hydrothermal alteration and fluid chemistry of the endako porphyry molybdenum deposit british columbia hydrothermal alteration and fluid chemistry data of the early cretaceous endako porphyry molybdenum deposit british columbia provide new information on the hydrothermal fluids associated with low fluorine molybdenite mineralization molybdenite mineralization and hydrothermal alteration occur as early quartz molydenite stockwork veins with k feldspar bearing selvages and paragenetically later quartz molybdenite ribbon veins with sericite bearing selvages late hydrothermal alteration is associated with the development of kaolinite and postore tertiary age calcite veins fluid inclusions in early formed quartz molybdenite stockwork veins with k feldspar bearing alteration assemblages are dominated by moderate salinity 5 to 15 wt nacl equiv liquid rich type 1 and rare high salinity 30 to 45 wt nacl equiv halite bearing type 3 fluid inclusions type 1 and type 3 fluid inclusions in early veins homogenize between 390 and 430 c and 375 and 420 c respectively secondary fluid inclusions type 2 of low salinity 1 to 5 wt nacl equiv in these early veins are minor and homogenize between 130 and 285 c fluid inclusions in quartz molybdenite ribbon veins with sericite bearing alteration assemblages are dominated by moderate salinity liquid rich type 1 inclusions with minor type 2 fluid inclusions type 1 fluid inclusions of ribbon veins homogenize between 360 and 400 c fluid inclusions in postore calcite veins are of only type 2 fluid inclusions which homogenize at 209 c hydrothermal fluids recorded by type 1 and type 3 fluid inclusions in early veins were trapped under lithostatic to hydrostatic conditions between 0 3 and less than or equal to 2 0 kbar and 360 and 560 c postore fluids recorded by type 2 fluid inclusions were trapped under conditions less than or equal to 0 5 kbar and between 190 and 300 c quartz stockwork and ribbon veins possess 18o values of 8 4 0 2 n 9 and 8 4 0 6 n 13 respectively hydrothermal k feldspar and biotite from k feldspar alteration assemblages possess 18o values of 6 8 0 4 n 7 and 3 5 0 8 n 8 respectively oxygen isotope geothermometry of quartz biotite and quartz k feldspar pairs from k feldspar alteration assemblages yield temperatures between 200 and 490 c which is similar to the trapping temperatures of hydrothermal fluids determined from fluid inclusion studies associated with molybdenite mineralization the development of kaolinite and calcite veins the oxygen isotope temperatures of the quartz biotite and quartz k feldspar pairs suggest that k feldspar and biotite either record the approximate 18o composition of hydrothermal fluids associated with k feldspar alteration or have undergone 18o exchange with late stage hydrothermal fluids hydrogen isotope composition of quartz stockwork and ribbon veins fluid inclusion waters range between 105 and 173 per mil solute chemistry studies of fluid inclusion waters indicate that ore forming fluids from endako have low br cl and br na ratios and high i cl and i br ratios in comparison to porgera epithermal babine lake porphyry cu and st austell capitan pluton vein deposits associated with magmatic processes na k ratios of fluid inclusion waters yield temperatures 308 to 429 c similar to those determined from type 1 and type 3 fluid inclusions and stable isotope thermometry results from fluid inclusion and solute chemistry studies indicate the involvement of hydrothermal fluids exsolved from a crystallizing melt in the formation of the endako molybdenum deposit however oxygen and hydrogen isotope values deviate from the generally accepted magmatic compositions which suggests the early involvement of meteoric water in the ore forming fluids and ore genesis

highly fractionated i type granites in ne china ii isotopic geochemistry and implications for crustal growth in the phanerozoic ne china is the easternmost part of the central asian orogenic belt caob the area is distinguished by widespread occurrence of phanerozoic granitic rocks in the companion paper part i we established the jurassic ages 184 137 ma for three granitic plutons xinhuatun lamashan and yiershi we also used geochemical data to argue that these rocks are highly fractionated i type granites in this paper we present sr nd o isotope data of the three plutons and 32 additional samples to delineate the nature of their source to determine the proportion of mantle to crustal components in the generation of the voluminous granitoids and to discuss crustal growth in the phanerozoic despite their difference in emplacement age sr nd isotopic analyses reveal that these jurassic granites have common isotopic characteristics they all have low initial 87 sr 86 sr ratios 0 7045f0 0015 positive end t values 1 3 to 2 8 and young sm nd model ages 720 840 ma these characteristics are indicative of juvenile nature for these granites other late paleozoic to mesozoic granites in this region also show the same features sr nd and oxygen isotopic data suggest that the magmatic evolution of the granites can be explained in terms of two stage processes 1 formation of parental magmas by melting of a relatively juvenile crust which is probably a mixed lithology formed by pre existing lower crust intruded or underplated by mantle derived basaltic magma and 2 extensive magmatic differentiation of the parental magmas in a slow cooling environment the widespread distribution of juvenile granitoids in ne china indicates a massive transfer of mantle material to the crust in a post orogenic tectonic setting several recent studies have documented that juvenile granitoids of paleozoic to mesozoic ages are ubiquitous in the central asian orogenic belt hence suggesting a significant growth of the continental crust in the phanerozoic d 2003 elsevier science b v all rights reserved

highly evolved juvenile granites with tetrad ree patterns the woduhe and baerzhe granites from the great xing an mountains in ne china abstract in ne china voluminous granitoids were emplaced in late paleozoic and mesozoic times we report here sr nd o isotopic and elemental abundance data for two highly evolved granitic plutons woduhe and baerzhe from the great xing an mountains they show a rather juvenile sr nd isotopic signature and a spectacular tetrad effect in their ree distribution patterns as well as non charac charge and radius controlled trace element behavior the emplacement ages are constrained at 130 4 ma for the woduhe and 122 5 ma for the baerzhe granites by rb sr and sm nd isotope analyses both granites are also characterized by low but imprecise initial 87sr 86sr ratios of about 0 703 the nd sr isotope data argue for their generation by melting of dominantly juvenile mantle component with subordinate recycled ancient crust this is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt the parental magmas for both the woduhe and baerzhe granites have undergone extensive magmatic differentiation during which intense interaction of the residual melts with aqueous hydrothermal fluids probably rich in f and cl resulted in the non charac trace element behavior and the tetrad effect of ree distribution both the woduhe and baerzhe granites show the characteristic trace element patterns of rare metal granites but their absolute abundances differ by as much as two orders of magnitude the oxygen isotope compositions of the two granites have been severely disturbed significant 18o depletion in feldspar but not so much in quartz suggests that the hydrothermal alteration took place in a temperature condition of 300 500 c this subsolidus hydrothermal alteration is decoupled from the late stage magma fluid interaction at higher temperatures despite the two distinct and intense events of water rock interaction the rb sr and sm nd geochronological systems seem to have maintained closed hence suggesting that the two events occurred shortly after the plutonic emplacements

zircon u pb ages of the metamorphic supracrustal rocks of the xinghuadukou group and granitic complexes in the argun massif of the northern great hinggan range ne china and their tectonic implications abstract the basement of the argun massif in the northern great hinggan range consists of the metamorphic supracrustal rocks of the xinghuadukou group and associated granitic complexes the metamorphic supracrustal rocks were previously interpreted as paleoproterozoic while the granitic complexes were considered mesoproterozoic in age this paper presents new zircon la mc icp ms u pb ages of biotite plagioclase leptynite and biotite schist from the xinghuadukou group in the lulin forest area heilongjiang province zircon shrimp u pb ages of biotite plagioclase gneiss from the xinghuadukou group in lulin forest and quartz diorite and monzogranite from the granitic complexes in mohe county heilongjiang province new geochronological data from the three metasedimentary rock samples of the xinghuadukou group can be preliminarily divided into five groups 1 2017 2765 ma 2 1736 1942 ma 3 1359 1610 ma 4 749 1239 ma and 5 448 716 ma except for the zircons of the 448 716 ma group belonging to a metamorphic origin the other age groups had the youngest age of 749 17 ma indicating that the xinghuadukou group formed during the neoproterozoic era at least

sims zircon u pb and molybdenite re os geochronology hf isotope and whole rock geochemistry of the wunugetushan porphyry cu mo deposit and granitoids in ne china and their geological significance abstract the geodynamic setting of magmatic rocks and geodynamic mechanism of cu mo fe sn pb zn ag polymetallic mineralization in northeastern ne china are attracting increasing attention this study explores these issues by providing sims zircon u pb dating whole rock geochemical hf isotopic data of magmatic rocks and molybdenite re os dating exposed in the wunugetushan porphyry cu mo deposit ne china this deposit is located in the western part of the great xing an range on the southeastern margin of the mongol okhotsk orogenic belt molybdenite re os and sims zircon u pb dating of the host monzogranitic porphyry and the wall rock of biotite granite in the wunugetushan porphyry cu mo deposit indicate that the ore formation host porphyry and wall rock emplacement occurred at 180 5 2 0 ma 180 4 1 4 ma and 203 5 1 6 ma respectively and the mineralization of the wunugetushan porphyry cu mo deposit occurred during the same period as that of the host monzogranitic porphyry geochemically the wunugetushan granitoids are characterized by strong lree hree fractionation and pronounced negative nb ta and ti anomalies with slightly negative eu anomalies eu eu 0 71 0 97 of the host monzogranitic porphyry and pronounced negative eu anomalies eu eu 0 29 0 32 of the wall rock of biotite granite in situ hf isotopic analyses of zircons from the host monzogranitic porphyry and the wall rock of biotite granite yielded ehf t values ranging from 0 5 to 8 2 and from 6 9 to 5 9 respectively the geochemical and isotopic data for the wunugetushan granitoids imply that the primary magmas of the host monzogranitic porphyry could have originated by partial melting of a thickened lower crust with input of mantle components while the primary magmas of the wall rock of biotite granite could have been derived by partial melting of a thickened lower crust that mixed with ancient crustal materials based on the regional geological history geochemistry of the wunugetushan granitoids and new isotopic age data we suggest that the formation of the wunugetushan porphyry cu mo deposit was possibly induced in the early jurassic during the period of the southeastward subduction of the mongol okhotsk oceanic plate beneath the erguna massif

niobium uranium evidence for early formation of the continental crust niobium uranium ratios in greenstone belt basalts and gabbros indicate that parts of the late archean mantle beneath western australia underwent a level of melt extraction resulting in formation of the continental crust comparable to that seen in the present mantle the implication is either that i the amount of continental crust that formed before 2 7 x 10 9 years ago was much greater than generally thought or ii crustal growth occurred by severe depletion of small volumes of the mantle rather than by moderate depletion of a large volume of mantle

early mesozoic southward subduction history of the mongol okhotsk oceanic plate evidence from geochronology and geochemistry of early mesozoic intrusive rocks in the erguna massif ne china abstract in this paper we present new zircon u pb ages hf isotope data and whole rock major and trace element data for early mesozoic intrusive rocks in the erguna massif of ne china and we use these data to constrain the history of southward subduction of the mongol okhotsk oceanic plate and its influence on ne china as a whole the zircon u pb dating indicates that early mesozoic magmatic activity in the erguna massif can be subdivided into four stages at 246 ma 225 ma 205 ma and 185 ma the 246 ma intrusive rocks comprise a suite of high k calc alkaline diorites quartz diorites granodiorites monzogranites and syenogranites with i type affinities the 225 ma intrusive rocks consist of gabbro diorites and granitoids and they constitute a bimodal igneous association the 205 ma intrusive rocks are dominated by calc alkaline i type granitoids that are accompanied by subordinate intermediate mafic rocks the 185 ma intrusive rocks are dominated by i type granitoids accompanied by minor amounts of a types these early mesozoic granitoids mainly originated by partial melting of a depleted and heterogeneous lower crust whereas the coeval mafic rocks were probably derived from partial melting of a depleted mantle modified by subduction related fluids the rock associations and their geochemical features indicate that the 246 ma 205 ma and 185 ma intrusive rocks formed in an active continental margin setting related to the southward subduction of the mongol okhotsk oceanic plate the 225 ma bimodal igneous rock association formed within an extensional environment in a pause during the subduction process of the mongol okhotsk oceanic plate every magmatic stage has its own corresponding set of porphyry deposits in the southeast of the mongol okhotsk suture belt taking all this into account we conclude the following 1 during the early mesozoic the mongol okhotsk oceanic plate was subducted towards the south beneath the erguna massif but with a pause in subduction at 225 ma and 2 the southward subduction of the mongol okhotsk oceanic plate not only caused the intense magmatic activity but was also favorable to the formation of porphyry deposits

bajo de la alumbrera copper gold deposit stable isotope evidence for a porphyry related hydrothermal system dominated by magmatic aqueous fluids alteration zones at the gold rich bajo de la alumbrera porphyry copper deposit in northwestern argentina are centered on several porphyritic intrusions they are zoned from a central copper iron sulfide and gold mineralized potassic biotite k feldspar quartz core outward to propylitic chlorite illite epidote calcite assemblages a mineralized intermediate argillic alteration assemblage chlorite illite pyrite has overprinted the potassic alteration zone across the top and sides of the deposit and is itself zoned outward into phyllic quartzinuscovite illite pyrite alteration this study contributes new data to previously reported delta 18 o and delta d compositions of fluids responsible for the alteration at bajo de la alumbrera and the data are used to infer likely ore forming processes measured and calculated delta 18 o and delta d values of fluids 8 3 to 10 2 and 33 to 81 parts per thousand respectively confirm a primary magmatic origin for the earliest potassic alteration phase lower temperature potassic alteration formed from magmatic fluids with lower delta d values down to 123 parts per thousand these depleted compositions are distinct from meteoric water and consistent with degassing and volatile exsolution of magmatic fluids derived from an underlying magma variability in the calculated composition of fluid associated with potassic alteration is explained in terms of phase separation or boiling if copper iron sulfide deposition occurred during cooling as proposed elsewhere this cooling was largely a result of phase separation magmatic water was directly involved in the formation of overprinting intermediate argillic alteration assemblages at bajo de la alumbrera calculated delta 18 o and delta d values of fluids associated with this alteration range from 4 8 to 8 1 and 31 to 71 per mil respectively compositions determined for fluids associated with phyllic alteration 0 8 to 10 2 and 31 to 119 parts per thousand overlap with the values determined for the intermediate argillic alteration we infer that phyllic alteration assemblages developed during two stages the first was a high temperature 400 degrees 300 degrees c stage with d depleted water delta d 66 to 119 parts per thousand this compositional range may have resulted from magma degassing and or the injection of new magmatic water into a compositionally evolved hydrothermal system the isotopic variations also can be explained by increased fluid rock interaction the second stage of phyllic alteration occurred at a lower temperature similar to 200 degrees c and variations in the modeled isotopic compositions imply mixing of magmatic and meteoric waters ore deposition that occurred late in the evolution of the hydrothermal system was probably associated with further cooling of the magmatic fluid in part caused by fluid rock interaction and phase separation changing ph and or oxygen fuoracity may have caused additional ore deposition the ingress of meteoric water appears to postdate the bulk of mineralization and occurred as the system at bajo de la alumbrera waned

assessing the reliability of the modified three component spatial autocorrelation technique summary analysis of seismic ambient vibrations is becoming a widespread approach to estimate subsurface shear wave velocity profiles however the common restriction to vertical component wavefield data does not allow investigations of love wave dispersion and the partitioning between rayleigh and love waves in this study we extend the modified spatial autocorrelation technique mspac to three component analysis 3c mspac by determination of love wave dispersion curves this technique provides additional information for the determination of shear wave velocity depth profiles furthermore the relative fraction of rayleigh waves in the total portion of surface waves on the horizontal components is estimated tests of the 3c mspac method are presented using synthetic ambient vibration waveform data different types of surface waves are simulated as well as different modes in addition different spatial distributions of sources are used we obtain rayleigh and love wave dispersion curves for broad frequency bands in agreement with the models used for waveform simulation the same applies for the relative fraction of rayleigh waves dispersion curves are observed at lower frequencies for love waves than for rayleigh waves while 3c mspac has clear advantages for determination of love waves velocities 3c mspac and conventional vertical frequency wavenumber analysis complement each other in estimating the rayleigh wave dispersion characteristics inversions of the dispersion curves for the shear wave velocity depth profile show that the use of love wave velocities confirms the results derived from rayleigh wave velocities in the presence of higher mode surface waves love waves even can improve results application of 3c mspac to ambient vibration data recorded during field measurements pulheim germany show dominance of love waves in the wavefield existing shear wave profiles for this site are consistent with models obtained from inversion of rayleigh and love wave dispersion curves

quantitative assessment of in situ salt karstification using shear wave velocity dead sea abstract the dead sea ds coastal areas have been dramatically affected by sinkhole formation since around 1990 such sinkholes along both israeli and jordanian shores are linked to karst cavities that form through slow salt dissolution a quantitative estimate of such in situ salt karstification would be an important indicator of sinkhole hazard one of the indications of salt karstification is its increased hydraulic conductivity caused by the development of dissolution cavities forming conducting channels within the salt layer we measured the hydraulic conductivity k versus shear wave velocity vs of ds salt in situ for estimating the actual salt karstification in areas of sinkhole development these parameters were measured with the magnetic resonance sounding mrs and multichannel analysis of surface waves masw methods respectively understanding of the field relationships was augmented by similar inter relations obtained in the laboratory on samples of ds salt in situ salt velocities vs vary from 750 m s to over 1650 m s while hydraulic conductivity k in the same zones varies between about 10 4 m s to slightly over 10 8 m s both field and laboratory k and vs values fit the exponential function ln k 0 0045 vs 5 416 with a determination coefficient r2 of 0 88 a classification based on vs and k was generated for salt conditions and the corresponding degrees of sinkhole hazard which was verified in the mineral beach sinkhole development area the mapping of sinkhole sites shows that they form within highly conductive zones with k 5 5 10 5 it is suggested that this methodology with some modification can be used for evaluating the conductive properties of karstified rock and associated sinkhole hazards

the importance of surface waves in vibration study and the use of rayleigh waves for estimating the dynamic characteristics of soils vibrations generated during civil engineering work are often dominated by prominent surface waves the propagation of which is strongly influenced by site conditions the effects of soil properties on the shape amplitude and duration of rayleigh waves are shown from synthetic seismograms surface waves are dispersive and may be processed to retrieve the shear characteristics shear wave velocityvs and shear quality factorqs of soil layers a seismic survey was conducted on a site limelette belgium to determine the dynamic characteristics of the ground layers from different seismic methods various refraction profiles and one cross hole test were performed to obtain shear wave velocity profiles the comparison of surface wave inversion method with other techniques shows that the former leads to slightly underestimatedvs values

reply to the comment by bolhar et al on growth and recycling of early archaean continental crust geochemical evidence from the coonterunah and warrawoona groups pilbara craton australia by green et al tectonophysics 322 2000 69 88

porphyry cu mo au deposits related to melting of thickened mafic lower crust examples from the eastern tethyan metallogenic domain abstract most porphyry cu deposits in the world occur in magmatic arc settings and are formed in association with calc alkaline arc magmas related to subduction of oceanic lithosphere this contribution reviews a number of significant porphyry cu deposits in the eastern tethyan metallogenic domain they widely occur in a variety of non arc settings varying from post late collisional transpressional and extensional environments to intracontinental extensional environments related to orogenic and anorogenic processes their spatial temporal localization is controlled by strike slip faults orogen transverse normal faults lineaments and their intersections in these non arc settings these deposits are dominated by porphyry cu mo deposits with minor porphyry cu au and epithermal au deposits and exhibit a broad similarity with those in magmatic arcs the associated magmas are generally hydrous relatively high fo2 high k calc alkaline and shoshonitic and show geochemical affinity with adakites they are distinguished from arc magmas and or oceanic slab derived adakites by their occurrence as isolated complexes high k2o contents 1 2 8 5 and much wider range of end t values 10 to 3 and positive ehf t values 4 6 to 6 9 these potassic magmas are most likely formed by partial melting of thickened juvenile mafic lower crust or delaminated lower crust but also involving various amounts of asthenospheric mantle components key factors that generate hydrous fertile magmas are most likely crust mantle interaction processes at the base of thickened lower crust in non arc settings rather than oceanic slab dehydration as in arc settings breakdown of amphibole in thickened lower crust e g amphibole eclogite and garnet amphibolite during melting is considered to release fluids into the fertile magmas leading to an elevated oxidation state and higher h2o content necessary for development of porphyry cu mo au systems copper and au in hydrous magmas are likely derived from mantle derived components and or melts which either previously underplated and infiltrated at the base of the thickened lower crust or were input into the primitive magmas by melt mantle interaction in contrast mo and part of the s in the fertile magmas are probably supplied by old crust during melting and subsequent ascent

comparisons of shear wave slowness in the santa clara valley california using blind interpretations of data from invasive and noninvasive methods many groups contributed to a blind interpretation exercise for the deter mination of shear wave slowness beneath the santa clara valley the methods in cluded invasive methods in deep boreholes as well as noninvasive methods using active and passive sources at six sites within the valley with most investigations being conducted at a pair of closely spaced sites near the center of the valley although significant variability exists between the models the slownesses from the various methods are similar enough that linear site amplifications estimated in several ways are generally within 20 of one another the methods were able to de rive slownesses that increase systematically with distance from the valley edge cor responding to a tendency for the sites to be underlain by finer grained materials away from the valley edge this variation is in agreement with measurements made in the boreholes at the sites

euro seistest determination of the geological structure of the volvi basin and validation of the basin response the volvi basin northern greece is a 5 km wide graben of neogene age it has been chosen by european union directorate general xii for science research and development in climatology and natural hazards as a test site euro seistest for studying site effects in one of europe s most seismic active areas the site is located in the epicentral area of the 1978 ms 6 5 earthquake that struck the city of thessaloniki the geometry velocity and stratigraphy of the basin were not well known consequently a number of geophysical and geotechnical studies were performed to determine the 2d geometry and the dynamic characteristics vp vs qs of the valley investigations included 78 refraction tests 20 surface wave inversions and 8 borehole seismic tests as well as geotechnical tests this article presents the methodology used for the geophysical investigation and the results in its center the graben depth reaches 190 m and at least four normal faults have been located along the section the overall graben structure and the fault locations have been confirmed by the records of a shot generated at one edge of the valley and by the measurements of a local earthquake wave propagation appears to be strongly influenced by the thickness of the sediments which in turn is controlled by fault displacements simple 2d modeling of the basin response was performed and the results are in good agreement with weak motion data confirming the validity of the seismic structure inferred from seismic prospecting

mineralogical and isotopic studies of base metal sulfides from the jiawula ag pb zn deposit inner mongolia ne china abstract the jiawula ag pb zn deposit is located in the northern part of the da hinggan mountains metallogenic belt in the eastern section of the central asian orogenic belt sphalerite galena pyrite chalcopyrite and arsenopyrite are the major sulfide minerals occurring in this deposit here we report results from electron probe micro analysis epma thermoelectricity and sulfur isotope studies of the constituent silver minerals and sulfide phases of the jiawula deposit petrographic observations and epma study reveal abundant silver mineralization in the ore especially within sphalerite and galena discrete grains of silver minerals including argentite pyrargyrite and canfieldite and isomorphism in silver bearing sulfides are identified silver and tellurium contents in galena are relatively high and show interrelationship significant substitution of s by te in the galena lattice facilitates silver entering the galena structure which might have been promoted by relatively low lg fs2 the thermoelectric coefficient of pyrite shows a marked gradient from n type to p type from pre to post metallogenic stages pyrites in jiawula are enriched in co and as and in the absence of ni displaying features typical of epithermal deposits the isotopic data present a close relationship between the sulfur source and magmatism

timing and evolution of jurassic cretaceous granitoid magmatisms in the mongol okhotsk belt and adjacent areas ne asia implications for transition from contractional crustal thickening to extensional thinning and geodynamic settings abstract the mongol okhotsk belt and adjacent areas are key areas to study the relationship between the okhotsk and paleo pacific tectonic regimes and their superposition on the older paleo asian regimes during late mesozoic times this paper summarizes the spatial temporal evolution of late mesozoic jurassic cretaceous granitoids and related intrusions in these areas and interprets the magmatic evolution in terms of a transition from contractional crustal thickening to extensional thinning according to 407 published zircon ages these granitoids were mainly emplaced during the intervals 200 180 ma 180 165 ma 165 145 ma 145 135 ma and 135 100 ma jurassic granitoids 200 145 ma predominately occur in the baikal ne mongolia bnem and great xing an range early cretaceous 145 100 ma granitoids are mainly occur in the great xing an range and display a southward younging migration significantly early cretaceous granitoids also extend into the trans baikal area across the mongol okhotsk suture far away from the paleo pacific plate margin in ne china thus they were more plausibly related to post orogenic collapse of the mongol okhotsk orogen from the late jurassic to early cretaceous the granitoids evolved compositionally from calc alkaline and high k calc alkaline i type with some adakite like features to high k calc alkaline and shoshonitic highly fractionated i transitional i a or a type characterized by a significant decrease in their sr y ratios this evolution coincided with a tectonic transition from contractional crustal thickening to extensional thinning combined with regional geology we speculate that the jurassic granitoids were likely derived from melting of the deep seated thickened lower continental crustal lcc sources whereas the cretaceous granitoids produced through crustal melting from an extensional thinning setting our results provide a case study demonstrating that the petrogenesis of granitic magmatism was closely associated with crustal tectonics early jurassic granitoids along the okhotsk belt formed in a subduction collision setting related to closure of the mongol okhotsk ocean whereas late jurassic granitoids in the great xing an range and in the northern north china craton may have formed in a syn or post collisional setting superposed by far field affects of subduction of the paleo pacific plate early cretaceous granitoids in these areas formed in response to post orogenic extensional collapse of the mongol okhotsk belt coupled with back arc extension related to paleo pacific plate subduction

early paleozoic metamorphic rocks of the erguna block in the great xing an range ne china evidence for the timing of magmatic and metamorphic events and their tectonic implications abstract the erguna block is a crustal unit located along the eastern margin of the central asian orogenic belt caob in the far north of china it contains a variety of khondalitic rocks that include sillimanite and garnet bearing gneiss biotite plagioclase gneiss and carbonate in association with hornblende plagioclase gneiss and a variety of granitic orthogneisses these rocks are collectively referred to as the mohe complex and make up the basement rocks in this poorly exposed terrane four samples were analyzed for this study including two samples of biotite plagioclase gneiss one sample of garnet sillimanite gneiss and a sample of hornblende plagioclase gneiss all samples provide evidence of metamorphism in the form of discrete zircon grains or metamorphic rims around detrital cores and they record remarkably consistent 206 pb 238 u ages between 495 2 ma and 497 6 ma detrital zircon cores with oscillatory zoning from the two biotite plagioclase gneiss samples yield magmatic ages that range from 608 8 ma to 1015 12 ma whereas those in the garnet sillimanite gneiss range from 678 8 to 1373 17 ma these results establish that a range of meso to neoproterozoic magmatic rocks were present in the source area and contributed to the sedimentary protoliths the youngest zircon core with an age of 608 8 ma limits the maximum possible age of deposition indicating that the rocks of the mohe complex cannot be late archean to early proterozoic as previously considered the 500 ma age for the granulite facies metamorphic event in the mohe complex is identical to that recorded in the mashan complex of the jiamusi block and the hutou complex of the khanka block 1000 km to the south southeast implying that an extensive early paleozoic khondalite belt extended across much of the eastern caob rocks of similar age and metamorphic grade have also been recorded from the sayang baikal orogen along the southern margin of the siberia craton 1000 km to the west it is unclear at present whether these two belts are directly related but whatever the relationship it is evident that extensive tracts of khondalitic rocks were present in the eastern caob they were subsequently affected by high grade metamorphism in the early paleozoic forming collisional accretionary terranes that were accreted during the late pan african global event

ages and petrogenesis of the late mesozoic igneous rocks associated with the xiaokele porphyry cu mo deposit ne china and their geodynamic implications abstract the genesis of igneous rocks associated with the newly discovered xiaokele porphyry cu mo deposit located in the eastern erguna block ne china can give insights into the regional geodynamic evolution during the late mesozoic several ore bodies have been identified in a granodiorite porphyry stock which intruded the rhyolite and was subsequently intruded by diorite porphyry and granite porphyry the u pb ages of zircons from rhyolite mineralized granodiorite porphyry diorite porphyry and granite porphyry associated with the xiaokele deposit are 152 5 1 7 150 0 1 6 147 9 1 3 and 123 2 1 7 ma respectively the rhyolite and granite porphyry have high sio2 and low mgo cr co and ni contents their isotopic data show negative end t values of 4 76 to 0 87 initial 87sr 86sr ratios of 0 7066 to 0 7134 and positive zircon ehf t values of 0 33 5 56 indicating that they were derived from a basaltic lower continental crust the mineralized granodiorite porphyry is characterized by high sr y values and low y 3 7 8 0 contents showing adakite affinity the low k2o na2o 0 51 0 7 ratios high cao contents weakly negative end t 1 17 to 0 27 and low zircon ehf t 1 49 5 4 values from the adakitic samples indicate that they were derived from the partial melting of an altered oceanic slab together with assimilation of mantle peridotite and crustal materials the 148 ma diorite porphyry has high mg 51 58 weakly negative and positive end t 0 09 to 0 01 values and lower 87sr 86sr i 0 7055 0 7057 ratios suggesting an enriched mantle wedge source considering the late mesozoic regional tectonic evolution of the erguna block and adjacent area we propose that the formation of the xiaokele deposit is linked to the southward flat slab subduction of the mongol okhotsk oceanic plate during the later jurassic early cretaceous

new evidence of magmatic fluid related phyllic alteration implications for the genesis of porphyry cu deposits the phyllic alteration in a number of circum pacific porphyry cu au deposits is related to high temperature saline magmatic fluids this contradicts the widely used genetic models wherein phyllic alteration formed as the result of mixing between magmatic and meteoric fluids at the endeavour 26 north porphyry deposit in eastern australia the transition from early potassic to the main stage phyllic alteration is associated with fluids that with time decline in total salinity nacl kcl and temperature from 600 to 550 degrees c calculated and measured delta 18 o and delta d compositions of fluids 5 1 8 5 parts per thousand 57 to 73 parts per thousand delta d confirm a primary magmatic origin for both the early potassic and main stage phyllic alteration these results are consistent with other recent studies e g el salvador chile far southeast philippines and panguna and porgera papua new guinea and suggest that rather than these results being unusual a major revision of porphyry cu genetic models is required

generation of sodium rich magmas from newly underplated basaltic crust sodium rich rocks of trondhjemite tonalite dacite ttd or granodiorite ttg suites form much of precambrian continental crust1 they are thought to have formed by partial melting of subducted oceanic crust2 3 a process that would have been much more widespread early in earth history than at present owing to the higher thermal gradients prevailing at that time4 phanerozoic ttd suites do exist however and seem also to relate to subduction zones5 defant and drummond6 proposed that these suites form where young 25 myr hot oceanic lithosphere is subducted and melts thus locally simulating the conditions that led to widespread crustal growth in the archaean here we describe plutonic and volcanic rocks from the cordillera blanca complex in peru which have characteristics of the high al ttd suite but which were produced above a subduction zone containing a 60 myr old slab we present evidence that the complex formed by partial melting of newly underplated basaltic crust and argue that this mechanism should be considered more generally as an additional way of generating sodium rich arc magmas

geochronology and isotopic geochemistry of the a type granites from the huanggang sn fe deposit southern great hinggan range ne china implication for their origin and tectonic setting abstract the huanggang sn fe deposit inner mongolia is located in southern great hinggan range metallogenic belt la icp ms zircon u pb dating show that the k feldspar granite and granite porphyry in the huanggang mine were formed at 136 7 1 1 ma and 136 8 0 57 ma respectively sr nd pb isotope of the rocks and in situ zircon hf isotopic systematics show that 87 sr 86 sr i values range from 0 70211 to 0 70729 close to the 87 sr 86 sr i of oceanic basalts and lower than those of continental crust the e nd t values and nd model ages t dm vary from 0 8 to 0 9 and 855 to 993 ma respectively the pb isotopic compositions are also variable with 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb values of 18 974 26 107 15 554 15 914 and 38 894 39 890 respectively suggesting that the lead is derived from a mixed source the 176 hf 177 hf values range from 0 282744 to 0 282922 with corresponding e hf t values ranging from 1 9 to 18 3 and two stage hf model ages t dm2 of between 561 and 888 ma the isotope composition shows that huanggang granites were derived from partial melting of juvenile lower crust that originated from depleted mantle perhaps contaminated by small amounts of ancient continental crust younger nd hf isotope model ages imply that an important crustal growth event took place in this area during the neoproterozoic integrating our data with previously published results and the late mesozoic regional tectonic setting we conclude that the huanggang granites were generated in an intraplate tectonic magmatic setting asthenospheric mantle upwelling due to lithospheric delamination and magma underplating caused the partial melting of a mantle wedge metasomatized by the fluids released from subducted oceanic crust or by decompression of depleted mantle this resulted in remelting differentiation and a continued evolution of the mafic juvenile crust producing a large quantity of granitic magma the tectonic setting for these processes may be linked to the nnw subduction of the pacific plate izanagi in the mesozoic which affected most of eastern china

origin of the badaguan porphyry cumo deposit inner mongolia northeast china constraints from geology isotope geochemistry and geochronology abstract the badaguan porphyry cu mo deposit is located in the derbugan metallogenic belt of northeastern inner mongolia china the host granodioritic porphyry and the wall rock granitic porphyry were emplaced at 230 ma and 238 ma respectively the granodioritic porphyry has 87 sr 86 sr i values of 0 70535 0 70549 e nd t values of 0 41 1 17 e hf t values of 1 30 6 51 and two stage model ages t dm2 of 1131 848 ma in contrast the granitic porphyry is characterized by e hf t values from 0 75 to 7 28 that yield t dm2 model ages of 1355 816 ma the geochemical and sr nd hf isotopic data for the magmatic rocks associated with the badaguan porphyry cu mo deposit indicate that these intrusions were generated by the partial melting of juvenile lower crust the 18 o values of ore fluids from different mineralizing stages are between 6 0 and 1 5 and the fluid d water values vary from 119 3 to 140 0 indicating a mixed fluid of magmatic and meteoric water the s pb isotopes show that the metal was mostly derived from a deep seated magma that involved some crustal materials with a narrow 34 s range 2 4 to 3 5 we infer that the badaguan porphyry cu mo deposit formed during a period of southeast directed subduction of the mongol okhotsk oceanic plate beneath the erguna block

high sr y magmas reflect arc maturity high magmatic water content and porphyry cu mo au potential examples from the tethyan arcs of central and eastern iran and western pakistan the temporal and geochemical evolution of arc magmatism that culminated in porphyry cu mo au deposit formation has been studied in three separate neo tethyan arc systems in central and eastern iran and western pakistan porphyry cu au deposits in the lut block of eastern iran formed in the middle eocene at the end of a period of extensive paleocene eocene volcanism porphyry cu mo deposits in the kerman belt of central iran formed in the middle miocene at the end of a period of voluminous eocene oligocene volcanism and porphyry cu au deposits in the chagai belt of western pakistan formed in four pulses during the eocene early miocene middle late miocene and late miocene pliocene after a prolonged period of arc magmatism that began in the late cretaceous and is still active in each region the late porphyry related magmas are more geochemically evolved and more hydrous as evidenced by the presence of hornblende phenocrysts than the preceding volcanic rocks we suggest that this reflects maturation of the arc magmatic system over a period of tens of millions of years leading to the generation of more evolved volatile rich magmas at later stages of the arc s history high magmatic water contents are a prerequisite for the shallow crustal emplacement of arc magmas and the subsequent generation of potentially ore forming subvolcanic magmatic hydrothermal systems it is thus suggested that the fertility of arc magmas within a given arc terrane can be assessed by observing the relative timing of plutonic suites later suites are more prospective noting the common presence of hornblende or biotite phenocrysts indicating high magmatic water contents and through lithogeochemical fingerprinting of magmatic fractionation processes relatively high sr y and la yb ratios and eun eu ratios 1 indicating abundant early hornblende fractionation and suppression of plagioclase crystallization in hydrous magmas

geophysical investigation of a large landslide in glaciolacustrine clays in the trieves area french alps abstract slope movements in clay deposits are spread all over the world and result from complex deformation processes including internal strains in the landslide body and slipping along rupture surfaces such mass movements are likely to generate changes in the geophysical parameters characterizing the ground which can be used to map the landslide body in the last decade geophysical techniques have been increasingly used for landslide investigation purposes however the success of any geophysical technique is overall controlled by the existence of a geophysical contrast differentiating the body to be mapped for landslides affecting thick clay materials from soft clay to shale or marl electrical and seismic techniques have been mainly applied in the past in this study we attempt to physically characterize the deformation within a large slide avignonet affecting laminated clays which were deposited in a glacially dammed lake during the wurm period clay deposits which cover an area of 300 km2 south of grenoble french alps and have a maximum thickness of 200 m overlay compact alluvial layers and marly limestone of mesozoic age piezometric data at avignonet show that the water table is very shallow implying that the slide developed in saturated clay several seismic and electrical profiles were performed in order to tentatively correlate the variations of p wave vp velocity s wave velocity vs and electrical resistivity with geotechnical data and morphological observations in such saturated and fine material it turned out that only the s wave velocity exhibits significant variations with the displacement rates and the morphological features vs values at shallow depth were found to be inversely correlated with displacement rates measured by gps with a division by at least a factor of 2 between the zones unaffected and strongly deformed by the landslide these results suggest that vs mapping could provide valuable information on the deformation state of the clay material and that the evolution of vs with time could be used as an indicator for characterizing the landslide activity in the subsurface including the evolution into a flow

extrapolation of irregular subsurface structures using the horizontal to vertical spectral ratio of long period microtremors one of the key problems in modeling the 3d subsurface structure of sedimentary basins is extrapolation and or interpolation from 2d models constructed from reflection and refraction surveys the use of microtremor horizontal to vertical h v spectral ratios allowing simple and quick microtremor measurements may be suitable for this purpose the validity and usefulness of long period microtremor h v spectral ratios are investigated as a possible tool for extrapolation in 3d basin structure modeling three component microtremor observations were conducted at 51 stations in the northern section of the osaka basin which encompasses the most complex geological structures in the basin the microtremor h v spectral ratios were measured in the range 1 to 5 sec to reproduce these observations three 2d finite element models have been developed that account for the irregular shape of subsurface structures deduced from seismic reflection studies microtremor array studies and deep drilling data the 3d model obtained by combining the 2d models is consistent with geological information for the area such as surface geology and the location of active faults furthermore compared with the basement structure derived from the gravity prospecting this 3d model is more detailed and offers higher resolution than the gravitational method therefore the microtremor h v spectral ratio represents a useful technique of extrapolation and interpolation for modeling 3d basin structures

fluid inclusions and h o s pb isotope systematics of the chalukou giant porphyry mo deposit heilongjiang province china abstract the chalukou giant porphyry mo deposit located in the northern great xing an range is the largest mo deposit in the xing an mongolia orogenic belt this deposit s ore bodies are mainly hosted in an intermediate felsic complex and jurassic volcanic sedimentary rocks of which late jurassic granite porphyry quartz porphyry and fine grained granite are closely associated with the mo mineralization three types of fluid inclusions fis are present in the quartz associated with oxide and sulphide minerals i e liquid rich two phase gas rich two phase and daughter mineral bearing multiphase fis the fis in the quartz phenocrysts of the granite porphyry contain liquid rich two phase gas rich two phase and daughter mineral bearing multiphase fis the homogenization temperatures vary from 230 c to 440 c and 470 c to 510 c and their salinities vary from 0 7 to 53 7 nacl eq and 6 2 to 61 3 nacl eq respectively the fis of k feldspar quartz magnetite veins of the early stage are composed of liquid rich two phase gas rich two phase and daughter mineral bearing multiphase fis with homogenization temperatures and salinities of 320 c to 440 c and 4 2 to 52 3 nacl eq respectively the fis of quartz molybdenite veins and breccia of the middle stage are composed of liquid rich two phase gas rich two phase and daughter mineral bearing multiphase fis with homogenization temperatures and salinities of 260 c to 410 c and 0 4 to 52 3 nacl eq respectively fis of quartz fluorite galena sphalerite veins of the late stage are liquid rich two phase fis with homogenization temperatures and salinities of 170 c to 320 c and 0 5 to 11 1 nacl eq respectively the ore forming fluids of the chalukou deposit are characterised by high temperature high salinity and high oxygen fugacity belonging to an f rich h 2 o nacl co 2 system the 18 o w values vary from 4 5 to 3 2 and the d w values vary from 138 to 122 indicating that the ore forming fluids were a mixture of magmatic and meteoric water the 34 s values range from 1 9 to 3 6 with an average of 1 6 the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb values of the metallic minerals are in the ranges of 18 269 18 501 15 524 15 567 and 38 079 38 264 respectively both the s and pb isotopic systems indicate that the ore metals and fluids came primarily from a deep seated magma source from the juvenile lower crust the mo mineralization in the chalukou deposit occurred at a depth of 0 5 to 1 3 km and multiple stages of phase separation or immiscibility of ore forming fluid was critical for the formation of the chalukou deposit

geochronology and geochemistry of early middle triassic magmatism in the erguna massif ne china constraints on the tectonic evolution of the mongol okhotsk ocean abstract in this paper we present new zircon u pb dating hf isotope major and trace elements and sr nd isotope data for early middle triassic intrusive rocks in the erguna massif of ne china in the eastern segment of the central asian orogenic belt caob our aim is to elucidate the tectonic evolution of the mongol okhotsk ocean and its influence on ne china zircons from five representative intrusions in the erguna massif are euhedral subhedral in shape display oscillatory growth zoning in cl images and have th u ratios of 0 17 1 54 and in combination these features indicate that the zircons are of igneous origin zircon u pb dating results demonstrate that the early middle triassic magmatism in the erguna massif took place between 241 and 247 ma the early middle triassic rocks are composed mainly of a suite of diorites quartz diorites granodiorites monzogranites and syenogranites they have sio 2 57 71 72 86 wt mg 19 52 al 2 o 3 14 27 17 23 wt and na 2 o k 2 o 0 67 1 59 chemically they are metaluminous to peraluminous and belong to the high k calc alkaline series moreover they are enriched in light rare earth elements and large ion lithophile elements and depleted in heavy rare earth elements and high field strength elements e g nb ta and ti the whole rock e nd t and zircon e hf t values of these samples range from 4 68 to 3 42 and from 2 0 to 6 6 respectively indicative of formation from primary magmas generated by partial melting of juvenile crustal material with a contribution from mantle derived mafic magmas these magmas subsequently underwent fractional crystallization contamination and magma mixing geochemically these early middle triassic intrusive rocks have affinities with intrusive rocks from active continental margin settings we conclude therefore that the early middle triassic magmatism in the erguna massif was generated within an active continental margin setting related to the southwards subduction of the mongol okhotsk oceanic plate beneath the erguna massif this conclusion is supported by the occurrence of early mesozoic porphyry and skarn deposits along the southeastern side of the mongol okhotsk suture belt

seismic imaging of the shallow subsurface shear wave case histories obtaining high resolution images of the geology and hydrogeology of the subsurface in the depth range from ground level to 50 m is one of the major challenges of modern geophysics the methods which are commonly used such as compressional wave surveys and ground penetrating radar often suffer from adverse effects caused by the near surface conditions changes in water saturation and various sources of noise this paper demonstrates some of the advantages offered by the use of shear wave seismology and by the combination of shear and compressional wave seismic methods in shallow subsurface investigations multicomponent shallow seismic tests were carried out at four different sites to examine the effectiveness of different acquisition geometries under a variety of near surface geological conditions near surface conditions encountered at the sites included thick clays clay sand sequences overlying chalk mudstone overlying granodiorite bedrock and landfill material under all conditions shear wave data acquisition was found to have advantages over compressional wave acquisition for the investigation of the shallow subsurface shear head waves being unaffected by water saturation achieved penetration to greater depths at a site in crewkerne dorset where compressional head wave penetration was limited to the near surface layers better vertical resolution was achieved at shallow depths using shear wave reflection energy at a landfill site shear wave reflections from shallow interfaces were in some cases less affected by noise compared with the equivalent compressional wave reflections combinations of shear and compressional wave data recording allowed the measurement of a poisson s ratio log and gave indications of seismic anisotropy at two sites where dipping clay layers were present

giant ore deposits formed by optimal alignments and combinations of geological processes giant ore deposits are priority targets for mining companies a review of the characteristics of several giant porphyry and epithermal deposits worldwide suggests that they formed from ordinary processes that were fortuitously operating at maximum efficiency

petrogenesis of adakitic porphyries in an extensional tectonic setting dexing south china implications for the genesis of porphyry copper mineralization the dexing adakitic porphyries quartz diorite granodiorite porphyries associated with giant porphyry cu deposits are located in the interior of a continent south china they exhibit relatively high mgo cr ni and sr contents high la yb and sr y ratios but low yb and y contents similar to adakites produced by slab melting associated with subduction however they are characterized by bulk earth like nd sr isotope compositions end t 1 14 to 1 80 and 87 sr 86 sr i 0 7044 0 7047 and high th 12 6 27 2ppm contents and th ce 0 19 0 94 ratios which are different from those of cenozoic slab derived adakites sensitive high resolution ion microprobe shrimp geochronology studies of zircons reveal that the dexing adakitic porphyries have a crystallization age of 171 3ma this age is contemporaneous with middle jurassic extension within the shi han rift zone and within plate magmatism elsewhere in south china indicating that the dexing adakitic porphyries were probably formed in an extensional tectonic regime in the interior of the continent rather than in an arc setting their high th contents and th ce ratios and middle jurassic age argue against an origin from a neoproterozoic 1000ma stalled slab in the mantle taking into account available data for the regional metamorphic magmatic rocks and the present day crustal thickness 31km in the area we suggest that the dexing adakitic porphyries were most probably generated by partial melting of delaminated lower crust which was possibly triggered by upwelling of the asthenospheric mantle due to the activity of the shi hang rift zone moreover the dexing adakitic magmas must have interacted with the surrounding mantle peridotite during their ascent which elevated not only their mgo cr and ni contents but also the oxygen fugacity fo2 of the mantle the high fo2 could have induced oxidation of metallic sulfides in the mantle and mobilization of chalcophile elements which are required to produce associated cu mineralization therefore the cu metallogenesis associated with the dexing adakitic porphyries is probably related to partial melting of delaminated lower crust similar to the metallogenesis accompanying slab melting

discrimination of productive and nonproductive porphyritic intrusions in the chilean andes a geochemical comparison between productive intrusions those associated with mineralization and nonproductive intrusions those unrelated to mineralization has been made on the basis of over 100 fresh granitoid rocks from the chilean porphyry copper belt the study was carried out on the scale of a mining district el salvador potrerillos then on the scale of a single traverse el salvador chilean coast and finally on the scale of the andes itself the productive intrusions are best characterized by large negative anomalies in y mn th and the heavy rare earth elements a discriminant diagram of y against mno is recommended for predicting whether an apparently fresh intrusion has associated peripheral mineralization the low values of y and mn in productive intrusions can be partly explained by the early crystallization of y and mn rich hydrous phases such as hornblende and by the loss of mn rich fluids from the magma the same elements make useful discriminants in other porphyry copper provinces although the exact position of the discriminant boundary varies from island arcs through continental margin to continental settings

an early cretaceous ag pb zn mineralization at halasheng in the south erguna block ne china constraints from u pb and rb sr geochronology geochemistry and sr nd hf isotopes abstract the halasheng deposit located in the southern erguna block is a vein type ag pb zn deposit in the derbugan metallogenic belt the orebodies hosted in middle late jurassic volcanic rocks show a close spatial and temporal relationship with early cretaceous granites zircon u pb dating suggests that the granites were emplaced at 134 128 ma rb sr dating of ore related sphalerite gives an imprecise age of 122 18 ma indicating that the halasheng deposit formed in the early cretaceous whole rock major and trace element analyses show that the cretaceous granites belong to the metaluminous to peraluminous shoshonite to high k calc alkaline series and can be classified as a type granites they are enriched in large ion lithophile elements lile and light rare earth elements lree but depleted in high field strength elements hfse and heavy rare earth elements hree the quartz monzonite which has a spatial relationship with mineralization has low initial 87sr 86sr 0 7058 0 7069 and positive end t 0 42 0 61 and ehf t 3 47 6 45 with nd and hf two stage model ages of 0 81 0 85 ga and 0 69 0 86 ga respectively these geochemical features are similar to those of major mesozoic granite intrusions in the erguna block we propose that these graintes originated from partial melting of juvenile crust in an intraplate extensional setting taken together the halasheng ag pb zn deposit formed in the early cretaceous after the orogeny related to closure of the mongol okhotsk ocean the relatively low temperature of ag pb zn ore and alteration mineralogy suggest that there is only a distal relationship if any to nearby potentially causative granite intrusions

evidence of two dimensional amplification effects in an alluvial valley valnerina italy from velocimetric records and numerical models abstract the results of field surveys velocimetric records and numerical models are reported with the goal of analyzing the local seismic response in a section of the nera river alluvial valley in central italy alluvial deposit geometry and dynamic properties were defined by geological and geophysical investigations 2d amplification effects were pointed out by horizontal to vertical spectral ratios hvsrs as well as by horizontal to horizontal spectral ratios hhsrs to a reference station hvsrs were derived from both noise and weak motion records while hhsrs were only computed from weak motions where travertine deposits are interlayered within the alluvia 2d amplification effects are shown only by hhsrs the observed amplifications 1 consist of peaks of the amplification functions a f in the range 1 10 hz 2 generally correspond to two frequency ranges whose values mainly depend on the valley shaped ratio and on the local heterogenities of the alluvial deposits and 3 can be regarded as due to a 1d resonance combined with lateral wave propagation numerical models via the finite difference method were performed by the italian national institute for geophysics and volcanology web interface for seismological application and by the fast lagrangian analysis of continua codes the obtained results 1 show a good agreement with hhsrs 2 prove that some 2d amplification effects are constrained by both the shape ratio of the valley and the heterogeneity of the alluvial deposits 3 reveal focalization effects within the alluvial deposits strictly related to the shape of the valley and 4 allow the comparison of the a f functions in both linear and nonlinear dynamic behavior and the computation of the shear strains due to ground motion within the alluvial deposits

the pre devonian tectonic framework of xing an mongolia orogenic belt xmob in north china abstract a new tectonic division of the xing an mongolia orogenic belt xmob in north china has been presented according to our research and a lot of new data of tectonics geochronology and geochemistry four blocks and four sutures have been recognized in the xmob including the erguna eb xing an airgin sum xab songliao hunshandake shb and jiamusi jb and xinlin xiguitu xxs xilinhot heihe xhs mudanjiang ms and ondor sum yongji sutures oys the framework of the xmob is characterized by a tectonic collage of the blocks and orogenic belts between them different precambrian basements have been found in the blocks including the neoproterozoic metamorphic rocks and plutons in the eb the neoproterozoic metamorphic rocks in western and eastern of segments of the xab mesoproterozoic and neoproterozoic metamorphic rocks in middle segments of the xab respectively the neoproterozoic metamorphic rocks and mesoproterozoic volcanic rocks and plutons in the shb and neoproterozoic metamorphic rocks in the jb the xxs resulted from a northwestward subduction of the xab beneath the eb during the cambrian which was followed by the forming of the xhs and oys in the northwest and south margins of the shb in the silurian respectively the ms was caused by a westward subduction of the jb beneath the east margin of the shb during the middle devonian the three cambrian silurian and middle devonian events indicate that the xmob belongs to a pre middle devonian multiple orogenic belt in the central asian orogenic belt caob forming of the xmob suggests that the southeast part of the paleo asian ocean closed before the middle devonian

evolution of middle late triassic granitic intrusions from the badaguan cu mo deposit inner mongolia constraints from zircon u pb dating geochemistry and hf isotopes abstract the great xing an range in the eastern part of the central orogenic belt is one of the major polymetallic metallogenic belts in china the badaguan cu mo deposit in the erguna massif forms part of this belt and is a typical porphyry deposit associated with multiple granitic intrusions which are temporally and genetically related to the formation of this deposit in this paper we present new zircon u pb ages hf isotopic data and whole rock major and trace element geochemistry on the badaguan granitoids zircon u pb data indicate that the intrusions formed during two major phases ca 244 237 ma and ca 232 229 ma the middle triassic ca 244 237 ma phase is represented by a suite of medium k calc alkaline granite k feldspar granite biotite granite and porphyritic granite with i type affinities in general they are enriched in light rare earth elements lrees and large ion lithophile elements liles and depleted in heavy rare earth elements hrees and high field strength elements hfses their zircon ehf t values and two stage model ages tdm2 range from 1 5 to 8 5 with a mean value of 4 9 and from 732 to 1366 ma with a mean value of 959 ma respectively in contrast the late triassic ca 232 229 ma intrusions dominantly comprise a suite of high k calc alkaline i type granite porphyry and granodiorite porphyry these rocks are enriched in liles and lrees but depleted in hrees and hfses such as nb ta and ti their ehf t and tdm2 values range from 3 4 to 6 2 with a mean value of 5 0 and from 865 to 1047 ma with a mean value of 942 ma respectively these results suggest that the primary magmas of the middle and late triassic intrusive rocks were co magmatic and were mainly derived from the partial melting of juvenile thickened lower crust in addition the primary magma forming the middle triassic complex also assimilated a small amount of ancient crustal material and experienced a remarkable degree of fractional crystallization prior to its emplacement in contrast the source magma of the late triassic complex probably underwent interaction between of minor mantle derived melt and crustal components prior to emplacement the cu in badaguan deposit was likely sourced from the mantle derived melt whereas the mo was contributed by the host rocks with high mo contents

trace element abundances of high mgo glasses from kilauea mauna loa and haleakala volcanoes hawaii we performed an ion microprobe study of eleven high mgo 6 7 14 8 wt tholeiite glasses from the hawaiian volcanoes kilauea mauna loa and haleakala we determined the rare earth re high field strength and other selected trace element abundances of these glasses and used the data to establish their relationship to typical hawaiian shield tholeiite and to infer characteristics of their source the glasses have trace element abundance characteristics generally similar to those of typical shield tholeiites e g l light ree h heavy reec1 1 the kilauea and mauna loa glasses however display trace and major element characteristics that cross geochemical discriminants observed between kilauea and mauna loa shield lavas the glasses contain a blend of these discriminating chemical characteristics and are not exactly like the typical shield lavas from either volcano the production of these hybrid magmas likely requires a complexly zoned source rather than two unique sources when corrected for olivine fractionation the glass data show correlations between cao concentration and incompatible trace element abundances indicating that cao may behave incompatibly during melting of the tholeiite source furthermore the tholeiite source must contain residual garnet and clinopyroxene to account for the variation in trace element abundances of the kilauea glasses inversion modeling indicates that the kilauea source is flat relative to c1 chondrites and has a higher bulk distribution coefficient for the hree than the lree

origin of the wunugetushan porphyry cu mo deposit inner mongolia ne china constraints from geology geochronology geochemistry and isotopic compositions abstract the wunugetushan porphyry cu mo deposit is located in the southeastern margin of the mongol okhotsk orogenic belt and in the northwestern segment of the great xing an range ne china the orebodies of this deposit are mainly hosted in the monzogranitic porphyry stock and in contact with the granitic porphyry dyke and biotite granite batholith the shrimp zircon u pb dating of the granitic porphyry dyke yielded ages of 201 4 3 1 ma 2 mswd 1 5 these results indicate that the magmatism in the wunugetushan area might have occurred at ca 201 ma in the early jurassic and that the mineralization age ca 181 ma of this deposit is later than the age of intrusive granitic porphyry in the area geochemically the wunugetushan granitoids belong to high k calc alkaline and shoshonitic series enriched in k rb nd and pb and depleted in sr nb ti and p with negative eu anomalies in situ hf isotopic analyses of zircons using la mc icp ms indicate that the ehf t values for zircons from a granitic porphyry sample vary from 2 4 to 11 8 and that the corresponding crustal model ages tdmc vary from 483 to 1088 ma the least altered monzogranitic porphyry granitic porphyry and biotite granite yielded relatively uniform end t values from 1 0 to 0 6 and low 87sr 86sr i ratios ranging from 0 704387 to 0 708385 the geochemical and sr nd hf isotopic data for the granitoids indicate that the source magma for these rocks could be derived from a juvenile lower crust the 34s values of sulfides show a narrow range 0 76 to 3 20 similar to those of magmatic sulfur further implying a lower crust origin based on the results of this study and the regional geodynamic evolution it is proposed that the formation of the wunugetushan deposit and associated granitoids should be linked to the southeastward subduction of the mongol okhotsk oceanic plate beneath the erguna massif during the early jurassic and that the monzogranitic porphyry intrusions in wunugetushan area probably provided important ore metals responsible for the large scale cu mo mineralization

giant porphyry deposits characteristics distribution and tectonic controls more than half of the 25 largest known porphyry copper deposits defined in terms of contained copper metal formed during three time periods the paleocene to eocene eocene to oligocene and middle miocene to pliocene these giant deposits are clustered within three provinces central chile northern chile and southwest arizona northern mexico other giant deposits occur in montana utah panama peru argentina irian jaya mongolia and iran compressive tectonic environments thickened continental crust and active uplift and erosion were associated with the formation of many of these deposits calc alkalic magmas are most favorable for the formation of giant porphyry copper deposits although several of the largest systems are associated with high k calc alkalic intrusions the 25 largest gold rich porphyry deposits are concentrated in the southwest pacific and south america with other occurrences in eurasia british columbia alaska and new south wales many of the deposits formed in the last 13 m y the largest of the deposits are associated with high k calc alkalic intrusions many calc alkalic porphyritic intrusions have also produced giant gold rich porphyries in the last 20 m y the formation of giant porphyry copper molybdenum and copper gold deposits in the circum pacific region has been closely associated with subduction of aseismic ridges seamount chains and oceanic plateaus beneath oceanic island and continental arcs in several examples these tectonic perturbations have promoted flat slab subduction crustal thickening uplift and erosion and adakitic magmatism coeval with the formation of well endowed porphyry and or epithermal mineral provinces similar tectonic features are inferred to be associated with the giant porphyry copper molybdenum provinces of northern chile eocene oligocene and southwest united states cretaceous paleocene topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation other factors such as sutures in the overriding plate permeability architecture of the upper crust efficient processes of ore transport and deposition and in some cases formation and preservation of supergene enrichment blankets are also vital for the development of high grade giant ore deposits a low grade geochemical anomaly may be the final product of mineralization if ore forming processes do not operate efficiently even in the most favorable geodynamic settings

origin of mesozoic adakitic intrusive rocks in the ningzhen area of east china partial melting of delaminated lower continental crust to the best of our knowledge modern adakites have not been documented in a nonarc environment we report geochemical and isotopic data for early cretaceous anjishan adakitic intrusive rocks that are in a continental setting unrelated to subduction the anjishan adakitic intrusive rocks which are exposed in the ningzhen area of east china have high sr y and la yb ratios coupled with low yb and y as well as relatively high mgo contents and mg numbers mg 0 4 0 6 similar to products from slab melting however low n d t values 6 8 to 9 7 and high 8 7 sr 8 6 sr i 0 7053 0 7066 are inconsistent with an origin by slab melting the tectonics and geochemistry lead us to conclude that adakitic magmas were most likely derived from partial melting of mafic material at the base of the continental crust high sr y and la yb ratios of the adakitic intrusive rocks suggest that garnet was stable as a residual phase during partial melting implying that the crustal thickness exceeded 40 km in the early cretaceous the present thickness of the crust in the ningzhen area is only 30 km and therefore the crust appears to have been thinned by at least 10 km since the early cretaceous the relatively high mgo contents and mg of the anjishan intrusive rocks suggest that adakitic magmas interacted with mantle rocks possibly coinciding with lower crustal delamination which would also account for the observed thinning

early jurassic porphyry copper mineralization in ne china a case study of the yanghuidongzi deposit abstract the yanghuidongzi cu deposit is located in the southeastern part of heilongjiang province in ne china and represents one of the few known early jurassic porphyry cu deposits within the eastern edge of the xing an mongolia orogenic belt here we present new whole rock major and trace element and sr nd isotopic data zircon u pb and hf isotopic data and molybdenite re os data for units associated with the deposit laser ablation inductively coupled plasma mass spectrometry la icp ms dating of zircons from the granodiorite porphyry in the study area yielded ages of 191 0 1 1 and 191 2 1 0 ma that are interpreted to be the emplacement age of this intrusion the molybdenite re os dating undertaken during this study yielded model ages of 192 7 187 0 ma an isochron age of 188 2 3 8 ma and a weighted mean model age of 190 2 2 6 ma representing the timing of formation of the cu mineralization in this area the yanghuidongzi granodiorite porphyry contains relatively high concentrations of sio 2 68 88 72 49 wt al 2 o 3 15 37 16 31 wt and sr 230 479 ppm but relatively low concentrations of y 7 97 9 87 ppm and yb 0 72 0 85 ppm suggesting that this intrusion has an adakitic affinity combining this with the positive end t 0 7 1 1 and ehf t values 4 0 6 9 low mg values 41 50 and the low concentrations of mgo 0 86 1 22 wt cr 3 17 4 37 ppm and ni 2 11 4 20 ppm within this intrusion suggests it formed from a magma generated by the partial melting of juvenile lower crustal material during the early jurassic subduction of the paleo pacific plate

geodynamic setting of gold deposits in eastern and central trans baikal chita region russia abstract it is proposed that there are three types of gold deposits in eastern and central transbaikalia trans baikal province namely i high sulphide intrusion related deposits with some signs of porphyry deposits ii low sulphide intrusion related deposits and iii low sulphide epithermal au ag deposits most of the gold deposits belong to the first two types and their ages are middle late jurassic deposits of the third type are not numerous and their age is early cretaceous the majority of the gold mineralization is spatially related to the two branches of the mongolia okhotsk suture along which siberia collided at the early middle jurassic boundary with the mongolia north china continent and the onon island arc terrane located between the two continents collision related thrusting folding and magmatism lasted until the latest jurassic when they gave way to post collisional rifting that continued until the end of early cretaceous according to their age relation to magmatism and tectonic framework the intrusion related deposits high and low sulphide were formed in a regional collisional setting extensional environments at that time existed only in local areas in the roofs of great magmatic chambers low sulphide epithermal deposits were formed during early cretaceous post collisional rifting

estimation of s wave velocity structures in and around the sendai basin japan using array records of microtremors we conducted array measurements of microtremors at six sites in and around the sendai basin to estimate deep s wave velocity structures above the seismological bedrock pre tertiary bedrock after estimating phase velocities of microtremors in the frequency range from about 0 5 to 3 hz we succeeded to estimate the deep structures above the pre tertiary bedrock at four soil sites kata okin arah and myg15 and only the upper part just beneath the pliocene layer at the other soil site trma using a rayleigh wave inversion technique at trma and a rock site tama we roughly estimate the deep s wave velocity structures using empirical site amplification factors derived from strong motion records the deepest bedrock depth is 1 km and the shallowest depth is 200 m among these six sites the difference of the bedrock depth between the eastern side and the western side of an active thrust fault the nagamachi rifu line is only 120 m the difference of the bedrock depth between two sites in the east of the basin reaches about 500 m although any geological boundaries or buried faults have not been mapped since the deep s wave velocity structure of the sendai basin had been basically unknown we delineate it for the first time in this article using array measurement of microtremors

influence of parameterization on inversion of surface wave dispersion curves and definition of an inversion strategy for sites with a strong vs contrast inversion of the fundamental mode of the rayleigh wave dispersion curve does not provide a unique solution and the choice of the parameterization number of layers range of velocity and thickness values for the layers is of prime importance for obtaining reliable results we analyzed shear wave velocity profiles derived from borehole tests at 10 sites where soil layers overlay bedrock in various geologic contexts one to three seismic layers with linear velocity laws could model all of them three synthetic models defined from this preliminary study were used to understand the influence of parameterization on the dispersion curve inversion this analysis resulted in the definition of a two step inversion procedure for sites exhibiting a strong impedance con trast in the first step the dispersion curve is inverted with an increasing number of layers over half space the evolution of the minimum misfit and bedrock depth with number of layers allows the estimation of the true bedrock depth range in the

geochronological isotopic and mineral geochemical constraints on the genesis of the diyanqinamu mo deposit inner mongolia china abstract the diyanqinamu mo deposit located in central inner mongolia in china is a newly discovered mo deposit due to the lack of detailed deposit scale studies the metallogenesis of the deposit has been a matter of debate in this study petrography zircon u pb geochronology sr nd and pb isotopes and apatite mineral geochemistry have been used to constrain the genesis of the diyanqinamu mo deposit petrographic evidence indicates that the granites in the diyanqinamu deposit have experienced fluid exsolution as demonstrated by the corroded quartz in the porphyritic granites skeletal quartz in the aplitic granites and the unidirectional solidification texture ust in the apex of the aplitic granites sr and nd isotopic data of the purple fluorite from the fluorite molybdenite veins showing the 87sr 86sr i 0 7046 0 7052 avg 0 7048 and end t values 2 4 3 8 avg 3 3 are similar to those of the porphyritic and aplitic granites this similarity implies that the mo ore forming fluids may have been derived from the granitic magmas the hypothesis is further supported by the fluorine content 3 79 5 48 wt avg 4 53 wt in apatite from the porphyritic granites and the widely distributed fluorite in the hydrothermal alteration mineral assemblages which indicate that the porphyritic granites contain high f content and the hydrothermal fluids are also f rich petrographic observation also shows that magnetite occurs commonly in the hydrothermal mineral assemblages indicating that the hydrothermal fluids are characterized by high oxygen fugacity fo2 it is important to note that the intruding granites are essentially barren and the mo is mainly hosted in the andesite and volcaniclastic rocks in comparison pb isotopic compositions of molybdenite are similar to those of both the andesite and k feldspar from the porphyritic granites which suggests that both the intruding granites and ore hosting andesite have contributed to the ore forming materials this hypothesis is further supported by the abnormally high mo for the andesite our new evidence suggests that the diyanqinamu mo deposit may have formed in a post collisional extensional environment ore forming materials may have been derived mainly from the granites and minimally from the host rocks the ore fluids are characterized by high fo2 and being f rich and the trigger for the mo mineralization has been attributed to the reduction of fo2 and or temperature for the ore fluids

geochronology and geochemistry of the wunugetushan porphyry cu mo deposit in ne china and their geological significance abstract the wunugetushan porphyry cu mo deposit is located in the manzhouli district of ne china on the southern margin of the mesozoic mongol okhotsk orogenic belt concentric rings of hydrothermal alteration and cu mo mineralization surround an early middle jurassic monzogranitic porphyry the cu mo mineralization is clearly related to the quartz potassic and quartz sericite alteration molybdenite re os and groundmass 40 ar 39 ar of the host porphyry dates indicate that the ore formation and porphyry emplacement occurred at 177 6 4 5 ma and 179 0 1 9 ma respectively geochemically the host porphyry of the deposit is characterized by strong lree hree fractionation enrichment in lile ba rb u th and pb and depletion of hfse nb ta ti and hree the sr nd pb isotopic compositions of the porphyry display an varied initial 87 sr 86 sr i ratio a positive e nd t values and high 206 pb 204 pb t 207 pb 204 pb t and 208 pb 204 pb t ratios these data indicate that the magmatic source of the host porphyry comprised two end members lithospheric mantle metasomatized by fluids derived from the subducted slab and continental crust we infer that the primitive magma of the host porphyry was derived from crust mantle transition zone based on regional geology and geochemistry of the host porphyry the wunugetushan deposit is suggested to form in a continental collision environment after closure of the mongol okhotsk ocean

recycling of orogenic arc crust triggers porphyry cu mineralization in kerman cenozoic arc rocks southeastern iran pre collisional eocene oligocene arc diorites quartzdiorites granodiorites and volcanic equivalents in the kerman arc segment in central iran lack porphyry cu mineralization and ore deposits whereas collisional middle late miocene adakite like porphyritic granodiorites without volcanic equivalents host some of the world s largest cu ore deposits petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment ore hosting kuh panj porphyry intrusions exhibit high sr 400 ppm low y 20 no negative eu anomalies eu eu 1 and relatively non radiogenic sr isotope signatures 87sr 86sr 0 7042 0 7047 relative to eocene oligocene granitoids mainly sr 12 la yb 15 eu eu 1 87sr 86sr 0 7053 0 7068 trace element modeling indicates peridotite melting for the barren eocene oligocene intrusions and a hydrous garnet bearing amphibolite source for middle late miocene ore hosting intrusions the presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30 35 to 40 45 km or 12 kbar the changes in residual mineralogy in the source of eocene to miocene rocks in the kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel underplating of cu and sulfur rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust mantle boundary and dehydration melting under oxidizing conditions produced syn and post collisional ore hosting intrusions while the lack of post collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur rich and oxidized adakitic magmas

characterization of earthquake strong ground motion some underwater landslides are triggered by strong ground motions caused by earthquakes this paper reviews current concepts and trends in the characterization of strong ground motion improved empirical ground motion models have been derived from a strong motion data set that has grown markedly over the past decade however these empirical models have a large degree of uncertainty because the magnitude distance soil category parameterization of these models often oversimplifies reality this reflects the fact that other conditions that are known to have an important influence on strong ground motions such as near fault rupture directivity effects crustal waveguide effects and basin response effects are not treated as parameters of these simple models numerical ground motion models based on seismological theory that include these additional effects have been developed and extensively validated against recorded ground motions and used to estimate the ground motions of past earthquakes and predict the ground motions of future scenario earthquakes

s wave velocity profiling by joint inversion of microtremor dispersion curve and horizontal to vertical h v spectrum a joint inverse analysis using both microtremor dispersion curve and horizontal to vertical h v spectrum is proposed for estimating the s wave velocity vs profiles of subsurface soils in the inversion both microtremor dispersion and h v data are assumed to be the rayleigh wave dispersion curve and the surface both rayleigh and love wave h v spectrum that have been theoretically derived by taking into account the effects of their fundamental and higher modes the proposed joint inversion as well as the conventional one using dispersion data alone is per formed at four sites where shallow vs profiles down to engineering bedrock are available the vs profiles estimated by the proposed joint inversion are more con sistent with available down hole velocity logs than those by the conventional method in particular the proposed inversion shows significant improvement in estimating bedrock vs structures compared to the conventional inversion sensitivity analyses indicate that the surface wave h v ratio is sensitive to the bedrock vs structure more than the rayleigh wave phase velocity confirming that the proposed joint inversion including h v spectrum is promising

distribution of porphyry deposits in the eurasian continent and their corresponding tectonic settings in the eurasian continent there are three huge metallogenic belts of cu and mo porphyry deposits comprising the paleozoic central asian ore belt in the north the tethyan eurasian ore belt of jurassic to cenozoic age in the southwest and the east margin ore belt of the eurasian continent of jurassic to cretaceous age in the east the latter is considered to be part of the vast circum pacific ore belt some of the main features of the spatial temporal distribution of cu and mo porphyry systems and related geodynamic processes of the three metallogenic belts are described in particular the key role of postsubduction related porphyry ore systems is emphasized comprising collisional and post collisional cu mo porphyry deposits during the geological history of the eurasian continent the recurrent feature of these ore systems and related felsic rocks is their derivation from partial melting of stagnant or residual oceanic slabs and mixing with a variable amount of crustal material during magma ascent to shallower levels 2013 published by elsevier ltd

determination of shallow shear wave velocity profiles in the cologne germany area using ambient vibrations summary we have used both single station and array methods to determine shallow shear velocity site profiles in the vicinity of the city of cologne germany from ambient vibration records based on fk analysis we assume that fundamental mode rayleigh waves dominate the analysed wavefield in the frequency range of 0 7 2 2 hz according to this view a close relation exists between h v spectral ratios and the ellipticity of the contributing rayleigh waves the inversion of the shape of h v spectral ratios then provides quantitative information concerning the local shear wave velocity structure however based on tests with synthetic data believed to represent a typical situation in the lower rhine embayment dispersion curves were found to provide stronger constraints on the absolute values of the velocity depth model than the ellipticities the shape of the ellipticities was found to be subject to a strong trade off between the layer thickness and the average layer velocity we have made use of this observation by combining the inversion schemes for dispersion curves and ellipticities such that the velocity depth dependence is essentially constrained by the dispersion curves while the layer thickness is constrained by the ellipticities in order to test this method in practice we have used array recordings of ambient vibrations from three sites where the subsurface geology is fairly well known and geotechnical information is at least partially available in order to keep the parameter space as simple as possible we attempted to fit only a single layer over a half space model however owing to earlier studies from the region we assume a power law depth dependence for sediment velocities for all three sites investigated the inversion resulted in models for which the shear wave velocity within the sediment layer both in absolute value at the surface and in depth dependence are found to be remarkably similar to the results obtained by budny from downhole measurements this is strong support for the interpretation of h v spectral ratios as rayleigh wave ellipticities for all three sites the predicted sh wave site amplification factors at the fundamental frequency are of the order of 5 6 with a slightly smaller value south of cologne

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

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

long duration asynchronous ground motions in the colfiorito plain central italy observed on a two dimensional dense array 1 in winter 1998 a small aperture 200 m four station array was operating in the middle of the colfiorito plain waveforms of seven small magnitude 2 1 m 3 7 local earthquakes are analyzed in this study the peculiarity of the array seismograms is a 2 min long duration of the horizontal ground motion the predominant frequency in the plain is around 1 hz in this frequency band earthquake induced ground shaking is synchronous for a few seconds during direct s waves after this time window wave trains show an increasingly chaotic behavior within the array the energy variation of the horizontal ground shaking between the array and a nearby rock outcrop exceeds a factor of 500 at 1 hz in order to help understanding of observations and construct models for future numerical simulations the buried structure of the colfiorito plain has been investigated through seismic refraction profiles and geoelectric measurements a three dimensional reconstruction of the basin structure reveals an extremely complex bedrock topography which is probably a recurrent feature for intermontane basins in tectonically active regions apparent velocities and backazimuths in the frequency band 0 5 1 5 hz indicate that a 180 m deep depression nw of the array is responsible for the generation of edge diffracted surface love waves their arrival to the array breaks the synchronism of vertically reverberating waves which predominate in the first seconds of the s wave window