major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

in situ la mc icp ms and id tims u pb geochronology of cassiterite in the giant furong tin deposit hunan province south china new constraints on the timing of tin polymetallic mineralization abstract the furong deposit located in southern hunan province china is a newly discovered giant tin deposit spatially associated with the a type qitianling granite the petrogenetic link between the giant furong tin deposit and the qitianling granite batholith remains controversial because of the lack of precise dating for the tin polymetallic mineralization here we report for the first time in situ u pb data on cassiterite obtained by la mc icp ms and the results are compared to id tims data the in situ la mc icp ms analyses of the cassiterites provide a reliable age constraint for tin polymetallic mineralization in the furong deposit yielding an isochron age of 159 9 1 9 ma at 95 confidence level mswd 18 which is indistinguishable from the id tims 206 pb 238 u weighted mean age of 158 2 0 4 ma the in situ u pb ages corroborate the ar ar dates published for the furong tin deposit which indicate that the mineralization is coeval with the emplacement of the qitianling granite batholith these results provide further evidence of a close temporal link between the pluton s emplacement and tin mineralization in the furong area the data obtained clearly demonstrate that in situ la mc icp ms u pb dating of cassiterite is a robust geochronometer for direct dating of tin polymetallic mineralization

isotopic geochemistry zircon u pb ages and hf isotopes of a type granites from the xitian w sn deposit se china constraints on petrogenesis and tectonic significance abstract zircon u pb geochronological geochemical and petrological analyses have been carried out on the xitian granite emplaced in the middle part of shi hang zone which is closely related to the economically important xitian tungsten tin deposit in hunan province southeast china la icp ms zircon u pb dating of two representative samples yielded weighted means 206 pb 238 u age of 151 7 1 2 ma and 151 8 1 4 ma these granites are comprised mainly of k feldspar quartz plagioclase fe rich biotite and minor fluorite and are characterized by enrichments in rb th rees total ree 159 351 ppm and hfses e g zr and y but depletions in ba sr p eu and ti they are metaluminous to weakly peraluminous and show a clear a type granite geochemical signature with high sio 2 73 44 78 45 wt total alkalis na 2 o k 2 o 2 89 8 98 wt fe 2 o 3 mgo ratios and low p 2 o 5 cao mgo and tio 2 contents in situ zircon hf isotope analysis suggests their e hf t values ranging from 7 43 to 14 69 sr nd isotope data show their e nd t values in the range of 9 2 to 7 3 with corresponding t dm2 ages of 1 72 1 56 ga these characteristics indicate that the xitian granite originated from partial melting of metamorphic basement rocks with a certain amount of mantle derived materials combined with previous geochemical and isotopic data it is derived that mantle crust interaction was gradually enhanced from the early to late stages of magmatism the ore forming materials and fluids of the xitian w sn deposit are mainly produced by the early yanshanian granitic magmatism which is also responsible for the late jurassic ca 152 ma a type granitic rocks that host the w sn polymetallic deposits distributed along the shi hang zone implying a significant mesozoic extensional event in southeast china likely caused by the subduction of the paleo pacific plate

mesozoic overthrust tectonics in south china whether south china was a platform or a para platform after the mid paleozoic deformation or whether the mountains of huanan south china form a mesozoic collision type orogen depends upon whether the ophiolite melange in the yangtze region is precambrian basement or was overthrust onto a foreland thrust belt during the mesozoic this paper presents evidence of tectonic windows under the melange and basement klippes above the melange in the yangtze region

petrology and geochemistry of late stage intrusions of the a type mid proterozoic pikes peak batholith central colorado usa implications for petrogenetic models abstract the 1 08 ga anorogenic a type pikes peak batholith front range central colorado is dominated by coarse grained biotite amphibole syenogranites and minor monzogranites collectively referred to as pikes peak granite ppg the batholith is also host to numerous small late stage plutons that have been subdivided into two groups e g wobus 1976 studies in colorado field geology colorado school of mines professional contributions colorado 1 a sodic series sio 2 44 78 wt k na 0 32 1 36 composed of gabbro diabase syenite quartz syenite and fayalite and sodic amphibole granite and 2 a potassic series sio 2 70 77 wt k na 0 95 2 05 composed of biotite granite and minor quartz monzonite differences in major and trace element and nd isotopic characteristics for the two series indicate different petrogenetic histories potassic granites of the late stage intrusions appear to represent crustal anatectic melts derived from tonalite sources based on comparison of their major element compositions with experimental melt products in addition nd isotopic characteristics of the potassic granites e nd 1 08 ga 0 2 to 2 7 overlap with those for tonalites granodiorites ca 1 7 ga boulder creek intrusions e nd 1 08 ga 2 4 to 3 6 exposed in the region some of the partial melts evolved by fractionation dominated by feldspar the late stage potassic granites share geochemical characteristics with most of the ppg which is also interpreted to have an anatectic origin involving tonalitic crust the origin of monzogranites associated with the ppg remains unclear but mixing between granitic and mafic or intermediate magmas is a possibility syenites and granites of the sodic series cannot be explained as crustal melts but are interpreted as fractionation products of mantle derived mafic magmas with minor crustal input high temperature and low oxygen fugacity estimates e g frost et al 1988 american mineralogist 73 727 740 support a basalt fractionation origin as do e nd values for sodic granitoids e nd 1 08 ga 2 2 to 0 7 which are higher than e nd values for colorado crust at 1 08 ga ca 1 0 to 4 0 enrichments in incompatible elements e g rare earth elements rb y and depletions in compatible elements e g cr sr ba in the sodic granitoids compared to coeval mafic rocks are also consistent with fractionation accessory mineral fractionation release of fluorine rich volatiles and or removal of pegmatitic fluids could have modified abundances of ce nb zr and y in some sodic granitoid magmas gabbros and mafic dikes associated with the sodic granitoids have e nd 1 08 ga of 3 0 to 3 5 which are lower than depleted mantle at 1 08 ga and their trace element characteristics suggest derivation from mantle sources that were previously affected by subduction related processes however it is difficult to characterize the mantle component in these magmas because assimilation of crust during magma ascent could also result in their observed geochemical features the pikes peak batholith is composed of at least two petrogenetically different granite types both of which exhibit geochemical characteristics typical of a type granites models proposed for the petrogenesis of the granitoids imply the existence of mafic rocks at depth and addition of juvenile material to the crust in central colorado at 1 1 ga

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

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

molybdenite re os and muscovite 40ar 39ar dating of the xihuashan tungsten deposit central nanling district south china abstract the xihuashan tungsten deposit in the central nanling region south china is an important vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions wolframite and molybdenite are the principal ore minerals the gangue minerals are mainly quartz and muscovite wolframite and molybdenite are products of the first stage hydrothermal activity whereas muscovite formed dominantly at the second stage molybdenite re os and muscovite 40ar 39ar dating have been carried out to investigate the age of mineralization re os isotopic dating for molybdenite associated with wolframite yield a precise well constrained isochron age of 157 8 0 9 ma mswd 1 5 ar ar isotopic analyses of muscovite yield a plateau age of 152 8 1 6 ma in agreement with an inverse isochron age of 152 8 1 6 ma which is 5 mys younger than the re os age the molybdenite re os age is interpreted as the age of tungsten mineralization this age coincides well with the zircon u pb age of the host granitic intrusion reported previously the 5 mys difference between molybdenite re os and muscovite 40ar 39ar ages probably represents the duration of hydrothermal activity the results show that the xihuashan tungsten deposit is one of many important tungsten tin deposits formed during 150 to 160 ma associated with large scale lithospheric extension in south china

tectonics and metallogeny of mainland southeast asia a review and contribution abstract the southeast asia region is endowed with a diversity of mineral resources notably porphyry related skarn epithermal and sediment hosted orogenic gold deposits formation of these deposits was associated with a long and complex tectonic history of gondwana supercontinent break up arc magmatism backarc basin development together with arc continent and continent continent collisions that created the present day mainland se asia this paper summarizes historical and current se asian geological research and ore deposit studies here we present a new tectonic and metallogenic model for phanerozoic mainland se asia from this model we conclude that incipient arc backarc basin magmatism is the key to the formation of many important ore deposits in the truong son and loei fold belts the two major metallogenic belts in mainland se asia in addition triassic to cenozoic arc continent and continent continent collisions have led to the formation of many sediment hosted orogenic gold deposits in the sukhothai and the sibumasu terranes oblique cretaceous to recent subduction along the andaman sunda trench was responsible for gold and copper gold molybdenum porphyry and epithermal mineralization along the kawlin wutho mt popa arc in myanmar in the north and the sumatran volcanic arc in the south we anticipate that the present emphasis on exploring for shallower level epithermal deposits will increasingly lead to exploration for deeper level porphyry and porphyry related skarn systems in the coming decades

a hybrid origin for the qianshan a type granite northeast china geochemical and sr nd hf isotopic evidence abstract major and trace element whole rock sr and nd isotope and zircon hf isotope data are reported for a suite of a type granites and mafic microgranular enclaves from the early cretaceous 126 2 ma qianshan pluton liaodong peninsula northeast china with the aim of investigating the sources and petrogenesis of a type granites the qianshan pluton includes hornblende alkali feldspar granite graphic biotite granite and mafic microgranular enclaves the hornblende alkali feldspar granites have high sio 2 fe 2 o 3t mgo k 2 o na 2 o rb zr and lree contents and low ba and sr concentrations with strongly negative eu anomalies their high rb sr 87 rb 86 sr 16 76 24 15 and initial 87 sr 86 sr ratios 0 7215 to 0 7283 negative e nd t values 14 1 to 16 5 and zircon e hf t values 18 9 to 11 5 indicate they were mainly derived from a crustal source but with involvement of high e nd t and e hf t materials graphic biotite granites have similar geochemical features and sr nd hf isotopic compositions to enclaves indicating they were the result of crystal fractionation of evolved mafic magmas but with involvement of low e nd t and e hf t materials the mafic enclaves have an igneous texture and contain acicular apatite suggesting quenching of mafic magmas that have co mingled with the host granites they have low initial 87 sr 86 sr ratios 0 7097 0 7148 negative e nd t 14 5 to 11 9 and zircon e hf t 17 1 to 6 9 values and are enriched in liles and lrees and depleted in hfses when coupled with the high mgo mg up to 54 this indicates derivation from an enriched lithospheric mantle source but contaminated by crustal materials geochemical and sr nd and zircon hf isotopic compositions rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead magma mixing of mantle derived mafic and crustal derived magmas coupled with crystal fractionation is compatible with the data this example shows that at least some a type granites formed through a complex process involving mantle and crustal derived magma mixing crystal fractionation and infracrustal melting

generation of metaluminous a type granites by low pressure melting of calc alkaline granitoids melting experiments on two calc alkaline rocks a tonalite and a granodiorite demonstrate that shallow dehydration melting of hornblende and biotite bearing granitoids generates metaluminous a type granitic melts profuse crystallization of calcic plagioclase orthopyroxene during low pressure p 4 kbar incongruent melting explains all of the major and trace element characteristics of a type granites e g their low al ca mg sr and eu contents and high ga al and k na ratios as well as their common association with anorthositic and mangeritic rocks the residual assemblage produced during melting of the same rocks in the deep crust p 8 kbar is dominated by clinopyroxene and as a consequence most of the chemical features diagnostic of a type granites are lost the high temperatures 900 c and low h 2 o contents 4 wt that are characteristic of a type magmas are adequately explained by the h 2 o poor nature of the granitoid source materials and require neither a granulitic nor a f rich source previous attempts to explain the origin of a type granites have focused on the nature of the source material these experiments show that pressure of melting is at least as important as source composition in engendering a type melts

formation of high δ18o fayalite bearing a type granite by high temperature melting of granulitic metasedimentary rocks southern china the genesis of a type granites has been controversial fayalite granite is a member of the most reduced a type granites commonly thought to have been primarily sourced from tholeiitic rocks in this paper we report petrography whole rock geochemistry sr nd isotope and in situ zircon hf o isotope results for a fayalite bearing a type granite suite at jiuyishan in southern china high zircon 18 o 8 0 9 8 negative zircon ehf t 6 2 to 2 3 and evolved whole rock sr nd isotopes i sr 0 7151 0 7181 end t 7 4 to 6 6 indicate the reworking of old supracrustal rocks isotopic and geochemical results particularly downward inflections of zr and ba at 70 wt sio 2 point to fractional crystallization rather than magma mixing as the controlling process for the evolution of the igneous suite integrated petrological geochemical and isotopic studies present the first convincing case that reduced a type granites can also be generated by high temperature 960 c melting of granulitic metasedimentary rocks likely related to the upwelling of the asthenosphere and or underplating and intrusion of basaltic melts we emphasize that key factors for the genesis of this unique rock type are low oxygen fugacity f o 2 low f h 2 o and high temperature

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

rutile saturation in hydrous siliceous melts and its bearing on ti thermometry of quartz and zircon the tio2 solubility of rutile saturated hydrous siliceous melts has been investigated at p 1 gpa and t 650 1000 c for several representative felsic compositions the dissolution of a rutile crystal into a tio2 undersaturated melt provides information on both tio2 solubility and ti diffusion results of this study confirm that tio2 solubility is strongly dependent on both temperature and melt composition but not on the amount of h2o present for a given t t io2 content decreases as the melts become more felsic the solubility of tio2 is given by log ti ppm 7 95 5305 t 0 124fm

kinematics of the central hellenides structural analysis along 24 cross sections crosscutting several windows in the central hellenides provides the sense of nappe movements as well as the location of destroyed oceans lying between the apulian and eurasian continents from the mesozoic orogeny took place in two phases the first phase the eo hellenic phase was initiated by convergence of the apulian and pelagonian plates with west directed subduction and closure of the pindos ocean late jurassic obduction of oceanic lithosphere over the western margin of the pelagonian plate was followed by footwall imbrication mylonites and sheath folds during the late cretaceous uplift was associated with ductile normal faulting at depth and tectonic unroofing at shallow crustal levels the second phase the meso hellenic phase comprised the closure of the ambelakia ocean at the eastern margin of the pelagonian plate and continental subduction along the eastern margin of the apulian plate west directed subduction of the ambelakia ocean was associated with eastward directed ductile thrusting folding and blueschist metamorphism blueschist formed within a simple duplex structure at depth and was subsequently overthrusted in the late eocene onto the olympos microcontinent which acted as a major obstacle to the eastward directed nappe movements up to 150 m thick cataclasites kink folds and a spaced cleavage were formed during the late stage of the continental collision a subduction along the eastern margin of the apulian plate caused kink folding and reimbrication of the western parts of the pelagonian basement since the oligocene the overthickened crust collapsed by means of low angle normal faults

characteristics of seismic waves composing hawaiian volcanic tremor and gas piston events observed by a near source array a correlation method specifically designed for describing the characteristics of a complex wave field is applied to volcanic tremor and gas piston events recorded by a semicircular array of geos instruments set at the foot of the puu oo crater on the east rift of kilauea volcano hawaii the spatial patterns of correlation coefficients obtained as functions of frequency for the three components of motion over the entire array are similar for gas piston events and tremor and clearly depict dispersive waves propagating across the array from the direction of puu oo the wave fields are composed of comparable amounts of rayleigh and love waves propagating with similar and extremely slow phase velocities ranging from 700 m s at 2 hz to 300 m s at 8 hz the highly cracked solidified lava flow on which the array was deployed and subjacent structure of alternating lava and ash layers formed during repeated eruptions of puu oo since 1983 appear to be responsible for the low velocities observed the results from puu oo stand in sharp contrast to those obtained in an experiment conducted in 1976 on the partially solidified lava lake of kilauea iki rayleigh waves were not observed in kilauea iki but well developed trains of love waves were seen to propagate there with velocities twice as high as those observed near puu oo these differences in the propagation characteristics of surface waves at the two sites may be attributed to the presence of a soft horizontal layer of molten rock in kilauea iki which may have lowered the phase velocity of rayleigh waves more drastically than that of love waves resulting in severe scattering of the rayleigh wave mode on the other hand the thin superficial pahoehoe flow under our array at puu oo may have favored the development of vertical columnar joints more extensively at this location than at kilauea iki which may have reduced the shear moduli controlling the love wave mode the average phase velocities in the frequency band from 2 to 5 hz found at puu oo are roughly similar to those determined for tremor at klyuchevskoy volcano kamchatka but the frequency dependence appears much stronger at puu oo

shrimp u pb zircon ar ar muscovite and re os molybdenite isotopic dating of the taoxikeng tungsten deposit south china block abstract the taoxikeng tungsten deposit is located in the jiangxi province in the southern part of china and is one of the largest wolframite quartz vein type tungsten deposits in the country the deposit is situated in sinian neoproterozoic to permian strata at the contact with the buried taoxikeng granite sensitive high mass resolution ion microprobe shrimp zircon u pb analysis of the granite has yielded dates of 158 7 3 9 and 157 6 3 5 ma which are interpreted as the emplacement age of the granite molybdenite separated from ore bearing quartz veins yields a re os isochron age of 154 4 3 8 ma and muscovite separated from greisen between the granite and country rocks yields 40ar 39ar plateau ages of 153 4 1 3 and 152 7 1 5 ma these dates obtained from three independent geochronological techniques constrain the ore forming age of the taoxikeng deposit and link the ore genesis to that of the underlying granite the taoxikeng deposit is an example of a jurassic regional scale tungsten tin ore forming event between 160 and 150 ma in the nanling region of the south china block the deposit s strikingly low rhenium contents 4 9 to 13 0 10 3 g g in molybdenite suggests that the ore was derived from a crustal source this conclusion is consistent with previously published constraints from s d and o stable isotopes sr nd systematics and petrogenetic interpretations of spatially related granites

mineral chemistry trace elements and sr nd hf isotope geochemistry and petrogenesis of cailing and furong granites and mafic enclaves from the qitianling batholith in the shi hang zone south china abstract the shi hang zone is an important ne trending mesozoic magmatic belt composed of granites with relative high end t values and young tdm model ages in south china however the petrogenesis and the tectonic environment for the shi hang zone magmatic rocks remain controversial we report here mineral chemistry geochemical and sr nd hf isotopic data for the cailing and furong granites and mafic microgranular enclaves mmes from the qitianling granite batholith in southern hunan province south china the qitianling granite batholith is a multi staged composite pluton with three phases cailing furong and huangtangling according to their ages and petrography the cailing 163 160 ma and furong 157 153 ma phases are mainly composed of porphyritic amphibole biotite monzogranite and they share similar geochemical and isotopic characteristics both of them show similar sio2 contents from 66 50 to 70 28 and metaluminous a cnk values of 0 80 to 0 98 the granites are characterized by high contents of large ion lithosphile elements lile such as rb th u pb high field strength elements hfse such as nb ta zr hf and zr nb ce y contents 350 ppm and high 10 000 ga al ratios 2 6 chondrite normalized ree patterns show relative enrichment of light rare earth elements lrees and significant negative eu anomalies mineralogical and geochemical features suggest that the cailing and furong granites are a type which can be further classified as a2 subtype they have relatively lower 87sr 86sr i ratios 0 7091 0 7132 higher end t values 5 5 to 7 6 and younger nd isotopic model ages 1 48 1 56 ga than those common s type granites in south china zircon ehf t values vary from 8 1 to 3 7 the mmes in the cailing phase show similar trace element and sr nd isotopic characteristics with the host granites but zircons from the mmes show different ehf t values 6 4 2 6 with those from the host granites 8 1 to 3 7 this indicates that the mmes and host granites were crystallized from different sources of magmas providing direct evidence for mafic felsic magma mixing processes the isotope data indicate that the cailing and furong granites from the qitianling batholith were derived from a hybrid magma consisting of about 80 felsic magma derived from old crust and about 20 mantle derived mafic magma the strong magma mixing at about 160 155 ma caused by intra arc rifting or back arc extension related to subduction of the paleo pacific plate is favored to explain the petrogenesis of the cailing and furong granites as well as the shi hang zone

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

the relationship between a type granites and residual magmas from anorthosite evidence from the northern sherman batholith laramie mountains wyoming usa abstract anorthosite complexes commonly are spatially and temporally associated with a type granite batholiths but their genetic relationship if any has been difficult to determine this study focuses on the northern portion of the 1 43 1 44 ga sherman batholith which is located adjacent to the 1 44 ga laramie anorthosite complex laramie mountains wyoming usa the northern sherman batholith is an ideal place to resolve the relationship of a type granite with anorthosite because of the age of the crust into which it is emplaced most a type granites are intruded into crust only slightly older than the granites themselves and there is little isotopic contrast between potential mantle and crustal source rocks the northern sherman batholith intrudes archean crust that by 1 44 ga had developed nd sr and pb isotopic compositions that differed greatly from contemporaneous mantle the northern sherman batholith is an iron enriched metaluminous alkalic to alkali calcic batholith most of the batholith is composed of fayalite granite with minor volumes of monzodiorite and olivine gabbro hypabyssal dikes of these compositions crop out in the highest structural levels exposed in the area the northern sherman batholith is less differentiated and has assimilated less felsic crust than the southern portions which intrude more fertile proterozoic crust northern sherman batholith rocks are compositionally and isotopically very similar to monzonitic and dioritic rocks of the laramie anorthosite complex none of these rocks have isotopic compositions similar to their archean host rocks precluding derivation solely from such sources instead northern sherman batholith granites like laramie anorthosite complex rocks are related to mantle derived tholeiitic magmas emplaced at the base of the crust the tectonic environment and magmatic processes that lead to the formation of massif anorthosite are also conducive to the formation of voluminous a type granite of which the northern sherman granite is a prime example

petrogenesis of malaysian granitoids in the southeast asian tin belt part 2 u pb zircon geochronology and tectonic model in our complementary geochemical study part 1 the malaysian granitoids of the southeast asian tin belt were divided into a middle permian to late triassic i type dominated eastern province indochina terrane and a triassic to early jurassic transitional i s type main range province sibumasu terrane separated by the bentong raub suture zone which closed in the late triassic previous geochronology has relied on only a few u pb zircon ages together with k ar and whole rock rb sr ages that may not accurately record true magmatic ages we pre sent 39 new high precision u pb zircon ion microprobe ages from granitoids and vol canics across the malay peninsula our results show that ages from the eastern province granitoids span 289 220 ma with those from the main range province granitoids being entirely late triassic spanning 227 201 ma a general westerly younging magmatic trend across the malay peninsula is considered to refl ect steepening and roll back of the bentong raub subduction zone during progressive closure of paleo tethys the youngest ages of subduction related granites in the eastern province roughly coincide with the youngest ages of marine sedimentary rocks along the paleo tethyan suture zone our petrogenetic and u pb zircon age data support models that relate the eastern province granites to pre collisional andean type magmatism and the western main range province granites to syn and post collisional crustal melting of sibumasu crust during the late triassic tin mineralization was mainly associated with the latter phase of magmatism two alternative tectonic models are discussed to explain the triassic evolution of the malay peninsula the fi rst involves a second late triassic to jurassic or early cretaceous east dipping subduction zone west of sibumasu where subduction related hornblende and biotite bearing granites along sibumasu are paired with main range crustal melt tinbearing granites analogous to the bolivia cordilleran tin bearing granite belt the second model involves westward underthrusting of indochina beneath the west malaya main range province resulting in crustal thickening and formation of tin bearing granites of the main ranges cretaceous granitoids are also present locally in singapore ubin diorite on tioman island in the noring pluton of the stong complex eastern province and along the sibumasu terrane in southwest thailand and burma myanmar refl ecting localized crustal melting

isotopic and paleomagnetic constraints on the mesozoic tectonic evolution of south china in order to better constrain the paleogeographic evolution of south china we measured sm nd and rb sr isotopic compositions for 23 mesozoic granites that crop out throughout the area tightly grouped neodymium depleted mantle model ages 1 4 0 3 ga suggest the region is underlain by relatively homogeneous proterozoic crust and fail to define crustal provinces neither the isotopic nor geologic data suggest that a mesozoic suture exists however granites possessing anomalously high sm 8 ppm and nd 45 ppm concentrations relatively high initial epsilon neodymium 4 to 8 and high but variable initial 87sr 86sr 0 759 to 0 713 form a northeast trending zone that coincides with two prominent mesozoic basins southeast of the zone lie the majority of mesozoic intrusives and upper triassic to lower cretaceous extensional basins found in south china mesozoic paleomagnetic poles are well clustered northwest of the zone pre cretaceous poles southeast of it are discordant with respect to those from the northwest the only recognized tectonostratigraphic terrane in south china lies southeast of the zone the terrane is bordered by a northeast trending sinistral fault that was active in the mesozoic other faults in south china have similar attitudes ages and sense of shear together the observations suggest that the mesozoic tectonic regime in south china consisted of strike slip activity plus concomitant rifting as terranes or fragments of similar crust were transported north along sinistral faults the zone defined by the granites enriched in nd and sm demarcates displaced terranes to the southeast from relatively stable land to the northwest

linking zircon u pb and garnet sm nd ages to date loading and metamorphism in the lower crust of a cretaceous magmatic arc swakane gneiss wa usa abstract synorogenic basin development and subsequent collapse and loading provide important constraints on the late cretaceous crustal structure of the north america cordillera high grade metasedimentary rocks of the swakane gneiss in the north cascades have been interpreted to include ca 73 ma detrital zircon that requires a protolith age considerably younger than metamorphic ages of adjacent terranes this detrital interpretation requires rapid loading rates of 7 8 mm yr heating to 750 c in garnet preserves compositional evidence for growth during high pressure amphibolite facies metamorphism and little subsequent modification new garnet rock sm nd isochrons of 73 5 1 2 71 3 2 8 and 65 8 0 7 ma tightly constrain the timing of garnet growth swakane gneiss zircons preserve complex magmatic detrital and metamorphic histories most zircons have distinct cores and homogeneous overgrowths detrital zircon cores include significant proterozoic and mesozoic components with low u th ratios homogeneous metamorphic zircon rims have high u th 5 and define an array of concordant u pb dates from 75 to 63 ma the new zircon u pb and garnet sm nd ages establish that the youngest regional metamorphism was diachronous and occurred between 75 and 63 ma our dataset precludes post 73 ma deposition and instead suggests that sedimentation occurred after ca 91 ma and ended before ca 75 ma using these age constraints for deposition and metamorphism we propose new loading rates of 1 3 mm yr and conclude that the swakane gneiss protolith was likely deposited in a small short lived intra arc basin that subsided filled in and collapsed quickly due to overthrusting of arc crust

solubility of cassiterite in evolved granitic melts effect of t fo2 and additional volatiles abstract the aim of this experimental study was to determine the solubility of cassiterite in natural topaz and cassiterite bearing granite melts at temperatures close to the solidus profiles of sn concentrations at glass crystal sno 2 interface were determined following the method of harrison t m watson e b 1983 kinetics of zircon dissolution and zirconium diffusion in granitic melts of variable water content contributions to mineralogy and petrology 84 66 72 the cassiterite concentration calculated at the sno 2 glass interface is the sno 2 solubility experiments were performed at 700 850 c and 2 kbar using a natural f bearing peraluminous granitic melt with 2 8 wt normative corundum slightly h 2 o undersaturated to h 2 o saturated melt compositions were chosen in order to minimize the loss of sn to the noble element capsule walls at the nickel nickel oxide assemblage ni nio oxygen fugacity buffer the solubility of cassiterite in melts containing 1 12 wt f increases from 0 32 to 1 20 wt sno 2 with an increasing temperature from 700 to 850 c at the ni nio buffer and a given corundum content sno 2 solubility increases by 10 to 20 relative to an increase of f from 0 to 1 12 wt sno 2 solubility increases by 20 relative to increasing cl content from 0 to 0 37 wt in synthetic granitic melts at 850 c we show that cl is at least as important as f in controlling sno 2 solubility in evolved peraluminous melts at oxygen fugacities close to the ni nio buffer in addition to the strong effects of temperature and f o 2 on sno 2 solubility an additional controlling parameter is the amount of excess al corundum content at ni nio and 850 c sno 2 solubility increases from 0 47 to 1 10 wt sno 2 as the normative corundum content increases from 0 1 to 2 8 wt at oxidizing conditions ni nio 2 to 3 sn is mainly incorporated as sn 4 and the effect of excess al seems to be significantly weaker than at reducing conditions

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

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

jurassic intraplate magmatism in southern hunan eastern guangxi 40ar 39ar dating geochemistry sr nd isotopes and implications for the tectonic evolution of se china the mesozoic geology of se china is characterized by intensive and widespread magmatism however the tectonic regime that accounted for the mesozoic magmatism has been an issue with little consensus a comprehensive study of ar 40 ar 39 dating geochemistry and sr nd isotopes has been conducted on basalts from southern hunan and syenite intrusions from eastern guangxi three episodes of jurassic magmatism i e alkaline basalts of c 175 ma in age syenitic intrusions of c 160 ma and high mg basalts of c 150 ma are identified the older c 175 ma alkaline basalts are characterized by low sr i sr 0 7035 0 7040 and high nd epsilon nd t 5 to 6 isotopic compositions and oib like trace element patterns e g nb la 1 in contrast the younger c 150 ma high mg basalts have high sr i sr c 0 7054 and low nd epsilon nd t c 2 isotopic compositions and incompatible trace element patterns of arc affinity the c 160 ma syenitic intrusions display a relatively large range of sr and nd isotopic compositions i sr 0 7032 0 7082 epsilon nd t 5 5 to 4 1 with the qinghu syenites having the lowest i sr highest epsilon nd t and oib type incompatible trace element patterns analogous to the c 175 ma alkaline basalts such a secular variation in rock types and geochemical and isotopic characteristics reveals changes in melt segregation depth and mantle sources which are inferred to have resulted from the post indosinian orogenic lithosphere extension and thinning the c 175 ma alkaline basalts are suggested to have formed by small degrees of decompression melting of the astheno sphere or an enriched lithospheric mantle source accreted by asthenosphere derived melts during the initial extension the c 160 ma syenitic and c 150 ma high mg basaltic rocks mainly originated from the enriched lithospheric mantle that melted owing to a raised geotherm caused by lithosphere thinning this interpretation is at odds with the active continental margin related to the subduction of palaeo pacific plate but consistent with continental rifting and extension for the mesozoic of se china

zircon u pb and sm nd geochronology and geochemistry of the sn w deposits in the northern guposhan ore field nanling range southern china abstract the guposhan ore field located in the central part of the nanling range and close to the giant central south peninsula tin ore belt is well known for its large scale sn w mineralization and hosts a series of middle to large scale sn w deposits in this study medium to fine grained biotite granite outcropped in the mining area have zircon u pb ages of 162 8 1 3 ma mswd 0 54 and 162 7 1 2 ma mswd 0 66 respectively these zircon ages are consistent to the sm nd isotopic age of minerals garnet hornblende clinopyroxene and orthopyroxene from the skarn type ores which is 160 4 4 8 ma mswd 1 3 these granites are characterized by high content of sio2 k2o na2o and rees and high ga al ratios indicating that they belong to highly fractionated a type granites with high k calc alkaline and aluminous peraluminous signatures the zircon lu hf isotopes of these granites have ehf t values and tdmc ages of 2 66 to 1 71 and 1 32 1 38 ga respectively combined with the previous studies it was proposed that the magma was formed by the mixing of crust mantle components ca 50 and ca 50 respectively in addition magmas are characterized by low temperatures of ca 710 c and oxygen fugacity log fo2 values of 18 5 to 16 4 formation of these granites were likely related to an intraplate extensional tectonic setting triggered by roll back of the subducted paleo pacific plate beneath the south china block scb these granites are in favor of the sn w mineralization making the guposhan ore district a large scale sn w mineralization ore field in the nanling range

geology and genesis of kafang cu sn deposit gejiu district sw china kafang is one of the main ore deposits in the world class gejiu polymetallic tin district sw china there are three main mineralization types in the kafang deposit i e skarn cu sn ores stratiform cu ores hosted by basalt and stratiform cu sn ores hosted by carbonate the skarn mainly consists of garnet and pyroxene and retrograde altered rocks these retrograde altered rocks are superimposed on the skarn and are composed of actinolite chlorite epidote and phlogopite major ore minerals are chalcopyrite pyrrhotite cassiterite pyrite and scheelite sulfur and pb isotopic components hint that the sources of different types of mineralization are distinctive and indicate that the skarn ore mainly originated from granitic magma whereas the basalt hosted cu ores mainly derived from basalt microthermometry results of fluid inclusions display a gradual change during the ore forming process the homogenization temperature of different types of inclusions continuously decreases from early to late mineralization stages the salinities and freezing temperatures exhibit similar evolutionary tendencies with the t homogenizaion while the densities of the different types keep constant the majority being less than 1 oxygen and hydrogen isotopic values o and d of the hydrothermal fluids fall within ranges of 3 1 to 7 7 with an average of 6 15 calculated at the corresponding homogenization temperature and 73 and 98 with an average of 86 5 respectively microthermometry data and h o isotopes indicate that the ore forming fluid of the kafang deposit is mainly derived from magma in the early stage and a mixture of meteoric and magmatic water in late stage molybdenite re os age of the skarn type mineralization is 83 4 2 1 ma and the stratiform ores hosted by basalt is 84 2 7 3 ma which are consistent with the la icp ms zircon age of the xinshan granite intrusion 83 1 0 4 ma the evidence listed above reflects the fact that different ore styles in the kafang deposit belong to the same mineralization system

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