application of geophysical borehole logging techniques to examine coastal aquifer palaeohydrogeology geophysical logging is shown to be a useful technique to support investigations of coastal aquifer hydrogeology formation logging can identify the geological layering and fluid logging can characterize the salinity distribution the measurements also reveal wellbore flow to be common in coastal boreholes which can mask the salinity stratification in the aquifer matrix geophysical logging can be used to guide water sampling and to provide information on the palaeohydrogeology in combination with water sampling and age determinations it has shown modern groundwaters overlying holocene age groundwaters in turn overlying groundwaters of pleistocene age within 150 m of the surface in some of the aquifers studied sea level change in response to pleistocene glaciations and deglaciations is recognized as a major control on the salinity of groundwaters and on the development of permeable flow routes in coastal aquifers the permeable routes that developed by groundwater circulation to older and deeper base levels are now partly or wholly occupied by groundwaters of modern flow systems and can be the focus for saline intrusion the effects of pleistocene sea level change on aquifer development appear to be worldwide and are being increasingly recognized examples are described to illustrate the development of flow horizons in relation to rock layering structure and base levels in coastal regions groundwaters of unconfined aquifers are in direct contact with modern sea water at a freshwater saline water interface in confined aquifers the interface with saline water may exist some distance offshore for both unconfined and confined aquifer systems sea level provides the minimum natural head reference for groundwater recharged at higher elevations inland and circulating to the coast the hydraulic potential of coastal aquifers therefore generally increases with depth and upward seepages and springs develop in coastal regions and sometimes offshore the continuous groundwater circulation from inland recharge areas to discharging base level at the coast establishes permeable flow routes it also develops the general permeability and storage of coastal groundwater flow systems changes in sea level directly influence the salinity of groundwater and the flow routes that are developed rising sea levels cause inundation of unconfined aquifers by marine waters from the seaward end groundwater flowsystem circulation to the rising river base levels develops the permeability of increasingly shallow flow routes falling sea levels promote freshwater flushing and the oxidation of aquifers from the landward end and the development of deeper permeable horizons through circulation to the lower and more remote base level outlets during the pleistocene hydraulic base level river and sea level changed dramatically both locally and globally in response to glaciation and deglaciation as polar ice expanded and retreated over northern land areas during periods of polar ice expansion recharge was lower in glaciated or permafrost areas fiver base levels and global sea level fell resulting in a greater continentality and more remote coastlines sea levels are believed to have fallen by as much as 130 m below present with recoveries and stillstands during interglacial periods for details see vaikmae et al 2001 the repeated changes introduced a complex 3d salinity and age distribution of groundwaters occupying coastal aquifers depending upon their elevation and degree of confinement the cycles of inundation drainage and freshwater flushing the present balance between the inland advance and from edmunds w m milne c j eds 2001 palaeowaters in coastal europe evolution of groundwater since the late pleistocene geological society london special publications 189 251 270 0305 8719101l 15 00 the geological society of london 2001 25 2012 at koebenhavns universitetsbibliothek on february 9 http sp lyellcollection org downloaded from

intraplate extension prior to continental extrusion along the ailao shan red river shear zone left lateral movement of the ailao shan red river shear zone lends support to the hypothesis of continental extrusion resulting from the collision of india with asia our new observations from northwestern yunnan china and northwestern vietnam on different sides of the shear zone demonstrate that the sinistral offset was 600 km according to correlations of permian triassic flood basalt successions and late paleogene highly potassic mafic magmas we conclude that the shear was propagating on the south china continental margin and does not correspond to a suture between south china and indochina furthermore the highly potassic magmas were emplaced from ca 40 to 30 ma before the shear movement which was caused by the late oligocene to early miocene ca 27 22 ma extrusion activity this suggests that a late eocene to early oligocene intraplate extension possibly induced by delamination of thickened continental lithosphere took place in northwestern yunnan or eastern tibet as a response to the india asia collision this extension and sea floor spreading of the south china sea that began ca 30 ma could have accounted for the initiation of the ailao shan red river shear zone

the western ailaoshan volcanic belts and their se asia connection a new tectonic model for the eastern indochina block the western ailaoshan wal volcanic belts mark the western boundary of the south china indochina suture zone along the ailaoshan fold belt geochronological and geochemical evidence suggests that the wal volcanic belts vary in ages and origins and includes 1 l carboniferous earliest m permian ca 300 270 ma incipient backarc basin magmatism 2 m permian ca 265 ma island arc mature backarc basin magmatism 3 early l permian ca 260 255 ma wal indochina arc continent collision and the associated syn collisional granitic magmatism as well as subsequent 4 e triassic ca 250 245 ma post collisional magmatism regional geological comparison indicates that the post l carboniferous wal tectonic evolution was closely related to the eastern indochina block we present a new g plate geodynamic evolution model for the ailaoshan fold belt and its surrounding south china indochina region based on new and published u pb zircon ages together with whole rock and pb isotope geochemical data

late quaternary sedimentary environments and landforms in the ganges delta abstract late quaternary sediments deposited since the lowest stand of sea level during the last glacial maximum in the ganges delta and its surrounding region were classified into five units according to their sedimentary facies these are the lowest unit of sandy gravels the lower unit of sand with a few gravels and the middle upper and uppermost units consisting mainly of sand and silt with occasional peat layers the contact between the lower and middle units is fairly sharp and the upper part of the lower unit is oxidized in some places this suggests a period of subaerial exposure after the deposition of the lower unit during the low stand of sea level about the time of the last glacial maximum rivers in the ganges delta and its surrounding region dissected the surfaces of the region and deposited the lowest unit on the valley floors the lower unit was deposited over the lowest unit during an early stage of the post glacial transgression between ca 12 000 yr bp and 10 000 yr bp the surface of the delta was slightly dissected and the top of the lower unit was weathered and oxidized following this period the middle and upper units of alluvial or deltaic sand and silt with occasional peat were deposited the coastline in the early holocene retreated towards the central part of the present ganges delta in the middle and late holocene the silt and clay with occasional peat layers of the uppermost unit indicate that the lowland gradually became marshy and poorly drained as the rate of transgression became slower

active circulation of saline ground waters in carbonate platforms evidence from the great bahama bank measurements of salinity temperature and ground water discharges within the great bahama bank provide evidence of active circulation of near normal ocean water beneath north andros island elevated salinity waters 38 42 derived by density refulx from the great bahama bank flow eastward beneath the island and mix with normal salinity cold ground waters 19 20 c from deeper than 250 m in the adjacent oceans east to west flow of water from the straits of florida may be driven by head differences generated by the florida current which impinges on the western margins of the platform alternatively density differences between the reflux and tongue of the ocean sea waters may cause more local circulation on the eastern flanks these flows have important diagenetic implications particularly in the explanation of pervasive secondary dolomitization widely reported at shallow depths in the bahamas

geochemical and sr nd isotopic characteristics of granitic rocks from northern vietnam abstract five major felsic igneous suites from northern vietnam with ages from mid proterozoic to early cenozoic were studied representative granitic rocks from the posen complex mid proterozoic and the dienbien complex late permian to early triassic show geochemical characteristics similar to those of calc alkaline to high k calc alkaline i type granites however the former located in the south china block has significantly higher initial nd isotopic ratios end t 0 7 to 1 5 and older nd isotopic model ages tdm 1 7 ga than the latter end t 4 7 to 9 7 tdm 1 3 1 5 ga which were emplaced south of the song ma suture and thus in the indochina block the generation of both complexes may be attributed to subduction related processes that occurred in two distinct crustal provenances with different degrees of mantle inputs on the other hand jurassic to cretaceous granitic rocks from the phusaphin complex contemporaneous rhyolites from the tule basin and late paleogene granitic rocks from the yeyensun complex all exposed in the south china block between the ailao shan red river shear zone and the song ma suture display geochemical features similar to those of a type granites with intermediate end t values 0 6 to 2 8 and younger tdm ages 0 6 1 1 ga these magmas are suggested to have been generated as a consequence of intraplate extension in the western part of the south china block yunnan and to have been transported to their present position by mid tertiary continental extrusion along the ailao shan red river shear zone related to the india asia collision overall the isotopic and model age data reported in this study indicate that in northern vietnam the most important crust formation episode took place in the proterozoic likewise repeated mantle inputs have played a role in the petrogenesis of phanerozoic granitic rocks

a recipe for microcontinent formation accreted slivers of continental margins are common in the geologic record but the processes that lead to their formation are poorly understood we observe an association of plume related microcontinent isolation and subsequent long term asymmetries in oceanic crustal accretion based on four recent examples the seychelles in the indian ocean jan mayen in the norwegian greenland sea and the east tasman plateau and the gilbert seamount complex in the tasman sea these microcontinents formed by rerifting of a young continental margin 25 m y old in the vicinity of a mantle plume stem followed by asymmetric seafloor spreading two dimensional numerical stochastic basin modeling suggests that a yield strength minimum along the landward edge of a rifted margin thermally enhanced by heating from a mantle plume may cause a spreading ridge to jump onto this zone of weakness this action isolates a passive margin segment the association of large igneous provinces and microcontinents should be useful for identifying similar events in the geological record

age and duration of the emeishan flood volcanism sw china geochemistry and shrimp zircon u pb dating of silicic ignimbrites post volcanic xuanwei formation and clay tuff at the chaotian section abstract the age and duration of the emeishan basalts sw china remain poorly constrained largely due to the severe thermo tectonic overprinting of the ar ar system and failure to obtain zircon separates from erupted basalts in an attempt to solve this problem geochemical analyses and shrimp zircon u pb dating have been carried out on rare felsic ignimbrite in the uppermost of the emeishan lava succession the xuanwei formation which immediately overlies the emeishan basalts and a clay tuff at the middle late permian boundary at the chaotian section clastic rocks of the lowermost xuanwei formation group 1 in eastern emeishan large igneous province lip have a geochemical affinity to the emeishan felsic volcanic rocks whereas the overlying sediments group 2 are compositionally more akin to mafic components of the emeishan traps this is the reverse of volcanic sequence of the central emeishan lip where the felsic extrusives sit above predominant mafic rocks it is likely that the clastic rocks are water transported sediments resulting from erosion of the volcanic rocks in the center of the emeishan lip this interpretation is further supported by the general agreement between the age of the lowermost xuanwei formation 257 4 ma 260 5 ma and that of the silicic ignimbrite 263 4 ma and the clay tuff at the middle late permian boundary at chaotian 260 5 ma these ages interpreted as the termination age of the emeishan volcanism are indistinguishable within error from the middle late permian boundary age 260 4 0 4 ma and the main stage 259 262 3 ma of the emeishan volcanism inferred from dating of mafic and alkaline intrusions in the emeishan lip all these suggest that the emplacement of the emeishan volcanism took place over a very short interval moreover the temporal link and geochemical analyses suggest that the chaotian clay at the middle late permian boundary was genetically related to the emeishan silicic volcanism this together with the fact at that both the emeishan basalts and the chaotian clay rest on the maokou formation leads us to infer that the emeishan basalt was emplaced at the middle late permian boundary in this sense the emeishan volcanism can be regarded as a boundary event and its age is presumed at 260 ma although more precise dating is required both stratigraphic correlation and chronologic data presented in this paper lend supports to the notion that the emeishan volcanism was one of likely causes of the end guadalupian mass extinction

ophiolite genesis and global tectonics geochemical and tectonic fingerprinting of ancient oceanic lithosphere ophiolites and discussions on their origin and significance in earth s history have been instrumental in the formulation testing and establishment of hypotheses and theories in earth sciences the definition tectonic origin and emplacement mechanisms of ophiolites have been the subject of a dynamic and continually evolving concept since the nineteenth century here we present a review of these ideas as well as a new classification of ophiolites incorporating the diversity in their structural architecture and geochemical signatures that results from variations in petrological geochemical and tectonic processes during formation in different geodynamic settings we define ophiolites as suites of temporally and spatially associated ultramafic to felsic rocks related to separate melting episodes and processes of magmatic differentiation in particular tectonic environments their geochemical characteristics internal structure and thickness vary with spreading rate proximity to plumes or trenches mantle temperature mantle fertility and the availability of fluids subduction related ophiolites include suprasubduction zone and volcanic arc types the evolution of which is governed by slab dehydration and accompanying metasomatism of the mantle melting of the subducting sediments and repeated episodes of partial melting of metasomatized peridotites subduction unrelated ophiolites include continental margin mid ocean ridge plume proximal plume distal and trench distal and plume type plume proximal ridge and oceanic plateau ophiolites that generally have mid ocean ridge basalt morb compositions subduction related lithosphere and ophiolites develop during the closure of ocean basins whereas subduction unrelated types evolve during rift drift and seafloor spreading the peak times of ophiolite genesis and emplacement in earth history coincided with collisional events leading to the construction of supercontinents continental breakup and plume related supermagmatic events geochemical and tectonic fingerprinting of phanerozoic ophiolites within the framework of this new ophiolite classification is an effective tool for identification of the geodynamic settings of oceanic crust formation in earth history and it can be extended into precambrian greenstone belts in order to investigate the ways in which oceanic crust formed in the archean

fore arc basalts and subduction initiation in the izu bonin mariana system recent diving with the jamstec shinkai 6500 manned submersible in the mariana fore arc southeast of guam has discovered that morb like tholeiitic basalts crop out over large areas these fore arc basalts fab underlie boninites and overlie diabasic and gabbroic rocks potential origins include eruption at a spreading center before subduction began or eruption during near trench spreading after subduction began fab trace element patterns are similar to those of morb and most izu bonin mariana ibm back arc lavas however ti v and yb v ratios are lower in fab reflecting a stronger prior depletion of their mantle source compared to the source of basalts from mid ocean ridges and back arc basins some fab also have higher concentrations of fluid soluble elements than do spreading center lavas thus the most likely origin of fab is that they were the first lavas to erupt when the pacific plate began sinking beneath the philippine plate at about 51 ma the magmas were generated by mantle decompression during near trench spreading with little or no mass transfer from the subducting plate boninites were generated later when the residual highly depleted mantle melted at shallow levels after fluxing by a water rich fluid derived from the sinking pacific plate this magmatic stratigraphy of fab overlain by transitional lavas and boninites is similar to that found in many ophiolites suggesting that ophiolitic assemblages might commonly originate from near trench volcanism caused by subduction initiation indeed the widely dispersed jurassic and cretaceous tethyan ophiolites could represent two such significant subduction initiation events

pollutant dispersal in groundwater and sediments of gaining and losing river reaches affected by metal mining the presented work couples groundwater and sediment chemistry in the metal mining polluted przemsza river valley in southern poland to reveal regularities in pollutant distribution and to relate them to sedimentary processes and surface water groundwater exchange ten piezometers were installed in transects across the low gradient meandering losing river reach and in the incised channelised gaining reach at each sampling site cores of sediments were sampled for heavy metals and groundwater samples were collected over a year for standard physicochemical analysis as well as zn pb cd mg and fe in the losing river reach the magnitude of pollution of groundwater in the levee zone was similar to that in the river and declined in the backswamp in the levee zone of the incised reach minimum groundwater pollution adjacent to the highly polluted river was related to gaining relatively clean groundwater in the losing reach the dispersal of heavy metals in the levee zone is controlled mainly by overbank accumulation of polluted sediments post depositional changes of metal concentrations in profiles of the losing reach indicate the important role of groundwater in metal dispersal in the gaining river reach the redistribution of metals in the profiles was not ascertained due to a much lower groundwater table

zircon u pb ages hf o isotopes and whole rock sr nd pb isotopic geochemistry of granitoids in the jinshajiang suture zone sw china constraints on petrogenesis and tectonic evolution of the paleo tethys ocean the jinshajiang suture zone located in the eastern part of the tethyan tectonic domain is noticeable for a large scale distribution of late jurassic to triassic granitoids these granitoids were genetically related to the evolution of the paleo tethys ocean beiwu linong and lunong granitoids occur in the middle zone of the jinshajiang suture zone and possess similar geochemical features indicating that they share a common magma source sims zircon u pb dating reveals that the beiwu linong and lunong granitic intrusions were emplaced at 233 9 1 4 ma 2 233 1 1 4 ma 2 and 231 0 1 6 ma 2 respectively all of these granitoids are enriched in abundances of si sio2t 65 2 73 5 wt and large ion lithophile elements liles but depleted in high field strength elements contents hfses e g nb ta and ti in addition they have low p2o5 contents 0 06 0 11 wt a cnk values molecular al2o3 cao na2o k2o mostly 1 1 and 10 000 ga al ratios 1 7 2 2 consistent with the characteristics of i type granites in terms of isotopic compositions these granitoids have high initial 87sr 86sr ratios 0 7078 0 7148 pb isotopic compositions 206pb 204pb t 18 213 18 598 207pb 204pb t 15 637 15 730 and 208pb 204pb t 38 323 38 791 zircon 18o values 7 3 9 3 and negative end t values 5 1 to 6 7 suggesting they were predominantly derived from the continental crust their nb ta ratios average value 8 6 are consistent with those of the lower continental crust lcc however variable ehf t values 8 6 to 2 8 and the occurrences of mafic microgranular enclaves mmes suggest that mantle derived melts and lower crustal magmas were involved in the generation of these granitoids moreover the high pb isotopic ratios and elevated zircon 18o values of these rocks indicate a significant contribution of the upper crustal composition we propose a model in which the beiwu linong and lunong granitoids were generated under a late collisional or post collisional setting it is possible that this collision was completed before late triassic decompression induced mantle derived magmas to be underplated and provided the heat for the anatexis of the crust hybrid melts including mantle derived and the lower crustal magmas were then generated the hybrid melts thereafter ascended to a shallow depth and resulted in some degree of sedimentary rock assimilation such three component mixing magma source and subsequent fractional crystallization could be responsible for the formation of the beiwu linong and lunong granitoids

paleomagnetism of the middle late jurassic to cretaceous red beds from the peninsular thailand implications for collision tectonics abstract jurassic to cretaceous red sandstones were sampled at 33 sites from the khlong min and lam thap formations of the trang syncline 7 6 n 99 6 e the peninsular thailand rock magnetic experiments generally revealed hematite as a carrier of natural remanent magnetization stepwise thermal demagnetization isolates remanent components with unblocking temperatures of 620 690 c an easterly deflected declination d 31 1 i 12 2 95 13 9 n 9 in stratigraphic coordinates is observed as pre folding remanent magnetization from north trang syncline whereas westerly deflected declination d 342 8 i 22 3 95 12 7 n 13 in geographic coordinates appears in the post folding remanent magnetization from west trang syncline these observations suggest an occurrence of two opposite tectonic rotations in the trang area which as a part of thai malay peninsula received clockwise rotation after jurassic together with shan thai and indochina blocks between the late cretaceous and middle miocene this area as a part of southern sundaland block experienced up to 24 5 11 5 counter clockwise rotation with respect to south china block this post cretaceous tectonic rotation in trang area is considered as a part of large scale counter clockwise rotation experienced by the southern sundaland block including the peninsular malaysia borneo and south sulawesi areas as a result of australian plate collision with southeast asia within the framework of sundaland block the northern boundary of counter clockwise rotated zone lies between the trang area and the khorat basin

geochemical constraints on the origin of bimodal magmatism at the okinawa trough an incipient back arc basin abstract the magmatism at the axial zone of the middle okinawa trough a young continental back arc basin comprises a bimodal basaltic rhyolitic suite accompanied by minor intermediate rocks we report major and trace element and sr nd isotopie data for the intermediate to silicic suites to provide constraints on their petrogenesis the rhyolites recovered as lava and pumice fall into three geochemical groups type 1 2 and 3 rhyolites type 1 rhyolites have 87sr 86sr 0 7040 0 7042 and 143nd 144nd 0 5128 0 5129 identical to those of associated basalts and are characterized by highly fractionated ree patterns petrogenesis of type 1 rhyolites is explicable in terms of fractional crystallization of the associated basalt in contrast type 2 rhyolites and andesite have slightly higher 87sr 86sr 0 7044 0 7047 but similar 143nd 144nd 0 5128 compared to those of the basalts the compositions of type 2 rhyolite and andesite can be explained by assimilation and fractional crystallization afc processes of the basalt magma quantitative analysis suggests assimilation fractional crystallization ma mc ratios of 0 05 hybrid andesite generated by mixing of evolved basalt and type 1 rhyolite is also present we emphasize that mechanical extension in this part of the okinawa trough involves gabbro ic lower crust that resulted from fractionation of mantle derived basaltic magmas type 3 rhyolite occurs only as pumice which makes its derivation questionable this rhyolite has major and trace element compositions and sr nd isotopie ratios which suggests that it may be derived from volcanic activity on the southern ryukyu volcanic front and arrived in the okinawa trough by drifting on the kuroshio current

fish suggests continental connections between the indochina and south china blocks in middle devonian time a yunnanolepiform antiarch placoderm fish is recorded from the givetian dong tho formation of quang binh province central vietnam this and other fishes from the same locality occur in marginal marine detrital facies with plant remains and lingulid brachiopods that indicate a nearshore to deltaic environment yunnanolepiform antiarchs were hitherto known exclusively from the lower devonian of the south china block the new occurrence of this group well south of the song ma suture suggests close links between the indochina and south china blocks in middle devonian time the massive sandstone exposures of the dong tho formation may be a southern extension of the do son sandstone formation of the hai phong area which is located on the south china block

paleomagnetism of the earliest cretaceous to early late cretaceous sandstones khorat group northeast thailand implications for tectonic plate movement of the indochina block abstract a total of 400 samples 33 sites were collected from the earliest cretaceous to early late cretaceous sandstones of the khorat group in the indochina block for paleomagnetic study to unravel the tectonic evolution of the region the sites were adopted from 3 traverses located in the northern edge of the khorat plateau northeastern thailand results indicate that almost all the sandstones exhibit similar magnetic values with an average declination d 31 7 inclination i 30 3 59 7 190 9 k 54 4 and a95 3 7 at reference point 17 30 n and 103 30 e the calculated paleolatitude points are inferred to deviate from the present latitude point by 1 2 2 3 only the lowermost part of the cretaceous sandstones can pass a positive fold test at 95 confidence level the relationship between the virtual geomagnetic poles vgps of cretaceous rocks of the indochina plate in thailand and those of the south china plate advocate that there is a major displacement of indochina along the northwest trending red river and associated faults by about 950 150 km with a 16 0 17 0 clockwise rotation relative to the south china plate during earliest cretaceous times paleomagnetic results of the early late cretaceous indochina plate point to a 20 25 clockwise rotation relative to the present occurring since very late cretaceous 65 myrs early neogene times which may be due to the collision between india and asia

tectonic implications of the nan suture zone and its relationship to the sukhothai fold belt northern thailand abstract the nan suture and the sukhothai fold belt reflect the processes associated with the collision between the shan thai and indochina terranes in southeast asia the shan thai terrane rifted from gondwana in the early permian as it drifted north a subduction complex developed along its northern margin the nan serpentinitic melange is a thrust slice within the pha som metamorphic complex and in total this unit is a late permian accretionary complex containing offscraped blocks from subducted oceanic crust of carboniferous and permian age the deformational style within the pha som metamorphic complex supports a west dipping subduction zone the late permian to late triassic fore arc basin sediments are preserved in the sukhothai fold belt and include a near continuous sedimentary record at least locally the whole sequence was folded and complexly thrust in the late triassic as a result of the collision late syn to post kinematic granites place an upper limit of 200 ma on the time of collision post orogenic sediments prograded across the suture in the jurassic

the ribe formation in western denmark holocene and pleistocene groundwaters in a coastal miocene sand aquifer the ribe formation is a regionally extensive miocene sand aquifer that is present in western denmark at depths ranging from 100 to 300 m below ground surface groundwater chemistry and isotope data collected from more than 40 wells show that the ribe formation mainly contains high quality ca bicarbonate type groundwater of holocene age 100 10 000 a bp pleistocene age groundwaters identified on the basis of stable isotopes noble gases and corrected 14c values are present below the island of r0m in discharge areas near the coast and in hydraulically isolated inland areas the groundwater age distribution in the ribe formation was successfully simulated with a numerical groundwater flow model and particle tracking only when the 14c content in groundwater was corrected for both geochemical reactions and diffusion the results indicate that geochemical and physical processes significantly influence the 14c content of groundwater and that the correction factors required for the two processes are of the same magnitude flow modelling results indicate that pleistocene groundwaters were emplaced at depth within the ribe fromation under low base level conditions that prevailed throughout the late pleistocene near the coast these waters are essentially isolated from the present flow system and pleistocene freshwater may be present offshore seismic surveys show that conditions offshore are favourable for the presence of pleistocene freshwater within the ribe formation and other aquifers

the impeller meter for measuring aquifer permeability variations evaluation and comparison with other tests a knowledge of the variation of horizontal hydraulic conductivity with vertical position k z is important in understanding the transport and dispersive properties of aquifers using an impeller meter to measure the discharge distribution in a screened well while pumping at a constant rate is a promising technique for obtaining the k z function such an application is described herein and the resulting k z functions are compared with those obtained previously using tracer tests and multilevel slug tests impeller meter data were the most convenient to obtain and tracer data the most difficult the k z functions obtained by the three methods were not identical but quite similar overall this similarity between both borehole tests and the larger scale tracer test showed that nonstationary hydraulic conductivity trends in a stochastic hydrologic sense exist in the test aquifer the impeller meter method was better able to detect the higher k layers than was the multilevel slug approach overall the results suggest that a practical strategy for fitting impeller meter tracer or multilevel slug test data to a given aquifer is to use the selected testing procedure to obtain a dimensionless distribution and then a standard pumping test to measure combining both types of information enables dimensional values for k z to be calculated in low permeability aquifers or near the bottom of a test well the fluid velocity due to pumping may be below the stall velocity of an impeller thus there is a definite need for the commercial development of more sensitive flow measuring devices such as heat pulse flowmeters hess 1986 which will extend the resolution of this field method

geochemical variation within the northern ryukyu arc magma source compositions and geodynamic implications the major and trace element and pb sr nd isotopic compositions of quaternary mafic lavas from the northern ryukyu arc provide insights into the nature of the mantle wedge and its tectonic evolution beneath the volcanic front in the northern part of the arc the subducted slab of the philippine sea plate bends sharply and steepens at a depth of 80 km lavas from the volcanic front have high abundances of large ion lithophile elements and light rare earth elements relative to the high field strength elements consistent with the result of fluid enrichment processes related to dehydration of the subducting slab new pb isotopic data identify two distinct asthenospheric domains in the mantle wedge beneath the south kyushu and northern ryukyu arc which in a parallel with data from the lau basin appear to reflect mantle with affinities to indian and pacific type mid ocean ridge basalt morb indian ocean morb type mantle contaminated with subducted ryukyu sediments can account for the variation of lavas erupted on south kyushu and probably in the middle okinawa trough in contrast magmas of the northern ryukyu volcanic front appear to be derived from sources of pacific morb type mantle contaminated with a sedimentary component along arc variation in the northern ryukyus reflects increasing involvement of a sedimentary component to the south compositions of alkalic basalts from the south kyushu back arc resemble intraplate type basalts erupted in nw kyushu since 12 ma we propose that the bending of the subducted slab was either caused by or resulted in lateral migration of asthenospheric mantle yielding indian ocean type characteristics from a mantle upwelling zone beneath nw kyushu and the east china sea this model also accounts for 1 extensional counter clockwise crustal rotation 4 2 ma 2 voluminous andesite volcanism 2 ma and 3 the recent distinctive felsic magmatism in the south kyushu region

volcanism in the earliest stage of back arc rifting in the izu bonin arc revealed by laser heating 40ar 39ar dating abstract the back arc region of the izu bonin arc has complex bathymetric and structural features which due to repeated back arc rifting and resumption of arc volcanism have prevented us from understanding the volcano tectonic history of the arc after 15 ma the laser heating 40ar 39ar dating technique combined with high density sampling of volcanic rocks from the back arc region of this arc successfully revealed the detailed temporal variation of volcanism related to the back arc rifting based on the new 40ar 39ar dating results 1 back arc rifting initiated at around 2 8 ma in the middle part of the izu bonin arc 30 30 n 32 30 n volcanism at the earliest stage of rifting is characterized by the basaltic volcanism from north south trending fissures and or lines of vents 2 following this earliest stage of volcanism at ca 2 5 ma compositionally bimodal volcanism occurred and formed small cones in the wide area this volcanism and rifting continued until about 1 ma in the region west of the currently active rift zone 3 after 1 ma active volcanism ceased in the area west of the currently active rift zone and volcanism and rifting were confined to the currently active rift zone the volcano tectonic history of the back arc region of the izu bonin arc is an example of the earliest stage of back arc rifting in the oceanic island arc age data on volcanics clearly indicate that volcanism changed its mode of activity composition and locus along with a progress of rifting

age of seychelles india break up many continental flood basalt provinces are spatially and temporally linked with continental break up establishing the relative timing of the two events is a key step in determining their causal relationship here we investigate the example of the deccan traps and the separation of india and the seychelles whilst there has been a growing consensus as to the age of the main phase of the deccan emplacement 65 5 1 ma chron 29r the age of the rifting has remained unclear we resolve this issue through detailed seafloor magnetic anomaly modeling supported by wide angle and reflection seismic results of the north seychelles and conjugate laxmi ridge gop rift margins and geochemistry and 40ar 39ar geochronology of rocks from the north seychelles margin we show that syn rift volcanics offshore the seychelles islands in the form of seaward dipping reflectors were most likely erupted during chron 28n and the first organized seafloor spreading at the carlsberg ridge also initiated during this chron at 63 4 ma the severing of the seychelles occurred by a south eastward ridge propagation that was completed by the start of chron 27n 62 ma a brief pre 28r phase of seafloor spreading occurred in the gop rift possibly as early as 31r 32n 71 ma initial extension at the margin therefore preceded or was contemporaneous with the deccan emplacement and separation of the seychelles was achieved less than 3 5 ma afterwards this is the shortest time interval between flood basalt emplacement and break up yet reported for any continental flood basalt rifted margin pair a contributing factor to the apparently short interval in the deccan case may be that rifting occurred by a ridge jump into already thinned continental lithosphere however we conclude that external plate boundary forces rather than the impact of a mantle plume were largely responsible for the rifting of the seychelles from india

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

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts