intermediate dykes have no genetic link to the granites and magma mixing was negligible eight dyke samples have low sio2 and high mgo ni and cr contents negative e nd t values 1 5 to 2 7 and positive e hf t values 2 7 to 7 6 suggest that the dykes were derived from residual basic lower crust after mafic crystal accumulation two samples of adakite like dykes are characterised by high sr y ratios 89 to 100 and high sio2 low k2o ni cr contents in combination with slightly negative e nd t values 1 7 to 1 8 and positive e hf t values 2 9 to 4 3 the adakite like dykes were derived from cumulate basic lower crust which had a mixed source between depleted mantle and crust derived melts based on our data combined with previously published work we suggest that extension induced middle lower crustal melting and underplating of mantle derived basaltic melts were the principal driving mechanisms for cretaceous granitic magmatism in coastal fujian province extension was related to subduction retreat whereas steep slab subduction caused underplating of mantle derived basaltic melts these processes were coupled and mainly responsible for the tectonic transition during the cretaceous from compression to extension in the coastal belt of the cathaysia plate

south flank of the yangtze delta past present and future abstract chenier plain and mudflat development in the south flank of the yangtze delta are examined by multi disciplinary methods over different spatiotemporal scales and changing human earth interactions the study site contains a narrow belt of elongated ridge complexes that formed along the sediment deficient open coast from 6500 to 4000 yr bp since then and until the past two decades shoreline progradation has accelerated due to increasing sediment supply fueling rapid deltaic expansion superimposed on this trend are a series of discrete sand dominated ridges deposited during several stormy intervals tidal flat development is regulated by complex estuarine processes short term morphodynamic variations at the site are caused by the alternations of tides and waves while intermediate morphodynamic variations are controlled by the multi decadal shifting of river stem channel and stormy climates the ongoing rapid accretion on the tidal flats is predicted to continue into the near future because the estuarine buffer effect is expected to balance the adverse impacts of decreasing riverine sediment discharge and rising sea level technological developments during the last 2000 years are exemplified by seawall construction against sea flooding marking a transition from passive to active dike construction has been used more frequently and intensively to reclaim land since the 1970s in support of the booming socioeconomic development in the region lessons from complex morphodynamic change and human earth interactions in the southern yangtze delta admonish us to not reclaim coastal wetland by lower flat enclosures constructing new dikes near the low waterline while an optimal alternative would be to implement upper flat enclosures constructing new dikes around the high waterline on the continuously accretionary tidal flats with auxiliary biological restoration engineering to satisfy both socioeconomic development and sustainable wetland conservancy

deformation of granitoid plutons in the dongshan area southeast china constraints on the physical conditions and timing of movement along the changle nanao shear zone the ne trending changle nanao shear zone has affected several granitoid plutons in the dongshan area southeast china microstructures in the granitoids range from undeformed to solid state lineations and foliation migmatitic textures are common in some units microprobe analysis of total al has been carried out on hornblende rims in four samples of gneiss from various points across the shear zone confining pressures calculated fall into range of 4 2 4 9 kb the average pressure 4 5 kb suggests that the shear zone may have reached at least 16 km depth fluid inclusion studies referred from the correspondent p t isochores indicate that the temperature of ductile deformation in the shear zone was 740 c observations on intrusive relations between the various granitic phases and their relative degrees of deformation suggest that emplacement of the different magma phases may be closely related in time and to movement along the changle nanao shear zone zircon from one deformed pluton yielded a crystallization u pb age of 121 5 2 8 ma field and microstructural data suggest the dated pluton is syntectonic which constrains the upper age of high temperature deformation in the orthogneiss along the changle nanao shear zone at that locality

sea level and storm control on the evolution of a chenier plain firth of thames new zealand abstract geological controls on the evolution of the miranda chenier plain firth of thames new zealand are investigated using high resolution stratigraphic information obtained from geophysical surveys two previous studies of the miranda chenier plain have provided disparate conceptual models of its development over the holocene one study evokes sea level oscillations to form individual cheniers while the other offers an alternate model based on the observed transgression of the modern chenier both studies agree that sea level has dropped between 4000 and 1000 years bp but the elevation of the highstand and nature of the fall are contentious this paper extends previous interpretations using data obtained from ground penetrating radar surveys and historical aerial photographs stratigraphic interpretation of the continuous high resolution sub surface radar data was used to infer a sea level curve for miranda these data enable four new inferences 1 sea level fell from 2 m around 4000 years ago mid holocene highstand to present about 1000 years ago 2 falling sea level influenced chenier spacing with the onset of alongshore rather than across shore chenier plain development coinciding with the termination of sea level fall after the formation of ridge six 3 all cheniers initially transgressed producing similar resultant spit morphologies but the evolution of the more recent ridges 1 5 differed from older ridges 6 13 in that transgression occurred over embayed tidal flat sediments while the older cheniers stabilized on foreshore mudflats and 4 storms exert an important control in initiating chenier genesis the miranda chenier plain is a site of global significance for understanding chenier evolution in this study the high level of subsurface detail unimagined in past decades presents greater insight into the morphology and stratigraphy of the chenier ridges shedding new light on the role of sea level and storms on the evolution of the plain

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

formation of chenier plain of the donana marshland sw spain observations and geomorphic model abstract the guadalquivir estuary is one of the most important in europe it is isolated from the sea by two important littoral spits donana and la algaida its sedimentary filling occurred as a result of deltaic contributions of the guadalquivir river giving rise to marshes primarily composed of mud deposits among which a succession of sandy and shelly ridges can be found the aim of this paper is to explain the genesis and evolution of these sandy and shelly ridges clarifying what types of ridges are found and their spatial distribution identifying the processes responsible for their formation these ridges extend in the form of long strands along the estuary influencing its evolution during the late holocene the geomorphologic and lithostratigraphic features of these ridges allow them to be defined as transgressive cheniers regressive cheniers and laterally accreted ridges spits as components of the guadalquivir estuary chenier plain complex this chenier plain has the peculiarity of developing on a semi enclosed shoreline contrary to other chenier plains in the world which develop on open coasts in the guadalquivir estuary the chenier plain formation is related to two relatively higher sea level 4200 2800 yr bp and 1400 1000 yr bp during which high energy events occur storms and tsunamis that transgressed the large littoral spits the carrizosa 4000 yr bp and vetalengua 1400 1300 yr bp spits have been formed across the inlet and prograded landwards of the estuary from here several sequences of cheniers mainly transgressive cheniers associated with these events were formed these cheniers form two groups las nuevas 1100 1000 yr bp and marilopez 3000 yr bp composed mainly of shells and shell fragments these cheniers were constructed by waves which reworked the shells above estuarine levees and led to their intense landward migration thus explaining the peculiar high inland position of the cheniers

sources and evolution of arc magmas inferred from coupled o and hf isotope systematics of plutonic zircons from the cretaceous separation point suite new zealand abstract coupled o and hf isotopic compositions of zircons from early cretaceous 113 124 ma granitoids of the separation point suite sps new zealand obtained by cathodoluminescence imaging guided micro beam methods sims la icpms are used as a record of evolving magma compositions in a prominent mesozoic arc system eight representative sps samples from individual plutons in the nelson and fiordland regions yield magmatic zircons with initial hf isotope ratios expressed in e hf ranging from 4 to 11 nelson and 5 to 12 fiordland respectively initial hf isotope ratios of zircons are extremely heterogeneous within individual samples with the vast majority of values distinctly less radiogenic than depleted mantle at 120 ma e hf 16 o isotope ratios are likewise variable with 18 o zircon smow values of 2 8 nelson and 0 7 fiordland the within rock variability in both zircon hf and o isotope ratios is testimony to open system processes that operated during magma evolution and zircon crystallisation average 18 o zircon for cores and rims allow constraints to be placed on the o isotopic composition of magmas from which zircon precipitated 18 o magma 4 8 elevated 18 o magma 6 5 require involvement of 18 o enriched supracrustal material weathered continental crust or low t seawater hydrothermally altered oceanic crust while 18 o magma 18 o depleted crustal component whole rock sr isotope nb ta and nd pb systematics are inconsistent with 18 o depleted slab melts 18 o 0 6 as a source component for sps magmas instead low 18 o values suggest incorporation of high t meteoric hydrothermally altered country rocks similar to those of the largs terrane presently exposed in northern fiordland in diagrams of sio 2 versus inferred 18 o magma the most primitive sps samples from the nelson and fiordland regions plot close to the expected composition for primitive arc magmas more evolved granitoids however show strongly divergent trends of o isotope composition as a function of sio 2 suggestive of assimilation coupled to fractional crystallisation afc in contrasting crustal environments emplacement level contamination by local crust is supported by age distributions of inherited zircons which indicate a predominance of palaeozoic and mesozoic zircons in nelson and fiordland granitoids respectively

response of wave dominated and mixed energy barriers to storms wave dominated and mixed energy barriers are extremely dynamic landforms responding to processes operating over a spectrum of time scales ranging from daily to monthly fluctuations related to storm and post storm conditions to century to millennium scale evolution driven by relative sea level change two types of storms are of particular relevance warm core tropical and cold core extratropical cyclones both are responsible for generating very large waves highly energetic surf zone dynamics and sediment transport elevated inshore water levels and extensive morphological responses all cyclones are affected by climate change which governs their frequency intensity and tracks barrier storm response is primarily governed by maximum storm runup and barrier morphology as conceptualised in abby sallenger s storm impact scale model sallenger 2000 this model defines four storm impact regimes and includes erosive as well as accretionary responses on the erosion side the swash regime drives bar and berm flattening the collision regime is marked by dune scarping and beach lowe the overwash regime leads to dune scouring and channel incision and the inundation regime may result in barrier destruction on the deposition side storm berms and beach ridges may form and accrete in the swash and collision regimes localised vertical beach and barrier accretion are associated with the collision and overwash regimes and washover deposition takes place in the overwash and inundation regimes site specific factors play a key role in moderating the morphological response and include storm characteristics type duration and track longshore sediment supply upwelling downwelling currents coastal setting and inner shelf topography the response of a barrier to a tropical or extratropical cyclone can however not be considered in isolation and has to be appreciated in a longer temporal context involving morphological preconditioning due to antecedent wave and water level conditions additionally a simple process response approach of the cause and effect type is inappropriate and a more complex conceptual framework involving thresholds feedbacks resilience and vulnerability will need to be adopted a useful way to visualise and conceptualise more complex storm behaviours and the longer term vulnerability of barriers is the resilience trajectory which maps out the changes in barrier geometry elevation and width over various time scales from weeks to years or even longer and under varying forcing conditions including changes in storminess and sea level rise an increased understanding of barrier response to storms and sequences of storms is required to better quantify long term barrier response to climate change high resolution and comprehensive decadal records of barrier response to storms are a prerequisite to achieve this ambition linking site specific coastal settings hydrodynamic drivers and morphological responses and allowing the recognition of recovery and impact dominated phases the enhanced insights in barrier response to extreme events must then be incorporated into improved coastal response models to help predict the impacts of future climate change on wave dominated and mixed energy barriers around the world 2013 elsevier b v

shoreline change analysis and its application to prediction a remote sensing and statistics based approach abstract shoreline change analysis and prediction are important for integrated coastal zone management and are conventionally performed by field and aerial surveys this paper discusses an alternative cost effective methodology involving satellite remote sensing images and statistics multi date satellite images have been used to demarcate shoreline positions from which shoreline change rates have been estimated using linear regression shoreline interpretation error uncertainty in shoreline change rate and cross validation of the calculated past shorelines have been performed using the statistical methods namely regression coefficient r 2 and root mean square error rmse this study has been carried out along 113 5 km of coast adjoining bay of bengal in eastern india over the time interval 1973 to 2003 the study area has been subdivided into seven littoral cells and transects at uniform interval have been chosen within each cell the past and future shoreline positions have been estimated over two time periods of short and long terms in three modes viz transect wise littoral cell wise and regionally the result shows that 39 of transects have uncertainties in shoreline change rate estimations which are usually nearer to cell boundaries on the other hand 69 of transects exhibit lower rmse values for the short term period indicating better agreement between the estimated and satellite based shoreline positions it is also found that cells dominated by natural processes have lower rmse when considered for long term period while cells affected by anthropogenic interventions show better agreement for the short term period however on regional considerations there is not much difference in the rmse values for the two periods geomorphological evidence corroborates the results the present study demonstrates that combined use of satellite imagery and statistical methods can be a reliable method for shoreline related studies

hybridization between felsic and mafic magmas in calc alkaline granitoids a case study in northern sardinia italy abstract two examples of felsic mafic association resulting from a magma mingling mechanism have been studied in carboniferous calc alkaline granitoids from sardinia using mineralogical and geochemical techniques 1 the centimetric to decimetric magmatic mafic enclaves from the reversely zoned tonalitic santa restituta pluton this type of enclave which is common in calc alkaline granitoids represents blobs of mafic magma incorporated into a silicic host magma 2 the osidda mafic complex about one kilometre in diameter enclosed in the benettuti granodiorite this study intends to compare these two types of felsic mafic association in order 1 to clarify the nature of the interaction processes which occurred between the two magmatic components 2 to test the influence of the degree of fragmentation of the mafic component into the felsic matrix on the intensity of such processes the santa restituta enclaves sre and the osidda mafic complex omc exhibit the same general mineral assemblage plagioclase biotite hornblende quartz this assemblage is similar to that of the corresponding host granitoids however the sre and the omc are characterized by a greater abundance of biotite and hornblende the mineralogical study reveals the presence of two types of crystals the first type corresponds to minerals typical of the mafic or the felsic component in the mafic magma they are represented by remnants of an rich plagioclase by hornblende clots presumably pyroxene relicts and by orthopyroxene observed only in one facies of the omc these crystals represent remnants of phenocrysts present in the mafic component prior to the mingling event in the felsic component the first type of crystals is represented by quartz ocelli which are sometimes incorporated in the mafic magma as xenocrysts surrounded by a reaction rim of biotite and hornblende the second type comprises minerals which are found indiscriminantly in both magmatic components and which formed during the mingling event mingling minerals they include plagioclase an52 35 biotite hornblende quartz mineralogical data indicate that thermal equilibrium occurred between the mafic magma and the felsic matrix that equilibration was reached in the sre is shown by the compositional similarity of the mingling minerals of the enclaves and their host rocks however due to a lesser degree of fragmentation thermal equilibration was not reached in the omc geochemical data however do reveal close relationships between the two magmas which appear therefore to have both been hybridized by mutual chemical interaction a chemical comparison between the sre and the omc shows that in both cases the same qualitative interaction mechanisms operated between the host granitoids and either a voluminous mafic body osidda or a highly fragmented mafic component santa restituta enclaves however the intensity of hybridization is minor in the omc as compared with the sre it is suggested that hybridization of the host granitoids involves 1 mass to mass mixing due to disaggregation and dispersal of the mafic magma in the host granitoid resulting from mechanical stirring during the pluton s genesis from the initial meeting of the two magmas to the pluton s final emplacement 2 loss of certain elements si k rb ba li zr p nb ree which migrated towards the mafic magma through diffusion due to compositional gradients fluid transfer as a consequence the composition of the host granitoids is linked to that of their magmatic enclaves the enclaves with the lowest feo tot mgo ratios are enclosed in the least felsic granitoids and vice versa hybridization of the mafic component involves 1 mechanical transfer of crystals quartz from the host granitoid 2 enrichment in numerous elements migrating from the felsic component this is expressed mineralogically by the crystallization of numerous anhedral phases such as quartz sio2 biotite k rb h2o hornblende h2o apatite p and zircon zr 3 loss of ca and sr by the mafic component the nature of the processes of chemical migration are discussed the importance of the continuous renewal of the contact surface between the two components is emphasized the original compositions of the interacting mafic and granitic components become therefore highly modified this phenomenon can probably be generalized to apply to calc alkaline granitoids as a whole which are in fact characterized by the common occurrence of magma mingling

high mg adakites from kadavu island group fiji southwest pacific evidence for the mantle origin of adakite parental melts we report here the compositions of primitive high mg adakite lavas from the kadavu island group fiji two distinctive high mg adakite compositions are present on kadavu and both are strongly enriched in sr and la with high sr y 120 and la yb 30 values the east kadavu high mg adakite is relatively enriched in k2o and depleted in tio2 and nb our results from kadavu suggest that there is an adakite magma series that is the result of complex open system magmatic processes including magma mixing between relatively low sio2 mantle derived melts of high mg adakite composition and high sio2 low mg adakite magma the results from kadavu island suggest that adakite magma suites worldwide are likely to include primitive high mg compositions despite the lack of fi eld evidence in many cases

geochronological and geochemical results from mesozoic basalts in southern south china block support the flat slab subduction model the debate on the mesozoic tectonics of the south china block scb featuring a broad orogenic belt and a large continental magmatic province has been rejuvenated in the past years there are a number of competing tectonic models each predicting different time space and compositional evolutional trends for the mesozoic igneous rocks including sporadic basalts in this paper we report high precision 40 ar 39 ar ages and geochemical and sr nd isotopic data for basaltic rocks in central eastern scb these results together with a data compilation indicate three evolutionary stages for the basalts stage 1 195 160 ma basalts occur only in inland scb they exhibit low initial 87 sr 86 sr ratios 0 7038 to 0 7078 high e nd t values 1 5 to 6 0 and ocean island basalt oib like geochemical characteristics such as low la nb ratios 0 6 to 1 4 implying negligible to minor lithosphere contamination stage 2 160 110 ma basalts mostly from the same inland region with minor occurrence closer to the coast are characterized by variable initial 87 sr 86 sr ratios 0 7053 to 0 7102 end t values 6 0 to 5 0 and low la nb ratios 0 9 to 1 8 indicating an enhanced asthenosphere lithosphere interaction stage 3 110 to 80 ma basalts can be further divided into two sub groups based on their geographic and geochemical variations basalts in the coastal regions are characterized by low end t values 8 1 to 3 7 and variably high la nb ratios up to 4 8 indicating a strong arc signature on the other hand basalts in the inland regions have high e nd t values 1 9 to 6 8 and low la nb ratios 0 6 to 1 2 that are similar to the stage 1 basalts we interpret these features as results of geodynamics processes related to the break up foundering and retreating of an early mesozoic flat subducted oceanic slab

upper mantle structure and dynamics beneath southeast china we applied teleseismic tomography to 5671 relative travel time residuals from 257 teleseismic events recorded by 69 seismic stations to determine the 3d p wave velocity structure of the upper mantle under southeast se china our results show prominent low p wave velocity low vp anomalies under se china which may reflect the remnant magma chambers and channels of the late mesozoic igneous rocks which may be reheated by the upwelling mantle flow from the lower mantle driven by the deep subduction in east asia during the cenozoic high vp anomalies are revealed in the upper mantle to the east of taiwan which represent the subducted eurasian plate our result also suggests the break off of the subducted eurasian plate caused by its interaction with the philippine sea plate under central and north taiwan the slab break off may have created a mantle window through which the asthenospheric flow arises causing the high heat flow and rapid uplift in the taiwan orogen

the amazon influenced muddy coast of south america a review of mud bank shoreline interactions the 1500 km long coast of south america between the amazon and the orinoco river mouths is the world s muddiest this is due to the huge suspended sediment discharge of the amazon river 106 754 tons yr 1 9 part of which is transported alongshore as mud banks mud bank formation is controlled by the physical oceanography of the continental shelf seaward of the amazon river mouth an initial seafloor storage area for much of the suspended sediment discharged from the river in this area rapid and sustained fluid mud concentration and trapping are associated with fresh water salt water interaction and estuarine front activity on the shelf due to the enormous amazon water discharge ca 173 000 m3 s 1 at obidos 900 km upstream of the mouth fluid mud is transported shoreward and then along the coasts of the guianas by a complex interaction of wave and tidal forcing and wind generated coastal currents the mud banks which may number up to 15 or more at any time are up to 5 m thick 10 to 60 km long and 20 to 30 km wide and each may contain the equivalent mass of the annual mud supply of the amazon as the banks migrate alongshore their interaction with waves results in complex and markedly fluctuating shorelines that are associated with space and time varying depositional bank phases and erosional inter bank phases bank zones are protected from wave attack as a result of wave energy dampening by mud and undergo significant albeit temporary coastal accretion accompanied by rapid mangrove colonization the dampening of waves in bank areas as they propagate onshore is accompanied by the shoreward recycling of mud commonly in the form of individual mud bars these bars progressively undergo desiccation and consolidation and thus constitute a major pathway for rapid and massive colonization by mangroves erosion by waves propagating across relatively mud deficient shoreface zones in inter bank areas can lead to muddy shoreline retreat rates of tens of metres to several kilometres over a few months to a few years accompanied by massive removal of mangroves notwithstanding the higher incident wave energy on inter bank shores inter bank shorefaces are permanently muddy due to the pervasive influence of the amazon muddy discharge inter bank and transitional bank to inter bank phases are associated with both periodic sandy chenier formation and extreme forms of rotation of rare headland bound sandy beaches the high mud supply from the amazon has been the overarching geological control on the quaternary evolution of the northeastern south american coast having led to the growth of a muddy shelf clinoform at the mouth of the amazon and more or less important progradation throughout this coast net progradation reflects an imbalance in favour of deposition during each mud bank inter bank cycle the high mud supply has presumably blanketed shelf sand deposited by smaller rivers during eustatic lowstand phases the shelf clinoform structure at the mouth of the amazon and the muddy coastal progradation throughout the coast of the guianas and into venezuela provide analogues of the geological record on muddy shorefaces

progradational and backstepping shoreface deposits in the ladinian to early norian snadd formation of the barents sea shoreface sandstone deposits within the early carnian part of the snadd formation of the norwegian barents sea can be traced for hundreds of kilometres in the depositional strike direction and for tens of kilometres in the depositional dip direction this study uses three dimensional seismic attribute mapping and two dimensional regional seismic profiles to visualize the seismic facies of these shoreface deposits and to map their internal stratigraphic architecture at a regional scale the shoreface deposits are generally elongate but show variable width from north east to south west which corresponds to a sediment source in the northern part of the basin and a southward decrease in longshore sediment transport the snadd formation presents an example of how large scale progradational shoreface deposits develop the linear nature of its shoreface deposits contrasts with more irregular cuspate wave dominated deltaic shorelines that contain river outlets and instead implies longshore drift as the main sediment source in map view discrete sets of linear features bounded by truncation surfaces scale directly to beach ridge sets in modern counterparts the shoreface deposits studied here are characteristic in terms of scale and basin wide continuity and offer insight into the contrast between shallow marine deposition under stable triassic greenhouse and fluctuating holocene icehouse climates findings presented herein are also important for hydrocarbon exploration in the barents sea because they describe a hitherto poorly understood reservoir play in the triassic interval wherein the most prominent reservoir plays have so far been considered to be found in channelized deposits in net progradational delta plain strata that form the topsets to shelf edge clinoforms the documented presence of widespread wave dominated shoreface deposits also has implications for how the relative importance of different sedimentary processes is considered within the basin during this period

dynamic changes and processes in the mississippi river delta research in the modern delta of the mississippi river has revealed short term changes and processes that are of significant magnitude deltaic lobes each lobe covering an area of 30 000 sq km and having an average thickness of 35 km switch sites of deposition on an average of every 1 500 yr through short periods of geologic time this process results in a relatively thick accumulation of stacked deltaic cycles covering extremely large areas within a single delta lobe and operating on an even higher frequency are bay fills and overbank splays bay fills having areas of 250 sq km and thickness of 15 m require only 150 yr to accumulate four major events have taken place in the modern balize delta since 1838 overbank splays are much smaller covering areas of less than 2 sq km and having thicknesses of 3 m but are associated with high floods on the river at the river mouth continued progradation of the distributary channel can form distributary mouth sand bodies that have dimensions of 17 km long 8 km wide and a thickness of 80 m in a period of only 200 yr differential sedimentary loading at the river mouth results in formation of diapirs that display vertical movements in excess of 100 m in a period of 20 yr on the subaqueous delta platform sediment instabilities operate nearly continuously mass moving large quantities of shallow water deposits to deeper water environments via arcuate rotational slides and mudflow gullies and depositional lobes all of these changes and processes operate at differing spatial and temporal scales but all result in deposition of large volumes of sediment over extremely short periods of time

aeolian beach ridges and their significance for climate and sea level concept and insight from the levant coast east mediterranean abstract relict beach ridges of aeolian origin and associated soils are often used for inferring relative sea level and climate with contrasting results most studies link the aeolian coastal deposits to regressive phases some to high sea level stands and a few to intermediate relative sea level positions we interpret the apparent contradictions as indicating the lack of an over arching concept and the inconsistent usage of sea level related terms in this paper we present an integrated morpho sedimentological concept for a microtidal mid latitudinal coast and review existing data from the levant east mediterranean coast to evaluate the concept and to eliminate nomenclatural confusion a coastal depositional environment in a semi arid environment consists of shallow marine aeolian and alluvial facies which together form an aeolian beach ridge complex as a package of strata which respond simultaneously to sea level change a transgressive complex forms through reworking or overstepping of the coastal foredune and a regressive complex forms by downstepping under transgression the aeolian beach ridge represents the highstand deposit and its adjacent shallow marine sediment is the transgressive deposit under regression the complex represents the falling stage and the associated downdip surface marks the lowstand on the levant coast we find chronologically well constrained offlapping aeolian beach ridges as parts of six downstepping beach ridge complexes formed between 200 ka and 10 ka the complexes represent the falling stage systems tract fsst of a short lived 5th order depositional sequence when the shoreline shifted from a position close to the modern coastline to the shelf or below the shelf edge three of these fssts and their up dip and down dip super bounding surface together form the 4th order 100 ka sequence of the last interglacial glacial cycle the absence of transgressive highstand and lowstand systems tract is explained by the poor preservation potential due to the small sediment budget of the complex the falling stage complex has a high preservation potential because sediment source area increases while the sand drift potential remains above the local threshold on the levant coast sand delivery to the backshore continued during relative sea level falls for distances of up to 10 km between dune and coastline which is unprecedented in most modern analogues the significance of the dune soil succession for climate is limited because the dunes are governed by relative sea level change the vegetation response to changes in precipitation is non linear and the dune dynamics are characterised by low resilience and hysteresis

the mississippi delta region past present and future the mississippi delta region of south louisiana houses a wealth of resources within a dynamic subsiding landscape foundations for the delta region reflect neogene evolution of the depocenter whereas details of the modern landscape reflect late pleistocene to holocene evolution of the alluvial deltaic plain the holocene delta plain was constructed by cyclical growth of deltaic headlands followed by avulsion and relocation of the fluvial sediment source abandoned headlands were then submerged and reworked while a new headland was created at the site of active fluvial sediment input historic period levees have decoupled the delta plain from its fluvial sediment source at the same time global sea level rise was accelerating which has accelerated delta plain submergence diversions of mississippi river water and sediment are necessary to achieve delta plain sustainability but upstream dams trap 50 of the total sediment load and there is not enough supply to keep pace with subsidence and accelerated

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent