residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

geochemical characteristics and magma fertility for the jurassic arc rocks in the gangdese belt tibet abstract jurassic arc magmatic rocks are widely distributed along the gangdese belt southern tibet however only one jurassic arc related porphyry cu deposit the xietongmen deposit has been found the jurassic arc magma fertility needs to be further constrained in order to understand the rarity of arc related porphyry cu deposits in this belt this paper seeks to combine new data on the jurassic granitoid rocks with all published data on the jurassic magmatic rocks in the gangdese belt to comprehensively explore their geochemical variation and magma fertility our new data show that the jurassic granitoid rocks have zircon u pb ages of 171 6 1 1 ma to 195 3 1 3 ma these jurassic granitoids are calc alkaline series with sio2 contents of 59 4 to 70 7 wt mg values of 35 to 53 and a cnk values of 0 72 1 25 mainly 20 v sc ratios 8 and high zircon eun eun 0 3 ce4 ce3 ratios 300 and low titanium in zircon temperatures

water fluxed crustal melting produces cordilleran batholiths most granites and related calc alkaline silicic volcanic rocks from the united states and new zealand cordillera are saturated with zircon between 65 and 70 wt sio2 for this silica interval zircon saturation temperatures t zr are universally lower 900 c the values contrast with t zr from alkaline rocks from the cenozoic u s cordillera which are typically 800 c for 65 70 wt sio2 case studies of titanium in zircon thermometry from the u s cordillera also suggest that alkaline magma injections into granitic magma chambers are hot but calc alkaline magma injections are usually cooler a model is presented suggesting that silicic cordilleran magmas form in magmatic arcs where hydrous basaltic magmas solidify in the arc root producing mafic underplates that exsolve aqueous fluids which transfer to the crust and promote water fluxed partial melting at ambient pressure temperature 750 800 c at 8 kbar conditions subsequent rock buffered melting reactions modulate the water content of arc magmas the granitic partial melts are water undersaturated rise adiabatically as increments but stall in the middle to upper crust building cool and hydrous crystal rich magma chambers batholiths however injections of hotter magmas are required to drive volcanic eruption in the backarc granitic magma chambers are intermittently recharged with hotter drier alkaline magmas which are produced mostly by decompression melting during lithospheric extension not hydrous fluxing this highlights the control of subduction dynamics on water content and consequently magmatic temperatures in silicic magma systems

s rich apatite hosted glass inclusions in xenoliths from la palma constraints on the volatile partitioning in evolved alkaline magmas the composition of s rich apatite of volatile rich glass inclusions in apatite and of interstitial glasses in alkaline xenoliths from the 1949 basanite eruption in la palma has been investigated to constrain the partitioning of volatiles between apatite and alkali rich melts the xenoliths are interpreted as cumulates from alkaline la palma magmas apatite contains up to 0 89 wt so3 3560 ppm s 0 31 wt cl and 0 66 wt ce2o3 sulfur is incorporated in apatite via several independent exchange reactions involving p5 ca2 vs s6 si4 na and ce3 the concentration of halogens in phonolitic to trachytic glasses ranges from 0 15 to 0 44 wt for cl and from 0 2 wt so3 dsapatite glass is only slightly dependent on the melt composition and can be expressed as so3 apatite wt 0 157 ln so3 glass wt 0 9834 the phonolitic compositions of glass inclusions in amphibole and hauyne are very similar to evolved melts erupted on la palma the lower sulfur content and the higher cl content in the phonolitic melt compared to basaltic magmas erupted in la palma suggest that during magma evolution the crystallization of hauyne and pyrrhotite probably buffered the sulfur content of the melt whereas the evolution of cl concentration reflects an incompatible behavior trachytic compositions similar to those of the water rich glass inclusions analyzed in apatite and clinopyroxene are not found as erupted products these compositions are interpreted to be formed by the reaction between water rich phonolitic melt and peridotite wall rock

tibetan tectonic evolution inferred from spatial and temporal variations in post collisional magmatism cenozoic magmatism on the tibetan plateau shows systematic variations in space and time that must be considered in models concerning tibetan tectonic evolution after the india asia collision which started in the early tertiary and terminated the gangdese arc magmatism in the lhasa terrane made of the southern tibetan plateau widespread potassium rich lavas and subordinate sodium rich basalts were generated from f50 to 30 ma in the qiangtang terrane of northern tibet subsequent post collisional magmatism migrated southwards producing ultrapotassic and adakitic lavas coevally between f26 and 10 ma in the lhasa terrane then potassic volcanism was renewed to the north and has become extensive and semicontinuous since f13 ma in the western qiangtang and songpan ganze terranes such spatial temporal variations enable us to elaborate a geodynamic evolution model which depicts when and how the indian continental lithospheric mantle started thrusting under asia by involving rollback and breakoff of the subducted neo tethyan slab followed by removal of the thickened lhasa lithospheric root we propose that only after the lithospheric removal which occurred at f26 ma could the indian mantle lithosphere have commenced its northward underthrusting and henceforth served as a pivotal control to the himalayan tibetan orogenesis consequently the tibetan plateau is suggested to have risen diachronously from south to north whereas the southern part of the plateau may have been created and maintained since the late oligocene the northern plateau would have not attained its present day elevation and size until the mid miocene when the lower part of the western qiangtang and songpan ganze lithospheres began to founder owing to the push of the underthrust indian mantle lithosphere d 2004 elsevier b v all rights reserved

apatite composition tracing petrogenetic processes in transhimalayan granitoids apatites crystallized from different types of igneous rocks show significant variations in the abundances of some minor and trace elements in this study electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry were used to determine the concentrations of 25 minor and trace elements in apatite separated from three principal rock types of thetranshimalayan igneous plutonic suite s type granites the i type gangdese batholith and postcollisional adakites f mn sr and rare earth elements ree in apatite vary systematically with the composition of the host magma and thus have high potential as petrogenetic tracers more specifically the f and mn contents of apatite can be used as an indicator of magma aluminosity or differentiation index combined with sr and ree data which show significant variations in apatite from different rock types these elements are useful for constructing discrimination diagrams this study also reveals that apatite has the capacity to retain geochemical information about the host magma through the course of magmatic evolution systematic variations of sr and ree in apatite with bulk rock aluminosity are the results of partition competition with pre existing and coexisting major and accessory minerals in silicate melts and thus are useful for more detailed investigations of petrogenetic processes such as fractional crystallization and magma mixing which is signaled by inconsistent eu anomalies sr abundances and ree patterns relative to bulkrock compositions

apatite chemical composition determined by electron microprobe and laser ablation inductively coupled plasma mass spectrometry as a probe into granite petrogenesis abstract major minor and trace element abundances in apatites from various i and s type igneous and sedimentary granites of the lachlan fold belt have been determined using electron microprobe and laser ablation inductively coupled plasma mass spectrometer the results show that apatite can accommodate many minor and trace elements whose concentrations and ratios are relatively sensitive to factors controlling many of the fundamental differences between i and s type granites apatites from s type granites generally have higher f but lower cl contents than those from i type granites which is ascribed mainly to the loss of cl during the weathering processes forming the source rocks of s type granites although fractional crystallisation can cause significant enrichment in f as well high mn and fe contents in apatites from s type granites and high s and as abundances in apatites from mafic i type granites result from different oxygen fugacities and degrees of al saturation or aluminosity between metaluminous mafic i type magmas and peraluminous s type and felsic i type magmas there are systematic and distinctive differences in absolute rare earth element ree abundances ree distribution patterns and element ratios e g la y sm nd etc between apatites from different types of granite the strong eu depletion that characterises apatites from s and felsic i type granites is interpreted here to be a result of the uniqueness of crystal chemistry of apatite and high eu2 eu3 ratios in s type and felsic i type magmas which are more reduced and peraluminous than mafic i type magmas strong ree la to eu and th enrichment in apatites from mafic i type granites and marked nd depletion in apatites from most s type and felsic i type granites are caused by the precipitation and fractionation of monazite in the parental magmas of the latter rocks substitution mechanisms are responsible for high na in apatites from s type and felsic i type granites and for high si in apatites from mafic i type granites and may also have important effects on ree partitioning between apatite and melt thus apatite chemistry can be used as an excellent indicator of granite petrogenesis the results have important implications for identifying different types of granite and are potentially significant for determining the provenance of sedimentary rocks

co variability of s6 s4 and s2 in apatite as a function of oxidation state implications for a new oxybarometer in this study we use micro x ray absorption near edge structures xanes spectroscopy at the s k edge to investigate the oxidation state of s in natural magmatic hydrothermal apatite durango mexico and mina carmen chile and experimental apatites crystallized from volatile saturated lamproitic melts at 1000 c and 300 mpa over a broad range of oxygen fugacities formula 1 fmq 1 2 fmq 3 fmq fayalite magnetite quartz solid buffer the data are used to test the hypothesis that s oxidation states other than s6 may substitute into the apatite structure peak energies corresponding to sulfate s6 2482 ev sulfite s4 2478 ev and sulfide s2 2470 ev were observed in apatite and the integrated areas of the different sulfur peaks correspond to changes in formula 2 and bulk s content here multiple tests confirmed that the s oxidation state in apatite remains constant when exposed to the synchrotron beam at least for up to 1 h exposure i e no irradiation damages to our knowledge this observation makes apatite the first mineral to incorporate reduced s2 intermediate s4 and oxidized s6 s in variable proportions as a function of the prevailing formula 3 of the system apatites crystallized under oxidizing conditions fmq 1 2 and fmq 3 where the s6 stotal peak area ratio in the coexisting glass i e quenched melt is 1 are dominated by s6 with a small contribution of s4 whereas apatites crystallizing at reduced conditions fmq contain predominantly s2 lesser amounts of s6 and possibly traces of s4 a sulfur oxidation state vs s concentration analytical line transect across hydrothermally altered apatite from the mina carmen iron oxide apatite ioa deposit chile demonstrates that apatite can become enriched in s4 relative to s6 indicating metasomatic overprinting via a so2 bearing fluid or vapor phase this xanes study demonstrates that as the formula 4 increases from fqm to fmq 1 2 to fmq 3 the oxidation state of s in igneous apatite changes from s2 dominant to s6 s4 to s6 s4 furthermore these results suggest that spectroscopic studies of igneous apatite have potential to trace the oxidation state of s in magmas the presence of three s oxidations states in apatite may in part explain the non henrian partitioning of s between apatite and melt our study reveals the potential to use the s signature of apatite to elucidate both oxygen and sulfur fugacity in magmatic and hydrothermal systems 1 embed mml math 1 gif 2 embed mml math 2 gif 3 embed mml math 3 gif 4 embed mml math 4 gif

derivation of mesozoic adakitic magmas from ancient lower crust in the north china craton three mesozoic plutons were intruded into the archean granulite terrains in northern margin of the north china craton adjacent to the granulite xenolith bearing tertiary hannuoba basalts they are triassic guzuizi and honghualiang granites and early cretaceous zhuanzhilian diorite rocks of the three intrusions are characterized by high sr 576 1216 ppm and na2o 4 0 low y 18 ppm and heavy rare earth elements yb 1 8 ppm these features are similar to modern adakites siliceous rocks with high sodium aluminum and strontium and low heavy rare earth element and yttrium contents from island arcs and archean high al tonalite trondhjemite granodiorite ttg however they are distinctly potassium rich and their evolved strontium neodymium and hafnium isotopic compositions and inherited zircon ages coincide with those of the archean granulites and the hannuoba granulite xenoliths such features cannot readily be explained with previous models of the origin of adakites and ttgs we propose that these adakitic rocks are formed by partial melting of ancient lower crust and that the restites are represented by some of the hannuoba granulite xenoliths we further argue that this could be one major mechanism to generate voluminous mesozoic adakitic magmas in the eastern north china craton our hypothesis can also explain the discrepancies in ages and compositions between the granulite terrains and xenoliths and implies that crustal anatexis may be one of the major processes controlling the chemical differentiation of the continental crust

so2 flux monitoring at stromboli with the new permanent ingv so2 camera system a comparison with the flame network and seismological data we installed a permanent so2 camera system on stromboli italy in may 2013 in order to improve our capacity to monitor the so2 emissions from this volcano the camera collects images of so2 concentrations with a period of similar to 10 s allowing quantification of short term processes such as the gas released during the frequent explosions which are synonymous with stromboli it also allows quantification of the quiescent gas flux and therefore comparison with the flame network of scanning ultraviolet spectrometers previously installed on the island analysis of results from the so2 camera demonstrated a good agreement with the flame network when the plume was blown fully into the field of view of the camera permanent volcano monitoring with so2 cameras is still very much in its infancy and therefore this finding is a significant step in the use of such cameras for monitoring whilst also highlighting the requirement of a favourable wind direction and strength we found that the explosion gas emissions are correlated with seismic events which have a very long period component there is a variable time lag between event onset time and the increase in gas flux observed by the camera as the explosion gas advects into the field of view of the camera this variable lag is related to the plume direction as shown by comparison with the plume location detected with the flame network the correlation between explosion gas emissions and seismic signal amplitude show is consistent with a gas slug driven mechanism for seismic event production comparison of the so2 camera measurements of the quiescent gas flux shows a fair quantitative agreement with the so2 flux measured with the flame network overall the so2 camera complements the flame network well as it allows frequent quantification of the explosion gas flux produced by stromboli whose signal is in general too brief to be measured with the flame network further work is required however to fully automate the calculation of so2 flux from the so2 images captured with the camera and to adequately account for scattering effects c 2015 elsevier b v all rights reserved

an apatite for progress inclusions in zircon and titanite constrain petrogenesis and provenance apatite has recently gained considerable attention as a mineral with many uses within the earth and planetary sciences apatite chemistry has recently given new insight into a wide range of geological processes and tools for example magmatism metasomatism planetary geochemistry and geochronology we expand the utility of apatite here by presenting a novel way to fingerprint magma chemistry and petrogenesis using apatite inclusions within robust titanite and zircon we present trace element data from apatite mineral inclusions shielded within magmatic zircon and titanite importantly apatite inclusion and host titanite chemistries detailed in this study allow estimation of the whole rock sr and sio2 we show how these data can be used to assess the degree of fractionation of the host magma and to calculate key trace element abundances and ratios we demonstrate that the inclusions can be linked to discrete periods in the crystallization history of the host phases thus providing insight into petrogenesis the results highlight that apatite compositions might discriminate modern granitoids younger than 2 5 ga from archean proterozoic transitional granitoid compositions sanukitoid signatures development of such a petrological tool has important potential for interpretation of provenance and a better understanding of the secular evolution of the continental crust including that of early earth

u pb and re os geochronological evidence for the jurassic porphyry metallogenic event of the xiongcun district in the gangdese porphyry copper belt southern tibet prc abstract two large copper gold porphyry deposits no i and no ii were discovered in the last decade within the xiongcun district which is located along the south margin of the gangdese porphyry copper belt these two deposits are hosted by two porphyries that were emplaced into the early jurassic volcano sedimentary rock sequences of the xiongcun formation the porphyries are both quartz diorite bodies with one of these distinguished by its large quartz eyes our new molybdenite re os and zircon u pb dates for no i and no ii deposits and host intrusions reveal the presence of two middle jurassic ore forming episodes in the xiongcun district the no ii deposit is related to the 181 175 ma quartz diorite porphyry and formed ca 172 6 2 1 ma the no i deposit is related to the 167 161 ma quartz diorite porphyry with large quartz eyes and formed ca 161 5 2 7 ma geochronological and geochemical features of the jurassic ore bearing porphyries in the xiongcun district indicate that the porphyry copper gold mineralization formed in an island arc setting which is related to the northward subduction of the neo tethys oceanic plate these observations in combination with geochronological data reported at gangdese porphyry copper belt indicated four major metallogenic events existed in the gangdese porphyry copper belt at 172 161 ma 65 48 ma 40 23 ma and 20 12 ma we have identified two mineralization episodes comprise middle jurassic metallogenic event 172 161 ma in the xiongcun district which provides new constrains for the middle jurassic metallogenic event in the gangdese porphyry copper belt

high sr y and la yb ratios the meaning of the adakitic signature abstract the name of adakite is used to describe a far too large group of rocks whose sole common feature is high sr y and la yb ratios however such a signature can be achieved via different processes melting of a high sr y and la yb source deep melting with abundant residual garnet fractional crystallization or afc or interactions of felsic melts with the mantle causing selective enrichment in lree and sr over hree a database of the compositions of adakitic rocks including high silica and low silica adakites martin h smithies r h rapp r p moyen j f champion d c 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 2 1 24 continental adakites and archaean adakites was assembled geochemical modeling of the potential processes is used to interpret it and reveals that 1 the classical model of slab melting provides the best explanation for the genesis of high silica adakites 2 low silica adakites are explained by garnet present melting of an adakite metasomatized mantle i e at depths greater than 2 5 gpa 3 continental adakites is a term encompassing a huge range of rocks with a corresponding diversity of petrogenetic processes and most of them are different from both low and high silica adakites 4 archaean adakites show a bimodal composition range with some very high sr y examples similar to part of the ttg suite reflecting deep melting 2 0 gpa of a basaltic source with a relatively high sr y while lower sr y rocks formed by shallower 1 0 gpa melting of similar sources comparison with the archaean ttg suite highlights the heterogeneity of the ttgs whose composition spreads the whole combined range of hsa and archaean adakites pointing to a diversity of sources and processes contributing to the ttg suite

relative oxidation states of magmas inferred from ce iv ce iii in zircon application to porphyry copper deposits of northern chile major and trace element compositions of zircons and whole rocks from 14 barren and seven ore bearing calc alkaline intrusions from the chuquicamata el abra porphyry copper belt of northern chile have been measured in situ by excimer laser ablation ela icp ms these data permit the ce iv ce iii ratio within zircon to be calculated using a lattice strain model for mineral melt partitioning of ce iv and ce iii zircon ce iv ce iii and eun eun ratios and by inference magmatic oxidation states generally increase from older mafic to younger felsic units within this sequence porphyry copper mineralization is directly associated only with intrusions with zircon ce iv ce iii 300 and eun eun 0 4 such trends can be understood in terms of interdependent relations between oxygen fugacity sulfur speciation and solubility and chalcophile element partitioning in silicate magmas because zircon occurs in most calc alkaline intrusions and is resistant to subsolidus alteration zircon ce iv ce iii ratios provide a useful tool for evaluating the economic potential of such rocks for magmatic hydrothermal cu au mineralization the approach is general and may provide a means to infer relative oxidation state in a wide range of intermediate to felsic igneous rocks

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

measurements of transient ground movements below a ballasted railway line this paper presents the results of a detailed investigation into the ground deformations that occur under a railway line during the passage of a train four horizontal boreholes were installed at different depths below a ballasted railway track ground deformations were measured using geophones at set distances from the centreline of the track within each borehole the results show vertical displacements reducing with depth from a maximum at the sleeper sleeper displacements are dominated by pairs of bogies at the ends of adjacent wagons which have a frequency of loading 1 hz although the effects of individual bogies 2 hz and axles 6 hz are also apparent higher loading frequencies attenuate with depth so that at a depth of 0 780 m below the sleeper soffit no axles are visible within the displacement data and by a depth of 1 98 m only the combined effect of pairs of adjacent bogies is apparent in contrast longitudinal horizontal motion is greatest at a depth of 0 78 m below the sleeper soffit

tectonic evolution of the qinghai tibet plateau abstract the qinghai tibet plateau composed of several continental slivers within the eastern tethyan domain is one of the pivotal sites to examine to better understand the theory of plate tectonics and the orogenic evolution on earth this plateau is generally inferred to be a collage of several continental blocks that rifted from gondwanaland and subsequently accreted to the asian continent however recent recognition of over twenty ophiolite melange zones and their associated island arcs indicates that the traditional model of tectonic evolution requires revision based on 177 recently finished 1 250 000 scale geological maps and related studies we summarize the main tectonic context of the qinghai tibet plateau and propose a new integrated model to account for the new findings the complex orogen of the immense qinghai tibet plateau consisting of multiple island arc basin systems that developed at different stages while surrounded by the north china yangtze tarim and indian plates is emphasized the entire orogen surrounded by suture zones that mark the locations of oceanic closure is investigated by examining i the first order tectonic units and ophiolitic melanges including arc arc continent collision zones and ii their internally enclosed blocks as the second order tectonic units therefore the qinghai tibet plateau is divided into three major orogenic systems namely from northeast to southwest the early paleozoic qinling qilianshan kunlunshan qin qi kun the late paleozoic triassic qiangtang sanjiang and the late paleozoic to cenozoic gangdese himalaya orogenic systems which are separated by the kangxiwa muzitagh maqin mianxian and the bangong shuanghu changning menglian sutures respectively we propose that the formation and evolution of the qinghai tibet plateau to have been intrinsically related to those of the eastern tethys recorded by the longmu co shuanghu ophiolite melange zone the southern qiangtang paleozoic accretionary arc basin system the bangong nujiang suture zone and their associated composite island arc basin systems the present day bangong shuanghu changning menglian suture system marks the final closure of the tethyan ocean the yarlung zangbo ocean opened as a back arc basin in response to the southward subduction of the tethyan ocean lithosphere in the middle triassic and closed as a result of the india asia collision at the end of cretaceous followed by the northward indention of the indian plate that resulted in significant intra continental deformation and plateau uplift in the cenozoic

sulfur partition coefficient between apatite and rhyolite the role of bulk s content experimental studies have been performed to constrain sulfur behavior during apatite crystallization and to determine sulfur partition coefficient between apatite and melt kd s apatite melt at oxidizing conditions crystallization experiments have been conducted with a hydrous rhyolitic melt and different bulk sulfur contents 0 15 to 2 wt s at 900 and 1 000 c 200 mpa and log f rm o 2 nno 3 6 the sulfur content in the glass increases with increasing amount of added s anhydrite crystallizes for s added 0 75 wt 0 10 and 0 13 wt so3 in glass at 900 and 1 000 c respectively the amount of anhydrite increases and the amount of apatite decreases with increasing amount of added sulfur the sulfur exchange reaction in apatite is influenced by the bulk composition of the melt e g p content however changing melt composition has only little effect on kd s apatite melt for the investigated rhyolitic composition the kd s apatite melt does not depend directly on temperature decreases from 14 2 to 2 7 with increasing s content in glass from so3 0 03 to 0 19 wt respectively and can be predicted from the following equation ln kd 0 0025 s in melt in ppm 2 9178 the combination of experimental data obtained for rhyolitic and andesitic melts reveals that the sulfur partition coefficient tends toward a value of 2 for high sulfur content in the glass 0 2 wt so3 using s in apatite as proxy for determining s content in melt is promising but additional experimental data are needed to clarify the individual effects of t f rm s 2 and p and ca content in the melt on s partitioning

apatite geochronology and chemistry of luanchuan granitoids in the east qinling orogen china implications for petrogenesis metallogenesis and exploration abstract the luanchuan granitoids in the east qinling orogen central china host multiple genetic types of mo w pb zn ag polymetallic deposits here we present results from systematic geochronological and geochemical investigations on apatite with a view to gain insights into the petrogenesis metallogenesis and potential for mineral exploration we analyzed 388 apatite grains from eight late mesozoic granitic plutons in the luanchuan ore district apatite u pb geochronology yields 206pb 238u mean ages in the range of 151 5 102 3 ma representing the crystallization ages through integrating our results with those from previous studies on the multi stage magmatism 160 130 ma 111 108 ma and metallogeny 150 139 ma 138 135 ma 114 ma the newly obtained apatite ages can be correlated with coeval magmatic and metallogenetic events of this ore district in comparison except for the nannihu pluton which is ca 19 ma younger than the corresponding zircon u pb ages the other studied plutons show almost consistent apatite and zircon u pb ages within error ranges suggesting rapid post magmatic cooling below 450 c in response to shallow emplacement apatite chemistry displays ree concentrations in the range of 2379 15 925 ppm characterized by rather high lree concentrations depleted to flat hree profiles and distinctive negative eu anomalies suggesting crust mantle mixing in the magma source prior to apatite crystallization which incorporated different degrees of sediment melting and slab melting components triggered by the subducted paleo pacific slab derived fluids in conjunction with element concentrations and ratios e g sr mn cl y la y eu eu sm nd n la sm n eu eu n ce ce n la yb n in apatite the luanchuan granitoids are classified as moderately oxidized and mineralized i type granites we suggest that the huangbeiling pluton and other igneous rocks in its vicinity likely have relatively higher potential for future w mo mo w exploration and that different degrees of magmatic differentiation might have generated the porphyry skarn mo w deposit in the yuku ore field moreover our study also demonstrates that the apatite ree concentrations and ratios can be used as potential indicators for mineral exploration

repeated crustal thickening and recycling during the andean orogeny in north chile 21 26 s posttectonic granitoids 2 lower crustal p wave velocities of 7 3 7 7 km s 1 compatible with underplated mafic crust and 3 results from recent experimental petrologic work showing garnet stability in mafic mineralogies 12 kbar 40 km crustal thickness analogous to older andean magmatic episodes in north chile newly underplated basaltic crust may account for the remaining deficit in neogene crustal thickening similar evolutionary patterns in geochemistry and initial sr and nd isotopic characteristics of andean 200 ma to present magmatic rocks suggest that the andean orogeny in this region evolved by a combination of processes of repeated arc migration tectonic and magmatic crustal thickening and igneous recycling which was controlled by periodically changing plate convergence rates and obliquity and corresponding changes in the rheologic behavior of the continental crust index terms 1020 geochemistry composition of the crust 1030 geochemistry geochemical cycles 0330 8159 evolution of the earth rheology crust and lithosphere 9360 information related to geographic region south america keywords andean orogeny continental crust recycling adakite ttg crustal thickening

zircon u pb and hf isotope constraints on the mesozoic tectonics and crustal evolution of southern tibet the first in situ hf and u pb isotope analyses of zircon separates from mesozoic granites in southern tibet identify a significant previously unknown stage of magmatism igneous zircons n 34 from a granite within the gangdese batholith show a weighted mean 206 pb 238 u age of 188 1 1 4 ma and e hf t the parts in 10 4 deviation of initial hf isotope ratios between the zircon sample and the chondritic reservoir values between 10 4 and 16 8 suggesting predominantly early jurassic intrusive activity with a juvenile mantle contribution of 40 inherited zircons from two cretaceous s type granites in the northern magmatic belt 23 delineate a slightly older 206 pb 238 u age cluster between 188 and 210 ma these zircons have e hf t values from 3 9 to 13 7 yielding crustal hf model ages from ca 1 4 to 2 1 ga suggesting a major episode of crustal growth in proterozoic time and remelting of this crust in early jurassic time combining these with literature data we interpret the jurassic gangdese magmatism as an early product of the neo tethyan subduction that played a long lasting role in the tectonic evolution of southern tibet prior to the india asia collision

partition coefficients of hf zr and ree between zircon apatite and liquid concentration ratios of hf zr and ree between zircon apatite and liquid were determined for three igneous compositions two andesites and a diorite the concentration ratios of these elements between zircon and corresponding liquid can approximate the partition coefficient although the concentration ratios between apatite and andesite groundmass can be considered as partition coefficients those for the apatite in the diorite may deviate from the partition coefficients the hree partition coefficients between zircon and liquid are very large 100 for er to 500 for lu and the hf partition coefficient is even larger the ree partition coefficients between apatite and liquid are convex upward and large d 10 100 whereas the hf and zr partition coefficients are less than 1 the large differences between partition coefficients of lu and hf for zircon liquid and for apatite liquid are confirmed these partition coefficients are useful for petrogenetic models involving zircon and apatite

petrogenesis of early to middle jurassic granitoid rocks from the gangdese belt southern tibet implications for early history of the neo tethys abstract the gangdese belt tibet records the opening and closure of the neo tethyan ocean and the resultant collision between the indian and eurasian plates mesozoic magmatic rocks generated through subduction of the tethyan oceanic slab constitute the main component of the gangdese belt and play a crucial role in understanding the formation and evolution of the neo tethyan tectonic realm u pb and lu hf isotopic data for tonalite and granodiorite from the xietongmen nymo segment of the gangdese belt indicate a significant pulse of jurassic magmatism from 184 ma to 168 ma the magmatic rocks belong to metaluminous medium k calc alkaline series characterized by regular variation in major element compositions with sio2 of 61 35 73 59 low to moderate mgo 0 31 2 59 with mg of 37 45 these magmatic rocks are also characterized by lree enrichment with concave upward trend in mree on the chondrite normalized ree patterns and also lile enrichment and depletion in nb ta and ti in the primitive mantle normalized spidergrams these rocks have high zircon ehf t values of 10 94 to 15 91 and young two stage depleted mantle model ages tdm2 of 192 ma to 670 ma the low mgo contents and relatively depleted hf isotope compositions suggest that the granitoid rocks were derived from the partial melting of the juvenile basaltic lower crust with minor mantle materials injected in combination with the published data it is suggested that northward subduction of the neo tethyan slab beneath the lhasa terrane began by the late triassic which formed a major belt of arc related magmatism

apatite in felsic rocks a model for the estimation of initial halogen concentrations in the bishop tuff long valley and tuolumne intrusive suite sierra nevada batholith magmas

trace element incorporation in titanite constraints from experimentally determined solid liquid partition coefficients titanite liquid partition coefficients for most of the trace elements relevant in petrogenetic studies are provided for titanite saturated liquids equilibrated at 1 5 gpa and 850 c starting from lamproitic compositions the high compatibility observed for ree hfse sr v and sc and the strong incompatibility observed for actinides large ion lithophile and light elements are discussed in terms of available crystal chemical mechanisms for incorporation and crystal structure control the exchange vectors na1ca 1 and al1ti 1 allow local charge balance to be achieved after incorporation of ree3 and r5 at the ca and ti site respectively the significant amounts of h measured are also relevant in this regard the exchange mechanism being oh 1o 1 at the o1 site the incorporation of u4 and th4 at the ca site is scarce and is likely balanced by that of mg2 at the ti site both these substitutions are responsible for strong structural strain titanite can thus be considered an important repository for ree and hfse in metamorphic and igneous rocks and its role must be accounted for when modelling trace element residence during metamorphic reactions and late magmatic crystallisation history due to the measured differences in compatibility titanite crystallisation increases the values of nb ta and lree hree ratios in residual liquids the similar compatibility of u and pb makes titanite suitable for u pb geochronology of igneous rocks only after common pb correction finally this study confirms that the titanite end member is not suitable for radioactive waste disposal due to the discussed crystal chemical constraints and that titanite based waste forms should contain high amounts of na and mg2

geological characteristics and genesis of the jurassic no i porphyry cu au deposit in the xiongcun district gangdese porphyry copper belt tibet abstract the xiongcun district located in the western segment of the gangdese porphyry copper belt gpcb hosts the only known jurassic mineralization in the gpcb tibet prc the no i deposit in the xiongcun district is related to the middle jurassic quartz diorite porphyry 167 161 ma and the mineralization was formed at ca 161 5 2 7 ma ore bearing middle jurassic quartz diorite porphyry emplaced into the early jurassic volcano sedimentary rock sequences of the xiongcun formation veinlets and disseminated mineralization developed within the middle jurassic quartz diorite porphyry and the surrounding metamorphosed tuff hosting a measured and indicated resource of 1 04 mt copper 143 31 t gold and 900 43 t silver with an average grade of 0 48 copper 0 66 g t gold and 4 19 g t silver the mineralization can be assigned to four stages including three main stages of hypogene mineralization and one epigenetic stage the main alteration associated with mineralization is potassic seven mineralization related hydrothermal veins have been recognized including quartz sulfide biotite sulfide magnetite sulfide quartz molybdenite sulfide chalcopyrite pyrite pyrrhotite pyrite and polymetallic veins the s and pb isotopic compositions of the ore sulfides and the re contents of the molybdenite suggest a mantle source for the ore forming materials with minor contamination from the subducted sediments hydrogen and oxygen isotope compositions of quartz in the ores suggest that both magmatic and meteoric waters were involved in the ore forming process the ore bearing porphyry 167 161 ma and ore forming 161 5 2 7 ma ages of the no i deposit correspond to the time of northward subduction of neo tethys oceanic slab the geochemical data of the ore bearing porphyry indicate that the no i deposit formed in an intra oceanic island arc setting and the ore bearing porphyry originated from the partial melting of mantle with limited contribution of subducted sediments the genesis of the ore bearing porphyry and no i deposit is interpreted as being related to northward intra oceanic subduction of neo tethys oceanic slab in the middle jurassic time 167 161 ma

thirty sixth canadian geotechnical colloquium advances in visualization of geotechnical processes through digital image correlation1 digital image correlation dic is an image processing technique that calculates fields of incremental displacement by comparing two digital images and locating numerous small regions in both image

extreme nb ta fractionation in metamorphic titanite from ultrahigh pressure metagranite abstract extremely high nb ta ratios up to 239 occur in metamorphic titanite from ultrahigh pressure metagranite in the sulu orogen this indicates significant nb ta fractionation in subduction zone fluids by means of u pb dating and trace element analysis of titanite we distinguish the metamorphic domains from the anatectic domains titanite u pb dating yields lower intercept ages of 215 12 ma to 222 27 ma for the metagranite samples with regardless of the compositional differences between the two types of titanite domains this indicates the two generations of titanite growth during exhumation of deeply subducted continental crust the metamorphic titanite shows significantly elevated nb but decreased ta and thus higher nb ta ratios than the anatectic titanite the increase of nb ta ratios for the metamorphic titanite is associated more with a decrease of ta than an increase of nb suggesting the control of fluid composition on the titanite nb ta ratios because the metamorphic titanite grew during the exhumation of deeply subducted continental crust its unusually high nb ta ratios are ascribed to the breakdown of hydrous minerals such as phengite and biotite that host much more nb than ta this implies that the composition of subduction zone fluids is primarily dictated by the geochemical property of hydrous minerals that break down during dehydration reaction at high pressure to ultrahigh pressure conditions therefore significant nb ta fractionation in ti rich accessory minerals such as titanite and rutile at least on the mineral scale during subduction zone processes is possibly much more common than previously thought

late alteration in titanite catisio5 redistribution and remobilization of rare earth elements and implications for u pb and th pb geochronology and nuclear waste disposal abstract translucent dark coloured titanites from a wide variety of geological environments are commonly partly replaced by very fine grained aggregates of ree rich minerals including allanite monazite and bastnasite rutile quartz calcite apatite and chlorite along grain fractures and boundaries the aggregates of ree rich minerals are bordered by an irregular zone of altered titanite which by secondary ion mass spectrometry sims is considerably lower in rees u and th than the adjacent unaltered matrix light rees and th are differentially depleted in the altered zone and correspondingly enriched in secondary minerals additionally hrees and u have been lost to the external system the loss of hrees being in proportion to the increase in atomic number natural radiation damage was not an important factor in promoting the late alteration of titanite titanite which has been subjected to late hydrothermal activity would not remain a closed system in respect to either u or th decay series and therefore cannot be used for u pb and th pb geochronology the observed leaching and partial dissolution of titanite under hydrothermal conditions are generally consistent with laboratory experimentation indicating that proper isolation from any communication with hydrothermal fluids is essential in the application of titanite based ceramics for the immobilization of radioactive waste

behaviour of saturated railway track foundation materials during undrained cyclic loading this paper presents results of a series of hollow cylinder tests carried out to investigate the undrained behaviour of saturated railway track foundation materials during cyclic loading involving p

zircon u pb geochronology and hf isotopic constraints on petrogenesis of the gangdese batholith southern tibet abstract during the mesozoic cenozoic northward neotethyan subduction and subsequent india asia collision gave rise to the extensive transhimalayan magmatism that stretches from burma and western yunnan through southern tibet to the ladakh and kohistan complexes to understand the age distribution and petrogenesis of the gangdese batholith the largest intrusive exposure along the transhimalayan magmatic belt fifty granitic samples were selected for in situ zircon u pb and hf isotopic analyses the u pb data suggest four discrete stages of magmatic activity i e 205 152 109 80 65 41 and 33 13 ma respectively with the 65 41 ma stage being the most prominent the hf isotopic data indicate that the gangdese batholith is overwhelmed by positive e hf t values which are comparable to those of the kohistan ladakh batholiths in the west but differ markedly from those of the chayu burma batholiths in the east most of the gangdese granites show similar and young hf model ages 1000 300 ma indicating their derivation from juvenile crust however those formed in the 65 41 ma stage exhibit more heterogeneous hf isotopic ratios with negative e hf t values being observed in some granites younger than 50 ma suggesting the involvement of old indian continental crust in their petrogenesis this age may thus mark the onset of the india asia collision the newly established zircon u pb age and hf isotope database of the gangdese batholith can be used as a powerful tracer or fingerprint when studying the source to sink relation of the sediments eroded from the southern tibetan plateau

field performance of a peat railway subgrade reinforced with helical screw piles rail tracks on peat subgrades can experience significant deflections which have led to derailments a potential ground stabilization strategy is to use screw piles to reduce rail displacements however limited research has been undertaken to investigate the effect of these piles and their performance under cyclic train loading a field site was instrumented and monitored before and after screw pile installation the piles were instrumented with strain gauges piezometers were installed in the peat and high speed cameras were used to measure track and subgrade displacements the load carried by each instrumented pile was approximately 50 60 kn three weeks after installation but reduced to approximately 30 kn after six months although one year s worth of piezometric data was collected before installation of the piles it is difficult to conclusively attribute the changes in pore pressures to the piles particularly because the piezometric data collected after the pile installation was only available for t

factors controlling sulfur concentrations in volcanic apatite apatite crystals from two types of samples were analyzed by electron microprobe for 15 major and trace elements 1 apatite in h2o and s saturated experimental charges of the 1982 el chichon trachyandesite and 2 apatite in volcanic rocks erupted from 20 volcanoes the so3 contents of the experimental apatite increase with increasing oxygen fugacity from 0 04 wt in reduced charges buffered by fayalite magnetite quartz o2 fmq to 1 0 2 6 wt in oxidized charges buffered by manganosite hausmanite mnh or magnetite hematite mth the so3 contents of mnh and mth buffered apatite also generally increase with increasing pressure from 2 to 4 kbar and decreasing temperature from 950 to 800 8c the partition coefficient for so 3 between apatite and oxidized melt increases with decreasing temperature but appears to be independent of pressure apatites in volcanic rocks show a wide range of so3 contents 0 04 to 0 63 wt our sample set includes one group known to contain primary anhydrite and a second group inferred to have been free of primary anhydrite no systematic differences in apatite s contents are observed between these two groups our study was initiated to define the factors controlling s contents in apatite and to evaluate the hypothesis that high s contents in apatite could be characteristic of s rich anhydrite bearing magmas such as those erupted from el chichon in 1982 and pinatubo in 1991 this hypothesis is shown to be invalid probably chiefly a consequence of the slow intra crystalline diffusion that limits re equil ibration between early formed apatite and the evolving silicate melt contributing factors include early crystallization of most apatite over a relatively small temperature interval common late stage magmatic enrichment of s progressive oxidation during magmatic evolution and strong controls on s contents in apatite exerted by temperature and o2 pressure

the lhasa terrane record of a microcontinent and its histories of drift and growth article i nfo the lhasa terrane in southern tibet has long been accepted as the last geological block accreted to eurasia before its collision with the northward drifting indian continent in the cenozoic but its lithospheric architecture drift and growth histories and the nature of its northern suture with eurasia via the qiangtang terrane remain enigmatic using zircon in situ u pb and lu hf isotopic and bulk rock geochemical data of mesozoic early tertiary magmatic rocks sampled along four north south traverses across the lhasa terrane we show that the lhasa terrane has ancient basement rocks of proterozoic and archean ages up to 2870 ma in its centre with younger and juvenile crust phanerozoic accreted towards its both northern and southern edges this finding proves that the central lhasa subterrane was once a microcontinent this continent has survived from its long journey across the paleo tethyan ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the qiangtang terrane to the north and with the indian continent to the south zircon hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks e g 50 90 0 70 and 30 100 to the mesozoic magmatism in the southern central and northern lhasa subterranes respectively we suggest that much of the mesozoic magmatism in the lhasa terrane may be associated with the southward bangong nujiang tethyan seafloor subduction beneath the lhasa terrane which likely began in the middle permian or earlier and ceased in the late early cretaceous and that the significant changes of zircon ehf t at 113 and 52 ma record tectonomagmatic activities as a result of slab break off and related mantle melting events following the qiangtang lhasa amalgamation and india lhasa amalgamation respectively these results manifest the efficacy of zircons as a chronometer u pb dating and a geochemical tracer hf isotopes in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics

fluid flux melting generated postcollisional high sr y copper ore forming water rich magmas in tibet miocene postcollisional porphyry cu deposits in southern tibet are genetically associated with dacitic rhyolitic intrusions with unusually high sr y ratios 40 which have been attributed to dehydration melting of garnet amphibolite in a thickened lower crust to test this hypothesis and examine the hydration state of copper ore forming high sr y magmas we utilize a geohygrometer for granitoid rocks entailing zircon saturation thermometry and h 2 o dependent phase equilibria the results show that these tibetan high sr y magmas had dissolved h 2 o contents 10 wt which considerably exceeds the water supply by dehydration melting of basaltic amphibolites maximum of 6 7 1 4 wt our results indicate that high sr y dacitic rhyolitic magmas cannot be produced by dehydration melting of basaltic amphibolites while h 2 o added melting of basaltic amphibolites can produce high sr y dacitic rhyolitic melts it does not yield high enough mg 50 to match the tibetan ore forming porphyries we propose an alternative model for the genesis of copper ore forming high sr y magmas in tibet and suggest that the high sr y dacitic rhyolitic porphyries in southern tibet are residually h 2 o enriched high pressure differentiation products of hydrous mafic partial melts of tibetan mantle this hypothesis is based on the previous investigation of miocene mafic microgranular enclaves mantle derived melts which define a fractionation trend with and have sr nd hf isotopic compositions similar to the host tibetan ore forming porphyries

trace element partitioning between apatite and silicate melts we present new experimental apatite melt trace element partition coefficients for a large number of trace elements cs rb ba la ce pr sm gd lu y sr zr hf nb ta u pb and th the experiments were conducted at pressures of 1 0 gpa and temperatures of 1250 c the rare earth elements la ce pr sm gd and lu y and sr are compatible in apatite whereas the larger lithophile elements cs rb and ba are strongly incompatible other trace elements such as u th and pb have partition coefficients close to unity

the different sources and petrogenesis of jurassic intrusive rocks in the southern lhasa subterrane tibet evidence from the trace element compositions of zircon apatite and titanite abstract the jurassic magmatism distributed in the southern lhasa subterrane slt has been recognized as a record of the early stage evolution of the neo tethys ocean however the magma compositions and detailed crystallization histories remain an enigma zircon apatite and titanite in igneous rocks can serve as effective petrogenetic indicators in this paper we present the whole rock geochemical zircon u pb data zircon hf isotopic analyses and major and trace elemental compositions of zircon apatite and titanite from baiga granite porphyry egp shanba granodiorite egd pengcuolin granodiorite porphyry mgp and dazhuqu monzonite lm rocks in the slt to constrain their source and petrogenesis the results from this study show that a combination of zircon ti th u hf and rare earth element ree contents apatite halogen ree and sr contents and titanite rees can be used to track the detailed magmatic crystallization histories higher sr contents are found in apatite srap from egp ca 192 ma and egd ca 176 ma than those in their host rocks srwr indicating that their magma genesis may have involved some mafic magma the magma genesis of lm ca 159 ma may have involved more reduced mafic or least evolved magma as evidenced by the higher th u but lower yb gd ratios higher zircon saturation and ti in zircon temperatures in zircon highest srap srwr ratios and large positive eu anomalies in titanite from lm the lower cl contents and higher la sm n values in apatite from mgp ca 172 ma are inherited from the low cl melts the mgp rocks have higher zircon ce4 ce3 and eun eun ratios a greater apatite so3 content and a higher titanite total ree content which indicates that mgp has a higher oxidation state than do egp egd and lm the mgp also exhibits a higher h2o content 11 wt dissolved in the melt greater ba la and nb ta ratios in whole rock and higher nb ta ratios in zircon however mgp demonstrates lower zircon saturation and ti in zircon temperatures which suggest that mgp was generated by fluid fluxed melting below 750 c the low ti in zircon temperatures but high la yb and sr y ratios of mgp indicate that a local thickened crust likely existed in the middle jurassic period in the slt due to mafic magma underplating during this time

sulfur partitioning between apatite and melt and effect of sulfur on apatite solubility at oxidizing conditions the effect of sulfur on phosphorus solubility in rhyolitic melt and the sulfur distribution between apatite anhydrite melt and fluid have been determined at 200 mpa and 800 1 100 c via apatite crystallization and dissolution experiments the presence of a small amount of sulfur in the system 0 5 wt s under oxidizing conditions increases the solubility of phosphorus in the melt probably due to changing calcium activity in the melt as a result of the formation of ca s complexing cations apatite solubility geothermometers tend to overestimate temperature in ca poor s bearing system at oxidizing conditions in crystallization experiments the sulfur content in apatite decreases with decreasing temperature and also with decreasing sulfur content of the melt the sulfur partition coefficient between apatite and rhyolitic melt increases with decreasing temperature kdsapatite melt 4 5 14 2 at t 1 100 900 c under sulfur undersaturated conditions no anhydrite the sulfur partition coefficient is lower in anhydrite saturated melt 8 at 800 c than in anhydrite undersaturated melt suggesting that kdsapatite melt depends not only on the temperature but also on the sulfur content of the melt these first results indicate that the sulfur content in apatite can be used to track the evolution of sulfur content in a magmatic system at oxidizing conditions

early jurassic volcanic rocks in the xiongcun district southern lhasa subterrane tibet implications for the tectono magmatic events associated with the early evolution of the neo tethys ocean abstract early mesozoic late triassic to middle jurassic igneous rocks in the southern lhasa subterrane tibet record important information on the early tectono magmatic evolution of the neo tethys ocean this paper presents petrological geochronological and geochemical data for the xiongcun formation ignimbrites to constrain the petrogenesis and tectonic setting of these rocks in the southern lhasa subterrane the xiongcun formation is dominated by andesitic and dacitic rocks these rocks yield early jurassic 195 176 ma zircon u pb ages and display typical arc like geochemical signatures being enriched in large ion lithophile elements e g rb ba and u and depleted in high field strength elements e g nb ta and ti sr nd pb hf isotopic compositions are highly depleted these chemical and isotopic data suggest that the xiongcun formation ignimbrites probably formed in an intra oceanic island arc setting related to the northward subduction of the neo tethys oceanic slab the parental magmas were derived from a depleted mantle source modified by fluids released from the neo tethys oceanic slab combined with previously reported data we suggest that the volcanic rocks in the early jurassic xiongcun and yeba formations of the southern lhasa subterrane were generated by a single subduction system but developed on oceanic and continental crust respectively

sulfur evolution of oxidized arc magmas as recorded in apatite from a porphyry copper batholith uniformly sulfur rich cores abruptly zoned to sulfur poor rims 1 to 0 2 wt so3 in apatite from the yerington batholith nevada indicate that early magma that is crystal poor oxidizing and sulfate rich evolved to sulfate poor magma via crystallization of anhydrite a mineral observed in magmas from pinatubo and el chichon we predict that the characteristic zonation to sulfur poor rims of apatite in the yerington batholith is common in other oxidized hydrous calc alkaline magmas and can be used to track cryptic anhydrite saturation as well as to monitor sulfur evolution sulfate rich arc magmas such as yerington magmas may crystallize to produce hydrothermal fluids rich in chlorine copper and sulfur and porphyry copper ores

in situ u pb zircon dating using laser ablation multi ion counting icp ms high resolution in situ u pb zircon geochronology on zoned grains can obtain isotope signatures from multiple growth or thermal events we present a method using laser ablation multicollector inductively coupled plasma mass spectrometry la mc icp ms to overcome complications associated with intricately zoned zircon crystals through in situ sampling of zircon volumes as small as 12 m 25 m and 40 m in diameter by about 10 m in depth high precision u pb age of a series of zircon standard covering a wide age range of 30 to 1 065 ma was acquired using la mc icp ms the precision of measured pb u ratios in homogeneous zircon is about 2 2 resulting in routinely achieved precision of u pb ages obtained by external calibration of 1 2 or better all masses of interest can be simultaneously recorded with a multi ion counting system mic operating in static mode and the short ablation required to achieve such precision results in spatial resolution that is superior to comparable u pb zircon analyses by single collector icp ms the resulting present u pb age for five zircon reference samples and two geological samples show an excellent agreement with the previously reported id tims or shrimp data

trace element composition of igneous zircon a thermal and compositional record of the accumulation and evolution of a large silicic batholith spirit mountain nevada hafnium u th and ree content of zircons from the spirit mountain batholith in southern nevada correlate with calculated temperatures from the ti in zircon thermometer to support field and petrologic evidence of rejuvenation of crystal mush and melt extraction events during the 2 million year accumulation of the granitoid batholith marked variation in zircon composition from sample to sample from grain to grain within individual samples and from zone to zone within individual grains documents in detail a history of fluctuating conditions with repeated episodes of replenishment reheating crystal mush rejuvenation fractional crystallization and melt segregation the zircons exhibit compositional and thermal variability indicative of variations in host melt composition due to 1 melt rejuvenation mixing and fractionation 2 coeval growth of other ree rich accessory minerals and possibly 3 fluctuation in fo2