structural and tectonic evolution of the eastern cayman trough caribbean sea from seismic reflection data the eastern cayman trough preserves a record of the late cretaceous to paleogene caribbean history that is largely affected by neogene strike slip tectonics of the current plate boundary we conducted an analysis of seismic data within the eastern cayman trough based upon single and multichannel seismic reflection profiles collected during the seacarib ii cruise in 1987 and the casis cruise in 1992 these data show that the basement of the eastern cayman trough can be divided into four domains from east to west with distinct morphologic and sedimentary character and inferred older to younger ages 1 a province of rifted mesozoic continental crust exhibiting seven parallel horst blocks striking northeast southwest 2 a continent ocean transition bet een provinces 1 and 3 that exhibits seamounts small hills and sedimentary basins 3 an eocene oceanic crust with rough basement but smoother relief than the rifted crust basement trends are roughly north south and oblique to the northwest trend in domain 1 and 4 the northern jamaica slope which forms an east west trending slope with northward dipping strata that flank the three deeper water domains of the cayman trough the domains are interpreted to be the product of the eocene east west opening of the cayman trough as a pull apart basin in a left lateral strike slip setting closure of the 1100 km of eocene and younger oceanic crust of the cayman trough places the fault block province adjacent to the belize margin of central america restoration of normal faults in the fault block province places an additional 190 km of left lateral offset along the cayman trough a neogene phase of transpression has reactivated structures in the four domains along with on land structures described by previous authors in jamaica the proximity of the eastern margin of the cayman trough to petroliferous continental rocks in central america suggests an improved possibility of hydrocarbon potential unfortunately s diment thicknesses of less than 1 km probably are not conducive to hydrocarbon formation

the fate and accumulation of bromide during playa salt deposition an example from lake frome south australia an advectivn diffusion model describing the distribution of br in porewaters underlying an accumulating deposit of halite on a playa lake can be used to predict the evolving composition of the accumulating salt growing as a result of evaporation the br cl ratio of the accumulating halite is proportional to the concentration or br at the surface of the brine body from which it is growing the evolution of interstitial br and therefore the composition of the accumulating salt is a function of 1 the diffusion coefficient of br in the brine saturated sediment 2 the advective velocity of the interstitial water 3 the initial concentration of br and cl at the onset of evaporation and 4 the distribution coefficient of br into the accumulating salt all of which can be estimated for the sediments and brines of lake frome south australia at lake frome the model is used to estimate mean evaporation rates for the salt covered surfaces which are found to be between 0 5 and 3 0 cm y these rates are lower than the rates estimated for the salt free surfaces of the lake by allison and barnes 1985 but are consistent with the expectation that groundwater input and therefore evaporation rates will be focused at the salt free lake margins rather than at the salt covered central regions of the playa and that the surface albedo of the salt covered zones will reduce energy penetration to the sediment and thus evaporation

an alternative interpretation of the cayman trough evolution from a reidentification of magnetic anomalies magnetic data were collected during the wilkes 1973 and seacarib ii 1987 cruises to the cayman trough a new interpretation of magnetic data is carried out an isochron pattern is drawn up from our anomaly identifications an early eocene age 49 ma ypresian for cayman trough opening is proposed instead of the late oligocene or middle eocene ages suggested by previous studies our plate tectonic reconstruction is simpler and fits the on land geology jamaica and cuba and the tectonics our reconstruction shows a southward propagation of the spreading centre between magnetic anomalies 8 and 6 26 and 20 ma the trough width increases by 30 km in this period the southward propagation of the cayman spreading centre from the middle oligocene to the early miocene induced the development of the restraining bend of the swan islands the formation of a 1 km high scarp on the eastern trace of the cayman trough transform fault walton fault and the formation of a pull apart basin hendrix pull apart magnetic anomalies and magnetization maps give information about the deformation and the rocks the proposed evolutionary model of the cayman trough from the inception of seafloor spreading to the present configuration is presented in relation to the tectonic escape of the northern boundary of the caribbean plate from the maastrichtian to the present

structural evolution of the la trocha fault zone oblique collision and strike slip basins in the cuban orogen 1 the la trocha fault zone acted as a major left lateral transfer zone and is bounded by the la trocha ltf zaza tuinicu ztf cristales ctf and taguasco tgf faults these faults were consistent with the clockwise rotation of convergence and shortening in central cuba from the paleocene to the early eocene 65 48 ma a ssw nne shortening produced transtension in the ltf and transpression in the ztf subsequently during the middle eocene 48 37 ma shortening shifted to a sw ne direction resulting in the normal component of the ltf and transpression in the ztf and ctf since the late eocene 37 ma central cuba has been welded to the north american plate the post welding deformation gave rise to transtension of the ltf and tgf this deformation is consistent with a wsw ene shortening and reflects activity in the transform boundary of the cayman trough both the normal and thrust displacements of these previous faults are corroborated by structural data whereas left lateral displacement is deduced from the concordance between oblique collision and structural features plate kinematics and the structural evolution of the la trocha fault zone indicate that the related central basin is a strike slip polygenetic basin and that the formation of this system i e fault zone strike slip basin was a consequence of the paleogene oblique collision between the caribbean volcanic arc and the bahamas borderland north american plate

origin of the penalver formation in northwestern cuba and its relation to k t boundary impact event abstract the uppermost maastrichtian penalver formation and its equivalents in northwestern cuba are characterized by thick normal graded calcarenite with distinct basal conglomerate and have been suspected as deposits related to the cretaceous tertiary boundary k t impact however its depositional mechanism is not well understood and clear evidence for its association with the impact has never been presented in this study detailed field survey and petrographic observations were carried out on the penalver formation in order to clarify its sedimentary processes and to test its relation to the k t impact the penalver formation at the type locality near havana is approximately 180 m thick and is subdivided into the basal lower middle upper and uppermost members based on its lithology the basal member consists of massive poorly sorted calcirudite with grain supported fabric which contains abundant macrofossils of shallow marine origin and occasional large intraclasts of the underlying strata suggesting that it was formed by a grain flow from a carbonate platform on the cretaceous cuban arc the lower to uppermost members consist of massive calcarenite and calcilutite that show upward fining composition of the calcarenite is distinctly different from that of the basal member the homogeneous appearance coarse tail normal grading abundant water escape structures and abundant reworked fossils in these members are consistent with those of the mediterranean homogenite a deep sea tsunami induced deposit that was formed by settling from a high density suspension repetition of thin conglomerate beds in the lower member that contain well sorted well rounded mud clasts and shallow marine fossils is considered to reflect intermittent lateral flow possibly induced by a series of tsunami waves during an early stage of settling of grains from a high density suspension altered vesicular glass of probable impact origin and shocked quartz are discovered in the basal and the lower to upper members respectively together with the biostratigraphically constrained age of the penalver formation this evidence suggests that the penalver formation has a genetic relation to the k t impact distribution of altered vesicular glass and shocked quartz grains can explain the sequence of the initial grain flow and the following tsunami waves

estimation of evaporation from the normally dry lake frome in south australia depth profiles of deuterium composition expressed as delta values have been used to make point estimates of evaporation from the floor of the normally dry lake frome a salt lake in northern south australia values from five sites varying between 90 and 230 mm yr 1 have been used to obtain a relatively crude approximation for mean evaporation rate from the lake of 170 mm yr 1 under the assumption that this represents discharge of water from the regional groundwater system the groundwater inflow into the lake is calculated as 5 108 m3 yr 1 two possible models which describe groundwater inflow into the lake are discussed

proximal cretaceous tertiary boundary impact deposits in the caribbean trace element isotopic and mineralogic studies indicate that the proposed impact at the cretaceous tertiary k t boundary occurred in an ocean basin although a minor component of continental material is required the size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact wave deposits suggest an impact between the americas coarse boundary sediments at sites 151 and 153 in the colombian basin and 5 to 450 meter thick boundary sediments in cuba may be deposits of a giant wave produced by a nearby oceanic impact on the southern peninsula of haiti a approximately 50 centimeter thick ejecta layer occurs at the k t boundary this ejecta layer is approximately 25 times as thick as that at any known k t site and suggests an impact site within approximately 1000 kilometers seismic reflection profiles suggest that a buried approximately 300 km diameter candidate structure occurs in the colombian basin

detrital zircon u pb age constraints on cretaceous sedimentary rocks of lingshan island and implications for tectonic evolution of eastern shandong north china abstract in order to clarify sedimentary environment and tectonic history of the sulu orogenic belt we date zircons from four sandstones and one interbedded rhyolite collected on lingshan island in east shandong north china u pb age distributions of detrital zircon populations from the newly named lingshandao formation resemble that of overlying fluvial sedimentary rocks age distributions exhibit four main populations of paleoproterozoic 2 5 2 3 ga mesoproterozoic 2 1 1 9 ga neoproterozoic 850 700 ma and early cretaceous 138 121 ma age accompanied by sporadic occurrences of archean paleozoic and early mesozoic aged grains data indicate a depositional age of 121 ma for the lingshandao formation which constrains the maximum depositional age of overlying fluvial sedimentary rocks the lingshandao formation thus more likely correlates to the uppermost laiyang group of the jiaolai basin proterozoic age populations indicate a mixture of material derived from the north china ncb and yangtze block yzb basement along with protolith material from the hp uhp metamorphic units of the sulu orogenic belt proterozoic age populations differ from those of the roughly coeval jiaolai basin which represents a terrestrial depositional environment to the north of the sulu terrane the yzb appears to be a significant source of detrital zircons consistent with field observations

evaporation rate from a salt pan estimates from chemical profiles in near surface groundwaters evaporation of water from saturated saline soils or sediments induces gradients of the solutes in the remaining interstitial solution these gradients lead to a systematic and predictable solute distribution in the soil solution which may be used in some cases to estimate the rate of evaporation simple one dimensional transport models for the distribution of cl and br indicate net evaporation rates from the salt covered surface of lake eyre south australia of between 0 9 and 2 8 cm yr 1 the former is a minimum estimate averaged over 20 yrs which includes the major 1974 filling event while the latter reflects the most recent summer evaporation period

evolution of middle america and the in situ caribbean plate model james k h 2009 evolution of middle america and the in situ caribbean plate model origin and evolution of the caribbean plate 328 127 138 james k h lorente m a pindell j l eds conference on geology of the area between north and south america with focus on the origin of the caribbean plate siguenza spain may 29 jun 02 2006

structure and tectonics of the upper cenozoic puerto rico virgin islands carbonate platform as determined from seismic reflection studies the puerto rico virgin islands carbonate platform was deposited over an area of 18 000 km2 from early oligocene to holocene on top of an inactive and subsiding cretaceous earliest oligocene island arc regional single channel and multichannel seismic reflection lines presented in this study provide the first information on the regional stratigraphy and structure of this platform that has previously been known mainly from onshore stratigraphic sections of a relatively small 2250 km2 portion of the platform exposed by late neogene tectonic uplift along the north coast of puerto rico seismic reflection lines are used to map the thickness of the carbonate platform strata and to correlate this thickness with onshore outcrop and well data from northern and southern puerto rico st croix u s virgin islands and the saba bank limestone thickness variations from a little over 2 km to almost zero are used to subdivide the puerto rico virgin islands platform into five distinct carbonate provinces 1 north puerto rico area including the onshore exposures 2 virgin islands area 3 st croix and saba bank area 4 south puerto rico area and 5 mona passage area carbonate thickness and structural information from each area are used to test five previously proposed models for the deformation and vertical movements of the platform the most prominent feature of the platform in the puerto rico virgin islands area is a large east west trending arch the northern limb of this arch exhibits a smoother more uniform dip than the steeper more abruptly faulted southern limb the core of the arch is responsible for the exposure of arc basement rocks on puerto rico the origin of this arch which occurs over a 300 km wide area is best explained by north south shortening and arching caused by interaction at depth of subducted slabs of the north america and caribbean plates other important evidence for this model can be found in the benioff zones observed in the earthquake profiles loading of the caribbean plate results in downward flexing of the north america plate and causes the 4 km subsidence of the carbonate platform north of puerto rico

zircon u pb geochronology and hf isotopes of major lithologies from the jiaodong terrane implications for the crustal evolution of the eastern block of the north china craton abstract as an important component of the western shandong complex in the eastern block of the north china craton the yishui terrane consists of neoarchean high grade supracrustal rocks granitoid gneisses and charnockites la icp ms zircon u pb dating and hf isotopic analyses on these lithologies have been carried out and the results provide new insights into the neoarchean crustal evolution of the eastern block of the north china craton new zircon dating results reveal that the magmatic precursors of the supracrustal metapelites and granitoid gneisses were generated at 2 54 2 53 ga and 2 57 2 55 ga respectively and the charnockites were emplaced contemporaneously around 2 56 2 53 ga single metamorphic zircon grains and overgrowth rims from these rocks document consistent metamorphic ages at 2 50 ga suggesting that the yishui terrane experienced a high grade metamorphic event at the end of the neoarchean detrital zircons from pelitic gneisses yield 207pb 206pb ages of 2 89 2 65 ga with a major age peak at 2 53 ga and a subordinate age peak at 2 70 ga implying that the sedimentary protoliths of the pelitic gneisses may have been sourced from 2 53 ga rocks in the yishui terrane and 2 70 ga rocks in the adjacent luxi granite greenstone terrane hf isotopic compositions show that the neoarchean magmatic zircons have positive ehf t values ranging from 1 4 to 7 8 and depleted mantle model ages of 2 92 2 60 ga with a prominent peak at 2 8 2 7 ga suggesting that the neoarchean crust was derived mainly from juvenile sources and partly from the recycling of old continental crust in the yishui area combined with previous data from the adjacent luxi granite greenstone terrane and other complexes in the eastern block it is concluded that the neoarchean was an important period of crust accretion in the eastern block of the north china craton

high precision 40ar 39ar age for the jehol biota abstract abundant fossils of the terrestrial jehol biota including plants insects dinosaurs birds mammals and freshwater invertebrates were discovered from the yixian formation and the overlying jiufotang formation in inner mongolia hebei province and liaoning province northeastern china because of the exceptional preservation of fossils the jehol biota is one of the most important mesozoic lagerstatten and is referred to as a mesozoic pompeii the jehol biota has provided a rare opportunity to address questions about the origin of birds the evolution of feathers and flight the early diversification of angiosperms and the timing of placental mammal radiation six tuff samples and two basalt samples collected from the tuchengzi the yixian and the jiufotang formations near the classic outcrops in western liaoning ne china yielded high precision 40 ar 39 ar ages we obtain an age of 129 7 0 5 ma for a basaltic lava from the bottom of the yixian formation and an age of 122 1 0 3 ma for a tuff from the lowermost part of the overlying jiufotang formation our age results provide an age calibration of the whole yixian formation and show that the whole formation was deposited entirely within early cretaceous time over an interval of 7 ma

lacustrine evidence of holocene environmental change from three faroese lakes a multiproxy xrf and stable isotope study the vegetation history of the faroe islands has been investigated in numerous studies all broadly showing that the early holocene vegetation of the islands largely consisted of fellfield with gravely and rocky soils formed under a continental climate which shifted to an oceanic climate around 10 000 cal yr bp when grasses sedges and finally shrubs began to dominant the islands here we present data from three lake sediment cores and show a much more detailed history from geochemical and isotope data these data show that the faroe islands were deglaciated by the end of younger dryas 11 700 10 300 cal yr bp at this time relatively high sedimentation rates with high 13c imply poor soil development 13c ti and data reveal a much more stable and warm mid holocene until 7410 cal yr bp characterised by increasing vegetation cover and build up of organic soils towards the holocene thermal maximum around 7400 cal yr bp the final meltdown of the laurentide ice sheet around 7000 cal yr bp appears to have impacted both ocean and atmospheric circulation towards colder conditions on the faroe islands this is inferred by enhanced weathering and increased deposition of surplus sulphur sea spray and erosion in the highland lakes from about 7400 cal yr bp from 4190 cal yr bp further cooling is believed to have occurred as a consequence for increased soil erosion due to freeze thaw sequences related to oceanic and atmospheric variability this cooling trend appears to have advanced further from 3000 cal yr bp a short period around 1800 cal yr bp appears as a short warm and wet phase in between a general cooling characterised by significant soil erosion lasting until 725 cal yr bp interestingly increased soil erosion seems to have begun at 1360 cal yr bp thus significantly before the arrival of the first settlers on the faroe island around 1150 cal yr bp although additional erosion took place around 1200 cal yr bp possibly as a consequence of human activities hence it appears that if humans caused a change in the faroe landscape in terms of erosion they in fact accelerated a process that had already started soil erosion was a dominant landscape factor during the little ice age but climate related triggers can hardly be distinguished from human activities

actively evolving microplate formation by oblique collision and sideways motion along strike slip faults an example from the northeastern caribbean plate margin abstract the pattern of folding faulting and late quaternary coral reef uplift rates in western and central hispaniola haiti and dominican republic suggest that the elongate gonave microplate a 190 000 km2 area of the northeastern caribbean plate is in the process of shearing off the caribbean plate and accreting to the north american plate late cenozoic transpression between the southeastern bahama platform and the caribbean plate in hispaniola has inhibited the eastward motion of the northeastern corner of the plate transpression is manifested in western and central hispaniola by the formation of regional scale folds that correspond to present day anticlinal topographic mountain chains continuous with offshore anticlinal ridges areas of most rapid quaternary uplift determined from onland coral reefs 125 ka and younger coincide with the axial traces of these folds offshore data suggest recent folding and faulting of the seafloor onshore reef data do not conclusively require late quaternary folding but demonstrate that tectonic uplift rates of the axial areas of the anticlines decrease from the northwest peninsula of haiti 0 37 mm yr to to the central part of the coast of western haiti 0 19 mm yr to the south central part of western haiti 0 mm yr formation of the 1200 km long enriquillo plantain garden walton fault zone as a bypass strike slip fault has isolated the southern edge of the gonave microplate and is allowing continued unimpeded eastward motion of a smaller caribbean plate past the zone of late neogene convergence and quaternary uplift of coral reefs in hispaniola offshore seismic reflection data from the jamaica passage the marine strait separating jamaica and haiti show that the enriquillo plantain garden fault zone forms a narrow but deep active fault bounded trough beneath the passage the active fault is continuous with active faults mapped onshore in western haiti and eastern jamaica the bathymetric deep is present because the jamaica passage fault segment represents a 50 km wide transtensional left step of the fault trace between haiti and jamaica onshore satellite imagery and field observations suggest that the enriquillo plantain garden fault forms a continuous trace extending from central hispaniola east of lake enriquillo dominican republic to the westernmost end of the southern peninsula of haiti the regional lineament corresponds to a recent fault scarp in quaternary alluvium of the clonard pull apart basin in the central part of the southern peninsula of haiti and suggests that at least this part of the lineament has undergone recent slip calmus 1983 has suggested a total offset of 30 50 km of the enriquillo plantain garden fault zone in the southern peninsula of haiti using the apparent offset of lithologic units seismic reflection data from lake enriquillo document recent deformation of quaternary lake sediments where the lineament crosses the lake leveling of the crest of a late holocene coral reef and associated algal tufa around lake enriquillo demonstrate late holocene vertical movement and tilting in a 1500 m wide zone parallel to the fault trend lateral offset is difficult to show in the enriquillo valley area because of rapid recent sedimentation into the valley the pattern of inactive strike slip faults and fold belts of cenozoic age in cuba and the yucatan basin suggest that two elongate microplates were sheared off the proto caribbean plate and accreted to the north american plate by a similar process in paleocene and eocene times age of terminal deformation in western central and eastern cuba is consistent with southeastward younging and migration of arc collision the similarity of the size and sequence of events in cuba suggests that the process of oblique collision and sideways motion of the plate along a new strike slip fault towards a free face may be an important process of microplate formation and interplate transfer in other areas

shrimp u pb dating of coesite bearing zircon from the ultrahigh pressure metamorphic rocks sulu terrane east china this paper provides further evidence for the ongoing discussion as to whether the dabie uhpm belt formed in triassic or palaeozoic time and whether the sulu uhpm belt formed in triassic or neoproterozoic time combined use of laser raman spectrometer lr cathodoluminescence imaging cl and ion probe u pb in situ dating shrimp provided accurate ages of uhpm from rocks collected from weihai ne sulu uhpm belt lr was used to identify coesite and other uhp minerals as inclusions in zircon separates from an amphibolized peridotite and an eclogite cl was used to examine the zoning structure of these zircon and shrimp dating was performed on specific spots on zircon to obtain ages of different geological events an age of 221 12 ma was obtained for coesite bearing zircon from the amphibolized peridotite an age of 228 29 ma for eclogite was obtained from the lower intercept of a concordia plot these ages are interpreted as the time of uhpm in the weihai region ultramafic rocks to the east of weihai yield a magmatic age at 581 44 ma the zircon in the ultramafic rocks possibly also records a thermal event at c 400 ma but no independent geological evidence for this event has been found the eclogite protolith formed in the middle proterozoic 1821 19 ma which is similar to the age of country rock gneisses of 1847 1744 ma the new geochronological data confirm that uhpm occurred in the triassic in the sulu area when subduction took the ultramafic body and the eclogite protolith together with the adjacent supracrustal rocks to mantle depths

geophysical profiling across the sulu ultra high pressure metamorphic belt eastern china abstract the largest ultra high pressure metamorphic uhpm belt in the world is located along the dabie sulu region which tectonically belongs to the east part of the central orogenic belt of china integrated geophysical investigations of using deep seismic reflection mt and geothermal observations have been carried out in the sulu area since 1997 the results of integrated interpretation suggest the existence of three features 1 a rift beneath the lianshui basin by the jiashan xionshui fault 2 a special crustal pattern called the magmatic multi arch structure occurs beneath the northern sulu uhpm zone and 3 a northwest dipping regional thrust crosses the sulu crust representing the intracontinental subduction of the yangtze craton beneath the sulu metamorphic belts after collision between the yangtze and sino korean cratons a magmatic multi arch structure consists of some arched reflectors that occur in both the lower and the upper crust where arched reflectors coincide with granitoid plutons the multi arch structures are common in eastern china where many mesozoic granitoid plutons of different scales occur the crustal structures in the sulu metamorphic belts resulted from intensive dynamic processes following the triassic collision between the yangtze and sino korean cratons the formation and exhumation of uhpm rocks followed the collision and then intracontinental subduction of the yangtze craton beneath the dabie sulu terranes took place in the early and middle jurassic in the late jurassic the sulu lithosphere turned to an extensional regime large scale granitic intrusions occurred in eastern china these likely resulted from lithospheric thinning and asthenospheric uplifting the granitic intrusions came to a climax during the cretaceous and were followed by rifting along existing faults in the early eogene resulting in many petroleum basins the granitoid emplacement that generated the magmatic multi arch structure and the rift were consequences of the lithospheric thinning process and deep intracontinental subduction of the yangtze craton beneath the sulu metamorphic belt might partially contribute to the lithospheric thinning

criteria for the recognition of salt pan evaporites layered evaporites can accumulate in 1 ephemeral saline pans 2 shallow perennial lagoons or lakes and 3 deep perennial basins criteria for recognizing evaporites deposited in these settings have yet to be explicitly formulated the characteristics of the ephemeral saline pan setting have been determined by examining eight holocene halite dominated pans salt pans and their deposits marine and non marine from the u s mexico egypt and bolivia these salt pans are typified by alternating periods of flooding resulting in a temporary brackish lake evaporative concentration when the lake becomes saline and desiccation which produces a dry pan fed only by groundwater the resulting deposits consist of alternating layers millimetres to decimetres of halite and mud the layers of halite are characterized by 1 vertical and horizontal cavities rounded crystal edges and horizontal truncation surfaces due to dissolution during flooding 2 vertical chevrons and cornets grown syntaxially on the bottom during the saline lake stage 3 halite cements overgrowths and euhedral cavity linings and disruption of layering into metre scale polygons produced during the desiccation stage the muddy interbeds are characterized by displacive growth of halite during the desiccation stage immediately below the surface of the pan the halite layers are matured by repeated episodes of dissolution and diagenetic crystal growth this results in porous crusts with patches of chevron and cornet crystals truncated by dissolution clear diagenetic halite cement and internal sediment these layers of mature halite closely resemble the patchy cloudy and clear textures of ancient halite deposits holocene salt pans are known to cover thousands of square kilometres and cap halite deposits hundreds of metres thick so they are realistic models for ancient evaporites in scale e g permian salado formation of new mexico texas which preserves many primary salt pan features

the thermal springs of aachen germany what charlemagne didn t know the aachen hot springs flow out from upper devonian limestones at the variscan thrust front of the rhenish massif hydrogeochemical analyses were used to determine the origin of the water and show that sodium chloride and sulfate originate from dissolving evaporites that are influenced by meteoric groundwater the circulation depths of the aachen thermal water is estimated to be 3500 m using sio2 geothermometry and the regional geothermal gradient of about 30 c km the deep circulation in paleozoic sandstones siltstones and shales and a considerable residence time allow rock water reactions which explain the concentrations of ba sr f and si while the thermal water rises into upper devonian limestones carbonates are dissolved cooler fresh water from the vicinity contributes to the thermal aquifer depending on the pressure head of the springs sulfate reduction coupled with methane oxidation can be observed as soon as the water temperature is below 65 c

collision between the north and south china blocks a crustal detachment model for suturing in the region east of the tanlu fault a crustal detachment model based on the interpretation of linear aeromagnetic anomalies surface geological observations and deep seismic profiles is proposed for the continent continent collision between the north and south china blocks east of the tanlu fault the model suggests that during the mid mesozoic collision between the two continental blocks the upper crust of the south china block in the subei yellow sea region was detached from the lower crust and thrust over the north china block for 400 km whereas the lower part of the lithosphere was subducted under the north china block along a subsurface suture running east from nanjing the sinistral offset of the qinling suture by the tanlu fault is only 110 120 km in the deep crust much less than previously suggested

petrochemistry and tectonic significance of cretaceous island arc rocks cordillera oriental dominican republic abstract cretaceous island arc rocks of the caribbean island arc system have been exposed by cenozoic faulting in the cordillera oriental in eastern hispaniola high k 2 o intermediate to felsic volcanic rocks loma la vega volcanics are interbedded with marine epiclastic sedimentary rocks and tuffs las guajabas tuffs and unconformably overlie pre aptian sedimentary rocks low k 2 o volcanic rocks guamira volcanics and a granodioritic to tonalitic intrusion el valle pluton the petrology and geochemistry of these units in conjunction with regional stratigraphic data are used to speculate on the tectonics of the newly developing caribbean island arc system during early and late cretaceous time the loma la vega volcanics are characterized by the presence of large phenocrysts of sanidine and minor amounts of clinopyroxene opaque oxides and rare leucite in a devitrified matrix of chlorite and clay although the volcanic rocks have undergone some low temperature alteration metamorphism which redistributed some major elements and large ion litho phile trace elements the high field strength elements rare earth elements and radiogenic isotopes appear to have been minimally affected based on abundances of the relatively immobile elements trace element enrichment patterns and isotopic compositions the loma la vega volcanics are considered part of the high k calc alkaline ca or shoshonitic island arc volcanic series in contrast pre aptian early cretaceous volcanic and plutonic rocks of the underlying los ranchos formation have chemical characteristics similar to rocks in the island arc tholeiitic or primitive island arc pia series that form coeval and along strike sections of the early cretaceous caribbean island arc in other parts of present day hispaniola cuba puerto rico and the virgin islands an abrupt and regional change in composition from island arc tholeiites to high k calc alkaline rocks is coincident with a hypothesized reversal in subduction polarity in pre aptian time as inferred from previously published tectonic models polarity reversal may have been triggered by attempted subduction of the caribbean oceanic plateau beneath this segment of the caribbean island arc the observed magmatic and tectonic effects of the proposed cretaceous caribbean arc reversal are similar to the better documented neogene subduction reversal event in the solomon islands arc in the southwest pacific

cenozoic tectonic history of the north america caribbean plate boundary zone in western cuba structural studies of well dated jurassic to lower miocene rocks in western cuba constrain the sequence of structural events affecting this oblique collisional zone between the late cretaceous island arc and the jurassic cretaceous north america passive margin in the southeastern gulf of mexico and straits of florida results of detailed mapping and collection of fault slip data at 34 sites define a regionally consistent five phase tectonic model for the period from the late paleocene to the post early miocene during the late paleocene to the early eocene the cuban island arc collided with the north american passive margin bahamas platform northwest ward overthrusting during the collision defines tectonic phase i a nne ssw compression concurrent with early eocene left lateral strike slip faulting along the pinar fault zone defines phase ii this result is consistent with structural mapping showing sinistral shear within the 065 striking pinar fault zone an ene wsw to e w compression defining phase iii overprinted phase ii faults in the lower eocene and older rocks post early miocene normal faulting characterizes phase iv inversion of fault slip data indicates two contemporaneous directions of tension of 120 and 170 strike slip faults that overprint phase iv normal faults yield a 120 compression phase v the direction of compression associated with the arc continent collision rotates clockwise from nw se in the late paleocene early eocene phase i to nne ssw phase ii and to ene wsw by the middle eocene phase iii the rotation in the compression direction occurred because the arc turned toward an oceanic area in the present day area of central and eastern cuba progressive collision led to complete subduction of the remnant oceanic crust by middle to late eocene time

sources of chloride and implications for 36cl dating of old groundwater southwestern great artesian basin australia we investigate the relative importance of a number of processes that affect cl and 36cl distribution in the southwestern flow systems of the great artesian basin australia to provide more precise estimates of age and flow and recharge rates in situ production of 36cl secular variations in the rate of production of 36cl and its subsequent fallout as well as rates of diffusion of stable cl from adjacent aquitards mask the interpretation of rates of decay of 36cl cl along hydraulic gradients and can preclude estimating absolute groundwater ages however mean flow velocities calculated from absolute cl concentrations are 0 24 0 03 m yr and are a more reliable parameter than calculated ages because fewer assumptions and approximations are required recharge rates to the main cadna owie formation and algebuckina sandstone aquifer of the great artesian basin estimated from cl mass balance in the unconfined aquifers are 0 16 0 08 mm yr and were probably up to a factor of 3 higher 30 kyr ago as indicated by decreasing cl and 18o concentrations along the head gradient

structural and tectonic evolution of western cuba fold and thrust belt 1 we present balanced and restored cross sections across the western cuba fold and thrust belt to illustrate its structure and tectonic evolution based on the interpretation of multichannel seismic profiles field data and balancing techniques the nnw sse trending soroa cross section intersects from south to north 1 the los palacios basin 2 the sierra del rosario antiformal stack 3 the bahia honda thrust unit 4 the frontal 3 km thick imbricated thrust sheets and 5 the foredeep basin at depth a duplex that links the sierra del rosario unit and the frontal imbricates is defined using the thickness of the cover thrust sheets of the imbricated north american margin the minimum calculated shortening is of 130 km in a sse or south direction to fit large scale plate tectonic reconstructions however a more allochthonous alternative using thinner cover sequences is also discussed which restores the bahia honda unit 220 km to the south of its present position syntectonic deposits in combination with a forward kinematic model provide a good constraint for the tectonic evolution of the orogen the internally deformed bahia honda unit overthrusted the north america margin cover successions during danian and selandian times 65 5 60 ma before the stacking of these cover rocks during selandian and thanetian times 60 56 ma the growth of a large antiformal stack beneath the sierra del rosario occurred at early middle eocene 56 45 ma generating about 4 km of structural relief between the paleoisland of cuba and the synorogenic seafloor before the final infill of the foredeep

oil and gas developments in south america central america caribbean area and mexico in 1982 petroleum developments in the region in 1982 had a more varied pattern than in 1981 when all aspects were upbeat with varying degrees of increases in 1982 brazil mexico and guatemala had striking increases in oil production bolivia chile and colombia had moderate increases and argentina trinidad and venezuela reported declines in exploration argentina reported several additional offshore tierra del fuego discoveries in the cretaceous springhill and 2 more encouraging gas discoveries in the noroeste basin bolivia reported an oil discovery from silurian rocks more generally considered a gas objective brazil extended and confirmed the western amazonas gas area with 2 discoveries colombia added 2 more spectacular oil discoveries in the llanos basin to follow up 2 similar finds in 1981 several countries reported that discoveries have increased the national reserves of hydrocarbons considering the social political and economic problems in several countries along with the worldwide depression and petroleum surplus developments in the region have been on the whole favorable

structure and tectonic evolution of the southwestern trinidad dome escambray complex central cuba insights into deformation in an accretionary wedge abstract the trinidad dome escambray complex cuba forms part of an accretionary wedge built during intra oceanic subduction in the caribbean from the late cretaceous to cenozoic the structure reflects syn subduction exhumation during thickening of the wedge followed by extension field mapping metamorphic and structural analysis constrain the tectonic evolution into five stages three ductile deformation events d1 d2 and d3 are related to metamorphism in a compressional setting and formation of several nappes d1 subduction fabrics are only preserved as relict s1 foliation and rootless isoclinal folds strongly overprinted by the main s2 foliation the s2 foliation is parallel to sheared serpentinised lenses that define tectonic contacts suggesting thrust stacks and underthrusting at mantle depths thrusting caused an inverted metamorphic structure with higher grade on top of lower grade nappes exhumation started during d2 when the units were incorporated into the growing accretionary wedge along nne directed thrust faults and was accompanied by substantial decompression and cooling folding and thrusting continued during d3 and marks the transition from ductile to brittle ductile conditions at shallower crustal levels the d4 5 events are related to extension and contributed to the final exhumation likely as a core complex d4 is associated with a regional spaced s4 cleavage late open folds and numerous extension veins whereas d5 is recorded by normal and strike slip faults affecting all nappes the p t path shows rapid exhumation during d2 and slower rates during d3 when the units were progressively incorporated into the accretionary prism the domal shape formed in response to tectonic denudation assisted by normal faulting and erosion at the surface during the final stages of structural development these results support tectonic models of sw subduction of the proto caribbean crust under the caribbean plate during the latest cretaceous and provide insights into the tectonic evolution of accretionary wedges in an intra arc setting

the belize margin revisited 2 origin of holocene antecedent topography the importance of antecedent topography in dictating holocene facies patterns has been generally recognized there is however disagreement as to origin or lithology of the antecedent topography particularly with respect to the siliciclastic or carbonate nature of the underlying topography and structural patterns to help resolve these problems published and unpublished information have been compiled to produce a structural fabric map of onshore and offshore belize that includes a new geologic map of the country the map along with illustrated seismic lines demonstrates the occurrence of a number of nne trending transpressional faults in which landward directed thrusting is consistently displayed along with tectonic inversion offshore wells in conjunction with the seismic lines document the inversion as post eocene suggesting a similar age for transpressional fault movement presumably the landward directed thrusting reflects the opposing force of eastward directed subduction along the western margin of central america relative to the westward seafloor spreading of the caribbean cayman ridge the belize faults show little current seismicity but nevertheless the resulting structures have affected quaternary carbonate deposition as evidenced on an illustrated seismic line by both seaward and landward bi directional progradation of the reef margin from an underlying structural high the structural influence on the development of holocene antecedent topography is further suggested by the occurrence of a bouguer gravity plateau in the same shelf area that marks the occurrence of the belize lagoon rhomboid shelf atolls the youngest documented lithology of 12 illustrated offshore exploration wells is miocene carbonate in some wells the carbonate is interpreted as extending into the pliocene and holocene although no age diagnostic criteria are in evidence in other wells siliciclastics of unknown age and thickness are identified as overlying neogene carbonates the regional distribution and age of onshore limestones suggests that unroofing of the cretaceous carbonate cap of the maya mountains siliciclastic sediment source did not occur until late in neogene time perhaps no earlier than late pliocene consequently the maya mountains could not have been a major offshore source of siliciclastics until the quaternary information on the lithology of the immediately underlying pre holocene is provided by limited penetration core data and shallow resolution seismic lines these show that antecedent pleistocene limestones beneath the holocene reefs were deposited around 130 000 b p isotope stage 5e the thickness of the overlying holocene shelf margin reef capped carbonates increases along depositional strike from a few meters in the north to more than 25 m in the south in contrast piston cores and seismic data from the southern shelf lagoon collectively document the occurrence of antecedent siliciclastic topography the southward dip of both carbonate and siliciclastic antecedent surfaces is presumably a reflection of increasing southerly subsidence increasing antecedent erosional relief in the same direction reflects the pronounced southerly increase in paleo rainfall that presumably paralleled that of present day rainfall

high temperature geochronology constraints on the tectonic history and architecture of the ultrahigh pressure dabie sulu orogen 1 new u pb zircon and th pb monazite ages are presented from the giant sulu ultrahigh pressure uhp terrane combined with sm nd ages rb sr ages inclusion relationships and geologic relationships they help define the timing of peak recrystallization the timing of subsequent amphibolite facies metamorphism and the architecture of the dabie sulu suture zone between the collided sino korean and yangtze cratons the data indicate a 15 myr record of uhp recrystallization the first clearly documented for a giant uhp terrane this requires that continental subduction in the dabie sulu orogen involved multiple uhp tectonic or recrystallization events a 244 236 ma precursor uhp event seen only in the dabie shan was followed by a second 230 220 ma main uhp event which was itself terminated by a 220 205 ma amphibolite facies overprint older eclogite facies events seen in the qinling segment of this orogenic belt raise the possibility that these rocks have undergone u hp metamorphism three or four times but at present there is no geochronological evidence in the dabie sulu area to support this the subduction of the lower yangtze plate did not proceed in a simple fashion the ages of inherited zircon cores demonstrate that a ribbon continent of yangtze affinity escaped subduction and became wedged against the sino korean plate hanging wall

cretaceous deformation history of the middle tan lu fault zone in shandong province eastern china abstract based on field analysis of fault slip data from different rock units of the cretaceous basins along the middle part of the tan lu fault zone shandong province eastern china we document polyphase tectonic stress fields and address the changes in sense of motion of the tan lu fault zone during the cretaceous the cretaceous deformation history of the tan lu fault zone can be divided into four main stages the first stage during the earliest cretaceous was dominated by n s extension responsible for the formation of the jiaolai basin we interpret this extension to be related to dextral strike slip pull apart opening guided by the tan lu fault zone the second stage during the middle early cretaceous was overwhelmingly rift dominated and characterized by widespread silicic to intermediate volcanism normal faulting and basin subsidence it was at this stage that the tan lu parallel yi shu rift was initiated by e w to wnw ese extension the tectonic regime then changed during the late early cretaceous to nw se oriented transpression causing inversion of the early cretaceous rift basin and sinistral slip along the tan lu fault zone during the late cretaceous dextral activation of the tan lu fault zone resulted in pull apart opening of the zhucheng basin which was subsequently deformed by ne sw compression this deformation chronology of the tan lu fault zone and the associated cretaceous basins allow us to constrain the regional kinematic models as related to subduction along the eastern margin of asia or related to collision in the tibet region

age and spreading history of the cayman trough as determined from depth heat flow and magnetic anomalies the opening of the cayman trough records aspects of relative motion between the north american and caribbean plates essential to accurate reconstruction of caribbean evolution assessment of opening rates based upon basement subsidence analysis as well as magnetic anomaly interpretation shows that the trough may have opened at one third to one half previously proposed rates depths to basement show that the crust has subsided away from the present axis in two stages a younger stage characterized by substantial and asymmetric greater to the east subsidence preceded by an older stage of slight increases of depth with distance depth to age relations calculated from subsidence curves which accommodate lateral as well as vertical cooling of the accreting slab indicate that the trough has opened at an overall rate of less than 15 mm yr since 25 30 ma and at 20 30 mm yr prior to 30 ma marine magnetic anomalies show lineations perpendicular to the trough including a distinct central anomaly but the pattern is neither well defined nor symmetrical about the present axis however partial anomaly sequences can be identified on both sides of the axis and the distribution of these sequences indicates that spreading may have involved frequent short ridge jumps mostly eastward the overall rate of opening as indicated by this interpretation of the magnetics is about 15 and 30 mm yr since and prior to 26 ma both subsidence and magnetics indicate that the trough opened by at least 45 50 ma

chlorine stable isotope studies of old groundwater southwestern great artesian basin australia abstract stable cl isotope ratios 37 cl 35 cl were measured in groundwater samples from the southwestern flow system of the great artesian basin australia to gain a better understanding of the cl sources and transport mechanisms 37 cl values range from 0 to 2 5 smoc and are inversely correlated with cl concentration along the inferred flow direction the cl isotopic compositions in conjunction with other geochemical parameters suggest that cl in groundwaters is not derived from salt dissolution mixing of the recharge water with saline groundwater cannot explain the relationship between 37 cl and cl concentration measured marine aerosols deposited via rainfall and subsequent evapotranspiration appear to be responsible for the cl concentrations observed in wells that are close to the recharge area and in groundwaters sampled along the southern transect 37 cl values measured in the leachate of the bulldog shale suggest that the aquitard is the subsurface source of cl for the majority of groundwater samples studied diffusion is likely the mechanism through which cl is transported from the pore water of the bulldog shale to the aquifer however a more detailed study of the aquitard rocks is required to verify this hypothesis

crustal velocity field of mexico from continuous gps measurements 1993 to june 2001 implications for the neotectonics of mexico 1 we combine velocities for 14 continuous gps stations spanning mexico and 173 additional continuous gps sites on the north american and pacific plates to study the large scale deformation of mexico the new station velocities which are derived from more than 6000 days of previously unused gps data provide the first ever view of the crustal velocity field of mexico key results are as follows 1 areas north of the mexican volcanic belt not including baja california move with the north american plate interior within the 1 2 mm yr 1 station velocity uncertainties station velocities for the mexican basin and range are consistent with no present day extension and yield an upper 95 limit of 1 3 mm yr 1 for any regional extension 2 south of the mexican volcanic belt five of the six sites move significantly relative to the north american plate all sites in the yucatan peninsula move toward the east at 3 4 mm yr 1 possibly defining an independent yucatan block 3 site velocities are consistent with limits of 0 4 mm yr 1 for present slip across the mexican volcanic belt 4 tampico on the gulf coast exhibits eastward motion consistent with gravity sliding known to occur in the adjacent mexican ridges fold belt 5 southeastward motion of la paz relative to the pacific plate is consistent with the hypothesis that the baja peninsula is not fully attached to the pacific plate 6 residual velocities for 160 north american plate gps stations outside of mexico exhibit no coherent regional patterns indicative of internal plate deformation

shrimp u pb dating trace elements and the lu hf isotope system of coesite bearing zircon from amphibolite in the sw sulu uhp terrane eastern china abstract in this study we link mineral inclusion data trace element analyses u pb age and hf isotope composition obtained from distinct zircon domains of complex zircon to unravel the origin and multi stage metamorphic evolution of amphibolites from the sulu ultrahigh pressure uhp terrane eastern china zircon grains separated from amphibolites from the ccsd mh drill hole g12 and niushan outcrop g13 were subdivided into two main types based on cathodoluminescence cl and laser raman spectroscopy big dusty zircons with inherited cores and uhp metamorphic rims and small clear zircons weakly zoned grey white luminescent inherited cores preserve mineral inclusions of cpx pl ap qtz indicative of a mafic igneous protolith dark grey luminescent overgrowth rims contain the coesite eclogite facies mineral inclusion assemblage coe grt omp phe ap and formed at t 732 839 c and p 3 0 4 0 gpa in contrast white luminescent small clear zircons preserve mineral inclusions formed during retrograde hp quartz eclogite to lp amphibolite facies metamorphism t 612 698 c and p 0 70 1 05 gpa inherited zircons from both samples yield shrimp 206 pb 238 u ages of 695 520 ma with an upper intercept age of 800 31 ma the uhp rims yield consistent triassic ages around 236 225 and 239 225 ma for g12 and g13 with weighted means of 229 3 and 231 3 ma respectively small clear zircons from both samples give 206 pb 238 u ages around 219 210 ma with a weighted mean of 214 3 ma interpreted as the age of retrograde quartz eclogite facies metamorphism matrix amphibole from both samples indicate ar ar ages of 209 0 7 and 207 0 7 ma respectively probably dating late amphibolite facies retrogression the data suggest subduction of neoproterozoic mafic igneous rocks to uhp conditions in middle triassic 230 ma times and subsequent exhumation to an early hp 214 ma and a late lp stage 208 ma over a period of 16 and 6 myr respectively thus early exhumation from a mantle depth of 120 100 km to about 60 km occurred at an average rate of 0 3 cm y while subsequent exhumation to a middle crustal level took place at approximately 0 54 cm y these exhumation rates are considerably slower than those obtained for uhp rocks in the dora maira and kokchetav massifs 2 3 cm y based on similar p t estimates and trace element and hf isotope compositions sulu amphibolites can be identified as retrograde uhp eclogites the ehf 800 of 8 implies a significant input from the depleted mantle to the sulu dabie terrane during the middle neoproterozoic overgrown rims are characterized by a distinct trace element composition with low lu hf and th u and significantly higher 176 hf 177 hf ratios than inherited cores consistent with formation during after garnet re crystallization and fractionation of the lu hf system during uhp metamorphism the combined dataset suggests homogenization of the 176 hf 177 hf ratio within the metamorphic mineral assemblage and during protolith formation observed variations are explained by mixing of material from both domains during laser ablation e g due to partial recrystallization of inherited cores

neoarchean to paleoproterozoic continental evolution and tectonic history of the north china craton a review rocks of archean age are widely distributed in the north china craton ncc and can be divided into high grade regions and granite greenstone belts even though most underwent amphibolite to granulite facies metamorphism quartzo feldspathic gneisses occupy 70 to 85 of the total exposure of archean rocks in the craton supracrustal rocks commonly consist of intercalated volcano sedimentary rocks including metabasites meta intermediate to acid rocks banded iron formations metapelites and minor marbles the oldest rocks outcrop over a small area of 4 km2 and are a quartzite amphibolite sequence that yield 3 8 3 5 ga isotopic ages chemical and geochronological data constrain the earliest main crust forming episode at ca 2 9 2 7 ga when most rocks were metamorphosed to upper amphibolite or granulite facies at moderate pressures mafic granulites can be classified into two textural types referred to as near isobaric cooling ibc and near isothermal decompression itd types high pressure granulites and retrograded eclogites occur mainly near the junction of the provinces of hebei shanxi and inner mongolia in the central ncc and in eastern shandong province of the eastern ncc as well as locally in henan province in the southern ncc these high pressure rocks show clockwise p t paths indicating decompression from 14 kb to 5 6 kb an exposed section interpreted as representing precambrian continental lower crust has also been identified in the northern part of the craton although some mafic ultramafic metamorphic rocks have been interpreted as remnants of ancient oceanic crust and mantle by a number of geologists geochemical and petrological evidence demonstrates that many supracrustal orthogneiss associations have island arc affinities therefore several tectonic models have been proposed including continent continent collision and island arc terrain accretion achieved by arc arc or arc microcontinent collision the ncc underwent multiple high grade metamorphic events of which the two most important took place during the intervals 2600 2450 ma and 1950 1750 ma which are considered to be related to early precambrian supercontinental cycles

pdf orientations in shocked quartz grains around the chicxulub crater we measured 852 sets of planar deformation features pdfs in shocked quartz grains in impactite samples of the yaxcopoil yax 1 core and from 4 cretaceous tertiary k t boundary deposits the monaca the cacarajcara and the pealver formations in cuba and dsdp site 536 within 800 km of the chicxulub crater in order to investigate variations of pdf orientations in the proximity of the crater orientations of pdfs show a broad distribution with peaks at 1013 1012 and 1112 plus r z 1011 orientations with minor c 0001 s 1121 t 2241 plus x 5161 and m 1010 plus a 11 20 orientations planar deformation features with c 0001 orientation are relatively more abundant in the proximity of the chicxulub crater than in distal sitessuch as north america the pacific ocean and europe this feature indicates that in the proximity ofthe crater part of the shocked quartz grains in the k t boundary deposits were derived from the lowshock pressure zones moreover the orientations of pdfs with 1122 plus r z 1011 are high in our studied sites and frequencies of these orientations decrease with increasing distance from the crater on the other hand absence of c 0001 and the rare occurrence of pdfs with 1122 plus r z 1011 orientations in the sample from the yax 1 core that was taken at the top of the impactite layer of the chicxulub crater suggests that the sampling horizon that reflects a certain cratering stage is also an important factor for variations in shocked quartz

yucatan karst features and the size of chicxulub crater summary the buried chicxulub impact structure is marked by a dramatic ring of sinkholes called cenotes if containing water and adjacent less prominent partial rings which have been shown to coincide with maxima in horizontal gravity gradients and a topographic depression these observations along with the discreteness and spacing of the features suggest a formation mechanism involving faulting in the outer slump zone of the crater which would thus have a diameter of approximately 180 km an opposing view based primarily on the interpretation of gravity data is that the crater is much larger than the cenote ring implies given the association of the known cenote ring with faults we here examine northern yucatan for similar rings in gravity surface features and elevation which we might expect to be associated with outer concentric faults in the case of a larger possibly multiring structure no such outer rings have been found although definite patterns are seen in the distribution of karst features outside the crater rim we explain these patterns as resulting mainly from deformation related to the block fault zone that parallels the shelf edge of eastern yucatan

extracting phreatic evaporation from remotely sensed maps of evapotranspiration 1 one of the most important parameters related to soil salinization is the direct evaporation from the groundwater phreatic evaporation if the groundwater table is sufficiently close to the surface groundwater will evaporate through capillary rise in recent years several methods have been suggested to map evapotranspiration et on the basis of remote sensing images these maps represent the sum of both transpiration of vegetation and evaporation from the bare soil however identifying the amount of phreatic evaporation is important as it is the dominant flux in the salt balance of the soil the interpretation of stable isotope profiles at nonirrigated areas in the unsaturated zone allows one to quantify phreatic evaporation independently of the transpiration of the vegetation such measurements were carried out at different locations with a different depth to groundwater the benefit is twofold 1 a relation between phreatic evaporation rates and the depth to groundwater can be established 2 by subtracting the measured values of phreatic evaporation from remotely sensed values of et vadose et consisting of transpiration and excess irrigation water in the unsaturated zone can be estimated at the sampling locations a correlation between the normalized differential vegetation index and the calculated vadose et rates could be established r2 0 89 with this correlation the contribution of phreatic evaporation can be estimated this approach has been tested for the yanqi basin located in western china finally the distribution of phreatic evaporation was compared to a soil salinity map of the project area on a qualitative basis

syn collisional transform faulting of the tan lu fault zone east china origin of the continental scale tan lu fault zone tlfz east china remains controversial about 550 km sinistral offset of the dabie orogenic belt dob and sulu orogenic belt sob is shown along the ne nne striking tlfz syn collisional sinistral ductile shear belts in the tlfz have been identified thirteen phengite bulk separates from the mylonites were dated by the 40ar 39ar method they gave cooling ages of the 198 181 ma for the shear belts along the eastern margin of the dob and 221 210 ma from the western margin of the sob distribution of the foreland basin deposits suggests that sinistral offset of the dob and sob by the tlfz took place prior to deposition of the upper triassic strata the marginal structures around the dob and sob support syn collisional faulting and indicate anticlockwise rotation of the dob during the displacement the folding and thrust faulting related to crustal subduction coeval with the tan lu faulting is older than the foreland basin deposition related to the orogenic exhumation several lines of evidence demonstrate that the tlfz was developed as a syn collisional transform fault during latest middle to earliest late triassic time when the dob and sob experienced crustal subduction of the south china block scb eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting

a model to estimate the depositional brine depths of ancient halite rocks implications for ancient subaqueous evaporite depositional environments a model is derived which allows a more general approach to the interpretation of bromine profiles in halite rocks than is possible with the models of kuhn or holser allowing for an open system with influx and reflux reduces the depth of brine necessary to generate a given salt deposit even very small and regular bromine gradients which historically have been interpreted as the result of deposition from deep brine bodies can be generated in an open system from brine no more than a few tens of metres deep the bromine gradient produced from a given depth of brine is strongly dependent on the composition and amount of influx but less so on the composition of brine already in the basin a zechstein profile is analysed which in a closed basin would require brine 2665 m deep it can equally be modelled by influx of normal seawater which fully replenishes a basin no more than 140 m deep a somewhat irregular profile from the paradox basin instead of requiring a basin 100 400 m deep can be modelled as being produced by deposition from brines only 10 m deep reflux in both cases can only be a few per cent of influx at a maximum

geology and timing of mineralization at the cangshang gold deposit north western jiaodong peninsula china the cangshang gold deposit of the north western jiaodong peninsula contains reserves of greater than 50 tonnes t and is developed by the largest open pit gold mine in china this deposit is a jiaojia style i e disseminated and veinlet deposit it is controlled by the san cang fault zone which trends 040 and dips 40 75 se at the mine site the main no 1 orebody lies between a hanging wall of precambrian metamorphic rocks mainly amphibolite of the fenzishan group and a footwall composed of the mesozoic linglong granitoid the ore zone is mainly composed of pyritized sericitized and silicified granitoid which has undergone variable degrees of cataclasis shrimp u pb dating of zircon indicates that the protolith of the hanging wall amphibolite was formed at 2530 17 ma and underwent metamorphism at 1852 37 ma the footwall granodiorite has been dated at 166 4 ma whereas zircons from the ore zone yield a younger age of 154 5 ma cathodoluminescence images of zircons from the granodiorite and ore zone show oscillatory zonation indicative of an igneous origin for both and the ages of these zircons therefore are all interpreted to be representative of magmatic crystallization dating of sericite by 40ar 39ar has been used to directly determine the timing of formation of the cangshang deposit providing the first time absolute age on formation of the jiaojia style gold deposits the well defined age of 121 3 0 2 ma provides the precise timing of gold mineralization at the cangshang deposit this age is consistent with those of linglong style vein type gold mineralization also from the north western jiaodong peninsula at between 126 and 120 ma therefore our work indicates that both styles of gold deposits in the jiaodong peninsula were formed during the same mineralization event

high arctic climate conditions for the last 7000 years inferred from multi proxy analysis of the bliss lake record north greenland the arctic is more vulnerable to climate change than are mid latitudes therefore palaeolimnological studies from the high arctic are important in providing insights into the dynamics of the climate system here we present a multi proxy study from one of the world s northernmost lakes bliss lake peary land greenland the early holocene 10 850 10 480 cal a bp is characterized by increased erosion and gradually more marine conditions full marine conditions developed from 10 480 cal a bp until the lake was isolated at 7220 cal a bp from its marine isolation at 7220 cal a bp bliss lake becomes a lacustrine environment evidence from geochemical proxies delta c 13 and total organic carbon suggests that warmer conditions prevailed between 7220 and 6500 cal a bp corresponding to the holocene thermal maximum and from 3300 until 910 cal a bp from 850 to 500 cal a bp colder climate conditions persisted the transition from warmer to colder climate conditions taking place around 850 cal a bp may be associated with the transition from the medieval warm period to the little ice age copyright c 2011 john wiley sons ltd

diachronous uplift and recycling of sedimentary basins during cenozoic tectonic transpression northeastern caribbean plate margin abstract four marine sedimentary sequences of late cretaceous to pleistocene age crop out in the 320 km long 1 to 30 km wide peralta rio ocoa belt of hispaniola haiti and dominican republic the four sedimentary sequences are dominated by marine turbiditic rocks ranging up to 11 5 km in apparent thickness and exhibit mainly northwest to southeast belt parallel paleocurrents the three younger sequences are generally in fault or unconformable contact with the underlying sequence from northwest to southeast the four belts become progressively wider younger less metamorphosed less folded and faulted and lower in topographic elevation we interpret the three younger sequences as a syn tectonic stratigraphic record of diachronous northwest to southeast transpressional closure of a coniacian danian back arc basin represented by the oldest exposed sedimentary sequence at the northwest end of the belt and inferred at depth beneath the three younger sequences using the stratigraphic record we infer the following three stages in the closure of the back arc basin and the overlying younger basins stage one latest cretaceous to early late eocene closure a minimum of 11 km of paleocene turbidites and limestone in the padre las casas area and a minimum of 11 5 km of early eocene to early late eocene pelagic limestone mudstone sandstone and siltstone in the peralta and sierra el numero areas was deposited in an elongate basin derived from the first stage of latest cretaceous early late eocene closure and erosion of the coniacian danian back arc basin to the northwest paleocene eocene turbidites in both areas contain large amounts of reworked campanian paleocene microfauna and exhibit northwest to southeast belt parallel paleocurrents syn deformational features in eocene sedimentary rocks in the peralta and sierra el numero area indicate that convergent deformation accompanied sedimentation witschard and dolan 1990 stage two middle eocene to early miocene closure up to 8 6 km of middle eocene to early miocene turbidites debris flows and olistostromes of the rio ocoa group of the dominican republic were deposited in an elongate basin derived from middle eocene to early miocene closure uplift and erosion of the peralta group to the west and northwest turbidites contain reworked eocene faunas and lithologies similar to those in the underlying peralta group and exhibit northwest to southeast belt parallel paleocurrents erosion of late cretaceous island arc and overlying paleogene carbonate rocks of the cordillera central provided additional belt perpendicular sources of coarser grained conglomerate and olistostromes following deposition of the rio ocoa group both the peralta and the rio ocoa group were deformed in a southwest verging fold and thrust belt during the early miocene stage three middle miocene to recent closure up to 1 5 km of middle miocene to pleistocene sandstone conglomerate and reefal limestone of the ingenio caei group of the dominican republic were deposited in an elongate basin above a pronounced angular unconformity developed on the older deformed rocks of the rio ocoa group sediments of the ingenio caei group were derived from middle miocene to recent closure uplift and erosion of the rio ocoa and peralta groups to the northwest onshore exposures of the ingenio caei group can be correlated with submerged strata seen on seismic reflection profiles across the offshore san pedro basin recent submarine clastic sedimentation in the san pedro basin is dominated by northwest to southeast influx of clastic turbidites derived from active erosion of onshore exposures of the rio ocoa and ingenio caei groups middle miocene to recent sediments of the san pedro basin are being actively shortened by northward to northeastward directed underthrusting along the muertos trench underthrusting at the muertos trench is suggested to represent ongoing closure of the back arc basin thought to be deeply buried beneath the san pedro basin tectonic transpression along the closing back arc basin marks one edge of an actively deforming microplate within the north america caribbean strike slip plate boundary zone

a plate tectonic model for the mesozoic and early cenozoic history of the caribbean plate abstract we present a model in which the caribbean plate is an intra american feature formed along the caribbean spreading center as opposed to the current model that considers the caribbean plate as a far travelled crustal segment that formed in the pacific region paleomagnetic data which cover an age range from jurassic through paleocene indicate the ophiolite complexes in costa rica and panama formed in an equatorial position the ophiolites did not fundamentally change their position relative to south america since their origin basaltic rocks of the lower part of the ophiolites are of mid ocean ridge type suggesting formation at a spreading center they are interpreted to have formed as part of the proto caribbean crust at a spreading axis in an intra american position during jurassic and early cretaceous times the upper part of the ophiolites is mainly built up by island arc and intraplate basalts the island arc basalts evolved at the central american landbridge which started in the middle cretaceous the intraplate basalts are related to the caribbean plateau basalt which thickened and stiffened the caribbean crust in middle cretaceous to probably campanian times changes in relative plate motions along the middle american convergent plate margin are reflected by orientations and time sequences of paleostress tensors calculated from fault slip data in southern mexico and costa rica kinematic indicators from mylonite zones display sinistral movement along secondary shear zones within the southern mexican crustal complexes and along the northern boundary of the chortis block in the motagua polochic fault system this reflects the eastward drift of the chortis block since the beginning of the cenozoic at this time the chortis block became part of the caribbean plate which moved more than 1000 km towards the east relative to the north and south american plates during the cenozoic

gravity anomaly map of north america the gravity anomaly map of north america is the product of a 12 year international effort to compile critically edit and merge gravity anomaly data on a continental and global scale this color pixel map printed on four quadrant sheets at a scale of 1 5 000 000 and including a fifth sheet showing a color index map with data references is the first such map at this large scale to include several hundreds of thousands of precise surface data of the united states canada mexico and central america as well as other high quality surface data from neighboring continental and oceanic areas the map which shows bouguer gravity anomalies on land and free air gravity anomalies over oceans is remarkable for its detail sixty six colors or shadings have been used in a carefully conceived nonlinear scheme to show anomalies at a 5 or 10 mgal interval over a dynamic range from about 300 mgal to 130 mgal

role of partial melting in the evolution of the sulu eastern china ultrahigh pressure terrane strongly deformed potassium feldspar rich dikes are widely distributed in the northern part of the sulu ultrahigh pressure uhp metamorphic terrane eastern china the fact that the crystallization ages of these dikes overlap with the age of peak uhp metamorphic conditions implies the presence of melt during metamorphism sr isotopic ratios of the dikes are compatible with their origin as partial melts of the dominant felsic sulu gneiss partial melting may be the key to solving several unusual features of the sulu and other uhp terranes such as the almost complete lack of mineralogical evidence for uhp conditions and the limited growth of zircon during uhp conditions in the dominant felsic gneiss in addition because partial melting will cause a drastic reduction in the strength of the uhp gneisses the most likely exhumation mechanism is diapiric rise of a low viscosity partially molten mass containing entrained blocks of eclogite and not a thin sheet as usually proposed

structural and geochronological evidence for early cretaceous orogen parallel extension of the ductile lithosphere in the northern dabie orogenic belt east china abstract the wnw trending north dabie dome ndd in the northern dabie orogenic belt is bounded by the xiaotian mozitan ductile shear zone xmsz in the north and the wuhe shuihou shear zone wssz in the south fabric geometries and kinematics of both the xmsz and the wssz are similar they both show a top to nw or wnw sense of shear and display similar microstructures which indicate that the deformation temperature was about 600 650 c 40 ar 39 ar dating of hornblende and biotite from the mylonites of the xmsz suggests that the shear zone was developed prior to 142 ma u pb zircon la icpms dating of undeformed granite dikes that cut the xmsz suggests that the ductile shearing occurred before 130 ma the wssz was also developed in the early cretaceous the interior of the ndd is dominated by top to nw or wnw sense of shear in the migmatitic gneiss and deformed plutons of the earliest early cretaceous ages we suggest that the xmsz the wssz and the interior of the ndd were involved in the same early cretaceous deformation the xmsz and the wssz were originally a single connected more flat lying zone which we call the east dabie detachment zone eddz it developed at a crustal level of over 18 km in depth kinematics of the eddz suggest that the ductile crust and possibly part of the lithospheric mantle in the eastern dabie orogen underwent pervasive orogen parallel and ese ward extension at the beginning of the early cretaceous large scale magmatic intrusions following this deformation and the resultant increase in buoyancy led to the exhumation of the ndd and the warping of the eddz erosion separated the eddz into two zones the xmsz and the wssz as observed today many metamorphic core complexes of early cretaceous were developed in the eastern north china craton most showing top to nw or wnw sense of shear we suggest that such a widespread uniform shear sense reflects a uniform flow direction of the ductile lithosphere in the east china that has also been documented in the liaonan yiwulushan and yumenshan metamorphic core complexes in the northeastern part of the north china craton

western caribbean intraplate deformation defining a continuous and active microplate boundary along the san andres rift and hess escarpment fault zone colombian caribbean sea the san andres rift sar located on the lower nicaraguan rise is a previously poorly studied active 015 trending bathymetric and structural rift basin that is 11 27 km 7 17 mi wide and extends for 346 km 215 mi across the western flank of the caribbean plate in this study we integrate bathymetric maps potential field data and high resolution two dimensional 2 d seismic lines to understand the crustal structure tectonic history and tectonic origin of the sar which is one of the active areas within the otherwise stable caribbean plate we compiled regional gravity and magnetic data that revealed a negative gravity anomaly and positive magnetic anomaly that we interpret as a result of crustal thinning and an elevated moho along the main rift axis of the sar forward models of gravity data show four possible interpretations for the origin of the crust underlying and surrounding the sar interpretations of 2 d seismic reflection data show structural features within the upper crust and sedimentary sections typical of other active rift systems including a sar parallel north south alignment of earthquakes with the larger events showing normal and strike slip focal mechanisms sequential kinematic restorations based on 2 d seismic profiles reveal three major phases of sar opening 1 the initial early eocene rifting stage 2 middle eocene extension and 3 a rapid middle miocene to early pliocene extension accompanied by emergence of the san andres island as a rift shoulder we propose slab rollback and intraplate extension as main tectonic mechanisms to explain all rift phases and neogene volcanism found in the western caribbean region

kinematic reconstruction of the caribbean region since the early jurassic abstract the caribbean oceanic crust was formed west of the north and south american continents probably from late jurassic through early cretaceous time its subsequent evolution has resulted from a complex tectonic history governed by the interplay of the north american south american and paleo pacific plates during its entire tectonic evolution the caribbean plate was largely surrounded by subduction and transform boundaries and the oceanic crust has been overlain by the caribbean large igneous province clip since 90 ma the consequent absence of passive margins and measurable marine magnetic anomalies hampers a quantitative integration into the global circuit of plate motions here we present an updated quantitatively described kinematic reconstruction of the caribbean region back to 200 ma integrated into the global plate circuit and implemented with gplates free software our reconstruction includes description of the tectonic units in terms of euler poles and finite rotation angles our analysis of caribbean tectonic evolution incorporates an extensive literature review to constrain the caribbean plate motion between the american continents we use a novel approach that takes structural geological observations rather than marine magnetic anomalies as prime input and uses regionally extensive metamorphic and magmatic phenomena such as the great arc of the caribbean the clip and the caribbean high pressure belt as correlation markers the resulting model restores the caribbean plate back along the cayman trough and major strike slip faults in guatemala offshore nicaragua offshore belize and along the northern andes towards its position of origin west of the north and south american continents in early cretaceous time we provide the paleomagnetic reference frame for the caribbean region by rotating the global apparent polar wander path into coordinates of the caribbean plate interior cuba and the chortis block we conclude that formation of the caribbean plate west of the north and south americas as a result of panthalassa pacific spreading leads to a much simpler plate kinematic scenario than proto caribbean atlantic spreading placing our reconstruction in the most recent mantle reference frames shows that the clip originated 2000 3000 km east of the modern galapagos hotspot and may not have been derived from the corresponding mantle plume finally our reconstruction suggests that most if not all modern subduction zones surrounding the caribbean plate initiated at transform faults two of these along the southern mexican and nw south american margins evolved diachronously as a result of migrating trench trench transform triple junctions

plate boundary readjustment in oblique convergence example of the neogene of hispaniola greater antilles the haitian fold and thrust belt is the major mountain belt of haiti western part of hispaniola greater antilles and resembles a compressive restraining bend between the two major faults which have driven the opening of the cayman basin since the eocene during the rifting stage from the middle to the late eocene this area underwent an extensional evolution with fissural volcanic activity along ne sw tilted blocks the haitian fold and thrust belt was constructed from the early miocene until the present by stacking sedimentary units into a collisional wedge perpendicular to the tilted blocks which was propagating to the southwest during the construction of the wedge piggyback basins were formed and progressively uplifted during the late neogene convergence is localized in the cul de sac enriquillo trough where the active front proceeds southward onto the beata ridge in this area miocene to quaternary wrench structures of the lower plate like the southern peninsula and the enriquillo plantain garden faults are reactivated as normal faults owing to the loading of the fold and thrust belt

environmental character and history of the lake eyre basin one seventh of the australian continent abstract one of the world s largest internally drained endorheic basins the 1 14 million km 2 lake eyre hydrological basin leb covers nearly 15 of the australian continent palaeoclimatic and associated flow regime variations are recorded in an archive of fluvial aeolian and lacustrine sediments that are particularly accessible for deposits from the past 300 ka and are especially relevant for the past 50 ka during which humans have inhabited australia due to its great size economic resources and diverse latitudinal extent it has for over six decades been the focus of environmental scientific and resource based studies across numerous disciplines with an emphasis on assessing the scientific and environmental research over this period this paper is divided into four parts part a provides an introduction and background part b provides the geological history including evidence of substantial tertiary and quaternary climate change part c covers the contemporary environmental conditions and part d presents a conclusion and summary this not only represents the first comprehensive review of current knowledge of any of the world s truly large dryland drainage basins but also highlights how more multi disciplinary research is required key remaining questions revolve around the impact of global weather systems on the leb the lake level story in relation to a more precise picture of late quaternary climate change the role of humans and climate in the demise of the megafauna modern hydrological changes the role of vegetation in altering channel morphology and flow efficiencies and nature of flood transmissions

shrimp u pb zircon dating of the wulian complex defining the boundary between the north and south china cratons in the sulu orogenic belt china abstract neoproterozoic metasedimentary and metavolcanic rocks of the wulian group are associated with gneissic granitoids at the northern margin of the sulu uhp belt adjacent to the wulian yantai fault and are collectively referred to as the wulian complex shrimp u pb dating of detrital zircon from the metasedimentary rocks of the wulian group indicates a range in age from 3478 to 625 ma based on zircons 3000 ma with the oldest age being 3339 ma 2700 2400 ma with a peak at 2436 ma 2200 1800 ma with a peak at 2156 ma and at 770 ma these results indicate that deposition of the wulian group was after 770 ma and that some detrital material most likely came from neoproterozoic sources in the south china craton scc shrimp u pb zircon dating of a metavolcanic rock defines a weighted mean 206 pb 238 u age of 761 8 ma which is consistent with other rocks of south china affinity and can be correlated with syn rift magmatism during the breakup of the supercontinent rodinia the wulian group together with neoproterozoic granites of the wulian complex constrains the location of the triassic suture zone between the north china and south china cratons based on our new data the suture must lie north of the wulian complex and is marked by the baichihe yantai fault

timing of the jiufotang formation jehol group in liaoning northeastern china and its implications the timing of the jiufotang formation remains speculative despite recent progress in the study of the jehol biota in this paper we contribute to this topic with ar 40 ar 39 dating on k feldspar sanidine and orthoclase from tuffs interbedded within the fossil bearing shales of the jiufotang formation from the upper part of the jehol group in chaoyang liaoning northeastern china ar 40 39 ar step heating analyses of k feldspar and the shrimp u pb zircon data indicate that tuffs at the shangheshou section erupted at 120 3 0 7 million years ago this result confirms an aptian age for the jiufotang formation that was mainly based on biostratigraphic evidence it also places stringent controls on the age of the fossils from the formation providing a minimum age 120 ma for the four winged dinosaur microraptor and the seed eating bird jeholornis

structure and tectonics of the yucatan basin caribbean sea as determined from seismic reflection studies the yucatan basin preserves a record of the late cretaceous to paleogene caribbean north american convergent history that is largely unaffected by neogene strike slip tectonics of the current plate boundary an examination of seismic basement within the yucatan basin based upon available seismic reflection data including extensive multichannel data shows that the basement comprises nine domains distinguished on the basis of internal reflection character and surface topography these domains encompass three distinct crustal types or blocks the first underlies the western flank of the basin and represents the offshore continuation of the adjacent yucatan platform the second includes the topographically heterogeneous domains of the eastern two thirds of the basin and is dominated by a subsided volcanic rise or arc cayman rise resting upon probable oceanic crust of pre tertiary age the eastern edge of the rise and adjacent basins dips northeast beneath the cuban margin along a sediment filled trench the third type of crust occupies a rectangular deep within the western third of the basin available evidence indicates that this crust is oceanic in character and represents a large mature pull apart basin set within a wide paleo transform zone between the western platform and eastern oceanic basin this zone defines the northwestern portion of the caribbean north american convergent plate boundary paleocene to middle eocene transform motion was left lateral along north south to nne ssw trends with a displacement of about 350 km a long middle eocene transcurrent fault of about 50 km left lateral displacement cuts the basin diagonally from sw to ne and continues onland in cuba as la trocha fault this reconstruction is consistent with known eocene regional tectonics but the timing of regional events raises questions about present interpretations of plate geometry in the northwestern caribbean

bromine geochemistry of salar de uyuni and deeper salt crusts central altiplano bolivia abstract the salar of uyuni in the central bolivian altiplano is probably the largest salt pan in the world 10 000 km 2 a 121 m deep well drilled in the central salar disclosed a complex evaporitic sequence of 12 salt crusts separated by 11 mud layers in the lower half of the profile thick halite beds alternate with thin mud layers the mud layers thicken upwards and show clear lacustrine features the thickness of the salt beds decreases markedly from the base upward the bromine content of the halite ranges from 1 3 to 10 4 mg kg the halite does not originate from the evaporation of the dilute inflow waters of the altiplano which would lead to br content of tens of mg kg the presence of halite of very low br content 2 mg kg in a gypsum diapir strongly suggests that most of the halite deposited at uyuni originated from the leaching of ancient salt formations associated with the numerous gypsum diapirs of the altiplano the deep and thick halite beds were probably deposited in a playa lake as suggested by their very low and fairly constant br content 1 6 2 3 mg kg and by the abundance of detrital minerals thereafter perennial salt lakes of increasing duration flooded the central altiplano increasing amounts of dilute inflow waters of low cl br ratio and the exhaustion of diapiric halite lead to an increase of both the thickness of the lacustrine layers and of the bromine content of the salt crusts 5 10 mg kg deposited as the lakes dried up paleolake levels in the central altiplano rose as those in the northern altiplano the titicaca basin were simultaneously falling the progressive fluvial erosion of the threshold between the northern and the central altiplano lowered the levels of the northern lakes and allowed more dilute waters of low cl br ratio to flood the central altiplano therefore both the thickness of lacustrine sediments and the bromine content of the salt crust increased to the present the three upper crusts show a decrease in bromine content which may reflect a recent modification of the inflow regime to the last lakes the salt crust deposited by the last salt lake 10 000 years ago shows a bromine distribution that unexpectedly increases with depth as the lake dried the salt crust was probably initialy distributed over a wider area than the present flat crust covering the topographic surface up to the level of the lake where halite reached saturation the dissolution of the initial salt of low br content from the margins of the lake to the center is probably responsible for the observed br distribution in the surface salt as in a playa during the holocene a severe drought hit the altiplano and drastically lowered the intracrustal brine table within the salt crust leaving a thin layer of high concentrated residual brine at the bottom of the crust bromine rich halite replaced primary halite by a temperature activated mechanism in the lower crust further increasing the br gradient with depth

exhumation tectonics of the ultrahigh pressure metamorphic rocks in the qinling orogen in east china new petrological structural radiometric insights from the shandong peninsula 1 in eastern china the sulu area is recognized as the eastern extension of the qinling dabie belt which is famous for its ultrahigh pressure uhp metamorphism although numerous petrologic and geochemical works are available structural data are still rare this paper provides the first extensive study of bulk geometry and kinematic analysis of the shandong peninsula the study area is divided into three tectonic areas by cretaceous faults namely a southern uhp belt or sulu area a northern migmatite area and an eastern eclogite and migmatite area or weihai area conversely to the deeply entrenched idea that the later area belongs to the north china belt and the two others to the south china block scb we argue that all three areas are parts of the scb structural petrologic 40ar 39ar and u pb data comply with this new interpretation in the north shandong area mafic granulites enclosed as blocks within gneissic migmatites do not significantly differ from the sulu and weihai eclogites which also experienced a granulite facies overprint before migmatization the circa 210 200 ma age of the main ductile deformation is related to an extensional event during the triassic or indosinian orogeny this date corresponds to the temperature climax but the time of the pressure peak i e the real age of the uhp metamorphism is discussed

hydrological and geochemical processes controlling variations in na mg2 cl so42 groundwater brines south eastern australia abstract evaporative discharge of regional groundwater from more than 50 playa lakes at the 400 km 2 raak plain groundwater discharge complex forms a very large reservoir of hypersaline na mg 2 cl so 4 2 type subsurface brine but very little salt precipitates the main processes controlling the formation and evolution of brine compositions are a evapo concentration of the regional groundwater b mixing between the high and low tds end members and c subsurface gypsum precipitation uniformity in these processes across the entire groundwater discharge complex coupled with the chemical similarity between the regional groundwater and local recharge sources has led to remarkably similar brine chemistries and evaporite compositions across raak plain the similarity between the source waters and the ultimate brine compositions indicates that solutes are generally conserved within the system the greatest variation in groundwater chemistry at raak plain was found to occur within the playa lakes particularly within the top 1 2 m of the subsurface brine body rather than amongst the different lakes this small scale variability is a result of 1 advective and diffusive mixing between the hypersaline shallow 20 kyr