the metal oxide fraction of pelagic sediment in the equatorial north pacific ocean a source of metals in ferromanganese nodules abstract pelagic sediment recovered at domes site a in the equatorial north pacific 151 w 9 15 n consists of a surface homogeneous layer approximately 10 cm thick overlying a strongly mottled layer that is lighter in color the radiolarian composition of both units is quaternary in areas where this sediment was only a few centimeters thick the underlying sediment was early tertiary clay mineralogy and major oxide composition of the two quaternary sediments are uniform their similarity to continental shale suggests that the sediment has a terrigenous source clay mineralogy and major oxide composition of the tertiary sediment also are uniform although they differ markedly from the quarternary sediment in contrast to the major oxides concentrations of mn co cu and ni soluble in hydroxylamine hydrochlorideacetic acid are strongly different in the surface and subsurface quaternary sediment mn and ni exhibit pronounced depletions in the subsurface sediment ni slightly more than mn cu is also depleted in the subsurface sediment but less than mn it is also depleted in the subsurface tertiary sediment whereas the mn concentration remains high concentration of co relative to mn increases into the subsurface quaternary sediment to a constant co mn ratio of 3 10 2 the trivalent ree the ree exclusive of ce and fe exhibit little down core variation distribution of elements in these sediments is closely related to their concentration in associated surface ferromanganese nodules the nodules are of two distinct types those from the area where the quaternary sediment is relatively thick have mno2 as the dominant manganese mineral the ratios of ni mn cu mn and fe mn in these nodules approximate the corresponding ratios of the soluble fraction of surface sediment todorokite is the dominant mineral of nodules recovered from areas where the quaternary sediment is thin relatively high cu mn ni mn and low fe mn ratios of these nodules mirror differences between the soluble fraction of surface and subsurface quaternary sediment these compositional trends of sediment and nodules at domes site a reflect a diagenetic origin for the todorokite nodules and a predominantly hydrogenous origin for the mno2 nodules

cyclic magnetite dissolution in pleistocene sediments of the abyssal northwest pacific ocean evidence for glacial oxygen depletion and carbon trapping the carbonate free abyss of the north pacific defies most paleoceanographic proxy methods and hence remains a blank spot in ocean and climate history paleomagnetic and rock magnetic geochemical and sedimentological methods were combined to date and analyze seven middle to late pleistocene northwest pacific sediment cores from water depths of 5100 to 5700 m besides largely coherent tephra layers the most striking features of these records are nearly magnetite free zones corresponding to glacial marine isotope stages miss 22 12 10 8 6 and 2 magnetite depletion is correlated with organic carbon and quartz content and anticorrelated with biogenic barite and opal content within interglacial sections and mid pleistocene transition glacial stages mis 20 18 16 and 14 magnetite fractions of detrital volcanic and bacterial origin are all well preserved such alternating successions of magnetic iron mineral preservation and depletion are known from sapropel marl cycles which accumulated under periodically changing bottom water oxygen and redox conditions in the open central northwest pacific ocean the only conceivable mechanism to cause such abrupt change is a modified glacial bottom water circulation during all major glaciations since mis 12 oxygen depleted antarctic bottom water aabw sourced bottom water seems to have crept into the abyssal northwest pacific below 5000 m depth thereby changing redox conditions in the sediment trapping and preserving dissolved and particulate organic matter and in consequence reducing and dissolving both biogenic and detrital magnetite at deglaciation a downward progressing oxidation front apparently remineralized and released these sedimentary carbon reservoirs without replenishing the magnetite losses

sedimentation at manop site h eastern equatorial pacific over the past 400 000 years climatically induced redox variations and their effects on transition metal cycling gravity cores recovered from manganese nodule project site h 6 33 n 92 49 w show marked downcore variations in the abundance of calcium carbonate organic carbon opal manganese and other components deposited over the past 400 000 years variations in the downcore abundance of organic carbon which ranges from 0 2 to 1 0 can be used to hindcast redox conditions in the surface sediments over this time the results indicate that the depth to the manganese redox boundary varied from about 5 to 25 cm below the seafloor during four major cycles downcore variations in solid phase mn ni and cu can be produced by such changes in redox conditions a model which predicts that solid phase mn can be trapped and buried when the mn redox boundary migrates rapidly upward is consistent with the observed organic carbon and mn records and supports the reconstructed redox variations the history of redox variations at site h can be explained by changes with time in surface water productivity major productivity variations at the site occur over 100 kyr cycles with relatively higher productivity occurring during glacial stages thus quaternary climate changes influence surface water productivity redox conditions in sediments and the cycling of transition metals

genesis of adakitic granitoids by partial melting of thickened lower crust and its implications for early crustal growth a case study from the huichizi pluton qinling orogen central china abstract adakitic rocks are often considered as a key to deciphering the genesis of archean ttgs and the early crustal growth granites from the huichizi pluton in the north qinling nq unit have high sr y and la yb n ratios similar to adakites their relatively high sio 2 k 2 o and na 2 o and very low mgo cr and ni contents are in the range of high sio 2 adakites and early archean ttgs and are compositionally similar to experimental melts derived from metabasalt sources new sims zircon u pb dating constrains the emplacement age of the huichizi pluton at 422 5 ma rock samples from the huichizi pluton have e nd t and zircon e hf t values similar to the neoproterozoic metabasalts in the nq unit in combination with their normal mantle like 18 o zir values these adakites are best explained by partial melting of the neoproterozoic mafic crustal root due to subduction of the shangdan ocean regional geological data suggest that the crust was probably thickened by a ca 490 ma arc collision process prior to the emplacement of the huichizi pluton our results confirm that underplating of mafic magma and its subsequent fusion triggered by slab subduction under high pressure conditions could be an important mechanism for the formation of early continental crust

precessionally forced productivity variations across the equatorial pacific 1 measurements of combustion oxygen demand cod in two sediment cores provide a record of paleoproductivity driven by surface ocean dynamics in the equatorial eastern and western pacific for the past 400 000 years the cod time series are well correlated with each other over this time span and show pronounced precessionally forced peaks of higher productivity during globally colder periods the phase of this signal in the two cores is identical to within chronological uncertainties suggesting a common insolation forcing mechanism for the upper ocean across the equatorial pacific cod is also in phase with the precessionally forced component of global ice volume as indicated by oxygen isotopes and with atmospheric methane in the vostok ice core these relationships imply that the cod relative paleoproductivity index provides an important diagnostic measure of the mechanisms of tropical ocean dynamics and climate change

zircon u pb ages ree concentrations and hf isotope compositions of granitic leucosome and pegmatite from the north sulu uhp terrane in china constraints on the timing and nature of partial melting granitic leucosome and pegmatite are widely distributed within biotite bearing orthogneiss in the northern part of the sulu ultrahigh pressure uhp metamorphic terrane eastern china a combined study of mineral inclusions cathodoluminescence cl images u pb shrimp dates and in situ trace element and lu hf isotope analyses of zircons provided insight into the nature and timing of partial melting in these rocks zircon grains separated from biotite bearing orthogneiss typically have three distinct domains 1 pre metamorphic magmatic cores with qtz kfs pl ap inclusions which record a neoproterozoic protolith age of 790 ma 2 mantles with coe phe ap inclusions that record triassic uhp age at 227 3 ma and 3 narrow rims with quartz inclusions that record hp granulite facies retrograde metamorphism at 210 3 ma in contrast zircons separated from granitic leucosome have only two distinct domains 1 the central uhp areas with coe phe ap inclusions record triassic uhp age of 227 3 ma and 2 outer magmatic areas with qtz kfs ab ap inclusions that record partial melting time of 212 2 ma zircons separated from pegmatite contain mineral inclusions of qtz kfs ap and show regular magmatic zoning from centre to edge the centres record partial melting time of 212 2 ma in line with the outer domains of granitic leucosome whereas the edges give a younger age of 201 2 ma related to pb loss and partial recrystallization during late triassic regional amphibolite facies retrogression these data indicate that partial melting in the north sulu uhp gneissic rocks took place during post uhp retrograde hp granulite facies metamorphism pre metamorphic magmatic zircon cores from biotite bearing orthogneiss give uniform 176hf 177hf of 0 28187 0 00003 2 sd standard deviation corresponding to ehf 790 and hf model ages tdm2 of about 16 3 and 2 41 ga respectively this is consistent with the generation of its protolith by reworking of paleoproterozoic to late archean crust in contrast uhp zircon domains from biotite bearing orthogneiss and granitic leucosome are characterized by distinct trace element composition with low lu hf 0 006 low th u 0 1 and considerably higher 176hf 177hf 0 28233 0 00002 2 sd than the pre metamorphic cores the uniform but significantly different hf isotope composition between the uhp ehf 227 14 6 0 8 2 sd and pre metamorphic ehf 227 27 7 domains indicates equilibration of the lu hf isotope system only within the uhp metamorphic mineral assemblage the disequilibrium between whole rock and uhp zircon suggests that about two thirds of the whole rock hf retained in the pre metamorphic zircon domains zircon domains crystallized during partial melting at 212 ma in granitic leucosome and pegmatites have a hf isotope composition indistinguishable from that of the uhp zircon domains this suggests that only hf and zr equilibrated during uhp metamorphism was remobilized during partial melting while pre metamorphic zircon remained stable or was not accessible in contrast the magmatic zircon edges from pegmatite have somewhat lower 176hf 177hf 0 28216 and ehf t 17 6 1 2 2 sd indicating some release of less radiogenic hf for instance by dissolution of pre metamorphic zircon during late regional amphibolite facies retrogression

isotopic variation in the tuolumne intrusive suite central sierra nevada california granitoid rocks of the compositionally zoned late cretaceous toulumne intrusive suite in the central sierra nevada california have initial87sr 86sr values sri and143nd 144nd values ndi that vary from 0 7057 to 0 7067 and from 0 51239 to 0 51211 respectively the observed variation of both sri and ndi and of chemical composition in rocks of the suite cannot be due to crystal fractionation of magma solely under closed system conditons the largest variation in chemistry ndi and sri is present in the outer most equigranular units of the tuolumne intrusive suite sri varies positively with sio2 na2o k2o and rb concentrations and negatively with ndi al2o3 fe2o3 mgo feo cao mno p2o5 tio2 and sr concentrations this covariation of sri ndi and chemistry can be modeled by a process of simple mixing of basaltic and granitic magmas having weight percent sio2 of 48 0 and 73 3 respectively isotopic characteristic of the mafic magma are sri 0 7047 ndi 0 51269 and 18o 6 0 and of the felsic magma are sri 0 7068 ndi 0 51212 and 18o 8 9 the rocks sampled contain from 50 to 80 of the felsic component an aplite in the outer equigranular unit of the tuolumne intrusive suite apparently was derived by fractional crystallization of plagioclase and hornblende from magma with granudiorite composition that was a product of mixing of the magmas described above siliceous magmas derived from the lower crust having a maximum of 15 percent mantle derived mafic component are represented by the inner prophyritic units of the tuolumne intrusive suite

response of manganese in the ocean to the climatic cycles in the quaternary profiles of the 230th concentration in mn crusts from the central pacific ocean measured at extremely high depth resolution reveal that the growth rates of mn crusts are influenced by climate based on a constant flux model the sections of maximum 230th concentration correspond to periods of slow growth during glacial stages fast growth occurred during interglacial stages 1 5 and 7 probably due to a larger supply of mn oxides from the water column high resolution profiles of 230th and 10be in sediment cores from high biological productivity areas display radioisotope maxima in the interglacial stages and minima during glacial periods the ratio of the fluxes of 10be 230th being 4 the only exceptions are observed at 135 and 270 kyr b p where the ratio of the fluxes is as low as 0 1 to 0 3 we presume that this 230th anomaly reflects short periods of time at the end of glacials when precipitation of mno2 occurred this hypothesis is confirmed by peaks of mn observed in sediment cores mainly at the transitions from glacial to interglacial stages the standing crops of mn in these layers suggest release of mn2 from the sediments during glacial stages and buildup of mn in the water column to concentrations of up to 10 mol l

what do we learn from peaks of uranium and of manganese in deep sea sediments abstract uranium and manganese are two redox sensitive trace elements with complementary behavior under anoxic conditions u is immobile while reduced mn is dissolved in pore water of sediments uranium diffuses from sea water into reducing sediments and is enriched there the depth of the reducing layers and the sediment accumulation rate determine the enrichment of authigenic uranium on the contrary mn is dissolved in the reducing sediment sections diffuses in pore water and forms peaks of mn oxide as soon as oxygen is available thus the profiles of both mn and authigenic u record the depth of the redoxcline during periods of oxygen limitation in the sediments estimates of the depth of incorporation of uranium during the last glacial were derived for several cores at localities in the atlantic numerical modeling of the redoxcline as a function of the oxygen content of the water column and of the flux of organic matter to the sediments constrains these values during periods of extreme shallow redoxcline depths burn down of organic matter and deepening of the redoxcline during the holocene may have significantly altered the organic matter and uranium signals of glacial sediments at present day conditions sediments accumulating at rates smaller than 2 cm ky 1 may have lost the u signals peaks of manganese are then the only reliable record for a less ventilated sediment column in the past

diatom productivity in the equatorial pacific ocean from the last glacial period to the present a test of the silicic acid leakage hypothesis 1 the silicic acid leakage hypothesis salh suggests that during glacial periods unused silicic acid escaped the southern ocean into the equatorial oceans causing an ecological shift favoring diatoms relative to coccolithophorids and a drawdown of co2 the 230th normalized opal fluxes and 231pa 230th ratios were measured in eleven equatorial pacific cores to reconstruct diatom productivity over the past 30 kyr and to test the salh holocene spatial patterns of opal flux are strongly correlated with 231pa 230th ratios and with satellite estimates of primary productivity down core opal flux records do not support the salh but show holocene opal burial to exceed that of the late glacial period by 35 or 2 8 gt opal kyr across the equatorial pacific this suggests that the salh may not account for lower atmospheric co2 levels during the late glacial however the data do support results from previous studies that invoke increased el nino like conditions during this time

descending ion layer property in the gadanki radar observations of 150 km echoes and its implication to the echoing phenomenon 1 gadanki radar observations of the daytime 150 km echoes displaying descending features resembling the descending ion layer behavior are presented the descending pattern is intriguing since it indicates the possible role of density gradient associated with the ion layer in generating the irregularities responsible for 150 km radar echoes not envisioned before unusually strong snr and narrow spectral features of these echoes clearly indicate the role of sharp density gradients in the echoing process given the fact that gadanki is located at magnetically low latitude it is argued that these descending echoing layers are produced by interchange instability on the gradient of daytime descending ion layer formed by meridional wind shear associated with tidal gravity waves quite similar to that observed during nighttime the observations reported here are first of its kind illustrating the role of density gradient layers and are important in furthering our understanding on the puzzling 150 km echoing phenomenon

productivity control of fine particle transport to equatorial pacific sediment accumulation rates of 3he from cosmic dust 230th produced in the water column barite produced in the water column during decay of organic matter and fe and ti arriving with wind borne dust all are positively correlated in an equatorial pacific core tt013 pc72 01 1 n 139 4 w water depth 4298 m these accumulation rates are also positively correlated with the accumulation rates of noncarbonate material they are not significantly correlated to the mass accumulation rate of carbonate which makes up the bulk of the sediment the fluctuations in accumulation rates of these various components from different sources thus must result from variations in some process within the oceans and not from variations in their original sources sediment focusing by oceanic bottom currents has been proposed as this process marcantonio et al 1996 we argue that the variations in the accumulation rates of all these components are dominantly linked to changes in productivity and particle scavenging 3he 230th fe ti by fresh phytoplankton detritus which delivers ba upon its decay in the equatorial pacific upwelling region we speculate that as equatorial pacific productivity is a major component of global oceanic productivity its variations over time might be reflected in variations in atmospheric levels of methanesulfonic acid an atmospheric reaction product of dimethyl sulfide which is produced by oceanic phytoplankton and recorded in antarctic ice cores

development of a sequential extraction procedure for iron implications for iron partitioning in continentally derived particulates abstract the development of a sequential extraction procedure for iron in modern and ancient sediments is presented the scheme recognizes seven operationally derived iron pools 1 carbonate associated fe fe carb including siderite and ankerite 2 easily reducible oxides fe ox1 including ferrihydrite and lepidocrocite 3 reducible oxides fe ox2 including goethite hematite and akaganeite 4 magnetite fe mag 5 poorly reactive sheet silicate fe fe prs 6 pyrite fe fe py and 7 unreactive silicate fe fe u as such this is the first extraction scheme specifically developed to allow the separate identification of magnetite and the first to allow a complete evaluation of fe carbonate phases such as siderite and ankerite the scheme was developed following tests on pure mineral phases to evaluate the minerals solubilized by each technique and to determine optimum extraction times further tests on mixtures of pure minerals and on grain size separated sediments from two major us rivers and two glacial meltwaters validate the specificity of the scheme for different pools of iron minerals and demonstrate a high degree of reproducibility for each analytical stage the data obtained for the riverine and glacial sediments are additionally discussed in relation to the dominant modes of transport of different iron minerals in fine grained continental sediments

energy constrained open system magmatic processes iv geochemical thermal and mass consequences of energy constrained recharge assimilation and fractional crystallization ec rafc 1 a wealth of geochemical and petrological data provide evidence that the processes of fractional crystallization assimilation and magma recharge replenishment dominate the chemical signatures of many terrestrial igneous rocks previous work spera and bohrson 2001 bohrson and spera 2001 has established the importance of integrating energy species and mass conservation into simulations of complex magma chamber processes an extended version of the energy constrained formulation energy constrained recharge assimilation fractional crystallization ec rafc tracks mass and compositional variations of melt cumulates and enclaves in a magma body undergoing simultaneous recharge assimilation and fractional crystallization spera and bohrson 2002 because many ec rafc results are distinct from those predicted by extant rafc formulations the primary goal of this paper is to present a range of geochemical and mass relationships for selected cases that highlight issues relevant to modern petrology among the plethora of petrologic problems that have important well documented analogues in nature are the geochemical distinctions that arise when a magma body undergoes continuous versus episodic recharge the connection between erupted magmas and associated cumulate bodies the behavior of recharge fractionation dominated systems rfc thermodynamic conditions that promote the formation of enclaves versus cumulates and the conditions under which magma bodies may be described as chemically homogeneous investigation of the effects of continuous versus episodic recharge for mafic magma undergoing rafc in the lower crust indicates that the resulting geochemical trends for melt and solids are sensitive to the intensity and composition of recharge suggesting that ec rafc may be used as a tool to distinguish the nature of the recharge events compared to the record preserved in melts the geochemical and mass characteristics of solids associated with particular rafc events may record a more complete view of the physiochemical history of an open system magma body the capability of ec rafc to track melts and solids creates a genetic link that can be compared to natural analogues such as layered mafic intrusions and flood basalts or mafic enclaves and their intermediate composition volcanic or plutonic hosts the ability to quantify chemical and volume characteristics of solids and melts also underscores the need for integrated field petrologic and geochemical studies of igneous systems while it appears that a number of volcanic events or systems may be characterized by continuous influx or eruption of magma steady state systems reports describing compositional homogeneity for products that represent eruptions of more than one event are relatively rare in support of this ec rafc results indicate that very specific combinations of recharge conditions bulk distribution coefficients and element concentrations are required to achieve geochemical homogeneity during cooling of a magma body undergoing rafc in summary critical points are that ec rafc provides a method to quantitatively investigate complex magmatic systems in a thermodynamic context it predicts complex nonmonotonic geochemical trends for which there are natural analogues that have been difficult to model and finally ec rafc establishes the link between the chemical and physical attributes of a magmatic system application of ec rafc promises to improve our understanding of specific tectonomagmatic systems as well as enhance our grasp of the essential physiochemical principles that govern magma body evolution

an experimental study of trace element partitioning between zircon and melt as a function of oxygen fugacity abstract the partitioning of p sc ti sr y nb the rare earth elements ree hf ta th and u between zircon and a synthetic andesitic melt was determined as a function of oxygen fugacity f o 2 over a range of fourteen log units from qfm 8 to qfm 6 where qfm is the quartz fayalite magnetite oxygen buffer at 1300 c and 1 atm using sims and la icp ms the partition coefficients of ce and eu were found to vary systematically with f o 2 relative to those of the other ree producing ce and eu anomalies similar to those that are characteristic of natural igneous zircon these anomalies coexist at terrestrial f o 2 s and were used to quantify eu 3 eu 2 eu 3 and ce 4 ce 3 ce 4 in the melt the partition coefficients of the redox invariant trivalent cations are in excellent agreement with lattice strain theory the values of d ree are related to those determined for natural samples by the expected dependence on temperature the incorporation of ree 3 in zircon was independent of the presence of p d u d th was found to vary systematically with f o 2 indicating the presence of u 4 u 5 and u 6 in the melt at terrestrial conditions d ti was independent of f o 2 despite an expectation of significant ti 3 in the most reduced experiments

post depositional manganese mobilization during the last glacial period in sediments of the eastern clarion clipperton zone pacific ocean abstract numerous studies have provided compelling evidence that the pacific ocean has experienced substantial glacial interglacial changes in bottom water oxygenation associated with enhanced carbon dioxide storage in the glacial deep ocean under postulated low glacial bottom water oxygen concentrations o 2 bw redox zonation biogeochemical processes and element fluxes in the sediments must have been distinctively different during the last glacial period lgp compared to current well oxygenated conditions in this study we have investigated six sites situated in various european contract areas for the exploration of polymetallic nodules within the clarion clipperton zone ccz in the ne pacific and one site located in a protected area of particular environmental interest apei3 north of the ccz we found bulk sediment mn maxima of up to 1 wt in the upper oxic 10 cm of the sediments at all sites except for the apei3 site the application of a combined leaching protocol for the extraction of sedimentary mn and fe minerals revealed that mobilizable mn iv represents the dominant mn oxyhydr oxide phase with more than 70 of bulk solid phase mn steady state transport reaction modeling showed that at postulated glacial o 2 bw of 35 m the oxic zone in the sediments was much more compressed than today where upward diffusing pore water mn2 was oxidized and precipitated as authigenic mn iv at the oxic suboxic redox boundary in the upper 5 cm of the sediments transient transport reaction modeling demonstrated that with increasing o 2 bw during the last glacial termination to current levels of 150 m 1 the oxic suboxic redox boundary migrated deeper into the sediments and 2 the authigenic mn iv peak was continuously mixed into subsequently deposited sediments by bioturbation causing the observed mobilizable mn iv enrichment in the surface sediments such a distinct mobilizable mn iv maximum was not found in the surface sediments of the apei3 site which indicates that the oxic zone was not as condensed during the lgp at this site due to two to threefold lower organic carbon burial rates leaching data for sedimentary fe minerals suggest that fe iii has not been diagenetically redistributed during the lgp at any of the investigated sites our results demonstrate that the basin wide deoxygenation in the ne pacific during the lgp was associated with 1 a much more compressed oxic zone at sites with carbon burial fluxes higher than 1 5 mg corg m 2 d 1 2 the authigenic formation of a sub surface mobilizable mn iv maximum in the upper 5 cm of the sediments and 3 a possibly intensified suboxic diagenetic growth of polymetallic nodules as our study provides evidence that authigenic mn iv precipitated in the surface sediments under postulated low glacial o 2 bw it contributes to resolving a long standing controversy concerning the origin of widely observed mn rich layers in glacial deglacial deep sea sediments

coordinated investigation of summer time mid latitude descending e layer es perturbations using na lidar ionosonde and meteor wind radar observations over logan utah 41 7 n 111 8 w 1 it is well known that there is a strong correlation between the formation of a descending sporadic e layer es and the occurrence of large upper atmospheric zonal wind shears most likely driven by solar thermal tides and or gravity waves we present new results of es perturbation events captured between 13 and 17 july 2011 ut days 194 198 as part of a coordinated campaign using a wind temperature na lidar at utah state university 41 7on 111 8 w and a canadian advanced digital ionosonde cadi scientific instrumentation ltd saskatoon saskatchewan canada and skiymet meteor wind radar both located at nearby bear lake observatory 41 9 n 111 4 w during this period the cadi detected strong descending es on 2 days 195 and 197 when large modulations of the top side mesospheric na layer occurred in synchronism with strong oscillations in the ionosonde e region echoes a weakening in the descending e layer echoes was observed on the other 2 days 196 and 198 coincident with a large reduction in the zonal diurnal and semidiurnal amplitudes above 95 km both tidal components were found to have comparable contributions to the total zonal wind shear that was critical for es formation and its downward propagation further investigation indicates that the weakening tidal amplitudes and the occurrence of the es events were also influenced by a strong quasi two day period modulation suggesting significant quasi two day wave qtdw interactions with the tides indeed a nonlinear wave wave interaction induced 16 hour period child wave was also detected with amplitude comparable to that of the prevailing tides these interaction processes and their associated effects are consistent with earlier thermosphere ionosphere mesosphere electrodynamics general circulation model studies of nonlinear interactions between the migrating tidal waves and the qtdw and were probably responsible for the observed damping of the tidal amplitudes resulting in the disruption of the es

ocean dynamics not dust have controlled equatorial pacific productivity over the past 500 000 years biological productivity in the equatorial pacific is relatively high compared with other low latitude regimes especially east of the dateline where divergence driven by the trade winds brings nutrient rich waters of the equatorial undercurrent to the surface the equatorial pacific is one of the three principal high nutrient low chlorophyll ocean regimes where biological utilization of nitrate and phosphate is limited in part by the availability of iron throughout most of the equatorial pacific upwelling of water from the equatorial undercurrent supplies far more dissolved iron than is delivered by dust by as much as two orders of magnitude nevertheless recent studies have inferred that the greater supply of dust during ice ages stimulated greater utilization of nutrients within the region of upwelling on the equator thereby contributing to the sequestration of carbon in the ocean interior here we present proxy records for dust and for biological productivity over the past 500 ky at three sites spanning the breadth of the equatorial pacific ocean to test the dust fertilization hypothesis dust supply peaked under glacial conditions consistent with previous studies whereas proxies of export production exhibit maxima during ice age terminations temporal decoupling between dust supply and biological productivity indicates that other factors likely involving ocean dynamics played a greater role than dust in regulating equatorial pacific productivity

a deeper respired carbon pool in the glacial equatorial pacific ocean article i nfo atmospheric pco2 was approximately 80 ppm lower during the last glacial period than during pre industrial times identifying the fate of that carbon has been one of the great challenges in paleoceanography we present evidence from ten equatorial pacific ocean sediment cores to show that the deep pacific ocean likely stored more carbon during the last glacial period than the holocene the concentration of the redox sensitive metal uranium u in sediments was systematically greater during the last glacial period than during the holocene indicating more reducing conditions in glacial age sediments reconstructions of biogenic opal flux indicate that changes in u distribution were not the result of changes in biological productivity and the ensuing rain of organic carbon to the sea floor which also affects the redox conditions of the sediments together these results lead to the interpretation that bottom water in the equatorial pacific during the glacial period had significantly lower oxygen concentration than during the holocene and a correspondingly greater level of respired co2 this conclusion is supported by evidence for greater preservation of brassicasterol a biomarker produced by diatoms in glacial age sediments of the eastern equatorial pacific the presence of additional respired co2 in the glacial deep ocean would have lowered atmospheric pco2 by 1 increasing the total storage of co2 in the glacial ocean and 2 increasing ocean alkalinity following a transient carbonate dissolution event our results are consistent with recently published data from the north pacific ocean this suggests that increased carbon storage in the glacial deep pacific ocean was a basin wide phenomenon consistent with a large scale transfer of carbon to the deep ocean during glacial periods

terdiurnal tidelike variability in sporadic e layers 1 time series analysis was performed on a large database of ionosonde recordings taken over 12 years for the 6 month period from the beginning of may to the end of october when sporadic e layer occurrence is frequent the results show that in addition to the well known 24 and 12 hour tidal variations there is also a weaker but regular 8 hour periodicity in midlatitude sporadic e layers es statistically this terdiurnal periodicity is significant and occurs in both the sporadic e layer critical frequency foes and the layer virtual height h es becoming strongest around summer solstice and later in october after a minimum in september at times a weak 6 hour periodicity can also be present in es but its effects are much less significant than those of the 8 hour oscillation the 8 hour periodicity in es is attributed to the terdiurnal tide presumably acting through its vertical wind shear forcing of the metallic ions in the lower thermosphere the relation to the terdiurnal tide was inferred from simultaneous ionosonde recordings from three widely spaced stations in the same midlatitude zone showing the 8 hour oscillation to be present simultaneously in all ionosonde stations and have phases which are consistent with a westward propagating terdiurnal wave of zonal wave number 3 the present study establishes the regular occurrence of a terdiurnal tidelike oscillation in es which needs to be incorporated into the physics and modeling of sporadic e layer formation and dynamics

diffusive transfer of oxygen from seamount basaltic crust into overlying sediments an example from the clarion clipperton fracture zone highlights geochemical evidence confirms exchange between sediments and the basaltic crust fluids o2 exchange between the sediment and the basaltic crust produces a fully oxic sediment column transport reaction modeling was performed to quantify the exchange of o2 and nutrients abstract the clarion clipperton fracture zone ccfz in the pacific ocean is characterized by organic carbon starved sediments and meter scale oxygen penetration into the sediment furthermore numerous seamounts occur throughout its deep sea plain which may serve as conduits for low temperature hydrothermal seawater circulation through the oceanic crust recent studies in deep sea environments of the pacific and atlantic oceans have suggested and presented evidence of dissolved constituent exchange between the seawater flowing in the basaltic crust and the pore water of the overlying sediments through high resolution pore water oxygen and nutrient measurements we examined fluxes and geochemical interactions between the seamount basaltic basement and pore waters of the overlying sediments at three sites located on a radial transect from the foot of teddy bare a small seamount in the ccfz at three sites located 1000 700 and 400 m away from the foot of the seamount we found that oxygen concentrations initially decrease with sediment depth but start to increase at depths of 3 and 7 m toward the basaltic basement nitrate view the mathml sourceno3 concentrations mirror the oxygen concentration profiles as they increase with sediment depth but decrease towards the basement these profiles suggest an upward diffusion of oxygen from seawater circulating within the seamount crust into the overlying basal sediments and a downward diffusion of view the mathml sourceno32 from sediment pore water into the basaltic crust at one site we determined that the 87sr 86sr ratios of the bottom water and of the deep sediment near the basaltic crust are similar further supporting diffusive exchange between basaltic crust fluids and sediment pore water transport reaction modeling performed at two of the study sites revealed that 1 the diffusive flux of oxygen from the basaltic basement outpaces the oxygen consumption through organic matter oxidation and nitrification in the basal sediments and 2 the nutrient exchange between the sediment and the underlying basaltic crust occurs at orders of magnitude lower rates than between the upper sediment and the overlying bottom water these results further show that the diffusion of oxygen from the seamount basaltic basement into the overlying pore waters affects the preservation of organic compounds and helps to maintain a completely oxygenated sedimentary column at all 3 sites near the seamount

correlative radar and airborne sodium lidar observations of the vertical and horizontal structure of gravity waves near the mesopause in november 1986 joint radar and na lidar observations were conducted in colorado to study mesopause dynamics the radar observations were conducted at platteville colorado with a stratosphere troposphere st radar in a meteor echo detection mode the na lidar observations included ground based observations at broomfield and denver colorado and airbome observations during three flights over the great plains rocky mountains and pacific coast both radar and lidar identified a 6 hour wave that was remarkably coherent during the november campaign the vertical wavelength of the 6 hour wave estimated from the radar data was 8 to 9 km the amplitude of the zonal wind component was 10 m s 1 and the amplitude of the meridional wind component was 4 m s 1 the vertical wavelength estimated from the ground based and airborne lidar data was 7 3 km and the amplitude of the scalar horizontal wind ranged from 13 to 16 m s 1 the zonal wavelength of this wave was approximately 772 km and the intrinsic zonal phase velocity was 35 m s 1 westward the 6 hour wave was dominant in the height range of 80 90 km which corresponds to the bottomside of the na layer an additional 2 hour wave was observed with the na lidar during both the ground based and airborne observations the vertical wavelength of this wave was about 12 km and the zonal wavelength was 260 km the intrinsic zonal phase velocity was 43 m s 1 westward this 2 hour wave was also present only on the bottomside of the na layer

an analysis of tidal and planetary waves in the neutral winds and temperature observed at low latitude e region heights we present an extensive analysis of tidal and planetary waves in the altitude range of 94 to 144 km for the january 20 30 1993 period using the temperature and winds measured by the arecibo incoherent scatter radar isr this is the first time that simultaneous observational results for the 6 8 12 24 hour tides and a quasi 2 day planetary wave at e region heights have been reported at tropical latitudes in order to derive the major oscillations from the mainly daytime data we fill in the nighttime periods with assumed data values and large error bars when valid measurements are not obtainable and then fit the data using the measured and assumed errors as weight simulated results show that such a method is demonstratively better than leaving the nighttime as a gap the salient features of the tidal analysis results include the following 1 despite their large day to day variabilities in amplitude the 6 8 hour oscillations are shown to be upward propagating tides 2 the vertical wavelength of the semidiurnal tide in the zonal wind lengthens from 25 to 110 km for the altitude range from 94 to 135 km while the vertical wavelength of the meridional wind remains constant the semidiurnal component of the meridional wind experiences little dissipation above 106 km which is indicative of the turbopause height 3 the diurnal tide which has often been assumed to be negligible in earlier observations can be quite substantial above 110 km 4 a 2 day planetary wave dominates the diurnal and semidiurnal tides in the meridional wind between 97 and 108 km continuous isr operation during the january 20 30 1993 campaign also provides an opportunity to examine the tidal variability both in phase and amplitude

excess argon in k ar and ar ar geochronology the k ar and ar ar dating techniques occasionally produce anomalously old ages attributed to excess argon and such data is often rejected as not offering any insight into the age thermal history or geochemistry of the rock however improvements in the quantification of argon geochemistry now provide a framework to model excess argon in both open and closed systems solubility data for argon in hydrous fluids melts and emerging data for minerals can be used to understand the behaviour of excess argon and provide valuable insights into the environment in which the samples cooled to their argon retention or closure temperature treating excess argon as a trace element also throws light on its behaviour in minerals above the closure temperature in deeply buried dry systems such as eclogites blueschists granulites and even in the lithospheric mantle extremely low partition coefficients between k feldspar and hydrous fluid phases predict lower excess argon susceptibility than micas and this is observed in fluid poor systems variation of partition coefficients can lead to excess argon in fluids being introduced into minerals or removed from minerals as grain boundary fluids change during flow through a rock however excess argon can also be introduced or removed from minerals by varying temperature without the need for fluid flow high mineral melt and mineral fluid partition coefficients are also the reason why excess argon is often concentrated in inclusions within minerals partition coefficients between minerals and hydrous fluids as low as 10 6 lead fluid inclusions to dominate the radiogenic argon budget particularly in low potassium minerals melt inclusions are less dominant but become critical in dating younger samples

the influence of suboxic diagenesis on the formation of manganese nodules in the clarion clipperton nodule belt of the pacific ocean abstract polymetallic nodules and a single fe mn crust from the clarion and clipperton zone ccz of the equatorial eastern pacific have been analyzed to determine their chemical and mineralogical compositions icp oes analyses of bulk nodules from the ccz indicate that the nodules formed under oxic diagenetic conditions with typical mn fe ratios of 4 6 ni cu values of 2 3 wt co contents of 0 12 0 17 wt however detail analyses of individual growth layers by electron microprobe analyses empa reveal much larger chemical heterogeneity of individual layers with mn fe ratios ranging from 800 two different genetic types of layers can be distinguished layer type 1 dense layer with average mn fe ratios of 1 80 average ni cu of 0 81 wt co contents of 0 30 wt hydrogenetic metal precipitation from oxic waters these layers consist of fe vernadite mno2 epitaxially intergrown with feroxyhyte feooh nanoparticles layer type 2 growth structures dendritic growth structures and dense layers with average mn fe ratios of 96 ni cu of 3 9 wt co contents of 0 08 wt and a distinct ni cu maximum of 6 51 wt at a mn fe ratio of 56 suboxic diagenetic metal precipitation from suboxic pore waters type 2 layers mainly consist of turbostratic phyllomanganates such as 10 a vernadite 7 a vernadite and todorokite are minor compounds mixed layer type 3 these layers can occur as zones of low reflectivity in the transition from layer type 1 to 2 or build up inhomogeneous growth structures of nm thin layers of low or high reflectivity the mn fe ratios of this material range between 3 and 11 ni cu of 1 4 6 wt and co contents are between 0 02 and 0 77 wt in most cases these growth structures represent a mixture of type 1 and 2 layers x ray photoelectron spectroscopy xps of the recent outermost nm layers of nodules top rim and bottom side indicates hydrogenetic accretion processes under recent oxic conditions both from seawater and pore water the mixed type ccz nodules are interpreted to consist of an oxic hydrogenetic and a suboxic diagenetic end member calculations of the proportions of the individual layer end members show that suboxic layers make up about 50 60 of the chemical inventory of the ccz nodules whereas oxic hydrogenetic layers comprise about 35 40 the remaining part 5 10 consists of incorporated sediment particles occurring along cracks and pores these results demonstrate that suboxic conditions alternate with oxic conditions during the growth of nodules in the eastern ccz this is probably due to fluctuating bioproductivity in the equatorial pacific surface waters during glacial interglacial periods which led to changing organic carbon flux to the sediment and changing oxygen consumption in near surface sediments furthermore reduced ventilation of the deep ocean during glacial periods may have led to suboxic conditions in near surface sediments our investigations prove that bulk chemistry data of whole nodules only provides an average of individual layers that build up the nodules and is inappropriate for genetic interpretation

pore water profiles and numerical modelling of biogeochemical processes in peru basin deep sea sediments abstract an extensive set of pore water profiles including o 2 no 3 no 2 nh 4 po 4 3 fe 2 mn 2 so 4 2 sio 4 4 ph and alkalinity as well as solid phase data on organic carbon content and porosity in 18 sediment cores obtained from five areas in the peru basin rv sonne 106 expedition in 1996 is presented the pore water profiles indicate that early diagenesis progresses through oxygen respiration denitrification and manganese iv reduction while the subsequent redox states iron iii reduction sulphate reduction and methanogenesis cannot be observed from the dissolved phase in these deep sea sediments a numerical diagenetic model was applied to the data in order to derive parameters such as the depositional flux of metabolizable organic matter or the bioturbation intensity that control the geochemical conditions in the deep sea floor and could not be obtained directly by measurements moreover the numerical simulations show that even those pore water no 3 profiles that decline non linearly to zero concentration are not compatible with a steady state assumption they can be explained only by transient downward progression of a nitrate front

geochronology geochemistry and isotope compositions of piaochi s type granitic intrusion in the qinling orogen central china petrogenesis and tectonic significance abstract s type peraluminous granite can crop out in various tectonic settings the paleozoic piaochi granitic intrusion is a large s type peraluminous intrusion located in the north qinling orogen and has important implication for its tectonic evolution though intensively studied the age and tectonic setting of this intrusion are still controversial in this study we carried out an integrated study of zircon u pb age major and trace elements and sr nd hf o isotope compositions for the piaochi intrusion with aims to constrain its petrogenesis and tectonic significance sims and la icpms u pb zircon data obtained from magmatic zircons indicate that the piaochi intrusion was emplaced at 473 4 ma and contained ca 490 ma inherited zircons the granite samples from the piaochi intrusion show typical s type characteristics such as the relatively moderate aluminum saturation index 1 00 1 08 low zirconium saturation temperatures occurrences of muscovite and high zircon 18 o values 8 70 to 9 54 the relatively low sm nd 0 13 0 20 and feo t mgo ratios 2 21 3 9 suggest that the granites are unfractionated the geochemical compositions reveal that they were derived from partial melting of a clay poor but plagioclase and biotite rich psammitic source similar to metasedimentary rocks outcropping in the north qinling unit moreover the piaochi granites are moderately depleted in eu and heavy rare earth elements and have relatively high la yb n values 22 8 56 8 implying a high pressure plagioclase poor and garnet rich residual assemblage the piaochi granites have high and variable initial 87 sr 86 sr ratios 0 72167 0 72511 and low e nd t from 10 23 to 8 71 values with two stage nd model ages t dm2 of 1 91 2 03 ga which are comparable with those of supracrustal materials in the north qinling unit in addition our results show that the ca 470 ma magmatic zircons display a narrow e hf t array within those of the inherited cores these imply that the piaochi granites inherited their isotopic characteristics wholly from their sources and the hf isotopes might have been differently homogenized during the partial melting our new zircon u pb ages indicate that the piaochi granites were emplaced after the climax of the uhp metamorphism coeval with later retrograde metamorphism during exhumation therefore we suggest that the formation of the early paleozoic piaochi intrusion was triggered by the exhumation of the uhp rocks

zircon u pb and k feldspar megacryst rb sr isotopic ages and sr hf isotopic composition of the mesozoic heyu pluton eastern qingling orogen china abstract mesozoic granitoids are ubiquitous in china and have attracted the interests of many geologists not only because of their mineralization potential but also because they carry information on source material emplacement mechanisms and crustal architecture most of the plutons were created by multi stage magma emplacement and offer particular challenge for unraveling the emplacement and cooling history a multi isotope approach combined with single grain dating analyses provides a means to understand magma geneses even in complex magmatic settings this study presents rb sr isotope data for k feldspar megacrysts and u pb ages and hf isotopic composition for zircons from the composite heyu pluton exposed in eastern qinling orogen central china zircon u pb concordia ages of 150 and 140 ma and single k feldspar rb sr isochron ages between 133 and 121 ma were obtained from early and late magmatic stages respectively consistent with slow cooling or isotopic re equilibration of the rb sr k feldspar system the distinct k feldspar morphology of early and late intrusive phases is controlled largely by the emplacement depth likely to be associated with a gravity driven sinking model corresponding zircon e hf t values are 21 8 to 18 0 and 17 2 to 10 3 for early and late intrusive phases respectively indicating different magma sources

late quaternary deep stratification climate coupling in the southern ocean implications for changes in abyssal carbon storage the southern ocean plays an important role in modulating pleistocene atmospheric co2 concentrations but the underlying mechanisms are not yet fully understood here we report the laser grain size distribution and mn geochemical data of a 523 kyr long sediment record core ant30 p1 02 off prydz bay east antarctica to trace past physical changes in the deep southern ocean the core sediments are predominantly composed of clay and silt sized material three grain size end members em as well as three sensitive grain size classes sc were discerned interpreted as ice rafted debris em1 and sc1 and coarse em2 and sc2 and fine em3 sc3 materials deposited from bottom nepheloid layers respectively ratios of em2 em2 em3 and sc2 sc3 reveal changes in the local bottom current strength which is related to the deep ocean diapycnal mixing rate showing higher values during interglacial periods and lower values during glacial periods mno was enriched at each glacial termination probably caused by abrupt elevations in antarctic bottom water aabw formation rate lower aabw formation rate and reduced deep diapycnal mixing during glacial periods enhanced deep southern ocean stratification contributing to glacial atmospheric co2 drawdown the elevated aabw formation and enhanced deep diapycnal mixing during glacial terminations alleviated such deep stratification promoting deeply sequestered co2 to outgas

early ordovician continental break up in variscan europe ndsr isotope and trace element evidence from bimodal igneous associations of the southern massif central france abstract the high grade marvejols group and the low grade albigeois cevennes sedimentary sequence contain bimodal igneous rocks of early ordovician age which are representative of a widespread thermal event in the european variscides comparison of their nd sr isotope and trace element characteristics provides additional evidence for their origin in an ensialic extensional setting as an alternative to the back arc model proposed by previous authors we propose that these associations record a continental break up episode unrelated to contemporaneous subduction in this model the widespread early paleozoic bimodal magmatism marks the birth of a mid european oceanic arm we propose that the break up was controlled by both transtensional processes and mantle plume activity high grade associations such as the marvejols group and low grade bimodal associations such as the albigeois cevennes might be regarded as representing opposite rifted passive margins the northern marvejols type margin was involved in a late ordovician silurian subduction like process with hp ht metamorphism in contrast the southern albigeois cevennes margin remained largely unaffected possibly as part of the overriding plate of the subduction zone pseudo calc alkaline signatures unrelated to subduction processes may occur in magmatic rocks associated with continental break up episodes in this case negative nb anomalies are produced by the addition of crustal components enriched in th and lree relative to nb this inferred alternative origin of nb anomalies has important bearing on the paleogeodynamic settings based on geochemical data

sm nd isotope systematics of high ree accessory minerals and major phases id tims la icp ms and epma data constrain multiple permian triassic pegmatite emplacement in the koralpe eastern alps abstract detailed sm nd mineral id tims empa and la icp ms analysis of meta pegmatite minerals from the koralpe stubalpe area austria involving single crystal separation step wise dissolution and acid leaching techniques yielded i information about the partitioning of ree between accessory and major mineral phases in meta pegmatites and ii age constraints on the long lasting permian triassic event in the austroalpine basement units of the eastern alps internal sm nd mineral isochrons performed on porphyroclast domains from the three localities rostockbach kuppergrund and wildbachgraben including garnet xenotime apatite monazite and feldspar indicate multiple emplacement of pegmatoid melts between 273 2 and 258 3 ma other localities yielded younger ages indicating that magmatic garnet crystallisation persisted from 251 7 to c 230 ma ages calculated between high ree accessories monazite apatite xenotime and the low ree major phases feldspar and garnet are largely consistent zircon however plots clearly off the internal regression line h 2 so 4 leaching experiments on meta pegmatite garnet rich in micron sized xenotime and apatite inclusions locally affected by dynamic recrystallisation yielded information about the behaviour of the sm nd system during strong tectono metamorphic overprinting the data suggest multiple injections of pegmatite melts at distinctly different times during protracted crustal thinning and heating in the permian triassic ky paramorphs after andalusite and micro inclusions of kyanite staurolite and sillimanite in magmatic garnet indicate crystallisation of the garnet at moderately high but variable pressure conditions during subsequent eclogite facies overprinting peak pt c 700 c 2 2 gpa and intense deformation in cretaceous time the magmatic chemical and isotopic signatures of porphyroclasts were largely preserved except for localized within grain micro shear zones and outermost rim domains whereas part of the feldspar rich matrix recrystallised during pervasive mylonitisation along the eclogite to amphibolite facies grade exhumation path

a middle silurian early devonian magmatic arc in the qinling mountains of central china an early to middle paleozoic magmatic arc was discovered in the qinling orogenic belt of central china that marks the boundary between the north china craton and the south china craton the arc was built on the deformed southern passive continental margin of the north china craton which has been modified by the accretion of an oceanic island arc in early paleozoic time u pb analyses of zircons from granites indicate short lived arc activity from middle silurian to early devonian time trace element analyses as well as ree analyses of i type granites are consistent with the interpretation that the magmatic arc developed above a north dipping subduction zone termination of magmatic activity was probably caused by the initiation of collision between the north china craton and the south china craton this interpretation is consistent with faunal data and places new constraints on the paleozoic tectonic evolution of the qinling belt

recycling processes in granite granodiorite complex genesis the querigut case studied by ndsr isotope systematics abstract using the isotopic rb sr and sm nd petrogenetic tracers we have studied the calc alkaline plutonic complex of querigut pyrenees france which is famous for its acid to mafic rock association and is a typical post tectonic hercynian granitoid its age of 280 m y is already known 2 23 24 and our purpose is to examine the relationship between its different petrographic units and the problem of their source composition the sm nd isotopic results rule out any genetic process involving a unique homogeneous source and imply the presence of old recycled continental materials in contrast the rb sr isotope system seems to have been homogenized by hot fluids maybe post magmatic this is also true for pb isotopes as shown previously by michard vitrac et al 18 on the basis of the isotopic results and the major element data a model of combined fractional crystallization assimilation of country rocks is proposed for the basic part of the complex in contrast acid parts are mainly the result of the continental anatexis this study also constrains the basement s age 1200 1900 m y of the area and suggests a scheme for the gological history of the eastern pyrenees

geochronology and magmatic oxygen fugacity of the tongcun molybdenum deposit northwest zhejiang se china the tongcun mo porphyry deposit in northwest zhejiang is hosted in three porphyry units huangbaikeng songjiazhuang and tongcun from southwest to northeast u pb zircon ages of 162 3 0 ma for the huangbaikeng porphyry 159 9 3 0 ma for the songjiazhuang porphyry and 167 6 155 6 ma for the tongcun porphyry indicate that these intrusions formed during the jurassic and are most likely associated with the northwestward subduction of the izanagi plate trace element compositions of zircons from the tongcun deposit constrain the oxygen fugacity fo2 of the magma using zircon ce anomalies and ti in zircon temperatures the average magmatic fo2 for the porphyries in the tongcun deposit is fayalite magnetite quartz fmq 2 7 which is similar to the shapinggou fmq 3 2 and dabaoshan fmq 3 5 mo porphyry deposits but much higher than that of the reduced cretaceous ore barren shangjieshou porphyry fmq 1 1 around 8 km away from the tongcun deposit the distinct difference in magmatic oxygen fugacity between the jurassic and cretaceous porphyries may help to explain the absence of mo porphyry mineralization in northwest zhejiang during the cretaceous

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

observations and modeling of the 6 hour tide in the upper mesosphere 1 this paper presents observations and modeling of the 6 hour tide radar observations of horizontal winds at esrange 68 n 21 e indicate that this tidal periodicity is a consistent part of the diurnal variation and is largest during midwinter vertical structure and phase coherence provide strong support that the observed oscillations are tidal model simulations generate a tide that has many similarities to the observed tide at esrange diagnostic model tests indicate that the tide is forced primarily by the 6 hour component of solar heating globally the monthly mean simulated tide is dominated by the migrating component except near the poles although the contribution from nonmigrating modes is not negligible according to the model both migrating and nonmigrating 6 hour tides have small amplitude in low latitudes

widespread seawater circulation in 18 22 ma oceanic crust impact on heat flow and sediment geochemistry on the basis of heat flow measurements seismic mapping and sediment pore water analysis we demonstrate widespread and efficient ventilation of the 18 22 ma oceanic crust of the northeast equatorial pacific ocean recharge and discharge appear to be associated with basement outcrops including seamounts and north south trending faults along which sediment cover thins out and volcanic rocks are exposed low temperature hydrothermal circulation through the volcanic crust leads to the reduction of heat flow through overlying sediments with measured heat flow values that are well below those expected from conductive cooling curves for lithosphere of this age typically dissolved pore water oxygen decreases from the sediment surface downward reaching minimum values at mid depth and rising again in the lower part of the cores investigated clearly indicating oxygen rich seawater circulation through the oceanic crust underneath the sediments if the residence time of the circulating fluids in the upper crust is short or the fluid flux is large oxic conditions may be preserved and oxygen can diffuse upwards into the sediments this process leading to widespread oxic conditions in the near basement sediments may cause the oxidation of residual reduced material stored in the deeper sediments resulting in downward fluxes of the reaction products into the basement and from there back into the oceans considering the widespread existence of this type of off axis ventilation the net effect of the resulting return flow of reaction products on biogeochemical cycles and element fluxes e g carbon and nitrogen may be very large

the dynamic ionosphere over arecibo a theoretical investigation numerical simulations of the f region ionosphere over arecibo puerto rico are presented we deduce from these simulations that the dynamic behavior of the arecibo ionosphere particularly the so called midnight collapse phenomenon is strongly influenced by the upward propagating semidiurnal tidal component of the neutral meridional wind excited below thermospheric levels presence of a terdiurnal component in the wind field improves the agreement with experiment and could result from nonlinear interactive coupling between the neutral wind and ion drag the steep underside density gradients occurring in conjunction with the collapse are due to vertical shear in the meridional wind field associated with the propagating semidiurnal tide these gradients are capable of triggering the gradient drift instability thus accounting for plasma irregularity formation and observations of vhf scintillations associated with the collapse phenomenon

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

subarctic pacific evidence for a glacial deepening of the oceanic respired carbon pool abstract measurements of benthic foraminiferal cadmium calcium cd ca have indicated that the glacial interglacial change in deep north pacific phosphate po4 concentration was minimal which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean here we present sedimentary redox sensitive trace metal records from ocean drilling program odp site 882 nw subarctic pacific water depth 3244 m to make inferences about changes in deep north pacific oxygenation and thus respired carbon storage over the past 150 000 yr these observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment our results suggest that the deep subarctic pacific water mass was depleted in oxygen during glacial maxima though it was not anoxic we reconcile our results with the existing benthic foraminiferal cd ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed rather than remineralized this change would have corresponded to an increase in the deep pacific storage of respired carbon which would have lowered atmospheric carbon dioxide co2 by sequestering co2 away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea the magnitude of change in preformed nutrients suggested by the north pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pco2

solid phase manganese in southeast atlantic sediments implications for the paleoenvironment abstract in many deep sea sediments mn rich layers are observed at various levels in order to investigate their formation and preservation as well as their use to reconstruct past changes in the depositional environment downcore profiles of manganese and manganese carbonate from different early diagenetic environments in the southeast atlantic ocean were examined by geochemical analysis x ray diffraction and sem analysis the results were compared to pore water data and productivity regimes in sediments underlying areas of high to moderate surface water fertility mn is reduced and recycled to overlying waters or precipitated at the oxic suboxic boundary within the sediment forming subsurface mn spikes manganese carbonate is a characteristic feature of these early diagenetic mn enrichments in the cores from the equatorial divergence where glacial interglacial productivity changes have been recorded by geochemical and isotopical evidence manganese carbonate peaks occur at deglaciation phases decreased supply of organic matter though the total manganese contents are nearly constant indicating that manganese carbonate survives burying to anoxic sediments better than mn iv phases in sediments of the central walvis ridge underlying nutrient poor surface waters peaks of mn iv and manganese carbonate occur in glacial sections thus giving evidence of higher reduction rates through increased supply of the reducing organic matter the higher flux of organic matter is attributed to a higher surface water productivity during glacials on the central walvis ridge since the evaluation of paleoproductivity proxies in that area is ambigous the interpretation of manganese and manganese carbonate profiles is an important qualitative tool supporting glacial interglacial changes in paleoproductivity

ree fractionation and nd isotope disequilibrium during crustal anatexis constraints from himalayan leucogranites abstract the processes controlling rare earth element ree behaviour during crustal anatexis have profound implications not only for ree abundances of crustally derived granites but also for their model nd ages for typical protoliths of anatectic granites such as are exposed in metapelites from the high himalayan crystalline series hhcs a high proportion 90 of bulk rock lree and mree are sited in the accessory phases apatite and monazite and of hree in garnet and apatite mass balance constraints indicate that observed ree abundances of himalayan leucogranites cannot be generated from ree deficient reactant phases in their metasedimentary protoliths muscovite biotite plagioclase and quartz but must result from the dissolution of accessory phases ree and th abundances in anatectic melts are modelled by combining empirical expressions for monazite apatite and zircon solubilities as a function of temperature melt composition and melt water content with analysed accessory phase ree abundances this approach which allows the contribution to the melt from each accessory phase to be identified successfully predicts himalayan leucogranite trace element abundances the lree and th concentrations of a metapelite derived melt are buffered by monazite stability although apatite dissolution contributes up to 10 of lree to the melt together with 50 of the mree and 90 of the hree zircon contributes a negligible proportion of ree to the melt during anatexis dissolution of monazite and apatite in the melt results in 1 increasing ree abundances and lree hree ratios with increasing temperature of melting 2 a negative eu anomaly in the melt 3 high sm nd ratios in the melt relative to its metasedimentary protolith and 4 nd isotope disequilibrium between the melt and its protolith all of these features are observed in the ree geochemistry of himalayan leucogranites the combined effects of sm nd fractionation and nd isotope disequilibrium during anatexis imply that model nd ages calculated for anatectic granites derived from apatite and monazite bearing protoliths should be treated with considerable caution

quantifying manganese and nitrogen cycle coupling in manganese rich organic carbon starved marine sediments examples from the clarion clipperton fracture zone extensive deep sea sedimentary areas are characterized by low organic carbon contents and thus harbor suboxic sedimentary environments where secondary autotrophic redox cycling becomes important for microbial metabolic processes simulation results for three stations in the eastern equatorial pacific with low organic carbon content 20 m concentrations

descending layer variability over arecibo descending layers of ionization over arecibo exhibit very diverse behavior from night to night that does not appear to be strongly correlated to geomagnetic activity solar forcing or average semidiurnal tidal winds on some nights three or more distinct layers are observed to form near 170 km over timescales of approx 2 hours rather than descending smoothly over periods of several hours these layers stall abruptly disappear or even reverse direction in the midst of their descent the time scales for their disappearance are examined and compared to loss rates arising from diffusion and recombination diffusion alone is found to be too slow to account for the observations but recombination is fast enough provided that the convergent wind shear that forms the layer is relatively weak coincident with their disappearance the continuity equation is solved in conjunction with a time sequence of radar profiles to estimate the vertical drift and horizontal neutral wind consistent with the observed behavior the resultant wind field is northward has an average speed of approx 80 m s and varies significantly near the altitude where the layers are observed these inferred winds are consistent with the presence of the observed layers and their magnitudes as obtained from the classical continuity and momentum equations are reasonable for this altitude range

sources of phanerozoic granitoids in the transect bayanhongor ulaan baatar mongolia geochemical and nd isotopic evidence and implications for phanerozoic crustal growth abstract the central asian orogenic belt caob is renowned for massive generation of juvenile crust in the phanerozoic mongolia is the heartland of the caob and it has been subject to numerous investigations particularly in metallogenesis and tectonic evolution we present new petrographic geochemical and sr nd isotopic analyses on phanerozoic granitoids emplaced in west central mongolia the data are used to delineate their source characteristics and to discuss implications for the phanerozoic crustal growth in central asia our samples come from a transect from bayanhongor to ulaan baatar including three tectonic units the baydrag cratonic block late archean to middle proterozoic the eo cambrian bayanhongor ophiolite complex and the hangay hentey basin of controversial origin the intrusive granitoids have ages ranging from ca 540 to 120 ma the majority of the samples are slightly peraluminous and can be classified as granite s s including monzogranite syenogranite and alkali feldspar granite most of the rocks have initial 87sr 86sr ratios between 0 705 and 0 707 late paleozoic to mesozoic granitoids 250 ma are characterized by near zero end t values 0 to 2 whereas older granitoids show lower end t values 1 5 to 7 the data confirm the earlier observation of kovalenko et al geochemistry international 34 1996 628 who showed that granitoids emplaced outside of the pre riphean basement rocks are characterized by juvenile positive end t values whereas those within the pre riphean domain and the baydrag cratonic block as for the present case show a significant effect of contamination by precambrian basement rocks nevertheless mass balance calculation suggests that the granitoids were derived from sources composed of at least 80 juvenile mantle derived component despite our small set of new data the present study reinforces the general scenario of massive juvenile crust production in the caob with limited influence of old microcontinents in the genesis of phanerozoic granitoids

an upper e region quarterdiurnal tide at arecibo studies of the time height trajectories of ionosphere e region layers at arecibo have revealed not only the usual diurnal sporadic e and semidiurnal intermediate layer structures but also that on occasion extra layers form and descend through the e region in particular during january 1981 four layers per day were observed to descend through the upper e region this four per day layer system was remarkably coherent over the 3 days of observation and suggests the existence of a 6 hour period or quarterdiurnal tidal wind system in the upper e region numerical simulations of ion trajectories in a realistic model atmosphere with diurnal semidiurnal and quarterdiurnal tidal wind systems of appropriate amplitude and phase structures confirm that the presence of a quarterdiurnal tide is sufficient to explain the observations

productivity patterns in the equatorial pacific over the last 30 000 years the equatorial pacific traverses a number of productivity regimes from the highly productive coastal upwelling along peru to the near gyre like productivity lows along the international dateline making it an ideal target for investigating how biogeochemical systems respond to changing oceanographic conditions over time however conflicting reconstructions of productivity during periods of rapid climate change like the last deglaciation render the spatiotemporal response of equatorial pacific productivity ambiguous in this study surface productivity since the last glacial period 30 000 years ago is reconstructed from seven cores near the line islands central equatorial pacific and integrated with productivity records from across the equatorial pacific three coherent deglacial patterns in productivity are identified 1 a monotonic glacial holocene increase in productivity primarily along the equator associated with increasing nutrient concentrations over time 2 a deglacial peak in productivity 15 000 years ago due to transient entrainment of nutrient rich southern sourced deep waters and 3 possible precessional cycles in productivity in the eastern equatorial pacific that may be related to intertropical convergence zone migration and potential interactions with el nino southern oscillation dynamics these findings suggest that productivity was generally lower during the glacial period a trend observed zonally across the equatorial pacific while deglacial peaks in productivity may be prominent only in the east

zircon trace element and isotopic sr nd hf pb effects of assimilation fractional crystallization of pegmatite magma a case study of the guangshigou biotite pegmatites from the north qinling orogen central china abstract evidence for open system magmatic processes related to wallrock assimilation accompanied by fractional crystallization afc is present in the guangshigou biotite pegmatites north qinling orogen the biotite pegmatite gneiss contacts generally coincide with the greatest enrichment of u and th zircon u pb dating constrains the crystallization ages of the biotite pegmatite rim zone 415 2 6 ma internal zone 413 5 2 5 ma in line with a pyrite pb pb isochron age 413 22 ma metamict areas in zircon show generally elevated concentrations of trace elements and expulsion of radioactive pb internal zone samples representing uncontaminated magma have negative to positive zircon 413 ma ehf t 1 53 3 24 low end t values 2 4 and old hf and nd model ages tdm2 1 5 1 19 ga t2dm 1 35 ga respectively indicating a dominantly recycled mesoproterozoic lower crustal material with involvement of some juvenile materials in the source region the magmatic oxygen fugacity fo2 and crystallization temperatures ranges from 24 81 to 13 34 of log fo2 and 570 c to 793 c respectively compared to the internal zone pegmatite rim samples display a variable and lower end t values 3 9 to 2 8 and t2dm 1 47 1 37 ga but similar hf isotopic compositions favouring a three component isotopic mixing model recycled mesoproterozoic lower crust materials juvenile materials and host gneiss pronounced variations of ti y u th hf and ree concentrations in zircon from grain to grain in individual samples and from area to area within individual grains suggest a fluctuating crystallization environment in hybridized magma from which the rim hosted zircons crystallized variable and high radiogenic pb ratios of pyrites forming in the hybridized magma were inherited from the matrix zircons from both zones exhibit similar hf isotope patterns indicating the rim hosted zircons crystallized during the early stage of hybridization of magma however the heterogeneous nd isotopic composition in individual pegmatites imply an incorporation of wallrock derived melt with less radiogenic nd

effects of progressive oxygen depletion on sediment diagenesis and fluxes a model for the lower st lawrence river estuary we applied a diagenetic model to examine the effects of a decadal timescale progressive decrease in bottomwater oxygen concentration on sediment geochemistry and fluxes across the sediment water interface the model was calibrated using geochemical data acquired over the last 30 yr in the lower st lawrence river estuary canada where the bottom water oxygen concentration has been decreasing at an average rate of 1 mmol l21 yr21 over the past 70 yr benthic fluxes calculated from the model are comparable to fluxes derived from shipboard sediment incubations by propagating the model forward in time and allowing the oxygen concentration to decrease further at 1 mmol l21 yr21 we predict changes in the distributions and fluxes of iron manganese phosphorus nitrogen and sulfur as the oxygen concentration decreases the concentrations and distributions of reactive phases in the sediment change at an accelerating pace fluxes of reduced substances out of the sediment increase reactive iron and manganese oxide phases become depleted and the sediment becomes progressively enriched in iron sulfides a notable exception is the efflux of phosphate which remains invariant at the study site these changes are likely to become measurable within the next 20 yr model results are sensitive to the effects of decreasing oxygen concentrations on the benthos the response of which we represent by two different approximations of the bioturbation and bioirrigation formulations a gradual decrease and a thresholdtype decrease the principal obstacle to reliable predictions of how sediments will respond is the lack of knowledge about the response of bioturbation and bioirrigation to decreasing oxygen in bottom waters

triassic granitoids of the qinling orogen central china genetic relationship of enclaves and rapakivi textured rocks abstract granitoids varying in composition from biotite amphibole granodiorite to monzogranite with rapakivi textures have recently been recognized in the qinling orogen central china the granitoids are magnesian calc alkalic and metaluminous a cnk 0 71 0 95 they contain many mafic to intermediate microgranular enclaves the enclaves are quenched mafic melts in granitic host magma as evidenced by fine grained sinuous margins against or transitional contacts with the host granitoids as well as disequilibrium textures and mineral assemblages u pb zircon dating of the granitoids yields 209 2 ma and 212 2 ma and the enclaves 210 2 ma and 211 2 ma respectively the host granitoids and enclaves show obvious silica gap but similar ree and trace element patterns the whole rock 87sr 86sr t end t and zircon ehf t values for the granitoids vary from 0 70516 to 0 70634 2 3 to 4 4 and 0 7 to 7 6 and for the enclaves from 0 70467 to 0 70600 1 1 to 4 0 and 1 2 to 8 8 respectively showing overlapped end t and zircon ehf t values all these suggest that the two magmatic systems represented by the host rock and enclave are probably derived from distinct sources with sufficient interaction or common origin but underwent different degrees of crustal contamination mineralogical and geochemical data point to enclave dissolution in silicic magma as a major process accounting for the origin of the rapakivi texture the possible bimodal magmatism suggested by the coeval granitoids and lamprophyre dykes combined with the structural pattern geochemical features and regional tectonics suggest a post collision setting for the qinling rapakivi textured granitoid plutons

monazite controlled sm nd fractionation in leucogranites an ion microprobe study of garnet phenocrysts rare earth element ree abundances in four garnet phenocrysts from two monazite bearing leucogranites from southern british columbia have been measured with an ion microprobe this study examines the effect of monazite crystallization on the lrees by using garnet as a monitor of elemental variations in the liquid this approach virtually eliminates uncertainties associated with source induced lree fractionation the garnets examined are spessartine rich alm70 75sps18 22pyp3 4grs3 4 phenocrysts that show primary igneous zoning and lack monazite inclusions garnet rims have zoning profiles i e eu to ce that are depleted by factors of five to ten relative to cores of the three models investigated to constrain processes controlling lree zoning in garnet 1 1 variations in the garnet melt distribution coefficients 2 2 liquid diffusion controlled partitioning and 3 3 crystal diffusion controlled partitioning the latter model best explains the observed zoning this model is consistent with experimental studies suggesting that monazite has a low solubility in granitic melts these results suggest that nd model ages calculated using measured 147sm144nd in leucogranites should be viewed with caution as is demonstrated by neodymium isotopic data from southern british columbia and the central nepalese himalaya

a study of tidal and planetary wave periodicities present in midlatitude sporadic e layers the diurnal and semidiurnal atmospheric tides are known to be of fundamental importance in the formation of midlatitude sporadic e layers acting through their vertical windshear forcing of the long living metallic ions in the lower thermosphere also recent studies suggested that planetary waves play a role on sporadic e generation as well a fact that went unnoticed in the long going research of sporadic layers in this paper a methodology is employed to investigate the tidal and planetary wave periodicities imprinted onto sporadic e critical frequencies foes in this approach standard analysis techniques used in neutral atmospheric dynamics are applied on foes time series obtained during summertime when sporadic e occurrence is nearly continuous it is shown that besides the dominant and known 24 hour and 12 hour tidal periodicities in foes there is often a weaker terdiurnal 8 hour oscillation present as well in addition there are planetary wave periodicites in foes with periods near the normal rossby modes that is 2 5 10 and 16 days it is also found that the tidal oscillations in foes undergo a strong amplitude modulation with periods comparable to the dominant planetary wave periodicities present in the data our results are in line with recent findings based on a single event study which suggested that sporadic e layers are affected indirectly by planetary waves through their nonlinear interaction and modulation of the atmospheric tides at lower altitudes the close relationship between neutral wave dynamics and midlatitude sporadic e periodicities suggests that the ionosonde data can be used as an alternative means of studying tidal and planetary wave characteristics and their climatology in the lower thermosphere

sequential leaching of peru basin surface sediment for the assessment of aged and fresh heavy metal associations and mobility abstract sequential leaching experiments were carried out using the upper 25 cm of oxic to suboxic sediment from the peru basin and ferromanganese nodules in order to assess potential mobility and the associations of heavy metals in the mineral phases the general leaching pattern confirmed that in the nodules as well as in the upper dark brown sediment layer significant proportions of heavy metals like mn co ni zn cu and cd are associated with mno2 and would be released under reducing conditions in the underlying mn poor layers mn oxide hosted metals are minor to distinguish the leaching behaviour of aged and fresh sorbents radiotracers were adsorbed on the solids before leaching the dominant role of the mn oxide phase for scavenging dissolved heavy metals was confirmed for the upper sediment layer and the nodules for sorption equilibration times of 5 h and 7 days respectively the sorption process was rapid freshly sorbed metals were leached mostly in the same fractions as those in aged sorbents and little difference was found for sorption times of 5 h and 7 days in contrast in the mn poor sediment layers a significant amount of adsorbed radiotracers was easily remobilised by simple ion exchange especially cs and cd and an ageing effect shift to less easily leachable fractions was observed after 7 days when surface sediment is resuspended into the bottom water the mn oxide rich surface layer and nodule particles represent a much more effective heavy metal scavenger under oxic conditions compared to other mn poor sediment phases however at the same time the mn rich particles are a stronger potential source of toxic heavy metals in a shift to more reducing conditions

energy constrained open system magmatic processes 3 energy constrained recharge assimilation and fractional crystallization ec rafc 1 geochemical data for igneous rock suites provide conclusive evidence for the occurrence of open system processes within thermally and compositionally evolving magma bodies the most significant processes include magma recharge with possible enclave formation and magma mixing assimilation of anatectic melt derived from wallrock partial melting and formation of cumulates by fractional crystallization rafc in this study we extend the energetically constrained assimilation and fractional crystallization ec afc model spera and bohrson 2001 bohrson and spera 2001 to include the addition of compositionally and thermally distinct recharge melt during simultaneous assimilation and fractional crystallization energy constrained recharge assimilation and fractional crystallization ec rafc tracks the trace element and isotopic composition of melt cumulates and enclaves during simultaneous recharge assimilation and fractional crystallization ec rafc is formulated as a set of 3 t i s coupled nonlinear differential equations where the number of trace elements and radiogenic and stable isotope ratios modeled are t i and s respectively solution of the ec rafc equations provides values for the average wallrock temperature ta mass of melt within the magma body mm mass of cumulates mct and enclaves men mass of wallrock involved in the thermal interaction mao mass of anatectic melt assimilated m a concentration of t trace elements and i s isotopic ratios in melt cm cumulates cct enclaves cen and anatectic melt ca as a function of magma temperature tm input parameters include the equilibration temperature teq the initial temperature and composition of pristine melt tmo cmo emo recharge melt tro cro ero and wallrock tao cao eao temperature dependent trace element distribution coefficients dm dr da heats of transition for wallrock ha pristine melt hm and recharge melt hr and the isobaric specific heat capacity of assimilant cp a pristine melt cp m and recharge melt cp r the magma recharge mass function mr tm is specified a priori and defines how recharge magma is added to standing magma the present ec rafc simulator incorporates a weak coupling to major element mass balance and phase relations based on laboratory experiments or gibbs energy minimization e g ghiorso 1997 ec rafc can be applied to a variety of magmatic systems including volcanic suites that show evidence of magma mixing layered mafic intrusions and granitoid plutons predictions for masses as well as compositions of magmatic products are part of the ec rafc solution the systems approach provides an opportunity to quantitatively assess the roles of assimilation fractional crystallization and magma recharge in magma evolution using trace element and isotopic constraints together with energy conservation

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

sediment delivery and depositional patterns off adelie land east antarctica in relation to late quaternary climatic cycles article i nfo this study focuses on the understanding of depositional patterns over late quaternary glacial interglacial cycles and of the influence of diagenesis on geochemical sedimentary records from the continental margin off adelie land east antarctica we provide a complete analysis of the 30 m long sediment core md03 2603 collected on a deep sea sediment mound deposit the lr04 benthic oxygen isotope stack vs down core records of ba al and ba ti atomic ratios reflectance data and micropaleontological evidence allow to determine a detailed chronology back to 490 ka bp long lived uranium and thorium 238 u 234 u 232 th and 230 th provide an assessment of lateral vs vertical sediment advection by constraining the sediment focusing factor is high in most glacial intervals when mostly detrital material was transported down slope and focused to the core area interglacials display highs in ba al and ba ti coupled to low values related to stronger contour current flow biogenic fractions are more abundant during interglacials and more diluted by detrital fractions during glacials the diatom assemblage is dominated by the open ocean species fragilariopsis kerguelensis but glacial intervals display an increase of sea ice related and coastal species the integrated approach high resolution record of major and minor elements uauth 15 n norg 13 c and corg provides key insights into how redox conditions affect glacial interglacial sedimentation processes our evidence shows that diagenetic effects due to development of reducing conditions and consequent higher preservation of organic matter may overprint the paleoclimatic significance of some proxies involved into a sequence of diagenetic remineralization pathways comparison of the marine record to ice core data epica dome c edc allows to extend the information to the whole east antarctic margin sediment proxies of increased burial of biogenic material or increased preservation of organic matter are linked to climatic amelioration on the continent highs in edc dust flux correlate with high mn al and mo al ratios within the sediment record confirming that establishment of colder conditions on the continent triggered changes in sedimentation rates at the glacial interglacial transition which in turn affected the development of reducing redox fronts within the sediment