microbial sulfate reduction in deep sea sediments at the guaymas basin hydrothermal vent area influence of temperature and substrates abstract microbial sulfate reduction was studied by a 35 s tracer technique in sediments from the hydrothermal vent site in guaymas basin gulf of california mexico in situ temperatures ranged from 2 7 c in the overlying seawater to 120 c at 30 cm depth in the hydrothermal sediment sulfate reduction was measured in intact cores of hydrothermal sediment at 3 20 35 50 70 and 90 c the maximum rates of sulfate reduction were found in the upper 0 2 cm of the sediment and ranged from 32 nmol cm 3 d 1 at 90 c to 1563 nmol cm 3 d 1 at 70 c the rates of sulfate reduction rapidly decreased with depth in the upper 0 10 cm of the sediment and the maximal depth integrated rate 0 10 cm was 70 3 mmol so 4 2 m 2 d 1 at 70 c in comparison the sulfate reduction rate in nonhydrothermal sediment from the vent area was 0 85 mmol m 2 d 1 at the in situ temperature of about 3 c the high subsurface rates of sulfate reduction in the hydrothermal vent area was attributed to an enhanced local substrate availability in slurries of hydrothermal sediment incubated at 10 120 c microbial sulfate reduction extended to 102 c and different temperature groups of microbial sulfate reducers had optimum temperatures at around 34 70 and 80 88 c the overall temperature response of thermophilic sulfate reduction was similar in hydrothermal sediment sampled at different sites addition of short chain fatty acids and yeast extract to the sediment slurries stimulated sulfate reduction rates at all incubation temperatures no sulfate reduction was detected in the temperature range from 102 120 c microbial rather than thermochemical sulfate reduction could be a possible source of h 2 s in sulfide deposits with formation temperatures at about 100 c

provenances of the mesozoic sediments in the ordos basin and implications for collision between the north china craton ncc and the south china craton scc abstract to constrain the provenance of the ordos basin and the evolution history of the qinling orogen belt from the triassic to the jurassic 10 samples from the dongsheng area and 28 samples from the yan an area were analyzed for u pb ages and lu hf and sm nd isotopic compositions the results indicate that middle jurassic sediments in the dongsheng area were derived from the khondalite belt langshan mountain and the yinshan terrane mesozoic sediments in the yan an area consist of two parts one part is derived from the north china craton ncc which has u pb age groups of 1 8 ga and 2 5 ga and hf model ages of 2 8 ga the other part is derived from the qilian qinling orogenic belt which has u pb age groups of 600 1500 ma and 100 500 ma and nd and hf isotopic model ages of less than 2 2 ga combining the u pb ages with the hf and nd isotopic model ages mesozoic detrital zircons with u pb age groups of 1 8 ga and 2 5 ga in the yan an area are found to also be derived from the khondalite belt langshan mountain and the yinshan terrane not from the trans china orogen belt from the late late triassic sediments of the yan an area the low average values of the hf 2 03 ga and nd 2 03 ga model ages and the characteristic age population of 600 1500 ma reveal that the main collision or continental subduction between the ncc and the south china craton scc occurred in the late late triassic after the main collision or continental subduction the proportion of sediments from the qinling qilian orogenic belt began to decrease recorded in the early jurassic samples which may be in response to the gradual slowing of the uplift speed of the qinling orogenic belt in the early middle jurassic the sediments have a main u pb age population of 100 500 ma low detrital zircon hf model ages average value is 1 17 ga and low whole rock nd model ages average value is 1 13 ga which suggests that the qilian qinling orogenic belt may have a fast uplift history in the early middle jurassic

remotely sensed debris thickness mapping of bara shigri glacier indian himalaya despite the important role of supraglacial debris in ablation knowledge of debris thickness on himalayan glaciers is sparse a recently developed method based on reanalysis data and thermal band satellite imagery has proved to be potentially suitable for debris thickness estimation without the need for detailed field data in this study we further develop the method and discuss possibilities and limitations arising from its application to a glacier in the himalaya with scarce in situ data surface temperature patterns are consistent for 13 scenes of advanced spaceborne thermal emission and reflection radiometer aster and landsat 7 imagery and correlate well with incoming shortwave radiation and air temperature we use an energy balance approach to subtract these radiation or air temperature effects in order to estimate debris thickness patterns as a function of surface temperature both incoming shortwave and longwave radiation are estimated with reasonable accuracy when applying parameterizations and reanalysis data however the model likely underestimates debris thickness probably due to incorrect representation of vertical debris temperature profiles the rate of heat storage and turbulent sensible heat flux moreover the uncertainty of the result was found to increase significantly with thicker debris a promising result since ablation is enhanced by thin debris of 1 2 cm

comparison of 14c ages of hydrothermal petroleums abstract in order to set limits on the time frame of formation of hydrothermal petroleum we have obtained 14 c ages on samples from three diverse regions gulf of california guaymas basin northeast pacific ocean escanaba trough and middle valley and the east african rift tanganyika trough the results date the source of carbon and therefore provide maximum ages for the formation and emplacement of the hydrothermal petroleums the youngest petroleum occurs iin the souther trough of guaymas basin 3200 6600 yr mean 4692 yr in the northern trough the petroleum is slightly older 7400 yr significantly older hydrothermal petroleum occurs in escanaba trough 17 000 yr and middle valley 29 000 yr a continental example from the east african rift has an age of 25 000 yr comparable to the ages observed in the oceanic samples from the northeast pacific ocean these ages affirm that hydrothermal petroleum formation is a very rapid process and took place some time between the latest pleistocene and the present in these active hydrothermal systems

local wind system in the rongbuk valley on the northern slope of mt everest 1 to better understand the local wind systems in the himalayas wind and related atmospheric parameters were observed in the rongbuk valley on the northern slope of mt everest during the hest2006 campaign from may 29 to june 29 2006 data analysis and a simple numerical simulation show that the dominating down valley flow in this valley is mainly formed by the thermally driven winds valley wind mountain wind and glacier wind the vertical air motion is composed of a descending flow from the morning to midnight and an ascending flow for the rest of the day with important modification from the vertical component of the above down valley flow and a compensation flow of the slope wind the analysis also shows that the local wind system is well confined in the rongbuk valley due to topographic shielding effects

geochemical implications of the lipid composition of thioploca spp from the peru upwelling region 15 s thioploca a genus of colorless sulphur oxidizing filamentous bacteria constitutes as much as 80 of the biomass in dysaerobic surface sediments o2 0 1 ml l bottom water in the coastal upwelling regimes of peru and chile the lipid composition of thioploca collected from sediments from the oxygen minimum zone in the peru upwelling region near 15 s is presented here and we provide the first assessment of the influence of thioploca on organic compound distributions in upwelling regime sediments since marine species of thioploca have been found only in dysaerobic surface sediments of upwelling regimes biomarkers for this organism may be useful in identifying similar depositional conditions in the sedimentary record thioploca dry was found to be 3 8 4 1 wt lipid three fatty acids cis 16 1 9 16 0 and cis 18 1 11 accounted for 69 72 of this lipid hydroxy fatty acids hopanoids and hydrocarbons were conspicuously absent from the thioploca the thioploca was found to contain cyclolaudenol a c31 sterol with an unusual structure diagenetic alteration products of this sterol may serve as markers for thioploca input to sedimentary organic matter and hence as markers for paleo upwelling depositional environments in the sedimentary record

crustal architecture and its controls on mineralisation in the north china craton abstract knowledge of the history of the earth s continents and the genesis of mineral deposits is poorly understood on a crustal scale this contribution combines geological and zircon hf isotopic data collected from igneous rocks associated with mineralisation to gain a better understanding of the nature of the growth of and mineral genesis in the north china craton the new zircon u pb dates reported here are 2587 62 ma for syenogranite at zanhuang in the northeast part of craton 2552 24 ma for trondhjemitic gneiss and 2554 29 ma for metadiorite at dengfeng in the eastern and central part of and 2820 6 and 2821 32 ma for tonalite at lushan in the southeast part of the craton lu hf isotopic data collected from granitic rocks for this study yield ehf t values and hf crustal model ages tdmc of 3 5 8 and 2580 2600 ma for the syenogranite at zanhuang 1 9 7 4 and 2550 2580 ma for trondhjemitic gneiss and metadiorite at dengfeng and 0 5 5 2 and 3120 2840 ma for tonalite at lushan six major magmatic events have been recognised throughout the region the crustal growth and reworking of the craton includes eo to mesoarchean early neoarchean and paleoproterozoic events the consistency in the evolution of neoarchean magmatism coupled with zircon hf isotope systematics indicate that similar crustal growth and reworking were in action in the eastern trans north china and western blocks the crust architecture indicated by hf isotopic mapping of the north china craton constrains the distribution of mineral deposits the bif hosted fe deposits are spatially related to juvenile or reworked crustal domains with groups of deposits located internal to and at the margins of archean terranes and orogenic au deposits are spatially associated with juvenile crustal domains

hydrothermal petroleum genesis migration and deposition in guaymas basin gulf of california hydrothermal activity and seabed mounds have been explored in guaymas basin by the deep sea drilling project dsdp piston coring dredging and diving with the deep submersible research vessel dsrv alvin sedimentary organic matter derived primarily from immature degraded microbial detritus is easily converted to petroleum under the hydrothermal regime these petroleums are mature and migrate in the fluids and by diffusion to the seabed the fluid migration is aided by near critical aqueous solution and supercritical carbon dioxide and hydrocarbons petroleum compositions vary from condensates to naphthenic to waxy all with significant amounts of asphaltenes and hydrothermal products such as olefins and toxic polynuclear aromatic hydrocarbons pah the heavy ends condense at the seabed depositing mainly as a cement with the sulfides and other minerals and to a lesser extent as entrapped oil and crystalline wax in vugs and conduits of the mounds the pah are high temperature resynthesis aromatiza

structural pattern of the wutai complex and its constraints on the tectonic framework of the trans north china orogen abstract wutai complex is a key to test controversial models for the tectonic evolution of the trans north china orogen tnco along which the eastern and western blocks amalgamated to form the north china craton three stages of deformation d 1 to d 3 were identified in the wutai complex d 1 is characterized by ne sw trending foliations s 1 and nw se orientated lineations l 1 indicating an initial nw se directed compression associated with d 1 was prograde metamorphism m 1 d 2 progressively overprinted d 1 and generated z shaped folds and nee sww trending ductile shear zones d 2 resulted in a fan shaped structural pattern of the complex with top to the nw thrusting in the northwestern part and opposite top to the se thrusting in the southeastern part during d 2 the crust was doubled through thickening leading to peak metamorphism m 2 d 3 developed during post collision exhumation and deformed the early fabrics to be open folds resulting in near isothermal decompression m 3 and late cooling metamorphism m 4 the overall structure of the wutai complex is characterized by a fan shaped pattern with structural divergence structural features of the wutai complex combined with those of the adjacent hengshan and fuping complexes indicate that the tnco is characterized by a fan shaped orogenic wedge with opposite senses of thrust this orogenic wedge could have resulted from an eastward subduction and collision between the western and eastern blocks to finally form the tnco at 1 85 ga

organic rich sediment alteration an experimental and theoretical study at elevated temperatures and pressures organic rich diatomaceous ooze was reacted with sea water at 200 and 300 c 500 bars and an initial fluid sediment mass ratio of 4 to evaluate the role of organic matter in sediment alteration processes at elevated temperatures and pressures decomposition of organic matter during the early stages of reaction dominated alteration and resulted in increased dissolved co2 corganic nh4 and h2s car ylic acids were identified as reaction intermediaries during the transformation of organic matter to ch4 and co2 extensive so42 reduction was observed at 300 c but not at 200 c sediment alteration at 300 c resulted in recrystallization of calcic plagioclase and diatoms to an assemblage containing albite pyrrohotite and quartz in addition to minor anhydrite and mg smectite in contrast sediment alteration at 200 c resulted in only minor anhydrite and mg smectite formation and there was no indication of recrystallization of diatoms to quartz rapid mg fixation during the early stages of alteration resulted in the complete removal of mg from solution at 300 c and partial removal at 200 c production of acidity associated with mg metasomatism was efficiently titrated by thermolytic and oxidative degradation of organic matter resulting in conspicuously low dissolved metal concentrations during the experiments in the later stages of sediment alteration at 300 c albitization of calcic plagioclase caused the continuous release of ca to solution while at 200 c fluid chemistry remained relatively constant speciation calculations for the 300 c experiment indicate an in situ ph of 5 11 and a highly reduced redox state likely controlled by organic matter decomposition experimental results permit us to evaluate fluid mineral equilibria in complex fluids containing high concentrations of dissolved organic species co2 and h2s and constrain better alteration processes in sub sea floor hydrothermal systems at sediment covered spreading centers such as the guaymas basin gulf of california

nd isotopic constraints on crustal formation in the north china craton abstract recent tectonic analysis suggests that the north china craton consists of two archean continental blocks called the eastern and western blocks separated by the paleoproterozoic trans north china orogen although the published geochronological data are not sufficient to constrain the detailed tectonothermal evolution of the craton the available nd isotopic data show some important differences in nd model ages between the tectonic units the eastern block shows two main nd model age peaks one between 3 6 and 3 2 ga and the other between 3 0 and 2 6 ga limited nd isotopic data from the western block show a large range of model ages between 3 2 and 2 4 ga these differences are consistent with the recently proposed model the nd isotopic data from mantle derived mafic rocks indicate that the mantle beneath the north china craton was depleted in the archean consistent with major crustal growth during this period in the paleoproterozoic however the mantle derived mafic rocks show negative end t values implying crustal contamination this may have resulted from subduction and collision between the eastern and western block implying that the mechanisms of crustal formation and evolution may have been different between the archean and paleoproterozoic the north china craton was re activated by addition of mantle derived magma into the lower crust in the late mesozoic resulting in rejuvenation of the lower crust this indicates that underplating is also an important mechanism for continental addition although in this case it may not equate to crustal growth since it was preceded by removal of lithospheric mantle and possible some lower crust

geochemical origin of hydrothermal fluid methane in sediment associated fields and its relevance to the geographical distribution of whole hydrothermal circulation abstract we investigated the chemical composition of hydrothermal fluids and deduced the origin of hydrothermal fluid methane in a sediment associated minami ensei me hydrothermal field the okinawa trough the endmember hydrothermal fluid of the me field contained isotopically 13 c enriched methane 26 0 to 24 7 which suggested a thermogenic origin however the observed methane dominating hydrocarbon compositions c 1 c 2 10 3 suggested that biogenic methane not thermogenic hydrocarbons is predominant the conflict between these geochemical indications can be resolved by the hypothesis that the thermal reaction of sedimentary organic matter initially generates the primary source of hydrocarbons and the secondary thermal decomposition of hydrocarbons increases the c 1 c 2 ratio as high as that of biogenic methane the low molecular hydrogen concentration 0 04 mmol kg in the me fluid suggests that the thermal fluid sediment interaction occurred in the recharge stage not the discharge stage of hydrothermal circulation less biogenic methane in the me fluid implies a laterally shrunken hydrothermal fluid circulation that reduced biogenic methane incorporation at the recharge stage a comparison of hydrothermal fluid chemistry and geological geographical settings among the global sediment associated hydrothermal systems also suggests representative patterns in the geochemical origins of hydrothermal fluid methane and their relevance to hydrothermal fluid circulation as a whole

episodic crustal growth in the southern segment of the trans north china orogen across the archean proterozoic boundary abstract the dengfeng and taihua complexes are well exposed neoarchean to paleoproterozoic units in the southern segment of the trans north china orogen tnco zircon u pb dating shows that the dengfeng complex records two episodes 2568 11 ma and 2306 6 ma of tonalite trondhjemite granodiorite ttg magmatism all of the ttg rocks are characterized by high sio2 66 7 75 4 wt na2o 3 20 5 06 wt and relatively low mgo 0 40 1 78 wt the late neoarchean ttg gneisses have very low contents of hree ybn 0 69 2 75 and y 1 73 7 07 ppm with moderate la yb n 24 1 53 8 and high sr y 65 1 291 3 ratios the early paleoproterozoic ttg gneisses have low contents of hree ybn 2 93 6 37 and y 6 7 11 0 ppm with moderate la yb n 10 1 27 0 and sr y 10 6 52 1 ratios both suites show pronounced negative nb ta p and ti anomalies but positive sr and pb anomalies the late neoarchean ttg gneisses all have similar bulk rock nd and zircon hf model ages with mainly positive nd t and are interpreted as resulting from the melting of dominantly juvenile thickened lower crust with residual garnet and amphibole the early paleoproterozoic ttg gneisses have extremely variable nd t 6 23 to 4 23 and heterogeneous zircon hf t 3 3 to 3 1 which are also best interpreted as resulting from the partial melting of thickened lower crust with residual amphibole and garnet the taihua complex in the xiaoqinling area records three episodes of early paleoproterozoic ttg magmatism 2 48 ga at caotan 2 31 ga at houjiacun and 2 16 ga at bayuan younger than the taihua complex in the lushan area 2 85 2 72 ga all rocks have relatively low contents of hree ybn 1 03 8 32 and y 2 84 24 ppm with moderate la yb n 8 7 88 4 and sr y 19 8 125 8 ratios and show negative ta nb and ti anomalies and positive sr and pb anomalies the caotan gneisses at 2 48 ga and the houjiacun ttg gneisses at 2 31 ga have low mg 0 14 0 45 low cr the geochronology of the dengfeng complex in the dengfeng area and the taihua complex in the lushan xiong er and xiaoqinling areas reveals at least four magmatic episodes in the southern segment of the tnco from the late mesoarchean to early paleoproterozoic 2 85 2 72 ga 2 57 2 48 ga 2 34 2 30 ga and 2 20 2 07 ga the rocks of the two early episodes are dominantly of juvenile compositions with mostly positive whole rock nd t and zircon hf t values suggesting two episodes of crustal growth formed in a subduction tectonic setting the magmatic rocks of the third episode consist of both the juvenile and pre existing crustal materials with variable whole rock nd t and zircon hf t values which were generated in a subduction zone during the initial assembly of the ncc within the columbia supercontinent cycle the final episode of magmatism lacks juvenile materials with whole rock nd t and zircon hf t values being consistently negative these may have resulted from the orogenic collapse the episodic continental growth recorded in the southern segment of the tnco was caused by subduction and consequent orogeny consistent with global supercontinent cycles within the late archean and early paleoproterozoic

role of bacterial mats in oxygen deficient marine basins and coastal upwelling regimes preliminary report bacterial mats play an important role in the sedimentation history of many marine biogenic regimes observations of the living mats suggest that in shallow waters they are dominated by photosynthetic cyanobacteria while in deeper waters the mats are dominated by nonphotosynthetic sulfur oxidizing bacteria fossilized remains of analogous mat structures from the miocene monterey formation are commonly associated with oil producing and phosphate rich zones preliminary observations suggest that bacterial mats may be a source of the organic matter that in time is thermally altered to hydrocarbons

crustal growth in the north china craton at 2 5ga evidence from in situ zircon u pb ages hf isotopes and whole rock geochemistry of the dengfeng complex abstract the dengfeng complex is located on the southern margin of the north china craton ncc and belongs to the southern portion of the trans north china orogen this terrane is important to understand the formation and evolution of ncc during late neoarchean 2 5 ga the dengfeng complex is well exposed in the junzhao region and comprises two distinct lithologic units supracrustal assemblage and plutonic rocks la icpms magmatic zircon u pb age data shows that the rocks formed within the range of 2547 2504 ma the available hf isotope data indicate that the majority of ca 2 5 ga zircons from the dengfeng complex have high e hf t values close to the initial hf isotope ratios of the contemporaneous depleted mantle these data indicate that the rocks in the dengfeng represent juvenile crust the ttg gneisses in the dengfeng complex display low mg 41 48 mgo 59 69 mgo 3 5 6 6 wt ni 82 130 ppm and cr 148 237 ppm abundances elevated sr 1759 1927 ppm and ba 1742 2289 ppm concentrations and high lree la n 38 487 such geochemical features are similar to archean sanukitoids a two stage model is applied here to explain the genesis of metadiorites of dengfeng complex 1 firstly the mantle is metasomatized either by melts or by aqueous fluids from a subducted slab 2 subsequently sanukitoid magmas were produced by partial melting of the hybridized mantle furthermore the amphibolites of supracrustal rocks have a mixture of morb and arc like geochemical affinities suggesting the development of a back arc in the southern ncc at ca 2 5 ga the contemporary late neoarchean ttgs sanukitoids and morb back arc association may represent a late neoarchean tectonic melange implying a neoarchean subduction accretion process which would suggest that modern style plate tectonics processes was probably initiated in the southern ncc by 2 5 ga

microbially catalyzed dolomite formation from near surface to burial abstract over the past century a number of models have been developed to explain the vast stratigraphic distribution of authigenic dolomite these models include hydrogeological geochemical and geomicrobiological interpretations that shed light on kinetic constraints on low temperature dolomite formation and in particular how certain microbes can overcome such limitations in this review we focus on the direct and indirect mechanisms by which microbes facilitate the nucleation and shallow burial diagenetic stabilization of dolomite in marine sediments we also consider the likely effects of local and global scale biogeochemical perturbations over the distribution and activities of subsurface microbes and thus potentially over the stratigraphic distribution of dolomite considering the many advances that have been made in the fields of geomicrobiology and biogeochemistry during the past 20 years investigating the important role microbes play in sedimentary systems will undoubtedly contribute to a more complete interpretation of dolomite formation in the rock record

climate and anthropogenic factors influencing an estuarine ecosystem from nw iberia new high resolution multiproxy analyses from san simon bay ria de vigo abstract two sedimentary sequences coastal and subtidal were studied in san simon bay ria de vigo situated on the atlantic coast of nw iberia the coastal record is a shallowing upward sequence which evidences a locally developed low marsh situated below the current beach and dated at the second half of the 4th century during the following decades this low marsh was progressively replaced by an alder swamp which formed on it this suggests an apparent stabilisation or slow down of the relative sea level rsl in this site at the beginning of the dark ages da the subtidal sequence studied reflects the main changes in the landscape the hydrological conditions climate and rsl affecting this part of nw iberia during the last 1250 years evidence of changing dinocysts content in the sediment reveals that two centennial or decadal scale episodes existed of shelf marine waters more intensely penetrating inside the bay between the 15th 18th centuries and at ca 1800 1930 ad besides we related different proxies with the occurrence of four main climatic stages namely the previously described dark ages da ca 350 750 ad the mediaeval climatic anomaly mca ca 750 1100 ad and the little ice age lia ca 1500 1930 ad in addition we propose a regional mca lia transition ca 1100 1500 ad that it has not been previously described our environmental characterization indicates a persistent north atlantic oscillation nao negative mode domain in ria de vigo during the mca but this became weaker during the lia and probably also during the earlier da nao mode become more irregular during the mca lia transition generally persisting in dominant negative mode except for a phase of minor upwelling intensification at ca 1150 1350 ad which mainly affected the external parts of the ria we postulate that an almost simultaneous phase ca 1100 1350 ad of stronger continental contribution in the sediments may be related to increasing storm intensities probably linked to a reinforcement of the easter atlantic ea pattern and also that the intertidal supratidal ecosystems inside san simon bay may have extended further in the past at least towards the end of the 5th century and between ca 1050 1350 ad and ca 1450 1750 ad a number of local historical references are consistent with our palaeoecological data and so support the chronology proposed as well as many of the environmental changes reconstructed this good agreement will help in the interpretation of other analogous sequences extending back in time

glacier winds in the rongbuk valley north of mount everest 2 their role in vertical exchange processes 1 high ozone concentrations combined with low humidity and strong persistent glacier winds were found at the surface of rongbuk valley north of mount everest with sharply increased ozone concentrations in their vertical profiles glacier winds and their roles in vertical exchange of the atmosphere were investigated numerically to understand the phenomena a lagrangian particle dispersion model was used to carry out numerical experiments forward in time simulations and footprint analysis backward in time simulations the meteorological data inputs for these experiments were derived from the advanced regional prediction system results showed that glacier winds may lead to significant downward transport of 1 5 2 km during the daytime from the northern slopes of mount everest glacier winds could advance down through the valley with strong upward motions shown as a rolling up in front of their leading edge combining with upslope winds at two sidewalls of the valley or up valley winds of tributaries the lifting flows produced strong mixing of the atmosphere to a depth of approximately 3 km three dimensional footprints derived from the particle dispersion model for the observational site rongbuk monastery clearly show influence from the mountainside of mount everest and from the southern part of the valley the vertical extension of influence was as much as 2 3 km good correlation was found between the influence height and the ozone concentration all the simulation results strongly indicate that the glacier winds and their related vertical exchange processes pump down ozone rich air from upper levels to the surface of the valley

palaeoproterozoic assembly of the napier complex southern india and western australia implications for the evolution of the cuddapah basin abstract a detailed examination of lithostratigraphic tectonothermal geochronologic and palaeomagnetic database of the dharwar bastar cratons of south india the yilgarn craton of western australia and the east antarctic shield has shown broad similarity two palaeomagnetic key poles of 2400 ma age from the dharwar and yilgarn cratons suggest near neighbor positions matching patterns of craton outlines orientation of mafic dyke swarms and palaeo north direction for 2400 ma have established a continental assembly of siwa an acronym for south india si and western australia wa at 2400 ma in this assembly the yilgarn craton fits against the bastar craton and the singhbhum craton the available geological data from the napier complex of the eastern antarctica and the dharwar craton of south india were used to prepare the barcode style reconstruction of archaean tectonostratigraphic events of both the cratons the method of matching continental outlines the internal features of two continental blocks and the palaeomagnetic data demonstrate that the napier complex was also a part of siwa during the period 2200 1900 ma and was located at the position of the cuddapah basin of india adjacent to the dharwar craton and the yilgarn craton the separation of the napier complex from the south indian block led to the development of the cuddapah basin at 1950 ma

formation age and genesis of the banded iron formations from the guyang greenstone belt western north china craton abstract previous studies focused on banded iron formations bifs from the eastern north china craton ncc few were conducted on those of the western ncc this paper concentrates on two bifs sanheming and gongyiming from the guyang greenstone belt gb western ncc sims u pb analyses of zircons from the amphibolite interlayers of sanheming and gongyiming bifs gave upper intercept ages of 2562 14 ma and 2569 78 ma respectively coupled with 2555 56 ma for the tonalite with bif xenoliths the formation age of the bifs is inferred to be 2 56 2 57 ga protolith reconstruction based on geochemistry and field occurrence of the amphibolites shows that they are originally basaltic trace elements reveal that the basalts of sanheming and gongyiming are t morb and n morb respectively metabasites from other locations of the guyang gb in previous studies display island arc geochemical characteristics plus the lithologic assemblage of komatiite basaltic komatiite boninite tholeiite high mg andesite and nb enriched basalt identified by previous work the geodynamic setting of the bifs from guyang gb is deduced to be a mantle plume erupting into the subduction zone and they were deposited in arc related basins relatively low contents of al 2 o 3 tio 2 and hfse for the bifs indicate negligible detritus involvement paas normalized rey profiles are characterized by lree depletion and hree enrichment positive la gd y and eu anomalies weak negative ce anomalies and y ho weight ratios of 26 41 indicating a mixture of submarine high temperature hydrothermal fluids and seawater chondrite normalized ree patterns for the bifs are similar to those of the komatiites occurring at the bottom of the gb collectively it is speculated that submarine high temperature hydrothermal fluids leached out the fe and si of oceanic volcanics during circulation and they deposited due to the changed physiochemical conditions when the fluids mixed with the seawater the hydrothermally altered amphibolites proximal to the gongyiming upgraded iron ores are enriched in various elements added by the hydrothermal fluids plus the 18 o values of magnetites and quartzs the genesis of the gongyiming upgraded iron ores is proposed to be hydrothermal interaction with low grade bif

neoarchean algoma type banded iron formations from eastern hebei north china craton shrimp u pb age origin and tectonic setting abstract algoma type bif hosted iron deposits occur in the shirengou xingshan erma lingshan and sijiaying areas of eastern hebei the deposits are hosted in archean rocks and their formation was related to volcanic and sedimentary processes in small volcano sedimentary basins supracrustal rocks of the qianxi and dantazi groups were metamorphosed from granulite facies to amphibolites facies available data indicate that these bif deposits mainly formed during paleoarchean and neoarchean times the paleoarchean bif hosted iron deposits are represented by the xingshan deposit that yielded a shrimp u pb zircon age of 3389 5 7 6 ma the other bif hosted iron deposits formed in the late neoarchean represented by the shirengou shuichang lingshan erma and sijiaying deposits that formed between 2605 ma and 2503 ma the late neoarchean bif iron deposits are considered to have formed under a mantle plume environment the eu anomalies of the ore samples from eastern hebei show that the bif ores formed in a hydrothermal related volcanic submarine environment where submarine hydrothermal effluents associated with volcanic activities may have supplied both the iron and silica for the bifs from eastern hebei

archean paleoproterozoic crustal evolution of the ordos block in the north china craton constraints from zircon u pb geochronology and hf isotopes for gneissic granitoids of the basement abstract the ordos block has been considered as an archean micro block in north china craton however its formation and evolution are poorly understood for a long time due to lack of available basement rocks our la icpms and sims zircon u pb dating of gneissic granitoids from the ordos block basement identified two distinct periods of granitic magmatism at 2 5 ma and 2 2 2 0 ga and two phases of metamorphisms at 1 95 ga and 1 85 ga respectively of which most zircons of 2 5 ga granitoids show positive hf t values ranging from 0 1 to 4 1 with a peak t dm of 2 7 ga minor zircons have negative hf t values from 3 8 to 0 02 and t hf c of 2 8 3 1 ga moreover the 3 40 ga inherited zircon and zircons with t hf c of 3 1 4 2 ga were found from 2 2 ga to 2 0 ga granitoids these suggest that there existed a neoarchean crust in the ordos block which underwent a major crustal growth at 2 7 ga and granitic magmatism at 2 5 ga highly consisting with 2 7 ga crustal growth and 2 5 ga magmatism resulted from juvenile crustal reworking in north china craton the zircons from 2 2 ga to 2 0 ga granitoids in ordos block basement display variable hf isotopic composition of positive to negative hf t values much similar to those of 2 2 2 0 ga granitoids related to continental margin arc setting in the trans north china orogen they were subsequently subjected to 1 95 and 1 85 ga metamorphisms which were widespread throughout the trans north china orogen based on the highly coherent zircon geochronology and hf isotopic composition between ordos block and other micro blocks of north china craton we propose that there is a neoarchean crust in ordos block which underwent a tectonic evolution similar to those in east block in later neoarchean and then experienced 2 2 2 0 ga granitic magmatism related to continental margin arc and 1 95 1 85 ga metamorphism resulted from collision between the east and west blocks along tnco

sulige field in the ordos basin geological setting field discovery and tight gas reservoirs abstract the sulige gas field in central ordos basin is one of the largest gas fields in china with about 860 7 billion cubic meters bcm of proven gas reserve this field covers an area of about 500 km 2 with largely tight clastic reservoirs the upper carboniferous lower permian deltaic sandstones and upper permian lacustrine mudstones deposited in a stable cratonic tectonic setting form an effective petroleum system that is favorable for gas accumulation in large scale stratigraphic lithologic traps based on wire line log response drilling stem test and core data a generalized classification system was developed for the gas reservoirs of the sulige field thus type i and ii rocks are capable of gas production without natural and or artificial fracturing type iii rocks are capable of gas production after artificial fracturing and type iv rocks are too tight to produce at commercial rates even with artificial fracturing the discovery of the sulige field not only adds large gas reserve in the ordos basin but strongly indicates the overlook potential of both tight sandstone reservoir rock and relatively porous and permeable sweet spots in it

geological framework of the archean and paleoproterozoic tanami region northern territory the tanami region a poorly exposed mostly paleoproterozoic province within the north australian craton hosts a number of significant gold deposits in diverse settings rare exposures of 2 520 2 500 ma amphibolite facies archean gneiss and metasedimentary rocks form basement to the thick overlying metasedimentary succession of the 1 880 1 830 ma tanami group the basal unit of the tanami group is the dead bullock formation a fining upward deep water succession dominated by siltstone carbonaceous siltstone iron rich siltstone and mafic sills carbonaceous and iron rich lithologies in the upper dead bullock formation represent important hosts for gold mineralization the conformably overlying killi killi formation represents turbiditic sedimentary rocks that are correlated with the widespread lander rock beds of the arunta region sedimentation of the tanami group was terminated by regional deformation and greenschist to amphibolite facies metamorphism during the tanami event d1 m1 at around 1 830 ma the tanami group is unconformably overlain by rhyolite siliciclastic sedimentary rocks and felsic ignimbrite of the ware group that were deposited at about 1 825 1 810 ma subsequent ese wnw to se nw directed shortening d2 followed by ne sw to e w directed shortening d3 has resulted in open ne f2 and nw f3 trending folds in both the tanami and ware groups voluminous granitoids dominated by i type biotite granodiorite and monzogranite were intruded in the interval 1 825 1 790 ma and have been subdivided using geochemical criteria into the birthday frederick and grimwade suites basalt and immature sedimentary rocks of the mount charles formation are restricted in extent to the tanami mine corridor and are interpreted to reflect a continental rift succession that was deposited around 1 800 ma with an early archean sedimentary provenance steep s to se dipping f4 fold structures of tanami and ware group metasedimentary rocks many spatially associated with 1 825 1 790 ma granitoid intrusions indicate a period of sse directed regional shortening d4 syn to post the regional granitoid intrusive phase a network of n to nw striking faults several of which are interpreted as oblique thrusts with a component of left lateral movement indicates a period of d5 convergence during wsw ene to e w directed shortening the tanami mine corridor fault system comprises a network of n ne to ene striking d5 faults that merge with n to nw striking faults and probably accommodated movement between granite core domains d5 faulting is associated with the main phase of gold mineralization in suitable structural lithological traps the paleoproterozoic basement of the tanami region is unconformably overlain by quartz sandstone lithic arenite and conglomerate of the pargee sandstone pargee sandstone may represent syn tectonic sedimentation related to the 1 730 ma strangways orogeny and is unconformably overlain by the late paleoproterozoic platform cover succession of the birrindudu group the paleoproterozoic basement and cover sequences have subsequently undergone several episodes of faulting collectively termed d6 the paleoproterozoic evolution of the tanami region is interpreted to have occurred in an intracratonic setting but was fundamentally influenced by tectonic events in the adjacent halls creek orogen 1 835 1 805 ma halls creek orogeny and arunta region 1 815 1 800 ma stafford event the boundaries between the tanami region and kimberley region to the northwest and the arunta region to the southeast are transitional and are largely defined by the presence or absence of identifiable dead bullock formation

bacterial incorporation of relict carbon in the hydrothermal environment of guaymas basin abstract radiocarbon analyses of bulk carbon and individual organic compounds are presented for the hydrothermal environment of the rebecca s roost vent in the southern trough of the guaymas basin hydrothermal field the 14 c values of co 2 and ch 4 in the hottest hydrothermal fluids 317 c are nearly radiocarbon dead 944 and 923 respectively in contrast the 14 c values of sediments and individual fatty acids 418 to 227 obtained from a bacterial mat located south of the vent site are similar to values previously reported for hydrothermal petroleum in this environment and are more depleted in 14 c than overlying waters hydrothermal fluids moving through the sediments appear to supply 14 c of intermediate age to the bacteria this carbon may take the form of or may be supplied by processes similar to the generation of hydrothermal petroleum although the bacterial mat visibly was dominated by beggiatoa spp such mats are known to include numerous other species individual compound data show that preaged carbon is being consumed by the integrated bacterial assemblage values of 13 c and 14 c indicate that petroleum derived carbon is incorporated directly into fresh bacterial biomass subsequently some of this newly synthesized material also is consumed by heterotrophs as eukaryotic sterols from the same sample also have 14 c depleted values 14 c 136 to 110 therefore the entire system may operate as a complex consortium to transform relict carbon back into biomass bacterial consumption of relict carbon occurs despite the ample supply of fresh carbon delivered from the productive overlying water column

radiocarbon studies of organic compound classes in plankton and sediment of the northeastern pacific ocean radiocarbon 14c and stable carbon isotopes 13c were measured in total hydrolyzable amino acid thaa total carbohydrate tcho total lipid and acid insoluble organic fractions that had been separated from phytoplankton zooplankton sediment floc and sediment samples from an abyssal site in the northeastern pacific ocean thaa tcho and lipid fractions accounted for 91 99 of the total organic carbon toc in phytoplankton and zooplankton 57 of toc in sediment floc and 18 38 of toc in sediment based on concentration profiles in sediment first order degradation rate constants below the bioturbation zone were calculated using a multi g model considering both labile and refractory organic fractions the calculated rate constants were in the order thaa tcho toc tn lipid indicating the relative reactivities of these compound classes in the sediment during early diagensis bioturbation affected the distribution of these compound classes in the top few centimeters of the sediment the 14c values of all organic fractions decreased in the order plantkon in surface water to sediment floc to sediments at 4100 m depth distinct differences of 14c exist among thaa tcho and lipid fractions in sediment floc and sediments the lipid fraction exhibited lower 14c signatures than thaa and tcho fractions differential decomposition of organic matter and sorption and or biological incorporation of old doc into sediment appear to be the major processes that likely control the observed 14c signatures and abundances 13c values of the organic compound classes in sediment are similar to their values in plankton indicating that organic matter input to sediment in the northeastern pacific is mainly from marine sources also distinct 13c signatures were found in each of the four organic fractions

shrimp u pb zircon ages of the fuping complex implications for late archean to paleoproterozoic accretion and assembly of the north china craton the fuping complex is situated in the central part of the north china craton and consists of four major lithological assemblages fuping tonalitic trondhjemitic granodioritic gneisses longquanguan augen gneisses wanzi supracrustal assemblage and nanying granitic gneisses shrimp u pb geochronology combined with u th and cathodoluminescence cl imaging of zircon enables resolution of magmatic and metamorphic events that can be directed towards understanding the late archean to paleoproterozoic history of the fuping complex cl images reveal the coexistence of magmatic and metamorphic zircons in nearly all rock types of the fuping complex the metamorphic zircons occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores and are all characterized by nebulous zoning or being structureless with extremely high luminescence and very low th contents these features make them distinct from magmatic zircons that are characterized by concentric oscillatory zoning comparatively low luminescence and high th and u contents shrimp u pb analyses on magmatic zircons reveal that the tonalitic trondhjemitic and granodioritic plutons of the fuping gneisses were emplaced at 2523 14 ma 2499 10 ma and 2486 8 ma respectively whereas the monzogranitic and granitic plutons of the longquanguan augen gneisses were intruded respectively at 2510 22 ma and 2507 11 ma prismatic and oscillatory zoned zircons dominate in the pelitic rocks of the wanzi supracrustal assemblage and are interpreted as detritus from igneous source rocks the concordant and discordant u pb ages of 2502 5 ma and 2507 14 ma obtained from two pelitic rock samples indicate these rocks must have been deposited no earlier than 2507 ma ago in addition a zoned zircon grain in one pelitic rock sample has a near concordant age of 2109 5 1 ma which may provide a maximum depositional age for the wanzi supracrustal rocks shrimp results also reveal that granitic magmatism assigned to the nanying granitic gneisses occurred over a protracted interval from 2077 13 ma to 2024 21 ma the nebulously zoned zircon grains and overgrowth recrystallization zircon rims from different rocks yielded similar concordant 207pb 206pb ages in the range 1875 to 1802 ma interpreted as approximating the age of regional metamorphism of the fuping complex timing of primary zircon crystallization and regional metamorphism of the fuping complex is in general agreement with recent u pb zircon ion probe results for the wutai and hengshan complexes that bound the fuping complex to the northwest these areas are characterized by the emplacement of major granitoid bodies at around 2 50 ga to 2 48 ga ago deposition of supracrustal rocks in the paleoproterozoic intrusion of paleoproterozoic granitic bodies at 2 1 to 2 0 ga and regional metamorphism at 1 875 to 1 802 ga these data indicate that the fuping and hengshan complexes do not represent an older crystalline basement to the wutai complex as suggested in previous tectonic models but together with the wutai complex represent elements of a single late archean to paleoproterozoic magmatic arc system that has been subsequently tectonically disrupted and juxtaposed during the collision of the eastern and western north china blocks at 1 85 ga which resulted in the final assembly of the north china craton

microbial carbon cycling in oligotrophic regional aquifers near the tono uranium mine japan as inferred from δ13c and δ14c values of in situ phospholipid fatty acids and carbon sources abstract microorganisms are ubiquitous in deep subsurface environments but their role in the global carbon cycle is not well understood the natural abundance 13c and 14c values of microbial membrane phospholipid fatty acids plfas were measured and used to assess the carbon sources of bacteria in sedimentary and granitic groundwaters sampled from three boreholes in the vicinity of the tono uranium mine gifu japan sample storage experiments were performed and drill waters analyzed to characterize potential sources of microbial contamination the most abundant plfa structures in all waters sampled were 16 0 16 1 7c cy17 0 and 18 1 7c a plfa biomarker for type ii methanotrophs 18 1 8c comprised 3 and 18 of total plfas in anoxic sedimentary and granitic waters respectively sampled from the kna 6 borehole the presence of this biomarker was unexpected given that type ii methanotrophs are considered obligate aerobes however a bacterium that grows aerobically with ch4 as the sole energy source and which also produces 56 of its total plfas as 18 1 8c was isolated from both waters providing additional evidence for the presence of type ii methanotrophs the 14c values determined for type ii methanotroph plfas in the sedimentary 861 and granite 867 waters were very similar to the 14c values of dissolved inorganic carbon dic in each water 850 this suggests that type ii methanotrophs ultimately derive all their carbon from inorganic sources whether directly from dic and or from ch4 produced by the reduction of dic in contrast 13c values of type ii plfas in the sedimentary 93 and granite 60 waters indicate that these organisms use different carbon assimilation schemes in each environment despite very similar 13 c ch 4 values 95 for each water the 13cplfa values 28 to 45 of non methanotrophic bacteria in the kna 6 ltl water do not clearly distinguish between heterotrophic and autotrophic metabolisms but 14cplfa values indicate that 65 of total bacteria filtered from the kna 6 ltl water are heterotrophs ancient 14c values 1000 of some plfas suggest that many heterotrophs utilize ancient organic matter perhaps from lignite seams within the sedimentary rocks the more negative range of 13cplfa values determined for the kna 6 granitic water 42 to 66 are likely the result of a microbial ecosystem dominated by chemolithoautotrophy perhaps fuelled by abiogenic h2 results of sample storage experiments showed substantial shifts in microbial community composition and 13cplfa values as much as 5 during 2 4 days of dark refrigerated aseptic storage however water samples collected and immediately filtered back in the lab from freshly drilled msb 2 borehole appeared to maintain the same relative relationships between 13cplfa values for sedimentary and granitic host rocks as observed for samples directly filtered under artesian flow from the kna 6 borehole of the tono uranium mine

generation of short chain acid anions in hydrothermally altered sediments of the guaymas basin gulf of california an initial investigation of the concentration distribution of short chain organic acid anions in hydrothermally altered sediments of the guaymas basin reveals the presence of high concentrations of acetate and propionate relative to normal marine sediments acetate and propionate concentrations appear to vary as a function of sediment temperature and reach concentrations 1100 and 200 m respectively at temperatures 100 c as in previously studied oil field formation waters these acid anions probably play a key role in the generation of co2 and hydrocarbons gases hydrogen ion ph buffering the complexing of aqueous ions and mineral dissolution and precipatation at temperatures 100 c these and other acid anions should be important substrates for heterotrophic bacterial processes including sulfate reduction

variations in the chemical and stable isotope composition of carbon and sulfur species during organic rich sediment alteration an experimental and theoretical study of hydrothermal activity at guaymas basin gulf of california organic rich diatomaceous ooze was reacted with seawater and a na ca k cl fluid of seawater chlorinity at 325 400 c 400 500 bars and fluid sediment mass ratios of 1 56 2 35 to constrain factors regulating the abundance and stable isotope composition of c and s species during hydrothermal alteration of sediment from guaymas basin gulf of california alteration of inorganic and organic sedimentary components resulted in extensive exchange reactions the release of abundant h2s co2 ch4 and corganic to solution and recrystallization of the sediment to an assemblage containing albitic plagioclase quartz pyrrhotite and calcite the 34scdt values of dissolved h2s varied from 10 9 to 4 3 during seawater sediment interaction at 325 and 400 c and from 16 5 to 9 0 during na ca k cl fluid sediment interaction at 325 and 375 c in the absence of seawater so4 h2s is derived from both the transformation of pyrite to pyrrhotite and s released during the degradation of organic matter in the presence of seawater so4 reduction of so4 contributes directly to h2s production sedimentary organic matter acts as the reducing agent during pyrite and so4 reduction requisite acidity for the reduction of so4 is provided by mg fixation during early stage sediment alteration and by albite and calcite formation in mg free solutions organically derived ch4 was characterized by 13cpdb values ranging between 20 8 and 23 1 whereas 13cpdb values for dissolved corganic ranged between 14 8 and 17 7 mass balance calculations indicate that 13c values for organically derived co2 were 14 8 residual solid sedimentary organic c showed small 0 7 depletions in 13c relative to the starting sediment the experimental results are consistent with the isotopic and chemical composition of natural hydrothermal fluids and minerals at guaymas basin and permit us to better constrain sources and sinks for c and s species in subseafloor hydrothermal systems at sediment covered spreading centers our data show that the sulfur isotope composition of hydrothermal sulfide minerals in guaymas basin can be explained by derivation of s from diagenetic sulfide and seawater sulfate basaltic s may also contribute to hydrothermal sulfide precipitates but is not required to explain their isotopic composition estimates of seawater sediment mass ratios based on sulfur isotopic composition of sulfide minerals and the abundance of dissolved nh3 in vent fluids range from 3 29 during hydrothermal circulation sources of c in guaymas basin hydrothermal fluids include thermal degradation of organic matter bacteriogenic methane production and dissolution of diagenetic carbonate

hydrothermal fluid flow system around the iheya north knoll in the mid okinawa trough based on seismic reflection data seismic reflection data around the iheya north knoll hydrothermal field provide insights into geological structures that control subseafloor hydrothermal fluid flow in the sediment covered continental backarc basin of the mid okinawa trough we identified the seismic expression of widespread porous volcaniclastic pumiceous deposits and intrusions as a result of silicic arc volcanism the porous and permeable volcanic deposits are distributed in an area extending updip from the thick succession of the deep trough to the seafloor at the hydrothermal field their regional structure focuses the flow of hydrothermal fluids derived from the surrounding trough fill sediments and directs them to the vents of the hydrothermal field the high concentrations of ch4 and nh4 in the fluids of the hydrothermal field are likely derived from the interaction of migrating fluids with trough fill sediments

diurnal winds in the himalayan kali gandaki valley part i observations abstract the diurnal wind system of the kali gandaki valley in nepal was explored in september and october 1998 in a field campaign using pilot balloons as the main observational tool this valley connects the plateau of tibet with the indian plains the river crosses the himalayas forming the deepest valley on earth intense upvalley winds blow up this valley during the day observations were made along the river at various spots selected between the exit point from the himalayas and the source close to the plateau of tibet the strongest upvalley winds were found between marpha and chuksang with typical speeds of 15 20 m s 1 the upvalley wind sets in first at the ground but an upvalley wind layer of 1000 2000 m depth forms quickly after the onset this deep inflow layer persists up to lo manthang a town located a few kilometers south of the plateau of tibet deceleration in the late afternoon and evening also appears to commence near the ground weak drainage flow forms late in the night the causes o

geochemistry of shallow sediments in guaymas basin gulf of california hydrothermal gas and oil migration and effects of mineralogy offset of prograde hydrothermal alterations by retrograde reactions is evident in sediments from a piston core pc6 8 m long from the guaymas basin gulf of california geochemical and mineralogical analyses of sediments and pore fluids show superimposed geochemical signals that indicate currently active reactions are modifying previously formed secondary solids hydrothermal barite was formed in a previously active flow channel between 150 and 250 cm depth hydrothermal gypsum is presently dissolving at depths 780 cm below which hydrothermal fluid flow is channeled by a secondary dolomite layer thermal stress of organic matter generates hydrothermal gas and petroleum having wide ranges of compositions and maturities a significant amount of hydrothermally generated oil has been transported laterally through a porous debris flow approx 240 cm subbottom overwhelming the indigenous bituminous matter water soluble petroleum constituents have disseminated throughout the cored sediments from 400 to 700 cm depth the immature organic matter continues to experience thermally enhanced diagenesis and an even higher thermal stress has occurred at the bottom of the core enhanced bacterial degradation of organic matter has led to depletion of pore water sulfate and enrichment of ammonium nh4 in both pore fluid and sediment resulting in formation of nh4 bearing secondary clay minerals at depths below 780 cm

tectonothermal history of the basement rocks in the western zone of the north china craton and its tectonic implications the basement of the north china craton can be divided into the eastern central and western zones based on lithological structural metamorphic and geochronological data the western zone comprises two different petrotectonic units archaean tonalitic trondhjemitic granodioritic ttg grey gneisses and metamorphic mafic rocks and palaeoproterozoic khondalite series the former is characterized by isobaric cooling ibc type anticlockwise p t paths in the north northwestern part of the zone and near isothermal decompression itd type clockwise p t paths in the eastern part adjacent to the central zone on the other hand the tectonothermal evolution of palaeoproterozoic khondalite series rocks is characterized exclusively by nearly isothermal decompression following the peak of metamorphism and then cooling defining clockwise p t paths the archaean ttg gneisses and associated mafic rocks with anticlockwise metamorphic p t paths reflects an origin related to underplating and intrusion of mantle derived magmas which may be derived from mantle plumes they represent a late archaean continental block in the western part of the north china craton the palaeoproterozoic khondalite series rocks represent passive continental margin deposits they were metamorphosed and deformed in the late palaeoproterozoic during the amalgamation of the western continental block with another continental block in the east part of the north china craton the itd type clockwise p t t paths of the palaeoproterozoic khondalite series rocks record the tectonothermal histories of the collision of the western and eastern continental blocks which resulted in the final assembly of the north china craton at c 1800 ma

tracing iron fueled microbial carbon production within the hydrothermal plume at the loihi seamount the loihi hydrothermal plume provides an opportunity to investigate iron fe oxidation and microbial processes in a system that is truly fe dominated and distinct from mid ocean ridge spreading centers the lack of hydrogen sulfide within the loihi hydrothermal fluids and the presence of an oxygen minimum zone at this submarine volcano s summit results in a prolonged presence of reduced fe within the dispersing non buoyant plume in this study we have investigated the potential for microbial carbon fixation within the loihi plume we sampled for both particulate and dissolved organic carbon in hydrothermal fluids microbial mats growing around vents and the dispersing plume and carried out stable carbon isotope analysis on the particulate fraction the 13 c values of the microbial mats ranged from 23 to 28 and are distinct from those of deep ocean particulate organic carbon poc the mats and hydrothermal fluids were also elevated in dissolved organic carbon doc compared to background seawater within the hydrothermal plume doc and poc concentrations were elevated and the isotopic composition of poc within the plume suggests mixing between background seawater poc and a 13 c depleted hydrothermal component the combination of both doc and poc increasing in the dispersing plume that cannot solely be the result of entrainment and doc adsorption provides strong evidence for in situ microbial productivity by chemolithoautotrophs including a likelihood for iron oxidizing microorganisms

stable carbon and nitrogen isotopic signatures of fauna associated with the deep sea hydrothermal vent system of guaymas basin gulf of california abstract potential food sources and the trophic position of some of the most conspicuous faunal components vent and non vent were examined in the deep hydrothermal vent system of guaymas basin in the gulf of california using carbon and nitrogen stable isotope analyses the isotopic signatures of 13 species collected by the dsrv alvin and nautile mostly from sulfide influenced habitats were analyzed the 13 c of nine vent species had a wide range 36 0 to 12 7 whereas the 15 n values varied from 5 0 to 9 4 the dual isotopic approach allowed the recognition of two main groups containing vent endemic fauna one was represented by an assemblage of eight species associated with sulfide deposits visually dominated by the siboglinid worm riftia pachyptila and characterized by enriched 13 c values means 13 7 to 21 0 the second group included a single species the bivalve vesicomya gigas an inhabitant of soft sediments which had depleted 13 c and 15 n signatures means 35 7 and 1 5 the galatheid munidopsis alvisca is an exception among the species in the r pachyptila aggregation due to its depleted 13 c 26 4 and an intermediate 15 n value 5 5 isotopic 13 c and 15 n signatures of four non vent species exhibited mostly enriched 15 n values means 13 c 27 8 to 13 6 15 n 14 5 to 17 9 expected for higher consumers and detritivores in a deep sea food web they may benefit from the vent production via microbial matter or decaying vent organisms vent and non vent fauna were assigned to five feeding guilds symbiont containing fauna bacterivores detritivores predator scavengers and suspension feeders based on isotopic values of vent and non vent fauna as well as that of surficial sediments it is inferred that the hydrothermal ecosystem in the guaymas basin is self supported with high energy efficiency and with low exporting capacity to the background deep sea food web

cretaceous cenozoic tectonic history of the jiaojia fault and gold mineralization in the jiaodong peninsula china constraints from zircon u pb illite k ar and apatite fission track thermochronometry the jiaojia fault jjf in the jiaodong area of eastern china is an important nne trending structure that is subsidiary to the regional tancheng lujiang tan lu fault zone and hosts 1200 t of gold reserves contained in disseminated and stockwork ore dominantly in the footwall of the fault we present new zircon u pb apatite fission track and illite k ar data along the jjf and have delineated its tectonic history focusing on its formation and reactivation zircon u pb dating shows that the shangzhuang granite is a composite body with ages between 132 1 and 127 1 ma illite k ar ages for the fault s gouge range from 83 2 to 68 2 ma and the measured apatite fission track ages for ores are between 55 and 21 ma previous zircon u pb geochronology and structural studies suggest that the jjf was originally activated in the jurassic during 160 150 ma as a sinistral fault the jjf was a normal fault in the early cretaceous due to nw se orientated tension and ne sw compression which lasted from 135 to 120 ma this was followed by sinistral strike slip faulting due to nw se compression and ne sw tension during 120 110 ma and it changed to normal displacement at ca 110 ma our apatite fission track data analysis and thermal modeling of representative samples suggest that there was a subsequent dextral reactivation of the fault at ca 55 ma previous age data of ca 130 110 ma for gold mineralization along the jjf coincides with the early cretaceous magmatism and is coeval with the transition from normal faulting to sinistral strike slip faulting of the jjf in early cretaceous which is interpreted to be due to changing direction of the subducting pacific plate

petrogenesis of the 2 1 ga lushan garnet bearing quartz monzonite on the southern margin of the north china craton and its tectonic implications abstract the lushan garnet bearing quartz monzonite was emplaced into the western taihua complex at 2134 17 ma on the southern margin of the north china craton ncc the rocks contain sio 2 contents of 56 98 59 05 wt with high k 2 o na 2 o 7 46 9 14 wt and al 2 o 3 15 87 17 58 wt and low cao 2 38 2 77 wt and mgo 1 18 1 50 wt contents and belong to an intermediate shoshonitic series magmatic garnet grains in the rocks are chemically homogeneous with relatively high cao 6 36 7 92 wt but low mno 1 45 1 94 wt and mgo 2 47 3 45 wt contents and high fe mn ratios they contain 61 94 66 39 mol almandine 18 60 23 40 mol grossular 10 06 15 11 mol pyrope and 1 09 4 32 mol spessartine similar to high pressure garnets formed from m type magma but different from those found in s type granites and metapelites phase equilibrium diagrams in combination with trace element distribution coefficients between zircon and garnet suggest whole rock zircon saturation temperatures varying from 891 c to 951 c and the mineral assemblage of garnet plagioclase amphibole or biotite in these rocks is stable at 15 kbar and 890 950 c with h 2 o t 800 c all of the rocks are enriched in lile and lree with low nb la ratios 0 24 0 61 similar to those of lithospheric mantle which has a nb la ratio of 0 5 therefore the garnet and whole rock chemical compositions indicate that the lushan quartz monzonite possibly formed by small degrees of partial melting of a phlogopite bearing lithospheric mantle the variable zircon hf t values 3 5 to 4 1 with t dm c from 2 34 ga to 2 51 ga suggest involvement of crustal materials the rocks have slightly negative nb and ta anomalies characteristics of island arc basalts iab however their high zr 598 926 ppm and zr y ratios 17 1 21 8 suggest an affinity with ocean island basalt oib hence the mixed iab and oib like geochemical signatures are indicative of continental intra plate rifting possibly related to extension and thinning of the lithosphere and upwelling of asthenosphere our study proposes that an intra continental rifting event occurred at 2 2 2 0 ga on the southern margin of the ncc after the final amalgamation of ncc

glacier winds in the rongbuk valley north of mount everest 1 meteorological modeling with remote sensing data 1 persistent glacier winds blowing from noon to midnight in summer are present in the rongbuk valley north of mount everest with a maximum speed of 10 m s 1 and a vertical thickness as high as 1 km these glacier winds may bring upper level atmosphere ozone to the surface having a significant impact on the atmospheric environment such phenomena may be typical of the tibetan plateau where most high mountains are covered by snow or glacier ice throughout the year the advanced regional prediction model was used to simulate the down valley flows using realistic topography but neglecting synoptic winds the modeling results agree well with the observations obtained in june 2002 revealing that the glacier winds are thermal flows primarily driven by the along valley temperature gradient between the colder air over the glacier surface and the warmer air over surface areas covered by rock debris which maintains air advection along the rongbuk valley downslope winds over the glacier slopes especially from the western valley side and the west rongbuk glacier were forced by their inertia farther down into the valley and would intensify the glacier winds the narrowing of the rongbuk valley could also speed up the glacier winds sensitivity tests showed that the detailed distribution of the rongbuk glacier delineated by data from the enhanced thematic mapper plus on landsat 7 plays an important role in glacier winds development the glacier winds could be much weaker in winter when the area is completely snow covered

diurnal winds in the himalayan kali gandaki valley part ii modeling abstract the penn state ncar mesoscale model mm5 is used to simulate and better understand the wind observations in the kali gandaki valley reported in the first part of this paper the kali gandaki river originates in nepal near tibet flows southward through the mustang basin crosses the himalayas in a gorge and descends to the lowlands of nepal extremely strong diurnal upvalley flow in the gorge and the basin alternates with rather weak drainage flow in the night as proposed in part i the mustang basin and the tibetan plateau can be considered as an elevated heat source driving the upvalley flow during the day however the extreme strength of the diurnal upvalley winds and the order of magnitude asymmetry between day and night cannot be explained with a simple plateau circulation theory the model is successful in simulating almost all aspects of the observations the simulations strongly suggest that the observed acceleration of the upvalley winds near the entrance to the mustang basin is linked

archean komatiite volcanism controlled by the evolution of early continents the generation and evolution of earth s continental crust has played a fundamental role in the development of the planet its formation modified the composition of the mantle contributed to the establishment of the atmosphere and led to the creation of ecological niches important for early life here we show that in the archean the formation and stabilization of continents also controlled the location geochemistry and volcanology of the hottest preserved lavas on earth komatiites these magmas typically represent 50 30 partial melting of the mantle and subsequently record important information on the thermal and chemical evolution of the archean proterozoic earth as a result it is vital to constrain and understand the processes that govern their localization and emplacement here we combined lu hf isotopes and u pb geochronology to map the four dimensional evolution of the yilgarn craton western australia and reveal the progressive development of an archean microcontinent our results show that in the early earth relatively small crustal blocks analogous to modern microplates progressively amalgamated to form larger continental masses and eventually the first cratons this cratonization process drove the hottest and most voluminous komatiite eruptions to the edge of established continental blocks the dynamic evolution of the early continents thus directly influenced the addition of deep mantle material to the archean crust oceans and atmosphere while also providing a fundamental control on the distribution of major magmatic ore deposits

u pb and hf isotopic study of zircons of the helanshan complex constrains on the evolution of the khondalite belt in the western block of the north china craton abstract the helanshan complex is located at the westernmost segment of the khondalite belt a continent continent collisional belt along which the yinshan block in the north collided with the ordos block in the south to form the western block of the north china craton the complex consists of s type granites and high grade pelitic granulite gneiss felsic paragneiss quartzite calc silicate rock and marble together called the khondalite series rocks la q icp ms u pb geochronology and la mc icp ms lu hf isotopic data of zircons combined with cathodoluminescence cl imaging enable the resolution of magmatic and metamorphic events that can be directed towards understanding the formation and evolution of the khondalite belt in the western block of the north china craton cl images reveal the coexistence of magmatic type detrital zircons and metamorphic zircons in most of the khondalite series rocks of which the metamorphic zircons occur as either single grains or overgrowth rims surrounding and truncating magmatic type detrital zircon cores la q icp ms u pb analyses on magmatic type detrital zircons reveal two distinct age populations with one in the archaean 2 85 2 53 ga and the other in the palaeoproterozoic 2 2 2 0 ga suggesting that the sedimentary protoliths of the khondalite series rocks in the helanshan complex must have been deposited at some time after 2 0 ga the hf analyses show that the archaean detrital zircons possess negative ehf t values from 7 64 to 0 15 with depleted mantle model ages ranging from 3 34 to 3 10 ga this implies the existence of a paleo mesoarchaean 3 34 3 10 ga crust in the western block which underwent a recycling event in the period 2 85 2 53 ga nearly all palaeoproterozoic 2 2 2 0 ga detrital zircons possess positive ehf t values 0 86 9 38 with depleted mantle model ages of 2 45 2 15 ga suggesting a significant crustal growth event in the western block in the palaeoproterozoic metamorphic zircons yield two groups of age with one at 1 95 ga and the other at 1 87 ga of which the former is considered as the timing of the collision between the yinshan and ordos blocks to form the western block whereas the latter is consistent with the age of 1 86 ga from two s type granites which are considered to have formed by the partial melting of pelitic granulites gneisses at the stage of the exhumation of the helanshan complex

carbon isotope systematics of individual hydrocarbons in hydrothermal petroleums from the guaymas basin gulf of california abstract individual aliphatic and aromatic hydrocarbons in hydrothermal petroleums from the guaymas basin were subjected to compound specific isotope analysis to trace their origins the carbon isotope compositions of the alkanes and polycyclic aromatic hydrocarbons means 23 1 and 21 2 respectively all reflect their marine source and confirm their generation from the sedimentary kerogen

growth and reworking of the early precambrian continental crust in the north china craton constraints from zircon hf isotopes abstract we synthesize more than 2600 hf isotope data on the archean paleoproterozoic zircons from the north china craton ncc recalculation of the data based on single stage and two stage hf model ages of the eastern block of the ncc shows peak ages of 3902 13 ma and 3978 18 ma respectively and also small peaks at 3 5 4 0 ga the majority of zircon ehf t values are positive suggesting the possibility of the crust and the mantle differentiation at ca 3 9 4 0 ga in the eastern block of the ncc most magmatic zircons from the whole of ncc have their hf model age range of 2 4 2 9 ga and the single stage model ages is cluster at 2698 4 ma whereas the two stage model ages concentrate at 2714 5 ma implying that the protoliths were juvenile crustal rocks the most prominent peak at 2 7 ga indicates that this period marks the most important stage of the crust mantle differentiation and crust formation of the ncc the widespread 2 5 ga rocks in the ncc and the absence of the 2 5 ga peaks in hf model ages are consistent with the partial melting and reworking of the juvenile rocks at 2 5 ga furthermore the 2 5 1 7 ga zircon hf isotope features are also related to the reworking of the crustal rocks our results from the integration of a large database suggest that the eastern block and the trans north china orogen have undergone similar crust mantle differentiation and magmatism leading to the conclusion that the essential cratonization of the north china took place at the end of neoarchean

metallogeny of the north china craton link with secular changes in the evolving earth abstract the north china craton ncc has experienced a complex geological evolution since the early precambrian and carries important records of secular changes in tectonics and metallogeny here we synthesize the salient geological and tectonic features of the evolution and destruction of the ncc vis a vis major metallogenic events and the formation of potential ore deposits we identify a close relationship between the major geological events in the ncc and those reported elsewhere on the globe we trace the records of a regular change in the pattern of metallogeny mineral deposit character spatial distribution and genetic mechanisms which closely match the timing and styles of the major geological and tectonic events in this craton the ncc went through five major tectonic cycles 1 neoarchean crustal growth and stabilization 2 paleoproterozoic rifting subduction accretion collision with imprints of the great oxidation event goe 3 late paleoproterozoic neoproterozoic multi stage rifting 4 paleozoic orogenesis at the margins of the craton and 5 mesozoic extensional tectonics associated with lithospheric thinning and decratonization coinciding with these major geological events are five major metallogenic systems identified as follows 1 an archean bif system 2 paleoproterozoic cu pb zn and mg b systems 3 a mesoproterozoic ree fe pb zn system 4 a paleozoic orogenic cu mo system and 5 mesozoic intracontinental au and ag pb zn and mo systems the ore deposit types in each of these metallogenic systems show distinct characteristics and tectonic affinities from early precambrian through late precambrian to paleozoic and mesozoic the ncc records a transition from primitive to modern style plate tectonics evidence for imbricated oceanic plate stratigraphy in a subduction accretion setting and collisional orogenesis along at least three major zones of ocean closure are documented major transitions in tectonic style and surface environmental changes recorded in other parts of the world are also reflected in the geological history and metallogenic events in the ncc large scale gold deposits formed through intraplate tectonics during the mesozoic provide important insights into mantle dynamics and crust mantle interaction associated with lithospheric thinning and craton destruction the ncc provides one of the best examples for documenting secular changes in the geological history and metallogenic epochs of an evolving earth

14c ages of hydrothermal petroleum and carbonate in guaymas basin gulf of california implications for oil generation expulsion and migration sup 14 c dates have been obtained by accelerator mass spectrometry and by conventional techniques from hydrothermally derived petroleum calcite and vent water from the southern trough of guaymas basin gulf of california the ages for petroleum range from 4240 to 5705 b p whereas those for calcite range from 7340 to 33 168 b p the co sub 2 in a sample of hydrothermal vent fluid 24 end member yielded an apparent age of 14 820 b p which is within the calcite age range these are not true ages but rather they reflect the age of carbon within these materials the data indicate that the conversion of sedimentary organic matter to petroleum occurs very rapidly and that the petroleum is mobilized from sedimentary organic matter in the upper 30 m of the sediment column le 500 m thick underlying the sea floor deposits the large difference in ages between the petroleum and most of the calcites indicates that the carbon source in the calcites is more complex the inorganic carbon pool probably originates from the dissolution of older detrital carbonates and autochthonous biogenic carbonates in the shallow sediments and or the decarboxylation of organic matter at greater depth with a magmatic component of dead carbon

petrogenesis and tectonic significance of paleoproterozoic meta mafic rocks from central liaodong peninsula northeast china evidence from zircon u pb dating and in situ lu hf isotopes and whole rock geochemistry abstract the central liaodong peninsula is located in the northwestern part of the jiao liao ji belt in the eastern block of the north china craton surface rocks in this region are voluminous meta mafic rocks which mainly comprise amphibolite and metamorphic gabbro or diabase we present zircon cathodoluminescence images u pb dates and lu hf isotope data as well as whole rock geochemical data for these rocks in order to constrain the tectonic nature and evolution of the jiao liao ji belt zircons from these meta mafic rocks can be divided into two groups with one having a typical magmatic origin and the other a metamorphic origin zircon u pb dating and lu hf isotopic results show that the magmatic zircons have two peak ages at 2503 and 2154 ma with the former have hf 7 1 to 8 1 and single stage model ages t hf 2 50 2 55 ga indicating that these captured or inherited zircons formed at ca 2 50 ga by partial melting of coeval juvenile crust the younger magmatic zircons have hf 3 2 to 9 6 mainly varying from 7 4 to 9 6 average 8 7 and t hf 2 15 2 34 ga peak at 2 19 ga suggesting that the meta mafic rocks were emplaced at ca 2 15 ga and derived by partial melting of depleted mantle the metamorphic zircons yield a peak age of 1897 ma and have hf 4 5 to 6 8 these zircons can be further divided into three groups on the basis of hf isotope data i e hf 4 5 to 2 3 0 6 to 1 0 and 3 1 to 6 8 t hf 2 39 2 54 2 26 2 39 and 2 03 2 11 ga respectively indicating they were derived by reworking of neoarchean paleoproterozoic ancient crust and some paleoproterozoic juvenile crust thus there existed two crustal growth events at 2 50 and 2 15 ga and one reworking event at ca 1 90 ga in the eastern block geochemical data show that these meta mafic rocks are characterized by sio 2 47 3 49 8 wt tio 2 0 97 1 59 wt k 2 o 0 39 1 95 wt na 2 o k 2 o 1 03 4 85 mg 39 52 cr 29 247 ppm and ni 24 4 73 4 ppm these features combined with low total rare earth element concentrations ree relative enrichment in light ree significant positive rb ba k and p anomalies and depletions in high field strength elements e g nb ta and ti indicate derivation by partial melting of depleted lithospheric mantle that had been metasomatized by subduction derived fluids with little or no crustal contamination during magma ascent given our dating results and the regional geological framework we propose that the subduction in the eastern longgang block took place at least in age of 2 15 ga and that the meta mafic rocks in the central liaodong peninsula may have formed in a back arc basin however the tectonic location of this magmatic arc and its relationship with the nangrim block need to be further studied to confirm this hypothesis

eoarchean ultra depleted mantle domains inferred from ca 3 81 ga anshan trondhjemitic gneisses north china craton abstract early mantle differentiation is yet to be well constrained because isotopic systems recorded in many ancient rocks are arguably susceptible to later disturbances although refractory zircon is of singular importance in deciphering early earth history a growing body of work on ancient zircons indicates that interpretations of their u pb ages and hf o isotopes are neither straightforward nor unique owing to these complexities the question of whether the anshan complex of north china craton ncc really preserves 3 8 ga rocks remains controversial to better understand these issues we conducted a systematic in situ zircon u pb hf and o isotopic study guided by detailed field mapping 1 50 scale and sampling at guodishan northern anshan complex three rock units were recognized and precisely dated a ca 3 13 ga massive trondhjemitic gneiss that dominates the outcrop a ca 3 36 3 30 ga migmatite complex that is intruded by the trondhjemitic gneiss and a ca 3 81 ga massive to weakly banded trondhjemitic gneiss that is enclosed by the migmatite complex u abundances u pb discordances apparent 207pb 206pb ages and 18o values of a single generation of magmatic zircons reveal that only low u generally u

combined u pb hafnium and oxygen isotope analysis of zircons from meta igneous rocks in the southern north china craton reveal multiple events in the late mesoarchean early neoarchean abstract we report the results of a comprehensive isotopic investigation of zircons from metamorphosed tonalites and amphibolites from lushan in the far south of the trans north china orogen of the north china craton that reveal the oldest rocks yet dated from the orogen a detailed investigation of the internal structures of zircons combined with targeted sims u pb and oxygen isotope analyses and icp ms hf zircon analyses has resulted in the discovery of previously unknown geological events in the north china craton magmatic zircon from the tonalite and amphibolite was found to be essentially coeval with a small spread of ages from 2829 18 ma to 2832 11 ma in the tonalites and from 2838 35 ma to 2845 23 ma in amphibolite hafnium isotope data suggest derivation of both tonalite and amphibolite from a depleted mantle source with minor crustal contamination oxygen isotope ratios in zircons range from 5 1 to 7 3 vsmow with high 18 o results recorded only from metamorphic domains the earliest stage of metamorphic zircon growth present in all four samples analyzed in this study occurred between 2772 17 22 in the tonalites and 2776 20 and 2792 12 ma in the amphibolites a younger metamorphic event at 2638 61 in the tonalite and between 2671 13 and 2651 13 ma in the amphibolites is recognized in zircons from three of the four samples investigated this is the first time that metamorphic events at either of these times have been recorded in the north china craton importantly there is no evidence for the 1 8 ga high grade metamorphic event that is manifest in the northern and central parts of the trans north china orogen

the composition and genesis of the mesoarchean dagushan banded iron formation bif in the anshan area of the north china craton abstract the dagushan bif hosted iron deposit in the anshan benxi area of the north china craton ncc has two types of iron ore quartz magnetite bif fe 2 o 3 t 2 o 3 t 90 wt chlorite quartz schist and amphogneiss border the iron orebodies and are locally present as interlayers with bifs chlorite quartz schist and bifs are enclosed by amphogneiss in some locations the quartz magnetite bifs are enriched in hrees heavy rare earth elements with positive la eu and y anomalies indicating their precipitation from marine seawater with a high temperature hydrothermal component moreover these bifs have low concentrations of al 2 o 3 tio 2 and hfses high field strength elements e g zr hf and ta suggesting that terrigenous detrital materials contributed insignificantly to the chemical precipitation the high grade iron ores exhibit similar geochemical signatures to the quartz magnetite bifs e g ree patterns and y ho ratios implying that they have identical sources of iron however these ores have different ree rare earth element contents and eu eu values and the magnetites contained within them exhibit diverse ree contents and trace element concentrations indicating that the ores underwent differing formation conditions and the high grade ores are most likely the reformed product of the original bifs the chlorite quartz schist and amphogneiss are characterized by high sio 2 and al 2 o 3 contents and exhibit variable abundances of rees enrichment in lrees light rare earth elements negative anomalies in hfses e g nb ta p and ti and positive anomalies in liles large ion lithophile elements e g rb ba u and k a protolith reconstruction indicates that the protoliths of the chlorite quartz schist are felsic volcanic rocks sims and la icp ms zircon u pb dating indicate that this schist formed at approximately 3110 to 3101 ma which could represent the maximum deposition age of the dagushan bif however two groups of zircons from the amphogneiss are identified 3104 to 3089 ma zircons that are most likely derived from the chlorite quartz schist and 2997 to 2995 ma zircons which are interpreted to represent the time of protolith crystallization thus the dagushan bif most likely formed before 2997 to 2995 ma the 3 1 ga zircons yield e hf t values of 8 07 to 5 46 whereas the 3 0 ga zircons yield e hf t values of 3 96 to 2 09 these geochemical features suggest that the primitive magmas were derived from the depleted mantle with significant contributions of ancient crust