tertiary flexural evolution of the beaufort mackenzie basin canada abstract seismic reflection data indicate that more than 14 16 km of clastic materials are preserved in the beaufort mackenzie basin these correspond to tectonic activity and sediment loading from the upper cretaceous to the present day to understand better how the basement movement responds to the thick sediment loading an inverse flexural model has been used to simulate the evolutionary process the results of the inverse flexural model simulation show that the basin subsidence developed dominantly as an elastic flexural response to sediment loading with a minor component due to lateral compressive stress the forward model results show that the late eocene to pleistocene subsidence of the basin included three stages with different rates of subsidence the koponoar kugmallit and iperk sequences represent products of two rapid subsidence stages whereas the mackenzie bay and akpak sequences reflect the products of a more stable and slower subsidence stage

chemical and isotopical characterisation of fluid manifestations of ischia island italy abstract between 1994 and 1995 gas samples from fumaroles and thermal waters were collected on ischia island the chemical composition of the shallow and deep natural hydrothermal fluids discharged is related to the main hydrological and lithological characteristics of the rock formations present in the reservoir a biphase reservoir liquid gas is identified where the dominant liquid has a temperature of about 280 c on the basis of 13ctdc values it was possible to hypothesize a deep source characterised by carbon isotopic values varying from 0 to 3 these values are noticeably more positive with respect to those attributed to magmatic co2 13 c co 2 ranging from 5 to 8 thus suggesting a magmatic source modified by crustal contamination this hypothesis is supported by the carbon isotopic composition of co2 in sampled gases which varied from 0 to 5 the inferred isotopic value of carbon of magmatic co2 would then be about 2 the observed differences in c isotopic composition between fumarolic and magmatic gases would be caused by kinetic and or equilibrium fractionation processes these processes would cause a fractionation of 13c of deep co2 towards more negative values down to 5 actually co2 removal or addition processes caused by the interaction between deep gases and shallow hydrothermal waters are likely to be responsible for the different chemical and isotopic compositions of gaseous emissions for these reasons and on the basis of the homogeneity of geothermometric values the existence of a single large reservoir that feeds all of the fluids discharged at ischia island can be hypothesised based on acquired data a new geochemical model of the geothermal system of ischia island is proposed

application of stochastic simulation to co2 flux from soil mapping and quantification of gas release 1 conditional sequential gaussian simulations sgs have been applied for the first time to the study of soil diffuse degassing from different volcanic and nonvolcanic systems the application regards five data sets of soil co2 fluxes measured with the accumulation chamber methodology at the volcanic areas of solfatara of pozzuoli italy vesuvio cone italy nisyros greece and horseshoe lake california and at the nonvolcanic degassing area of poggio dell olivo italy the sgs algorithm was used to generate 100 realizations of co2 flux for each area probabilistic summaries of these simulations together with the information given by probability plots were used 1 to draw maps of the probability that co2 fluxes exceed thresholds specific for a background flux i e to define the probable extension of the degassing structures 2 to calculate the total co2 output and 3 to quantify the uncertainty of the estimation the results show that the sgs is a suitable tool to model soil diffuse degassing producing realistic images of the distribution of the co2 fluxes that honor the histogram and variogram of the original data moreover the relation between the sample design and the uncertainty of estimation was investigated leading to an empirical relation between uncertainty and the sampling density that can be useful for the planning of future co2 flux surveys

cenozoic deformation of the tarim plate and the implications for mountain building in the tibetan plateau and the tian shan 1 the tarim basin in nw china developed as a complex foreland basin in the cenozoic in association with mountain building in the tibetan plateau to the south and the tian shan orogen to the north we reconstructed the cenozoic deformation history of the tarim basement by backstripping the sedimentary rocks two dimensional and three dimensional finite element models are then used to simulate the flexural deformation of the tarim basement in response to the sedimentary loads and additional tectonic loads associated with overthrusting of the surrounding mountain belts the results suggest that uplift of both the western kunlun shan and the tian shan orogens started during or before oligocene since the miocene mountain building accelerated in the western kunlun shan but showed segmented development in the tian shan the results also indicate reduced tectonic load along the altyn tagh fault since late miocene consistent with geological and geophysical evidence of the fault cutting the entire lithosphere and migrating southward during its cause of the cenozoic evolution

tectonic evolution of a composite collision orogen an overview on the qinling tongbai hong an dabie sulu orogenic belt in central china abstract the formation of collisional orogens is a prominent feature in convergent plate margins it is generally a complex process involving multistage tectonism of compression and extension due to continental subduction and collision the paleozoic convergence between the south china block scb and the north china block ncb is associated with a series of tectonic processes such as oceanic subduction terrane accretion and continental collision resulting in the qinling tongbai hong an dabie sulu orogenic belt while the arc continent collision orogeny is significant during the paleozoic in the qinling tongbai hong an orogens of central china the continent continent collision orogeny is prominent during the early mesozoic in the dabie sulu orogens of east central china this article presents an overview of regional geology geochronology and geochemistry for the composite orogenic belt the qinling tongbai hong an orogens exhibit the early paleozoic hp uhp metamorphism the carboniferous hp metamorphism and the paleozoic arc type magmatism but the three tectonothermal events are absent in the dabie sulu orogens the triassic uhp metamorphism is prominent in the dabie sulu orogens but it is absent in the qinling tongbai orogens the hong an orogen records both the hp and uhp metamorphism of triassic age and collided continental margins contain both the juvenile and ancient crustal rocks so do in the qinling and tongbai orogens in contrast only ancient crustal rocks were involved in the uhp metamorphism in the dabie sulu orogenic belt without involvement of the juvenile arc crust on the other hand the deformed and low grade metamorphosed accretionary wedge was developed on the passive continental margin during subduction in the late permian to early triassic along the northern margin of the dabie sulu orogenic belt and it was developed on the passive oceanic margin during subduction in the early paleozoic along the northern margin of the qinling orogen three episodes of arc continent collision are suggested to occur during the paleozoic continental convergence between the scb and ncb the first episode of arc continent collision is caused by northward subduction of the north qinling unit beneath the erlangping unit resulting in uhp metamorphism at ca 480 490 ma and the accretion of the north qinling unit to the ncb the second episode of arc continent collision is caused by northward subduction of the prototethyan oceanic crust beneath an andes type continental arc leading to granulite facies metamorphism at ca 420 430 ma and the accretion of the shangdan arc terrane to the ncb and reworking of the north qinling erlangping and kuanping units the third episode of arc continent collision is caused by northward subduction of the paleotethyan oceanic crust resulting in the hp eclogite facies metamorphism at ca 310 ma in the hong an orogen and low p metamorphism in the qinling tongbai orogens as well as crustal accretion to the ncb the closure of backarc basins is also associated with the arc continent collision processes with the possible cause for granulite facies metamorphism the massive continental subduction of the scb beneath the ncb took place in the triassic with the final continent continent collision and uhp metamorphism at ca 225 240 ma therefore the qinling tongbai hong an dabie sulu orogenic belt records the development of plate tectonics from oceanic subduction and arc type magmatism to arc continent and continent continent collision

co2 diffuse emission from maar lake an example in changbai volcanic field ne china abstract numerous maars and monogenetic volcanic cones are distributed in northeast china which are related to westward deep subduction of the pacific ocean lithosphere comprising a significant part of the pacific ring of fire it is well known that diffuse co2 emissions from monogenetic volcanoes including wet e g maar lake and dry degassing systems e g soil diffuse emission fault degassing etc may contribute to budget of globally nature derived greenhouse gases however their relationship between wet e g maar lake and concomitant dry degassing systems e g soil diffuse emission fault degassing etc related to monogenetic volcanic field is poorly understood yuanchi maar one of the typical monogenetic volcanic systems is located on the eastern flank of tianchi caldera in changbai volcanic field of northeast china which displays all of three forms of co2 degassing including the maar lake soil micro seepage and fault degassing measurements of efflux of co2 diffusion from the yuanchi maar system yms indicate that the average values of co2 emissions from soil micro seepage fault degassing and water air interface diffusion are 24 3 23 3 g m 2 d 1 39 2 22 4 g m 2 d 1 and 2 4 1 1 g m 2 d 1 respectively the minimum output of co2 diffuse emission from the yms to the atmosphere is about 176 1 88 3 ton yr of which 80 4 results from the dry degassing system degassing from the fault contributes to the most of co2 emissions in all of the three forms of degassing in the yms contributions of mantle crust air and organic co2 to the soil gas are 0 01 0 10 10 20 32 36 and 48 54 respectively which are quantitatively constrained by a he c isotope coupling calculation model we propose that co2 exsolves from the upper mantle melting beneath the tianchi caldera which migrates to the crustal magma chamber and further transports to the surface of yms along the deep fault system during the transportation processes the emission of gas experiences crustal contamination influence of magma chamber beneath the yms sub surface processes and air dilution

neoproterozoic granitoid in northwest sulu and its bearing on the north china south china blocks boundary in east china 1 middle neoproterozoic granitoid rocks are found in the wulian region that is located in the northwestern part of the sulu orogen and is approximately bounded by the wulian yantai fault in southeast zircon u pb dating yields concordant ages of 738 10 to 758 5 ma for three granites and one gabbro hornblende ar ar dating on the gabbro gives consistent plateau and isochron ages of 719 1 3 7 and 717 9 7 2 ma respectively this suggests that the wulian granitoids correspond to bimodal magmatism during the mid neoproterozoic in the northern margin of the south china block in response to the breakup of rodinia supercontinent they were tectonic slices scraped off from the upper part of the south china block during the triassic continental subduction this demonstrates that the suture location between the north china block and the south china block lies north of the wulian and penglai groups rather than along the wulian yantai fault that marks the northern margin of ultrahigh pressure metamorphic belt

flexural plate subsidence sedimentation rates and structural development of the super deep south caspian basin abstract on a 270 km long seismic line across the west central and central parts of the south caspian basin an inverse flexural plate method is used to recover original uploaded plate parameters the original plate shows remarkable consistency of parameters determined from the 12 second deep seismic line with average rigidity d 1023 6nm bending moment m 1016n dip angle 0 14 and in line compressive stress of 1012 3n m 1 by sequentially adding the sedimentary units to the average bare basement it is shown that the geometry of the basin at jurassic time had a major downward warp and high sedimentary fill to the west leaving the eastern section open to possible erosion during early and middle cretaceous time the deep western part of the basin was then filled by sediments during late tertiary quaternary time and a new depocenter created across the central and western parts of the basin this newer depocenter was then filled during pliocene quaternary time the combined flexure of the basement plate and corresponding sediment fill behaviors with time are indicative of corresponding lithologic variations across the basin and with suspected organic rich sediments the integrated description of basement sediments and depocenter behavior points to the utility of the inverse procedure for improving our understanding of basinal evolution the value of rigidity is comparable to estimated oceanic crust values in line with the suspected tethys oceanic fragment of an island arc below the sediments the shift in depositional behavior with time from west to more northerly across the line of section is tied to the orogenic rise of the caucasus mountains to the north of the section and to the continued subduction of the talysh vandam plate fragment northward today the transpressional nature of the basin and the resolution of the in line compressive stress into components perpendicular to the great caucasus 70 and also perpendicular to the west caspian deep laid fault 25 30 are both in accord with the 25 30 km of present day sedimentary cover including the variations of thicknesses of seismic stratigraphic units along the section from azerbaijan in the west to nearly the turkmenian border in the east

high resolution water column survey to identify active sublacustrine hydrothermal discharge zones within lake rotomahana north island new zealand abstract autonomous underwater vehicles were used to conduct a high resolution water column survey of lake rotomahana using temperature ph turbidity and oxidation reduction potential orp to identify active hydrothermal discharge zones within the lake five areas with active sublacustrine venting were identified 1 the area of the historic pink terraces 2 adjacent to the western shoreline subaerial steaming cliffs boiling springs and geyser 3 along the northern shoreline to the east of the pink terrace site 4 the newly discovered patiti hydrothermal system along the south margin of the 1886 tarawera eruption rift zone and 5 a location in the east basin northeast of patiti island the pink terrace hydrothermal system was active prior to the 1886 eruption of mount tarawera but venting along the western shoreline in the east basin and the patiti hydrothermal system appear to have been initiated in the aftermath of the eruption similar to waimangu valley to the southwest different combinations of turbidity ph anomalies both positive and negative and orp responses suggest vent fluid compositions vary over short distances within the lake the seasonal period of stratification limits vertical transport of heat to the surface layer and the hypolimnion temperature of lake rotomahana consequently increases with an average warming rate of 0 010 c day due to both convective hydrothermal discharge and conductive geothermal heating a sudden temperature increase occurred during our 2011 survey and was likely the response to an earthquake swarm just 11 days prior

interpretation of gravity and magnetic anomalies at lake rotomahana geological and hydrothermal implications abstract we investigate the geological and hydrothermal setting at lake rotomahana using recently collected potential field data integrated with pre existing regional gravity and aeromagnetic compilations the lake is located on the southwest margin of the okataina volcanic center haroharo caldera and had well known pre 1886 tarawera eruption hydrothermal manifestations the famous pink and white terraces its present physiography was set by the caldera collapse during the 1886 eruption together with the appearance of surface activities at the waimangu valley gravity models suggest that subsidence associated with the haroharo caldera is wider than the previously mapped extent of the caldera margins magnetic anomalies closely correlate with heat flux data and surface hydrothermal manifestations and indicate that the west and northwestern shore of lake rotomahana are characterized by a large well developed hydrothermal field the field extends beyond the lake area with deep connections to the waimangu area to the south on the south the contact between hydrothermally demagnetized and magnetized rocks strikes along a structural lineament with high heat flux and bubble plumes which suggest hydrothermal activity occurring west of patiti island the absence of a well defined demagnetization anomaly at this location suggests a very young age for the underlying geothermal system which was likely generated by the 1886 tarawera eruption locally confined intense magnetic anomalies on the north shore of lake rotomahana are interpreted as basalt dikes with high magnetization some appear to have been emplaced before the 1886 tarawera eruption a dike located in proximity of the southwest lake shore may be related to the structural lineament controlling the development of the patiti geothermal system and could have been originated from the 1886 tarawera eruption

heavy minerals and garnet geochemistry of stream sediments and bedrocks from the almklovdalen area western gneiss region sw norway implications for provenance analysis abstract detrital heavy minerals commonly document the geological setting in the source area hence they are widely used in sedimentary provenance analysis in heavy mineral studies the 63 125 and 63 250 m grain size fractions are most commonly used heavy mineral data and garnet geochemistry of stream sediments and bedrocks from the catchment area draining the almklovdalen peridotite massif in sw norway reveal that a wider grain size spectrum needs to be considered to avoid misleading interpretations the almklovdalen peridotite massif consists mainly of dunite and harzburgite as testified by the heavy mineral suite at the outlet of the main river the heavy mineral spectrum is very monotonous due to dilution by a strong influx of olivine heavy minerals like apatite and epidote characterising the host gneisses have almost disappeared mgo rich almandine garnets are more frequent in the coarser grain size fractions whereas mno rich almandine garnets are more frequent in the finer grain size fractions garnets with pyrope content exceeding 50 are only found in the 500 1000 m grain size fraction therefore the sample location and the selected grain size fraction are of paramount importance when dealing with heavy minerals and mineral geochemical data otherwise provenance sensitive information may be missed

variability of passive gas emissions seismicity and deformation during crater lake growth at white island volcano new zealand 2002 2006 1 we report on 4 years of airborne measurements of co2 so2 and h2s emission rates during a quiescent period at white island volcano new zealand beginning in 2003 during this time a significant crater lake emerged allowing scrubbing processes to be investigated co2 emissions varied from a baseline of 250 to 2000 t d 1 and demonstrated clear annual cycling that was consistent with numbers of earthquake detections and annual changes in sea level the annual variability was found to be most likely related to increases in the strain on the volcano during sea level highs temporarily causing fractures to reduce in size in the upper conduit so2 emissions varied from 0 to 400 t d 1 and were clearly affected by scrubbing processes within the first year of lake development scrubbing caused increases of so42 and cl in lake waters and the ratio of carbon to total sulphur suggested that elemental sulphur deposition was also significant in the lake during the first year careful measurements of the lake level and chemistry allowed estimates of the rate of h2o g and hcl g input into the lake and suggested that the molar abundances of major gas species h2o co2 so2 and hcl during this quiescent phase were similar to fumarolic ratios observed between earlier eruptive periods the volume of magma estimated from co2 emissions 0 015 0 04 km3 was validated by cl increases in the lake suggesting that the gas and magma are transported from deep to shallow depths as a closed system and likely become open in the upper conduit region the absence of surface deformation further leads to a necessity of magma convection to supply and remove magma from the degassing depths two models of convection configurations are discussed

evidence of early cretaceous transpression in the sulu orogenic belt eastern china abstract recent studies have documented marine turbidites with syn sedimentary deformation features in the central sulu orogenic belt of eastern china these units preserve essential information on the late mesozoic evolution of the sulu orogenic belt referred to as the baxiandun formation the turbidites exhibit similar lithologic characteristics to nearby units such as the lingshandao formation that have been well studied even though precise geochronologic constraints are lacking for a more precise correlation this study reports detrital zircon u pb age data that correlate the baxiandun formation turbidites of the central sulu orogenic belt to the early cretaceous lingshandao formation we also report al in hornblende emplacement depth estimates for granitic intrusions of the sulu orogenic belt s laoshan mountain a sharp contact between the laoshan granites and the marine baxiandun formation indicates that the baxiandun basin rapidly subsided to the emplacement depth of the laoshan plutons lateral correlation among the marine turbidites the lingshandao and baxiandun formations combined with information established by previous studies indicates initiation of transpressional tectonics at 122 121 ma transpression ceased with the emplacement of the laoshan granites whose a1 type composition indicates a return to extensional tectonics at ca 111 ma

late paleozoic mesozoic tectonic evolution of sw japan a review reappraisal of the accretionary orogeny and revalidation of the collisional model abstract this paper makes a review of the interpretations of the tectonic evolution of sw japan during the last three decades in the late 1970s the dominant model was the so called pacific type orogeny emphasizing the purported absence of nappes and the contrast with the alpine chains and interpreting the evolution as due to a steady oceanic subduction since the paleozoic time in the 80s the discovery of the actual structure made of a pile of large thrust sheets led authors to propose collisional models involving the intermittent underthrusting of buoyant blocks like micro continents at the same time the use of high resolution biostratigraphy allowed several authors to recognize ancient accretionary wedges with a reconstructed ocean plate stratigraphy of individual accreted units especially in the tanba and shimanto zones also precise radiometric dating permitted the distinction of metamorphosed units especially in sanbagawa and shimanto belts as a result of these new data since the 1990s the plate tectonic interpretation of the history of the japanese islands was revised by japanese scientists and presented again in terms of accretionary processes linked to a steadily oceanic subduction with an episodic ridge subduction the so called miyashiro type orogeny the review of different data leads to the following conclusions the structure of sw japan is made of a pile of sub horizontal nappes polydeformed with a geometry similar to the one encountered in collisional orogens the geodynamic mechanisms advocated for the tectonic building within the accretionary orogeny concept miyashiro type orogeny are inappropriate a permanent oceanic subduction with the intermittent collision actually subduction of an active ridge or seamount chain is unable to build such structures as this process induces in fact an acceleration of the tectonic erosion and collapse of the upper plate the underthrusting of a micro continent or mature arc is likely needed the exhumation story of sanbagawa hp schists suggests the setting of a continental subduction the petrological and new geochemical data from the literature strongly support the existence beneath the nappes of accretionary complexes of continental bodies showing affinities with south china from which they were once separated the episodic collision underthrusting of such blocks was responsible for the tectonic piling tectonic erosion plaid likely a major role in removing material during the intervening subduction stages a revised geodynamic model implying the collision of the honshu south kitakami kurosegawa and shimanto blocks is proposed for explaining the three orogenic crises which took place respectively at around 240 130 and 80 60 ma ago in sw japan the paleogeographic position and affinity of the hida block with surrounding units in the hinterland are still unclear more work is needed to solve this question

u pb dating of zircons from granitic leucosomes in migmatites of the jiaobei terrane southwestern jiao liao ji belt north china craton constraints on the timing and nature of partial melting abstract in the jiaobei terrane of the jiao liao ji belt eastern china layers and irregular lenses of granitic leucosomes are widely distributed within high pressure hp mafic granulites medium pressure mp granulites amphibolites ttg gneisses and hp and mp pelitic granulites the layers and lenses may be parallel to or cross cut the foliation in the host rocks on different scales and they show evidence of coalescence and migration in the formation of centimeter to decimeter scale segregations the migmatized rocks extend over an area of at least 120 km 75 km from laixi through laiyang and qixia to sw yantai a combined study of mineral inclusions cathodoluminescence cl images and zircon u pb la icp ms dates provides clear evidence on the nature and timing of the partial melting in these granulite facies metamorphic rocks most zircons from the granitic leucosomes are either inherited crystals igneous or detrital with distinct overgrowths or are simply new euhedral crystals both the overgrowths and the new crystals commonly exhibit perfect euhedral shapes pronounced oscillatory zoning and contain mineral inclusions of qtz kfs pl ap in contrast the inherited cores are rounded or irregular in shape and exhibit signs of dissolution these observations suggest that the new zircons are anatectic in origin and that they crystallized from melts derived from dehydration melting reactions and partial melting of the host granulite facies rocks numerous u pb spot analyses of anatectic zircons reveal that the jiaobei terrane experienced a major episode of partial melting in the paleoproterozoic with crystallization of the melt occurring in two distinct periods from 1860 9 2 2 to 1852 1 2 8 ma and 1839 9 2 9 to 1833 3 5 3 ma as represented respectively by the magmatic cores and rims of the anatectic zircons the first age group probably represents the initial crystallization of melts derived from partial melting within the jiaobei terrane while the second age group may represent the completion of migmatization and crystallization of granitic leucosomes this significant partial melting event was genetically associated with the paleoproterozoic mp granulite facies hot stage of exhumation of the southwestern part of the jiao liao ji belt and it induced extensive retrogression of the ttg gneisses and mafic and pelitic granulites as well as the formation of regional migmatites

early cretaceous exhumation of the sulu orogenic belt as a consequence of the eastern eurasian tectonic extension insights from the newly discovered wulian metamorphic core complex eastern china the mechanisms of thinning of the lithosphere and destruction of the north china craton have been debated in recent decades their causal link with regional tectonic extension is well exemplified by the exhumation of the wulian metamorphic core complex mcc along the sulu orogenic belt to the se of the north china craton the wulian mcc is a cordilleran type mcc with a northwestward dipping low angle master detachment fault zone the wulian detachment fault zone an early cretaceous supradetachment basin the zhucheng basin and a lower plate of ultrahigh pressure metamorphic rocks in the sulu orogenic belt synthetic structural fabric and thermochronological data suggest that tectonic extension is responsible for the exhumation of the lower plate and triggered syn and post tectonic magmatisms a new cooling path for the lower plate rocks indicates that the lower plate was exhumed at a high rate of 2 0 km ma 1 from before c 128 ma to 123 ma and at a moderate rate of 0 35 km ma 1 from 81 to 61 ma the rapid exhumation is consistent temporally with the sedimentation of terrestrial deposits of the laiyang group in the zhucheng supradetachment basin the post kinematic granitic intrusions are dated as c 122 ma which marks the cessation of rapid exhumation of the lower plate vast amount of andesitic volcanic rocks from 120 to 105 ma in the qingshan group in the zhucheng basin may be related to the peak of lithospheric thinning in the wulian area these data highlight the importance of regional tectonic extension in the formation of the detachment fault zone and the exhumation of the wulian mcc and in triggering syn and post kinematic magmatisms the scenario is consistent with the parallel extension tectonics model in which tectonic extension of the lithosphere led to detachment faulting in both the crust and mantle resulted in the loss of some of the subcontinental roots gave rise to the exhumation of the mccs and triggered plutonic emplacement and volcanic eruptions of hybrid magmas

forecasting etna eruptions by real time observation of volcanic gas composition it is generally accepted but not experimentally proven that a quantitative prediction of volcanic eruptions is possible from the evaluation of volcanic gas data by discussing the results of two years of real time observation of h2o co2 and so2 in volcanic gases from mount etna volcano we unambiguously demonstrate that increasing co2 so2 ratios can allow detection of the pre eruptive degassing of rising magmas quantitative modeling by the use of a saturation model allows us to relate the pre eruptive increases of the co2 so2 ratio to the refilling of etna s shallow conduits with co2 rich deep reservoir magmas leading to pressurization and triggering of eruption the advent of real time observations of h2o co2 and so2 combined with well constrained models of degassing represents a step forward in eruption forecasting

late cretaceous climate changes recorded in eastern asian lacustrine deposits and north american epieric sea strata abstract cretaceous climate data of the long lived cretaceous songliao basin sb in eastern asia is correlated and compared with the western interior seaway wis on the northern american plate in order to understand better the dynamics of the earth s past greenhouse climates nearly continuous late cretaceous terrestrial deposition in the songliao basin is represented by two cores totaling 2431 m in length the turonian maastrichtian age of the section is based on integrated stratigraphy and is comparable in age with upper cretaceous strata in the wis being consistent with global trends the dynamic late cretaceous climates of both the sb and wis gradually cooled from the warmest albian cenomanian time to the end of the maastrichtian with several intervening warm periods as did the global climate however regional differences existed the songliao basin climate was humid to semi humid warm temperate subtropical and the western interior seaway was in the humid warm temperate zone and experienced only moderate climatic changes the shifts of oxygen isotope data in the songliao basin were frequent and abrupt whereas wis records more gradual change affected mainly by fresh water runoff mixing with southern tethyan and northern arctic waters sedimentary cycles of eccentricity obliquity and precession bands are recorded in both the sb and wis basins the sedimentary cycles in the wis and sb are interpreted to be related to variations of the wet dry runoff cycles which indicate that orbital forcing played an important role in global climate change in late cretaceous the most favorable condition for organic carbon burial in both the sb and wis basin was bottom water anoxia regardless of the cause of the anoxia but the organic carbon burial rate was usually much higher in the songliao lake than in the wi epeiric sea suggesting that giant lakes may serve as important sinks of atmospheric co 2 in both basins organic rich deposits formed during a rise in water level and incursion of saline waters the integration of paleoclimate data from cretaceous marine deposits and terrestrial sedimentary record will promote our understanding of the cretaceous greenhouse climate change and may provide insights for a future greenhouse world

the pink and white terraces of lake rotomahana what was their fate after the 1886 tarawera rift eruption abstract the pink and white terraces that once stood regally on the shores of old lake rotomahana and which were unique in their beauty as a natural wonder of the world were regarded by the local m ori as a taonga or treasure because of the therapeutic qualities of the waters and their majestic appearance the eruption of mt tarawera on june 10 1886 is commonly cited as the cause of their demise with the lake rapidly rising soon thereafter to drown the large newly formed rotomahana crater and other volcanic edifices shaped during the excavation of the old lake thus the effects of the eruption have been masked from onlookers for more than 125 years however application of state of the art survey techniques usually applied in the marine realm to modern lake rotomahana including auv surveys with numerous sensors seismic profiling water column surveys and deployment of deep sea cameras has provided a wealth of new information about the state of hydrothermal systems in the lake and the probable fortunes of the pink and white terraces we believe that the majority of both sets of terraces were destroyed during the eruption however some tantalizing evidence remains for remnants from both sites to exist to this day high resolution bathymetric mapping of the lake floor clearly recognizes some features of the post 1886 landscape including a prominent landmark known as the pinnacle if we accept the postulated location of the pinnacle on a pre 1886 map of lake rotomahana then we appear to have captured a photograph of one of the buttresses to a tier of the nearby white terraces more revealing are side scan sonar images of structures located in the correct position of the pink terraces with respect to the pinnacle albeit 20 m deeper than expected if the pre 1886 lake level of 292 m above sea level is to be believed this work clearly shows that the greater pink terraces hydrothermal system survived the eruption and is very active today whereas that part of the system that supplied hydrothermal fluids to the white terraces has largely ceased activity altogether

subaerial and sublacustrine hydrothermal activity at lake rotomahana abstract lake rotomahana is a crater lake in the okataina volcanic centre new zealand that was significantly modified by the 1886 tarawera rift eruption the lake is host to numerous sublacustrine hydrothermal vents water column studies were conducted in 2011 and 2014 along with sampling of lake shore hot springs and crater lakes in waimangu valley to complement magnetic seismic bathymetric and heat flux surveys helium concentrations below 50 m depth are higher in 2014 compared to 2011 and represent some of the highest concentrations measured at 6 10 7 ccstp g with an end member 3he 4he value of 7 1 ra the high concentrations of helium when coupled with ph anomalies due to high dissolved co2 content suggest the dominant chemical input to the lake is derived from magmatic degassing of an underlying magma the lake shore hot spring waters show differences in source temperatures using a na k geothermometer with inferred reservoir temperatures ranging between 197 and 232 c water 18o and d values show isotopic enrichment due to evaporation of a steam heated pool with samples from nearby waimangu valley having the greatest enrichment results from this study confirm both pre 1886 eruption hydrothermal sites and newly created post eruption sites are both still active

mechanism of subsidence of ancient cratonic rift basins cratonic basins commonly occur over ancient rift zones these inactive rift basins are recognizable by a positive linear bouguer gravity anomaly that may correspond to the axial gravity high found in modern rift valleys many of these basins undergo discrete periods of increased subsidence rates or reactivations long after the mass excess responsible for the linear gravity high was emplaced furthermore the reactivation of many cratonic basins occurs simultaneously with large scale compressional tectonics it is suggested that the driving force for subsidence is the isostatically uncompensated ancient mass excess the subsidence of these basins is modelled by a lithospheric flexure model with a nonlinear maxwell viscoelastic rheology solutions to this model indicate that basins may experience a low subsidence rate throughout geologic time the subsidence of a basin will stop only when isostatic compensation of the mass excess is achieved since ancient rift mass excesses may be uncompensated over long geologic time intervals the early thermal and structural evolution of rifts may not significantly influence later basin subsidence the models suggest that basins may be reactivated by any mechanism which lowers the effective viscosity of the lithospheric material allowing the uncompensated basin to settle toward an isostatic compensation depth faster than normal since viscosity is a strong function of temperature reactivation by a world wide increase in heat flow is suggested as a possible mechanism for the synchroneity of basin subsidence throughout a continent an increase of 15 in the geothermal gradient for example from 16 5 18 9 k km will cause about a 5 increase in subsidence this increase in heat flow however seems unlikely of producing by itself the magnitude of basin subsidence during a reactivation phase that is observed in the geologic record where up to 100 increase in subsidence might occur since the rheology of the lithosphere is nonlinear effective viscosity is also a strong nonlinear function of stress the presence of a regional compressive stress during periods of tectonism of 1 1 108 pa about 2 8 of the buckling strength of the lithosphere produces a short period of reactivated subsidence 105 yr during the reactivated subsidence the newly imposed regional stress relaxes sufficiently in the lower lithosphere to restore the effective viscosity to values similar to that before reactivation this suggests that reactivated subsidence caused by regional compression can be maintained as long as the stress level remains high in the lower lithosphere this may be accomplished by an intermittent application of the regional stress over time

imaging the deep source of the rotorua and waimangu geothermal fields taupo volcanic zone new zealand abstract magnetotelluric data were recorded in a 45 10 km band crossing the rotorua and waimangu geothermal fields in the northern part of the taupo volcanic zone in the central north island of new zealand 3 d inverse modelling of these data show that beneath the low resistivity areas marking the near surface geothermal fields localised electrically conductive zones are present in the crust below about 2 5 and 3 5 km depth at rotorua and waimangu respectively at increasing depth these conductive zones broaden and appear to merge with a larger conductive zone at 8 km depth situated between the geothermal systems at rotorua the top of the conductive zone is situated directly beneath the area of greatest surface heat and gas discharge at waimangu the uppermost part of the deeper conductive zone is situated beneath the western part of lake rotomahana also an area of intense surface thermal activity and high heat flux the localised conductive zones are interpreted to be high temperature quasi magmatic fluids rising from a broader zone of partial melt at deeper levels

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

from static to dynamic provenance analysis sedimentary petrology upgraded abstract the classical approach to sandstone petrology established in the golden years of plate tectonics and based on the axiom that detrital modes of sandstone suites primarily reflect the different tectonic settings of provenance terranes has represented a benchmark for decades the composition of sand and sandstone however simply provides us with a distorted image of the lithological structure of source terranes and gives us little clue whether they are allochthonous or autochthonous orogenic or anorogenic young or old what we may able to see reflected in detrital modes is the nature of source terranes continental arc oceanic and the tectonostratigraphic level reached by erosion in space and time the proposed new approach to the petrology of sand and sandstone 1 starts with a simple classification scheme circulated since the 1960s which is purely descriptive objective and free of ill defined ambiguous terms and 2 focuses on the nature and tectonostratigraphic level of source terranes further steps are essential to upgrade provenance analysis acquiring knowledge from modern settings is needed to properly identify and wherever possible correct for physical and chemical processes introducing environmental and diagenetic bias and thus address nature s complexities with adequate conceptual tools equally important is the integration of multiple techniques ideally including bulk sediment multi mineral and single mineral methods bulk sediment petrography remains the fundamental approach that allows us to capture the most precious source of direct provenance information represented by the mineralogy and texture of rock fragments bulk sediment geochemistry applicable also to silt and clay carried in suspension is a superior method to check for hydraulic sorting chemical weathering and fertility of detrital minerals in different sediment sources detrital geochronology thermochronology and isotope geochemistry reveal the diverse time structures of source rocks and have become necessary complementary techniques in modern provenance analysis inferences on geodynamic processes need independent geological information and come last but if tackled properly they can lead us much farther than the standard label obtained by using triangular diagrams uncritically as if they were infallible oracles

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

composition and sediment dispersal pattern of the upper triassic flysch in the eastern himalayas china significance to provenance and basin analysis the paleogeography and basin type of upper triassic flysch langjiexue group in the eastern himalayan orogen are disputed in order to shed new light on the flysch s origin we applied different sedimentological methods assemblages of heavy minerals and clastic components of sandstones were utilized to determine the primary depositional composition heavy mineral indices s m ratios thickness of sandstone siltstone s versus slate mudrock m and paleocurrent data were combined to reveal the sediment dispersal pattern and the location of the source areas in the analyzed sandstones heavy minerals such as zircon rutile tourmaline apatite and anatase are most common and zircon is predominant most over 60 ztr values range from 60 to 98 and systematically increase southward as a provenance sensitive parameter ruzi values vary in large magnitude and are significantly higher in both the east and west 20 than in the center the majority of s m ratios decrease from north to south suggesting an overall decrease in grain size to the south paleocurrent directions vary between 120 and 270 main vector 205 and 185 after 20 counterclockwise correction displaying a radial curved pattern variable heavy mineral assemblages indicate different sources and the sandstones fall in the recycled and mixed arc orogeny fields of dickinson triplots together supporting the view of multiple sources results of the ztr values s m ratios and paleocurrent directions illustrate a dispersal pattern corresponding to a submarine fan system the provenance and submarine fan dispersal pattern along with the basin configuration deep basin with oceanic affinities suggest that the langjiexue group accumulated in a remnant basin between lhasa greater india and australia where the sediments dispersed into the basin toward the developing orogen suture zone and not away from the orogen challenging the provenance direction for the traditional remnant basin model

an active thermoelastic rift mechanism finite element solutions for stresses and displacements during rift development are obtained for a variable thickness elastic lithosphere plate subjected to thermoelastic loading by conductive heating from an axial line source in the asthenosphere the asthenosphere is modelled as a fluid foundation the prerift lithosphere is modelled as an infinite continuous plate a semi infinite plate is used to characterize the rifted lithosphere horizontal restraints are removed at the rift axis to model the transition from a continuous to separated lithosphere plate during rifting lithosphere strength envelope curves derived from olivine flow laws are used to determine the elastic lithosphere depth in the solutions conductive heating of a variable thickness continuous lithosphere plate by a 2000 w m line source at 60 km depth produces high stresses oriented orthogonal to the forming rift axis and small vertical displacements the maximum uplift obtained in the continuous lithosphere plate models subjected to thermoelastic loading was 0 12 km at a distance of 120 km from the forming rift axis this small uplift is accompanied by shallow tensile stresses of 80 mpa at a distance of 5 km from forming rift axis which decrease to 6 mpa at a distance of 210 km shallow horizontal thermoelastic tensile stresses are over 5 times greater than the horizontal stresses produced by thermal buoyancy loads near the forming rift axis the transition from a continuous to rifted lithosphere is accompanied by an increase in lithosphere uplift at the rift axis from 0 11 to 0 42 km and a reduction in shallow horizontal stress magnitude by a factor of 30 thermoelastic loading may be a source of shallow tensile stress in the lithosphere and a contributing factor for the initiation of rifting thermal loading may also produce postrifting topography changes thermoelastic loading of the lithosphere is proposed as a possible driving mechanism for rift formation which produces separation and the transition from a continuous to rifted lithosphere plate

in situ evaluation of air sea gas exchange parameterizations using novel conservative and volatile tracers measurements of air sea gas exchange rates are reported from two deliberate tracer experiments in the southern north sea during february 1992 and 1993 a conservative tracer spores of the bacterium bacillus globigii var niger was used for the first time in an in situ air sea gas exchange experiment this nonvolatile tracer is used to correct for dispersive dilution of the volatile tracers and allows three estimations of the transfer velocity for the same time period the first estimation of the power dependence of gas transfer on molecular diffusivity in the marine environment is reported this allows the impact of bubbles on estimates of the transfer velocity derived from changes in the helium sulphur hexafluoride ratio to be assessed data from earlier dual tracer experiments are reinterpreted and findings suggest that results from all dual tracer experiments are mutually consistent the complete data set is used to test published parameterizations of gas transfer with wind speed a gas ex change relationship that shows a dependence on wind speed intermediate between those ofliss and merlivat 1986 and wanninkhof 1992 is found to be optimal the dual tracer data are shown to be reasonably consistent with global estimates of gas exchange based on the uptake of natural and bomb derived radiocarbon the degree of scatter in the data when plotted against wind speed suggests that parameters not scaling with wind speed are also influencing gas exchange rates

helium isotope evidence for magmatic gases in lake nyos cameroon we have measured he 4he and 4he 20ne ratios of gas samples collected at lake nyos where a toxic gas disaster occurred on august 21 1986 and at lake monoun in cameroon west africa the he 4he ratios corrected for air contamination are 5 39 5 75 ratm where ratm is the atmospheric ratio of 1 40 10 6 for lake nyos and 3 56 ratm for lake monoun the data suggest a significant contribution of mantle derived helium in these cameroon volcanic crater lakes the origin of co2 gas erupted during lake nyos disaster is inferred to be of magmatic origin based on the high he 4he ratio

discovery of active hydrothermal venting in lake taupo new zealand the horomatangi geothermal system of lake taupo new zealand is a sub lacustrine equivalent of subaerial geothermal activity nearby in the taupo volcanic zone tvz the setting of this system is rare within the tvz as it is directly associated with an individual volcanic feature that of the 1 8 ka taupo eruption vent two distinct hydrothermal vent areas named te hoata and te pupu have been discovered during dives with the submersible jago venting of gases was seen at both sites and hot water up to 45degreesc discharges at the te pupu site dilute water samples have concentrations of so4 cl na and sio2 above ambient lake water values gas samples have compositions similar to other tvz geothermal systems gas geothermometers indicate the existence of a high temperature hydrothermal environment beneath the lake with reservoir temperatures in excess of 300degreesc chimney structures were found at the te pupu site they are up to 30 cm tall and mineralized by an epithermal suite of elements including s hg as sb and tl the walls of the chimneys are largely composed of diatoms and strands of silicified filamentous bacteria embedded in an amorphous silica groundmass bacterial mats are commonly associated with the gas vents and also occur at two hot springs close to the vents commonly perched on top of dead chimneys and or exposed outcrops are dense assemblages of what are probably a new species of sponge of the genus heterorotula the sponges host a notably diversified associated invertebrate fauna and represent a previously unseen biomass on the lake floor the sponges appear to have bored into the mineralized chimneys c 2002 elsevier science b v all rights reserved

millennial timescale resolution of rhyolite magma recharge at tarawera volcano insights from quartz chemistry and melt inclusions most rhyolite eruption episodes of tarawera volcano have emitted several physiochemically distinct magma batches 1 10 km3 these episodes were separated on a millennial timescale the magma batches were relatively homogeneous in temperature and composition at pumice scale 4 cm but experienced isolated crystallisation histories at the sub cm scale matrix glasses have trace element compositions sr ba rb that vary by factors up to 2 5 indicating incomplete mixing of separate melts some quartz hosted melt inclusions are depleted in compatible trace elements sr ti ba compared to enclosing matrix glasses this could reflect re melting of felsic crystals deeper in the crystal pile individual quartz crystals display a variety of cathodoluminescence brightness and ti zoning patterns including rapid changes in melt chemistry and or temperature 50 100 c and point to multi cycle crystallisation histories the tarawera magma system consisted of a crystal rich mass containing waxing and waning melt pockets that were periodically recharged by silicic melts driven by basaltic intrusion

shrimp u pb zircon dating of the neoproterozoic penglai group and archean gneisses from the jiaobei terrane north china and their tectonic implications abstract archean basement gneisses and supracrustal rocks together with neoproterozoic sinian metasedimentary rocks the penglai group occur in the jiaobei terrane at the southeastern margin of the north china craton shrimp u pb zircon dating of an archean ttg gneiss gave an age of 2541 5 ma whereas metasedimentary rocks from the neoproterozoic penglai group yielded a range in zircon ages from 2 9 to 1 8 ga the zircons can be broadly divided into three age populations at 2 0 1 8 ga 2 45 2 1 ga and 2 5 ga detrital zircon grains with ages 2 6 ga are few in number and there are none with ages

shrimp u pb zircon geochronology of palaeoproterozoic metasedimentary rocks in the north china craton evidence for a major late palaeoproterozoic tectonothermal event abstract although metasedimentary successions are widely distributed across the north china craton those of palaeoproterozoic age are restricted to three orogenic belts namely the trans north china orogen the khondalite belt and the jiao liao ji belt prior to this work some of those successions were considered to be archaean in age the palaeoproterozoic metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 0 to 2 1 ga with the majority recording an age between 2 3 and 2 0 ga this latter group define a series of magmatic events that occurred between formation of the archaean basement and deposition of the metasedimentary rock protoliths the metasedimentary rocks occur as two associations older volcano sedimentary units that formed between 2 37 and 2 0 ma and younger sedimentary units that formed mainly between 2 0 and 1 88 ga all these rock associations were then subjected to metamorphism during the late palaeoproterozoic 1 88 and 1 85 ga tectonothermal event named the luliang movement in early chinese literature which was a continent continent collision that led to the amalgamation of the north china craton

u pb ages and trace elements of detrital zircons from early cretaceous sedimentary rocks in the jiaolai basin north margin of the sulu uhp terrane provenances and tectonic implications abstract the dabie sulu orogen in east central china is the largest uhp belt in the world many studies have dealt with detrital minerals from sedimentary basins surrounding the dabie belt in order to constrain the tectonic unroofing of this terrane on the other hand still few are the works focused on detritals from the basins associated with the sulu belt the jiaolai basin adjacent to the sulu belt is made of mesozoic sedimentary rocks two sandstone samples collected from the early cretaceous laiyang group in the northern and southern margins of the jiaolai basin were selected for zircon u pb dating and trace element analysis the zircons show main u pb age clusters at ca 2500 2400 2000 1700 850 700 and 330 130 ma with a minor peak at ca 1100 ma and a few archean ages most zircons show texture features reflecting a magmatic origin whereas several late paleoproterozoic and triassic zircons show homogeneous cl images and low th u ratios indicating a metamorphic origin the neoproterozoic ages are consistent with the protolith ages of the metamorphic rocks in the sulu terrane implying that the sulu tarrane may be a major source for this component whereas most neoproterozoic zircons are euhedral to subhedral or angular in shape and are not surrounded by overgrowths this implies that low grade metamorphic neoproterozoic metaigneous rocks ocurring along the northern margin of the sulu terrane or metasediments overlying the hp uhp rocks in the sulu terrane might provide source materials to these detrital zircons the late and early paleoproterozoic age peaks are consistent with the thermal events occurred in the jiaobei terrane slightly younger than those in the yangtze block these suggest that the jiaobei terrane was a potential source for the paleoproterozoic to archean detrital zircon components only two early paleozoic zircon grains were found in the studied samples indicating the early paleozoic arc did not extend into the sulu terrane according to the distribution of different kinds of rock adjacent to the sulu terrane the early cretaceous detrital zircons may be potentially derived from cretaceous plutons from the sulu belt eight detrital zircons including six metamorphic grians and two metamorphic overgrowth rims yield the triassic ages which might be derived from hp uhp rocks from the sulu terrane a metamorphic overgrowth rim yields a metamorphic age of 246 3 ma probably recording the timing of the prograde metamorphism of the sulu terrane one metamorphic grain yields an age of 212 2 ma which is interpreted to record a retrograde metamorphic event based on the ree patterns the remaining six triassic analyses can be subdivided into two groups four of them record a weighted mean age of 230 6 ma and show nearly flat hree patterns and slight negative or positive eu anomalies the last two grains are enriched hree considering their ages and the ree patterns it is suggested that they may originate from other diverse uhp rocks the triassic metamorphic zircons were detected in the laiyang group indicating that the sulu uhp rocks were exposed to the surface before the early cretaceous

the ad1315 tarawera and waiotapu eruptions new zealand contemporaneous rhyolite and hydrothermal eruptions driven by an arrested basalt dike system a series of large hydrothermal eruptions occurred across the waiotapu geothermal field at about the same prehistoric time as the ad1315 kaharoa rhyolite magmatic eruptions from tarawera volcano vents 10 20 km distant triggering of the waiotapu hydrothermal eruptions was previously attributed to displacement of the adjacent ngapouri fault the kaharoa rhyolite eruptions are now recognised as primed and triggered by multiple basalt intrusions beneath the tarawera volcano a 1000 t day pulse of co2 gas is recorded by alteration mineralogy and fluid inclusions in drill core samples from waiotapu geothermal wells this co2 pulse is most readily sourced from basalt intruded at depth and although not precisely dated it appears to be associated with the waiotapu hydrothermal eruptions we infer that the hydrothermal eruptions at waiotapu were primed by intrusion of the same arrested basalt dike system that drove the rhyolite eruptions at tarawera this dike system was likely similar at depth to the dike that generated basalt eruptions from a 17 km long fissure that formed across the tarawera region in ad1886 fault ruptures that occurred in the waiotapu area in association with both the ad1886 and ad1315 eruptions are considered to be a result rather than a cause of the dike intrusion processes

co2 discharge from the bottom of volcanic lake rotomahana new zealand 1 from april 2010 to february 2011 co2 flux surveys were performed on lake rotomahana new zealand the area has been hydrothermally active with fumaroles and sublacustrine hydrothermal activity before and since the eruption of mt tarawera in 1886 the total co2 emission from the lake calculated by sequential gaussian simulation is 549 72 t d 1 two different mechanisms of degassing diffusion through the water air interface and bubbling are distinguished using a graphical statistical approach the carbon dioxide budget calculated for the lake confirms that the main source of co2 to the atmosphere is by diffusion covering 94 5 of the lake area mean co2 flux 25 g m 2 d 1 and to a lesser extent bubbling mean co2 flux 1297 g m 2 d 1 mapping of the co2 flux over the entire lake including over lake floor vents detected during the survey correlates with eruption craters formed during the 1886 eruption these surveys also follow regional tectonic patterns present in the southeastern sector of lake rotomahana suggesting a deep magmatic source 10 km for co2 and different pathways for the gas to escape to the surface the values of 13cco2 2 88 and 2 39 confirm the magmatic origin of co2

high elevation of jiaolai basin during the late cretaceous implication for the coastal mountains along the east asian margin abstract a large body of evidence suggests that there were extensive coastal mountains along the east asian margin during the late cretaceous however current knowledge of the paleo mountains the period range and elevation is limited therefore direct paleoaltimetry is needed to validate and evaluate the paleo mountains in east asia our study area is jiaolai basin which is located at the east asian continental margin we estimate the paleoelevation of jiaolai basin during the late cretaceous using carbonate clumped isotope paleothermometry after correcting for seasonal preference latitudinal difference and secular climate change we conclude that the paleoelevation of jiaolai basin was almost certainly 2 0 km at 80 ma combined with the evidence from stratigraphy paleogeography and paleoclimatology our results suggest that the existence of coastal mountains along east asia during the late cretaceous is likely and the model of okhotomorsk east asia collision is preferred

geochronology and geochemistry of metamorphic rocks in the jiaobei terrane constraints on its tectonic affinity in the sulu orogen abstract tectonic affinity of tectono lithological units close to ultrahigh pressure metamorphic belt is a key issue for understanding the geodynamics of continental collision this is particularly so for the jiaobei terrane northeast of the dabie sulu orogenic belt in china new data from la icpms zircon u pb dating whole rock elements and nd sr isotopes and mineral o isotopes are presented for metamorphic rocks from this terrane the results place geochronological and geochemical constraints on their protolith nature and metamorphic timing and thus on its tectonic affinity to one of the two triassic collided continents the north and the south china blocks protolith ages for ttg gneiss amphibolite and mafic granulite are 2 7 2 5 and 2 4 ga respectively regional metamorphism took place extensively at 1 76 ga protolith of the ttg gneiss was generated by partial melting of mantle derived rocks at the root of a thickened crust protolith of the amphibolite was probably a product of arc like magmatism protolith of the mafic granulite was derived from a depleted mantle source both of them were locally contaminated by supracrustal materials protoliths of paragneiss and schist in the fenzishan group were mostly derived from supracrustal sources but protolith of amphibolite in the fenzishan group is of mantle derived signature unlike the uhp metaigneous rocks in the dabie sulu orogenic belt that show unusual 18 o depletion the jiaobei metamorphic rocks have basically preserved their original mantle like o isotope compositions in general the nature and timing of geological events recorded in the metamorphic rocks from the jiaobei terrane are comparable with those from the north china block rather than the south china block thus the jiaobei terrane is concluded to have tectonic affinity to the former but behave like a micro continent during the triassic continental collision the 1 76 ga regional metamorphism in the jiaobei terrane is likely related to reworking of the arc continent collisional orogen in the periphery of the north china block rather than the 1 85 ga collision event between the eastern and western north china blocks the present study lends support to the common assumption that the suture boundary between the north and south china blocks in the sulu orogen is located along the wulian yantai fault tectonic mingling along the wulian yantai fault is probably related to subduction erosion during the continental collision

a model of thick plate deformation and its application to the isostatic movements due to surface subsurface and internal loadings summary a model of thick plate deformation is presented without any restriction on stress or strain conditions in the plate an analytical solution is given for the vertical displacement of a thick elastic plate the present method is exact and applicable to 3 d plate deformation problems associated with surface subsurface and internal loadings the conventional thin plate theory which ignores the variation of vertical strain of a plate may not be appropriate to be used as a basic model to study deformation problems of the continental lithosphere since it is shown that the actual surface isostatic adjustment due to surface loading could reach an amount twice as much as predicted by thin plate theory even on a relatively thin plate with 30 km thickness and young s modulus e lo00 kbar and poisson s ratio y 0 25 the isostatic adjustment due to surface load depends on the stress condition at the lower boundary of the elastic lithosphere if there is an active mantle upwelling or downwelling force acting on the boundary then the isostatic adjustment depending on the magnitude of the mantle force is either greatly hindered or amplified to a degree that is beyond the normal prediction of isostatic movements in addition the viscous effect of mantle material on the isostatic movements is shown to be negligible on geological time scales if the mantle viscosity is below ld4poise it is also shown that the airy isostasy of the total sediment load in a surface depression with small wavelength could be achieved only if a considerable period of geological time is allowed for the stress relaxation of viscoelastic or viscous material in the lithosphere the rheological property of the continental lithosphere has a significant effect on basin subsidence caused by sediment loading alone while pure elastic lithosphere restricts surface basin development because of the strong basement support throughout the evolution history

co2 and he degassing at el chichon volcano chiapas mexico gas flux origin and relationship with local and regional tectonics during 2007 2008 three co2 flux surveys were performed on el chichon volcanic lake chiapas mexico with an additional survey in april 2008 covering the entire crater floor including the lake the mean co2 flux calculated by sequential gaussian simulation from the lake was 1 190 march 2007 730 december 2007 and 1 134 g m 2 day 1 april 2008 with total emission rates of 164 9 5 march 2007 59 2 5 december 2007 and 109 6 6 t day 1 april 2008 the mean co2 flux estimated from the entire crater floor area was 1 102 g m 2 day 1 for april 2008 with a total emission rate of 144 5 9 t day 1 significant change in co2 flux was not detected during the period of survey and the mapping of the co2 flux highlighted lineaments reflecting the main local and regional tectonic patterns the 3he 4he ratio as high as 8 1 ra for gases in the el chichon crater is generally higher than those observed at the neighbouring transmexican volcanic belt and the central american volcanic arc the co2 3he ratios for the high 3he 4he gases tend to have the morb like values 1 41 109 and the co2 3he ratios for the lower 3he 4he gases fall within the range for the arc type gases the high 3he 4he ratios the morb like co2 3he ratios for the high 3he 4he gases and high proportion of morb co2 m 25 15 at el chichon indicate a greater depth for the generation of magma when compared to typical arc volcanoes

a technique for incorporating geothermal gradients and nonlinear creep into lithospheric flexure models a beam flexure model for the lithosphere which employs a nonlinear viscous creep constitutive relation has been developed for time dependent flexure caused by surficial loads the lithosphere is buoyantly supported by the underlying asthenosphere which is modeled as an elastic winkler foundation creep is highly dependent on temperature and melting point which in turn vary with depth these factors are incorporated into the beam lithospheric model by using weertman s constitutive relation for creep of rock at elevated temperature a typical value of the creep power n in the weertman equation is 3 for rock but the value of n may be varied in the model the governing nonlinear partial differential equations for moment and deflection are solved by an analytical procedure for the spatial coordinate and by a numerical marching procedure in the time coordinate stresses in the lithosphere are also evaluated with special attention given to an iterative technique for locating the neutral axis which will not be at the centroid because of the nonlinearity and the geothermal gradient

an unrecognized major collision of the okhotomorsk block with east asia during the late cretaceous constraints on the plate reorganization of the northwest pacific abstract interactions at plate boundaries induce stresses that constitute critical controls on the structural evolution of intraplate regions however the traditional tectonic model for the east asian margin during the mesozoic invoking successive episodes of paleo pacific oceanic subduction does not provide an adequate context for important late cretaceous dynamics across east asia including continental scale orogenic processes significant sinistral strike slip faulting and several others the integration of numerous documented field relations requires a new tectonic model as proposed here the okhotomorsk continental block currently residing below the okhotsk sea in northeast asia was located in the interior of the izanagi plate before the late cretaceous it moved northwestward with the izanagi plate and collided with the south china block at about 100 ma the indentation of the okhotomorsk block within east asia resulted in the formation of a sinistral strike slip fault system in south china formation of a dextral strike slip fault system in north china and regional northwest southeast shortening and orogenic uplift in east asia northeast striking mountain belts over 500 km wide extended from southeast china to southwest japan and south korea the peak metamorphism at about 89 ma of the sanbagawa high pressure metamorphic belt in southwest japan was probably related to the continental subduction of the okhotomorsk block beneath the east asian margin subsequently the north northwestward change of motion direction of the izanagi plate led to the northward movement of the okhotomorsk block along the east asian margin forming a significant sinistral continental transform boundary similar to the san andreas fault system in california sanbagawa metamorphic rocks in southwest japan were rapidly exhumed through the several kilometer wide ductile shear zone at the lower crust and upper mantle level accretionary complexes successively accumulated along the east asian margin during the jurassic early cretaceous were subdivided into narrow and subparallel belts by the upper crustal strike slip fault system the departure of the okhotomorsk block from the northeast striking asian margin resulted in the occurrence of an extensional setting and formation of a wide magmatic belt to the west of the margin in the campanian the block collided with the siberian margin in northeast asia at about 77 ma a new oceanic subduction occurred to the south of the okhotomorsk block ending its long distance northward motion based on the new tectonic model the abundant late archean to early proterozoic detrital zircons in the cretaceous sandstones in kamchatka southwest japan and taiwan are interpreted to have been sourced from the okhotomorsk block basement which possibly formed during the late archean and early proterozoic the new model suggests a rapidly northward moving okhotomorsk block at an average speed of 22 5 cm yr during 89 77 ma it is hypothesized that the okhotomorsk east asia collision during 100 89 ma slowed down the northwestward motion of the izanagi plate while slab pull forces produced from the subducting izanagi plate beneath the siberian margin redirected the plate from northwestward to north northwestward motion at about 90 89 ma

volcanic lake systematics ii chemical constraints abstract a database of 373 lake water analyses from the published literature was compiled and used to explore the geochemical systematics of volcanic lakes binary correlations and principal component analysis indicate strong internal coherence among most chemical parameters compositional variations are influenced by the flux of magmatic volatiles and or deep hydrothermal fluids the chemistry of the fluid entering a lake may be dominated by a high temperature volcanic gas component or by a lower temperature fluid that has interacted extensively with volcanic rocks precipitation of minerals like gypsum and silica can strongly affect the concentrations of ca and si in some lakes a much less concentrated geothermal input fluid provides the mineralized components of some more dilute lakes temporal variations in dilution and evaporation rates ultimately control absolute concentrations of dissolved constituents but not conservative element ratios most volcanic lake waters and presumably their deep hydrothermal fluid inputs classify as immature acid fluids that have not equilibrated with common secondary silicates such as clays or zeolites many such fluids may have equilibrated with secondary minerals earlier in their history but were re acidified by mixing with fresh volcanic fluids we use the concept of degree of neutralization as a new parameter to characterize these acid fluids this leads to a classification of gas dominated versus rock dominated lake waters a further classification is based on a cluster analysis and a hydrothermal speedometer concept which uses the degree of silica equilibration of a fluid during cooling and dilution to evaluate the rate of fluid equilibration in volcano hydrothermal systems

boiling and dilution in the shallow portion of the waiotapu geothermal system new zealand abstract the waiotapu geothermal system is the largest in terms of surface extent and heat flow 17 km2 and 600 mw respectively of the 20 major geothermal systems in the taupo volcanic zone new zealand two extinct dacite cones and a rhyolite dome rise about 500 m above the waiotapu valley the majority of thermal features occurs in the valley over a relief of only 100 m and lies within coincident apparent resistivity and 30 m depth thermal anomalies thermal features comprise near neutral ph chloride springs often boiling acid sulfate springs and mud pools and mixed waters the latter including both bicarbonate chloride and acid sulfate chloride springs the majority of the sulfate discharges to the surface in the northern higher altitude area while most chloride that reaches the surface does so in the southern portion of the system comparison of measured and calculated surface chloride flux the latter from measured heat flow and reservoir chloride concentrations indicates that at least half of the deep chloride does not discharge at the surface but flows laterally to the south at shallow depths mixing with groundwater the composition of well discharges indicates a shallow 400 m reservoir of chloride fluid about 1350 mg cl kg at 230 c is diluted by a co2 rich steam heated water nil chloride at about 160 c the latter located on the margins of the system this same dilution trend is apparent from the compositional variation and k na and k mg geothermometry of hot spring waters however there is chemical and stable isotope evidence from hot springs that cold groundwater also acts as a diluent at shallow levels and very near the surface steam heated acid sulfate waters mix with the upflow boiling of the deep chloride fluids prior to dilution results in the stabilization of k feldspar in contrast dilution at shallower depths by the steam heated waters both co2 rich and acid sulfate leads to the water compositions initially shifting to k mica and interstratified clay stability and to kaolinite stability with further dilution and temperature decrease the composition and distribution of these fluids are consistent with alteration mineralogy and zonation observed in drill core although boiling occurs at deeper levels and up to the surface in the upflow zone at waiotapu mixing is also common and is the dominant process on the margin and in the near surface portion of the system boiling of deep chloride fluid is very common in the upper 1 2 km of the upflow zone of most geothermal systems though it may be quenched by mixing with marginal waters either cold groundwater in high relief terrane or steam heated waters in areas of lower relief co2 rich steam heated waters are common on the margins of systems and will generally underlie the near surface acid sulfate steam heated waters interaction with co2 rich waters will form k mica and interstratified clays while acid sulfate waters cause kaolinite and even alunite to form the former assemblage is commonly associated with typical low sulfidation epithermal gold mineralization as wallrock alteration where gold bearing veins comprise adularia and illite in contrast kaolinite is rare and alunite absent from a direct spatial and genetic association with gold mineralization in this environment this implies that mixing of the deep neutral ph chloride fluid with surficial acid sulfate waters does not commonly lead to ore grade gold deposition mixing with and cooling by co2 rich steam heated waters leads to clay stability accounting for the large halos of clay alteration and low grade metal anomalies which often surround veins of high gold grade in contrast mixing with surficial acid sulfate waters is unlikely to cause precious metal mineralization because the chloride fluids have already lost the majority of their gold through deeper boiling and dilution

silurian clastic sediments in the north qilian shan nw china chemical and isotopic constraints on their forearc provenance with implications for the paleozoic evolution of the tibetan plateau abstract the north qilian shan is an accretion collision orogenic belt in the northeastern margin of the tibetan plateau that connects the north china plate to the north with the tethyan orogenic assemblage to the south its early paleozoic temporal spatial tectonic evolution has been extensively studied but the nature and tectonic setting of its silurian deposition is poorly understood our new petrological analysis suggests that the clast composition of fan conglomerates is complex in the danbanshan and zhongdabanshan sections abundant lenticular conglomerate beds contain mainly subrounded rounded metamorphic clasts whereas the tongziba and haichaoba sections contain volcanic chert limestone ultramafic and granitoid clasts however in the sunan area clast types are relatively simple dominated by basalt and granitoids and at tongziba gabbro and basalt clasts are subrounded and angular indicating two different types of provenance ultramafic limestone and abundant chert clasts in the haichaoba and tonghe conglomerates indicate an ophiolitic source whereas subrounded rounded quartzite and granitoid gneiss clasts were probably derived from the central qilian basement geochemical data from the volcanic and granitoid clasts suggest an arc related source and their zircon u pb ages of 515 429 ma suggest that the arc magmatism did not end in the mid silurian sandstone petrology and detrital modes suggest that the silurian sediments were deposited in a forearc basin paleogeographic reconstructions inferred from nnw nne paleocurrent data indicate that an island arc was present off the southern margin of the silurian basin and that southward subduction of oceanic crust between north china and the qilian shan was active or continued in the silurian

timing of metamorphism in the paleoproterozoic jiao liao ji belt new shrimp u pb zircon dating of granulites gneisses and marbles of the jiaobei massif in the north china craton abstract the paleoproterozoic jiao liao ji belt lies in the eastern block of the north china craton with its southern segment extending across the bohai sea into the jiaobei massif high pressure pelitic and mafic granulites have been recently recognized in the paleoproterozoic jingshan group jiaobei massif new shrimp u th pb geochronology combined with cathodoluminescence cl imaging of zircon has been applied to the determination of the timing of the metamorphism of the high temperature and high pressure granulites and associated gneisses and marbles metamorphic zircons in these high pressure granulites gneisses and marbles occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores metamorphic zircons are all characterized by nebulous zoning or being structureless with high luminescence and relatively low th u values metamorphic zircons from two high pressure mafic granulites yielded 207pb 206pb ages of 1956 41 ma and 1884 24 ma one metamorphic zircon from a garnet sillimanite gneiss also gave an apparent 207pb 206pb age of 1939 15 ma these results are consistent with interval of ages of c 1 93 1 90 ga already obtained by previous studies for the north and south liaohe groups and the laoling group in the northern segment of the jiao liao ji belt metamorphic zircons from a high pressure pelitic granulite and two pelitic gneisses yielded weighted mean 207pb 206pb ages of 1837 8 ma 1821 8 ma and 1836 8 ma respectively two diopside olivine phlogopite marbles yielded weighted mean 207pb 206pb ages of 1817 9 ma and 1790 6 ma these paleoproterozoic metamorphic ages are largely in accordance with metamorphic ages of c 1 85 ga produced from the ji an group in the northern segment of the jiao liao ji belt and c 1 86 1 80 ga obtained for the high pressure pelitic granulites from the jingshan group in the southern segment as this metamorphic event was coeval with the emplacement of a type granites in the jiao liao ji belt and its adjacent areas it is interpreted as having resulted from a post orogenic or anorogenic extensional event

sedimentology geodynamics resources and environments of china and adjacent areas a special issue in memory of professor shu sun for his scientific contributions and academic services

axisymmetric finite element analysis of an elastic lithosphere subjected to thermal loading summary an axisymmetric finite element was used to model the lithosphere as an infinite 40 km thick circular elastic plate on an elastic foundation asthenosphere subjected to concentrated thermal loading thermal loading is produced by a point heat source of 4 184 lo8 watts located 60 km beneath the plate within the asthenosphere increased nodal temperatures within the lithospheric finite element mesh were obtained from a solution to the steady state heat conduction equation for a point source in a semi infinite half space vertical as well as radial thermal expansion coefficients of 1 33 x lo k were utilized in the solutions thermoelastic loads as well as isostatic uplift forces are applied as nodal loads in the finite element lithosphere model thermoelastic loads are produced from uneven heating of the lithosphere and differential expansion isostatic uplift forces result from radial expansion and the diminished density of heated lithosphere columns uplift of the lithosphere due to the point heat source and vertical expansion is reduced because of radial expansion and flexure this occurs because material at the base of the lithosphere is closer to the point heat source and experiences greater radial expansion for sediment infdl thermoelastic loading reduces the surface uplift produced by isostatic uplift forces from 3 11 to 192m thermoelastic lithosphere models yield significantly higher radial stress profiles than density models without thermoelastic stresses the neutral plane for radial stress is displaced towards the surface in the thermoelastic models due to greater radial expansion of basal lithosphere material which is closer to the point heat source the finite element model has several advantages over the classical thin plate approach stresses and strains can be evaluated at any point within the lithosphere this capability was used in this study to determine vertical lithosphere expansion thickening non linear variation of stress with depth and the stress neutral plane position

deciphering the early cretaceous transgression in coastal southeastern china constraints based on petrography paleontology and geochemistry abstract the occurrence of a transgression in coastal southeastern china during the early cretaceous has been debated this question was addressed here through the use of petrographic paleontological and geochemical studies of ten representative lower cretaceous outcrop sections in the study area the petrographic results suggest that limestones in the shipu section of northeastern zhejiang province were predominantly deposited in a tidal flat environment the paleontological study reveals marine red and brown algae in black shales and mudstones of the yong an and chong an sections of the western fujian province in the biomarker study of black shales and mudstones the widespread detection of gammacerane in combination with ratios of tricyclic terpane c 26 c 25 35 s c 34 s 0 8 and hopane c 29 c 30

intense magmatic degassing through the lake of copahue volcano 2013 2014 here we report on the first assessment of volatile fluxes from the hyperacid crater lake hosted within the summit crater of copahue a very active volcano on the argentina chile border our observations were performed using a variety of in situ and remote sensing techniques during field campaigns in march 2013 when the crater hosted an active fumarole field and in march 2014 when an acidic volcanic lake covered the fumarole field in the latter campaign we found that 566 to 1373 t d 1 of so2 were being emitted from the lake in a plume that appeared largely invisible this combined with our derived bulk plume composition was converted into flux of other volcanic species h2o 10989 t d 1 co2 638 t d 1 hcl 66 t d 1 h2 3 3 t d 1 and hbr 0 05 t d 1 these levels of degassing comparable to those seen at many open vent degassing arc volcanoes were surprisingly high for a volcano hosting a crater lake copahue s unusual degassing regime was also confirmed by the chemical composition of the plume that although issuing from a hot 65 c lake preserves a close to magmatic signature eq3 6 models of gas water rock interaction in the lake were able to match observed compositions and demonstrated that magmatic gases emitted to the atmosphere were virtually unaffected by scrubbing of soluble s and cl species finally the derived large h2o flux 10 988 t d 1 suggested a mechanism in which magmatic gas stripping drove enhanced lake water evaporation a process likely common to many degassing volcanic lakes worldwide

cyclic processes and factors leading to phreatic eruption events insights from the 25 september 2007 eruption through ruapehu crater lake new zealand abstract a dangerous block ash eruption occurred without warning from ruapehu crater lake on 25 september 2007 ending a 6 month period of temperature decline in the lake the northerly directed blast sent ballistics of up to 2 m diameter more than 2 km from the source the ejecta comprised a variety of volcano lacustrine lithologies many showing evidence of intense hydrothermal alteration petrographic studies of the ballistics reveal numerous examples of pores vesicles being filled with assemblages of elemental sulphur anhydrite pyrite and natroalunite and many ballistics exuded liquid sulphur from their pores during cooling at atmospheric pressure up to 5 of the ash was comprised of fine grained juvenile glass material confirming the presence of magma in the shallow vent environment a long recognised characteristic of this volcano is the thermal cycling behaviour of the crater lake behaviour which has remained effectively unchanged through two magmatic eruption events in 1945 and in 1995 96 airborne measurements of co2 and so2 flux from the volcano since 2003 show a strong positive correspondence with temperature cycling in the lake pointing to a definitive link between heat and mass discharge through the system low so2 emission rates and c s mole ratios 30 were typical of the period 2003 to early 2007 and appear to reflect vigorous scrubbing of s gases in the hydrothermal system during this time to better understand the chemical and physical processes operating in this very dynamic volcanic hydrothermal system and its propensity to develop potentially dangerous hydrothermal seals we have developed an integrated finite difference tough2 heat mass transport simulation of the hydrothermal environment the model which is constrained by observed heat and mass flux characteristics of the volcano demonstrates the transient nature of the heating cycles on the vent lake system of particular interest is the role of co2 as a relatively inert pressure transmitting medium in the hydrothermal environment seal formation was simulated using the reactive transport code x1t which showed that condensation of magmatic vapour into a highly porous medium of andesitic composition leads to rapid formation of an elemental sulphur anhydrite natroalunite mineral assemblage and a drastic reduction in permeability we suggest that since the 1995 96 vent clearing eruptions a shroud of elemental sulphur and other alteration phases formed along the margins of the 2 phase liquid vapour region enclosing the conduit this effectively seals the upper portion of the vent from the adjacent hydrostatically controlled environment and allows for development of pressurised vapour static gas columns beneath the northern and central vents

the lake nyos gas disaster chemical and isotopic evidence in waters and dissolved gases from three cameroonian crater lakes nyos monoun and wum abstract to better understand the cause of the nyos gas disaster of august 21 1986 we conducted geochemical and limnological surveys in october 1986 of three lakes nyos monoun and wum which are located in the cameroon volcanic zone that is characterized by a prevalence of young alkaline basalts and basanitoids lake wum was studied as a non active control co2 is dissolved in significant concentrations about 1 5 of saturation in gas active lakes nyos and monoun but is virtually absent in lake wum stable isotopic ratios of total dissolved carbon 13c 3 for nyos and 5 5 for monoun and of helium 5 7 ratm for nyos and 3 6 ratm for monoun indicate a mantle origin of these gases however so42 and cl concentrations are found to be very low concentrations of dissolved chemical species like fe2 mg2 ca2 and hco3 are high in the two gas active lakes whereas they are very low in the gas inactive lake high salinities in the gas active lakes are probably due to dissolution of indigenous mafic rocks and transported lateritic soil in acidic co2 rich warm water the gas active lakes are characterized by increasing temperature and salinity with increasing depth indicating an active influx of heat and dissolved materials at the bottom density estimates show that the lake water is stably stratified in spite of the inverse temperature profile of the lakes on account of dissolved chemical species the concentrations of dissolved carbonate species co2 aq and hco3 are positively correlated with those of ionic dissolved species indicating their common occurrence in the bottom water the august 1986 gas bursts from lake nyos were most likely caused by rapid exsolution of dissolved co2 within the lake an explosive process such as a phreatic eruption or a co2 gas jetting from beneath the bottom is unlikely because of low concentrations of cl and so42 no oxygen isotopic shift low turbidity and no reported perturbation of the bottom sediments exsolution of co2 bubbles could occur if co2 saturated bottom water was displaced upwards by an increased influx of high salinity water from the bottom during the rainy season exsolution of co2 at the upper layers was possibly accelerated by upwelling of a two phase fluid co2 bubbles and solution a mechanism known as a pneumatic lift pump resulting in discharge of a large amount of co2 gas the h2s concentration in the gas cloud must have been kept far below the lethal level because of a high fe2 concentration of the lake water

earthquake swarm activity highlights crustal faulting associated with the waimangu rotomahana mt tarawera geothermal field taupo volcanic zone abstract the waimangu rotomahana mt tarawera geothermal field wrtgf in the taupo volcanic zone new zealand experiences frequent but sporadic earthquake swarms with durations of less than 1 day here we examine detailed locations of the seismic activity using precise double difference relative location techniques we utilize a combination of cross correlation derived arrival times and catalogue based arrival times from 582 earthquakes recorded in the area between 2004 and 2015 for the relocation analysis the new earthquake locations highlight a 6 km long ne sw lineation which we infer to represent a sub surface fault that extends along the northern side of waimangu geothermal system and the north western end of lake rotomahana we suggest that this structural feature acts as a permeable pathway for aqueous fluid and co2 release up to the surface geothermal field and lake rotomahana from a deeper magmatic source

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

global co2 emission from volcanic lakes the global co 2 discharge from subaerial volcanism has been estimated at 300 mt yr 1 however estimates of co 2 emissions from volcanic lakes have not been considered in order to improve this information extensive research on co 2 emissions of volcanic lakes worldwide has been performed the observed normalized average co 2 emission rates increase from alkaline 5 5 t km 2 d 1 to neutral 201 2 t km 2 d 1 to acid 614 2 t km 2 d 1 in volcanic lakes taking into account 1 normalized co 2 emission rates 2 the number of volcanic lakes in the world 769 and 3 the fraction and average areas of the investigated alkaline neutral and acid volcanic lakes the estimated global co 2 emission from volcanic lakes is 117 19 mt yr 1 with 94 17 mt yr 1 as deep seated co 2 this study highlights the importance of a revision of the actual global co 2 discharge from subaerial volcanism

late cretaceous provenance change in the jiaolai basin east china implications for paleogeographic evolution of east asia abstract east china experienced crustal extensions during the early cretaceous and the latest cretaceous cenozoic for a long time previous studies have recognized a short lived compressional event between these two extensional regimes during the early late cretaceous but not much attention has been paid to it although it may shed new light on the tectonic evolution of east asia and the mechanism of the north china craton destruction the jiaolai basin located at the margin of east china consists of a thick succession of cretaceous sedimentary rocks and thus may help in further interpreting the mechanism and influence of the short lived compressional event here we apply integrated sedimentological methods to sandstone samples of both the lower cretaceous laiyang group and upper cretaceous wangshi group our findings suggest that there was a provenance change in the jiaolai basin from the early cretaceous granitic and metamorphic rock origin to the late cretaceous basic intermediate volcanic origin combined with the zircon u pb ages we conclude that the provenance change was caused by the uplift of the coastal mountains along the east asian margin from the relatively distal sulu orogenic belt and jiaobei terrane during the early cretaceous to the intra basinal volcanic rocks of the qingshan groupduring the late cretaceous after careful evaluation of the provenance histories orogenic exhumations widespread unconformities and paleoclimate changes that occurred in sedimentary basins both along the east asian margin and in the hinterland we finally estimate the possible range of influence and extent of the short lived compression event during the early late cretaceous

tarawera 1886 new zealand a basaltic plinian fissure eruption abstract new zealand s biggest and most destructive volcanic eruption of historical times was that of tarawera in 1886 the resulting scoria fall has a dispersal very similar in extent to that of the vesuvius a d 79 pumice fall and is one of the few known examples of a basaltic deposit of plinian type a new estimate of the volume 2 km 3 is significantly greater than previous estimates the basalt came mainly from a 7 km length of fissure and emission and exit velocity were fairly uniform along at least 4 km of it this is one of the few documented examples of a plinian eruption from a fissure vent primary welding of the scoria fall resulted where the accumulation rate exceeded about 250 mm min 1 a model of the eruption dynamics is proposed which leads to an estimate of 28 km for the height of the eruption cloud and implies a magma volatile fraction of 1 5 3 violent phreatic explosions occurred in the southwestern extension of the fissure across the rotomahana geothermal field and it is thought that some of the water responsible for the power of the plinian eruption came from this source though its amount was not sufficient to turn the eruption into a phreatoplinian one

reconstruction of the geology and structure of lake rotomahana and its hydrothermal systems from high resolution multibeam mapping and seismic surveys effects of the 1886 tarawera rift eruption abstract present day lake rotomahana is one of the two focal points of the most destructive eruption in new zealand s historical record i e that of mt tarawera on 10 june 1886 with devastating loss of life and presumed destruction of the iconic pink and white terraces that adorned the margins of the lake basaltic dikes are considered to have ascended near surface in the area intruding into hydrothermally altered and water saturated ground beneath the existing lake the consequential hydrothermal and phreatomagmatic eruptions ejected 0 5325 km 3 of material from the lakefloor and below plastering the nearby landscape for several kilometers with mud and other debris the eruption buried the natural outlet of the lake with the bottom of the craters becoming filled by water within months and completely concealed from view within years today lake rotomahana has depths up to 118 m high resolution 0 5 m bathymetric mapping when combined with a 2 d seismic reflection survey enables us to see details of the maar craters on the lakefloor including those parts subsequently buried by sediment the large rotomahana crater described by workers immediately after the eruption measures 2 5 km in diameter near its southwestern end and excavated ground to 155 m below present day lake level the vent system as revealed by the present study forms an array of right stepping dextral craters with the main crater being host to two sub craters rotomahana west crater and rotomahana east crater today buried beneath the lakefloor and which are in filled by 36 and 37 m of sediment respectively subordinate craters along the same 057 tarawera rift trace include hochstetter crater 11 m of infill waingongongongo crater 14 m and rotomakariri crater 26 m these craters host a total 0 0268 km 3 of sediment other features highlighted by the bathymetric data include craters not filled by sediment sediment fan deltas volcanic ridges and dikes submerged wave cut terraces formed during times of lower lake levels and gas pockmarks all either related to the 1886 eruptive episode or post eruption hydrothermal and erosional processes application of results from bubble plume co 2 flux magnetic and heat flux surveys of lake rotomahana to this study when combined with regional earthquake relocation analysis and broadband magnetotelluric data suggest an explanation in terms of a magmatic heat source located south of waimangu and a corresponding convective water heat transport system extending thence to beneath the western end of the lake a holistic approach has provided a coherent context for the eruption and its effect on the historical pink and white terraces hydrothermal system that appears to have been the eastern most extension of a larger system that lay beneath the waimangu area before the eruption the newly named pink terraces hydrothermal system 1 5 km 2 is a continuation of the historical hydrothermal activity that was concentrated on the western shores of the old lake and together with the formation of the new post 1886 patiti hydrothermal system 1 km 2 located sw of patiti island mark the two distinct areas of hydrothermal activity in the lake today

sediment generation in humid mediterranean setting grain size and source rock control on sediment geochemistry and mineralogy sila massif calabria abstract grain size control on sediment composition is investigated in modern proximal sediment from the sila massif where basic to felsic intrusive rocks are exposed in a mediterranean humid temperate upland climate samples were taken from small creeks and weathering profiles from three areas reflecting different bed rock compositions samples were separated into eleven grain size fractions from very coarse sand to clay and analyzed by i x ray fluorescence for chemical composition and ii x ray diffraction and mineral liberation analysis for mineralogical composition the chemical composition vs grain size relations were modeled by compositional linear regression mineralogical composition of selected samples is used to substantiate the interpretations based on geochemistry results reveal a high degree of chemical weathering with chemical index of alteration cia up to 92 high cia values are restricted to the fine grained fractions while sand sized sediment average at low to moderate cia values 60 although strongly weathered the three sample suites reflecting basic to felsic plutonic bed rock can be effectively discriminated across all grain size classes using trace elements such as v rb and sr linear trend modeling and mineralogical data reflect similar patterns for all sample suites implying similar processes independent of source rock composition this includes overall decrease of quartz and k feldspar over the full grain size range from very coarse sand to clay which is contrasted by overall increase of sheet silicates from coarse to fine among the latter increase of clay minerals strongly outpaces the increase of micas in silt to clay fractions a more complex behavior is shown by plagioclase which is most abundant in intermediate grain size fractions for all sample suites this is likely caused by initial hydrolysis along cleavage and twinning planes and subsequent breakage of plagioclase crystals into smaller fragments towards finer grain size intense hydrolysis has destroyed most feldspars

a forward approach to the problem of nonlinear viscoelasticity and the thickness of the mechanical lithosphere the physical significance of the mechanical lithosphere is clarified using a nonlinear maxwell flexure model this model reconciles high temperature creep data for rock with the observed long term strength of the mechanical lithosphere an approximate correspondence is established between the nonisothermal maxwell model and an elastic flexure model to define an effective lithosphere thickness he the model calculations are essentially forward since he does not depend in a significant way upon the nominal or prescribed value of beam thickness depending rather upon such variables as temperature and creep activation energy the effective thickness of the maxwell model though a function of time is stable enough over appropriate time scales to explain the long term integrated strength of the lithosphere the strength index is defined as the ratio of axial stress to the axial stress that would be present in a purely elastic fiber suffering the same strain the base of the effective lithosphere is marked by a critical isopleth of strength c 0 3 this critical level though not its position is independent of time since loading the strength index also maps out zones of predominant rheology the narrowness of the transition zone between the elastic lithosphere and the viscous asthenosphere explains the success of the elastic plate in modeling many examples of lithosphere flexure the elastic plate approximation may apply best where the lithosphere is relatively young and hot isolated weak zones in the continental crust may or may not weaken the lithosphere as a whole depending upon the distribution of these zones and the manner in which they deform in general such weakening is likely to be most effective when the base of the crust occurs at midlithospheric depths

a novel heat flux study of a geothermally active lake lake rotomahana new zealand abstract a new technique for measuring conductive heat flux in a lake was adapted from the marine environment to allow for multiple measurements to be made in areas where bottom sediment cover is sparse or even absent this thermal blanket technique pioneered in the deep ocean for use in volcanic mid ocean rift environments was recently used in the geothermally active lake rotomahana new zealand heat flow from the lake floor propagates into the 0 5 m diameter blanket and establishes a thermal gradient across the known blanket thickness and thereby provides an estimate of the conductive heat flux of the underlying terrain this approach allows conductive heat flux to be measured over a spatially dense set of stations in a relatively short period of time we used 10 blankets and deployed them for 1 day each to complete 110 stations over an 11 day program in the 6 3 km lake results show that lake rotomahana has a total conductive heat flux of about 47 mw averaging 6 w m2 over the geothermally active lake the western half of the lake has two main areas of high heat flux 1 a high heat flux area averaging 21 3 w m2 along the western shoreline which is likely the location of the pre existing geothermal system that fed the famous pink terraces mostly destroyed during the 1886 eruption 2 a region southwest of patiti island with a heat flux averaging 13 1 w m2 that appears to be related to the explosive rift that formed the lake in the 1886 tarawera eruption a small rise in bottom water temperature over the survey period of 0 01 c day suggests the total thermal output of the lake is 112 132 mw and when compared to the conductive heat output suggests that 18 42 of the total thermal energy is by conductive heat transfer